RFC 8859
A Framework for Session Description Protocol (SDP) Attributes When Multiplexing
RFC 8859: A Framework for Session Description Protocol (SDP) Attributes When Multiplexing ✨
Okay bestie, this is RFC 8859 🎀 It was written by S. Nandakumar from Cisco, and it's on the Standards Track, so it's an actual Internet Standards Track document 💅. It's dated January 2021, and its ISSN is 2070-1721 🌸. The header has no "Obsoletes" or "Updates" line, so there's nothing it replaces or changes 🙈
Abstract ✨
So the whole point of this spec is to give us a framework for checking how SDP attributes behave when they're multiplexed 🦋 This happens when SDP negotiates one single 5-tuple to send and receive media for several media descriptions. Main character energy, literally 👑
It also sorts the existing SDP attributes into categories using that framework 💜
Status of This Memo ✨
This is an Internet Standards Track document 🌈
It's a product of the Internet Engineering Task Force (IETF) 🧚 It reflects the consensus of the IETF community, got public review, and was approved for publication by the Internet Engineering Steering Group (IESG). If you want more on Internet Standards, check Section 2 of RFC 7841 📚
For the current status, any errata, and how to send feedback, go to https://www.rfc-editor.org/info/rfc8859 🔗
Copyright Notice ✨
Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. 💖
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) as they stand on the date this document was published. Please read these carefully, because they explain your rights and restrictions for this document 🫶 Code Components pulled out of this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions, and they come without warranty, as described in the Simplified BSD License 🍓
Table of Contents 🌸
1. Introduction
2. Terminology
3. Motivation
4. SDP Attribute Analysis Framework
4.1. Category: NORMAL
4.2. Category: CAUTION
4.3. Category: IDENTICAL
4.4. Category: SUM
4.5. Category: TRANSPORT
4.6. Category: INHERIT
4.7. Category: IDENTICAL-PER-PT
4.8. Category: SPECIAL
4.9. Category: TBD
5. Analysis of Existing Attributes
5.1. RFC 4566: SDP
5.2. RFC 4585: RTP/AVPF
5.3. RFC 5761: Multiplexing RTP and RTCP
5.4. RFC 3312: Integration of Resource Management and SIP
5.5. RFC 4574: SDP "label" Attribute
5.6. RFC 5432: QoS Mechanism Selection in SDP
5.7. RFC 4568: SDP Security Descriptions
5.8. RFC 5762: RTP over DCCP
5.9. RFC 6773: DCCP-UDP Encapsulation
5.10. RFC 5506: Reduced-Size RTCP in RTP Profile
5.11. RFC 6787: Media Resource Control Protocol Version 2
5.12. RFC 8445: ICE
5.13. RFC 5285: RTP Header Extensions
5.14. RFC 3605: RTCP Attribute in SDP
5.15. RFC 5576: Source-Specific SDP Attributes
5.16. RFC 7273: RTP Clock Source Signaling
5.17. RFC 6236: Image Attributes in SDP
5.18. RFC 7197: Duplication Delay Attribute in SDP
5.19. RFC 7266: RTCP XR Blocks for MOS Metric Reporting
5.20. RFC 6285: Rapid Acquisition of Multicast RTP Sessions
5.21. RFC 6230: Media Control Channel Framework
5.22. RFC 6364: SDP Elements for FEC Framework
5.23. RFC 4796: "content" Attribute
5.24. RFC 3407: SDP Simple Capability Declaration
5.25. RFC 6284: Port Mapping between Unicast and Multicast RTP
Sessions
5.26. RFC 6714: MSRP-CEMA
5.27. RFC 4583: SDP Format for BFCP Streams
5.28. RFC 5547: SDP Offer/Answer for File Transfer
5.29. RFC 6849: SDP and RTP Media Loopback Extension
5.30. RFC 5760: RTCP with Unicast Feedback
5.31. RFC 3611: RTCP XR
5.32. RFC 5939: SDP Capability Negotiation
5.33. RFC 6871: SDP Media Capabilities Negotiation
5.34. RFC 7006: Miscellaneous Capabilities Negotiation in SDP
5.35. RFC 4567: Key Management Extensions for SDP and RTSP
5.36. RFC 4572: Comedia over TLS in SDP
5.37. RFC 4570: SDP Source Filters
5.38. RFC 6128: RTCP Port for Multicast Sessions
5.39. RFC 6189: ZRTP
5.40. RFC 4145: Connection-Oriented Media
5.41. RFC 6947: The SDP "altc" Attribute
5.42. RFC 7195: SDP Extension for Circuit-Switched Bearers in
PSTN
5.43. RFC 7272: IDMS Using the RTP Control Protocol (RTCP)
5.44. RFC 5159: Open Mobile Alliance (OMA) Broadcast (BCAST) SDP
Attributes
5.45. RFC 6193: Media Description for IKE in SDP
5.46. RFC 2326: Real Time Streaming Protocol
5.47. RFC 7826: Real-Time Streaming Protocol
5.48. RFC 6064: SDP and RTSP Extensions for 3GPP
5.49. RFC 3108: ATM SDP
5.50. 3GPP TS 183.063
5.51. 3GPP TS 24.229
5.52. ITU T.38
5.53. ITU-T Q.1970
5.54. ITU-T H.248.15
5.55. RFC 4975: The Message Session Relay Protocol
5.56. Historical Attributes
6. bwtype Attribute Analysis
6.1. RFC 4566: SDP
6.2. RFC 3556: SDP Bandwidth Modifiers for RTCP Bandwidth
6.3. RFC 3890: Bandwidth Modifier for SDP
7. rtcp-fb Attribute Analysis
7.1. RFC 4585: RTP/AVPF
7.2. RFC 5104: Codec Control Messages in AVPF
7.3. RFC 6285: Unicast-Based Rapid Acquisition of Multicast RTP
Sessions (RAMS)
7.4. RFC 6679: ECN for RTP over UDP/IP
7.5. RFC 6642: Third-Party Loss Report
7.6. RFC 5104: Codec Control Messages in AVPF
8. group Attribute Analysis
8.1. RFC 5888: SDP Grouping Framework
8.2. RFC 3524: Mapping Media Streams to Resource Reservation
Flows
8.3. RFC 4091: ANAT Semantics
8.4. RFC 5956: FEC Grouping Semantics in SDP
8.5. RFC 5583: Signaling Media Decoding Dependency in SDP
8.6. RFC 7104: Duplication Grouping Semantics in the SDP
9. ssrc-group Attribute Analysis
9.1. RFC 5576: Source-Specific SDP Attributes
9.2. RFC 7104: Duplication Grouping Semantics in the SDP
10. QoS Mechanism Token Analysis
10.1. RFC 5432: QoS Mechanism Selection in SDP
11. k= Attribute Analysis
11.1. RFC 4566: SDP
12. content Attribute Analysis
12.1. RFC 4796
12.2. 3GPP TS 24.182
12.3. 3GPP TS 24.183
13. Payload Formats
13.1. RFC 5109: RTP Payload Format for Generic FEC
14. Multiplexing Considerations for Encapsulating Attributes
14.1. RFC 3407: cpar Attribute Analysis
14.2. RFC 5939 Analysis
14.2.1. Recommendation: Procedures for Potential Configuration
Pairing
14.3. RFC 6871 Analysis
14.3.1. Recommendation: Dealing with Payload Type Numbers
14.3.2. Recommendation: Dealing with Latent Configurations
15. IANA Considerations
15.1. New "Multiplexing Categories" Subregistry
15.2. "Mux Category" Column for Subregistries
15.2.1. Table: SDP bwtype
15.2.2. Table: attribute-name
15.2.3. Table: content SDP Parameters
15.2.4. Table: Semantics for the "group" SDP Attribute
15.2.5. Table: "rtcp-fb" Attribute Values
15.2.6. Table: "ack" and "nack" Attribute Values
15.2.7. Table: "depend" SDP Attribute Values
15.2.8. Table: "cs-correlation" Attribute Values
15.2.9. Table: Semantics for the "ssrc-group" SDP Attribute
15.2.10. Table: SDP/RTSP Key Management Protocol Identifiers
15.2.11. Table: Codec Control Messages
15.2.12. Table: QoS Mechanism Tokens
15.2.13. Table: SDP Capability Negotiation Option Tags
15.2.14. Table: Timestamp Reference Clock Source Parameters
15.2.15. Table: Media Clock Source Parameters
16. Security Considerations
17. References
17.1. Normative References
17.2. Informative References
Acknowledgements
Author's Address1. Introduction 🦋
Okay so SDP has a bunch of attributes for describing things that apply to each individual media description (the ones marked by "m=" lines) and to the whole multimedia session 💖 Usually, different media types like audio and video each get their own media description and their own RTP session, and each session rides on its own transport-layer flow 🌸
But [RFC8843] lets you use one single address:port combo (a BUNDLE address) to receive media for several SDP media descriptions. That's so iconic, because one set of Interactive Connectivity Establishment (ICE) [RFC8445] candidates can cover multiple media descriptions. The catch is that now we have to figure out what the SDP attributes actually mean when they're multiplexed 🧚
There are so many SDP attributes registered with the [IANA], and more can show up later, so we need a framework to check whether each attribute even makes sense for transport multiplexing 💅
The document kicks off by explaining why we need this framework 🎀 Then it introduces the framework and its procedures, and after that, several sections apply the framework to the SDP attributes registered with the [IANA] 📚
2. Terminology 🌈
5-tuple: A collection of these values: source address, source port, destination address, destination port, and transport-layer protocol ✨
3GPP: Third Generation Partnership Project. More info is at https://www.3gpp.org 🌍
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be read as described in BCP 14 [RFC2119] [RFC8174], but only when they appear in all capitals, as shown here 🫶
3. Motivation 💜
Cutting down on the number of transport-level flows is kind of a must-do, because setting up Secure Real-time Transport Protocol (SRTP) [RFC5763] transports for RTP takes time and gets complicated when you're using ICE [RFC8445] and Datagram Transport Layer Security (DTLS) 😭 These procedures make conserving port bindings on Network Address Translators (NATs) super important 🙈 That's why people came up with ways, like the one in [RFC8843], to multiplex RTP over a single transport flow and save network resources such as port numbers 🔥 But this adds more restrictions on how the SDP attributes can be used, as they're defined today 💀
Here's the real problem: some attribute combos make perfect sense on independent "m=" lines, the way classic SDP works, but make zero sense once those "m=" lines get multiplexed over the same transport 🤯 For an obvious example, ICE lets each "m=" line have its own independently specified "ice-ufrag" attribute. But if media from several "m=" lines is multiplexed over the same ICE component, the meaning of media-level "ice-ufrag" attributes gets totally muddled 😵💫
Right now there are close to 250 SDP attributes registered with the [IANA], and more are coming 🌸 There's no clearly defined procedure for checking whether these attributes are valid or applicable when used with transport multiplexing 🥺
Part 1 of 21 ✨ Part 2 is next, bestie 💖
4. SDP Attribute Analysis Framework ✨
okay so attributes in an SDP session description can live at the session level, the media level, or the source level 🎀 informally, there are a bunch of semantic groupings for them. One vibe could look like this:
- Attributes about the media content itself, like media type, encoding schemes, and payload types 🎵
- Attributes about how the media gets transported, like RTP/RTP Control Protocol (RTCP) port numbers, network addresses, and QoS 🚚
- Metadata description attributes that capture session timing and origin info ⏰
- Attributes that set up relationships between media descriptions, like the grouping framework [RFC5888] 🫶
this framework looks at how SDP attributes behave under multiplexing, and it assigns each attribute to a multiplexing category 💅 since these categories are totally separate from those informal groupings, the category assignments are normative (so they're the actual rules, not just vibes).
4.1. Category: NORMAL 😌
the NORMAL attributes are the chill ones. they can be specified independently when multiplexed, and they keep their original semantics.
in the example below, the direction and label attributes are specified independently for the audio and video "m=" lines. multiplexing these media streams over a single transport-layer flow doesn't mess with them 🙌
v=0
o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
s=
c=IN IP4 host.atlanta.example.com
t=0 0
m=audio 49172 RTP/AVP 99
a=sendonly
a=label:1
a=rtpmap:99 iLBC/8000
m=video 49172 RTP/AVP 31
a=recvonly
a=label:2
a=rtpmap:31 H261/900004.2. Category: CAUTION 🚨
it's not advisable to multiplex with the CAUTION attributes, bestie. using them under multiplexing might lead to incorrect behavior 💀
Example: multiplexing media descriptions over a single Datagram Congestion Control Protocol (DCCP) transport [RFC5762] is not recommended, since DCCP is a connection-oriented protocol and therefore doesn't allow multiple connections on the same 5-tuple. big no 🙅♀️
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=
c=IN IP4 client.biloxi.example.com
t=0 0
m=video 5004 DCCP/RTP/AVP 99
a=rtpmap:99 h261/9000
a=dccp-service-code:SC=x52545056
a=setup:passive
a=connection:new
m=video 5004 DCCP/RTP/AVP 100
a=rtpmap:100 h261/9000
a=dccp-service-code:SC=x5254504f
a=setup:passive
a=connection:new4.3. Category: IDENTICAL 🔁
the IDENTICAL attributes (and their values, if they have any) MUST be repeated across all the media descriptions under multiplexing. no skipping, periodt 💖
stuff like rtcp-mux lands in this category ✨ bc RTCP reporting happens per RTP session, RTCP multiplexing MUST be enabled for both the audio and video "m=" lines if they're transported over a single 5-tuple 🎧
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=
c=IN IP4 client.biloxi.example.com
t=0 0
m=audio 34567 RTP/AVP 97
a=rtcp-mux
m=video 34567 RTP/AVP 31
a=rtpmap:31 H261/90000
a=rtcp-muxNote: even tho IDENTICAL attributes must be repeated across all media descriptions under multiplexing, they might not always be explicitly encoded across all of them. [RFC8843] defines rules for when attributes and their values are implicitly applied to a media description 🧠
4.4. Category: SUM 🧮
the SUM attributes can be set the way they're normally used, but software using them in the multiplexing scenario MUST apply the sum of all the attributes being multiplexed instead of trying to use them independently. this is typically used for bandwidth or other rate-limiting attributes to the underlying transport. math era 📊
the software parsing the SDP sample below should use the aggregate Application Specific (AS) bandwidth value from the individual media descriptions to determine the AS value for the multiplexed session. so the calculated AS value would be 256+64 kilobits per second for the given example ✨
v=0
o=test 2890844526 2890842807 IN IP4 client.biloxi.example.com
c=IN IP4 client.biloxi.example.com
t=0 0
m=audio 49170 RTP/AVP 0
b=AS:64
m=video 51372 RTP/AVP 31
b=AS:2564.5. Category: TRANSPORT 🚀
the TRANSPORT attributes can be set normally for multiple items in a multiplexed group, but the software MUST pick the one that's associated with the "m=" line whose information is used for setting up the underlying transport. one pick, no drama 🎯
in the example below, the "a=crypto" attribute is defined for both the audio and video "m=" lines. the video media line's "a=crypto" attribute gets chosen since its MID value (bar) appears first in the "a=group:BUNDLE" line. this happens because of the BUNDLE grouping semantic [RFC8843], which mandates that the values from the "m=" line corresponding to the mid appearing first on the "a=group:BUNDLE" line be considered for setting up the RTP transport 🫶
v=0
o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
s=
c=IN IP4 host.atlanta.example.com
t=0 0
a=group:BUNDLE bar foo
m=audio 49172 RTP/AVP 99
a=mid:foo
a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:d0RmdmcmVCspeEc3QGZiNWpVLFJhQX1cfHAwJSoj|2^20|1:32
a=rtpmap:99 iLBC/8000
m=video 51374 RTP/AVP 31
a=mid:bar
a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:EcGZiNWpFJhQXdspcl1ekcmVCNWpVLcfHAwJSoj|2^20|1:32
a=rtpmap:96 H261/900004.6. Category: INHERIT 🎁
the INHERIT attributes are the ones that wrap up other SDP attributes or parameters. they inherit their multiplexing characteristics from whatever they encapsulate. these ones are defined in [RFC3407], [RFC5939], and [RFC6871] as part of a generic framework for indicating and negotiating capabilities in the SDP related to transport, media, and media format 🧃
the inheritance shows up when the encapsulated attribute or parameter is actually being used. with SDP Capability Negotiation [RFC5939], for example, this happens when a capability (the encapsulating attribute) is used as part of a configuration. the configuration inherits the multiplexing category of each of its constituent (encapsulated) attributes and parameters. the inherited attributes MUST be coherent in order to form a valid configuration from a multiplexing point of view (see Section 14 for further details) 👀
v=0
o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
s=
c=IN IP4 host.atlanta.example.com
t=0 0
m=video 3456 RTP/AVP 100
a=rtpmap:100 VP8/90000
a=fmtp:100 max-fr=30;max-fs=8040
a=sqn: 0
a=cdsc: 1 video RTP/AVP 100
a=cpar: a=rtcp-mux
m=video 3456 RTP/AVP 101
a=rtpmap:101 VP8/90000
a=fmtp:100 max-fr=15;max-fs=1200
a=cdsc: 2 video RTP/AVP 101
a=cpar: a=rtcp-muxin this example, the IDENTICAL category gets inherited by the cpar-encapsulated "rtcp-mux" attribute 🌸
4.7. Category: IDENTICAL-PER-PT 🎬
the IDENTICAL-PER-PT attributes define the RTP payload configuration based on the payload type, and they MUST have identical values across all the media descriptions for a given RTP payload type when repeated. these payload types identify the same codec configuration as defined in Section 9.1 of [RFC8843] under this context 🎥
in the SDP example below, Payload Types 96 and 97 are repeated across all the video "m=" lines, and all the payload-specific parameters (for example, rtpmap and fmtp) are identical. (note: some line breaks are due to formatting only 🙈)
v=0
o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
s=
c=IN IP4 host.atlanta.example.com
t=0 0
a=group:BUNDLE cam1 cam2
m=video 96 97
a=mid:cam1
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42400d; max-fs=3600; max-fps=3000;
max-mbps=108000; max-br=1000
a=rtpmap:97 H264/90000
a=fmtp:97 profile-level-id=42400a; max-fs=240; max-fps=3000;
max-mbps=7200; max-br=200
m=video 96 97
a=mid:cam2
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42400d; max-fs=3600; max-fps=3000;
max-mbps=108000; max-br=1000
a=rtpmap:97 H264/90000
a=fmtp:97 profile-level-id=42400a; max-fs=240; max-fps=3000;
max-mbps=7200; max-br=2004.8. Category: SPECIAL 🪄
for the SPECIAL attributes, the text in the specification defining the attribute MUST be consulted for further handling when multiplexed. read the fine print, babe 📖
as an example, for the "extmap" attribute [RFC5285], the specification defining the extension needs to be consulted to understand the multiplexing implications.
