/////////////////////////////////////////////////////////////////////////// // // // Unit eXchange Digital 5B // // The Phinal Phile? // // // // By Keltic Phr0st // // // /////////////////////////////////////////////////////////////////////////// OK folks, here it is: The LAST ever UXD5b file from yours truly where ALL will be revealed... But first a word of warning... The excerpt itself is quite old, but nonetheless, technically accurate. And I havent seen anyone else working on this type of switch or punting any of this info around, so out it goes for consumption by the HP Masses. (Excerpeted from British Telecommunications Engineering) UXD5b : A 600 Line Digital Local Telephone Exchange =================================================== The UXD5b is a Microprocessor controlled digital switching telephone exchange designed for worlwide applications where the exchange capacity is not expected to grow much above 600 lines. The System offers a wider range of modern facilities over its predecessor, the UXD5A. This article also decsribes a compact rural version of the exchange for applications where the exchange availability is less stringent than that normally specified for higher order exchanges. INTRODUCTION ============ UXD5b is the latest addition to the UXD5 range of small digital local telephone exchanges, and follows the UXD5A, which is now an established system in the British Telecom (BT) Network serving rural communities in Scotland. The UXD5A has already been described in earlier issues of this Journal. The UXD5A system provided basic telephony facilities suited mainly to rural communities wher the exchange capacity did not exceed 150 connections. In the BT Network this confined its use to a modern replacement for the aging Strowger Unit Automatic Exchange (UAX) 12. The UXD5B extends the network modernisation program to cover UAX13's 14's. Whereas most UAX12's are located in Scotland, the larger UAX's are found in most areas of the BT Network, particularly in Wales and South West England. The costs of developing this larger size UXD5 system have been kept to a minimum by interchanging many of the most recent design advances with BT's Monarch PABX thereby continuing the practise adopted for the UXD5A, which itself was based on the original PABX design. The UXD5b is a BT development, which commenced mid-1980, with the co-operation of Plessey and the General Electric Company, whose involvement covered export-market requirements. The public service trial of the first production exchange is now well advanced at MuckHart, near Dundee in Scotland. BT's confidence in the design has led to substantial initial supply contracts being placed with industry in advance of completion of the trial. This article describes the main features of the UXD5b and outlines BT's program for its introduction into the network. BACKGROUND TO THE DEVELOPMENT OF THE UXD5B ========================================== The Dual BT/Export role of the UXD5b has been paramount from the outset of the development. The product specification, formulated at the start of the development, specified a system capable of operaying both in the BT network and also in telecommunications networks worldwide with the minimum of adaptive engineering. It was recognised that a wide range of modern telecommunications facilities would be required and available on an optional basis and that the system must be capable of interworking in either a wholly analogue or mixed analogue/digital enviroment. The concept of a flexible design approach has, therfore, been a major consideration throughout the development. The UXD 5a was taken as the base for the new design, and the development of the UXD5b proceeded in 2 Distinct stages; namely, expanding the exchange connection capacity and widening the range of facilities offered. The Objective of the first stage was achieved, by the development of a 96 port line shelf. By this means, the capacity of a single cabinet containing 6 line shelves was doubled from 150 lines to 300 lines. The extended capacity required an increase in processing power, and the 8085 microprocessor used as the main control in the UXD5A was replaced by the more powerful 8088 device. At the same time, the principle of a main or or central processing unit (CPU) and pre-processing unit (PPU) was retained. Provision of a second 300-line cabinet and the interposition of a pulse code modulation (PCM) interface card, specially developed for the UXD5B, between the respective control units enables the two 300 line units to function as a single 600-line exchange. The second but parallel stage of development included the replacement of standard electromechanical subscribers meters with an electronic bulk billing system, provision of a wider range of maintennance and Diagnostic (M and D) aids and man machine Interface (MMI) facilities. A Universal signalling junction card was developed to give a greater flexibility in the allocation of circuits to routes and signalling systems than had been possible with the dedicated junction units developed for the UXD5A. This new design also has the capability of interworking with signalling systems more appropriate to the export enviroment. Again, for the export market, the system can offer CCITT R2 signalling facilities. In common with other modern nowbeing introduced in the BT network, the UXD5B offers 6 of the top 8 star services (supplementary services). The complexity of the devlopment and the extremely short timescales set for its completion required that the work be partioned into convenient development packages and allocated between BT and industry on a functional basis. For example, industry