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1、Fiber Access NetworkA Cable Operators PerspectivebyJohn A. Brouse, Jr.Director of Network ImplementationCharter Communications, Inc.IntroductionDuring the late 1980s, cable television operators in the United States reached a critical point where bandwidth demands and physical extensions to their coa
2、xial-based, tree and branch service delivery networks stressed the technical limits for signal quality and platform reliability. In response to the cable operators demand for a solution that addressed both signal quality and reliability, the industry looked toward adapting existing fiber optics tech
3、nologies to accommodate frequency division multiplexed analog video distribution. The initial application of broadband fiber based platforms was targeted to simply reduce the cascading effects of active electronic devices. Within a short time, the cable industry migrated fiber beyond this initial ap
4、plication and considered other services beyond traditional broadcast video. As other economic forces emerged, such as the launch of direct broadcast satellite service and the threat of telcos entering the video market, cable operators recognized the need to evolve their networks to support two-way i
5、nteractive services and growing customer expectations. The result was development of a hybrid network which integrated fiber optic cables and devices with coaxial cables and RF based devices as a function of service based network requirements. This architecture was named the Hybrid Fiber-Coax (HFC)
6、network and moved fiber closer to the customer, usually supporting service groups of 500 homes or less. The current list of services which the cable television multi-system operator (MSO) is offering include traditional video entertainment, video on demand, high speed connections to the Internet, lo
7、cal and long distance telephony, with many more in development. While deployment of the HFC network has certainly been the principal enabler for these high end two-way services, it has not adequately addressed nor resolved other operational issues now coming to the forefront. Todays two major concer
8、ns areq escalating outside plant operation and maintenance costs negatively impacts cash flow growthq evaluating and readying outside plant for new service launches negatively impacts product time-to-marketBringing broadband to the homeGeneva, 19 November 2001 Two major building blocks for all-optic
9、al networks have been agreed by the International Telecommunication Union with the adoption of two draft new global standards for increasing the efficiency and survivability of optical fibre access networks based on Passive Optical Network (PON) techniques. The draft new standards are designated ITU
10、-T Recommendations G.983.4 and G.983.5.A passive optical network (PON) is a system that brings optical fiber cabling and signals all or most of the way to the end user in residential and new small/medium business networks. Depending on where the PON terminates, the system can be described as fibre-t
11、o-the-curb (FTTC), fiber-to-the-building (FTTB), Fibre To The Cabinet (FTTCab), Fibre To The Office (FTTO) or fiber-to-the-home (FTTH). Passive Optical Networks (PONs) utilize light of different colours (wavelengths) over strands of glass (optical fibres) to transmit large amounts of information bet
12、ween customers and network/service providers. The passive simply describes the fact that optical transmission has no power requirements or active electronic devices once the signal is going through the network. With PONs, signals are carried by lasers and sent to their appropriate destination by dev
13、ices that act like highway interchanges, without the use of any electrical power, eliminating expensive powered equipment between the provider and the customer. PONs offer customers video applications, high-speed Internet access, multimedia and other high-bandwidth capabilities.Although the techniqu
14、e of PONs has been known for around 20 years as an alternative to traditional wire pair and coaxial cable, it is only now, with the need for fast internet access, that they are looking attractive for mass deployment in, for example, new building developments. Line rates are up to 622 Mbit/s in both
15、the upstream direction (customer to network/service provider), and the downstream (network/service provider to customer) direction over three to four orders of magnitude (or 1,000 to 10,000 times) faster than a state-of-the-art modem which provides for network access at up to 56 kbit/s. In addition
16、to speed, another advantage of optical technology is that it is flexible and is expected to require less maintenance than older cable technologies. Moreover, the costs of fibre and much of the equipment located with the service provider is shared among several customers, making it more cost-attractive.Because PON is independent from bit rates, signal format (digital or analogue), and protocols (SONET/SDH, Internet Protocol, Et
