SIP Devices & Your Network - Disabling SIP-ALG

SIP-ALG is not recommended for use with CircleLoop.

What is SIP-ALG?


SIP-ALG is a feature of many popular routers, that allows the router to inspect and rewrite the SIP messages sent to and from SIP desk phones. It is designed to help desk phones communicate outside of the local network, but in practice can actually cause more problems than it solves. To use a SIP desk phone with CircleLoop, SIP-ALG must be disabled.
Most routers that support SIP-ALG will have it enabled by default.

How does SIP-ALG affect CircleLoop calls?


  • Call Receiving, Dropped Calls, and Failed Call Transfers​

Calls may not come through, or be dropped when answered. You won’t be able to transfer calls, put calls on or off hold, or park calls.

  • Non-Functioning Call Groups

Certain devices fail to register on to the CircleLoop platform or are incapable of receiving data. Phones in call groups won’t ring as required.

  • Direct-to-Voicemail

Inbound calls may be directed straight to voicemail or receive and error message and the call cut off.

If you're experiencing any of the above issues, we recommend checking whether your router supports SIP-ALG, and if so, confirm that the feature is disabled.

    How to disable SIP-ALG?


    To find out exactly how to disable SIP-ALG on your router, you will need to refer to the router manufacturer's documentation, however, most routers have this option available under the "Advanced", "Network" or "NAT" Settings. The option is generally presented as a checkbox that can be toggled on or off.