We present a novel egocentric visual localization algorithm for an indoor navigation system, called PERCEPT -V, which is designed to assist the blind and visually impaired users traveling independently in an unfamiliar indoor space. Through the integration of a background extraction module based on Robust Principle Component Analysis (RPCA) into the localization algorithm, we successfully improve the resilience of camera localization to the presence of crowds in the observed scene. Experiments using datasets of videos containing various levels of crowd activity show that the proposed algorithm can increase prominently the reliability of localization performance.

mHealth (healthcare using mobile wireless technologies) has the potential to improve healthcare and the quality of life for elderly and chronic patients. Many studies from all over the world have addressed this issue in view of the aging population in many countries. However, there has been a lack of any consolidated evidence-based study to classify mHealth from the dual perspectives of healthcare and technology. This paper reports the results of an evidence-based study of mHealth solutions for chronic care amongst the elderly population and proposes a taxonomy of a broad range of mHealth solutions from the perspective of technological complexity. A systematic literature review was conducted over 10 online databases and the findings were classified into four categories of predominant mHealth solutions, that is, self-healthcare, assisted healthcare, supervised healthcare and continuous monitoring. The findings of the study have major implications for information management and policy development in the context of the Millennium Development Goals (MDGs) related to healthcare in the world.

In this paper, we propose a system capable of detecting and identifying people in videos captured by smart phones. We discuss the challenges to extend existing location aware multimedia applications from annotating static landmarks in distance to annotating dynamic people in close range with significant pose variations. We propose to use a hybrid video and RF tracking system to enable accurate observer and target localization, and extract part models comprised of Maximally Stable Color Regions for each target. The model can efficiently detect possible positions of targets in the video, which are then used as dynamic landmarks to calibrate the camera orientation. Finally, positions of all targets in the video are jointly estimated using both visual features and spatial constraints. Experiments show that our approach can locate identified targets in video with significantly higher accuracy than back-projection using camera orientation estimations from accelerometers and magnetometers.

Reliable tracking of people in video and recovering their identities are of great importance to video analytics applications.For outdoor applications, long range identity sensors such as active RFID can provide good coverage in a large open space, though they only provide coarse location information. We propose a probabilistic approach using noisy inputs from multiple long range identity sensors to globally associate and identify fragmented tracklets generated by video tracking algorithms. We extend a network flow based data association model to recover tracklet identity efficiently. Our approach is evaluated using five minutes of video and active RFID measurements capturing four people wearing RFID tags and a couple of passersby. Simulation is then used to evaluate performance for larger number of targets under different scenarios.identities are of great importance to video analytics applications.For outdoor applications, long range identity sensors such as active RFID can provide good coverage in a large open space, though they only provide coarse location information. We propose a probabilistic approach using noisy inputs from multiple long range identity sensors to globally associate and identify fragmented tracklets generated by video tracking algorithms. We extend a network flow based data association model to recover tracklet identity efficiently. Our approach is evaluated using five minutes of video and active RFID measurements capturing four people wearing RFID tags and a couple of passersby. Simulation is then used to evaluate performance for larger number of targets under different scenarios.

RFIDs are becoming ubiquitous in our social and economic lives, gradually transforming the environment into a smart space. In this paper we introduce SCOUT system built on a novel decentralized architecture for massive scale smart environments. SCOUT provides an underlying framework for efficient management of runtime activities and querying of smart object attributes. The architecture fulfills the need for dynamic attribute detection across a wide range of applications and can be deployed in diverse settings. The proposed SCOUT system can help management and attribute detection in scenarios such retailing, manufacturing, transportation and distribution industries. The advantage of the framework lies in its simplicity and ease of implementation. We present a set of results, by building a simulation environment as well as a workload generator, which highlight the proposed framework scalability.

We propose a middleware called BuddyShare to automatically form an overlay group of nearby friends' mobile phones to collaboratively download data by sharing mobile internet. This system is hypothetical in nature and only work on certain assumptions such as: 1) frequent availability of friends' phone nearby, 2) Sufficient social trust among physically close users to share internet and 3) sufficient social networking information available in phones. In order to validate these hypotheses, we collected human centric dataset of cellular phone users of university environment to study the user behavior. In this paper, we present certain social and proximity behaviors of these users that validate these hypotheses and show the practical feasibility of a BuddyShare system. We also study the usefulness of BuddyShare by virtually leveraging it on this user network, which concludes around three times scaling in download rate on average.

In this paper, we investigate the problem of scheduling flows for fair stream allocation in ad hoc networks utilizing multiple antennas at the transmitter and receiver side known as Multiple Input Multiple Output (MIMO) antenna technology. Our main contributions include: i) the concept of stream allocation to flows based on their traffic demands or class, ii) achieving the proportional fairness of the stream allocation in the minimum possible schedule length. We first formulate demand-based fair stream allocation as an integer linear programming (ILP) problem whose solution is a schedule that is guaranteed to be contention-free. We then solve this ILP in conjunction with binary search to find a minimum-length contention-free schedule that achieves the fairness goals. We also show that an implementation of our algorithm for a number of sample topologies in fact yields minimum length schedules that achieve the fairness goals.

