RFC 3524

Mapping of Media Streams to Resource Reservation Flows

📅 published April 2003, from ietf

RFC 3524: Mapping of Media Streams to Resource Reservation Flows 🎀

Network Working Group 💖 Request for Comments: 3524 Authors: Gonzalo Camarillo and Atle Monrad, both at Ericsson ✨ Category: Standards Track 🦋 Date: April 2003 🌸 Obsoletes / Updates: the title block doesn't list anything it obsoletes or updates 🧚

Status of This Memo 📜

This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice ©️

Abstract 🫶

This document adds an extension to the Session Description Protocol (SDP) grouping framework. It lets you ask for a group of media streams to get mapped into one single resource reservation flow. It defines the SDP syntax you need for that, plus a brand new "semantics" attribute called Single Reservation Flow (SRF). 💅

Table of Contents 📚

1.  Introduction ........................................    2
    1.1  Terminology ....................................    2
2.  SRF Semantics .......................................    2
3.  Applicability Statement .............................    3
4.  Examples ............................................    3
5.  IANA Considerations .................................    4
6.  Security Considerations .............................    4
7.  Acknowledgements ....................................    4
8.  Normative References ................................    5
9.  Informative References ..............................    5
10. Authors' Addresses ..................................    5
11. Full Copyright Statement ............................    6

1. Introduction ✨

Okay so, resource reservation protocols give network resources to specific flows of IP packets. When a router gets an IP packet, it runs a filter to figure out which flow that packet belongs to, and then it gives the packet the Quality of Service (QoS) that goes with that flow. Routers usually filter on the source and destination IP addresses and the port numbers. 🦋

Multimedia sessions usually have several media streams, like an audio stream and a video stream. To give QoS to a whole multimedia session, you have to map all of those streams onto resource reservation flows, and there's more than one way to do it. You can map every stream onto a single reservation flow, or you can give every stream its own flow. Some apps need the first option, some need the second, and a single session can even need a mix of both. Like, a session with three streams might want two of them sharing one reservation flow while the third gets a second flow. Main character energy 👑

This document defines the SDP [1] syntax you need to say how media streams should be mapped into reservation flows. To do that, it uses the SDP grouping framework [2] and defines a new "semantics" attribute called Single Reservation Flow (SRF). 🎀

1.1 Terminology 🌈

In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119 [3] and indicate requirement levels for compliant SIP implementations. 📖

2. SRF Semantics 💜

We define a new "semantics" attribute inside the SDP grouping framework [2], and it's called Single Reservation Flow (SRF). 🧚

Media lines grouped with SRF semantics SHOULD be mapped into the same resource reservation flow. Media lines that aren't part of a given SRF group SHOULD NOT be mapped into the reservation flow used for that SRF group. 🔥

Note that an SRF group MAY have just one media line. In that case, following the definition above, that media line will be mapped into one reservation flow. That flow carries traffic from that media line and from no other media lines. 🍓

3. Applicability Statement 🦋

Some resource reservation setups don't need the mechanism in this document at all. Some resource reservation protocols let the entity that generates the SDP session description reserve resources in both directions (that's sendrecv) for the session. When that happens, the generator can choose any mapping of media flows to reservation flows it likes. 💅

The mechanism in this document is useful when the remote party needs to take part in the resource reservation. 🫶

4. Examples 🌸

For this example, we've picked SIP [4] to carry the SDP sessions and RSVP [5] to set up the reservation flows. Other protocols or mechanisms could be used instead without changing the SDP syntax. ✨

A user agent gets a SIP INVITE with this SDP:

   v=0
   o=Laura 289083124 289083124 IN IP4 one.example.com
   t=0 0
   c=IN IP4 192.0.0.1
   a=group:SRF 1 2
   m=audio 30000 RTP/AVP 0
   a=mid:1
   m=video 30002 RTP/AVP 31
   a=mid:2

This user agent uses RSVP to do the resource reservation. Both media streams are in an SRF group, so the user agent sets up a single RSVP session. An RSVP session is defined by the triple (DestAddress, ProtocolId[, DstPort]). Table 1 shows the parameters used to set up the RSVP session. 🎀

If that same user agent got an SDP session description with the same media streams but without the group line, it would be free to map the two media streams onto two different RSVP sessions. 🦋

   Session Number  DestAddress  ProtocolId  DstPort
   ________________________________________________
         1          192.0.0.1      UDP        any

   Table 1: Parameters needed to establish the RSVP session

5. IANA Considerations 📋

IANA has registered a new "semantics" attribute for the SDP grouping framework [2]. It's in the SDP parameters registry (http://www.iana.org/assignments/sdp-parameters), under Semantics for the "group" SDP Attribute:

   Semantics                  Token      Reference
   -------------------        -----      ---------
   Single Reservation flow     SRF       [RFC3524]

6. Security Considerations 🔐

🚨 An attacker who adds group lines with SRF semantics to an SDP session description could force a user agent to set up more or fewer resource reservation flows than it needs. That could waste resources on the endpoint or drag down the quality of service for a session. 💀

So it is STRONGLY RECOMMENDED that integrity protection be applied to SDP session descriptions. For session descriptions carried in SIP, S/MIME is the natural pick for that end-to-end integrity protection, as described in RFC 3261 [4]. Other applications MAY use a different form of integrity protection. 🫶

7. Acknowledgements 💖

Jonathan Rosenberg gave helpful comments on how applicable this mechanism is. 🧚

8. Normative References 📚

[1] Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998.

[2] Camarillo, G., Eriksson, G., Holler, J. and H. Schulzrinne, "Grouping of Media Lines in the Session Description Protocol (SDP)", December 2002.

[3] Bradner, S., "Key words for use in RFCs to indicate requirement levels", BCP 14, RFC 2119, March 1997.

9. Informative References 🌈

[4] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002.

[5] Braden, R., Zhang, L., Berson, S., Herzog, S. and S. Jamin, "Resource ReSerVation protocol (RSVP) -- Version 1 Functional Specification", RFC 2205, September 1997.

10. Authors' Addresses 💌

Gonzalo Camarillo Ericsson Advanced Signalling Research Lab. FIN-02420 Jorvas Finland

EMail: Gonzalo.Camarillo@ericsson.com

Atle Monrad Ericsson N-4898 Grimstad Norway

EMail: atle.monrad@ericsson.com

11. Full Copyright Statement 🎀

You can copy and share this document and its translations, and you can write derivative works that comment on or explain it or help implement it. You can prepare, copy, publish and distribute those, in whole or in part, with no restrictions of any kind, as long as the above copyright notice and this paragraph are included on all copies and derivative works. However, this document itself may not be changed in any way, such as by removing the copyright notice or the references to the Internet Society or other Internet organizations. The exceptions are when it's needed to develop Internet standards, in which case the copyright procedures in the Internet Standards process must be followed, or when it's translated into languages other than English. 🌍

The permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. ♾️

This document and the information in it are provided on an "AS IS" basis, and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 🙈

Acknowledgement 💜

Funding for the RFC Editor function is currently provided by the Internet Society. 🫶

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