Battery injection and loop supervision for DSL environment

Details Battery injection and loop supervision for DSL environment Battery injection and loop supervision for DSL environment

2000-01-28

2001-09-18

Nguyen, Duc (Department: 2643)

Telephonic communications

Diagnostic testing, malfunction indication, or electrical...

Using portable test set

C379S027010, C379S029010, C379S030000

Reexamination Certificate

active

06292540

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a system and method for connecting copper loops to a central office in a digital subscriber loop (DSL) environment. More particularly, the present invention is directed to a system and method for connecting a battery to copper loops and for supervising the status of such loops from the central office in the DSL environment. In addition, the present invention discloses circuitry allowing a field technician using a conventional butt set to detect the presence of a battery and to receive an audible tone from the cooper loops in the DSL environment.
BACKGROUND OF THE INVENTION
Digital Subscriber Loop, or DSL, is one of the most promising new technologies for delivering superior service and higher speed connections over existing infrastructure in the telecommunications industry. Recent changes in the telecommunications industry such as the deregulation of local markets has brought on the emergence of new technologies such as DSL. In addition, the growing demand for faster, more reliable Internet access has increased the demand for technologies that deliver higher speed connections over existing infrastructure.
In general, DSL uses the existing copper loop that is currently used for conventional telephony to deliver data at high bandwidth. Currently, the transmission rates for DSL technologies are dependent on the distance between a central office and a particular customer. Moreover, depending on the type of DSL technology, the transmission rate downstream to the customer and upstream to the central office may vary. For example, for asymmetric DSL, the transmission rate is faster downstream to the customer than upstream to the central office, and thus is well suited for Internet usage and video on demand. On the other hand, for symmetric DSL, the transmission rate is about the same for both downstream and upstream.
As is well known, DSL uses packet switching technology that operates independently of voice telephone system, allowing telephone companies to provide Internet service and not lock up circuits for telephone calls. DSL can carry both voice and data signals simultaneously, in both directions, allowing the customer to log onto the Internet and make a telephone call at the same time. Thus, it is easy to understand why DSL is becoming the preferred system and method for sending/receiving analog and digital data/signals in the telecommunications industry.
One major problem for those in this industry is the installation and maintenance of DSL using the existing infrastructure and standard operational tools. This problem is better understood by first describing the installation/testing process in a conventional POTS (plane old telephone system) environment, which is described in greater detail hereinafter with reference to
FIGS. 1-3
.
FIG. 1
illustrates a simplified diagram of a POTS environment having a butt set connected to a copper loop for maintenance and testing purposes. In the conventional POTS environment, a central office (CO)
2
is connected to a customer's telephone
8
at the customer's premise
6
(home, office, etc.) using a copper loop
4
(pair of copper wires). In between the CO
2
and the customer's premise
6
, a field technician
12
uses a conventional butt set
10
or any other maintenance instrument to test the copper loop. The butt set
10
is generally a standardized device that the technician
12
uses to determine which copper loop is active and/or available for customers. The butt set
10
is essentially a portable and rugged telephone set. For example, once the butt set
10
is connected to a cooper loop via electrical clips, the technician
12
can simulate a telephone going off-hook to draw audible tones. A voice switch (not shown) in the CO
2
recognizes an off-hook condition through its loop supervision circuit and applies audible tones to the loop allowing the technician
12
to confirm proper connectivity.
The butt set
10
illustrated herein is equivalent to a telephone handset to test/maintain communication wires. The term butt set is used in this field, presumably because the butt set
10
includes a hook for fastening it to a tool belt and tends to hand down along the technician's buttocks. The butt set
10
generally includes a microphone, earphone, and a speaker.
FIG. 2
illustrates a diagram of an existing circuit used in the POTS environment as shown in FIG.
1
. The CO
2
typically includes a SLIC (subscriber loop interface circuit)
20
for interfacing with a pair of wires, tip and ring, from the outside plant. The SLIC
20
includes an amplifier AT
22
connected in series to a resistor R
b1
26
, and an amplifier AR
24
connected in series to a resistor R
b2
28
. The amplifier AT
22
and resistor R
b1
26
, and the amplifier AR
24
and resistor R
b2
28
form a balance drive interface circuit to the tip and ring wires. As known, the SLIC
20
can be implemented with transformers instead of amplifiers AT
22
, AR
24
. Further connected in between the resistor R
b1
26
and the resistor R
b2
28
is a detector
30
. Typically, the ohm values of the resistors R
b1
26
and R
b2
28
are equal (50 to 400 ohms). The voltage V
b
is the effective battery voltage across the tip and ring wires.
The detector outputs a signal voltage V
s
(which is proportional to the DC current flow in the loop, which in turn is proportional to the length of the loops and is reflected as resistance) into a comparator C
32
, while a reference voltage V
r
is also inputted into the comparator C
32
. The comparator C
32
then outputs a loop status indication signal (SHD) based on voltages V
s
and V
r
.
In the outside plant, there also exist resistors R
11
34
and R
12
36
, where each resistor is connected in series to the tip and ring wires, respectively. As is well known, tip and ring are terms used to describe the two wires that are used to set up a telephony/DSL connection. Typically, the ohm value of resistors R
11
34
and R
12
36
are the same, which is also dependent on the length of the loop.
In the customer's premise
6
, the telephone
8
can be represented with an off-hook switch S
p
38
connected in series with a resistor R
p
40
. The resistor R
p
40
typically has a value of, preferably, between 100 to 200 ohms (off-hook resistance is less than or equal to 400 ohms). Further, the sum of the resistors R
11
34
, R
12
36
, and R
p
40
should be less than or equal to 1900 ohms, as per conventional telephony standards.
The butt set
10
includes a monitor mode switch S
m
50
connected in series with a monitor mode resistor R
m
52
(typically greater than 100 K ohms), which switch S
m
50
and resistor R
m
52
are further connected in parallel with a talk mode switch S
t
54
and a talk mode resistor R
t
56
(typically less than 400 ohms). Thus, the butt set
10
can provide two different modes of operation, as described in greater detail hereinafter. The butt set
10
also includes two leads, where one lead is connected to the tip at position a and the other lead is connected to the ring at position a′.
During operation in the POTS environment, a battery is used to provide a DC path or current flow beginning from the amplifier AT
22
through resistors R
b1
26
, R
11
34
, R
p
40
, R
12
36
, R
b2
28
to the amplifier AR
24
. Thus, the current flowing through this circuit is inversely proportional to the sum of the resistors R
b1
26
, R
11
34
, R
p
40
, R
1
2
36
, and R
b2
28
. When the customer picks up the telephone
8
to make a call, the detector
30
detects that the telephone
8
is off hook, a DC path is generated, and the CO
2
recognizes an off-hook condition, thereby providing a dial tone to the customer. In this environment, the frequency signals in the copper loop operate within the voice/audio bandwidth and the DC current path is used for loop supervision.
During the maintaining, testing, or installing stage, the technician
12
uses the butt set
10
to connect to the tip and ring wires at points a, a′. The butt se

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