assumed responsibility for export facilities not required on BT applications, electronic bulk billing (Call Accounting Sub-System), MMI, subscribers private meters (SPM) and ringer developments. BT undertook the majority of main software and hardware development, junction cards and new line cards, and cabinet unit development. A new DC-DC convertor was developed under contract with a firm specialising in this type of design. UXD5B SYSTEM ORGANISATION ========================= A system Block Diagram of the UXD5B is shown in Figure 1 (External file UXDFIG1.ASC). Line Shelves ------------ The combination of 2 types of line shelves and backplanes is unique to the UXD5 Application. The 2 Types have 32-port and 96-port capacities respectively. The 32 port shelves accomodate 2-port and 4-port line cards providing an analogue interface to subscribers 2-wire lines. The usual arrangement on a shelf is six 4-port cards and four 2-port cards, though 2-port cards can be fitted in the 4-port positions to provide other combinations if required. The 4-port positions accomodate mostly PBX line cards, each of which serves 4 PBX Lines. These can be configured on-board to cater for either loop calling or earth calling PBX groups. The line card provides digital speech and signalling at 72 Kbit/s, to and from the shelf multiplex at which speech and signalling are seperated into 2.048Mbit/s and 256Kbit/s highways respectively to the control shelf. Exceptionally, spare 4-port positions can be equipped with ordinary-subscribers line cards of the type use on the UXD5A if required. Lines allocated to the 4-port positions would normally have calling rates well above average for this type of exchange. The 2-port positions serve Coinbox (CCB) lines and junction units. The CCB Line card is designed to interwork with the standard BT Pay-on answer payphones and each card serves 2 lines. The BT Self contained payphone is treated as an ordinary line with signalling from the exchange by means of the 50hz signals used for SPM. The junction units provide 2 junction circuits on a card and these can be arranged as either 2 incoming, 2 Outgoing or 1 Bothway according to the traffic requirements of a particular exchange application. The 96-port line shelf accomodates only one type of line card, namely the 8-port line card. Each card provides connection to eight 2-wire customer's lines and a fully equipped shelf houses 12 cards serving a total of 96 lines. Most subscribers lines are connected to this shelf type and the originating and terminating traffic levels allow the 96 lines to be concentrated on to 32 Channels to the control shelf. In this case, each line unit converts to 2.048 Mbit/s PCM, which is inserted directly into the appropriate timeslot under control of a shelf interface unit. The particular speech channel/time-slot that is used is freely allocated by the microprocessor-controlled interface unit, but it is arranged to allocate low-order numbered time-slots first. For a call terminating at a port on the shelf, the main processor will allocate a time-slot starting at the higher ordered time-slots. Thus, there is contention only between originating and terminating calls when the 32 Channel highway is nearly full. In this event, the terminating call takes priority. When all time slots are full, an equipment engaged tone is returned on a terminating call and silence is transmitted to originating calls. The actual concentration is performed by time-slot assignment codecs whose active time-slots are controlled by a microprocessor on each line card. This is instructed with which time slot to use by the shelf interface unit. Signalling between the concentrating-shelf interface unit and the line card uses an 8 bit paralell bidirectional bus that is time shared between the line cards. Each line card is given a unique address determined by the wiring on the back plane. Signalling and speech are passed to and from the concentrating line shelf in the same format as for a non-concentrating 32-line port shelf, enabling the same control algorithms to be used in each case. Control Shelves --------------- The 4 identical control shelves on the exchange (two on each 300 line unit) provide the main processing power and switching capability of the exchange. Only one control shelf on each 300-line unit of a pair of control shelves is active at any one time, the other control operates in the standby mode. Each control shelf includes a change-over card, which provides the switching function neccesary to allow a pair of shelves to operate in active and stand-by mode. All inputs to the control shelves are wired in parallel to both shelves, but the outputs pass through the change-over card. The cards are interlinked and the stand-by card can be activated under the control of a microprocessor on its control shelf. The change-over cards are also linked into a hardware watchdog circuit on the control-shelf processor cards. If any control-shelf microprocessor should should become inactive or faulty in its behaviour, this is detected by the watchdog and the condition is signalled to the change-over card. The change-over card is designed so that it will not allow its shelf to become active if it is receiving a fault signal from any watchdog. Thus, under fault conditions, control will automatically pass to the other shelf only if all is in order. Change-over causes calls in progress to be lost. Periodic routine change-over is effected under software control and is therefore arranged to occur when no calls are in progress. Digitally encoded speech the shelf interface units and shelf multiplexers is applied to a non-blocking time switch