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Fast Fault Isolation and Restoral Key to Info Management-Control.

The weakest link in an information-processing network is neither the data processing system nor the data communications system per se. In terms of network reliability and quality of service, the weakest link is whether or not a systems or network operator--data processing or data communications--can quickly track a fault to its source and then correct it. The uncertainties in isolating, identifying and restoring faults and failures represent the weakest link.

However, as a discipline, data communications management is a much more recent industry development than data processing management. Therefore it is often less understood. In fact, data communications users over the years have demanded from data communications designers and manufacturers greater utilities to determine network performance, problem identification and restoration, as well as communications management information. The data communications industry has responded well. Not only has it developed the utilities called for, but it has also designed advancements in the human engineering of communications management systems and the types of information provided to network operators. In addition, data communications designers and manufacturers would hope to encourage among users a management commitment to keep their operators and managers knowledgeable in diagnostic and control techniques--not only for those in immediate use, but also for state-of-the-art. The technology has advanced remarkably during the past few years and will unquestionably continue to do so. Some of the more advanced technologies will be discussed very generally here.

Ten years ago the data communications network control of nearly every organization depended almost entirely upon the common carrier. In the recent past the actual management of a network may have involved little or no sophistication on the part of many small and medium size users. Today, however, as the cost of network management has decreased and the need has increased, even small users consider network management a requirement. Most medium-size users and nearly all large-scale users consider it mandatory. They have literally taken control of their networks and, in so doing have expanded their tech control center in many cases into rooms almost as large as the computer room itself. While neither a tech control center nor a data communications systems will dictate the configuration of a data processing environment, communications management today has nonetheless come to point out new directions and new dimensions in network economics and flexibilities.

Early concepts in data diagnostics implemented by Racal-Milgo, for example, consisted of techniques to send queries from testing devices to modems and other components and receive indications on the status of EIA RS-232 signals. Such qualitative techniques monitored network performance for faults between preset points. One of the simplest of these early qualitative device is Racal-Milgo's Model 220 test set, a microprocessor-based device still in use today. It continues to serve small links for such purposes as line patching, which merely determines if line faults exist. Significant here is the fact that the Model 220 technique requires personnel intervention to implement tests, and in many cases the device proves impractical for testing remote locations. Equally important, it does not permit the operator to perform preventative maintenance or to run tests on one portion of the network while looking for problems in another.

This led to the development of more quantitative techniques that extract specific information on network faults or irregularities and incorporate many network restoral functions, all from a central site. The development of this technique came as a result of user demands for the performance of preventative maintenance and for running multiple tests so as not to impede main-channel data or in-band throughput. It was made possible by refinement of secondary or subchannel operations that can not interfere with main-channel data, that can poll modems simultaneously and that can take unsolicited alarms from network equipment at any time. The techniques became popular following a fundamental breakthrough in high-speed, narrowband data communications.

The narroband techniques concentrated high-speed, main-channel data transmission within a very narrow (800 Hz) portion of the available bandwidth (300 Hz to 3300 Hz) and centered it at 1700 Hz. As a result, channels beyond the 800-Hz spread, such as 315 to 420 Hz, could be used well for asynchronous diagnostics. The low-speed, frequency-shift-keying secondary channel, called T-7 by Racal-Milgo, transmits data at 75 bits per second and permits an operator at the central site to manually monitor remote modem terminal interfaces. No Main-Channel Data Interference

The technique also allows diagnostic data to proceed without interference with main-channel data. The insertion of diagnostic information does not affect the ability of the network to transfer data. Nor does it create a situation in which main-channel data security is compromised. If diagnostic data were inserted into main-channel data, the diagnostic equipment would then have access to the main-channel data, which might conceivably be damaged or otherwise impacted as a result.

Racal-Milgo's diagnostics grew quickly for use in two PROM microprocessor-based controllers, the System 180 and 185 and then to the company's minicomputer-based Communications Management Series (CMS) controller, used in medium and large-scale networks. The PROM controllers, and even to a greater extent the CMS controllers, enable operators to scan entire networks for various faults and degraded line condition and, in many cases, to alert service teams even before interruptions occur. They can spot line or equipment problems before or after working hours and on weekends, and they often permit automatic network restoral procedures.

