suresh@cheme.caltech.edu (Suresha Guptha B.A.) (05/30/91)
Hi fellow netters,
before I had requested information about 9600 V.32bis modems. I got
enough replies for my posting and wish to thank all of them.
US Robotics V.32bis modem and Prometheus Pro modem ultima were
some of the choices mentioned in the responses that I got. US Robotics was
mentioned because of the reputation of the company and also its performance.
Prometheus because of its fax capabilities, price/performance. I am including
both my original posting and the responses that I got below.
*******My original posting******
I am considering buying a 9600 V32.bis modem. Fax capabilities
of the modem are not important to me. Could some one suggest a good
modem that I should purchase ? I would appreciate if you can share the
experiences you had or the reviews you have read about the available
9600 baud modems. If I get enough replies I will summarize it to the
net.
Thanks in advance.
*******Responses that I received*********
**************
I have tried using ProModem Ultima from the Promotheus. It is
capable of sending data up to 14,400 bps and Fax Group III at 9600 baud
It is v.32 compatible, and I think this is a great Modem.
However, I personally have problem with its Fax Software.
The interface is not very user-friendly. Besides, its capability is only
for not-so-fancy fax-document editor. The editor allow me to include the
cover page for every document I want to send. And I did try receiving
and sending document from/to overseas' node.
I have heard from people around me that the best modem is the
USRobotic Courier HST Dual Standard which is also v.32 compliant modem.
However the price is very expensive. What you get, though, is a good
modem with the backup from a reputable company in the modem industry.
USRobotic usually give 2 year warranty for their modem. It is not a
FaxModem, but its throughput is usually higher than the other modems.
If you have access to the computer magazines like Macworld or
MacUser, try looking at their issue on Nov. 1990 issue of MW on page
190 about High-Speed Modems, and on Jan 1990 issue of the MU on page
180 about Modems: 9600 bps and counting. I think they are doing a good
job in describing the technology and the products as well as the measure
of performance of several different modems avaiable on the market at
that time.
Off course, time has change and the price for the modems listed
on those articles are not accurate anymore. They are getting cheaper
all the time.
*************
I use a US Robotics Courier V.32 modem. I can get the free upgrade to
V.32bis but I haven't. This modem actually belongs to the government and
I will have to return it to them some time so I will have to buy one of
my own.
This modem does V.32 and V.42bis. With the free upgrade it will do
V.32bis. This modem does one thing that the others don't do. It has the
ability to negotiate the speed in the two directions (transmit and receive)
separately (if both modems are from US Robitics). I am sure that at some
time you have been talking on a long distance line and asked the other
person of they could hear another conversation in the background or a funny
sound. And the other person has said that they hear nothing strange. This
is where this is important. This way either the transmit or the receive
speed will slow down but not both. AGAIN, this *only* works if both modems
are from US Robotics. US Robotics made their money providing proprietary,
high speed modems before V.32 was inexpensive enough. These modems were
asymetric. They transmitted at 14.4Kbps in one direction and 300bps in the
other and worked better (and *considerably* faster) that Hayes V series
modems which ran at 9600bps but only one direction at a time (and achived
throughput of about only 4800bps). They are using this technique to add
additional abilities to their modem.
This is good for the government because we will be out in the Australian
outback with several of these modems. It is very important that we get the
best possible speeds. US Robotics also sells HST modems (Their proprietary
pre V.32 modems which are in wide use at BBS sites across the country).
They also sell a Dual Standard modem which has V.32 and HST for maximum
compatibility. This is for the person who wants everything and can afford it.
For myself, I may purchase the Promethius Ultima modem (V.32bis, V.42bis,
and send/receive FAX). I think that it would be neet to be able to FAX
a quick message to some fax machine without going to the office. But I might
just have the other person fax it to the office so I can pick up the paper
printout there.
If you don't already know:
V.32 = 9600bps, 4800bps
V.32bis = 14.4Kbps, 12Kbps, 9600bps, 7200bps, 4800bps
V.42 = MNP 4 and LAP/M modem to modem error correction
V.42bis = LAP/M and 4 to 1 data compression.
