Call Timeouts - Snom 4S NAT Filter Admin Manual

The value directly influences the keep-alive traffic caused by the
NAT Filter.
The Registration Logging Time is the time after which it moves
the backup file to the primary location. See preparing recovery above.

4.4.2 Call Timeouts

Unfortunately, in SIP little attention has been put on the problem
when a user agent just disconnects from the network without further
notification. This situation typically occurs on power failure, system crash
or when the Internet connection becomes unavailable. In these cases the
filter needs to disconnect the call.
Even more unfortunate, there is not a single way that this
problem can be addressed. Therefore, the filter uses several mechanisms
that check if the call is still alive.
The first way to find out if the call is still alive is to send OPTIONS
requests to the user agents that are directly connected to the filter. The
OPTIONS are sent outside of the dialog, because sending them inside
the dialog would cause a sequence numbering problem. If no response is
coming back, that is an indication that the user agent is not connected any
more (the reverse it not necessarily true: some user agents boot up so fast
that options responses might be returned in time). The Refresh Interval
tell the filter after how many seconds it should send; the No Response
Timeout tells the filter how long it should wait for a response.
If there is absolutely no media, this is also a fairly good indication
that the call is over. The setting No Media Timeout defines how many
seconds the filter tolerates calls without media. This setting only applies
of any media has been received at all. That means if you for example start
a instant messaging session without any media, the filter will not remove
this session because of a media timeout.
Another famous case is one way audio. Imagine a user agent
calling a mailbox and then crashing/rebooting. The media server will play
one-way audio possibly for a long time. Because of this scenario, we added
the One-Way Audio Timeout. In contrast to the no media timeout, this
setting only looks at audio media. This timeout is also only started upon
reception of the first media packet. This setting should consider that some
user agents do silence suppression. Please keep in mind that some users
are very quiet and don't say anything for a relatively long time. However,
44 • Confi guration
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