To reap the benefits of advances in wireless technologies as well as provide backward compatibility with current investments, future wireless routers that constitute the backbone of Wireless Mesh Networks (WMNs) will be equipped with multiple radios of different technology standards. The multiplicity of channels, radios and technology standards makes the problem of efficient network utilization in a WMN more challenging. Unlike previous works that focused only on homogeneous WMNs, in this paper, we focus on determining an effective routing, channel assignment and scheduling scheme that maximizes the network capacity, while maintaining node level fairness in a heterogeneous network setting. We first introduce a novel graph model that captures the WMN heterogeneity in terms of the number of radios and radio technologies. Using this model, we provide an optimization formulation that determines the effective routing scheme and traffic values on each edge. To determine an interference-free channel assignment of these traffic values, we introduce a joint channel assignment and scheduling algorithm that preserves node level fairness. We perform an extensive evaluation of our solution in homogeneous and heterogeneous networks and study the impact of the number of orthogonal channels, radios, gateways and the aggregate traffic demand on the performance of our solution. Our results show that the proposed scheme obtains node level fairness while maximizing the network capacity.

In this paper, we present a collision free MAC protocol for wireless ad-hoc networks with multiple input multiple output (MIMO) links. The proposed MAC protocol provides proportional service differentiation to various classes of traffic based on their respective bandwidth demands. It exploits the spatial multiplexing and interference suppression capability of MIMO links in order to activate multiple links in the same collision domain. Simulation results show that the proposed MAC protocol achieves strict fairness in maintaining the proportional service differentiation among contending links. Then we introduce the concept of proportional fairness deviation which can be used as a tuning knob for assigning the leftover bandwidth to different traffic classes in proportion to their differentiation parameters. This tuning knob will adjust the quality of service assigned to users in a particular traffic class for a specific cost.

In this paper, we study the use of IEEE 802.11e for priority based safety messaging for inter-vehicle communications (IVC) in vehicular ad-hoc networks (VANET). The message priorities, which are assigned based on message urgency, are associated with different quality of service in terms of average delay and normalized throughput. We investigate the use of IEEE 802.11e to provide priority based service differentiation. To increase the communication reliability we also apply a repetitive transmission mechanism that provides proportional reliability differentiation for each prioritized message. We evaluate the performance of our proposed protocol using OPNET Modeler, in terms of average delay and normalized throughput as a function of the number of repetitions, number of vehicles, bit error rates, data rates, percentage of priority 1 vehicles and packet size. The results show that using proper parameter setting for IEEE 802.11e and appropriate number of repetitions per priority class will result in an efficient solution for IVC that supports different priority safety messaging.

In this paper we propose a MAC (Medium Access Control) protocol (named MACQUE) that provides QoS support for multimedia applications in the MI- UWB (Multiband Impulse-based Ultra Wideband) based wireless networks. The proposed MAC protocol utilizes the advantages provides by the MI-UWB including multiple non-overlapping frequency channels, simultaneous transmissions in same channel as well as dynamical reconfiguration of transmission parameters. The resource allocation algorithm of the proposed MAC protocol uses a two-phase procedure to provide explicit QoS support and optimize resource utilization in a dense medium-size MI-UWB network. The performance of the proposed MAC protocol is evaluated by extensive simulation study.

The growing convergence among mobile computing devices and smart sensors boosts the development of ubiquitous computing and smart spaces, where localization is an essential part for realizing the big vision. Due to their large size, high cost, and high power consumption, the current widely accepted outdoor localization methods based on GPS and cellular techniques are not suitable for tracking numerous small size and limited power objects. In this paper, we present Scout, an easy-setup and cost- effective outdoor localization system based on off-the- shelf active RFID systems and a probabilistic localization algorithm, which is compatible with the future smart spaces and ubiquitous computing systems. The proposed algorithm is robust to measurement uncertainty and self-adjustive to varying outdoor environments. Using MATLAB simulations, we investigate the system performance dependence on a number of system and environmental parameters. The simulation results prove that the proposed system is an accurate and cost-effective candidate for outdoor localization.

In this paper, we propose Multi-Channel Time Division Multiple Access (MC/TDMA) scheme which provides proportional service differentiation while achieving high throughput in a multichannel wireless network. Proportional service differentiation is achieved by scheduling traffic over multiple non-overlapping channels using the modified open-shop scheduling problem analogy. This analogy allows us to use known optimal algorithms that have been previously developed for the open-shop scheduling problem. With extensive performance evaluation using OPNET simulator, we show that the proposed MC/TDMA scheme provides proportional service differentiation while achieving high throughput. To the best of our knowledge, this is the first work for provisioning proportional service differentiation in wireless networks using multiple channels.

203-207

In this paper we propose an adaptive MAC protocol that provides QoS support for multimedia applications in UWB-based wireless networks. The proposed protocol accounts for the UWB unique characteristics while considering the QoS requirements. The resource allocation algorithm of the proposed protocol assigns the transmission parameters (data rate and power) to nodes in the network based on the current traffic conditions. We present a thorough performance evaluation of the proposed protocol in terms of throughput, admission ratio, energy consumption and delay. The proposed protocol is studied for different system loads and traffic distributions.