4.9. Category: TBD 🕰️
the TBD attributes haven't been analyzed under the proposed multiplexing framework yet, so they SHOULD NOT be multiplexed. not yet, bestie 🙃
5. Analysis of Existing Attributes 📚
this section analyzes attributes listed in [IANA], grouped under the IETF document that defines them 🗂️
the "Level" column indicates whether the attribute is currently specified as:
S-- Session levelM-- Media levelB-- Both (implies either a session level or a media level attribute)SR-- Source-level (for a single SSRC) [RFC5576]
the "Mux Category" column identifies the multiplexing category assigned to each attribute, and the "Notes" column captures additional informative details about the assigned category wherever necessary 💜
5.1. RFC 4566: SDP 🎀
okay so [RFC4566] is literally the SDP spec itself 🧚 It's built for describing multimedia sessions, whether you're announcing one, inviting someone to one, or starting one up in some other way. Here's how its attributes shake out:
+================+=====================+=======+==================+
| Name | Notes | Level | Mux Category |
+================+=====================+=======+==================+
| sendrecv | Not impacted | B | NORMAL |
+----------------+---------------------+-------+------------------+
| sendonly | Not impacted | B | NORMAL |
+----------------+---------------------+-------+------------------+
| recvonly | Not impacted | B | NORMAL |
+----------------+---------------------+-------+------------------+
| inactive | Not impacted | B | NORMAL |
+----------------+---------------------+-------+------------------+
| cat | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| ptime | The attribute value | M | IDENTICAL-PER-PT |
| | MUST be the same | | |
| | for a given codec | | |
| | configuration. | | |
+----------------+---------------------+-------+------------------+
| maxptime | The attribute value | M | IDENTICAL-PER-PT |
| | MUST be the same | | |
| | for a given codec | | |
| | configuration. | | |
+----------------+---------------------+-------+------------------+
| orient | Not impacted | M | NORMAL |
+----------------+---------------------+-------+------------------+
| framerate | The attribute value | M | IDENTICAL-PER-PT |
| | MUST be the same | | |
| | for a given codec | | |
| | configuration. | | |
+----------------+---------------------+-------+------------------+
| quality | Not impacted | M | NORMAL |
+----------------+---------------------+-------+------------------+
| rtpmap | The attribute value | M | IDENTICAL-PER-PT |
| | MUST be the same | | |
| | for a given codec | | |
| | configuration. | | |
+----------------+---------------------+-------+------------------+
| fmtp | The attribute value | M | IDENTICAL-PER-PT |
| | MUST be the same | | |
| | for a given codec | | |
| | configuration. | | |
+----------------+---------------------+-------+------------------+
| keywds | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| type | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| type:broadcast | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| type:H332 | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| type:meeting | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| type:moderated | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| type:test | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| tool | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| charset | Not impacted | S | NORMAL |
+----------------+---------------------+-------+------------------+
| sdplang | Not impacted | B | NORMAL |
+----------------+---------------------+-------+------------------+
| lang | Not impacted | B | NORMAL |
+----------------+---------------------+-------+------------------+
Table 1: RFC 4566 Attribute Analysis5.2. RFC 4585: RTP/AVPF 💜
[RFC4585] is the one that extends the Audio-visual Profile (AVP) so receivers can send feedback to senders way more quickly 🔥 That means short-term adaptation and feedback-based repair can actually happen. The one attribute here is rtcp-fb, and it's giving "scoped per payload type" energy:
+=========+===========================+=======+==================+
| Name | Notes | Level | Mux Category |
+=========+===========================+=======+==================+
| rtcp-fb | Since RTCP feedback | M | IDENTICAL-PER-PT |
| | attributes are scoped by | | |
| | payload type (PT), their | | |
| | values MUST be identical | | |
| | for a given PT across the | | |
| | multiplexed "m=" lines. | | |
+---------+---------------------------+-------+------------------+
Table 2: RFC 4585 Attribute Analysis5.3. RFC 5761: Multiplexing RTP and RTCP 🦋
[RFC5761] is all about the drama of putting RTP data packets and RTP Control Protocol (RTCP) packets on one single UDP port 😭 It explains when that multiplexing is a yes and when it's a hard no, and how SDP signals a multiplexed session.
+==========+=================================+=======+==============+
| Name | Notes | Level | Mux |
| | | | Category |
+==========+=================================+=======+==============+
| rtcp-mux | RTP and RTCP multiplexing | M | IDENTICAL |
| | affects the entire RTP session. | | |
+----------+---------------------------------+-------+--------------+
Table 3: RFC 5761 Attribute Analysis5.4. RFC 3312: Integration of Resource Management and SIP ✨
[RFC3312] sets up a generic framework for preconditions, and it's extensible through IANA registration 🍓 It also covers how network quality of service can be a precondition before a Session Initiation Protocol (SIP) session gets established. So the participant has to reserve network resources before the session can keep going. Very responsible, very iconic.
+======+======================+=======+==============+
| Name | Notes | Level | Mux Category |
+======+======================+=======+==============+
| des | Refer to notes below | M | CAUTION |
+------+----------------------+-------+--------------+
| conf | Refer to notes below | M | CAUTION |
+------+----------------------+-------+--------------+
| curr | Refer to notes below | M | CAUTION |
+------+----------------------+-------+--------------+
Table 4: RFC 3312 Attribute AnalysisNOTE: A mismatched set of preconditions across media descriptions results in session establishment failures due to inability to meet the requested resource reservations. 🙈
5.5. RFC 4574: SDP "label" Attribute 🌸
[RFC4574] adds a brand new media-level attribute called "label" 🧚 It carries a pointer to a media stream, for any network application that uses SDP. The sender can attach it to one stream or several, and the application can then use that pointer to refer to each stream in its own context. Simple, cute, useful.
+=======+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+=======+==============+=======+==============+
| label | Not impacted | M | NORMAL |
+-------+--------------+-------+--------------+
Table 5: RFC 4574 Attribute Analysis5.6. RFC 5432: QoS Mechanism Selection in SDP 👑
[RFC5432] is the procedure for negotiating QoS mechanisms using the SDP offer/answer model. Choosing your QoS mechanism with a friend, honestly so iconic 💅
+===============+======================+=======+==============+
| Name | Notes | Level | Mux Category |
+===============+======================+=======+==============+
| qos-mech-send | Refer to Section 10. | B | TRANSPORT |
+---------------+----------------------+-------+--------------+
| qos-mech-recv | Refer to Section 10. | B | TRANSPORT |
+---------------+----------------------+-------+--------------+
Table 6: RFC 5432 Attribute Analysis5.7. RFC 4568: SDP Security Descriptions 🔥
[RFC4568] defines an SDP cryptographic attribute for unicast media streams 🔐 The attribute describes a cryptographic key and other parameters that configure security for a unicast media stream, whether that's in one message or a roundtrip exchange. This one's serious, bestie, so pay attention 🫶
+========+=================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+========+=================================+=======+===========+
| crypto | crypto attribute MUST be the | M | TRANSPORT |
| | one that corresponds to the | | |
| | "m=" line chosen for setting up | | |
| | the underlying transport flow. | | |
+--------+---------------------------------+-------+-----------+
Table 7: RFC 4568 Attribute Analysis5.8. RFC 5762: RTP over DCCP 💖
okay so RTP is basically the go-to transport for real-time multimedia on IP networks 🎥, and DCCP is a transport protocol that gives real-time apps some really desirable services 🫶. [RFC5762] is the spec that maps RTP onto DCCP, plus the signaling that goes with it, so real-time apps can actually use what DCCP offers ✨. it's giving teamwork 🤝
+===================+======================+=========+==========+
| Name | Notes | Current | Mux |
| | | | Category |
+===================+======================+=========+==========+
| dccp-service-code | If RFC 6773 is not | M | CAUTION |
| | being used in | | |
| | addition to RFC5762, | | |
| | the port in the "m=" | | |
| | line is a DCCP port. | | |
| | Being a connection- | | |
| | oriented protocol, | | |
| | DCCP does not allow | | |
| | multiple connections | | |
| | on the same 5-tuple. | | |
+-------------------+----------------------+---------+----------+
Table 8: RFC 5762 Attribute AnalysisNOTE: ok bestie, this one's a bit of a plot twist 🙈. if RFC 6773 is being used alongside RFC 5762, and the DCCP-in-UDP layer has extra demultiplexing going on, it might be possible to give each DCCP flow its own service code, since each one uses a different DCCP port 🧚. BUT doing that could clash with the media type on the "m=" line 💀. none of this is standardized yet, and honestly it wouldn't work the way I just described 😭. so multiplexing is not recommended even in this alternate scenario 🚫
5.9. RFC 6773: DCCP-UDP Encapsulation 🦋
so [RFC6773] comes in with an alternative way to encapsulate DCCP, called DCCP-UDP 🌈. the main slay here is that it lets DCCP travel through today's generation of Network Address Translation (NAT) middleboxes without anyone having to modify those boxes 💅
+===========+==============================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+===========+==============================+=======+==========+
| dccp-port | Multiplexing is not | M | CAUTION |
| | recommended due to potential | | |
| | conflict between the port | | |
| | used for DCCP encapsulation/ | | |
| | decapsulation and the RTP. | | |
+-----------+------------------------------+-------+----------+
Table 9: RFC 6773 Attribute AnalysisNOTE: so RFC 6773 allows DCCP-UDP encapsulation, where the UDP port is the port of the DCCP encapsulation/decapsulation service 🎀. this lets arbitrary DCCP packets get encapsulated, and the DCCP port you pick could collide with the port you picked for the RTP traffic 😬. if you multiplex several DCCP-in-UDP encapsulations on the same UDP port, with no RTP traffic on that port, you're basically squishing several DCCP port spaces together 🫠. whether that works depends on the nature of the DCCP encapsulation and the port choices, so it's super application dependent 🔮
5.10. RFC 5506: Reduced-Size RTCP in RTP Profile 🌸
[RFC5506] is all about the benefits and the issues that show up when RTCP packets are allowed to be sent at reduced size 📦. it's a whole vibe with real tradeoffs 🧐
+============+===========================+=======+==============+
| Name | Notes | Level | Mux Category |
+============+===========================+=======+==============+
| rtcp-rsize | Reduced-size RTCP affects | M | IDENTICAL |
| | the entire RTP session. | | |
+------------+---------------------------+-------+--------------+
Table 10: RFC 5506 Attribute Analysis5.11. RFC 6787: Media Resource Control Protocol Version 2 🎀
okay the Media Resource Control Protocol Version 2 (MRCPv2) lets client hosts control media service resources like speech synthesizers, recognizers, verifiers, and identifiers that live on servers in the network 🗣️. MRCPv2 is not a "stand-alone" protocol, no cap 🙅♀️. it leans on other protocols, like SIP, to coordinate MRCPv2 clients and servers and manage the session between them, and on SDP to describe, discover, and exchange capabilities 🧩. it also relies on SIP and SDP to set up the media sessions and their parameters between the media source or sink and the media server 📞. once that's done, the MRCPv2 exchange runs over the control session set up above, so the client can control the media-processing resources on the speech resource server 🫶. [RFC6787] defines the attributes for this purpose ✨
+==========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+==========+==============+=======+==============+
| resource | Not impacted | M | NORMAL |
+----------+--------------+-------+--------------+
| channel | Not impacted | M | NORMAL |
+----------+--------------+-------+--------------+
| cmid | Not impacted | M | NORMAL |
+----------+--------------+-------+--------------+
Table 11: RFC 6787 Attribute Analysis5.12. RFC 8445: ICE 🧚
[RFC8445] describes a NAT traversal protocol for UDP-based multimedia sessions set up with the offer/answer model 🌐. ICE uses the Session Traversal Utilities for NAT (STUN) protocol and its extension, Traversal Using Relay NAT (TURN) 🔁. and ICE can be used by any protocol that uses the offer/answer model, like SIP 📞
+===================+===========================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+===================+===========================+=======+===========+
| ice-lite | Not impacted | S | NORMAL |
+-------------------+---------------------------+-------+-----------+
| ice-options | Not impacted | S | NORMAL |
+-------------------+---------------------------+-------+-----------+
| ice-mismatch | Not impacted | S | NORMAL |
+-------------------+---------------------------+-------+-----------+
| ice-pwd | ice-pwd MUST be the one | B | TRANSPORT |
| | that corresponds to the | | |
| | "m=" line chosen for | | |
| | setting up the | | |
| | underlying transport | | |
| | flow. | | |
+-------------------+---------------------------+-------+-----------+
| ice-ufrag | ice-ufrag MUST be the | B | TRANSPORT |
| | one that corresponds to | | |
| | the "m=" line chosen | | |
| | for setting up the | | |
| | underlying transport | | |
| | flow. | | |
+-------------------+---------------------------+-------+-----------+
| candidate | ice candidate MUST be | M | TRANSPORT |
| | the one that | | |
| | corresponds to the "m=" | | |
| | line chosen for setting | | |
| | up the underlying | | |
| | transport flow. | | |
+-------------------+---------------------------+-------+-----------+
| remote-candidates | ice remote candidate | M | TRANSPORT |
| | MUST be the one that | | |
| | corresponds to the "m=" | | |
| | line chosen for setting | | |
| | up the underlying | | |
| | transport flow. | | |
+-------------------+---------------------------+-------+-----------+
| ice2 | Not impacted | S | NORMAL |
+-------------------+---------------------------+-------+-----------+
Table 12: RFC 8445 Attribute Analysis5.13. RFC 5285: RTP Header Extensions ✨
[RFC5285] gives us a general mechanism for using RTP's header-extension feature 🧩. (heads up: [RFC5285] has been obsoleted by [RFC8285] 🙈.) it lets each RTP packet carry a small number of small extensions, where the universe of possible extensions is huge and registration is decentralized 🌍. the extensions actually in use for a session get signaled in that session's setup information 📝
+========+================================+=======+==============+
| Name | Notes | Level | Mux Category |
+========+================================+=======+==============+
| extmap | Refer to the document defining | B | SPECIAL |
| | the specific RTP extension. | | |
+--------+--------------------------------+-------+--------------+
Table 13: RFC 5285 Attribute Analysis5.14. RFC 3605: RTCP Attribute in SDP 👑
okay so originally, SDP assumed that RTP and RTCP were carried on consecutive ports 🙃. but that's not always true once NATs are involved 🌀. [RFC3605] specifies an early mechanism for indicating the RTCP port 🎯
+======+================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+======+================================+=======+===========+
| rtcp | RTCP port MUST be the one that | M | TRANSPORT |
| | corresponds to the "m=" line | | |
| | chosen for setting up the | | |
| | underlying transport flow. | | |
+------+--------------------------------+-------+-----------+
Table 14: RFC 3605 Attribute Analysis5.15. RFC 5576: Source-Specific SDP Attributes ✨
okay so [RFC5576] is all about the SSRC (synchronization source) IDs that name each RTP media source 🎀. It lets you describe those sources inside SDP, attach attributes to each one, and show how sources relate to each other 💅. It also defines a bunch of source-level attributes for describing properties of each media source 💜.
+===============+=====================+=======+==================+
| Name | Notes | Level | Mux Category |
+===============+=====================+=======+==================+
| ssrc | Refer to notes | M | NORMAL |
| | below. | | |
+---------------+---------------------+-------+------------------+
| ssrc-group | Refer to Section 9 | M | NORMAL |
| | for specific | | |
| | analysis of the | | |
| | grouping semantics. | | |
+---------------+---------------------+-------+------------------+
| cname | Not impacted | SR | NORMAL |
+---------------+---------------------+-------+------------------+
| previous-ssrc | Refer to notes | SR | NORMAL |
| | below | | |
+---------------+---------------------+-------+------------------+
| fmtp | The attribute value | SR | IDENTICAL-PER-PT |
| | MUST be the same | | |
| | for a given codec | | |
| | configuration. | | |
+---------------+---------------------+-------+------------------+
Table 15: RFC 5576 Attribute AnalysisNOTE: If SSRCs are repeated across "m=" lines being multiplexed, they MUST all represent the same underlying RTP Source. 🫶
5.16. RFC 7273: RTP Clock Source Signaling ⏰
[RFC7273] is the clock one 🕰️. It specifies SDP signaling that identifies timestamp reference clock sources, plus SDP signaling that identifies the media clock sources in a multimedia session. Lowkey a lot of attributes, but they're all the same vibe 🌈.
+===================+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+===================+==============+=======+==============+
| ts-refclk | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| mediaclk | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| ts-refclk:ntp | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| ts-refclk:ptp | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| ts-refclk:gps | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| ts-refclk:gal | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| ts-refclk:glonass | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| ts-refclk:local | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| ts-refclk:private | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| mediaclk:sender | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| mediaclk:direct | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
| mediaclk:IEEE1722 | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
Table 16: RFC 7273 Attribute Analysis5.17. RFC 6236: Image Attributes in SDP 🖼️
[RFC6236] proposes a new generic session setup attribute so you can negotiate different image attributes, like image size 🌸. The big use case is a low-end handheld that wants to show video without rescaling the image, which can gobble up memory and processing power 😭. It also helps keep the bitrate sensible, because only the image size the receiver actually wants gets sent 🦋.
+===========+==========================+=======+==================+
| Name | Notes | Level | Mux Category |
+===========+==========================+=======+==================+
| imageattr | The attribute value MUST | M | IDENTICAL-PER-PT |
| | be the same for a given | | |
| | codec configuration. | | |
+-----------+--------------------------+-------+------------------+
Table 17: RFC 6236 Attribute Analysis5.18. RFC 7197: Duplication Delay Attribute in SDP 🍓
[RFC7197] defines an attribute that tells you whether there are temporally redundant media streams, and what the duplication delay is, all in SDP ⏳.
+===================+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+===================+==============+=======+==============+
| duplication-delay | Not impacted | B | NORMAL |
+-------------------+--------------+-------+--------------+
Table 18: RFC 7197 Attribute Analysis5.19. RFC 7266: RTCP XR Blocks for MOS Metric Reporting 📊
[RFC7266] defines an RTCP Extended Report (XR) Block with two new segment types and matching SDP parameters, so you can report mean opinion score (MOS) metrics across a range of RTP applications 🌟. Basically it's how you grade call quality, and it's giving main character energy 👑.
+============+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+============+==============+=======+==============+
| calgextmap | Not impacted | B | NORMAL |
+------------+--------------+-------+--------------+
Table 19: RFC 7266 Attribute Analysis5.20. RFC 6285: Rapid Acquisition of Multicast RTP Sessions 🚀
[RFC6285] describes a way to reuse the existing RTP and RTCP machinery so that acquisition delay goes down ⚡. The trick is an auxiliary unicast RTP session that carries the reference info to the receiver, arriving before or alongside the multicast stream. That unicast flow can even be sent faster than its natural bitrate to speed things up even more 🏎️. The motivating use case is multicast apps carrying real-time compressed audio and video 🎶.
Heads up bestie: the table below marks this attribute as "Not recommended" with a CAUTION mux category, so read that one carefully 🙈.
+==============+=================+=======+==============+
| Name | Notes | Level | Mux Category |
+==============+=================+=======+==============+
| rams-updates | Not recommended | M | CAUTION |
+--------------+-----------------+-------+--------------+
Table 20: RFC 6285 Attribute Analysis5.21. RFC 6230: Media Control Channel Framework 🎛️
[RFC6230] describes a framework and protocol for app deployments where the application logic and media processing are split up 🧩. That means the app logic can seamlessly reach resources that aren't on the same physical box. The framework uses SIP to set up an application-level control channel between application servers and their external servers, like media servers 💜.
+========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+========+==============+=======+==============+
| cfw-id | Not impacted | M | NORMAL |
+--------+--------------+-------+--------------+
Table 21: RFC 6230 Attribute Analysis5.22. RFC 6364: SDP Elements for FEC Framework 🛡️
[RFC6364] specifies how to use SDP to describe the parameters needed to signal the Forward Error Correction (FEC) Framework Configuration Information between senders and receivers 📡. It also includes examples showing how to group multiple source and repair flows together for apps that run several instances of the FEC Framework at once 🧁.
