Maxotel

SIP ALG

SIP ALG stands for "Session Initiation Protocol Application Layer Gateway".


What is SIP ALG?

Breaking this down: 

  • SIP is the industry standard protocol for VoIP (the standard used by MaxoTel)
  • ALG is a common feature of routers designed to assist in managing certain types of internet traffic (in this case SIP traffic).

In short, SIP ALG is designed to facilitate the flow of VoIP traffic through your router, but often it creates more problems than it solves.  Most vendors ship their routers with SIP ALG enabled by default.



Why Disable SIP ALG?

By design, SIP ALG places itself in the middle of the communication path between your phones and MaxoTel.  This means that all communications and instructions relating to your VoIP service will be filtered through ALG.

Many different router vendors have their own varied implementations of SIP ALG, each of which has it's on quirks and limitations.  While most won't cause any noticeable problems most of the time, over time they can start to cause problems.


Common problems associated with SIP ALG include:

  • Phones ringing, but no audio when the call is connected (either one-way audio or no audio)
  • Sporadic issues with phones not ringing
  • Random phones losing their connection / not registering to the PBX


MaxoTel's service is designed to operate in such a way that SIP ALG is not required, so in almost all cases it is better to have it off than leave it on.



How to Disable SIP ALG:

The process for disabling SIP ALG varies depending on the router.  Please see the guides below for common routers. 

If your router is not listed, please Contact Us for help.




Other Possible Causes

If disabling SIP ALG doesn't resolve any issues you may be encountering, the next most likely cause may be NAT Issues.