Internet Engineering Task Force (IETF) C. Holmberg

Internet Engineering Task Force (IETF) C. Holmberg
Request for Comments: 8262 I. Sedlacek
Updates: 5368, 5621, 6442 Ericsson
Category: Standards Track October 2017
ISSN: 2070-1721

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.

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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) 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.

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

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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:

o [RFC6442] specifies how a Geolocation header field references a
body part using a Content-ID URL for providing location
information.

o [RFC5368] specifies how a Refer-To header field references a body
part using a Content-ID URL to provide a list of targets.

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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.

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Example message (SIP INVITE):

INVITE sips:[email protected] SIP/2.0
Via: SIPS/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bK74bf9
Max-Forwards: 70
To: Bob <sips:[email protected]>
From: Alice <sips:[email protected]>;tag=9fxced76sl
Call-ID: [email protected]
Geolocation: <cid:[email protected]>
Geolocation-Routing: no
Accept: application/sdp, application/pidf+xml
CSeq: 31862 INVITE
Contact: <sips:[email protected]>
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...

--boundary1
Content-Type: application/pidf+xml
Content-ID: <[email protected]>

<?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:[email protected]"
>
<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>

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<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:[email protected];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:[email protected]>
From: Carol <sip:[email protected]>;tag=32331
Call-ID: d432fa84b4c76e66710
CSeq: 2 REFER
Contact: <sip:[email protected]>
Refer-To: <cid:[email protected]>
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: <[email protected]>

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<?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:[email protected]?method=BYE"/>
<entry uri="sip:[email protected]?method=BYE"/>
<entry uri="sip:[email protected]?method=BYE"/>
</list>
</resource-lists>
--boundary1--

1.5. Solution

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

o Specifies and registers the Content-ID header field as a SIP
header field.

o 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.

o Updates [RFC5621] to enable a Content-ID URL to reference a
complete message-body and the metadata provided by some additional
SIP header fields.

o 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.

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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:

o A MIME-Version header field, if included in the header fields of
the SIP message.

o 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.

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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:[email protected];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:[email protected]>
From: Carol <sip:[email protected]>;tag=32331
Call-ID: d432fa84b4c76e66710
CSeq: 2 REFER
Contact: <sip:[email protected]>
Refer-To: <cid:[email protected]>
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: <[email protected]>

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<?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:[email protected]?method=BYE" />
<entry uri="sip:[email protected]?method=BYE" />
<entry uri="sip:[email protected]?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.

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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").

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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

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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>.

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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: [email protected]

Ivo Sedlacek
Ericsson
Sokolovska 79
Praha 18600
Czech Republic

Email: [email protected]

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