Register Timeouts - Snom 4S NAT Filter Admin Manual

4.4.1 Register Timeouts

The Refresh Interval for the UA is the number of seconds
between NAT refreshes from the NAT Filter. The NAT Filter keeps track
of registered user agents and keeps their NAT port binding with packets
alive. Typically, a port timeout is 60 seconds; however because this value
must handle the smallest timeout. Therefore, a value of 15 seconds seems
more appropriate. The filter sends the keep-alive packets regardless of
the transport layer. Although on TCP most implementations keep the
connection alive for a much longer time, some implementations close
their ports after a short timeout. Therefore, also TCP connections must
be refreshed.
You may use two different methods for the refreshing. If you
Use OPTIONS for refresh, the filter sends out OPTIONS SIP requests to
the registered user agents. This method has much more traffic overhead
than other methods. But it is the only one that ensures compatibility
with existing implementations and guarantees that the user agent sends
something back from the inside NAT. This is important in some NAT types
as they do not allow refreshing NAT bindings from the outside. If you turn
the flag off, the filter will send short white space packets to the registered
user agent.
[ 4 S N A T F
S N O M
]
I L T E R
snom technology AG • 43