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List:       sip-implementors
Subject:    Re: [Sip-implementors] Loose routing & Error Information
From:       sshetti () hss ! hns ! com
Date:       2004-07-29 12:40:11
Message-ID: OFD3208971.654DC5E5-ON65256EE0.00437065-65256EE0.00447F9E () hss ! hns ! com
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some correction on the example mentioned...

strict router always expects its address in the request uri, and not in the
route header list.
if a client is sending request to a strict router and client understands
loose routing, it shall first push the reqURI (which is contact address of
callee) as last route header. now it pops the next hop strict router's
route header from the route set and places the same in the request URI. now
it sends request to the strict router.
strict router pops the topmost route and makes it request URI and sends it
to same location as per old rfc.

if the next hop is loose router, then it understands that previous hop was
strict one as it finds reqURI pointing to itself. therefore it removes last
route which is the end point's contact and makes it request URI. now it
sends the request to wherever next route points (I assume next route has
"lr", else it has to repeat the same steps which client did before sendign
to strict router!).

in the example mentioned below, it would cause the strict router to send
the message to itself and then send to next hop (as its route header is
presnt in the route list as well as req URI).

regards,
Shetti



                                                                           
             Ramachandran Iyer                                             
             <rama14@yahoo.com                                             
             >                                                          To 
             Sent by:                  Suresh P <psuresh@tataelxsi.co.in>, 
             sip-implementors-         "Sip-Implementors \(E-mail\)"       
             bounces@cs.columb         <sip-implementors@cs.columbia.edu>  
             ia.edu                                                     cc 
                                                                           
                                                                   Subject 
             07/29/04 04:52 PM         Re: [Sip-implementors] Loose        
                                       routing & Error Information         
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           





Loose Routing, Strict Routing: The difference between the 2 is basically
how the proxy (router) behaves or is intelligent enough to decipher the
messages coming to it. Loose router being the more intelligent of the two.
This router will always add a (;lr) field on its record-route, which will
then be part of the Route list as well.

For Strict Routers.. the msg coming to them shoudl be STRICTLY add to them
in the request-URI... where as for a Loose Router its ok,, to send the msg
as it is, with the term party being in the req-URI..

If for ex, a route list  (A, B,C)has been formed, wih an intermediate
Router (B) being a strict router. So A will copy the B's URI from the route
list, put it on the req-URI and send it to B. B upon receiving, will remove
itself from the route list and send it to C. C now be a loose router,
understand that even though the msg is sent to it, but the term party is
some1 else.. so picks up the last element in the route list, puts it in the
req-URI and sends it to the next on the route list.

There is some document which shows complete flow with example,, i dont
remember which 1.. i guess you could search and find that easily though.

Rama


Suresh P <psuresh@tataelxsi.co.in> wrote:
Hi all,

The following SIP protocol features is relevant in a UA
development? If so, why it is required and what is the application in a
deployed scenario?

1. Loose routing & strict routing support
2. Error information support.

Comments are highly appreciated.

Regards,
-Suresh

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