In this paper, we propose an adaptive contention-based MAC scheduling scheme called Multi-channel Contention-based TDMA (MC/TDMA) for Multichannel wireless networks which provides proportional service differentiation while achieving high resource utilization. The MC/TDMA scheme adaptively schedules the traffic over multiple non-overlapping channels by controlling the number of competing nodes on a common channel based on the system load. The scheduling problem of MC/TDMA scheme is solved in two phases. The first phase called the Timeslot Allocation phase is reduced to a modified open-shop scheduling problem which allows us to use known efficient open-shop scheduling algorithms. For the second phase called Channel Allocation Phase, which is a non-convex Non-linear Programming (NL-P) problem (an NP-Hard problem) we develop a greedy heuristic. In order to maximize the utilization of the network resources while achieving proportional service differentiation, we propose a tuning knob called the collision factor 'a' which can be adaptively adjusted based on the network load. Through extensive simulations using OPNET we show that the proposed MC/TDMA scheme can provide proportional service differentiation in a multichannel wireless network while optimizing the utilization of the network resources.

Demand for broadband access networks has grown rapidly with the increased demand for Internet connectivity and multimedia services. Fixed broadband wireless access systems based on the IEEE 802.16 standard may become a viable alternative to wired systems. In particular, the mesh networking capability added into the standard will potentially provide significantly wider broadband wireless coverage without requiring line-of-sight. In this paper, we present a transmission scheduling algorithm for the IEEE 802.16 mesh mode standard. To the best of the authors' knowledge, this is the first scheduling algorithm for a multihop network based on the 802.16 standard. Simulation results show that the proposed algorithm achieves high channel efficiency while providing equal transmission opportunity (i.e., fair access) to all nodes in the network. This study will aid network designers in fine-tuning the details of the communication system for satisfactory performance in the field

In a multirate wireless network, low data rate nodes consume proportionately more channel resources than high data rate nodes, resulting in low overall network performance. The use of multiple non-overlapping frequency channels in multirate wireless networks can overcome the performance degradation by having nodes communicate on different channels based on their data rates. However, no effort has been invested to utilize the multiple channels for a multirate wireless network. In this paper, we introduce the data rate adaptive channel assignment (DR-CA) algorithm for a multichannel multirate single-hop wireless network to provide higher network throughput and network efficiency. The main idea is to assign links having same or comparable data rates on the same channel to minimize the wastage of channel resources due to interference between high data links and low data rate links. We also design a new intermediary multichannel layer (IML) which resides between network layer and link layer, at which we implement the DR-CA algorithm. The IML design requires no modifications to the underlying MAC layer and upper layers of the network stack. To evaluate the proposed algorithm we define new performance metrics-channel efficiency for a multichannel multirate wireless network. Using OPNET simulations, we show that the multichannel enhancement using our proposed algorithm provides significant performance improvement in terms of network throughput and channel efficiency over existing approaches in multirate wireless networks. Under heavy load condition, the channel efficiency using DR-CA algorithm reaches 90% of the maximum limit. To the best of our knowledge, this is the first work to utilize the benefits of multiple channels in the multirate wireless network environment.

In this paper, we exploit the benefit of multiple orthogonal channels in multihop wireless access networks (MWANs) from the aspect of network topology control. Between medium access control and network layers, we propose a novel protocol named multi-channel coordinated temporal topology control (MOTTO). Controlling the temporal network topology through coordinated multi-channel assignments, MOTTO decomposes the contending multihop traffic in a single channel MWAN into small groups of single hop traffics over different channels, epochs and spaces. Such network decomposition effectively reduces the traffic contention and leads to significant capacity improvement in MWANs. Our scheme assumes a single half-duplex radio per node and can be implemented in software over standard off-the-shelf wireless network interface cards (NIC) without changes to MAC and network layers. Simulation results show that MOTTO significantly improves network performance in a number of MWANs scenarios.

In this paper, we present a collision free MAC protocol for wireless networks with smart antennas that provides proportional service differentiation to various classes of traffic based on their respective bandwidth demand. The proposed protocol works for diverse physical parameters such as number of interfaces at each node, number of communication frequencies, and antenna beamwidth. To the best of our knowledge, this is the first work that provides link layer differentiated services for wireless networks with smart antennas and explores the influence of the physical parameters and network topology on the performance of the MAC layer.

To meet the growing demand for broadband wireless connectivity, integrating 3G and IEEE 802.16 networks is a clear and viable solution. To the best of the authors' knowledge, this is the first solution proposed for the integration of 3G and 802.16 wireless networks. We present a novel network and mobile client architecture that provides seamless roaming and mobility while maintaining connectivity across these heterogeneous wireless networks and provides quality of service (QoS) support. To provide QoS support to the application in the integrated network environment, the proposed architecture incorporates the procedures for activating a QoS session, the translation between network-specific QoS classifications, and network and session layer QoS support. We provide simulation results that show the viability and performance of the proposed QoS architecture.

The main contribution of this paper is the design and implementation of Archies, a generic and open end-to-end architecture for adaptive streaming of live MPEG-4 video over last hop wireless networks. The distinguishing features of our architecture include support for end-to-end source rate adaptation, feedback control from the client and end-to-end packet loss differentiation. We also present a prototype implementation of Archies and evaluate its performance over a real network testbed. Archies serve as a generic and open end-to-end video streaming architecture and experimental real network testbed that provides an excellent platform to the research community to develop, evaluate and compare various algorithms for adaptive video streaming over wireless networks. The components of the architecture are designed to be lightweight and modular that could be easily extended and evolved in the future with better algorithms for video compression and source rate adaptation.

