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Re: connection speed when using pon

On Monday 31 January 2005 14:26, Paul wrote:
>John Hasler wrote:
>> I wrote:
>>>But they do not take into consideration the compression done by
>>> the modem.
>> Gene Heskett writes:
>>>Oh, but it does.
>> Those numbers represent the raw bit rate (not baud rate) between
>> the modems.  The effective data transfer rate can be much higher
>> but depends on the compressibility of the data.
>OK, explain why I can only download at 4.5-5.5 kbps when my
> connection is 48000?  And, is there any way to get the speed up?

Very simple Paul, you are getting a 4.5 to 5.5 KiloBYTES per second 
perfomance out of a circuit whose advertising dweebs call 56k, 
because that 56k is in kiloBITS (or kilobaud, where a baud generally 
equals a bit) per second.  Generally if the modems can maintain 
synchronization, the start and stop bits can be dispensed with *most* 
of the time, but there has to be an occasional marker to maintain 
synch, so I expect that while the 8 bits per byte plus a start and 
stop bits=10 bits per byte sent is cheated a little bit, the amount 
of gain by so doing is relatively marginal, and going back to full 
useage of start and stop bits per byte sent is probably the first 
step down from 56k to 48k as the modems negotiate their comm speeds 
for a reasonable error rate.  I believe, and its been a while since I 
read up on the particular details, that the modems are, when at full 
speed, sending the data in 128 bit (16 byte) packets as opposed to 8 
bit packets, with a start(1) and stop(0) bit on each end of the 
packet as a synch check.  My info on that might be dated, but I 
haven't noticed modem makers touting a new, improved protocol for use 
on POTS lines in several years now.

So, no, if you are getting 4.5-5.5 kilobytes per second, your are 
pretty much getting your monies worth.  Should the line goto hell and 
drop you to below 4k bytes a second, then I would call ma bell or 
whoever owns the copper to your place and request they take a look 
see at the line with a TDR.  Back when I was useing a modem over 
POTS, I suddenly dropped all the way to around 1.4k bytes and stayed 
there.  I eventually called, they tdr'd the line and found one of 
their linemen in doing some repairs, had tagged a branch circuit onto 
mine with an open on the far end, and the far end was nearly a mile 
away.  I'd like to have taken a picture of that tdr screen just for 
grins.  No way in hell that was the optimum flat line clear to the 
end.  It had to have more ringing than an uncracked liberty bell 

TDR=Time Domain Reflectometer, a means of measureing a cable whose 
technology somewhat resembles a radar in that you can see every 
putz'd joint, hammer or wrench ding in the outer conductor and bad 
connection, even the teflon rings that support the center conductor 
in big coax, from one end to the other, and nail it down in terms of 
where to dig almost to the exact foot.  I've used it on coax cables 
1000 feet long and told the tower crew which joint to take apart 720 
feet up and fix.  Easy when the accuracy is an inch or so, and the 
joints are 20 feet apart. :-)

I forgot to mention, I'm a broadcast engineer with about 56 years of 
chaseing electrons for a living, now semi-retired at age 70.

Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
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Yahoo.com attorneys please note, additions to this message
by Gene Heskett are:
Copyright 2005 by Maurice Eugene Heskett, all rights reserved.

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