Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!ucsd!ucbvax!agate!shelby!decwrl!wam.UMD.EDU!stripes
From: stripes@wam.UMD.EDU
Newsgroups: comp.protocols.misc
Subject: Re: Xmodem problems at high speeds?
Message-ID: <8905210046.AA04404@cscwam.UMD.EDU>
Date: 21 May 89 00:46:21 GMT
References: <187@chiron.UUCP>
Organization: (Who me?)
Lines: 22

In article <187@chiron.UUCP> capron@chiron.UUCP (Michael P. Capron) writes:
>
>I had heard a rumor that Xmodem breaks down at high baud rates (>2400),
>something about the checksum algorithm.  Does anyone know if there is any truth
>to this? 

The checksum does not cause it to breakdown at high speeds, but is not as good
at finding errors as a CRC (a 16-bit CRC is supported by most XMODEM programs).
It is not a good protocall for higher speeds, because the RTD becomes more and
more important (or over LONG distantances, or through packet switched/mutiple
networks, etc.).  Ymodem (basicly 1K blocked XMODEM) is better at this, but
still suffers with high RTD (Round Trip Delay).  ZMODEM does not suffer from
this (except durring error recovery, I think, and at inital handshakeing time),
it also has a bunch of other goodie, but is a bit harder to implment.  Sorces
for a PD implimation of Xmodem, Ymodem, and Zmodem are all available
*somewhere*, mabie SIMTEL20.
-- 
           stripes@wam.umd.edu
      Josh_Osborne@Real_World,The
      "The dyslexic porgramer"
        "Bones, help this man, He's hurt!"  <->
                 <->  "Dammit, Jim, I'm a DOCTOR, not a.... Oh, yeah."