Pulse or digital communications – Repeaters – Testing
Patent
1982-07-29
1986-08-26
Safourek, Benedict V.
Pulse or digital communications
Repeaters
Testing
370 85, 364900, H04B 300
Patent
active
046087001
DESCRIPTION:
BRIEF SUMMARY
This application is based upon, and claims priority of, International Appliation No. PCT/US81/00896 filed July 23, 1981.
TECHNICAL FIELD
The field of this invention is data communications and more specifically apparatus and methods for linking components in distributed communication systems.
BACKGROUND ART
There is a need for an efficient, simple and economical means of communication between controllers, sensors, and controlled devices in distributed systems. The types of systems which would benefit greatly from such a communications system include, but are not limited to, distributed energy systems such as heating and air conditioning, other process systems, distributed alarm systems for fire and intrusion, and many others. The requirements for such a communication system are economy, for obvious reasons, simplicity of interconnection, to make the system useful for a wide range of applications, and efficiency of message arbitration and addressing, to allow use with low bandwidth media.
There have been several different local communications links developed in recent years. Some of these local networks provide one-way communications from a single, fixed terminal. These links, for example, the one marketed by BSR, Inc., are adaptable to a variety of applications.
Another form of local network uses a single data path and an arbitration scheme which depends upon detection of collisions and re-transmission with a random time delay. This type of system is typified by ETHERNET, presently marketed by Xerox Corporation.
Another form of local network avoids most collisions by assigning each port a time slot, which rotates through all terminals in the network. Such networks are known as "token" networks, because the time-slot assignment is mediated by passing around a "token", or special symbol. This type of network is typified by CHAOSNET.
Yet another form of local network is the IEEE STD-488 instrumentation bus, which uses a master controller to handle all communications.
The subject invention is intended to fill a need which is not quite met by any of the above mentioned local networks. It provides two-way communications with low cost and high utilization of the communications medium.
DISCLOSURE OF THE INVENTION
In general this invention comprises a communications network and in particular a linked network which permit efficient communication among associated components. In a simple embodiment, there are two paths for information transfer. These are referred to herein as the data and control paths. The data path carries, in the preferred embodiment, three types of information, which are handled differently by the network ports. The control path carries bus access requests of different immediacy levels. The second part of the communication network is the collection of ports. These ports are identical to each other, and are of such nature as to be producible as large-scale integrated circuits. The ports and the data and control paths are collectively referred to as the link herein.
Each of the ports is connected to a device which the port serves, referred to here as the associated component. The associated components may be as simple as a switch, or as complicated as a computer. The associated component initiates any action of the link port, and accepts information transferred to it from the link by the link port.
Access to the link is requested by a link port by sending a signal on the control path. One of the most important features of this link is distributed arbitration. For example, when one link port requests access to the link, all ports may be made aware of the request. Each port can then keep track of all pending requests at each immediacy level. When a device is in control of the data path (or "bus"), it is known as the master. When the master reliquishes control, it sends a special symbol on the data path, this special symbol being the end of function (EOF). When the link ports receive an EOF, they decrement their count of pending requests. A port with a pending request knows that it can become m
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Kirtley, Jr. James L.
Sterling Thomas L.
Williams Ronald D.
Chin Stephen
Engellenner Thomas J.
Maslow James E.
Massachusetts Institute of Technology
Safourek Benedict V.
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