Re: [AVTCORE] Mandatory nature of RTCP

[Magnus Westerlund <[e-mail]>]

On 2011-05-09 13:20, Schwarz, Albrecht (Albrecht) wrote:
> RTCP is NOT MANDATORY according RFC 3550.
> I fail to see any normative statement, too.
> I could also imagine RTP use cases which do not need at all RTCP. 

I think I agree that RTCP is not mandated directly. However, in reality
it is required. Only in a few very limited usages can one skip to use RTCP.

If one uses UDP as underlying transport then RTCP is needed to fulfill
the congestion control requirements in RFC 3550 and the profiles
(RFC3551). Both has a SHOULD requirement and that SHOULD exist to allow
cases where you have dedicated resource.

Then we have all the binding information that RTCP provides, like time
synchronization (RTCP SR), which to be synchronized (SDES CNAME). Some
single media applications can live without this, but any multi-media do
need some of this.

There is a reason why RTP doesn't contain so much hard requirements. RTP
is a toolbox and applications are suppsed to pick the pieces it needs.
And general RTCP is needed in most cases. So I would recommend any one
deciding on RTP/RTCP should start with describing what application
requirements they have. Then pick the RTP parts.

But I will guess that SIPREC is likely to need RTCP. But please do your
analysis of what you need.

Cheers

Magnus Westerlund

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