Internet Engineering Task Force (IETF)
Request for Comments: 8262
Updates: 5368, 5621, 6442
Category: Standards Track
ISSN: 2070-1721

C. Holmberg
I. Sedlacek
Ericsson
October 2017

Content-ID Header Field in the Session Initiation Protocol (SIP)

Abstract

This document specifies the Content-ID header field for usage in the Session Initiation Protocol (SIP). This document also updates RFC 5621, which only allows a Content-ID URL to reference a body part that is part of a multipart message-body. This update enables a Content-ID URL to reference a complete message-body and metadata provided by some additional SIP header fields.

This document updates RFC 5368 and RFC 6442 by clarifying their usage of 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.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8262.

Copyright Notice

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as 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.

   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  . . . . . . . . . . . . . . . . . . . . . . .  14

1. Introduction

1.1. Identifying a Body Part

A SIP message consists of a start-line, one or more header fields, an empty line indicating 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 define in [RFC2045].

A body part in the multipart message-body is described using header fields such as Content-Disposition, Content-Encoding, and Content- Type, which provide information on 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 uniquely identifying 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 referenced by a Content-ID URL. The Content-ID URL value is included in the Content-ID header field of the body part.

Examples of SIP header fields referencing 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 for providing 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

How to uniquely identify a complete message-body of a SIP message using a Content-ID header field and how to reference a complete message-body using a Content-ID URL are not currently specified.

Note: In [RFC5621], the Content-ID URL references a specific body part only.

Some existing specifications, such as [RFC5368], contain examples that show usage of a SIP Content-ID header field referencing a complete message-body, even though such usage has never been specified. Many implementors have interpreted these examples to indicate that such usage is allowed by the corresponding specification, despite the absence of language allowing it. 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 needs to include only one MIME entity in the INVITE request. This MIME entity can be, for example, of the 'application/pidf+xml' MIME type.

However, due to [RFC6442] requiring inclusion of a Geolocation header field referencing the body part with the location information, the UAC includes a multipart message-body with a single body part in the INVITE request, and includes the location information of 'application/pidf+xml' MIME type and an associated Content-ID header field in the body part.

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 including a list of targets as specified in [RFC5368], then the UAC needs to include only one MIME entity in the REFER request. This MIME entity is of the 'application/resource-lists+xml' MIME type.

However, due to [RFC5368] requiring inclusion of a Refer-To header field referencing the body part containing the list of targets, the UAC includes a multipart message-body with a single body part in the REFER request and includes the list of targets of 'application/ resource-lists+xml' MIME type and an associated Content-ID header field in the body part.

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

In order to solve the problems described above, this document:

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

If an existing specification only defines the usage of a multipart message-body to carry a single body part to be referenced by a Content-ID URL, implementations MUST NOT carry the MIME entity in a non-multipart message-body unless the specification is updated to explicitly allow it.

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.

3. Content-ID Header Field

3.1. Introduction

This section defines the usage of the Content-ID header field for SIP.

3.2. Syntax

The ABNF [RFC5234] for the Content-ID header field is:

    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.

3.3. Semantics

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.

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.

3.4.3. Example: Referencing the Message-Body of a SIP Message

The 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:

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

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.

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 8262

9. 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

   [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

   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.com

Content-ID Header Field in the Session Initiation Protocol (SIP)

Abstract

Status of This Memo

Copyright Notice

Table of Contents

1. Introduction

1.1. Identifying a Body Part

1.2. Referencing a Body Part

1.3. Problem Statement

1.4. Consequences

1.4.1. Example 1: SIP INVITE

1.4.2. Example 2: SIP REFER

1.5. Solution

1.6. Backward Compatibility

2. Conventions

3. Content-ID Header Field

3.1. Introduction

3.2. Syntax

3.3. Semantics

3.4. Procedures

3.4.1. User Agent (UA) Procedures

3.4.2. Proxy Procedures

3.4.3. Example: Referencing the Message-Body of a SIP Message

4. Update to RFC 5368

5. Update to RFC 5621

6. Update to RFC 6442

7. Security Considerations

8. IANA Considerations

8.1. Header Field

9. References

9.1. Normative References

9.2. Informative References

Authors' Addresses