Contents

Ed1tor: Ron Quinney (ES5.4.3) Editorial Publ1shed by BTHO/ NE / ES543. Testing SSAC15 Pr1vate C1rcu1ts Room 301. at TMCCS 203 High Holborn Improvement plan for overhead LONDON WC1 V 7BU network 3 01 -432 2806 Special serv1ces maintenance 4 Maintenance News D1g1tal transmiSSion- coded mark ISSN 0143-6627 1nversion 5 How computers keep their cool 6 Regent call connect system 7 The Irish connection 10 Register translator 14 11 Close encounters of the 4A kind 14 On reflection. 15 New generation test equipment for the fault repair serv1ce 17 Faster RATES for private circuitS 20 Automatic testmg methods 21 New cable alarm saves money 24 New electroniC work bench 25 Introducing reg1onal service 1mprovement centres 26 Letters 26 Editorial Testing SSACIS private eireuits at TMCCs My editorral functrons on thrs magazine take by Roy Smith BTM/SM1.4 Operation up only a small part of my BTHO duties. The success of the patching relay set In operatror1. orther the local or drstar1t~end lnevrtably. therefore. time does not permrt used with the signalling system AC13 of the crrcurt to be tested rs patched from the complete checkrng of the technical accuracy (SSAC13) at Trunk Maintenance test Jack frame ( T J F) appear a 11 ce to the test of all authors' submrtted drafts. This was Control Centres (TMCCs) resulted in set. due regard bern~l grverl to the TMCC brought home after the drstrrbution of the decision to introduce a similar standard levels. The patch should. therefore. MN19 by my training colleagues who were device for circuits equipped with the rncl ude ar1y r1ecessary a mplrfrers and becomrng bombarded wrth querres on AC15 equipment. The facilities offered attenuators. The AC15 rs r10rmally strapped Herald trainrng courses- all because two by the tester and some constructional to present relatrve levels of 1 dBm and course numbers had been transposed. The details are described in this article. It -4d Bm. Having done thrs. testrng can start. Edrtorral Board have 11ow decrded that a should be noted that this BT version ..J Outgoing call disclaimer should be rncluded in the has identical electrical characteristics The two~wrre lrne test cord rs plugged into magazine in future. In my other dutres. to the Northern Telecom equipment. the two~wrre Jack and, after operating the concerned with the reparr of electronic Facilities 'speak' and 'loop hold' keys, the required equipment. I am aware of the wrde variety of outgomg call-rr1cludrr1g dralling to local number is dialled. Wrth restoratron of the new customer apparatus. systems and e or drstant~er1d 'dral' key, supervrsory tones are heard. When technology enterrng servrce with British rncomrrlg call-rr1cludrng recording of the drstant~end answers. the lamp lrghts­ Telecom- many in large numbers. The e dralled drgrts on a 10 or 16~digit drs play rndrcatrng Called Subscrrber Answer (CSA) exciting and challenging era we have been unrt -and corwersation can take place. waiting for has arrived. and it rs up to all of us supervrsory condrtions When the called~er1d clears (CSA lamp to keep ourselves informed of developments. e -rncoming call (1/C Call) off) the crrcurt can be released by restoring Maintenance News arms to do all it can to -called subscrrberanswer (CSA) the 'loop hold' key. help in this important aspect of today's ~-called subscrrber clear world.- Edrtor. J Incoming call e M onrtor of cr rcu rt- tone on idle The customer or engrneer at the drstant~end Equipment can then be rnstructed to call back. In thrs As shown in the crrcuit diagram. the rnarn case the lamp mdrcates an rncoming call features are: (1/C Call). The procedure already e interface relay set -loop drscor1nect/E mentruned rs followed. but thrs trrne the and M rr1comrng dralled drgrts can be detected and e transformer unrt stored 011 the drsplay unit. e break~type Jacks and lamp The crrcurtrs released wher1 the callrng~ e SSAC1 5 equrpment end clears. Benefits • elimination of abortive visits to customers Several benefits arise using this test-set, e improved serviceability. including: 021-262 4040 e fault localisation before involving other maintenance staff Edge connector T1 .------~5

+6 4 R4 s

British Telecom LS SSACIS 2 Equipment Diag SA/SAW 702060 -50v 0 35

II~

LS2

1 111 _-/ ... riD lJI,1 -ve .., E2 .., ~S:,1 I 212~1 Digit e---'-"------~ I ~II 1 Display Reset 21 22 1 2 I A::: r<:/\ _/(2 Unit ~~~------~ 11H1vvv~ E---111 1/C Caii/CSA lamp Improvement plan for overhead netUJork

by John Stoddart BTSW/SV1.3.2 wrre. such actron often manifests rtself as an when they encounter or provide more than New developments over the past 10 rntermittent norse fault. Wmk practices two drop wires in line of route years have steadily improved the considered to contrrbute to premature drop e too low a priority given to dealing with any performance of the overhead network. wire failures are: ofthese causes. But this performance tends to e too many drop-wrre clamps frxed to a deteriorate rapidly during bad weather. srngle Bracket 22 often result rn abrasron Improvements required This inability to withstand bad weather e strippmg rrlsulation unnecessanly or failing . j More reliable drop wire not only stretches the manpower to use the cmrect tool- Wire Stnpper 2- BTHO seem to have accepted this and a drop resources beyond the limits of the results in damage to the conductor wtre wtth cadmtum-copper conductors, to be normal repair service organisation, but e JOtntt ng drop w1 res wtth Wire Insulated known as Drop Wtre 7, is to be introduced also has a catastrophic effect on BT's Connector 1 A- which is for underground natronally. ability to restore customer service use rapidly enough to achieve the TIP 2 e failure to use an Aerial 32A and Tester 132 _j Improved workmanship target. Consequently, as BT is soon to to locate a disconnection fault can result in Even wrth the Introduction of a more rei table aim for a 95 per cent TIP 2 target and the creation of unnecessary JOints. drop wtre. staff need to become aware of also has a longer term Tl P 1 objective Srmilarly, unwillingness to open aerial preventive matntenance aspects, such as: of 0·29 fault reports per station per cable couplings results in additional joints e The prevention of drop wtre fat lures which annum, further effort must be directed external to the couplings are a result of abrastorl by trees, lamp towards reducing the overhead plant • insufficienttree pruning. standards. roofs and so on fault rate. Other causes are: e J ornts 111 drop wtre must be kept to a elack of a suitable lead-in cable at block mirlrmum and, whenever practical. a faulty Factors affecting performance wiring points drop wire should be replaced in its entirety. Wrth the exceptron of Drop Wrre 4, other • ageing of open wires and the inability of Where Joints are unavoidable, the correct recent types have been rnadequate. The staff to carry out their work rtem- Wire Connector 2A- must be used situatron rs further aggravated when there rs • insufficient use of spiral eyes to restrict the e Staff should carry S!Jare terminal block an accumulatio11 of drop wrres on a route. movement of drop wires to reduce covers and strip-contact gas-discharge Frequer1t failures occur because drop wires termination failures on DPs tubes which should be replaced when they are unable to withstand abrasron and are thus • the conductors of both an aerial cable and are found to be corroded susceptible to any fmm of abuse arrsing drop wires terminated on the face of a e Terminal blocks should be treated with from pom corlstructrorl or work practices. terminal block often results in the drop srlrcon spray as a matter of course Resultir1g damage to the copper-coated steel wires being severed by the aerial cable • Frnally, good field supervision and conductor soon causes rt to cmrode or rust • failure of maintenance and installation staff adequate trainrng are essential ingredrents away. Before the complete far lure of the drop to subm rt either forms A 1 024 or A2887 to improve the quality of workmanship. 3 Speeial serviees naaintenanee

