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SIP ALG Settings

Last Updated: May 29, 2014 04:10PM PDT
Many routers, that are either provided by your Internet Service Provider or that you can buy at the store, come with what is called SIP ALG, or a SIP Application Layer Gateway. This article will discuss what SIP ALG settings are and what effect they can have on your VoIP service.
What does SIP ALG do?

In the simplest terms, SIP ALG is like an all-access keycard for Voice over IP information to get through the outer security of your router and to the correct Private, or internal, IP address that belongs to the VoIP Adapter, softphone, or other device you are using to make and receive calls. SIP ALG resolves any "NAT related issues" or the translation process from the large network of the world wide web to the one in your home. 

What kind of issues can SIP ALG cause?

While the above sounds like a good thing to have on your router, and it was original implemented with good intentions, often it is not configured correctly and is not a "one ALG fits all" solution. This means that SIP ALG usually causes more trouble that it solves. 

If SIP ALG is not configured correctly it can make the information sent by your device unreadable to our server, or the other way around.

This can cause issues such as
  • One Way Audio - When you call someone and you can hear them, but they can not hear you.
  • Incoming Call Failure - Incoming calls do not ring and seem not to reach your device at all.
  • Call Dropping - if the call suddenly drops after any length of time without being terminated by either members of the call.

How do I disable SIP ALG settings on my router?

All routers, whether they are set up at your home by your Internet Service Provider or one that you bought from an electronics store, are different. Each brand of router that have SIP ALG settings enabled usually have a different way to configure or disable them. 

If your Internet Service Provider installed your router, the easiest and best first step would be to contact their Internet technical support staff and see if they can either disable the SIP ALG settings for you or walk you through how to change them yourself.

If you bought your router yourself, you can check the user manual that came with it to see how to disable the SIP ALG settings. Your router's manufacturer also might have a website that has either a knowledge base for your router or online manual. If not, simply search the web, I guarantee the information on how to disable those settings are out there if your router does have SIP ALG.

Does my router have SIP ALG?

Below is a non-exhaustive list of routers that are known to have SIP ALG settings, enabled by default, that cause issues with VoIP service if not disabled. Your router type may not be on this list but it may still have SIP ALG. Check to make sure with the manual or manufacturer.

  • D-Link - DIR-655 models
  • Motorola - SBG6580 models ** SIP ALG cannot be disabled on this router, users must disable NAT and put the router in bridge mode.
  • SpeedTouch - ST530 v6 models
  • Zyxel - 660 series models
  • Netgear - WRG614v9 Wireless-G Router, DGN2000 Wireless-N ADSL2+ Modem Router
  • SMC - ToDo routers
  • Linksys - WRV200, WRT610N
  • Peplink Multi-WAN routers
  • Fortinet
  • Cicso - 800 series
  • Juniper / Netscreen - SSG series
I have disabled SIP ALG on my router and am still having problems!

If you have disabled SIP ALG and are still experiencing trouble such as Call Dropping, One Way Audio, and Incoming Calls not working while you are able to make calls out then it is likely a different issue with the router's firewall. Please make sure that UDP ports 8891 and 5060 are unblocked or forwarded to your adapter in your router or try placing your VoIP adapter in the router's DMZ or assign it a public IP address so that it is not behind a firewall.

If you have any other questions about SIP ALG settings and their affect on VoIP Internet Telephony please contact us as we would be happy to assist you!

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