http://groups.google.com/d/topic/comp.sys.amiga/RT6luTnu9aA/discussion
`comp.sys.amiga ›
`19.2k baud modems
`6 posts by 6 authors
`Harald Milne
`12/17/87
` Yes, there is such a beast. We just got one, on order for 3 months.
`We got it at discount for $700 plus bucks. The discount is applied to uunet
`subscribers. Else, pay a hefty $1500.
` Its called a TrailBlazer. Want to know more?
`--
`Work: Computer Consoles Inc. (CCI), Advanced Development Group (ADG)
` Irvine, CA (RISCy business! Home of the CCI POWER 6/32)
`UUCP: uunet!ccicpg!harald
`N Weinstock
`12/18/87
`- hide quoted text -
`In article <7403@ccicpg.UUCP> harald@ccicpg.UUCP writes:
` Yes, there is such a beast. We just got one, on order for 3 months.
`>We got it at discount for $700 plus bucks. The discount is applied to uunet
`>subscribers. Else, pay a hefty $1500.
` Its called a TrailBlazer. Want to know more?
`--
`>Work: Computer Consoles Inc. (CCI), Advanced Development Group (ADG)
`> Irvine, CA (RISCy business! Home of the CCI POWER 6/32)
`>UUCP: uunet!ccicpg!harald
`Thought I'd stick my $.02 in. The TrailBlazer is supposed (haven't actually
`touched one myself) to be a very spiffy unit which will likely become a
`standard for 19.2Kbps modems. (By the way, BAUD rate is the signalling
`frequency, not the data rate. The TrailBlazer is a 19.2K bits per second
`modem, NOT 19.2Kbaud. Sorry to be nitpicky, but I just learned this
`distinction recently :-)
`This modem constantly checks the quality of the line, and adjusts data
`rate accordingly. It has supposedly been clocked at an average of about
`14Kbps over random long-distance lines. Pretty impressive. I would guess
`that if a conditioned line were available, it could probably make 19.2.
`My understanding is that this thing works by subdividing the 3KHz voice band
`into a large number of subchannels, and transmitting many bits in "parallel."
`Well, that's all the hearsay I've heard said. If this posting is a giant
`glob of misinformation, please correct (or flame) me. I'm very interested in
`how the TrailBlazer works.
`--
`+_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_+
`| |
`| Neil Weinstock UUCP: ...!codas!cord!nsw |
`| AT&T Bell Labs, Liberty Corner NET: n...@cord.att.com |
`| Warren, NJ (which one? I DON'T KNOW) |
`| |
`| DISCLAIMER: My views are entirely my own, I think |
`| |
`+_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_+
`Bill Mayhew
`12/19/87
`I'd suggest reading comp.dcom.modems to follow the lively
`discussion of the Telebit Trailblazer and other modems of various
`types.
`The Trailblazer supports the normal 0-300, 1200, and 2400 buad
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`transmission formats up to v22.bis standard. If desired MNP error
`correction can be applied to 1200 and 2400 baud connections with
`other modems that support MNP. With MNP in effect, transmission
`errors virtually disappear; MNP also achieves a 2:1 data
`compression, resulting in an effective 4800 baud connection.
`In addition to ISO transmission modes, the Trailblazer also has a
`proprietary Trellis coded multi carrier system. Data are
`transmitted up up to 512 carriers of 7.6 Hz bandwidth. An initial
`handshake procedure determines what mode is it be used. If the
`"FAST" Trellis transmission mode is selected, the line profile is
`examined to decide which of the 512 carriers will be employed. The
`Trellis mode is half duplex. In theory, if all 512 carriers are in
`operation, the instantaneous throughput is 19200 bits/sec.
`Typically between me and the vax about 20 miles away, I get 14500
`to 16500 bits/sec as claimed by the status report from the modem
`(ATs70?). When two Trailblazers are talking in Trellis mode, AT
`commands can be sent to the remote Trailblazer via a supervisory
`data channel (AT%...). This latter feature is very handy.
`An optional ROM can be installed to support the uucp g protocol or
`kermit. With the option ROM, the Trailblazers have the ability to
`spoof the local host into nearly continuous throughput. The
`Trailblaizers have faily be internal buffers. They can send
`appropriate checksums back to the local host to keep filling their
`buffers before a large block is actually sent between the modems.
`I've found that I typically get 550 characters / sec in this mode
`for uucp. Most of the limit seems to be with the vax which just
`can't keep sending data for sustained periods any faster than that.
