RFC 8262
Content-ID Header Field in the Session Initiation Protocol (SIP)
RFC 8262: Content-ID Header Field in the Session Initiation Protocol (SIP) 🎀
Okay bestie, let's start with the title block 💅 It's from the Internet Engineering Task Force (IETF) and it's RFC 8262. The authors are C. Holmberg and I. Sedlacek, both from Ericsson 🦋 It's a Standards Track document, dated October 2017, with ISSN 2070-1721. It updates RFC 5368, RFC 5621, and RFC 6442 ✨ The title block doesn't list anything it obsoletes, so nothing is replaced here.
Abstract
Okay so this doc specifies the Content-ID header field for use in the Session Initiation Protocol (SIP) 🌸 It also updates RFC 5621, which only lets a Content-ID URL point at a body part that's inside a multipart message-body. This update lets a Content-ID URL point at a complete message-body, plus the metadata that some extra SIP header fields provide 🔥
It also updates RFC 5368 and RFC 6442 by clarifying how they use the SIP Content-ID header field 💜
Status of This Memo
This is an Internet Standards Track document. 🌈
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.
Info about the current status of this document, any errata, and how to give feedback on it can be found at https://www.rfc-editor.org/info/rfc8262. 🧚
Copyright Notice
Copyright (c) 2017 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 in effect on the date of publication of this document. Please review these documents carefully, since they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions, and are provided without warranty as described in the Simplified BSD License. 🫶
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Identifying a Body Part . . . . . . . . . . . . . . . . . 3
1.2. Referencing a Body Part . . . . . . . . . . . . . . . . . 3
1.3. Problem Statement . . . . . . . . . . . . . . . . . . . . 4
1.4. Consequences . . . . . . . . . . . . . . . . . . . . . . 4
1.4.1. Example 1: SIP INVITE . . . . . . . . . . . . . . . . 4
1.4.2. Example 2: SIP REFER . . . . . . . . . . . . . . . . 6
1.5. Solution . . . . . . . . . . . . . . . . . . . . . . . . 7
1.6. Backward Compatibility . . . . . . . . . . . . . . . . . 7
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Content-ID Header Field . . . . . . . . . . . . . . . . . . . 8
3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 8
3.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. Semantics . . . . . . . . . . . . . . . . . . . . . . . . 8
3.4. Procedures . . . . . . . . . . . . . . . . . . . . . . . 9
3.4.1. User Agent (UA) Procedures . . . . . . . . . . . . . 9
3.4.2. Proxy Procedures . . . . . . . . . . . . . . . . . . 9
3.4.3. Example: Referencing the Message-Body of a SIP
Message . . . . . . . . . . . . . . . . . . . . . . . 9
4. Update to RFC 5368 . . . . . . . . . . . . . . . . . . . . . 10
5. Update to RFC 5621 . . . . . . . . . . . . . . . . . . . . . 11
6. Update to RFC 6442 . . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8.1. Header Field . . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 141. Introduction ✨
1.1. Identifying a Body Part
Okay so a SIP message is made up of a start-line, one or more header fields, an empty line that marks the end of the header fields, and an optional message-body, as specified in [RFC3261] 💖
The message-body can be a non-multipart message-body or a multipart message-body, as specified in [RFC3261] 🎀
[RFC5621] defines generic handling of a multipart message-body in a SIP message 🦋
A multipart message-body contains zero, one, or several body parts, encoded using the format defined in [RFC2045] 🌸
A body part in the multipart message-body is described using header fields such as Content-Disposition, Content-Encoding, and Content-Type. These give info about the content of the body part, as specified in [RFC5621] 💅 A body part in the multipart message-body can also contain a Content-ID header field, with an ID value that uniquely identifies the body part, as specified in [RFC2045] 🫶
1.2. Referencing a Body Part
A SIP header field can reference a body part using a Content-ID URL, as specified in [RFC5621] 🧚
The Content-ID URL is specified in [RFC2392]. [RFC2392] specifies how to identify the body part that a Content-ID URL refers to. The Content-ID URL value is included in the Content-ID header field of the body part. 💜
Examples of SIP header fields that reference a body part using a Content-ID URL are:
- [RFC6442] specifies how a Geolocation header field references a body part using a Content-ID URL to provide location information. 🌈
- [RFC5368] specifies how a Refer-To header field references a body part using a Content-ID URL to provide a list of targets. ⭐
1.3. Problem Statement
Right now, it's not specified how to uniquely identify a complete message-body of a SIP message using a Content-ID header field, or how to reference a complete message-body using a Content-ID URL. 😭
Note: In [RFC5621], the Content-ID URL references a specific body part only.
