Overview through the RFC 4028- Session Timers in the Session Initiation Protocol (SIP)

Session-Expires, which conveys the lifetime of the session, and Min-SE, which conveys the minimum allowed value for the session timer.

Session-Expires Header Field Definition

The Session-Expires header field conveys the session interval for a SIP session. It is placed only in INVITE or UPDATE requests, as well as in any 2xx response to an INVITE or UPDATE.  Like the SIP Expires header field, it contains a delta-time. The absolute minimum for the Session-Expires header field is 90 seconds.  This value represents a bit more than twice the duration that a SIP transaction can take in the event of a timeout.  This allows sufficient time for a UA to attempt a refresh at the halfpoint of the session interval, and for that transaction to complete normally before the session expires.

However, 1800 seconds (30 minutes) is RECOMMENDED as the value for the Session-Expires header field.  In other words, SIP entities MUST be prepared to handle Session-Expires header field values of any duration greater than 90 seconds, but entities that insert the Session-Expires header field SHOULD NOT choose values of less than 30 minutes.

422 Response Code Definition

This extension introduces the 422 (Session Interval Too Small) response code.  It is generated by a UAS or proxy when a request contains a Session-Expires header field with a duration below the minimum timer for the server.  The 422 response MUST contain a Min-SE header field with the minimum timer for that server.

-- Marco Mouta

On Wed, Feb 23, 2011 at 2:00 PM, Mino Haluz mino.haluz@gmail.com wrote:

Hi, I see in my cdrtool rarely 422 Session Timer too small - the reason why the call was not initiated. Do you have some suggestion how to fix this ? Maybe SST module ? What is the default value of this timer, so that I could increase it ?  kamailio 3.1.0 (i386/linux) 1e204f Thank  you, Mino _______________________________________________ SIP Express Router (SER) and Kamailio (OpenSER) - sr-users mailing list sr-users@lists.sip-router.org http://lists.sip-router.org/cgi-bin/mailman/listinfo/sr-users