| SIPCORE Working Group | C. Holmberg |
| Internet-Draft | I. Sedlacek |
| Updates: 5621 (if approved) | Ericsson |
| Intended status: Standards Track | May 8, 2017 |
| Expires: November 9, 2017 |
Content-ID header field in Session Initiation Protocol (SIP)
draft-ietf-sipcore-content-id-04
This document specifies the Content-ID header field for usage in the Session Initiation Protocol (SIP). The document also updates RFC 5621, to enable a Content-ID URL to reference a complete message-body and metadata provided by some additional SIP header fields.
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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 [RFC2045] format.
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].
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:
It is currently not specified 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.
The examples below shows the consequences of the problem described above.
If a UAC sends an INVITE request conveying location as specified in [RFC6442], if the UAC decides not to include an SDP offer, and if the location is conveyed by value, then the UAC needs to include only one MIME entity in the INVITE request. This content can be e.g. 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 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.
If a UAC sends an 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 content 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 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.
In order to solve the problems described above, this document:
NOTE: In [RFC5621], the Content-ID URL references a specific body part only.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
This section defines the usage of the Content-ID header field for SIP.
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].
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:
The Content-ID header field can be included in any SIP message which is allowed to contain a message-body.
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.
The UA MUST set the value of the Content-ID header field to a globally unique value.
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.
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 creating 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).
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.
This specification registers a new SIP header field according to the procedures in [RFC3261].
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:
[RFC EDITOR NOTE: Please replace XXXX with the RFC number of this document when publishing]
Header Name: Content-ID
compact:
Reference: RFCXXXX
[RFC EDITOR NOTE: Please remove this section when publishing]
Changes from draft-ietf-sipcore-content-id-03
Changes from draft-ietf-sipcore-content-id-02
Changes from draft-ietf-sipcore-content-id-01