In this paper, token-based security protocols with dynamic energy-security level tradeoff for Internet of Things (IoT) devices are explored. To assure scalability in the mechanism to authenticate devices in large-sized networks, the proposed protocol is based on the OAuth 2.0 framework, and on secrets generated by on-chip physically unclonable functions. This eliminates the need to share the credentials of the protected resource (e.g., server) with all connected devices, thus overcoming the weaknesses of conventional client-server authentication. To reduce the energy consumption associated with secure data transfers, dynamic energy-quality tradeoff is introduced to save energy when lower security level (or, equivalently, quality in the security subsystem) is acceptable. Energy-quality scaling is introduced at several levels of abstraction, from the individual components in the security subsystem to the network protocol level. The analysis on an MICA 2 mote platform shows that the proposed scheme is robust against different types of attacks and reduces the energy consumption of IoT devices by up to 69% for authentication and authorization, and up to 45% during data transfer, compared to a conventional IoT device with fixed key size.

Devices in the Internet of Things (IoT) produce large amounts of sensitive data. However, the use of the public Internet for data transfer by IoT devices makes them susceptible to cyber attacks. Among these attacks, data tampering or modification attacks to disrupt or bias the states of applications using these data may result in widespread damage and outages. To detect such attacks, this paper proposes an efficient and simple technique to detect data tampering in IoT systems. The proposed mechanism uses a random time hopping sequence and random permutations to hide validation information. We also present a formal security analysis of the proposed protocol. Performance analysis of the proposed protocol shows that it has low computational complexity and is suitable for IoT systems.

One of the most important and critical requirements for Internet-of-Things (IoT) based systems is security under limited resources. The simple and low-cost nature of many IoT devices makes them a prime target for physical, side-channel, and cloning attacks. To address this issue, this paper presents an efficient protocol for mutual authentication in IoT systems. The proposed protocol uses a Physical Unclonable Function to provide the desired security characteristics. An analysis of the protocol shows that it is not only robust against different kind of attacks, but also very efficient in terms of memory, computations, energy, and communication overhead.

The Internet of Things (IoT) represents a great opportunity to connect people, information, and things, which will in turn cause a paradigm shift in the way we work, interact, and think. IoT devices are usually small, low cost, and have limited resources, which makes them vulnerable to physical, side-channel, and cloning attacks. Therefore, any protocol designed for IoT systems should not only be secure but also efficient in terms of usage of chip area, energy, storage, and processing. To address this issue, we present light-weight mutual authentication protocols for IoT systems based on physical unclonable functions. Protocols for two scenarios are presented, one when an IoT device and server wish to communicate and the other when two IoT devices want to establish a session. A security and performance analysis of the protocols shows that they are not only robust against different types of attacks, but are also very efficient in terms of computation, memory, energy, and communication overhead. The proposed protocols are suitable for real time applications and are an attractive choice for implementing mutual authentication in IoT systems.

Increased power usage and network performance degradation due to best-effort bandwidth sharing significantly affect tenancy cost, cloud adoption, and data center efficiencies. In this article, we propose a novel Sliding-Scheduled Tenant request model which enables tenants to specify the required duration of their application within a certain window, in addition to its resource requirement graph. We investigate the sliding-scheduled application placement and routing problem, which selects the start-time of requests within their specified time-window to reserve both server and network resources for their required duration, and therefore provide resource guarantees with predictable performance. Using the multi-component utilization-based power model, we formulate the problem as an optimization problem that maximizes the acceptance rate while consuming as low power as possible. We develop fast online heuristics that adopt power, acceptance and adaptive spread-based scheduling policies while allocating the resources with the consideration of request duration and current shutdown-time of the devices. We demonstrate the effectiveness of the proposed algorithms in terms of power saving and acceptance rate, 1) for small data centers, by comparing their performance with the numerical results obtained from solving the optimization problem using CPLEX and 2) for large data centers using comprehensive simulation results.

Increased power usage and network performance variation due to best-effort bandwidth sharing significantly affect tenancy cost, cloud adoption, and data center efficiencies. In this paper, we propose a novel time-aware request model which enables tenants to specify an estimated required time-duration, in addition to their required server resources for Virtual Machines (VMs) and network bandwidth for their communication. We investigate the VM-placement and routing problem, which allocates both server and network resources for the specified time-duration, to provide resource guarantees. Further, we exploit VM-migration while considering its power consumption overhead, to improve power saving and resource utilization. Using the multi-component utilization-based power model, we formulate the problem as an optimization problem that maximizes the acceptance rate while consuming as low power as possible. We develop fast online heuristics that allocate resources for requests, considering their duration and bandwidth demand. We also develop migration policies augmenting these heuristics. For migration heuristics, we propose server-migration and switch-migration approaches, which migrate the VMs between the powered-on servers only if their migrations result in turning-off at least one server and switch, respectively. We demonstrate the effectiveness of the proposed heuristics in terms of power saving, acceptance ratio, and migration overhead using comprehensive simulation results.

