Xmodem problems at high speeds?

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3 total messages Started by Michael P. Capron Fri, 19 May 1989 00:58

#965

Author: Michael P. Capron
Date: Fri, 19 May 1989 00:58

9 lines
606 bytes

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? 

				Thanks in advance,
				Mike Capron

...uunet!chiron!capron

Re: Xmodem problems at high speeds?

#966

Author: stripes
Date: Sun, 21 May 1989 00:46

22 lines
1567 bytes

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."

Re: Xmodem problems at high speeds?

#967

Author: Tim Pozar
Date: Sun, 21 May 1989 21:37

16 lines
1100 bytes

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? 
>

    No truth, but turn-around gets a bit ridiculous at speeds
at or greater than 9600 with current high-speed modems.

	    Tim

-- 
 ...sun!hoptoad!\                                     Tim Pozar
                 >fidogate!pozar               Fido:  1:125/406
  ...lll-winken!/                            PaBell:  (415) 788-3904
       USNail:  KKSF / 77 Maiden Lane /  San Francisco CA 94108

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