which switches eight 2048 Kbit/s 32 Channel PCM highways. The timeswitch inputs also include digitally encoded tones generated on the services card. This card provides up to 12 tones which can be either BT Standard tones, CCITT standard or any combination of tones required by an administration. The tones are programmed in electrically programmable read-only memory (EPROM) and a logic gate array formats the tones for a particular application under the control of the EPROM. The services card also contains 6 press-button multi-frequency (PBMF) Receivers for use with press-button telephones employing multi frequency (MF) Signalling. (KpT : PBMF Receiver = KRD. Savvy?) These telephones are allocated a special port type so that the operating system automatically associates a PBMF receiver whenever MF dialling is required. The receivers decode the received digits into a form required by the main control. Where a high percentage of press-button telephones are in use, additional receivers can be equipped on cards accomodated on non-concentrating line shelves. Several facilities on the exchange require interconnection of more than 2 speech paths; for example, 3-party service, and trunk offering. This requirement is met by using a conference bridge in which a digital summation is performed on up to 4 speech paths giving 4 outputs. Each output excludes one of the incoming speech paths such that it can be connected to a subscriber without increasing his sidetone levels by excluding his own speech. The sum is linear so that the same transmission rules apply for a multi-party call as or a 2-party call. Four conference bridges are provided on each services card. Signalling from the shelf interface units and shelf multiplexers is applied to the signalling-in card on each control shelf. This card stores the information in a 256 byte random access memory (RAM) with each byte containing the current signalling information from a port. The processors scan the store for this information. The outgoing signalling is taken from the signalling-out card, which is another 256 byte RAM store, that can be written to by the processor. As the address of each byte corresponds to a port number on the exchange, the microprocessors can readily read and write to any port in sequence. The exchange continually monitors the performance of the speech and signalling paths by performing a loop-round test. To test the speech path, a tone is switched to an IDLE line and, as the telephone is ON-HOOK, the 2-wire/4-wire hybrid balance circuit on the line card is mismatched sufficiently to allow a proportion of the tone to be reflected back through the system. A Circuit on the services card detects the reflected tone and, by switching the output from the line card to the services card, the analogue-to-digial functioning of the line card is verified. A similar arrangement is used to check the signalling paths. Each control shelf uses two 8088 microprocessors and the main program is stored in two 128Kbyte EPROM Cards. Exchange configuration data and subscribers class-of-service (COS) information is held in battery backed RAM. As a back-up-facility, the battery-backed RAM card includes and EPROM device mounted on an internal daughter board. This is automatically programmed in situ under MMI Control. The microprocessors are arranged as a mian processor and a pre- processor. The pre-processor provides fast scanning of those ports which require it and controls the input/output with the billing processors. The main processor provides the main call billing function, and uses the majority of the program store. The processors are closely coupled and share a common bus. Both processors use the same design of board, the different functions being implemented by means of links. Two 300-line abinets are linked together to form a signle 600-line exchange by means of a 30-channel PCM link. The Link uses standard CCITT frame definitions and a common channel signalling protocol in time-slot 16. Low-level signal processing, synchronisation and alignment are performedon-board under microprocessor control. The same basic card is also used for standard 30-channel channel-associated junction PCM systems. For the inter cabinet application, the card is located in a control-shelf position. For interworking with a junction PCM line system, the card replaces a shelf multiplex on a non-concentrating line shelf. The 32 available ports on the shelf are allotted to 30 junction connections with ports 0 and 16 being reserved for synchronisation and signalling operations respectively. Billing Shelf ------------- The billing, or call-accounting subsystem, is a duplicated microprocessor-controlled system which calculates and records the charge data for each call in progress on the exchange. The duplicated systems are linked to each control shelf by a pair of serial asynchronous links. The dialled-digit information, COS of the calling subscriber and time-of-day are passed from the main system control active control shelf to both billing planes. Each processor uses this information independently in a complex algorithm to determine the correct charging rate for a call. At the end of a call, the 2 values are compared and the final data is recorded on the subscribers 'software' meter. Any discrepancy is in the recorded data is conveyed to the M and D routine for analysis and fault reporting. Billing records are stored in battery-backed CMOS RAM to maintain the integrity of the data under power-failure conditions. The system caters for a variety of charging schemes; for example, singke shot; Variable time Intervale (VTI); and metering-over-junction, which, if required, can also