-=> Quoting Russell Brooks to Mark Griffiths <=-



 RB>> up. One day I would like to see 117% efficiency at 33600.
 
 BG>> Unlikely on the copper where you live.  Wait for co-ax and you'll be
 BG>> OK.  
 
 MG> I have seen a 117% transfer using ordinary Zmodem on a 31.2k connect. 
 MG> 3650cps on a file several meg long.  The modems definitely did not speed
 MG> shift up to 33.6k, although the line was quite clean with very few BLERS.

 RB> That is good, but I bet you wont see 117% at 33600

I've never managed a 33.6k connect to that number...

 RB> I dont think the bandwidth is there anymore

The bandwidth is there - I get 3429 symbol rate connects to it, but the 
SNR is a bit low at between 36.5 and 37dB.
 
 BG>> True, but I'm still also convinced that it's protocol dependant too, as 
 BG>> Binkley has never quite managed 4000cps on large zips with its 8Kb 
 MG> ZedZap.
 MG>  
 RB>> I think along the same lines, I am not a strong 
 RB>> believer that ZedZap is THE 
 RB>> most efficient.  A lot of changes can take place in the time it takes 
 MG> for 
 RB>> 8kb to go through
 
 BG>> I'd have thought that the Courier's SREJ would have made a 
 BG>> slight difference with 8Kb blocks, but that just didn't 
 BG>> seem to happen.
 
 MG> The 8KB blocks mean less protocol overhead so in the absence of errors 
 MG> (as 
 MG> should be the case when using an error correction protocol in the modem)
 MG> the transfer should be quicker.  The Courier's SREJ has nothing to do 
 MG> with
 MG> the 8KB block size since its at a different protocol layer.  SREJ is most
 MG> useful on noisy lines which is exactly what you don't want to be able to 
 MG> achieve 4000 cps.

 RB> Are you saying.... turn off SREJ and use only ZedZap and if your
 RB> bandwith permits... you could get closer to 4000cps

No, I'm not saying that, in fact the opposite would be more likely the case
Having SREJ will not (shouldn't anyway) degrade error free performance in 
any way.
 
 MG> Has is occurred to anybody that a 33.6k connect may not exactly equal
 MG> 33600 bits per second?

 RB> Never thought about it

I would say that the most likely reason why you can't get as high performance
out of a 33.6k connection as a 31.2k connection is due to this reason.  The
only other likely reason is that a 33.6k connection is likely to have more
BLERs.

If you really desperately wanted to see a true 4000 cps mark, your best 
chance would be to connect 2 modems back to back via a telephone cable
and transfer a very large file using the most efficient protocols at each
layer.  I would suggest using MNP 4 with no compression and probably 
Zed-Zap although I have never used it so I can't comment on how good it is.
Zmodem MobyTurbo would probably be better if it had 8KB blocks, but it would
probably still be worth a try anyway.

By bypassing the PSTN you will guarantee no BLERs.  The only thing 
stopping you from getting the same transfer rates on the PSTN when you
do connect at 33.6k is line noise because the bandwidth must be there for
you to get a 33.6k connect in the first place...

Regards,
Mark Griffiths.

... Not tonight, dear.  I have a modem.
___ Blue Wave/QWK v2.12

--- Squish/386 v1.11