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Path: sserve!newshost.anu.edu.au!munnari.oz.au!yoyo.aarnet.edu.au!myall.awadi.com.au!myall!blymn From: blymn@awadi.com.au (Brett Lymn) Newsgroups: comp.os.386bsd.bugs Subject: Re: Problems with patchkit 0.2.4 Date: 28 Jul 1993 08:54:59 GMT Organization: AWA Defence Industries Pty. Ltd. Lines: 72 Message-ID: <BLYMN.93Jul28182459@siren.awadi.com.au> References: <1993Jul20.012738.2952@fcom.cc.utah.edu> <CAHvz0.38s@cyb.cojones.com> <BLYMN.93Jul25173659@siren.awadi.com.au> <1993Jul25.220104.13519@fcom.cc.utah.edu> NNTP-Posting-Host: siren.awadi.com.au In-reply-to: terry@cs.weber.edu's message of Sun, 25 Jul 93 22:01:04 GMT >>>>> On Sun, 25 Jul 93 22:01:04 GMT, terry@cs.weber.edu (A Wizard of Earth C) said: TL> In article <BLYMN.93Jul25173659@siren.awadi.com.au> blymn@awadi.com.au (Brett Lymn) writes: TL> [ ... modems that lie about the number of CPS they can transfer ... ] >In this case you definitely need the flow control because the data you >pump at the modem may not be uniformly compressible so you can overrun >the modem. Use either stty crtscts or get a slattach that sets this >for you. TL> The initial issue that has yet to be addressed is that the current CTS/RTS TL> implementation in the driver matches neither the Bell-103c standard, nor TL> matches what Telebit and other modems expect. I do not know if it was changed by CGD or what but CTS/RTS flow-control works fine with the setup I have (dataplex modem/386bsd 0.1/CGD com-beta patches...old I know but it works) TL> It also neglects the fact that many compressing modems (but not Microcomm TL> or Telebit) put less RAM in the modem than they should, and then, in clear TL> violation of the MNP-5 definition, turn on flow control *in band* when TL> MNP-5 is on, with no way to turn it off. These modems can *never* be TL> used at high data rates with binary data, since 1/128th of the data stream TL> (statistically) will match the in-band flow control characters "^s" and TL> "^q". The only choice these manufacturers would have would be raising the TL> price of their modems to match their competitors by way of adding enough TL> RAM that buffer overruns don't occur... then why buy a knock-off when you TL> can buy a real Microcomm (since they invented MNP)? In modems, you will TL> definitely get what you pay for. Why buy MNP? IMHO it has too many problems to be worth it. Apart from, as you correctly state, the implementation varying between manufacturers (I have experienced some MNP5 modems not talking to each other at all) but also MNP will happily compress the data irrespective of whether the data size is increased by the compression or not. Much better to get a v.42bis modem, they seem more reliable (from my experience) and do not try to compress uncompressible data. Besides from what I see of the modem market MNP is a bit passe most high end ones support v.42bis. As for in-band flow control, I have an option on my modem to turn it off, I have done so. TL> In any case, it is not safe to use CTS/RTS flow control until the driver TL> has been fixed, and it hasn't been fixed yet. When* it has been fixed, TL> *then* your advice will be applicable. Ummmm depends, the problem you stated is correct if you are accepting incoming calls on a 386bsd system with a compressing modem. In this case I agree there is a possibility of a security problem BUT I only use my modem for outbound v.42bis slip traffic. I can see no problem with this. TL> Until then, don't set the connection to the modem to 19200 baud unless you TL> *know* the modem will *always* be able to push 1920 characters a second TL> down the line. I run my link at 38400 (I have a 16550 and some com patches). I was able to quite easily destroy my slip link by attempting to ftp stuff from my home machine to work without flow control - the ftp would just hang and time out. With CTS/RTS flow control I can run my link at 38400 without problems (In fact I have a friend with a DOS box that had the same problems using z-modem, the same fix worked for him) I think you need to qualify your advice Terry. From what you said RTS/CTS on an incoming line could be a BAD THING, I can see not problem with using it on an exclusively out-going line. Comments? -- Brett Lymn