nd public-key cryptosystems, Commun. slow-hopping, and if the hop rate is faster it is referred to as fast ACM, pp. 120-126. This page intentionally left blank Telecommunication cables PJ Howard Telecommunication Consultant Contents Introduction 15/3 Symmetrical pair cables 15/4 Coaxial pair cables 15/5 Line plant for copper cables 15/9 Optical fibres 15/9 Optical fibre cables 15/11 Cable design 15/13 15.8 Line plant for optical cables 15/16 15.9 CCITT standardised optical fibre 15/16 15.10 Future developments 15/16 15.11 References 15/17 15.12 Acknowledgements 15/17 This page intentionally left blank Introduction 15/3 Introduction APL sheath provides an effective moisture barrier and electrostatic screen. Cables provide the transmission medium for the majority of tele- Cables of this design can be supplied with conductor diameters communication systems. The installed cost of cables is a significant ranging from 0.32mm to 0.9mm, and in sizes ranging from 100 pairs proportion of total investment in any network. A fascinating aspect to 3200 pairs or more. The maximum average resistance and mutual of telecommunication transmission history has been the achieve- capacitance is shown in Table 15.1. Overall cable diameters are in ment of progressive upgrades in traffic capacity over existing cable the range 17mm to 70mm, depending on conductor gauge and links. For example, the application of 30 channel systems to de- number of pairs. The capacitive unbalance at voice frequency is loaded audio pairs, the operation of coaxial cables initially with 300 generally less than 275pF in a 500m length. channel (1.3MHz) systems and many years later with either 2700 For longer circuits, cables with a lower mutual capacitance and channel (12MHz) systems or 1920 (140Mbit/s) digital systems. less capacitance unbalance are required. These requirements are Today, virtually all new cables except for the local area, are of met with a star quad construction i.e. diagonally opposite conduc- optical fibre and of single mode design. Not only 