-=> Quoting Dan Bridges to Rick Collins <=-
-=> FidoMail to 1:163/215, please.-=<
DB> DCE/8*10 * data_bits_per_packet/(data_bits_per_packet+7) * 60/61
DB> At 31,200 DCE with no compression (&K0) and with a LAP-M data
DB> frame size of 128+7 bytes there should be a DTE transfer rate of
DB> 36,372 bps and with 244+7 byte frames (USR V.Everything) it
DB> should reach 37,291 bps. This is still under the 38,400 bps DTE
DB> rate.
That sounds right.
DB> Since the tramsfer rate is below the DTE speed I think there
DB> should be no need for hardware flow control.
I've run with no receive flow control just to prove that point, with
no problems.  Transmit is another story, though. :-)
RC>I won't dispute your findings, but I'd suggest the reason is not
RC>simply the DTE speed being overwhelmed by the data rate.
DB> I can only assume that there must be "jerkiness" in the
DB> modem->comms program data flow as well as a straight time delay
DB> so that 37,291 DTE effective DTE transfer rate requires more than
DB> a fixed 38,400 bps DTE rate. (Although the DTE channel is async I
DB> presume that "38,400 bps" would only be attainable with a
DB> constantly flowing data stream.) Might try and put my 35MHz
DB> oscilloscope on the data line and take a look, but it might be
DB> hard to sync to it.
I guess something to keep in mind is when a particular speed is set
what _actually_ happens is the length of each signal element is set. 
In other words, the time duration of a "bit" is configured and _that_
results in some number of "bits per second".  I've explained this to
the less technically inclined by discussing the "speed" of the data
when connected to a BBS and typing your name in response to the Name:
prompt:  Assuming a 38,400 bps port speed, how "fast" is the name
sent?  Well, how fast a typist are you? :-)
Lets make some assumptions.  The data (real data, not the overhead)
is arriving at a constant rate of 3600 bytes per second, and the comm
port is operating at 38,400 bps.  The PC and the comm program know
nothing of this - they only "know" that there are 400 (we're assuming
an 8-byte FIFO buffer) interrupts per second being generated by the
comm port.  Up the port speed to 57,600.  What's changed?  The
interrupts are _still_ arriving at 400 per second.
Hmmm.  Does that lead anywhere productive in relation to what you've
seen?
TTFN. Rick.
Ottawa, ON 19 May 15:56 
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