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With the constant increase in public transit coverage in Bangkok Metropolitan Area in Thailand, many people are still hesitant to switch from using private to public transit, with one potential cause being the unavailability and difficulty in accessing accurate and timely information about their itineraries, while they are commuting. To assess and tackle such issues, the researchers adopted the user-centric Design Thinking methodology to empathize with target users' pain points in this study. They proposed a solution in a user-centric manner by assessing the usability flaws of existing mobile navigation applications, such as Google Maps and ViaBus. By developing a holistic mobile application called 'Disgovery' that covers all modes of public transit in the Bangkok Metropolitan Area and provides relevant information about their trips, the researchers aim to help commuters in Bangkok easily access it in a timely fashion. Through the user-friendly interface, commuters can eliminate the difficulty of finding routes and prices suitable to their needs. By making public transit more accessible with the help of ubiquitous mobile computing, commuters are also encouraged to switch from using private vehicles to public transit, which also can reduce accidents and carbon emissions. The findings from the usability testing in this study suggest that 'Disgovery' is an effective and user-friendly application for daily commuters in Bangkok that can help them achieve their goals without difficulties. The findings also indicate the importance of user interface and user experience guidelines in designing such applicationS. [ABSTRACT FROM AUTHOR]

An optical wavelength division multiplexing metro access network is proposed in this paper. With the design of flexible distribution node (FDN), three kinds of reconfigurable networks can be flexibly built to achieve intra- and inter-optical network unit (ONU)-direct communications. With the adoption of multiple tangent twin-ring topologies, four-level shared protections covering both feeder and distribution fibers are also supported. Moreover, the network can be smoothly expanded by adding express ONUs connected to FDNs. Thus, the network can not only achieve capacity increasing but also support full-duplex reconfigurable communication. A reconfigurable transmission algorithm is also set to avoid wavelengths conflict. [ABSTRACT FROM AUTHOR]

Improving the performance of electronic and optoelectronic components has enabled the investigation of transmitting optical channels with data rates greater than 40 Gb/s, over infrastructures that were initially supporting 10 Gb/s transport. However, for transporting high capacity channels, over long distances, considerable signal processing is necessary, with current emphasis being on digital techniques. Meanwhile in the context of optical networking where spectrally adjacent channels may cross different routes to interconnect the same source destination nodes, adaptive transmission systems become vital. This paper will suggest, compare and develop the necessary transponder technologies that enable transportation of 40 Gb/s channels over deployed Metropolitan Area optical Networks (MAN) infrastructure with emphasis on the interplay between realistic performance, feasibility and complexity/cost. Specifically it will investigate utilizing deployed optical infrastructure for transporting 40 Gb/s DQPSK channels in conjunction with various high performance, low complexity electronic equalizers that can compensate the corresponding linear impairment enhancement that accompanies this upgrade, namely Chromatic Dispersion and Polarization Mode Dispersion while they can be implemented in a single FPGA. It is shown that resource constraint performance evaluation is vital and the exact technology choice is related to the deployed infrastructure. [ABSTRACT FROM AUTHOR]

Popular network applications (e.g. web access, social network apps) are mostly delay sensitive. Therefore, understanding the characteristics of latency in broadband network is of extreme importance for SPs, ISPs and individual users as well. The previous studies show that last-mile latency is the bottleneck of network latency in developed countries. In this paper, we analyze network latency in China from three perspectives: last-mile latency, MAN latency and backbone latency. We deploy specific measurement tools at the home gateway on several hundred users' side to measure the latency with LAN and ADSL access technology. Based on the measured results of 4 months, we found that: (i) compared to the backbone latency, the last-mile latency is not the bottleneck in China, and it is even less than the MAN latency with LAN access technology; (ii) more interestingly, due to the tree architecture that has been widely adopted in China, the port selection of backbone router which the MAN network connected to has a distinctly effect on the MAN latency; (iii) furthermore, we present the study of what factors and how they influence the three parts of end-to-end network latency. [ABSTRACT FROM AUTHOR]

This study aims to put forward an extensive discussion about the increasing demand for available bandwidth to serve the multiple types of traffic in modern wavelength division multiplexing (WDM) metropolitan area networks (MANs). A traffic-depended multi-buffer node architecture in conjunction with an efficient asynchronous transmission WDM access (WDMA) protocol to serve the variable size Internet packets in ring MANs is proposed. The structure of the multi-buffer node architecture is determined by the probability distribution of each packet size category in the MAN traffic, providing storage and dropping events equity among the nodes. The adopted WDMA algorithm satisfies the requirement for high performance efficiency especially under high offered load, by taking care to optimally face the bandwidth fragmentation problem and to maximize the bandwidth exploitation, while it effectively avoids both the packets collisions over the wavelengths and the destination conflicts. Numerical results prove that the proposed network model achieves throughput improvement up to 334% as compared with the relative study of Pranggono and Elmirghani (2011). An analytical framework is developed for the protocol throughput predictions under both symmetric and asymmetric IP traffic scenarios. Also, the proposed protocol performance is thoroughly investigated through simulation results based on Poisson and self-similar traffic model statistics, for both traffic scenarios. [ABSTRACT FROM AUTHOR]

