Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!iuvax!cica!tut.cis.ohio-state.edu!ucbvax!unisoft!hoptoad!hsfmsh!daemon From: tnixon@hsfmsh.UUCP (Toby Nixon) Newsgroups: comp.dcom.modems Subject: Re: v.42? v.32? v.va espana!! Message-ID: <3183@hsfmsh.UUCP> Date: 6 Jun 90 19:15:44 GMT Sender: daemon@hsfmsh.UUCP Organization: Hayes Microcomputer Products, Inc. Norcross, Georgia Lines: 106 In article <3931@milton.acs.washington.edu>, amigo@milton.acs.washington.edu (Michael Robertson) writes: - MNP is just a early protocol used to boost the modem's - throughput beyond what a non-MNP modem would do. MNP is just a - built-in hardware protocol much like any other software ones used in - terms (Zmodem, Xmodem, etc.). MNP (Microcom Networking Protocol) was, as the name suggests, developed by Microcom, Inc., of Norwood, MA, as a point-to-point error correction protocol between modems. It was originally an async start-stop protocol only (MNP2), but has always had the advantage over XMODEM or ZMODEM of allowing data transfer in both directions simultaneously and of "streaming" operation rather than fixed-length blocks. - It also has some advantages in that it is designed specifically for - modem transfers of course, and it does compression (if on). Anyhow, - there is MNP classes 1 to 5, and supposedly 7 was developed, but - never used much in modems until >V.42< Actually, MNP classes now go up to 10. Class 3 introduced synchronous transmission on the phone line (HDLC framing); Class 4 allows longer frames and shorter headers for less protocol overhead; Class 5 is data compression based on the frequency of occurrence of inidividual characters; Class 6 is a fast-turnaround ping-pong modulation scheme for operation up to 9600bps, based on CCITT V.29; Class 7 is a data compression scheme based on the frequency of occurrence of pairs of characters; Class 8 doesn't exist anymore; Class 9 adds some protocol enhancements including multiple selective reject and piggybacked acknowledgements; Class 10 adds some procedures to help the protocol work over real noisy lines like cellular radio (more aggressively reduces maximum frame size, has more retries before giving up). - What V's are is the CCITT standards institute's way of - defining how a modem operates, and calling that a standard of sorts. - They recognize only a few that they can agree apon, such as V.32, or - 2400 baud modems all work on V.22. (V.32 is defined as a two-way - full duplex 9600 baud transfer state). The International Telegraph and Telephone Consultative Committee (CCITT) is part of the United Nations, and has considerably more power than you seem to think. They are the one and only internationally recognized standards organization for telephone system operation, including data transmission over the telephone network (which is what is defined by the V series Recommendations). CCITT standards have the force of law in many countries. Nations are bound by treaty to abide by CCITT Recommendations for interconnection of telephone systems. Because the Bell System controlled data communications in the USA for many decades, only in the past 10 years or so has compatibility with CCITT Recommendations been a major issue for modem users in the US. There are MANY MANY CCITT standards (not "only a few") that US modem manufacturers comply with today: V.1, V.2, V.4, V.14, V.21, V.22, V.22bis, V.23, V.24, V.25, V.25bis, V.28, V.32, V.33, V.42, V.42bis, V.54, etc. And this is only a small subset of the entire family of V series standards, and doesn't begin to mention all of the others in Series A through Series Z! - But back to V.42/V.42bis, V.42 is just the CCITT's standard - for what was MNP-7. It gives you 3 times the modems throughput, so - you can expect to get into the 350-400 characters per second data - transfer rates if your connection is made to a V.42 modem. Huh? V.42 is the CCITT standard for error control. It defines two protocols: Link Access Procedure for Modems (LAPM) in the main body of the standard, and an Alternative Protocol defined in Annex A of the recommendation which provides backward compatibility with modems implementing MNP2-4. It has nothing whatsoever to do with MNP7. LAPM is the basis for future extensions to V.42, one of which is the V.42bis international standard for data compression. V.42bis is based on the Lempel-Ziv data compression technique, which compresses variable-length strings of characters into fixed-length tokens. On text files, we often see throughput approaching 4-to-1 (e.g., 9600bps throughput on a 2400bps V.22bis modem). While MNP7 was proposed by Microcom for consideration during the development of V.42bis, as well as a number of other techniques, the Lempel-Ziv technique as enhanced by British Telecom and Hayes was selected because of its superior performance, reduced microprocessor requirement, ability to quickly adapt to changing data patterns, flexibility to work in varying amounts of memory with proportional degrees of compression, and relative simplicity of design and description. Anyway, I've written about five times what I intended, but simply want to caution you about presenting as facts information with which you are obviously not very familiar. Toby Nixon Principal Engineer, Hayes Microcomputer Products Inc. Standards Committee Representative Chairman, TIA standard committee TR-30.4 Special Rapporeur on Q.14 in CCITT Study Group XVII ----------------------------------------------------------------------------- Toby Nixon, Principal Engineer Fax: +1-404-441-1213 Telex: 6502670805 Hayes Microcomputer Products Inc. Voice: +1-404-449-8791 CIS: 70271,404 Norcross, Georgia, USA BBS: 1-800-US-HAYES MCI: TNIXON Telemail: T.NIXON/HAYES AT&T: !tnixon UUCP: ...!uunet!attmail!tnixon Internet: 70271.404@compuserve.com MHS: C=US / AD=ATTMAIL / PN=TOBY_L_NIXON / DD=TNIXON -----------------------------------------------------------------------------