To quote RFC3261:
To quote RFC3261:

  If the response for a request within a dialog is a 481
  (Call/Transaction Does Not Exist) or a 408 (Request Timeout), the UAC
  SHOULD terminate the dialog.  A UAC SHOULD also terminate a dialog if
  no response at all is received for the request (the client
  transaction would inform the TU about the timeout.)

Instead of relying on originating UA to DTRT, tear down session by
ourselves upon receiving 408 or 481 in response to re-INVITE.

sippy/b2bua,AVOXI/b2bua,sippy/b2bua,AVOXI/b2bua