Ian, at 02:54 on Nov 28 1996, you wrote to Bill Grimsley...

> Two USR Couriers with a 33k6bps connect, probably due to
> their unique 256 byte LAPM frames and SREJ (Rockwells only
> use 128 byte LAPM frames, but similar cps rates may be
> possible with MNP4, which also uses 256 byte frames).

IS> Nope, even MNP4 won't take you past about 118% (1700 cps at 
IS> 14400, 3400 at 28800, so about 3967 cps at 33600). 

That still doesn't explain the 4000cps which was physically seen here on
one particular 1.5Mb file transfer between David's Courier and mine (and
which was witnessed by Russell Brooks at the time).

IS> No modem that complies with V.34 does anything 'unique' with frame 
IS> sizes, and most modern modems will respond to a request for 
IS> larger than default frames.

Dunno, when I call Rockwells, most aftecall stats show the frame size as
being 128 bytes, and only a handful indicate 256 byte frames or SREJ, so
I'm not convinced that this applies to "most" modems just yet.

IS> LAPM with 256 byte frames is still a percent or so slower than MNP4. 

Is this due to 32-bit CRC checking?

IS> SREJ isn't relevant to error-free throughput.

True.

IS> A 48K file will give you about a +/-8% error in recording 
IS> (ie, +/-300cps!) at one second resolution, at 33600.  Even 
IS> 480K is too small for really definitive throughput figures 
IS> at that rate (still approx +/-30cps).  Quoting transfers of 
IS> 1Mb or greater starts to make timing artifacts look 
IS> relatively insignificant.

Agreed.  In fact, several smaller log entries here (say 50Kb or so) show
speeds in excess of 4000cps, but these are obviously inaccurate. Not so
with 1500Kb though, where a second or two either way is not likely to make
much difference at all to the calculated overall cps rate.

IS> So close to seeing those (some say) 'magic' extra zeroes, but so far :)

Still reckon the 4000cps I saw with Russ was genuine...  :)

Regards, Bill

--- MsgedSQ/2 3.50