4.1 Introduction and Review of Previous Attempts

This chapter looks at how the condition of existing access networks can be modelled.

The PSTN copper access network forms a major transport channel for successful delivery of broadband services to residential customers in Britain [1]. Using asymmetric digital subscriber line (ADSL) technology, the twisted copper pair used for telephony can also carry digital data traffic by passing higher frequencies down the line. In theory, a copper pair has well-defined characteristics for signals up to several megahertz. However, BT has a PSTN network that was installed primarily for low-frequency voice traffic, some of which has been in service for over 30 years. Clearly, it is impossible to know the physical characteristics of all copper pairs but this information along with their age and condition have a real effect on high-bandwidth traffic (in terms of attenuation, crosstalk and noise). Consequently, within an aging network this can result in an increased fault rate and poor customer satisfaction.

For many reasons it is sensible to assume that the fixed line network will still be the transport of choice for some time to come. With the promise of the data wave sweeping the nation, people will inevitably become more data hungry. Despite the great advances in technology BT has made in the development of digital techniques, optical devices and transport, reliance is still made on the copper access network which represents a considerable proportion of BT's fixed assets. Although this technology is...