jiro@shaman.com (Jiro Nakamura) (02/28/91)
I have a question for the peanut gallery. I know that PEP uses a number
of different frequencies for DAMQAM, achieving an average throughput of
10,000 to 18,000 bps in one direction, with a smaller opposite channel
in the opposite direction (I think it was about 30bps?)
Now, this is great raw throughput. But a v.32 achieves 9600 bps in
each direction, so theoretically it *could* do 19200 in one direction.
No? If v.32 was set up as a half-duplex system with all of its resources
going one way, it could do 19200 easily.
I don't know if v.32bis is full duplex or not, but it does 14,400 bps.
I would think PEP, using more of the available frequency bandwidth
should be able to get consistently 18,000 bps or higher. Why not?
- Jiro Nakamura
jiro@shaman.com
ps. I own a T2500 and love it, so this isn't meant to be a flame on
Telebit. I just want to know.
pps. To the fellow at helios.tamu.edu who is forging articles and hates
Telebits: don't bother replying to this, please.,.. :-)
--
Jiro Nakamura jiro@shaman.com
Shaman Consulting (607) 253-0687 VOICE
"Bring your dead, dying shamans here!" (607) 253-7809 FAX/Modemccplumb@rose.uwaterloo.ca (Colin Plumb) (02/28/91)
jiro@shaman.com (Jiro Nakamura) wrote: > > I have a question for the peanut gallery. I know that PEP uses a number >of different frequencies for DAMQAM, achieving an average throughput of >10,000 to 18,000 bps in one direction, with a smaller opposite channel >in the opposite direction (I think it was about 30bps?) Well, on local connections I usually get 18,500 bps or so raw, but there is some protocol overhead for error correction. I think the reverse channel is more than 30 bps, though. > Now, this is great raw throughput. But a v.32 achieves 9600 bps in >each direction, so theoretically it *could* do 19200 in one direction. >No? If v.32 was set up as a half-duplex system with all of its resources >going one way, it could do 19200 easily. No! V.32 uses the same frequencies to send in both directions, and a complex echo cancelling scheme whereby you listen carefully, and subtract off your own shouting to hear the comparative whisper of the other end. Putting it all in one direction would require complete re-engineering, and while it is probably possible to achieve 19,200 bps unidirectional, the existence of V.32 doesn't particularly help. You'd have to eliminate the echo-cancellation and use the improved noise margins to use a denser constellation (512 points) if you wanted it to resemble V.32. But decoding a 512-point constellation is hugely computationally expen$ive. > I don't know if v.32bis is full duplex or not, but it does 14,400 bps. > I would think PEP, using more of the available frequency bandwidth >should be able to get consistently 18,000 bps or higher. Why not? It is full duplex, using the same echo-cancelling scheme. Again, it uses the entire frequency spectrum in both directions. BTW, this makes V.32 and V.32bis connections very hard to wiretap. Your assertion that PEP uses more of the available frequency bandwidth may be true, but I for one don't know it. Toby Nixon posted a while ago that Telebit was going to present a paper to the V.fast commitee about a PEP-like 28,000 baud full duplex modem. There were other proposals in the same wonderful performance range for the meeting... I wonder what happened? -- -Colin
tnixon@hayes.uucp (02/28/91)
In article <1991Feb27.185340.3897@shaman.com>, jiro@shaman.com (Jiro Nakamura) writes: > Now, this is great raw throughput. But a v.32 achieves 9600 bps in > each direction, so theoretically it *could* do 19200 in one direction. > No? If v.32 was set up as a half-duplex system with all of its resources > going one way, it could do 19200 easily. No. You're making the assumption that V.32 uses frequency division multiplexing, dividing the available bandwidth in half in order to be able to transmit both directions at once. Most modulation schemes at 2400bps and below do this, but not V.32. V.32 uses echo cancellation, so both modems use the FULL bandwidth SIMULTANEOUSLY. They subtract their transmitted signal from the received signal, leaving only what the remote modem sent. So, while we are studying how to do 19200bps, it is by no means "easy". > I don't know if v.32bis is full duplex or not, but it does 14,400 bps. V.32bis also uses echo cancellation for full duplex (it is). It acheives 14,400bps by using four times as many possible signal states as V.32. This signal is much more complex than V.32, requiring considerably better receiver circuitry