270 lines
12 KiB
Plaintext
270 lines
12 KiB
Plaintext
/////////////////////////////////////////////////////////////////////////////
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// //
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// Keltic Phr0st / Fit-Of-Boredom Productions Inc. Presents: //
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// AXE 10 : Architecture //
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// //
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// An Overview of the AXE 10 System Architecture and functional Structure //
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// //
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/////////////////////////////////////////////////////////////////////////////
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INTRODUCTION
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============
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In march 1985, after a detailed evaluation of digital switching systems, BT
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placed a contract with Ericsson Limited for the development of AXE10 for the
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BT Network and for the supply of a quantity of exchanges.
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AXE10 is a duplicated-processor stored-program controlled digital
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switching system developed by Telefon AB LM Ericsson of Sweden. The system
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is structured for local, tandem, transit and combined exchange applications.
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It can also be configured as a cewllular mobile or as an international
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switching centre.
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SWITCHING ARCHITECTURE
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======================
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The system architecture is logically divided into two main parts, the
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switching system (APT) and the control system (APZ). See Figure 1.
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The switching system (APT) performs traffic and operation/
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maintennance functions. It comprises four main hardware subsystems:
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Subscriber Switching SubSystem (SSS)
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Group Switching SubSystem (GSS)
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Trunk and Signalling SubSystem (TSS)
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Common-Channel Signalling SubSystem (CCS)
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and the following software subsystems :
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Traffic Control SubSystems (TCS)
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Charging SubSystem (CHS)
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Operation and Maintennance SubSystem (OMS)
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Subscriber Services SubSystem (SUS)
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Network Management SubSystem (NMS)
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All Hardware subsystems have a hardware component.
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The control system (APZ) is made up of centralised and distributed
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logic achieved through the following subsystems:
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Central Processor SubSystem (CPS)
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Regional Processor SubSystem (RPS)
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Maintennance SubSystem (MAS)
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Support Processor SubSystem (SPS)
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Data Communication SubSystem (DCS)
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File Management SubSystem (FMS)
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Man-Machine Communication Subsystem (MCS)
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In Earlier Exchanges the input/output subsystem was used instead of SPS, FMS,
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MCS and DCS. See Figure 2 for the Subsystem structure.
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FUNCTIONAL STRUCTURE
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====================
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The division of the systems (APT and APZ) into subsystems is determined by
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conditions and requirements that arise from features, traffic handling and
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operations and maintennance functions. See Figure 3.
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The subsystems, including their interfaces, are designed such that
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they can be used for different applications with the minimum of adaptation.
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Each subsystem is built from a number of function blocks which in themselves
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comprise hardware, central software, regional sofware and data components,
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or just central software and data components. Each function block is designed
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to execute a specific set of functions or sub-functions. A library of
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several hundred functional blocks exists to satisfy all applications and
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individual exchange requirements. Standardised interface signalling is
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extensively used between blocks not only to achieve the neccesary flexibility
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to satisfy customer's requirements, but to also enable new technology to be
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introduced within the system in an efficient manner. See Figure 4.
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To meet the twin needs of high capacity and low cost, the complex
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executove tasks neccesary to operate the system are executed by the
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duplicated central processor (CP) working in a paralell synchronous mode.
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The routine, high volume tasks, such as scanning operations and for the
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direct control of hardware, are distributed across a dimensionable number
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of small regional processors (RPs). Regional Processors controlling several
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hardware units are configured in a load sharing mode. The software driving
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the APT functions, therefore, has both APT and APZ elements.
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THE APT SUBSYSTEMS
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==================
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Subscriber Switching SubSystem (SSS)
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------------------------------------
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The subscriber switching subsystem contains the digital subscriber switch
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and is built up of 16 line switch modules (LSMs). An LSM serves 128 analogue
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subscribers or can support four 30-Channel systems for ISDN Customers.
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Its principal function is to supervise the state of connected subscriber
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lines, and to set up release connections by sending and receiving signals
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to and from subscribers. The SSS comprises both hardware and Software. To
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allow for the possibility of reducing line-plant costs, the local exchange
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may be engineered with distributed switching in the form of a remote
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subscribers switch (RSS).
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Trunk and Signalling SubSystem (TSS)
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------------------------------------
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The trunk and signalling subsystem includes the equipment for connecting
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trunks to the group switch. It supervises the state of trunks to other
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exchanges by measn of the signals it receives and sends. The TSS consists
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of both hardware and software.
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Group Switching SubSystem (GSS)
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-------------------------------
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The group switching subsystem houses a time-space-time digital switch built
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up of duplicated time switch modules (TSMs) and duplicated space switch
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modules (SPMs). Its primary purpose is to set yp a 64Kbit/s path between
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SSS and TSS devices through the group switching network. It is also
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responsible for network synchronisation functions. The GSS comprises
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hardware and software.
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Traffic Control SubSystem (TCS)
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-------------------------------
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The Traffic Control SubSystem is wholly software, and controls and supervises
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the set-up and release of connections. The TCS stores and analyses digit
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information received from the SSS and TSS, and then, after checking against
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previously recorded information, for example, subscriber categories, routing
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and tariff classes, decides how the call should be handled.
