Performance evaluation of access methods for Local Area Networks (LAN), can only be partially studied by the mean of classical mathematical methods. Random simulation, based on discrete events, can take into account all the specifications without simplifying them. A study of the simulation language SLAM has demonstrated that this tool can be easily studied for this kind of problem. The first part of the paper will deal with a short description of SLAM facilities. In the second part, we will discuss of the modelling of the most common used methods for access control for LAN, token-passing and CSMA/CD. The third part will give examples of protocol analysis and model validations.

A common optical local oscillator scheme for distributing radio signals over fiber in a microcellular system is proposed. Remodulation scheme is used at the radio port to eliminate the need of active optical source. Theoretical analysis and experiment prove that the suitable IF frequency can prevent uplink radio signal from the additional distortions caused by remodulation. The system capacity is also calculated, where the linearization of amplitude modulator and the thermal noise reduction technique are employed to enhance the capacity.

Scheduling mechanisms and admission policies play an important role in optimizing resource allocation in networks offering integrated services. The scheduler mediates the low-level contention for service between cells of different classes, while admission control regulates the acceptance or blocking of incoming traffic on a connection-by-connection basis. These two levels of control are of course closely related in the sense that if too much traffic is allowed to enter the network by an overly lax admission control policy, then no scheduler will be able to provide the requested Quality of Service (QoS) for all traffic classes. A functioning admission control is a prerequisite for any guarantee of cell-level QoS while its merit is to guarantee QoS efficiently and fairly. We focus on a DQDB and an ATM switch to demonstrate these principles.

This paper presents R-Daisy, a scalable all-optical packet network where each node is equipped with one wavelength-tunable transmitter and one fixed-wavelength receiver. Network scalability is obtained with a novel multifiber ring topology that allows for wavelength spatial reuse and requires an optical transmitted power proportional typically to the square root of the number of nodes. The topology of R-Daisy provides one logical channel per destination node. Each channel is shared in statistical time division by all nodes transmitting to a given destination. A channel inspection capability allows the implementation of slotted ordered access protocols. Three collision-free multichannel access protocols are proposed in the paper, and their performance comparison is carried out through simulation.

Simple solutions to stabilize the frequency of the transmitter lasers and to eliminate the influence of the state of polarization on the receiver gain and frequency control signals and on the channel identification in a High Density Wavelength Division Multiplexing environment has been theoretically investigated and experimentally verified. It has been proved that, by using the proposed technique, the separation of such frequency is maintained constant within the limit of the beat linewidth. It has been proved also the ability of a mixer-based system in keeping constant the power of the control signal at the receiver. An improved scheme for channel identification based on a low pass filter, a zero-bias diode and a frequency-to-voltage converter is finally proposed and test results are presented. All the above-mentioned solutions have been tested on a 622 Mbit/s FSK multichannel coherent optical system.

In this paper, low-speed ATM cell-based physical layer function is designed. Unshielded Twisted Pair (UTP) is used for the transmission medium for this function. This is designed to be used in the B-NT2 system that is being developed at Electronics & Telecommunications Research Institute (ETRI) in Korea. Current standardization activities at ITU-T and ATM- Forum for the low-speed ATM transmission are described briefly. The designed function has four units: (1) ATM Cell Transmission Unit (ACTU), (2) Twisted-Pair TRansmission Unit (TPTU), (3) ATM Cell Receive Unit (ACRU), and (4) Twisted-Pair Receive Unit (TPRU). The ACTU receives ATM cells from the ATM Layer Block, generates HEC, idle pattern, sync pattern, and send the ATM cells to the TPTU for transmission. The TPTU receives ATM cells from the ACTU, performs scrambling, 4B/5B encoding, and parallel to serial conversion, and transmits the encoded data over the twisted-pair. The TPRU receives the data through the twisted-pair, recovers the clock, performs word delineation, serial-to-parallel conversion, 4B/5B decoding, and descrambling, and send the data to the ACRU. The ACRU delineates the cell boundary using the sync pattern, checks the HEC, and sends the ATM cells to the ATM Layer Block. When there is no cell to be transmitted, the idle patterns are generated and transmitted. One of the special bytes of the 4B/5B codes is used for the byte alignment and cell delineation. The block diagrams and their functional description are given in detail.

In this paper we present a rigorous treatment for evaluating the performance of a differential phase shift keying system using optical preamplification and optical demodulation. This treatment is based on the characteristic function an allow us to analyze the influence of the post-detection filtering on the non-Gaussian noise sources, resulting from amplified spontaneous emission noise beats. Both lumped and distributed Erbium-Doped Fiber Amplifiers with single and dual pumping schemes have been considered. Our results, when compared with the Gaussian approximation, indicate that this approximation overestimates the bit error rate and becomes inadequate as the bit rate increases.

