SIP (Session Initiation Protocol) ALG (Application Layer Gateway) is a feature in many routers/hubs which inspects any VoIP traffic to prevent problems caused by firewalls and if necessary, modifies the VoIP packets. Routers and some broadband hubs will often have SIP ALG enabled as a default setting.
If SIP ALG is enabled, it can affect your BT Cloud Voice SIP trunks:
- It can interfere with the SIP signalling on incoming and outgoing calls.
- Registering to the BT Cloud Voice SIP platform.
- One way audio transmission.
The feature SIP ALG can also be known as SIP Aware or SIP Transformations. This feature must be disabled when using BT Cloud Voice SIP Trunks.