Power efficiency and predictable performance have become major concerns for cloud service providers as they significantly affect cloud adoption and tenancy cost. Providing guaranteed resources for predictable performance in data centers drives the need for a request model which abstracts the traffic characteristics as well as the resource requirements of tenant applications. In this paper, we propose a novel Sliding Scheduled Tenant (SST) request model which enables tenants to request their resources for an estimated required time duration which can slide within a certain time-window. We investigate the power-efficient resource-guaranteed Virtual Machine (VM) -placement and routing problem for dynamically arriving SST requests. The problem requires provisioning of the specified resources in a data center for the required duration of requests by choosing an appropriate start- and end-time within their specified time-window, so as to maximize the number of accepted requests while consuming as low power as possible. We develop a mixed integer linear programming (MILP) optimization problem formulation based on the multi-component utilization-based power model. Since this problem which is a combination of VMplacement, scheduling and routing problems, is computationally rohibitive, we develop a fast and scalable heuristic algorithm. We demonstrate the effectiveness of the proposed algorithm and SST request model in terms of power saving and acceptance ratio through comprehensive simulation results.

The newly emerging wireless powered communication networks (WPCNs) have recently drawn significant attention, where radio signals are used to power wireless terminals for information transmission. In this paper, we study a WPCN where one multi-antenna access point (AP) coordinates energy transfer and information transfer to/from a set of single-antenna users. A harvest-then-transmit protocol is assumed where the AP first broadcasts wireless power to all users via energy beamforming in the downlink (DL), and then, the users send their independent information to the AP simultaneously in the uplink (UL) using their harvested energy. To optimize the users' throughput and yet guarantee their rate fairness, we maximize the minimum throughput among all users by a joint design of the DL-UL time allocation, the DL energy beamforming, and the UL transmit power allocation, as well as receive beamforming. We solve this nonconvex problem optimally by two steps. First, we fix the DL-UL time allocation and obtain the optimal DL energy beamforming, UL power allocation, and receive beamforming to maximize the minimum signal-to-interference-plus-noise ratio of all users. This problem is shown to be still nonconvex; however, we convert it equivalently to a spectral radius minimization problem, which can be solved efficiently by applying the alternating optimization based on the nonnegative matrix theory. Then, the optimal time allocation is found by a one-dimensional search to maximize the minimum rate of all users. Furthermore, two suboptimal designs of lower complexity are also proposed, and their throughput performance is compared against that of the optimal solution.

Variation in network performance due to the shared resources is a key obstacle for cloud adoption. Thus, the success of cloud providers to attract more tenants depends on their ability to provide bandwidth guarantees. Power efficiency in data centers has become critically important for supporting larger number of tenants. In this paper, we address the problem of time-aware VM-placement and routing (TVPR), where each tenant requests for a specified amount of server resources (VMs) and network resource (bandwidth) for a given duration. The TVPR problem allocates the required resources for as many tenants as possible by finding the right set of servers to map their VMs and routing their traffic so as to minimize the total power consumption. We propose a multi-component utilization-based power model to determine the total power consumption of a data center according to the resource utilization of the components (servers and switches). We then develop a mixed integer linear programming (MILP) optimization problem formulation based on the proposed power model and prove it to be N P-complete. Since the TVPR problem is computationally prohibitive, we develop a fast and scalable heuristic algorithm. To demonstrate the efficiency of our proposed algorithm, we compare its performance with the numerical results obtained by solving the MILP problem using CPLEX, for a small data center. We then demonstrate the effectiveness of the proposed algorithm in terms of power consumption and acceptance ratio for large data centers through simulation results.

The dual use of radio signals for simultaneous wireless information and power transfer (SWIPT) has recently drawn significant attention. To meet the practical requirement that energy receivers (ERs) operate with much higher received power than information receivers (IRs), ERs need to be deployed closer to the transmitter than IRs. However, due to the broadcast nature of wireless channels, one critical issue is that the messages sent to IRs cannot be eavesdropped by ERs, which possess better channels from the transmitter. In this paper, we address this new secrecy communication problem in a multiuser multiple-input single-output (MISO) SWIPT system where a multi-antenna transmitter sends information and energy simultaneously to one IR and multiple ERs, each with a single antenna. By optimizing transmit beamforming vectors and their power allocation, we maximize the weighted sum-energy transferred to ERs subject to a secrecy rate constraint for the information sent to the IR. We solve this non-convex problem optimally by reformulating it into a two-stage problem. First, we fix the signal-to-interference-plus-noise ratio (SINR) at the IR and obtain the optimal beamforming solution by applying the technique of semidefinite relaxation (SDR). Then the original problem is solved by a one-dimension search over the optimal SINR value for the IR. Furthermore, two suboptimal low-complexity beamforming schemes are proposed, and their achievable (secrecy) rate-energy (R-E) regions are compared against that by the optimal scheme.

