Line sharing multipoint POTS splitter masking noise

Details Line sharing multipoint POTS splitter masking noise Line sharing multipoint POTS splitter masking noise

2000-12-27

2004-08-10

Kuntz, Curtis (Department: 2643)

Telephonic communications

Diagnostic testing, malfunction indication, or electrical...

For detection of eavesdropping device

C379S022030, C379S031000, C379S035000

Reexamination Certificate

active

06775355

ABSTRACT:

TECHNICAL FIELD
The present invention relates generally to data communications, and more particularly, to a system and method for enabling a multiple line communication device to communicate over a plurality of different subscriber loops in a manner which prevents a potential third-party eavesdropper from detecting a leakage signal.
BACKGROUND OF THE INVENTION
With the increasing bandwidth demands from the advent of the Internet, service providers have looked for ways to increase data transmission performance over the copper wire local loop transmission lines that connect telephone central offices (COs) to customer premises (CPs). In conventional telephony networks, customer premises equipment (CPE) are coupled to CO switches over the above mentioned transmission lines, which are commonly known as “local loops,” “subscriber lines,” “subscriber loops,” “loops,” or the “last mile” of the telephone network. In the art, the term “line” and “loop” are used interchangeably, both terms referring to the copper wire pair used in a typical telephone transmission line conductor. Historically, the public switched telephone network (PSTN) evolved with subscriber loops coupled to a telephone network with circuit-switched capabilities that were designed to carry analog voice communications. “Central office” or “CO” means any site where a subscriber loop couples to a telephony switching unit, such as a public switched telephone network (PSTN), a private branch exchange (PBX) telephony system, or any other location functionally coupling subscriber loops to a telephony network. Digital service provision to the CP is a more recent development. With it, the telephone network has evolved from a system capable of only carrying analog voice communications into a system that can simultaneously carry voice and digital data.
Historically, the POTS subscriber loop was designed with the functions needed to communicate analog voice-conversation signals and subscriber loop signaling. The CO switch uses subscriber loop signaling to notify the customer premises about events in the telephone network, while customer premises equipment (CPE) use subscriber loop signaling to inform the CO to perform actions for the customer. Some examples of subscriber loop signaling include: the CO switch signaling to the CPE that an incoming call has arrived by ringing the phone, the CPE (e.g., a telephone) signaling to the CO switch that the CPE is initiating a call by an on-hook to off-hook transition of the telephone handset, and the CPE signaling to the CO switch that a call should be connected to a location by transmitting the phone number of the location.
Because of the prohibitive costs of replacing or supplementing existing subscriber loops, technologies have been implemented that utilize existing subscriber loops to provide easy and low cost migration to digital technologies. Subscriber loops capable of carrying digital signals are known as digital subscriber lines (DSLs). Various digital technologies provide customers with additional flexibility and enhanced services by utilizing frequency-division multiplexing and/or time-division multiplexing techniques to fully exploit the transmission capability of a subscriber loop. These newer DSL technologies provide digital service to the customer premises without significantly interfering with the existing plain old telephone service (POTS) equipment and wiring by utilizing portions of the available frequency spectrum not used by a POTS signal. These portions of the frequency spectrum are often referred to as “logical channels.” Logical channels within a subscriber line that carry digital signals are known as “DSL channels,” while logical channels within a subscriber line which carry POTS analog signals are known as “POTS channels.”
DSL technologies, such as but not limited to integrated services digital network (ISDN), high-bit-rate digital subscriber line (HDSL), HDSL2 and symmetric digital subscriber line (SDSL), utilize different frequencies of the available frequency spectrum and therefore do not coexist with a POTS signal, which typically utilizes the 0-4 kilohertz (KHz) portion of the available frequency spectrum. These DSL technologies accomplish this functionality by frequency-division multiplexing (FDM) a single data signal onto a logical channel above (at higher frequencies than) the 0 KHz to 4 KHz frequency range used by the analog POTS signals. Such multiplexing techniques and terminology are common to those skilled in the art, and are not described in detail herein.
Several variations of new multiple channel DSL technology exist, such as, but not limited to, Asymmetric Digital Subscriber Line (ADSL), Rate Adaptive Digital Subscriber Line (RADSL), Very High Speed DSL (VDSL), Multiple Virtual Lines (MVL™) and Tripleplay™, with this group generally referred to as xDSL. Communications systems employing xDSL technology may multiplex a plurality of data signals and a single POTS signal onto a single subscriber line. An xDSL system employing frequency-division multiplexing would multiplex a plurality of data signals onto a corresponding plurality of logical channels, each logical channel utilizing a different portion of the available frequency spectrum. An xDSL system employing time-division multiplexing would multiplex a plurality of data signals onto a single logical channel with each different data signal allocated to a predefined portion of time in a predefined, repeating time period.
For example, an xDSL system employing time-division multiplexing of four data signals would subdivide a predefined time period into four sub-periods. Each one of the four data signals would be allocated to one of the four sub-periods. During the first sub-period, the first data signal would be communicated across the subscriber loop. During the second sub-period, the second data signal would be communicated. Likewise, the third and fourth data signals would be communicated during the third and fourth sub-periods, respectively. When the fourth sub-period has ended, the predefined time period repeats, and the first data signal is communicated during a new first sub-period. Thus, four individual data signals can be transmitted sequentially by allocating one of the signals to one of the four sub-periods.
FIG. 1
is a simplified illustrative block diagram of a portion of an existing telephony system
20
which includes a telephone company CO
22
coupled to a CP
24
via a single subscriber loop
26
. Subscriber loop
26
may be any suitable connection for communicating electrical signals, but is typically a copper wire pair, as is well known in the art, that was originally designed to carry a 0-4 KHz analog voice channel (POTS signal). Located within the CO
22
is the CO telephony POTS switching unit
28
which communicates POTS signals with the telephone(s)
30
residing in CP
24
via the subscriber loop
26
. In some instances, filter(s)
32
may be coupled between subscriber loop
26
and telephone(s)
30
.
CO digital equipment
34
and low pass filter
36
may be added at the CO to facilitate transmission of digital data. Digital equipment
34
transmits and receives data signals over subscriber loop
26
. When a copper wire pair is used for data signal transmission, the wire pair is often referred to as a digital subscriber loop (DSL).
Low pass filter
36
separates, or splits out, the POTS signal for delivery to POTS switching unit
28
. Low pass filter
36
is designed to pass the 0-4KHz analog POTS signal. In some applications, a POTS splitter(not shown) may be used. Such a POTS splitter may also include a high pass frequency filter designed to pass the data signals, which utilize the portion of the available frequency spectrum above 4 KHz, to the digital equipment
34
. Thus, a POTS splitter may split off the data signal from the subscriber loop for delivery to digital device
38
, thereby separating the data signal from the POTS analog signal. POTS splitter technology is well known in the art, and is therefore not described in detail herein.
Located within the CP
24
may be

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