[Fwd: Force remote to start H.245 session?]

[Chris Wayman Purvis]

Reply intended for the list unintentionally sent to Paul personally, so here
you all are!

Chris

Chris Wayman Purvis wrote:
>
> Paul,
>
> First of all, sorry for the fact that this seems to be a week-old mail I'm
> finally responding to...
>
> I may have misunderstood, but I don't understand why this is necessary.  If
> both endpoints have expressed willingness to use tunnelled H.245, why can an
> endpoint not simply start sending H.245 messages (of COURSE starting with TCS,
> and potentially tunnelled in purpose-built FACILITY messages) when it wishes to
> start a tunnelled H.245 session?  I would have thought that would be a pretty
> clear indication of intent to start a tunnelled H.245 session!
>
> FACILITY/reason=startH245 is required for separate H.245 connections because an
> endpoint may not know an address at its interlocutor to use to initiate an
> H.245 connection.  This problem doesn't exist in tunnelled H.245, so I see no
> necessity for the extra interpretation!
>
> We may want some extra text specifying behaviour at the start of an H.245
> session, to ensure that the destination of the initial tunnelled H.245 message
> actually does something constructive (sends a TCS) rather than non-constructive
> (merely Acking the TCS it's been sent and not advancing anything useful).
>
> Regards,
> Chris
>
> Paul Long wrote:
> >
> > How does an EP force the remote EP to bring up a tunneled H.245 session?
> >
> > Consider this call scenario: Fast Connect was enough to establish the
> > desired media between two EPs. Both support H.245 Tunneling but neither has
> > initiated an H.245 session because neither had any need to. One EP now needs
> > to use H.245 procedures. It doesn't matter, but reasons include DTMF
> > transmission via UII and requesting a different video format or different
> > audio bit-rate via RequestMode. That EP can initiate its own H.245
> > procedures, e.g., TCS and MSD, but how does it force the other EP to bring
> > up an H.245 session?
> >
> > H.323 and H.225.0 say that Facility/reason=startH245 is just for switching
> > from Fast Connect or H.245 Tunneling to a separate H.245 channel, not for
> > initiating an H.245 session via tunneling. Is it just hoped that when an EP
> > sees that the other EP is bringing up an H.245 session, it will do the same?
> > Seems like a pretty weak assumption. It would be nice if
> > Facility/reason=startH245 without an h245Address meant to bring up an H.245
> > session on whatever transport is already established, i.e., tunneled or
> > separate channel. Seems like we could do this in v4 because startH245
> > without an h245Address currently has no meaning. Whadya think?
--
Dr Chris Purvis -- Development Manager
ISDN Communications Ltd, The Stable Block, Ronans, Chavey Down Road
Winkfield Row, Berkshire.  RG42 6LY  ENGLAND
Phone: +44 1344 899 007
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