Hi, I'm Magic, and thanks for asking your question on JustAnswer. I will be glad to help you.

what you will need to do is login to the Interface of your Linksys SPA2102 and setup the IP of of the router interface

The "Outside" interface will be setup on the Linksys in the setup screen.

It will be on the Wan Setup page that will face the "outside" interface of the Cudatel PBX.

well, actually....taking a second look at the way this Linksys works and its interfaces, I don't see where it's possible to do the setup you are requiring, unless you are using an Ethernet cable between the Cudatel PBX and your Linksys SPA2102.

You will need to configure a static IP address on your Linksys SPA2102 and make sure to connect it to the Cudatel PBX using the blue Ethernet port (Internet port) and NOT the yellow one. Make sure you are using the correct settings for IP address, subnet mask, gateway and (optional) DNS servers.

The static IP address will be setup on Router > Wan Setup.

Next, go into the Voice menu.

then click Advanced.

Click SIP, and set the RTP port range to 16384 - 32768.

Click “Line 1” to configure the FXS port or “PSTN Line” to configure the FXO port. The FXS port is
labeled “Phone” on the ATAand is marked with a light green border. (A telephone or a fax
machine plugs into the “Phone” port.) The FXO port is labeled “Line” and is marked with a dark
green border. (A telephone line from the phone company usually plugs into the “Line” port.)
Scroll down to “Proxy and Registration”
Set Proxy to x.x.x.x:5065 (Same as the value in “Domain” in phone
Set Outbound Proxy to x.x.x.x:5065 (where x.x.x.x = CudaTel IP address)
Scroll down to “Subscriber Information”
Set Display Name as desired (Can be user’s name or extension or anything else)
Set User ID to the extension number of the generic SIP device
Set Password XX the password XXXXX of the generic SIP device
Set Auth ID to the Auth. Username value of the generic SIP device
Set Use Auth ID to yes

scroll to the bottom of the page and click "Submit all Changes" and wait for the Linksys SPA2102 to boot.

Make sure that when you are configuring your Linksys SPA2102 that you use the LAN (yellow) Ethernet port and not the blue (Internet) port.

This information is being pulled from here:

http://www.cudatel.com/docs/CudaTel-TB-Linksys-PAP2T.pdf

Let me know if you have any difficulties and we'll troubleshoot the issue where you are getting hung up at.

Great!! Sorry if I had missed a step there. I was trying to respond as quickly as possible.

Let me know if I can be of any further assistance in the future.

Please remember to rate my service if you were satisfied.

I just wanted to follow up and see how everything is going. Is everything working properly?