Why Many Companies Have Their SIP ALGs Disabled
Before disabling your SIP ALG, ensure you know how it works. SIP ALGs are enabled only by your VoIP provider or router manufacturer. They will tell you how to optimize your VoIP experience. You need bandwidth, latency, and stability to get the most out of VoIP. Enabled SIP ALGs can enhance your call quality and connectivity.
Application Layer Gateway (ALG)
If you’re experiencing problems with the quality of VoIP calls, you may want to disable your Application Layer Gateway (ALG) for SIPS. This is a device that helps VoIP users connect to other devices. However, it isn’t a substitute for your VoIP provider. You should check with them before disabling your ALG.
The ALG works by replacing the SIP header with an IP address. The m= field is used to create pinholes. During outbound communication, the ALG will pass on the SIP client’s response message to the C2.
An ALG is a proxy server, sitting between the client and the real server. It facilitates the exchange without the need to configure the client application. The client connects to the proxy instead of the real server.
Problems with default SIP ALG
SIP ALGs are standard VoIP routers that feature inspecting VoIP traffic as it passes through. Unfortunately, these filters can change VoIP messages on the fly, resulting in problems when using the service. In particular, SIP ALGs can cause issues with VoIP messages, handset registration, audio, and Busy Lamp Field and Message Waiting Indicators. If you’re having trouble with these issues, you should disable SIP ALG on your router to fix them.
There are several ways to test if your SIP ALG is causing problems. The simplest and quickest way is to use a SIP ALG detector, which can be downloaded free from the internet. However, the tool needs to be run from the same network as the VoIP device you’re trying to diagnose. Otherwise, the test results can be inaccurate.
Most common routers come with an inbuilt SIP ALG. Unfortunately, they often have bugs that make SIP registration and call flow impossible. These issues can cause the outbound call status to stay in “Dialing” status.
Switching to TCP for SIP ALGs
TCP for SIP ALGs is incompatible with SIP ALGs. A standard workaround is to use a full Session Border Controller. If your SIP traffic frequently re-transmits, something is amiss.
While SIP ALGs are not fatal in themselves, they can affect the quality of your calls. Depending on the manufacturer, you may have to disable this feature. The process varies from manufacturer to manufacturer, but VoIP-Info has an extensive guide to help you disable SIP ALGs.
Better than switching to TLS-encrypted calls
The TLS standard provides message security by providing both encryption and confidentiality. It is also used for unlocking SIP calling on many mobile networks, including 3G and LTE. However, some areas have restrictive environments and may not allow you to use SIP without encryption. Nevertheless, switching to TLS can make your VoIP calling more secure and available to your customers.