to work reliably. > I would think PEP, using more of the available frequency bandwidth > should be able to get consistently 18,000 bps or higher. Why not? PEP already uses virtually all of the available bandwidth; some standards engineers complain that PEP tries to actually use frequencies outside of the range permitted in many countries. The "typical" throughput is lower because a "typical" phone line doesn't provide good enough signal quality at the band edges for PEP (DAMQAM) to actually use those portions of the band. Also, PEP is limited because it wastes bandwidth by using guard times between symbols to reduce intersymbol interference. Other companies that promote multicarrier modulation have eliminated ISI through other methods, allowing throughput well over 20kbps. -- Toby Nixon, Principal Engineer | Voice +1-404-840-9200 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net
root@zswamp.fidonet.org (Geoffrey Welsh) (03/01/91)
>From: tnixon@hayes.uucp > I would think PEP, using more of the available frequency bandwidth > should be able to get consistently 18,000 bps or higher. Why not? >PEP already uses virtually all of the available bandwidth; I think the question here is, why does V.32bis (or the newer HST modulation) get 14,400 bps raw carrier throughput on all decent lines, while PEP may reach 16,000 bps only under very rare 'ideal' lines. I've often wondered what could be done to improve DAMQAM modulation. It is, after all, the oldest of the current high speed dialup modem technologies, predating the HST, the V-9600, and even the widespread public acceptance of 2400 bps! For instance, I've noticed that the trend in 9600+ bps modems is to increase the resolution in the coding constellation. PEP still uses sixteen point QAM; has DSP technology not improved enough to enable us to code more than four bits per baud in a multicarrier scheme? I've also wondered about the overlap of the bandwidth; if their carriers are 7.8 Hz apart and operating at 8 baud, does this not make their outside harmonics, according to Fourier's theorems, overlap the next carriers' (both up and down) fundamental frequencies? If these harmonics are subject to a significant reduction in amplitude, could they perhaps be crammed a bit closer or operated at higher baud rates? Bottom line: I can imagine multicarrier technology benefitting from the application of improved technology, but there seems to be no move on Telebit's part to do so. From this I can only conclude that the future of multicarrier technology lies with maintaining compatibility with existing PEP installations... I do not think that we will see improvements in DAMQAM from Telebit. PEP is coasting. <sigh> >Other companies that promote multicarrier modulation have >eliminated ISI through other methods, allowing throughput >well over 20kbps. I was not aware that any companies were promoting, in a large way, general purpose multicarrier modems... -- UUCP: watmath!xenitec!zswamp!root | 602-66 Mooregate Crescent Internet: root@zswamp.fidonet.org | Kitchener, Ontario FidoNet: SYSOP, 1:221/171 | N2M 5E6 CANADA Data: (519) 742-8939 | (519) 741-9553 The mile is traversed not by a single leap, but by a procession of coherent steps; those who insist on making the trip in a single element will be failing long after you and I have discovered new worlds. - me
gandrews@netcom.COM (Greg Andrews) (03/01/91)
In article <1991Feb27.185340.3897@shaman.com> jiro@shaman.com (Jiro Nakamura) writes: > > I have a question for the peanut gallery. I know that PEP uses a number >of different frequencies for DAMQAM, achieving an average throughput of >10,000 to 18,000 bps in one direction, with a smaller opposite channel >in the opposite direction (I think it was about 30bps?) > You're confusing PEP with HST. HST has the low speed back channel while PEP is completely half-duplex (data flows in only one direction at a time). I believe the HST 14400 modulation uses a 450 bps back channel. > Now, this is great raw throughput. But a v.32 achieves 9600 bps in >each direction, so theoretically it *could* do 19200 in one direction. >No? If v.32 was set up as a half-duplex system with all of its resources >going one way, it could do 19200 easily. I can't speak directly to that (perhaps Toby can help us with the details), but I'm fairly certain that V.32 can't increase the bit rate. At least not V.32 *as such*. > I would think PEP, using more of the available frequency bandwidth >should be able to get consistently 18,000 bps or higher. Why not? Error correction. PEP does consistently get 16,000-18,000 bps over phone lines in the US. The overhead of the error correction protocol is what gives you throughput of just 12,000-14,000 bps. -- .-------------------------------------------. | Greg Andrews | gandrews@netcom.COM | `-------------------------------------------'