+=================+======================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+=================+======================+=======+==========+
| fec-source-flow | Refer to the | M | SPECIAL |
| | document defining | | |
| | specific FEC scheme. | | |
+-----------------+----------------------+-------+----------+
| fec-repair-flow | Refer to the | M | SPECIAL |
| | document defining | | |
| | specific FEC scheme. | | |
+-----------------+----------------------+-------+----------+
| repair-window | Refer to the | M | SPECIAL |
| | document defining | | |
| | specific FEC scheme. | | |
+-----------------+----------------------+-------+----------+
Table 22: RFC 6364 Attribute Analysis5.23. RFC 4796: "content" Attribute 🎬
[RFC4796] adds a new SDP media-level attribute called "content" ✨. It describes the content of a media stream in more detail than the media description line does 🌷. The sender can attach it to one or more media streams, and then the receiving app can treat each stream differently, like putting it on a big screen or a small one, based on what it contains 📺.
+=========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+=========+==============+=======+==============+
| content | Not impacted | M | NORMAL |
+---------+--------------+-------+--------------+
Table 23: RFC 4796 Attribute Analysis5.24. RFC 3407: SDP Simple Capability Declaration ✨
okay so [RFC3407] gives SDP a set of attributes for declaring capabilities 🎀 It's minimal, and it's backwards-compatible, so older SDP parsers aren't going to freak out over it 💖
+=========+======================+=======+==============+
| Name | Notes | Level | Mux Category |
+=========+======================+=======+==============+
| sqn | Not impacted | B | NORMAL |
+---------+----------------------+-------+--------------+
| cdsc | Not impacted | B | NORMAL |
+---------+----------------------+-------+--------------+
| cpar | Refer to Section 14 | B | INHERIT |
+---------+----------------------+-------+--------------+
| cparmin | Refer to notes below | B | SPECIAL |
+---------+----------------------+-------+--------------+
| cparmax | Refer to notes below | B | SPECIAL |
+---------+----------------------+-------+--------------+
Table 24: RFC 3407 Attribute AnalysisNOTE: the attributes "a=cparmin" and "a=cparmax" define minimum and maximum numerical values for the attributes described in "a=cpar" 📏✨
NOTE: "cpar" can define a "b=" attribute or any "a=" attribute, so its multiplexing category depends on which attribute it's wrapping and what the numbers end up meaning 🤔 That's why it's recommended to check the spec that defines "cparmin" and "cparmax" to see how they behave under multiplexing. It's a whole vibe, bestie 🧠💅
5.25. RFC 6284: Port Mapping between Unicast and Multicast RTP Sessions 🦋
okay this one is so cool 😭 [RFC6284] has a port-mapping solution that lets RTP receivers pick their own ports for an auxiliary unicast session, in apps that use both unicast and multicast 🌸 It also protects against denial-of-service or packet amplification attacks that could be used to send one or more RTP packets to a victim client. Not me being impressed 💀🔥
+=================+=========================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+=================+=========================+=======+==========+
| portmapping-req | Not recommended if port | M | CAUTION |
| | mapping is required by | | |
| | the application | | |
+-----------------+-------------------------+-------+----------+
Table 25: RFC 6284 Attribute Analysis5.26. RFC 6714: MSRP-CEMA 🌈
[RFC6714] defines an extension to the Message Session Relay Protocol (MSRP) called Connection Establishment for Media Anchoring (CEMA) 🧚 Supporting it is optional, so it's totally your call bestie 💜 The extension lets middleboxes anchor the MSRP connection without having to modify the MSRP messages themselves. That means it also enables secure end-to-end MSRP communication in networks where those middleboxes are deployed, which is honestly iconic 👑 The document also defines an SDP attribute, "msrp-cema", that MSRP endpoints use to say they support the CEMA extension ✨
+===========+======================+=======+==============+
| Name | Notes | Level | Mux Category |
+===========+======================+=======+==============+
| msrp-cema | Refer to notes below | M | TBD |
+-----------+----------------------+-------+--------------+
Table 26: RFC 6714 Attribute AnalysisNOTE: as per Section 9 of [RFC8843], there isn't any publicly available spec yet that defines how to multiplex or demultiplex MSRP flows over a single 5-tuple 😩 Once one shows up, the multiplexing category assignments for the attributes in this section could be revisited 🫶
5.27. RFC 4583: SDP Format for BFCP Streams 🎀
[RFC4583] explains how to describe Binary Floor Control Protocol (BFCP) streams in SDP descriptions 📝 User agents that use the offer/answer model to set up BFCP streams use this format in their offers and answers, so it's a big deal for them 💅
+===========+======================+=======+==============+
| Name | Notes | Level | Mux Category |
+===========+======================+=======+==============+
| floorctrl | Refer to notes below | M | TBD |
+-----------+----------------------+-------+--------------+
| confid | Refer to notes below | M | TBD |
+-----------+----------------------+-------+--------------+
| userid | Refer to notes below | M | TBD |
+-----------+----------------------+-------+--------------+
| floorid | Refer to notes below | M | TBD |
+-----------+----------------------+-------+--------------+
Table 27: RFC 4583 Attribute AnalysisNOTE: [RFC4583] has been obsoleted by [RFC8856], which redefines the SDP attributes listed in this section, including the "Mux Category" values 🔄 However, [RFC8856] doesn't change the "Mux Category" values of the attributes, so the plot stays the same 🌸
NOTE: as per Section 9 of [RFC8843], there isn't any publicly available spec that defines how to multiplex or demultiplex BFCP streams over a single 5-tuple 🙈 Once that spec exists, the multiplexing category assignments for the attributes in this section could be revisited 💜
5.28. RFC 5547: SDP Offer/Answer for File Transfer 📁
okay file transfer era 🦋 [RFC5547] gives you a way to negotiate transferring one or more files between two endpoints, using the SDP offer/answer model from [RFC3264] 🚀 It's giving organised sharing energy ✨
+==================+======================+=======+==============+
| Name | Notes | Level | Mux Category |
+==================+======================+=======+==============+
| file-selector | Refer to notes below | M | TBD |
+------------------+----------------------+-------+--------------+
| file-transfer-id | Refer to notes below | M | TBD |
+------------------+----------------------+-------+--------------+
| file-disposition | Refer to notes below | M | TBD |
+------------------+----------------------+-------+--------------+
| file-date | Refer to notes below | M | TBD |
+------------------+----------------------+-------+--------------+
| file-icon | Refer to notes below | M | TBD |
+------------------+----------------------+-------+--------------+
| file-range | Refer to notes below | M | TBD |
+------------------+----------------------+-------+--------------+
Table 28: RFC 5547 Attribute AnalysisNOTE: as per Section 9 of [RFC8843], there isn't any publicly available spec that defines how to multiplex or demultiplex MSRP flows over a single 5-tuple 😭 Once one is available, the multiplexing category assignments for attributes in this section could be revisited 🫶
5.29. RFC 6849: SDP and RTP Media Loopback Extension 🔁
[RFC6849] adds new SDP media types and attributes so you can set up media sessions where the media gets looped back to the transmitter 🎀 These sessions work as monitoring and troubleshooting tools, giving you ways to measure more advanced Voice over IP (VoIP), real-time text, and Video over IP performance metrics. Measurement main character energy 📊👑
+====================+================+=======+==================+
| Name | Notes | Level | Mux Category |
+====================+================+=======+==================+
| loopback rtp-pkt- | The attribute | M | IDENTICAL-PER-PT |
| loopback | value MUST be | | |
| | same for a | | |
| | given codec | | |
| | configuration. | | |
+--------------------+----------------+-------+------------------+
| loopback rtp- | The attribute | M | IDENTICAL-PER-PT |
| media-loopback | value MUST be | | |
| | same for a | | |
| | given codec | | |
| | configuration. | | |
+--------------------+----------------+-------+------------------+
| loopback-source | Not impacted | M | NORMAL |
+--------------------+----------------+-------+------------------+
| loopback-mirror | Not impacted | M | NORMAL |
+--------------------+----------------+-------+------------------+
Table 29: RFC 6849 Analysis5.30. RFC 5760: RTCP with Unicast Feedback 💌
[RFC5760] extends RTCP so receivers can send unicast feedback to a multicast sender 💖 This is super useful for single-source multicast sessions, like source-specific multicast (SSM) communication, where the usual many-to-many group model isn't available or isn't wanted 🌟
+==============+=========================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+==============+=========================+=======+===========+
| rtcp-unicast | The attribute MUST be | M | IDENTICAL |
| | reported across all | | |
| | multiplexed "m=" lines. | | |
+--------------+-------------------------+-------+-----------+
Table 30: RFC 5760 Attribute Analysis5.31. RFC 3611: RTCP XR 📈
[RFC3611] defines the Extended Report (XR) packet type for RTCP 🎀 It also explains how an application can signal the use of XR packets if it uses the Session Description Protocol (SDP) 🫧
+=========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+=========+==============+=======+==============+
| rtcp-xr | Not impacted | B | NORMAL |
+---------+--------------+-------+--------------+
Table 31: RFC 3611 Attribute Analysis5.32. RFC 5939: SDP Capability Negotiation
[RFC5939] is the big daddy of SDP capability negotiation 💅 It gives us a general framework, and it also explains how to package up attributes and transport protocols as capabilities and then negotiate them with that framework. Other kinds of capabilities, like media types and media formats, can be added later in other documents, so this is just the starting lineup 🦋
+========+=====================+=======+==============+
| Name | Notes | Level | Mux Category |
+========+=====================+=======+==============+
| pcfg | Refer to Section 14 | M | SPECIAL |
+--------+---------------------+-------+--------------+
| acfg | Refer to Section 14 | M | SPECIAL |
+--------+---------------------+-------+--------------+
| csup | Not impacted | B | NORMAL |
+--------+---------------------+-------+--------------+
| creq | Not impacted | B | NORMAL |
+--------+---------------------+-------+--------------+
| acap | Refer to Section 14 | B | INHERIT |
+--------+---------------------+-------+--------------+
| tcap | Refer to Section 14 | B | INHERIT |
+--------+---------------------+-------+--------------+
| cap-v0 | Not impacted | B | NORMAL |
+--------+---------------------+-------+--------------+
Table 32: RFC 5939 Attribute Analysis5.33. RFC 6871: SDP Media Capabilities Negotiation
Okay so SDP capability negotiation already gives you a framework for indicating and negotiating capabilities 🌸 But the base version only handles transport protocols and attributes. [RFC6871] levels up by adding media capabilities, which means you can negotiate media types and their related parameters too ✨
+========+======================+=======+==================+
| Name | Notes | Level | Mux Category |
+========+======================+=======+==================+
| rmcap | Refer to Section 14 | B | IDENTICAL-PER-PT |
+--------+----------------------+-------+------------------+
| omcap | Not impacted | B | NORMAL |
+--------+----------------------+-------+------------------+
| mfcap | Refer to Section 14 | B | IDENTICAL-PER-PT |
+--------+----------------------+-------+------------------+
| mscap | Refer to Section 14 | B | INHERIT |
+--------+----------------------+-------+------------------+
| lcfg | Refer to Section 14 | B | SPECIAL |
+--------+----------------------+-------+------------------+
| sescap | Refer to notes below | S | CAUTION |
+--------+----------------------+-------+------------------+
| med-v0 | Not impacted | S | NORMAL |
+--------+----------------------+-------+------------------+
Table 33: RFC 6871 Attribute AnalysisNOTE: The "sescap" attribute is not recommended for use with multiplexing 🙈 The reason is that it needs unique configuration numbers across the entire SDP (per [RFC6871]), whereas [RFC5939] only needs them within a single media description. As Section 14 explains, using identical configuration numbers across multiplexed (bundled) media descriptions is the default way to say "these configurations are compatible" in a bundle 💜
5.34. RFC 7006: Miscellaneous Capabilities Negotiation in SDP
[RFC7006] stretches the SDP Capability Negotiation framework so endpoints can negotiate three more SDP capabilities 🎀 Specifically, it gives us a way to negotiate bandwidth (the "b=" line), connection data (the "c=" line), and session or media titles (the "i=" line for each session or media) 🧚
+=========+==================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+=========+==================================+=======+===========+
| bcap | Inherit the category SUM as | B | INHERIT |
| | applicable to the "b=" attribute | | |
+---------+----------------------------------+-------+-----------+
| bcap-v0 | Not impacted | B | NORMAL |
+---------+----------------------------------+-------+-----------+
| ccap | The connection address type MUST | B | IDENTICAL |
| | be identical across all the | | |
| | multiplexed "m=" lines. | | |
+---------+----------------------------------+-------+-----------+
| ccap-v0 | Not impacted | B | NORMAL |
+---------+----------------------------------+-------+-----------+
| icap | Not impacted | B | NORMAL |
+---------+----------------------------------+-------+-----------+
| icap-v0 | Not impacted | B | NORMAL |
+---------+----------------------------------+-------+-----------+
Table 34: RFC 7006 Attribute Analysis5.35. RFC 4567: Key Management Extensions for SDP and RTSP
[RFC4567] adds general extensions for SDP and Real-Time Streaming Protocol (RTSP) so they can carry messages from a key management protocol, which helps secure the media 🔐 It's basically a framework, so one or more key management protocols can plug into it. That means it only really works once it's paired with an appropriate key management protocol 💅
+==========+==========================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+==========+==========================+=======+===========+
| key-mgmt | Key management protocol | B | IDENTICAL |
| | MUST be identical across | | |
| | all the "m=" lines. | | |
+----------+--------------------------+-------+-----------+
| mikey | Key management protocol | B | IDENTICAL |
| | MUST be identical across | | |
| | all the "m=" lines. | | |
+----------+--------------------------+-------+-----------+
Table 35: RFC 4567 Attribute Analysis5.36. RFC 4572: Comedia over TLS in SDP
[RFC4572] explains how to set up secure connection-oriented media transport sessions over Transport Layer Security (TLS) using SDP 🔒 It introduces a new SDP protocol identifier, "TCP/TLS", and defines the syntax and semantics for an SDP "fingerprint" attribute that identifies the certificate that will be presented for the TLS session. This works out securely, as long as the integrity of session descriptions is assured 🫶
NOTE: [RFC4572] has been obsoleted by [RFC8122] 😭
+=============+=================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+=============+=================================+=======+===========+
| fingerprint | fingerprint value MUST be | B | TRANSPORT |
| | the one that corresponds | | |
| | to the "m=" line chosen | | |
| | for setting up the | | |
| | underlying transport flow. | | |
+-------------+---------------------------------+-------+-----------+
Table 36: RFC 4572 Attribute Analysis5.37. RFC 4570: SDP Source Filters
[RFC4570] shows how to adapt SDP to express one or more source addresses as a source filter for one or more destination "connection" addresses 🌈 It defines the syntax and semantics for an SDP "source-filter" attribute that can reference IPv4 or IPv6 addresses, as either an inclusive or exclusive source list, for multicast or unicast destinations. Inclusive source filters are the ones that can specify a source-specific multicast (SSM) session ✨
+===============+=========================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+===============+=========================+=======+===========+
| source-filter | The attribute MUST be | B | IDENTICAL |
| | repeated across all | | |
| | multiplexed "m=" lines. | | |
+---------------+-------------------------+-------+-----------+
Table 37: RFC 4570 Attribute Analysis5.38. RFC 6128: RTCP Port for Multicast Sessions
SDP has an attribute that lets RTP applications specify an address and a port for the RTCP traffic 💖 In RTP-based source-specific multicast (SSM) sessions, that same attribute is used to designate the address and the RTCP port of the Feedback Target in the SDP description. But the RTCP port tied to the SSM session itself can't be specified with that attribute, because it would cause ambiguity, so it is required to be derived from the "m=" line of the media description. Deriving it from the "m=" line is an unnecessary restriction, though, and [RFC6128] fixes that by introducing a new SDP attribute 🙌
+================+==========================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+================+==========================+=======+===========+
| multicast-rtcp | Multicast RTCP port MUST | B | IDENTICAL |
| | be identical across all | | |
| | the "m=" lines. | | |
+----------------+--------------------------+-------+-----------+
Table 38: RFC 6128 Attribute Analysis5.39. RFC 6189: ZRTP
[RFC6189] defines ZRTP, a protocol for a media path Diffie-Hellman exchange. It agrees on a session key and parameters for setting up unicast SRTP sessions for VoIP applications 📞
+===========+=================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+===========+=================================+=======+===========+
| zrtp-hash | The zrtp-hash attribute MUST be | M | TRANSPORT |
| | the one that corresponds to the | | |
| | "m=" line chosen for setting up | | |
| | the underlying transport flow. | | |
+-----------+---------------------------------+-------+-----------+
Table 39: RFC 6189 Attribute Analysis5.40. RFC 4145: Connection-Oriented Media ✨
Okay bestie, [RFC4145] is all about getting media to travel over TCP using SDP 🧦. It defines the SDP "TCP" protocol identifier 💖, the SDP "setup" attribute (which covers the connection setup procedure 🔌), and the SDP "connection" attribute (which handles re-establishing the connection 🔁). Iconic.
+============+==================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+============+==================================+=======+===========+
| setup | The setup attribute MUST be the | B | TRANSPORT |
| | one that corresponds to the | | |
| | "m=" line chosen for setting up | | |
| | the underlying transport flow. | | |
+------------+----------------------------------+-------+-----------+
| connection | The connection attribute MUST | B | TRANSPORT |
| | be the one that corresponds to | | |
| | the "m=" line chosen for | | |
| | setting up the underlying | | |
| | transport flow. | | |
+------------+----------------------------------+-------+-----------+
Table 40: RFC 4145 Attribute Analysis5.41. RFC 6947: The SDP "altc" Attribute 🌸
So [RFC6947] came up with a way for one SDP offer to carry multiple IP addresses from different address families, like IPv4 and IPv6 🌐. The new "altc" attribute fixes the backward-compatibility headache that Alternative Network Address Types (ANAT) gave everyone because of their syntax 🙈. Literally a glow-up.
+======+=================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+======+=================================+=======+===========+
| altc | The IP address and port MUST be | M | TRANSPORT |
| | the ones that correspond to the | | |
| | "m=" line chosen for setting up | | |
| | the underlying transport flow. | | |
+------+---------------------------------+-------+-----------+
Table 41: RFC 6947 Attribute Analysis5.42. RFC 7195: SDP Extension for Circuit-Switched Bearers in PSTN 📞
[RFC7195] is the one that covers use cases, requirements, and protocol extensions for using the SDP offer/answer model to set up audio and video streams over circuit-switched bearers in the Public Switched Telephone Network (PSTN) 📼. Old-school phone calls, but make it SDP 💅.
+=========================+=============+=======+==============+
| Name | Notes | Level | Mux Category |
+=========================+=============+=======+==============+
| cs-correlation:callerid | Refer to | M | TBD |
| | notes below | | |
+-------------------------+-------------+-------+--------------+
| cs-correlation:uuie | Refer to | M | TBD |
| | notes below | | |
+-------------------------+-------------+-------+--------------+
| cs-correlation:dtmf | Refer to | M | TBD |
| | notes below | | |
+-------------------------+-------------+-------+--------------+
| cs-correlation:external | Refer to | M | TBD |
| | notes below | | |
+-------------------------+-------------+-------+--------------+
Table 42: RFC 7195 Attribute AnalysisNOTE: [RFC7195] defines SDP attributes for establishing audio and video media streams over circuit-switched bearers by defining a new nettype value, "PSTN". However, Section 7.2 of [RFC8843] requires the "c=" line nettype value to be "IN". If there exists in future a specification that defines procedures to multiplex media streams over nettype "PSTN", the multiplexing categories for attributes in this section could be revisited.
