Once promoted as an all-digital replacement for the PSTN, ISDN
is widely available in Australia from Telstra Corporation (although
not from other telcos). Most Telstra customers now have the option
of choosing it instead of the analog PSTN. An ISDN service provides
two "B channels", each of which can be used
to carry either a digitised voice (or video, FAX, etc) call, or a
64 kbps data call. Its takeup has been limited by extremely high
prices, and is now something of a technological curiosity...
ADSL
Asymmetric Digital Subscriber Line provides a high-speed (in
the hundreds-of-kbps to low-Mbps range) data service over an
existing phone line. The "Asymmetric" aspect is that the
"downstream" data rate is usually much higher than the "upstream"
rate -- an arangement which is suitable for most home users. It's
also often possible to configure an "SDSL" link if preferred. This
service is becoming increasingly available in Australia, and will
probably dominate the market in future years.
Cable Modem
For areas which have an existing Hybrid Fibre-Coax (HFC) "Pay
TV" infrastructure, the cable modem provides access to a shared
high-speed medium (eg Optus@Home), in much the same
(conceptual) way that traditional Ethernet works. Cable modems are
limited by the fact that many areas do have a cable TV service.
Wireless Systems
A variety of systems have been proposed, none yet dominant.
Watch this space...
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