Optical fiber technology is firmly established as an economic preference for long-haul and interoffice telephony transmission applications. For the local network, fiber optics has been less pervasive to date, primarily due to the issue of return on capital plant investment. The fiber optics market growth for telephony has been relatively flat for the past few years while the industry has pondered ways of penetrating the network for local services distribution. Having proven itself in high performance usage, such as long distance and high capacity trunk routes, fiber optic systems must now evolve to meet the "Local Loop Challenge". The migration of fiber from the local switching office or wire center toward the home has been slower than many had hoped, but according to the number of field trials (at last count 12-15 in the USA alone) there is a significant commitment by the Operating Telephone Companies to the implementation of such systems. Perhaps the state of the market for fiber optics in local applications can be compared with the evolving ISDN (integrated services digital network) environment. The core technology readily exists, yet there is debate among the industry as to the form the applications of the technology will take. Thus these local loop trials are intended to help the industry identify the most promising services and architectures for the subscriber network.

High power 1300nm edge emitting LED's (ELED) will be required for spectrally sliced optical transmission systems. However, wavelength shifts caused by variations in ambient conditions and drive current will cause a degradation in system performance. We show that using current technology wavelength division multiplexers the use of uncooled transmitters causes a reduction in operating margin of 50% in a four channel system and that significant performance limitations occur when operating with multi-level line codes.

Presently, single mode optical fiber technology is being utilized in systems to supply telephone service to the subscriber. However, in an attempt to be competitive with copper based systems, there are many development programs underway to determine the most cost effective solution while still providing a service that will either satisfy or be upgradeable to satisfy the demands of the consumer for the next 10 to 20 years. One such approach is to combine low cost laser transmitters and silicon receivers, which have been developed for the "compact disc" industry, with fiber that operates in the single mode regime at 1300 nm. In this paper, an optical transceiver will be presented, consisting of a compact disc laser, a silicon detector and a single mode coupler at 1300 nm. A possible system layout is presented which operates at 780 nm bi-directionally for POTS and upgradeable to 1300 nm for video services. There are several important design criteria that have to be considered in the development of such a system which will be addressed. These include: 1. Optimization of coupled power from laser to fiber while maintaining stable launched conditions over a wide range of environmental conditions. 2. Consideration of the multimode operation of the 1300 nm single mode fiber while operating in the 780 nm wavelength region. 3. Development of a low cost pseudo-wavelength division multiplexer for 1300 nm single mode/780 nm multimode operation and a low cost dual mode 50/50, 780 nm splitter using 1300 nm fiber. Details will be given of the design criteria and solution in terms of optimized design. Results of the performance of several prototype devices will be given with indications of the merits of this approach and where further development effort should be applied.

A novel optical distribution system suitable for providing a large number of channels is proposed. Its characteristics are theoretically analyzed and experimentally examined. In this system, 150 Mb/s digital HDTV channels are time and wavelength multiplexed on a single mode fiber by an optical star coupler and distributed to each subscriber. Each subscriber selects one HDTV channel using an acoustooptic tunable wavelength filter and an electrical time-slot selector. This system can easily provide a large number of HDTV channels, since it simultaneously utilizes two multiplexing dimensions. In addition, the acoustooptic tunable wavelength filter, a key device in the system, is a stable and well-established device. The loss and crosstalk characteristics of the acoustooptic tunable filter are theoretically analyzed by Gaussian beam approximation. They show that one system can distribute 320 HDTV channels to 256 subscribers with a minimum wavelength spacing of 2 nm. An experimental 12 channel( 4 time division x 3 wavelength division) system with a wavelength spacing of 20 nm in the 1.3 μm region demonstrates that it can operate a data rate of 1.2 Gb/s with only 4dB loss and 20 dB crosstalk at the tunable filter. The access time to select one channel is 4 Rs . The minimum optical power at the optical receiver is 30 dBm, which means that this prototype can handle 256 subscribers. The experimental loss and crosstalk characteristics agree well with the theoretical analysis.

Design philosophy of a fiber optic transmission line terminal circuit (LTC) module for digital subscriber loops is described. A small, cost effective LTC module has been developed that realizes a 52 to 156 Mb/s fiber-to-the-home system. The salient points are ; various combinations of LDs and PDs/APDs can be used to match the subscriber line length requirements, CMI or scrambled NRZ line codes can be used, the module is suitable for single mode fiber (SMF) or graded index fiber (GIF) cables, high density LSI techniques can be used to develop single chip components. The volume of the contructed module is 92.6cm3 with a dispersion power of 3W. A single low power IC chip has been developed that includes decision and timing circuits. Thus timing phase adjustments are not needed. Differential amplification created between the pre-amplifer IC and the main amplifier IC is employed to yield a high common mode rejection ratio and suppress the effects of external noise. The double loop of the auto-power-control (APC) for the LD is adopted to separately control the d.c. bias current (Is) and the pulse modulation current (Ip). The CMI-CODEC-IC is fabricated by a Bi-CMOS process. It includes a PLL circuit that doubles input clock frequency for CMI signal coding. The CMI line code can be adopted to maintain bit sequence independence, facilitate hardware implementation of the timing-extraction circuit, and prevent bit errors caused by received optical power fluctuations. Received optical power fluctuations can happen when fibers are manually handled during cable installation or mid-span branching.