Some existing specifications, such as [RFC5368], have examples that show a SIP Content-ID header field referencing a complete message-body, even though that usage has never been specified. Lots of implementors read these examples as meaning the corresponding specification allows that usage, even though there's no language saying so. This document updates the normative language in the affected documents to explicitly allow such usage. 🙈
1.4. Consequences
The examples below show the consequences of the problem described above. 🔥
1.4.1. Example 1: SIP INVITE
If a User Agent Client (UAC) sends an INVITE request that conveys location by value (as specified in [RFC6442]) and decides not to include a Session Description Protocol (SDP) offer, then the UAC only needs to include one MIME entity in the INVITE request. This MIME entity can be, for example, of the 'application/pidf+xml' MIME type. 🍓
But because [RFC6442] requires including a Geolocation header field that references the body part with the location information, the UAC ends up including a multipart message-body with a single body part in the INVITE request. That body part has the location information of 'application/pidf+xml' MIME type, plus an associated Content-ID header field. 😤
Example message (SIP INVITE):
INVITE sips:bob@biloxi.example.com SIP/2.0
Via: SIPS/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bK74bf9
Max-Forwards: 70
To: Bob <sips:bob@biloxi.example.com>
From: Alice <sips:alice@atlanta.example.com>;tag=9fxced76sl
Call-ID: 3848276298220188511@atlanta.example.com
Geolocation: <cid:target123@atlanta.example.com>
Geolocation-Routing: no
Accept: application/sdp, application/pidf+xml
CSeq: 31862 INVITE
Contact: <sips:alice@atlanta.example.com>
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
--boundary1
Content-Type: application/pidf+xml
Content-ID: <target123@atlanta.example.com>
<?xml version="1.0" encoding="UTF-8"?>
<presence
xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:gbp="urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xmlns:gml="http://www.opengis.net/gml"
xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
entity="pres:alice@atlanta.example.com"
>
<dm:device id="target123-1">
<gp:geopriv>
<gp:location-info>
<gml:location>
<gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
<gml:pos>32.86726 -97.16054</gml:pos>
</gml:Point>
</gml:location>
</gp:location-info>
<gp:usage-rules>
<gbp:retransmission-allowed>no
</gbp:retransmission-allowed>
<gbp:retention-expiry>2010-11-14T20:00:00Z
</gbp:retention-expiry>
</gp:usage-rules>
<gp:method>802.11</gp:method>
</gp:geopriv>
<dm:deviceID>mac:1234567890ab</dm:deviceID>
<dm:timestamp>2010-11-04T20:57:29Z</dm:timestamp>
</dm:device>
</presence>
--boundary1--1.4.2. Example 2: SIP REFER
If a UAC sends a REFER request that includes a list of targets, as specified in [RFC5368], then the UAC only needs to include one MIME entity in the REFER request. This MIME entity is of the 'application/resource-lists+xml' MIME type. 💖
But because [RFC5368] requires including a Refer-To header field that references the body part containing the list of targets, the UAC ends up including a multipart message-body with a single body part in the REFER request. That body part has the list of targets of 'application/resource-lists+xml' MIME type, plus an associated Content-ID header field. 🌸
Example message (SIP REFER):
REFER sip:conf-123@example.com;gruu;opaque=hha9s8d-999a SIP/2.0
Via: SIP/2.0/TCP client.chicago.example.com;branch=z9hG4bKhjhs8ass83
Max-Forwards: 70
To: "Conference 123" <sip:conf-123@example.com>
From: Carol <sip:carol@chicago.example.com>;tag=32331
Call-ID: d432fa84b4c76e66710
CSeq: 2 REFER
Contact: <sip:carol@client.chicago.example.com>
Refer-To: <cid:cn35t8jf02@example.com>
Refer-Sub: false
Require: multiple-refer, norefersub
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
Allow-Events: dialog
