Session Initiation Protocol – Application-Level Gateway, or SIP ALG, is a protocol used in VoIP telephony services. A lot of routers have their own SIP ALG enabled by default that will attempt to re-write SIP packets with their own information. This makes it impossible for the messages to get to their destination. Most routers only affect SIP ALG messages sent on port 5060. For this reason Nextiva signals using port 5062 allowing us to bypass the routers own SIP ALG.
NOTE: Some routers will allow you to disable SIP ALG, but for those that don’t, using port 5062 for registration is a must.
You may be affected by SIP-ALG if you run into these scenarios:
- One-way audio on calls
- No audio
- Phones dropping registration
- Calls going straight to voicemail for no known reason
- Random error messages when your number is called (e.g. “The caller you have dialed is no longer in service”)
Here is our Nextiva SIP-ALG Detector Tool (must be used on a Java-capable device).
If SIP-ALG is detected, many routers allow users to disable it. Otherwise use port 5062 for registration.