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Back-Up Modem Switching Controlled by EIA Interface

IP.com Disclosure Number: IPCOM000044496D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Jones, MD: AUTHOR [+2]

Abstract

This article describes a system for providing back-up support for a failed modem within a group of identically configured modems. The circuits provide means for switching the analog lines from a failed modem to a spare or back-up modem. The spare or back-up modem can provide normal service on its own dedicated telephone line during periods of normal operation. When a modem connected to a given telephone line is suspected of failure, a second mode of operation is entered. During this second mode, the telephone line is routed to a particular spare connection bus which is connected to a designated spare modem.

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Back-Up Modem Switching Controlled by EIA Interface

This article describes a system for providing back-up support for a failed modem within a group of identically configured modems. The circuits provide means for switching the analog lines from a failed modem to a spare or back-up modem. The spare or back-up modem can provide normal service on its own dedicated telephone line during periods of normal operation. When a modem connected to a given telephone line is suspected of failure, a second mode of operation is entered. During this second mode, the telephone line is routed to a particular spare connection bus which is connected to a designated spare modem. Activation of the back-up mode is controlled by respective EIA (Electronic Industries Association) channels connected to the Data Terminal Equipment (DTE) associated with the failed modem channel and with the spare modem channel, as will be described in greater detail. Fig. 1 illustrates schematically a configuration of three identical modems 1, 2 and N. The first modem has been set up as a normal modem channel and is illustrated as normally serving the telephone line 1 and the EIA port 1. A set of switches A, B and C control the configuration of the modem as either a normal-mode or a spare-mode modem. Relays D are selected under program control to reconfigure the connection to the telephone lines 1, 2 and N. In the example shown, modem 1 is configured as a normal-service modem in which data on telephone line 1 passes through the closed contacts of switch B, relay D, switch A into modem 1 and out of modem 1 to the EIA interface. Data outbound from the DTE connected to the EIA interface 1 can enter the port 1 and pass through the EIA driver receiver (D/R) circuit onward to the EIA wrap test logic and from there to the modem 1. From the output of the modem, the signals pass through the closed contacts of switch A, the closed contacts of the relay D, the closed contacts of switch B and out to the telephone line 1. This illustrates normal operation. For back-up operation in the event that modem 1 fails, a sequential code detector circuit 4 receives input from the EIA interface, and when a specific code is detected, it initiates the relay driver circuit 5 to switch the relay D into the back-up or spare configuration mode. This is illustrated more clearly for the modem 2 which has been shown as being configured in the normal mode but relay D has been activated so that the closed contacts are switched relative to those shown for relay D associated with modem 1. In this configuration, telephone line 2 has signals that pass through switch B closed contacts and the closed contacts of relay D to feed the contact of switch C which is connected through its closed contacts to bus rail 1, thus isolating modem 2 from the telephone line. This is achieved by appropriate code sent over the EIA interface 2 and received in the sequential code detector circuit 4 which initiates the relay driver cir...