J Comprehensive plant improvement by Don Beckley T5 much more cooperation and extra effort w1ll scheme Private circuits are the most important be needed. There is a need to introduce an all-embracing part of Special Services, of which Even before the threat of competition it scheme which will- amplified external extensions and Datel was recogn1sed that BT may not be showing • include procedures to identify sections of services are the other large elements. enough concern. but with competition now overhead plant which are in need of Because of their importance private with us we have greater reasons for remedial attention circuits have been under the spot-light satisfying our pr1vate circuit customers. In e be complementary to LOCAMS recently due to the long delays in the Bell system, one-third of the revenue • have a mechanism to control the priority of provision. Consequently there has not comes from spec1al services. compared with the planning and execution of plant been much attention focused on four per cent in the UK. wh1ch illustrates the improvement work. maintenance. This is not to say that all considerable potent1al for shift of revenue by To conclude. adequate numbers of the our customers are satisfied with their our business customers. correct size working parties will be required service, indeed, the need to improve the to support such a plant improvement repair service still exists- especially in TIP2A programme. London. In 1979/80 TIP 2A- the percentage of all 0272 295240 Private circuits have always presented fault reports cleared by the end of next problems. but during the last five years their working day-was introduced as a 1m porta nee has gained increasing perform a nee indicator designed to 1mprove recognition within BT. Among the speed of repair. What has been achieved? In difficulties in maintaining private circuits is early 1980 the national performance was 60 Corrections the large variety of customer terminating per cent compared w1th 79 per cent in Phil Darcy's article in MN19 on London's equipment. Some of this equipment is December 1981. During the period October TXE4 contained a mis-print on page 7, customer-owned. and many customers use 1 980 to September 1 981 the number of column three. The·second line gave a figure i the equipment for non-speech transmissions Areas achieving 80 percent increased from of 0.5 per cent.- this should have been 1 which makettjstlng difficult. But the 62 to 78; those achiev1ng 90 per cent 0.05 per cent. fundamental drawback is that private increased from 21 to 59; and those achieving Due to an error in the author's draft. the circuits do notfall1nto the patterns of 95 per cent increased from 6 to 20. So there course numbers for the Herald training responsibility so well defined for the PSTN has been a steady improvement. However. courses were incorrect. Herald Newsf/ash and so well served with interfaces and Areas achieving the best results do not have No. 49 was issued by ICS7.2.2 to overcome test po1nts. automatic routiners. and so on. many private circuits. the immediate problems experienced by Clearly then. to overcome these deficiencies So a very substantial proportion of faults training officers.- Editor. -absence of clear boundaries of is still not being repaired by the end of the responsibilities and facilities of control- next working day. The majority of these 4 Digital transmission faults are in the large crtres. more especrally performance and to brrng action to bear -eoded mark London. and we clearly have a long way to when things are clearly not happenrng as go to achieve the target of 95 per cent. If the they should. To do this JOb he needs good anversaon- - target seems ambitious. let me say at once responses from all around hrm. whether they by George Clark T5.1 .4 that our customers really want 'same day' be rnternal or external. Hrs JOb rs to provrde Previous MN articles on digrtal transmission clearance. conscience to the ser·vrce. have referred to coded mark inversion ( C M I) Speed of repair r n itself rs rlot the only Reg ronal Datec teams on the other hand without descrrbrng the technrque. criterion- abrlrty to deal with repeat faults rs were set up to deal with obscure faults not CMI is an internationally agreed standard another. It rs a sad fact that many crrcurts are easrly located by the regular staff wrth their interface srgnal conforming to the general poorly installed wrth unsoldered JOints, lrmrted facrlrties. The teams have done much outline shown in the figure. Technically, it is causing intermrttent problems whrch are valuc:ble work. mcluding dealrrlg wrth a two-level non-return-to-zero code, in hard to rdentrfy. They cause confusion and problems of pmtocols rn data transmrssron. which Binary 0 is coded so that both much wasted trme. especrally when data , Unfortunately, their presence rs not wr dely amplitude levels A 1 and A 2 are attained transmrssron rs rnvolved. because the proper enough known and they are not called upon consecutively- each for half a unit time functionrng of the circurt rs only finally for help as often as they might be. Any interval (t/2). Binary 1 is coded so that proven with customer's cooperation. Faults article on Specral Servrces marnterlzmce either of the amplitude levels A 1 and A 2 are of this kind urldoubtedlytestthe patrence of would be rncomplete wrthout merltron of attained alternately for one full unit time the customer·s who cannot understand why remote test access. but this is the subject of a interval (t). we cannot do better· If they were aware of special article (RATES) rn thrs issue. the real cause and the comparatrvely srmple To summarrse. we have accomplrshed a Binary remedy, they would have even less great deal. but much more remarns to be Level A sympathy I We do not deal wrth repeat faults done on reparr and maintenance of prrvate 2 as energetically as we should. Currently circuits. New servrces (X- Stream) are being about 25 per cent of all fau!ts are repeats. introduced in 1982 and will make demands having been reported prevrously wrthrn the at least as great as the exrstrng ones; these last two months. new services are rntended to match the competition in technical innovation. We Level A 1 1...- .__ Teamworl< is essential must match the competition in the servrce 1 1 During the last 18 months two rmportant we give. I -"•1 i'ol events have occurred. namely the t establishment of Specral Servrce Managers ~ f4-----+1 (SSM s) and the Datec teams. The role of the Example of CMI coded bmary signal SSM rs to marntar rl an oversrght of 01-4321328 5 Hotv eonaputers keep their eool

by Dennis Brewer ETA5.3.1 significant part in dust and odour control. functions are camed out on the incoming The provision of process cooling for large In large data processing centres the main fresh -a1 r stream. In typical winter conditions computer installations has been necessary computer room is usually split into a number the fresh-air content will be extremely dry ever si nee the introduction of early I C L Leo of zones where each zone copes with and. when mixed w1th return air. the mixture 326 computers in the mid-1960s. The approximately 1 00 kilowatts of machine heat. w1ll absorb mo1sturefrom personnel and exacting standards of temperature, humidity Each zone has its own re-circulation plant or equipment thus caus1ng the room's relative (50%RH) and dust levels specified for air handling unit fully equipped with fans, hum1dity to begin to drop. The humidity computers have required OPE to provide and cooling coils filters and 1ts own set of detector will, under these conditions, operate purpose-designed and built controls. Temperature control is achieved by respond by switch1ng on steam humidifiers computer centres throughout the country. proportional control of the cooling coil. A until the correct spec1f1ed, balance is The purpose-built centres are designed to temperature sensor is placed in the zone's achieved. mamtai n computer rooms at 21 oc ( ± 3 °C) return-air stream producing a signal which is Because each computer centre was built and 50% ( ±5%) RH continuously, passed to a controller which contains the set or refurbished when the need arose. BT now 1rrespect1ve of heat from machines. personnel point signal and a comparator mechanism has a great var1ety of buildings, refrigeration, and fabnc. and solar gains to the building. that proportionally drives an output signal to air handling units and controls. However. a In BT's larger centres the process cooling the valve actuator on the cooling coil. The common element at most larger centres is load is provided at 600 watts per square cooling coils usually contain chilled water. pneumatic control of air conditioning. And metre. thus the standard 1 000 square metre The chilled water is maintained at a flow these controls have proved to be extremely computer room IS capable of dissipating temperature of approximately 1 ooc- chosen useful. s1mple and reliable. The basic system about 600 kilowatts of process heat. to restrict the latent (moisture removed by uses a pressure range of 3-1 3psi (0.2-09 bar The purpose of a1r conditioning is, of the coil) duty of the coil. This is because the approximately) operating sensor controller course, to establish and ma1nta1n the dew-point of a room held at 21 oc and systems wh1ch actuate pneumatic valves. appropriate environmental conditions, which 50% RH is about 1 0°C, so in these conditions dampers. motors and micro-switches. In 1nclude retaining a static moisture level. To coil temperatures below 1 ooc incur recent years, electrolliC controls have greatly help achieve this level- and thus simplify the excessive latent duty. 1rnproved and much more use is being made control and ducting arrangements-fresh air Provided the moisture level in the room of the modular systems offered by specialist 1ntake is l1m1ted to between 2-5 per cent of remains constant the relat1ve humidity will f1rms. the total re-circulated air. The fresh air is not exceed the specified limits of control usually provided via special equipment which while the temperature stays within its limits. Engineer's role also ensures the temperature of the incoming Control of relat1ve humidity is achieved The role of a build1ng serv1ces maintenance air is 1n the region of 13°C all the year round. either by add1ng moisture with steam engineer in a BT computer centre is an The fresh-air plant also provides a positive electrode boilers, or dehumidifying by using extremely exacting one. H1s skills must pressure to the room and so plays a a fixed fresh air input temperature. Both encompass all aspects of electrical 6 1 Regent eall eonneet s~stena by Roger lsted BTE S1.3.3.1 Space division switching Regent is the name given to this new Regent is an advanced electronic PABX w1th PABX recently launched by BT in drg1tal stored program control but, unlike engineering from high voltage mains to low selected areas of the country. It is Monarch uses CMOS space-division voltage control c1rcu1ts, and from pneumatic based on a proprietary switching swrtching The system capac1ty is 256 ports to electronic controls. He must also be able system and is complementary to the of whrch 184 are available for assignment to to understand the basics of refrigeration to BT developed Monarch 120 described in extensions. exchange l1nes or private circuits. run and maintain the large quant1t1es of MN15. The rema1nder are used for receivers. special ch1ll1ng plant under his control. BT has been The Regent call connect system­ funct1ons. and the common control. served well by its present mallltenance force initially available in BTE, BTNW and The system's capacrty depends upon the w1th only a few hours of computing time lost BTL/City Area- offers similar capacity way the ports are used. as an extension uses 1n recent years. to Monarch and is being marketed to one port. arl exchange line two, and a private !VIr Brewer has now left ETA5 and has give customers increased choice of BT crrcuit four. The maxrmum size of the system become a Fiald Sales Manager in Exeter PABXs. It has recently become available rs 24 exchange l1nes and 134 extensrons. Area- Editor nationally. Areas burld a system to order from a basic