In this paper the economic viability of alternative architectures for optical access networks providing broad band services to different subscriber classes in a metropolitan environment, is investigated by a specific tool, NEVE (Network Economic Viability Evaluator), developed for broad band multiservice network planning, service evolutionary scenarios assessment, evaluation of tariff strategies and other actions taken at stimulating the demand growth. As the viability target can be achieved in different ways, different studies can be carried out by NEVE. In the paper some of them are discussed, particularly the ones addressed: to evaluate the impact on viability of alternative service scenarios; to determine the critical mass of broad band subscribers and the critical joint service adoption cost; to evaluate cross subsidiary policies among different subscriber classes and services; to perform sensitivity analysis with respect to variations of demand parameters and tariffs.

Crosstalk induced interferometric noise has been found to constrain the performance of optical switching networks. A computer design and simulation package has been used to analyze the effect of this noise on optical TDM crossconnects. This software tool is able to calculate all possible routes that a signal may traverse within a crossconnect for a given input/output assignment, and also incorporates a theoretical analysis of interferometric noise. It has been found that for a crossconnect capable of switching 512 independent channels, the constituent 2 x 2 crosspoints must possess isolations better than -20 dB, and the switch architecture must be dilated.

The capacity of local area networks (LAN) can be substantially increased by amalgamating different access techniques. Wavelength Division Multiplexing (WDM) and Code Division Multiple Access (CDMA) both offer and asynchronous mode of communications. Integration of WDM and CDMA could offer increases in the network capacity whilst still attaining asynchronous operation. Here, a different kind of integration is proposed, similar to the hybrid system used in electrical CDMA. A novel optical CDMA concept using wavelength hopping and time spreading is described employing prime sequences for both hopping and spreading and proof is given that the autocorrelation function has zero side-lobes and that the crosscorrelation function is at most 1. Code generation and correlation is achieved efficiently, the number of possible stations is greatly increased as is the number of simultaneous users. It is shown that the system offers unprecedented security leading to a very secure communications. The system is suitable for truly asynchronous highly secure LAN applications.

The ATM technology can be used to implement the future B-ISDN as well as broadband LANs. The advanced characteristics of such networks, e.g. very high speed and integrated services support, are putting challenging requirements on the related management systems. This paper presents solutions currently adopted or under study within the relevant standardization bodies distinguishing between management systems for public and private ATM networks. Furthermore some major issues regarding ATM management systems coming up on the market are analyzed.

The successes of B-ISDN project depend on attractive application services. Thus, it is very important to analyze application services which users desire, and to study the customer access network for applications. Especially, because the cost of the constructions for the customer access network need high, it is very important to configure this network economically and effectively. We recognize the importance how to provide B-ISDN application services and to configure the customer access network. This paper describes the Interactive Distance Education Service (IDES) requirements in the user and network aspects. The requirements include the service definition, reference configuration, procedure and Quality Of Service. And also this paper proposes the configuration of customer access network for providing IDES using the Centralized Access Node system which is a kind of the B-NT system. There are many applications area in IDES, we describe the three scenarios--for rural area, between the major and minor campus and for joint education including the university, research institute and enterprise.

We categorize broadband multimedia services according to their required bit rates and their transport symmetries. We also describe typical access networks, their service coverages and migrations. According to our analysis, we propose ATM-based Multimedia Information and Communication System (AMICS) as an ATM based multimedia multi-service platform. AMICS consists of ATM backbone networks, ATM ring regional transport networks, and ATM access networks. The access network has an active double star configuration and provides multicast/statistical multiplexing functions. The multicast function in AMICS is evaluated using near-video-on-demand and CATV service simulations.

The provision of broadband services at a reasonable cost to residential and small business customers is one of the major challenges facing operators. The introduction of cost-effective systems considering the existing infrastructure is an important study. Within the RACE project 2024 Broadband Access Facilities, the economic and evolution aspects of different introduction scenarios of a broadband access system suitable for providing these services are investigated. This paper presents the final results of this study.

ATMR (Asynchronous Transfer Mode Ring) is a media access control (MAC) protocol for local and metropolitan area networks (LANs and MANs) working in a Gbit/s range. The ATMR network architecture is based on a combination of a slotted ring network, spatial slot reuse and a distributed cycle reset mechanism. The performance evaluation is based on simulation results which have been obtained in homogeneous and heterogeneous traffic scenarios. Particularly user throughputs are compared with those of a pure slotted ring network. We demonstrate that the fairness mechanism employed in the ATMR MAC protocol regulates the access to the medium in a global and fair manner. Furthermore we illustrate the throughput advantage obtained by the introduction of a special bandwidth allocation scheme.