Okay so the tea here is the nettype clash 🫢. [RFC7195] brings in a new nettype called "PSTN", but Section 7.2 of [RFC8843] says the "c=" line has to be "IN". If a future spec ever sorts out how to multiplex over "PSTN", the multiplexing categories in this section could get another look 🔍.
5.43. RFC 7272: IDMS Using the RTP Control Protocol (RTCP) 🎵
[RFC7272] defines a new RTCP packet type and an RTCP Extended Report (XR) Block Type, both made for Inter-Destination Media Synchronization (IDMS) ⏱️. Everyone playing in sync, it's giving harmony 🎶.
+===========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+===========+==============+=======+==============+
| rtcp-idms | Not impacted | M | NORMAL |
+-----------+--------------+-------+--------------+
Table 43: RFC 7272 Attribute Analysis5.44. RFC 5159: Open Mobile Alliance (OMA) Broadcast (BCAST) SDP Attributes 📡
[RFC5159] gives us descriptions of SDP attributes used by the Open Mobile Alliance's "Service and Content Protection for Mobile Broadcast Services" specification 📻. Broadcast-level security, bestie 🔐.
+====================+===============+=======+==============+
| Name | Notes | Level | Mux Category |
+====================+===============+=======+==============+
| bcastversion | Not impacted | S | NORMAL |
+--------------------+---------------+-------+--------------+
| stkmstream | Not impacted | B | NORMAL |
+--------------------+---------------+-------+--------------+
| SRTPAuthentication | Needs further | M | TBD |
| | analysis | | |
+--------------------+---------------+-------+--------------+
| SRTPROCTxRate | Needs further | M | TBD |
| | analysis | | |
+--------------------+---------------+-------+--------------+
Table 44: RFC 5159 Attribute Analysis5.45. RFC 6193: Media Description for IKE in SDP 🔑
[RFC6193] explains how to set up a media session that represents a virtual private network using the Session Initiation Protocol, for on-demand media and application sharing between peers 🤝. It extends the protocol identifier of SDP so it can negotiate use of the Internet Key Exchange Protocol (IKE) for media sessions in the SDP offer/answer model 🗝️. VPN vibes, but make it cute.
+==================+============================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+==================+============================+=======+==========+
| ike-setup | Unlikely to use IKE in the | B | CAUTION |
| | context of multiplexing | | |
+------------------+----------------------------+-------+----------+
| psk-fingerprint | Unlikely to use IKE in the | B | CAUTION |
| | context of multiplexing | | |
+------------------+----------------------------+-------+----------+
| ike-esp | Unlikely to use IKE in the | B | CAUTION |
| | context of multiplexing | | |
+------------------+----------------------------+-------+----------+
| ike-esp-udpencap | Unlikely to use IKE in the | B | CAUTION |
| | context of multiplexing | | |
+------------------+----------------------------+-------+----------+
Table 45: RFC 6193 Attribute Analysis5.46. RFC 2326: Real Time Streaming Protocol 🎬
The Real Time Streaming Protocol, or RTSP, is an application-level protocol for controlling the delivery of data that has real-time properties 🎥. It gives you an extensible framework for controlled, on-demand delivery of real-time data, like audio and video 🍿.
+=========+=======================+=======+==============+
| Name | Notes | Level | Mux Category |
+=========+=======================+=======+==============+
| etag | RFC 2326 is obsolete. | B | CAUTION |
+---------+-----------------------+-------+--------------+
| range | RFC 2326 is obsolete. | B | CAUTION |
+---------+-----------------------+-------+--------------+
| control | RFC 2326 is obsolete. | B | CAUTION |
+---------+-----------------------+-------+--------------+
| mtag | RFC 2326 is obsolete. | B | CAUTION |
+---------+-----------------------+-------+--------------+
Table 46: RFC 2326 Attribute AnalysisNOTE: [RFC2326] defines SDP attributes that are applicable in the declarative usage of SDP alone. For the purposes of this document, only the offer/answer usage of SDP is considered to be mandated by [RFC8843].
Heads up, bestie 🚨: [RFC2326] is obsolete, and the attributes here are only in the declarative usage of SDP. For this document, the only usage that counts is the offer/answer one that [RFC8843] mandates 📋.
5.47. RFC 7826: Real-Time Streaming Protocol 🌈
The Real-Time Streaming Protocol, or RTSP, is an application-level protocol for controlling the delivery of data with real-time properties ⏯️. It gives you an extensible framework for controlled, on-demand delivery of real-time data, such as audio and video 📺.
+=========+===========================+=======+==============+
| Name | Notes | Level | Mux Category |
+=========+===========================+=======+==============+
| range | RTSP is not supported for | B | CAUTION |
| | RTP stream multiplexing. | | |
+---------+---------------------------+-------+--------------+
| control | RTSP is not supported for | B | CAUTION |
| | RTP stream multiplexing. | | |
+---------+---------------------------+-------+--------------+
| mtag | RTSP is not supported for | B | CAUTION |
| | RTP stream multiplexing. | | |
+---------+---------------------------+-------+--------------+
Table 47: RFC 7826 Attribute AnalysisNOTE: [RFC7826] defines SDP attributes that are applicable in the declarative usage of SDP alone. For the purposes of this document, only the offer/answer usage of SDP is considered to be mandated by [RFC8843].
Same tea as the last one 🫖. [RFC7826] covers attributes for the declarative usage of SDP alone, and for this document, only the offer/answer usage that [RFC8843] mandates counts. RTSP just isn't supported for RTP stream multiplexing, so the mux category stays CAUTION 🙅♀️.
5.48. RFC 6064: SDP and RTSP Extensions for 3GPP
okay so 3GPP's Packet-switched Streaming Service (PSS) and Multimedia Broadcast/Multicast Service (MBMS) 💖 both run on SDP and RTSP, but with their own extra bits added on top. 🎀 [RFC6064] is the doc that explains those extensions, and it also registers them with IANA 🧚 so they're officially on the list.
+==============================+=============+=======+==============+
| Name | Notes | Level | Mux |
| | | | Category |
+==============================+=============+=======+==============+
| X-predecbufsize | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| X-initpredecbufperiod | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| X-initpostdecbufperiod | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| X-decbyterate | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3gpp-videopostdecbufsize | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| framesize | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-Integrity-Key | Refer to | S | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-SDP-Auth | Refer to | S | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-SRTP-Config | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| alt | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| alt-default-id | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| alt-group | Refer to | S | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-Adaptation-Support | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-Asset-Information | Refer to | B | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| mbms-mode | Refer to | B | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| mbms-flowid | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| mbms-repair | Refer to | B | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics | Refer to | M | CAUTION |
| | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Corruption | Refer to | M | CAUTION |
| duration | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Rebuffering | Refer to | M | CAUTION |
| duration | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Initial | Refer to | M | CAUTION |
| buffering duration | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Successive | Refer to | M | CAUTION |
| loss of RTP packets | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Frame rate | Refer to | M | CAUTION |
| deviation | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Jitter | Refer to | M | CAUTION |
| duration | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Content | Refer to | B | CAUTION |
| Switch Time | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Average | Refer to | M | CAUTION |
| Codec Bitrate | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Codec | Refer to | M | CAUTION |
| Information | notes below | | |
+------------------------------+-------------+-------+--------------+
| 3GPP-QoE-Metrics:Buffer | Refer to | M | CAUTION |
| Status | notes below | | |
+------------------------------+-------------+-------+--------------+Table 48: RFC 6064 Attribute Analysis 🌈
NOTE: ngl this one's a big deal 💅 [RFC6064] defines SDP attributes that are applicable in the declarative usage of SDP alone. For the purposes of this document, only the offer/answer usage of SDP is considered to be mandated by [RFC8843]. 🫶
5.49. RFC 3108: ATM SDP 💖
okay so [RFC3108] is all about using SDP to describe ATM bearer connections and whatever ATM Adaptation Layer (AAL) they're riding on 🦋✨ it's basically the SDP dress code for ATM 💅
+=======================+=============+=======+==============+
| Name | Notes | Level | Mux Category |
+=======================+=============+=======+==============+
| aalType | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| eecid | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| capability | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| qosClass | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| bcob | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| stc | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| upcc | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| atmQOSparms | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| atmTrfcDesc | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| abrParms | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| abrSetup | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| bearerType | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| lij | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| anycast | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| cache | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| bearerSigIE | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| aalApp | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| cbrRate | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| sbc | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| clkrec | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| fec | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| prtfl | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| structure | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| cpsSDUsize | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| aal2CPS | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| aal2CPSSDUrate | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| aal2sscs3661unassured | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| aal2sscs3661assured | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| aal2sscs3662 | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| aal5sscop | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| atmmap | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| silenceSupp | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| ecan | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| gc | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| profileDesc | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| vsel | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| dsel | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| fsel | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| onewaySel | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| codecconfig | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| isup_usi | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| uiLayer1_Prot | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| chain | Refer to | B | CAUTION |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
Table 49: RFC 3108 Attribute AnalysisNOTE: okay so, RFC 3108 is the convention for describing ATM bearer connections that use an AAL1, AAL2, or AAL5 adaptation layer 🌸 with AAL1, AAL2, and AAL5, a bearer connection can carry a single media stream 🎀 and with AAL1 and AAL2 specifically, you can multiplex several media streams into one bearer connection 💜 across all three adaptation types, bearer connections can be bundled into a single media group 🧚 in every case RFC 3108 covers, a real-time media stream (voice, video, voiceband data, pseudowire, and others) or a multiplex of streams gets mapped straight into an ATM connection ✨ what it does NOT cover is ATM acting as a low-level transport pipe for IP packets, which can then carry one or more real-time (e.g., VoIP) media sessions with a life cycle that's different from the underlying ATM transport 🙈
5.50. 3GPP TS 183.063 🎀
[TISPAN] describes Telecommunications and Internet converged Services and Protocols for Advanced Networking (TISPAN); 🌈
+====================+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+====================+==============+=======+==============+
| PSCid | Not impacted | S | NORMAL |
+--------------------+--------------+-------+--------------+
| bc_service | Not impacted | S | NORMAL |
+--------------------+--------------+-------+--------------+
| bc_program | Not impacted | S | NORMAL |
+--------------------+--------------+-------+--------------+
| bc_service_package | Not impacted | S | NORMAL |
+--------------------+--------------+-------+--------------+
Table 50: 3GPP TS 183.063 Attribute Analysis5.51. 3GPP TS 24.229 💖
okay so [IP-CALL] specifies an IP multimedia call control protocol built on Session Initiation Protocol and Session Description Protocol. it's giving full call setup energy ✨
+=================+============================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+=================+============================+=======+===========+
| secondary-realm | secondary-realm MUST be | M | TRANSPORT |
| | the one that corresponds | | |
| | to the "m=" line chosen | | |
| | for setting up the | | |
| | underlying transport flow. | | |
+-----------------+----------------------------+-------+-----------+
| visited-realm | visited-realm MUST be the | M | TRANSPORT |
| | one that corresponds to | | |
| | the "m=" line chosen for | | |
| | setting up the underlying | | |
| | transport flow. | | |
+-----------------+----------------------------+-------+-----------+
| omr-m-cksum | Not impacted | M | NORMAL |
+-----------------+----------------------------+-------+-----------+
| omr-s-cksum | Not impacted | M | NORMAL |
+-----------------+----------------------------+-------+-----------+
| omr-m-att | Not impacted | M | NORMAL |
+-----------------+----------------------------+-------+-----------+
| omr-s-att | Not impacted | M | NORMAL |
+-----------------+----------------------------+-------+-----------+
| omr-m-bw | Not impacted | M | NORMAL |
+-----------------+----------------------------+-------+-----------+
| omr-s-bw | Not impacted | M | NORMAL |
+-----------------+----------------------------+-------+-----------+
| omr-codecs | Not impacted | M | NORMAL |
+-----------------+----------------------------+-------+-----------+
Table 51: 3GPP TS 24.229 Attribute Analysis5.52. ITU T.38 🍓
[T.38] defines procedures for real-time Group 3 facsimile communications over IP networks. fax, but make it IP 📠💅
+=======================+=============+=======+==============+
| Name | Notes | Level | Mux Category |
+=======================+=============+=======+==============+
| T38FaxVersion | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38MaxBitRate | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxFillBitRemoval | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxTranscodingMMR | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxTranscodingJBIG | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxRateManagement | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxMaxBuffer | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxMaxDatagram | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxUdpEC | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxMaxIFP | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxUdpECDepth | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38FaxUdpFECMaxSpan | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38ModemType | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
| T38VendorInfo | Refer to | M | TBD |
| | notes below | | |
+-----------------------+-------------+-------+--------------+
Table 52: ITU T.38 Attribute AnalysisNOTE: As per Section 9 of [RFC8843], there exists no publicly available specification that defines procedures for multiplexing/demultiplexing fax protocol flows over a single 5-tuple. Once such a specification is available, the multiplexing category assignments for the attributes in this section could be revisited. 🙈
5.53. ITU-T Q.1970 🦋
[Q.1970] defines Bearer Independent Call Control (BICC) IP bearer control protocol. bearer control, but make it iconic 👑
+=======+=====================================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+=======+=====================================+=======+==========+
| ipbcp | ipbcp version identifies the types | S | SPECIAL |
| | of IP bearer control protocol | | |
| | (IPBCP) message used in BICC (ITU-T | | |
| | Q.1901) environment that are | | |
| | limited to single-media payload. | | |
| | Refer to the pertinent ITU-T | | |
| | specifications while multiplexing. | | |
+-------+-------------------------------------+-------+----------+
Table 53: ITU-T Q.1970 Attribute Analysis5.54. ITU-T H.248.15 🧚
ITU-T H.248.15 [H.248.15] defines the Gateway Control Protocol SDP H.248 package attribute. so this one is all about gateways being told which extension packages to use 🌸
+==========+=====================================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+==========+=====================================+=======+==========+
| h248item | It is only applicable for | B | SPECIAL |
| | signaling the inclusion of H.248 | | |
| | extension packages to a gateway | | |
| | via the local and remote | | |
| | descriptors. The attribute | | |
| | itself is unaffected by | | |
| | multiplexing, but the package | | |
| | referenced in a specific use of | | |
| | the attribute can be impacted. | | |
| | Further analysis of each package | | |
| | is needed to determine if there | | |
| | is an issue. This is only a | | |
| | concern in environments using a | | |
| | decomposed server/gateway with | | |
| | H.248 signaled between them. The | | |
| | ITU-T will need to do further | | |
| | analysis of various packages when | | |
| | they specify how to signal the | | |
| | use of multiplexing to a gateway. | | |
+----------+-------------------------------------+-------+----------+
Table 54: ITU-T H.248.15 Attribute Analysis5.55. RFC 4975: The Message Session Relay Protocol 💜
[RFC4975] describes the Message Session Relay Protocol, a protocol for transmitting a series of related instant messages in the context of a session. message sessions get treated like any other media stream when they're set up through a rendezvous or session-creation protocol, like the Session Initiation Protocol. it's the group chat of media streams, honestly 💬✨
+======================+=============+=======+==============+
| Name | Notes | Level | Mux Category |
+======================+=============+=======+==============+
| accept-types | Refer to | M | TBD |
| | notes below | | |
+----------------------+-------------+-------+--------------+
| accept-wrapped-types | Refer to | M | TBD |
| | notes below | | |
+----------------------+-------------+-------+--------------+
| max-size | Refer to | M | TBD |
| | notes below | | |
+----------------------+-------------+-------+--------------+
| path | Refer to | M | TBD |
| | notes below | | |
+----------------------+-------------+-------+--------------+
Table 55: RFC 4975 Attribute AnalysisNOTE: As per Section 9 of [RFC8843], there exists no publicly available specification that defines procedures for multiplexing/demultiplexing MSRP flows over a single 5-tuple. Once such a specification is available, the multiplexing categories assignments for the attributes in this section could be revisited.
5.56. Historical Attributes 🕰️
this section looks at the attributes that are only kept around for historic usage, as listed by the [IANA]. vintage vibes, but make it analysis 📼
+=========+=====================+=======+==============+
| Name | Notes | Level | Mux Category |
+=========+=====================+=======+==============+
| rtpred1 | Historic attributes | M | CAUTION |
+---------+---------------------+-------+--------------+
| rtpred2 | Historic attributes | M | CAUTION |
+---------+---------------------+-------+--------------+
Table 56: Historical Attribute Analysis6. bwtype Attribute Analysis 🌈
this section is where we get into how specific bandwidth attributes get handled when multiplexing is involved. bandwidth drama, and I am here for it 👀💖
6.1. RFC 4566: SDP
Okay so [RFC4566] is the SDP spec, and it's built for describing multimedia sessions 📣✨ for announcing them, inviting people in, and all the other ways of kicking off a multimedia session. Iconic behavior, honestly.
+===========+=================================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+===========+=================================+=======+==========+
| bwtype:CT | Not impacted | S | NORMAL |
+-----------+---------------------------------+-------+----------+
| bwtype:AS | For media-level usage, the | B | SUM |
| | aggregate of individual | | |
| | bandwidth values is considered. | | |
+-----------+---------------------------------+-------+----------+
Table 57: RFC 4566 bwtype Analysis6.2. RFC 3556: SDP Bandwidth Modifiers for RTCP Bandwidth
[RFC3556] adds two new modifiers to the bandwidth attribute in SDP 🎀. They're there so you can say how much bandwidth RTCP packets are allowed to use in an RTP session. Very organized of them, no cap.
+===========+================================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+===========+================================+=======+==========+
| bwtype:RS | Session-level usage represents | B | SUM |
| | session aggregate, and media- | | |
| | level usage indicates SUM of | | |
| | the individual values while | | |
| | multiplexing. | | |
+-----------+--------------------------------+-------+----------+
| bwtype:RR | Session-level usage represents | B | SUM |
| | session aggregate, and media- | | |
| | level usage indicates SUM of | | |
| | the individual values while | | |
| | multiplexing. | | |
+-----------+--------------------------------+-------+----------+
Table 58: RFC 3556 bwtype Analysis6.3. RFC 3890: Bandwidth Modifier for SDP
[RFC3890] brings in the TIAS bandwidth modifier 🦋. It leaves out transport overhead on purpose, and instead there's a separate packet-rate attribute doing the work. Put the transport-independent bitrate together with the maximum packet rate and you can calculate the real bitrate over whatever transport is actually being used. Main character math energy 🧮💅.
+=============+==================================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+=============+==================================+=======+==========+
| bwtype:TIAS | The usage of TIAS is not | B | SPECIAL |
| | defined under offer/answer | | |
| | usage. | | |
+-------------+----------------------------------+-------+----------+
| maxprate | The usage of TIAS and | B | SPECIAL |
| | maxprate is not well | | |
| | defined under multiplexing. | | |
+-------------+----------------------------------+-------+----------+
Table 59: RFC 3890 bwtype AnalysisNOTE: Okay, this one's important bestie 👀. The whole point of TIAS is that you take the media-level bitrate, multiply it by the known per-packet overhead for the transport you picked, and then multiply that by the maxprate value. That gives you the worst-case bitrate coming off the transport, which is a much more accurate picture of what you're really using. If you sum the TIAS values separately across each "m=" line and then multiply that total by maxprate and the per-packet overhead, the number gets wildly inflated 💀. Multiplying first and then adding the individual values is the way to go, iykyk.
