Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
1999-01-15
2001-03-27
Hsu, Alpus H. (Department: 2738)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S389000, C370S395430, C709S227000
Reexamination Certificate
active
06208637
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for the generation of analog telephone signals in digital subscriber loop access system.
BACKGROUND OF THE INVENTION
The increasing demand for bandwidth has resulted in a need for equipment which can transmit both telephony and data signals from telephone central offices to subscriber residences and businesses. Because of the tremendous number of twisted wire pairs which are in place for the delivery of traditional phone services, telecommunications manufacturers have developed digital subscriber loop transmission systems which support the transport of digital data from telephone central offices to subscribers. Such systems offer the advantage that they can make use of the existing twisted wire pairs, although it is sometimes necessary to place electronics for sending and receiving these signals outside of the telephone central office and closer to the subscribers.
Digital subscriber loop systems offer the advantage of being able to provide data signals to subscribers, and in many instances allow traditional telephone services to be transmitted simultaneously with a digital signal. This allows the subscriber to have a primary phone line along with a high-speed digital data service.
However, if a twisted wire pair is being used to simultaneously provide a traditional analog phone service and high-speed data it cannot be used to provide additional phone lines using existing digital subscriber loop systems. This requires that a separate twisted wire pair be used if the subscriber wants to have a second phone line in addition to the primary phone line and high-speed data service.
For the foregoing reasons, there is a need for a method and apparatus which can provide analog phone service in a residence or business in a digital subscriber loop access system.
SUMMARY OF THE INVENTION
The present invention describes a method and apparatus for the simultaneous transport of data and telephony services over a fiber optic based infrastructure in which digital telephony signals and data signals are received at a telephone central office unit and combined for transmission over a fiber optic link to a second unit which can be located either in the telephone central office or in the field. At the second unit a digital subscriber loop signal is formed which has Asynchronous Transfer Mode (ATM) cells which contain either digital telephony signals or data signals. The ATM cells are transmitted to a residential receiving device which reconstructs the data signal for presentation at a user data interface and reconstructs an analog telephony signal for presentation at a user telephony interface.
In a preferred embodiment ATM cells which contain digital telephony information are spaced by 5 ms and can contain a single 64 kb/s channel formed using Pulse Code Modulation (PCM) techniques, two 32 kb/s channels formed using Adaptive Differential Pulse Code Modulation(ADPCM)techniques, or four 16 kb/s channels using ADPCM techniques.
The present invention also encompasses an ATM cell mapping for supporting the delivery of telephony services in a digital subscriber loop architecture which is based on a digital telephony signal payload, a signaling payload, and an overhead payload. The digital telephony payload is used to transport the telephony services, the signaling payload is used to transport signaling for generation of ringing, dial-tone, and other standard telephony functions, and the overhead payload transports control and maintenance messages.
Another feature of the present invention is that it supports echo cancellation which can be used in conjunction with ADPCM techniques to guarantee an acceptable voice quality.
An advantage of the present invention is that the service provider can deliver multiple voice circuits in addition to a high-speed data service over one twisted wire pair, and can provide the customer with traditional telephony services connected via the PSTN. In addition, the service provider can continue to provide the primary phone line as an analog service compatible with the data service, and offer one or more additional phone lines. Depending on the quality of service desired, these phone lines can use compression, and up to four additional phone lines can be supported in the residence or business, along with the data service.
These and other features and objects of the invention will be more fully understood from the following detailed description of the preferred embodiments which should be read in light of the accompanying drawings.
REFERENCES:
patent: 4819228 (1989-04-01), Baran et al.
patent: 4970721 (1990-11-01), Aczel et al.
patent: 5583863 (1996-12-01), Darr, Jr. et al.
patent: 5946323 (1999-08-01), Eakins et al.
patent: 5999525 (1999-12-01), Krishnaswamy et al.
Covington & Burling
Hsu Alpus H.
Next Level Communications, L.L.P.
Qureshi Afsar M.
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