This paper proposes the ATM (Asynchronous Transfer Mode) Multiplexing/Demultiplexing Processing Module (ATM MDPM) in the broadband subscriber access node which connects a number of customer premise equipments to the broadband backbone network with the rate more than 155.52 Mbps. In the viewpoint of modular concept, ATM MDPM is implemented using basic cells which mainly perform multiplexing/demultiplexing, concentration, header translation, and traffic monitoring of ATM layer functions. We also suggest the functional architecture of ATM MDPM for accommodating the loss-sensitive video and the delay- sensitive data traffic and for supporting intelligent connection control capability including the point-to-multi-point and the multicast connections.

In this paper, we investigate the multiplexing algorithm for broadband ATM access network based on the quality-of-service (QOS) level of the input source traffics. We suggest an appropriate ATM multiplexing algorithm in order to satisfy their QOS requirements for the loss-sensitive traffic and the delay-sensitive traffic. For this purpose, we first study the service requirements of ATM multiplexer and the definition of QOS based on the ITU-T white recommendations. Second, we suggest a functional architecture of the broadband ATM multiplexer and the multiplexing algorithm to satisfy various QOS requirements in B-ISDN. Finally, the performance measures of interest, namely steady-state cell loss probability and average delay, are discussed by simulation results.

A fiber optic distribution system for phased array antennas containing optical amplifiers is analyzed. The position of the optical amplifier layers inside the distribution network is investigated in terms of microwave insertion loss and signal-to-noise ratio. The proposed solution uses one layer of optical amplifiers to feed several hundred (> 500) T/R modules of a phased array antenna. The output signal-to-noise ratio is 120 dB/Hz which exceeds the required specification.

Economical communication services can be realized with the Passive Double Star (PDS) system, which shares optical fiber cables and telephone office equipment among several users. By using the ATM transmission technique, the economy of the PDS system can be enhanced and the full flexibility of the PDS system can be realized. Our assumption is that POTS and Narrowband ISDN (N-ISDN) must be supported for a while. This paper shows the outline of a PDS system based on the ATM transmission technique (ATM-PDS) that also supports POTS and N-ISDN.

Many kinds of fiber access systems are being used to offer various services economically. They are based on different transmission technologies and fabricated by different vendors. A fiber access network operation system (OpS) must achieve common management of different type transmission equipment to offer all services efficiently. Since the network termination equipment called Optical Network Unit (ONU) is placed in or near the customer's premise, the fiber access network OpS must utilize a remote operation mechanism to manage the ONU. This paper proposes the assignment of management functions for the equipment of fiber access systems, from the view point of OpS efficiency. An NE (Network Element) has a management portion and manages different types of equipment in a common manner. This paper also describes the interface between management portion and network element body in the transmission equipment, which allows us to use the same management block between different vendor equipment sets. We show the efficiency of this management function assignment by discussing the alarm surveillance function of the NE. Additionally, we describe a remote control mechanism that achieves ONU operation in the management portion of the central office.

A unique optical access technique is described in which the features of coherence multiplexing and code division multiple access (CDMA) are combined. For the realization of this technique, the transmitted data is precoded and modulated by PSK onto an optical carrier, to achieve self-homodyne detection. This technique is described and demonstrated experimentally. The detailed theoretical analysis of the system performance in coherent optical CDMA for asynchronous communication is carried out and compared with incoherent optical CDMA system which use intensity modulation and required unipolar codes.

A novel optical technique, combining the coherence property of optical sources and the mathematical properties of digital code families is demonstrated. This technique not only exploits the large bandwidth available in single mode optical fibers but also provides a secure, asynchronous communication system.

This paper is concerned with the analysis of the output phase noise of a network which employs the coherence property of short coherence length optical sources and aspects of the code division multiple access technique. The analysis shows that the limitations imposed on the SNR can be improved by increasing the maximum code length.

Video on Demand is expected to be the first of many Video Dial Tone services that will bring broadband connections to residential customers. While significant research has been undertaken to identify cost effective access architectures, much less effort has been expended on video servers and backbone architectures, and it may be here that competitive advantage can be obtained. This paper focuses on the placement of key architectural elements within the network to show that a network topology which balances centralized and distributed storage of content minimizes backbone costs. Intuitively, storing copies of popular movies close to consumers reduces demand on the network, while centralizing titles reduces the amount of server resources required due to sharing and hence the cost of storage.