`Nonetheless, this is about 5-1/2 times the throughput that I get
`with a Hayes 1200 modem. As such, the Telebit should be able to
`save its cost in terms of reduced phone bills in about threee months.
`(Assuming a commercial rate in-state long distance news feed that
`operates 4 hours a day.)
`For me, the Trailblaizer has made talking to our vax *possible*.
`Our dial-up suffers a strong high-frequency roll-off somewhere in
`the web of wiring between the CO that serves the vax and the CO
`that serves me. As such a Hayes 1200 is useless. The answer
`carrier is the higher frequency, which is attenuated by the poor
`circuit. The result is a continuous stream of ~r~r~r_{... at my
`end. The Trailblazer has an adaptive equalizer that is able to
`work around the line impairment at even 1200 baud from a Hayes
`modem on the vax. Of course a Trailblazer will not cure all types
`of line impairment. The TelCo was totally unsympathetic with our
`complaints about the line. They said (roughly quoting) "If it's
`good enough to hold a voice conversation, that's all we care about.
`Tough."
`Naturally, I don't have any financial interest in Telebit other
`than reduced financial assests on my account. It is a product that
`does indeed do what it say it will in the glossy ads.
`--Bill
`John Russell
`12/22/87
`In article <503@cord.UUCP> nsw@cord.UUCP (59455-N Weinstock) writes:
`>This modem constantly checks the quality of the line, and adjusts data
`>rate accordingly. It has supposedly been clocked at an average of about
`>14Kbps over random long-distance lines. Pretty impressive. I would guess
`>that if a conditioned line were available, it could probably make 19.2.
`My understanding is that this thing works by subdividing the 3KHz voice band
`>into a large number of subchannels, and transmitting many bits in "parallel."
`I have heard figures of 100K bits/second for modems using this technique, but
`I was under the impression you needed the same model on the other end due to
`the specialized encoding used. Maybe like you say the Trailblazer will become
`the standard.
`John
`--
`"...and intuition, in a case such as this, is of crucial importance."
` -- William Gibson, _Count_Zero_
`Peter da Silva
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`12/28/87
`In article <4310@garfield.UUCP>, john13@garfield.UUCP (John Russell) writes:
`> I have heard figures of 100K bits/second for modems using this technique, but
`> I was under the impression you needed the same model on the other end due to
`> the specialized encoding used. Maybe like you say the Trailblazer will become
`> the standard.
`And I was under the impression that Shannon's Theorem said that the hard limit
`for a voice line was 50K bits/second. I could be wrong (been known to happen,
`just ask anyone here), but I believe the person who told me this. He's a jerk,
`but a knowledgable one.
`--
`-- Peter da Silva `-_-' ...!hoptoad!academ!uhnix1!sugar!peter
`-- Disclaimer: These U aren't mere opinions... these are *values*.
`George Robbins
`1/3/88
`In article <1329@sugar.UUCP> peter@sugar.UUCP (Peter da Silva) writes:
`> In article <4310@garfield.UUCP>, john13@garfield.UUCP (John Russell) writes:
`> > I have heard figures of 100K bits/second for modems using this technique, but
`> > I was under the impression you needed the same model on the other end due to
`> > the specialized encoding used. Maybe like you say the Trailblazer will become
`> > the standard.
` And I was under the impression that Shannon's Theorem said that the hard limit
`> for a voice line was 50K bits/second. I could be wrong (been known to happen,
`> just ask anyone here), but I believe the person who told me this. He's a jerk,
`> but a knowledgable one.
`Shannon had to assume that the data was random. If the data has patterns
`that compression or other algorithms can take advantage of, then you can
`obtain higher equivalent "bit rates", however you can probably argue that the
`actual amount of theoretical "information" being transmitted is still less
`than Shannon's limits.
`Practically, the USR type 9600 baud or Trailblazer type modems may offer
`you considerable cost savings if you transfer a lot of data, or the pleasure
`of "direct connect" data rates even though you're dialed into your sites
`host computer. The tradeoff is currently between maximum data rate and
`interactive turn-around/echo time, but both sides are still fighting hard.
`--
`George Robbins - now working for, uucp: {uunet|ihnp4|rutgers}!cbmvax!grr
`but no way officially representing arpa: cbmvax!g...@uunet.uu.net
`Commodore, Engineering Department fone: 215-431-9255 (only by moonlite)
`
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