[MMUSIC] SDPCapNeg-06 Issue #3: More Fine-grained Control of Required Extensions
Flemming Andreasen <fandreas@cisco.com> Tue, 11 September 2007 21:32 UTC
Return-path: <mmusic-bounces@ietf.org>
Received: from [127.0.0.1] (helo=stiedprmman1.va.neustar.com) by megatron.ietf.org with esmtp (Exim 4.43) id 1IVDLN-0007uk-BN; Tue, 11 Sep 2007 17:32:25 -0400
Received: from [10.91.34.44] (helo=ietf-mx.ietf.org) by megatron.ietf.org with esmtp (Exim 4.43) id 1IVDLM-0007u4-7X for mmusic@ietf.org; Tue, 11 Sep 2007 17:32:24 -0400
Received: from sj-iport-3-in.cisco.com ([171.71.176.72] helo=sj-iport-3.cisco.com) by ietf-mx.ietf.org with esmtp (Exim 4.43) id 1IVDLK-0007if-Td for mmusic@ietf.org; Tue, 11 Sep 2007 17:32:24 -0400
X-IronPort-AV: E=Sophos;i="4.20,240,1186383600"; d="scan'208";a="522836124"
Received: from sj-dkim-3.cisco.com ([171.71.179.195]) by sj-iport-3.cisco.com with ESMTP; 11 Sep 2007 14:32:22 -0700
Received: from sj-core-5.cisco.com (sj-core-5.cisco.com [171.71.177.238]) by sj-dkim-3.cisco.com (8.12.11/8.12.11) with ESMTP id l8BLWMY4032532 for <mmusic@ietf.org>; Tue, 11 Sep 2007 14:32:22 -0700
Received: from xbh-sjc-231.amer.cisco.com (xbh-sjc-231.cisco.com [128.107.191.100]) by sj-core-5.cisco.com (8.12.10/8.12.6) with ESMTP id l8BLW4of006696 for <mmusic@ietf.org>; Tue, 11 Sep 2007 21:32:22 GMT
Received: from xfe-sjc-211.amer.cisco.com ([171.70.151.174]) by xbh-sjc-231.amer.cisco.com with Microsoft SMTPSVC(6.0.3790.1830); Tue, 11 Sep 2007 14:32:20 -0700
Received: from [10.21.88.23] ([10.21.88.23]) by xfe-sjc-211.amer.cisco.com with Microsoft SMTPSVC(6.0.3790.1830); Tue, 11 Sep 2007 14:32:20 -0700
Message-ID: <46E70963.9050604@cisco.com>
Date: Tue, 11 Sep 2007 17:32:19 -0400
From: Flemming Andreasen <fandreas@cisco.com>
User-Agent: Thunderbird 1.5.0.13 (Windows/20070809)
MIME-Version: 1.0
To: mmusic <mmusic@ietf.org>
Content-Type: text/plain; charset="ISO-8859-1"; format="flowed"
Content-Transfer-Encoding: 7bit
X-OriginalArrivalTime: 11 Sep 2007 21:32:20.0956 (UTC) FILETIME=[3C35A9C0:01C7F4BB]
DKIM-Signature: v=0.5; a=rsa-sha256; q=dns/txt; l=3430; t=1189546342; x=1190410342; c=relaxed/simple; s=sjdkim3002; h=Content-Type:From:Subject:Content-Transfer-Encoding:MIME-Version; d=cisco.com; i=fandreas@cisco.com; z=From:=20Flemming=20Andreasen=20<fandreas@cisco.com> |Subject:=20SDPCapNeg-06=20Issue=20#3=3A=20More=20Fine-grained=20Control= 20of=20Required=20Extensions |Sender:=20; bh=iLOtGjKFfJ9PZU/QiDNjuOR42YOUpgbfWojXoHeBpqc=; b=G3SLXewy7QHC1ASoR0pZsxQ2XrnJVZwTYQAVT4DwwFULq6g/KHrS4zmcdYJuhKwf1fLwytLY 3lxexa6dc8X4J5m+4GB3Vv3SjFHx24F0jka7eoau/U57DOAJB91JIwMj;
Authentication-Results: sj-dkim-3; header.From=fandreas@cisco.com; dkim=pass ( sig from cisco.com/sjdkim3002 verified; );
X-Spam-Score: -4.0 (----)
X-Scan-Signature: fb6060cb60c0cea16e3f7219e40a0a81
Subject: [MMUSIC] SDPCapNeg-06 Issue #3: More Fine-grained Control of Required Extensions
X-BeenThere: mmusic@ietf.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Multiparty Multimedia Session Control Working Group <mmusic.ietf.org>
List-Unsubscribe: <https://www1.ietf.org/mailman/listinfo/mmusic>, <mailto:mmusic-request@ietf.org?subject=unsubscribe>
List-Post: <mailto:mmusic@ietf.org>
List-Help: <mailto:mmusic-request@ietf.org?subject=help>
List-Subscribe: <https://www1.ietf.org/mailman/listinfo/mmusic>, <mailto:mmusic-request@ietf.org?subject=subscribe>
Errors-To: mmusic-bounces@ietf.org