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Charging SubSystem (CHS)
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------------------------
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The Charging SubSystem consists of central software blocks and is responsible
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for the task of charging calls by means of very accurate pulse metering
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techniques. In addition to normal charging, special subscribers charging
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facilities are available such as itemisation and advice duration and charge
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(AD&C) information. The CHS also provides the administration with charging
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statistics and per-event charging information. It functions by monitoring and
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then analysing call information from the TCS or SUS (for service information).
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Output to the FMS follows execution of the charging function.
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Operation and Maintennance SubSystem (OMS)
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------------------------------------------
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The Operation and maintennance SubSystem mainly comprises software blocks.
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Its function is one of system supervision, fault location, collection of
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statistics and for dealing with the administration's operation and
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maintennance functions. It can be operated either in the local or in remote
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mode, say from a remote operation and maintennance centre.
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Subscriber Services SubSystem (SUS)
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-----------------------------------
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The subscriber services system consists entirely of central software. Its
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function blocks provide a variety of subscriber services. Typical SUS
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services include:
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Abbreviated Dialling
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Three-Party Services (Enquiry, hold and transfer)
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Diverion (Immediate, On Busy and and on no-reply)
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Malicious Call Trace
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Call Barring
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Automatic Alarm Call
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Common Channel Signalling SubSystem (CCS)
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-----------------------------------------
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The Common-channel signalling subsystem implements the message transfer part
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(MTP) of CCITT Signalling Systems No. 6 and No. 7. The subsystem consists
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of hardware and software blocks, the hardware devices (signalling terminals)
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being connected to the external signalling links via a semi-permanent
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connection through the group switch.
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Network Management Subsystem (NMS)
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----------------------------------
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The functions of the network management subsystem are implemented in
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software. The role of NMS is to provide access via the normal input/output
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devices for the administration to monitor continuously the state of the
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network.
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THE APZ SUBSYSTEMS
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==================
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Central Processor SubSystem (CPS)
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---------------------------------
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The Central Processor subsystem is realised in both hardware and software.
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The CPS executes the complex software tasks which are stored in the various
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APT blocks. The main hardware parts of the central processor, which is
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duplicated and runs in the synchronous mode, are the central processing unit
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(CPU) and the memory stores. These stores comprise the main store (MS) or
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program store (PS), reference store (RS) and the data store (DS).
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The purpose of the CPS is to execute the following functions:
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o Program Control including supervision of functions and for measuring
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processor load.
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o Loading and storage of tasks
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o Output and updating reloading information
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o Controlling fault tracing programs resident in the MAS or RPs.
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Regional Processor SubSystem (RPS)
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----------------------------------
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The regional processor subsystem consists of both hardware and software
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blocks. The purpose of the RPS is to run the simple, routine and very
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frequent tasks to drive the RP part of the APT software and hardware. The
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number of functions performed by an RP pair depends upon the complexity
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of these functions. The number of RP pairs required for a given exchange
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depends upon its size and the complexity of its signalling systems.
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Maintennance SubSystem (MAS)
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----------------------------
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The maintennance subsystem consists of both hardware and software. The major
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role is to supervise the operation of the APZ control system and takes the
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appropriate action should a malfunction occur.
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Support Processor SubSystem (SPS)
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---------------------------------
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The support processor subsystem consists of one or more independent
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processors which drive input/output equipment such as personal computers,
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visual display units and disc drives which are connected to the subsystem.
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Data Communications System (DCS)
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--------------------------------
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The software for the data communications system resides in the SPS. It also
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has a hardware element to support protocols such as X.25. Its function is to
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support remote operation and maintennance, and transfer of itemised call
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accounting data.
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File Management SubSystem (FMS)
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-------------------------------
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The file management subsystem consists wholly of software. It provides
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storage in the event that a data link failure occurs.
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Man-Machine Communications SubSystem (MCS)
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------------------------------------------
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The man-machine communications subsystem consists of software. It provides
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security checking and authorises I/O devices and the operator for a
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particular function. It routes data output from the exchange to the presel-
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-ected terminal(s). In addition, the MCS controls the generation of alarm
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printouts or displays.
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RELIABILITY
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===========
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System Performance is determined by both hardware and software reliability.
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Hardware reliability is achieved by choice of components and by duplication
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of units which perform a task affecting a proportion of the exchange
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function.
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Software reliability exists through system recovery functions which
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rely on three restart levels namely:
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o Small Restart - The APZ clears all jobs in process of being established.
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The status of all existing calls is maintained.
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o Large Restart - If the smll restart is rapidly followed by a new software
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error then a more extensive restart involving a reset of all dynamic data
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will take place. All existing calls are cleared.
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o Restart with reload - The highest level of restart is enacted when the
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restart fails to lead to a succesful program execution. The system then
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automatically reloads programs and data from an external store. All
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existing calls are cleared.
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