f lexibil ity in understanding equipment and retraining. (Arthur D Little Ltd, Berkeley Square House, Berkeley Square, London WlX 6EY, UK. Tel: 01-493 6801). []

Signalling in telecommunications networks S Welch, lEE Te lecommunica t ions Series, UK (1979) £12

Signalling systems link the various switching machines in a telecommuni- cations network to enable the network to function as a whole, and must be compatible with the various types of switching and transmission systems with which a given network may be equipped. A good understanding of sig- nalling is thus essential in network de- sign. The book is intended to present and analyse the various possible signall- ing techniques. This is particularly im- portant in view of the impact that new techniques (stored program control, intregrated digital transmission and switching etc.) may have. Although dealing mainly with public telephone systems the signalling principles form the basis of private and data networks. Signalling in both the analogue and digital environments is included.

Also covered are subscribers' (cus- tomers') lines and local exchange area junction networks; PCM systems are dealt with when relevant. This leads to long-distance DC and low-frequency AC signalling, trunk (toll) network, DC voice frequency, outband and inter- register multifrequency signalling, and includes the influence of transmission and switching. Requirements and pre- ference for common channel signalling in both analogue and digital stored pro- gram control environments are covered, as are the CCITT international signall- ing systems, their evolution and the rea- sons for their existence. (Peter Peregrinus Ltd., PO Box 26, Hitchin, Herts., SG5 ISA, UK) []

Interfacing the automated maritime mobile telephone system with the US public switched telephone network

R F L inf ie ld and T de Haas, N T I A Report 78-7 (1978) ($5.25)

The functional requirements, opera- tional characteristics and technical specifications of automated maritime mobile telephone systems are being studied by the International Radio Consultative Committee of the ITU. In a related study, the authors describe the characteristics of both the US public switched telephone network and the maritime radio service. The features and performance parameters, both operational and technical, desirable in an automatic maritime mobile tele- phone systems are reviewed. Rate structures of both US domestic common-carrier and maritime mobile services are outlined.

Emphasis is laid on: land sub-

scribers calling a ship; communications in a fully automated system when the customer has no knowledge of the ship's location; accomplishing the goal of making a ship-to-coast station link appear to be an extension of the tele- phone plant's local loop.

A number of issues pertinent to the domestic-telephone/maritime-mobile interface are grouped under the follow- ing headings; channel allocation, co- channel interference and sharing, range extension, performance, internetting, location registration, costs, rates and rate structure. (National Technicd ~n- formation Service, 5285 Port Royal Road, Springfield, VA22161, USA. Tel: (202) 39S-SSO0) []

Computer equipment

ICe Business Rat io Report UK (1979) £44

The financial performance of the 60 leading UK computer equipment com- panies is analysed for the period 1975 -78. The sector showed continued growth with a 20% total sales increase and a total pre-tax profit improve- ments of 50%. Disturbing features are evident, however, with regard to work- ing capital management. The overall liquidity position as summarized by the current ratio, indicates that only 16 out of 47 firms have an acceptable level of 2:1, the average being 1.6:1. The com- ponents of current assets are examined for credit period and stock levels. These factors imply that current assets, excluding cash, are growing more than current liabilities, which could lead to

short term liquidity problems. A discussion of the destination of the

industry's scales shows that the largest recipient is itself, followed by the office equipment industry. Machine tools, education and business services are, as yet, relatively unimportant customers. The computer equipment sector ex- ports a very high proportion of its out- put, the UK being in a good position despite being a net importer. The mar- ket oriented companies should concen- trate on the developing nations, es- pecially Latin America, the Middle East, Africa and the Peoples Republic of China. (ICC Ltd, 81 City Road, London ECI Y IBD, UK. Tel." 01-638 2946) []

134 computer communications