Modems, the best choice Ready to buy your first modem or upgrading? The following paper tries to explain BRIEFLY about the various choices available. In order of cost, least to most: 1200 Hayes Compatible (Atari has a sale on this) $39.00 2400 Hayes Compatible (This is the most common choice) $89.00 2400+ Hayes Compatible (This modem has MNP5) $120.00 9600 Hayes Compatible (V.32 MNP5 V.42 V.42bis) $350.00 The above prices are as of 08/23/91 and may be more or less at your local dealer. The modems are all External and don't include a RS-232 cable (average cost $8.00) or communications software. Your choice will depend on your pocketbook and what you intend to use it for. Your online time will be less, of course, with the faster modems (more cost). If you do a lot of long distance BBS'ing then your best buy in the long run would be the 9600 baud modem provided that the BBS you call supports it with one of their own. (9600 baud modems just came down in price about $100 and we expect to see more of them installed in BBS systems over the standard 2400 baud modems) If you plan to connect to systems using higher level terminal emulations like VT-100 thru VT-300 or GUI interfaces (Graphical User Interface) you would be advised to purchase a modem with error correction. Transmission Errors can severely affect one of these types of terminal emulations. Line noise and data error when telecomputing are quite common so a special modem is necessary, a modem with ERROR CORRECTION built in. Several types are available; MNP (Microcom networking Protocol) and V.42. Almost all nodes for Genie and Compuserve are now supported by MNP level 4 modems. These provide error free communications when two such modems are connected to each other. One would almost think that they have something planned for the future in the way of GUI interfaces. MNP level 5 provides data compression as well as error correction. With uncompressed files or ASCII transfers you can usually get a 2:1 compression ratio or an effective transfer rate twice the connect rate. For example at 2400 baud your transfer rate could approach 4800 baud. V.42 is an International error correction protocol and is found in the more expensive modems. In any case it's a better and more expensive protocol than MNP4. Usually the more expensive 9600 baud modems have both MNP and V.42 support. V.42bis is an International error correction (V.42) and data compression protocol that provides 4:1 compression on uncompressed data. With ascii or uncompresed files you can get an effective (best case) transfer rate of four times your connect rate or 38,400 baud. Very few computers are capable of transfers over the RS-232 port at 38,400 baud. The ST sure isn't and most 386 and 486 PC's can't either (note: one of the TT's Rs-232 ports can transfer at 91000 baud). For now it's kind of wasted except where your modem falls back to a lower speed because of bad telephone line conditions and your modem carrier is at 2400 instead of 9600 baud. In this case you are still transferring data at an effective rate of 9600 baud when using V.42bis. v.32 is an International standard for 9600 baud modems. In the USA 1200 and 2400 modems are pretty standard but if you are really using the long distance phone lines and calling Europe you may have a problem connecting. There are several standards in Europe that US modems can't connect to unless they support those standards. Most 9600 baud modems support both US and European telecommunication standards. When two modems are connected to each other over the phone line the first thing they have to do is to talk to each other to find out what speed (baud rate) or error correction and Compression protocols they have in common (so they can be used). This is the warbling computer associated tone you hear upon connecting with the other modem. With a 9600 baud modem a try at communication at 9600 baud is attempted. If the correct answering tone isn't received in a few seconds or is corrupted (bad phone line) a 2400 baud tone is generated/sent. This is called fall back. If connection can't be made at 2400 baud then a fall back to 1200 baud takes place. Once the modems establish a common carrier speed the 9600 baud modem tries to establish a common error correction/compression protocol. Starting with V.42bis falling back to v.42 then MNP5 then MNP4 through MNP1. Another nice feature of the 2400+ and 9600 baud modems is that they Auto baud detect and convert the carrier speed to a fixed Rs-232 speed. You can leave your Rs-232 speed at 19,200 and the modem takes care of the rest. You no longer have to watch for the connect speed and change your RS-232 settings. **************************************** In summary if you plan on buying a 9600 baud modem make sure it supports the following: V.32, V.42bis, V.42, MNP 5 Or if a 2400 baud modem connected to a UNIX or other Mainframe then by all means get the 2400+ modem with MNP error correction. If just hobbying over the phone line and the wife controls the purse strings then the Atari 1200 baud modem is probably the only one she will let you buy....but try for the 9600 baud, tell her that you will really be saving money by reducing your on-line (long distance) time . ***************************************