ZyXEL Routers

If you are using a Zyxel router and experiencing dropped calls, we recommend disabling the SIP ALG feature of the router. Models which may follow these instructions include the P-660HW, the P-729H, and the PK5001Z. Not every firmware is the same and some variation in these instructions may occur.

Using the Web Interface

Navigate to the NAT tab and uncheck the box for SIP ALG.

Using Telnet

  1. Telnet into the route
  2. Select menu items 24 then 8
  3. To display current SIP ALG status run the following command:
    • ip nat service sip active.
  4. To turn off sip alg:
    • ip nat service sip active 0

ZyWALL USG 50/80/100

  1. Select Gears Icon
  2. Click on ALG
  3. Uncheck the boxes for Enable SIP ALG and Enable SIP Transformations to disable these options


  1. Click on Advanced
  2. Click on ALG
  3. Uncheck Enable SIP ALG to disable SIP ALG