Subject: [Sip] Outbound: must Registrar also reuse flow?

From: Fredrik Thulin <[email-masked]>
Date: Mon, 3 Apr 2006 17:24:56 +0200

Hi

In the following setup, if the client does Outbound and send a REGISTER 
towards the Registrar via the edge-proxy EP,

 UA --|-- EP -- Registrar
     NAT

does the Registrar have to reuse the exact same flow to EP when a new 
request arrives at Registrar, targeted for UA?

The EP obviously has to do so, but does the Registrar also have to?

Section 6.1 definately says the Registrar must do so

  "The registrar MUST store enough information to uniquely identify the
   network flow over which the request arrived. "

but I can't see the point in mandating the exact same flow being used to 
send subsequent requests from Registrar to EP, if both of them are on 
the open Internet?

/Fredrik

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From: Hisham Khartabil <[email-masked]>
Date: Mon, 3 Apr 2006 17:41:25 +0200

There can be multiple EPs that connect to the registrar/proxy. So to 
ensure that an INVITE, for examples, arrives at the correct EP, you 
need the registrar/proxy to store such information.

Regards,
Hisham

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From: Fredrik Thulin <[email-masked]>
Date: Mon, 3 Apr 2006 18:09:01 +0200

> need the registrar/proxy to store such information.

The registrar stores the RFC3327 Path, where the edge-proxys can put 
their unique hostnames instead of the common name for all the 
edge-proxys.

The registrar then uses the Path information to send the subsequent 
requests to the right edge-proxy.

/Fredrik