`
`
`
`Published by Chapman & Hall, 2—6 Boundary Row, London SE1 SHN, UK
`
`Chapman & Hall, 2—6 Boundary Row, London SE1 8HN, UK
`Chapman & Hall GmbH, Pappelallee 3, 69469 Weinheim, Germany
`Chapman & Hall USA, 115 Fifth Avenue, New York, NY 10003, USA
`
`Chapman & Hall Japan, ITP-Japan, Kyowa Building, 3F, 2—2-1 Hirakawacho,
`Chiyoda-ku, Tokyo 102, Japan
`Chapman & Hall Australia, 102 Dodds Street, South Melbourne, Victoria 3205,
`Australia
`Chapman & Hall India, R. Seshadri, 32 Second Main Road, CIT East, Madras
`600 035, India
`
`3 ’C I
`714
`.4
`I V
`L) i 0 2v,
`[7, (A) /
`\ .
`/ 9‘,
`
`'
`
`/
`
`\ '
`/ .
`
`First edition 1997
`
`© 1997 Nick Burd
`
`Printed in Great Britain by Cambridge University Press
`ISBN 0 412 49730 1
`
`Apart from any fair dealing for the purposes of research or private study, or
`criticism or review, as permitted under the UK Copyright Designs and Patents
`Act, 1988, this publication may not be reproduced, stored, or transmitted, in any
`form or by any means, without the prior permission in writing of the publishers,
`or in the case of reprographic reproduction only in accordance with the terms of
`the licences issued by the Copyright Licensing Agency in the UK, or in
`accordance with the terms of licences issued by the appropriate Reproduction
`Rights Organization outside the UK. Enquiries concerning reproduction outside
`the terms stated here should be sent to the publishers at the London address
`printed on this page.
`The publisher makes no representation, express or implied, with regard to the
`accuracy of the information contained in this book and cannot accept any legal
`responsibility or liability for any errors or omissions that may be made.
`
`A catalogue record for this book is available from the British Library
`
`‘
`@Printed on permanent acid-free text paper; manufactured in accordance with
`lANSIgNISO Z39.48-1992 and ANSI/NISO Z39.48—l984 (Permanence of
`aper .
`
`
`
`
`
`126 The U interface
`
`be applied by splitting each line-side transformer winding into two equal halves
`and connecting them with a capacitor. The capacitor enables AC signals to pass
`without attenuation but blocks DC voltages. Components are added to this
`configuration to protect the circuitry from excessively high voltages caused by
`lightning strikes.
`
`to N.“
`U transceiver
`
`
`
`
`
`to Iinecard
`
`U transceiver
`
`protection
`curcunry
`
` '
`
`'
`D391?tge
`
`‘ DC voltage
`.
`source
`
`Fig. 4.13 Power feed configuration at the U interface.
`
`In European ISDNs, the U transceiver side of an NT] for both 2B1Q and 4B3T
`systems will
`typically be powered remotely from the network across
`the
`transmission cable, thus allowing the network operator to maintain full control
`over the U transmission system at all times. The S/T user—network interface may
`under normal conditions be powered locally from the NTl using a local power
`source such as mains or batteries, and is backed-up with remote power from the
`network under emergency power conditions where the local power source fails.
`When active, the NTl must consume no more than SOOmW of power from the
`network, and in a deactivated state must consume no more than 120 mW. Under
`emergency power conditions when the NTl is expected to also power the user's
`designated terminal
`across
`the user—network interface,
`then the power
`consumption of an active NTl is allowed to rise to a maximum of 1.1W8. This
`power is delivered as a DC voltage and current that varies between different
`ISDNs due to the different safety requirements and subscriber loop configurations.
`' The minimum voltage at the NT] required for correct operation is 28V, while the
`feed voltage at the exchange may vary from network to network from 51 V
`to 115V.
`
`
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