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The Telecom Digest for March 23, 2012
Volume 31 : Issue 76 : "text" Format
Messages in this Issue:
Re: What Hath Bell Labs Wrought? The Future (Jim Bennett)
FCC sues AT&T for Nigerian TDD scams (John R. Levine)

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Date: Thu, 22 Mar 2012 19:38:58 -0400
From: ajbcommconsulting@frontier.com (Jim Bennett)
To: telecomdigestmoderator.remove-this@and-this-too.telecom-digest.org.
Subject: Re: What Hath Bell Labs Wrought? The Future 
Message-ID: <4F6BB812.6020107@frontier.com>

On 2012-03-21 11:02, Eric Tappert wrote:
>
> The problem with these frequencies is that they do not toggle all the
> bits in the encoding, thus testing at those frequencies is incomplete.
> Accordingly, the test sets for digital circuits test at 1015 Hz,
> wihich causes all the bits to toggle in the encoding.
>
> There is nothing "magic" about 1 kHz.  It does sort of correspond to
> the peak energy in voice (even though every voice is a bit different).
> Note that any sampling rate would have the same problem with
> frequencies that are, as Bill put it, "even sub-multiples" of the
> sampling frequency.
>
> I doubt that most engineers would consider this a big screw up by Bell
> Labs, and certainly there are lots of other cases where the impact was
> greater.  All in all, they did a pretty good job of designing the
> telephone network...
>
> ET

Every "milliwatt" test tone I have seen is set at 1004 hertz.  I am not 
saying there is no such thing as a 1015 hertz source, just that this is 
the first I am hearing of it.  Maybe I just need to get out more.

Over the years I have heard at least three different explanations for
why the 1000 hertz test tone was changed to 1004 hertz.  It is
certainly true that sampling a 1000 hertz tone at 8000 samples per
second will result in the exact same eight patterns, repeating ad
nauseum. [assuming that the test tone is stable].  This is one of the
explanations I have heard, i.e., that it is not a rigorous enough test
for the A/D converters and/or the actual line drivers.  I have always
found this somewhat dubious, as my experience with these things is
that they either work or they don't.  Timing slips and jitter were the
primary problems in the days of true DS-1 signaling over copper, and
testing often involved sending "all ones."

Another explanation I have heard is that 1000 hertz was never a problem 
until ESF came along.  Extended Super Frame finds the framing bit by 
looking for the one bit out of 193 that consistently alternates between 
a "one" and a "zero" with each frame.  Apparently the 1000 hertz tone 
would result in actual time slot bits doing the same thing, and bumping 
it up to 1004 solved the problem.  I am not saying this is fact, just 
relating what I have heard over the years.

Jim
==================================================
Speaking from a secure undisclosed location.




Date: 22 Mar 2012 23:38:30 +0100
From: "John R. Levine" <johnl@iecc.com>
To: telecomdigestmoderator.remove-this@and-this-too.telecom-digest.org.
Subject: FCC sues AT&T for Nigerian TDD scams 
Message-ID: <alpine.BSF.2.00.1203222334460.67350@joyce.lan>

AT&T provides a TDD relay service for which the government reimburses the 
costs.  According to the WSJ, the Justice Department is suing AT&T for 
fraudulent reimbursement claims.

TDD relay has a dreadful problem with Nigerians calling and defrauding 
people.  The FCC required that operators register users and verify that 
they're in the US.  The suit claims that AT&T deliberately uses a 
registration scheme that doesn't keep out crooks, and as a result 95% 
(NINETY FIVE PERCENT) of their TDD calls are Nigerian fraud.

http://online.wsj.com/article/SB10001424052702304636404577297454154404874.html

Regards,
John Levine, johnl@iecc.com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail.
http://jl.ly






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