On  1 Sep 98 at 6:41, Earl Truss wrote:

> At 01:13 AM 9/1/98 -0700, you wrote:
> >And Earl says:
> >>This sounds quite slow.  A typical "average" transfer rate is about
> >>one-tenth of the modem's rating.  That is, a 33.6Kbps (thousand bits
> >
> >"about one-tenth of the modem's rating" is true; but, correct me if I'm
> >wrong, exactly one-eighth.
>
> No, you cannot get exactly one-eighth of the rating because a byte
> of data transferred over a phone line has more information included
> with it than just the eight data bits.  In fact, each byte of data
> transferred over a modem is at least ten bits long.  There is a
> "start bit" which is used to signal the beginning of the data byte
> followed by seven or eight data bits then a parity bit if only
> seven bits of data were transferred and followed up by one or two
> "stop bits" used to signal the end of the "byte".  The 8N1 protocol
> most commonly used with modems indicates that each byte has eight
> data bits, no parity bit and one stop bit.  This does not include
> the start bit which is always present.  Another common protocol
> used by some systems is 7E1 that indicates that each byte has seven
> data bits, one parity bit and one stop bit and the always-present
> start bit.

  The 10-bits-per-byte rule of thumb (explained above) doesn't really
apply *in detail* since the introduction of modem compression and, I
think, 14.4Kbps signalling.  It is, however, likely to be closer to
the mark than dividing by 8, and it's also far easier.

  While we're thinking about this, though, it occurs to me that
1.38KB/sec is almost 1/10 of 14.4Kbps.  I wonder what Winston (the
guy with the problem...) has the speed of his COM port set to?  [Go
into Settings|Control Panel|System|Device Manager.  Find the port
that the modem is on, and check its "Settings" properties.  The speed
defaults to 9600bps; for a modem, you almost certainly want it to be
115Kbps.  [Thanks to compression, there may be *more* data between
modem and PC than over the phone line, so this setting should be AT
LEAST as big as your expected phone line speed.]

David G

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