Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04Q—SELECTING
  • H04Q11/00—Selecting arrangements for multiplex systems
  • H04Q11/04—Selecting arrangements for multiplex systems for time-division multiplexing

Definitions

• the present invention relates to a digital switching system which performs the Matrix Switch function for Circuit Switching applications. BACKGROUND ART
• a Matrix Switch or Crosspoint Switch is a device used in a Space Division Switching System to enable any two or more attached circuits to be interconnected as required.
• a Space Division Switching System normally has a large number of electrical conductors or circuits terminating at a Matrix or Crosspoint Switch. By selectively connecting one or more switching nodes or crosspoints of the Matrix Switch an electrical connection is established between any two of these circuits. • The most common example of a Space Division
• Switching System is the analogue telephone exchange where a Matrix or Crosspoint Switch is used to interconnect subscriber telephones to each other on an "as requested" basis.
• a data communications switching system example is the requirement for a number of terminal devices to be able to be connected to more than one communications channel or host computer.
• Circuit switching systems implement a physical connection between two attached devices. This is accomplished by mechanical switches and relays or by electronic circuits. Circuit switching systems are normally arranged as a Switch Matrix enabling two or more circuits attached to the matrix to be physically and/or electrically connected via the Switch Matrix. This type of switching system establishes a permanent circuit through the switching system for the duration of the connection.
• Switch Matrix As the number of individual circuit connections increases the size of the Switch Matrix expands as a power function, which rapidly escalates the equipment size and cost.
• a 4x4 matrix switch which can connect any two of the eight circuits, requires 16 individual switching nodes or crosspoints while a 32x32. atrix requires 1024 switching nodes. Each switching node may be required to connect more than one signal line for each circuit connection thus, the number of actual switching circuits can be very large for even a small number of circuit connections.
• the signal paths need not be symmetric, which further complicates the matrix if unidirectional electronic switching is used.
• the present invention provides the information transparent, circuit switching function of a Space Division switching system at a size and cost more comparable to that of a Time Division or Message switching system.
• the present invention differs from current switching system implementations in that it provides both matrix circuit switching and information transparency without requiring a large number of physical switching nodes or crosspoints.
• a Virtual Matrix Electronic Switch which implements the circuit switching function of electrical signals present on electrical circuit conductors terminating at the Matrix Switch.
• the majority of switching systems are used to route low information bandwidth signals and are therefore very amenable to the use of high speed sampling and multiplexing techniques to enable a number of low information bandwidth channels to efficiently share a high bandwidth channel with negligible loss of information content.
• the present invention employs the said high speed sampling and multiplexing techniques to achieve the same switching function without the requirement of a permanent circuit.
• the electrical signals are preconditioned to appropriate signal levels before being switched. If the incoming signal is of an analogue type it is first converted to a digital representation at a sample rate consistent with maintaining the original information content.
• the conversion of analogue type signals to a digital format is not a precondition of the invention, as appropriate sample and hold techniques would allow the signals to be switched as amplitude varying discrete samples of the analogue signal.
• the preferred embodiment consists of one Timing and Control Module and a number of Switch Modules interconnected by three, multiple conductor, parallel signal Buses. Two of the Buses, known as the Switch Buses, are used to transfer information between Switch Modules installed in the system. The third bus, known as the Control Bus, is used by the Timing and Control Module to provide system timing and control signals to all Switch Modules.
• the Timing and Control Module can include a Keyboard and Display Unit, or have an attached interactive terminal . device, such as a CRT display, to allow direct operator control of the circuit connections.
• the circuit connection request can be provided by the attached device, such as a telephone handset.
• each Switch Module Associated with each Switch Module is a Line Interface Unit which provides the demarcation between the switching system and attached external circuit.
• the Line Interface Unit provides the conversion between the electrical, or other types of signals, used by the attached devices and the electrical signals processed by the switching system.
• the Switch Modules perform the actual switch function and exchange information via the Switch Buses.
• the two Switch Buses are equally accessible to each Switch Module installed in the system. Access by a Switch Module to the Switch Buses is determined by the Timing and Control Module. Binary encoded timing signals are generated by the Timing and Control Module and are monitored by each Switch Module.
• the switching system's basic time period is known as the Transfer Slot period and is the time period required for two Switch Modules to execute an information exchange on the Switch Buses.
• the timing section of the Timing and Control Module generates the Transfer Slot count which is received by all Switch Modules.
