bob@MorningStar.Com (Bob Sutterfield) (02/01/91)
(Listen in on comp.dcom.modems sometime, where these issues are often discussed. I've included c.d.m in the Newsgroups: line, and directed followups there.) In article <56917@eerie.acsu.Buffalo.EDU> v082mv5d@ubvmsd.cc.buffalo.edu (William M Utter) writes: In article <1991Jan21.204216.27162@engin.umich.edu>, chau@caen.engin.umich.edu (Hin Fai Chau) writes... (2) What do V.42, V.42bis, Hayes and MNP-5 mean? V.42 and MNP are methods of error correction and DATA compression. MNP5 can make you modem go "twice" as fast... v.42 is a much better compression and might get you 9600. Just to be picky... V.42 and MNP4 are error correction protocols. They are very similar if not identical, and I know of no technical advantage of one over the other. V.42bis and MNP5 are data compression protocols. MNP5 will yield a best-case throughput improvement of 2:1, and V.42bis will manage a 4:1 speedup. Of course, not many people send megabytes of "A"s every day, so you won't see those theoretical values. All the above are independent of the underlying carrier technology, whether V.22 (1200), V.22bis (2400), V.32 (9600), V.32bis (14400) or whatever. Hayes is a company that makes modems and other stuff. They invented and popularized the modem control command set that starts every instruction with "AT". To be "Hayes-compatible" means that your modem's instructions must begin with "AT" too. (4) What is the limit of ordinary phone lines? Can it handle 9600 baud data transmission? We use Telebit T1600s to carry TCP/IP over PPP between SPARCstations over regular voice-grade telephone lines. The DTEs are set at 38400, and we use V.32/V.42/V.42bis (9600 carrier with error correction and data compression). We see FTP throughput figures of 1.7 to 2.8 Kbytes/sec in a one-way transfer, or 1.5 to 2.2 Kbytes/sec if files are being shipped both directions at the same time. The variance reflects the degree of compressibility of the data being transferred. I'm looking forward to trying out a V.32bis modem someday!