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Distributed Time Division Switching Network Diagnostic Method

IP.com Disclosure Number: IPCOM000042288D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 3 page(s) / 16K

Publishing Venue

IBM

Related People

Combes, J: AUTHOR [+2]

Abstract

This article describes a method for diagnosing the time slot buffers of a distributed time division switching network by applying a specific data pattern to a selected ring slot and checking with a variable time delay the correct return of the specific data pattern. Fig. 1 shows a typical distributed time division switching network comprising several ring buses (high/low), each one closed by a ring control logic (RCL), time switch modules (TSM) attached to each ring bus and stations connected to each of the links (in and out) of each TSM via line interface modules (LIM). Each link is a time multiplex (MPX; DMPX) channel of as many slots as there are stations. The functional principle of a distributed time division network is based on several time multiplexed frames of 8-bit slots.

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Distributed Time Division Switching Network Diagnostic Method

This article describes a method for diagnosing the time slot buffers of a distributed time division switching network by applying a specific data pattern to a selected ring slot and checking with a variable time delay the correct return of the specific data pattern. Fig. 1 shows a typical distributed time division switching network comprising several ring buses (high/low), each one closed by a ring control logic (RCL), time switch modules (TSM) attached to each ring bus and stations connected to each of the links (in and out) of each TSM via line interface modules (LIM). Each link is a time multiplex (MPX; DMPX) channel of as many slots as there are stations. The functional principle of a distributed time division network is based on several time multiplexed frames of 8-bit slots. These frames transport voice/data samples from a LIM attached to a TSM to another LIM attached to another TSM, and vice-versa. The major problem in a distributed time division switching network is the diagnosis of the numerous time slot buffers in the various TSMs constituting it (outbound buffers, inbound buffers, local buffer) and in the frame buffers of the RCL. Therefore, two diagnostic functions are added to the TSM and RCL hardware to allow testing of the switching buffers and associated control logic with a minimum of additional circuits. The TSM outgoing and incoming links to/from the LIMs can be wrapped inside each TSM under a diagnostic program command. The RCL is added the capability to inject, under diagnostic program control a specific data pattern in a selected ring slot and to check, with a predetermined delay (which is controlled by the diagnostic program) or later by a diagnostic read command, that the specific pattern is returned to the RCL in the selected ring slot. The predetermined delay depends on the path the ring slot is programmed to follow within the TSMs of the switching network. If the ring slot is not intercepted by any TSM, it returns to the RCL in the next ring bus frame. If the ring slot is intercepted by a TSM, it enters in the current time frame the first outbound buffer. At the next time frame, it is extracted from that outbound buffer and (with the TSM links being wrapped) sent to the inbound buffer. At the third time frame, it is returned from that inbound buffer to the ring bus frame and received by the RCL. The ring slot under test can be similarly programmed to enter the local buffer, from the outbound buffers, prior to exit to the inbound buffers and then to go back to the ring bus frame. In that case four time frames are necessary prior to receiving that ring slot at the RCL. When such paths are programmed, any premature or lack of reception of the ring slot content by the RCL is detected by the RCL itself and reported to the diagnostic program as a fault. Of course, this mechanism can only be used with an initial content of the ring slot under test di...