tnixon@hayes.uucp (03/01/91)
In article <1991Feb28.050506.7297@watdragon.waterloo.edu>, ccplumb@rose.uwaterloo.ca (Colin Plumb) writes: > Toby Nixon posted a while ago that Telebit was going to present a paper > to the V.fast commitee about a PEP-like 28,000 baud full duplex modem. > There were other proposals in the same wonderful performance range for > the meeting... I wonder what happened? Since you asked... Telebit didn't come through. They did present a fairly detailed technical paper (the kind you'd see in IEEE Transactions on Communications, full of formulas and such) on how to do echo cancellation in a multicarrier modem, but no details on their proposal and no testing results. Codex, on the other hand, presented a very detailed and specific proposal on a single-carrier scheme that goes up to 24,000bps on most phone lines in the US, and they included extensive and detailed testing results to prove it. The technology in the Codex modem to improve performance allows it to transmit between 16,800 and 19,200 on the same lines that V.32bis can just barely send 14,400. Pretty good! I _still_ want to hear what Telebit has to say, but it looks like it will be April or later before we see any details. Also, it was fascinating that Intelligent Modem Corporation (Forval) has now stepped forward with a counter-proposal to Telebit for a _different_ multicarrier scheme (and we all thought only Telebit did those kind of modems!). I actually like what I've heard about the IMC proposal better than Telebit -- higher throughput, easier to implement, etc. But, again, they didn't lay it all out on the table and didn't have any testing results, but gave a "conceptual" presentation. There were several other contributions from Racal-Milgo, IBM Europe, and others, giving specific details about the single-carrier approach. We should get a lot more contributions for the meeting of Study Group XVII at the end of April. Remind me again the first week of May, and I'll try to summarize for you what happened there. -- Toby Nixon, Principal Engineer | Voice +1-404-840-9200 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net
bob@MorningStar.Com (Bob Sutterfield) (03/02/91)
In article <3818.27ccf3f4@hayes.uucp> tnixon@hayes.uucp writes:
V.32 uses echo cancellation, so both modems use the FULL bandwidth
SIMULTANEOUSLY.
In my simple-minded testing of various modems with our typical traffic
requrements, I can attest that this is powerful stuff. Running
RFC1171 PPP with RFC1144 TCP header compression over V.32/V.42/V.42bis
between SPARCstation-1s with their DTEs latched at 38400bps, I do FTP
transfers and check the overall and burst throughput when shipping a
copy of the SPARC UNIX kernel. The bursts happen when sending those
sections of the file that are particularly compressible by the V.42bis
implementation in the modems. Various brands of modems don't seem to
vary much in this test, so I'll cite my results for Telebit T1600s.
Running one FTP, I see a sustained rate of 1.8 Kbytes/sec with gusts
to 2.8. Running simultaneous FTPs (one in each direction) over the
same link, they slow down only to 1.5 overall with gusts to 2.2. This
is impressive in that there isn't much degradation. I don't know if
the slowdown is caused by limits on the signalling capacity of the
line, or by limits on the CPU and/or DSP capacity of the modems, or by
limits in the Sun serial port or in the current STREAMS-based PPP
implementation. (I doubt the latter, but I haven't yet run between
directly-connected Suns with no modems involved.)
By comparison, the same exercise between a T2500 and a TB+ running PEP
with DTEs clocked at 19200 (maximum for today's PEP modems) yields a
one-way throughput of around 1.3-1.5Kb/sec. I haven't tried the
simultaneous two-way torture test yet, but I suspect PEP won't fare
nearly so well.
Between two modems running V.32/V.42/V.42bis but with one side clocked
at 19200 and one at 38400, I see around 1.6 Kb/sec one-way either
direction.
Things still to try:
1) direct 38400 connection to see if the Sun's the limiting factor
2) bidirectional FTP over a PEP connection
3) V.32bis/V.42/V.42bis connection, at 38400 and 56K DTE rates
4) sync PPP
5) non-STREAMS, user-space PPP implementation
6) any other variables I'm forgetting?