be sourced to a lower-order exchange; allowing for local, national and International dialling. The billing system contains its own accurate real-time clock for local generattion of charging rates. For current BT applications, Bulk Billing information only is stored; However, the interfaces are designed to allow for the introduction of itemised billing. Full access to the system is available via the MMI and the data is presented in tabular form for administrative use. (KpT : I shall be releasing,at some point in the future, a guide on how to decipher and read tabular billing records, as well as EMPIRE line monitor readings [very similar to billing records] ) Main Control Software --------------------- Most of the source code for the programs is written in CORAL using a computer-aided design (CAD) facility called SX1. This is a code generator which automatically produces CORAL code from Program flow charts. This procedure has ensured that the code produced is easily maintainable and reduced development time. Apporximately 80% of the software is written in CORAL, and the rest in 8088 assembler language. The assembler is used where either time is critical or input/output routines are being used. The majority of the software is run by the main processor, and this is best described under the following main process headings: Operating System : ------------------ The Operating system provides the link between all the other programs run on the main processor. It can start programs running either after responding to an interrupt (known as foreground programs) or on request from a program (known as background programs). Several programs perform a similar class of function and in this case, they are given a similar class name, as, for example, exchange scan, which has foreground programs that scan the ports and a background program that provides the output function to the ports. The operating system also provides general routine requests such as providing the real time clock. It can start background programs after set delays or at specific times. It also causes the the microprocessor to output a pulse every 100ms so that the hardware watchdog can verify that it is still running. Exchange Scan : --------------- There are 4 programs associated with exchange scanning. The main program is run in foreground and scans the complete exchange every 128ms. Subsidiary exchange-scan programs run at 8ms intervals and 24ms Intervals. These subsidiary programs scan ports which need a faster response to their signalling changes than the 128ms scan can provide. Examples that require this are the detection of loop-disconnect pulses from a standard telephone and the detection of digits received by the PBMF receivers. The exchabge-scan backgorund program provides the software interface to the signalling output to the ports. It also provides an interface from other programs such as call processing and M and D to the method of scanning the signalling input provided by the foreground exchange scan programs. Call Processing : ----------------- Call Processing is the program that controls the main functions of the exchange. It is a background program and acts in response to a request from other programs. It responds mainly to exchange scan programs as its main purpose is to interpret the changes in telephonic functions reported to it and to decide what action the exchange should take. Inter-Shelf Link : ------------------ Three Programs are associated with controlling the serial link between the 2 control shelves on the same 300-line rack. As for exchange scan, a background program acts as the interface to other programs and controls the output across the link, and 2 foreground programs control the reception of data from the other shelf. At present, the link is used only to communicate changes in the exchange configuration and changes in the fault status from one control to another. Billing : --------- Billing also has 3 programs used to communicate between call processing and the billing processors over the serial links from the pre-processor. The programs are for a similar purpose to that decsribed above and comprise one background program and 2-foreground programs. Maintennance and Diagnostics : ------------------------------ This group of programs control the automatic testing and fault reporting features of the exchange. The background program is started by the operating system every 15s when it starts a test on one card on the exchange. As it goes through a testing schedule automatically, the complete exchange is tested every few hours. A control shelf that is in the NON-ACTIVE state cannot test line cards, but it can perform tests on its own cards, and sufficient spare processing power is available to perform more extensive tests on areas such as the RAM. A fault found on the non-active shelf is reported to the active shelf via the inter-shelf link programs so that the neccesary alarm indication action can be taken. A foreground M and D program runs every 128ms to provide validation of time critical events. The background program can also be started under request from other programs so that tests can be run independently of the routine 15 second test and so that it can decide what action to take on errir conditions being reported by other programs. Man-Machine Language : ---------------------- This is a background program that provides the control and decides the action to take in response to commands from the administration's terminal that have been passed on to the control shelf by the MMI Processor. List : ------ The 3 programs associated with the interface to the man-machine processor are all referred to