H.323 Fast Connect and Versioning
Paul E. Jones
paulej at PACKETIZER.COM
Fri Sep 26 13:20:34 EDT 2003
> I thought it would happen from the conversion among us.
> I do not understand well. One of my understanding is that the version 1
> is not aware of our syntax issue and it could accept any Setup and return
> Connect irrespective of the version. Am I right?
That is correct. That's the problem we are looking at.
> Why are there issues in Fast Connect only?
With regular H.245 capability exchange and the use of OLCs, both sides will
know the actual capabilities. Version 2 devices should then only send an
OLC with a version that it knows the remote side can accept.
We potentially have this same problem with SIP and other SDP-based systems.
They must change the version number in the "answer" to an "offer".
> The 2002 ASN.1 syntax is for t30-data.
> Before V.21 signal starts, i.e. during CNG and CED exchange,
> I do not believe there are issues.
> If we use Fast Connect and V.21 signals are exchanged during Fast Connect,
> it would be a problem. Is this one of the problems?
The problem has to do with sending a Fast Connect proposal (channel
proposal) for T.38v2 (2002 syntax) to a version 0 device (1998) syntax and
that device accepting the proposal and, subsequently, sending 2002-encoded
IFP packets. The version 0 device cannot decode the IFP packets.
In short, there is a potential for sending the wrong ASN.1 PER encoded
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