Thursday, April 16, 2009

Cap'n Crunch, In-band Management and the CSR

Jason Lackey

In the good old days before computer hacking, malware, botnets and distributed denial of service attacks, there were things like ham radio and phone phreaking. One of the things that make phone phreaking, or hacking the phone system, possible was the use of in-band signalling. This is where signals in the phone call itself were used to control the switching equipment. This is in contrast to out of band signalling, a more secure approach where data and control are on different channels.

You may have seen 2600: The Hacker Quarterly at the news stand. If you are old enough, you may be tempted to believe that name has roots in the game console world with the Atari 2600, which for many was their first game machine after Pong. As it turns out, 2600 comes from 2600 hz, the frequency of certain switching commands used by old AT&T (and other) switching systems to release trunk lines. Interestingly, John Draper, a legendary hacking figure, somehow figured out that the plastic whistle that was packaged in some boxes of Cap'n Crunch breakfast cereal could be readily modified to produce a 2600 hz tone which could then be used to do interesting and illegal things to the phone system.

What does this have to do with mobile phone CSRs? Well, interestingly I was on the phone with TMobile support, who really are a delightful bunch, somehow managing to be cheeful, friendly and helpful in the face of dealing with the general public. Anyway, during the call I was surprised when I was temporarily cut off. The CSR came back on the line and was all over herself apologizing when she explained that there was something about her voice which caused their phone system to do funny things. Evidently the systems they have in place use some kind of in-band control, and just like Cap'n Crunch and his 2600hz whistle, she was causing the phone system to do unexpected things.

Funny how seemingly unrelated things can sometimes end up having connections.


  1. This sounds like a case of talk-off. (see:

    When I worked at Octel in the early nineties, we had to select voice talents to record our voicemail phrases in various languages -- and part of the selection process involved talk-off tests (for obvious reasons!).

    On another historical footnote, one of Octel's voice talents was also the Time Lady, Jane Barbe. (see: Just a random factoid that always delighted me...

    Thanks for the interesting post, Jason.

  2. Hey Susan, thanks for bit on talk-off! My vocab is now +1. Very cool that you had the Time Lady.

    Speaking of voice talent - did you know the voice of the London underground got canned a while back?