In improvement for medical facilities in lives of human, the information technology (IT) has been playing important roles in developments of new systems that will be more reliable in conquering of critical diseases and also in terms to provide the medical facilities and remote monitoring of patients, also called telemonitoring systems. Due to the development of telemonitoring systems, the medical treatments for remote located patients are possible and also beneficial in case to handle the patient health while in emergency conditions. In past two decades, there were several telemonitoring systems that deployed to access and monitor the remote located patient's health. For further enhancements, this study first makes a survey on existing telemonitoring systems and then proposes a new system that will be accounted as an enhancement to the existing once. This study only proposes an idea to access and monitor the remote located patients, and corresponding implementation will be a part of future development. [ABSTRACT FROM AUTHOR]

Looking in to the modern technology, we see new inventions and innovations which are unique. As an example, during the past years, new technologies have been created in computer networks like metropolitan area network (MAN) that has had a noticeable advance in urban communication. Therefore the aim of this article is to provide and compile information regarding MAN technology and MPLS. Utilizing Ethernet in urban networks needs a developing potential and strength that only exists in MPLS and IP levels. Two layer and three joint networks are the solutions that join simplicity and economy of Ethernet at IP/MPLS scale. Different transfer technologies have been used in MAN so metropolitan services should be given on a mixture of optic and data switches, MPLS have been developed for this work and using generalized-MPLS makes MPLS deployments possible even on none-IP-aware switches. At first, theories about using MAN technology to produce urban networks are explained. Then a set of problems regarding the management of resources and provisioning barriers are introduced following the solutions by means of IP/MPLS network which have been implemented and validated in eSNP simulator. [ABSTRACT FROM AUTHOR]

A new four wave mixing (FWM) model for an optical network with amplifiers and a comparative analysis among three proposed amplifiers placement techniques have been presented in this paper. The FWM model is validated with the experimental measured data. The novelty of this model is its uniqueness that on direct substitutions of network parameters like length, it works even for unequal inter amplifier separations. The novelty of the analysis done among three schemes is that it presents fair choice of amplifiers placement methods for varied total system length. The appropriateness of these three schemes has been analyzed on the basis of critical system length, critical number of amplifiers and critical bit error rate (10 −9 ) in presence of four wave mixing (FWM) and amplified spontaneous emission noise (ASE). The implementation of analysis done has been given with the help of an example of a regenerative metropolitan area network (MAN). The results suggest that the decreasing fiber section scheme should be avoided for placements of amplifiers and schemes IUFS and EFS shows their importance interchangeably for different set of parameters. [ABSTRACT FROM AUTHOR]

Worldwide interoperability for Microwave Access (WiMAX) is based on the IEEE 802.16 standard. This technology provides broadband wireless last-mile access in a Metropolitan Area Network (MAN). The IEEE 802.16-2004 standard (i.e. Fixed WiMAX) provides specification for the Medium Access Control (MAC) and Physical (PHY) layers for WiMAX. A critical part of the MAC layer specification is scheduling, which resolves contention for bandwidth and determines the transmission order of users. The algorithms are researched under different mixes of traffic and for various characteristics of the IEEE 802.16 MAC layer. In this research the focus is on the WiMAX uplink traffic scheduling. A scheduling algorithm's task in a multi-class network is also to categorize the users into one of the pre-defined classes. In this research, the algorithms are tailored at enhancing the collective performance of hybrid algorithms in the WiMAX domains which complement the assigned priorities. The spectrum of constraints which have been extracted from the hybrid Earliest Deadline First(EDF) + Weighted Fair Queuing (WFQ) + First in First out (FIFO) EDF+WFQ+FIFO algorithm include the static nature by which priorities are assigned and maintained during the entire duration of a transmission time and the core attributes of absolute dependence on deadline. The second constraint is embedded within the EDF scheduling algorithm and the perseverance of pursuing deadline associated weightages. In this research, the reengineering of the scheduling mechanics governing the EDF algorithms has been pursued. The dominance of the pre-stipulated deadline of the EDF algorithm is indeed acknowledged in the proposed and developed enhanced algorithm. The simulation results indicate that the legacy algorithms are not suitable for the multi-class traffic systems of WiMAX. This is because these algorithms do not explicitly incorporate the WiMAX QoS parameters into their mechanisms and are highly static. Extensive discrete - event simulation experiments have been done for the purpose of performance analysis. The performance metrics used are average throughput, average delay, missed deadline ratio and average queue size utilization ratio. The acquired results have proven that the proposed algorithms have successfully enhanced the static constrained algorithm. [ABSTRACT FROM AUTHOR]

We review several node architectures for optical slot switching ring networks, which can be used in metropolitan or datacenter applications, and compare them for their networking aspects. The dimensioning, quality of service, latency, and protection issues are discussed for the different approaches. The main devices, i.e. fast wavelength-tunable laser, burst-mode coherent receiver (which is required to enable high data rate transmission at 100 Gb/s and above), and a slot blocker for improved wavelength usage efficiency are described, and available technologies for each key building block are reviewed. [ABSTRACT FROM PUBLISHER]