7. rtcp-fb Attribute Analysis ✨
This section is all about the rtcp-fb SDP attributes 💖.
7.1. RFC 4585: RTP/AVPF
[RFC4585] extends the Audio-Visual Profile (AVP) so receivers can send feedback to senders way more quickly 🏃♀️💨. Statistically speaking, anyway. That means short-term adaptation becomes possible, plus feedback-based repair mechanisms that are actually efficient. Big brain era 🧠.
+=========+=============================+=======+==================+
| Name | Notes | Level | Mux Category |
+=========+=============================+=======+==================+
| ack | The attribute value MUST be | M | IDENTICAL-PER-PT |
| rpsi | the same for a given codec | | |
| | configuration. | | |
+---------+-----------------------------+-------+------------------+
| ack app | Feedback parameters MUST be | M | SPECIAL |
| | handled in the app-specific | | |
| | way when multiplexed. | | |
+---------+-----------------------------+-------+------------------+
| nack | The attribute value MUST be | M | IDENTICAL-PER-PT |
| | the same for a given codec | | |
| | configuration. | | |
+---------+-----------------------------+-------+------------------+
| nack | The attribute value MUST be | M | IDENTICAL-PER-PT |
| pli | the same for a given codec | | |
| | configuration. | | |
+---------+-----------------------------+-------+------------------+
| nack | The attribute value MUST be | M | IDENTICAL-PER-PT |
| sli | the same for a given codec | | |
| | configuration. | | |
+---------+-----------------------------+-------+------------------+
| nack | The attribute value MUST be | M | IDENTICAL-PER-PT |
| rpsi | the same for a given codec | | |
| | configuration. | | |
+---------+-----------------------------+-------+------------------+
| nack | Feedback parameters MUST be | M | SPECIAL |
| app | handled in the app specific | | |
| | way when multiplexed. | | |
+---------+-----------------------------+-------+------------------+
| trr-int | The attribute value MUST be | M | IDENTICAL-PER-PT |
| | the same for a given codec | | |
| | configuration. | | |
+---------+-----------------------------+-------+------------------+
Table 60: RFC 4585 Attribute Analysis7.2. RFC 5104: Codec Control Messages in AVPF
[RFC5104] adds a few extensions to the messages defined in the Audio-Visual Profile with Feedback (AVPF) 🎬. They're especially helpful in conversational multimedia where centralized multipoint functionality is in use, but some of them also work in smaller multicast environments and point-to-point calls 📞.
+======+==========================+=======+==================+
| Name | Notes | Level | Mux Category |
+======+==========================+=======+==================+
| ccm | The attribute value MUST | M | IDENTICAL-PER-PT |
| | be the same for a given | | |
| | codec configuration. | | |
+------+--------------------------+-------+------------------+
Table 61: RFC 5104 Attribute Analysis7.3. RFC 6285: Unicast-Based Rapid Acquisition of Multicast RTP Sessions (RAMS)
[RFC6285] uses the RTP and RTCP machinery you already have to cut down acquisition delay 🚀. An auxiliary unicast RTP session carries the Reference Information to the receiver, and it arrives right before or alongside the multicast stream. That unicast flow can even go faster than its natural bitrate, which speeds up acquisition even more ⚡. The main use case is multicast apps carrying real-time compressed audio and video 🎶📺, and honestly that's the most slay use case ever.
+======+==========================+=======+==================+
| Name | Notes | Level | Mux Category |
+======+==========================+=======+==================+
| nack | The attribute value MUST | M | IDENTICAL-PER-PT |
| rai | be the same for a given | | |
| | codec configuration. | | |
+------+--------------------------+-------+------------------+
Table 62: RFC 6285 Attribute Analysis7.4. RFC 6679: ECN for RTP over UDP/IP
[RFC6679] spells out how Explicit Congestion Notification (ECN) works with RTP running over UDP, using RTCP as the feedback mechanism 🌈. It defines a new RTCP Extended Report (XR) block for periodic ECN feedback, a new RTCP transport feedback message for timely reporting of congestion events, and a STUN extension that's used in the optional initialization method using ICE 🧚. Three features, one RFC, zero chill 💜.
+=================+============================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+=================+============================+=======+===========+
| ecn-capable-rtp | ECN markup is enabled at | M | IDENTICAL |
| | the RTP session level. | | |
+-----------------+----------------------------+-------+-----------+
| nack ecn | This attribute enables ECN | M | IDENTICAL |
| | at the RTP session level. | | |
+-----------------+----------------------------+-------+-----------+
Table 63: RFC 6679 Attribute Analysis7.5. RFC 6642: Third-Party Loss Report 💌
okay so picture a big RTP session 🌸 using the RTCP feedback mechanism from [RFC4585]. some event hits and suddenly a ton of receivers all want to send feedback at the same time. the feedback target gets slammed, and that's the transient overload we're worried about 😭
usually this gets avoided by forwarding feedback reports to everyone, so receivers can skip sending their own duplicates. super smart! but there are cases where forwarding is NOT recommended, and that's where feedback implosion can sneak in 💀
that's the tea [RFC6642] spills. it digs into those cases and creates a brand new RTCP Third-Party Loss Report. it lets the receivers know the feedback target already knows about a loss event, so they can hold back their feedback ✨ it also defines the SDP signaling that goes with it 🎀
+=======+==========================+=======+==================+
| Name | Notes | Level | Mux Category |
+=======+==========================+=======+==================+
| nack | The attribute value MUST | M | IDENTICAL-PER-PT |
| tllei | be the same for a given | | |
| | codec configuration. | | |
+-------+--------------------------+-------+------------------+
| nack | The attribute value MUST | M | IDENTICAL-PER-PT |
| pslei | be the same for a given | | |
| | codec configuration. | | |
+-------+--------------------------+-------+------------------+Table 64: RFC 6642 Attribute Analysis 🦋
7.6. RFC 5104: Codec Control Messages in AVPF 🧚
[RFC5104] adds a few extensions on top of the messages from the Audio-Visual Profile with Feedback (AVPF). 💅 these are especially useful in conversational multimedia setups where centralized multipoint stuff is happening. some of them also work in smaller multicast setups and point-to-point calls, so they're lowkey versatile 🙈
+=======+==========================+=======+==================+
| Name | Notes | Level | Mux Category |
+=======+==========================+=======+==================+
| ccm | The attribute value MUST | M | IDENTICAL-PER-PT |
| fir | be the same for a given | | |
| | codec configuration. | | |
+-------+--------------------------+-------+------------------+
| ccm | The attribute value MUST | M | IDENTICAL-PER-PT |
| tmmbr | be the same for a given | | |
| | codec configuration. | | |
+-------+--------------------------+-------+------------------+
| ccm | The attribute value MUST | M | IDENTICAL-PER-PT |
| tstr | be the same for a given | | |
| | codec configuration. | | |
+-------+--------------------------+-------+------------------+
| ccm | The attribute value MUST | M | IDENTICAL-PER-PT |
| vbcm | be the same for a given | | |
| | codec configuration. | | |
+-------+--------------------------+-------+------------------+Table 65: RFC 5104 Attribute Analysis 🌈
8. group Attribute Analysis 👑
this section is all about the SDP "group" attribute semantics from [RFC5888] 🫶
8.1. RFC 5888: SDP Grouping Framework 🍓
[RFC5888] sets up a framework for grouping "m=" lines in SDP, and each grouping has its own purpose 💖
+===========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+===========+==============+=======+==============+
| group:LS | Not impacted | S | NORMAL |
+-----------+--------------+-------+--------------+
| group:FID | Not impacted | S | NORMAL |
+-----------+--------------+-------+--------------+Table 66: RFC 5888 Attribute Analysis ✨
8.2. RFC 3524: Mapping Media Streams to Resource Reservation Flows 🦋
[RFC3524] extends the SDP grouping framework. it lets you ask for a group of media streams to be mapped into one single resource reservation flow 🙌 it defines the SDP syntax for that, plus a new "semantics" attribute called Single Reservation Flow (SRF) 💜
+===========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+===========+==============+=======+==============+
| group:SRF | Not impacted | S | NORMAL |
+-----------+--------------+-------+--------------+Table 67: RFC 3524 Attribute Analysis 🌸
8.3. RFC 4091: ANAT Semantics 🥀
[RFC4091] defines ANAT semantics for the SDP grouping framework. (heads up bestie: [RFC4091] has been obsoleted by [RFC8445].) ANAT semantics let alternative types of network addresses be used to establish a particular media stream 🗝️
+============+==============================+=======+==============+
| Name | Notes | Level | Mux Category |
+============+==============================+=======+==============+
| group:ANAT | ANAT semantics is obsoleted. | S | CAUTION |
+------------+------------------------------+-------+--------------+Table 68: RFC 4091 Attribute Analysis 💀
8.4. RFC 5956: FEC Grouping Semantics in SDP 🔥
[RFC5956] defines how to group associated source and FEC-based repair flows in SDP. these semantics are meant to be used with the SDP Grouping Framework [RFC5888]. they let you describe grouping relationships between source and repair flows when one or more source and/or repair flows show up in the same group, and they also support additive repair flows 🧁 SSRC-level grouping semantics are defined here too, for RTP streams that use SSRC multiplexing ✨
+==============+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+==============+==============+=======+==============+
| group:FEC-FR | Not impacted | S | NORMAL |
+--------------+--------------+-------+--------------+Table 69: RFC 5956 Attribute Analysis 🫧
8.5. RFC 5583: Signaling Media Decoding Dependency in SDP 🎀
[RFC5583] defines semantics for signaling the decoding dependency between media descriptions that share the same media type in SDP. this is required, for example, if media data gets separated and sent over different network streams because of a layered or multiple descriptive media coding process 🌈
+===========+==========================+=======+==================+
| Name | Notes | Level | Mux Category |
+===========+==========================+=======+==================+
| group:DDP | Not impacted | S | NORMAL |
+-----------+--------------------------+-------+------------------+
| depend | The attribute value MUST | M | IDENTICAL-PER-PT |
| lay | be the same for a given | | |
| | codec configuration. | | |
+-----------+--------------------------+-------+------------------+
| depend | The attribute value MUST | M | IDENTICAL-PER-PT |
| mdc | be the same for a given | | |
| | codec configuration. | | |
+-----------+--------------------------+-------+------------------+Table 70: RFC 5583 Attribute Analysis 💜
8.6. RFC 7104: Duplication Grouping Semantics in the SDP 🌷
[RFC7104] defines semantics for grouping redundant streams in SDP. these semantics are meant to be used with the SDP Grouping Framework. grouping semantics at the synchronization source (SSRC) level are also defined in this document, for RTP streams that use SSRC multiplexing 🫶
+===========+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+===========+==============+=======+==============+
| group:DUP | Not impacted | S | NORMAL |
+-----------+--------------+-------+--------------+Table 71: RFC 7104 Attribute Analysis 💅
9. ssrc-group Attribute Analysis 🧚♀️
this section breaks down "ssrc-group" semantics 🦄
9.1. RFC 5576: Source-Specific SDP Attributes 🌟
[RFC5576] gives us a way to describe RTP media sources in SDP. those sources are identified by their synchronization source (SSRC) identifiers. it lets you attach attributes to these sources and express relationships among them ✨ it also defines a bunch of source-level attributes for describing the properties of media sources 💖
+===================+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+===================+==============+=======+==============+
| ssrc-group:FID | Not impacted | SR | NORMAL |
+-------------------+--------------+-------+--------------+
| ssrc-group:FEC | Not impacted | SR | NORMAL |
+-------------------+--------------+-------+--------------+
| ssrc-group:FEC-FR | Not impacted | SR | NORMAL |
+-------------------+--------------+-------+--------------+Table 72: RFC 5576 Attribute Analysis 🎀
9.2. RFC 7104: Duplication Grouping Semantics in the SDP 🍒
[RFC7104] defines semantics for grouping redundant streams in SDP. these semantics are meant to be used with the SDP Grouping Framework. grouping semantics at the synchronization source (SSRC) level are also defined in this document, for RTP streams that use SSRC multiplexing 💫
+================+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+================+==============+=======+==============+
| ssrc-group:DUP | Not impacted | SR | NORMAL |
+----------------+--------------+-------+--------------+Table 73: RFC 7104 Attribute Analysis 🌺
10. QoS Mechanism Token Analysis 🎀
this section looks at the QoS tokens specified with SDP 🫧
10.1. RFC 5432: QoS Mechanism Selection in SDP 🎀
[RFC5432] is the one that lays out how to negotiate QoS mechanisms using the SDP offer/answer model. 💅
+======+================================+=======+===========+
| Name | Notes | Level | Mux |
| | | | Category |
+======+================================+=======+===========+
| rsvp | rsvp attribute MUST be the one | B | TRANSPORT |
| | that corresponds to the "m=" | | |
| | line chosen for setting up the | | |
| | underlying transport flow. | | |
+------+--------------------------------+-------+-----------+
| nsis | rsvp attribute MUST be the one | B | TRANSPORT |
| | that corresponds to the "m=" | | |
| | line chosen for setting up the | | |
| | underlying transport. | | |
+------+--------------------------------+-------+-----------+Table 74: RFC 5432 Attribute Analysis
NOTE: A single Differentiated Services Code Point (DSCP) for each flow being multiplexed doesn't impact multiplexing, since QoS mechanisms are signaled/scoped per flow. For scenarios that involve having different DSCP code points for packets being transmitted over the same 5-tuple, issues as discussed in [RFC7657] need to be taken into consideration. 🙈
11. k= Attribute Analysis ✨
11.1. RFC 4566: SDP 🌸
[RFC4566] defines SDP, which is meant for describing multimedia sessions for session announcement, session invitation, and other forms of multimedia session initiation. 🦋
+======+===================================+=======+==============+
| Name | Notes | Level | Mux Category |
+======+===================================+=======+==============+
| k= | It is not recommended to use this | S | CAUTION |
| | attribute under multiplexing. | | |
+------+-----------------------------------+-------+--------------+Table 75: RFC 4566 Attribute Analysis
12. content Attribute Analysis 💖
12.1. RFC 4796 🧚
[RFC4796] defines a brand new SDP media-level attribute, content. It describes the content of the media stream in more detail than the media description line does, which is so useful. ✨ The sender of an SDP session description can attach the content attribute to one or more media streams, and then the receiving application can treat each media stream differently (for example, showing it on a big screen or a small one) based on what the content actually is. 👑
+=================+==============+=======+==============+
| Name | Notes | Level | Mux Category |
+=================+==============+=======+==============+
| content:slides | Not impacted | M | NORMAL |
+-----------------+--------------+-------+--------------+
| content:speaker | Not impacted | M | NORMAL |
+-----------------+--------------+-------+--------------+
| content:main | Not impacted | M | NORMAL |
+-----------------+--------------+-------+--------------+
| content:sl | Not impacted | M | NORMAL |
+-----------------+--------------+-------+--------------+
| content:alt | Not impacted | M | NORMAL |
+-----------------+--------------+-------+--------------+Table 76: RFC 4796 Attribute Analysis
12.2. 3GPP TS 24.182 🔥
[IMS-CAT] specifies an IP multimedia subsystem for customized alerting tones. Cute, right? 🎶
+============+=========================+=======+==============+
| Name | Notes | Level | Mux Category |
+============+=========================+=======+==============+
| g.3gpp.cat | Usage defined for the | M | NORMAL |
| | IP multimedia subsystem | | |
+------------+-------------------------+-------+--------------+Table 77: 3GPP TS 24.182 Attribute Analysis
12.3. 3GPP TS 24.183 🌈
[IMS-CRS] specifies an IP multimedia subsystem for customized ringing signal. Ringtones, but make it standards-compliant. 💜
+============+=========================+=======+==============+
| Name | Notes | Level | Mux Category |
+============+=========================+=======+==============+
| g.3gpp.crs | Usage defined for the | M | NORMAL |
| | IP multimedia subsystem | | |
+------------+-------------------------+-------+--------------+Table 78: 3GPP TS 24.183 Attribute Analysis
13. Payload Formats 🦋
13.1. RFC 5109: RTP Payload Format for Generic FEC 🛡️
[RFC5109] describes a payload format for generic Forward Error Correction (FEC) for media data encapsulated in RTP. It's based on the exclusive-or (parity) operation, and it lets end systems apply protection using various protection lengths and levels, plus various protection group sizes, so it can adapt to different media and channel characteristics. ✨ Depending on the packet loss situation, it enables complete recovery of the protected packets or partial recovery of the critical parts of the payload. Honestly, that's a whole main character move. 👑
+==============+=====================+=======+==========+
| Name | Notes | Level | Mux |
| | | | Category |
+==============+=====================+=======+==========+
| audio/ulpfec | Not recommended for | M | CAUTION |
| | multiplexing due to | | |
| | reuse of SSRCs. | | |
+--------------+---------------------+-------+----------+
| video/ulpfec | Not recommended for | M | CAUTION |
| | multiplexing due to | | |
| | reuse of SSRCs. | | |
+--------------+---------------------+-------+----------+
| text/ulpfec | Not recommended for | M | CAUTION |
| | multiplexing due to | | |
| | reuse of SSRCs. | | |
+--------------+---------------------+-------+----------+
| application/ | Not recommended for | M | CAUTION |
| ulpfec | multiplexing due to | | |
| | reuse of SSRCs. | | |
+--------------+---------------------+-------+----------+Table 79: RFC 5109 Payload Format Analysis
14. Multiplexing Considerations for Encapsulating Attributes 🌸
This section is all about recommendations for defining the multiplexing characteristics of SDP attributes that encapsulate other SDP attributes or parameters. 🍓 As of today, attributes like these are defined in [RFC3407], [RFC5939] and [RFC6871] as part of a generic framework for indicating and negotiating transport-, media-, and media-format-related capabilities in SDP. It's giving framework, fr fr. 🫶
The behavior of these attributes under multiplexing is, in turn, defined by the multiplexing behavior of the attributes they encapsulate. Those are made known once the offer/answer negotiation process is completed, so you have to wait for the final result to see the full picture. ⭐
14.1. RFC 3407: cpar Attribute Analysis 🧁
The [RFC3407] capability parameter attribute a=cpar encapsulates a b= (bandwidth) or an a= attribute. For bandwidth attribute encapsulation, the category SUM is inherited. For the case of an a= attribute, the category corresponding to the SDP attribute being encapsulated is inherited. 💅
v=0
o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
s=
c=IN IP4 host.atlanta.example.com
t=0 0
m=video 3456 RTP/AVP 100
a=rtpmap:100 VP8/90000
a=sqn: 0
a=cdsc: 1 video RTP/AVP 100
a=cpar: a=rtcp-mux
m=video 3456 RTP/AVP 101
a=rtpmap:101 VP8/90000
a=fmtp:100 max-fr=15;max-fs=1200
a=cdsc: 2 video RTP/AVP 101
a=cpar: a=rtcp-muxIn this example, the category IDENTICAL is inherited for the cpar-encapsulated rtcp-mux attribute. Okay, so the encapsulated attribute just gets the same category, and that's the whole vibe. 🦋
14.2. RFC 5939 Analysis 🌈
[RFC5939] defines a general SDP capability negotiation framework. It also specifies how to provide transport protocols and SDP attributes as capabilities, and how to negotiate them using the framework. 💖
For this purpose, [RFC5939] defines the following:
- A set of capabilities for the session and its associated media-stream components, supported by each side. The attribute
a=acapdefines how to list an attribute name and its associated value (if any) as a capability. The attributea=tcapdefines how to list transport protocols (e.g.,RTP/AVP) as capabilities. 🎀 - A set of potential configurations (
a=pcfg) provided by the offerer to indicate which combinations of those capabilities can be used for the session and its associated media stream components. Potential configurations aren't ready for use until they're fully negotiated. They provide an alternative that MAY be used, subject to SDP capability-negotiation procedures. In particular, the answerer MAY choose one of the potential configurations for use as part of the current offer/answer exchange. 🔥 - An actual configuration (
a=acfg) for the session and its associated media stream components. The actual configuration identifies the potential configuration that was negotiated for use. Using an actual configuration doesn't require any further negotiation. 🧚 - A negotiation process that takes the current actual configuration and the set of potential configurations (combinations of capabilities) as input, and provides the negotiated actual configurations as output. In [RFC5939], the negotiation process is done independently for each media description. Each m-line gets its own little negotiation moment. 👑
14.2.1. Recommendation: Procedures for Potential Configuration Pairing 💖
okay so this part is all about how the offerer should set up potential configurations so the answerer can pick a combo that works across every multiplexed stream 🎀 it's giving teamwork 🫶 this section is written for entities that generate and process SDP under the generic capability-negotiation framework from [RFC5939], specifically in the context of media-stream multiplexing ✨
the whole point is letting the offerer make sure the potential configurations across multiplexed streams can (easily) be negotiated so they stay consistent with each other 💅 the goal is to make life easier for the answerer when it's picking potential configurations that line up across all the multiplexed media descriptions 🦋
a potential configuration picks a set of attributes and parameters that get added to the media description once it's negotiated 🌸 when you're multiplexing media descriptions that have potential configurations, there MAY be a need to coordinate that selection between the multiplexed media descriptions so the multiplexing behaves the way it should 👑
you could analyze every potential configuration in the multiplexed media descriptions to hunt for combinations that satisfy those constraints 🙈 but ngl that gets messy really fast 💀
here's the thing: [RFC5939] says each potential configuration in the SDP has a unique configuration number, but uniqueness is only scoped to each media description 🧚 so to make it simple for the answerer to chose valid combinations of potential configurations across the media descriptions in a given BUNDLE group, we give you a straightforward rule for building them 🍓
- Let m-bundle be the set of media descriptions that form a given bundle.