Energy harvesting is a promising solution to prolong the operation time of energy-constrained wireless networks. In particular, scavenging energy from ambient radio signals, namely wireless energy harvesting (WEH), has recently drawn significant attention. In this paper, we consider a point-to-point wireless link over the flat-fading channel, where the receiver has no fixed power supplies and thus needs to replenish energy via WEH from the signals sent by the transmitter. We first consider a SISO (single-input single-output) system where the single-antenna receiver cannot decode information and harvest energy independently from the same signal received. Under this practical constraint, we propose a dynamic power splitting (DPS) scheme, where the received signal is split into two streams with adjustable power levels for information decoding and energy harvesting separately based on the instantaneous channel condition that is assumed to be known at the receiver. We derive the optimal power splitting rule at the receiver to achieve various trade-offs between the maximum ergodic capacity for information transfer and the maximum average harvested energy for power transfer, which are characterized by the boundary of a so-called "rate-energy (R-E)" region. Moreover, for the case when the channel state information is also known at the transmitter, we investigate the joint optimization of transmitter power control and receiver power splitting. The achievable R-E region by the proposed DPS scheme is also compared against that by the existing time switching scheme as well as a performance upper bound by ignoring the practical receiver constraint. Finally, we extend the result for optimal DPS to the SIMO (single-input multiple-output) system where the receiver is equipped with multiple antennas. In particular, we investigate a low-complexity power splitting scheme, namely antenna switching, which achieves the near-optimal rate-energy trade-offs as compared to the optimal DPS.

Energy harvesting is a promising solution to prolong the operation of energy-constrained wireless networks. In particular, scavenging energy from ambient radio signals, namely wireless energy harvesting (WEH), has recently drawn significant attention. In this paper, we consider a point-to-point wireless link over the narrowband flat-fading channel subject to time-varying co-channel interference. It is assumed that the receiver has no fixed power supplies and thus needs to replenish energy opportunistically via WEH from the unintended interference and/or the intended signal sent by the transmitter. We further assume a single-antenna receiver that can only decode information or harvest energy at any time due to the practical circuit limitation. Therefore, it is important to investigate when the receiver should switch between the two modes of information decoding (ID) and energy harvesting (EH), based on the instantaneous channel and interference condition. In this paper, we derive the optimal mode switching rule at the receiver to achieve various trade-offs between wireless information transfer and energy harvesting. Specifically, we determine the minimum transmission outage probability for delay-limited information transfer and the maximum ergodic capacity for no-delay-limited information transfer versus the maximum average energy harvested at the receiver, which are characterized by the boundary of so-called "outage-energy" region and "rate-energy" region, respectively. Moreover, for the case when the channel state information (CSI) is known at the transmitter, we investigate the joint optimization of transmit power control, information and energy transfer scheduling, and the receiver's mode switching. The effects of circuit energy consumption at the receiver on the achievable rate-energy trade-offs are also characterized. Our results provide useful guidelines for the efficient design of emerging wireless communication systems powered by opportunistic WEH.

Energy harvesting is a promising solution to prolong the operation of energy-constrained wireless networks. In particular, scavenging energy from ambient radio signals, namely wireless energy harvesting (WEH), has recently drawn significant attention. In this paper, we consider a point-to-point wireless link over the flat-fading channel subject to the time-varying co-channel interference. It is assumed that the receiver has no fixed power supplies and thus needs to replenish energy via WEH from the unintended interference and/or the intended signal sent by the transmitter. We further assume a single-antenna receiver that can only decode information or harvest energy at any given time due to the practical circuit limitation. As a result, it is important to investigate when the receiver should switch between the two modes of information decoding (ID) and energy harvesting (EH), based on the instantaneous channel and interference conditions. In this paper, we derive the optimal mode switching rule at the receiver to achieve various tradeoffs between the minimum transmission outage probability for ID and the maximum average harvested energy for EH, which are characterized by the boundary of a so-called “outage-energy” region. Moreover, for the case when the channel state information (CSI) is known at the transmitter, we investigate the joint optimization of transmit power control and scheduling for information and energy transfer with the receiver's mode switching. Our results provide useful insights to the optimal design of emerging wireless communication systems powered by opportunistic WEH.

Characterizing the global maximum of weighted sum-rate (WSR) for the K-user Gaussian interference channel (GIC), with the interference treated as Gaussian noise, is a key problem in wireless communication. However, due to the users' mutual interference, this problem is in general non-convex and thus cannot be solved directly by conventional convex optimization techniques. In this paper, by jointly utilizing the monotonic optimization and rate profile techniques, we develop a new framework to obtain the globally optimal power control and/or beamforming solutions to WSR maximization problems for the GICs with single-antenna transmitters and single-antenna receivers (SISO), single-antenna transmitters and multi-antenna receivers (SIMO), or multi-antenna transmitters and single-antenna receivers (MISO). Different from prior work, this paper proposes to maximize the WSR in the achievable rate region of the GIC directly by exploiting the facts that the achievable rate region is a "normal" set and the users' WSR is a strictly increasing function over the rate region. Consequently, the WSR maximization is shown to be in the form of monotonic optimization over a normal set and thus can be solved globally optimally by the existing outer polyblock approximation algorithm. However, an essential step in the algorithm hinges on how to efficiently characterize the intersection point on the Pareto boundary of the achievable rate region with any prescribed "rate profile" vector. This paper shows that such a problem can be transformed into a sequence of signal-to-interference-plus-noise ratio (SINR) feasibility problems, which can be solved efficiently by applying existing techniques. Numerical results validate that the proposed algorithms can achieve the global WSR maximum for the SISO, SIMO or MISO GIC, which serves as a performance benchmark for other heuristic algorithms.

