Published on internetnews.com

May 4, 2007
Zork Returns! Thanks to Open Source Asterisk PBX
By Sean Michael Kerner

TORONTO -- A voice PBX (define) system is typically thought of as being all work and no play. How much fun can you have with a system that is designed to provide voicemail and call extensions, right?

Turns out that when you open up the code and let developers run wild, strange things can happen.

Such is the case with the open source Asterisk PBX, which has at least a few strange implementations that developers explained in a session at the IT360 conference here. The session was officially called "Exploring Your Phone System," but Asterisk developer Simon Ditner called it "Crazy Things You Can Do With Your Phone System."

The crazy thing Ditner wanted to do was play Zork over the telephone.

Zork is a text-based adventure game that debuted in the late 1970s. It became a popular series in the early 1980s with versions for the IBM PC, Apple II and Commodore 64 systems. Ditner tried to take that game and make it playable over the phone using only your voice.

His effort is called Zoip (a hybrid of Zork VoIP). In order to build his phone-based game system, Ditner started with a stock Asterisk installation and then added a number of items to do speech recognition and text to speech.

In the game, the Zoip system reads out a Zork description using the Festival text-to-speech engine. For instance: "This is a small room with passages to the east & south. Bloodstains & deep scratches mar the walls."

The user would then say either "east" or "south" to move to the next area. In order to do the speech-recognition part, Ditner used the Spinx2 open source speech-recognition technology.

To glue the Asterisk, Festival, Sphinx2 and Zork text all together, Ditner used Perl. He said it only took him 48 hours to get the project done, thanks to the openness of Asterisk and the community that surrounds it.

"Asterisk is three things," Ditner said. "It's an IVR (define), a PBX (define) and a media gateway."

Ditner explained that at first he began his project as an approach to implementing an Asterisk interface. "Gradually it became less about Asterisk and more about my application and the limit of my imagination," Ditner said. "Asterisk can step out of your way and let you do what you want."

The same can't be said of traditional commercial PBXs, such as those from Nortel or Avaya. Ditner said his effort and other such experimental efforts just aren't easily possible by hobbyist developers like himself.

But there is one pesky little limitation of Ditner's Zoip application: copyrights. Though no one has developed Zork in over two decades, the original publisher, Infocom, still holds the copyrights. As such, Zoip is just a hobby project for nonprofit use.

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