In this paper, we study the effect of three fiber geometrical parameters- cladding diameter, cladding noncircularity, and core concentricity error- on two generic types of splicing or connectorization systems. For the first geometry, based upon a cylindrical ferrule, the cladding outside diameter is the most important single parameter, and the performance of the splice can be improved significantly if the width of the distributions of cladding diameters can be reduced. The second geometry, based upon a multifiber array splice, is more sensitive to cladding noncircularity. For both types of splices, the core concentricity error is relatively unimportant.

Various techniques for restricting the bandwidth of a single mode fiber are discussed. The limitations of a fiber optic delay line bandwidth limiter are addressed and several alternatives proposed.

The last road-block to unlimited bandwidth service to the customer has fallen with the introduction of fiber cables into the distribution plant. AT&T's Fiber-To-The-Home system, which first went into residential service in New Jersey Bell in August 1988, is a new feature of the SLC® Series 5 Digital Loop Carrier System. The architecture of SLC Series 5 has been extended from a fiber feeder only system to include fiber cable in the distribution plant, both fiber distribution cable and fiber drop cable. Immediately following the first cutover, three other SLC Series 5 Fiber-To-The-Home systems in Southwestern Bell, South Central Bell and CONTEL of California were turned up and placed into service before the end of 1988. The SLC Series 5 Fiber-To-The-Home architecture has been developed to be upgradeable from a POTS only vehicle to a wide-band service vehicle, with a minimum of reconfiguration. This all fiber network will position the Local Exchange Carriers to provide wide-band services in an economical manner, and set the stage for tomorrows intelligent network, where higher bandwidth services will be needed.

Midspan branching of metallic cables has been performed extensively, largely because of the ease of connectorization of metallic cables. Now that metallic cables are being replaced by fiber optic cables, midspan branching of fiber optic cables has become important. This report considers various methods of midspan branching of fiber optic cables. The optimum cable system for ease of midspan branching was selected based on the optical cable structure, minimum fiber length needed at a splice and the Performance of the mechanical splice itself.

An experimental shared fibre access system for subscriber loop application is described. The system known as MACNET, involves the use of a passive optical coupler located in the street near the cluster of customers served by the network. The experimental system was designed primarily for the delivery of narrowband telecommunication services but the overlay of distributive video has also been demonstrated. The successful development and the experience gained from the experimental system has led to detailed studies for a trial system based on the provision of a fixed access capacity. A particular implementation of this trial system is discussed, as well as an overlay for bi-directional video transmission.

The Broadband Integrated Services Digital Network (BISDN) is a new concept for exchange area communications. Based on lightwave technology, high-speed circuit and packet switching, and intelligent networking, BISDN will integrate services such as voice, data, video, LAN (Local Area Network), and MAN (Metropolitan Area Network) under the same umbrella as POTS (Plain Old Telephone Service). Among various components of the BISDN, the cell-based ATM (Asynchronous Transfer Mode) multiplexing technique is a powerful vehicle for providing integrated services effectively. Among various services envisaged for BISDN, high-quality video may be the most attractive new service for the majority of residential customers. Therefore, the digital coding of high-quality video signals in a form suitable for transmission through the proposed BISDN network is of great interest and importance. The coding of ATV (advanced television) for digital transmission is of particular importance since it may represent the most viable means for avoiding transmission impairments and delivering very high image quality. The target rate for the coding of the ATV signal is the currently proposed CCITT H4 rate of roughly 135 Mbps, which is the BISDN payload of the SONET channel. In this paper, we review the structure of the BISDN and effective digital coding of ATV at about 135 Mbps. We also address issues related to transmission of compressed ATV over the cell-based ATM networks.

Today, it's not easy to find a telecommunications publication that doesn't have a feature article on fiber to the home. Not only do these articles appear in telecommunications publications but in newspapers like in the Wall Street Journal and USA Today. What concerns me about these articles is the immediate emphasis on CATV and video on demand services. Fiber is indeed a broadband transmission medium. However, from BellSouths point of view, the video services are not necessary to the economic equation for placing fiber to the subscriber. Our objective is to place fiber in the network for POTS like services first and upgrade the electronics based on customer demand.

