Subject: [SIP] How Expire field works in this case ?

From: "rafi" <[email-masked]>
Date: Sat, 24 Jun 2000 13:50:42 +0530

Hi,

                 Consider a call set up between  UAC and 
     UAS  passing through 'n' number of proxies. When
    UAC  generated  INVITE message it used   Expire
    field with time  't'.  All the intermediate proxies  upon receiving
    INVITE message decided  to use time 't' in order to limit their 
    search. When  INVITE finally arrives at UAS (assuming user is
   presently unavailable),   it decides to wait for time duration 't'.
    Now, before timer of duration 't' really expires  at UAS, timer at proxy (first proxy 
    in the call setup) expires first resulting in call being released. Thus call 
    MAY be released  much earlier than call waiting time promised at UAS. 
    Thus, how  should  UAS use  time 't' present in INVITE request when 
    user is  currently not available?.

       Second question is how does UA handles the 
case of INVITE crossing each other for a given pair of
user ?.  Is this decision is left to user of SIP stack ?

Thank You
Rafi Assadi H.M.
Silicon Automation Systems
Bangalore,  INDIA

---

From: Henning Schulzrinne <[email-masked]>
Date: Sat, 24 Jun 2000 13:04:45 -0400

> rafi wrote:

The timer is not suitable for microsecond timing. If forwarding your
call takes more than a second, something is seriously broken (and your
call throughput is going to be pretty low). Thus, the window where the
call gets terminated by the first proxy rather than the UAS is going to
be measured in units of milliseconds. In addition, even if the first
proxy cancels the call, the total search time is still the expiration
time, so this is correct behavior. The phone will stop ringing either
way. (This can happen in any event if a proxy has a shorter
pre-configured patience than the UAS.)

> user ?.  Is this decision is left to user of SIP stack ?

This question has been discussed several times on the list, at great
length. Please take a look at the archives.

> Silicon Automation Systems

_______________________________________________
SIP mailing list
[email-masked]
http://lists.bell-labs.com/mailman/listinfo/sip