ZyXEL Communications ZyXEL ZyWALL 5 - Manual (Page 595)

ZyWALL 5 User’s Guide
594 Appendix H SIP Passthrough
If the primary WAN connection fails, the SIP client needs to re-register with the SIP server
through the secondary WAN port to have the SIP connection go through the secondary WAN
port.
When the ZyWALL uses both of the WAN ports at the same time, you can configure a routing
policy to have the voice traffic from any IP address with UDP port 5060 and the RTP ports go
over a specified WAN port.
Enabling/Disabling the SIP ALG
The ZyWALL SIP ALG is turned off by default to avoid retranslating the IP address of an
existing SIP device that is using STUN. If you want to use a SIP client device (a SIP phone or
IP phone for example) behind the ZyWALL without STUN, use the ip alg enable
ALG_SIP command to activate the SIP ALG.
Signaling Session Timeout
Most SIP clients have an “expire” mechanism indicating the lifetime of signaling sessions.
The SIP UA 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 call during the ZyWALL SIP
timeout default (60 minutes), the ZyWALL SIP ALG drops any incoming calls after the
timeout period. You can use the ip alg siptimeout command to change the timeout
value.
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.