Rod, at 10:41 on Mar 05 1996, you wrote to Bill Grimsley...

BG> Sure, but even fibre-optic has inherent line loss (attenuation), which must 
BG> be reamplified every so often.

RS> Not in the sense of affecting the calls call by call. Once its digital, 
RS> that that, what goes in one end, comes out perfect at the other end.

BG> Theoretically.

RS> Aint no theory, thats the whole POINT of going digital. Thats why you HAVE 
RS> digital telephone exchanges etc.

BG> Nope,

RS> Yep, you havent grasped what digital is all about Bill.

I've grasped it just fine thanks, but if you're still not sure about
digital theory, ask your dog.  I'm sure he'll set you straight.

BG> FO digital square waves will eventually degrade to low-amplitude
BG> sinusoidal waves, without regeneration.  Usually within 150Km too.

RS> Completely irrelevant when you HAVE regeneration at a MUCH closer
RS> spacing than that Bill. So you DONT get degradation of the digital
RS> DATA no matter how many repeaters the data goes thru. Thats the
RS> WHOLE POINT of digital, it DOESNT degrade the data.

I KNOW that, Rod.  What I'm saying is that WITHOUT regeneration, the
digital signal WILL (and does) degrade.  The whole point (if there is one)
is that because Telstra regenerates the FO data at least every 60-80km or
so, there should be no degradation of the signal, regardless of the total
distances involved.  That's the theory, and indeed, it works well in
practice.

BG> However, I just called Alan Kennedy, my senior engineer
BG> mate with Telstra, and the reality can be rather different
BG> (although for the most part, there should be no appreciable
BG> loss along the entire length of FO).

RS> You are garbling the story considerably,

BG> Nope.

RS> Yep, totally mangling the significance of how FO works. While what
RS> you talk about does happen, you DONT get degradation of the digital
RS> DATA in that approach and thats the WHOLE POINT of going digital.

Are we arguing the same point?  I'm agreeing that you DON'T see the
degradation which is inherent in FO, BECAUSE of frequent signal
regeneration.

RS> the whole POINT of a digital system is that you DONT get increased
RS> degradation of the data when it moves thru more repeaters. Tho you
RS> certainly still need them just because you cant currently run a fibre optic
RS> cable repeaterless for the 1000Km class distances we are talking about.

BG> Exactly.  If you did, there'd be nothing but a tiny sine wave left.

RS> And so your claims on the path VARYING from call to call have imploded.
RS> Once the call is digitised in the phone exchange line card at each end
RS> of the session, with a completely digital system BETWEEN the exchanges,
RS> there aint no variation in the DATA between the exchanges, BECAUSE
RS> its digital, and thats the WHOLE POINT of modern digital exchanges.

Once again, theoretically.  And before you spack out completely, I'll once
again agree that this is what happens in practice too (or should), provided
that the inter-exchange paths are indeed digital.  Brisbane certainly is
now, but I can't speak for all of Sydney.

BG> The actual FO design specs call for an exchange transmit level of
BG> -10dBm, with automatic regeneration once the level drops to -47dBm.

RS> Thats says nothing useful at all tho about whether a digital system
RS> gets any degradation at all. The whole POINT of it is that you dont.

BG> Without occasional regeneration, you most certainly will.

RS> And you ALWAYS have regeneration, SO YOU DONT.

Or, barring failure of the regenerator, you SHOULDN'T.  You're falling into
the trap of speaking in definites, and ignoring Murphy.

BG> Now comes the tricky bit.  The maximum allowable inter-exchange
BG> losses are 12dB on a normal copper pair, with a further allowable
BG> loss of up to 7dB to each subscriber.

RS> That NOT a fibre optic cable. The vast bulk of
RS> the inter exchange links are fibre optic now.

I'll have to take your word for that, but that's not what I'm talking about.

BG> But not the exchange-to-sub links.  They're still copper.

RS> Crap, the vast bulk of them ARENT now.

ROFL!  You have FO to your door, do you?  Bullshit.  Up here, the vast bulk
of exchange-to-subscriber lines are copper pair, just as in Sydney.  And
THAT'S where the attenuation is occurring, not on the FO (as I've said
repeatedly).

BG> And THAT'S where the greatest attenuation occurs.

RS> Nope, not when you have FO between exchanges.
RS> And thats what the vast bulk of them are now.

Sure, that overcomes the old 12dB maximum accepted loss between exchanges,
but it still says nothing useful about the maximum acceptable loss of 7dB
between the exchange and the subscriber.  On EACH end.  That's up to 14dB,
Rod.

RS> You are comprehensively mangling the considerations on repeater spacing
RS> in a digital system and the question of degradation OF THE DATA.

I think you've focussed on a particular aspect of my earlier comments, and
have totally ignored my main complaint, the 14dB loss between subs.

Will a graphical representation make it easier for you to grasp?

==========================================================
 Me      my exchange            Paul's exchange    Paul

  A----------B--------------------------C-----------D
     copper         fibre-optic            copper
==========================================================

Maximum acceptable loss from A to B = 7dB, from B to C = 0dB, and from C to
D = 7dB.  The total is obviously 14dB.  With an initial Tx level from my
end of say -11dBm, one would expect the Rx level at Paul's end to be
-25dBm.  But it's not, it's actually hovering around -35dBm with the M34F. 
So tell me, where the fuck is the extra 10dB loss coming from?  One theory
proposed by Alan is that because Paul lives in units, there could be high
resistance joints in the building, or in fact anywhere between either of us
and our respective exchanges.  The bottom line is that this loss is
unacceptable, even by Telstra's standards, and at this stage, cannot be
adequately explained.

Regards, Bill

--- Msgedsq/2 3.20