1.01 In early 1987, Fujitsu began the development of the second generation low capacity lightwave multi-plexer. This product was to be an integral part of a loop electronics package, which included a new generation of Fujitsu Digital Loop Carrier (FDLC), two new outdoor cabinet designs, a Ti Extension Shelf (TEXT) and the Fiber Loop Multiplexer (FLM).

Recognition of the impact of the emerging North American Standard for building wiring is growing rapidly. The standard-ization of topology, distances, media, number of crossâ€"connects and connector loss define a physical and performance template for the design of future communication systems. A study was completed in June 1989 by ISO/IEC, JTC 1, SC 25 which proposes that work commence on an International Standard for building wiring. This paper describes the building wiring standard and addresses the use of fiber in the backbone and to the desktop.

In recent years the reliability of optical fibers in special environments has become of great concern in military, government and other specialty high performance applications. With the first exploratory installations of fiber-to-the-home confirming the inherent requirements for a robust optical fiber, the telecommunications market and operating companies have had to begin considering how to minimize long term maintenance of optical fiber systems, which are subjected to a much broader range of dangers than in long haul or station to station installations. This paper discusses some background information on the strength and fatigue of optical fibers/cables, their reliability issues and several points concerning design and lifetime predictions for such components/systems. It includes information on standards efforts in fiber reliability and environmental testing as well as on SPIE efforts to present up-to-date information on these topic areas. Its intent is to point out problem areas for long term maintenance and present current approaches to minimize these problems rather than present solutions.

During the late '70s and early '80s two exciting communication technologies evolved. One was a network technology dealing with computer integration called Local Area Networks (LAN), and the other was a transmission media, fiber optics, which offered data integrity in addition to increased transmission speed and distance for the data communication network. Local Area Networks are designed and installed to allow many different computing devices to communicate with one another. LANs, considered premise-based networks, provide high-speed reliable data communication within a specific geographical area such as individual buildings and/or campus environments. Advances in fiber optic communication technologies and a continued increase in business requirements for distributed data processing, offered by LANs, ironically set the stage for a natural relationship of the two technologies.

A new synchronization method called Synchronous Frequency Encoding Technique (SFET) is introduced. SFET can be used to recover the source clock frequency when an isochronous service is emulated on an ATM network. By taking advantage of the synchronization of the network, SFET recovers the source clock frequency almost instantaneously. Simulation shows that the recovered clock is independent of the network cell jitter and has jitter performance comparable to that of the present network.

The actual and future B-ISDN situation is described, together with the field trial of IBIS in JAPAN. The CCITT recommendation of B-ISDN is being published in 1989. The basic NNI (network node interface) of 155.52 Mbps is applicable for the video signal transmission, together with the audio service, N-ISDN service, POTS and other data information services. When the STM-1 signal is induced to the subscriber by optical fiber, the interactive and integrated service will be realized. The interactive and integrated service of field trial is being performed in Osaka Japan. The field trial of "IBIS", which will open up the way to interactive network, is now operating.

The SONET concept started with a method of synchronous multiplexing for high speed transmission. It was originally intended for transport of the most prevalent bulk transmission signal - DS3. The concept allowed most of the multiplexing and demultiplexing effort to be confined to low speed operations where CMOS could be employed for low cost and low power consumption. The concept was not allowed to remain at that level, but was expanded through the efforts of many participants in the T1X1 committee of Exchange Carriers Standards Association. SONET offers several important improvements over current transport concepts for the telecommunications network and should be viewed as the benchmark for the development and deployment of all future transmission products.

Integrated Digital Loop Carrier (IDLC) and Synchronous Optical Network (SONET) technologies have taken significant steps forward during the past year. There appears to be widespread consensus in the telecommunications industry on generic interface definitions for both IDLC and SONET network elements. Each of these technologies will respond to the mix-and-match needs of the telephone companies; IDLC in the area of integrated access and SONET in the area of optical interfaces. Individually, mix and SONET technologies should help to solve several of the immediate concerns of telephone companies. Together however, the synergy between the two technologies is opening up new opportunities for integrated access in feeder loop applications. The marriage of IDLC and SONET technologies has enabled a generic SONET-based IDLC interface to be defined. This paper reviews the status of that interface and discusses some of the integrated access opportunities it makes possible.

This paper discusses some functional requirements of a SONET (Synchronous Optical NETwork) 1 framer chip when used in an application for a 13-ISDN User Network Interface (UM), particularly the necessary physical layer Operations and Maintenance (O&M) capabilities which provide a basis for higher layer operations and maintenance functions. O&M functions include performance monitoring, failure state indications, and maintenance signals. This work is related to a SONET framer chip research prototype project at Bellcore, and the O&M functions described in this paper will be implemented in the framer chip.

