Path: utzoo!attcan!uunet!wang!bu-tyng!oneill From: oneill@bu-tyng.bu.edu (Brian O'Neill) Newsgroups: comp.dcom.modems Subject: Re: v.42? v.32? v.va espana!! Message-ID: <4013@bu-tyng.bu.edu> Date: 11 Jun 90 18:33:22 GMT References: <2669790120204258@vms.huji.ac.il> <3931@milton.acs.washington.edu> Organization: Boston University Corporate Education Center, Tyngsboro MA Lines: 67 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