- Let m-bundle-pcfg be the set of media descriptions in m-bundle that include one or more potential configurations.
- Each media description in m-bundle-pcfg MUST have at least one potential configuration with the same configuration number (e.g., "1").
- For each potential configuration with configuration number x in m-bundle-pcfg, the offerer MUST ensure that if the answerer chooses configuration number x in each of the media descriptions in m-bundle-pcfg, then the resulting SDP will have all multiplexing constraints satisfied for those media descriptions.
- Since it is nearly impossible to define a generic mechanism for various capability extensions, this document doesn't provide procedures for dealing with the capability-extension attributes. However, Section 14.3 provides analysis of media-capability-extension attributes as defined in [RFC6871].
the above lets the answerer find multiplexing-compatible combos super easily 🥰 it just picks a potential configuration number that shows up in every media description with potential configurations in the bundle 🌈
also, the offerer is still allowed to provide additional potential configurations with independent configuration numbers ✨ the answerer will have to do more complicated analysis to figure out which multiplexed combos of those are valid 😭
14.2.1.1. Example: Transport-Capability Multiplexing 🦋
v=0
o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
s=
c=IN IP4 host.atlanta.example.com
t=0 0
a=tcap:1 RTP/SAVPF
a=tcap:2 RTP/SAVP
a=group:BUNDLE audio video
m=audio
a=mid:audio
a=pcfg:1 t=1
a=pcfg:2
m=video
a=mid:video
a=pcfg:1 t=1
a=pcfg:2 t=2in this example, the potential configurations offering the RTP/SAVPF transport-protocol capability both have configuration number "1" in the audio and video media descriptions 💜 that's the matching pair, bestie 🫶
14.2.1.2. Example: Attribute-Capability Multiplexing 🌸
v=0
o=alice 2890844526 2890844527 IN IP4 host.atlanta.example.com
s=
c=IN IP4 host.atlanta.example.com
t=0 0
a=acap:1 a=rtcp-mux
a=acap:2 a=crypto:1 AES_CM_128_HMAC_SHA1_80
inline:EcGZiNWpFJhQXdspcl1ekcmVCNWpVLcfHAwJSoj|2^20|1:32
a=group:BUNDLE audio video
m=audio 49172 RTP/AVP 99
a=mid:audio
a=pcfg:1 a=1
a=pcfg:2
m=video 560024 RTP/AVP 100
a=mid:video
a=pcfg:1 a=1
a=pcfg:2 a=2in this one, the potential configuration number "1" gets repeated for the a=rtcp-mux attribute capability, because the behavior is IDENTICAL for a=rtcp-mux under multiplexing 🙈✨ same vibe, same number, no drama 💅
14.3. RFC 6871 Analysis 🧚
[RFC6871] extends the capability negotiation framework described in [RFC5939] by defining media capabilities that can be used to indicate and negotiate media types and their associated format parameters 🎀 it also lets you indicate latent configurations and session capabilities 🌈
14.3.1. Recommendation: Dealing with Payload Type Numbers 🍓
[RFC6871] defines a new payload type parameter ("pt") to be used with the potential, actual, and latent configuration parameters 💖 the parameter associates RTP payload type numbers with the referenced RTP-based media-format capabilities ("a=rmcap") defined in [RFC6871], and it's only appropriate when the transport protocol uses RTP 🦋 this means the same payload type number can be assigned as part of potential or actual configurations in different media descriptions in a bundle ✨ there are rules for using identical payload type values across multiplexed "m=" lines, described in [RFC8843], which must be followed here, as well 👑 and as described in Section 14.2.1, using identical configuration numbers for compatible configurations in different bundled media descriptions gives the answerer a way to easily pick compatible configurations here too 🫶
14.3.1.1. Example: Attribute Capability under Shared Payload Type 💜
The attributes "a=rmcap" and "a=mfcap" follow the above recommendations under multiplexing 🌸
v=0
o=- 25678 753849 IN IP4 192.0.2.1
s=
c=IN IP4 192.0.2.1
t=0 0
a=creq:med-v0
m=audio 54322 RTP/AVP 96
a=rtpmap:96 AMR-WB/16000/1
a=fmtp:96 mode-change-capability=1; max-red=220;
mode-set=0,2,4,7
a=rmcap:1,3 audio AMR-WB/16000/1
a=rmcap:2 audio AMR/8000/1
a=mfcap:1,2 mode-change-capability=1
a=mfcap:3 mode-change-capability=2
a=pcfg:1 m=1 pt=1:96
a=pcfg:2 m=2 pt=2:97
a=pcfg:3 m=3 pt=3:98
m=audio 54322 RTP/AVP 96
a=rtpmap:96 AMR-WB/16000/1
a=fmtp:96 mode-change-capability=1; max-red=220;
mode-set=0,2,4,7
a=rmcap:4 audio AMR/8000/1
a=rmcap:5 audio OPUS/48000/2
a=mfcap:5 minptime=40
a=mfcap:4 mode-change-capability=1
a=pcfg:1 m=4 pt=4:97
a=pcfg:4 m=5 pt=5:101in this example, the potential configuration number "1" gets repeated when referring to the media and media-format capabilities used for Payload Type 96 🎀 that means media capabilities 2 and 4, along with their media-format capabilities, MUST refer to the same codec configuration, per the definition of IDENTICAL-PER-PT 😭💅
14.3.2. Recommendation: Dealing with Latent Configurations 🦋
[RFC6871] adds the notion of a latent configuration, which provides configuration information that may be used to guide a subsequent offer/exchange, e.g., by adding another media stream or using alternative codec combinations not currently offered 🌈 latent configurations have configuration numbers that cannot overlap with the potential configuration numbers [RFC6871] 🧚 supported combinations of potential and latent configurations are indicated with the "a=sescap" attribute, but use of this attribute is not recommended with multiplexed media, since it requires unique configuration numbers across the SDP 💀 taken together, there's no well-defined way to indicate supported combinations of latent configurations, or combinations of latent and potential configurations, with multiplexed media 🙈 it's still allowed to use the latent configuration attribute, but the limitations above will apply 🍓 to figure out valid combinations, actual negotiation will have to be attempted subsequently instead ✨
15. IANA Considerations 👑
Section 15.1 defines a new subregistry, added by the IANA, for identifying the initial registrations for the various multiplexing categories applicable as described in this document 🌸
IANA has added a new column named "Mux Category" to several of the subregistries in the "Session Description Protocol (SDP) Parameters" registry 💖 the tables in Section 15.2 identify the names of entries in the existing subregistries and specify the value to be put in the new "Mux Category" column of the associated IANA registry for each one 🦋
15.1. New "Multiplexing Categories" Subregistry 🎀
A new subregistry has been created 💜 it's called "Multiplexing Categories" and it has the following registrations initially:
+=========================+===========+
| Multiplexing Categories | Reference |
+=========================+===========+
| NORMAL | RFC 8859 |
+-------------------------+-----------+
| CAUTION | RFC 8859 |
+-------------------------+-----------+
| IDENTICAL | RFC 8859 |
+-------------------------+-----------+
| TRANSPORT | RFC 8859 |
+-------------------------+-----------+
| SUM | RFC 8859 |
+-------------------------+-----------+
| INHERIT | RFC 8859 |
+-------------------------+-----------+
| IDENTICAL-PER-PT | RFC 8859 |
+-------------------------+-----------+
| SPECIAL | RFC 8859 |
+-------------------------+-----------+
| TBD | RFC 8859 |
+-------------------------+-----------+Table 80 🍓
further entries can be registered using the Standard Actions policies outlined in [RFC8126], which requires IESG review and approval and Standards Track IETF RFC publication 👑
each registration needs to indicate the multiplexing category value to be added to the "Multiplexing Categories" subregistry, as defined in this section 🌈
such a registration MUST also indicate the applicability of the newly defined multiplexing category value to the various subregistries defined in the "Session Description Protocol (SDP) Parameters" registry 💀
15.2. "Mux Category" Column for Subregistries 🧚
each subsection identifies a subregistry of the "Session Description Protocol (SDP) Parameters" registry 🦋 the tables list the column that identifies the SDP attribute name/Token/Value from the corresponding subregistries, plus the values to be used for the new "Mux Category" column being added ✨
entries in the existing subregistries of the "Session Description Protocol (SDP) Parameters" registry that lack a value for "Mux Category" in this specification will get a value of "TBD" 💖
the registration policy for updates to the "Mux Category" column values for existing parameters, or for registering new parameters, is beyond the scope of this document 🫶 the registration policy for the affected table is defined in [RFC8866] 🌸
15.2.1. Table: SDP bwtype ✨
okay so this is where we add new rows to the "bwtype" subregistry of the "Session Description Protocol (SDP) Parameters" registry 🎀 and the references get updated to point at this RFC too, right alongside the older ones, so nobody loses their place 💖
+==========+==============+
| SDP Name | Mux Category |
+==========+==============+
| CT | NORMAL |
+----------+--------------+
| AS | SUM |
+----------+--------------+
| RS | SUM |
+----------+--------------+
| RR | SUM |
+----------+--------------+
| TIAS | SPECIAL |
+----------+--------------+
Table 8115.2.2. Table: attribute-name 💅
same energy here 🦋 the new values go into the "attribute-name" (formerly "att-field") subregistry of that same registry, and the references get updated to include this RFC along with the previous ones 🌸
NOTE: the attributes from [FLUTE] ("flute-tsi", "flute-ch", "FEC-declaration", "FEC-OTI-extension", "content-desc") were not analyzed for their multiplexing behavior 😭 because that draft has expired. so for the purposes of this spec, they get the multiplexing category of TBD 🫶
+==========================+==================+
| SDP Name | Mux Category |
+==========================+==================+
| cat | NORMAL |
+--------------------------+------------------+
| keywds | NORMAL |
+--------------------------+------------------+
| type | NORMAL |
+--------------------------+------------------+
| type:broadcast | NORMAL |
+--------------------------+------------------+
| type:H332 | NORMAL |
+--------------------------+------------------+
| type:meeting | NORMAL |
+--------------------------+------------------+
| type:moderated | NORMAL |
+--------------------------+------------------+
| type:test | NORMAL |
+--------------------------+------------------+
| charset | NORMAL |
+--------------------------+------------------+
| charset:iso8895-1 | NORMAL |
+--------------------------+------------------+
| tool | NORMAL |
+--------------------------+------------------+
| ipbcp | SPECIAL |
+--------------------------+------------------+
| group | NORMAL |
+--------------------------+------------------+
| ice-lite | NORMAL |
+--------------------------+------------------+
| ice-options | NORMAL |
+--------------------------+------------------+
| bcastversion | NORMAL |
+--------------------------+------------------+
| 3GPP-Integrity-Key | CAUTION |
+--------------------------+------------------+
| 3GPP-SDP-Auth | CAUTION |
+--------------------------+------------------+
| alt-group | CAUTION |
+--------------------------+------------------+
| PSCid | NORMAL |
+--------------------------+------------------+
| bc_service | NORMAL |
+--------------------------+------------------+
| bc_program | NORMAL |
+--------------------------+------------------+
| bc_service_package | NORMAL |
+--------------------------+------------------+
| sescap | CAUTION |
+--------------------------+------------------+
| rtsp-ice-d-m | TBD |
+--------------------------+------------------+
| recvonly | NORMAL |
+--------------------------+------------------+
| sendrecv | NORMAL |
+--------------------------+------------------+
| sendonly | NORMAL |
+--------------------------+------------------+
| sdplang | NORMAL |
+--------------------------+------------------+
| lang | NORMAL |
+--------------------------+------------------+
| h248item | SPECIAL |
+--------------------------+------------------+
| sqn | NORMAL |
+--------------------------+------------------+
| cdsc | NORMAL |
+--------------------------+------------------+
| cpar | INHERIT |
+--------------------------+------------------+
| cparmin | SPECIAL |
+--------------------------+------------------+
| cparmax | SPECIAL |
+--------------------------+------------------+
| rtcp-xr | NORMAL |
+--------------------------+------------------+
| maxprate | SPECIAL |
+--------------------------+------------------+
| setup | TRANSPORT |
+--------------------------+------------------+
| connection | TRANSPORT |
+--------------------------+------------------+
| key-mgmt | IDENTICAL |
+--------------------------+------------------+
| source-filter | IDENTICAL |
+--------------------------+------------------+
| inactive | NORMAL |
+--------------------------+------------------+
| fingerprint | TRANSPORT |
+--------------------------+------------------+
| flute-tsi | TBD |
+--------------------------+------------------+
| flute-ch | TBD |
+--------------------------+------------------+
| FEC-declaration | TBD |
+--------------------------+------------------+
| FEC-OTI-extension | TBD |
+--------------------------+------------------+
| content-desc | TBD |
+--------------------------+------------------+
| ice-pwd | TRANSPORT |
+--------------------------+------------------+
| ice-ufrag | TRANSPORT |
+--------------------------+------------------+
| stkmstream | NORMAL |
+--------------------------+------------------+
| extmap | SPECIAL |
+--------------------------+------------------+
| qos-mech-send | TRANSPORT |
+--------------------------+------------------+
| qos-mech-recv | TRANSPORT |
+--------------------------+------------------+
| csup | NORMAL |
+--------------------------+------------------+
| creq | NORMAL |
+--------------------------+------------------+
| acap | INHERIT |
+--------------------------+------------------+
| tcap | INHERIT |
+--------------------------+------------------+
| 3GPP-QoE-Metrics | CAUTION |
+--------------------------+------------------+
| 3GPP-Asset-Information | CAUTION |
+--------------------------+------------------+
| mbms-mode | CAUTION |
+--------------------------+------------------+
| mbms-repair | CAUTION |
+--------------------------+------------------+
| ike-setup | IDENTICAL |
+--------------------------+------------------+
| psk-fingerprint | IDENTICAL |
+--------------------------+------------------+
| multicast-rtcp | IDENTICAL |
+--------------------------+------------------+
| rmcap | IDENTICAL-PER-PT |
+--------------------------+------------------+
| omcap | NORMAL |
+--------------------------+------------------+
| mfcap | IDENTICAL-PER-PT |
+--------------------------+------------------+
| mscap | INHERIT |
+--------------------------+------------------+
| 3gpp.iut.replication | TBD |
+--------------------------+------------------+
| bcap | INHERIT |
+--------------------------+------------------+
| ccap | IDENTICAL |
+--------------------------+------------------+
| icap | NORMAL |
+--------------------------+------------------+
| etag | CAUTION |
+--------------------------+------------------+
| duplication-delay | NORMAL |
+--------------------------+------------------+
| range | CAUTION |
+--------------------------+------------------+
| control | CAUTION |
+--------------------------+------------------+
| mtag | CAUTION |
+--------------------------+------------------+
| ts-refclk | NORMAL |
+--------------------------+------------------+
| mediaclk | NORMAL |
+--------------------------+------------------+
| calgextmap | NORMAL |
+--------------------------+------------------+
| ptime | IDENTICAL-PER-PT |
+--------------------------+------------------+
| orient | NORMAL |
+--------------------------+------------------+
| orient:portrait | NORMAL |
+--------------------------+------------------+
| orient:landscape | NORMAL |
+--------------------------+------------------+
| orient:seascape | NORMAL |
+--------------------------+------------------+
| framerate | IDENTICAL-PER-PT |
+--------------------------+------------------+
| quality | NORMAL |
+--------------------------+------------------+
| rtpmap | IDENTICAL-PER-PT |
+--------------------------+------------------+
| fmtp | IDENTICAL-PER-PT |
+--------------------------+------------------+
| rtpred1 | CAUTION |
+--------------------------+------------------+
| rtpred2 | CAUTION |
+--------------------------+------------------+
| T38FaxVersion | TBD |
+--------------------------+------------------+
| T38MaxBitRate | TBD |
+--------------------------+------------------+
| T38FaxFillBitRemoval | TBD |
+--------------------------+------------------+
| T38FaxTranscodingMMR | TBD |
+--------------------------+------------------+
| T38FaxTranscodingJBIG | TBD |
+--------------------------+------------------+
| T38FaxRateManagement | TBD |
+--------------------------+------------------+
| T38FaxMaxBuffer | TBD |
+--------------------------+------------------+
| T38FaxMaxDatagram | TBD |
+--------------------------+------------------+
| T38FaxUdpEC | TBD |
+--------------------------+------------------+
| maxptime | IDENTICAL-PER-PT |
+--------------------------+------------------+
| des | CAUTION |
+--------------------------+------------------+
| curr | CAUTION |
+--------------------------+------------------+
| conf | CAUTION |
+--------------------------+------------------+
| mid | NORMAL |
+--------------------------+------------------+
| rtcp | TRANSPORT |
+--------------------------+------------------+
| rtcp-fb | IDENTICAL-PER-PT |
+--------------------------+------------------+
| label | NORMAL |
+--------------------------+------------------+
| T38VendorInfo | TBD |
+--------------------------+------------------+
| crypto | TRANSPORT |
+--------------------------+------------------+
| eecid | CAUTION |
+--------------------------+------------------+
| aalType | CAUTION |
+--------------------------+------------------+
| capability | CAUTION |
+--------------------------+------------------+
| qosClass | CAUTION |
+--------------------------+------------------+
| bcob | CAUTION |
+--------------------------+------------------+
| stc | CAUTION |
+--------------------------+------------------+
| upcc | CAUTION |
+--------------------------+------------------+
| atmQOSparms | CAUTION |
+--------------------------+------------------+
| atmTrfcDesc | CAUTION |
+--------------------------+------------------+
| abrParms | CAUTION |
+--------------------------+------------------+
| abrSetup | CAUTION |
+--------------------------+------------------+
| bearerType | CAUTION |
+--------------------------+------------------+
| lij | CAUTION |
+--------------------------+------------------+
| anycast | CAUTION |
+--------------------------+------------------+
| cache | CAUTION |
+--------------------------+------------------+
| bearerSigIE | CAUTION |
