Disable SIP ALG on (most) ASUS routers

Login to your router
  1. Open your browser such as Firefox, Chrome etc, and enter the address (this is the default IP address)
  2. When requested enter the username and password details.
    default username: admin
    default password: admin
    (Once logged in for the first time you may be prompted to change your password)
  3. Under the Advanced Settings side menu click on WAN
  4. Click on NAT Passthrough tab on the top sub menu
  5. Set SIP Passthrough to Disable
  6. Click Apply