,-~---·-···---···----··--- ·-- ·-·· ., : Parallel working of a M ic 21 with 1 i carbon microphones

1 The carbon microphone can shunt the M1c 21 and cause 1t to cut off when two or more handsets are off-hook. This can apply w1th Plan numbers and 2/ PM BXs. The remedy for 7 46 type 1nstru ments 1s to change all transmitters to M1c 21. Th1s is llOt poss1 ble 1n the case of tr1 mphones (for wh1ch no I ~near microphone solution has been developed) or certa1n spec1al range telephones employing other carbon microphones; Ill such cases the solution 1s to burld out the m1crophone w1th zener r adaptors or su1table resistors. Further l1nformat1on on M1c 21 1s conta1ned 1n : ICS7.2.2 Newsflash 1073 dated March ~ 982. --·· ___j 7 8+48 unit by the provision (or removal) of Microprocessor ..,..---- / apparatus slide-in units (AS Us). The Regent's 256 ports are scanned sequentially Ma1nt en anee I T'fL£COf'·\ Regent ] operator's console is used to configure the for detection of signals. each port being panel ' -~-~cJ ... ; j j .I '==' system-operating program. Extension AS Us scanned for 12.5 microseconds. All ports are have eight circuits. exchange line AS Us four, therefore scanned every 3.2 milliseconds. Equ1p ment and private circuit AS Us two. During scann1ng, detection of call shelf 2 Regent cons1sts of a single floor-standing orig1nation causes a microprocessor interrupt ]it cab1net (about the s1ze of a domestic Signal to be generated. and a speech path and refrigerator) wh1ch can also house an rece1verto be assigned to the originating Equip ment optional, standby, power supply of between extens1on. After dialling, the rece1ver is shelf 1 two and six hours. All connections to the released and the called party is connected l~lli J~ "~n equ1pment cabmet use three-metre cables to the same speech path as the originator. , n n 1"1 n,. terminating in a wall-mounted connection There are 31 speech paths available in Secon dary box (box connection 350). Regent, and each of the 256 ports has access ~- . powe rshelf- - The connection box uses insulat1on access to all of them. ~ displacement connectors to terminate the The ma1n processor with overall system Fr ontview 1/ building distribution wirtng and a combined control. is an MC6800. It is supported by ~ connect1on box and building distribution 8k bytes of Random Access Memory (RAM) frame (BDF) 1s also ava1lable as a wall used as a call processing transient memory­ mounting unit (Box connection 520 or 530). such as remembering which extensions are The front door of the equipment cabinet busy. Also. 4k bytes of RAM- battery gives access to the maintenance panel. protected- contains installation-dependent AS Us and standby power. The rear door Information, such as access codes and holds the systems primary power supply and extension numbers. The system also gives access to connections for extending provides up to 56k bytes of programmable the system. emergency switching circuitry Read Only Memory (PROM) containing the and standby power controls. Cable entry is system-operating program. Particular through holes at either side at the bottom of versions of operating program are known as the cabinet. generics. The operator's console contains an He-engineered M C6800 microprocessor with 2k of ROM Regent was developed by M itel Telecom which controls the displays and monitors Limited and is manufactured in the such things as keystrokes. company's South Wales factory. It is based Regent uses a specially developed large on Mitel's SX-200, but has been extensively scale integrated (LSI) c1rcuitto implement re-eng1neered to suit Brit1sh Telecom a space-division switching matrix. The basis Primary power supply requirements and network characteristics. of this space d1v1sion is a four-by-eight bit analogue crosspoint switch ( M I TEL Regent Cabinet Layout MT8804) which is used throughout the 8 system to connect any one of 31 speech range of features and facilities to meet paths to any one or more extension. customers needs. exchange l1ne. console. receiver or tone 020645206 generator circu1ts under the control of the microprocessor.

Maintenance Regent System Conf1guratton The modular design of the equipment permits 1------l rapid location and replacement of defective , 31 speech paths 1 parts. Circuit malfunctions are detected ~------~ I by diagnostic routines automatically I 1nitiated by the central processor unit (CPU). Extensions Preventive maintenance 1s limited to the Tone control replacement of the Random Access Memory Extensions (RAM) battery packs every 18 months and the optional standby power every four years.

Automatic diagnostics To local Exchange In addition to 'power-up' diagnc3t1cs which Exchange Line Trunks checks the RAMs and PROMs. an automatic Processor & diagnostic rout1ne runs at all times except Memory when there are four or fewer speech paths free in the system or when an operator's console is being used to configure the system. The automatic diagnostics tests the speech path connections. MF and dial pulse generators. supervisory tones. and speech Scanner path 'biasing'. Faults found are reported as non- urgent alarms. and the fai I i ng unit is Console Common control busied out. if possible. The automatic L ______j diagnostics will not busy out more than half the receivers. generators. or speech Receiver Data/address buss paths. so guard1ng against the poss1bility that an error in the fault detection circuitry could shut down the system. Commercial ~-+~~~- Regent- which is exclusive to British power ·~------~-~-~----il Pownpply I Telecom- is an advanced sol1d-state PABX of exceptionally small size. noiseless in operation. and offers a comprehensive L ______J 9 The Irish eonneetion

by Douglas Gregory T5.3.1 present procedures rely on individual procedure. An agreement has been reached with 1nterpretatio11 of old working arrangements iJ First stage. contact between the the Irish telecommunications wh1ch had never been ratified by the two Superv1sing Off1cer of UK Control and the administration which should improve administrations. Inevitably problems often Inspector-in-Charge of Dublin Control the handling of Private Services got out of hand and serv1ce detenorated due __ Second stage: contact between Executive between the two countries. Within BT, to the lack of agreed technical standards Engineer or Spec1al Serv1ce Manager in UK these services- now to be recognised and escalation procedures. and the Executive Engineer of Dublin Control as 'international type connections'­ o Third stage: contact between will remain the responsibility of the Proposed procedures BTHO/NEjT5.3.1 and the Eire P and T Inland Division. The proposed new procedures are based on Department of the Engineer-in- Chief. The procedures agreed are contained in those currently used for maintenance of In addition, the procedures include the following Tis: 83 K0037 (Marketing). private circuits to other countries. Each guidance to staff on the kind of information AB K1504 (Planning and Works) and circuit will be planned and commissioned that may he I p customers who are very EB K1175 (Maintenance). Under the with a national section in each country, and dissatisfied with the service given by either agreement three types of private circuits will a connecting international section. The administration. be provided: international section w1ll be the Group link u Ordinary quality point-to-point between the respective H F terminals, one of Implementation c:: Special quality point-to-point which will be designated the Terminal The new procedures are expected to be o Special quality multipoint International Circuit Control. implemented from about mid-1982 for new The technical requirements will be based This will reduce the total number of Circuit c1rcuits. Exist1ng circu1ts will be programmed CC/TT Recommendations M 1020 and Controls in the UK need1ng to make contact for re-designat1on and possibly re­ M1040, and the c1rcuits Will be identified by with Dublin Control to about 13, and will englneering in the near future. But even standard international designations, such as g1ve more scope for cooperation between before this work has been completed, NC- DU1 (denoting thef1rst circuit between terminal staffs. The responsibilities of Circuit maintenance staff will find the information Norwich and Dublin, the next being NC­ Controls and sub-controls have been re­ in T/ EB K1175 a useful aid when dealing DU2, and so on). defined and identical wording reproduced in with the Eire administration. both administrations' maintenance 01-432 9194 Present procedures instructions. In January 1 982 there were 250 private circuits serving UK and Eire customers. The1r Escalation maintenance responsibilities rested w1th Should a problem arise in the future, about 65 Circuit Control centres in the UK, engineering staff in both countries will be but with only one in Eire. To a large extent able to invoke a three-stage escalation 10 Register translator ~4 by Brian Harris ES9.2.1 Development of a new processor­ components, and Signal Conversion dur1ng installation. commissioning, or under controlled register translator to replace Electronics (SCE) powered by+ 5v and fault conditions when the R/T14 is out of the magnetic-drum type { R/T4) is now using transistor-transistor logic (TTL) and service. When the R/T14 is in service the nearing completion. It is known as discrete component relay drivers. One R/T maintenance console is disconnected by a R/T14, and 95 have been ordered for 14 is provided with 96 sees whrch are Yale-type lock and the key is stored in a safe. installation in Director Central connected to the Central Processing Unit All program and data- for example Switching Units {CSU) starting in (CPU) via an Input/Output (I/O) and translation rnformat1on- is held in dynamic September 1982. One R/T14 will replace highway interface unit. Random Access Memory (RAM) within the two magnetic drums. An R/T14 can be Thirty SSM F2 sender-receivers are store system. An area of store is also installed very quickly, and though the provided on theM F rack, 1 5 for each R/T 14. allocated for each sec, known as sec first installations will be supplied and A sender-recerver (SR) is connected via a working store. where all the information for a installed by the manufacturers, MFelectronic unit (MFE) to the 1/0 and particularcall1s stored. The CPU counts subsequent installation and then to the CPU. The CPU scans all the SCCs rncoming d1gits and stores them in the commissioning will be done by British and M F SRs every 11.1 ms and will do a appropriate sec working store along with Telecom staff. lrmited amount of work for any SCC or SR class-of-service and translation information The rlumber of R/T14 processors at any on which a call is being set up during every when sufficient digits have been received to srte wrll depend on local requrrements but 11 .1 ms scan period. Because the CPU is obtain a translation. the mrnimum installatron comprises of two working at a very fast rate (1OM Hz) it is able For any processor a program of processors and one rack of SSM F 2 sender­ to control up to 96 sees, albeit one at a time. rnstructions must be written and stored rn recervers; the two processors and one M F2 machine-readable form to tell the processor rack berng referred to as a cabrnet triple. The CPU what to do for any given set of Existing regrster access relay sets will The CPU is a G EC M K1 P Processor. circumstances. Most of the store is used

