VOIP with Telstra Thompson Modem

Recently we cut over a over a customer from their existing VSP to Ipera due to a range of issues. While most phones where at their central office their accountant had a Snom phone in their Brisbane office and it wasn’t registering.

It was reporting network failure and all the logs showed it trying to register however receiving no response. Ipera could see no data coming from the the IP. After shipping a new preconfigured and having the same issue we had to do some more digging.

It turned out that by default Telstras Thompson ADSL Modem/Router has SIP ALG enabled and this was causing issues. There is no way to disable it in the web interface so you need to log in through telnet to do it. These are the steps to disable it:

  1. Telnet into the router, the default username is administrator and the password is blank
    C:\Users\User>telnet 10.0.0.138
    
  2. At the prompt disable SIP ALG buy entering the command
    connection unbind application=SIP port=5060
    
  3. Now save the configuration by entering the command
    saveall
    
  4. You can then exit by entering the command
    exit
    

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