Chapter 6: The Powering of Access Networks

Chapter 6: The Powering of Access Networks

?Power corrupts.?

?Anonymous

Overview

For access networks, it may well be that the things that are most corrupted by power are the grand visions that people have had about the future. In one case at least, the problem of powering has been blatantly dismissed as a mere detail. In the real world, before the advent of reliable cold fusion, antimatter containment, or the tapping of the quantum vacuum, it may be a less trivial problem.

The discussion of powering given here is at a higher level than that of the transmission technologies, since the purpose of this chapter is to identify the problems and their possible solutions.

6.1 The Traditional Balance

In the traditional approach to PSTN, the telephone handsets are powered from the exchanges to which they are connected. The exchange supplies dc power across the same pair of copper wires that carries the voice signal. There is no need for the power to be supplied by the customer unless a special terminal, such as a fax or an answering machine, is used. The PSTN service is also made independent of the mains electricity supply by having a backup power source, typically an independent generator, in the exchange building.

It is important for PSTN to continue to operate during a mains failure because voice communication is needed during emergencies when mains power is not available. The PSTN service was designed to be independent of local mains power, because local mains power was...

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Chapter 6: The Powering of Access Networks

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