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 Busy Lamp Field (BLF) and Message Waiting Indicators (MWI).

For our Hosted VoIP service, including out Single User services, SIP ALG must be disabled on your TP-LINK router.

This guide explains how to disable SIP ALG on most TP-LINK routers where specific instructions are not available.

The instructions do differ between different TP-LINK routers. Click here for more specific instructions for your particular TP-LINK router.

1. Press the Windows Start button and in the search box type in cmd and hit Enter
2. Type in
   

   telnet 192.168.1.1

   and hit Enter
   Note Windows Vista/7 may not have Telnet installed by default. Please click on Start → Control Panel → Programs → Programs and Features → Turn Windows Features on or off → Ensure TELNET CLIENT is checked and click OK.

3. When prompted, the default password is admin
   Note that no symbols may appear when typing in the password, but continue anyway.
4. Type in
   

   ip nat service sip sw off

   and hit Enter
   If successful, it should say Nat SIP v2 switch off!

NOTE The settings are temporary and the SIP ALG service will be turned back on if your router reboots for any reason.

We suggest purchasing a router more suitable for business use, such as the Technicolor or DrayTek.

Different TP-LINK routers may have different instructions. Please see list below for instructions for your particular device.

Further information can be found at TP-Link FAQ.