MNP 5 = 2 to 1 data compression.
MNP = Microcomm Networking Protocol (Proprietary to Microcom)
LAP/M = Link Access Protocol/Modem.
bps = Bits per second.
Kbps = Thousands of bits per second.
NOTES:
A V.32 and V.32bis modem will work together. V.32bis will be able
to speed up or slow down to more speeds. If 9600bps is to fast for the noise
on the line, it will try 7200bps rather than dropping to the much slower
4800bps.
V.42bis data compression is not only twice as good at compression, it also
checks to see if the compression is doing any good. For files that are
already compressed (e.g. StuffIt or CompactPro) the modem compression will
actually make the file bigger to send *and* it may even crash the link.
V.42bis will check and not compress the file on the fly if already compressed,
MNP 5 won't do this and may crash the link.
**************
> I am considering buying a 9600 V32.bis modem. Fax capabilities
I have a Hayes 9600 UltraSmartModem v42bis (read 38.4k throughput) modem. I'd
definitely go for v42 as it allows 4;1 compression vrs 2:1 allowed by
MNP5. I paid around $800.00 for it and have been thorougly pleased
with it's performace. I use White Knight as the modem program. I can
get _real_ throughput of about 22K with other v42 modems during
transfers of files that were already compressed (.sit.hqx). The
documentation is excellent. Learned more than I ever needed to know
about modems.
**************
My impression is that the current V.32bis modems aren't very reliable yet.
I'm still buying V.32/V.42bis only. Note that V.32bis is 14Kb, not just a
9600b modem.
**************
Try the new US Robotics V32.bis. It is state of the art and runs as low as
$575 (I think?).
**************
-Sureshfolta@tove.cs.umd.edu (Wayne Folta) (05/31/91)
>>My impression is that the current V.32bis modems aren't very reliable yet. >>I'm still buying V.32/V.42bis only. Note that V.32bis is 14Kb, not just a >>9600b modem. I have had no problems with my Prometheus Ultima and V.32b. In fact, I did some experiments with another Ultima owner the other night, and the results were very encouraging. Using V.32b and MNP5, we got 1480 cps throughput on a sound file that had already been compressed! Ultimas had some problems with receiving FAXs until the upgrade to MaxFax 2.0.4. Now everything appears to work fine. Note also that the Ultima is the only modem with send/receive FAX that I know of that has a higher non-FAX data rate than 2400bps. I disagree with the gentleman that found the MaxFax software to be non user-friendly. It is intuitive enough for me, and it has enough options to do anything I might need. Its only drawback is that making cover pages is awkward. (You create the page templates in a drawing program... it doesn't have any built-in graphics abilities.) -- Wayne Folta (folta@cs.umd.edu 128.8.128.8)
conrad@popvax.uucp (M20400@c.nobili) (05/31/91)
<1991May30.000326.22453@nntp-server.caltech.edu> suresh@cheme.caltech.edu (Suresha Guptha B.A.): >I am including both my original posting and the responses that I got below. >*******My original posting****** > I am considering buying a 9600 V32.bis modem. Fax capabilities >of the modem are not important to me. Could some one suggest a good >modem that I should purchase ? I would appreciate if you can share the >experiences you had or the reviews you have read about the available >9600 baud modems. If I get enough replies I will summarize it to the >net. >*******Responses that I received********* > I use a US Robotics Courier V.32 modem. I can get the free upgrade to >V.32bis but I haven't. ... No, you can't. No such thing. Check it out with USR. >************** >I have a Hayes 9600 UltraSmartModem v42bis (read 38.4k throughput) modem. I'd >definitely go for v42 as it allows 4;1 compression vrs 2:1 allowed by >MNP5. I paid around $800.00 for it and have been thorougly pleased >with it's performace. I use White Knight as the modem program. I can >get _real_ throughput of about 22K with other v42 modems during >transfers of files that were already compressed (.sit.hqx). ... Hmmm. Your "_real_ throughput of about 22K" on "files that were already com- pressed" seems questionable. I believe your modem supports a maximum link rate of 9,600 bps. So with a pair of such modems, connected at 9,600 bps and using V.42bis compression your could _hope_ for a maximum throughput of 38,400 bps if you believed the manufacturers' claims of 4:1 