[SIPForum-discussion] How to use lr parameter in URI

[hemanth kumar]

Hi
   
  Please find my answers inline

harish T <harish0611 at gmail.com> wrote:
  
While reading RFC 3261 i could not make out the difference between "URI that contain   the lr parameter" and 
"URI does not contain lr parameter"

case 1:
   if first URI doen't contain lr parameter then   
          <sip:proxy1>,<sip:proxy2>,<sip:proxy3;lr>,<sip:proxy4>

   The request will be formed with the following Request-URI and Route
   header field:

   METHOD sip:proxy1
     Route: <sip:proxy2>,<sip:proxy3;lr>,<sip:proxy4>,<sip:user at remoteua>
  If the lr parameter is absent, it means that it is a strict router. Strict router expects its entry( that it added in the Record Route of the initial Request) in the Request URI. So the UA gets the entry from the route set and puts it in the Request URI. It adds the end point's info as the last entry in the record route.
   
  case 2: (is this correct?)


 if first URI contain lr parameter then 
          <sip:proxy1;lr>,<sip:proxy2>,<sip:proxy3>,<sip:proxy4>

   The request will be formed with the following Request-URI and Route
    
   header field:

   METHOD sip:proxy1
   Route: <sip:proxy2>,<sip:proxy3>,<sip:proxy4>,<sip:user at remoteua>

Is this correct?...

I could not understand the lr concept ...if any one knows please explain how to use lr  parameter...  
if possible please provide simple example

  If the UA finds from route set that the next hop is a loose router, It then uses the end point's info (obtained from the contact header in the initial request) in the Request URI and sends it. when it reaches the loose router, it looks for its entry in the route set and removes its entry from the route list and forwards it to the next hop. Before forwarding it checks in the route set if the next hop is a loose router or a strict router. if it is a strict router, it replaces the Request URI with the next hops entry in the route list and removes that entry in the route list. It also adds the destination's entry from the request URI to the route set as the last entry.

  Hope this answers your question

  Regards
  Hemanth




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With regards 
Harish.T _______________________________________________
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