On Thu, 2008-11-20 at 09:40 +0000, Gabor Paller wrote:
> Hi,
> 
> It took some time but I went after the re-registration issues.
> The NCH Express Talk softphone, Basic Free Version, V3.08 does the wrong
> thing. It requests 1 hour subscription expiration period and ignores the
> expiration period returned by SipX. Therefore its subscription will
> expire and it will not be accessible until its hourly re-registration.
> It's a pity because we had the best experiences with this softphone.
> 
> 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.
> 
> Would it be possible for SipX to "lie" in its subscription expiration
> time, e.g. report back X seconds to the endpoint and set its internal
> timeout to X+D seconds? Minor clock differences between the device and
> the endpoint could be then overcome.

It's software... anything is possible.

Even if we were to provide for some skew, I wouldn't call a minute a
"minor" difference, and wouldn't want to make the skew nearly that big -
a few seconds at most.  We have seen other phones that try to refresh
"exactly" on the expiration... not very clever, IMHO.


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