Subject: About Timer

From: "yinshaohua" <[email-masked]>
Date: Tue, 22 Feb 2000 20:51:42 +0800

Hi:

     When reading RFC 2543, I have a question regarding path of ACK and BYE.
     In section 4.2.4, there writes "If the INVITE request contained a
contact header, the callee should send a BYE request to that address rather
than the from address ".
And in section 10.5.1, there has " If the response contained a Contact
header field, the ACK may be sent to the address listed in that Contact
header field."  So I can draw a following call flow chart :

user A          Proxy          User B
   INVITE
  ----------->  INVITE
                      --------->
                             200
                      <---------
                200
   <----------
   ACK
   ----------------------------->
      The call is established
                          BYE
   <----------------------------
  In the example ,when do I release the call resource in the Proxy Server ?
  Thanks !

  Shaohua Yin

---

From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 22 Feb 2000 09:24:31 -0500

> header field."  So I can draw a following call flow chart :

Correct.

>   In the example ,when do I release the call resource in the Proxy Server ?

What call resource? If the proxy doesn't record-route, it can't maintain
call state, and thus there is no call resource to release. The proxy
will probably maintain transaction state in this case (what we call
stateful). That state is released after some short period of time after
the 200 OK has been forwarded; 32 seconds is reasonable based on the
timers defined in the spec. In the case of a stateless proxy, there is
no state at all to maintain or release.

If the proxy record-routes, it will see the ACK and the BYE. If its
maintaining call state, it can release that state upon the BYE. Also,
the usage of the session timer
(http://www.ietf.org/internet-drafts/draft-ietf-sip-session-timer-00.txt)
is recommended in case the BYE never gets sent or is lost. 

-Jonathan R.

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