Shufflenet and MONET are compared in order to find the best solutions as regards the traffic management performance. Using simple mathematics, throughput and efficiency of both networks are derived and numerically evaluated under the constraint of a limited number of overall channels. It is shown that when the number of users is small shufflenet exhibits the best behavior, but MONETs only are able to connect a large number of users with satisfactory performance. Furthermore, the latter become more and more efficient when the hypothesis of uniform traffic is removed.

A concept for a business customer premises network using both coherent multi-channel transmission and ATM is presented. It is shown that a flexible, upgradable high capacity network can be realized, well-suited for the provision of distributive, retrieval, and interactive broadband services. Based on this concept a complete demonstrator is being realized, addressing all broadband communication aspects like network control, wavelength management, network security, field installation, broadband signaling etc.

In this paper, we propose the EM-CRMA media access protocol which supports a multi- channel wavelength-division-multiplex (WDM) network architecture with a ring topology for high-speed LAN and MAN networks. EM-CRMA-II is an enhancement of the CRMA-II (cycle-reservation-media access) protocol. In a single physical WDM network, it supports both a high speed circuit-switched network and a moderate speed packet-switched network. In EM- CRMA-II, various services including unicasting, multicasting, and broadcasting are efficiently supported in the circuit-switched network; datagram traffic with different speed and continuity characteristics is supported in the packet-switched network. Backed by effective scheduling algorithms of our design, EM-CRMA-II provides an integrated support for multimedia traffic.

In classical massively parallel computers, the complexity of the interconnection networks is much higher than the complexity of the processing elements themselves. Optical interconnections may provide a way to reconsider very large parallel architectures. We compare some optically interconnected parallel multicomputer models with regard to their communication capabilities. We first establish a distinction of such systems, based on the independence of the communication elements embedded in the processors (transmitters and receivers). Then, motivated by the fact that in multicomputers some communication operations have to be very efficiently performed, we study two fundamental communication problems, namely, one-to-all and all-to-all, under the hypothesis of bounded fanout. Our results take also into account a bounded number of available wavelengths.

The present paper describes the advantages of the combination of optical Code Division Multiple Access and Polarization Shift Keying direct detection. It is shown by means of a new receiver model that the normally disturbing statistical fluctuations of the State of Polarization on a single-mode fiber result in an attenuation of the crosscorrelation functions at the receiver. Thereby an average process gain of 4.7 dB in signal-to-crosstalk ratio is obtained. A receiver with optical signal processing unit for the chip-synchronous case is derived. Finally some simulation results concerning multi user interference and receiver noise are presented.

Optical integration of sensing and communication traffics is proposed. Time division multiplexed digital sensor signals are optically combined with communication traffic in an extended LAN environment. The composite signal is transmitted over a common optical fiber ring. The operational procedures of the integrated system and methods for signal separation and detection are explained. The degree of degradation of each traffic as a result of the spectral overlapping is analyzed and power penalties evaluated. It is shown that the communication traffic may be recovered with negligible power penalty employing direct detection techniques, whereas for the sensor traffic the power penalty may be minimized by the whitened matched filter detection. Under these conditions an optimum solution for system integration can be derived for the limiting case.

The introduction of Wavelength Division Multiplexing techniques into fiber networks opens perspectives for a global transport optical telecommunication backbone. By using signal transparent optical crossconnects, based on space and wavelength routing, a rearrangeable network topology can be achieved. Local exchanges could, in principle, be connected directly to each other through end-to-end transparent optical paths. Nevertheless, to attain a full- meshed interconnection, a relatively large number of wavelength channels is required between two nodes, growing rapidly to unrealistic numbers. Therefore, in order to achieve a more scalable network architecture, it is necessary to improve the routing granularity, without compromising too much the optical transparency and network simplicity. The architecture proposed introduces the required granularity by dividing the network in overlapping partitions, accessing the time domain at partition boundaries. The result is a scalable, flexible and simple high-capacity network architecture, ready to cope with future telecommunication demands well into the next century.

A minimal routing strategy for a new network architecture, named Starring, is presented. The simplicity of the proposed algorithm optimizes the expected average number of hops and hence the efficiency, of the network. Estimates of the network diameter and of the average number of hops in the Starring architecture show that, in the optimized operating mode, they compare fairly well with those related to other known photonic structures. The self-minimal routing behavior of the Starring and the possibility of an easy design and implementation of all-optical switching circuit make the Starring structure attractive and competitive.