Ethernet is becoming a preferred technology to be extended to metropolitan area networks (MANs) due to its low cost, simplicity, and ubiquity. However, current Ethernet lacks a fast failure recovery mechanism as it reconstructs the spanning tree after the failure is detected, which commonly requires tens of seconds. Some fast failure-handling methods based on multiple spanning trees have been proposed in the literature, but these approaches are either centralized or require periodic message broadcasting over the entire network. In this paper, we propose a local restoration mechanism for metro Ethernet using multiple spanning trees, which is distributed and fast and does not need failure notification. Upon failure of a single link, the upstream switch locally restores traffic to preconfigured backup spanning trees. We propose two restoration approaches, connection-based and destination-based, to select backup trees. We formulate the tree preconfiguration problem that includes working spanning tree assignment and backup spanning tree configuration. We prove that the preconfiguration problem is NP-complete and develop an integer linear programming model. We also develop heuristic algorithms for each restoration approach to reduce the computation complexity. To evaluate the effectiveness of our heuristic algorithms, we carry out the simulation on grid and random networks. The simulation results show that our heuristic algorithms have comparable performance close to the optimal solutions, and both restoration approaches can efficiently utilize the network bandwidth to handle single link failures.

In Optical Burst Switching (OBS) network architecture, edge nodes assemble bursts and send them to the core network arbitrarily, which will lead to inevitable collisions and low network utilization in the core network. Our objective is to achieve high performance burst transmission for bursty traffic while avoiding the use of wavelength converters and excessive optical buffers. To achieve this objective, we propose a novel optical burst chain switching (OBCS) mechanism, which combines the merits of optical circuit switching and optical burst switching with affordable signaling overhead. In the proposed mechanism, switching unit is a burst chain which consists of multiple non-periodic and non-consecutive bursts in one wavelength. Theoretical analysis for the throughput and queuing delay of the proposed scheme is carried out and is also verified by simulation results. We present extensive simulation results to demonstrate its superior performance over OBS networks with/without wavelength converters.

Ethernet is becoming a preferred technology to be deployed in metro domain due to its low cost, simplicity and ubiquity. However, traditional spanning tree based Ethernet protocol does not meet the requirement for metro area networks in terms of network resilience. In the work of Qiu et al. (2009), we proposed a fast spanning tree reconnection (FSTR) mechanism for metro Ethernet networks to handle single link failures. Upon failure of a link on a spanning tree, FSTR mechanism activates a reconnect-link to reconnect the broken spanning tree. FSTR mechanism has the features of fast recovery, simplicity, and guaranteed protection. However, when more than one link fail in the network, the FSTR mechanism would generate unexpected loops and cannot function properly. In this paper, we propose a fast spanning tree reconnection mechanism to handle double-link failures with protection grade guarantees. The mechanism is distributed and can alleviate the problem in previous FSTR mechanism. We formulate the reconnect-link pre-configuration problem for double-link failures as an integer linear programming problem. Through numerical results we demonstrate that the proposed mechanism can satisfy the protection grade required for each connection by efficiently utilizing the network capacity.

Ethernet is becoming a preferred technology to be deployed in metro domain due to its low cost, simplicity and ubiquity. However, spanning tree based Ethernet protocol does not meet the requirement for Metro Area Networks in terms of network resilience, despite the advancement of Ethernet standardization and commercialization. In this paper, we propose a fast spanning tree reconnection (FSTR) mechanism for Metro Ethernet networks to handle any single link failure, which has features of fast recovery, backup capacity guarantees and ease of implementation. Upon failure of a link on a spanning tree, a distributed failure recovery protocol is activated to reconnect the broken spanning tree using a reconnect-link not on the spanning tree. We present the details of the protocol, including failure notification and forwarding table reconfiguration procedures. The pre-configuration of the reconnect-links to reconnect each spanning tree is formulated as an integer linear programming (ILP) problem. The optimization results show that with lower implementation cost, fast spanning tree reconnection mechanism can achieve comparative or considerably better performance than other resilient mechanisms for Metro Ethernet networks.

Protected working lightpath envelope (PWLE) is a promising path-oriented protection strategy developed by us to provision survivable services for dynamic traffic. Partitioning the network capacity into a working layer and a protection layer by means of lightpath-protecting p-cycles, PWLE possesses the advantages of high capacity efficiency, avoidance of wavelength conversion, good blocking performance and guaranteed optical transmission quality. Nevertheless, the impact of network connectivity on the actual utilization of the working layer has been overlooked. Hence, we propose connectivity aware protected working lightpath envelope (CAPWLE) to augment the actual utilization of the working layer whilst retaining its high capacity efficiency. To fulfill the goal, we propose effective envelope, developed based on the maximum concurrent flow problem (MCFP), to evaluate the protection capability of lightpath-protecting p-cycles from a combined perspective of connectivity and volume. By virtue of effective envelope, CAPWLE is optimized by a mixed integer linear programming (MILP) model. Numerical results show that the actual utilization of the working layer is enhanced by CAPWLE under both dynamic stationary and non-stationary traffic patterns.