1 n rtrally be retained 1 n the CS U together with identical to that used in the processor for this program information. Each program the regrster hunters. The outlets of the controlling TXK1 GSC equipment. The CPU 1nstructron IS stored in one word of store, a regrster hunter are cabled to Signal rs the heart of the system where program word being 16 b1nary d1gits (bits) and Conversron Circurts(SCC) on the R/T14 racks. instructrons are decoded and executed to having a particular location. or address, The sec provrdes the Interface between control all the actrons wrthin the R/T14. It within the store. For every step of the the 50v electromechanical equipment and consists of an oscillator and clock timing program the instruction word has to be the electron rc processor equipment. The circuit; a registerfile and arithmetic unit; a located and the 16 bits of information sec is analogous to a register but the mrcro-program from which all control transferred from the store to the command register functron rs performed by the sequences a1·e derrved; and a store address word register 1n the CPU where it IS decoded processor. The SCC consrsts of two separate circuit by which the store-system is accessed. and used to initiate action by the micro­ units: Srgnal Conversron Relays (SCR) A maintenance console and console program which sends out control pulses, powered from the exchange-50v supply and interface ci rcu 1t are 1ncorporated in the CPU each 1 OOns long, to perform the action usrng type-23 relays and drscrete to g1ve corr,plete manual control ofthe CPU required. Extractrng the program word from 11 TK 1st

To SCR's on all { available processors ------~

MF access switches

MF access switches

sec

96 SCCs and 15 MF2 S/Rs Etc. as shown on left

Inter processor highway

Teletypewnter highway 0 l/0 1/0 Teletypewriter highway 1 I

TTYPO

R/T14 12 store- known as the instruction fetch translat1on editor program wh1ch is staff as 'systems engineers' because a total­ sequence- takes about 1.6 micro-seconds, accessed via the teletypewriter whenever system understanding is necessary to enable the average time taken to execute an translation changes are required. The faults to be located. The processor can Instruction being 4 micro-seconds. The translation editor enables translation carry out various tests on SCCs and S Rs, processor thus can execute about 250000 changes to be entered into the processor and which can be initiated from the teletypewriter Instructions every second. stored for up to seven days before they are and the test results printed. Three testers required; the time and date they are to will be provided at every installation; a power The Store become operational being entered in supply unit tester for the DC/DC converters; Because the store system uses dynamic response to a question from the processor. a sender-receiver tester which performs full RAM. the store contents would be lost if Translation changes entered into one I i mit testing of all M F frequencies, and a 50v power was to be interrupted, so a reserve processor are automatically passed to others. unit tester for use with the 50v relay units. store is necessary. This store used in R/T14 thus simplifying the translation change Maintaining R/T14 will be a very useful is a Tandberg digital recorder which has a procedure. introduction to processor control of copy of all program and data on a magnetic Should a processor fail, such that the telephone exchanges and the change from tape cartridge. Should it be necessary, the teletypewriter is unable to access the R/T14 to System X will be more easily store system can be reloaded in about 90 processor. control of the processor is accomplished. seconds. achieved from the maintenance console. Other uses To enable the program and data to be Any failures in SCCs or SRs, or in areas of The possibility of using R/T14 as a loaded from the digital cartridge recorder, the processor. are reported as fault messages replacement for types 2, 3 and 5 a small loader program is stored on on the remote teletypewriter. A second electromechanical register translators is Programmable Read Only Memory (PROM) trolley-mounted teletypewriter- known as presently being considered. The use of devices which are not affected by loss of power. the serv1ce teletypewriter- is used during R/T141n non-d1rector GSCs requires the Use of Teletypewriters fault location orfor all unsolicited fault use of a new register access circuit which Control of a R/T14 by maintenance staff is by prints should the remote machine fail. The has already been developed using type-23 means of a teletypewriter. First a processor is pair of teletypewriters can control up to relays w1th all functions controlled by a 1dentif1ed by 1ts number 1n the range 01 to 1 5. 1 5 processors. microprocessor. One rack can accommodate then a password is entered to unlock 128 reg1ster access Circuits (RAC) using facil1ties according to the status level of the Maintenance and repair JUSt one-tenth the space of the equivalent password entered. A fully tra1ned member Maintenance of R/T14 1s on the same basis electromechanical equipment plus givmg of staff has password status Ieveil which as M Kl processors in TXK1 GSCs, 50v relay savings on initial capital cost and g1vesfullfacil1t1esofthe Man Mach1ne units being repaired on site and printed considerable savings on maintenance costs. Language (MML). wiring boards being sentto an Area Repair For use 1n the non-director exchange Individual SCCs or SRs can be 'busied' Centre (ARC) for analysis by a Membra in w1th the new RAC, the processor performs out of serv1ce. returned to service. meter automatic test system. A complete set of the routmer function on the RAC under readings can be taken and alarms can be spare printed wiring boards is held at every program control. with any fault information controlled from the teletypewriter. It will be site for maintenance purposes. It being the being pr1nted on the teletypewriter. rare to make changes to the program. but task of maintenance staff to identify which A decision on R/T14 non-director changes to data. particularly translation board 1s faulty when a processor fails. application is expected soon. changes, will be frequent. The R/T14 has a Courses at BTTC Stone have started to train 01-4321332 13 Close eneounters of the 4A kind

