The present invention relates to broadband networks and systems, and more particularly to Digital Subscriber Line (DSL) technology.
The demand for broadband communication at higher bandwidth, to accommodate multimedia information, is growing. Telecommunication and Cable networks are providing these services to subscribers, in increasing numbers.
Telecommunication networks and Cable networks use a central Distribution Center [DC] such as a Central Office in telecommunications or a Head end in cable networks, to house the network equipment to serve a community of subscribers. The equipment in DCs are interconnected to each other using a backbone or core network, form a larger network. Typically, the subscribers are located with in five-mile radius of the DC. The equipment located at the DC and the equipment located at subscriber locations are connected using drop cables. Typically, the drop cables in a telecommunication network are twisted pair copper wires and Coaxial Cables are used in the Cable networks.
The Digital Subscriber Loop [DSL] technology is widely used in the Telecommunication networks for broadband services. There are a number of variations of DSL technologies such as high bit-rate digital subscriber line (HDSL), Symmetric or Single pair Digital Subscriber Line (SDSL, symmetric high bit-rate digital subscriber line (SHDSL), asymmetric digital subscriber line (ADSL), very-high-bit-rate digital subscriber line (VDSL)and rate adoptive digital subscriber line (RADSL). The term “xDSL” is used in art to include all of the variations of DSL Technology. Each of this xDSL technology is suited to a different application with trade-off made between transmission distance and bandwidth. The broadband service data rate ranges from 300 Kilobits per second [Kbps] to 52 Megabits per second [Mbps]. The trade off and capability of each variation of xDSL technology is well known in the art.
The transmission from a Distribution center (DC) to a subscriber is termed “downstream” and the transmission from a Subscriber to the DC is termed “upstream”. The system is asymmetrical when the upstream and downstream bandwidths differ. The system is symmetrical when the upstream and downstream bandwidths are equal. Both symmetrical and asymmetrical xDSL services are in use. The upstream and downstream services are carried over either a single twisted pair copper wire, termed duplex transmission, as is ADSL, VDSL and are carried over multiple pairs of twisted pair wires as in HDSL, termed dual-duplex transmission.
The DSL technology uses a variety of modulation techniques, such as, Two binary one quaternary (2B1Q), Carrierless Amplitude and Phase modulation (CAP), Discrete Multitone (DMT) and Quadrature Amplitude Modulation (QAM). These modulation techniques are standardized by the international standards bodies and are well know in the art.
Narrowband signals such as voice signals are frequency multiplexed with the broadband signals. These multiplexing techniques are well known in the art.
Thus, the DSL technology allows data, voice, and video to be transmitted simultaneously over standard twisted-pair copper wiring at multi-megabit rates, to form a complete converged communication network.
In a typical DSL based network, the Digital Subscriber Access Concentrator (DSALM) and switching equipment is located at a DC. The subscriber equipment such as a DSL modem is coupled to the DSLAM by twisted pair copper wires.
The direct wire service limits the bandwidth of the chosen xDSL service. Typically, less than 6 Mbit upstream and 760 kilobits upstream data can be transmitted up to a 18 Kilo Feet. This distance reduces to 1,500 ft to services over 25 megabits. These xDSL technology dependent limitations are well known in the art. The Other factors such as line impairment, bundling of wires in a binder group, Load Coils, stubs either makes it impossible or adds further limitation to the distances of the services.
Several techniques such as improved xDSL signals, mid-span repeaters and loop extenders are being tried in the art.
Digital Loop Carrier (DLC) have been in use to overcome the high cost of adding new copper wires either to overcome the impairments or to meet growing service demands of telecommunication services. These DLCs are typically used to provide Voice lines from an Out Side Plant (OSP). A high capacity link carrying multiple voice lines such as T Carrier system or OC3 line is used from the DC to a DLC located at remote site. At the DLC Plain Old Telephone Services (POTS), service is derived and distributed to subscribers. However, these high-speed links are not able to carry xDSL signals, to offer combined broadband services.
To serve these subscribers with broadband services, DSLAM or Remote Access Modules (RAM) are being used. These remote systems are either located with in the DLC cabinet or housed next to the DLC in another Outside Plant equipment cabinet. The xDSL signal generated at the remote systems is additionally frequency division multiplexed with Voice at the DLC and distributed to subscribers.
Newer DLC equipment that can house the DSLAM line cards with in the DLC cabinets are also in use.
For these solutions, the xDSL Processing Electronics needs to be at the remote site requiring: Out Side Plant environment hardened equipment, Space, Network Management System, Power and Maintenance.
A subscriber can be served by high bandwidth transmission capable media such as Fiber from DC all the way to the subscriber location. However, it is extremely costly to connect every user with high bandwidth media.
Commercially practical alternatives using, combination of fiber cables feeding neighborhood Optical Network Unit (ONU) and subscriber connected by existing or new copper from the ONU, are being discussed in the art. This topology is called Fiber to the Neighborhood (FTTN). This topology also encompasses Fiber to the Curb (FTTC) with short drops of copper to individual subscriber or Fiber to the Basement (FTTB), serving tall buildings with vertical copper drops to individual subscribers.
It would be desirable for FTTN networks to make use of the DSLAM equipment and or include the present DLC served subscriber.
It would be desirable for FTTN networks to reduce the processing electronics like remote DSLAM or RAM, Line cards or ONU, which add electrical power, space, service provisioning and maintenance complexity.
It would be desirable that such a network to deliver variable bandwidth connections and multiple types of service to the subscribers, to deliver the voice, Data and Video services, using twisted pair copper, multiple twisted pair copper, coaxial cable, free air or fiber media.