Path: utzoo!mnetor!tmsoft!torsqnt!news-server.csri.toronto.edu!rpi!usc!elroy.jpl.nasa.gov!jarthur!nrossi
From: nrossi@jarthur.Claremont.EDU (Nick Rossi)
Newsgroups: comp.sys.cbm
Subject: Re: Kermit Question
Message-ID: <11595@jarthur.Claremont.EDU>
Date: 7 Apr 91 22:26:15 GMT
References: <1991Apr5.201357.7658@noose.ecn.purdue.edu> <11571@jarthur.Claremont.EDU> <1991Apr7.205934.20408@alchemy.chem.utoronto.ca>
Organization: Harvey Mudd College, Claremont, CA 91711
Lines: 46

In article <1991Apr7.205934.20408@alchemy.chem.utoronto.ca> mroussel@alchemy.chem.utoronto.ca (Marc Roussel) writes:
>In article <11571@jarthur.Claremont.EDU> nrossi@jarthur.Claremont.EDU
>(Nick Rossi) writes:
>>For standard Kermit, the maximum packet length is 94 bytes.  Yes, there is
>>a lot of overhead in Kermit which makes it a very inefficient protocol (which
>>characters and such.  I seem to recall using a Kermit program on an IBM which
>>was sending 1024 byte packets, but perhaps I was looking at the wrong thing
>>on the screen or something, as I haven't been able to reproduce it.

>     I don't think that this is quite right.  The packet length in Kermit is
>arbitrary.  In fact, the initial handshake between the two computers
>includes packet length information.  (Transmission is then undertaken at
>the largest packet length allowed by both Kermits.  The "set send/receive
>packet length" commands merely tell Kermit how large a packet you wish to
>allow it to use.  Why you'd ever want this to be less than the maximum,
>I don't know.)  Kermit-65 can't handle packets any greater than 96 bytes
>(according to my manual).  This maximum has to do with the amount of memory
>available for buffering I think.  On the other hand, the latest versions of
>MS-Kermit and C-Kermit can handle packets up to 1Kbytes.
>     I hope I got this right.  (I'm relaying second-hand information
>here, not first-hand knowledge.)  If I didn't, I hope someone will set me
>straight.

				Marc R. Roussel
                                mroussel@alchemy.chem.utoronto.ca


The reason Kermit (standard Kermit, anyway) won't support packet lengths
longer than 96 bytes is because only one byte in a packet is
available for negotiating the packet size.  This byte must be in the
printable character range (as are all bytes in Kermit packets), and so
it must have a value between 32 and 126.  Subtract 32 from this range, and
you have a value between 0 and 94.  The packet length represents the
length of everything after the length byte, so the actual maximum size is
96 (packet plus length byte plus start-of-header).  The maximum length is
determined by the buffering size of the receiving computer.  For some systems
this is not a problem, but again, Kermit was designed to work on ANY
environment, some of which may have smaller buffers.


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        Nick Rossi, '93                |              SONY               |
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      Harvey Mudd College              |   Because caucasians are just   |
 (ooo HELL is a place on earth)        |         too damn tall.          |
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