3 Sep
2009
3 Sep
'09
3:57 p.m.
Ben wrote:
This is 1976 ... did they have 9600 modems back then
that a human could
afford!
Yes, but they only worked on point-to-point leased lines with
significantly greater bandwidth than normal voice-grade PSTN (Public
Switched Telephone Network) lines. Expensive stuff.
AFAIK, the first commercially available modem for voice-grade PSTN to
achieve 9600 bps or more was the Telebit Trailblazer, introduced in
1985. It was half-duplex at approximately 18,000 bps (peak) with a low
bit rate reverse channel. The firmware automatically did line
turnarounds based on buffer depths, so it simulated full duplex but with
relatively high latency.
The Trailblazer used proprietary Packetized Ensemble Protocol (PEP),
which used up to 512 narrow-band carriers. It was a forerunner of OFDM
modulation, which is now used for 802.11a/g/n and many other high
performance data radio applications.
The Trailblazer is a 6 baud modem! :-)
A baud is a symbol per second, NOT a bit per second. A symbol can
encode multiple bits, and in PEP modulation a symbol encodes thousands
of bits. For comparison, a V.32 9600 bps modem actually communicates at
2400 baud, with four bits per symbol (16-point constellation).
Eric