Excavating
Patent
1994-12-14
1997-09-02
Beausoliel, Jr., Robert W.
Excavating
H04L 1226
Patent
active
056639686
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to test apparatus for integrated services digital networks, and more particularly to a test apparatus for measuring a set of margins, or proximities to failure, of a number of analogue transmission and reception parameters of two-wire lines and their associated termination units in integrated services digital networks.
BACKGROUND
Information relating to quality of service obtained from two-wire lines and their associated termination units in integrated services digital networks usually includes measurements of bit-error rates. Such information is digital in nature, and supplies little intuitive insight into the state of various components associated with the two-wire line. Specifically, from a measured bit-error rate for a two-wire line, particularly if the bit-error rate lies close to a normal range, it is very difficult to make meaningful inferences about the state of the line and how robust it would be if conditions such as temperature and humidity were to change. This is particularly important for technicians who are trying to locate intermittent faults which occur only under rare circumstances.
Probably of more interest to a technician involved in fault-finding and maintenance of such two-wire lines would be a set of analogue figures-of-merit. For a two-wire line terminated at a customer's premises in a network termination unit, and terminated at an exchange in a line termination unit, such a set could, for example, include any of the following: (a) the tolerable increase in two-wire line attenuation, (b) the tolerable decrease in receiver sensitivity in the line termination unit, and (c) the tolerable decrease in receiver sensitivity in the network termination unit.
Equipped with this possible set of figures for the two-wire line, the technician could easily determine whether a fault was present, or was likely to become apparent, in the two-wire line itself, the line termination unit, or the network termination unit.
Thus, it is desirable to provide a test apparatus for integrated services digital networks for providing analogue figures-of-merit which can help a technician to locate faults in two-wire lines and their associated termination units.
SUMMARY OF THE INVENTION
The present invention comprises a margin test method and apparatus for use in an integrated services digital network, the margin test apparatus comprising: a network termination unit including means for coupling a two-wire line to a four-wire line, the two-wire line carrying a composite signal, and the four-wire line carrying a transmitted signal and a received signal; a first adjustable attenuator for adjustably attenuating the received signal; and a second adjustable attenuator for adjustably attenuating the transmitted signal.
Preferably, the network termination unit further includes: a receiver for converting the received signal to a received data stream, the received signal having a level; and a transmitter for converting a transmitted data stream to the transmitted signal; and wherein the network termination unit is calibrated such that it is in a failure mode if the level of the received signal is less than a predetermined threshold level.
The failure mode may comprise a state in which the bit-error rate is greater than a preselected rate, or a state in which the network termination unit is not synchronised with a second unit, or a state in which communication between termination units is substantially unreliable.
Preferably, the network termination unit further comprises failure detection means for determining if the network termination unit is in the failure mode.
A method for determining a line margin using the margin test apparatus preferably comprises the steps of: coupling the two-wire line to a line termination unit; placing the line termination unit in a first test mode in which the transmitted signal is looped back through the line termination unit to become the received signal; measuring the level of the received signal to determine an initial reception level; vary
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Patents Abstracts of Japan E-1308, p. 5, JP, A, 4-249935 (NEC Eng Ltd.) Sep. 4, 1992.
Beausoliel, Jr. Robert W.
Elmore Stephen C.
H. Heuer Instruments Pty Ltd.
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