Method and system for combining symmetric DSL signals and...

Details Method and system for combining symmetric DSL signals and... Method and system for combining symmetric DSL signals and...

1999-10-22

2004-02-17

Nguyen, Chau (Department: 2663)

Multiplex communications

Communication techniques for information carried in plural...

Combining or distributing information via frequency channels

C370S493000, C375S222000

Reexamination Certificate

active

06693916

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to generic Digital Subscriber Line systems and voice communications systems and more particularly to methods and systems for combining symmetric Digital Subscriber Line signals and analog voice signals.
2. Description of Related Art
With the increased usage of Internet services and the desire or need for other high data rate signals, consumers require equipment that can handle data signals at a rate greater than that available via traditional analog voice modems, which currently have a maximum data rate of 56K bits per second (“BPS”). Recently, business and residential consumers are using Digital Subscriber Line (“DSL”) modems as part of a system for getting high speed access to the Internet. DSL type of service is currently being offered by many telecommunication access service providers, which include numerous independent access providers and traditional telephone companies. There are many variations of DSL including High-Bit-Rate Digital Subscriber Line (“HDSL”), Asymmetric DSL (“ADSL”), and Symmetric DSL (“SDSL”). (“Asymmetric” refers to the fact that the upload and download bit rates are not equal and “Symmetric” refers to the fact that the upload and download bit rates are the same.) HDSL and SDSL are both symmetrical DSL signals that use the same modulation technique. HDSL systems use two pairs of twisted wire, operate at a fixed data rate (equivalent rate to T
1
in North America and E
1
outside North America) and are mainly used as a replacement for T
1
and E
1
network connections. ADSL and SDSL systems use a single twisted pair of wires and are capable of operating at variable data rates. A description of an exemplary DSL system employing 2B
1
Q modulation is described in Bellcore TA-NWT-001210 Issue 1, Oct. 1991, Generic Requirements for High-Bit-Rate Digital Subscriber Lines which is hereby incorporated by reference for its teachings on DSL systems and 2B
1
Q modulation.
These DSL services are generically called xDSL. xDSL service reaches its customers by using copper wires that extend from a telephone company's Central Office (“CO”) to a residence or business. Currently, telephone companies mostly offer ADSL service, which is a service targeted at their consumer or residential customer base and offer businesses T
1
service using HDSL. Independent or alternative access providers are also in the access market and offer mostly SDSL. There are several types of SDSL and HDSL modems available. The most common type of modulation format the modems employ is a 2B
1
Q (two bits per quadrant or symbol) format, which is a simple four level signal modulation format known as Pulse Amplitude Modulation (“PAM”). For the sake of clarity, during the remainder of the document, only SDSL will be described although the invention applies equally to both SDSL systems and single wire pair HDSL systems that use 2B
1
Q modulation.
FIG. 1
(Prior Art) is a diagram of a prior art communication system
270
in which both voice and data (via SDSL access) are delivered through independent means and equipment to an individual customer. Voice and SDSL is delivered in this way because of the inability of voice and such data signals to coexist on the same connection. As shown in this figure, Customer premise equipment (“CPE”)
240
and Central Office (“CO”) equipment
250
receive (a) traditional voice communication via a twisted pair of wires
173
and (b)SDSL communication via a separate twisted pair of wires
214
commonly dedicated to transferring only SDSL signals. The CPE
240
includes call signal destination equipment
144
, an SDSL modem
212
, and digital signal destination equipment
148
. The CO equipment
250
includes a telephone switch
174
and an SDSL Modem and DSL Access Multiplexer (“DSLAM”)
213
. As shown in
FIG. 1
, the SDSL Modem/DSLAM
213
is coupled to the Internet
180
by a Router/Internet Service Provider (“ISP”)
260
, the connection thereto is known to one of skill in the art.
In this FIGURE, the central office (“CO”) equipment
250
of a telephone company provides voice communication on the twisted pair of wires
173
between the call signal destination equipment
144
in the CPE
240
and a public switch telephone network (“PSTN”)
190
. The call signal destination equipment
144
may be any voice signal processing apparatus or telephone system such as a telephone keyset, public branch exchange (“PBX”), or voice band modem or fax. It is noted that the PSTN
190
may be any telephone system including PSTN, PBX, or plain old telephone system (“POTS”). As noted above, the CO equipment
250
includes a telephone switch
174
that transfers or switches analog voice signals to the twisted pair of wires
173
when the signal is addressed to the CPE
240
and to a connection into the public switched telephone network (“PSTN”)
190
. Voice and signaling signals appear on wires
173
and consist of voice band signals whose frequency ranges from zero to 3.4 kHz, a battery feed voltage (DC at −48 volts) and an AC ringing high voltage (20 Hz at 90 volts RMS). Transient signals may also appear on the twisted pair of wires
173
during changes in line conditions such as at the beginning and end of a ringing signal, the taking of a phone off-hook during ringing and not during ringing, the placement of a phone on-hook, the switching of ringing to battery feed signal and the switching of the battery feed signal to the ringing signal.
As also shown in this FIGURE, an SDSL access provider (either the telephone company or an alternative service provider) uses additional equipment, an SDSL Modem/DSLAM
213
inside the CO
260
for providing data communication on the twisted pair of wires
214
between the CPE
240
and the Internet
180
via a Router/ISP
260
. The SDSL Modem/DSLAM
213
includes a digital subscriber line access multiplexer (“DSLAM”) with SDSL modems.
The SDSL (2B
1
Q modulation format) modem inside the SDSL Modem/DSLAM
213
converts SDSL signals (which are modulated analog data signals) on the twisted pair of wires
214
to digital signals. The SDSL Modem/DSLAM
213
also multiplexes many SDSL modem signals into a single high-speed signal and passes that signal on to the ISP/Router
260
. The ISP/ router
260
interconnects the SDSL Modem/DSLAM
213
to the Internet
180
.
Similarly, when a digital data signal is transmitted from the Internet
180
to the CPE
240
via line
214
, the ISP/router
260
transfers the Internet traffic to the SDSL Modem/DSLAM
213
. Any digital data that is addressed to the CPE
240
is then sent to the appropriate SDSL modem of the SDSL Modem/DSLAM
213
. The SDSL modem in the SDSL Modem/DSLAM
213
converts this digital data to an SDSL signal where the SDSL signal is modulated analog signal. The SDSL signal is transmitted to the CPE
240
via the twisted pair of wires
214
. The SDSL (2B1Q) signals have a frequency range starting from DC (0 Hz) to an upper frequency that is one half of the assigned data rate. For example: when the data rate of the service being offered is 384 kbps, the frequencies generated are may range from 0 Hz to 192 kHz.).
As noted above, the CPE
240
includes an SDSL modem
212
and digital signal destination equipment
148
. The SDSL modem
212
demodulates SDSL signals (as noted, the SDSL signals are analog data signals) received on the twisted pair of wires
214
and provides a digital signal that is transferred to the digital signal destination equipment
148
via line
145
. Line
145
may be an Ethernet cable or serial cable capable of transferring a digital signal. The digital signal destination equipment
148
may be networking equipment such as a hub, router or switch or an individual computer. The SDSL modem
212
also modulates digital signals received from the digital signal destination equipment
148
, using a modulation or encoding technique compatible with that used by the SDSL modem of SDSL Modem/DSLAM
213
, and transmits them to the SDSL Modem/DSLAM
213
on the twisted pair of wires
214
.
The twisted p

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