Introduction

If you use VoIP for business or personal calls, you might have heard about SIP ALG. It is a feature in many routers that is supposed to “help” with internet phone calls. The problem is that in most cases, it does the opposite, causing dropped calls, poor quality, or connection errors. That is why understanding SIP ALG is important for anyone who wants stable online communication.

Definition

SIP ALG, short for Session Initiation Protocol Application Layer Gateway, is a setting in many routers and firewalls. It works by scanning and rewriting SIP packets, which carry information about your VoIP calls. The intention is good — to solve issues with NAT and private IP addresses — but the execution often causes problems.

How It Works in Practice

Routers with SIP ALG enabled automatically interfere with your VoIP traffic. For example, if you are running a virtual PBX or using SIP trunks, SIP ALG may try to “fix” your call data but ends up breaking it instead. Typical problems include calls not connecting, one-way audio, or sudden disconnections.

Imagine running a small support team that relies on VoIP numbers. Customers call in, but some of them cannot hear your agents or the line drops mid-conversation. In many cases, SIP ALG is the hidden cause. Disabling it often brings instant improvement in call stability and sound quality.

Business Relevance

For companies, reliable communication is everything. Whether it’s a call center, a startup serving clients abroad, or a freelancer working with international partners, VoIP is a lifeline. SIP ALG can silently disrupt that lifeline. That is why many providers, including Freezvon, recommend checking your router settings during VoIP setup. With SIP ALG disabled, your virtual numbers, SIP trunks, and hosted PBX will run without unnecessary interruptions.

FAQ

What is SIP ALG?

SIP ALG is a router feature that changes VoIP traffic in an attempt to help with network translation. Instead of helping, it usually breaks calls.

Should I disable SIP ALG?

Yes, in most situations. Turning it off prevents common call problems such as failed connections or one-way audio.

How to disable SIP ALG?

It depends on your router. Usually, you can find it in the firewall or advanced settings. On some models it is hidden, and you may need to check the manual or contact your ISP.

Does every router use SIP ALG?

Not all, but many popular routers come with SIP ALG enabled by default. If you experience VoIP issues, this should be one of the first settings to check.

In Simple Terms

SIP ALG is a router feature meant to improve VoIP, but in reality it often makes things worse. For smooth business calls and reliable virtual numbers, it is usually best to turn it off.