In H.323 v4 there will be a boolean in the Setup message called symmetricOperationRequired, relevant only to fast connect, that indicates whether symmetric operation is required. This will allow you to offer multiple codecs and still ensure symmetric operation between v4 endpoints.
- Rich
Anatoli Levine wrote:
Chris,
if you originate the fast start and you offer only one codec for both receive and transmit (g711Ulaw = 60, for instance), the receiving side can either accept this or drop the call, but it can't use any other codec and also can't change parameters for the codec which was offered.
Anatoli
Chris Wayman Purvis wrote:
This may be a silly question, but how is symmetry enforced in fastStart?
Regards, Chris
Roni Even wrote:
Hi, I think the issue is very important, there is no clear way to achieve symmetric operation today. In H.323 it states that if a terminal supports H.263 CIF it implies that it support H.261 CIF. On the other hand it states that a terminal can use the receive capabilities to signal which codec it supports, it is not clear if for example a terminal signal that it can receive H.263 CIF, if the transmitter can send H.261 CIF since it is implied but is less preferable, or does it mean that it can only receive H.263 CIF. I think that we can use this change also to make the text correct at least for the symmetric mode. It should state that these are the modes that the terminal can do in symmetric mode and not the implied ones. Roni Even -----Original Message----- From: Mike Nilsson [mailto:mike.nilsson@BT.COM] Sent: Thursday, September 07, 2000 11:47 AM To: ITU-SG16@MAILBAG.INTEL.COM Subject: Enforcing symmetric operation in the context of slow start for H. 323v4
At the Portland rapporteur's meeting of Q12-14, document APC-1881, 'Enforcing symmetric operation in the context of slow start for H.323v4', was discussed. The outcome of the discussion, as described in the meeting report, is:
This was accepted for the H.323 IG and also H.323 V4. It wasagreed that this was meritorius, but that some further discussion was needed. See TD-47. The agreement is that APC-1881 is adopted for changes to H.323 V4, and TD-47 for H.245 V7, with the redefinition of the receiveAndTransmitt capability being the preferred approach. It was noted that the rejectReason needs to be mentioned in TD-47. Text will also be added to note that the procedures of TD-47 only apply if the slave has detected a conflict. All are urged to look very closely at this, and to consider if there are any issues with this. If any are found, we will make changes in November. The editor will post this discussion on the mailing list to ensure broad discussion.
The purpose of this mail is simply to do as the meeting report stated, and highlight the issue and to try to get broad agreement on the proposed solution. As far as H.245 is concerned the proposed solution is to include text from TD-47a that is labelled as 'Proposal for immediate action' and the first option (redefinition of the receiveAndTransmitt capability) from the section labelled 'Longer term options'.
The documents are available at:
ftp://standard.pictel.com/avc-site/0008_Por/APC-1881.zip ftp://standard.pictel.com/avc-site/0008_Por/TD-47a.zipBest regards
Mike Nilsson
Mike Nilsson Multimedia Applications B81 Room 102 pp14 BT Advanced Communications Technology Centre Adastral Park, Martlesham Heath, Ipswich, IP5 3RE, UK Tel: +44 1473 645413 Mobile: +44 7808 635412 Fax: +44 1473 646589 Email: mike.nilsson@bt.com
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-- Dr Chris Purvis -- Development Manager ISDN Communications Ltd, The Stable Block, Ronans, Chavey Down Road Winkfield Row, Berkshire. RG42 6LY ENGLAND Phone: +44 1344 899 007 Fax: +44 1344 899 001
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