• the Transfer Slot count is cyclic and the time taken to increment through every Transfer Slot is known as the Transfer Slot Rotation period.
• Transfer Slot Rotation period depends on the total number of Transfer Slots, a smaller number of Transfer Slots provides a faster external circuit sample rate and vice versa.
• the minimum number of external circuit connections active at any one time is equal to the number of Transfer Slots in the Transfer Slot Rotation period.
• the Transfer Slot period is normally a fixed system parameter dependant on the physical implementation of the system switching circuits. The number of individual Transfer Slots and hence the Transfer Slot
• Rotation time can be a fixed or variable system parameter as required.
• the Timing and Control Module allocates a Transfer Slot time and Switch Bus selection to. each active Switch Module. Each Switch Module monitors the Transfer Slot count signals on the Timing and Control Bus. When the Transfer Time Sloi: value matches the allocated Slot number the Switch Module outputs the current state of the input signals present at its Line Interface Unit onto the allocated Switch Bus. At the same time it transfers the information present on the other Switch Bus to its Line Interface Unit. As Switch Modules are normally paired for any one Transfer Slot, the same procedure occurs at the other Switch Module, with the exception that the alternate Switch Buses are used for input and output. The information representing the instantaneous external circuit signals at the inputs of the pair of communicating Switch Modules are transferred to the outputs of the alternate Switch Module of the pair.
• the Timing and Control Module communicates with each Switch Module via the Control Bus and can allocate each individual Switch Module a specific Transfer Slot time and the Switch Buses to be used for input and output.
• Timing and Control Module allocates the Transfer Slot times for all Switch Modules it ensures that for any one Transfer Slot time only one pair of Switch Modules will have access to the Switch Buses.
• the Transfer Slot time and Switch Bus allocations are not specific to any individual Switch Module and are allocated as required.
• the Switch Modules involved in a transfer have no synchronisation or interaction with each other except for the recognition of a valid Transfer Slot count.
• the Line Interface Units convert the data received from the Switch Module into the form required by the external signal circuits. For a digital circuit the signals are converted to the appropriate digital levels while for an analogue circuit a digital to analogue conversion is performed and the resulting time continuous signal is conditioned to the required bandwidth and signal level.
• the Switch Buses form part of the switching system and are normally an integral part of•the Matrix Switch Printed Circuit backplane.
• the design of the Switch Bus backplane depends on the logic family used to implement the system.
• Each signal conductor of the Switch Bus is terminated at its characteristic impedance to minimise signal noise and cross coupling.
• the information bandwidth of a Switch Buses during a Transfer Slot period is related to the number of parallel signal paths making up the Switch Bus.
• the preferred embodiment has eight parallel signal paths for each Switch Bus however, this is not a restriction on the Matrix Switch architecture as the Switch Buses can be extended to any number of parallel signal paths required.
• Each Switch Module in the Matrix Switch is identical and can occupy any position on the Switch and Control Buses.
• a Switch Module position is known to the Timing and Control Module by a unique address which, in turn, is the address of the corresponding external circuit.
• any two external circuits can be interconnected via their corresponding Switch Modules. Allocation of the same Transfer Slot time to any two Switch Modules in the system initiates a virtual connection between their associated external circuits.
• the two Switch Modules operating in synchronism via the Switch Buses perform a high speed digital sample of their respective external circuits.
• the data is then transferred between the two Switch Modules to their outputs and held for one Transfer Slot Rotation period.
• the output signals are time sampled replicates of the input signals the transfer is completely transparent to the Switch Modules and the system Timing and Control Module.
• the transfer function When the Matrix Switch is considered at the Line Interface Module inputs and outputs the transfer function is very similar to a permanent connection system.
• the switching transfer function does have an amount of non- cumulative error introduced due to the sampling function, which is directly related to the Transfer Slot rotation period.
• the number of external circuit connections that can be supported by the Switch Matrix at any one time is bounded by the sampling error tolerance of the external circuit and its attached device.
• the Transfer Time Slot Count is sequenced at a high rate, typically Megahertz.
• rate of binary information change on any one signal line is relatively slow, typically up to 20 Kilobits/second while the analogue to digital conversion rate for telephone quality speech is 8000 conversions/second.
• the maximum period between successive sample is 125 microseconds.
• the Matrix Switch can transfer the resulting binary word between Switch Modules in one Transfer Slot time the maximum Transfer Slot Rotation period is also 125 microseconds. If a typical Transfer Slot period of 100 nanoseconds, is assumed then the maximum number of Transfer Slots in one Transfer Slot Rotation period, or alternatively, the maximum number of active external circuit connections possible at any one time, is 1250.