If your phone lines are clean enough, use V.32 or V.32bis modems for
PPP. If you must fight dirty lines or international connections,
consider using PEP. Don't use any serial line IP software without TCP
header compression.grr@cbmvax.commodore.com (George Robbins) (03/02/91)
In article <3820.27ce2ea5@hayes.uucp> tnixon@hayes.uucp writes: > > Also, it was fascinating that Intelligent Modem Corporation (Forval) > has now stepped forward with a counter-proposal to Telebit for a > _different_ multicarrier scheme (and we all thought only Telebit did > those kind of modems!). I seem to recall the NEC and one or two others had also played around with multi-carrier modem technology, though not neccessarily in the Asynchronous low-price modem market. -- George Robbins - now working for, uucp: {uunet|pyramid|rutgers}!cbmvax!grr but no way officially representing: domain: grr@cbmvax.commodore.com Commodore, Engineering Department phone: 215-431-9349 (only by moonlite)
grr@cbmvax.commodore.com (George Robbins) (03/02/91)
In article <6895.27CDE02A@zswamp.fidonet.org> root@zswamp.fidonet.org (Geoffrey Welsh) writes: > > >From: tnixon@hayes.uucp > > > I would think PEP, using more of the available frequency bandwidth > > should be able to get consistently 18,000 bps or higher. Why not? > > >PEP already uses virtually all of the available bandwidth; > > I think the question here is, why does V.32bis (or the newer HST > modulation) get 14,400 bps raw carrier throughput on all decent lines, while > PEP may reach 16,000 bps only under very rare 'ideal' lines. I think you need to examine closely the relation between these "ideal" lines and "all decent" lines. There's not a lot of user evidence on what percentage of call attempts will work at 14.4 and some contention even about 9600. > I've often wondered what could be done to improve DAMQAM modulation. It > is, after all, the oldest of the current high speed dialup modem technologies, > predating the HST, the V-9600, and even the widespread public acceptance of > 2400 bps! Yes/No. The underlying technologies and the product implementations have distinctly different timelines. I hope Telebit does manage to come out with a second generation scheme that combines the apparent benefits of multi-carrier technology with the full- duplex nature that echo-cancellation supports. It's hard to predict whether they will do so while there is still a reasonably window of opportunity... -- George Robbins - now working for, uucp: {uunet|pyramid|rutgers}!cbmvax!grr but no way officially representing: domain: grr@cbmvax.commodore.com Commodore, Engineering Department phone: 215-431-9349 (only by moonlite)
pete@Octopus.COM (Pete Holzmann) (03/02/91)
In article <3820.27ce2ea5@hayes.uucp> tnixon@hayes.uucp writes: > >Also, it was fascinating that Intelligent Modem Corporation (Forval) >has now stepped forward with a counter-proposal to Telebit for a >_different_ multicarrier scheme (and we all thought only Telebit did >those kind of modems!). I actually like what I've heard about the >IMC proposal better than Telebit -- higher throughput, easier to >implement, etc. But, again, they didn't lay it all out on the >table and didn't have any testing results, but gave a "conceptual" >presentation. I saw the Forval/IMC modem at COMDEX/Fall, and spoke with an engineer about it. It *doe* sound very interesting, with a number of technological improvements over PEP, and other modems in general: - multicarrier protocol, with full data speed in both directions simultaneously - 19200 baud base data rate (on pre-compressed data); interface speeds up to 56Kb when the modem is compressing on the fly - modem firmware is downloadable. You never have to order a new PROM set; just call up their BBS and download a new program. (There are certain aspects to this that make me a bit nervous, but if it is done properly with proper handling of security/reliability issues, it sounds like a really Good Thing...) I hadn't heard of Forval/IMC before; I'm glad to hear that they are more thann just an invisible taiwan-clone company. Pete -- Peter Holzmann, Octopus Enterprises |(if you're a techie Christian & are 19611 La Mar Ct., Cupertino, CA 95014 |interested in helping w/ the Great UUCP: {hpda,pyramid}!octopus!pete |Commission, email dsa-contact@octopus) Voice: 408/996-7746;FAX=408/985-0859
gandrews@netcom.COM (Greg Andrews) (03/02/91)
In article <6895.27CDE02A@zswamp.fidonet.org> root@zswamp.fidonet.org (Geoffrey Welsh) writes: > > For instance, I've noticed that the trend in 9600+ bps modems is to >increase the resolution in the coding constellation. PEP still uses sixteen >point QAM; has DSP technology not improved enough to enable us to code more >than four bits per baud in a multicarrier scheme? > PEP isn't limited to a 16 point constellation. In the cleanest parts of the line you'll see carriers using a 64 point (6 bit) constellation. Unless the modem decides the line won't support that kind of signal resolution... -- .-------------------------------------------. | Greg Andrews | gandrews@netcom.COM | `-------------------------------------------'