by Graham Winter BTM/SM 2.2 Fault printout for ma1n control un1t exchange. The first TXE4A exchange, at Belgrave (MCU). supervising process1ng unit (SPU) e Component failures have all been lower in Leicester, has now been in service for marker SWitChing network and rout!!ler than the predicted failure rate (except for over 12 months. It is a six-plane unit output IS sim1lar to TXE R D but 1n some cases diodes of a part1cular type, a problem with 5000 installed connections utilises a sl1ghtly different format. Additional which became apparent during the early serving a mainly residential urban area. fault pnntout generated by the OPU 1s output years ofTXE4 RD). Extension 1 -adding an additional 7400 on to the teletype used for day-to-day e It is interesting to note that only one connections- is currently being alterations to exchange data. Analysis of transistor failed in the first 12 months, and installed with integration starting switching, MCU, marker and SPU printout that Integrated Circuits failed at an average shortly. The TXE4A system was IS at present undertaken manually, but a of only one per month. described in M N16, and in this article method of computerised analysis using a • There have been no major service fai I ures. we look at the maintenance of TXE4A Small Business Computer is being We are now on the threshold of the TXE4A and Belgrave's performance so far. developed. Installation programme. with about 300 Location of a faulty PI U is undertaken exchanges being ordered up to 1 985/6, plus Maintenance w1th the a1d of a fault d1agnost1c flow-chart. extensions to TXE4 RD exchanges using The maintenance philosophy IS Similar to start1ng w1th a particular alarm or occurrence. TXE4A equipment. As the system will take us that ofTXE4 RD. 1n that a faulty plug-in unit YES/NO decisions lead to e1ther replacing 1nto early next century, 1t is encouraging to (PI U) is located and replaced by a spare faulty un1ts or the application of further see from the 1nitial performance that the held in the exchange. The faulty un1t is then tests. Figure 1 shows part of a diagnostic objective of a more reliable service to the repaired on or off site, depending on its chart. customer can be obtained from TXE4A. type. complexity or type of fault. 027-22634004 Preventive maintenance 1n the form of Performance so far routmers for links, outgoing JUnctions, Over the first year of service the following reg1sters and marker sub-systems. are run points have been observed: overnight. Further preventive maintenance • Customer-reported faults per exchange such as dormant fault checks and periodic connection were approximately 25 per routines are applicable to TXE4 RD racks cent of those for TXE4 R D, or 20 per cent only. A small additional amount of routine of those reported for all systems combined. work is camed out on the magnetic tape • 97 per cent of all faults on exchange mach1nes assoc1ated w1th the operations equipment were found as a result of 1nbuilt processmg un1t ( 0 PU) and to ensure that check1ng circuits. rout1nes and the like. the exchange master and reserve data tapes The remaining faults were found as a are kept up-to-date. result of reports onginat1ng outside the 14 Figure 1 Part of TXE4A fault diagnos ( Start flowchart tic On refleetion I SER LEV 3' This time authors (or their successors) Prompt alarm have looked back and reported on their I articles which appeared in M N 10 TP AA6 and AA7 (Autumn 1976). No TXE 4. Mike Robards ES8.1 .1 informs us on SBCC (E1-3) I at earth that si nee the bringing into service of the first I Replace I TXE4 at Rectory. Birmingham in February /Yes 5BBC (E1-3) 1 976, some 179 similar exchanges have opened. These exchanges- known as the Waveforms on TP's Rectory Design, or TXE4( R D)- provide for No AA4, AA 1 3 and AA 14 on 2BNS's (F16 over 1.7 million connections. A further and E24) compare 162RD types and 176 extensions are on Replace l 2BNS (E24) I I order and should be completed during the lYes next three years, providing a total capacity of MonltorTP'sAAB.AA18 TP AA7 on 2BNS No l 1 over 4. 6 million connections. and AA19 on 2BNS (F16)1 (F16) high To improve service performance of the earlier RD exchanges, those currently under Yes I construction are being modified to overcome Waveforms on TP's most of the known design deficiencies. It is No AA1 and AA12 on expected that those already in service will I 2BNR's (E23 and also be upgraded. F15) compare TP AA6 on 2BNO's TX£4A-theversion using more modern (F14 and E22) Yes I Yes electronic components -was described in compare r- {Set scope to 1OOms MN16 (Spring 1980). One exchange with TP AA7 on 2BNQ's ~o timebase, store. single sweep some 5000 connection capacity (or I No (E22 and F14) compare multi pie size) is operating at Belgrave- see l this issue- and 86 more are on order as well as three extensions. During the next three IYes r Replace I 2BNO (E22) years. over one million connections will _ 100 ms timbase. become available on TXE4A exchanges. Waveforms on TP's "' store. single AA6.AAS,AA9,AA13 {$"'"''" sweep International subscriber dialling­ on 2BNO's (E22 and F14) compare now known as International Direct Dialling (I D D)- has developed extensively since I Yes MN10. says Paul Taylor. of BT International 15 I N4.1.3. Now 92 per cent of the world's Call offices London Broadcasting Company (LBC) to all telephones are available on I DD from the UK. Geoff Balls. ICS7.1.2, admits that when he companies. w1th a central BT control at In May 1982, Egypt and the Yemen AR were wrote the article for MN 70 six years ago he 'London PWs' (Faraday Building). Only the added, raising the total number of did not foresee such dramatic developments enthusiasm and expertise of the Faraday staff participating countries to 118. Three more taking place in such short time. The far­ enabled the changeover to proceed as are due to be added in July, and further reaching changes in payphone technology smoothly as it did. expansion is anticipated. have hastened the obsolescence of the In addition. a 'News Contribution' network At present. 99.2 per cent of UK telephones Pay-on-Answer (POA) system. is now being provided from aiiiLR stations have access to I D D and all customers are Although we have succeeded with the back to LBC, with remote switching facilities scheduled to have the facility by July this handset cords and door closers we expect at programme company premises. year. During last April. outgoing I D D calls of that POA. with its remaining intractible The I LR network is now as big as the lTV over 60 mill1on paid minutes went through problems, wi II be replaced over the next six network- and is still growing. UK transit centres. Most of this traffic was years with a family of electronic self­ routed through Mondial House and Stag contained payphones. No doubt they will NCC news Lane. bring their own problems. but the first few Terry Farres, ofthe National NCC (T5.2.3). hundred are performing well. reports that the declining trend of non­ Dataplex. According to Roger availability of hyper-group links continues; Whitbread, T5.3.2, Dataplex has had mixed Remote printout for CF DEs it has dropped to about half what it was six fortunes over the past few years. Dataplex 2 Since the early equipment described in years ago- just as was forecast. There has was based on soundly designed equipment, MN70, BT South East Region have also been a general improvement in failure but service was prone to interruptions caused developed an electronic version which uses rate. Apart from these encouraging signs not by local voltage variations and transmission two-tone signal I i ng to accept the printout much impact has been made on working path disturbances. Most of these systems information from 25 remote CFDEs. party overloads. We hope to give more details have now been ceased, although several are Following earlier tests in Brighton. plans for a in the next issue. still in service. feasibility study in Slough are well in hand. It will be of interest to readers to learn that An improved design known as Dataplex 3, BTSE/SM1.3. work has begun using Prestel for showing also based on proprietary equipment has. bookings for dedicated S PN and spare plant. s1nce MN7 0, entered service. But the Local radio It is hoped this will be of use to Regional introduction of the Packet Switched Service Bill Atkinson, of T5.2.2, states that 1 980 saw NCCs in planning future work. IS likely to take most of the data multiplexing a further expansion of Independent Local business. However. Prestel will continue to Radio (ILR) from the origina119 stations. use Dataplex 3 to provide extended Prestel About seven new stations are likely to computer access at local call rates to other come 'on air' each year up to the mid-1980s, areas. bringing the total to 69. I LR will then be Smaller. less complex, equipment with available to 90 per cent of the UK population. similarfacilit1es is being investigated which Major changes have been the introduction w1ll prov1de up to eight low bit-rate channels. of multipoint programme circuits (as opposed This may lead to a Dataplex 4 service. to point-to-point) for news distribution from

16 New generation test e4uipment for the fault repair serviee

by lan Blake ES5.1.2 as a fault diagnosis and distribution control. from an RLT Controller in the RSC. All test A field trial of Remote Line Test ( R LT) Being microprocessor controlled, R LT also result informat:on and details of line equipment is now well under way at has the potential to keep pace with the conditions are returned to the RSC in this two Repair Service Controls (RSCs)­ evolution of customer apparatus and the form for subsequent display on the Guildford in BTSE and Carmarthen in local network. Controller. The remote unit has been BTWM.It is hoped that, having proved Before the field trial Guildford and desrgned to work into all existing exchange its merit, RL Twill become an integral Carmarthen RSCs were equipped with types capable of providing test access- with part of the repair service strategy­ Modular RSC Equipment which consisted of the exception of System X which mentioned in M N18- contributing to three modules providing the Test Test incorporates its own test facilities. the modernisation and service Access and Reception functions mounted on Included in the tests and conditions improvements sought for the repair an office-style desk. When RL Twas which can be applied by the RL T remote unit service. introduced, a visual display terminal (VDT) are: known as an R LT Controller was provided in e automatic check for ac mains contact Present limitations place of the Test and Test Access modules. immediately a line is accessed for test Engineers who have worked in RSCswill be The Reception module was retained to purposes aware of the I imitations of the present test provide all the incoming and outgoing call e several automatic line test sequences gear whether mounted on test desks or requirements of the RSC. which can include insulation resistance rncluded in modular RSC equipment-as As shown in the diagram (Figure 3), the across the pair, wire to earth and wire to well as the difficulties involved in testing system consists of R LT Controllers at each exchange battery in all combinations over long test junctions. This is no criticism RSC position which obtain access to remote e measurement of capacitance in all of the old style test desks which achieved the test units in the local exchanges through a configurations which can also be included orrginal designer's aim of testing local lines switch block and speech-band private in an automatic test sequence from local exchanges. Buttoday's repair circurts. Most exchanges in the RSC area e measurement of ac and de volts, current service needs equipment which can be used will be equipped with one or more of these and loop resistance from one or more central locations. This may remote units. The remote unit consists of a e check of dial and M F4 signals. also coin rnclude an RSC, a centralised fault shelf of electronic equipment mounted on a pulses from pay-on-answer coin boxes reception point or an out-of-hours RSC. miscellaneous apparatus rack, and is e application of interrupted ringing current connected to the existing test access and battery and earth conditions to enable The RLT equipment equipment and the exchange common speech over the system As its name implies, R LT has been designed services. Like the RLT Controller, the remote e high impedance monitoring to resolve these problems. It also provides unit is microprocessor controlled. It sets the e howler the accuracy and range of tests needed to test access equipment and performs all test e 50Hz longitudinal pulses to check enable an RSC to achieve its full potential functions under the control of data received operation of customers' private meters 17 e ability to make calls into the exchange over which are permanently engaged. lists of lines found faulty during the night the test access. onto a printer in the RSC or External Plant In addition, there are some novel tests Night routining Maintenance Centre (EPMC). Service­ which have not previously been available to RLT can be programmed to carry out night affected lines will be indicated on the the repair service. For example, a means of routining of the local network and so take printout. identifying if all bells have been turned off or over from the existing fault-prone local line telephones unplugged on a 'new-plan' insulation routine (LLIR) equipment. One Other benefits installation; and a way of forcing full test R LT Controller will be capable of driving During the course of the field trial it may be access to I i nes on Strowger exchanges about 1 0 remote units and 'downloading' possible to provide and evaluate further test F1gure 1. The desk layout used at Guildford- the Reception module is at the left and the RL T Controller in the centre. The pigeon holes are used for storage of fault cards and umesheets.

