Zeroscan

What is Zeroscan?

Zeroscan is a wardialer. It was first developed in 1993 on an Apple //e with an AppleCat ][ modem. Recent improvements in modem technology have made it possible to bring the primary feature of Zeroscan-- logging interesting data, be it a modem or a telephone anomaly-- to the modern modem world.

Most wardialers operate on a single premise: finding carriers. Some can also find tones, and most can locate busy numbers. This is because the modems themselves have the ability to detect busy, tone, and carriers. Furthermore, most modems can't expect carriers *and* tones; meaning the wardialer must make two sweeps of an exchange -- one to log carriers, another to log tones. With the exception of carrier detection, these modems use cadence to detect call progress tones. Cadence is simply measuring the presence of audio vs. the presence of silence. IE; to detect a busy signal with cadence, the device would simply look for .5 seconds of noise followed by .5 seconds of silence repeated x times (increment x to improve accuracy.)

While cadence is good for detecting static call progress tones, it's awful at detecting speech or other interesting tones (DTMF outpulses, clicks, etc.). One of the benefits of using the AppleCat modem was the fact that I had absolute control over what cadence corrosponded to what call progress tone. The AppleCat didn't detect call progress tones internally; rather it handed a cadence bit back up to some more intelligent application. This let me write Zeroscan in such a way that it detected tones, busy signals, rings, reorder, and clicks. I then was able to define anything that fell between a click and a reorder as voice (as voice cadence is extremely sporadic) and refine these values over time. This gave me a definite speed advantage over my friend running Toneloc with a USR Courier HST; the courier had its own idea about what voice and busy signals were, and would often misinterpret (and hence, hang up) short rings or busies, and would many times not "hear" voices that were too soft or otherwise outside the cadence detection range of the modem.

One of the early problems I had when writing Zeroscan for my Apple // is that my AppleCat couldn't detect carrier (!) This almost made me abandon Zeroscan until I realized that I didn't really care about finding carriers as much as I wanted to throw away everything I knew about (ringouts, busies, and people shouting "hello? hello?!") and log everything else. As it turned out, "everything else" was all sorts of interesting things..

Zeroscan has the ability to detect audio based on both cadence and frequency. To detect call progress tones, it isolates individual streams of audio and subjects them to an FFT analysis. The output of the analysis and the cadence results are matched against a set of easily modifyable values for busy, dialtone, ring, and voice. Audio data that does not match these cadence & frequency requirements can be further analyzed for data (carrier) information and/or logged to disk for later playback.

What do I need to run Zeroscan?

Zeroscan is written in perl and C under Linux. It also requires an ADPCM "voice modem" to send & receive arbitrary audio data. I have a PCMCIA Zoom 56k that uses the Rockwell chipset, but other modems should be able to be supported with a few minor AT command changes.

A significant portion of Zeroscan uses "pvfutils", part of the vgetty package by Marc Eberhard <Marc.Eberhard@Uni-Duesseldorf.DE>, in particular, all the audio format conversions and a FFT analysis program.

Progress

• Dial engine complete
• Cadence engine complete
• FFT engine complete

• Tone database
• User interface
• DTMF decoder
• Demodulator