Accept: application/sdp, message/sipfrag
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
--boundary1
Content-Type: application/resource-lists+xml
Content-Disposition: recipient-list
Content-ID: <cn35t8jf02@example.com>
<?xml version="1.0" encoding="UTF-8"?>
<resource-lists
xmlns="urn:ietf:params:xml:ns:resource-lists"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
>
<list>
<entry uri="sip:bill@example.com?method=BYE"/>
<entry uri="sip:joe@example.org?method=BYE"/>
<entry uri="sip:ted@example.net?method=BYE"/>
</list>
</resource-lists>
--boundary1--1.5. Solution 🎀
okay so to fix all those problems, this doc does four things 💅
- Specifies and registers the Content-ID header field as a SIP header field.
- Specifies that, when used as a SIP header field, the Content-ID header field identifies the complete message-body and the metadata provided by some additional SIP header fields of the SIP message.
- Updates [RFC5621] to enable a Content-ID URL to reference a complete message-body and the metadata provided by some additional SIP header fields.
- Updates [RFC5368] and [RFC6442] by adding text that explicitly states that a SIP Content-ID header field can be used.
1.6. Backward Compatibility 🦋
okay this one is important, bestie 😭 If an existing specification only defines using a multipart message-body to carry a single body part that a Content-ID URL points to, implementations MUST NOT carry the MIME entity in a non-multipart message-body unless the specification is updated to explicitly allow it. no sneaky workarounds 🙅♀️
2. Conventions 📜
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 interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. so the caps are doing the heavy lifting 💅✨
3. Content-ID Header Field 💖
3.1. Introduction 🌸
This section defines how the Content-ID header field gets used for SIP. 🧚
3.2. Syntax 🍓
the ABNF [RFC5234] for the Content-ID header field looks like this:
Content-ID = "Content-ID" HCOLON msg-id
msg-id = "<" id-left "@" id-right ">"Note: id-left and id-right are specified in [RFC5322]. HCOLON is defined in [RFC3261].
Note: When used in a SIP header field, the msg-id syntax has been simplified, compared to the syntax in [RFC5322], to disallow the use of comments and to adopt to the SIP usage of leading white space. 🫶
The value of the Content-ID header field value must be unique in the context of a given SIP message, including any embedded MIME Content-ID header field values. Note that the SIP Content-ID header field value is not expected to be unique among all SIP messages; it has no meaning outside of the message in which it is included. so it only has to be unique inside its own message, not across the whole internet 🌈
3.3. Semantics 💜
this is the part where it gets fun ✨ The Content-ID header field included in the header fields of a SIP message identifies the message-body of the SIP message and the metadata provided by:
- A MIME-Version header field, if included in the header fields of the SIP message.
- Any 'Content-' prefixed header fields (including the Content-ID header field itself) included in the header fields of the SIP message.
The Content-ID header field can be included in any SIP message that is allowed to contain a message-body.
Note: The message-body identified by the Content-ID header field can be a non-multipart message-body or a multipart message-body. 🦋
3.4. Procedures 👑
3.4.1. User Agent (UA) Procedures 💅
A UA MAY include a Content-ID header field in any SIP message that is allowed to contain a message-body.
A UA MUST NOT include a Content-ID header field in any SIP message that is not allowed to contain a message-body. no putting it where it doesn't belong 🙈
A UA MUST set the value of the Content-ID header field to a value that is unique in the context of the SIP message. 🔥
3.4.2. Proxy Procedures 🧚
A proxy MUST NOT add a Content-ID header field in a SIP message.