In this paper, we investigate the problem of multipath traffic engineering in optical burst switching (OBS) networks. The main goal of this work is to minimize burst loss rate in the network by adaptively balancing the burst traffic among multiple paths based on the measurement and analysis of path congestion. We develop three distributed traffic splitting algorithms by considering the special features of OBS networks. Among these three algorithms, one algorithm considers burst level traffic distribution, and the other two algorithms consider flow level traffic distribution to avoid packet reordering problem. The proposed multipath traffic engineering algorithms achieve significant performance improvement in reducing burst loss probability in a distributed manner in OBS networks. Further, through theoretical analysis and simulations, we show that the proposed algorithms converge quickly on a sudden traffic increase in the network.

Abstract In this paper, we study the problem of scheduling sensor activity to cover a set of targets with known locations such that all targets can be monitored all the time and the network can operate as long as possible. A solution to this scheduling problem is to partition all sensors into some sensor covers such that each cover can monitor all targets and the covers are activated sequentially. In this paper, we propose to provide information coverage instead of the conventional sensing disk coverage for target. The notion of information coverage is based on estimation theory to exploit the collaborative nature of geographically distributed sensors. Due to the use of information coverage, a target that is not within the sensing disk of any single sensor can still be considered to be monitored (information covered) by the cooperation of more than one sensor. This change of the problem settings complicates the solutions compared to that by using a disk coverage model. We first define the target information coverage (TIC) problem and prove its NP‐completeness. We then propose a heuristic to approximately solve our problem. Simulation results show that our heuristic is better than an existing algorithm and is close to the upper bound when only the sensing disk coverage model is used. Furthermore, simulation results also show that the network lifetime can be significantly improved by using the notion of information coverage compared with that by using the conventional definition of sensing disk coverage. Copyright © 2008 John Wiley & Sons, Ltd.

Protected working lightpath envelope (PWLE) is a promising scheme developed by us to provision survivable services for dynamic traffic. As a a path-oriented protection strategy based on lightpath-protecting p-cycles, PWLE has the advantages of high capacity efficiency, avoidance of wavelength conversion, good blocking performance and guaranteed optical transmission quality compared with conventional schemes. It partitions the total network capacity into a working layer and a static protection layer in which a set of lightpath-protecting p-cycles are configured. The lightpath-protecting p-cycles in PWLE are not designed particularly for a set of pre-defined paths. Instead, they are selected to protect an envelope of working channels that can be used flexibly for working routing. The protected working channels are grouped based on the related attach nodes which are defined as the nodes one-hop away from the on-cycle nodes. To design PWLE, pre-computation of a subset of candidate cycles and cycle selection within the subset are crucial. Due to the uniqueness of the lightpath- protecting p-cycle, no existing algorithms can be applied directly for cycle selection for PWLE. Moreover, existing algorithms for pre-computation of candidate cycles are mostly span-protection- oriented. Therefore, we propose the attachnode-based cycle generation (ANCG) algorithm for pre-computation of candidate cycles and three algorithms for lightpath-protecting p-cycle selection for PWLE. Numerical results show that ANCG can generate a small subset of cycles with high capacity efficiency. Meanwhile, the algorithms for cycle selection work well with much reduced computational time.

Unlike the terrestrial wireless networks that utilize the radio channel, underwater networks use the acoustic channel, which poses research challenges in the medium access control (MAC) protocol design due to its low bandwidth and high propagation delay characteristics. Since most of the MAC protocols for wireless terrestrial networks have been designed with negligible propagation delay in mind, they generally perform poorly when applied directly in underwater acoustic networks, especially for the case of handshaking-based protocols. In this paper, we propose a MACA-based MAC protocol with packet train to multiple neighbors (MACA-MN). It improves the channel utilization by forming a train of packets destined for multiple neighbors during each round of handshake, which greatly reduces the relative proportion of time wasted due to the propagation delays of control packets. This approach also reduces the hidden terminal problem. Our simulations show that the MACA-MN is able to achieve much higher throughput than the MACA protocol.

Although there are many MAC protocols that have been proposed for terrestrial wireless networks with a wide variety of aspects, these protocols cannot be applied directly in underwater acoustic networks due to the channel's uniqueness of having low data rate and long propagation delay. In order to achieve a high throughput, both characteristics must be taken into account in the MAC design. We propose a random access MAC protocol for multi-hop underwater acoustic networks based on receiver reservation, which we shall call the "Receiverinitiated Packet Train" (RIPT) protocol. It is a handshakingbased protocol that addresses the channel's long propagation delay characteristic by utilizing receiver-initiated reservations, as well as by coordinating packets from multiple neighboring nodes to arrive in a packet train manner at the receiver. Our simulation results have confirmed that the RIPT protocol can achieve our goal of having high and stable throughput performance while maintaining low collision rate.