18 NUMBER 35290 TIME. 21-AUG-81 0949 04

A-8 8-A A-E B-E A-E BE B·E AE

RECEIVER ON

A C VOLTAGE ov OV OV OV faci I ities. For example, identifying the presence and approximate location of ser1es --DV rOV --DV -5V D.C VOLTAGE high resistance faults, and enabling the RESISTANCE 647KO remote unit to test lines on more than one exchange using test junctions. This may BATIERY CONTACT 923KO sound contradictory for a remote I i ne test CAPACITANCE system but the microprocessor in the remote

CURRENT unit could be programmed to take into accou ntthe affects of any test Junction AUTOMATIC TEST 1 -TEST 0 K before returning the test results to the RSC. The results displayed on the RLT Controller 1n the RSC would then relate only to the STATUS HOLD TEST customer's line and not include the parameters of the test junction. Th1s capability would reduce the number of Controller Figure 2. A typical VDTscreen display remote units needed in rural areas and To Remote represent a large f1nancial saving nationally. Units in Further phases of development planned } other local for RLT are: to integrate it with the RSC exchanges computerised administration system To other { Switch (ARSCC) -also mentioned in MN18- and RLT to enable it to 1nterwork with the System X Controllers test network to provide comparable test facilities on customers' lines served by Remote Unit System X exchanges. 01-4322351

Customer

Repair Service Control Private (RSC) Circuit

Local Exchange 19 Faster RATES for private eireuits by David Kennard- N E/T5.3.1

Computer-controlled relay equipment I ______I ~rivate I ______I is now on trial for intercepting and lrCUitS testing private circuits from a distant centre. The equipment, known as cess RATES (Remote Access and Test cess ays ays Equipment System). can bejumpered ~~~ ~~~ into existing private circuits or other I I I Exchange I I Exchange I special circuits in local exchanges. and I A B LTP Controller I I LTP Controller J I will be controlled over dial-up or I I I I dedicated circuits from a central fault I I I I I I I reporting point. I Remote I I Remote I Until now, it has not been possible to test Test Test I interface I I Interface I private circuits automatically from a central unit modules unit modules point- as can be done on telephone circuits I I I I I _l using test selectors. Of course, private I I I circuits can be tested over tie-lines or test­ I Modeml I I ModemJ I ____ _j ______j trunks. but there is a limit to the distance over L ______- L ______wh1ch successful tests can be made, and the Data Analogue Data Analogue connection between the tie-line and private line line line line circu1t has to be applied manually. The delay I-- (:~;;:~1-;-e;;tr;--- I PSTN in conducting manual testing at MDFs or I I Control or TJFs-which often requires a visit to an I I terminal dedicated I unattended exchange-contributes to the l J I lines high outage times forfault reports. The I I I I national outage average for private circuits at _l Control l present is about 20 hours. and the RATES _j_ interface : IModemJ un1t ~Modem! facilities could help to reduce this, as well as I I the number of intermittent and repeated I l l I faults which occur. I I Printer I I Several different types of equipment are L ______j being examined, and the most notable version at the moment is based on an American design, shown in the Figure 1. This version is on trial at Manchester, and current plans are to install the equipment in 1 5 RATES- Remote Access Test Eqwpment System 20 Automatic exchanges to intercept about 18 000 are received at the control centre. the testing circuits, which can then be tested remotely officer keys-in the commands on a visual testing from one of two control centres. If this stage display terminal (VDT) to operate the of the trial is successful. it may be system, after first look1ng up the customer expanded to about three times the size later, and circuit details on card records. Once the methods which will include most of the large exchange and circuit number is known, a exchanges in the Manchester conurbation. data cartridge tape for the exchange is Other trials, using a simpler type of plugged into the terminal. and the equipment developed by BTLR, have been appropriate section of the tape is selected for by Steve Plumb ES 5.4.1 started at Albert Docks (London) and ident1fying and operating the relevant access MN13 introduced readers to Automatic Test Reading. In each case. the equipment is relays. A dial-up or ded1cated l1nk is then set Systems (ATS). This article gives some idea fitted in a single exchange to intercept up to up between the control interface unit and the of the testing methods used to locate faults about 1000 circuits. The simplification stems remote interface unit at the exchange. on such complex digital electronic units as from the application of short-distance control Control signals and return signals pass over System X or Herald central processors. It circuits to operate the relays indirectly, a 300 baud data line, while a second line can relates particularly to the Membrain M 87700 rather than utilise longer-distance data lines be connected for monitoring, speaking or series of ATS now installed at some Area as in the Manchester scheme. exchanging other analogue signals. The Repair Centres (ARCs). These ATS are not The equipment at Manchester will be data signals are abbreviated to speed up the generally equipped to test analogue units fitted near the MD Fin each exchange, and operations, and all the normal test such as Mobile Radio Sets or frequency will consist of one or two racks of the access­ parameters can be applied or measured by division multiplex (FDM) units. relays and control units which are cabled to activating the particular test module at the There are many different types of digital the MD F to intercept existing JUmpers for the local exchange. The control terminal has units containing general purpose logic private circuits as shown in the F1gure. Each duplicated facilities which permit two devices- such as the Texas 7 400 series of relay is a miniature-type which will switch separate exchanges to be accessed at a time, integrated circuits (ICs)- and these are up to three pairs at a t1 me, to cater for two­ so that end-to-end tests between exchanges normally straightforward to test. Other units wire, four-wire and signalling circuits. The can be made over a long-distance private contain 'custom made' devices such as relays are selected and operated from the circuit. Once tests have been completed, the Uncommitted LogicArrays (ULAs),wherea local controller unit which is a full test log can be printed out at the control single chip provides all the logic found on an microprocessor activated either indirectly centre, 1f a record is needed. entire plug-in unit (PIU) of about four or five from the control centre or directly from a local The results of the trials so far are very years ago. Other complex devices such as test panel ( LTP). The local test panel has a promising, and full evaluat1on will continue Read Only Memories (ROMs) and Random key-pad which will allow all the normal to determine to what extent the equipment Access Memories (RAMs) all present testing facilities to be made, usually for sub­ can contribute to reducing the outages of problems to the fault diagnostician. The location work, or where faults are referred to private-circuits due to faults. types of components used, and the way they the local exchange for initial testing. 01-432 9148 have been connected, therefore influences With the majority of fault reports which the test method used with a particular unit. 21 Testability generated using the simulator that have the High speed tests Testability means designing a circuit so that necessary accompanying information Most ATS generally apply tests to a PIU at a it can be tested and faulted using an ATS, as enabling the ATS to automatically locate the rate of tens-of-thousands per second. well as performing its intended system task. fault in a circuit. The automatic fault location However, there is often the facility of loading Typical problems for an ATS include long is mainly carried out by the ATS operator the test information into a fast memory and counter chains, microprocessors, oscillators placing a 'guided probe' on components as then 'firing' it at the Unit Under Test (UUT). and the complex devices already mentioned requested bytheATS. With this technique the M embrai n ATS can which require many logic inputs for complete A simulated test program is normally change any or all of the pin states frve million testing- especially where they are 'hidden' written to test as much of the circuit as is times per second. This allows testing of a in the circuit by other complex devices. possible and practical. However, certain tests U UTwith clock signals and data running at Testability can involve electrically breaking and techniques cannot be used wrth the typical system speeds. Because modern long counter chains into manageable lumps, simulator. The test programs written without circuit speeds are increasing ATS providing additional connections into the the simulator are usually referred to as manufacturers are trying to speed up their circuit to enable control of microprocessors 'manual' programs. This stems from the fact machines, but at high speeds various timing and oscillators, as well as the ability to test that although error messages can be included difficulties can arise. Just addmg a foot or so some parts of a circuit in isolation from other in such a program to indicate the expected of wire to a sensrtive high speed area of a parts. problem orfault confirmation and frnal UUT can stop the crrcuitfunctioning diagnosis normally has to be carried out altogether. So high-frequency transmissron Test programs manually by the operator. Usually, manual concepts also have to be considered when Test programs and other relevant information programs are only wrrtten where operator testing. -such as the full circuit description including interaction is required (such as to operate component types, names, pin connections switches. observe LEOS, and so on.) A non­ General logic tests and so on- are created for particular circuits. simulated test program also lacks the As already mentioned, testrng circuits Modifications to a circuit often require a new information confirming which faults are containing generallogrc devices is normally database with some changes to the original detected and the resultrng quality figures. straightforward, although poor testabrlity can test program as well as to the associated When a circuit is tested, the idea is to cause problems. information. detect any faults relating to disconnected or When tackling general logic. test programs Generating test programs is a time­ high resistance component connections, are written to frnd the possrble faults rather consuming task so, where possible, various device output stages stuck at logic '1 ·or '0'. than to immitate the system from which the aids are used. One main aid is a simulator timing devices, and to carry out full circuit came. In this way the programmer which lists the possible faults that could functional checks of each device. The does not have to learn the intrmate system occur on the PIU. then indicates the parts of simulator indicates which faults are detected, details of every crrcuit he sees. but instead the circuit that have been adequately tested. but it is not able to state whether all the should be very conversant wrth logic It also generates a 'fault dictionary' for the function checks have been made. To help principles and have the basic informatron particularfaults that can be detected. The the program confirm that function tests about the circuit. simulator can then inform the operator of the produce the expected results. the simulator program's 'qualrty' -that is, the difference outputs all device output states related to the between those faults detected and those programmed input states. undetected. Usually it is only test programs 22 Complex devices socket) a further problem arises as it cannot instruction. for example add one number to :::J ULA tests easily be removed. another. then acquires any extra information The main problem with U LAs is that there To test RAMs. each cell must have both required (the two numbers. say) and finally might be only very small quantities of the logic value ·o· written in and read out. outputs the result. particular types depending on the number of then the value 1. However. to properly check It has been estimated that to fully test a PIUs made. For such unique devices there a RAM for faults between the cells. a pattern typical microprocessor with every will not be a model of its operation in the of 1 sand Os should be written and read. combination of function. data and speed ATS simulator's library. This means using Much debate exists on which patterns are limit. would take 10 years. (by which time the much effort to generate a model otherwise it best. Normally a 'chequer-board' pattern of system it came out of may well have been prevents a simulated test program from being 1 sand Os is used. which is then reversed. scrapped). We obviously have to settle for a generated. To check ROMs and RAMs. the principles realistic set of tests that give a high degree of Again. testability is a major consideration, used to write the tests can be fairly simple. confidence that the microprocessor is but in this case it should have been thought but the length of the test program. and time working well. This normally means a check of when the complex chip was designed. taken to write it. can be formidable and even of each function with its fixed set, in addition Often data sheets and full functional unrealistic. In very large programs the floppy to trying a pattern of logic Os and 1 sin each descriptions are available for simple devices. disc storage can be exceeded, requiring two memory element (register cell). but not for custom ones. This can make the or more discs to hold the full program. If the ATS has sufficient control of the test programming task much harder. However. one facility that is available­ microprocessor then the tests are easily especially when the circuit diagram for the called Live Data Compression (LDC)­ manageable. custom device is not available. carries out a time-related summation of all the logic state changes ofthe circuit. Bus structured PI Us DRAM and ROM tests With LDC, short routines used in a An electronic BUS is a set of communication Large memory devices such as these are very repetitive manner can often replace lengthy l1nes taken to various devices- such as the common in modern PIUs. Typically. ROMs continuous patterns. This saves much floppy ROMs. RAMs and microprocessors (which contain fixed data) have 16.384 disc storage space and shortens the time mentioned above. The BUS allows any separate cells. each hold1ng the logic value taken to write the tests. at the expense of a device connected to it to communicate with 0 or 1. RAMs (in which the data can slightly longer testing time. LDC is only any other device. constantly be changed) can contain 2.000 geared to indicating a failure and does not Obviously some controlling logic ensures cells. allow automatic diagnosis of the fault. the correct devices are 'talking' and 'listening' ROMs are tested by reading a II the cells although failure messages can be included at any one time. It is common to have an and checking that the correct data is present. as in a manual test program. In this way a 'address' and 'data' BUS on such PIUs which This is fine when all the PIUs of a particular simulated program can be used first to check typically consist of eight or 16 lines each. The type have identical data in the ROMs. but most of a PIU. followed by an LDC program. address BUS is used to selectthe required sometimes the data differs from system site to with messages to state which particular device (memory element. for example) and site. In cases where there are many variants of ROM/RAM has failed. the data BUS to convey any information or the data. the Ideal solution is to remove the results. ROM from the PIU and check it separately. LJ Microprocessor tests A well-designed testable PIU operating with a test ROM inserted 1n the PIU. If the A microprocessor by itself is basically a data mainly on the BUS principle is relatively ROM is soldered-in (instead of being in a manipulator. It functions by taking in an straightforward to test. The number of tests 23 NeUJ eallle alartn savestnone~

