Information to help your business benefit from telecommunications

Taking a SIP

two cans connected by an ethernet cable

How often do you ever stop to think about those mechanical or electrical things we take completely for granted? A car engine, for instance, with pistons travelling up and down those cylinders thousands of times a minute with only the thinnest layer of oil between performance and disaster…or, as we’re about to explain, making a ‘phone call via the internet, something so simple it hardly bears thinking about. Until there’s a problem, which, as it happens, can be quite common.

The initiation of every internet call (or VoIP, Voice over Internet Protocol to give it its proper name) involves a series of behind the scenes steps. Collectively these steps are known as SIP, or Session Initiation Protocol. Think of them like this,

  1. Hi, I’m X’s phone and I want to talk to you.
  2. Hi X, I acknowledge that you want to talk to me.
  3. I’ll just prep up this end so I can receive your call.
  4. Thanks, this is to confirm that X’s phone really does want to talk to you.
  5. Formalities completed. Call placed.

So you can see that there’s a potential for things to go wrong…but there’s more.

To help with this process, all routers have a feature know as SIP ALG (Session Initiation Protocol – Application Layer Gateway). This is something clever that changes private IP addresses and ports into public IP addresses and ports…and, working together, they act as to prevent any firewall related issues that could crop up as a result of your internet router playing tricks. Theoretically having SIP-ALG ensures call quality.


BUT! In most cases having SIP ALG is similar to having too many cooks, because what happens is that there’s more chance of poor call quality or calls not connecting and general scrambling (packet loss) when ALG is engaged, and so most VoIP providers suggest you turn SIP ALG off on your router.

How do you know if you’re affected?

  • If you fail to get through to the person you’re calling
  • If you can hear them, but they can’t hear you
  • If you get an echo, or the line is fuzzy
  • If you get cut-off during a call

What to do?

It will depend on your router, but most allow you to disable the SIP ALG feature. Start by calling the company that supplied your router. If they can’t help, try searching the internet for your router manufacturer’s name and model, i.e. “Disable SIP-ALG on Netgear R6850”.

If you still have problems, you may need a better internet connection or a router that’s more suitable for VoIP use. Give us a ring on 033 33 58 33 33 and we will try and help.

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