Optical burst switching (OBS) is a promising technique for wavelength division multiplexing (WDM) networks. In practice, wavelength converters (WCs) are either absent or only sparsely deployed in WDM networks due to economic and technical limitations. Thus, wavelength assignment is expected to be an important component of OBS networks. In this paper, an offline wavelength assignment scheme in OBS networks without wavelength conversion capability is proposed. The key idea of the scheme is to decide the wavelength searching order of each traffic connection at edge nodes according to the wavelength priorities determined by the calculated burst loss probabilities on different wavelengths. Simulation results indicate that the proposed scheme can reduce the network-wide burst loss probability significantly compared with other schemes. It is also illustrated that the performance of the proposed scheme can be further enhanced by a larger number of wavelengths per link and a reasonable delay bound at edge nodes.

As a prevalent reliable transport protocol in the Internet, TCP uses two key functions: the additive-increase multiplicative-decrease (AIMD) congestion control and a cumulative ACK technique for guaranteeing delivery. However, these two functions lead to the inefficiency of TCP in ad hoc networks where the TCP connections have very small bandwidth-delay products (BDPs) and there are frequent packet losses in the network due to various reasons such as route breakages and radio interference. In this paper, we show that if the BDP of a path is as low as several packets and is known before the connection establishment, any AIMD-style congestion control is costly and is hence not necessary for ad hoc networks. On the contrary, a technique for guaranteeing reliable transmission and recovering packet losses plays a more critical role in the design of a transport protocol over ad hoc networks. With this basis, we propose a novel effective datagram-oriented end-to-end reliable transport protocol for ad hoc networks, which we call Datagram Transport Protocol for Ad hoc networks (DTPA). The proposed scheme incorporates two techniques: a fixed-size- window-based flow-control algorithm and a cumulative bit-vector-based selective ACK strategy. We then develop a mathematical model for evaluating the performance of DTPA based on these two techniques. An optimum transmission window is determined for an n-hop chain and is computed to be the BDP of the path plus 3. The protocol is verified using GloMoSim, and simulation results show that our proposal substantially improves the network performance in terms of throughput, round-trip time, number of retransmissions, and IP queue size.

In centralized wireless networks, reducing the transmission power normally leads to higher network transport throughput. In this paper, we investigate power control in a different scenario, where the network adopts distributed MAC layer coordination mechanisms. We first consider widely adopted RTS/CTS based MAC protocols. We show that an optimal power control protocol should use higher transmission power than the "just enough" power in order to improve spatial utilization. The optimal protocol has a minimal transmission floor area of Theta(dijdmax), where dmaxis the maximal transmission range and dijis the link length. This surprisingly implies that if a long link is broken into several short links, then the sum of the transmission floors reserved by the short links is still comparable to that reserved by the long link. Thus, using short links does not necessarily lead to higher throughput. Another consequence of this is that, with the optimal RTS/CTS based MAC, rate control can at best provide a factor of 2 improvement in transport throughput. We then extend our results to other distributed MAC protocols which uses physical carrier sensing or busy-tone as the control signal. Our simulation results show that the optimal power controlled scheme outperforms other popular MAC layer power control protocols.

This paper considers the coverage problem for hybrid networks which comprise both static and mobile sensors. The mobile sensors in our network only have limited mobility, i.e., they can move only once over a short distance. In random static sensor networks, sensor density should increase as O(log L + k log log L) to provide k-coverage in a network with a size of L. As an alternative, an all-mobile network can provide k-coverage with a constant density of O(k), independent of network size L. We show that the maximum distance for mobile sensors is O( 1/radic(k) log3/4(kL)). We then propose a hybrid network structure, comprising static sensors and a small fraction of O( 1/radic(k)) of mobile sensors. For this network structure, we prove that k-coverage is also achievable with a constant sensor density of O(k). Furthermore, for this hybrid structure, we prove that the maximum distance which any mobile sensor has to move is bounded as O(log(3/4)L). We then propose a distributed relocation algorithm, where each mobile sensor only requires local information in order to optimally relocate itself. We verify our analysis via extensive numerical evaluations and show an implementation of the mobility algorithm on real mobile sensor platforms.

Target tracking and localization are important applications in wireless sensor networks. Although the coverage problem for target detection has been intensively studied, few consider the coverage problem from the perspective of target localization. In this paper, we propose two methods to estimate the lower bound of sensor density to guarantee a bounded localization error over the sensing field. We first convert the coverage problem for localization to a conventional disk coverage problem, where the sensing area is a disk centered at the sensor. Our results show that the disk coverage model requires 4 times more sensors for localization compared to detection applications. We then introduce the idea of sector coverage to tighten the lower bound. The lower bound derived through sector coverage is 2 times less than through disk coverage. A distributed sector coverage algorithm is then proposed in this paper. Compared to disk coverage, sector coverage requires more computations. However, it provides more accurate density estimations than the disk model. Numerical evaluations show that the density bound derived through our sector coverage model is tight.

