"Leased line" service can be provided by a variety of
technologies:
Traditionally: a permanently connected (or "nailed up") 'phone
line and two modems -- in Australia, the ancient DATEL service
worked this way. Bit rates up to 72kbps were available. Note that
the term "nailed up" has survived to this day to describe any
permanently available data circuit. Many businesses use a
modern-day equivalent of this technology by taking advantage of
Australia's "untimed local call" charging scheme, using a dial-in
modem but holding the connection permanently open.
DDS was an early (and fiendishly expensive) digital "leased
line" service in Australia, with bit rates between 2400 and 48kbps.
The original AARNet was
based on this service.
ISDN-based services. For example, a Telstra ISDN service can
dedicate one or more B Channels as a permanently available data
link, see later.