Emerging non-traditional data (NTD) such as transit agencies' smartcard data and Google's General Transit Feed Specifications (GTFS) have made it easier to unveil the way in which public transit remains relevant, reveal how it facilitates daily mobility, and highlight the way in which different locales across a metropolitan area are connected by public transit. Based on a 24-h period of smartcard data for Brisbane (4 March 2014) allied with GTFS data, we retrieved 205,560 distinct transit riders' trip trajectories by direction (AM/inbound vs. PM/outbound) in Brisbane, Australia. It visualises the trajectories using a waterpark metaphor, in that, like water, people flow downhill. [ABSTRACT FROM AUTHOR]

Wireless mesh networks (WMNs) are considered as a promising alternative to wired local, or metropolitan area networks. However, owing to their exposure to various disruptive events, including natural disasters, or human threats, many WMN network elements located close to the failure epicentre are frequently in danger of a simultaneous failure, referred to as a region failure. Therefore, network survivability, being the ability to provide the continuous transmission after a failure, is of great importance. In this paper, we define three new measures of wireless mesh networks survivability for a region failure scenario, including the region failure survivability function, p-fractile region survivability function, and the expected percentage of total flow delivered after a failure as a function of region radius r. These measures are next used to evaluate the vulnerability of example wireless mesh networks to region failures. [ABSTRACT FROM AUTHOR]

This article presents a novel bidirectional wavelength reconfigurable optical network utilizing a remotely pumped erbium-doped fiber amplifier and tunable fiber Bragg gratings. The system is experimentally demonstrated at a 10-Gb/s per channel over 20-km fiber span that verifies the metro-network range system performance. The achieved power penalty is less than 1 dB when compared to the back-to-back transmission link. An example of practical application where the proposed module is used as an add/drop multiplexer and a remote node in the bidirectional wavelength division multiplexing passive optical network system is described. [ABSTRACT FROM PUBLISHER]

This article reports the operation of a cost-effective, colorless, dense wavelength-division multiplexing metropolitan network based on self-seeded reflective semiconductor optical amplifiers. All reflective semiconductor optical amplifiers used in the experiments are packaged in commercial small form-factor pluggable modules. The proposal architecture is simple and symmetric thanks to utilization of two cyclic array waveguide gratings. Downstream link functions in the C-band wavelength range and the upstream link functions in the L-band wavelength range. By using erbium-doped fiber amplifiers to extend the reach, an error-free transmission over 90 km for 16 channels at 2.5 Gb/s was experimentally demonstrated for both directions, and an optical budget over 35 dB was obtained. [ABSTRACT FROM PUBLISHER]

An understanding of epidemiological dynamics is important for prevention and control of epidemic outbreaks. However, previous studies tend to focus only on specific areas, indicating that application to another area or intervention strategy requires a similar time-consuming simulation. Here, we study the epidemic dynamics of the disease-spread over a commute network, using the Tokyo metropolitan area as an example, in an attempt to elucidate the general properties of epidemic spread over a commute network that could be used for a prediction in any metropolitan area. The model is formulated on the basis of a metapopulation network in which local populations are interconnected by actual commuter flows in the Tokyo metropolitan area and the spread of infection is simulated by an individual-based model. We find that the probability of a global epidemic as well as the final epidemic sizes in both global and local populations, the timing of the epidemic peak, and the time at which the epidemic reaches a local population are mainly determined by the joint distribution of the local population sizes connected by the commuter flows, but are insensitive to geographical or topological structure of the network. Moreover, there is a strong relation between the population size and the time that the epidemic reaches this local population and we are able to determine the reason for this relation as well as its dependence on the commute network structure and epidemic parameters. This study shows that the model based on the connection between the population size classes is sufficient to predict both global and local epidemic dynamics in metropolitan area. Moreover, the clear relation of the time taken by the epidemic to reach each local population can be used as a novel measure for intervention; this enables efficient intervention strategies in each local population prior to the actual arrival. [ABSTRACT FROM AUTHOR]

This paper analyzes long duration overvoltages due to backfeeding currents from the low-voltage network to the medium-voltage network through network protectors in heavily meshed underground distribution networks. Overvoltages above 3 p.u. may be developed as a result of a simultaneous occurrence of three phenomena: neutral displacement, Ferranti effect, and current chopping. A detailed model of a typical distribution network is utilized for the study. Time-domain simulations are performed using an Electromagnetic Transients Program-type program. The results demonstrate that overvoltages due to backfeeding last longer during peak load operating conditions, and the largest peak overvoltages occur at no load. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we study a slotted WDM ring network architecture with a suitable access protocol that avoids both data channels collisions and destination conflicts and decreases the packets dropping probability. Our intention is to increase throughput and to decrease transmission delay. The key idea of this paper is the exploitation of a number of buffers at each access node, in conjunction with the appropriate allocation of the incoming traffic among them and the effective decision algorithm for the appropriate buffer selection for transmission. Simulation results approximate the necessary number of buffers at each access node that maximizes the fiber bandwidth utilization. [Copyright &y& Elsevier]

