How does PAP2 work without port forwarding?

Posts: 19 · Posted: Thu Mar 10, 2005 8:42 pm Post subject:

millieaux wrote:

<newbie alert> So what about incoming calls? Are you saying that the PAP2 maintains an 'always on' connection to the Vonage servers so that it can receive a connection when there is an inbound call and the phone should ring?

Your adapter maintains a constant "heartbeat" connection to the call managers at Vonage. The call managers use SIP to broker the connection between your home adapter and a PSTN voice gateway.

SIP messages are transmitted via UDP -- what's unique about that is that UDP maintains no state information. There are no establishment / acknowledgement / finish states like there are on TCP sessions, so when you make your outbound connection most firewalls/routers just watch for activity on those UDP ports. They have no awareness if it is a single conversation taking place on that port pair, or if multiple short conversations are taking place. If nothing happens for 180 seconds or so it will stop forwarding those ports. With your voice adapter, it is talking to the Vonage call manager every few seconds thus keeping that connection open.

When you get an incoming call, the PSTN switch hands the call over via a SS7 connection to a Voip gateway (most likely a Cisco MGX8xxx box). The Voip gateway then signals the call manager that there is an inbound call for your phone number. That is where the real magic happens, and it decides how to handle the call:

If you have call forwarding turned on, it tells the MGX telco gateway to forward the call back out the PSTN to that number.

If your phone adapter isn't on the network (no internet connection / no power), it checks to see if there is a Network Availability number listed. If there is it tells the MGX gateway to forward the call out the PSTN to that number. If not it sends a SIP invite message to the voicemail server out east, which then establishes a connection to the gateway and takes your message.

If your phone adapter is on the network, it receives a SIP invite message from the call manager that triggers it to ring your phone. If you pick up, it makes an outbound connection to the voice gateway that is holding your inbound call and playing ring tones to the caller. If you don't pick up in your configured voicemail wait time, the call manager sends a message to your voice adapter to stop ringing your phone and sends a SIP invite message to the voicemail server at Vonage. The voicemail server will then establish that connection to your waiting call and play your greeting / take a message.

The only case where port forwarding starts to get sticky is Vonage-to-Vonage calls, because it is likely that both parties are behind firewalls / routers that restrict inbound counnections. In this case, one side would need to forward UDP ports 10,000-20,000 to the voice adapter to ensure that this connection could be made.

Posts: 2 · Posted: Fri Mar 11, 2005 12:58 am Post subject: I cheated....

I used TWO routers.... One for my Router pluged into my cable modem FIREWALL OFF DHCP ON. The Vonage adapter pluged into to first router and the second router pluged into the first.... The second router has firewall and dhcp on.

Of course if the damn Vonage adapter would work being pluged directly into the modem I would not need two routers.