• the preferred embodiment demonstrates a switching system whereby the information transfers between external circuits are symmetrical and bidirectional. This is not a limiting factor of the invention and other arrangements such as asymmetrical switching or unidirectional switching to one or more external circuits from a single external circuit are within the scope of the invention.
• Timing and Control Module could be programmed to handle a number of higher level system functions not associated with the present invention's basic switching function.
• Figure 1 is a schematic block diagram of a limited Virtual Matrix Electronic Switching System according to the preferred embodiment of the present invention.
• Figure 2. is a schematic block diagram of the Timing and Control Module of the system of Figure 1.
• FIG. 3 is a schematic block diagram of the Switch Module of the system of Figure 1.
• Figure 4. is a schematic block diagram of a typical digital Line Interface Unit.
• Bus 100 is the control bus which is the primary system bus and is used by the timing and control module 110 to distribute commands and timing information to switch modules 210, 310, 410
• Buses 101 and 102 are the two switch buses used by the switch modules for the exchange of external circuit information. Each signal conductor of each bus is terminated in its characteristic impedance by terminating resistors 103 and 104 to minimise signal reflections during a bus operation.
• Each switch module is connected to the control bus and both switch buses and can receive or transmit information on either switch bus.
• Line interface units 220, 320, 420 provide the physical and electrical interface between switch modules and the external circuits. The line interface units also provide signal conditioning, conversion, isolation and medium translation, such as optical to electrical, if required.
• Fig 2. shows detail of the timing and control module (110).
• a microcomputer (111) is used to provide the system management functions including the allocation of switch module transfer slot periods and switch bus selection.
• the microcomputer would normally be a single chip device however any implementation of a stored program computer which can perform the required functions is applicable.
• the microcomputer connects to the control bus via a bus interface (112) which provides appropriate buffering of the bus signals.
• the timing generator (113) provides the basic system timing signals and the transfer slot count used by the switch modules to accurately synchronise information transfers on the switch buses.
• the timing generator also connects to the control bus via the bus interface.
• the control interface (114) is the user interface to the switching system to establish the required external circuit connections.
• the parameters can be provided directly to the switching system via a keyboard or terminal device. Alternatively, the request for an external circuit connection can be derived from the external circuits themselves with appropriate signal detection circuits, normally incorporated into the line interface unit.
• Fig 3. shows detail of the switch module.
• the Transfer Slot latch (211) is accessible to the timing and control microprocessor and holds the Transfer Slot and the switch buses allocations to be used by the Switch Module for an information transfer.
• the timing decode logic (212) continuously monitors the Transfer Slot count on the control bus and compares it with the allocated value held in the Transfer Slot latch. When a match is detected the timing decode logic activates the bus switch control logic (213).
• the switch input latch (219) is closed, freezing the instantaneous value of the external circuit information in the latch for the duration of the transfer. An information transfer is then executed on the allocated Switch Buses. If, for example, switch bus 101 has been allocated as the switch module output bus then the switch bus control enables bus receiver 215 and bus driver 217.
• switch bus 102 has been allocated as the output bus then bus receiver 214 and bus driver 216 are enabled.
• the transfer procedure is identical in both cases except for the switch buses used in the transfer.
• the external circuit information held in latch 219 is output onto switch bus 101 via bus driver 217.
• bus receiver 215 allows information on switch bus 102 to pass to the inputs of latch 218.
• the timing decode logic deactivates the bus switch control and the switch module is disconnected from the switch buses.
• the function of the line interface unit can vary depending on the signal type and transmission medium used for the external circuits.
• a typical line interface unit for digital signals is shown on Fig 4.
• Signal level translators and conditioners 221 and 222 perform the signal conversion between the external circuit signal levels and the switch module signal levels.
• the line interface unit would normally provide the physical connection (223) to the external circuits.
• Other types of line interface units could include analogue to digital and digital to analogue converters, optical to electrical and electrical to optical converters or other transmission medium or signal conditioning and conversion functions as required.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Use Of Switch Circuits For Exchanges And Methods Of Control Of Multiplex Exchanges (AREA)
• Data Exchanges In Wide-Area Networks (AREA)

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• 1986
  • 1986-05-26 WO PCT/AU1986/000149 patent/WO1986007228A1/en unknown
  • 1986-05-26 EP EP19860903147 patent/EP0221962A1/de not_active Withdrawn

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