for each device on the BUS might be by Eric Woodgate BTE/Colchester Area C R E and cable pressure failures- costs considerable, but the approach is basically A new cable-pressure alarm system, devised about £1,000, excluding installation charges. that of tackling one device at a trme. in Colchester Area and developed in BTE, 0206 72960 has paid for itself in just one day. A final word The system. which uses Zener diodes, has ATS programmers are to be found in some been on field trial at Ipswich since April1 980. WHATISTIER2? Area Repair Centres, BTHO, BT Factones It was devised by a Precision Test Officer Trer 2 is the next generatron of corn and outside consultants. Although an ATS and developed by staff in the External Plant telephone for PCO' s-and there wrll be does not solve all our problems, as a general­ Maintenance Centre (EPMC). a Renters' versron. It rs the marn purpose software-controlled tester it is One January morning the pressure failure replacement for POA. capable of very effective fault dragnosrs. Thrs detection equipment at Ipswich EPMC It rs nearly readyfortrral. Plessey, THO naturally depends on good qualrty test issued a deferable alarm on the 542-pair Development and THO Marntenance programs and operation of the ATS torts best Ipswich to London No 2 cable. This was Groups (and many others) are working advantage. Also, once a test program has followed almost immedrately by an urgent very closely to develop one of the best been generated- often with a signrficant alarm locatrng the Mannrngtree area. A coin telephones rn the world. The latest mvestment in skilled programmers' time- it JOinting team was promptly directed to the rn technology and the grottrestfrom every is always avarlable when required for that scene. On arrival they discovered the day freld experrence have been fed rnto typeofPIU. manhole full of water, and on pumping it out, the electro nrc, mechanical and physrcal It is hoped this rather long artrcle has the team found a very large fracture in the desrgn to produce a payphone whrch wrll helped readers apprecrate something of the cable's lead sheath. grve every modern facrlrty and stay in various ATS techniques that can be used to Timely warning and the quick action by servrce come whatever. thoroughly test a PI U- assuming that staff had prevented a total failure of this very Of course, we shall not produce the testability has been desrgned-rrl. ATS important cable with, in this case, little more perfect PCO- but we hope to get nearer techniques are used typically when other than half-an-hourto spare. Certainly had the than ever before.

methods would take too long or be old type of alarm system still been in use, the When 7 Wrth luck, Trral starts rn October, 1 1 excessively complicated. inevitable delay in detecting the fault would product1on starts early '83 w1th general 1 01-932 2894 have resulted in considerable loss of service avarlabrlrty by mrd 1 983.

in the trunk network. The repair cost would ICS 7.1.2 I also have been more than £2,000.

1 The Zener alarm system- which employs 1 01D POPHAM-432 9178 ____l just two pairs from the EPMC to test up to I Head of Payphone Marntenance Group 1000 circuits, and can discriminate between L_ 24 New eleetronie work beneh

