On Thu, 2008-11-20 at 09:40 +0000, Gabor Paller wrote:
> The Cisco 7940 (SIP image, P0S3-08-5-00) is a more complicated issue.
> The phone processes SipX expiration response correctly but it tries to
> re-register exactly after that time period. It seems that due to minor
> differences between the clock of the PC running SipX and the clock of
> the Cisco phone, the Cisco phone is regularly late. Not by much, the
> maximum time it spent unsubscribed was less than 1 minute. It still
> happens, however, and when it happens, the endpoint is unregistered and
> cannot receive calls.

This problem has been understood for a very long time, at least since
DHCP was devised.  And RFC 3261 gives explicit instructions that the UA
must re-register before its registration expires:

   10.2.4 Refreshing Bindings

   [...]  The UA then issues a REGISTER request for each
   of its bindings before the expiration interval has elapsed.  [...]

Dale


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