Re: [SIP] SIP - H.323 - INVITE - No media line.

[Vladislav Zubarev <[e-mail]>]

The annswers to most of your question in developing such a gateway you
can find in:

http://search.ietf.org/internet-drafts/draft-singh-sip-h323-01.txt

Have fun. :)

"Maddux, Michel" wrote:

> In constructing a gateway connecting Sip to 323, the process of signalling a
> call and then negotiating channels, for a Sip caller to 323 callee, is
> relatively straightforward. Only one temporizing step is required, and that
> is to not provide an RTCP address in opening channels from gateway (actually
> Sip) to 323 callee.
>
> The reverse case, of implementing 323 caller to Sip callee, is not so
> straightforward. Signalling is tractable, but media channel negotiation is
> murky. Two models occur:
>
> 1) When 323 calls, wait until it opens first media channel. Then issue the
> INVITE, noting only a media line of that media type but with a phony port.
> When Sip replies (200 OK presumed), complete the 323 media channel being
> negotiated, giving it the Sip's media port. Then negotiate the reverse
> channel with 323, saving its port, which is then transmitted to Sip via an
> ACK with a message body correcting the 323 media port. If the 323 caller
> then opens another media channel, repeat the above process via re-INVITE,
> and continue to do so as long as 323 requests media channels.
>
> 2) Depend upon language from the 2543 spec, particularly section B.4 and the
> ACK section, which state that an INVITE could be sent with NO media lines,
> upon receipt of which the Sip callee would respond with a list of its
> supported media (AND presumably providing a port for each of these). In this
> scenario, an INVITE devoid of media would be issued immediately on receipt
> of call from the 323 caller. The resulting 200 OK media list would then be
> used to negotiate the media channels with the 323 caller, and would be
> returned in final form in the message body of the ACK. [It is possible that
> this model would devolve to the first model since it is not known when the
> 323 caller is through opening channels. Should a mid-call media change be
> initiated by the 323 caller, the re-INVITE process would need be used,
> anyway.]
>
> We are interested in a recommendation as to how to do this. Are either of
> the above models viable, or does a better model exist? What is the spec
> status of section B.4?
>
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--
Vladislav Zubarev        mailto:[e-mail]
Software Engineer
Vovida Networks, Inc.    http://www.vovida.com