Synchronous microprocessor-based series (MPS) modems used with many of Racal-Milgo's PROM controllers contain a microprocessor-based T-7 test card with a unique electronic address. In this way, the controller can initially determine the location of each modem and distinguish it from all others. The feature includes a transmitter/receiver that provides the separate 75 b/s secondary channel over which modems, central and remote, communicate with the controller. It also allows the addressed modems to decode test-command words transmitted by the diagnostic controller, to perform the test requested and to frame, format and transmit the results back to the controller. The T-7 can also be programmed to detect unusual modem conditions and to automatically transmit appropriate alarms to the controller, which can receive external alarm signals, including ones for power failures, from modems while tests are in progress.

As powerful fault-isolation tools, the controllers can promptly conduct tests without equipment changes. Included are end-to-end tests, self-test, line loop tests, DTE loop tests and many others. In the event of line problems, the controller permits operators to switch an affected remote modem from dedicated to dial operation.

While the PROM controllers support up to 16 channels, the CMS controllers support from 16 to 256. In addition, the CMS controllers in some cases permit four operators to perform up to 16 functions on 256 channels, which can serve from 5,000 to 10,000 modems. The controllers permit central site operators to perform all the tests and simultaneous modem polling performed by the PROM controllers, as well as to restore service and delegate and coordinate repair.

The PROM controllers serve well in small to medium-sized networks. Continual network expansion raised the question of network expansions raised the question of whether to expand the capabilities of the System 185-type controller and the T-7 cards in the MPS modems or to design a computer system in itself to handle all the System 185 functions, keep the T-7 feature and add more comprehensive diagnostics, such as analog parameters including phase jitter, signal quality and line impairment, as well as serial-number reporting, recording and other management capabilities. The latter course was chosen following evaluations that revealed the computer system would make the price of network management for large-scale networks low in terms of per-modem cost--lower, in fact, than a more complicated System 185 that would require continual modification.

The T-7 feature was retained in the CMS controller as T-7 Version One, which serves MPS modems and is compatible with CMS series operations. A new T-7 Version two, introduced for CMS series modems, provides enhancements to diagnostic function, yet its compatible with T-7 Version One. Flexible System

All factors considered, the minicomputer-based systems were conceived as flexible computers in themselves. They have their own CPUs, disks, I/O, terminals and associated equipment. However, the system controller takes care of the diagnostic and management controls only. The controller communicates with remote devices--modems, switches and others. A popular medium-to-large-scale minicomputer-based network controller, for example, might contain a 10-Mb hard disk that retains on-line information about modems, switches and other devices, their physical location in a network and their relationship to each other. It has the ability to support four concurrent tasks on a single terminal. The largest of the system controllers would offer up to 16 concurrent tasks among as many as four operators. Microprocessor-driven backbone and remote modems have programming capabilities for such tasks as transmitting serial numbers, reporting faults that have occurred within or around them, the nature of the fault and in some cases line level performance, or analog parameters.

Essentially the minicomputer-based system functions as a tester, a controller, a data-base manager, a file organizer and a report generator. As a tester, it reports failures, and it initiates a full complement of remote tests. As a controller, it controls and monitors special equipment, such as modem switches. As a data-base manager, it keeps records on sites, units, and channels, and it can maintain, modify and display them--in which case the data base could be automatically compared with the network. As a file organizer, the system kesps a significant event file, which records the occurrence of tests and other system events. Also, the system can keep a pending work file, which records network problem maydays. As a report generator, it can generate hard-copy reports on every major data-base item, including the significant event file.

Looking a future network and product support, custom-system features are being designed to further enhance the capabilities of minicomputer-based systems and, at the same time, to provide systems that meet specialized user requirements. A wide range of supplementary dial backup, switching and diagnostic equipment can be coupled with a basic system to increase the flexibility and control capabilities of any given network. Increased ability to restore and reconfigure network components from central site are also under development, as are increased dial backup, switching, diagnostic and reporting capabilities. In addition, as networks continue to expand, other associated management situations are being anticipated, as is the feasibility of in-band diagnostics for specified applications.

The discipline continues to develop and provide innovative diagnostic and actual management and control functions, which permit information-processing personnel--both data processing and data communications--to better optimize the use of their own time and talents.
COPYRIGHT 1984 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1984 Gale, Cengage Learning. All rights reserved.

 
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Author:Atkins, J.
Publication:Communications News
Date:May 1, 1984
Words:1757
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