Browse Prior Art Database

Loop Transmission Controller

IP.com Disclosure Number: IPCOM000087231D
Original Publication Date: 1976-Nov-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Bono, RC: AUTHOR [+3]

Abstract

Described is an improvement in the operation of the loop disclosed in U. S. Patent 3,752,932. The system disclosed in this patent is capable of operation in synchronous data loop control (SDLC) protocol wherein the central or primary station issues an enable signal, commonly known as a go-ahead signal, which is immediately followed by a continuous stream of 1 bits. The terminals on the loop recognizing the go-ahead signals search for seven continuous 1 bits. Upon detecting this condition, if the terminal has data, it changes the seventh received 1 bit to a 0 bit and starts its message with an address code, control code and data and block checking characters, if desired. Loop protocol further requires that every transmission by a primary station or a terminal ends in a flag or F byte, i.e., 0 111 111 0.

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Loop Transmission Controller

Described is an improvement in the operation of the loop disclosed in U. S. Patent 3,752,932. The system disclosed in this patent is capable of operation in synchronous data loop control (SDLC) protocol wherein the central or primary station issues an enable signal, commonly known as a go-ahead signal, which is immediately followed by a continuous stream of 1 bits. The terminals on the loop recognizing the go-ahead signals search for seven continuous 1 bits. Upon detecting this condition, if the terminal has data, it changes the seventh received 1 bit to a 0 bit and starts its message with an address code, control code and data and block checking characters, if desired. Loop protocol further requires that every transmission by a primary station or a terminal ends in a flag or F byte,
i.e., 0 111 111 0.

If a terminal malfunctions, it may not produce an F byte, but may instead transmit random signals or a go-ahead sequence, either of which may hang up the loop. A system illustrated in the drawing is utilized to prevent a malfunctioning terminal from passing a go-ahead to the next terminal, and to inhibit the terminal from further transmissions until it rerequests permission to transmit. In addition, the illustrated embodiment allows the terminal to assume an idle mode if the terminal has information to transmit but is unable to respond within the time frame established by the first go-ahead it receives. In the idle mode, the controller produces continuous F bytes to whi...