Xref: utzoo comp.dcom.modems:10132 comp.sys.mac.comm:4001 Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!spool.mu.edu!cs.umn.edu!uc!apctrc!voyager!zjdg11 From: zjdg11@hou.amoco.com (Jim Graham) Newsgroups: comp.dcom.modems,comp.sys.mac.comm Subject: Re: Summary of 9600 V.32 bis modem info Message-ID: <1991Jun2.233826.29382@hou.amoco.com> Date: 2 Jun 91 23:38:26 GMT Article-I.D.: hou.1991Jun2.233826.29382 References: <1CE00001.gxxd0m@tbomb.ice.com> Sender: news@hou.amoco.com Distribution: na Organization: Amoco Lines: 81 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 ------------------------------------------------------------------------------