[SR-Users] Kamailio integration - Registration issue

[Alex Balashov]

On 07/07/2010 03:37 AM, rupert.organ at bt.com wrote:

> I have SER sitting in front of Asterisk.
> It is useful to me for Call Forking purposes as I do not think
> Asterisk handle multiple registered endpoints (against a single username)

You are correct.

> However, since both SER and Asterisk are Registrars, and
> Asterisk need toknow register info to work properly, I need to
> forward Registers from SER to Asterisk....

There is an element of this reasoning that is flawed: it is not 
"since" SER and Asterisk are "both" registrars.  In this scenario, SER 
is not acting a UAS;  it is not the logical target of the REGISTER 
request.  Therefore, it is not behaving as a "registrar."  Only 
Asterisk is the registrar in that scenario.

There is nothing in RFC 3261 preventing you from fronting a registrar 
with a proxy and statefully relaying REGISTER requests; in principle, 
a proxy can forward any request.  However, proxies (and UASs) cannot 
add Record-Route headers to the request, and since REGISTER does not 
establish a dialog, route sets have no meaning in relation to it 
anyhow.  This means there is no way to establish a pre-determined 
route set in any scenario ("trapezoid") involving one or more proxies 
between the registrant and the registrar.

The solution to that problem is Path (RFC 3327).



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Alex Balashov - Principal
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