as list programs. They control the serial link to the MMI processor and have a background program and 2 foreground programs. Pre-processor Software : ------------------------ The pre-processor has a small operating system that schedules foreground programs. The programs that run on the pre-processor are the 2 fast exchange scan programs runningat 8 and 24ms and the fast 8ms billing program. The firmware for these programs is contianed on-board the pre-processor so as to minimise the activity of the pre-processor on the main-control-shelf microprocessor bus. Database Handler : ------------------ The function of this process is to carry out maintennance tasks on the exchange configuration database both during intialistaion and during the operational life of the exchange. PHYSICAL REALISATION OF UXD5B ============================= The UXD5B system consists of 3 cabinet units, 2 A-units holding the line cards and central processing shelves and a B-uni holding ancilliary equipment such as the billing system, MMI processor, SPM equipment, alarm display and spare shelf positions for exchange specific equipment. The overall dimensions of a 3-cabinet exchange are 1680mm X 600mm X 2080mm. Up to about 300-line capacity, a single A-cabinet provides the necessary line equipment accomodation which, together with the B-cabinet, gives dimensions of 1120mm X 600mm X 2080mm. A front view of a 3-cabinet unit is given in Fig. 2 (NOT shown) A-Cabinet equipment : --------------------- The A-Cabinet (The Outer Cabinets in Fig. 2) provides accomodation for 9 equipment shelves given positional designations A-J, reading upwards. The power shelf is located at the bottom (Shelf Position A) and this houses 3 DC-DC convertors serving the 6 line shelves above. Two ringing units, operating in main and standby mode, are also equipped on the power shelf. The 6 line shelves are alternate 96-port and and 32-port types. The 2 control shelves serving this unit occupy shelf positions G and H. The equipment cards on both types of line shelf are interconnected by means of printed-wiring backplanes. These backplanes contain connectors for terminating the plug-ended cabling to the MDF. The backplane used on the control shelf is a wired type where the wiring is automatically wrapped during production.The 2-A cabinets used in a 600-Line exchange have identical equipment arrangements. B-Cabinet equipment : --------------------- The B-Cabinet provides accomodation for the exchange ancilliary equipment. Referring to the middle cabinet shown in Fig. 2 and reading from bottom to top, the equipped shelf positions are : SPM, MMI/Power, billing, miscellaneous, fuse panel. The spare shelf positions are available for optional facilities such as remote line testing, call logger or for use as additional miscellaneous or SPM equipment positions. A visual alarm display unit occupies 2 card positions on the miscellaneous shelf. This shelf is also designed to house a range of exchange-specific equipment and, to achieve maximum flexibility, each card position on the backplane is fitted with a 64-way edge connector for wiring on and off shelf connections. Unlike the earlier UXD5A, the main distribution frame (MDF) is not included in the B-Cabinet. For BT applications a standard cable length of 15m has been adopted for cabling between the A-Cabinet Line shelves and seperately sited MDF. Line shelf equipment is provided with secondary surge voltage protection on-board. Primary protection, either in the form of gas-discharge tubes or 3-terminal solid state devices, is required at the MDF Line side. An intermediate distribution frame (IDF) is not required since exchange number - directory number (EN-DN) translation is performed by the exchange software and, under normal traffic conditions and line card disposition, the exchange is not sensitive to the distribution of traffic load between individual line units or shelves. Line cable pairs are therefore jumpered from the line side of the MDF directly to the exchange side where terminations are arranged in EN order. Power Supplies : ---------------- The equipment is powered from a conventional -50v DC exchange battery supply. All other voltages required are derived by using specially designed efficient DC-DC convertors. Details of the construction of the convertor can be seen in Fig. 3. Each convertor provides up to 150W of output power made up of 102W at +5V, 24W at +12V and 24W at -12V. The outputs are protected against inout voltage transients. Thirteen convertors are distributed throughout the system to provide the required exchange availability. On the A-Cabinet, each control shelf is powered by a dedicated convertor mounted on the shelf. Line shelves are powered on a paired basis, the pairing arrangement being one 32-port and one 96-port shelf. On the B-Cabinet, each call-accounting subsystem has its own convertor and these are located on the adjacent MMI/Power Shelf. A third convertor on the MMI/Power shelf supplies the miscellaneous equipemtn shelf and the SPM shelf. Typical power consumption figures for a 600-line exchange under specific traffic loadings are given in Table 1. TABLE 1 Typical Power Consumption Traffic Loading (Erlangs) Power Consumption (W) Idle 1400 40 1900 64 2200 100-LINE SINGLE-CABINET RURAL VERSION ===================================== A 100-line single-cabinet system has been developed. This system uses a single control shelf and is primarily intended for applications where the system availability achieved with duplicated controls and multiple line shelves is not a major requirement of the administration. With such an arrangement the mean-time-between-failures resulting