The interactive multimedia service is expected to be a cornerstone of success in deploying the ATM-based access transport network. A hybrid access network architecture, which is combined with ring topology for the special community such as government and double star topology for the residential subscribers, would satisfy both service requirements of interactive multimedia-on-demand and economic opportunities of an access transport network. The adoption of different topology according to subscriber segments in one access network system results from user's requirements with different network reliability and evolutionary path. Because each subscriber segment needs different traffic class in different busy hour, the utilization of the common switching platform named as head node would be maximized. The cost evaluation is performed on five alternatives of access transport network based on the sum of cabling and network node cost. The result of evaluation is that only for an economic solution the double star is recommended for both the special community and the residential, while with consideration of serveability a hybrid with double star would be the optimized choice.

With the emergence of Broadband ISDN and the adoption of ATM as its transport mechanism there is a growing interest in slotted ring networks both for high speed packet switching and for multimedia LAN applications. This paper describes a slotted ring testbed which uses a modified Orwell protocol for media access, and which has enabled a study of the modified Orwell protocol under symmetrical and asymmetrical traffic flow distributions. The architecture of the slotted ring testbed is outlined, and analytical models for the protocol are presented for different traffic flow distributions. The analytical results are compared to experimental results obtained from the testbed. The suitability of the reset rate as an indicator of available bandwidth in an access control mechanism is considered, and it is shown that for constant traffic flow and traffic statistics the reset rate works well as an indicator of potential network congestion. Under changing traffic distributions and traffic arrival statistics, additional indicators of congestion are required. On-going work into access control for the test-bed in a integrated services environment is outlined.

The implementation of optical fiber networks will require a range of low cost and high functionality passive optical components. Silica on silicon is an important integrated optics technology that is ideally suited for developing such components. This paper describes the components that BNR Europe Limited is currently developing, together with examples of systems architecture. Passive Optical Networks currently being deployed will require power splitter components. Progress on both Y junction based 1 X N splitters and radiative star based 2 X N splitters will be given. Results on insertion loss, wavelength sensitivity and environmental stability of fiber pigtailed devices will be presented. More advanced optical systems will require the introduction of wavelength multiplexing to increase system capacity. The simplest case of wavelength multiplexing will involve the 1300 nm and 1550 nm wavelength. A more complex example of wavelength multiplexing is the optical router pilot system being installed at the Norwegian Broadcasting Company, in Oslo in 1995, as part of the RACE 2001 project. This system includes a fiber pigtailed 8 channel WDM with 4 nm channel spacing, which BNR Europe Limited has recently developed. Results on insertion loss, crosstalk and polarization sensitivity, together with the effect of temperature cycling over the range -55 C to +125 C will be reported at the conference.

Algorithms and structures of parallel-pipeline systems with instruction-stream pattern organization are suggested, theoretical basis of their development, prospective macroelement base in the shape of units (modules) executing operations of pattern matrix logics are considered.

Satellites are expected to play an important role in the future IBC and UMTS; owing to their flexibility and also their capability of covering large areas they are expected to complement the terrestrial component of the mobile networks and could be successfully exploited in all phases of the IBC deployment. The EU sponsored Programme for Research in Advanced Communications for Europe (RACE) has, since its start in 1 984, been conceived in two phases. Phase I, started in 1989, was concentrating on the system engineering, specifications and key technologies, while Phase II, which started in 1993, is concentrating on integration and the prototyping of new services and applications. The second Phase of the Programme has now reached full maturity and some of the results being achieved by Projects, are contained in this paper. The Consensus Management Project (CMP)1is responsible for consensus management activities within RACE II; this includes the management of the TG and STG structure for the preparation of the RACE Common Functional Specifications/Common Practice Recommendations (CFS/CPR) and contributions to the standardisation bodies. RACE CFS and CPR are published at the end ofeach year by CMP. Since 1994 an Addendum, collecting the latest results, is published in August. (see note in section 8). Within the RACE community, STG2.5 "Satellite Systems", building on the results achieved by the Project R1044 "IBC Development and Implementation Strategies", has developed more detailed Reference Configurations for satellites2; a similar activity is now starting in STG 2.4 "Mobile Communications"3 . Activities are currently in progress within RACE and ETSI SMG5 on the different aspects of integration of Satellite Systems into IBC and UMTS. This paper presents some of the results so far achieved in this work but it does not necessarily reflect fully the views of RACE or of SMGS.

