[AVTCORE] Header Compression and RFC5285bis

Magnus Westerlund <magnus.westerlund@ericsson.com> Sat, 02 April 2016 15:47 UTC

Return-Path: <magnus.westerlund@ericsson.com>
X-Original-To: avt@ietfa.amsl.com
Delivered-To: avt@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id E750212D12C for <avt@ietfa.amsl.com>; Sat, 2 Apr 2016 08:47:34 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -4.221
X-Spam-Level:
X-Spam-Status: No, score=-4.221 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id hJGXORpUr76e for <avt@ietfa.amsl.com>; Sat, 2 Apr 2016 08:47:33 -0700 (PDT)
Received: from sessmg23.ericsson.net (sessmg23.ericsson.net [193.180.251.45]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 3772C12D0FE for <avt@ietf.org>; Sat, 2 Apr 2016 08:47:33 -0700 (PDT)
X-AuditID: c1b4fb2d-f79c06d000005960-de-56ffe993a480
Received: from ESESSHC007.ericsson.se (Unknown_Domain [153.88.183.39]) by sessmg23.ericsson.net (Symantec Mail Security) with SMTP id 90.15.22880.399EFF65; Sat, 2 Apr 2016 17:47:31 +0200 (CEST)
Received: from [127.0.0.1] (153.88.183.153) by smtp.internal.ericsson.com (153.88.183.41) with Microsoft SMTP Server id 14.3.248.2; Sat, 2 Apr 2016 17:47:30 +0200
From: Magnus Westerlund <magnus.westerlund@ericsson.com>
To: IETF AVTCore WG <avt@ietf.org>, Stephen Casner <casner@acm.org>
Message-ID: <56FFE98E.2070406@ericsson.com>
Date: Sat, 2 Apr 2016 12:47:26 -0300
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0
MIME-Version: 1.0
Content-Type: text/plain; charset="windows-1252"; format=flowed
Content-Transfer-Encoding: 8bit
X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFprJLMWRmVeSWpSXmKPExsUyM2K7uu7kl//DDLr2q1m87FnJbvFi1RwW ByaPy1e8PZYs+ckUwBTFZZOSmpNZllqkb5fAlXF72hPmgl8CFW/6zjI3MF7m7WLk5JAQMJGY Oe0ZK4QtJnHh3nq2LkYuDiGBI4wSmw9/ZYVwljFKtF7fyAhSxSZgIXHzRyMbiC0soCVx9scJ IJuDQ0TAWeLmnyCQMK+AtsT3ea+YQWwWARWJw+cmgpWLCsRIHH93jhGiRlDi5MwnLCCtzAL2 Eg+2loGEmQXkJZq3zgZrFQIa09DUwTqBkW8Wko5ZCB2zkHQsYGRexShanFpcnJtuZKyXWpSZ XFycn6eXl1qyiREYYAe3/Nbdwbj6teMhRgEORiUe3gXq/8OEWBPLiitzDzFKcDArifDaPgcK 8aYkVlalFuXHF5XmpBYfYpTmYFES582J/BcmJJCeWJKanZpakFoEk2Xi4JRqYDRjj5y14mFZ iOoBPbfIYqVn6htMdjsv4/8svFDj/c4bNSwaHsrv78hKu3xPP1bt58L7LcbZ0C2MxePC89KM oqeNC67r2y5hvqlRsKBb0GzRkcSU7b/3x+YuiyxJq9/AzLml1vTTkeMm83psMjSfhB17zPDG OzVWpMzzVo/j6S8mt4xeXEoJVmIpzkg01GIuKk4EANrX6UksAgAA
Archived-At: <http://mailarchive.ietf.org/arch/msg/avt/UU-1kCgJ6eGH4vuNYimKpfX66_Y>
Subject: [AVTCORE] Header Compression and RFC5285bis
X-BeenThere: avt@ietf.org
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: Audio/Video Transport Core Maintenance <avt.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/avt>, <mailto:avt-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/avt/>
List-Post: <mailto:avt@ietf.org>
List-Help: <mailto:avt-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/avt>, <mailto:avt-request@ietf.org?subject=subscribe>
X-List-Received-Date: Sat, 02 Apr 2016 15:47:35 -0000

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
----------------------------------------------------------------------