LinuxSA Mailing list archives

  From: Daryl Tester <dt@picknowl.com.au>
  To  : Richard Walford <rwalford@picknowl.com.au>
  Date: Sat, 25 Nov 2000 21:18:13 +1030

Re: ADSL Enabled Exchange Areas: Updated 20/11/2000

Richard Walford wrote:

> Sorry, the latest documentation from Telstra available on their web sites
> (now If I could rember where, umm maybe USO pages) explicitly states 2400
> bps.

The USO that I downloaded makes no mention of this.  And if Telstra
have stated this, then that means that they've got it wrong, and that
they are now unable to distinguish the difference between baud and
BPS.  Baud is not the same as BPS (technically untrue, as most
signalling that occurs below 2400 bps the two are the equivalent rate).

> In fact I don't believe the USO (Universal Service Offering) actually
> defines what speed Telstra has to supply - I think you will find that
> Telstra only has to supply a voice grade service.

Which is where the 2400 baud comes in - it's pretty much the maximum
bandwidth that you can squeeze out of a voice grade (3.3 Khz from
memory, but I may be out by a few hundred Hertz here) due to Nyquist.
Any bitrate over 2400 bps is done "by signalling trickery", like
QAM and run length encoding/compression, but the _baud rate_ cannot
exceed half the available bandwidth without sampling errors being
introduced.  Yet people keep making the same mistake (on both sides
of the fence) over and over again.

> Feel free to correct me, but please supply a reference to a document that
> supports your position.

Elementary communications, and my dealings with Telecom/Telstra and
modems in the mid 80's.

BTW, an Altavista site-limited search cannot find any relevant
matches for "2400" on either www.telstra.com or www.bigpond.com.
I'm keen to see where Telstra have this in print.


-- 
Regards,
  Daryl Tester,  Software Wrangler and Bit Herder, IOCANE Pty. Ltd.

"Who knows what men lurk in the heart of eval?"

-- 
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