Issues such as one way audio, lack of incoming calls, registration issues and etc. can be due to SIP ALG

To disable SIP ALG telnet into the router and enter the following command.

1. > sys sip_alg 0 — Disables sip alg

2. > sys commit — Apply changes

3. > sys reboot — Reboot router

Once router is back online, reboot the ip phone or press re-register.

To re-enable SIP ALG run the following command:

sys sip_alg 1 — enables sip alg

 

Update: SIP ALG is now disabled by default and can be enabled/disabled using the GUI interface under NAT >> ALG