root@zswamp.fidonet.org (Geoffrey Welsh) (03/04/91)
In a letter to All, Greg Andrews (gandrews@netcom.COM ) wrote: >In article <6895.27CDE02A@zswamp.fidonet.org> >root@zswamp.fidonet.org (Geoffrey Welsh) writes: > > For instance, I've noticed that the trend in 9600+ bps modems is to >increase the resolution in the coding constellation. PEP still uses sixteen >point QAM; has DSP technology not improved enough to enable us to code more >than four bits per baud in a multicarrier scheme? > >PEP isn't limited to a 16 point constellation. In the >cleanest parts >of the line you'll see carriers using a 64 point (6 bit) >constellation. >Unless the modem decides the line won't support that kind of >signal resolution... My disappointment has doubled. At first I believed that Telebit & co. were simply not pushing the technology. Now I that I have reason to believe that they are, I can't avoid the conclusion that they are doing so poorly! If there are 511 carriers operating at a maximum of 8 baud with 4 bit QAM, the maximum possible raw throughput is in the vicinity of 16000 bps, a figure which I have seen Telebit modems approach on clean lines. If, as you say, they're using a 64 point constellation, the maximum raw throughput should be around 24000 bps, and I've never seen a TB come even close to that. -- UUCP: watmath!xenitec!zswamp!root | 602-66 Mooregate Crescent Internet: root@zswamp.fidonet.org | Kitchener, Ontario FidoNet: SYSOP, 1:221/171 | N2M 5E6 CANADA Data: (519) 742-8939 | (519) 741-9553 The mile is traversed not by a single leap, but by a procession of coherent steps; those who insist on making the trip in a single element will be failing long after you and I have discovered new worlds. - me
tnixon@hayes.uucp (03/04/91)
In article <6895.27CDE02A@zswamp.fidonet.org>, root@zswamp.fidonet.org (Geoffrey Welsh) writes: > For instance, I've noticed that the trend in 9600+ bps modems is to > increase the resolution in the coding constellation. PEP still uses sixteen > point QAM; has DSP technology not improved enough to enable us to code more > than four bits per baud in a multicarrier scheme? Telebit has proposed adding trellis coding to acheive better performance. The coding would go "vertically" across the frequencies, rather than "horizontally" from symbol to symbol. I believe the contraint on more constellation density has to do with the amount of time available to process each symbol more than anything else. > Bottom line: I can imagine multicarrier technology benefitting from > the application of improved technology, but there seems to be no move on > Telebit's part to do so. From this I can only conclude that the future of > multicarrier technology lies with maintaining compatibility with existing PEP > installations... I do not think that we will see improvements in DAMQAM from > Telebit. PEP is coasting. <sigh> > > >Other companies that promote multicarrier modulation have > >eliminated ISI through other methods, allowing throughput > >well over 20kbps. > > I was not aware that any companies were promoting, in a large way, general > purpose multicarrier modems... In presentations before the CCITT and TIA TR-30, Intelligent Modem Corporation appears to have some innovative techniques to improve the performance of PEP. For example, they propose using much fewer characters (64 or less), sending more bits per carrier, sending each symbol for much less time, and sending no guard period (dead time) between symbols. The result is (supposedly, since we haven't seen actually test results) throughput up to 24,000 bps synchronous, or even higher. They also propose echo cancellation for full-duplex. I've always thought that Telebit tried to make multicarrier appear much more "magical" and "obscure" than it needed to be, in presentations before standards committees. They've never been really willing to "open the kimono", if you know what I mean; have avoided showing real test results; and have not been at all forthcoming with proposals to handle synchronous transmission or full duplex. They killed the "asymmetrical modem" standards proposal in the process. I'm very pleased that there's now an additional player in the multicarrier field who is willing to explain it adequetely and work with established experts to improve it, without being (1) constrained to maintaining backward compatibility with existing devices, and (2) so concerned about public image, maintaining venture-capital investor confidence, and trying to tie up the technology with existing patents. IMC hasn't shipped their multicarrier modem yet, because they want to see what happens with the V.fast standard. But I expect it will be a good product, if it is at all consistent with the descriptions we've been given. -- Toby Nixon, Principal Engineer | Voice +1-404-840-9200 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net
