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`Published by Cbapmn a Hall, 2—6 Botmdary Row, tendon El 3H1“. UK
`
`Chapman E: Hall. 2-6 Boundary Row. London SE] EHN. UK
`
`Chapman 3t Hall {'3th. Pappelallee 3. 69-4159 Weinheim. li'iertrnnt}.I
`
`Chapman & Hall USA. “5 Fifth Avenue. New York. NY 10303. USA.
`
`Chapman & Hall Japan. lTPJapan. Kyom Building. 3F. 2—2-1 Himltawacho.
`Chiyoda-l'u. Tokyo “12. Japan
`
`Chapman d: Hail Australia. 102 Dodds Street. South Meiboume. Victoria 3205.
`Australia
`
`Chapman $1 Hall India. R. Seshadri. 31'. Second Main Road, CIT East. Madras
`GUI] 035. lndia
`
`First edition 199?
`
`"El
`
`1997 Nick Bun]
`
`Printed in Great Britain by Cambridge Universily Press
`ISBN I] fill man 1
`
`Apart from any fair dealing for the purposes of research or private smdy, or
`criticism or review. as pennined under the UK Copyright Designs and Patents
`Aer. [988. this publication may not be reproduced. stored. or nansmitted. in an:-r
`form or by any means, without the prior permission in writing of the publishers.
`or in the case of reprognphic reproduction uni:-r in accordance with the let-ins of
`the licences issued by the Copyright Licensing Agency in the UK. or in
`accordance widt tlte tentta or" lioences 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 represeonation. express or implied. with regard to the
`accuracy of the information contained in Eli: book and. cannot accept any legal
`responsibility or liability {or an}.r errors or omissions that Ina} be made.
`
`A. catalogue record for this book is available from the British Library
`
`:Eéif'riotod on
`rtnanent acid-free test
`a
`r, manufaemreti in accordance with
`EJSENISO 2 9.434991 and ANSUNFSSEZSQAS-IQBII (Pennanenee of
`per .
`
`
`
`

`

`I26 TheUinterface
`
`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.
`
`
`
`Fig. 4.13 Power feed configuration at the U interface.
`
`In European ISDNs, the U transceiver side of an NT] for both ZBIQ and 4331‘
`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 St’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 NT! must consume no more than sac mw of power from the
`network, and in a deactivated state must consume no more than IZDmW. Under
`
`emergency power conditions when the MI is expected to also power the user's
`designated terminal
`across
`the user—network interface.
`then the power
`consumption of an active NTI is allowed to rise to a maximum of Li W. 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 23V, while the
`feed voltage at the exchange may vary from network to network from 511'
`to 115V.
`
`aSlightly higher values of less than 600ml? and LEW respectively were allowed during
`an interim period until the end of 1994 provided the power is available From the network.
`
`
`
`

`

`U interface standards
`
`12?
`
`In America, it is expected that remote powering of the NT! is not provided and
`both primary power and emergency, or secondary, power rrluaqlr have to be sourced
`locally at the customer premises. Primary power will usually be derived from a
`local mains source while euuergencg.r power will come from local batteries. The
`status of power at the N“ is indicated in both ETSI and ANSI IBIQ systems
`using the psl and p52 bits of the lat-channel, and Table 4.1 shows the four
`messages defined by the value of these bits. In particular, the value 00 indicates to
`tlte network that both primer}r and emergency power sources have failed and that
`the NTl will shortlyr cease normal operations. This value is referred to as the
`dying gasp message. for which the American NTl must have sufficient energy
`storage to ensure that it continues operation long enough after failure of the power
`sources to send this status to the network.
`
`Apart from the delivery of remote power. the continuous supply at the exchange
`of a small amount of current through the subscriber loop helps to prevent the
`build-up of oxidation at cable joints that could otherwise lead to bad connections.
`This is known as sealing current as it helps to seal the connection.
`
`Table 4.1 Power supply bits of the It! 10 system
`
`NT! status
`
`pr!
`
`ps2
`
`Definition
`
`All power nonnal
`Secondanrpouerun
`
`Primnrvpowerout
`
`Dyinggasp
`
`l
`l
`
`0
`
`0
`
`l
`(I
`
`l
`
`fl
`
`Primary and emergency power sqtpliee are both nonnal
`PrimarypooernonnalJutemergemypowet-ismarginll.
`mavalldsle or not provided
`Mmpowismminnlonmavnilablemrmmm
`is nonnal
`
`flothprinwyandemergencppowaremuginalor
`unavailable. The NT roamr sleuth:I muse nonnal operuion
`
`4.5.3 Test and maintenance functions
`
`in
`As a result of the NT! being considered customer premises equipment
`American ISDNs. American operating companies can place the NTl
`in quiet
`mode as described in section 4.3.].4 in order to perform tests on the subscriber
`loop using test equipment tapped onto the line either at the local exchange or at
`some point along the length of the subscriber loop to the NTl. Return loss.
`insertion loss and impedance measurements can be performed while the NT! is in
`quiet mode. In quiet mode. the NT] is effectively placed in an idle state. ignoring
`requests for activation from the user or terminal side of the interface.
`
`
`
`