A proxy MUST NOT modify a Content-ID header field included in a SIP message.
A proxy MUST NOT delete a Content-ID header field from a SIP message.
the proxy is basically the hands-off friend here 🫣 it doesn't add, touch, or delete the Content-ID 💀
3.4.3. Example: Referencing the Message-Body of a SIP Message 🎀
this figure shows an example from [RFC5368], where the SIP Content-ID header field is used to reference the message-body (non-multipart) of a SIP message. 🌸
REFER sip:conf-123@example.com;gruu;opaque=hha9s8d-999a SIP/2.0
Via: SIP/2.0/TCP client.chicago.example.com
;branch=z9hG4bKhjhs8ass83
Max-Forwards: 70
To: "Conference 123" <sip:conf-123@example.com>
From: Carol <sip:carol@chicago.example.com>;tag=32331
Call-ID: d432fa84b4c76e66710
CSeq: 2 REFER
Contact: <sip:carol@client.chicago.example.com>
Refer-To: <cid:cn35t8jf02@example.com>
Refer-Sub: false
Require: multiple-refer, norefersub
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
Allow-Events: dialog
Accept: application/sdp, message/sipfrag
Content-Type: application/resource-lists+xml
Content-Disposition: recipient-list
Content-Length: 362
Content-ID: <cn35t8jf02@example.com>
<?xml version="1.0" encoding="UTF-8"?>
<resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<list>
<entry uri="sip:bill@example.com?method=BYE" />
<entry uri="sip:joe@example.org?method=BYE" />
<entry uri="sip:ted@example.net?method=BYE" />
</list>
</resource-lists>4. Update to RFC 5368 🌈
this section updates the second paragraph in Section 7 of [RFC5368] by allowing usage of either a MIME Content-ID header field or a SIP Content-ID header field to label the body part or the message-body carrying the URI list. 💖
OLD TEXT:
The Refer-To header field of a REFER request with multiple REFER-
Targets MUST contain a pointer (i.e., a Content-ID Uniform
Resource Locator (URL) as per RFC 2392 [RFC2392]) that points to
the body part that carries the URI list. The REFER-Issuer SHOULD
NOT include any particular URI more than once in the URI list.NEW TEXT:
The Refer-To header field of a REFER request with multiple REFER-
Targets MUST contain a pointer (i.e., a Content-ID Uniform
Resource Locator (URL) as per RFC 2392 [RFC2392]) that points to
the body part or message-body that carries the URI list. The
REFER-Issuer SHOULD NOT include any particular URI more than once
in the URI list. The REFER request can use either a MIME Content-
ID header field [RFC4483] or a SIP Content-ID header field
[RFC8262] to label the body part or the message-body.5. Update to RFC 5621 ✨
this section updates Section 9.1 of [RFC5621] by allowing a Content-ID URL to reference a message-body and the related metadata (Section 3.3) in addition to allowing a reference to a body part. 🦋
OLD TEXT:
Content-ID URLs allow creating references to body parts. A given
Content-ID URL [RFC2392], which can appear in a header field or
within a body part (e.g., in an SDP attribute), points to a
particular body part.NEW TEXT:
Content-ID URLs allow the creation of references to body parts or
message-bodies (and the header fields describing the message-
bodies). A given Content-ID URL [RFC2392], which can appear in a
header field or within a body part (e.g., in an SDP attribute),
points to a particular body part or the message-body (and the
header fields describing the message-body).6. Update to RFC 6442 🧚
this section updates the second paragraph in Section 3.1 of [RFC6442] by allowing usage of either a MIME Content-ID header field or a SIP Content-ID header field to label the body part or the message-body carrying the location data. 📍
OLD TEXT:
In Figure 1, Alice is both the Target and the LS that is conveying
her location directly to Bob, who acts as an LR. This conveyance
is point-to-point: it does not pass through any SIP-layer
intermediary. A Location Object appears by-value in the initial
SIP request as a MIME body, and Bob responds to that SIP request