compression for V.42bis.... You would probably have to "cook" a file to get anything close to this (i.e., make a big file of just spaces, or the letter x or something). Consensus seems to be that ratios of 2.5:1 to 2.7:1 are more usual. Your claimed throughput works out to a ratio of 2.3:1, which is pretty close to what one should expect for "normal" compressible text. On stuff that was _already_ compressed (as tightly as V.42bis can compress things) you will see "real throughput" of _no greater than_ 9,600 bps! No (further) compression possible = 1:1 compression ratio => throughput of 1 X link rate = 9,600 bps.... Perhaps your files are in fact somewhat compressible. After all, it looks like they have been put through BinHex. (The whole point of which is to _avoid_ a bunch of sequences of eight bits when encoding things, and _must_ not be very "efficient" at representing information....) It just strikes me that your ratio seems higher than could be explained by just the expansion of the StuffIt file by BinHex. Perhaps StuffIt is also not as efficient as V.42bis? Or are you not measuring the right thing? At any rate, I have seen lots of misleading info about compression ratios and expected throughputs, and didn't want any people to think that their V.42bis modems can further compress efficiently compressed files.... >documentation is excellent. Learned more than I ever needed to know >about modems. Try a USRobotics manual! Truly impressive.... >************** >My impression is that the current V.32bis modems aren't very reliable yet. >I'm still buying V.32/V.42bis only. ... Hmmm. _I_ am overwhelmed by the pair of USRobotics Courier V.32bis modems I just bought. I have found the new modems to be rock solid and the expected 1.5 times as fast as the V.32-only modems on clean links (note that this ratio would be even larger on noisy links, as the V.32bis modems don't have to fall back nearly as far _and can fall forward again when the link improves_).... _Way_ superior to the USRobotics Courier V.32 and Telebit T2500 modems that I had been using. Perhaps this neanderthal would like to buy a used USR Courier V.32 from me? ;-) >************** >Try the new US Robotics V32.bis. It is state of the art and runs as low as >$575 (I think?). Indeed. Quite awesome. Where did you see that price?! Lots of people would be interested. Best I've seen is $599 from a mail-order house that does not provide after-sale support.... >************** >-Suresh I have put comp.dcom.modems in the Followup-To: field of this message. You should really read that group if you are interested in modems! There are some wonderfully knowledgeable people there (I don't include myself in that category...). You will get very thorough answers to all kinds of modem-related questions there in a timely fashion. Questions like this one should probably be posted there for best results. If you are not asking about the hardware, but rather the software or cable or other interface for the Mac, then this _is_ the place to ask.... Really, you will be pleasantly surprised at the quality of the information and the signal-to-noise ratio there (just use K in rn if you see an article about a Hayes lawsuit...). +---- C o n r a d C . N o b i l i ----+ | | | Harvard University | Internet: conrad@harvarda.harvard.edu | | Office for Info. Tech. | conrad@popvax.harvard.edu | | Information Services | BITNET: CONRAD AT HARVARDA | | Technical & User Services | CONRAD AT HARVSPHB | | 1730 Cambridge Street | voice: (617) 495-8554 | +---- Cambridge, MA 02138 | fax: (617) 495-0715 ----+
time@ice.com (Tim Endres) (05/31/91)
In article <6913@husc6.harvard.edu>, conrad@popvax.uucp (M20400@c.nobili) writes: > Hmmm. Your "_real_ throughput of about 22K" on "files that were already com- > pressed" seems questionable. I believe your modem supports a maximum link rate > of 9,600 bps. So with a pair of such modems, connected at 9,600 bps and using > V.42bis compression your could _hope_ for a maximum throughput of 38,400 bps if > you believed the manufacturers' claims of 4:1 compression for V.42bis.... You > would probably have to "cook" a file to get anything close to this (i.e., make > a big file of just spaces, or the letter x or something). Consensus seems to > be that ratios of 2.5:1 to 2.7:1 are more usual. Your claimed throughput works > out to a ratio of 2.3:1, which is pretty close to what one should expect for > "normal" compressible