Stage one of the TransACT network

The original network laid by TransACT involved running high capacity fibre-optic cables via power poles into suburbs, close to people's homes. Each fibre-optic cable services a small area of around 45 to 65 homes and businesses.

At the end of each cable is a junction box (or 'node') that is located on, or very close to, a power pole within each service area. These nodes convert information transmitted across the network from light into electricity.

From each node, an individual pair of copper wires connects each home or office subscribing to TransACT. These wires are quite short - at most a few hundred metres long - and are of very high quality. This type of wiring is often described as "star" wiring because the connections radiate from a central point.

VDSL (Very high data rate DSL) technology is used on these copper wires to transmit information. Because the wires are dedicated to each home, as well as their quality and short length, they are capable of transmitting information at extremely high speeds - much faster than the ADSL (Asynchronous DSL) used across Telstra's much older copper phone wires. Without this high speed, it would not be possible for TransACT to deliver subscription television to homes.

Collectively, this type of network is known as Fibre-to-the-Curb (FTTC) architecture. It balances the cost of building a new fibre-optic network, rather than using an existing phone network, with the need to allow individual households to choose whether or not to subscribe to the service.

It would be possible to run fibre-optic cables to each home. However, every home and office would require an extremely expensive converter to transform the data carried by light on the fibre-optic network, into signals carried by electricity that can be used by televisions and computers in the home. Instead this is done cost-effectively at each node on the network.

Nodes and Super nodes

There are several types of nodes used in TransACT's Stage I network. Most (about 85 per cent) are small nodes mounted either on a regular power pole or on a short, special-purpose pole. You may see these around your suburb.

The remaining nodes are larger and could be called 'super nodes'. They are erected as freestanding, ground-mounted units.

The key difference between the two types is that the super nodes contain extra equipment for TransACT's telephone services, such as batteries to ensure that phones continue to work if there is a power failure.

Hubs

The fibre-optic cables from groups of nodes meet at 'hubs'. Each hub services between 15,000 and 25,000 homes and offices. The hubs are in turn connected to each other and to a central 'gateway' that connects the TransACT network to the rest of the internet. TransACT's gateway is located in a purpose-built high security bunker at TransACT House in Dickson.

How cable networks outside Canberra do it

TransACT's Stage I network is different to the cable networks in other parts of Australia.

These other networks may also use fibre-optic cables, but rather than nodes with up to around 60 homes like TransACT's, each node serves typically between 500 and 2,000 homes. In each serving area, the nodes handle the conversion from optical to electrical signals.

However, instead of using individual copper wires from the node to the customer, as TransACT does, all signals for all customers are broadcast on a common coaxial cable. Individual subscribers are then connected to this common cable and 'tune' into that part of the signal that is of interest to them.

Called a Hybrid Fibre Coax (HFC) network, this type of system is suitable for simple broadcast services such as basic subscription television. However, it is not particularly suitable for delivering individual subscriber services such as video-on-demand.

HFC networks provide less capacity, or bandwidth, for each subscriber, and have a greater risk of signal interference reducing the quality of transmissions - particularly when a large number of people in the same area subscribe.

This means that constant broadband internet speeds cannot be guaranteed and other issues regarding television reception can result, due to line interference.