Multiplex communications – Wide area network – Packet switching
Patent
1986-12-29
1989-12-12
Orsino, Joseph A.
Multiplex communications
Wide area network
Packet switching
H04J 316
Patent
active
048872660
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a communication system and in particular to a radio communication system capable of supporting a network of intercommunicating points with a variety of communication paths therebetween. The invention has particular utility in applications where a relatively large number of devices are required to intercommmunicate, such as in industrial plant and process monitoring and control, but the benefits and advantages of the invention are by no means restricted to such applications.
Communication networks employing cable (electrical and optical) connections and radio links are of course well known. Cable systems have the disadvantage that the capital cost of the equipment and the installation costs are relatively high. Whilst switched systems can provide great flexibility in the communication paths which are established, the provision of communications to a point not served by the original network may involve considerable difficulty and expense. Radio systems have the advantage that a transmitting and/or receiving station can normally be set up relatively easily in any location but there may be difficulty in providing a power supply to the station and often a radio station is relatively large and in particular may require a large antenna. There are many applications where it is desirable to provide a communications system in which the transmitting and receiving apparatus is small, may be easily installed in any location, and is of very low power consumption so as to mitigate the problem of power supplies. For example, on a site such as a refinery there may typically be of the order of 4000 points between which it is desired to provide data communication for process control purposes. There may, for example, be 3000 sensors at various points in the plant and perhaps 1000 receiving devices, such as data recording devices or actuators, such as valves. Data integrity and security are of course of great importance in such an application and this factor, together with the need to avoid any danger of electromagnetic interference, etc., has led to the use of complex cable systems often employing protected cables laid underground. Such installations are extremely costly (typically several millions of pounds for an oil refinery) and further high costs arise when it is desired to alter the system, for example when adding or moving a sensor.
SUMMARY OF THE INVENTION
Viewed from one aspect the invention provides a communication system operating on a single channel including a device at each of a plurality of nodes between which it is desired to establish communication, one device including means for transmitting synchronisation information and each other device having means for providing a synchronisation signal in synchrony with said synchronisation information, said one device being capable of transmitting an address of another device in one of a cyclically repeating series of consecutive time slots, at least one of said time slots in each cycle being reserved so that no such address may be transmitted, whereby any of said other devices may transmit in such a reserved time slot to request communication on said channel. Preferably, each said other device has a pre-assigned address and operates to decode transmitted information on said channel only in a particular time slot dependent on said address. Said other device is preferably arranged to transmit its address in said reserved time slot when it requests communication.
Viewed from another aspect, the invention provides a radio transmitter and receiver apparatus for providing data communication with an electrical device, comprising a transmitter circuit, a receiver circuit and an interface circuit, said interface circuit including a processor controlled by a stored program and being arranged to control the transfer of data from said device to the transmitter circuit and/or from the receiver circuit to the device, and said interface circuit being operable in a condition in which data transfer can take place or in a lower
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Lawrence Peter J.
Neve Brian D.
Owen Lyndon N.
Orsino Joseph A.
Process Automation & Computer Systems Ltd.
Scutch III Frank M.
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