Pete,

I am having difficulty with what it is that you are trying to convey. Let me try to summarise:

- An empty CS is transmitted "as a TCS message" containing only a sequence number and a protocol identifier. - The effect of receiving such a message does not effect the stored caps of the sending EP at the receiving EP - You (and the team you're working with) would have liked the effect to have been that all caps are removed.

I do not think that I understand your statement on "Re-cap" providing 90% of the functionality in the case that you do not understand empty CSs, could you elaborate on that?

Frank

Mailing list for parties associated with ITU-T Study Group 16 ITU-SG16@MAILBAG.INTEL.COM on 02/11/99 13:05:18 Please respond to Mailing list for parties associated with ITU-T Study Group 16 ITU-SG16@MAILBAG.INTEL.COM @ SMTP To: ITU-SG16 ITU-SG16@MAILBAG.INTEL.COM @ SMTP cc: Subject: Re: The meaning of the reception of a "new" capability set Classification: Restricted I think H.245 covers the delta aspects, although it goes on more about how to add caps and how to delete caps rather than explicitly saying that the caps are a delta.

The definition of an empty cap set is defined in the revised text in the "Third party pause..." section. Basically its only seqNum and protocolIdentifier. I think the team I'm working with would have preferred to have an empty cap set as one that explicitly removed all the existing caps. Even if you don't know about empty cap sets, as long as you can re-cap, you get 90% of the functionality this way. That was the originally intended method when the text said something like "a cap set that indicates that there are no more receive caps". (It seemed obvious to me what it was!!!) However, it became clear that this wasn't clear to everybody and hence consensus from the list moved to the revised text which adopts the other definition. The 'initial' method is also much more complex to explain, which I felt could also lead to interoperability issues. (Even if you don't like the method chosen, you will probably prefer it to the other solution we came up with which was for an endpoint to accept both methods!!!)

And another note, you only have to comply with RequestMode when under control of an MC. Without an MC it's optional. We assumed that that would be a big enough excuse for implementors not to implement anything to do with RequestMode!

Pete

============================================= Pete Cordell pete@tech-know-ware.com =============================================

-----Original Message----- From: frank.derks@PHILIPS.COM frank.derks@PHILIPS.COM To: ITU-SG16@MAILBAG.INTEL.COM ITU-SG16@MAILBAG.INTEL.COM Date: 02 November 1999 09:16 Subject: Re: The meaning of the reception of a "new" capability set

Hi Paul,

thanks for the reply. Is there any work going on to more clearly describe

that "delta" is the desired behaviour? The next question that this brings is: "what is an "empty CS", because I can see several ways of achieving this. Again I do not see a clear

specification on what an empty CS looks like.

I fully agree with your statement about the third-party initiated pause and

re-routing, but at the moment it is the only "lightweight" method of achieving certain behaviours that would otherwise require H.450.

Frank

Mailing list for parties associated with ITU-T Study Group 16

ITU-SG16@MAILBAG.INTEL.COM on 01/11/99 17:29:54

Please respond to Mailing list for parties associated with ITU-T Study

Group 16 ITU-SG16@MAILBAG.INTEL.COM @ SMTP

To: ITU-SG16 ITU-SG16@MAILBAG.INTEL.COM @ SMTP cc: Subject: Re: The meaning of the reception of a "new" capability set Classification: Restricted 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