Since the beginning of this century the issue of `quality' has been gaining increasing importance in a number of fields of human activities. For telecommunication services, too, the quality perceived by customers has been taken into account early on as an issue of strategic importance. Whilst for telephony the Quality of Service (QoS) has been already investigated and identified in terms of parameters and related test methodology, the situation for high speed data services (i.e. CBDS/SMDS, Frame Relay, etc.), provided by means of high speed network based on Asynchronous Transfer Moe (ATM) or Metropolitan Area Network technologies, can still be considered `under study'. There is a death of experience not only in terms of measurement instruments and procedures, but also in terms of knowledge of the relationship between the QoS provided at a network level and the quality perceived by the user on his or her terminal. The complexity of the equipment involved in setting up an end-to-end solution based on high speed data communications makes the problems of knowledge and supply of quality very hard to solve. Starting from the experience gained in carrying out high- speed network field trials based on Metropolitan Area Networks and, more recently, on ATM technology, the paper mainly deals with the problem of defining, measuring and then offering a specific QoS. First, the issue of what the user expects from the `high-speed network' is addressed. This analysis is carried out trying to gather what is peculiar to high-speed data communications from the user standpoint. Next, the focus is on how to cope with the requirements due to users' expectations, while carefully considering the basic principles of quality. Finally, a solution is proposed, starting from the experience gained from high speed networks installed in Italy.

FIRST is a RACE project where 5 main European telecoms operators, 4 equipment manufacturers and one university have joined up to define and test in a field trial in Portugal a cost effective Optical Access Network. The main design target has been a system which gives cost effective provision of wideband services for small and medium business customers. The system however, incorporates provision of telephone, ISDN and analog and digital video for residential customers as well. Technologies have been chosen with the objective of providing a simple, robust and flexible system where initial deployment costs are low and closely related to the service take up. The paper describes the main technical features of the system and network applications which shows how the system may be introduced in network planning. The system is based on Passive Optical Network technology where video is distributed in the 1550 nm window and telecoms services transmitted at 1300 nm in full duplex mode. The telecoms system provides high capacity, flexibility in loop length and robustness towards outside plant performance. The Subcarrier Multiple Access (SCMA) method is used for upstream transmission of bi-directional telecoms services. SCMA has advantages compared to the Time Division Multiple Access technology used in other systems. Bandwidth/cost tradeoff is better and the lower requirements to the outside plant increases the overall cost benefit. Optical beat noise due to overlapping of laser spectra which may be a problem for this technology has been addressed with success through the use of a suitable modulation and control technique. This technology is further validated in the field trial. The video system provides cost effective long distance transmission on standard fiber with externally modulated lasers and cascaded amplifiers. Coexistence of analog and digital video on one fiber with different modulation schemes i.e. BPSK, QPSK and 64 QAM have been validated. Total life cycle cost evaluations based on availability data, maintenance requirements and expectations for service development have been made. The field trial will be running for two years.

This paper proposes different models to describe a bursty source; models are based on Markov chains whose complexity is increasing with the accuracy of the description. The effectiveness of the proposed models is evaluated by varying statistical description parameters of sources like peak bandwidth and burstiness. The effect of the models presented on an ATM cell admission strategy is evaluated; the latter is suited to guarantee quality of service requirements like lost and delayed cell rates in ATM networks with multi-rate bursty traffic. The efficiency of the admission control is verified by a simulation tool.

Optical amplifiers have already deeply affected current thinking on optical fiber communications, and are likely to play an increasing role in the design of future systems. In this paper we review the principles of optical amplification and discuss briefly the operational characteristics of the main types of optical amplifiers and their main advantages and drawbacks.

This paper gives an overview of the type of ATM equipment currently being designed which fits in with the strategy of offering both a cost effective way to provide ATM in the public access network during the early phase of its implementation and the capability of evolving towards a fully optimized large capacity ATM node for future applications.

In optical fiber networks, the semiconductor laser source may be subjected to unavoidable optical feedback from fiber pigtails, fiber connectors and other components, unless expensive optical isolators are used. Therefore, a good understanding of external optical feedback phenomena in semiconductor lasers is required. This paper will review these phenomena, including linewidth narrowing and broadening, mode hopping phenomena and the transition to the so-called coherence-collapse regime. In particular, laser designs with high endurance against optical feedback will be discussed.

This paper describes the latest technological advances in passive components and related network accessories for optical access networks. Several architecture and service options exist everyone having a different impact on the implementation of the physical layer of the network. In this paper the requirements, the technologies and the performances of the following components and accessories are reviewed: splices and related components and hardware, connectors, attenuators, splitters and closures.

The preventive congesting control method of ATM is rather intolerant of traffic profile distortions in the multiplexing stages. Thus medium access protocols for tree Passive Optical Networks can not ignore that the cell clustering introduced by the arbitration method can not be distinguished from peak rate violations by the policing unit, the result is either unwarranted rejections of conforming cells or unacceptably low utilization. By recording and efficiently transmitting the arrival timing of cells the proposed system maintains a cell jitter comparable to a concentrated FIFO multiplexer.

