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From: phil%portal@portal.UUCP
Newsgroups: net.dcom
Subject: Re: Response to <1703@sdcsvax.UUCP> <11465@amdcad.UUCP>
Message-ID: <142@portal>
Date: Wed, 30-Apr-86 13:32:00 EDT
Article-I.D.: portal.142
Posted: Wed Apr 30 13:32:00 1986
Date-Received: Sun, 11-May-86 16:29:22 EDT
References: <1703@sdcsvax>
Lines: 35

In article <280@mit-vax.UUCP>, romkey@mit-vax.UUCP (John Romkey) writes:
> 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
...
> >> 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
> 
> 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
> ARPA: romkey@borax.lcs.mit.edu	Boston, MA, 02142

I talked to someone from Telebit recently and depending on the PC involved
the throughput limit can be PC system/software related, but in any case will
be related to the higher level acknowledgements for protocols such as
xmodem.  The problems of protocol interaction can I was told be solved by
chaging the high level protocol to avoid the unnecessary acks.  Some of the
PC throughput limits can be avoided by writing software that does not use
some of the more CPU expensive system facilities such as a BDOS call or
Macintosh 'resources' for doing things like updating the screen.

If anyone is considering trying to use V.32 modems I would recommend you 
try them first. I have heard from users there are big difficulties getting
the things to work over the switched network and they may become unusable
when the interoffice (CO) links start using lower bandwidth (32k) adaptive
PCM.  Anyone got any experience or info on this?