SIP ALG (Application Layer Gateway) is a feature which is enabled by default in most routers and firewall devices, which inspects VoIP traffic as it passes through and modifies the messages on-the-fly.

In few situations this is useful, but in most situations SIP ALG can cause problems using the service. Very often, SIP ALG is poorly implemented causing VoIP messages to be modified in a harmful way or simply corrupts them. In such cases you may experience issues registering your handset, one-way or no audio, unable to receive calls, and issues with BLF and Message Waiting Indicators.

For our Hosted VoIP service, including out Single User services, SIP ALG must be disabled on your router or firewall device.

This article is relevant to any relevant SonicWALL firewall device running SonicOS.

If you are using the SureVoIP Single User or SureVoIP Hosted VoIP service and you use a SonicWALL firewall then you will need to make the adjustments as described in this guide.

Fire up a browser (Firefox, Chrome etc) and access your SonicWALL web interface.

• If using the SureVoIP Hosted service, you may need to disable SIP Transformations on your device.
• To do so, you will need to access the web interface and go to the SIP Settings page and ensure Enable SIP Transformations is NOT enabled.

• The Consistent NAT setting will ensure the same NAT port is used. If this is disabled, you may experience undesired call behaviour.
• Ensure Consistent NAT is Enabled.

• The full SonicOS manual can be found at SonicWALL SonicOS 5.8 Administrator's Guide
• If you are having difficulty, please contact your supplier or seek professional support.