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rfc-6128

RTP Control Protocol (RTCP) Port for Source-Specific Multicast (SSM) Sessions

A. Begen
date2011-02 streamIETF arearai wgavt statusPROPOSED STANDARD pages6 canonicalhttps://www.rfc-editor.org/rfc/rfc6128 doi10.17487/RFC6128
The Session Description Protocol (SDP) has an attribute that allows RTP applications to specify an address and a port associated with the RTP Control Protocol (RTCP) traffic. In RTP-based source-specific multicast (SSM) sessions, the same attribute is used to designate the address and the RTCP port of the Feedback Target in the SDP description. However, the RTCP port associated with the SSM session itself cannot be specified by the same attribute to avoid ambiguity, and thus, is required to be derived from the "m=" line of the media description. Deriving the RTCP port from the "m=" line imposes an unnecessary restriction. This document removes this restriction by introducing a new SDP attribute. [STANDARDS-TRACK]

updates

Extracted elements (7)

design-rationale §1

The existing 'rtcp' attribute could not be reused to specify the SSM session's RTCP port because it was already used for the Feedback Target address and port, creating potential ambiguity. A new attribute 'multicast-rtcp' was introduced to remove the unnecessary restriction imposed by the +1 rule.

rtp, multicast, realtime

interoperability-note §2

This document updates RFC 5760. The distribution source may alternatively use RTP/RTCP port muxing per RFC 5761, in which case RTP and RTCP packets share the same destination port in the SSM session.

rtp, multicast, realtime

normative-requirement §2 MUST

In the absence of the 'multicast-rtcp' attribute, the +1 rule applies following RFC 5760, meaning the RTCP port is derived from the 'm=' line of the media description.

rtp, multicast, realtime

protocol-element §2

The 'multicast-rtcp' SDP attribute specifies the RTCP port for an SSM session, allowing the distribution source to use a desired port rather than deriving it from the 'm=' line via the +1 rule. It is defined as both a media-level and session-level attribute.

rtp, multicast, realtime

registry §5.1

This document registers a new SDP attribute named 'multicast-rtcp' in the SDP att-field registry. It is a media or session level attribute that specifies the port for the SSM RTCP session and is not subject to charset.

registry, rtp, multicast

security-consideration §4

A malevolent third party could use the 'multicast-rtcp' attribute to redirect RTCP traffic by intercepting and rewriting SDP packets. To mitigate this, the SDP description should be integrity protected and source authenticated, using mechanisms such as S/MIME, HTTPS, or SAP authentication.

security, rtp, multicast

wire-format §2

The ABNF syntax for the 'multicast-rtcp' attribute is: `rtcp-attribute = "a=multicast-rtcp:" port CRLF`, where 'port' is defined as specified in Section 9 of RFC 4566.

rtp, multicast, realtime