Dsl- compatible pots line card

Details Dsl- compatible pots line card Dsl- compatible pots line card

2000-07-17

2004-12-28

Le, Amanda T. (Department: 2634)

Pulse or digital communications

Transceivers

Transmission interface between two stations or terminals

C379S093050, C379S399010, C379S414000

Reexamination Certificate

active

06836509

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to telephone switching systems and to high-speed data communications, and, more specifically to a line card for analog telephone service that is compatible with high-speed data service on the same line.
BACKGROUND OF THE INVENTION
Once upon a time, the Bell System wired almost every home and business in the United States for telephone service by one (or more) tip-ring pair of copper wires. This original physical plant provided plain old telephone service (“POTS”). As time passed, more and more features and services were offered over the same copper wire. The tip-ring pair was originally intended for voice-band service of between (approximately) 0 and 4 kHz. This rather narrow bandwidth (by today's standards) provides high-quality voice communication and high quality in-band communication in general, i.e., dual tone multifrequency (DTMF) signaling. In more recent times, however, home and business use of computers (and data transmission in general) has taxed this tip-ring infrastructure to the maximum amount of data that can be passed through the voiceband (approximately 53 kbps). Consumers, especially business consumers, are demanding greater data rates. Several new technologies have been tried in an attempt to fulfill this demand. Coaxial cable and optical fiber have been tried, both of which have much higher bandwidth than copper wire. The one major drawback to both is that, unlike the copper wire infrastructure, there is no universal cable or optical infrastructure.
One relatively new technology that can be implemented over the embedded copper networks is digital subscriber line (DSL). DSL comes in many varieties such as asymmetrical DSL (ADSL) (upstream and downstream have different bandwidth requirements) and other varieties of service (herein XDSL). Many XDSL technologies provide high speed data service over current tip-ring pairs by encoding the signals in frequency ranges above the POTS frequency. Thus, one tip-ring pair can provide both POTS service and high-speed data service.
The local service providers (who are no longer part of a universal Bell System), however, have to make major changes in their central office to provide XDSL service.
FIG. 1
is a block diagram of a current central office providing XDSL service. Central office
10
includes a local telephone switching system (switch)
12
that provides the usual POTS telephone services and features. In order to provide XDSL, central office
10
also includes digital subscriber line access multiplexer (DSLAM)
14
which sends and receives digital signals to and from the subscribers and intefaces to the digital network
16
. A main distribution frame
20
, as is known in the art, connects outside plant tip-ring pairs
22
to switch
12
and DSLAM
16
.
In order to serve both a POTS telephone and XDSL on one tip-ring pair
22
, a splitter
24
is required. Splitter
24
, in general, causes the XDSL signal to be sent towards the DSLAM
16
and the POTS signal to be sent towards local switching system
12
. More specifically, splitter
24
includes a 4
th
to 6
th
order low pass filter
28
. A connection
30
is made to the incoming tip-ring pair and rerouted back through MDF
20
to DSLAM
16
at XDSL line card
32
for providing XDSL services. The POTS connection passes through the low pass filter
28
and then back through MDF
20
to POTS line card
36
in local switching system
12
. Splitter
24
, and more specifically low pass filter
28
, are required in order to filter the high frequency signal used by XDSL from the POTS circuit so that POTS line card
36
may process the incoming (and outgoing) signal properly. Furthermore, and more importantly, XDSL has a higher voltage (approximately 18 volts peak to peak) as opposed to POTS 3 to 5 volts peak to peak. Therefore, the low pass filter is also required to reduce the voltage sent to POTS line card
36
so that the line card is not damaged due to over voltage. The opposite is not true of XDSL line card
32
, in that the POTS communication is so far outside of its frequency band and of such low voltage that such signals require minimal filtering and are taken care of by normal XDSL analog interfaces.
Several issues arise when splitter
24
is introduced into central office
10
. Splitter
24
takes up office space, which is increasingly at a premium as new DSLAMs
16
and other services are incorporated into central office
10
. Furthermore, wiring in the office becomes more complex. Wherein an original POTS line passed through MDF
20
directly to POTS line card
36
, in order to provide XDSL service, the wiring passes through MDF at least three times for distribution of the various signals. In some instances, splitter
24
may be a part of the DSLAM
16
and separate wires run to switch
12
in some cases bypassing MDF
20
. This scenario, however, further complicates the wiring distribution in the office and is generally avoided. In either example, if the POTS line card
36
or the XDSL line card
32
(and switch
12
and DSLAM
16
respectively) malfunction, it may affect the other equipment, and the attached subscriber can use neither the POTS telephone nor the DSL service.
In U.S. patent application Ser. No. 08/767,138, entitled “Telecommunication Equipment Support Of High Speed Data Services” which is assigned to the assignee of this invention, a new line card is disclosed that incorporates both POTS and DSL service. This is a superior solution to the above-described problem provided that switch
12
switches both POTS and XDSL service. Furthermore, many data service providers that are not the incumbent POTS service provider want to provide XDSL service. This requires that a DSLAM of the alternate service provider be connected to the switch in some manner, such as that shown in FIG.
1
.
Therefore, there is a need in the art for a system that does not require additional equipment in order to provide XDSL service over POTS telephone lines.
SUMMARY OF THE INVENTION
This problem is solved and a technical advance is achieved in the art by an improved plain old telephone service (POTS) line card that may be directly connected to a customer line that is also connected to a digital subscriber line access multiplexer. A second order filter is added to the front end of the POTS line card in order to attenuate XDSL signals and to lower its amplitude. A new digital signal processor (DSP) includes further low pass filtering functions, gain compensation and termination impedance compensation to provide the proper balanced network as is known in current POTS cards but not provided in current XDSL services. This card may also be used alone without a XDSL equipped line. Thus, if the line is XDSL equipped maintenance may be performed on one without affecting the other of the two services. Further, these cards may be used in areas wherein DSL service is likely to be added as a feature and/or in areas with alternative XDSL providers.


REFERENCES:
patent: 5802169 (1998-09-01), Frantz et al.
patent: 6067316 (2000-05-01), Amrany et al.
patent: 6295343 (2001-09-01), Hjartarson et al.
patent: 2003/0156632 (2003-08-01), Dowling
patent: 197 25 572 A 1 (1999-01-01), None
patent: 0 503 528 (1982-09-01), None
EPO Search Report; No. EP 01 30 0758; dated Jan. 25, 2002; Examiner M. Vandevenne; place of search, The Hague.
U.S. patent application Ser. No. 08/767,138, Nye et al., filed May 22, 2000.

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