by Ron Quinney ES5.4.3 e half-length bench available (1 050mm x The first 100 benches have been delivered Repair of modern electronic equipment 1 050mm) to various ARCs direct from the manufacturer demands a high standard of workmanship e full or half-length upstand to support test and assembled on site. Further contracts and often requ1res a large amount of bench equipment have been placed by PSA and the bench area to accommodate test equipment and e all insulated construction components listed in the furniture catalogues. other fault diagnostic aids. e concealed housing for mains isolation Local accommodation staff ought to have all With the introduction of Area Repair transformers relevant information. Centres (ARCs)- see MNJ 7- it was e rear insulating barrier to give electrical The benches have been well received by apparent that there was a need to satisfy both isolation between benches sited back-to­ staff in ARCs, and Union representatives, these factors. There was also a pressing need back and it can be expected that many other users to meet the newly-def1ned min1mum e plastic tru nki ng to house wiring to 1 3A will be quick to see the benefits. standards laid down in the safety Tis. So, ill power sockets, with removable panel for Retrospective demands will also arise from cooperation w1th the Property Services optional use, local signal sources and so on the need to satisfy the new safety Agency (PSA) -who supply all furniture to e optional raised box to bring power sockets requirements. BT- ARC staff were asked about their needs. forward if required 07-432 2806 Note was taken ofthe1r experiences of the variety of types of benching available. as well as the required safety features, and a compromise design was produced for an electronic work bench. The prototype shown in the photograph differs slightly from the production items, but illustrates the general style. It does not show , the optional box which f1ts along the rear of the bench-top to allow the 13A power sockets to be brought forward for the convenience of the technician, and allows • small items of test equipment to be raised to a more convenient height The main features of the new electronic work bench are- e modularconstructioll e choice of pedestals- drawers or cupboard elarge lino-covered surface area (2•1 OOmm x 1 050mm) 25 Introducing regional Letters servieeiftlproveftlent ... .John Vidler of BTSW writes on the A346/349 procedure eentres Our colleagues ill the Installation and Works groups are continually providing new plant and equipment. Once provided, this becomes by Alan Kelly ES9.1.3 Staff who are brought together within the a maintenance respons1bil1ty for the rest of In the past, BTHQ held onto the region to take on this work will all belong to its l1fe- poss1bly 30 or 40 years. So not only is national responsibility for the same group- unlike BTHO where jobs 1t necessary for maintenance staff to know in development, planning, service and are spread over various divisions. These new advance what IS be1ng provided, and how, works for all exchange systems long groups are known as Regional Service but also- because our colleagues do not give after they had become well established Improvement Centres (RSICs). us a guarantee- it IS absolutely essential that -in fact, for as long as the systems had we should have the opportunity of inspecting been in the network. First for north east it before we accept it. Naturally, this meantthatvanous BTHO Different regions will set up RSICs to take Service targets- which have to be d1v1sions had the responsibil1tl( of committing over the national responsibility for different achieved if we are to stand the test of staff to an ever-increasing number of systems- the first being BTN E, dealing with competitiveness- are constantly hampered established systems. At the same time, new TXK1 Local and GSC systems. By the time by the lack of records, so often caused by systems and facilities were putting greater this article appears, BTM should have taken I ittle or no knowledge of the work being demands on the available resources. over the Strowger (TXS) system. earned out. Working party interruptions and Commitment to the new systems was given These are not the only systems likely to be damage to exist1ng plant both contribute to top priority by BTH 0, and it was felt that affected. Any system- once it is fully the failure to meet our aims and cause support for established systems would suffer established -will be considered as a customer dissatisfaction, things we can ill unless methods were changed. candidatefortheformationofan RSIC.In afford to tolerate. Two procedures exist to It was decided that once a system was this way BTH 0 will always be able to put its assist maintenance. fully established within the national network, major effort into the evolution of new The A346 procedures are not new and all responsibility for development planning, systems. have been .or should have been, used for serv1ce and works forth at system would be In the next issue of MN, we shall be notify1ng the Maintenance AEE of all works transferred to a specific Region. BTHO would taking a look at BTN E's RSICs at Leeds. of construction, renewal, and rearrangement thus be better able to concentrate on the new 01-4321300 taking place within his maintenance area. systems. The A349 is the relatively new procedure A region allocated the control of a system, for accepting into maintenance new or w1ll, among other cntena, be one with a altered external plant. It is set out to advise large proportion of that system. so will be the Maintenance AEE of the pending works able to provide system-trained staff from through to complet1on. A check is made to w1thin the region. ensure that all works have been carried out 26 1n a standard manner. and handed overto ... stores liaison Many thousands of Date I 200 users gain maintenance with all items correct. Dear Editor. access to their computer via the PSTN and it It is of paramount importance that internal Maintenance Heads of Division in Areas who is these customers that seem to have most and external plants are of the highest require to know how things are doing on their trouble in identifying the problems. operational order at all times. To find that new patch. could learn a lot from a chat with their How much better it would be if the circuits. racks. or cable networks are of such local Section Stock small-stores man. Many customers could do a simple 'go or no-go' a poor standard that they 1mmediately I am certain. would be amazed to learn of the test for themselves. but to do so effectively become a maintenance problem is not only cases where the storeman has to dust-off needs access to another computer. with a illogical and budget-consuming. but is essential items. knowledge of its operating procedure and guaranteed to lose customer confidence. In addition to this, what better way is there passwords. Construction staff often question the need to assess the amount of lead-sheathed cable In Reading we have developed a program for maintenance staff to check their work. still in the ground, than to study the solder for a NASCOM 1 microcomputer that But consider. if the result of a maintenance demand rate? allows it to be connected to a modem 2 Band check proves the need for improved Wei n the stores have a few good tips to exchange line. It answers an incoming call. workmanship then unnecessary expenditure offer too. introduces itself and, without the use of will be reduced and. more importantly, a David Watkins. EC 252. Cardiff. (0222 access codes or passwords. allows the better standard of service will result. And 398396). customer to perform a go/no-go test of that's what our customers will appreciate You have a good point there. David. The modem and terminal. At least when we are and be prepared to pay for. contributions Stores people can make are called in. we know that the fault is T1 L5 A0025. A2 C1202 refer. often overlooked, but we have always somewhere local. John Vidler regarded the Area Stores Liaison duties as To use the system, all our customers have BTSW/GR03 being a key point. Maybe maintenance to do is call Reading 861670 and when they Thanks, John, for bringing to our notice divisions should make more use of this get the data tone, put their terminal 'on line', once again the need for promoting the basis expertise.- Editor. then type 'Z' until the system responds. From for reliable and satisfactory customer the ·z· the microcomputer decides which ... Datel200 modem testing. service. -Editor. speed is in use (11 0 or 300 baud), and will Engineer:" I have completed my tests on echo back what is typed in, or send 'Quick ... call for a TRT119- once again your modem Sir. it passed with flying Brown Fox' messages or alphabets. An Can any reader help me please? colours" engineering option (protected by a I continue to have a need for a TRT11 9 Customer: "But you can't leave yet my password) is included. This allows us- if the Test Call Sender. The item is obsolescent in terminal still doesn't work. Now what do customer's term mal is suitable- to change the Vocabulary and stock is exhausted. I do." speed or parity when. having repaired any Enquiries throughout the area and regional Anyone involved in Datel installation or faults, we use the system ourselves as a final offices have drawn a blank. I would be maintenance will be familiar with a dialogue check that all is well. or to demonstrate to pleased to hear from anyone who knows the along these lines. and if a customer distrusts customers that the repairs were effective. location of a TRT11 9 which is. for one your tester (that box full of flashing lights) The system is very popular with Reading reason or another. no longer required. you are at a distinct disadvantage. To have to Area customers. and goes some way to R S King, Mtce AEE. M35 Cambridge T.A. tell him that your unnecessary visit will also reducing unnecessary visits, improving our 0223 353648. cost him money just adds insult to injury. 27 Maintenance News am1s to provide a medrum for two-way communication- that rs. between Headquarters and the field. If you want to wrrte about illlythrng you may have seenrn Maintenance News. or mdeed. about ar1y marr1tenance toprc. send your letter to· image. and savrng money. Future systems The t:drtor. Muir11enance News. Room 301. can be provided for a cost of less than £200. 203 High Holbom. London. WC1 V 7BU. Much better than saying "Sorry Sir. I have Say what you lrke. but the Edrtor may tone done alii can. perhaps rts the computer?" comments downrf he decides to publrsh. R. A. Collins Do please grve your full address. M4.9 Reading Area 0734 866353. If you have a contribution to offer to Maintenance News other than a letter -It's good to hear of mstances where local to the editor, please forward it through imtiative has been applied, not onlv to give a normal channels to the Maintenance better customer satisfaction but also in News agent for your Region or making better use of maintenance staffs· Telecommunications Board. The list is valuable time- Editor. shown below. The Editor cannot publish anything to do with current awards suggestions, neither can he be held responsible for technical inaccuracies in authors' submitted text.

Send ~our eontrillutions to.. EASTERN Mr B A Pearce S1 .1 .1 0206 89588 INTERNATIONAL EXEC. Mr D A Bardouleau IN4.1.3 01 -353 8380 LON DON MrEJones SM1.1 01-587 8000x7489 MIDLAND Mr DC M Coshan SLX3 021-262 4052 NORTH EAST Mr R Mundy s 1 .1.1 0532 467 529 N IRELAND Mr J McLarnon Sv2.3 0232 31 594 NORTH WEST Mr A Bunnis S2.1 061-863 7458 SCOTLAND Mr P McElroy S1 .4.1 .1 031-222 2390 SOUTH EAST Mr R Bayfreld SM1 0273 201 218 SOUTH WEST Mr J 0 West Sv1.3 0272 295337 WALES & MARCHES Mr E H Slrght S3.2.2 0222 391456 28

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PR011 ( 7/1982) Printed by Camgate Litho Ltd 68 Willow Walk London SEt