Subject: RE: [SIP] RE: about proxy

From: Ge Yu <[email-masked]>
Date: Thu, 25 May 2000 11:21:44 +0800

hi, Jonathan,

Thanks for your fast reply.

Actually it can be shown as following:

The SIP original operation:

           (1)       (2)       (3)       (4)       (5)
(caller)UAC--->proxy1--->proxy2--->proxy3--->proxy4--->UAS(callee)

Different proxy provides different service, the services are provided
sequentialy, all the (1),(2),(3),(4),(5) are standard SIP INVITE messages.

And another scheme:
           proxy2  proxy3  proxy4   
             (2)\  (3)/    (4)/  
(caller)UAC---->(local)proxy1---->UAS(callee)
            (1)               (5)

Now the services of proxy2, proxy3, proxy4 can be provided parallelly. The
(1),(5) 
are still standard SIP INVITE messages. But the (2),(3),(4) are simplified
requests which
only include the service provided by individual proxy, so (2),(3),(4)
messages are different 
and only part of original INVITE. Proxy1 sends out 3 requests
simultaneously, after it gets
the 3 reponses from 3 proxies, it rewrite the original INVITE and sends it
to UAS. 

By primarily consideration, the scheme can reduce call setup time, but is it
possible in SIP?

thanks
Yu

-----Original Message-----
From: Jonathan Rosenberg
To: Ge Yu
Cc: [email-masked]
Sent: 5/25/00 2:35 AM
Subject: Re: [SIP] RE: about proxy

Ge Yu wrote:
> 
> hi, all,
> 
> If a UAC sends out an INVITE, which will tranverse 4 proxy servers
until it
> reaches the callee, the servers provide different services, this is
standard
> method of SIP.
> 
> There is another approach: UAC sends out an INVITE to the first proxy
> server, which may be its local proxy, then the proxy acts as a client
and
> sends the different service requests to the other 3 proxy servers.
Upon the
> first server receives the responses, it forwards the INVITE directly
to the
> callee, so the INVITE only need to tranverse ONE proxy.

I think you are talking about forking, but I'm not certain. SIP allows a
proxy to receive one request, and forward more than one request out. IN
this case, the local proxy would fork and send three INVITEs. These
would hit three separate servers, each of which tries to contact the
user. As they receive responses, these responses are forwarded upstream
to the forking proxy. The first call acceptance that the forking proxy
receives is forwarded upstream towards the caller.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (732) 741-4778
http://www.cs.columbia.edu/~jdrosen         PHONE: (732) 741-7244
http://www.dynamicsoft.com

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From: Neil Deason <[email-masked]>
Date: Thu, 25 May 2000 09:11:26 +0100

> The SIP original operation:

In the first example the service being performed by the SIP proxies is trying to
locate the callee, by routing the INVITE on to the next appropriate hop.

What are the services of P2, P3, P4 in your second example?

Whatever they are I think describing nodes 2,3,4  as SIP Proxy Servers is
leading to confusion. However, if they are SIP nodes offering services, that
fall within the solution space of SIP, it might be possible to add a new SIP
request method to do what you are describing.

hth,
Neil.
--
Ubiquity Software Corporation, UK           http://www.ubiquity.net