To cut the costs of providing service to areas with a low number of subscribers per wire-mile, Telstra originally installed only a single copper pair from the Central Office (CO) to the subscriber residence. Telstra avoids installing an additional copper line by using ‘pair gain‘ technologies. Pair gain works either by time division multiplexing (TDM) or frequency division multiplexing (FDM) to facilitate carrying an additional voice signal on the existing copper pair. The signals are chopped up and stuffed into the single copper pair. The mixed signals are carried to and de-multiplexed at the CO and fed on into the ‘PSTN’ or ‘Public Switched Telephone Network.’
Standard copper wire ‘twisted pair’ telephone lines are known as ‘Plain Old Telephone Service’ or ‘POTS’ lines. POTS is capable of a bandwidth (or frequency response) of around 300Hz to 7000Hz (7kHz), which is about twice what is needed for basic intelligibility of voice signals- in fact, 300Hz-3kHz will do for standard quality voice transmission. The full frequency response (or bandwidth) of a single POTS line is good enough to carry a ~52kbit/sec signal from a modem or a fax machine. This is all well and good until a subscriber wants to add a separate line for a computer modem or a fax machine.
To avoid installing a second copper wire pair, which may require new aerial or buried cabling, Telstra installs a multiplexer (MUX) at the subscriber end which provides two voice-quality connections. The MUX then connects through a single copper pair to a de-multiplexing device at the CO. However, the bandwidth available at those two ports is only good for about 300Hz-3kHz. That level of bandwidth will only support a maximum data speed of around 19.2kbit/sec- or worse if there are any ‘repeaters’ or analog to digital (AD) converters in the path. Speeds can be as slow as 9.2-14.4kbit/sec if traffic has to be run through an AD (or DA) converter. Regardless, subscribers on pair gain are still billed for two full capacity telephone lines!
Rural and regional subscribers on pair gain systems are thus unable to use the full capacity of 56kbit/sec modems- bush subscribers will have a hard time getting 19.2kbit/sec. Copper based broadband technologies like ADSL (which require two copper pairs, 4 wires in sum) are impossible. Furthermore, you don’t have to be out ‘past the black stump’ to be affected. Subscribers in metropolitan Sydney suburbs like South Sydney and Glenhaven often cannot get ADSL or have troubles with even POTS lines for typical voice service.
Fairly simply, Telstra have been getting away with not improving their infrastructure for quite some years. Australia desperately needs a fibre-optic based system to provide broadband internet services to all subscribers, but Telstra’s profits have been going elsewhere.
Rookie National Party senator Barnaby Joyce looks like he just might take a stand in the new Lieberal operated Senate to hold up HoWARd on the full privatisation of Telstra.
You might consider sending Senator Joyce a thank you note if he’s able to stop the already inadequate Telstra services from getting any worse.
-weez
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