Active star/point-to-point

Written on 2:30 PM by ooe

Point-to-point systems use one or two fibres to connect a pair of nodes. The full bandwidth of the fibre is available for future upgrades and a high power budget is available for long-distance transmission. A drawback is that the network is not well-suited to broadcast services.

As the number of nodes in a network grows it is desirable to concentrate traffic to avoid the huge proliferation of fibre, which would arise with an unlimited mesh size. The choice of concentration point will affect the cost of the network. For example, if the concentration is nearer the customer the amount of fibre required can be reduced. However, point-to-point systems require a concentration point with active electronics. Consideration of environmental issues such as powering and temperature control and water ingress is then needed. These issues can be solved more easily if there is an existing building such as a central office offering environmental control. In the green field or overbuild situation these buildings may not exist and an external plant solution such as a pedestal or cabinet will be required at some cost.

The benign environment of an existing central office can perform this concentration function for point-to-point systems. The location of this building has been chosen to suit the needs of twisted-pair transmission. With fibre access using point-point technology, it is almost inconceivable to replace the wire pairs with fibre on a one-for-one basis because of disruption to existing services. Alternatively the installation of a new cables as an overlay containing massive numbers of fibres is very costly

For the mass market, operators are considering alternative architectures than traditional point-to-point for the local loop – the passive star that avoids the cost of active concentrators and can reduce opto-electronics costs by resource sharing.