Path: utzoo!attcan!uunet!husc6!mailrus!ames!lll-tis!lll-ncis!lll-lcc!pyramid!csg From: csg@pyramid.pyramid.com (Carl S. Gutekunst) Newsgroups: comp.dcom.modems,pyr.syseng.comm Subject: Re: Break definition (Some Answers from the Standards, LONG) Message-ID: <39163@pyramid.pyramid.com> Date: 12 Sep 88 08:23:54 GMT References: <39157@pyramid.pyramid.com> Followup-To: comp.dcom.modems Organization: Pyramid Technology Corp., Mountain View, CA Lines: 28 Someone's gonna flame me for it elsewise, so I suppose I should mention how a Telebit TrailBlazer works. (I suppose this is preaching to the choir, but if you've carried through this far I might as well finish the job.) The TrailBlazer uses a proprietary modulation scheme called Dynamic Adaptive Multicarrier Quadrature Amplitude Modulation (DAMQAM). Rather than the single high-frequency carrier used by other modulation schemes, the TrailBlazer uses 511 different low-frequency carriers. Each is QAM modulated at a rate of 12 baud (that is, 12 state changes per second); so each carrier has a data rate of 48 bits per second. Each carrier can be slowed down to 8 or 4 baud (32 or 16 bps), or dropped entirely. On real phone lines, quite a few carriers are dropped, and a number are slowed down to 8 baud; so the theoretical speed of 24528 bits per second is reduced to a real maximum of 18031. (Why an odd num- ber? I don't know.) Note that since DAMQAM modulation broadcasts across the entire bandwidth of the telephone line, it is half duplex -- only one end can be transmitting at a time. On top of DAMQAM, Telebit uses a proprietary data packetizing scheme, the Packetized Ensemble Protocol (PEP) that we've all come to know and love. PEP incorporates error correction, and a family of dataflow prediction schemes that make the modem appear to be full-duplex. This latter process is called "Adaptive Duplex," a term to which both Telebit and Racal-Vadic claim trade- marks (the latter for the RV 9600-VP modem). PEP and DAMQAM are trademarks of Telebit Corp, too. MNP is a trademark of Microcom. But you knew that, didn't you?