The telecommunications industry has been in place in the US for over a century. The network needed to sustain the industry has evolved through several paths to be a good workable network. A new Synchronous Optical Network SONET is being defined to bring the best parts of the network together into one consistent set. Several features are provided which make maintenance part of the network rather than a separate entity. The maintenance features of SONET, taken together, provide new possibilities in unified maintenance philosophy. The set of these features will be referred to in the following discussion as a Continuous In-Service Virtual Loopback (CIVL). The key to this philosophy is the built-in non-blocking use of overhead to administer and maintain a network. The following discussion has been limited to the first level SONET signal. It has also been limited to a relatively narrow set of simple network examples. The principles can and should be expanded as work proceeds toward the implementation of the network.

In considering the deployment of fiber optics to the residence, two critical questions arise: what are the leading services that could be offered to justify the required investment; and what is the nature of the business that would offer these services to the consumer ? This talk will address these two questions together with the related issue of how the "financial engine" of today's television distribution infrastructure - TV advertising - would be affected by an open access system based on fiber optics coupled with broadband switching. On the business side, the talk concludes that the potential for open ended capacity expansion, fair competition between service providers, and new interactive services inherent in an open access, switched broadband system are the critical items in differentiating it from existing video and TV distribution systems. On the question of broadband services, the talk will highlight several new opportunities together with some findings from recent market research conducted by BNR. The talk will show that there are variations on existing services plus many new services that could be offered and which have real consumer appeal. The postulated open access system discussed here is visualized as having ultimately 1,000 to 2,000 video channels available to the consumer. Although this may appear to hopelessly fragment the TV audience and destroy the current TV advertising infrastructure, the technology of open access, switched broadband will present many new advertising techniques, which have the potential to be far more effective than those available today. Some of these techniques will be described in this talk.

Driven by the pace of technological innovation, broadband telecommunications services are being defined that will lead to a new generation of public telecommunications services over the next decade. The interrelated progress in standards forums on Broadband ISDN, IEEE 802.6, and SONET is leading to the definition of services that will be well-matched to serving an extremely diverse set of current and emerging communications applications. This paper will focus primarily on the Asynchronous Transfer Mode (ATM) of Broadband ISDN to show the remarkable potential of this approach. Two perspectives will be developed to facilitate the understanding and positioning of the public telecommunications services that will result: 1. applications span, and 2. telecommunications attributes. Much research and development remains before broadband services can be deployed pervasively. However, the key attributes of the long term vision show promise for the introduction of interim services both to validate the vision and to begin the transition to making these services a reality.

The FDDI standard provides a high speed optical channel for interconnection among mainframes and peripherals, and for use as a backbone network between lower speed local area networks (LANs). As FDDI networks move out of the data center environment, detailed engineering rules are required to construct and administer the dual ring architectures for building and campus applications. This paper examines generic building and campus layouts, and demonstrates the implementation of the logical rings within the star physical topology of the AT&T Premises Distribution System (PDS). A companion paper presents optical performance models to determine distance limitations of the cable plant for these networks, with or without optical bypass switches.' The networks addressed range from a single closet, to a single multi-floor building, to a campus involving multiple buildings. Standard interfaces to the distribution system are defined for each administrative location in the generic building layout. Uniform jumper configurations are specified for cross-connections among the interfaces, which form the network into a dual ring architecture. Using the design guidelines presented, networks of any size and configuration can be constructed which conform to the FDDI dual ring standard.

A loss budget model to predict optical performance of Fiber Distributed Data Interface (FDDI) type networks in the premises distribution environment has been developed. This model tailors existing statistical loss budget models to the FDDI standard. It is expected that as FDDI becomes popular, fiber based distribution systems will become common. When designing a fiber distribution system it is important to understand the constraints placed on link performance by the cable plant. To determine these constraints, the model is examined numerically using a large range of initial conditions. The total link length is used as the dependent variable. This set of initial conditions corresponds to an ensemble of possible link configurations. These link configurations are studied in the context of the premises distribution environment. The model is extended to include the use of optical bypass switches. Laboratory measurement data is presented to verify the accuracy of the bypass switch model. The extended model, including the bypass switch, is examined numerically for a similar set of initial conditions. These constraints are applied to the use of bypass switches in wiring closets, between floors, and at the work location. Distance limitations are determined for FDDI links utilizing optical bypass switches.

An interoperability test between multiple vendors using AMD's SUPERNETTM chipset in their hardware imple-mentations with vendor specific software implementing the protocols and services defined by FDDI. The various tests performed and problems encountered are presented. A brief introduction to FDDI and general definition of terms is provided. For more detailed information of FDDI, the reader is referred to the American National Standards documents specifying FDDI and Advanced Micro Devices "SUPERNET tm for Fiber Distributed Data Interface Articles" document number PID# 10062A.

