GB1272978A - A data transmission system - Google Patents

Abstract

1,272,978. Data transmission systems. INTERNATIONAL BUSINESS MACHINES CORP. 4 Dec., 1969 [20 Dec., 1968], No. 59161/69. Heading H4P. [Also in Division G4] A data transmission system comprises a central station 1 and a plurality of area stations 2- 17 arranged in a closed loop around which signals are transmitted; each station 2-17 includes a by-pass (not shown in Fig. 1) that can be broken when the corresponding area station 2-17 receives or transmits signals; when a number of area stations simultaneously request communication with the central station 1, then these are interrogated sequentially around the loop. As described in relation to airline seat reservation, the stations 1-17 are interconnected through modulators 18, 20, 22, 24 and demodulators 19, 19, 21, 23, 25. All signals are transmitted counterclockwise around the loop in serial form, but are connected to parallel mode in each area station 2-17. When the central station 1 wishes to receive data, it sends a POLL signal around the loop, whereon those area stations desiring communication break their by-pass. Each sends a RESET signal, so reconnecting the by-pass of every calling area station except that nearest to the output of the central station 1, for example, area station 4. Data communication then occurs between area station 4 and central station 1. Communication then proceeds sequentially with the remaining calling area stations counterclockwise around the loop, by successive transmission of POLL and of RESET signals. In an alternative embodiment, communication proceeds sequentially with calling area stations, clockwise around the loop. The central station 1 may alternatively exchange data with any selected area station 2-17 by alerting all area stations 2-17 with a CALL signal, followed by an address signal for the selected area station, that will break the corresponding by-pass. Figs. 2 and 3 (not reproduced) illustrate area stations that are suitable for sequential communication between area stations and the central station, respectively counterclockwise and clockwise around the loop.