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From: mcc@WLV.IMSD.CONTEL.COM (Merton Campbell Crockett)
Newsgroups: comp.sys.laptops,comp.sys.ibm.pc.misc
Subject: Re: Comm programs, Crosstalk Mk IV
Message-ID: <1991Apr27.154039.6656@wlbr.imsd.contel.com>
Date: 27 Apr 91 15:40:39 GMT
References: <1991Apr21.085326.28167@agate.berkeley.edu> <1991Apr27.031643.23049@wlbr.imsd.contel.com> <1991Apr27.053539.10761@agate.berkeley.edu>
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In article <1991Apr27.053539.10761@agate.berkeley.edu> c60b-1eq@e260-1e.berkeley.edu (Noam Mendelson) writes:
>In article <1991Apr27.031643.23049@wlbr.imsd.contel.com> mcc@WLV.IMSD.CONTEL.COM (Merton Campbell Crockett) writes:
>>				In file transfers through a 2400 baud
>>modem link using 512 byte packets and 3 windows, an effective baud rate of
>>2510 to 2560 is typical transfer rate for text files.  The effective baud
>>rate decreases as you decrease the packet size; however, I haven't noticed
>>any improvement in the effective baud rate as you increase the packet size
>>from 512 bytes.
>
>The 2510-2560 bps figure for text data is due to Kermit's RLE compression,
>_not_ due to windowing.  It's fairly difficult to get around the 240 cps
>maximum for 2400 bps transfers.

Sorry about that.  I should have indicated that setting the windows to 1--ie
disabling the sliding windows option--yields an effective transfer rate in
the 2280-2340 bps range for text data.  Kermit's automatic compression was
involved in the transfers; however, the effective transfer rate was not due
to the effects of compression but the effects of sliding windows.

Probably should have also noted that MS-Kermit 3.10 now provides an automatic
detection and notification of a 7 bit data link in the path between the local
and remote system.  When a 7 bit data link is detected and the file type
is set to binary, the binary data is encoded to traverse the 7 bit data link
segment.  A useful feature when you forget the -8 switch to rlogin.

Another tacit assumption in this discussion is that the remote station is
using C-Kermit 4E, 4F, 5A, or equivalent version of Kermit.  Also, to be
noted is that the remote stations run 2.11 BSD, 4.3 BSD, and VMS 5.1 oper-
ating systems.  (The remote station running C-Kermit 4E is a 4.3 BSD system
which is reached over a transcontinental 56Kb X.25 packet switched link.
I tried it a couple of times but as it doesn't support windows and I had
difficulty figuring out the link latency, the transfer would typically be
aborted due to an excessive delay at some point.)

Another remote station running System V R3 something or another and using
an earlier version of C-Kermit goes Tango Uniform when it finds the window
option in the negotiation packet.

Of the various systems I use only the VMS system has C-Kermit 5A which has
support for windows.  It also requires an rlogin connection from my home
system.

At 9600 and 19.2K, the 1024 packet size improves performance when the remote
station does not use windows or they are disabled over that obtained from
using 512 byte packets.  In my experience the difference is nominal when
using sliding windows.  Performance may decrease with larger packets due
to resource limitations on the remote station.

Merton Campbell Crockett