Conventionally, in intelligent buildings in a metropolitan area network and in small-scale facilities in the optical access network, optical connectors are joined manually using an optical connection board and a patch panel. In this manual connection approach, mistakes occur due to discrepancies between the actual physical settings of the connections and their management because these processes are independent. Moreover, manual cross-connection is time-consuming and expensive because maintenance personnel must be dispatched to remote places to correct mistakes. We have developed a fiber-handling robot and optical connection mechanisms for automatic cross-connection of multiple optical connectors, which are the key elements of automatic optical fiber cross-connect equipment. We evaluate the performance of the equipment, such as its optical characteristics and environmental specifications. We also devise new optical connection mechanisms that enable the automated optical fiber cross-connect module to handle and connect angled physical contact (APC) optical connector plugs. We evaluate the performance of the equipment, such as its optical characteristics. The evaluation results confirm that the automated optical fiber cross-connect equipment can connect APC connectors with low loss and high return loss, indicating that the automated optical fiber cross-connect equipment is suitable for practical use in intelligent buildings and optical access networks. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to present principles from the complex approach in education and describe some practical pedagogic experiences enhancing how "real world" perspectives have influenced and contributed to curriculum development. Design/methodology/approach – Necessity of integration in terms of knowledge modeling is an historical trend in Engineering and Computer Sciences curricula. Integration of particular technical aspects with wide global aspects is a response to globalization demands. Globalization demands require new approaches, at both educational and teaching levels. Also, educational level embeds a wide range of pedagogical proposals or teaching proposals. Since the 1990s, Engineering and Computer Sciences curricula have emphasized, increasingly, the project-oriented approach in the Engineering field of knowledge and software engineering contents has migrated to beginners or fresh-man level in Computer Sciences courses. This approach is called the Complex Approach in education. COOL – "Comprehensive Object-Oriented Learning" – is an educational project mentored by Emeritus Professor Kristen Nygaard, from the Department of Informatics at Oslo University, which deals with the complex approach in education. Professor Nygaard passed away in 2002. This project was published in 2006 under the title of "Comprehensive Object-Oriented Learning: the Learner's Perspective". This paper analyses theoretical aspects in Nygaard's project and also compares aspects with the author's work teaching Object Oriented Modeling in Computer Sciences and Engineering, at Federal University of Santa Catarina – UFSC, Florianopolis, Brazil. The author's pedagogic proposal, developed on those contexts, since 1997, is supported by Nygaard theory and also by Edgar Morin "Complex Thought" theory adopted by UNESCO, titled Complex Thought cathedra. Findings – Innovation, in terms of Engineering and Computer Sciences curriculum development, is deeply related to the complex approach educational paradigm. Consequently, innovation in terms of pedagogic practices is also deeply related to the complex approach perspective. Complex approach overpasses fragmented view of knowledge towards integrative view concerning curriculum development in technological areas. Research limitations/implications – The comprehensive object-oriented learning presented here is applied to Computer Science and Engineering. However its development and application could impact other disciplines and education, especially in relation to technology integration in education. Originality/value – The paper presents and discusses COOL as a concept and approach for enhanced learning, in a novel manner, taking account of theoretical underpinnings developed aligned to modern thinking. [ABSTRACT FROM AUTHOR]

Use of Wireless communications for Metropolitan Area Network (MAN) in consumer electronics has increased significantly in the recent past. This paper, presents the performance analysis of four different channel coding and interleaving schemes for MIMO-OFDM communications systems. A comparison is done based on the BER, hardware implementation resources requirement, and power dissipation. It also presents a memory-efficient and low-latency interleaver implementation technique for the MIMO-OFDM communication system. It is shown that among the four coding and interleaving schemes studied, the crossantenna coding and per-antenna interleaving performs the best under all SNR conditions and for all modulation schemes. It is also the best scheme as far as the hardware resource implication and power dissipation are concerned, which are particularly important in the context of consumer electronics. Next, using the proposed interleaver, a MIMO-OFDM based transmitter employing a double data stream 2?2 MIMO spatial multiplexing system is built. [ABSTRACT FROM PUBLISHER]

Abstract: Storage area networks (SANs) are becoming an important part of optical MANs (metropolitan area networks). Growing storage and business-continuity needs; high-bandwidth, low latency requirements for SANs; storage infrastructure consolidation; and post-9/11 regulatory issues are among the several driving factors to push this trend. We, in this paper, consider a metro wavelength division multiplexing (WDM) SAN that allows the transmission of variable packet size such as Internet protocol (IP) datagram and evaluate its performance by means of discrete-event simulation. The network is based on one fixed transmitter and multiple fixed receivers. Beginning with an introduction and the context of this work, we describe the network and node architectures; and introduce the medium access control (MAC) protocols. Subsequently, using the Poisson and self-similar traffic, we present and discuss performance of the proposed network architecture in terms of throughput and queuing delay under symmetric and asymmetric traffic scenarios. The simulation results suggested that the proposed architecture is suitable for SAN applications which demand low queuing delay and high throughput. [Copyright &y& Elsevier]

