Re: [Dart] draft-ietf-dart-dscp-rtp-02 - Section 5.3 RTCP multi-stream optimization text
Colin Perkins <csp@csperkins.org> Thu, 28 August 2014 11:02 UTC
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From: Colin Perkins <csp@csperkins.org>
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Date: Thu, 28 Aug 2014 12:02:01 +0100
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Cc: Ben Campbell <ben@nostrum.com>, "draft-ietf-dart-dscp-rtp.all@tools.ietf.org" <draft-ietf-dart-dscp-rtp.all@tools.ietf.org>, "dart@ietf.org" <dart@ietf.org>, "avt@ietf.org WG" <avt@ietf.org>, "Paul E. Jones" <paulej@packetizer.com>
Subject: Re: [Dart] draft-ietf-dart-dscp-rtp-02 - Section 5.3 RTCP multi-stream optimization text
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David, On 26 Aug 2014, at 17:27, Black, David <david.black@emc.com> wrote: > <editor hat OFF> > > Colin writes: > > The discussion of the multi-stream-optimisation draft is a separate > issue, and is correct as it is. > > Looking closer, that discussion in the current DART draft currently says: > > RTCP multi-stream reporting optimizations for an RTP session > [I-D.ietf-avtcore-rtp-multi-stream-optimisation] assume that the RTP > streams involved experience the same packet loss behavior. This > mechanism is highly inappropriate when the RTP streams involved use > different PHBs, even if those PHBs differ solely in drop precedence. A quick follow-up to ensure this is clear: the multi-stream-optimisation cannot be used when reporting on received RTP streams where the different streams have different markings, since those streams are treated differently in the network. The marking I use for the RTP streams I send (and hence the marking I use for my RTCP packets) doesn’t influence whether I can use the multi-stream-optimisation, however. Colin > That's based on this text from the last paragraph of Section 1 > (Introduction) of the multi-stream optimization draft: > > This memo defines such an RTCP extension, RTCP Reporting Groups. > This extension is used to indicate the SSRCs that originate from the > same endpoint, and therefore have identical reception quality, hence > allowing the endpoints to suppress unnecessary RTCP reception quality > reports. > > When different DSCPs are used for SSRCs (RTP streams) that originate > from the same source, the statement that they "therefore have identical > reception quality" is clearly incorrect, so it looks like the current > DART draft text is correct, IMHO. > > Harald? > > </editor hat OFF> > > Thanks, > --David > >> -----Original Message----- >> From: Colin Perkins [mailto:csp@csperkins.org] >> Sent: Tuesday, August 26, 2014 11:54 AM >> To: Black, David >> Cc: Ben Campbell; Paul E. Jones; dart@ietf.org; avt@ietf.org WG; draft-ietf- >> dart-dscp-rtp.all@tools.ietf.org >> Subject: Re: Treatment of RTCP (was Re: [Dart] Colin Perkins comments - WGLC: >> draft-ietf-dart-dscp-rtp-02) >> >> >> On 26 Aug 2014, at 16:39, Black, David <david.black@emc.com> wrote: >> >>>>> Since not all the media sent by a single SSRC has the same marking, my >>>> suggestion would be that each SSRC mark the RTCP packets it sends with one >> of >>>> the same code points as it uses to mark the media. Since RTCP is somewhat >>>> important, it would make sense for each SSRC to mark the RTCP packets it >> sends >>>> using the highest priority code point it uses to mark the RTP media packets >> it >>>> sends. >>>> >>>> That makes sense to me. Paul, and others, do you agree with that last >>>> paragraph? >>> >>> <editor hat off> >>> >>> Sure, when there's a notion of priority or importance. There won't always >>> be one (e.g., is CS2 higher priority than AF2x? That depends ...). OTOH, >>> we don't need to say much here, e.g., the class selector codepoints (CSx) >>> are ordered, and adding a pointer to draft-ietf-tsvwg-rtcweb-qos will be >>> helpful. >>> >>> </editor hat off> >>> >>> Turning to the other RTCP issue, [F] on multi-stream optimization, I wonder >>> whether we inadvertently framed that issue backwards. Given the above, a >>> single RTCP report on multiple RTP streams that use rather different DSCPs >>> may not result in representative RTT values for all of the streams, because >>> the report has to be sent with one DSCP. If that outcome is a problem, >>> one should send separate RTCP reports (duh!). >> >> Each reporting SSRC sends a separate RTCP report block for each SSRC it >> receives, so this is not a problem. The question is what marking an SSRC uses >> for the RTCP packets it sends, given that it uses several different markings >> for the RTP media packets it sends. >> >>> That statement seems valuable to make and can be made with a citation of >>> RFC 3530, as opposed to the multi-stream optimization draft. >>> >>> Harald and Colin - what do you think? >> >> The discussion of the multi-stream-optimisation draft is a separate issue, and >> is correct as it is. >> >> -- >> Colin Perkins >> http://csperkins.org/ >> >> > -- Colin Perkins http://csperkins.org/
- Re: [Dart] draft-ietf-dart-dscp-rtp-02 - Section … Black, David
- Re: [Dart] draft-ietf-dart-dscp-rtp-02 - Section … Colin Perkins