H.323 Annex E

Kishore Ramisetty kish at TRILLIUM.COM
Fri Nov 20 14:57:50 EST 1998

H.323 Annex E proposes using simultaneous (or a little later)
TCP and UDP transport connections to provide seamless
interoperability with non-Annex E devices. This results in
inefficiencies because we now have to transmit two kinds of
PDUs for the same call. (Q.931 headers are present for TCP
transport and they are absent for UDP). This again has the
unfortunate consequence of mandating higher layers to be aware
of the transport because upper layers have to deal with
duplicates arriving from TCP and UDP connections.
(Section E.5.3 para 4 and 5)

A simpler solution to this problem is, Annex E compliant
end points should register with gatekeeper about their
capability of supporting Annex E in RRQ message and
gatekeeper propogates this in ACF messages. So, it is
easy to determine apriori whether to attempt UDP/TCP
connection to the destination end points (because non
Annex E devices won't register anything with gatekeepers).
This will also require some additions to GK-GK communication
so that such kinds of profiles can be communicated across

This solution of course requires V3 GKs. If a V3 GK (or
GK itself) is absent, then end points could have the
option of trying simultaneous connections or simply falling
back to TCP. This solution would make sure that going
forward to V3 we can get rid of this simultaneous connection
establishment procedures.

I would like some comments from the group.


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