MARX@vms.huji.ac.il (06/04/90)
Hi Netters, Recently I purchased the ATI 2400etc. Modem, In the brochure it says the MNP class 5 Data Compression abilities and also, the CCITT V.42 Error Control Protocol. I am starting to get mixed between the v's the MNPs and the x's. can anyone explain what is the difference, what are the features and what's good and what's bad on those protocols? Michael M. Marx, The Hebrew Univ. Of Jerusalem, ISRAEL marx@vms.huji.ac.il / marx@hujivms.bitnet
amigo@milton.acs.washington.edu (Michael Robertson) (06/05/90)
In article <2669790120204258@vms.huji.ac.il> MARX@vms.huji.ac.il writes: >Hi Netters, > >Recently I purchased the ATI 2400etc. Modem, In the brochure it says the >MNP class 5 Data Compression abilities and also, the CCITT V.42 Error >Control Protocol. >can anyone explain what is the difference, what are the features >and what's good and what's bad on those protocols? 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.). 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<. 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). 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.
tnixon@hsfmsh.UUCP (Toby Nixon) (06/07/90)
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 -----------------------------------------------------------------------------
oneill@bu-tyng.bu.edu (Brian O'Neill) (06/12/90)
In article <3931@milton.acs.washington.edu> amigo@milton.u.washington.edu (Michael Robertson) writes: >In article <2669790120204258@vms.huji.ac.il> MARX@vms.huji.ac.il writes: >>Hi Netters, >> >>Recently I purchased the ATI 2400etc. Modem, In the brochure it says the >>MNP class 5 Data Compression abilities and also, the CCITT V.42 Error >>Control Protocol. >>can anyone explain what is the difference, what are the features >>and what's good and what's bad on those protocols? > > 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.). >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<. > Sorry, but you are a bit mistaken. MNP is a suite of protocols. Levels 1 through 3 deal with error-correction, as does V.42, CCITT's standard error-correcting protocol. MNP levels 1 and 2 did error-correction with a loss on throughput. Level 3 managed to keep the same throughput. Level 4 added variable-sized packets. Level 5 is not an error correcting protocol, but a data compression scheme which can increase throughput up to 100%. CCITT's V.42bis is a similar but better and I believe offers up to 200% throughput. MNP Level 7 is also a data-compression scheme offering approximately the same throughput, but isn't very common. V.42 if fact includes MNP levels 1 through 4, so it is compatible with MNP class modems as far as error correction goes. > 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). > Unfortunately, CCITT's V.XX naming can be difficult to understand at times. V.32, as Mr. Robertson stated above, is a method of communication between hish-speed modems. V.42, on the other hand, is a method of error-correction between modems regardless of speed. V.XXbis is usually some sort of extension to a previous standard. The standard for 2400 baud communications is V.22bis, whereas the standard for 1200 baud is V.22 in Europe, but Bell 212A in the United States. There is also a variety of synchronous standards such as V.29 for leased-line applications. > 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. > V.42bis is what you are referrring to here. V.42, as stated above, is only error-correction. V.42 can actually work with MNP version 5 and 7 to get better throughput. Incidentally, I own an ATI 2400etc/e as the original poster has. It is an excellent modem. It has V.42 error-correction and MNP level 5 compression. I just talked to ATI last Thursday, and there is a planned upgrade for V.42bis, but it is still in the works, and may be available in a month or so. -- =========================================================================== Brian O'Neill - Boston University Corporate Education Center, Tyngsboro, MA UUCP: {decvax|ulowell}!bu-tyng!oneill Internet: oneill@bu-tyng.bu.edu (508) 649-9731 x14