A multi-time-hopping (MTH) binary pulse position modulation (PPM) ultra-wideband (UWB) system with Rake receivers is considered. Based on the system capacity, an admission scheme at the connection level is formulated to relate the number of multipath fingers to the number of different classes of users that can be supported and to the blocking probability of each class in the system. With this analytical framework, the minimum number of multipath fingers that are needed in the physical layer while maintaining prescribed outage probability requirements in the link layer and prescribed blocking probability requirements at the connection level in the network layer for each traffic class can be determined. The outage probability in terms of bit error rate specification, with Gaussian monocycles supporting variable bit rate (VBR) multiclass services, is presented. The analytical framework is formulated for the general case in which different traffic classes have different varying bit rates. Closed- form expressions for the signal at the correlator's output during a frame interval and the power of the interference resulting from one of the active time hopping sequences from the interfering users on one pulse are explicitly derived. The indoor channel model used is based on IEEE 802.15.3a.

We propose a new scheme, called protected working lightpath envelope (PWLE), for dynamic provisioning of survivable services without requiring any wavelength conversion. PWLE is a path-oriented protection strategy based on lightpath-protecting rho-cycles. It partitions the total network capacity into a static protection layer and a working layer available for dynamic routing. To deal with the new issues raised by lightpath-protecting p-Cycles, we propose compatible grouping so that the PWLE can be formulated as an mixed integer linear programming (MILP) model. Based on compatible grouping, we further propose compatible group routing (CGR), a distributed routing algorithm tailored for PWLE. Compared with rho-Cycle-based protected working capacity envelope (PWCE), PWLE has the advantages of high capacity efficiency, avoidance of wavelength conversion, good blocking performance and guaranteed optical transmission quality. We evaluate the performance improvement of PWLE in capacity efficiency and blocking performance through the numerical results obtained from CPLEX and simulations.

Unlike terrestrial networks that mainly rely on radio waves for communications, underwater networks utilize acoustic waves, which have comparatively lower loss and longer range in underwater environments. However, the use of acoustic waves pose a new research challenge in the networking area. While existing network schemes for terrestrial sensor networks are mainly designed for negligible propagation delay and high data rate, underwater acoustic communications are characterized by high propagation delay and low data rate. These terrestrial schemes, when directly applied to the underwater channel, will under-utilize its already limited capacity. We investigate how the underwater channel's throughput may be enhanced via medium access control (MAC) techniques that consider its unique characteristics. Specifically, we study the performance of Aloha-based protocols in underwater networks, and propose two enhanced schemes, namely, Aloha with collision avoidance (Aloha-CA), and Aloha with advance notification (Aloha-AN), which are capable of using the long propagation delays to their advantage. Simulation results have shown that both schemes can boost the throughput by reducing the number of collisions, and, for the case of Aloha-AN, also by significantly reducing the number of unproductive transmissions.

In this paper we consider the coverage problem for target detection applications in wireless sensor networks. Unlike conventional coverage problems which assume sensing regions are disks around sensors, we define the sensing region according to detection constraints in terms of false alarm probability and missing probability. We show that exploiting cooperation between sensors can extend the overall sensing region while maintain the same constraints on false alarm probability and missing probability. We then propose an energy efficient cooperative detection scheme and study the trade-offs on energy consumption between cooperative and non-cooperative schemes. The cooperative scheme can use half the number of sensors to monitor the whole fleld compared to disk model in networks deployed on grids. We also study the communication overheads incurred by the co-operative scheme, and show that only cooperation between limited number of nearby sensors is profitable in terms of energy consumption. In our simulations on randomly deployed networks, cooperation reduces the number of sensors to cover the area by 30% and nearly doubles the number of disjoint sensor sets where each can fully cover the area. Appropriately trading off energy consumption with coverage extension, our cooperative detection scheme can increase the network lifetime by nearly 70%.

This paper studies the problem of how to maximize the network lifetime while preserving network coverage for an energy constrained wireless sensor network. We consider network coverage from an our recently proposed information coverage model [1] other than the conventional sensing disk model. The lifetime maximization problem is modeled as a nonlinear programming problem and is shown NP-Complete. We then propose a family of greedy algorithms to allocate sensors different roles such that different sensors may consume different amount of energies in different intervals to prolong network lifetime while still guaranteeing application requirements. Simulation results suggest that the algorithm with the best balancing between communication energy consumption and area coverage requirement has the highest network lifetime.

In this paper, we study the coverage problem for hybrid networks which comprise both static and mobile sensors. We consider mobile sensors with limited mobility, i.e., they can move only once over a short distance. Such mobiles are simple and cheap compared to sophisticated mobile robots. In conventional static sensor networks, for a random deployment, the sensor density should increase as O(log L + k log log L) to provide k-coverage in a network with a size of L. As an alternative, an all mobile sensor network can provide k-coverage over the field with a constant density of O(k), independent of network size L. We show that the maximum distance that any mobile sensor will have to move is O(1 over √k log 3 over 4 (kL)). We then propose a hybrid network structure, comprising static sensors and a small fraction of O(1 over √(k)) of mobile sensors. For this network structure, we prove that k-coverage is achievable with a constant sensor density of O(k), independent of network size L. Furthermore, for this hybrid structure, we prove that the maximum distance which any mobile sensor has to move is bounded as O(log3 over 4 L). We then propose a distributed relocation algorithm, where each mobile sensor only requires local information in order to optimally relocate itself and characterize the algorithm's computational complexity and message overhead. Finally, we verify our analysis via extensive numerical evaluations.