In this paper, we propose Spacing-based Channel Occupancy Regulation (SCORE) MAC protocol that provides proportional service differentiation in terms of normalized throughput in wireless LANs. As shown by our system model and simulation study, SCORE provides consistent, scalable and adjustable proportional differentiation for any network size, any service class distribution, any node data rate and any packet size. Compared to state-of-the-art prioritized service differentiation schemes like Enhanced Distributed Coordination Function, SCORE can quantitatively control the channel sharing between different service classes with significant performance gain in terms of higher network throughput and lower packet collision probability.

This paper introduces a cost-effective portable teletrauma system that assists health-care centers in providing prehospital trauma care. Simultaneous transmission of a patient's video, medical images, and electrocardiogram signals, which is required throughout the prehospital procedure, is demonstrated over commercially available 3G wireless cellular data service. Moreover, the physician can remotely control the information sent from the patient side. Such a technology will allow a trauma specialist to be virtually present at the remote location and participate in prehospital care, which improves the quality of trauma care and can potentially reduce mortality and morbidity. To alleviate the limited and fluctuant bandwidth barriers of the wireless cellular link, the system adapts to network conditions through media transformations, data prioritization, and application-level congestion control methods. Experimental evaluation of the system prototype over real network conditions, transmitting different media types between the trauma patient and hospital unit, is encouraging. The teletrauma system reported in this paper is the first of its kind and it provides a basis for future enhancements.

A large number of Internet service providers (ISP) view wireless technology as an attractive option to replace all or part of the hard-wired infrastructure that currently dominates the local loop/last mile. Therefore, these ISP must provide quality of service support to these applications consistent with that offered by the backbone. However, this is a very challenging task in the wireless environment due to the instability of the wireless channel and the diverse quality of service requirements dictated by different multimedia applications. We introduce a resource allocation algorithm for the wireless link that distributes information from the ISP facility to the homes. The algorithm takes into account the wireless channel characteristics, the quality of service required by the applications as well as a pricing value function. Our solution is based on 'time-value' scheduling algorithms originally developed for scheduling real-time processes during transient faults.

Advances in optical networking reveal that all optical networks offering a multigigabit rate per wavelength will soon become economical as the underlying backbone in wide-area networks, in which the optical switch plays a central role. One of the central issues is the design of efficient signaling protocols which can support diversified traffic types, in particular the bursty IP traffic. This paper introduces a novel signaling protocol called the sampling probe algorithm (or SPA) to be used in a class of optical packet switching systems based on wavelength division multiplexing (WDM). The proposed scheme takes a drastically different approach from all existing signaling protocols. The salient features are 1) the pretransmission coordination is using an in-band signaling protocol, and thus does not require separate control channel(s) for transmission coordination; 2) the protocol is based on a reservation (connection) scheme which is capable of supporting multimedia traffic; 3) a gated service is adopted in which each successful reservation allows multiple packets (train of packets) to be transmitted, which can significantly reduce the per packet overhead; 4) the scheduling algorithm is adaptive by allowing flexible assignment of bandwidth on-demand; 5) the channel status gathering is done in a distributed fashion, and uses a passive listening mechanism, which itself does not interfere with packet transmissions. The results demonstrate that the proposed in-band signaling protocol can achieve high throughput and stability under heavy traffic condition.

We consider the problem of supporting multiple classes of real-time and non-real-time traffic on a WDM-based local-area network. We present a demand-adaptive algorithm which schedules transmission according to the quality-of-service requirements of the various traffic classes. The algorithm requires one control channel, on which a single token circulates. This token is used both as a means of communicating status information between the nodes and of controlling access to each of the multiple channels. Numerical examples are provided to illustrate the performance of the algorithm.

Future distributed systems are expected to support mo-bile computing through wireless extensions. In such environments, the spatial location of system resources, such as servers, can change dynamically as a result of host mobility. Consequently, a search or discovery cost is incurred when-ever a client requests use of a mobile resource whose location is unknown. In addition, because of the acute dependence of radio link performance on the characteristics of indoor operating environments, the Quality of Service experienced by a client that utilizes a mobile resource can depend on the resource’s specific location. The work reported in this paper proposes and evaluates a statistical framework for resource discovery in distributed computing environments with mo-bile hosts. Specifically, taking the peculiar attributes of wireless segments of the distributed system into account, we investigate the interplay between the cost of search for po-tentially mobile resources and the utility or benefit accrued to clients that require such resources. This interplay has im-portant ramifications for resource allocation in distributed mobile computing environments.

Considerable interest has been focusing on the possibility of employing a large number of low Earth orbit (LEG) satellites to provide an overall global coverage. However, there has been no performance study of such systems. The authors investigate the performance of low Earth orbit-satellite systems in terms of the system capacity, the average number of beam-to-beam handoffs and satellite-to-satellite handoffs the channel occupancy distribution and the average call drop probability. These performance measures are obtained as a function of: (1) the network constellation, (2) the satellite speed, (3) the cell size, and (4) the average transaction duration. These metrics are exemplified on the Iridium system. The results derived provide useful and simple tools for system design as well as for system analysis.>

Presents time-wavelength scheduling algorithms for WDM star based networks. The algorithms incorporate the unique aspects of WDM communication such as a number of tunable transmitters and receivers at each node, the tuning time, and a limited number of wavelengths. The transmission duration is composed of two elements: 1) the packet transmission time and 2) the tuning time of the system's transmitters and receivers. Based on the ratio between these two elements, the authors designed two scheduling algorithms. The first algorithm provides a minimal packet transmission duration, while trying to minimise the tuning time. The second algorithm obtains a schedule with a minimal tuning duration, while minimising the packet transmission time of the schedule.>

