Using VOIP to Connect Older Phones and Phone Systems to One Another

Image of Candlestick Phone with Asterisk Logo on its Dial

Background
In the fall of 2004, an email conversation began on the Telephone Collectors International mailing list. Several folks who had restored older PBXes and CO switching systems had begun to wonder, now that Voice Over IP was beginning to be viable, if there was a way to connect their switches together via the internet.

Someone mentioned the Asterisk VoIP PBX , and, with a little experimentation, the project took off, with several of the switchers creating Asterisk switches as tandems to their switches. A central switching scheme was established, office codes were assigned, and an automated method of looking up call routing was put in place. The Collectors' Net , or CNET , was born.

Since then, we've built a private network that includes more than just electromechanical switches connected to Asterisk PBXes. So far, we have older PBXes and CO switches, key systems of various sorts, and individual telephones.

These are connected not only by Asterisk VoIP PBXes, but also by other VoIP PBXes, Analog Terminal Adapters, VoIP telephones, and soft phones. There has also been some successful experimentation involving embedding Asterisk, pre-configured, into a standard residential firewall/DSL Modem.

We have our own mailing list , where we can cuss and discuss challenges and solutions, as well as pretty much anything telephony or VOIP related. The discussions so far have produced a wealth of information, available in the mailing list archives .

How It Works

There various ways of connecting to the CNET . Here are some:

Except for the soft phone, all connection types require a piece of hardware at your location. Here are two different call flow sequences, based on the most common types of connection methods: Asterisk PBXes and Analog Terminal Adapters (aka ATAs).

Typical Call Flow for the "Asterisk Tandem" means of connection to the CNET

A simple graphical representation of this call flow is available by clicking here.

Typical Call Flow for the "Analog Telephone Adapter" means of connection to the CNET

A simple graphical representation of this call flow is available by clicking here.

Which Connection Method Should You Use?

Let's Compare

Using a PC to create a tandem of your own:
Pretty much any old PC will do, as long as it is modern enough to support the FXS/FXO card(s) that you choose. Also, any Zapata -compliant PC telephony FXO and FXS cards will work -- one of each. These cards are available, brand new, from Digium , the folks who wrote the Asterisk program. Used Digium cards and brand new Zapata-compliant clones are available on eBay, in case you're the type who doesn't feel the need for tech support from the hardware manufacturer. From the software and operating system perspective, it's all free. Linux and Asterisk are the two necessary elements here. A detailed tutorial will get a generic VoIP switch up and running for you, and the sample configurations on our site will give you a template to use to configure your switch to join the Collectors' Net.
 
Using an Analog Terminal Adapter to home back to the ckts.info tandem, or someone else's PC:
This method invovles the use of a combination FXO/FXS device, also known as an Analog Terminal Adapter or ATA, such as the Sipura 3000 . Once your ATA is configured, your legacy switch will make outgoing calls through the FXS portion of the device, and receives calls on the FXO portion. The FXO/FXS device is programmed to connect through a host tandem (Asterisk PBX) at ckts.info or another switcher's site.

Putting Your System Together

Here we get into the nuts and bolts of getting your legacy PBX (or CO Switch) onto the CNET network. You've probably decided by now which connection method will work best for you. Now is when you make your choice.
 

Getting an Office Code

Okay, so you've got your ATA or Asterisk box mostly configured, and now you need to be reachable on the CNET . Here, then, is the dialing scheme:

UK switchers should refer to the UK Policy White Paper.

In the North American CNET scheme, the country code is the digit '1,' the next three digits are the office code, and the last four digits are the 'line' digits. This gives North American switchers a "1+7-digits" dialing pattern. (We don't use area codes, yet). The line digits are switchable at the collector's site; e.g., extensions, milliwatt, silent term, time-of-day, redirects to cell phones, etc.

Similar structures exist in other countries as well, with the first few digits comprising the 'city code' and 'exchange code", and the trailing digits switched in the individual PBX, CO switch, or key system.
 

These are the steps you need to be assigned an Office Code:

  1. Check for availability, and stake your claim. at the Collectors' Net WIKI.
  2. Register yourself with the group. This is how we tie it all together. The username you choose will link your office code to your directory entries to your switch to yourself. It's the glue behind the rest of it. (Just so you know, we do NOT share any of your contact information with anyone else, even other telecom-related sites.)
  3. Register and Activate your Office Code in our ENUM (DNS) registry. It's a manual process, though. Once you register, it will take an actual human to put it into the system.

Testing Your Installation

At this point, you've assembled your Asterisk box and programmed it, or you've obtained an ATA and programmed it. Now, it's time to test it. Here's how to test your connectivity on the net.

Troubleshooting

Let's face it, there are probably going to be a few glitches that you'll need to work out in order to get your system to 100%. And, if you're like me, you'll always be fiddling with things, and then needing to fix the damage that you did.

Help is available, from a variety of sources. The best kind? other collectors. We're all doing the same thing as you are, and most of us have "been there, done that." This help can be had by joining our mailing list. Once subscribed, you can ask the other members for the answers to your questions. Of course, many answers are already availabe, by searching the mailing list archives .

We are also in the process of trying to put together an FAQ based on questions posed to the mailing list, and will announce it both here and on the list when it's ready.

For those Asterisk and VoIP questions, a good place to search is the VoIP-Info.ORG website.

Additional Resources / External Links

These are a few of the outside sources we have found helpful. If you stumble across another one that is not listed here, please email us with that information, and we'll add it to this list.

      Helpful Links

Asterisk.ORG .   - -   The Asterisk website. Includes hardware compatibility list as well as downloads of Asterisk
Digium.COM .   - -   The folks who wrote Asterisk. They gave Asterisk away in hopes that you would buy their FXS, FXO, and T1 PC plug-in cards.
Guide To Asterisk   - -   An excellent step-by-step tutorial on getting Asterisk up and running. Add the CNET configs, and you're off and running.
Max's Hacks   - -   Max's hardware schematics and Asterisk (zaptel) hacks to make it all work.
VoIP-Info.ORG   - -   A TIKI on VoIP in General, but with emphasis on Asterisk
Zapata Telephony   - -   The authors of the "Zapata" voice-to-PC drivers, used in Asterisk.


 

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CNET is a project of participating members of TCI , ATCA, the UK's Telecom Heritage Group, and interested others.

Voice Over IP Tandem for Analog Switches