Multiplex communications – Wide area network – Packet switching
Patent
1983-03-02
1985-04-30
Safourek, Benedict V.
Multiplex communications
Wide area network
Packet switching
370 86, H04J 308
Patent
active
045148414
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a method and arrangement in a telecommunications system for obtaining, in transmitting information between terminals commonly connected by a ring bus, an adaption at the interface between the bus and respective terminal, where the terminals may assume different logical conditions.
BACKGROUND ART
In the known art, units with a simple repeater function are customarily used, i.e., the signals pass straight through the unit, only obtaining a correction of the signal shape in relation to the distortion in the line. As an example of such a connecting unit, reference is made to a circuit made by EXAR INTEGRATED SYSTEMS INC, type XR-C277. The circuit has a regenerating repeater function utilized in PCM systems.
DISCLOSURE OF INVENTION
A problem with arrangements in the known art is that a fault, e.g., in the form of an interruption in any of the terminals connected to the ring bus, also causes a breakdown of the entire bus, and in the case of a series bus this stops all traffic on the bus. The inventive arrangement, characterized by the claims, solves this problem by each of the terminals being connected to the bus via a connecting unit. The terminals can assume different conditions in relation to the bus. With the power supply unavailable the terminal is not connected, and can neither receive nor monitor the data flow on the bus. With power being supplied, but in the OFF LOOP condition the terminal is not connected to the bus, but it can monitor the data flow. In the PASSIVE condition the terminal is connected to the bus for receiving the data flow, and the terminal can also interrupt the data flow if it is commanded to go active. In the ACTIVE condition the terminal has access to the bus and also the initiative in the traffic occurring.
The connecting unit functions as a switch between the ring bus and terminal such that when the terminal is not supplied with power, the data flow on the bus goes straight through the unit, the latter then functioning purely as a repeater, whereas when power is supplied to the terminal and it is in the ACTIVE condition, for example, switching takes place in the unit preventing the data flow on the bus from passing through the unit, the flow passing instead through the terminal through the output transformer of the unit and out on to the bus.
In the terminal there is transceive logic coacting with the connecting unit, for receiving information from the unit for analysis. The signal on the bus also continues straight through the unit, which has a repeater function. The terminal awaits connection to the bus until it has received a particular code combination in the incoming data flow. When this combination is received the terminal sends an inhibition signal to the connecting unit, thereby interrupting the data flow through it. In comformity with received information the terminal subsequently sends data out to the bus via the output transformer of the unit. Information on the bus now flows through the terminal and may be affected by the latter. The inhibition signal is also triggered by absence of power.
The aim of the arrangement in accordance with the invention is thus to obtain a security function against faults, this function maintaining the data flow through the ring bus, even if a break should occur in any of the terminals connected to the bus.
BRIEF DESCRIPTION OF DRAWINGS
The inventive arrangement will now be described in detail with the aid of an embodiment, while referring to the appended drawings, on which:
FIG. 1 is a block diagram of a system in which the arrangement is included; and
FIG. 2 is a logic diagram of a connecting unit in accordance with the invention and indicates the transceive logic in the terminal for the sake of clarity.
MODE FOR CARRYING OUT THE INVENTION
As will be seen from FIG. 1, a plurality of terminals T1-T6 are each connected to a common ring bus RB via a connecting unit CU. The bus is of the single direction series type, which means that data only flow through the connecting unit in one directi
REFERENCES:
patent: 3825896 (1974-07-01), Obenhaus
patent: 4121054 (1978-10-01), Popkin
patent: 4402075 (1983-08-01), Bargeton et al.
Safourek Benedict V.
Telefonaktiebolaget LM Ericsson
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