in a total loss of service is expected to be in excess of 5 years. Fig 4. Shows the equipment cabinet arrangement. The reduced-height cabinet has provision for 7 shelves of standard height. The power shelf occupies the bottom shelf position and the order of shelves above this reading upwards is : MMI, Call Accounting, 32-port line shelf, 96-port line shelf, control shelf and miscellaneous / SPM shelf. A fuse panel is mounted to the rear of the power shelf and an insulation-displacement type MDF is located at the rear of the line shelves. In this arrangement, the duplicated call-accounting subsystem has been retained to avoid the nedd for a special design for this application. Each line shelf is seperately powered from a DC-DC convertor mounted on the power shelf. The power shelf also includes a main and stand-by ringer unit. The MMI shelf accomodates the call-accounting subsystem and miscellaneous / SPM shelf convertors. The control shelf includes its own dedicated convertor. UXD5B FACILITIES ================ It has already been mentioned that the UXD5B provides a wider range of facilities than was available on UXD5A as well as additional facilities specifically for export requirements. Subscribers Lines have the options of 2 Line-card types. The standard 8-port line card provides a nominal 25mA constant-current feed to line. On-board gain adjustment is provided to cover lines with up to 10dB loss. (The 4-port UXD5A long-line card is used on lines exceeding 10dB loss.) Certain types of customer apparatus require line current in excess of 25mA. To Cater for these a card is being developed giving a nominal 40mA line feed. This card can also provide test access to the line or exchange where remote line test equipment is fitted. Both card types provide for a limited number of shared-serice subscribers. A multiple-signalling junction card, controlled by an on-board microprocessor, is the standard analogue junction circuit for the UXD5B. It can be configured to interwork with all BT Local-Network Analogue junction signalling systems and Caters for E and M signalling for export applications. A standard message protocol is used for communication between the card and the main processor and the system therefore does not need to know the type of signalling system in use. Where CCITT R2 signalling is required, 2 card types are provided : The receiver, and the control/sender. Four receivers are mounted on a card each handling both incoming and outgoing traffic. The control/sender card provides the control functions (The software for which presides in PROM), the MF tones and 4 Senders. The control handles 4 sender/receivers, and both card types are fitted in 4-port positions on the non-concentrating line shelf. The UXD5B provides as options several advanced customer facilities. These are provided by additional software in the call processing program and are available to a maximum of 200 subscribers on the exchange. The facilities offered and their function are described below. Call Waiting Indication ----------------------- A Tone is transmitted to a busy subscriber's line to indicate that another subscriber is attempting to contact him. The other subscriber receives an announcement informing him to wait. Repeat Last Call ---------------- This enables the last digits dialled by a subscriber to be repeated by using a short special code. Call Diversion -------------- The subscriber can have 3 forms of diversion which he can set up himself: divert all calls, divert on no reply (his phone will ring for a few seconds during which time he must answer or else the call will be diverted to another number), and divert on busy (if he is already engaged on another call). In all cases, diversions can be set up only to another number on the same exchange. 3 Way Calling ------------- While a subscriber is engaged on a call he may dial up another subscriber and put the original call into a wait state. He then has the option of speaking to both parties in a conference mode, or clearing down from one party and continue speaking to the other. For this service to have satis- -factory transmission standards the conference facility is allowed only to have one party outside the exchange service area. Call Barring (Subscriber Controlled) ------------------------------------ The subscriber can bar certain outgoing calls made from his telephone. This is performed on recognition of the first few digits dialled and not specifically on call type. Code Calling ------------ A personal store is allocated to the subscriber in the exchange RAM for dialling frequently used codes. By applying a short dialling code these numbers are recalled and passed to the switching system as though he had dialled the complete number. EXCHANGE MAINTENNANCE AND DIAGNOSTICS ===================================== The main software of the exchange contains control options for both routine self diagnostics and fault finding and operator controlled fault finding. The aim of the M and D facilities is to detect any faults on the exchange and give their location down to plug-in unit level. On-site maintennance is confined to plug-in unit replacement. Lower levels of maintennance and repair are performed off-site. The diagnostic software operates in 2-ways. For hardware that has no, or limited, microprocessor control, all tests are performed by the main control shelf processor. Those units that have more microprocessor control instigate their own tests and report on failure of any test to the main control shelf processor. Some units that can have catastrophic failure (for example, a fuse blowing) report errors automatically to the main processor via the