Abstract: The concept of the all-fiberized multi-wavelength regenerator is analyzed, and the design methodology for operation at 40Gb/s is presented. The specific methodology has been applied in the past for the experimental proof-of-principle of the technique, but it has never been reported in detail. The regenerator is based on a strong dispersion map that is implemented using alternating dispersion compensating fibers (DCF) and single-mode fibers (SMF), and minimizes the nonlinear interaction between the wavelength-division multiplexing (WDM) channels. The optimized regenerator design with +0.86ps/nm/km average dispersion of the nonlinear fiber section is further investigated. The specific design is capable of simultaneously processing five WDM channels with 800GHz channel spacing and providing Q-factor improvement higher than 1dB for each channel. The cascadeability of the regenerator is also indicated using a 6-node metropolitan network simulation model. [Copyright &y& Elsevier]

Abstract: We report on an experimental demonstration of a frequency swept local oscillator-based spectral amplitude coding (SAC) label detection for DQPSK signals after 40km of fiber transmission. Label detection was performed for a 10.7Gbaud DQPSK signal labeled with a SAC label composed of four-frequency tones with 500MHz spectral separation. Successful label detection and recognition is achieved with the aid of digital signal processing that allows for substantial reduction of the complexity of the detection optical front-end. [Copyright &y& Elsevier]

Abstract: In this paper, we have demonstrated the quality-of-service offered by the metropolitan area network which is based on optical cross connect (OXC) and arrayed waveguide grating (AWG) demultiplexer operating at 10Gb/s with 0.1nm channel spacing for NRZ signal transmission. The data is successfully transmitted to a distance of 40km with a reasonably good BER of 2.388×10−35. The OXC and AWG demultiplexers in the proposed architecture allow incremental expansion in terms of the number of wavelength channels to be transmitted. Dispersion and crosstalk are the main signal-degrading factors arising from the operation of the OXC and the effectiveness of each factor is individually investigated. [Copyright &y& Elsevier]

Abstract: In this paper, we have analyzed the performance and feasibility for the metropolitan area network based on arrayed waveguide grating (AWG) multiplexers and arrayed waveguide grating (AWG) demultiplexers operating at the bitrate of 10Gb/s. In the network, the data is successfully transmitted to a distance of 50km with a very low BER of 1×10−40 thus improving the performance over AWG star based networks. Here, we have observed that arrayed waveguide gratings based multiplexers and demultiplexers for WDM applications prove to be capable of precise multiplexing and demultiplexing of a large number of channels with relatively low losses. This paper also presents the comparative investigation and suitability of various data formats like NRZ Rectangular, NRZ Raised cosine, RZ Rectangular, RZ Raised cosine and RZ super Gaussian for optical transmission link. It has been shown that RZ Raised cosine yields the highest value of Q, good eye opening and lowest BER. [Copyright &y& Elsevier]

Abstract: Due to the fact that a metro network market is very cost sensitive, direct modulated schemes appear attractive. In this paper a CWDM (Coarse Wavelength Division Multiplexing) system is studied in detail by means of an Optical Communication System Design Software; a detailed study of the modulated current shape (exponential, sine and gaussian) for 2.5Gb/s CWDM Metropolitan Area Networks is performed to evaluate its tolerance to linear impairments such as signal-to-noise-ratio degradation and dispersion. Point-to-point links are investigated and optimum design parameters are obtained. Through extensive sets of simulation results, it is shown that some of these shape pulses are more tolerant to dispersion when compared with conventional gaussian shape pulses. In order to achieve a low Bit Error Rate (BER), different types of optical transmitters are considered including strongly adiabatic and transient chirp dominated Directly Modulated Lasers (DMLs). We have used fibers with different dispersion characteristics, showing that the system performance depends, strongly, on the chosen DML–fiber couple. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a wavelength division multiplexing multi-ring architecture with a separate control wavelength for metropolitan area networks. We study the critical problem of low fiber bandwidth utilization that many access ring protocols introduce, especially at high load conditions. In our study this problem is effectively faced by: (1) applying an efficient slotted access algorithm to avoid both data wavelengths and receiver collisions, (2) introducing a number of buffers at each node to effectively allocate the incoming traffic into them, and (3) applying an efficient algorithm for buffer selection for transmission that combines the priority criteria of packet age and receiver collisions avoidance. In this way, we obtain maximum fiber bandwidth utilization. Especially, our aim is to achieve not only significant throughput enhancement, but also essential dropping probability and total delay reduction. Also, the number of transmission buffers per node is investigated in order to manage maximum throughput improvement, while considering the financial cost. Finally, a discrete-event simulation model based on Poisson statistics is developed for the performance measures evaluation. [ABSTRACT FROM AUTHOR]

