6. Private Circuit Links

A private circuit is a link between two locations joining two or more pieces of customer equipment. The need for these type of links arise from the communications requirements of the network customers. The physical link is provided by the network provider and is exclusively for the use of the customer leasing it. This exclusivity means that there is a premium placed upon these types of circuit because they must be maintained by the network provider for a single customer. This maintenance commitment is costly. The benefit is derived from high usage of the link as the calls are free once the rental has been paid. It is therefore only a practical proposition between sites where the call traffic is heavy and normal network
charges for the calls would exceed the cost of circuit rental.

With modern digital services and routing equipment a dial on demand service can be used for lower traffic users, where each call is charged at the usual rates. This provides similar functionality to the permanent connection at a lower cost.

6.1 Private Wires And Access Lines

A private wire or access line is the simplest form of private circuit. It is a straight wire pair from point A to point B. The wires will be routed along the runs used by the network carrier for other telephone lines in the area.

The circuit is a plain pair of wires with signalling being supplied from the equipment located at its ends. Although it shares the ducts of the network provider and is maintained by the same there is no physical connection between the two.

The length of a private wire is limited by the ability of the connected equipment to drive power down the line. This gives a practical length of upto 2 kilometres. The line will have a typical loop resistance of between 500 ohms and 1600 ohms. Equipment which cannot operate with these levels of resistance cannot be used with private wires.