SIP ALG Detection Tool

What is SIP ALG and Why Disabling It is Important for VoIP Services

Introduction to SIP ALG

Session Initiation Protocol Application Layer Gateway (SIP ALG) is a feature found on many routers. Its purpose is to help manage the initiation and handling of voice calls made over the internet (VoIP). SIP ALG acts as an intermediary that modifies the SIP packets as they pass through your router, intending to assist with issues related to NAT (Network Address Translation) traversal.

However, in practice, SIP ALG can often cause more problems than it solves. It tends to alter the SIP packets in a way that can disrupt VoIP communications, leading to issues such as dropped calls, one-way audio, or the inability to establish a direct call at all. For this reason, it is generally recommended that SIP ALG be disabled, especially when using professional VoIP services like those provided by Approved Systems.

Why SIP ALG Should Be Disabled for Approved Systems Hosted PBX and VoIP Services

For customers using Approved Systems’ Hosted PBX and VoIP services, it is essential to ensure that SIP ALG is disabled on your router. Disabling SIP ALG allows the VoIP traffic to pass through your network without unnecessary alterations, ensuring the highest quality of service and minimising issues with your phone system.

When SIP ALG is enabled, it can interfere with the proper functioning of your VoIP system by:

Altering SIP headers: This can prevent the VoIP service from correctly identifying and routing calls.
Causing one-way audio: If SIP packets are incorrectly modified, you might experience one-way audio, where one party can hear the other, but not vice versa.
Dropping calls: The interruption and modification of SIP packets can lead to calls being dropped unexpectedly.
Inability to receive direct Extension Calls: Approved Systems cusotmers using Call Queues or Call Centre related processes can lead to having issues receiving direct extension calls.

For these reasons, we strongly advise all customers using Approved Systems Hosted PBX and VoIP services to check if SIP ALG is enabled on their routers and disable it if necessary.

How to Check if SIP ALG is Enabled

To determine whether SIP ALG is enabled on your router, you can use a simple detection tool, such as the SIP ALG Detection Tool provided by dlinders.nl.

Steps to Use the SIP ALG Detection Tool:

Download the Tool: Click here to download the SIP ALG Detection Tool.
Run the Tool: Once downloaded, run the tool on your computer. It will attempt to make a SIP request and analyze the results.
Interpret the Results: The tool will display whether SIP ALG is detected as enabled or disabled. If it is enabled, you will need to disable it to ensure optimal VoIP performance.

Disabling SIP ALG on Common Routers

While the process of disabling SIP ALG can vary depending on your router’s make and model, here are general steps that apply to many routers: