Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
1998-09-11
2004-08-24
Duong, Frank (Department: 2666)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S356000, C370S395530
Reexamination Certificate
active
06781981
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to the field of data communications in the local access loop of the telephone network. In particular, a system and method are disclosed for providing high-speed data and voice services over standard twisted-pair voice-lines in a digital loop carrier (“DLC”) system.
In a typical DLC system, the digital transport capabilities of the phone network are extended from the central office switch into a particular neighborhood or business location. A remote digital terminal (“RDT”) is placed at a remote location from the central office and is connected to it via a fiber-optic cable, or some other high-bandwidth connection. The remote digital terminal receives PCM-modulated voice information from the central office switch, converts the digital PCM signals into analog voice signals, and routes the analog voice signals to a particular customer location via a plurality of line-cards that connect the RDT to the customer's location. Similarly, the RDT converts analog voice information from the customer to a digital PCM format for transport back to the central office switch. An example of a digital loop carrier system is set forth in U.S. Pat. No. 5,046,067 (“the '067 patent”), which is assigned to the assignee of the present invention. The teaching of this patent is hereby incorporated into the present application by reference.
The RDT typically includes an interface terminal for communicating with the central office over the fiber-optic connection, a common equipment shelf for housing equipment that is capable of exchanging PCM voice signals with a digital switch at the central office and that can also demultiplex high-bandwidth signals (such as DS-1 signals) into lower-bandwidth signals (such as DS-0) signals, and a plurality of copper shelves for housing line-cards (also known as channel units). The line-cards convert the PCM digital voice signals from the common equipment shelf into analog signals, and vice versa, for each customer that is connected to the RDT.
Dial-up Internet access is a presently available technique for transporting data to local customers. This mode of data communication transmits digital data over an analog voice line using a low-frequency (voice range) modem. Presently, the highest-bandwidth that such modems are capable of communicating is about 53 Kbps. This is not sufficient for many Internet applications, such as video-conferencing, interactive gaming, large file downloads, etc.
Another presently available technique for transporting data to a local user is via a dedicated digital line, such as a T-1 line, or an ISDN line. Although these alternatives provide higher-bandwidth capabilities than an analog modem, they are very costly to the average consumer, and therefore have met with minimal market penetration.
Recently, a series of new techniques for transporting data over voice lines, known as digital subscriber line (or DSL) have been proposed. DSL technologies use advanced digital modulation schemes to transport orders-of-magnitude more information over copper phone lines than analog modems or ISDN lines. The primary mechanisms for achieving such high throughput are higher-frequency transmission and advanced modulation schemes. Because of the promise of higher transport speeds, DSL is very desirable for Internet applications. In addition, DSL technology should be available at a fraction of the cost of dedicated T-1 lines, since no dedicated link is required.
Regardless of what DSL technique is implemented, problems exists with integrating DSL technology into existing digital loop carrier systems. Power is a primary concern. Typical DSL technologies require 4-8 watts per line-card to operate the complicated modulation algorithms, thus limiting their applicability to existing DLC installations, which are power-limited. Limited range is another concern. Some customers are at significant distances from the RDT, and if the DSL line-card range is limited, then additional hardware may be required to connect to a particular customer that is far from the RDT. Noise introduced into the system is yet another concern. But perhaps the most vexing problem is how to adapt the existing DLC infrastructure to support high-bandwidth digital data without reducing the voice-bandwidth capabilities of the system, or without having to replace the RDT equipment already installed in the field. The present invention solves this problem, as well as many others.
Thus, there remains a general need in this field for a system and method for integrating DSL capabilities into existing DLC systems.
There remains a more particular need for such a system and method in which an auxiliary bus is converted into a digital data bus for transporting data directly between the interface terminal and the DSL line-cards in the RDT, thereby bypassing the common equipment shelf and minimizing the impact to the voice-carrying capabilities of the DLC system.
There remains an additional need for such a system and method in which multiple digital signals from the DSL line-cards are switched at the RDT, prior to transmission to the central office switch.
There remains yet another need in this field for a combination voice/DSL line-card for use in a DLC system.
There remains still another need for such a combination voice/DSL line-card that utilizes low-power modulation technology, such as quadrature-phase shift keying (“QPSK”).
SUMMARY OF THE INVENTION
The present invention overcomes the problems noted above and satisfies the needs in this field for a digital loop carrier system that is capable of transporting both voice and DSL data signals. The digital loop carrier system includes a remote digital terminal having an interface terminal, a common equipment shelf for interfacing digital voice signals to the central office switch, and at least one copper shelf coupled to the common shelf for holding voice line-cards that convert digital voice signals into analog voice signals (and vice versa) for transport to customer premises. At least one copper shelf is configured to include an auxiliary digital data bus (preferably a packet data bus) for connecting combination voice/DSL line-cards and at least one data uplink card. The data uplink card is coupled directly to the interface terminal-to enable DSL data transport without impacting digital voice capabilities through the common equipment. Also disclosed is an optional Ethernet switch in the remote digital terminal for concentrating multiple DSL signals prior to transport back to the central office.
As described in more detail below, the present invention can be used with any DSL modulation scheme. However, because of the inherent power limitations of existing DLC installations, the preferred embodiment of the present invention utilizes a low-power QPSK-modulation technique. It is to be understood that this is only one example of the many types of modulation schemes that could be integrated into the combination voice/DSL line-cards, and the overall system of the present invention.
One embodiment of the present invention provides a system for transporting voice and digital subscriber line (DSL) data in the local telephone loop, comprising: (a) a central office switch coupled to voice and data sources; (b) a plurality of customer interface devices; and (c) a remote digital terminal (RDT) coupled between the central office switch and the customer interface devices, comprising: (1) an interface terminal for communicating voice and data signals between the central office switch and the RDT; (2) a common equipment shelf coupled to the interface terminal for transmitting and receiving voice signals; and (3) at least one copper equipment shelf coupled to the common equipment shelf, the copper equipment shelf including a plurality of communication cards and a digital data bus for transporting data between the cards, wherein one of the communication cards is a data uplink card coupled to the interface terminal for transmitting and receiving data signals, and another one of the communication cards is a combin
Advanced Fibre Access Corporation
Duong Frank
Jagannathan Melanie
Jones Day
LandOfFree
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