The core SDP Capability Negotiation Framework includes support for extensions. Unknown extensions are by default ignored, however extensions can have an option tag associated with them, and support for those can be required. The way this is done currently is by including a single "a=creq" at the session-level and/or media-level(s), which indicate the option tags that MUST be supported in order to process the SDP Capability Negotiation extensions. When provided at the session-level, the extensions must be supported throughout the entire SDP, and when provided at the media-level, the extensions must be supported for that particular media description ("m=" line). As part of the media capabilities discussion, Magnus expressed some concerns about forward compatibility and not having enough flexibility for later (if media capabilities are not included in the core, which they are not). Proper extensibility support is key to address this IMO, and the question here is whether the current extension mechanism is flexible enough. The design team had originally discussed "required" option tags being supported not only at the session and media level (as is done currently), but to also support them at the individiaul potential configuration level. This way, rather than requiring support for a particular extension throughout the entire SDP or in a particular media description in order to even use the SDP capability negotation framework, we can simply skip individual potential configuration attributes where the necessary extensions are not supported. At the time, it was felt that we could get by without such functionality, however I'd like to reconsider that here. The basic question is whether there ever is a need to require support for a particular extension in one potential configuration, but not another one in the same media description. I believe the answer to that is yes once we start considering combinations of capabilities. Consider the following example: a) If the transport protocol is AVPF, and media capabilities are supported, then use H.264 with the RFC 4588 RTP retransmission payload format. The RTP retransmission uses session-multiplexing and we have another extension in place to indicate an inter-media stream synchronization dependency. This extension must be supported as well. b) If the transport protocol is regular AVP, and media capabilities are supported then use H.264 with FEC (RFC 2198 and draft-ietf-avt-ulp-23.txt) The two alternatives above each correspond to a potential configuration which uses transport protocol capabilities (core) and media capabilities (extension), however the first one requires support for an additional capability (which the second does not). Thus, indicating required capabilities at the media-level alone does not produce the desired result (consider the case where the answerer supports only the media capabilities). While the use cases for this functionality may not be that common, they are nevertheless there, and will be important to some. I believe the functionality is important to have, it doesn't add much additional complexity, and if we are to have it, it needs to be in the core. Based on this, I'd like to suggest we add this functionality in the core. Please let me know if you agree or disagree with this. Thanks -- Flemming _______________________________________________ mmusic mailing list mmusic@ietf.org https://www1.ietf.org/mailman/listinfo/mmusic
- [MMUSIC] SDPCapNeg-06 Issue #3: More Fine-grained… Flemming Andreasen
- RE: [MMUSIC] SDPCapNeg-06 Issue #3: More Fine-gra… Stach, Thomas
- Re: [MMUSIC] SDPCapNeg-06 Issue #3: More Fine-gra… Flemming Andreasen
- RE: [MMUSIC] SDPCapNeg-06 Issue #3: More Fine-gra… Stach, Thomas
- RE: [MMUSIC] SDPCapNeg-06 Issue #3: More Fine-gra… Even, Roni