The design of a Gigabit Local Area Network is discussed from the top down and from the bottom up. The needs of potential users of such systems are described and related to candidate implementation techniques. Then, the performance achievable with various algorithms are compared. Finally, implementation of signaling techniques suitable for use on fiber optic LANs are discussed.

The term Metropolitan Area Network lends itself to defining a constantly changing environment in which equipment must be able to survive and operate with a high degree of flexibility. This environment is naturally outdoors with a variety of climatic extremes. Equipment may often be sheltered thru burial or vault techniques, or be subjected to direct exposure in aerial installations. Typically, system distances exceed what we consider to be the Local Area Network envelope of 2 kilometers and extend out to 40 kilometers or more.

In today's fast-paced communications environment, a variety of alternatives are presented to users and standards committees. Two of these are Fiber Distributed Data Interface (FDDI) and Metropolitan Area Network (MAN). This paper examines the characteristics and uses of both.

Metropolitan area networks are intended to serve organizational sites scattered around a metropolitan area, interconnecting local area networks, large computers, and PBX's. Standards work under IEEE Project 802 is now nearly complete for the basic standard, which will be used in the Bell operating companies' SMDS service offering. Recent coordination with other standards bodies have provided a level of compatibility that will enable "seamless" integration with Broadband ISDN.

SMDS is a connectionless, high performance, public, packet switched data service which may be initially made available in the early 1990's by the Bell Operating Companies. SMDS will be able to interconnect computers, and Local Area Networks (LANs), including very high speed LANs such as FDDI networks, over wide geographical areas. This paper provides an introduction to SMDS, its features and some of its technical details.

The IEEE 802.3 10BASE-F Task Force is currently working on two approaches for 10 Megabit per second CSMA/CD networks using fiber optic media. The two approaches have distinct application spaces. One approach is based on Passive Fiber Optic Star technology, the other on Active Star technology. One standard, covering both application spaces, is expected sometime in 1991. This paper will summarize the proposals presented to the committee, and its predecessors, over the last two years. Three types of proposals were considered for the Active Star application space. These included CSMA/CD on a ring topology, an Active Star based on the Fiber Optic Inter Repeater Link, and an Active Star based on a synchronous signaling scheme. Three proposals were considered for the Passive Star application space. These included techniques for detecting collisions via special pulses, code rule violations, and amplitude sensing techniques. The paper concludes with a summary of the proposals being standardized by the 10BASE-F Task Force.

The approach that IEEE 802.3 10 Mbps Baseband Fiber Media (10BaseF) task force adapted is synchronous links wired in an active star topology. The synchronous link, the star topology, and the active star component itself contribute to a unique and optimal LAN performance that is suitable for backbone connections for other media (Ethernet, Cheapernet, et cetra) as well as for fiber local distributions.

In the last few years the IEEE 802.3 committee has developed fiber optics inter-repeater link standard called FOIRL. This standard defines the "Fiber Optics Media Access Unit" (FOMAU) which is used to connect two IEEE 802.3 repeaters that are up to 1Km apart. The IEEE 802.3 lOBaseF task force is currently standardizing a full F/O system in two directions: passive and active. The active approach is a compromise between the FOIRL (Asynchronous) approach and the Synchronous approach. As a result of this activity the IEEE 802.3 standard will define three different F/O interfaces and several devices that will not inter-operate. Such a standard will lower the credibility among the IEEE 802.3 user community, as customers will be confused amidst the many chapters and devices with no clear choice. This paper describes a method that can reduce the number of standards to two (passive and active), while proposing a solution for all the requirements of 802.3 F/O LAN. (The question of passive vs active approach will be discussed in this paper).

This decade has seen extensive use of fiber in the telephone network. Fiber is already pervasive in interoffice facilities, and is now being introduced into the local loop, which represents 90% of telephone circuit miles. In the feeder portion of the loop, the connection between the central office and remote terminals, fiber has already made significant inroads. In fact, Ameritech has more route miles of fiber in each of its five states than is in the entire network of the interexchange carrier whose advertisements stress their use of fiber.

Topologies for economically bringing fiber to the home are under investigation. This paper examines the outside plant (OSP) costs of five different fiber to the home topologies and compares them to the cost of existing copper topology for the delivery of telephone service to the home. The costs were analyzed for a newly built subdivision. The topologies include, two fiber star, one fiber star, splitter-star, active pedestal, and bus. The costs examined are for fiber optic cable, hardware, and interconnect devices. Topology costs are calculated from current and projected prices for fiber optic components. The calculations for each topology include the components from the connector in the Central Office (CO) or Remote Terminal (RT) to the connector at the home or pedestal for the fiber system. The component parts include terminating equipment inside the CO or RT, feeder, distribution, and drop cables, splices, connectors, cross connect, taper hardware, and pedestals. Electronics (opto-electric conversion at CO/RT and pedestal/home) costs and installation costs are not included in the analysis. Addition of electronics and installation costs for each topology will allow telco planners to determine the overall topology cost. The analysis reveals the active pedestal and bus topologies as the most efficient deployment of OSP equipment and suitable economic candidates for fiber to the home systems in the near term. Splitter based systems become viable later on and one fiber systems are possible if additional revenue is available.