+--------------------------+------------------+
| aalApp | CAUTION |
+--------------------------+------------------+
| cbrRate | CAUTION |
+--------------------------+------------------+
| sbc | CAUTION |
+--------------------------+------------------+
| clkrec | CAUTION |
+--------------------------+------------------+
| fec | CAUTION |
+--------------------------+------------------+
| prtfl | CAUTION |
+--------------------------+------------------+
| structure | CAUTION |
+--------------------------+------------------+
| cpsSDUsize | CAUTION |
+--------------------------+------------------+
| aal2CPS | CAUTION |
+--------------------------+------------------+
| aal2CPSSDUrate | CAUTION |
+--------------------------+------------------+
| aal2sscs3661unassured | CAUTION |
+--------------------------+------------------+
| aal2sscs3661assured | CAUTION |
+--------------------------+------------------+
| aal2sscs3662 | CAUTION |
+--------------------------+------------------+
| aal5sscop | CAUTION |
+--------------------------+------------------+
| atmmap | CAUTION |
+--------------------------+------------------+
| silenceSupp | CAUTION |
+--------------------------+------------------+
| ecan | CAUTION |
+--------------------------+------------------+
| gc | CAUTION |
+--------------------------+------------------+
| profileDesc | CAUTION |
+--------------------------+------------------+
| vsel | CAUTION |
+--------------------------+------------------+
| dsel | CAUTION |
+--------------------------+------------------+
| fsel | CAUTION |
+--------------------------+------------------+
| onewaySel | CAUTION |
+--------------------------+------------------+
| codecconfig | CAUTION |
+--------------------------+------------------+
| isup_usi | CAUTION |
+--------------------------+------------------+
| uiLayer1_Prot | CAUTION |
+--------------------------+------------------+
| chain | CAUTION |
+--------------------------+------------------+
| floorctrl | TBD |
+--------------------------+------------------+
| confid | TBD |
+--------------------------+------------------+
| userid | TBD |
+--------------------------+------------------+
| floorid | TBD |
+--------------------------+------------------+
| FEC | NORMAL |
+--------------------------+------------------+
| accept-types | TBD |
+--------------------------+------------------+
| accept-wrapped-types | TBD |
+--------------------------+------------------+
| max-size | TBD |
+--------------------------+------------------+
| path | TBD |
+--------------------------+------------------+
| dccp-service-code | CAUTION |
+--------------------------+------------------+
| rtcp-mux | IDENTICAL |
+--------------------------+------------------+
| candidate | TRANSPORT |
+--------------------------+------------------+
| ice-mismatch | NORMAL |
+--------------------------+------------------+
| remote-candidates | TRANSPORT |
+--------------------------+------------------+
| SRTPAuthentication | TBD |
+--------------------------+------------------+
| SRTPROCTxRate | TBD |
+--------------------------+------------------+
| rtcp-rsize | IDENTICAL |
+--------------------------+------------------+
| file-selector | TBD |
+--------------------------+------------------+
| file-transfer-id | TBD |
+--------------------------+------------------+
| file-disposition | TBD |
+--------------------------+------------------+
| file-date | TBD |
+--------------------------+------------------+
| file-icon | TBD |
+--------------------------+------------------+
| file-range | TBD |
+--------------------------+------------------+
| depend | IDENTICAL-PER-PT |
+--------------------------+------------------+
| ssrc | NORMAL |
+--------------------------+------------------+
| ssrc-group | NORMAL |
+--------------------------+------------------+
| rtcp-unicast | IDENTICAL |
+--------------------------+------------------+
| pcfg | SPECIAL |
+--------------------------+------------------+
| acfg | SPECIAL |
+--------------------------+------------------+
| zrtp-hash | TRANSPORT |
+--------------------------+------------------+
| X-predecbufsize | CAUTION |
+--------------------------+------------------+
| X-initpredecbufperiod | CAUTION |
+--------------------------+------------------+
| X-initpostdecbufperiod | CAUTION |
+--------------------------+------------------+
| X-decbyterate | CAUTION |
+--------------------------+------------------+
| 3gpp-videopostdecbufsize | CAUTION |
+--------------------------+------------------+
| framesize | CAUTION |
+--------------------------+------------------+
| 3GPP-SRTP-Config | CAUTION |
+--------------------------+------------------+
| alt | CAUTION |
+--------------------------+------------------+
| alt-default-id | CAUTION |
+--------------------------+------------------+
| 3GPP-Adaption-Support | CAUTION |
+--------------------------+------------------+
| mbms-flowid | CAUTION |
+--------------------------+------------------+
| fec-source-flow | SPECIAL |
+--------------------------+------------------+
| fec-repair-flow | SPECIAL |
+--------------------------+------------------+
| repair-window | SPECIAL |
+--------------------------+------------------+
| rams-updates | CAUTION |
+--------------------------+------------------+
| imageattr | IDENTICAL-PER-PT |
+--------------------------+------------------+
| cfw-id | NORMAL |
+--------------------------+------------------+
| portmapping-req | CAUTION |
+--------------------------+------------------+
| ecn-capable-rtp | IDENTICAL |
+--------------------------+------------------+
| visited-realm | TRANSPORT |
+--------------------------+------------------+
| secondary-realm | TRANSPORT |
+--------------------------+------------------+
| omr-s-cksum | NORMAL |
+--------------------------+------------------+
| omr-m-cksum | NORMAL |
+--------------------------+------------------+
| omr-codecs | NORMAL |
+--------------------------+------------------+
| omr-m-att | NORMAL |
+--------------------------+------------------+
| omr-s-att | NORMAL |
+--------------------------+------------------+
| omr-m-bw | NORMAL |
+--------------------------+------------------+
| omr-s-bw | NORMAL |
+--------------------------+------------------+
| msrp-cema | TBD |
+--------------------------+------------------+
| dccp-port | CAUTION |
+--------------------------+------------------+
| resource | NORMAL |
+--------------------------+------------------+
| channel | NORMAL |
+--------------------------+------------------+
| cmid | NORMAL |
+--------------------------+------------------+
| content | NORMAL |
+--------------------------+------------------+
| lcfg | SPECIAL |
+--------------------------+------------------+
| loopback | NORMAL |
+--------------------------+------------------+
| loopback-source | NORMAL |
+--------------------------+------------------+
| loopback-mirror | NORMAL |
+--------------------------+------------------+
| chatroom | TBD |
+--------------------------+------------------+
| altc | TRANSPORT |
+--------------------------+------------------+
| T38FaxMaxIFP | TBD |
+--------------------------+------------------+
| T38FaxUdpECDepth | TBD |
+--------------------------+------------------+
| T38FaxUdpFECMaxSpan | TBD |
+--------------------------+------------------+
| T38ModemType | TBD |
+--------------------------+------------------+
| cs-correlation | TBD |
+--------------------------+------------------+
| rtcp-idms | NORMAL |
+--------------------------+------------------+
| cname | NORMAL |
+--------------------------+------------------+
| previous-ssrc | NORMAL |
+--------------------------+------------------+
| fmtp | IDENTICAL-PER-PT |
+--------------------------+------------------+
| ts-refclk | NORMAL |
+--------------------------+------------------+
| mediaclk | NORMAL |
+--------------------------+------------------+
Table 8215.2.3. Table: content SDP Parameters ✨
okay so the "content SDP Parameters" subregistry of the "Session Description Protocol (SDP) Parameters" registry just got a glow-up 🎀 these values are new bestties in there, and the references now point to this RFC too, alongside the old ones 💖
+============+==============+
| SDP Name | Mux Category |
+============+==============+
| slides | NORMAL |
+------------+--------------+
| speaker | NORMAL |
+------------+--------------+
| sl | NORMAL |
+------------+--------------+
| main | NORMAL |
+------------+--------------+
| alt | NORMAL |
+------------+--------------+
| g.3gpp.cat | NORMAL |
+------------+--------------+
| g.3gpp.crs | NORMAL |
+------------+--------------+
Table 8315.2.4. Table: Semantics for the "group" SDP Attribute 🧚
the "Semantics for the 'group' SDP Attribute" subregistry of the "Session Description Protocol (SDP) Parameters" registry is getting new tokens 🌸 same deal as before: the references now point to this RFC as well as the previous ones ✨
+========+==============+
| Token | Mux Category |
+========+==============+
| LS | NORMAL |
+--------+--------------+
| FID | NORMAL |
+--------+--------------+
| SRF | NORMAL |
+--------+--------------+
| ANAT | CAUTION |
+--------+--------------+
| FEC | NORMAL |
+--------+--------------+
| FEC-FR | NORMAL |
+--------+--------------+
| CS | NORMAL |
+--------+--------------+
| DDP | NORMAL |
+--------+--------------+
| DUP | NORMAL |
+--------+--------------+
Table 84ANAT is the one with the CAUTION category here, so it's the token to keep an eye on 👀
15.2.5. Table: "rtcp-fb" Attribute Values 💅
the "'rtcp-fb' Attribute Values" subregistry of the "Session Description Protocol (SDP) Parameters" registry gets these values 🦋 the references now point to this RFC as well as the previous references.
+============+==================+
| Value Name | Mux Category |
+============+==================+
| ack | IDENTICAL-PER-PT |
+------------+------------------+
| app | SPECIAL |
+------------+------------------+
| ccm | IDENTICAL-PER-PT |
+------------+------------------+
| nack | IDENTICAL-PER-PT |
+------------+------------------+
| trr-int | IDENTICAL-PER-PT |
+------------+------------------+
Table 8515.2.6. Table: "ack" and "nack" Attribute Values 🫶
the "'ack' and 'nack' Attribute Values" subregistry of the "Session Description Protocol (SDP) Parameters" registry got new values too 🔥 and yes, the references point to this RFC now as well as the older ones.
+============+==================+
| Value Name | Mux Category |
+============+==================+
| sli | IDENTICAL-PER-PT |
+------------+------------------+
| pli | IDENTICAL-PER-PT |
+------------+------------------+
| rpsi | IDENTICAL-PER-PT |
+------------+------------------+
| app | SPECIAL |
+------------+------------------+
| rai | IDENTICAL-PER-PT |
+------------+------------------+
| tllei | IDENTICAL-PER-PT |
+------------+------------------+
| pslei | IDENTICAL-PER-PT |
+------------+------------------+
| ecn | IDENTICAL |
+------------+------------------+
Table 8615.2.7. Table: "depend" SDP Attribute Values 🌈
the "'depend' SDP Attribute Values" subregistry of the "Session Description Protocol (SDP) Parameters" registry gets two new values 💜 the references now point to this RFC as well as the previous ones.
+=======+==================+
| Token | Mux Category |
+=======+==================+
| lay | IDENTICAL-PER-PT |
+-------+------------------+
| mdc | IDENTICAL-PER-PT |
+-------+------------------+
Table 8715.2.8. Table: "cs-correlation" Attribute Values 🙈
the "'cs-correlation' Attribute Values" subregistry of the "Session Description Protocol (SDP) Parameters" registry gets four new values. Their Mux Category is TBD, which means they haven't been decided yet 🍓 the references point to this RFC as well as the previous references.
+==========+==============+
| Value | Mux Category |
+==========+==============+
| callerid | TBD |
+----------+--------------+
| uuie | TBD |
+----------+--------------+
| dtmf | TBD |
+----------+--------------+
| external | TBD |
+----------+--------------+
Table 8815.2.9. Table: Semantics for the "ssrc-group" SDP Attribute 🎀
the "Semantics for the 'ssrc-group' SDP Attribute" subregistry of the "Session Description Protocol (SDP) Parameters" registry gets four tokens 💖 the references now point to this RFC as well as the previous references.
+========+==============+
| Token | Mux Category |
+========+==============+
| FID | NORMAL |
+--------+--------------+
| FEC | NORMAL |
+--------+--------------+
| FEC-FR | NORMAL |
+--------+--------------+
| DUP | NORMAL |
+--------+--------------+
Table 8915.2.10. Table: SDP/RTSP Key Management Protocol Identifiers 🔐
the "SDP/RTSP key management protocol identifiers" subregistry of the "Session Description Protocol (SDP) Parameters" registry gets mikey 🦋 it's marked IDENTICAL and the references point to this RFC as well as the previous ones.
+============+==============+
| Value Name | Mux Category |
+============+==============+
| mikey | IDENTICAL |
+------------+--------------+
Table 9015.2.11. Table: Codec Control Messages 🎬
the "Codec Control Messages" subregistry of the "Session Description Protocol (SDP) Parameters" registry gets four new values ✨ the references now point to this RFC as well as the previous references.
+============+==================+
| Value Name | Mux Category |
+============+==================+
| fir | IDENTICAL-PER-PT |
+------------+------------------+
| tmmbr | IDENTICAL-PER-PT |
+------------+------------------+
| tstr | IDENTICAL-PER-PT |
+------------+------------------+
| vbcm | IDENTICAL-PER-PT |
+------------+------------------+
Table 9115.2.12. Table: QoS Mechanism Tokens 🚀
the "QoS Mechanism Tokens" subregistry of the "Session Description Protocol (SDP) Parameters" registry gets rsvp and nsis, both in the TRANSPORT category 💅 the references point to this RFC as well as the previous ones.
+===============+==============+
| QoS Mechanism | Mux Category |
+===============+==============+
| rsvp | TRANSPORT |
+---------------+--------------+
| nsis | TRANSPORT |
+---------------+--------------+
Table 9215.2.13. Table: SDP Capability Negotiation Option Tags 🌸
the "SDP Capability Negotiation Option Tags" subregistry of the "Session Description Protocol (SDP) Parameters" registry gets five new option tags 🫶 they're all NORMAL, and the references point to this RFC as well as the previous references.
+============+==============+
| Option Tag | Mux Category |
+============+==============+
| cap-v0 | NORMAL |
+------------+--------------+
| med-v0 | NORMAL |
+------------+--------------+
| bcap-v0 | NORMAL |
+------------+--------------+
| ccap-v0 | NORMAL |
+------------+--------------+
| icap-v0 | NORMAL |
+------------+--------------+
Table 9315.2.14. Table: Timestamp Reference Clock Source Parameters ⏰
the "Timestamp Reference Clock Source Parameters" subregistry of the "Session Description Protocol (SDP) Parameters" registry gets seven values, and every single one is NORMAL 💜 the references now point to this RFC as well as the previous ones.
+=========+==============+
| Name | Mux Category |
+=========+==============+
| ntp | NORMAL |
+---------+--------------+
| ptp | NORMAL |
+---------+--------------+
| gps | NORMAL |
+---------+--------------+
| gal | NORMAL |
+---------+--------------+
| glonass | NORMAL |
+---------+--------------+
| local | NORMAL |
+---------+--------------+
| private | NORMAL |
+---------+--------------+
Table 9415.2.15. Table: Media Clock Source Parameters 🎧
the "Media Clock Source Parameters" subregistry of the "Session Description Protocol (SDP) Parameters" registry gets three values 🌈 they're all NORMAL, and the references point to this RFC as well as the previous references.
+==========+==============+
| Name | Mux Category |
+==========+==============+
| sender | NORMAL |
+----------+--------------+
| direct | NORMAL |
+----------+--------------+
| IEEE1722 | NORMAL |
+----------+--------------+
Table 9516. Security Considerations 🔒
okay, serious moment 😤 the main security stuff for RTP, including how it's being used here, is covered in [RFC3550] and [RFC3711]. go read those, periodt.
when you multiplex SDP attributes that have the "CAUTION" category, the implementations should be aware of the possible issues described in this specification. no cap, that's the vibe check you don't want to fail 💀
17. References 📚
17.1. Normative References 💖
[RFC2119]: Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>.[RFC4566]: Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, DOI 10.17487/RFC4566, July 2006, <https://www.rfc-editor.org/info/rfc4566>.[RFC8126]: Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www.rfc-editor.org/info/rfc8126>.[RFC8174]: Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>.[RFC8843]: Holmberg, C., Alvestrand, H., and C. Jennings, "Negotiating Media Multiplexing Using the Session Description Protocol (SDP)", RFC 8843, DOI 10.17487/RFC8843, January 2021, <https://www.rfc-editor.org/info/rfc8843>.
17.2. Informative References 🧠
[FLUTE]: Walsh, R., Peltotalo, J., Peltotalo, S., Curcio, I. D., and H. Mehta, "SDP Descriptors for FLUTE", Work in Progress, Internet-Draft, draft-ietf-rmt-flute-sdp-03, 12 September 2012, <https://tools.ietf.org/html/draft-ietf-rmt-flute-sdp-03>.
[H.248.15] ITU-T, "Gateway control protocol: SDP ITU-T H.248 package attribute", ITU-T Recommendation H.248.15, March 2013, <https://www.itu.int/rec/T-REC-H.248.15>.
[IANA] IANA, "Session Description Protocol (SDP) Parameters", <https://www.iana.org/assignments/sdp-parameters>.
[IMS-CAT] 3GPP, "IP Multimedia Subsystem (IMS) Customized Alerting Tones (CAT); Protocol specification", Specification 24.182, Specification 24.182, January 2015, <https://www.3gpp.org/ftp/Specs/html-info/24182.htm>.
[IMS-CRS] 3GPP, "IP Multimedia Subsystem (IMS) Customized Ringing Signal (CRS); Protocol specification", Specification 24.183, September 2016, <https://www.3gpp.org/ftp/Specs/html-info/24183.htm>.
[IP-CALL] 3GPP, "IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3", Specification 24.229, September 2016, <https://www.3gpp.org/ftp/Specs/html-info/24229.htm>.
[Q.1970] ITU-T, "Q.1970: BICC IP bearer control protocol", ITU-T Recommendation Q.1970, September 2006, <https://www.itu.int/rec/T-REC-Q.1970-200609-I/en>.
[RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming Protocol (RTSP)", RFC 2326, DOI 10.17487/RFC2326, April 1998, <https://www.rfc-editor.org/info/rfc2326>.
[RFC3108] Kumar, R. and M. Mostafa, "Conventions for the use of the Session Description Protocol (SDP) for ATM Bearer Connections", RFC 3108, DOI 10.17487/RFC3108, May 2001, <https://www.rfc-editor.org/info/rfc3108>.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, DOI 10.17487/RFC3264, June 2002, <https://www.rfc-editor.org/info/rfc3264>.
[RFC3312] Camarillo, G., Ed., Marshall, W., Ed., and J. Rosenberg, "Integration of Resource Management and Session Initiation Protocol (SIP)", RFC 3312, DOI 10.17487/RFC3312, October 2002, <https://www.rfc-editor.org/info/rfc3312>.