gandrews@netcom.COM (Greg Andrews) (03/05/91)
In article <6927.27D24513@zswamp.fidonet.org> root@zswamp.fidonet.org (Geoffrey Welsh) writes: >In a letter to All, Greg Andrews (gandrews@netcom.COM ) wrote: > > >PEP isn't limited to a 16 point constellation. In the > >cleanest parts > >of the line you'll see carriers using a 64 point (6 bit) > >constellation. > > >Unless the modem decides the line won't support that kind of > >signal resolution... > > My disappointment has doubled. At first I believed that Telebit & co. were >simply not pushing the technology. Now I that I have reason to believe that >they are, I can't avoid the conclusion that they are doing so poorly! > > If there are 511 carriers operating at a maximum of 8 baud with 4 bit QAM, >the maximum possible raw throughput is in the vicinity of 16000 bps, a figure >which I have seen Telebit modems approach on clean lines. If, as you say, >they're using a 64 point constellation, the maximum raw throughput should >be around 24000 bps, and I've never seen a TB come even close to that. > Geoffrey, I'm sorry you're disappointed, but I think your disappointment stems from a misunderstanding. You say "If there are 511 carriers... with 4 bit QAM...", but there *aren't*. First of all, the modem typically uses only about 400 carriers. Those at the top and the bottom extremes of the frequency range aren't often used because the line isn't good enough. Second, the signal quality of the phone line looks something like a bell curve. The best reponse is found in the middle range and the quality falls off as you go higher and lower. This results in the best transmission through the middle of the frequency range, and poorer transmission as you go farther into the fringes. PEP follows the line quality, using the most complex modulation in the middle ranges where quality is best (the 6-bit, 64 pint QAM), dropping to a simpler modulation where quality is a little worse (the 4-bit 16 point QAM), dropping further down to the simplest modulation where the line is bad (the 2-bit 4 point QPSK), and finally abandoning the carrier frequency where the line is really awful. The modem doesn't automatically use the same modulation across the whole frequency range. It uses the fastest modulation on each carrier that it can. On clean lines I typically see a mass of 6-bit carriers in the middle of the range, with 4-bit ones on the outside, and a few 2-bit ones toward the fringes. (this is shown by querying the S71 and S73 registers) The upper and lower extremes aren't used. Just as you'd expect, an adaptive modulation uses the fastest method where the line is cleanest, in the midrange. -- .-------------------------------------------. | Greg Andrews | gandrews@netcom.COM | `-------------------------------------------'
tnixon@hayes.uucp (03/06/91)
In article <6927.27D24513@zswamp.fidonet.org>, root@zswamp.fidonet.org (Geoffrey Welsh) writes: > My disappointment has doubled. At first I believed that Telebit & co. were > simply not pushing the technology. Now I that I have reason to believe that > they are, I can't avoid the conclusion that they are doing so poorly! > > If there are 511 carriers operating at a maximum of 8 baud with 4 bit QAM, > the maximum possible raw throughput is in the vicinity of 16000 bps, a figure > which I have seen Telebit modems approach on clean lines. If, as you say, > they're using a 64 point constellation, the maximum raw throughput should > be around 24000 bps, and I've never seen a TB come even close to that. Of course, the problem is that your assumptions are wrong. If you had 511 carriers with 8Hz frequency separation, you'd need at least 4088Hz of bandwidth -- and a typical telephone channel only has about 3400Hz of usable bandwidth (and that's pushing it). In reality, DAMQAM only uses 395 carriers, sending about 7.6 symbols per second per carrier, with 6 bits per carrier MAXIMUM, for just a tad over 18,000bps maximum throughput (less protocol overhead). Two additional carriers are used for "pilot tones" for timing recovery. To use all 397 tones at their maximum bit capacity would require a perfect circuit over a bandwidth of 3100Hz. In the real world, such circuits simply do not exist. Even if they did, PEP still couldn't achieve this full throughput, because you have to subtract out roughly 3% for protocol overhead, and a few percent (I don't know exactly how much) for line turnarounds to acknowledge data (it is, after all, a half-duplex modulation scheme). I'd say that 16,000bps was pretty good, considering. Not that I'd compliment Telebit or anything. God forbid. What _I_ want to see is their new V.fast proposal with echo cancellation that supposedly really does run at 24,000 bps! But, based on their track record of not submitting promised CCITT contributions on schedule, I'll believe it when I see it. -- Toby Nixon, Principal Engineer | Voice +1-404-840-9200 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net