This paper presents a technology and architecture perspective of the cost of evolving today's copper access network, optimized for POTS, to a fiber access network providing both narrowband and broadband services. Architectures are assessed using application studies based on cost models for actual routes in North America. This study identifies three architectures as serious candidates (i.e., close to copper in cost) for providing POTS service in 1992: the double star, the active pedestal and the star-bus.

To meet the challenges of the future telecommunications networks will consist predominately of single-mode optical fibre systems. Playing a leading role in realizing the full potential of this developing network will be the central switching nodes including trunk and local exchanges. However, to date there has been little general investigation into the interconnection medium to be used within the exchange environments and therefore there is the possibility that the full benefits of the external optical networks and current equipment modernization will not be fully effective due to the restrictions of the copper pair and coaxial interconnection architectures used. The most evident limitations of copper interconnections are: physical size and weight, small bandwidth (when compared with fibre), restricted transmission distances, EMI and EMC problems, limited networking opportunities, inflexible termination technology, and crosstalk between adjacent connectors and cables etc.

Redundancy in communication systems is vital for providing customer satisfaction and a cost effective network. If a line is cut in present systems, the traffic on that line must be routed to other channels while an emergency repair is made. If the operating company cannot provide the bandwidth to satisfy this rerouting, it must rent information capacity from its competitors. Presently, fiber is being installed in the metropolitan and subscriber loop networks, and consideration is being taken to provide redundancy in network reconfiguration to reduce fiber breakage problems. In a full duplex communication network, individual optical waveguides are utilized for transmission and reception of signals. Figure 1 illustrates a typical metropolitan network link from office to office. If a cable is severed by accident during construction work, discontinuity of service would result. When there are thousands of premium-paying customers at the other end of that cable, this situation can achieve crisis level immediately. In this paper details of a route protection or diversification scheme will be presented that will incorporate an intelligent fiber optic system that will automatically detect a cable fault and switch traffic to redundant fiber cables.

Two high speed data bus networks have been analyzed and compared to determine their relative performances with respect to throughput and message latency. The two networks are the SAE Linear Token Passing Data Bus and the SAE High Speed Ring Bus. Simulation programs were created to emulate the message passing protocols for each network and to generate a file of messages of random sizes and queue times for each station. The parameters used to generate these files were varied to simulate various bus loading conditions. The sensitivity of the buses was measured against such parameters as mean-time-between-message, message size, transmission rate, and number of message priority levels. Networks with different numbers of stations were simulated for each case. For each set of conditions the throughput and latency of the two networks were compared. The results of the analysis indicate that the latency of the ring is lower at light bus loading but as the loading increases the ring saturates more quickly than the linear bus, except in the case where the mean message sizes exceed 100 words.

Fibre optics will be introduced in the public subscriber loop network only for technical or economical reasons. In a model calculation the economical effects of fibre optics in the subscriber loop network are evaluated. Based on a single star shaped network a complete fibre optic subscriber loop solution is proposed.

An increase in demand for broadband services, coupled with a significant reduction in the cost of single-mode fiber (SMF) technology, makes the utilization of fiber optics desirable for subscriber loop applications.

To meet the near term requirements for narrowband digital services and to position our networks to meet the future demand for broadband services, the Local Exchange Carriers must begin to create an all digital, software controlled, switched network from Network Interface Network Interface. This paper discusses the transition to that all digital network.

The fiber optic cable and interconnection requirements for the subscriber loop are considerably different from interoffice outside plant needs. In general, the subscriber network will require higher fiber counts, significantly more interconnection and more frequent rearrangements. These unique needs demand products specifically designed for the subscriber loop. This paper discusses a complete fiber optic cable system and the economic considerations in designing this system. Optical fibers, high count feeder cables, "free access" (distribution) cables, drop cables, and multifiber connectors and multifiber fusion splicing are discussed. The performance of the various components and termination techniques are presented. This cable design, multifiber connectors, and multifiber splices have significant impact on reducing labor time and cost. Cost trends for this outside plant system are discussed. Particular attention is paid to the labor savings available because it is the major cost of any subscriber cable system.

This paper gives rules describing when to taper splice distribution cable and how many subscribers to serve from a service access point. It also describes a methodology for determining system maintenance charges for fiber loops .