text. On stuff that was _already_ compressed (as tightly > as V.42bis can compress things) you will see "real throughput" of _no greater > than_ 9,600 bps! No (further) compression possible = 1:1 compression ratio => > throughput of 1 X link rate = 9,600 bps.... Remember that V.32 (from what I remember) does not need the framing bits that 2400 baud uses, giving something on the order of a 20% increase in real throughput. If someone knows the details about this, please post. ------------------------------------------------------------- Tim Endres | time@ice.com ICE Engineering | uupsi!ice.com!time 8840 Main Street | Voice FAX Whitmore Lake MI. 48189 | (313) 449 8288 (313) 449 9208
zjdg11@hou.amoco.com (Jim Graham) (06/03/91)
First, let me say this --- I don't speak for my employer here....all of these comments are based on what I've seen with my own modem, at home, and with personal use. (standard disclaimer, in other words) In article <6913@husc6.harvard.edu>, conrad@popvax.uucp (M20400@c.nobili) writes: > So with a pair of such modems, connected at 9,600 bps and using > V.42bis compression your could _hope_ for a maximum throughput of 38,400 bps > if > you believed the manufacturers' claims of 4:1 compression for V.42bis.... I've got a Telebit T2500, which of course, has V.32 and V.42/V.42bis. With this, when I connect to V.32/V.42/V.42bis modems, and assuming a clean phone line (obviously, re-transmissions over a lousy line will reduce throughput), my brain-dead serial link, which thinks 19.2 is the end of the world, is the bottelneck. Now, when I connect to a 2400/V.42/V.42bis modem, my eyes see roughly the same throughput as a v.32/nothing link --- roughly 4:1 compression (in that area, at least). Now, for file transfers (each case refers to ZIPped [with implosion] files, Zmodem xfer w/o Zmodem compression, and no errors) I typically see the following type stats: a) no V.42: 95 -- 97 % efficiency b) V.42/V.42bis: 116 % efficiency typical, 127 % efficiency max. now, I had heard such claims for a long time, and never believed them...until I started seeing the results...with remarkable consistency. These figures, btw, remain constant among 3 different software packages.... > You > would probably have to "cook" a file to get anything close to this (i.e., > make > a big file of just spaces, or the letter x or something). No, these were real files. They vary from ZIPed GIFs, ZIPed text, ZIPed binaries, and combinations of the above. > Consensus seems to > be that ratios of 2.5:1 to 2.7:1 are more usual. Your claimed throughput > works > out to a ratio of 2.3:1, which is pretty close to what one should expect for > "normal" compressible text. ok --- why do I consistently see so much higher throughput than this? (this is intended as a serious, not sarcastic, question.) As another example, when on a different terminal, which did support 38.4 on the serial link, and a different V.32/V.42/V.42bis modem (which also did 38.4 serial), I can't say for sure that the throughput looked just like 38.4...not having seen exactly that speed like I have 9.6 so often, but it was ** WELL ** beyond 19.2 (2:1). > On stuff that was _already_ compressed (as tightly as V.42bis can compress > things) and that, folks, is the key phrase.... text is far, far from being compressed as much as V.42bis can compress it.... :-) Now, having said all that --- I do see considerably less throughput on noisy phone lines (the kind where you can hear the impulse noise while the modems train....really bad). That's where all the statements I'm disagreeing with are absolutely true. But, if you DO have a good line..... Again, this is all based on what I see with my own eyes. I didn't believe a word of this until I did see it. No company (including my employer) is in any way compensating me or prompting me to make these remarks. --jim ------------------------------------------------------------------------------ Share and Enjoy! (Sirius Cybernetics Corporation, complaints division) 73, de n5ial Internet: jdgraham@hou.amoco.com grahj@gagme.chi.il.us Amateur Radio: TCP/IP: jim@n5ial.ampr.org (44.72.47.193) Packet: bbs went qrt....no new bbs yet ------------------------------------------------------------------------------
andyb@stb.info.com (Andy B.) (06/03/91)
I just missed this summary. Did anyone happen to save it? Thanks! Andy -- If it's not broken...your girlfriend will get bored with it anyway.
