Abstract: Requirements on detection technology are examined from the system and economic perspectives. The two possible detection approaches, direct and coherent, are described, and their theoretical detectability limits are considered. Examples of both types of networks that have been demonstrated are presented. Direct detection networks are then considered, and examples of demonstrated networks are presented. The same is then done for coherent networks. The relative advantages and disadvantages of direct and coherent networks are discussed, and it is concluded that for some time to come, direct detection will be the solution of preference, particularly for networks. >

Abstract: The use of fiber-optic links to reinforce the coaxial network by reducing the average number of series-connected repeater amplifiers is compared with an evolutionary tapped-fiber approach based on a tree-and-branch network structure. This latter strategy utilizes fiber transmission all the way to the curb in a shared architecture that yields a high degree of granularity and then uses the resultant segmentation to provide greater effective bandwidth through selective switching. The advantages and limitations of both approaches are examined. A representative tapped-fiber topology and ultrawideband fiber-reinforced systems are considered, and their advantages and limitations are discussed. Hybrid broadcast/switched tapped-fiber and a hybrid broadcast/controlled access/switched system are also examined. Some options for service expansion are briefly described. >

Abstract: The history of cable television in the US is reviewed. The opportunity for reuse of frequencies assigned for other purposes in the over-the-air environment is discussed in the context of the crowding of the radio spectrum. The problem of loss in coaxial systems is briefly examined. The tree-and-branch topology used by cable systems is described. Signal quality issues are addressed. Tradeoffs in cable system design and cable system economics are discussed. >

Abstract: The relative strengths of optical and electronic technology are discussed with a view to identifying the optimum mix applicable at the discrete logic gate or chip level. It is proposed that an optimum high-speed processor should be partitioned into synchronous electronic islands, interconnected by optics. The use of free-space optical wiring and its limitations are discussed. The characteristics required of optoelectronic interfaces are delineated. A self-routing switching matrix is considered as a test case for the hybrid optoelectronic approach. By partitioning the complex self-routing circuit in the manner described, all the electrical pathways are very nearly equalized, favoring very-high-bit-rate operation. Information flow is also very streamlined. >

Abstract: Recent research into optical amplifiers and their future applications is described, focusing on the erbium-doped fiber amplifier. The characteristics of the amplifiers are briefly described, and their use in long-haul transmission systems, undersea transmission systems, optical frequency-division-multiplexed systems, subscriber loops, and functional circuits is examined. Their potential role in broadband communication networks is briefly considered. >

Abstract: A forecast is provided of the cost of realizing an all-fiber network. It is based on the successful histories of fiber penetration into the trunk and feeder networks and is intended to help build a framework against which local or regional strategies for network evolution can be tested. Starting with the early trend data for fiber to the home (FTTH), the pattern for the complete conversion of the lop network to fiber is estimated. No attempt has been made to factor in the impact that greater demand for broadband, particularly in the business sector, may have in accelerating the process; the impact of unforeseen new technologies in reducing costs; or the effect of the European and Asian markets in driving down costs. The results do, however, suggest a smooth transition to broadband as part of the normal improvement and evolution of the network, with a time-frame consistent with other views on the evolution of broadband. >

Abstract: The advantages of heterodyne detection are reviewed, and a historical summary aimed at showing that this technology is on track toward increasing commercialization over the next five to ten years is given Solutions to many important problems are described, and the remaining problems are examined Heterodyne detection is briefly compared with an alternative technique using direct detection, and a reasonable evolutionary path toward the incorporation of heterodyne techniques in various types of communication systems is discussed >

Abstract: Design considerations for capacity expansion are described, and requirements for photonic switch matrices, optical memories, and tunable-wavelength filters are examined. The present status of photonic switching devices and system experiments is discussed, covering space-, wavelength-, and time-division switches. Hybrid switching systems and coherent optical detection are considered as examples of system technology that will facilitate line capacity expansion. >

Abstract: The design of a broadband central office (CO) switch based on the SONET standard and the asynchronous transfer mode (ATM) protocol is addressed. An overview is given of the next generation switch (NGS), which has been proposed as a functional architecture for broadband networks and switching systems. The NGS consists of a number of different functional modules (interface, control, operations, service, and fabric), interconnected by open interfaces, that together form a high-speed large-throughput switching system. The interface modules and fabric modules, which embody some of the more difficult technological problems encountered in realizing terabit-per-second switches, are examined in detail. >

Abstract: Current CATV broadband networks are described, and a simplified model of these AM systems is given. AM systems performance metrics are examined from a CATV perspective. Noise sources are summarized, and the effects of intermodulation noise and laser nonlinearity are discussed. It is shown that the rigorous signal quality objectives associated with the CATV trunking application can, in principle, be satisfied with lightwave technology. The successful transmission of 42 carriers over 12 km of fibre while maintaining a C/N of 52 dB and composite distortions of less than -70 dBc is reported. >