root@zswamp.fidonet.org (Geoffrey Welsh) (03/09/91)
Greg Andrews (gandrews@netcom.COM ) wrote: >First of all, the modem typically uses only about 400 >carriers. Those >at the top and the bottom extremes of the frequency range >aren't often >used because the line isn't good enough. I'm fully aware of how a *typical* Telebit connection works, and you are doing nothing but distract attention from the issue, which is that Telebit has not introduced any improvements in the carrier technology since the introduction of V2 ROMs (and the emergence of the Telebit Trailblazer, as opposed to the DCA IRMA FastLink... I *do* go back that far, thank you) I feel that the multicarrier approach is inherently superior to any single-carrier approach (with the possible exception of the relative difficulty of echo cancellation), and am disappointed that Telebit has not demonstrated this by advancing their technology to outdistance the HSTs, V-96s, V.32s, and V.32bis in terms of throughput. -- UUCP: watmath!xenitec!zswamp!root | 602-66 Mooregate Crescent Internet: root@zswamp.fidonet.org | Kitchener, Ontario FidoNet: SYSOP, 1:221/171 | N2M 5E6 CANADA Data: (519) 742-8939 | (519) 741-9553 The mile is traversed not by a single leap, but by a procession of coherent steps; those who insist on making the trip in a single element will be failing long after you and I have discovered new worlds. - me
gandrews@netcom.COM (Greg Andrews) (03/11/91)
In article <6957.27D86C0A@zswamp.fidonet.org> root@zswamp.fidonet.org (Geoffrey Welsh) writes: >Greg Andrews (gandrews@netcom.COM ) wrote: > > >First of all, the modem typically uses only about 400 > >carriers. Those > >at the top and the bottom extremes of the frequency range > >aren't often > >used because the line isn't good enough. > > I'm fully aware of how a *typical* Telebit connection works, and you are >doing nothing but distract attention from the issue, which is that Telebit has >not introduced any improvements in the carrier technology since the >introduction of V2 ROMs (and the emergence of the Telebit Trailblazer, as >opposed to the DCA IRMA FastLink... I *do* go back that far, thank you) > Gee, I'm sorry Geoffrey. I was under the impression that I was addressing an aspect of PEP where someone was displaying some misconceptions (i.e. the fastest modulation available on a carrier and the distribution of modulation types across the various carriers). I see Toby also responded to that very same point. Are you going to accuse him of attempting to distract attention from the issue of PEP improvements also? -- .-------------------------------------------. | Greg Andrews | gandrews@netcom.COM | `-------------------------------------------'
root@zswamp.fidonet.org (Geoffrey Welsh) (03/11/91)
Greg Andrews (gandrews@netcom.COM ) wrote: >Gee, I'm sorry Geoffrey. I was under the impression that I >was addressing an aspect of PEP where someone was displaying >some misconceptions (i.e. the fastest modulation available >on a carrier and the distribution of modulation types >across the various carriers). I made two errors. One, which you pointed out, was to extrapolate details from some early Telebit propoganda and come to inaccurate conclusions about the exact numbers involved in a DAMQAM connection. The other, more serious, error was to put numbers in the message in the first place. Rather than discuss my assertion (which I have yet to see countered, though I wouldn't mind being corrected on this matter) that Telebit have not increased their modems' raw throughput in years, the net's attention is focused on numerical errors. >I see Toby also responded to that very same point. Are you >going to accuse >him of attempting to distract attention from the issue of >PEP improvements also? There is no need to accuse anyone; the deed is done and the fault is with my foolishness. -- UUCP: watmath!xenitec!zswamp!root | 602-66 Mooregate Crescent Internet: root@zswamp.fidonet.org | Kitchener, Ontario FidoNet: SYSOP, 1:221/171 | N2M 5E6 CANADA Data: (519) 742-8939 | (519) 741-9553 The mile is traversed not by a single leap, but by a procession of coherent steps; those who insist on making the trip in a single element will be failing long after you and I have discovered new worlds. - me