With the ever increasing importance of the possibility to exchange electronic information an important attempt has been taken to base the next generation of communication network on a concept that seems enable to cover the need for future communication. The concept selected for this purpose is called ATM, that with its flexibility and potential good utilization of the network resources is expected to be `the solution to every demand.' However, it still remains to be solved how the statistical multiplexing, that insures a good network utilization, can be applied without strong restriction specially on the bandwidth side. This paper covers some of the aspects of being able to provide broadband services and still gain from statistical multiplexing.

This paper gives a status report on signaling specifications for ATM networks, focusing on the activities of international standardization bodies like ITU-T and ETSI, and on the implementation agreements drafted by the ATM-Forum. It shows that for ATM networks, the envisaged signaling specifications--besides providing the basic signaling functions of call establishment and release known from current networks--will provide a powerful network support system for advanced ATM applications like multimedia co-operation, teleconsulting and telemonitoring, teleparticipation, etc. For these applications, sophisticated support functions will be specified, e.g. procedures for point-to-multipoint connections, modifications of connection characteristics, look-ahead functions, multiconnection calls, etc. Such signaling functions for ATM networks are currently specified by international standardization bodies. The work of these bodies can roughly be classified into three consecutive steps: (1) Signaling for `B-ISDN capability set 1'. These functions allow for the establishment and release of a simple ATM connection between two parties. They are the basis for all further specifications. The standardization work for `Capability Set 1' has been finalized in 1994. (2) Signaling for `B-ISDN capability set 2'. These functions provide for a powerful support system for multimedia and multiparty applications. The current standardization work focuses on these specifications. (3) Signaling for `B-ISDN capability set 3'. Currently, only some vague ideas exist for this 3rd capability set, e.g. related to integration between B-ISDN and `Intelligent Networks', or related to the integration of TV-distribution. This paper gives an overview of the available signalling protocols of capability set 1, and of the future extensions currently being specified.

During 1994 IDC has finished an enduser survey among over 3000 companies in Western Europe (Germany, UK, France, Italy, Sweden and Benelux) with more than 100 employees on their evaluation of high speed networks. The aim of this study was to understand the current status of these services and the applications IT managers have in mind when applying these services. In this paper IDC provides a summary of this survey with major findings and conclusions.

By applying a Chernoff bound to the error probability of an optically preamplified pulse position modulation (PPM) receiver we are able to present sensitivity results for various length PPM words. In exhibiting a potential sensitivity benefit of 7.1 dB these results compare extremely well to those obtainable from an equivalent on-off keyed non-return to zero (OOK NRZ) system. The results further demonstrate the possibilities of such a receiver configuration by surpassing the fundamental limit of an optically preamplified OOK NRZ receiver and approaching the sensitivity of coherent systems. Additionally a Gaussian approximation is formulated and we compare the Chernoff bound results with those obtainable from the approximation.

A new hybrid pulse position modulation code division multiple access is proposed for the indoor infrared channel. The system performance is analyzed in terms of bit rate, number of users, and the error rate due to the optical orthogonal code correlations. It is demonstrated that this hybrid can offer improved performance in terms of bit rate and promised to accommodate more used than the equivalent ON OFF Keying CDMA (OOK-CDMA).

An original analysis is presented for the performance of a self-synchronized optical fiber pulse position modulation (PPM) system. The results indicate that the PPM system can offer a significant sensitivity improvement over a comparable PCM system. an original expression is presented for the power spectral density of the cyclostationary PPM format and the results are used to analyze the system self-synchronization and performance under jitter.

A new strategy for modelling asymmetric traffic load distributions on local area networks (LANs) is outlined. Mathematical analysis utilizing the statistical characteristics of traffic loads offered to LANs is presented which provides a mechanism for the prediction of network performance under asymmetric traffic load distributions. Discrete event computer simulations of the token passing protocol are used to verify the predictions made by the new modelling strategy, and hence the potential value of this tool for network planners and operators is illustrated.

This paper reports on the investigation of the traffic throughput performance of passive optical networks using both time division multiplexing (TDM) and asynchronous transfer mode (ATM) transmission techniques. In particular discrete event computer simulation techniques are utilized to study the performance of these networks under asymmetric traffic loading conditions. The performance characteristics obtained demonstrate the degradation of the network traffic throughput using TDM, whereas ATM transmission proves resilient to even high levels of asymmetric traffic loading on the passive optical network.

