These can be a real hurdle when setting up VoIP, help others by posting your configs, tips and tricks or simply ask others for help if you're stuck.
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By GoofyCyborg
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Firewalls in routers (if you are using a physical telephone or adapter) and in your PC (if you are using a softphone) can cause problems for VoIP because it's their job to prevent un-asked for external data entering your network - they do their best to stop it.

Many modern routers are becoming clever at detecting the sort of traffic VoIP sends and allows it in but some others don't.

Some have a process running called SIP ALG which is supposed to help your router handle VoIP traffic but generally it just gets into a tangle with it. If it's switched on in your router, please turn it off.

If you're still having problems, most VoIP service providers have a service called 'NAT Proxy' which sorts out problems of one way calls.

If you experience one way audio or you are able to make outbound calls but not receive inbound, just enter your VoIP providers NAT proxy address as your Outbound Proxy. It will look something like this:

Adding the NAT Proxy in a telephone or adapter
To do this you will need to enter the IP address of your phone into the web browser of a PC that your telephone shares a network with and find the Outbound Proxy field. If you don't know how to do this please consult the manual for your telephone or adapter, otherwise ask us and we will try to help.

Adding the NAT Proxy in the X-Lite Softphone
To do this in X-Lite softphone press F8 when the phone is open and you will see the menu. Add the NAT address of your VoIP service provider into the outbound proxy field shown there.

Note: Please try your phone without the outbound proxy first; most equipment will not need it and adding it unnecessarily may cause problems. If you have the proxy added and experience problems please remove it & often it does the opposite of what you would expect!
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By kaiuk
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Just to reiterate one of the points above. Some firewalls (especially enterprise ones) have ports pre-configured with a name and port number associated with it. SIP ALG is one of the options but this should not be used. The firewall will apparently open it when in use and then close the ports when not in use in order to improve security.

However, VoIP providers will tell you not to use it and instead just to permanently open the ports otherwise calls may be cut off and other problems may occur.
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By froggy666
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Hi, I have a quick question about firewalls in that I have a weird connection and was looking for help.

See my problems is that I need to use a university's internet called Janet due to the fact I live in halls of residence. I'm part of quite a serious 'dota' team that is one of the best in the UK at the moment and are looking to move away from using PC communication to purely VoIP so there is nothing interfering with the connection and ping in the slightest way. (It's overkill but I got outvoted).

The weird bit is Janet likes to block ports and webpages. To the point Steam has a data transfer cap. Sites that are age gated are banned and blocked. It even blocks quite a bit of pop up ads (which is good as it means I can go without adblock and help youtubers). So does anybody know if this will haven an effect on me or is the best way to just but a set and try and set it up?
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By WelshPaul
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If the ISP block the default ports used for VoIP then yes it will have an impact on you! However...

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