Abstract: A broadband fiber network that provides voice, data, and switched-video services to residential subscribers is described. To achieve low installed costs, the proposed network takes advantage of recent advances in broadband electronic switching, subcarrier multiplexed broadband fiber transmission, and passive optical splitting, and uses a fiber-to-the-curb topology. The network is designed to provide high-quality broadband services while simultaneously achieving low installed first costs and affording graceful migration to high-definition television and digital video, and finally to broadband integrated services digital network (BISDN) services. >

Abstract: The evolution of standards and link specification methodology, spurred by the rapidly increasing interest in utilizing fiber-optic local area networks (LANs) and metropolitan area networks (MANs), is summarized. Issues that interrelate LAN and MAN architecture, protocol, and fiber-optic link performance are examined, particularly as concerns information transfer modes, framing, and overhead. The internetworking of LANs and MANs is discussed. The impact of architecture and protocol on link performance is addressed; receiver and link dynamics, the use of data scrambling versus block coding, clock distribution, and link error statistics are considered. A methodology for fiber-optic link specification that accounts for distortion and jitter is defined, and link analysis is discussed. Directions for future standards development are indicated. >

Abstract: The competitive forces that are motivating the cable industry to change are examined. The prominent sources of competition discussed are direct broadcast satellite, multichannel multiport distribution service, and the telephone companies. The characteristics of the two transmission media offering realistic choices for the delivery of video over a terrestrial network, namely, coaxial cable and optical fiber, are described. Fiber-optic supertrunks used in the cable television industry for point-to-point delivery of video signals and the tree-and-branch architecture used in current cable systems are also described. An evolutionary concept for the integration of fiber into cable systems, called fiber backbone, is presented. It consists of overlaying most of the existing trunk system with optical fiber cables. A direct passive optical fiber path is established from the headend to a number of feed points in the cable television distribution network. At these points, broadband multichannel information is converted from the optical back to the RF broadband domain, and, from that point on, the existing coaxial plant is utilized. The design and implementation of such a hybrid system are discussed. >

Abstract: The development of a specification for a standardized optical interface, the synchronous optical network (SONET), is described The initial project goals, most of which were accomplished with the release of the initial SONET specifications, ANSI T1105-1988 and ANSI T1106-1988, are discussed ANSI T1105-1988 contains specifications for the rate and format of the SONET interface ANSI T1106-1988 contains the optical parameter specification needed to complete the interface specification Differences between the SONET standard and other interface specifications are examined The CCITT standardization effort and its relationship to SONET are considered The second and current phase of SONET, namely, the development of a standard for communicating operations support information across the data communications channel, is described Related standards activities are summarized, and plans for future SONET standards are outlined The likely network impact of the planned evolution of the SONET standard over a number of years is assessed >

Abstract: The history of cable television in the UK is briefly summarized, and the current communications environment is described, focusing on the factors affecting the provision of broadband services. Existing cable television technology in the UK is examined. The modern networks that have adopted a conventional tree-and-branch framework have typically been built as 450-MHz systems (or are under consideration for upgrade in this level) with a capacity for 30 channels, adequate for the presently available program sources. The latest systems are looking to 550 MHz, to allow for future expansion; such a network might carry 34 PAL channels and 6 MAC channels at maximum capacity. For the most recent franchise awards, the 860-MHz systems are now a consideration. Some switched star networks, aimed at allowing interactive services, have also been built. The likely course of development of cable television in the 1990s is outlined, and the three network types that seem to be the main contenders-coaxial tree-and-branch, distributed-star, and passive optical networks-are discussed. >

Abstract: The likely direction for broadband switching evolution is reviewed to determine areas of application for optical technologies. The traffic characteristics of services available on broadband networks are examined, and the requirements they place on switching are discussed. Particular attention is given to the use of asynchronous transfer mode (ATM), which provides access and switching for services with a much wider variety of bit rates, connection holding times, and burstiness than other forms of switching. The limitations of electronic switching components are discussed, and opportunities for optical technology in future terabit-per-second throughput ATM switches are identified. >

Abstract: The current direction Bellcore is pursuing in the development of proposals for fiber-in-the-loop (FITL) system generic requirements is reviewed, and it is shown how the necessary tradeoffs are likely to be resolved. The reference model to be used in developing requirements for delivery of existing services and new services through FITL systems is discussed. The FITL system is defined in terms of the three external interfaces it must meet with the customer, the fiber-optic distribution network, and the larger Bellcore client company (BCC) transmission and operations networks. This reveals where innovation and product evolution can most profitably focus. Additional technical constraints that tend to narrow the technological and architectural choices available and set certain common directions for FITL systems are summarized. A generic interface between FITL systems and the larger BCC networks is proposed, and considerations for intervening transport and crossconnect systems are examined. >

Abstract: At issue in the delivery of broadband cable television services is whether their promise will be realized through the adoption of a revolutionary switched distribution system or an evolutionary upgrade to the existing broadcast, tree-and-branch coaxial cable television systems. This issue is examined in the context of the key factors of economics and consumer demand. Architectural objectives established to satisfy likely cable television system requirements five to ten years in the future are highlighted. A high-quality switched video system optimized for the likely cable television requirements of the later 1990s is described, both as conceptualized and as proven in the laboratory. The headend, switch and upconverters, optical link, tap, set-top unit, and link performance are described, and laboratory results are presented. Hurdles standing in the way of large-scale commercial viability are identified. >

