Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!elroy.jpl.nasa.gov!lll-winken!aunro!alberta!edson!news From: ewaniu@ee.ualberta.ca (Darren Ewaniuk) Newsgroups: comp.sys.amiga.datacomm Subject: Re: What's the difference between a Supra MNP and MNP-plus? Message-ID: <1991May19.211752.16918@ee.ualberta.ca> Date: 19 May 91 21:17:52 GMT References: Sender: news@ee.ualberta.ca Organization: University of Alberta Electrical Engineering Lines: 105 In article Reid_Bishop@a68k.UUCP (Reid Bishop) writes: >In a message dated Fri 17 May 91 05:50, Billsey!nesbbx@agora.uucp (bill Sey >wrote: > BS> But there's a difference on precompressed files... With MNP5, you get an BS> actual *slowdown* on BS> precompressed files, since it doesn't know enough to shut itself off > >I disagree here. In theory, this _should_ be true, but tests I have >conducted prove just the opposite. My BBS has MNP-5 modems on all lines, and >tests show that file transfers of compressed files (typically LHArced >files...) are _always_ faster using MNP-5 than not. My BBS is locked at 9600 >baud regardless of the connect rate, so BBS output is always constant. If I >call my BBS with straight 2400 baud, I get around 240 CPS under ideal >conditions. If I call using MNP-5, I get closer to 250-260 CPS, and >sometimes better when downloading LHarced files. > >In addition, I used to run a straight 2400 baud modem on the FIDO line, and >transfers never went over 240 CPS. Now, they go well over 250 CPS, again >these files are LHarced. These transfers are with a USR DS modem on the >other end. > >In a sense, MNP5 _can_ and _does_ improve transfer rates on compressed files. Yes, compared to straight 2400, but not as much as turning compression off but leaving MNP4 active (see below). BS> You'll get that with either modem, although if you're transfering BS> compressed files, you'll want to disable the MNP5. > >I would run tests before actually disabling MNP5 Turn off compression only, and you'll see the difference. MNP4 increases throughput of a 2400 Supramodem Plus to about 272 CPS. This is due to the stripping of start/stop bits, and transmitting everything in packets. However, MNP5 compression DOES expand archived files. The net result is that archived files have a lower throughput for MNP5 as opposed to MNP4. MNP5 rates are close to the 250 CPS or so that you stated above. Compared to MNP4 (272 CPS) it is slower. However, you do gain a bit over straight 2400 baud files (232 CPS) because of the MNP4 packetizing that is part of MNP5. But, since all MNP5 modems also do MNP4, to get maximum throughput, you will want to turn MNP5 data compression off to use MNP4. With the Supramodem Plus (or MNP), you can do this with the AT command %C0. This can be in your startup string, or you can place it in your dial command string after the AT and before the D###-####. If you are using the excellent JR-Comm telecommunications package, then you can put this in the modem parameters' alternate dial prefixes and then select this alternate prefix, so that this will be used only for the boards that you download archived files from. Since you run a bulletin board, I would suggest that you disable compression in dial-out mode only, and put this in your dial command string rather than the modem setup string, then tell your users how to disable compression on their systems for file transfer. This will then enable them to use compression when they log on to read messages, and by disabling compression from their end, they could increase throughput when they know they are going to download archived files. However, V.42 modems are a lot simpler, since you just don't have to worry about compression or not, because it will never decrease throughput like MNP5 does. That all said, I'd like to add my three months' experience with my Supramodem Plus to the original purpose of this thread. First, I would probably recommend against the average person upgrading to a MNP/V42 modem if you already have 2400 baud. You don't get much extra for throughput. I've never seen the Supramodem Plus go above about 520 CPS for text, and about the maximum for archived files is 272 CPS. All you gain is about 40 CPS over a normal 2400 baud modem. Bulletin board sysops could use the extra speed a bit more, but most already use the 9600+ baud modems. For the new modem user, or for those upgrading from slow 300 or 1200 baud modems, MNP or V42 could be useful. If you intend on a lot of text reading it proves useful (and since this is usenet, most of you do a lot of text reading!). If you intend to mainly download, only go MNP or V42 if you want to spend the extra money, as there won't be much gain. Finally, If you do decide to go for an error correcting modem, I'd probably recommend the V42 one, (a Supramodem Plus over a Supramodem MNP), as it is faster for text and does not decrease throughput in compression mode. (eliminating the need to disable compression while downloading) One final note: MNP and V42 are quite well supported for dialing into local bulletin board systems. All USRobotics modems that I know of support at least MNP4, with about half supporting MNP5/V42. Most other 9600 baud systems also support at least MNP4. However, there are some boards that are just plain 2400, and no modem will increase this speed. Before buying that MNP or V42 modem, be sure that the main systems that you will use will support it. I hope this helps. -- // AMIGA Darren Ewaniuk Graduating student of \\ // the power ewaniu@bode.ee.ualberta.ca University of Alberta \X/ is yours! Proud Amiga 2000 owner Electrical Engineering program