Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ihnp4!ptsfa!lll-lcc!pyramid!csg From: csg@pyramid.UUCP Newsgroups: comp.dcom.modems Subject: Re: 9600 bps dialups Message-ID: <2886@pyramid.UUCP> Date: Fri, 5-Jun-87 10:09:55 EDT Article-I.D.: pyramid.2886 Posted: Fri Jun 5 10:09:55 1987 Date-Received: Sun, 7-Jun-87 02:08:52 EDT References: Reply-To: csg@pyramid.UUCP (Carl S. Gutekunst) Distribution: world Organization: Pyramid Technology Corp., Mountain View, CA Lines: 111 Here's my by-now-somewhat-dated article on ultra-high speed modems, that I've sent out to various people from time to time. I hope it helps. I assume you are interested in what you can buy today for under $2000; Codex will sell you a marvelous V.32 9600 bps full duplex modem for $3500 or so.... Here's the four modems I'd suggest that you take a look at, in my order of preference. All have been demonstrated to provide dependable UUCP transfers at speeds of 750 characters per second or greater. All provide error correction. All have many quirks that are a direct consequence of their design: you really need hardware flow control; all use a packetizing strategy at high speed; you pretty much have to use the UUCP 'f' protocol or Zmodem; you must provide your own end-to-end error correction; most have gone through *many* firmware revs, so be sure to get the latest; all are incompatible with everything else. All support the Hayes command set and provide line progress monitoring. - Telebit Trailblazer ($1445). Provides Bell 103, Bell 212, V.22, V.22bis, and a proprietary multi-carrier modulation technique that dynamically adjusts the speed, based on line conditions; theoretical maximum is 18000 bps. High- speed is half duplex, with a turnaround delay that makes interactive sloppy but passable. Real data rate varies from 900 cps (California to New Jersey) to 1550 cps (locally). It can drop to 500 cps or less on really bad lines (which is still much better than the fallback of the other modems), but is otherwise generally unaffected by line noise. This is the only 9600bps voice-grade modem I've used that is dependable in- ternationally; works well to the Pacific Rim, poorly to Europe. Excellent performance with SLIP; Kermit unusable due to the packetizing. Reliable. The modem is also made by DCA under the name "Fastlink." Incidentally, the Trailblazer is also by far the best V.22bis modem I've ever tested -- even better than the AT&T 2224. Anyone looking for a really solid industrial V.22bis modem should look seriously at the Trailblazer. Telebit is also promising MNP Level 3 on the slow speeds Real Soon Now. - Racal-Vadic 9600VP ($1195). Provides Bell 103 and 212, plus 9600bps V.29 QAM half-duplex MNP level 3 (with Vadic mods). Fallback to 4800 and 2400 if line conditions are bad. In high-speed mode, the modem automatically switches be- tween 212 and V.29, depending on the amount of buffered data; interactive performance is exceptionally good. V.29 is still half duplex. Data rate is a very constant 740 cps with good lines. Sensitive to line noise. Excellent performance with SLIP, except poor with Telnet; Kermit unusable. Uucico 'g' protocol actually gets errors because of the modem's sloppy implementation of flow control. Reliable, although not as well built as the Trailblazer. - U.S. Robotics 9600HST ($999). I have not used one of these yet (I'm getting one soon) but the hearsay follows. Bell 103, 212, V.22, V.22bis; high-speed is V.32 trellis-coded 9600bps forward channel, with 7200, 4800, and 2400bps fallback, 300bps back channel, and MNP Level 3 for error correction. Inter- active performance is good. Data rate around 900cps. Extremely sensitive to line noise. Kermit is passable. Unreliable. This is a new product, and the initial units have been flakey. - Microcom AX9624 ($999). Again, I have not used one of these, although I've been satisfied with other Microcom products. Bell 103, 212, V.22, V.22bis, with MNP Level 6 that Microcom claims will get up to 19.2Kbps. Real data rates vary widely, being sensitive to the data passed, although I've never seen anyone do better than 900cps. Interactive is good. Somewhat sensitive to line noise. Kermit works OK, and even the 'g'-protocol will truck along at a reasonable clip. VERY UNRELIABLE. Every one of the half dozen people I know who have these report many DOAs (high as 75%) and many failures in use. It appears that they overheat and burn themselves out. Surprising, since the chassis is the same as for the AX2400, which was quite reliable. Possibly Microcom tried to stuff too much logic in their sealed metal box. Finally, I have a friend who swears by his Codex 208 synchronous half-duplex V.29 9600bps modems, with a $100 Inmac asynch protocol converter. Interactive is claimed to be as good as with conventional modems, since the turnaround is very fast and there is no packetizing. No error correction either, but a fair case can be made that error correction doesn't belong in the modem. These may be available used at bargain-basement prices (they list $1500 or so, but are widely used by IBM shops), so they could be just the thing for users dialing in from home. ______________________________________________________________________________ I you want to buy a modem today, I'd give the edge to Trailblazer. It is the fastest and most dependable of the ultra-high-speed modems, and also the most reliable. Interactive performance is its big weakness, although a sure typist will not be bothered. (Why the %@?&#! Telebit refuses to use just a little of that huge bandwidth for a reverse channel is beyond me.) If you insist on waiting for every character to echo, then you will be happier with the 9600VP; my *BIG* gripe with it is the lack of V.22bis. The USR 9600 HST looks like it will be good when the early production problems are shaken out, although it is much more affected by line conditions than the others. The suicidal tendencies of the AX9624 looks like a design flaw that may require major reworking by Microcom. For all these modems, there is no way of knowing whether or not they'll work from your location until you try them. These high-tech marvels are all subject to line problems and variations to which good ol' slow 1200bps modems are immune. The Trailblazer, the most technologically advanced modem anywhere, is by far the best on paper and appears to have the largest number of successes. Its design also allows most connection problems to be corrected in software, while the others may require hardware changes. (For example, our 9600VP would not work through our ROLM CBX until Vadic hand-tweaked the equalization.) In article (Keith Petersen) writes: >It wouldn't surprise me if the HST becomes the defacto standard for >9600 bps. It beats those pseudo full duplex (really half duplex) modems. Perhaps, but I doubt it and I certainly hope not. I'd really like to see modem manufacturers get off ancient analog standards and develop some modern digital encoding techniques like that used by the Trailblazer. Clearly this technology is in its infancy, but it holds great promise for all kinds of communications applications, if only a few more companies had the will to research it. What good are the current standards when different vendor's modems using allegedly identical standards won't talk to each other? Stuff 'em, and lets get on to the next generation.