In this paper we present a new approach to the design of multihop lightwave networks with connectivity patterns that can be dynamically reconfigured. We introduce a practical algorithm that efficiently reconfigures the connectivity diagram by reassigning wavelengths to best fit the current traffic pattern. A newly developed stochastic optimization algorithm is used to obtain the mapping of a regular structure into a WDM star, while optimizing the system performance measures. The optimization tool is generated and can be used with any objective function which is a function of the traffic patterns, the system control and the system configuration. The results show that this is a practical tool and the resulting structures have a superior system performance.>

One of the major challenges in the virtual topology design of a WDM star based system, is to incorporate in the optimization process both realistic objective functions and real system behavior. The authors present an efficient discrete optimization algorithm that meets these goals while incorporating the prevailing traffic conditions. They simulate the real system and then approximate the objective function by a short term simulation. The optimization process is based on an ordinal optimization approach, i.e., is insensitive to the approximation of the objective function obtained by short term simulation. Another crucial issue in virtual topology design is how to evaluate the quality of the solution obtained by the algorithm. They propose a new metric to evaluate the solution quality, the so called suboptimal quality, obtained by deriving the solution's relative position in the state space according to the performance order. The experiments presented in the paper attest to the quality (efficiency and robustness) of the optimization algorithm and its suitability to solve the wavelength assignment problem.>

An approach to the design of multihop lightwave networks with connectivity patterns that can be dynamically reconfigured is presented. A practical algorithm that efficiently reconfigures the connectivity diagram by reassigning wavelengths to best fit the current traffic pattern is introduced. A stochastic optimization algorithm is used to obtain the mapping of a regular structure into a wavelength-division-multiplexed (WDM) star, while optimizing the system performance measures. The optimization tool is general and can be used with any objective function which is a function of the traffic patterns, the system control, and the system configuration. The results show that this is a practical tool and that the resulting structures have a superior system performance.>

A cost-efficient metropolitan area network (MAN) based on a two-level structure is introduced. The physical topology of each level is a wavelength-division-multiplexing (WDM) passive star. The system design incorporates both the restrictions imposed by the unique features of the metropolitan environment, such as a relatively large number of nodes and large propagation delays, and the hardware limitations dictated by the WDM technology, such as a limited number of transceivers per node and the unavailability of wide-range rapidly tunable transceivers. A multicontrol channel-based protocol that is particularly suitable for packet switched communications is proposed. An analytical model is presented, and the system performance in terms of throughput and average delay is obtained.>

The proposed HIPPI standard, a connection-oriented communication standard for very-high-speed interconnection systems connecting high-end computing systems, is discussed. The problems of managing connections and of configuring the interconnection system as either a single crossbar switch or as a clique of crossbar switches are considered. Three connection management policies are introduced: a centralized policy, a broadcast policy, and a distributed policy. To compare these policies for different system configurations, a set of models is introduced and used to evaluate a range of interconnection system configurations. The results of these models and the use of a cost measure make it possible to compare the cost and performance of different configurations and alternative connection management policies.>

The first time-wavelength assignment algorithm for wavelength division multiplexing (WDM) star-based local and metropolitan area networks is presented. The algorithm incorporates the unique aspects of WDM communication such as a number of tunable transmitters and receivers at each concentrator, the tuning time, and a limited number of wavelengths. The transmission duration is composed of two elements: the packet transmission time, and the overhead incurred due to the tunability of the system's transmitters and receivers. For a given traffic matrix, the algorithm obtains a TDM/WDM schedule with minimal packet transmission duration, while minimizing the tuning time.>

The design of a wavelength division multiplexing (WDM) passive star network must address the following limitations of the optical hardware technologies: a limited number of transmitters and receivers at each node; the unavailability of rapidly tuning transmitters and receivers; and the mismatch between the electronic processing rates and the optical transmission bandwidth. The authors investigate the use of regular virtual topologies as an efficient solution that incorporates the above hardware limitations, while providing high system utilization and low end-to-end delays. The following regular topologies are investigated: Shufflenet, binary hypercube, generalized hypercube, and two-dimensional torus. A number of performance and hardware related metrics are introduced that reflect the use of these topologies in a high speed optical environment. Based on these metrics, along with upper and lower bounds developed for performance and hardware requirements, the authors evaluate and compare the selected regular topologies. They also address the issue of mapping the regular virtual topologies into a WDM star network.>

The authors introduce an approximate performance model for a packet switched satellite cluster consisting of m satellites interconnected through intersatellite links. The satellite cluster performance is expressed in terms of mean delay, throughput, and overflow probability. These performance measures are obtained as a function of the system load, traffic distribution, and system configuration in terms of the number of uplinks, number of buffers, number of transponders, and the intersatellite link capacity. The results obtained from the analytical model were within the confidence intervals of the simulation results obtained with a 99% confidence level. The analysis can be used to investigate the sensitivity of the system performance as a function of the system configuration.>

An architectural approach that meets high bandwidth requirements by introducing a communication architecture based on lightpaths, optical transmission paths in the network, is introduced. Since lightpaths form the building block of the proposed architecture, its performance hinges on their efficient establishment and management. It is shown that although the problem of optimally establishing lightpaths is NP-complete, simple heuristics provide near optimal substitutes for several of the basic problems motivated by a lightpath-based architecture.>

