Matthew,

After a deeper investigation, I see that we are both partly correct in our
statements about 56K technology, but we were both more wrong than right. <g>

There is a white paper available at the 3com web site which details the 56K
"process", but it is written in "engineer-speak" .  Following is excerpt
from an article I found at the WHATIS,COM site which (I think) explains the
process in a much simpler and clearer manner.
(Much better than I did anyway <grin>).

> 56 Kbps technologies exploit the fact that most telephone company
> offices are interconnected with digital lines. Assuming your Internet
> connection provider has a digital connection to its telephone company
> office, the downstream traffic from your local Internet access provider
> can use a new transmission technique on your regular twisted-pair phone
> line that bypasses the usual digital-to-analog conversion.
>A V.90-equipped modem doesn't need to demodulate the downstream
> data. Instead, it decodes a stream of multi-bit voltage pulses generated
> as though the line was equipped for digital information.

I still disagree on point 2.  I beleive the USR test line is of dubious
value.

Lets assume a very simplistic topology for the telephone network that has:
POINT A is the dialing modem.
POINT B is the TelCo switch center.
POINT C is USR's test facility (or whatever you want to call it)
POINT D is the ISP.

As stated above (and in the white paper), the 56K data stream bypasses the
A/D converters and feeds a "digital-like" signal directly to the modem.
Ergo, the wiring from POINT B to POINT A is just as critical as the wiring
from POINT C to POINT B.  Now consider that (in the "real" circuit) it is
POINT D that is sending the data back to POINT A, and - obviously - no test
of the wiring from C to B to A will ever account for the wiring from POINT D
to POINT B.   And that is why I said the line test is not a complete test.

As you pointed out, each time you make a connection from POINT A to POINT C
you are at the whim/mercy of the TelCo network and may or may not use the
exact same circuit.  Which supports the other part of my statment that the
line test is inconclusive.

Further, IMHO, unless you live in a small town, there are probably two or
more switch centers involved in routing the "call" from POINT A to POINT D.
In other words, for many (some?) of us, the full path is POINT A to POINT B1
to POINT B2 to POINT Bx to POINT D.

So I still maintain that the USR test line can only confirm that you have a
good connection - but only for this one connection - from POINT A to POINT
C.

Jim Meagher
Staff Editor


----- Original Message -----
From: "Matthew Ballard" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Sunday, March 05, 2000 1:44 AM
Subject: Re: [PCBUILD] Internet connection speed


> A response to inaccuracies of a previous post.
>
> >56K is the result of data compression technology, not actual transmission
> >speed.
>
> 56k is NOT the result of data compression technology, it is the result of
> taking advantage of the digital nature of phone lines, at least from the
> phone company central office to the modem you are connecting to, and
> requires that the other end have a digital phone company connection, such
> as via ISDN, T-1, etc.  When you add compression, it's possible to reach
> speeds of up to around 5 times the throughput of the raw speed of the
modem
> with a highly compressable file, but with a basically uncompressable file,
> such as a zip file set to maximum compression, it is possible to get up to
> around 2 kilobytes per second in additional speed when downloading a file.
> One restriction of 56k modem technology is that it can only survive ONE
> Analog/Digital conversion, and if a second conversion takes place, the
> connection is not possible at 56k speeds.
>
> >Point 2.
> >The USR "line test" merely attempts to negotiate a connection at the
highest
> >possible speed AND compression technology.  .  The line quality is only
one
> >half of the equation.  The other half of the equation is the data
> >compression algorythm.  If the two modems are not using compatible
> >algorythms, then 56K will not be acheived.
>
> This is NOT what the USR line test tests, it tests to see if the the
> connection between the test modems on USR's end and your phone company
> central office is entirely digital or not.  It may have taken a different
> route with the new modem, which would cause the difference in the test
> results, and therefore may not always be accurate, but it does NOT test
> compression technology at all, nor does it care about the speed it
acheives.
>
> >Point 3.
> >When a phone call is made, the telephone (modem) dials a number and
connects
> >to the Telephone Company's  (TelCo) switching center, which then makes a
> >connection to one or more switching center OR to the dialed number.  When
a
> >modem "calls" the local ISP, or calls the USR line test, the first part
of
> >the connection path (from the modem to the switching center) remains
> >constant, but from the switch center outward, there are very different
> >circuits.  USR is testing (and I use that term VERY loosely) the
connection
> >from the dialing modem to the switch center.  It can not "test" the
circuits
> >from the switch center to the ISP.  Therefore it is only a partial test.
>
> The line test does NOT test your lines, which doesn't matter as much as
the
> connection from your local Central Office to the end modems, in this case
> at USR.  It can't test the lines to your ISP, only to their modems.
>
> Matthew Ballard
> Computer Consultant
>
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