more on the HFC saga
Marc Weinstein
mhw at fithp
Wed May 22 14:21:43 AEST 1991
>From article <103431 at becker.UUCP>, by bdb at becker.UUCP (Bruce D. Becker):
> In article <1991May18.170853.2649 at fithp> mhw at fithp (Marc Weinstein) writes:
> |From article <101141 at becker.UUCP>, by bdb at becker.UUCP (Bruce D. Becker):
> |
> |Well, sort of...The place where HFC on the UNIXPC really works is when your
> |PC can send chars out faster than the remote modem can handle them. For
> |instance, if either the DCE-to-DCE speed or the DCE-to-DTE speed on the far
> |end are less than the host DTE-to-DCE speed, then the modems will apply
> |HFC and the UNIXPC will properly halt data transmission. HFC does NOT
> |seem to work for handling overflow on incoming PC ports.
>
> I'm having a hard time understanding why
> speed changes are necessary.
Most modems now support the ability to nail your port rate to something
(9600 or 19200) and vary the modem-to-modem rate to suit the remote
system. This makes administration much easier - one rate in gettydefs,
one rate in your Systems file.
> For most
> things compression is irrelevant, or they
> are done in the host as in news batches
> or uucp files. Doing compression in the
> modem seems wasteful of resources due
> to the fact that uncompressed data gets
> pumped thru the serial interface with
> an interrupt service routine invocation
> for each character!
Hmmm - don't understand the logic here. If I want to send a file to
someone, and I know my modem will compress the file anyway, then I don't
have to bother with compressing the file before the fact. Less wory,
less bother.
> Naturally on a little beastie like the 3B1
> this is pretty ferocious CPU consumption
> at high baud rates. Better to have direct
> end-to-end transfers at the same speed,
> with no buffering in the modems.
True, if both ends use the same speed.
--
Marc Weinstein
{simon,royko,tellab5}!linac!fithp!mhw Elmhurst, IL
-or- {internet host}!linac.fnal.gov!fithp!mhw
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