The authors introduce analytic models for evaluating demand assignment protocols in realistic finite-buffer/finite-station network configurations. A solution for protocols with gated and nongated service disciplines that enables one to model demand assignment protocols as found, for example, in local and metropolitan area networks and in satellite communication systems is presented. A tractable approximate solution based on linear equations whose number is also linear is given. It is demonstrated that in addition to its computational efficiency, the presented approach does not incur a significant penalty in terms of accuracy.>

The authors present a novel approach to the optimal time-slot assignment problem for a general satellite-switched time-division multiple-access (SS/TDMA) satellite cluster with intersatellite links (ISLs) interconnection. The proposed allocation algorithm accounts for the following: systems with any number of satellites; each satellite covers an arbitrary number of zones; no onboard buffering at the satellites; and ISLs with arbitrary capacities. They present an analogy between the satellite cluster scheduling problem and the modified openshop scheduling problem. Using this analogy the authors introduce a heuristic algorithm and an optimal branch-and-bound algorithm. They investigate the performance of the proposed heuristic both by theoretical bounds and by comparing the simulation results produced by the heuristic with the optimal results. In all cases the heuristic algorithm results are within 10% of the optimum.>

Efficient scheduling algorithms for the slot assignment problem in a satellite-switched time-division multiple-access (SS/TDMA) system are presented. This problem is translated into a modified open-shop scheduling problem, allowing the use of known optimal algorithms. Their complexity is expressed as a function of the following parameters: the number of nonzero entries in the demand matrix, the number of uplinks, and the number of downlinks. According to the values of these parameters, the algorithm with the lowest computational complexity can be adopted. Although the computational complexity of previously published algorithms is drastically reduced, simulation results show that the results are close to previously presented solutions in terms of the assignment duration and the number of switching matrices.>

The problem addressed arose from the evolution of broadband applications and the design of networks that service them. An emerging approach optimizing the transport mechanism in these networks is based on the establishment of virtual topologies. The problem of determining the set of physical links for each virtual link routing is studied. These sets are chosen so as to minimize delay and maximum physical link congestion. A lower bound on the problem and a heuristic solution that achieves near-optimal results when compared with the bound are developed.>

A wavelength division multiplexing (WDM) transmissive star network is investigated, in which each node has one tunable transmitter with limited tuning capability and multiple fixed receivers. Two synchronous channel access protocols requiring no pretransmission penalty are considered: random access and fixed transmission scheduling. An efficient approximate analysis with drastically reduced computational complexity is presented. In spite of the reduced complexity, the presented approach produces very accurate results and can serve in producing the most cost-effective system design for given performance requirements.>

A performance study of two onboard stored, baseband switched, TDMA satellites interconnected through intersatellite links is presented. The uplinks are operated under the slotted ALOHA policy, while the downlinks and intersatellite links are operated using TDM policy. Each satellite has a finite buffer capacity for successful packets arriving, on the uplinks and on the intersatellite links. The authors introduce an approximate analytical model that determines the satellite cluster performance in terms of mean delay, throughput, and overflow probability. The system performance is obtained as a function of the system load, traffic distribution, number of uplinks, number of buffers, number of Earth zones, number of transponders at each satellite, and the intersatellite link capacity. The analytical results were within the confidence intervals of the simulation results obtained with 99% confidence level. Using this model, the system designer can obtain the minimal system configuration for a required system performance.>

The authors introduce two techniques for allocating and managing buffers in support of distributed system operation and evaluate the resulting system behavior. For this evaluation a methodology that permits the development of an analytic model is introduced. With the help of this model, it becomes possible to fine-tune the buffer allocation policies in realistic system configurations.>

An inherent problem of conventional point-to-point wide area network (WAN) architectures is that they cannot translate optical transmission bandwidth into comparable user-available throughput due to the limiting electronic processing speed of the switching nodes. A solution to wavelength division multiplexing (WDM)-based WAN networks that addresses this limitation is presented. The proposed lightpath architecture trades the ample bandwidth obtained by using multiple wavelengths for a reduction in the number of processing stages and a simplification of each switching stage, leading to substantially increased throughput. The principle of the lightpath architecture is the construction and use of a virtual topology network in the wavelength domain, embedded in the original network. A study is made of the embedding of virtual networks whose topologies are regular, using algorithms which provide bounds on the number of wavelengths, switch sizes, and average number of switching stages per packet transmission.>

An approach to communication architectures for high-speed networks which provides efficient, adaptive communication for any traffic distribution is presented. It is based on a concept of dynamic sharing of communication resources which is obtained from the following three-tier SWIFT architecture. At the physical layer the high-speed communication system is based on the use of several lower speed channels or frequencies. At the data link layer, driven by hardware simplicity considerations, the SWIFT architecture uses a fixed time-slotted allocation of subchannels, in which each node is required to transmit or receive over only a single, predetermined, subchannel at a time. To provide adaptive channel access control, while preserving the data link hardware simplicity, a network layer is added. This layer introduces multihop adaptive channel (frequency) routing on the inherently broadcast communication medium. The routing concept provides dynamic sharing of communication channels and buffers, leading to a fully distributed adaptive bandwidth control. An analytic model for analyzing the performance of the multilayered architecture is developed. It shows that for homogeneous or heterogeneous traffic requirements the approach provides throughput/delay performance superior to that found in existing communication systems.>

