See my comments below...
-Qiaobing
"Paul E. Jones" wrote:
Archana,
The ACK packet certainly follows the line of thinking that I had. However, one issue with implementing this approach is that there are no fields in H.323 to provide a "sequence number". I suppose this could easily be overcome.
I want to change direction just a bit. I have been pushing for Annex E, but I got resistance: people want to be able to use TCP or another transport. I understand that desire. People have also expressed concerns that we're not clearly separating the transport and application layers. To some extent, that is true. However, I believe that with Annex E, we can draw that line a little clear-- but it means modifications to Annex E. Another issue is that some people have disagreed with modifying Annex E :-)
I'd count myself as one of those disagreeing with modifying Annex E. With the proposed end-to-end ack and Annex E level keeping call state changes as we discussed in the last two robustness conf. calls, the line btw transport and application will be further blurred.
Here's a thought: how about introducing a new session layer between the transport and below the H.323 application? This session layer would actually encode messages in a special format for transmission on the wire. For example, for TCP, we could modify the TPKT header and the payload to carry not only the H.323 message, but also sequencing data and other information. We can allow fail-over addresses to be carried in this layer and allow this layer to completely handle connection recovery.
When robustness is not available end-to-end, this layer in the middle would send and receive messages as normal. However, when robustness is available end to end, it would "get in the middle" and transparently handle robustness issues for the H.323 application.
The goal, of course, is to minimize the application changes and to minimize changes to the transports below.
DDP is exactly a session layer protocol btw the transport and the application. It is designed to perform all the functions you just described and more. You get network level redundancy with SCTP replacing TCP (multi-homing and fast fail-over) and node level redundancy from DDP (transparent server pooling at GKs). All this can be achieved with little change to H.323 protocol. Randy Stewart and myself at Motorola are going to have a contribution to details this architecture at the coming Osaka SG16 meeting this May.
Certainly, this is a shift from my previous thinking, but it represents an attempt to address all of the concerns people have raised. What is your opinion on this type of approach?
Paul
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