rdippold@cancun.qualcomm.com (Ron Dippold) (06/04/91)
In article <1CE00001.gxxd0m@tbomb.ice.com> time@ice.com writes: > >In article <6913@husc6.harvard.edu>, conrad@popvax.uucp (M20400@c.nobili) writes: >> Hmmm. Your "_real_ throughput of about 22K" on "files that were already com- >> pressed" seems questionable. I believe your modem supports a maximum link rate >> of 9,600 bps. So with a pair of such modems, connected at 9,600 bps and using >Remember that V.32 (from what I remember) does not need the framing >bits that 2400 baud uses, giving something on the order of a 20% increase >in real throughput. If someone knows the details about this, please >post. Expected throughput on a V.32 modem with V.42bis is about 1100 cps. Some are slightly slower or faster, but that has always been my experience with ZIPed and ARJed files. -- Standard disclaimer applies, you legalistic hacks. | Ron Dippold
conrad@popvax.uucp (M20400@c.nobili) (06/04/91)
-- Again, note comp.dcom.modems in the Followup-To: field -- most appropriate. <1991Jun2.233826.29382@hou.amoco.com> zjdg11@hou.amoco.com (Jim Graham) writes: ><6913@husc6.harvard.edu>, conrad@popvax.uucp (M20400@c.nobili) writes: >> So with a pair of such modems, connected at 9,600 bps and using >> V.42bis compression you could _hope_ for a maximum throughput of 38,400 bps >> if you believed the manufacturers' claims of 4:1 compression for V.42bis.... >I've got a Telebit T2500, which of course, has V.32 and V.42/V.42bis. With ^^^^^^^^^^^^^^^^^^^^^^^^ >this, when I connect to V.32/V.42/V.42bis modems, and assuming a clean phone >line (obviously, re-transmissions over a lousy line will reduce throughput), >my brain-dead serial link, which thinks 19.2 is the end of the world, is the ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ >bottelneck. Now, when I connect to a 2400/V.42/V.42bis modem, my eyes see ^^^^^^^^^^^ >roughly the same throughput as a v.32/nothing link --- roughly 4:1 >compression (in that area, at least). A couple of things so far. You've got a Telebit T2500. I had one too. Your brain-dead _modem_ thinks 19.2 is the end of the world. (I've got my flame- retardant unders on in case any of you think that I _really_ think that T2500s are brain-dead....) You should use more accurate measuring tools. I hope you're not an engineer! (Oops -- didn't have room for the ;-) !) Ok, now comes some stuff I really am not sure I follow. Beware. I may extract the wrong sense from this confusion, but I will try.... Background for c.d.m people: This started in c.s.m.c, but it was really just modem stuff, so I sent it here (sorry now, I guess). Someone had made a claim of "_real_ throughput of about 22K" on "files that were already compressed" with a V.32 & V.42bis modem, and I didn't want people to expect magic. It turned out that the person was transferring ".sit.hqx" files. So I explained lots of the issues, and that although ".sit" files are compressed pretty efficiently, ".hqx" files are by necessity not so. Which makes the 22K throughput _not_ really a figure for compressed data. I was a little puzzled because 22K / 9,600 = 2.3, which seems like a very good compression ratio for a ".sit.hqx" file. I had thought it would be lower than that. I was hoping for more data from others. I explained why this person really _did_ have a 9,600 bps modem.... (Note that I do believe in data compression, and am squeezing about 35Kbps through my pair of USRobotics Courier V.32bis modems even (especially?) as I type....) >Now, for file transfers (each case refers to ZIPped [with implosion] files, >Zmodem xfer w/o Zmodem compression, and no errors) I typically see the >following type stats: > > a) no V.42: 95 -- 97 % efficiency > b) V.42/V.42bis: 116 % efficiency typical, > 127 % efficiency max. > >now, I had heard such claims for a long time, and never believed them...until >I started seeing the results...with remarkable consistency. These figures, >btw, remain constant among 3 different software packages.... >> You would probably have to "cook" a