Multiplex communications – Wide area network – Packet switching
Patent
1984-11-27
1987-08-18
Safourek, Benedict V.
Multiplex communications
Wide area network
Packet switching
379 5, H04J 116
Patent
active
046882090
ABSTRACT:
Method and apparatus for looping around a digital transmission line (150) at a predetermined channel unit (172) to test the line from either end of the line. Each channel unit in the line is responsive to a first and a second received control code to perform one of two operations. When the first and second received control codes are both first predetermined control codes from one end of the line, the data channel assumes a state to pass the second received first control code and any subsequently received control codes to the next channel unit. However, when the first and second received control codes are first and second predetermined control codes from the one end of the line, respectively, the data channel unit connects the transmit path from the one line end to the receive path back to the one line end, thus looping back to the digital transmission line. To loop around a line at a predetermined channel unit, a maintenance circuit (152) at one line end applies an individual first predetermined control code for the predetermined channel unit and each of the intermediate channel units followed by the application of a second predetermined control code for the predetermined channel unit. The first channel unit from the end of the line passes the second received first control code and any subsequently received control codes to the next channel. This continues for each unit until the predetermined channel unit receives only a first and a second predetermined control code. The second received second control code causes the unit to loop around the transmission line. A maintenance circuit at the other end of the line can likewise loop around the line at any channel unit. A third predetermined control code causes each of the receiving channel units to return to their previous data transmission state.
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IEEE Transactions on Communications, vol. COM-30, No. 9, Sep., 1982, New York, L. W. Campbell et al., "Maintenance Operations for the Circuit-Switched Digital Capability", pp. 2053-2056.
The Bell System Technical Journal, vol. 61, No. 4 Apr., 1982, F. H. Keeve et al., "No. 10A Remote Switching System: System Maintenance", pp. 597-625.
Banzi, Jr. Frederick J.
Dugan Michael J.
Johnson Randolph W.
Saylor Douglas D.
Sharper Craig A.
American Telephone and Telegraph Company AT&T Bell Laboratories
Godlewski Richard J.
Huseman M.
Safourek Benedict V.
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