Public Switched Telephone Network (PSTN).
- Traditional CAN Layout
The Customer Access Network (CAN or PSTN) was built by the Postmaster-General’s Department (PMG) of the Australian Government during the 20th century. It was designed for basic telephony services, and connects a dedicated cable pair (or pairs) from the local telephone exchange to each residential or business customer.
The figure above illustrates the CAN network. Essentially a copper cable pair from the exchange up to each premise is used. Pillars are the point of connection between the Feeder Network and the Distribution Network. They are constructed with a number of cable pairs from the Feeder Network terminating on the exchange side and a generally larger number of cable pairs terminating on the Distribution side of the pillar. Provision is made for a connection or jumper wire to connect pairs from the feeder network to pairs in the distribution network. This allows a point of flexibility between the two parts of the network and allows different provisioning schemes to be used in each.
Around the beginning of the 21st century as more and more customers required an internet connection, ADSL equipment was installed at the exchanges and ADSL modems supplied to customers to provide high-speed broadband services over the existing copper wire network at relatively low-cost. This equipment allowed sharing of the telephone line spectrum between voice traffic and high-speed data access.
When Telstra was privatised, ownership of this network was transferred to them. Telstra are responsible for any maintenance or connection activities in this network. Other service providers are allowed by law to install DSLAM equipment inside Telstra telephone exchanges, and lease a cable path from Telstra, to connect their equipment to the customer’s premises (the so called unconditioned local loop service, aka ULLS, allows service providers to connect their own networks to communications wires in order to deliver services).
This helped to some extent, but created continuous friction and problems, with the third parties constantly complaining that they did not get a fair deal and that Testra had an unfair advantage because of their “vertical integration” (controlling the last mile as well as providing retail services to customers).