CM> but how do you know your modem hasn't done any damage ? just
CM> because your line is ok doesn't mean the exchange is undamaged.

RS> If it keeps killing the line interface, you will find out Chris.
RS> One obvious indication is that your phone line stops working.

CM> Not quite

Fraid so.

CM> although the physical line (cable) never changes it logical
CM> path through the exchange is rarely the same for each call.

Ah come on Chris, this is crap. In a digital exchange the digital
data out of the line card cant be killing stuff like that.

CM> In fact you could call every day for a month and still not hit
CM> the same logical path, So in essance if through some act of god
CM> a large voltage or somthing else goes wrong with your modem then
CM> it is quite possible that you could kill one of these logical
CM> paths and that in turn would look like an intermittent problem.

Fantasy Chris. The reality is that its the line card thats
vulnerable, and its protected because its not exactly a terrific
idea that the line cards die like flys with lightning around etc.

And why would an FCC approved modem be killing anything anyway ?
It clearly doesnt kill the exchanges in the US etc.

CM> I was having a chat to the designer (netcomm) who is designing
CM> a new PCMCIA modem for netcomm and he said that in order to
CM> pass (one) Austel test modems are fried (electricaly) with about
CM> 12,000 vac and they must not pass any more than 200 vac down
CM> the phone line, if they do then they fail (and are not approved).

RS> And non austel approved modems are normally FCC approved and that
RS> requires them to pass a similar test with a lower voltage, which is
RS> STILL perfectly adequate since it requires it to survive a 1.5KV test.

CM> perfectly adequate for WHO, You or AUSTEL ?

Perfectly adequate to ensure that it doesnt damage the exchange.
Austel is apparently moving to the use of the international standards
on that voltage isolation requirement stuff now as we speak. Funny that.

CM> If it was adequate then why would Austel want another approval
CM> at a larger voltage. Maybe because of the differing Locale.

It was just the usual approach taken in those days, mindless over
specification without regard to compliance cost. Pluck a number
out of the air whose higher value cant be justified on technical
grounds. Which is why they are moving to toss it in the bin now.

RS> And the phone exchange line interfaces have to
RS> be able to survive lightning and stuff anyway.

CM> There is currently NO WAY to design electrical equipment
CM> to survive a lightning strike. The voltages and ampres
CM> are just too great for the current components to handle.

Fact remains tho, while its certainly not possible to design it so
that it cant possibly ever be damned by a very close strike, its
quite feasible to design it so that it survives the less drastic stuff
that will inevitably be seen on actual cables entering the exchange.

Same applys to even TV transmitter towers, sure, you cant ensure
that never ever will any damage occur, but you can certainly do
heaps to drastically minimise the times when damage actually occurs.

CM> If telecom (telstra) get constant faults on one circuit (ie yours for
CM> instance) then they WILL search for a cause and trace it back to your
CM> line and come out to inspect your line, and if they find a non-austel
CM> approved modem (or other device) connected then they (austel) can give
CM> your a rather large (4 figure) fine and telstra would probably also take
CM> a dim view of it and charge you for repairs to the exchange circuit.

RS> Yes, its theoretically possible. Pity that you cant actually nominate
RS> too many non austel approved modems ever getting into that situation tho.
RS> And the reason they dont is very very simple, the FCC approval requirements
RS> are perfectly adequate to ensure they dont kill the exchange.

CM> See my above comment.

Useless.

RS> Even in a worst case scenario where your PC goes kaput and puts the full
RS> 240V onto say the bus connector of the internal modem, the 1.5KV voltage
RS> isolation to the phone line itself ensures no 240V on the phone line.

RS> Ditto with say an external modem if the plug pack fails and puts 240V
RS> onto the modem. And if you are paranoid there is no reason whatever why
RS> you cant use an Austel approved plug pack and a non austel approved modem.

CM> I can think of one reason strait away. Insurance, I wonder
CM> what the insurance company would say if your $3000 pentium
CM> (for example) was toasted by a non approved modem ?

Gets sillier by the minute. Austel approval for a modem has
nothing whatever to do with any potential to damage the PC itself.

CM> Is it really worth the effort to save a few measily dollars
CM> (say $200) to risk your expensive hardware ($2000 +) ?

You havent actually established that there *IS* an increased risk Chris.

--- PQWK202