Direct ATA to ATA Calling With The PAP2T-NA

As mentioned in my previous post, I have not abandoned plain old telephone service. It is very well engineered and integrates well with 911 service. There are, however, advantages to the flexibility of adding voip to your choices. My preferred home phone solution is to have two phones. One connected to the phone company and one (the long distance phone) connected to a flexible voip service like Voip.ms. My preferred ATA is the Cisco PAP2T-NA. I have family in other parts of the country. We tend to call them frequently so it is cost effective for all of us to adopt the dual phone strategy. Either ATA can be configured to dial a “hotline number” direct to the other ATA over the Internet before using the voip service in the dial plan. To make direct ATA to ATA calls work over the Internet you need to do the following:

  1. Setup and use a service like DynDNS.com to get a free domain name for your dynamic ip address.
  2. Configure the ATA to make and answer direct (unregistered) calls.
  3. Forward UDP ports on your router to the ATA.
  4. Configure the dial plan on the ATA be able to call the other ATA(‘s).

Most home internet service providers dynamically assign ip addresses so you need to get a domain name that doesn’t change. A service like DynDNS.com offers free domain names for situations like this. If your IP address is static then you do not need this and can just use that in the ATA’s dial plan.

You need to log into your PAP2T-NA as admin and go to line 1 and/or line 2 and change in the “Proxy and Registration” section the “Make Call Without Reg:” and “Ans Call Without Reg:” options to “yes” and save your changes at the bottom of the configuration screen by clicking on “Save Settings”.

The next thing you need to do is forward the necessary ports for an SIP call to work. I found the PAP2T-NA needed UDP 5060-5061, UDP 5004 and UDP 16384-16482 (since this was the way rtp was setup on my ATA in the SIP settings). Keep in mind that if you are unsure about the risks of forwarding ports on your router you probably should not do this. You have been warned.

The next step is to change the dial plan for Line 1 and/or Line 2. It would be a good idea to it write down or copy and paste & save it before making any changes. Here is an example of what mine would be like:

(<123:5194321111@domain.dyndns-remote.com>S0|*xx|[3469]11|0|00|[2-9]xxxxxx|1xxx[2-9]xxxxxxS0|xxxxxxxxxxxx.)

When I dial 123 (my hotline number) the first rule in the dial plan is matched so it sends the call to 5194321111@domain.dyndns-remote.com. 5194321111(not the real number) is the “User ID:” on the other ATA. In this case it happens to be the DID number of the voip service on the other ATA. For Voip.ms it would be the account number. domain.dyndns-remote.com is the newly assigned dyndns.com domain name.

For this to work the “Enable IP Dialing:” option must also be “yes”. Remember to save your changes at the bottom of the configuration screen by clicking on “Save Settings”. Any other number will be processed by the other rules in the dialing plan and be sent out to the regular registered voip service. The next example demonstrates a dial plan rule for a second ATA:

(<123:5194321111@domain.dyndns-remote.com>S0|124:123456_7@domain2.dyndns-remote.com>S0|*xx|[3469]11|0|00|[2-9]xxxxxx|1xxx[2-9]xxxxxxS0|xxxxxxxxxxxx.)

Hotline number 124 will match the second rule and send the call to 123456_7@domain2.dyndns-remote.com.

So there you have direct ATA to ATA calling. Setting it up is the hard part once that has been completed the person just has to pick up the phone at the other end when it rings.

Cicso ATA Administration Guide (pdf)
Linksys Dial Plan Tips and Tricks by Mango
Configure your Linksys VoIP ATA the right way! by Mango

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2 thoughts on “Direct ATA to ATA Calling With The PAP2T-NA”

  1. Hi I read your very detailed and interesting post but I have few questions.
    1) I already have a static ip so do I still need to do the dysdns setup?
    2) Does this method bypass the voip service? ie. if the voip service is down (internet is up), can I still make a call?

    Thanks

  2. Dyndns is not required if you have static ip. In the dial pattern you would use that static ip instead of the domain name from dyndns.

    Yes, this is a way to avoid a voip service by calling another ata direct. The negative aspects are that you need to open so many ports through your router and it is somewhat difficult to setup.

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