[RFC3407] Andreasen, F., "Session Description Protocol (SDP) Simple Capability Declaration", RFC 3407, DOI 10.17487/RFC3407, October 2002, <https://www.rfc-editor.org/info/rfc3407>.
[RFC3524] Camarillo, G. and A. Monrad, "Mapping of Media Streams to Resource Reservation Flows", RFC 3524, DOI 10.17487/RFC3524, April 2003, <https://www.rfc-editor.org/info/rfc3524>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, July 2003, <https://www.rfc-editor.org/info/rfc3550>.
[RFC3556] Casner, S., "Session Description Protocol (SDP) Bandwidth Modifiers for RTP Control Protocol (RTCP) Bandwidth", RFC 3556, DOI 10.17487/RFC3556, July 2003, <https://www.rfc-editor.org/info/rfc3556>.
[RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute in Session Description Protocol (SDP)", RFC 3605, DOI 10.17487/RFC3605, October 2003, <https://www.rfc-editor.org/info/rfc3605>.
[RFC3611] Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed., "RTP Control Protocol Extended Reports (RTCP XR)", RFC 3611, DOI 10.17487/RFC3611, November 2003, <https://www.rfc-editor.org/info/rfc3611>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, DOI 10.17487/RFC3711, March 2004, <https://www.rfc-editor.org/info/rfc3711>.
[RFC3890] Westerlund, M., "A Transport Independent Bandwidth Modifier for the Session Description Protocol (SDP)", RFC 3890, DOI 10.17487/RFC3890, September 2004, <https://www.rfc-editor.org/info/rfc3890>.
[RFC4091] Camarillo, G. and J. Rosenberg, "The Alternative Network Address Types (ANAT) Semantics for the Session Description Protocol (SDP) Grouping Framework", RFC 4091, DOI 10.17487/RFC4091, June 2005, <https://www.rfc-editor.org/info/rfc4091>.
[RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the Session Description Protocol (SDP)", RFC 4145, DOI 10.17487/RFC4145, September 2005, <https://www.rfc-editor.org/info/rfc4145>.
[RFC4567] Arkko, J., Lindholm, F., Naslund, M., Norrman, K., and E. Carrara, "Key Management Extensions for Session Description Protocol (SDP) and Real Time Streaming Protocol (RTSP)", RFC 4567, DOI 10.17487/RFC4567, July 2006, <https://www.rfc-editor.org/info/rfc4567>.
[RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session Description Protocol (SDP) Security Descriptions for Media Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006, <https://www.rfc-editor.org/info/rfc4568>.
[RFC4570] Quinn, B. and R. Finlayson, "Session Description Protocol (SDP) Source Filters", RFC 4570, DOI 10.17487/RFC4570, July 2006, <https://www.rfc-editor.org/info/rfc4570>.
[RFC4572] Lennox, J., "Connection-Oriented Media Transport over the Transport Layer Security (TLS) Protocol in the Session Description Protocol (SDP)", RFC 4572, DOI 10.17487/RFC4572, July 2006, <https://www.rfc-editor.org/info/rfc4572>.
[RFC4574] Levin, O. and G. Camarillo, "The Session Description Protocol (SDP) Label Attribute", RFC 4574, DOI 10.17487/RFC4574, August 2006, <https://www.rfc-editor.org/info/rfc4574>.
[RFC4583] Camarillo, G., "Session Description Protocol (SDP) Format for Binary Floor Control Protocol (BFCP) Streams", RFC 4583, DOI 10.17487/RFC4583, November 2006, <https://www.rfc-editor.org/info/rfc4583>.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, "Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, DOI 10.17487/RFC4585, July 2006, <https://www.rfc-editor.org/info/rfc4585>.
[RFC4796] Hautakorpi, J. and G. Camarillo, "The Session Description Protocol (SDP) Content Attribute", RFC 4796, DOI 10.17487/RFC4796, February 2007, <https://www.rfc-editor.org/info/rfc4796>.
[RFC4975] Campbell, B., Ed., Mahy, R., Ed., and C. Jennings, Ed., "The Message Session Relay Protocol (MSRP)", RFC 4975, DOI 10.17487/RFC4975, September 2007, <https://www.rfc-editor.org/info/rfc4975>.
[RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, "Codec Control Messages in the RTP Audio-Visual Profile with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104, February 2008, <https://www.rfc-editor.org/info/rfc5104>.
[RFC5109] Li, A., Ed., "RTP Payload Format for Generic Forward Error Correction", RFC 5109, DOI 10.17487/RFC5109, December 2007, <https://www.rfc-editor.org/info/rfc5109>.
[RFC5159] Dondeti, L., Ed. and A. Jerichow, "Session Description Protocol (SDP) Attributes for Open Mobile Alliance (OMA) Broadcast (BCAST) Service and Content Protection", RFC 5159, DOI 10.17487/RFC5159, March 2008, <https://www.rfc-editor.org/info/rfc5159>.
[RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 2008, <https://www.rfc-editor.org/info/rfc5285>.
[RFC5432] Polk, J., Dhesikan, S., and G. Camarillo, "Quality of Service (QoS) Mechanism Selection in the Session Description Protocol (SDP)", RFC 5432, DOI 10.17487/RFC5432, March 2009, <https://www.rfc-editor.org/info/rfc5432>.
[RFC5506] Johansson, I. and M. Westerlund, "Support for Reduced-Size Real-Time Transport Control Protocol (RTCP): Opportunities and Consequences", RFC 5506, DOI 10.17487/RFC5506, April 2009, <https://www.rfc-editor.org/info/rfc5506>.
[RFC5547] Garcia-Martin, M., Isomaki, M., Camarillo, G., Loreto, S., and P. Kyzivat, "A Session Description Protocol (SDP) Offer/Answer Mechanism to Enable File Transfer", RFC 5547, DOI 10.17487/RFC5547, May 2009, <https://www.rfc-editor.org/info/rfc5547>.
[RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific Media Attributes in the Session Description Protocol (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009, <https://www.rfc-editor.org/info/rfc5576>.
[RFC5583] Schierl, T. and S. Wenger, "Signaling Media Decoding Dependency in the Session Description Protocol (SDP)", RFC 5583, DOI 10.17487/RFC5583, July 2009, <https://www.rfc-editor.org/info/rfc5583>.
[RFC5760] Ott, J., Chesterfield, J., and E. Schooler, "RTP Control Protocol (RTCP) Extensions for Single-Source Multicast Sessions with Unicast Feedback", RFC 5760, DOI 10.17487/RFC5760, February 2010, <https://www.rfc-editor.org/info/rfc5760>.
[RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and Control Packets on a Single Port", RFC 5761, DOI 10.17487/RFC5761, April 2010, <https://www.rfc-editor.org/info/rfc5761>.
[RFC5762] Perkins, C., "RTP and the Datagram Congestion Control Protocol (DCCP)", RFC 5762, DOI 10.17487/RFC5762, April 2010, <https://www.rfc-editor.org/info/rfc5762>.
[RFC5763] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework for Establishing a Secure Real-time Transport Protocol (SRTP) Security Context Using Datagram Transport Layer Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May 2010, <https://www.rfc-editor.org/info/rfc5763>.
[RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description Protocol (SDP) Grouping Framework", RFC 5888, DOI 10.17487/RFC5888, June 2010, <https://www.rfc-editor.org/info/rfc5888>.
[RFC5939] Andreasen, F., "Session Description Protocol (SDP) Capability Negotiation", RFC 5939, DOI 10.17487/RFC5939, September 2010, <https://www.rfc-editor.org/info/rfc5939>.
[RFC5956] Begen, A., "Forward Error Correction Grouping Semantics in the Session Description Protocol", RFC 5956, DOI 10.17487/RFC5956, September 2010, <https://www.rfc-editor.org/info/rfc5956>.
[RFC6064] Westerlund, M. and P. Frojdh, "SDP and RTSP Extensions Defined for 3GPP Packet-Switched Streaming Service and Multimedia Broadcast/Multicast Service", RFC 6064, DOI 10.17487/RFC6064, January 2011, <https://www.rfc-editor.org/info/rfc6064>.
[RFC6128] Begen, A., "RTP Control Protocol (RTCP) Port for Source-
Specific Multicast (SSM) Sessions", RFC 6128,
DOI 10.17487/RFC6128, February 2011,
<https://www.rfc-editor.org/info/rfc6128>.
[RFC6189] Zimmermann, P., Johnston, A., Ed., and J. Callas, "ZRTP:
Media Path Key Agreement for Unicast Secure RTP",
RFC 6189, DOI 10.17487/RFC6189, April 2011,
<https://www.rfc-editor.org/info/rfc6189>.
[RFC6193] Saito, M., Wing, D., and M. Toyama, "Media Description for
the Internet Key Exchange Protocol (IKE) in the Session
Description Protocol (SDP)", RFC 6193,
DOI 10.17487/RFC6193, April 2011,
<https://www.rfc-editor.org/info/rfc6193>.
[RFC6230] Boulton, C., Melanchuk, T., and S. McGlashan, "Media
Control Channel Framework", RFC 6230,
DOI 10.17487/RFC6230, May 2011,
<https://www.rfc-editor.org/info/rfc6230>.
[RFC6236] Johansson, I. and K. Jung, "Negotiation of Generic Image
Attributes in the Session Description Protocol (SDP)",
RFC 6236, DOI 10.17487/RFC6236, May 2011,
<https://www.rfc-editor.org/info/rfc6236>.
[RFC6284] Begen, A., Wing, D., and T. Van Caenegem, "Port Mapping
between Unicast and Multicast RTP Sessions", RFC 6284,
DOI 10.17487/RFC6284, June 2011,
<https://www.rfc-editor.org/info/rfc6284>.
[RFC6285] Ver Steeg, B., Begen, A., Van Caenegem, T., and Z. Vax,
"Unicast-Based Rapid Acquisition of Multicast RTP
Sessions", RFC 6285, DOI 10.17487/RFC6285, June 2011,
<https://www.rfc-editor.org/info/rfc6285>.
[RFC6364] Begen, A., "Session Description Protocol Elements for the
Forward Error Correction (FEC) Framework", RFC 6364,
DOI 10.17487/RFC6364, October 2011,
<https://www.rfc-editor.org/info/rfc6364>.
[RFC6642] Wu, Q., Ed., Xia, F., and R. Even, "RTP Control Protocol
(RTCP) Extension for a Third-Party Loss Report", RFC 6642,
DOI 10.17487/RFC6642, June 2012,
<https://www.rfc-editor.org/info/rfc6642>.
[RFC6679] Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P.,
and K. Carlberg, "Explicit Congestion Notification (ECN)
for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August
2012, <https://www.rfc-editor.org/info/rfc6679>.
[RFC6714] Holmberg, C., Blau, S., and E. Burger, "Connection
Establishment for Media Anchoring (CEMA) for the Message
Session Relay Protocol (MSRP)", RFC 6714,
DOI 10.17487/RFC6714, August 2012,
<https://www.rfc-editor.org/info/rfc6714>.
[RFC6773] Phelan, T., Fairhurst, G., and C. Perkins, "DCCP-UDP: A
Datagram Congestion Control Protocol UDP Encapsulation for
NAT Traversal", RFC 6773, DOI 10.17487/RFC6773, November
2012, <https://www.rfc-editor.org/info/rfc6773>.
[RFC6787] Burnett, D. and S. Shanmugham, "Media Resource Control
Protocol Version 2 (MRCPv2)", RFC 6787,
DOI 10.17487/RFC6787, November 2012,
<https://www.rfc-editor.org/info/rfc6787>.
[RFC6849] Kaplan, H., Ed., Hedayat, K., Venna, N., Jones, P., and N.
Stratton, "An Extension to the Session Description
Protocol (SDP) and Real-time Transport Protocol (RTP) for
Media Loopback", RFC 6849, DOI 10.17487/RFC6849, February
2013, <https://www.rfc-editor.org/info/rfc6849>.
[RFC6871] Gilman, R., Even, R., and F. Andreasen, "Session
Description Protocol (SDP) Media Capabilities
Negotiation", RFC 6871, DOI 10.17487/RFC6871, February
2013, <https://www.rfc-editor.org/info/rfc6871>.
[RFC6947] Boucadair, M., Kaplan, H., Gilman, R., and S.
Veikkolainen, "The Session Description Protocol (SDP)
Alternate Connectivity (ALTC) Attribute", RFC 6947,
DOI 10.17487/RFC6947, May 2013,
<https://www.rfc-editor.org/info/rfc6947>.
[RFC7006] Garcia-Martin, M., Veikkolainen, S., and R. Gilman,
"Miscellaneous Capabilities Negotiation in the Session
Description Protocol (SDP)", RFC 7006,
DOI 10.17487/RFC7006, September 2013,
<https://www.rfc-editor.org/info/rfc7006>.
[RFC7104] Begen, A., Cai, Y., and H. Ou, "Duplication Grouping
Semantics in the Session Description Protocol", RFC 7104,
DOI 10.17487/RFC7104, January 2014,
<https://www.rfc-editor.org/info/rfc7104>.
[RFC7195] Garcia-Martin, M. and S. Veikkolainen, "Session
Description Protocol (SDP) Extension for Setting Audio and
Video Media Streams over Circuit-Switched Bearers in the
Public Switched Telephone Network (PSTN)", RFC 7195,
DOI 10.17487/RFC7195, May 2014,
<https://www.rfc-editor.org/info/rfc7195>.
[RFC7197] Begen, A., Cai, Y., and H. Ou, "Duplication Delay
Attribute in the Session Description Protocol", RFC 7197,
DOI 10.17487/RFC7197, April 2014,
<https://www.rfc-editor.org/info/rfc7197>.
[RFC7266] Clark, A., Wu, Q., Schott, R., and G. Zorn, "RTP Control
Protocol (RTCP) Extended Report (XR) Blocks for Mean
Opinion Score (MOS) Metric Reporting", RFC 7266,
DOI 10.17487/RFC7266, June 2014,
<https://www.rfc-editor.org/info/rfc7266>.
[RFC7272] van Brandenburg, R., Stokking, H., van Deventer, O.,
Boronat, F., Montagud, M., and K. Gross, "Inter-
Destination Media Synchronization (IDMS) Using the RTP
Control Protocol (RTCP)", RFC 7272, DOI 10.17487/RFC7272,
June 2014, <https://www.rfc-editor.org/info/rfc7272>.
[RFC7273] Williams, A., Gross, K., van Brandenburg, R., and H.
Stokking, "RTP Clock Source Signalling", RFC 7273,
DOI 10.17487/RFC7273, June 2014,
<https://www.rfc-editor.org/info/rfc7273>.
[RFC7657] Black, D., Ed. and P. Jones, "Differentiated Services
(Diffserv) and Real-Time Communication", RFC 7657,
DOI 10.17487/RFC7657, November 2015,
<https://www.rfc-editor.org/info/rfc7657>.
[RFC7826] Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M.,
and M. Stiemerling, Ed., "Real-Time Streaming Protocol
Version 2.0", RFC 7826, DOI 10.17487/RFC7826, December
2016, <https://www.rfc-editor.org/info/rfc7826>.
[RFC8122] Lennox, J. and C. Holmberg, "Connection-Oriented Media
Transport over the Transport Layer Security (TLS) Protocol
in the Session Description Protocol (SDP)", RFC 8122,
DOI 10.17487/RFC8122, March 2017,
<https://www.rfc-editor.org/info/rfc8122>.
[RFC8285] Singer, D., Desineni, H., and R. Even, Ed., "A General
Mechanism for RTP Header Extensions", RFC 8285,
DOI 10.17487/RFC8285, October 2017,
<https://www.rfc-editor.org/info/rfc8285>.
[RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", RFC 8445,
DOI 10.17487/RFC8445, July 2018,
<https://www.rfc-editor.org/info/rfc8445>.
[RFC8856] Camarillo, G., Kristensen, T., and C. Holmberg, "Session
Description Protocol (SDP) Format for Binary Floor Control
Protocol (BFCP) Streams", RFC 8856, DOI 10.17487/RFC8856,
January 2021, <https://www.rfc-editor.org/info/rfc8856>.
[RFC8866] Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP:
Session Description Protocol", RFC 8866,
DOI 10.17487/RFC8866, January 2021,
<https://www.rfc-editor.org/info/rfc8866>.
[T.38] ITU-T, "Procedures for real-time Group 3 facsimile
communication over IP networks", ITU-T
Recommendation T.38, November 2015,
<https://www.itu.int/rec/T-REC-T.38/e>.
[TISPAN] ETSI, "Telecommunications and Internet converged Services
and Protocols for Advanced Networking (TISPAN); IMS-based
IPTV stage 3 specification", Technical Specification 183
063 V2.1.0, June 2008, <https://www.etsi.org/deliver/
etsi_ts/183000_183099/183063/02.01.00_60/
ts_183063v020100p.pdf>.
# Acknowledgements 🫶
Okay bestie, time for the big thank-yous! 💖 I would love to thank Cullen Jennings and Flemming Andreasen for suggesting the categories, contributing text, and reviewing the draft of this document. I would also like to thank Magnus Westerlund, Christer Holmberg, Jonathan Lennox, Bo Burman, Ari Keränen, and Dan Wing for suggesting structural changes that improved the document's readability. ✨
I would also like to thank the following experts for their inputs and reviews, as listed: 🌸
Flemming Andreasen (5.24, 5.32, 5.33, 14), Rohan Mahy (5.54), Eric Burger (5.26), Christian Huitema (5.14), Christer Holmberg (5.21, 5.26, 12.2, 12.3), Richard Ejzak (5.44, 5.50, 5.51), Colin Perkins (5.7, 5.8, 5.9, 5.55), Magnus Westerlund (5.2, 5.3, 5.9, 5.27, 5.47, 6.1 - 6.3, 8.3, 7), Roni Even (5.12, 5.27, 8.4), Subha Dhesikan (5.6, 10), Dan Wing (5.7, 5.12, 5.35, 5.39, 5.45), Cullen Jennings (5.40), Ali C Begen (5.1, 5.20, 5.22, 5.25, 5.38, 7.3, 8.2, 8.4, 8.6, 9.2, 13.1), Bo Burman (7.2, 7.6), Charles Eckel (5.15, 5.27, 5.28, 9.1, 8.5), Paul Kyzivat (5.24), Ian Johansson (5.15), Saravanan Shanmugham (5.11), Paul E Jones (5.30), Rajesh Kumar (5.48), Jonathan Lennox (5.36, 5, 15, 9.1, 11.1), Mo Zanaty (5.4, 5.5, 5.23, 8.1, 8.3, 8.5, 12.1), Christian Huitema (5.14), Qin Wu (5.47, PM-Dir review), Hans Stokking (5.43, 5.16), Christian Groves (5.48, 5.52), and Thomas Stach.
Huge shoutout to everyone listed above! 🦋 I would like to thank Chris Lonvick for the SECDIR review, Dan Romascanu for the Gen-ART review, and Sabrina Tanamal for the IANA review. 💅
Thanks to Ben Campbell for Area Director review suggestions. 👑 Thanks to Spencer Dawkins, Stephen Farrel, Alissa Cooper, Mirja Kühlewind, and the entire IESG for their reviews. 🧚
# Author's Address 🎀
Here's where you can find the author, Suhas Nandakumar, at Cisco! 💜
Suhas Nandakumar Cisco 170 West Tasman Drive San Jose, CA 95134 United States of America
Email: snandaku@cisco.com
📦 where this page comes from
- ietf: rfc8859 2021-01
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms