Browse Prior Art Database

Highly Available Loop Carrier System

IP.com Disclosure Number: IPCOM000077243D
Original Publication Date: 1972-Jun-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 3 page(s) / 68K

Publishing Venue

IBM

Related People

West, LP: AUTHOR

Abstract

This is a method and apparatus for modifying loop communications upon the detection of one or more faulty links or terminals, using a dial up capability between each terminal with a local unit of the public switched network.

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Highly Available Loop Carrier System

This is a method and apparatus for modifying loop communications upon the detection of one or more faulty links or terminals, using a dial up capability between each terminal with a local unit of the public switched network.

Referring to Fig. 1, there is shown a simplex loop communication system comprising a central station and a plurality of terminals 1-5 connected in series over a corresponding plurality of leased line segments a, b, -- t. Each terminal is provided with a dial up connection to a telephone central office switching exchange A, B, C, and D. The switching exchange for each terminal, (A-CPU, D- Terminal 1, C-Terminals 4 and 5, E-Terminals 2 and 3) is shown as the same one that the leased line loop is routed through. A two-way dial up local line S connects each terminal to a corresponding telephone central office. In the preferred form, each terminal of the loop is provided with an auto answer capability. Additionally, each terminal is provided with a switching capability to switch either the input or the output from the leased line segment, to the dial up line switched interface.

Operationally, the central station periodically transmits a special character around the loop. Each operative terminal periodically looks for the presence of the special character on the loop. In the event that the ith terminal does not detect the special character within a predetermined time period, then it transmits the special character plus its address to the i+1 and remaining downstream terminals. Upon receipt of the special character and address by the central station, there is initiated a dial up talking path connection between the i/th/-1 terminal (the nearest operative upstream terminal) and the i/th/ terminal through the public switched network. The upstream terminal is conditioned in this regard by signals sent through the loop from the central station.

Referring to Fig. 2, there is shown a loop system in which the telephone central office E has suffered a catastrophic failure. This means that both the leased and dial up lines g, h, i, j, & S cannot connect either terminals 2 or 3 into the loop. The central receives notification of this via downstream terminal 4. The downstream half of the loop (terminals 4 and 5) would be reconnected via the switch network. This is implemented by the CPU initiating a dial up connection between central office A to central office C and further establishing a dial up connect...