In this paper it has been shown that by using a time division multiple access/code division multiple access (TDMA/CDMA) hybrid scheme with matched filter receivers, this will greatly improve the number of users which can be accommodated in the PON local access network architecture. This paper will also demonstrate the overall bit error rate and delay against throughput characteristics for the resulting TDMA/CDMA hybrid data stream compared with that of TDMA.

This paper describes a software system that can be used to predict the spectral performance of optical networks. The system can be used by the planners and designers of such networks to assess the spectral performance of existing or proposed optical networks. The software package combines the theoretical models developed in the course of a research program with experimental data obtained from the devices used in the UK field trials of fiber in the local access network. Using this package, a planner or designer is able to construct networks on actual location maps and then obtain forward and return loss spectral characteristics on any paths throughout the network. Since the development of the system is based on object oriented technology, it is future-proofed to the extent that any changes in the technology of the local access network can readily be incorporated into the existing modelling process.

A novel scheme for the classification and reproduction of packet channel burstiness is presented. Channels are described by burst-length--loading pairs, and an algorithm is presented which can faithfully reproduce any traffic characteristic for use in packet-level discrete time packet switch simulation studies.

Recently much interest has been shown in the design of very low noise tuned front-end optical receivers for use in Lightwave Sub-carrier Multiplex Systems as well as Coherent Lightwave Systems. This paper looks at the requirements that need to be considered to enable the accurate design of such tuned front-end optical receivers. Simplified design expressions are presented for a number of tuning configurations and theoretical results as well as practical measured results are presented for one of the designs. The design was realized at GaAs MMICs using the GEC/Marconi F20 foundry process.

In this paper we consider the design of broadband optical receivers for use in free-space local area networks. After a brief introduction to the relatively new topic of optical wireless LAN's, our attention turns to the design of receivers for use in these wireless systems. Mathematical models of the noise performance of optical wireless receivers are used to compare two different receiver topologies. This allows us to determine which type of receiver is best suited to a particular operating environment.

With the advent of Optical Fibers the role of Microwave radio has changed dramatically: from providers of backbone heavy traffic route, i.e. transportation of many messages among major switching centers, to provider of `last mile' connections, i.e. distribution of a few messages among peripheral points, often outside the switched network, and outside the practical reach of fibers. A portion of the microwave spectrum, referred to as millimeterwave spectrum, has gained considerable interest in this new role of microwave radios, due to a favorable match between network requirements and propagation features. The access mission of millimeterwave radios can be further enhanced by technological features which impact favorably in the economical and technical issues often related to access solutions. This paper surveys the concepts that make millimeterwave radio suitable to an access role in the network, and describes the technologies that enhance the natural fit of such radios in the network access environment, both from a technical and from an economical viewpoint.

This paper presents a Multimedia Art Directory, that has been developed for an ATM network, by describing its main characteristics and the creation environment and the network facilities used.

ATM network will support new multimedia services that will require new protocols, those services and protocols will need different test strategies and tools. In this paper, the concepts of functional and non-functional testers of ATM networks are discussed, a multimedia service and its requirements are presented and finally, a summary description of an ATM network and of the test tool that will be used to validate it are presented.

This paper describes a board-level realization of 2.5 Gb/s clock and data regenerator circuit, where the clock recovery function is implemented by a phase locked loop configuration. In order to use a low cost commercially available voltage controlled oscillator (VCO) a Richman quadricorrelator frequency-difference discriminator has been designed. The resultant frequency and phase locked loop (FPLL), makes possible the frequency acquisition even if the VCO starting frequency were out of the PLL pull-in range. All components used are cheap commercially available silicon devices. Measurements, at 10^-9 bit error rate, give an input electrical sensitivity less of 5 mV_pp with 2^23-1 pseudo-random input data stream. The recovered clock jitter is compliant with SONET STM-16.

Multiple access technology is important for wireless mobile radio communication systems to improve the system performance and capacity. According to the indoor radio channel characteristics we propose a multiple access scheme--the Time Code Division Multiple Access (TCDMA) for indoor wireless applications with a carrier frequency 2.4 GHz by combining advantages of both Time Division Multiple Access and Code Division Multiple Access. For implementation of a TCDMA system we use Surface Acoustic Wave devices with delays less than 5 microsecond(s) as analog Matched Filter in the receiver. The indoor multipath fading channel is modeled taking into account the measurement results for investigation of the TCDMA system capacity. Spreading codes for synchronization with maximal linear code sequences and for user data with Gold code sequences are selected according to their properties of autocorrelation and crosscorrelation. Additionally, data detection techniques are used to combat the multipath fading. Simulation results presenting bit error rate versus number of the active users are provided to prove the feasibility of TCDMA system for indoor applications.