DSL has several flavours. XYZed currently provides business class ADSL and SHDSL services.
ADSL (G. 992.1)
Asymmetric DSL. Offers a different transmission rate for each direction (upstream/downstream). Allows for more bandwidth downstream, towards the user supporting rates of up to 9Mbps and upstream transmission rates of 640Kbps. This compares with a maximum of 56Kbps for analog modems.
HDSL (G. 991.1)
High-speed DSL. Capable of carrying T1 or E1 (1.5 or 2Mbps) worth of traffic symmetrically over two copper pairs in fractions of n x 64K streams.
Symmetric DSL. Offers speeds of more than 192Kbps and up to 2Mbps in fractional n x 64Kbps speeds.
Symmetric DSL. A more advanced form of HDSL that allows for symmetric transmission supporting speeds up to 2Mbps over a single copper pair.
While the majority of Australians will be able to access DSL services from late 2001, technical limitations prevent the service being made available to every office or household that has a copper phone line.
The two key limitations are that the subscriber must be within a limited distance from their local telephone exchange and that the line between the two must be in good shape.
In borderline cases, customers may find that they can obtain some types of DSL but not others. This will depend upon:
- The distance of the customer’s premises from the local exchange.
- The quality of the copper line and whether it has any ‘bridges’ or ‘taps’ that prevent DSL deployment.
- The presence of remote integrated multiplexers, or RIMs, between a customer’s premises and the nearest exchange. RIMs are mini-exchanges that enable Telstra to extend fibre-optic links closer to consumers. However, it may prove difficult for XYZed to ‘co-locate’ its equipment within these RIMs, making it impossible to offer its DSL to subscribers in that area.