Re: The meaning of the reception of a "new" capability set
I believe every new capability set should be treated as a complete replacement for the previously received one. Otherwise conferencing servers (MCS) and Gateways will not be able exercise enough control over the media modes of the multipoint conferences and gateway sessions. Ilya Freytsis -----Original Message----- From: frank.derks@PHILIPS.COM [mailto:frank.derks@PHILIPS.COM] Sent: Monday, November 01, 1999 8:31 AM To: ITU-SG16@mailbag.cps.intel.com Subject: The meaning of the reception of a "new" capability set Neither H.323 nor H.245 are too clear about what it means when an endpoint receives another set of capabilities after having already received one. In previous E-mail messages on this list, I have read that capability sets are cumulative, i.e. anything "new" received in a TCS message adds to the capabilities transmitted in a previous TCS message. I have, however, found nothing in the recommendations that backs this up. So what is the intended procedure? Does a newly received set of capabilities replace the previously received set? Do capabilities received in a TCS message add to the already received capabilities? How are capabilities removed? What constitutes an "empty capability set" etc. I would appreciate it if somebody could point me in the right direction. Regards, Frank
Ilya, No, no, no!!! :-) Each TCS message is a _delta_ to be applied to the remote EP's current capability set stored in the EP. This issue was discussed a few months ago on the reflector. My reply follows my signature. BTW, the pause feature added to H.323v2 redefines the meaning of an empty TCS. In H.323v1, an empty TCS causes no change to the current cap set--a NO-OP, so to speak. As of v2, however, an empty TCS means close all outgoing channels, assume that the remote EP has no receive or transmit caps (flush the current capapbility set for the remote EP), and upon receipt of the next presumably non-empty TCS, re-open outgoing channels based on the possibly new set of receive caps. From what I've heard, though, many if not all v2 EPs still exhibit v1 behavior in this regard. I doubt whether "pause" will ever be a dependable feature. IMO, overloading a message like this is just asking for trouble. The same thing could have been better accomplished with RequestMode. Paul Long Smith Micro Software, Inc.
>>> My reply from July 1, 1999 Ramana, Chris, et al.:
An incoming terminalCapabilitySet message _modifies_ the current capability set in the receiving EP. The entire set is not necessarily transmitted within every message. This has been true since H.245v1. In fact, H.245 says that one should not transmit unchanged capabilities. One starts out with an empty set of descriptors. Incoming descriptors replace any extant ones with the same descriptor number. If one does not already exist with the same number, this adds a new descriptor; if one does exist, the new one replaces the old one; if the new descriptor does not contain simultaneousCapabilities, this removes any existing descriptor for the given number. (This is the same scheme used to modify the capability table.) Here is an illustrative chronological scenario: Current capability set: <empty> Incoming termCapSet 1 0: {{H.261qcif},{G.711}} 1: {{H.261cif},{G.711}} Current capability set: 0: {{H.261qcif},{G.711}} 1: {{H.261cif},{G.711}} Incoming termCapSet 2 1: {} Current capability set: 0: {{H.261qcif},{G.711}} Incoming termCapSet 3 1: {{H.261cif},{G.711}} 2: {{H.263sqcif&qcif&cif},{G.723,G.711}} Current capability set: 0: {{H.261qcif},{G.711}} 1: {{H.261cif},{G.711}} 2: {{H.263sqcif&qcif&cif},{G.723,G.711}} Incoming termCapSet 4 1: {} 0: {{H.261qcif&cif},{G.723.1,G.711)} Current capability set: 0: {{H.261qcif&cif},{G.723.1,G.711)} 2: {{H.263sqcif&qcif&cif},{G.723,G.711}} Paul Long Smith Micro Software, Inc. <<<<<<<<< -----Original Message----- From: Ilya Freytsis [mailto:IFREYTSIS@VIDEOSERVER.COM] Sent: Monday, November 01, 1999 8:57 AM To: ITU-SG16@MAILBAG.INTEL.COM Subject: Re: The meaning of the reception of a "new" capability set I believe every new capability set should be treated as a complete replacement for the previously received one. Otherwise conferencing servers (MCS) and Gateways will not be able exercise enough control over the media modes of the multipoint conferences and gateway sessions. Ilya Freytsis -----Original Message----- From: frank.derks@PHILIPS.COM [mailto:frank.derks@PHILIPS.COM] Sent: Monday, November 01, 1999 8:31 AM To: ITU-SG16@mailbag.cps.intel.com Subject: The meaning of the reception of a "new" capability set Neither H.323 nor H.245 are too clear about what it means when an endpoint receives another set of capabilities after having already received one. In previous E-mail messages on this list, I have read that capability sets are cumulative, i.e. anything "new" received in a TCS message adds to the capabilities transmitted in a previous TCS message. I have, however, found nothing in the recommendations that backs this up. So what is the intended procedure? Does a newly received set of capabilities replace the previously received set? Do capabilities received in a TCS message add to the already received capabilities? How are capabilities removed? What constitutes an "empty capability set" etc. I would appreciate it if somebody could point me in the right direction. Regards, Frank
participants (2)
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Ilya Freytsis -
Paul Long