25.1 Introduction

The purpose of a chapter on analog instruments and measurements is to describe what is required to make analog measurements on digital networks. Instruments such as cable testers and Transmission Impairment Measurement Sets TIMS) make general analog measurements, i.e., voltage, resistance, and frequency, but display results in terms that indicate the health or acceptability of specific network systems. Only those network-specific measurements will be dealt with here. Readers with an interest in how fundamental measurements are made should consult the reference [1] on general test equipment.

Analog parameters exist only at the Physical layer, level 1 (sometimes incorrectly referred to as level 0 ) of the OSI Reference Model for networks. Analog instruments have evolved into three classes: low-cost, general-purpose, and high-performance. The separation of the classes becomes blurred, however, by continuing cost reduction and the appearance of more sophisticated technology in smaller, easier-to-use configurations. Further measurement categorization will be by transport media (copper or fiber optics) and then by LAN vs. WAN within the specified media.