Abstract: A future integrated broadband network that can deliver video to the home is discussed. The data component of the network is not addressed; the focus is on the transport, distribution, and switching of video services. The impact of advancing technologies, changing economics, and dynamic market forces on the network's development is considered. The system is envisioned for the year 2000 and beyond. Although digital distribution of video to the home is technically possible today, it is not yet economically feasible. The benefits such a system offers to the consumer are examined. >

Abstract: The overall topology of the AT&T fiber to the home (FTTH) system is reviewed with particular emphasis on power. The focus is on the issues that arise in powering the customer end of the fiber, i.e., the distant terminal. It is shown that flexible power arrangements are required for distant terminals in the fiber system in the local plant. Architectures must be able to accommodate local exchange carrier preferences for AC or DC pedestal operation. The system must readily accommodate new as well as existing applications in growth areas and also rehabilitation applications. >

Abstract: Results obtained with analytical models of erbium-doped fiber amplifiers (EDFAs), which have potential as repeaters in lightwave transmission system, are summarized. The results pertain to the dispersion and noise characteristics of the amplifiers. Experimental results that verify some of the analysis are examined. The results show that EDFA systems are promising for undersea applications. Large dispersion penalties can be avoided by using dispersion-shifted fiber and transform-limited pulses placed close to the fiber's zero dispersion wavelength. Noise can be controlled by optical filters between the amplifiers or in front of the receiver, or both. >

Abstract: An innovative distributed queue dual bus (DQDB) concept for media access control is the subject of a standardization effort by IEEE Subcommittee 802.6, which has been assigned the task of developing a standard to meet metropolitan area network (MAN) requirements. A unique characteristic of the DQDB standard that differs from the other IEEE 802 (local area network) standards is its intent to support a relatively large set of physical layer interface rates. The viability of the large variety of rates and formats is permitted by physical layer convergence procedures (PLCPs), which provide adaptation functions between a single common DQDB layer and the supported transmission systems. An overview of the dual bus structure of a DQDB subnetwork and background information on the DQDB layer services are provided. The PLCPs are defined in more detail, and the PLCPs for public network transmission systems and customer premises extensions are examined. An example of a stable DQDB subnetwork that experiences a link failure is described. >

Abstract: In July 1989, Southern Bell began deploying a fiber access system capable of carrying 54 cable television (CATV) channels, as well as plain old telephone service (POTS) and integrated services digital network (ISDN) services in Heathrow, Florida. Four areas that must be addressed before these services can be successfully deployed in volume are discussed. They are integrating narrowband and broadband services on the same fiber, choosing a fiber architecture, designing the optical-network interface for multiple services, and designing a centralized digital video-selector switch. >

Abstract: Demands that must be met if cable system network architectures in urban centers are to adequately meet the transmission requirements of the next decade and provide an infrastructure for new revenue-producing transmission services are addressed. An upgrade, using fiber-optic technology, to an initial architecture based on current coaxial technology, utilizing high-performance feedforward configured trunk-line amplifiers, multiple AM microwave links to distribution nodes (hubs), backup supertrunks, and other conventional approaches, is described. The architecture adopted is explained, focusing on hub deployment. The requisite very-high-capacity, high-reliability feeder design is discussed. >

Abstract: Component, system, and network reliability are examined. With respect to component and system reliability, device operating temperatures (which could extend down to -40 degrees C in the winter or up to +85 degrees C in the summer) demand extraordinary attention to basic design and manufacturing reliability-assurance practices. Reliability of the telecommunications network, including the loop segment, is often described in terms of availability, which depends on several factors: network architecture, including media redundancy; system architecture, including hardware redundancy or protection switching; hardware and software reliability; and time to repair failures. The problems faced in dealing with each of these factors are discussed. >

Abstract: Common supertrunking practices employed in transmission system design are discussed. To provide a basis for appreciating the issues, a brief description of current trunking is provided. Approaches introduced recently in preparation for the introduction of high-definition and extended-definition television (HDTV and EDTV) and the resulting need for greater signal-to-noise ratios and wider bandwidths are covered. >

Abstract: The potential of photonic integrated circuits (PICs) for meeting the requirements of high-connectivity optical communication architectures (where there is a variety of cascaded, interconnected optical devices at each station) at a reasonable cost is discussed. PICs refer to the monolithic (single-substrate) integration of optically interconnected guided-wave devices. PIC technology replaces the separate, sequential alignment of single-mode fiber interconnections between the discrete devices with lithographically produced single-crystal waveguides, eliminating the cost of individual alignments through a wafer-scale batch process and providing a lower-loss connection, a low-reflection connection, and a very robust, small package. To illustrate the application of PIC techniques, a balanced heterodyne receiver, a wavelength-division-multiplexing source, and tapered waveguide output couplers are considered. >