Background and references on LMOS from the following patent. More good information at http://www.uspto.gov (external link)

Method and apparatus for testing communication systems

United States Patent 4,611,101, Walter , et al. September 9, 1986

BACKGROUND OF THE INVENTION

This relates to the maintenance and testing of communication lines and, in particular, to the maintenance and testing of conventional telephone lines.

Communication lines require periodic testing, maintenance and repair. At first, telephone system operators employed an entirely manual process of accessing, testing and servicing subscriber lines. However, these manual procedures frequently resulted in a substantial delay between the initial report of trouble on a line and the verification and identification of that trouble. Thus, a rapid, accurate and intelligent response to a trouble report or a subsequent inquiry was impossible in the majority of circumstances. In addition, the speed and accuracy of certain line tests depended on the experience of the tester and upon how quickly information about the subscriber's telephone equipment could be manually retrieved from a file; and the whole process was very much labor intensive.

In an effort to acquire better line testing, maintenance and repair capabilities, in the 1970's American Telephone and Telegraph, Inc. developed and implemented Automatic Repair Service Bureaus (ARSBs) in the predecessors of the Regional Bell Operating Companies (RBOCs). See P. S. Boggs and M. W. Bowker, "Automated Repair Service Bureau: Evolution", Bell System Technical Journal, Volume 61, No. 6, Part 2, pp. 1097-1114 (July-August, 1982). The ARSBs utilized a Loop Maintenance Operating System (LMOS) and a Mechanized Loop Testing (MLT) system.

LMOS provides four basic services to the ARSBs. First, the system generates and maintains a data base containing very detailed information, such as the identity of the telephone equipment in use at a subscriber's site, the electrical characteristics of this equipment, whether there are any unresolved reports of trouble on the line, and whether the subscriber's account shows an unpaid balance.

Second, LMOS performs computerized trouble report processing. When a trouble on a line is reported by a subscriber, an entry is made in the applicable line record. The telephone company employee receiving the subscriber's call can then use the MLT system, described below, to perform some preliminary tests on the line and verify or discount the report. If the tests disclose no line trouble, the employee will inform the subscriber that the line is in working order and make an entry in the line record reflecting that fact. Alternatively, if the test results indicate that a trouble does exist, the employee's entry will indicate that further testing by the MLT system is required. Thus, LMOS allows the existence and status of a pending trouble report to be readily determined.

The third basic service provided by LMOS involves the generation of management and analysis reports utilizing the information stored in its data base. These reports include analyses of the ARSBs' efficiency and the prediction and identification of problem areas in repair operations.

Finally, because LMOS keeps track of repair force locations and commitments, the system allows for efficient repair force deployment. This is particularly important when a subscriber is requested to remain at a site for repair operations.

An MLT system essentially performs computer controlled tests on the communication lines and interprets the results of those tests. These tests may be performed as a response to a subscriber's trouble report, or alternatively, as part of an automatic testing and maintenance program. The MLT system obtains information about the normal electrical characteristics of a subscriber's line from the LMOS date base and uses it to generate a series of adaptive tests in order to determine the current status of the line. For example, the subscriber may use what is referred to as "inward-only" service, in which outgoing calls on the line are not permitted, and thus no dial tone is provided. There would be little point in running a test to detect a dial tone on such a line. In addition to information about the subscriber's termination equipment, LMOS also contains data describing central office equipment and outside plant equipment on the line. This data is also required for meaningful MLT testing.

MLT accesses selected lines at and through communication test head hardware. Preliminary tests are performed to ascertain whether a given line is available for testing, including for example, whether the line is on intercept, whether it is currently in use (busy signal test) and whether the voltage on the line is hazardous to the testing equipment. If the line is available, MLT performs a series of diagnostic tests designed to determine the line's operational status. These tests typically include measurements of AC and DC voltage and current, resistance, and capacitance, dial tone detection, dial pulse and DTMF tests, a noise check and an off-hook test. In addition, the MLT system can detect the existence of an open wire and determine the location of the break.

MLT then interprets the results of these tests in accordance with information acquired from the LMOS data base. Frequently, these results can be used to respond to a subscriber trouble report or inquiry while he is still on the line. In addition, a detailed analysis of the test results can be routed to repair service personnel to enable repair operations to be accomplished quickly and efficiently.

Because of cost and efficiency considerations, however, present implementations of the MLT systems are best suited for use only where the number of lines to be served exceeds 10,000. Each MLT currently relies extensively on the processing power of a single minicomputer, and failure of that machine results in a total failure of the MLT system. Furthermore, present MLT systems require as many as five or six circuit boards to contain the components dedicated to actual line testing.

References Cited:

U.S. Patent Documents
3842218 Oct., 1974 DeLuca et al. 179/175.
3969594 Jul., 1976 DeLuca et al. 179/175.
4446341 May., 1984 Rubin 179/175.


Other References

Installation Guide, 4T-880, Manual Part, No. 997-880-00, Jul 1981, Teradyne, Inc.
Microcomputer Interactive Test System 70, Lardel, 40 pp.
Repair Bureau, Microcomputer Systems, Feb. 1983, 12 pp.
Automatic Line Test Set, Lordel T-9/15, pp. 1, 2, 13 and 25.
4TEL, Automatic Subscriber Loop Test System, Teradyne, pp. 1-18.
LRS-1 Automated Loop Reporting System, Northeast Electronics Instruction Manual, A3798-80601, Issue 1, Jun. 1979, 4 pp

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