[LINK] Battery back-up mandatory for NBN?

Paul Brooks pbrooks-link at layer10.com.au
Wed Nov 3 10:27:43 AEDT 2010

On 3/11/2010 8:55 AM, Tom Worthington wrote:
> As far as I am aware, there is no requirement for mobile providers to
> supply a service during a blackout. In practice they do (the US material
> I found suggested eight hours for cell towers), but as far as I know
> there is no law to say how long the service will operate for. So having
> a mobile phone does not guarantee you will have phone or data access
> during a blackout.
>> The fact that copper-line phones continue to function when mains
>> power fails is convenient serendipity. ...
> No. The system was designed to continue to operate when mains power
> failed. What competent professional would design a telecommunications
> system which relied on mains power?
No. To pick up on your comments above, just as with mobiles there is no requirement 
for fixed-line service providers to supply a service during a blackout.
In practice they do, and outside the exchanges (where the batteries are backed up by 
generators), the fixed-line terminals such as the CMUX cabinets in the basement
of office builtings which provide the data and ISDN PRI services over fibre also have 
batteries to last between 4 and 8 hours at a minimum.
There is no law to say how long a fixed-line service might operate for - if at all - 
under a mains power failure.

This telecommunications system wasn't designed to rely on mains power because it 
predates reticulation of mains power,  being designed back when gas lighting was normal.

> In the earliest days phones where powered by batteries in the exchanges.
> But later when mains power was available the phone company could have
> simply used that and saved money. Instead they provided battery and
> generator backup for blackouts.
No. They retained exchange powering of the line because that is how the analog phone 
standard achieves making the bell ring, and how the exchange
detects the handset is 'off hook', to retain backwards compatibility with the millions 
of conventional telephone handsets that are not themselves powered from mains.

They retained battery backup and generator backup _at the exchange_ to keep the 
exchange equipment alive during a mains power failure _at the exchange_. It is a 
useful byproduct that this backup
capability is also extended down the line to the customer premises by the simplicity 
of the analog off-hook/ring-bell signalling mechanism, which does not require any 
other device between the (battery-and-generator-backed) line card in the exchange 
providing dial-tone, and the handset itself which needs no other supply.


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