HDSL
HDSL simply stands for High bit-rate Digital Subscriber Line and is an earlier incarnation of DSL than ADSL. Typically HDSL is used for wideband digital transmission within a large corporate site, and between the telephone company and a customer. The main difference between ADSL and HDSL is that the latter is symmetrical: an equal amount of bandwidth is available in both directions. For this reason, the maximum data rate is lower than for ADSL-HDSL can carry as much as 2.32Mbps.
There are vendors offering HDSL in Australia at the moment. However, they don't widely promote it as the infrastructure is so limited that many potential customers are likely to be disappointed by the lack of support in their area. The CBDs of capital cities such as Sydney, Melbourne, and Brisbane have HDSL service but it is limited to just 1.9km from an enabled exchange. Telstra is the only provider of the service, but does not sell directly to end-users, instead wholesaling it to other vendors.
SHDSL
Yet another DSL, Symmetrical High bit rate Digital Subscriber Line (SHDSL) is also known as G.SHDSL and G.991.2. It has the distinction of being the first of the DSLs to have been designed from the ground up as an international standard.
This has been a fairly new development as the standard ITU G991.2 was only defined in February this year. Like the other DSL technologies, SHDSL sends and receives symmetrical data streams over a single copper pair at rates between 192Kbps and 2.31Mbps. SHDSL also has the ability to transport T1, E1, ISDN, ATM, and IP signals.
Because of the symmetrical nature of this technology and its high speed, it is better suited to the needs of remote LAN access, Web hosting and videoconferencing, for example. It also has the ability to transport multiple voice and data channels simultaneously.
I was sure you couldn't get T1 and T3 services in Australia, that it's a US standard, instead we have 2Mb links instead of their 1.54 ?