Costs for active double-star fiber networks for local exchange service are compared with the costs of copper twisted-pair single-star networks and copper coaxial-line tree networks with switching at the customer's premises. For both existing and new neighborhoods, it appears that delivery of broadband services through tree networks (possibly using fiber) and delivery of narrow band services through copper twisted-pair star networks will be the minimum cost approach for low market penetrations of the broadband service market. For near 100 percent market penetrations there is relatively little difference in the costs of the two approaches.

In formulating strategy for installation of fiber facilities, the decision-maker should have a clear focus on policy developments which could affect his investment. This paper reviews developments as of August 1989 at the national level, and draws preliminary conclusions as to the implications for the industry.

Electric utilities are beginning to make heavy use of fiber for a number of applications beyond transmission of voice and data among operating centers and plant facilities which employed fiber on the electric transmission systems. These additional uses include load management and automatic meter reading. Thus, utilities are beginning to place fiber on the electric distribution systems which, in many cases covers the same customer base as the "local loop". This shift to fiber on the distribution system is due to the advantages offered by fiber and because of congestion in the radio bands used for load management. This shift to fiber has been facilitated by a regulatory policy permitting utilities to lease reserve capacity on their fiber systems on an unregulated basis. This, in turn, has interested electric utilities in building fiber to their residential and commercial customers for voice, data and video. This will also provide for sophisticated load management systems and, possibly, generation of revenue.

The provision of telecommunications products and services in the United States has been dominated by AT&T and the Bell System for more than one hundred years. From the early days of telephones, it was clear that some framework of logic was required to provide "universal" telephone services to the vast majority of American citizens. The concept was known as "natural monopoly", and for the most part, has served us well. We are all aware of statements concerning absolute power corrupting absolutely, and AT&T has not been immune to this law of human nature. Several times during the past century, action has been required by the Federal Government to regulate and constrain AT&T and the Bell System from anti-competitive and predatory actions. These have been called consent decrees, Computer Inquiry II, Computer Inquiry III, and the Modified Final Judgment. The regulations and constraints imposed upon AT&T, with good reason, are now becoming eroded. The perception of a more highly competitive marketplace capable of accommodating an unrestrained AT&T, the impact of uncoordinated national and regional government policies, and unilateral actions by AT&T themselves are bringing us to the edge of an abyss. There are substantial reasons to believe that AT&T will use its considerable might to eliminate its competitors, once free to do so. Must we be doomed to repeat history with still another antitrust case against AT&T some years from now? Logic demands that we learn from the past, and that telecommunications policies be based upon that knowledge.

An engineering cost model has been constructed to examine the economics of using fiber optics to upgrade existing coaxial cable networks in order to provide on-demand video service. Two fiber backbone alternatives have been considered: a mixed digital/analog subcarrier multiplexing system and a fully digital pulse code modulation, time division multiplexed system. The results suggest that to provide an on-demand video service, the cable company will have to depart from their traditional approach of employing a high degree of common plant and move in the direction of providing a dedicated channel for each subscriber. The extent to which common plant can be shared among multiple subscribers decreases in proportion to the increase in ODV usage, with correspondingly higher costs per subscriber. Model calculations suggest that serious economic barriers exist to realizing an ODV service through simple fiber backbone upgrades to existing cable networks.

Southwestern Bell Telephone Company (SWBT), the main subsidiary of Southwestern Bell Corporation, is the Bell operating telephone company serving five states; Arkansas, Kansas, Missouri, Oklahoma and Texas. It has more than 8 million customers, 60,000 employees and more than 5,000 work locations within its territory. It is a major corporation by anyone's standards.

Midland Group have determined that the objectives for technology infrastructure in new and refurbished office buildings are best satisfied by the use of point-to-point fibre optic cabling to each users desk. The costs are compared with alternative solutions, the business justification demonstrated and some implementation issues discussed.

Geographically distributed government and industrial organizations are being faced with an increasingly complex set of problems related to multi-media information flow between distributed functions, heterogeneous hardware and software environments, and unsophisticated (in terms of modern information system technology) user cultures. As we enter the decade of the nineties, the integrated answer to this set of problems is being identified as the Enterprise Solution.. While many of the recent technology advances in multi-media hardware and software address the technical aspects of the enterprise solution, significant progress has not been realized in the area of transferring that emerging technology to the user environment. This paper will address the issues related to the technology transfer process as well as the education and evolution of the user culture. It will also show how the MIS manager can play a significant role in both the technology transfer and culture change process.

