rfc-5688

A Session Initiation Protocol (SIP) Media Feature Tag for MIME Application Subtypes

J. Rosenberg

date2010-01 streamIETF wgnon working group statusPROPOSED STANDARD pages7 canonicalhttps://www.rfc-editor.org/rfc/rfc5688 doi10.17487/RFC5688 errataview

The caller preferences specification for the Session Initiation Protocol (SIP) allows a caller to express preferences that the call be routed to a User Agent (UA) with particular capabilities. Similarly, a specification exists to allow a UA to indicate its capabilities in a registration. Amongst those capabilities are the type of media streams the agent supports, described as top-level MIME types. The 'application' MIME type is used to describe a broad range of stream types, and it provides insufficient granularity as a capability. This specification allows a UA to indicate which application subtypes the agent supports. [STANDARDS-TRACK]

Extracted elements (8)

design-rationale §1

The existing 'application' top-level media feature tag in RFC 3840 provides insufficient granularity because application streams for different applications are wildly different, unlike audio/video where common codecs exist. A new tag indicating specific application subtypes is needed for useful call routing.

sip, realtime

interoperability-note §3

The sip.app-subtype tag indicates only streaming media types a UA can support, not the functionality of the UA itself or MIME types it can send/receive in SIP messages or emails. To indicate support for SIP request bodies of a given type, the 'type' media feature tag from RFC 3840 must be used instead.

sip, realtime

normative-requirement §3 SHOULD

An application subtype is supported if the user agent would be capable of processing an SDP offer that contained that subtype as a format in the m-line of the SDP.

sip, realtime

normative-requirement §3 SHOULD

As new streaming media type formats are defined (such as game stream formats, whiteboard session formats), they SHOULD be defined using the SDP application stream and utilize a MIME application subtype.

sip, realtime

normative-requirement §3 SHOULD

When included in the Contact header field of a REGISTER request, an agent SHOULD include all application subtypes that it can support as streaming formats.

sip, realtime

protocol-element §3

The 'sip.app-subtype' media feature tag is of type token with a case-insensitive equality relationship. Its value can be any registered or private MIME application subtype compliant to the subtype-name grammar defined in RFC 4288.

sip, realtime

registry §6

This specification adds the 'sip.app-subtype' media feature tag to the SIP Media Feature Tag Registration Tree defined in RFC 3840, with ASN.1 Identifier 1.3.6.1.8.4.24.

sip, registry, realtime

security-consideration §5 SHOULD

The sip.app-subtype tag in a REGISTER request reveals the set of supported application media streams, which may be sensitive information giving insight into product capabilities. Applications utilizing this tag SHOULD provide means for ensuring its integrity and SHOULD provide a mechanism for guaranteeing authenticity.

sip, security, realtime