Abstract: A scheme of quantum network based on multiuser differential phase shift quantum key distribution system (DPS–QKD) is proposed. In this quantum network, arbitrary two users can achieve secret bits sharing by point-to-multipoint quantum key distribution and secret bits comparison. A protocol of secret bits sharing between arbitrary two users is presented. This network can implement secret bits distribution over 200km with higher key generation rate by today''s technologies. In theory, the capacity of user numbers in this network is unlimited. Hence, our proposed quantum network can serve for a metropolitan QKD network. A wide area QKD network can be constructed with this metropolitan QKD network. [Copyright &y& Elsevier]

The high-frequency segment (10-66 GHz) of the IEEE 802.16 standard seems promising for the implementation of wireless backhaul networks carrying large volumes of Internet traffic. In contrast to wireline backbone networks, where channel errors seldom occur, the TCP protocol in IEEE 802.16 Worldwide Interoperability for Microwave Access networks is conditioned exclusively by wireless channel impairments rather than by congestion. This renders a cross-layer design approach between the transport and physical layers more appropriate during fading periods. In this paper, an adaptive coding and modulation (ACM) scheme for TCP throughput maximization is presented. In the current approach, Internet traffic is modulated and coded employing an adaptive scheme that is mathematically equivalent to the replicator dynamics model. The stability of the proposed ACM scheme is proven, and the dependence of the speed of convergence on various physical-layer parameters is investigated. It is also shown that convergence to the strategy that maximizes TCP throughput may be further accelerated by increasing the amount of information from the physical layer. [ABSTRACT FROM AUTHOR]

Abstract: We propose a new technique that uses parametric amplification in optical fibers to combine two binary signals into a single quaternary amplitude-shift keying (4-ASK) signal. We develop a theoretical model to predict the power level distribution of the 4-ASK signals as a function of the extinction ratios of the input binary signals. Computer simulation results agree with the predictions of this theoretical model within a 0.9dB margin. We also analyze the application of this technique to the generation of quaternary-amplitude optical packets, which are attractive for allowing the label to be transmitted in the same bandwidth and simultaneously to the payload. Our results indicate that such optical packets may be propagated through lengths comparable to those involved in metropolitan area networks. [Copyright &y& Elsevier]

No abstract is available for this article. [ABSTRACT FROM AUTHOR]

Wireless metropolitan area sharing networks (WMSNs) are wide-area wireless networks with nodes owned and managed by independent wireless Internet service providers (WISPs). To support seamless roaming in emerging WMSNs, in this paper, we propose a localized and distributed authentication and billing architecture that aims at enabling efficient and privacy-preserving mutual authentication between mobile users (MUs) and WISPs. User anonymity and identity privacy can be protected, even in the presence of collusion between WISPs and a roaming broker (RB), which is considered to be the strongest user privacy protection. An efficient billing architecture is introduced and performed in the same stage of roaming, where U-tokens are defined and can be purchased by MUs from an RB as authentication credentials for the MUs to access the wireless network. The WISPs, thus, can cash the collected U-tokens in the RB for payment. We show that the proposed authentication and billing architecture can support localized inter-WISP authentication through the divisible blind signature scheme and a local witness strategy. A detailed analysis on a number of performance metrics, such as computation time and power consumption, is given to validate the performance of the proposed architectures. [ABSTRACT FROM AUTHOR]

Abstract: In this study we focus on the serious scalability problems that many access protocols for WDM ring networks introduce due to the use of a dedicated wavelength per access node for either transmission or reception. We propose an efficient slotted MAC protocol suitable for WDM ring metropolitan area networks. The proposed network architecture employs a separate wavelength for control information exchange prior to the data packet transmission. Each access node is equipped with a pair of tunable transceivers for data communication and a pair of fixed tuned transceivers for control information exchange. Also, each access node includes a set of fixed delay lines for synchronization reasons; to keep the data packets, while the control information is processed. An efficient access algorithm is applied to avoid both the data wavelengths and the receiver collisions. In our protocol, each access node is capable of transmitting and receiving over any of the data wavelengths, facing the scalability issues. Two different slot reuse schemes are assumed: the source and the destination stripping schemes. For both schemes, performance measures evaluation is provided via an analytic model. The analytical results are validated by a discrete event simulation model that uses Poisson traffic sources. Simulation results show that the proposed protocol manages efficient bandwidth utilization, especially under high load. Also, comparative simulation results prove that our protocol achieves significant performance improvement as compared with other WDMA protocols which restrict transmission over a dedicated data wavelength. Finally, performance measures evaluation is explored for diverse numbers of buffer size, access nodes and data wavelengths. [Copyright &y& Elsevier]