as appropriate. There is a 'Bad Location Information' response
code introduced within this document to specifically inform Alice
if she conveys bad location information to Bob (e.g., Bob "cannot
parse the location provided", or "there is not enough location
information to determine where Alice is").NEW TEXT:
In Figure 1, Alice is both the Target and the LS that is conveying
her location directly to Bob, who acts as an LR. This conveyance
is point-to-point: it does not pass through any SIP-layer
intermediary. A Location Object appears by-value in the initial
SIP request as a MIME body, and Bob responds to that SIP request
as appropriate. Either a MIME Content-ID header field [RFC4483]
or the SIP Content-ID header field [RFC8262] MUST be used to label
the location information. There is a 'Bad Location Information'
response code introduced within this document to specifically
inform Alice if she conveys bad location information to Bob (e.g.,
Bob "cannot parse the location provided", or "there is not enough
location information to determine where Alice is").7. Security Considerations 🔐
this part is serious, bestie 😭🚨 The Content-ID header field value MUST NOT reveal sensitive user information.
If the message-body associated with the Content-ID header field is an encrypted body, it MUST NOT be possible to derive a key that can be used to decrypt the body from the Content-ID header field value. 🔑💀 no leaking keys through the header!!
8. IANA Considerations 🌸
This specification registers a new SIP header field according to the procedures defined in [RFC3261].
8.1. Header Field 🎀
The header field described in Section 3 has been registered in the "Header Fields" sub-registry of the "Session Initiation Protocol (SIP) Parameters" registry by adding a row with these values:
Header Name: Content-ID
compact:
Reference: RFC 82629. References 📚
9.1. Normative References 💜
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
<https://www.rfc-editor.org/info/rfc2045>.
[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>.
[RFC2392] Levinson, E., "Content-ID and Message-ID Uniform Resource
Locators", RFC 2392, DOI 10.17487/RFC2392, August 1998,
<https://www.rfc-editor.org/info/rfc2392>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<https://www.rfc-editor.org/info/rfc3261>.
[RFC4483] Burger, E., Ed., "A Mechanism for Content Indirection in
Session Initiation Protocol (SIP) Messages", RFC 4483,
DOI 10.17487/RFC4483, May 2006,
<https://www.rfc-editor.org/info/rfc4483>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
DOI 10.17487/RFC5322, October 2008,
<https://www.rfc-editor.org/info/rfc5322>.
[RFC5621] Camarillo, G., "Message Body Handling in the Session
Initiation Protocol (SIP)", RFC 5621,
DOI 10.17487/RFC5621, September 2009,
<https://www.rfc-editor.org/info/rfc5621>.
[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>.9.2. Informative References ✨
Okay bestie, these are the "for your reading list" refs 📚 💅
[RFC5368] Camarillo, G., Niemi, A., Isomaki, M., Garcia-Martin, M.,
and H. Khartabil, "Referring to Multiple Resources in the
Session Initiation Protocol (SIP)", RFC 5368,
DOI 10.17487/RFC5368, October 2008,
<https://www.rfc-editor.org/info/rfc5368>.
[RFC6442] Polk, J., Rosen, B., and J. Peterson, "Location Conveyance
for the Session Initiation Protocol", RFC 6442,
DOI 10.17487/RFC6442, December 2011,
<https://www.rfc-editor.org/info/rfc6442>.Authors' Addresses 🎀
Meet the people who wrote this whole thing, lowkey the real MVPs 👑 Here's where you can find them:
Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: christer.holmberg@ericsson.com
Ivo Sedlacek
Ericsson
Sokolovska 79
Praha 18600
Czech Republic
Email: ivo.sedlacek@ericsson.comThat's the end of RFC 8262!! 🦋 You made it, bestie, you're literally a SIP legend now 🫶✨
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