Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via frequency channels
Reexamination Certificate
1999-02-04
2001-07-10
Vu, Huy D. (Department: 2664)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via frequency channels
C370S201000, C370S521000, C370S524000, C370S271000, C375S295000, C375S377000
Reexamination Certificate
active
06259708
ABSTRACT:
TECHNICAL FIELD
The present invention relates in general to communications using existing telephone wire and more particularly to a system that digitizes voiceband signals and transmits them over a digital subscriber line (DSL) using a DSL modem or other similar DSL device.
BACKGROUND OF THE INVENTION
The increased use of telephone twisted pair wiring for data communications has resulted in a push for faster modems and improved signaling protocols compatible with the public switch telephone network (PSTN). An example includes the emerging variety of the DSL communications protocols including asymmetric digital subscriber line (ADSL), symmetric digital subscriber line (SDSL), high bit rate digital subscriber line (HDSL), and very high rate digital subscriber line (VDSL). Each DSL variant represents a different transmission speed over possibly different distances of copper pair wiring usually for different applications.
In principle, a DSL modem and a plain old telephone system (POTS) or other voiceband device can operate simultaneously over the same twisted pair connection since they use different frequency bands. The connection, however, of a POTS to the same wire line pair as a DSL modem can suffer from several problems that result from the change in input impedance of the POTS equipment as it is added to the line. In essence, most POTS equipment is not designed to handle frequencies outside the voiceband of 300-3.4 kHz. In addition, POTS equipment often contains nonlinear components that may create intermodulation and harmonic interferences. Examples of such nonlinear components include Zener diodes, transistors, varistors, triacs, and other devices used for overvoltage protection, sidetone generation and overvolume protection.
As the shift to all digital communications continues, the POTS, due to its large installed base and widespread application may represent the final analog domain of telephony. Eventually, the industry may adopt a network that is entirely digital and DSL will eventually be the standard of choice. However, with the rapid growth of the Internet, high speed DSL modems might first dominate the telephone wires. One of promised DSL techniques is Asymmetrical Digital Subscriber Lines (ADSL). ADSL is an ANSI standard (T1E1.4-T1.413) issued in 1995 which presents the electrical characteristics of the Asymmetric Digital Subscriber Line signal appearing at the network interface.
While a known prior art technology, called Digital Pair Gain Device, can utilize one wire line pair to carry multiple voice channels, it requires that the connection be routed through an Integrated Service Digital Network (ISDN). The central office terminal emulates a telephone set for ring detection and hold purposes. On the other hand, the remote terminal at home drives a real analog phone by providing battery feed, off-hook detect, ring-trip detect, and ringing generation. The system requires a high frequency modem solely for its voice channels.
While ISDN is another typical DSL application, its limited data rate is not good for future Internet access. A fully digital telephony solution based on DSL, however, would be more advantageous. The integration of high speed modems and digital voice is important in today's consumer market and for applications such as 6-Mbps ADSL and voice over IP.
SUMMARY OF THE INVENTION
The invention provides a system for digitizing voiceband signals at the remote end of a Digital Subscriber Line (DSL) connection and embedding the digitized voice component into an active DSL data stream using a DSL modem. Voiceband transmissions between the remote terminal and the central office occur in the analog domain when the DSL modem is OFF and in the digital domain when the DSL modem is ON with the digital voiceband signals transmitted over a DSL link. With the DSL link active, the remote terminal communicates directly with the analog telephone equipment connected to the in-house 4-wire lines by providing battery feed, ring-trip detection, off-hook detection and ringing generation. In-house 4-wire lines provide connections between the DSL modem, telephones and computer or home networking equipment. A switching scheme enables a powered up DSL modem to control the analog equipment.
According to one embodiment, disclosed is a remote terminal for transmitting voiceband signals over a digital subscriber line (DSL) with the DSL coupled to a wire line pair connection providing a communications link from at least one voiceband device (such as a standard subscriber side telephone) and one digital data device (such as a desktop computer) to a central office facility. The remote terminal comprises a voice frequency interface with first and second terminals, the first terminal coupled to the voiceband device. A digital data interface with first and second terminals is also provided, the first terminal coupled to the digital data device. The device also includes a means of digitizing voiceband signals, such as an analog-to-digital signal converter, with an input terminal coupled to the second terminal of the voice frequency interface and an output terminal.
The device further includes a DSL compliant device, such as a DSL modem, with first, second and third terminals, the first terminal being coupled to the digital data interface for communicating with a digital data device such as a computer, the second terminal coupled to the output terminal of the means of digitizing voiceband signals and the third terminal coupled to the wire line pair connecting the customer premise to the central office. Essentially, the DSL compliant device is configured to receive digitize voiceband signals and intersperse them into the upstream DSL signal stream to the central office facility. The means for digitizing voice band signals is configured to present the same line conditions to the voice band component as it expects to see when the DSL compliant device is turned OFF.
According to another embodiment, disclosed is a central office call switching device comprising a line interface and a signal converter with analog and digital terminals, the analog terminal coupled to the line interface in a first operating state of the device. A digital subscriber line (DSL) compliant device with first, second and third terminals is also provided, the first terminal coupled to the digital terminal of the signal converter, the second terminal coupled to the line interface in a second operating state.
The central office call switching device also includes a digital interface with first and second terminals, the first terminal coupled to the third terminal of the DSL compliant device, the second terminal providing a signal pathway to at least one digital backplane, such as an Internet Protocol (IP) network. A voice frequency interface with first and second terminals is further provided, the first terminal coupled to the analog terminal of the signal converter.
Further disclosed are wiring configurations for coupling a remote terminal capable of digitizing voiceband signals and transmitting them in a DSL data stream utilizing the wire line pairs existing on the subscriber side of the network. According to one configuration, a voice frequency interface has a first terminal coupled to the subscriber POTS and a second terminal to a digitizing voiceband function through an existing, often unused, wire line pair. The switching mechanism, depending on the state of the remote terminal, can create a signal path from the POTS through a DSL compliant device in the remote terminal. If the remote terminal DSL complaint device is powered down, the switching mechanism will bypass the remote terminal entirely for normal voiceband operation.
According to another configuration, the voice frequency interface is split into two interfaces with the POTS coupled to one of the interfaces and a digital processing system to the second interface. Instead of coupling the processing system to the DSL device, the switching mechanism operates the transitions between the all-DSL state and the normal POTS voiceband operation.
According to anot
Chen Walter Y.
Cheng Yaqi
Franz Warren L.
Polley Michael O.
Brady III W. James
Moore J. Dennis
Phan M.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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