On Tue, 2006-03-28 at 07:09 -0700, Barker, Mark wrote:
> Does anybody know if a Proxy can initiate a REGISTER query client
> transaction
> to lookup the contact info for a "To:" Address of Record?
> 
> i.e. the REGISTER request has a blank Contact header to denote a lookup
> query
> 
> what would be in the From, branch, tag, Call-ID, Cseq header fields???

Well, your proxy application can generate such a REGISTER request.  But
when it is doing so, it is acting as a User Agent, and should follow all
the rules for User Agents.  In practice, your problem will be in getting
your SIP stack to handle this correctly -- the response to the REGISTER
has to be returned to the application code that wants to discover the
contact addresses, not to the proxy logic which will attempt to forward
it upstream.  You may have to open a different port and initialize a
separate instance of your SIP stack to do User Agent tasks.

But if all the components of your system obey the SIP rules, and are
aware of what sort of SIP agent they are, everything "should just work".

(Amusingly, your proxy, acting as a UA, will send a REGISTER request --
which will first go to your proxy, acting as a proxy!)

Dale

--- 
interop.pingtel.com -- the public SIP phone interoperability test server

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