grr@cbmvax.commodore.com (George Robbins) (03/13/91)
In article <6993.27DC6082@zswamp.fidonet.org> root@zswamp.fidonet.org (Geoffrey Welsh) writes: > > The other, more serious, error was to put numbers in the message in the > first place. Rather than discuss my assertion (which I have yet to see > countered, though I wouldn't mind being corrected on this matter) that Telebit > have not increased their modems' raw throughput in years, the net's attention > is focused on numerical errors. It's not a debating salon here, is it? Anyway, in a sense your assertion is essentially correct. Since the TB+ pep enhancements and protocol spoofing, they haven't done scratch as far as improving the basic technology and shipping it in a new dial-line modem They've "wasted" their time on the T1000 (competitive pricing), T2500 (V.32), Cellblazer (chance to corner a market), Netblazer (ditto?)... Much as I'd like to see improvements to the basic technology, I think it's up to the company to decide how to budget their R&D resources between basic technology and broadening the product base. In the real world, it isn't always possible to apply maximum effort on multiple fronts and Telebit is not the worlds largest modem company. -- George Robbins - now working for, uucp: {uunet|pyramid|rutgers}!cbmvax!grr but no way officially representing: domain: grr@cbmvax.commodore.com Commodore, Engineering Department phone: 215-431-9349 (only by moonlite)
root@zswamp.fidonet.org (Geoffrey Welsh) (03/14/91)
George Robbins (grr@cbmvax.commodore.com ) wrote: >They've "wasted" their time on the T1000 (competitive >pricing), T2500 (V.32), >Cellblazer (chance to corner a market), Netblazer >(ditto?)... I don't begrudge them the development of the T2500, Cellbalzer or Netblazer... they've got to make inroads into other markets because, frankly, the general purpose dialup market for PEP will probably die out. The T1000 *was* a waste of time. I believe that multicarrier modems are inherently more expensive to develop and build than single-carrier, and that the feature cutting on the 1000 makes it a less powerful brother to an already niche-oriented product. They'd have done much better working on increasing volume and cutting costs on the TB+. > Much as I'd like to see improvements to the basic >technology, I think it's >up to the company to decide how to budget their R&D >resources between basic >technology and broadening the product base. In the real >world, it isn't >always possible to apply maximum effort on multiple fronts >and Telebit is not the worlds largest modem company. ... nor will they ever be. I can't help but wonder how long a future the company has in manufacturing dialup modems. -- UUCP: watmath!xenitec!zswamp!root | 602-66 Mooregate Crescent Internet: root@zswamp.fidonet.org | Kitchener, Ontario FidoNet: SYSOP, 1:221/171 | N2M 5E6 CANADA Data: (519) 742-8939 | (519) 741-9553 The mile is traversed not by a single leap, but by a procession of coherent steps; those who insist on making the trip in a single element will be failing long after you and I have discovered new worlds. - me
grahj@gagme.chi.il.us (jim graham) (03/16/91)
In article <19796@cbmvax.commodore.com> grr@cbmvax.commodore.com (George Robbins) writes: > >They've "wasted" their time on the T1000 (competitive pricing), T2500 (V.32), >Cellblazer (chance to corner a market), Netblazer (ditto?)... Not quite sure how this was intended, whether was support for Telebit or flame.... I only have this to say --- I just bought a T2500, and have been very pleased since day 1 with the fact that it not only does PEP, but also V.32. It also adds MNP 4 and 5, as well as V.42 and V.42bis. All of this adds up to basically one thing --- I connect to just about any high-speed modem out there at high speed. In some cases (sorry, Telebit), V.42bis compression, combined with V.42 error detection and V.32 gets better throughput than PEP. My serial port, which crawls along at a maximum speed of 19.2 ( :-) :-) ), becomes the major limiting factor in how fast I can go...... As an owner of the T2500, regardless of how the original note was intended, I must state that this clearly was not a waste of time in my books. For what it's worth (or isn't worth)...... --jim ------------------------------------------------------------------------------ Share and Enjoy! (Sirius Cybernetics Corporation, complaints division) 73, de n5ial Amateur Radio: TCP/IP: jim@n5ial.ampr.org --- 44.72.47.193 Packet: n5ial@wb9mjn (Chicago, IL USA) Internet: grahj@gagme.chi.il.us ------------------------------------------------------------------------------