SIP ALG (Application Layer Gateway) is a feature which is enabled by default in most TP-LINK routers and 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, SIP ALG must be disabled on your TP-LINK router.
This guide explains how to disable SIP ALG on the following models:
Step-by-Step Guide
Further Reading
Further information can be found at TP-Link TD-W8968 User Guide.