howler and alarm board. Any faults found are entered into the recent fault history list which gives details relating to the type of fault, the unit that was faulty, the time the fault was found, the number of occurences of the fault and the associated alarm category. Another main action taken by the M and D software is the reporting of faults. If an alarm-extension junction is provided, faults deemed serious cause alarm conditions to be extended over the junction. Several categories are catered for and for BT applications these are given the following titles : Prompt alarm, deferred alarm, and in-station alarm. The category of alarm determines what level of action should be taken. MAN-MACHINE COMMUNICATIONS ========================== The 4 Processors on the control shelves and 2 on the billing shelf have communication links that require interface to an administration terminal. An MMI processor is provided on the the MMI shelf to link one terminal to any of the baove mentioned processors. To allow for multiple usage of the MMI, several input lines are provided. Up to 4 Modem-interface lines can be provided for remote interface to the MMI processor, one local terminal, a transaction recorder and a printer so that the MMI processor gives the administration complete flexibility on the type of interface it requires. Several levels of interface to the processor are allowed: A) Fault Status Level --------------------- The administration can access the MMI processor such that a brief form of the fault record for each control shelf on the exchange can be printed out (referred to as the active alarm list) B) Billing Access Level ----------------------- By using different passwords (Which are rarely enforced... KpT) the administration can gain access to the billing information and enable a dump of the billing records to be given. At this level no access is permitted to the main processor MMI. C) Main MMI Level ----------------- By using Different Passwords again (Which are rarely enforced... AGAIN!), the administration can gain access to the man-machine language on the main processors. By using this, full access is gained to the M and D facilities on the exchange and the exchange configuration can be altered and listed. D) Specialist User Level ------------------------ This allows designers to interrogate the system for debugging, etc. To avoid conflict between simultaneous users, only one user is allowed access to a particular exchange function at any one time. Remote access to the exchange MMI is provided via Modems. These can be either switched or on private wires. To prvide extra security on switched connections, the logon procedure is as follows. A special code is dialled into the exchange and the exchange recognises it as a special type requiring MMI Access. The call is cleared down and the exchange dials out on a pre-configured number and connects the modem when a satisfactory connection has been achieved. Several of these numbers can be configured, one to each MMI access Number, to allow access for a number of administration sites. Full access is still not attained until the neccesary logging in procedure has been followed. FUTURE DEVELOPMENTS =================== In conjunction with British Industry, The UXD5B development is continuing further, mainly in the areas of customer services and administration facilities. Advanced Customer services such as call reminder and call-charge advice require a voice guidance and announcement system to ensure that the service is correctly set up and responding in the required manner. These are currently under development for BT applications. A number of systems already exist and work is currently in hand to adapt the most suitable to UXD5B. BT Have embarked on a trial program of fitting call-logging equipment in all local exchanges. In the case of the UXD5B, the intention is to produce an equipment having a hardware and software interface with the exchange identical with those of the normal billing system so that it can be fitted as an alternative on an optional basis. Some additional changes to the main system software will be required for handling the message protocol between associated equipment provided on a common basis in the network. A development projected for the longer term is a new customer interface card capable of providing Integrated Services Digital Network (ISDN) facilities. New administration facilities include the provision of the CCITT No. 7 common channel signalling system (ARRRRRGGGHHHH) and a message transmission sub-system ((MTS). These will offer UXD5B customers the use of co-operative supplementary services in common with System X in an Integrated Digital Network. CONCLUSION ========== The development of the UXD5B is a joint BT and British Industry activity. In the case of BT it continues the program of rural-network modernisation, which began with the introduction of the UXD5A. The larger capacity UXD5B will be used mainly as a replacement for the older UAX13s, 14s and SAX exchanges in Scotland, Wales and South West England. To meet this program, initial orders have been placed with industry for over 350 exchanges covering a 3 year supply period. Not only is the UXD5B suitable for integration into an eventually all digital network, the wide range of advanced facilities it can offer, together with the continuing development program, mean that it will meet the future needs of the customer for the forseeable future with minimal change to the overall system architecture. Much interest is being shown in the UXD5B by overseas administrations, and BT's own commitment to it should enhance the success of the product in export markets.