An approximate solution to slotted communication systems with finite population and finite buffer capacity is presented. The authors assume symmetric systems and present for the first time a linear solution involving linear equations whose number is a linear function of the total buffer capacity. They show that the model can be applied to existing multiaccess channel protocols in which a single successful transmission can be affected per slot. They further show that, unlike solutions based on existing nonlinear models, the proposed solution can be extended to communication systems in which several successful transmissions can take place in parallel, such as multibus communication networks and multichannel satellite systems.>

Emerging applications require a substantially higher bandwidth than the one offered by current networks. The authors propose a novel architectural approach that meets the high bandwidth requirements by introducing a communication architecture based on lightpaths, which are purely optical transmission paths in the network. Since lightpaths form the building block of the proposed architecture, its performance hinges on their efficient establishment and management. The authors shown that although the problem of optimally establishing lightpaths is NP-complete, distributed heuristics provide near-optimal solutions for several of the basic problems presented by the lightpath architecture.>

A path-oriented channel allocation management approach is introduced for the emerging high-bandwidth fiber optic star networks. In the proposed approach, the transmission channel of the source node and the reception channel of the destination node are synchronized at the central switching node, creating a virtual path for packet communication between any two nodes. The number of virtual paths that can be established simultaneously, i.e. the number of concurrent packet transmissions, equals the number of channels in the network. The proposed path allocation thus provides maximum spatial reuse not found in existing fiber optic star systems. The provision of a virtual path for every packet eliminates the need for buffering at the central node and provides bounded delays.>

The authors consider a path-oriented channel allocation management. As opposed to multiaccess protocols of existing fiber-optic systems, in the proposed approach the outgoing channel of the source node and the incoming channel of the destination node are allocated time-sequentially, creating a time-dependent virtual path for all pairs of users. Using the time-oriented path allocation, the need for packet buffering at the central node is eliminated multiple channels can be utilized simultaneously for different transmissions, and packet delays are bounded. The authors demonstrate that the same approach is feasible for efficient control of multibeam satellite systems. They introduce a tractable analytic model for the evaluation of communication systems based on this approach. The model is used to evaluate the proposed system performance under different switching functionalities of the central node. In addition to providing the throughput/delay characteristics of the system, the model shows a relation between the degree of star symmetry and the system performance, with the equidistant node arrangement yielding the optimal performance.>

Emerging high speed networks are using optical fibers employing time division synchronous communication. In these systems the use of optical switching is strongly advocated due to the bottleneck created by store and forward in electronic components. Switching solutions geared toward optical systems have been proposed so far only for packet switching networks.

This paper introduces analytic models for evaluating demand assignment protocols in realistic finite buffer/finite station network configurations. We present a solution for implicit and explicit token passing systems enabling us to model local area networks, such as Token Bus. We provide, for the first time, a tractable approximate solution by using an approach based on restricted occupancy urn models. The presented approximation involves the solving of linear equations whose number is linear and equal only to the number of buffers in the system. It is demonstrated that in addition to its simplicity, the presented approximation is also highly accurate.

A multibus train (ordered demand assignment) communication architecture, using the AMTRAC protocol (for efficient utilization of fiber-optic-based very-high-speed networks) is presented. Taking advantage of the emerging WDM (wavelength-division multiplexing) and FDM (frequency-division multiplexing) technologies, the proposed solution introduces a coordinated multichannel control combining the performance advantages of two known approaches for high-speed communication: multichannel and train protocols. As a result an AMTRAC-based high-speed network achieves channel utilization significantly higher than previous approaches. For a network consisting of N stations, with propagation delay to packet transmission time ratio given by a, the AMTRAC architecture reaches a capacity of 1/(1+a/N/sup 2/).>

Communication architectures for very-high-speed networks are dealt with. The use of high communication speed increases the ratio between the end-to-end propagation delay and the packet transmission time. This increase restricts the utilization of the high system bandwidth in broadcast channel-based systems, causing a rapid performance deterioration. A communication system architecture characterized by the use of several parallel channels and design of the nodes' channel interface is presented. The channel-division approach is introduced, showing that for a given system bandwidth the total system capacity will be increased by bandwidth division and parallel communication. An analytic model of this system is developed, from which the proposed system's performance is obtained and performance bounds determined for multichannel slotted finite systems. The results show that the architecture has a potential to improve significantly the system performance compared to conventional single-channel-based systems. Furthermore, for a given network configuration an optimal architecture can be found which simultaneously maximizes the system throughput and minimizes the average packet delay.>

In conventional high-speed systems, the high ratio between the end-to-end propagation delay and the message transmission time severely restricts the system performance. Thus, the increase in channel bandwidth may be accompanied by only a marginal increase in actual system capacity. A combined frequency-time division-based control of the high-speed channel that significantly reduces this problem is proposed. The design of protocols subject to the unique channel control penalties of the resulting multichannel system is considered. The allocation of channels on a demand assignment basis is hindered in the multichannel configuration by the time penalty involved in locating an idle channel and by practical limitations on the transmit/receive multichannels mode interface. A new class of fixed allocation protocols is introduced in which the channel access is obtained without the aforementioned penalties. The protocols build on the allocation of source and destination oriented transmission rights, taking into account the implementation aspects of multichannel networks. It is shown that this class of protocols covers the whole range of random-access to fixed-channel-access control policies. An analytic approach for a uniform analytic treatment is introduced, showing the potential for a significant improvement in the system capacity and the average message delay.>

