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Browse Prior Art Database

Automatic Loop Reconfigurator

IP.com Disclosure Number: IPCOM000087759D
Original Publication Date: 1977-Mar-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 4 page(s) / 63K

Publishing Venue

IBM

Related People

Laurer, GJ: AUTHOR [+2]

Abstract

Serial data transmission loops have found increasing usage in recent years and provide certain, now well-known, operational advantages over other network forms. However, one serious drawback is total system failure whenever one component fails or when one or more breaks occur in the serial looped network. This article describes a technique for automatically reconfiguring the loop to provide operation under the above conditions which are also illustrated in Fig. 1.

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Automatic Loop Reconfigurator

Serial data transmission loops have found increasing usage in recent years and provide certain, now well-known, operational advantages over other network forms. However, one serious drawback is total system failure whenever one component fails or when one or more breaks occur in the serial looped network. This article describes a technique for automatically reconfiguring the loop to provide operation under the above conditions which are also illustrated in Fig. 1.

The controller may be provided with a variety of mechanisms for detecting a break or failure of a component in the loop. For example, loss of input, beacon signals or other irregularities which are permitted are the result of such a break. When this condition is detected, the controller divides the network into two subsystems A and B and initiates a number of steps which result in the substantially simultaneous half-duplex operation of subsystems A and B illustrated in Fig. 1. Periodically, the controller tries the loop system to determine whether a repair has been effected. When this condition is detected, a return to loop operation is initiated.

When the loop breaks, error recovery will allow, for example, end of poll timeouts to occur at the controller with repoll attempts.

After two repoll attempts, the controller will do a self test (wrap) on its adapter and driver/terminators. If they operate successfully, the controller will attempt to issue polls again (at least two end of poll timeouts) and if recovery does not occur, switch to backup operation (to T1 on the timing chart\ Fig. 2). Time elapsed is 15 to 20 seconds.

The first step in backup operation (T1 on the timing chart, Fig. 2) is achieved by the controller sending an SCM (System Control Message) to an "all addresses" address (all terminals that can receive it in front of the break in the loop) telling them that they are "A" terminals. This tells them how to handle polls and transmissions for the half-duplex arrangement that will now be operating. This is followed by a poll to which all the terminals will now respond. The first terminal receives the poll and sees end of poll (EOP). It now connects the driver to the line (which was previously the receive line) and sends in its response (an ACK which includes its address). This terminal will now connect its driver to the next terminal down line (Terminal 2). After passing the poll, it switches its terminator toward 2 and its driver toward the controller which is still listening. Terminal 2 now connects its driver to terminal 1's terminator via the loop wire pair and transmits its ACK (including its address) back through 1 to the controller. When it is finished, it switches its driver to terminal 3 and sends "end of poll" down line to terminal 3. It now switches its terminator to listen to terminal 3. Terminal 3 sends its ACK and tries to send the poll to the next terminal. At this point, the break is encountered and the controller...