Of late, Optical Code Division Multiple Access (OCDMA) has attracted much attention because of its vast bandwidth availability and for allowing simultaneous users to access the same optical channel with less delay. The construction of codes with good auto and cross correlation properties with low Multiple Access Interference (MAI) is a big challenge in OCDMA system. Hence, there is increasing research in this area. In this paper, we propose a reliable simulated model for OCDMA system with improved performance as compared to previous designs. The system has been designed for a Metropolitan Area Network (MAN) with optical fiber length of 60 km. In this paper, the optical CDMA system has been designed and simulated by using redesigned W/T matrix code and WDM-type components for high data rates, i.e., 1 Gbps, 1.25 Gbps, 2.5 Gbps and 5 Gbps. A comparative Bit Error Rate (BER) and eye diagram analysis of high speed OCDMA system for asynchronous concurrent communication of multiple users at the above-mentioned data rate has been carried out. Results show that this proposed system can accommodate 16 simultaneous users for 2.5 Gbps for BER e-10. Previous designs have been on a bit rate of 1.25 Gbps for 16 users with BER e-9 (Mendez et al., 2004). With -19 db received power, 16 simultaneous users can be accommodated at the BER of e-16, e-13, e-10 and e-4 for 1 Gbps, 1.25 Gbps, 2.5 Gbps and 5 Gbps respectively. Hence, the system designed in the present work is well-suited for 16 simultaneous users for the data rates, i.e., 1 Gbps, 1.25 Gbps and 2.5 Gbps, and can accommodate up to eight numbers of simultaneous users for data rate 5 Gbps. [ABSTRACT FROM AUTHOR]

In this paper, a packet pre-classification media access control protocol based on a carrier sense multiple access with idle detection (CSMA/ID) scheme is investigated for supporting IP packets over all-optical WDM ring networks. The purpose of the protocol is to increase throughput and to decrease the packet transmission delay of IP packets over optical networks in a metropolitan area network. This protocol avoids both packet collision and packet fragmentation. In order to improve the utilization of the network, the packets transmitted from a local area network are first pre-classified into various class queues of an access point (AP) according to their length. After checking the available space based on the wavelength received by the receivers of the AP, the packets in the queues are transmitted. An analytical model is developed to evaluate the performance of the protocol, with simulation results showing good network efficiency. The proposed network has short-term variations that introduce unfairness conditions. This problem could be overcome by assigning a quota on individual queues to allow all queues fair access. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A time difference of arrival (TDOA) location scheme for the orthogonal frequency division multiplexing (OFDM) based wireless metropolitan area networks (WMANs) is presented. A novel TDOA estimation algorithm for OFDM signals is proposed and adopted in this scheme. The algorithm enhances the location performance by utilizing the information in the time and frequency domains obtained from the received location OFDM signals. The simulations are implemented with an 802.16e configuration considering an outdoor wireless scenario. The simulation results show that the scheme can meet the E911 requirements in even complex multipath channel conditions, and outperform the location schemes with traditional correlation detection TDOA estimations. [ABSTRACT FROM AUTHOR]

Simultaneous measurements with 10 MHz bandwidth at 2.5, 3.5 and 5.8 GHz were performed in a rural/semi-rural environment in the UK. The measurements were processed to generate power delay profiles to estimate the root mean square delay spread of the channel. The frequency range of the orthogonal frequency division multiplexing (OFDM) symbol bandwidth that has dropped below a predefined level, termed herein as average fade bandwidth, and the corresponding level crossing are employed to quantify the severity of frequency selectivity. The channel data were used to estimate the bit error rate, for the 256 carrier-OFDM IEEE802.16 standard using a frequency domain channel simulator especially designed for the study. It was found that the performance of quasi-stationary wireless broadband systems depends mainly upon the frequency selectivity and the channel coding rate with 1/2 rate coding giving a superior performance to 3/4 rate coding. Puncturing was found to weaken the capability of forward error correction coding in the presence of series of deep fades in the channel transfer function. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the correlation between attitude and self efficacy with regard to computer assisted education. Sample of the study was 125 teacher candidates in Gazi University Education Faculty. Data of the study was collected with the help of attitude and self efficacy scale. At the end of study, it was found that self efficacy and attitude with regard to computer assisted education was very high. Also, there was moderate correlation between self efficacy and attitude with regard to computer assisted education. [ABSTRACT FROM AUTHOR]

For the past few years, the evolution of electro-optical technology has driven change in optical networks in the access and backbone areas. Optical bypassing and traffic aggregation mitigate the scalability problem in backbone networks, and burst mode transmission can provide a cost-efficient solution for access networks. Using those technologies, a new solution can be found for metro area networks, which interconnect access and backbone networks. In this article, we introduce a new solution for metro area networks, called optical burst transport (OBT). OBT is designed to use the promising technologies of backbone and access networks so that it provides all benefits, such as dynamic bandwidth provisioning, scalability, and robustness for unbalanced traffic. The performance evaluation of OBT also is verified by means of a testbed implementation. [ABSTRACT FROM AUTHOR]

