Re: [AVTCORE] Header Compression and RFC5285bis
Stephen Casner <casner@acm.org> Wed, 11 May 2016 05:49 UTC
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Date: Wed, 11 May 2016 06:49:07 +0100
From: Stephen Casner <casner@acm.org>
To: Roni Even <ron.even.tlv@gmail.com>
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Cc: 'Magnus Westerlund' <magnus.westerlund@ericsson.com>, 'IETF AVTCore WG' <avt@ietf.org>
Subject: Re: [AVTCORE] Header Compression and RFC5285bis
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Roni, I think it would be appropriate to include another sentence before the one you propose: "The use of RTP header extensions may reduce the effectiveness of header compression." -- Steve On Tue, 10 May 2016, Roni Even wrote: > Hi Magnus, > I am updating the document based on other comments from Colin. > The current text says "The interactions of the RTP header extension and > header compression is explored further in [RFC2508] and [RFC3095]." > Do you think we need more text here? Any suggestions > Roni > > > -----Original Message----- > > From: avt [mailto:avt-bounces@ietf.org] On Behalf Of Magnus Westerlund > > Sent: Saturday, April 02, 2016 6:47 PM > > To: IETF AVTCore WG; Stephen Casner > > Subject: [AVTCORE] Header Compression and RFC5285bis > > > > Hi, > > > > Stephen Casner raised a private comment on the > > draft-ietf-avtext-sdes-hdr-ext-05 when he did the IANA expert review. > > This was that both > > draft-ietf-avtext-sdes-hdr-ext-05 and RFC5285bis doesn't discuss impact of > > header compression due to the presence of RTP header extensions. > > > > I have to agree that this is something that at least RFC5285bis should > have a > > discussion on. There are some impact. > > > > In the case of Robust Header Compression (ROHC) (RFC 5795 and RFC 5225) > > the impact to my understanding is the following. RFC5225 and the RTP > > profile don't compress the actual header extension at all. The X bit in > the > > header is compressed and it is classified in Section A.5 as Rarely > changing. > > The assumption here is that what value is set on a previous packet will be > > maintained on the next. > > > > Looking at the emerging usages that is mostly right, but there will be > periods > > where the x bit may be flipping its value. The usage I am considering is > these > > initial inclusion of the MID, CNAME etc. However for example a video > > stream, it is sufficient to include the header extension in a single > packet out > > potentially many for an particular video image/frame. Thus one might have > a > > on, off, next TS, on, then off on subsequent packets. > > > > The impact of the classification as Rarely changing is that when a change > is > > needed a larger header than otherwise needed will be sent. > > Thus the impact will be that each on and off behaviour will result in one > and > > maybe two larger ROHC headers to get the change across compared to if no > > RTP header extensions would have been present. > > > > I haven't looked at CRTP, but I would guess similar impact. > > > > Cheers > > > > Magnus Westerlund > > > > ---------------------------------------------------------------------- > > Services, Media and Network features, Ericsson Research EAB/TXM > > ---------------------------------------------------------------------- > > Ericsson AB | Phone +46 10 7148287 > > Färögatan 6 | Mobile +46 73 0949079 > > SE-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com > > ---------------------------------------------------------------------- > > > > _______________________________________________ > > Audio/Video Transport Core Maintenance > > avt@ietf.org > > https://www.ietf.org/mailman/listinfo/avt > > >
- [AVTCORE] Header Compression and RFC5285bis Magnus Westerlund
- Re: [AVTCORE] Header Compression and RFC5285bis Roni Even
- Re: [AVTCORE] Header Compression and RFC5285bis Stephen Casner
- Re: [AVTCORE] Header Compression and RFC5285bis Roni Even
- Re: [AVTCORE] Header Compression and RFC5285bis Roni Even
- Re: [AVTCORE] Header Compression and RFC5285bis Stephen Casner