Xref: utzoo comp.dcom.modems:10096 comp.sys.mac.comm:3962 Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!apple!mips!zaphod.mps.ohio-state.edu!caen!ox.com!heifetz!tbomb!time From: time@ice.com (Tim Endres) Newsgroups: comp.dcom.modems,comp.sys.mac.comm Subject: Re: Summary of 9600 V.32 bis modem info Message-ID: <1CE00001.gxxd0m@tbomb.ice.com> Date: 31 May 91 15:56:58 GMT Reply-To: time@ice.com Distribution: na Organization: ICE Engineering, Inc. Lines: 26 X-Mailer: uAccess - Mac Release: 1.1.b9 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