What is SIP-ALG and when should it be disabled?

Updated by Tech Support

SIP (Session Initiation Protocol) ALG (Application Layer Gateway) is an application within many routers. It inspects any VoIP traffic to prevent problems caused by firewalls and if necessary modifies the VoIP packets. Routers will often have SIP ALG activated by default.

How can it affect SIP calls and registration?

If SIP ALG is activated, it can stop your SIP trunks & Hosted VoIP Extensions from:

  • registering to the platform
  • making and receiving incoming or outgoing call
  • and result in One way audio transmission

SIP ALG must be disabled

If your router and/or firewall are "SIP Aware" / has a SIP ALG enabled, then this functionality must be turned OFF so that the device does not interfere with any signalling.

Teleproject UK Disclaimer

Your Active iPBX SIP & Hosted VoIP Extension services together has been designed to appropriately support a quality voice service alongside the use of data. In order to maintain the quality, it is essential that the internal network components suitably support the service for delivery of your voice calls. If this is not implemented correctly then this may result in a degraded service.

If faults are reported to Teleproject UK which are found to be caused by end user customer equipment for example a home or office router that we do not manage, then we do reserve the right to apply a charge.

The information in this document is provided for general guidance only. It is recommended that your firewall maintainer, switch maintainer or retained IT consultant is consulted on all matters relating to your communications network including, but not limited to Local Area Network and firewall configuration. This is particularly important in connection with any issues which may impact on your network security or local IT policies.

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