c60b-1eq@e260-1g.berkeley.edu (Noam Mendelson) (04/17/91)
In article <1991Apr16.110136.6239@wam.umd.edu> bjahn@wam.umd.edu (Guess ??? ) writes: >In general, what is the standard in 9600 modems, and is there much difference >in int/ext modems beside personal preference? Most 9600 bps modems today are V.42bis. External/internal is really a matter of personal choice. > What is difference between v32, v32.bis, v42, v42.bis and MNP5? The MNP (Microcom Networking Protocol) is a protocol which is available on various levels (1-10). Each level has the benefits of its predecessors plus some added features. All levels incorporate error correction for error-free transmission. MNP-4 is a slight improvement over MNP-3, which strips the start and stop bits before transmitting data. The modem on the other end adds them before relaying the data to the serial port. On the average this will increase throughput by a concrete 20% or so. By concrete I mean that this value doesn't change and is independent of the type of data being transmitted. MNP-5 also incorporates data compression which can increase throughput by up to 100%, depending on the type of data transmitted. Text data will be transmitted approximately 2x faster than if you were using MNP-4. Compressed data (i.e., .ZIP files) will take _longer_ to transmit since the MNP-5 protocol is 'dumb' in that it attempts to compress all of the outgoing data. CCITT V.32 is a protocol designed for 9600 bps modems that doesn't offer the error control and data compression that is demanded by most of today's users. CCITT V.42 uses the LAPM (Link Access Procedure for Modems) error control protocol to insure that transmissions are error-free. CCITT V.42bis adds data compression that yields up to a 4x increase in throughput. Unlike MNP-5, V.42bis is a 'smart' protocol which only compresses data when the resulting block is smaller. Therefore, there is no decrease in throughput if compressed data is transmitted. >What would be a good buy for a modem that won't be outdated or will be off >standard in the future? Before true standards such as CCITT V.32 and V.42, 9600 bps modems used different protcols which made communicating a nightmare. You had to buy modems from the same manufacturer if you wanted to be sure that they would communicate effectively. However, since the introduction of CCITT standards, this problem has reduced in magnitude. So I would recommend that you buy a modem which offers V.42bis, V.32 and MNP-5. Although MNP-5 is an inferior protocol which will be obsoleted soon by V.42bis, many sites today offer only MNP-5 and not V.42. And MNP-5 is better than nothing. I admit that I know very little about HST modems. I believe they offer 14Kbps connections, but I may be wrong. -- +==========================================================================+ | Noam Mendelson ..!agate!ucbvax!web!c60b-1eq | "I haven't lost my mind, | | c60b-1eq@web.Berkeley.EDU | it's backed up on tape | | University of California at Berkeley | somewhere." |
sjs@gnv.ifas.ufl.edu (04/20/91)
From: bjahn@wam.umd.edu (Guess ??? ), University of Maryland at College Park >I am wondering about the various 9600 modems. Escpecially the US Robotic >modems. What is the difference between the USR v.32 modems and the HST modems? >In general, what is the standard in 9600 modems, and is there much difference >in int/ext modems beside personal preference? > What is difference between v32, v32.bis, v42, v42.bis and MNP5? >What would be a good buy for a modem that won't be outdated or will be off >standard in the future? > Thanks in advance! All I know (others will have to fill in the blanks): V.21: CCITT standard for 300 bps modems. V.22: CCITT standard for 1200 bps modems. V.22 bis: CCITT standard for 2400 bps modems. V.32: CCITT standard for 9600 bps modems. MNPx: MNP = Microcom Networking Protocol, a modem error-correction protocol. CCITT: Consultative Committee International Telegraph and Telephone. An organization established by the United Nations to develop worldwide standards for communications technology. +---------------------------------------------+------------------------------+ | ~~~ Borco | "Time to wake up! | | / \ ~~~ at the Mountains of Madness | Time to rise!" | | / / \ | | | / / \ Bitnet: sjs@ifasgnv | - Silver Lady, | | / \ Internet: sjs@gnv.ifas.ufl.edu | Intergalactic Touring Band | +---------------------------------------------+------------------------------+