TCS is always first message, not TCSAck

Chris Wayman Purvis cwp at ISDN-COMMS.CO.UK
Mon Nov 6 13:23:09 EST 2000


Doug,

If you don't like Paul's solution (it does have the flaw that a device
controlled by UIIs looks like something that doesn't terminate the call - not
that I see WHY that is a problem), then you do have an alternative.  If you
don't know the capabilities of the final destination of the call by this point
you won't lose a lot by using good old-fashioned
H.245-in-a-separate-TCP-stream!

Regards,
Chris

Douglas Clowes wrote:
>
> Paul,
>
> Ugly! That leaves open the decision, for the receiver of the TCS, of when
> you give up on a call because you do not have compatible capabilities.
>
> I can see that an empty-ish TCS could be distinguished from a TCS that
> isn't empty, but contains codecs I can't match. But how many EPs out there
> would already appreciate the distinction? If I send TCS 0.5, will my peer
> drop the call?
>
> Ugly!
>
> Douglas
>
> At 21:13 04/11/2000 -0600, Paul Long wrote:
> >Regarding Douglas' concern, regardless of whether "an EP _should_ be able to
> >ack a received message, even before sending TCS" (emphasis mine), the fact
> >remains that it _shall not_ do this, except when indicating that it
> >understands earlyH245Control. The solution to the particular problem he
> >mentions is for the endpoint to send an "almost empty" TCS, or "TCS=0.5"
> >:-). All it contains is sequenceNumber, protocolIdentifier, and--here's the
> >important part--multiplexCapability. In particular, it doesn't need to
> >contain capabilityTable or capabilityDescriptors, and the
> >multiplexCapability can provide only minimal information. Including
> >multiplexCapability means that it is not an empty TCS and therefore cannot
> >be mistaken for one, but the endpoint also does not need to know its
> >eventual capabilities at call-startup time.
>
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Dr Chris Purvis -- Development Manager
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