Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – Testing of subscriber loop or terminal
Utility Patent
1999-07-27
2001-01-02
Kuntz, Curtis A. (Department: 2443)
Telephonic communications
Diagnostic testing, malfunction indication, or electrical...
Testing of subscriber loop or terminal
C379S001040, C379S022000, C379S010030, C702S118000
Utility Patent
active
06169785
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method for testing a subscriber line connected between an exchange and a subscriber terminal.
2. Description of the Related Art
One example of such a prior art apparatus for testing a subscriber line will be described.
FIG. 1
illustrates system arrangement of a communication network including a subscriber line to be tested by an apparatus for testing a subscriber line. The communication network system includes a network (NW)
1
in which connection and switching of line are performed through an exchange, various subscriber terminals (TE)
2
such as a telephone set and a data communication terminal, and the like, a subscriber line (LN)
3
connected between the exchange and each subscriber terminal, and a line circuit (LC)
4
having an interface function between the subscriber terminal
2
and the network
1
for supplying communication electric power to the subscriber terminal through the subscriber line
3
.
The subscriber line
3
is constructed by pairing forward and backward two wire conductors a, b for each line. A twisted pair line obtained by twisting two wire conductors is typically used. Sometimes, a coaxial cable composed of a central conductor and a coaxial conductor are used. For signals transmitted through the subscriber line
3
both an analog signal such as a sound and an encoded digital signal are used.
The line circuit
4
includes an interface unit (I/F)
41
for interfacing the subscriber line
3
and the network
1
, and a power supply circuit (PW)
42
composed of a DC power supply for supplying DC voltage E to the subscriber terminal
2
through the subscriber line
3
and power supply resistors Rp1, Rp2, and a transformer (TR)
43
and a codec (CD)
44
for separating, coding, and decoding a transmission/reception signal between the subscriber line
3
and the interface unit
41
.
The subscriber terminal
2
includes not only conventional telephone sets and facsimiles, but also an in-band ringer (IBR) provided between a leased line and PBX, and a terminal apparatus of an integrated service digital network (ISDN) capable of data communication connected with the subscriber line through digital service unit (DSU) of a subscriber line terminal apparatus, and terminal processing for the subscriber line
3
following respective predetermined protocols.
For example, if the subscriber terminal
2
is a telephone set, and in an on-hook state, DC current is interrupted owing to capacitance of a bell circuit, while in an off-hook state the control is changed over to the communication circuit to permit a communication current to flow. When a subscriber intends to communicate, the subscriber first holds up a handset or brings the control into the off-hook state, and once a destination number is dialed, the call is connected with another telephone set through an exchange, which includes a processor CPU, for analogue speech communication between the telephone sets.
In case the terminal apparatuses are IBR, ISDN, by protocol the on-hook/off-hook state is controlled through the terminal apparatuses. In the case of a data terminal, the control becomes off-hook state during communication as in the case of telephone sets, while control becomes on-hook state during non-communication. For communications, codec
44
connected with the exchange through interface
41
converts communication signals.
Construction of the prior art subscriber line testing apparatus includes line lead-in relay (RE)
51
, adapter (AP)
52
, measuring apparatus (ME)
53
, and processor CPU, as illustrated in FIG.
1
.
The line lead-in relay
51
branches the subscriber line
3
from the line circuit
4
and leads it in to the measuring apparatus
53
. The adapter
52
connects the led-in line to the measuring apparatus
53
. The measuring apparatus
53
measures line constants such as resistance of the subscriber line
3
to which the subscriber terminal
2
is connected. The processor CPU is connected with the measuring apparatus
53
through the network. The processor CPU is also forms a part of the exchange of the network
1
, so that subscriber line testing is achieved by applying the CPU part of the exchange to the measuring apparatus.
When the line is normal, and the subscriber terminal is not in communication, only DC voltage supplied from the power supply circuit exists on the subscriber line but when the subscriber terminal is in communication, voltage on the subscriber line becomes the DC voltage of the power supply circuit onto which sound frequency or encoded high frequency transmission/reception signal voltage is superimposed.
Testing of such a subscriber line
3
is executed as follows. A tester first confirms that the subscriber of the line
3
, the object to be tested, is not in communication. Then, the line lead-in relay
51
is actuated to once separate and close the line
3
from the exchange. Then, the line
3
is led into the measuring apparatus
53
through the adapter
52
to measure various line parameters such as AC/DC voltage and resistance. Since the measured result is transmitted to the processor CPU through the network
1
other more indirect line parameters can be calculated with arithmetic operation of the processor CPU.
For an improvement of the testing method that extends a measurement range of a subscriber line the following prior art technique has been proposed.
Japanese Laid-Open Patent Publication No. 59-92661 (issued May 28, 1984), discloses “Subscriber Line Testing Method”. Prior art testing methods simply demonstrate the existence of external voltage when external voltage of a specified value or more on a subscriber line exists, but fails to measure the line constants of the subscriber line. The present technique ensures measurement of the line constant of the subscriber line even when external voltage exists. There is provided solving means as illustrated in
FIG. 2
wherein a and b conductor lines of a subscriber line are connectable to either a testing apparatus or earth, and monitoring is usually done by a voltage detector circuit to determine whether or not any external voltage above the specified value exists on either line.
When an external voltage above the specified value is detected on either one of the conductor lines of a subscriber line, these voltages are indicated, while when the external voltage on only one conductor line exceeds the specified value, one line is connected with earth and the other line is connected with the testing apparatus, and circuit constants such as line resistance of the line when the external voltage is the specified value or lower are automatically measured and displayed.
The aforementioned prior art method however has the following problem.
First, it is necessary to check whether the subscriber of a line to be tested is in communication. Even after it is confirmed that a subscriber is not in communication, a command input operation to a measuring apparatus for line testing in accordance with the kind of subscriber terminal and labor are required.
A measuring apparatus for performing line testing and exclusive testing apparatus such as an adapter are also required. In addition a line lead-in relay RE, a testing adapter AP, and a measuring apparatus ME must be controlled to achieve line testing.
SUMMARY OF THE INVENTION
To solve the difficulties with the prior art, it is an object of the present invention to provide an apparatus and a method for testing a subscriber line not only when the subscriber line is not in communication but also when in communication and wherein line constants are easily measured at all times irrespective of the kind of a subscriber terminal monitoring whether or not the line is normal.
To achieve the above object, an apparatus for testing a subscriber line according to the present invention includes two high resistance line monitoring resistors inserted between each of the two conductor lines of the subscriber line and earth, and an arithmetic operation unit for calculating a predetermined
Foley & Lardner
Kuntz Curtis A.
NEC Corporation
Tieu Binh K.
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