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- From: jwoods@cmptrc.lonestar.org (Jeff Woods)
- Subject: Re: Why would Zmodem not work on a 286-12?
- Message-ID: <BxCBt3.KCz@cmptrc.lonestar.org>
- Date: Sat, 7 Nov 1992 10:00:39 GMT
- References: <1992Nov5.080031.23093@netcom.com>
- Organization: CompuTrac Inc., Richardson TX
- Keywords: modem serial
- Lines: 49
-
- In article <1992Nov5.080031.23093@netcom.com> jeffgus@netcom.com (Jeffrey Gustafson) writes:
- | A friend of mine has a Everex 286-12. When he downloads with
- |the zmodem protocol it gives CRC errors every 10 seconds or so
- |(irradic). It is a problem with his 2400 w/MNP-4 and his
- |V.32bis/V.42bis modem. The both modems were in error-correcting
- |modes. I took all cards that could interfere (scanner, mouse, Sound
- |Blaster) and removed the config.sys and autoexec.bat and nothing
- |helped. When he used the same modem and I/O card in a Delta Gold
- |286-10, he had no problems. He has no problems or errors with the
- |files when he uses Ymodem/G (no CRC errors when unzipping). There are
- |no visible errors when he's online.
- | What could be the problem? I have no clue. Any suggestions?
-
- The problem is almost certainly, that hardware flow control is not
- functioning correctly. Hardware flow control is fairly tricky to
- set up correctly, especially without modem specific and comm software
- specific manuals. When using hardware datacompression (ala v.42bis or
- MNP5 or LAPM) or even error correction (ala MNP 2-4, or v.42, or LAPM)
- transfer rates in excess of the rated speed of the modem connection are
- not only possible, but likely. Getting hardware flow-control working
- and "nailing" the speed at a high rate between the modem and PC is the
- ideal solution, but doing so is non-trivial. I don't think I can explain
- how to solve the problem without being very modem and software specific.
-
- The reason Ymodem doesn't have the problem is because Ymodem sends packets
- all of which are acknowledged by the receiver before the next packet is
- sent. Zmodem normally doesn't do this. It sends a stream of data and
- only retransmits if it gets an error message from the other end. In other
- words, Ymodem has a pause and wait point frequently, but Zmodem never waits
- unless there's a problem (like data overrun).
-
- Some possible alternatives to the ideal, but difficult hardware flow control
- solution include:
-
- Use Ymodem or other packet type protocols.
-
- Disable data compression in the modem (error correction may have to go too)
-
- Find someone local who can help solve the problem.
-
- Hope that someone else on the net can explain it better than I can.
-
- I hope you get it working well.
- I love those high speed zmodem transfers!
- Good Luck and Happy Modeming!
- --
- jwoods@cmptrc.lonestar.org (Jeff Woods at CompuTrac, Inc.)
- stdinfo: "My opinions are my own."
- "You don't need a programmer so much as you need a exorcist." - A. Chambers
-