port forwarding

[Bort]

How does the Obi200 work without port forwarding? I understand dialing out because the connection is going out but when receiving a call, I assume the connection is generated from outside, so it is incoming traffic that must be allowed by the firewall.

[drgeoff]

The OBi is in regular communication with the ITSP SIP server, typically on port 5060. That can keep it open for incoming SIP messages. The media ports can be opened as required for a call.

In many cases, there is no need to configure any port forwarding on the router.

[Bort]

So it keeps the connection open forever? Does it use a polling mechanism to listen to incoming calls rather than event driven?

"In many cases" you say? In what cases would you need port forwarding then?

[drgeoff]

Port 5060 (or whichever) is continuously open.  SIP INVITE messages come in on that to initiate incoming calls.

Google Voice uses XMPP rather than SIP so the exact mechanism and port numbers will be different

Port forwarding may sometimes be used in stubborn cases of no incoming audio.  Don't worry about setting up port forwarding unless it proves necessary.

[Mango]

"In many cases" you say? In what cases would you need port forwarding then?

If you have a cheap or otherwise low quality router that doesn't perform well with VoIP, port forwarding may be necessary.

Forwarding the SIP port may solve the problem of your phone failing to ring.

Forwarding the RTP ports may solve the problem of no inbound audio, or slow audio setup.

Forwarding ports will NOT impact poor audio quality.

However, drgeoff is correct.  Port forwarding should be done as a last resort to solve a specific problem - as it is a security risk.