PW>> So HST is very tolerant of noisy lines?
DH>> Yes.  VERY.

PW> What sort of modulation, encoding, etc. does it employ to do that?

Jaw breaking stuff that goes well beyond the descriptive abilities of
language.  It's only easily describable in terms of deltas on rotating
vectors. (Yeah.)

The math is simple.  The circuits aren't.  The test gear DEFINITELY isn't.

If you want a brain strain, try and imagine amplitude modulation applied to
a series of FM carriers.  (None of which actually exist, other than as a
momentary snapshot, or a mathematical abstraction.  What you actually have
is a single voltage value that hops around like a flea on a hot griddle.)

Complicate the dickens out of this by bandpass and notch filtering, so a
small amount of bandwidth is available for a low data rate signal going the
other direction, and you get to HST.

PW>>> of modem users connect with HST?  Are the olde USR
PW>>> dual-standard modems still in popular use?
DH>> V-Everything has HST.  It's the current delivered model.

PW> And the top speed for HST is 16.8Kbps?  How come development stopped on it?

More or less ran out of gas.  End of the line for easy progress in that
particular technology - and another was opening at the time.

PW> Too many people moving to ITU-T standards?

Regrettably, the "standards" usually wind up being a means for
the poorer manufacturers to pull down the leader(s) to their performance
level.

PW>> Would people ever have bought HST-only modems in the past -- was it ever
PW>> THAT popular???
DH>> Yep.  Once.

PW> What caused the movement away from HST?  Improvement of phone lines, better
PW> modulation techniques, etc.???

More speed.  Even 14400 full duplex was capable of better throughput with
JANUS on good lines.  When v34 appeared, HST was history, unless you had
Telstra delivering rusty barbwire as your phone line.

Regards,
Dave Hatch.

--- Msgedsq 3.20