Static IP address

[Adam Funk]

I figured other people would come up with a lot more uses for it.

[John Walliker]

Well, there are plenty, but most are fundamentally what has already been mentioned. If you want some kind of incoming connection then a static IP address is highly desirable. This could be a server on your premises or a VoIP phone which needs to be able to receive incoming audio connections. The issue with VoIP phones is that signalling and voice are usually separated, with the SIP protocol handling the signalling and the RTP protocol handling the audio. The SIP protocol is used to register with a VoIP server and uses one port in the phone. When a call comes in it is necessary to send audio to a different target port in the phone for the RTP which carries the audio. If there is network address translation (NAT) the router may not know what to do with that incoming audio stream. However, the phone will generally send the router hints to help it. If there is CG-NAT there are two or more NAT-ing routers in series and the phone can only talk directly to the nearest one, making things very difficult. As ever, there are workarounds. A common one is for the phone to create a VPN tunnel to an end-point at the VoIP server. Phones vary in their capabilities. VoIP providers vary in what methods they support. Its a horrible mess with many workarounds and bodges which usually work most of the time. In contrast, a static IP address for the phone with appropriate firewall rules in the router "just works" every time. If you have other remote sites that you need to access securely then having firewalls at those sites which know about your static address is a good approach. Running your own VPN between sites requires at least one end to have a static IP address unless you involve other services in the process. I could go on... John

[The Natural Philosopher]

VOIP phones do not need static IP.

They can register with a STUN server

[John Walliker]

Yes, they can, but that isn't always enough. The kind of NATing and router behaviour do affect the reliability of incoming audio in particular. There are lots of nasty bodges that usually work. All I am saying is that with a static IP address and sensible firewall settings everything works very reliably. Sadly, this isn't always possible. I look after a lot of VoIP phones scattered around the world, many behind NAT and CG-NAT and I have come across most of the problems going at various times and have plenty of nasty workarounds in place for some of them.

John

[The Natural Philosopher]

I have been using NATed VOIP for years with sipgate, It works flawlessly

[John Walliker]

I don't for a moment doubt it. However, that doesn't mean that all VoIP phones using a variety of VoIP providers and different internet service providers and different routers will work flawlessly over NAT and especially CG-NAT. The reality is that they often don't - unless special measures like VPN tunnels for example are used.

John

[John Rumm]

And from that one example you extrapolate to all there other systems out there?