file to get anything close to this (i.e. >> make a big file of just spaces, or the letter x or something). By "this" I mean 4:1 compression ratios, not the paltry, believable ones above! >No, these were real files. They vary from ZIPed GIFs, ZIPed text, ZIPed >binaries, and combinations of the above. I don't know much about PeeCee compression formats. Are they so inefficient as to allow "116 % efficiency typical"? I had pointed out that if the same com- pression algorithm were used on the files as V.42bis would use if they were not compressed, then one should see 1:1 compression ratios on clean lines.... ;-) I tend to use GNU compress on UNIX, MacOS, and DOS, so I don't know about the ones mentioned above.... >> Consensus seems to be >> that ratios of 2.5:1 to 2.7:1 are more usual. Your claimed throughput works >> out to a ratio of 2.3:1, which is pretty close to what one should expect for >> "normal" compressible text. This is just the rough sense that I have gleaned from my own observations and stuff I see on c.d.m. I was hoping that we could get a better handle on these figures in c.d.m.... I guess I also have a sort of morbid curiosity about the ratios that you get, Geoffrey, with your one-megabyte files of nulls.... >ok --- why do I consistently see so much higher throughput than this? (this >is intended as a serious, not sarcastic, question.) As another example, when >on a different terminal, which did support 38.4 on the serial link, and a >different V.32/V.42/V.42bis modem (which also did 38.4 serial), I can't say >for sure that the throughput looked just like 38.4...not having seen exactly >that speed like I have 9.6 so often, but it was ** WELL ** beyond 19.2 (2:1). This is the throughput that you "see"? What do the bits look like? ;-) Also, am I correct when I read this to mean that you _aren't_ using a T2500 here -- a necessity for "38.4 on the serial link"? Or are you being deceived by more than your eyes? The mention of a _single_ different modem makes me wonder.... >> On stuff that was _already_ compressed (as tightly as V.42bis can compress >> things) This is the kind of data that the original "_real_ throughput of about 22K" was _by definition_ not talking about.... >and that, folks, is the key phrase.... text is far, far from being compressed >as much as V.42bis can compress it.... :-) Yes, exactly. Nor, apparently (if we are to believe that the guy with the "_real_ throughput of about 22K" had a better yardstick than you have (don't have?)) are ".sit.hqx" files. Note that ".sit" files have often been compressed using LZW and should be about as efficient/inefficient as V.42bis. (Right?) I am unsure whether BinHex (produces ".hqx" files) expands ".sit" files to as much as the 2.3X size that would seem to be implied by the original figures.... My network traffic seems to be compressible by anywhere from 1.8:1 to 2.5:1.... I still want numbers on _just how much_ "normal text" can be compressed by V.42bis modems.... Were the numbers I tossed out a fair impression from c.d.m? >Now, having said all that --- I do see considerably less throughput on noisy >phone lines (the kind where you can hear the impulse noise while the modems >train....really bad). That's where all the statements I'm disagreeing with >are absolutely true. But, if you DO have a good line..... I think you actually agree with what I was saying -- you just weren't sure what I was saying.... >Again, this is all based on what I see with my own eyes. I didn't believe a >word of this until I did see it. No company (including my employer) is >in any way compensating me or prompting me to make these remarks. Really, consider some _measurements_! And I _hope_ nobody is compensating you for most of those remarks! ;-) (Sorry, I guess I am just in a frisky mood!) > --jim > > >------------------------------------------------------------------------------ >Share and Enjoy! (Sirius Cybernetics Corporation, complaints division) >73, de n5ial > >Internet: jdgraham@hou.amoco.com > grahj@gagme.chi.il.us >Amateur Radio: > TCP/IP: jim@n5ial.ampr.org (44.72.47.193) > Packet: bbs went qrt....no new bbs yet >------------------------------------------------------------------------------ +---- C o n r a d C . N o b i l i ----+ | | | Harvard University | Internet: conrad@harvarda.harvard.edu | | Office for Info. Tech. | conrad@popvax.harvard.edu | | Information Services | BITNET: CONRAD AT HARVARDA | | Technical & User Services | CONRAD AT HARVSPHB | | 1730 Cambridge Street | voice: (617) 495-8554 | +---- Cambridge, MA 02138 | fax: (617) 495-0715 ----+
