Metallic testing of a subscriber loop that provides both...

Details Metallic testing of a subscriber loop that provides both... Metallic testing of a subscriber loop that provides both...

2000-09-29

2002-12-17

Tieu, Binh (Department: 2643)

Telephonic communications

Diagnostic testing, malfunction indication, or electrical...

Of trunk or long line

C379S001040, C379S009000, C379S015010, C379S027030, C379S027060, C379S028000, C379S029050, C370S248000

Reexamination Certificate

active

06496566

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the field of telephone subscriber loops that provide high speed data service and voice service, and, more particularly, to metallic testing of such loops.
BACKGROUND OF THE INVENTION
A relatively new technology uses the embedded voice telephone infrastructure to provide high speed data service. This service, generally referred to as “Digital Subscriber Line”(DSL) service, is available in many markets. DSL is implemented in several different ways, such as asymmetrical DSL (ADSL where upstream and downstream have different bandwidths), symmetrical DSL (SDSL where upstream and downstream have the same bandwidth) and other varieties of services (herein “XDSL” or “DSL”). Many XDSL technologies provide high speed data service over the current tip-ring pairs by encoding high speed data signals into frequency ranges well above the frequency range that carries both plain old telephone service (“POTS”) or integrated services digital network (ISDN) service. Thus, one subscriber loop comprising a tip-ring pair can provide both voice service and high speed data service.
One problem facing service providers in this fast growing market is loop maintenance. Specifically, most regulatory bodies require that each subscriber loop is tested for power cross, over-voltage, etc. as is known in the art. However, because incumbent voice service providers may be a different entity from the DSL service provider, testing the loop over the entire frequency spectrum (known in the art as “D.C. to light”) requires new and relatively sophisticated and expensive equipment.
Turning now to
FIG. 1
, a current metallic test system is illustrated in the context of metallic testing of a subscriber loop
5
. Subscriber loop
5
subscribes to both voice and DSL services. In a switching office
10
, there is a voice switch
12
and a digital subscriber line access multiplexer (DSLAM)
14
, which provide voice and data service for subscriber loop
5
, respectively. Voice switch
12
is connected to subscriber loop
5
by line card
16
as is known in the art. Line card
16
includes processing unit
18
which sends and receives analog signals over subscriber loop
5
and processes the signals to/from pulse code modulated (PCM) data, as used in the switching network as is known in the art. DSLAM
14
includes a line card
20
which sends and receives data from loop
5
to and from the data network via transceiver
22
.
Voice switch
12
and, more specifically, processing unit
18
supports analog signals in the 0-4 kHz band over subscriber loop
5
. Generally, DSLAM
14
, and more specifically transceiver
22
on line card
20
, supports signals in the 32-1,100 kHz range over subscriber loop
5
.
DSL introduces frequency and, more importantly, power characteristics that are incompatible with most current art voice service line cards. Conversely, voice service uses DC power with characteristics that interfere with DSL data. Therefore, a splitter
24
is provided in order to filter unwanted characteristics from the subscriber loop
5
for processing at processor
18
on voice line card
16
and DSL line card
20
. To enhance the voice signal, splitter
24
includes low-pass filter
26
, which attenuates the high voltage of DSL and generally filters out the high frequency DSL signal. To enhance the DSL signal, the DC component of signals on subscriber loop
5
are filtered by a capacitor
28
on line card
20
and a further capacitor
30
in splitter
24
.
It is known in the art that voice switches include a voice switch metallic test unit
32
that tests loop
5
for various faults. Metallic test unit
32
is connected to line card
16
via metallic test bus
34
. Metallic test bus
34
is connected through a set of relays
36
comprising a normally closed relay
38
and a normally open relay
40
. This set of relays
30
is reversed when voice switch metallic test unit
32
tests loop
5
to protect the circuitry of processing unit
18
on line card
16
. Likewise, DSLAM
14
includes DSLAM metallic test unit
42
which is connected to line card
20
via metallic test bus
44
to relays
46
including normally closed relay
48
and normally opened relay
50
.
In order to effect a usable path through splitter
24
for either metallic test unit
32
or
42
, several additional components must be included in splitter
24
. For example, in order to test loop
5
from voice switch metallic unit
32
, a signature
52
must be present in order to alert voice switch metallic unit
32
of the voltage loss that will occur because of the presence of splitter
24
. If signature
52
were not present, then any estimates of broken cable etc. would be incorrect.
Further, a detector
54
needs to be added to splitter
24
in order to detect whether the voice path is currently in use. An additional detector
56
is needed to detect signals from DSLAM metallic test unit
42
which will inform processor
58
that metallic test unit
42
is going to test loop
5
. When this occurs, processor
58
closes normally open relay
60
and opens normally closed relay
62
in order to permit testing from DSLAM metallic test unit
42
without interfering with line card
16
on voice switch
12
. All of these additional units not only are costly but also require a power supply
64
in order to operate. All of these units also then need to be diagnosed, fused, maintained, alarmed, etc. as is known in the art.
SUMMARY OF THE INVENTION
This problem is solved and a technical advance is achieved in the art by a system and method for metallic testing of a subscriber loop that provides voice and DSL services. Voice services are provided by a voice switch and DSL services are provided by a digital subscriber line access multiplexer (DSLAM); each of which includes a metallic test unit. A voice line card in the voice switch has a connection to a first metallic test bus connected to the voice switch metallic test unit via a first set of relays configured to connect the metallic test bus to the subscriber loop and to disconnect the subscriber loop from voice on the line card when testing is performed. A DSL line in the DSLAM card has a connection to a second metallic test bus, which is connected between the DSLAM metallic test unit and the subscriber loop. A second set of relays control the connection of the metallic test bus to the subscriber loop.
In this environment, the voice switch metallic test system is configured to send signals to control the second set of relays to disconnect the DSL line card and to provide metallic tests over the entire wireline spectrum (DC to light). The DSL metallic test unit connected to the second metallic test bus is configured to send signals to control the first set of relays to disconnect the DSL line card and to provide metallic tests from DC to light. Advantageously, a determination is made whether there is traffic on either the voice line or the DSL line prior to metallic testing. The metallic test may then be run and then, for example, a timer may cause the relays to reset to their original state. Further, a detector on each of the line cards may receive out-of-band signaling from the metallic test units and cause the relays to operate.


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Rowe, Martin, Senior Technical Editor; “ADSL Testing Moves Out of The Lab”; Test and Measurement World; (Inc. Electronics Test), Cahners Publishing, Denver, Colorado, vol. 19, No. 5, Apr. 1999, pp. 46-48, 50, 52

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