Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-12-02
2002-03-26
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S107000, C359S199200, C359S199200
Reexamination Certificate
active
06362908
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to the field of fiber-to-the-curb (“FTTC”) digital loop carrier (“DLC”) systems for communicating information in the local access loop between a central office switching station and a plurality of customer locations. In particular, a novel optical network unit (“ONU”) for use with such an FTTC system is described, in which the ONU includes at least one multi-service common card coupled to a plurality of service cards via a plurality of high-speed serial interconnections. The high-speed serial interconnections are preferably arranged in a separate point-to-point “star” configuration in which each service card includes a separate high-speed point-to-point serial interface with the one or more multi-service common cards. A family of adaptable multi-service common cards and a scalable FTTC system for delivering present and future multi-media services in the local loop are also disclosed.
By eliminating the traditional backplane found in present ONUs, the ONU of the present invention provides a modular, easily-reconfigurable (i.e. adaptable) architecture that extends the operating life of the ONU far beyond that of traditional ONU designs, and thus enables the system to adapt to unknown services that may or may not be anticipated at the time of installation. Due to the inherent limitations of a backplaned ONU, such adaptability to future services is not possible. Using the features and principles of the present invention, a future-proof, expandable FTTC system can be installed that is capable of providing a multitude of multi-media services over a single fiber-optic connection, such as telephony, high-speed data, CATV, video-on-demand, as well as any number of future services that may require extremely high-bandwidth.
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 (“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 (or service cards) that connect the RDT to the customer's equipment. 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.
An FTTC system is an extended version of the DLC system described above, in which the fiber-optic capabilities are extended further into the local loop by fiber-coupling a plurality of ONU telecommunication terminals to the RDT (which is then referred to as a Host Digital Terminal, or HDT), wherein the ONUs are located very close to the customer locations. An example FTTC system is set forth in
FIG. 1
, discussed in more detail below. The system shown in
FIG. 1
is also described in U.S. patent. application Ser. No. 08/794,723, titled “Distributed Ethernet Hub” (the “'723 application”). This application is commonly assigned to the assignee of the present invention and the teaching of this application is hereby incorporated into this disclosure by reference. As shown in
FIG. 1
, in a typical FTTC system the RDT is converted into an HDT, which, in many respects, is similar to the RDT, except that the HDT is further connected to a plurality of ONU telecommunication terminals via fiber-optic cable. The HDT includes appropriate circuitry and programming for routing signals to and from the plurality of ONUs and the central office switching station.
The ONUs are relatively small pedestal terminals that are physically located in close proximity to a customer's location, such as 500′ or less. By placing the ONU in close physical proximity to the customer, high-bandwidth communications can be managed through the ONU over traditional wiretypes. Each ONU typically services a plurality of customers, such as 4 to 8, although, in the future, more customers may be serviced from a single ONU. The ONU provides many functions. It converts optical signals from the HDT into appropriate electrical signals that correspond to the customer's equipment, such as analog phone signals, or high-speed data signals. It provides voltage surge protection for the physical connections to the customer's premises, such as twisted-pair copper or coaxial cable. It provides built-in test capabilities so that the lines to the customer's premises can be tested from the central office. It receives power from the HDT, and converts the received power into a conditioned power level that serves the ONU circuitry, as well as many other functions.
Presently, FTTC systems including ONUs are typically deployed for Plain Old Telephone Service (“POTS”), with the intention of getting fiber-optic cable close to the customer's premises so that present and future broadband services can be provided as they are defined, or as they become economically feasible. One example of these types of broadband services is high-speed Internet access. The '723 application provides a solution to delivering these types of services using presently available ONU technology. Other types of broadband services include CATV, video-on-demand, video conferencing, xDSL, interactive television, digital TV and radio, ISDN, as well as many other yet to be defined high-bandwidth applications. Companies seeking to deploy FTTC systems would like to be sure that future services, which have not even been defined, can still be handled by the FTTC system hardware in place. Thus, a future-proof architecture is desirable for the ONU, which provides the critical link between the FTTC system and the customer premesis. Presently known ONUs are not future-proof.
Presently known ONUs are not capable of being future-proof because they utilize a backplane architecture.
FIGS. 2A and 2B
, discussed in more detail below, set forth such an ONU incorporating a backplane architecture. In these types of ONUs, the common cards and service cards plug into a circuit-board backplane that includes a plurality of connectors for mating to corresponding connectors on the common or service cards and one or more electrical busses that connect the cards together. The one or more busses are metal interconnections (or traces) embedded in the backplane circuit board. The cards communicate with each other primarily via the backplane traces. Because the structure of the backplane inherently limits the services that can be handled by the ONU, any backplane architecture is not capable of being future-proof.
There are many problems associated with using a backplane structure. First, there is no modularity built into the system, since the position and spacing of the backplane connectors is mechanically fixed. Thus, the backplane can only accept circuit cards of a particular dimension and width. Second, the bandwidth of the backplane is limited by its electrical properties. These electrical properties that limit the bandwidth include the impedance of the interconnections between the circuit boards and the backplane and the impedance limitations of the metallization traces that connect the connectors together. In addition, termination resistors may limit the speed of the backplane bus. Because of these physical and electrical limitations, at higher frequencies it becomes very difficult to accurately distribute any type of clocking (or other data) signals over the backplane, due to skewing of the signals that may render the system inoperable.
In summary, it is not feasible to design a backplane ONU that is future-proof. Unle
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