lord_zar@ucrmath.ucr.edu (wayne wallace) (11/16/90)
Hello there. I'm struggling along on 2400 baud (GVC, not GVP, Super Modem 2400) and have been considering a modem upgrade. I saw a recent reply to some article in alt.bbs mentioning such modes of operation for a 9.6K modem as v.22, v.24, v.30, v.44, etc. I need: A nice summary of the various Amiga/IBM(bleah!) compatible modems (I do have my RS-232C cable) which can operate at 9.6K and what all the v.## means. Email quite preferred. If other people are interested in knowing such things, I'll post a summary, otherwise, I do thank you for your help. And yes, my modem prog can handle 9.6K. Anyways, Pax, Wayne.
Marcus@cup.portal.com (Mark W Shnayer) (11/18/90)
The following is captured from local BBS I call and re-edited to remove all the BBS prompts. Hope this helps clear up some of the confusion of Modem Standards. You know the old saying.... Standards are great, thats why theres so MANY of them! --------------------------------------------------------------------------- What is v.32, v.42, and v.42bis? The international standards committee, CCITT, based in Geneva, has defined the following, totally different standards, which are commonly confused. This is a definiton, in my own words, and is accurate: V.32: V.32 is a 9600 bps standard employing trellis coded quadrature amplitude modulation at 2400 baud, encoding 4 bits per baud. Using echo cancellers, it attains full duplex. In plain language, it means that v.32 is a 9600 bps data transmittion protocol. V.42: V.42 is an error correction protocol, more commonly known as LAP-M, or link access protocol for modems. It ensures that transmission of data is done without error. Annex A to this standard includes MNP 2 through 4, another common error correction method from Microcom. This protocol, v.42, also increases throughput by eliminating excess start and stop bits. V.42bis: V.42bis is a data compression standard, using lumpel-ziv encoding, which typically can achieve a 4:1 compression ratio, meaning four times as much data can be sent for the same actual transmission rate. Included in its Annex A is MNP 5, which ensures backwards compatibility with this older 2:1 ratio compression. I hope you understand this, and no longer call a v.32 modem a v.42 modem, because just because it's v.42 doesn't mean it's v.32. ------------------------------------------------------------------------------ What is HST and PEP? HST and PEP, like V.32, are high speed modulation techniques. However, HST and PEP are proprietary techniques belonging to US Robotics and Telebit, respectively, and thus require licencing before other manufacturers can use them (such as Ven-Tel). Here is what they are: HST: The HST modulation is similar to V.32 in the fact it uses a Trellis Coded Quadrature Amplitude Modulation technique. Unlike the V.32, it is not full duplex, with either a 300 or 450 bps Frequency Shift Keyed reverse channel. This makes it an "Assymetrical Duplex" modem. The main TCM/QAM channel encodes up to 7 bits per baud, at 2400 baud, with one bit used as parity, forming a maximum of 14,400 bps in one direction, with up to 450 in the reverse. The modem will switch channels as the data demands. PEP: The PEP modulation is totally unsimilar to both V.32 and HST. It uses DAMQAM, which I believe stands for Dynamic Adaptive Quadrature Amplitude Modulation. Effectively, it splits the phone line into 511 sections, and puts a 34 baud carrier on each, encoding up to 4 bits per baud, achieving maximum speeds of 18,000 bps (uncompressed). Each channel can be going one direction, so full duplex operation can be had at 9,000 bps. But, they also use something called "Adaptive Duplex" meaning that the various bps rates will be determined by the data being sent. If there is nothing going one direction, it will go 18,000 in that direction. However, if full duplex is needed, it will go 9,000 either way, with increments in between. Thus, maximum throughput is always ensured. As a note of curiosity, HST stands for High Speed Transmission, and PEP for Packetized Ensemble Protocol. -------------------------------------------------------------------------- What is MNP? MNP stands for Microcom Networking Protocol. They vary. MNP 1: This was the first data correction. It slowed down the transmission, due to overhead. MNP 2, 3: Further refinements on MNP 1. MNP 4: This data correction protocol eliminated the leading and trailing start and stop bits, thus guarenteeing error-free data, at about a 15% data throughput increase. MNP 5: This is a data compression protocol. It compresses data using RLL - I mean RLE- Run Length Encoding- type of protocol, I believe, attaing about a 2:1 data compression. MNP 6-8: I'm not sure; I even have an MNP 6 modem! MNP 9: This was the prime competitor against V.42bis. It is also a 4:1 data compression standard. MNP 10, 11: I believe these were developed for use by cellular modems, providing error correction and data compression standards more strict, yet more lienient, suitable for terrible cellular lines. Marcus@cup.portal.com (i think....)