dsiebert@icaen.uiowa.edu (Doug Siebert) (06/04/91)
In article <6937@husc6.harvard.edu> conrad@popvax.uucp (M20400@c.nobili) writes: > >I don't know much about PeeCee compression formats. Are they so inefficient as >to allow "116 % efficiency typical"? I had pointed out that if the same com- >pression algorithm were used on the files as V.42bis would use if they were not >compressed, then one should see 1:1 compression ratios on clean lines.... ;-) >I tend to use GNU compress on UNIX, MacOS, and DOS, so I don't know about the >ones mentioned above.... > I'm no expert on modems, but my own personal theory on compressed files being sent with > 100% efficiency is that the start/stop bits are eliminated for the most part, allowing potential gains (if all such bits were removed, which would be impractical) of 25%, leading to efficencies in excess of 120% Some correct me if I'm wrong (like I have to ask for this! :-) )
hoepfner@heawk1.gsfc.nasa.gov (Patrick Hoepfner) (06/17/91)
Doug.Siebert@f98.n250.z1.FidoNet.Org (Doug Siebert) writes: >In article <6937@husc6.harvard.edu> conrad@popvax.uucp (M20400@c.nobili) >writes: >> >>I don't know much about PeeCee compression formats. Are they so inefficient >>as to allow "116 % efficiency typical"? I had pointed out that if the same >>compression algorithm were used on the files as V.42bis would use if they >>were not compressed, then one should see 1:1 compression ratios on clean >lines... ;-) >>I tend to use GNU compress on UNIX, MacOS, and DOS, so I don't know about >>the ones mentioned above.... >I'm no expert on modems, but my own personal theory on compressed files being >sent with > 100% efficiency is that the start/stop bits are eliminated for >the most part, allowing potential gains (if all such bits were removed, which >would be impractical) of 25%, leading to efficencies in excess of 120% Some >correct me if I'm wrong (like I have to ask for this! :-) ) Just to add my 2 cents... The compression routines that are used on your computer Un*x compress, PC arc, and Mac StuffIt (to name a few), basically do the same as MNP5 or V.42bis. The only difference is that MNP5 (up to 2 to 1 compression) and V.42bis (up to 4 to 1 compression) do the compression on the fly. They don't require you to compress the program on your end and have the person on the other end uncompress them (also meaning the person on the other end doesn't have to worry about having the correct uncompression program - just the correct modem). Because these 'on the fly' compression techniques have to worry about working quickly, they probably won't ever keep up with the stand alone applications. But then again, you don't have to spend your time compressing and un- compressing them. The 2x1 and 4x1 compression is idealized. And significant compression can only be had on text files (with lots of repeated strings). If the file is already compressed the MNP5 compression will actually make the file longer. V.42bis looks to see if it is doing any good and will not compress a file if the resultant file is getting bigger. (I have read that MNP5 can actually crash the link if the file is already compressed). The answer is the 2x1 and 4x1 compression is idealized and will never be realized in real life situations, but text file will transfer significantly faster with MNP5 or V.42bis than without (and V.42bis is not only faster than MNP5, but also safer). -- Pat --------------------------------------> hoepfner@heasfs.gsfc.nasa.gov