Subject: [MMUSIC] RTSP 2.0: Mandating Circuit breakers for RTP

From: Magnus Westerlund <[email-masked]>
Date: Mon, 2 Sep 2013 09:00:14 +0200

WG,

Robert commented on the need to implement RTCP. This was in fact already
mandated in the text. However, maybe not as clearly as desired. So that
has been clarified.

This comment however leads to another issue. Using RTP/UDP does have
congestion control implications. We already had requirements on having
something. However, that something was unspecified as we didn't have
anything to point at. This has now changed with the work on circuit
brekaers (draft-ietf-avtcore-rtp-circuit-breakers).

Thus, I do suggest that we update the text on bandwidth adaptation to
state that circuit breakers are mandated to implement if one uses
non-congestion controlled unicast transport, such as UDP. And that the
circuit breakers form a outer envelope.

Proposed text below:
C.1.6.3.  Bit-rate adaption

   RTCP Receiver reports and any additional feedback from the client
   MUST be used to adapt the bit-rate used over the transport for all
   cases when RTP is sent over UDP.  An RTP sender without reserved
   resources MUST NOT use more than its fair share of the available
   resources.  This can be determined by comparing on short to medium
   term (some seconds) the used bit-rate and adapt it so that the RTP
   sender sends at a bit-rate comparable to what a TCP sender would
   achieve on average over the same path.

   To ensure that the implementation's adaptation mechanism has a well
   defined outer envelope, all implementations using a non-congestion
   controlled unicast transport protocol, like UDP, MUST implement
   Multimedia Congestion Control: Circuit Breakers for Unicast RTP
   Sessions [I-D.ietf-avtcore-rtp-circuit-breakers].

Cheers

Magnus Westerlund

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