Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!caip!unirot!halloran From: halloran@unirot.UUCP (Bob Halloran) Newsgroups: net.micro,net.micro.atari16,net.micro.ti Subject: Re: Optimum transmission speed over telephone lines Message-ID: <830@unirot.UUCP> Date: Tue, 8-Jul-86 08:02:30 EDT Article-I.D.: unirot.830 Posted: Tue Jul 8 08:02:30 1986 Date-Received: Wed, 9-Jul-86 02:00:45 EDT References: <1207@mhuxo.UUCP> <542@ecn-pc.UUCP> Reply-To: halloran@unirot.UUCP (Bob Halloran) Organization: Public Access Un*x, Piscataway NJ (The Soup Kitchen) Lines: 42 Xref: watmath net.micro:15014 net.micro.atari16:1268 net.micro.ti:210 In article <542@ecn-pc.UUCP> sandersr@ecn-pc.UUCP (Robert C Sanders) writes: >In article <1207@mhuxo.UUCP> gjphw@mhuxo.UUCP (WYANT) writes: >>and read mention of 9600 bps modems becoming available. Where does >>the retransmission rate due to lost bits negate the higher data >>transmission rate? > >Yes, there are 9600 baud modems out. Two major manufacturers are marketing >them (net- help me with the names!). From the articles that I have read >(PC World, BYTE, MAC World), the modems use a mathematical coding scheme to >encode the data to acheive an equivilant 9600-baud thoughput. Then, they >adjust themselves by testing the line and determining the optimum speed -- >they will drop to lower rates (8400, 5600, 4800, etc) in a continuously >variable manner to get the maximum speed realiably. Because of this constant >variability and change, both ends have to use the type modem from the same >manufacturer, unless of course you set the modems to use the industry standard >speeds of 2400, 1200, or 300. These modems, if I remember right, are Hayes >command set compatible, with extensions for their own capabilities. The modem in question is the Telebit Trailblazer, marketed under an OEM agreement by Digital Communications Assoc. (makers of IRMA PC-3270 card) as the 'DCA Fastlink'. The only difference is the faceplate. The modem uses an on-board 68K plus the TI signal processing chip plus lotsa RAM. It breaks up the bandwidth of the phone line into something like 512 subchannels, then moves data through them at roughly 18kbps. On the receiving end, the subchannels are recombined, CRC checks are performed, and the data stream is presented at 9600 baud. The major advantage of this modem over the CCITT V.32 modems now reaching the market is that under less-than-ideal line conditions (i.e. most of the time), the CPU will drop only those subchannels showing poor signal-to-noise, allowing falloff in increments of < 100 bps. The V.32 modems fall back by halving (9600 to 4800 to ...). It emulates 103, 212 and V.22bis (300, 1200 and 2400 respectively) modems and uses the Hayes command set. Friends have used them and love them for bulk data transfer. In a 'worst-case' test they did, they 'looped back' between two Fastlinks in their office via MCI, SPRINT, and ATT and still got > 7Kb throughput. Bob Halloran, Consultant ========================================================================= UUCP: topaz!caip!unirot!halloran DDD: (201)251-7514 USPS: 19 Culver Ct, Old Bridge NJ 08857 ATTmail: RHALLORAN Disclaimer: I speak for myself. Quote: "No matter where you go, there you are." - Buckaroo Banzai