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From: romkey%mit-vax@mit-vax.UUCP
Newsgroups: net.dcom
Subject: Re: Response to <1703@sdcsvax.UUCP> <11465@amdcad.UUCP>
Message-ID: <280@mit-vax>
Date: Sun, 27-Apr-86 04:23:00 EDT
Article-I.D.: mit-vax.280
Posted: Sun Apr 27 04:23:00 1986
Date-Received: Sun, 11-May-86 16:02:51 EDT
References: <1703@sdcsvax>
Lines: 29

In article <137@portal.UUcp> phil@portal.UUcp (Phil Sih) writes:
>In article <1703@sdcsvax.UUCP>, brian@sdcsvax.UUCP (Brian Kantor) writes:
>> In microcomputer file transfer use (kermit and xmodem) it works pretty
>> well.  Unfortunately, it doesn't seem to run all that fast!  Apparently
>> the packetising and turnaround delay are enough that the protocol
>> doesn't run at anywhere near full speed because its waiting for the
>> acknowledgement of the previous packet.  Undoubtably a protocol that
>> allows for more than one packet to be in flight would work much
>> better.  Telebit has a version of Crosstalk for the IBM PC that they
>> claim makes very fast file transfers - I guess its tuned for use with
>> their modem's time delays and error correction characteristics.  I
>> didn't test it.
>
>The limit on file xfers in this case may not be the modem/comm line. I heard
>Telebit needed the special version of Crosstalk because the PC could not
>keep up with the data rate from the modem. Also, since the Trailblazer
>protocol is reliable, there is no need for host level packet acks. You
>just dump the data and it comes out correct on the other end. That's what
>their "Packetized Enesmble Protocol" is supposed to do for you. This makes
>me think they just cut out the file level packet acks all together in
>their Xtalk.

Must be something to do with the way Crosstalk handles interrupts, then,
because I've run a (normal) PC's serial line at 19.2kbps without much problem.

John Romkey			FTP Software, Inc.
(617) 868-4878			PO Box 150
UUCP: romkey@mit-vax.UUCP	Kendall Square Branch
ARPA: romkey@borax.lcs.mit.edu	Boston, MA, 02142