"The nation which most completely assimilates high performance computing into its economy will very likely emerge as the dominant intellectual, economic, and technological force in the next century", Senator Albert Gore, Jr., May 18, 1989, while introducing Senate Bill 1067, "The National High Performance Computer Technology Act of 1989". A national network designed to link supercomputers, particle accelerators, researchers, educators, government, and industry is beginning to emerge. The degree to which the United States can mobilize the resources inherent within our academic, industrial and government sectors towards the establishment of such a network infrastructure will have direct bearing on the economic and political stature of this country in the next century. This program will have significant impact on all forms of information transfer, and peripheral benefits to all walks of life similar to those experienced from the moon landing program of the 1960's. The key to our success is the involvement of scientists, librarians, network designers, and bureaucrats in the planning stages. Collectively, the resources resident within the United States are awesome; individually, their impact is somewhat more limited. The engineers, technicians, business people, and educators participating in this conference have a vital role to play in the success of the National Research and Education Network (NREN).

High definition television is fast becoming a public interest in search for a larger clear vision television field of view. This paper discusses the past work and current prospectives of obtaining more detailed sharper television images and current options for implementation of HDTV.

Liquid crystal displays (LCD's) have developed from the original black on yellow calculator and watch products through many intermediate stages to the present generation backlit, black on white computer screens and full color, miniature televisions. The evolution of the technology is still continuing and promises to deliver larger and better displays which will open up many new application areas. High Definition Television (HDTV) liquid crystal displays are expected to be realised in the next decade.

Various levels of data transfer bandwidth allow for a variety of image transmission types and uses. The types of image transfer and interaction which are possible at each level of data bandwidth are characterized herein. Factors which affect the image which results from the transmission are govemed by issues such as image compression, as well as the possibility of local re-synthesis of portions of the imagery utilizing computing power which may be available at the destination. The ability to transmit varying qualities and types of images can be utilized for purposes ranging from still image transmission, to motion in portions of the image area, to various frame update rates of full screen moving imagery. The application of digital transmission to possible formats for HDTV are also explored.

The authors review data from cost analyses of fiber loop networks. It is argued that fiber in the local loop will provide cost-effective transport of services to about the T1 rate, making videophone and similar video services attractive and cost-effective in the near term. In contrast, it is suggested that fiber networks will not provide cost competition with coaxial cable TV networks for five to ten years.

Broadband systems, using well developed coaxial cable and amplifier technology are noted for versatility and flexibility. Networks of infinite variety may be assembled using couplers, taps and filters. Every signal is available simultaneously throughout the network. Intricate timing and switching schemes of high rate digital networks are avoided. Broadband long distance fiber optic systems became practical about 1983 when single mode fiber optimized for operating at 1300 nm became the fiber of choice for long haul digital telephone service. Removing the bandwidth limits imposed by multimode fibers, which had confined link limits to 6 miles and transmission rates to 45 Mbps, opened the way for development of systems transmitting at rates above 500 Mbps. At the same time development of laser diodes,emitting at 1300 nm,with excellent optic power, allowed extension of link distances to 25 miles and greater. Single mode fibers have been refined to have attenuation of less than 0.5 dB/km at 1300 nm. CATV operators had long sought ways of reducing the noise and distortion caused by repeated amplification in extending systems to new subscribers. Efforts at using fiber optic systems in the multimode era were relatively futile. 4 or 5 channels and 3-4 mile links using FM video modulation were all that could be achieved. With single mode fiber development these limitations were partially removed. In 1984, installation began of the present generation of FM modulated CATV fiber optic trunk lines. FM produces superior transmission at the greatest distance, but is quite expensive because of the cost of FM modulation and demodulation. Costs are typically in excess of $4,000/channel, with a practical limit of 16 channels per fiber. For distances shorter than 12 miles,FM is often considered too expensive.

Medical image communications is becoming a subject of interest within the telecommunications industry as a leading edge application for broadband technologies. In this paper we explore the communications requirements, and issues associated with with this application. We attempt to map both public and private communications solutions onto a variety of medical image communication scenarios and identify the opportunity for Broadband ISDN.

This paper describes an ongoing General Motors of Canada pilot project intended to resolve factory floor communication problems in the Oshawa, Ontario Car Body Assembly Plant. This was initially a university research and development project, but some results are being moved into the full production environment. We start by introducing the problems faced in computer integrated manufacturing (CIM) in general, and then concentrate on the specific problems encountered in the Oshawa plant. After this overview, we discuss the reasons behind using the Manufacturing Automation Protocol (MAP) Local Area Network and fiber optic media to solve these problems. The design philosophy and some technical aspects of these implementations are also included in this paper. There are several areas which need further work; we will discuss present efforts and future directions.

One Bell Center is a 44 story building in the heart of St. Louis. It is occupied by Southwestern Bell Corporation and Southwestern Bell Telephone Company. Today the building is totally occupied with about 4,000 people.

This paper will present an overview of the benefits and the emerging trends in fiber connectivity to the desktop environment. It will highlight the different application segments where that might be applied. It also addresses the cost issues of high speed connectivity in the desktop market.