Expires header in INVITE shall be used. 

Excerpt from RFC3261:
The UAC MAY add an Expires header field (Section 20.19) to limit the
validity of the invitation. If the time indicated in the Expires header
field is reached and no final answer for the INVITE has been received, the UAC
core SHOULD generate a CANCEL request for the INVITE, as per Section 9.

Best Regards,
Mohammed Hanifa

“In theory, there is no difference between theory and practice. But, in 
practice, there is."
  ----- Original Message ----- 
  From: Iñaki Baz Castillo 
  To: M. Ranganathan 
  Cc: sip-implementors 
  Sent: Saturday, July 10, 2010 9:33 AM
  Subject: Re: [Sip-implementors] How long can a Dialog be in Early state.


  2010/7/10 M. Ranganathan <[email protected]>:
  > Consider the following scenario :
  >
  > UAC sends INVITE, receives 1xx response and creates a Dialog which is
  > now in Early state.
  >
  > UAS dies and no final response is received.
  >
  > Client Transaction is stuck in Proceeding state and Dialog is stuck in
  > early state.
  >
  > I would like to generate a timeout alert at this point so that the
  > application can be alerted that the UAS died and hence it should
  > perform cleanup. What is the recommended timeout period for this? In
  > other words what is the max time for which the Dialog can remain in
  > Early state?


  There is no limits. Usually PSTN providers terminates the call after
  60-120 seconds ringing. A proxy can also terminate the INVITE
  transaction by sending a CANCEL to the ringing branches and a 408 to
  the UAC.
  Also, most of the UA's can be configured to cancel a call after N
  seconds ringing.


  -- 
  Iñaki Baz Castillo
  <[email protected]>

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