[SIPForum-techwg] Question re Application Server

[Paul Kyzivat]

I have another related question - the relationship of registration to 
routing of requests.

Section 7.2 says:

"SIP Application Servers MUST be prepared to accept (but MUST NOT 
require) registrations for any valid URI that the
Service Provider has assigned to an Enterprise. This interface 
specification does not define any specific action that is triggered by a 
successful registration; however one possible use of this information 
might be to update a DNS entry associated with the PBX in a DNS zone 
managed by the Service Provider."

This isn't specific enough to create an interoperable pair of nodes.

According to 3261, registration updates an abstract location service 
with the provided contact(s). Subsequent routing addressed to the AOR 
results in the request URI being replaced by a registered contact. The 
receiving UAS then determines the target of the request by the value of 
the R-URI.

But section 13.3 specifies what the R-URI should be, without regard to 
whether registration has happened or not.

This seems to suggest that you *forbid* the registration from causing a 
request addressed to the target of the registration from being 
retargeted to the registered contact. There is in fact no clear 
indication that the registered contact has any relevance to how requests 
are routed.

Yet it seems there is some implication that this will determine where 
requests to the enterprise are routed, though without influencing the 
value of the R-URI.

WIthout getting overly normative, can you clarify what expectations an 
anterprise server (pbx) can expect?

Does registration to *any* enterprise number affect the routing of 
requests addressed to *all* enterprise numbers? What if there is 
registration ot more than one enterprise number, using different contact 
addresses? If the registered contact contains a user part, or URI 
parameters, will the UAS receive those in the requests that result?

	Thanks,
	Paul

P.S. I'm also still hoping for an answer to my first set of questions, 
below.

Paul Kyzivat wrote:
> I am trying to understand the nuances of draft 5, and there is something 
> I am unsure of: Is the Application Server required to act as a B2BUA, or 
> is it permitted to act as a proxy? There is no mention of B2BUAs in the 
> document, but I think it may be implied.
> 
> In particular, suppose we have one service provider servicing two 
> enterprises: acme.com and bozo.com.
> 
> Acme has a phone number +12125551234, and Bozo has +14085556789. Then 
> Acme calls Bozo. According to the spec, the call from Acme is addressed as:
> 
> 	INVITE sip:+14085556789 at serviceprovider.net;user=phone SIP/2.0
> 	To: <sip:+14085556789 at serviceprovider.net;user=phone>
> 	From: <sip:+12125551234 at acme.com;user=phone>
> 
> But then the instructions for service provider addressing say that when 
> this is sent to Bozo that it should be addressed as:
> 
> 	INVITE sip:+14085556789 at bozo.com;user=phone SIP/2.0
> 	To: <sip:+14085556789 at bozo.com;user=phone>
> 	From: <sip:+12125551234 at serviceprovider.net;user=phone>
> 
> To change the To and From fields in this way requires that the 
> Application Server be a B2BUA. If this is routed using proxy routing, 
> then the message going to Bozo would perhaps look like:
> 
> 	INVITE sip:+14085556789 at bozo.com;user=phone SIP/2.0
> 	To: <sip:+14085556789 at serviceprovider.net;user=phone>
> 	From: <sip:+12125551234 at acme.com;user=phone>
> 
> So, is it a requirement to have a B2BUA in the path, or is proxy routing ok?
> 
> 	Thanks,
> 	Paul
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