G'Day all,

The [H.323-SIP/Internet] thread has lead to some interesting discussion. Being personally involved in the H248 "success" and having actually having had to fight through the process of having to work between SG16 and IETF I think there's a few steps that need to be taken before we go into mapping information elements.

I believe the first thing we need to do is define what architecture and call scenarios we are working with. H323 has several architectural elements, SIP is not so strong on architecture so we need to show what elements are talking to each other. Only then we can define what interfaces need to be interworked. In H248 this was relatively easy as the interface was between an MGC and MG. The H323-SIP interworking would be another degree of difficulty as there are potentially several interfaces. This architecture work would not slow down the work but would lead to a structured way of working were people agree on a problem space. One of the issues with H248 was that the problem space was not agree on and we went back and forth trying to figure out where we were.

As I mentioned at the SG16 I invite people to make contributions on this. Anything more detailed at this stage I believe is counter productive. Even Orit's first proposal I think is too detailed at this stage. Look at the early H248 work where we had many detailed protocols. There was an inordinate amount of work spent (and many late nights) trying to get from details to architecture. Then we had to go back again and define the protocol.

The 2nd thing to do is to define the set of capabilities we intend to interwork. This needs to be a clear statement of scope. Interworking basic audio with no conferencing and services is significantly different than interworking full audio, video and data conferencing. In H248 the scope was so large that people were working on completely different things without appreciating the other people's requirements.

Thirdly, we must choose our base. What H323version will be interwork with what SIP flavour and functionalities? Of course in today's world there needs to be flexibility to address new functionality but we shouldn't add a new work item every time of version 0 of an internet draft from Joe Bloggs comes out.

Fourthly, I believe that once the above is done, then we have a very good idea of what functional interworking work needs to be done. Once we have an idea of the work we can also figure out where the responsibilities would lie.

Once we know the work and who is responsible for the work then we MUST make sure this is agreed upon and documented in both the ITU and IETF by the people who can make decisions. Too many things were hidden in the H248 work and people that could make decisions were not at the appropriate meetings.

Finally we can then produce the detailed documents in a way that everyone understands.

I do think that at the end of the day H.248 was a success and that the co-operation between the IETF and ITU was made to work. This was because of the large amount of work and sacrifices made by a few individuals and companies who wanted to make this happen. Many of the individuals working on H248 will probably contribute on H323/SIP interworking so lets learn from the mistakes and have another go at making H323-SIP interworking work without having to kill ourselves to achieve the goal.

Cheers, Christian

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