A class of message-based or station-based priority protocols for demand-assignment-based local area networks (LANs), such as Token Bus, HYPERbus, LCN, etc., is defined. It is shown how existing priority protocols can be represented within this class and how they can be extended for a more efficient realization with regard to both delay and capacity of prioritized channel access in LANs. An analytic approach for analyzing multiple-access systems operating under prioritized demand assignment protocols is introduced. The approach permits the modeling of station-dependent and priority-dependent arrival rates and generally distributed transmission times. The introduced finite-population model is especially appropriate for prioritized systems where the number of users per priority class is typically small and users place different service demands on the system. For modeling systems with large populations of users, an approximate model, which is shown to be significantly more computationally efficient than the exact model without imposing additional modeling restrictions, is introduced.>

In high-speed communication networks, the ratio between the end-to-end propagation delay to packet transmission time is large, causing increased scheduling overhead in demand assignment protocols and increased collision probabilities in random access schemes. These lead to rapid degradation of the channel utilization in both channel access control approaches. In this paper, we present a "random token" oriented protocol where channel access is scheduled by random, implicit token passing leading to lower channel access control penalty. By optimally balancing the collision and scheduling penalties, the protocol allows the network to reach better performance than that obtained from random access schemes in networks with and without collision detection, without imposing additional system operational assumptions. Specifically, the random token protocol does not require knowledge of the number of stations, their identities, or synchronization in periods of silence. Therefore, the protocol is also suitable for high-speed networks with frequent reconfiguration and for mobile radio networks.

The HYPERchannel communication network based on one to four trunks, or channels is considered. We develop closed queueing models with dependent servers which characterize the network performance as a function of the number of channels, the channel load, the number of stations and the packet length distribution. For analyzing the network behavior with constant packet length we introduce techniques for representing the actual asynchronous network operation by a tractable "sequential synchronous" model. Throughput and delay measures are in this way obtained for asynchronous systems operating with constant or exponential service times. The developed approach can also be used for obtaining tractable analyses of other asynchronous systems, such as multiprocessors employing multiple-bus interconnection. In the case of HYPERchannel networks, we apply the introduced models for analyzing multi- trunk network behavior and for predicting the number of channels needed to obtain a required packet-delay/trunk-utilization performance. In HYPERchannel networks the observed results are of special significance since they are most pronounced when the number of stations is small, the situation found in the majority of operational networks.

The development of “very high speed” networks is being motivated by emerging applications and is therefore attracting increasing attention. As demonstrated in the past, in conventional high speed systems the high ratio between the end-to-end propagation delay and the message transmission time severely restricts the system performance. Thus the increase in channel bandwidth may be accompanied by only a marginal increase in actual system capacity. In this paper we propose a network architecture which eliminates this problem by introducing a combined Frequency - Time Division based control of the high speed channel. We consider the implementation characteristics of the resulting multichannel system and show that the design of protocols in these systems is subject to unique channel control penalties. Specifically, we show that in addition to the relatively high cost of channel sensing, the allocation of channel on a demand assignment basis is hindered in the multichannel configuration by the time penalty involved in locating an idle channel and by practical limitations of multichannel node interface design. We therefore introduce a new class of “allocation” protocols in which the channel access is obtained without the aforementioned penalties. The allocation protocols build on message source and destination oriented transmission rights allocation, taking into account the implementation aspects of multichannel networks. We show that the class of “multichannel allocation” protocols covers the whole range of random access to fixed channel access control policies and introduce an analytic approach for a uniform analytic treatment. The analysis demonstrates the potential for a significant improvement in the system capacity and the average message delay, when compared to a conventional single (undivided) channel system.

Demand assignment protocols have been implemented in a large number of operational LANs. However, the analytic models for protocol evaluation currently capture only a limited range of LAN operational circumstances. In this paper we present an analytic tool for evaluating fair and prioritized demand assignment protocols with a relatively general workload model. We consider arbitrary and station dependent message size distributions and arrival rates. This allows the modeling of LANs with heterogeneous workloads, thus permitting a larger correspondence between the modeled system and the real life network.

The concept of a multibeam satellite system With on-board processing and memory is studied. In this system multiple slotted ALOHA uplinks carry the traffic to the satellite. Packets are accepted at the satellite, when memory is available, and are routed to their destination zones using a TDM protocol. We present a model which can be used to evaluate a satellite system with conflict-free scheduling, i.e., a system in which several packets can be simultaneously chosen for downlink transmissions, given each earth zone is served by at most one satellite transponder in each slot. We compute the system throughput, packet delays, and buffer overflow probabilities for a general configuration. It is shown that for some configurations the one beam per zone restriction can have a significant effect on the system performance. The presented model can be also used to evaluate satellite systems when this restriction is removed and to evaluate a variety of other satellite systems.

The HYPERchannel communication network configured around one to four channels is considered. We develop a queueing model which characterizes the network performance as a function of the number of channels, the channel load and the number of stations in the network. The model is used to analyze the multichannel system performance and to evaluate the effect of the channel selection mechanism, as implemented by the HYPERchannel station interface units, on the performance.