Abstract: IEEE 802.16 wireless Metropolitan Area Network (MAN) is expected to revolutionize the broadband wireless access technology. Efficient resource management is essential in providing scalability in such large IEEE 802.16-based wireless network and Quality of Service (QoS) for multimedia applications (VoIP, MPEG, FTP, WWW) is usually achieved by appropriate classification of scheduling services and grant/request mechanism. In this paper, we firstly discuss the QoS issue in IEEE 802.16 wireless MANs and propose a dynamic admission control scheme for scheduling services defined in the 802.16 specification. The proposed scheme provides the highest priority for Unsolicited Grant Service (UGS) connections and maximizes the bandwidth utilization by employing bandwidth borrowing and degradation. We develop an approximate analytical model to evaluate the system performance by assuming that the traffic processes of all scheduling services are Poisson processes. In fact, the self-similarity of non-voice traffic makes its traffic process far from Poisson process and should be modeled by Poisson Pareto Burst Process (PPBP). Therefore, in the later part of the paper, we analyze upper bound blocking probabilities of all scheduling services above the packet level using PPBP model for fractal traffic and Gaussian model for aggregated traffic in large wireless network as well as using the Chernoff bound method. Based on the analytical results, we give another admission control and bandwidth allocation mechanism above the packet level so as to minimize the blocking probability of each type of service in IEEE 802.16 wireless MAN. Analytical and simulation results are obtained and compared to demonstrate the effectiveness of proposed schemes and validate our analytical models. [Copyright &y& Elsevier]

This paper focuses about the results of the simulation and analysis of a network model that it implements differentiated services techniques in the MAC layer using a Traffic Shaping model. We have used Metropolitan Area technologies like ATM as reference, but in our case we have adapted the new IEEE 802.17 protocol knows as Resilient Packet Ring as a mechanism that assures Quality of Services over the Metropolitan network. [ABSTRACT FROM AUTHOR]

The design of the medium-access control (MAC) protocol is the most crucial aspect for high-speed and high-performance local and metropolitan area networks, since the decisions made at this level determine the major functional characteristics of these networks. Most of the MAC protocols proposed in the literature are not suitable for multimedia applications, since they have been designed with one generic traffic type in mind. As a result, they perform quite well for the traffic types they have been designed for, but poorly for other traffic streams with different characteristics. In this paper, we propose an integrated MAC protocol called the Multimedia-MAC (M-MAC), which integrates different MAC protocols into a hybrid protocol in a shared-medium network to efficiently accommodate various types of multimedia traffic streams with different characteristics and quality-of-service demands, namely, a constant-bit-rate traffic, bursty traffic (say, variable-bit-rate traffic), and emergency messages (say, control messages). We have developed a mathematical framework for the analysis and performance evaluation of our M-MAC protocol, which involves a queueing system with vacation. We have applied our M-MAC design approach to a wavelength-division multiplexing network, and evaluated its performance under various traffic conditions. [ABSTRACT FROM AUTHOR]

This article provides an overview of the Resilient Packet Ring (RPR) protocol with a focus on medium access and fairness. The RPR IEEE 802.17 standard is under development as a new high-speed technology for metropolitan backbone networks. A key performance objective of RPR is to simultaneously achieve high utilization, spatial reuse, and Fairness. The core technical challenge for RPR is the design of a fairness algorithm that dynamically throttles traffic to achieve these properties. The IEEE 802.17 RPR working group was formed in early 2000 to develop a standard for bidirectional packet-switched metropolitan rings. In this article the authors describe the RPR fairness algorithm as defined in the IEEE 802.17 protocol. The article presents the algorithm's design objectives, describes the RPR node architecture, outlines the key components of the fairness algorithm, and presents a set of simulation results regarding fairness, throughput, and convergence times. The article presents the design objectives of the RPR fairness algorithm in the context of legacy technologies, Gigabit Ethernet, and synchronous optical network.

IEEE Working Group 802.17 is standardizing a new ring topology network architecture, called the Resilient Packet Ring, to be used mainly in metropolitan and wide area networks. This article presents a technology background, gives an overview, and explains some of the design choices behind RPR. Some major architectural features are illustrated and compared by showing performance evaluation results using the RPR simulator developed at Simula Research Laboratory using the OPNET Modeler simulation environment. [ABSTRACT FROM AUTHOR]

Today's metro networks have evolved from the need to support traditional voice and private line services. However, the tremendous growth in access to frame relay, ATM, IP, and Ethernet services, coupled with the desire of enterprise customers to interconnect via Ethernet interfaces, suggests the need for a new approach. This article proposes a new architecture for packet-aware transport network (PATN) that supports both packet and traditional TDM services and leverages an assemblage of emerging technologies to provide efficient aggregation and switching of packet traffic in metro networks. The PATN has the potential of provide significant cost savings to carriers by reducing the number of network elements, reducing transport costs through statistical multiplexing, and eliminating the need for redundant multiplexing operations. [ABSTRACT FROM AUTHOR]

Currently, LAN technology is predominantly Ethernet-based and offers packet-optimized switched technology. With more than 90 percent of Internet traffic originating from Ethernet-based LANs, efforts are underway to extend Ethernet beyond LANs into MANs and further into WANs. However, native Ethernet protocols need extensions or support from other technologies in order to succeed as MAN technology in terms of scalability, QoS, resiliency, OAM, and so on. The two emerging trends to carry Ethernet traffic across the MAN can be classified into native Ethernet (IEEE) protocol extensions, and encapsulation by another transportation technology such as MPLS networks. The goal is to offer new and challenging services such as virtual private LAN service, also known as transparent LAN service (TLS). This article presents a comprehensive overview of the required extensions/support of the Ethernet with an emphasis on the emerging provider bridge technology. [ABSTRACT FROM AUTHOR]