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The following example shows SIP signaling and audio sessions between SIP clients A and B
and the SIP server (1).
Figure 235 SIP ALG Example
29.5.3 SIP Signaling Session Timeout
Most SIP clients have an "expire" mechanism indicating the lifetime of signaling sessions.
The SIP user agent sends registration packets to the SIP server periodically and keeps the
session alive in the ZyWALL.
If the SIP client does not have this mechanism and makes no calls during the ZyWALL SIP
timeout default (60 minutes), the ZyWALL SIP ALG drops any incoming calls after the
timeout period.
29.5.4 SIP Audio Session Timeout
If no voice packets go through the SIP ALG before the timeout period (default 5 minutes)
expires, the SIP ALG does not drop the call but blocks all voice traffic and deletes the audio
session. You cannot hear anything and you will need to make a new call to continue your
conversation.
29.6 ALG Screen
Click ADVANCED, ALG to open the ALG screen. Use the ALG screen to turn individual
ALGs off or on and set the SIP timeout.
Note: If the ZyWALL provides an ALG for a service, you must enable the ALG in order
to perform bandwidth management on that service's traffic.
Chapter 29 ALG Screen
Signaling session
over UDP port 5060
Audio session using RTP
ZyWALL 5/35/70 Series User's Guide
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