Importance

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Abstract

Information originating at a plurality of terminal units is transmitted to a common information sink via a concentrator coupled between a plurality of terminal units and the common information sink. In one embodiment, used in a time reporting system, the information originates at a token reader at each of the terminals which is arranged to read pre-recorded information on an identification badge or time card. Each terminal is connected to the concentrator over a dedicated duplex communication link, and when the terminal has information to transmit, a first word is transmitted to the concentrator, the concentrator, in addition to being coupled to each of the terminals, is coupled to the information sink via a dedicated duplex communication link. Assuming the concentrator is idle, when a first word is received at a concentrator from a terminal, the concentrator attempts to seize the link between it and the common information sink. If successful, it transmits an address word corresponding to the address of the terminal from which it received the transmitted word. The information sink, upon receipt of an address, echoes the same to the concentrator. The echoed address is checked at the concentrator and on a favorable result, the concentrator transmits the word received from the terminal to the sink. Upon receipt of the word at the sink, the sink echoes the word to the concentrator. The concentrator, then transmits a copy of the echoed word to the terminal. Assuming the word received back at the terminal is an echo of the word it transmitted, it transmits a second word. If the concentrator detects an error in the address echo, or if the terminal detects an error in the word echo, the erroneously received address or word is retransmitted. If the error is not corrected in one of several retries, the attempt at transmission is terminated. In the time reporting system, a real time clock periodically sends time information to both the information sink and each of the terminals, thus obviating the necessity for any of the terminals to include time information in the message transmitted to the sink.

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First Claim