Energy limitations in wireless sensor networks and the need for low latency in many applications require a unified approach in the design of network protocols. In this paper, we propose a distributed wakeup schedule to accomplish a new topology control scheme. The aim is to increase the longevity of the network for a given upper bound on the average end-to-end delay. In the proposed scheme neither localization nor synchronization is required and only local information is used. In addition to its simplicity of implementation, its energy overhead is negligible and it implicitly determines the routing paths. Our simulation results show that this protocol achieve significant improvement in the network lifetime compared to SPAN, an existing topology control mechanism.

Bandwidth delay product (BDP) represents the maximum amount of allowed unacknowledged data in flight at any moment in the network. Due to the spatial reuse property of 802.11 MAC protocol in multi-hop ad hoc networks, the BDP of the path approximates 1/4 of the path length and is a value of several packets. With such a small BDP, TCP cannot work efficiently since its congestion window increases far beyond BDP most of the time, which can generate heavy congestion in the network. This paper presents a mathematical approach to derive an optimum maximum congestion window for TCP Reno over 802.11 based ad hoc networks. We adopt a Markov renewal approach to analyze the behavior of TCP Reno, which incorporates an accurate and realistic modelling of the fast-recovery process. Through analysis, we find that the optimum maximum congestion window is 6 packets for a multi-hop chain with any path length.

In order to meet the requirements of real-time applications, Optical Burst Switched backbone networks need to provide quantitative edge-to-edge loss guarantees to traffic flows. For this purpose, there have been several proposals based on the relative differentiation quality of service (QoS) model. However, this model has an inherent difficulty in communicating information about internal network states to the edge in a timely manner for making admission control decisions. In this paper, we propose an absolute QoS framework to overcome this difficulty. The key idea is to offer quantitative loss guarantees at each hop using a differentiation mechanism and an admission control mechanism. The edge-to-edge loss requirement is then translated into a series of small per-node loss probabilities that are allocated to the intermediate core nodes. The framework includes a preemptive differentiation scheme, a node-based admission control scheme and an edge-to-edge reservation scheme. The schemes are analyzed and evaluated through simulation. It is shown that the framework can effectively offer quantitative edge-to-edge loss guarantees under various traffic conditions.

We propose a packet-level model to investigate the impact of channel error on the transmission control protocol (TCP) performance over IEEE-802.11-based multihop wireless networks. A Markov renewal approach is used to analyze the behavior of TCP Reno and TCP Impatient NewReno. Compared to previous work, our main contributions are listed as follows: 1) modeling multiple lossy links, 2) investigating the interactions among TCP, Internet Protocol (IP), and media access control (MAC) protocol layers, specifically the impact of 802.11 MAC protocol and dynamic source routing (DSR) protocol on TCP throughput performance, 3) considering the spatial reuse property of the wireless channel, the model takes into account the different proportions between the interference range and transmission range, and 4) adopting more accurate and realistic analysis to the fast recovery process and showing the dependency of throughput and the risk of experiencing successive fast retransmits and timeouts on the packet error probability. The analytical results are validated against simulation results by using GloMoSim. The results show that the impact of the channel error is reduced significantly due to the packet retransmissions on a per-hop basis and a small bandwidth delay product of ad hoc networks. The TCP throughput always deteriorates less than ~ 10 percent, with a packet error rate ranging from 0 to 0.1. Our model also provides a theoretical basis for designing an optimum long retry limit for IEEE 802.11 in ad hoc networks.

Coverage is an important issue in wireless sensor networks. The most commonly used coverage model in the literature defines a point to be covered if its Euclidian distance to at least one sensor is less than a fixed threshold. This is a conservative definition of coverage which implicitly assumes that each sensor makes a decision independent of other sensors in the field. Sensors can cooperate to make an accurate estimation, even if any single sensor is unable to do so. We have previously proposed a new notion of information coverage and investigated its properties. In this paper, we study sensor density requirements for complete information coverage of a field with random sensor deployment. We provide an upper bound on the probability that an arbitrary point in a randomly deployed sensor field is not information covered and find the relationship between the sensor density and the average field vacancy. Simulation results validate our theoretical analysis and show that significant savings in terms of sensor density for complete coverage can be achieved with information coverage.

The type of services and the manner with which multiple access is performed have a tremendous impact on the system capacity. The capacity region for video services Ui the uplink of a round-robin carrier-hopping multi-rate multi-carrier (MC) DS-CDMA cellular system is derived by formulating and analyzing the outage probabilities in terms of bit error rate specifications. The subcarriers of the MC-DS-CDMA system are dynamically allocated to evenly distribute their usage. Three management schemes are used to perform subcarrier allocation: complete sharing (CS), dynamic complete partitioning (DCP) and dynamic complete group partitioning (DCGP). The analytical framework is formulated for the general case in which different traffic classes have different spreading gains in each of the subcarriers. Numerical results show that the capacity of DCGP is larger than that of CS or DCP.

We consider the problem of offline route optimization in optical burst switching (OBS) networks to determine a route layout for a given traffic demand to minimize the overall burst loss. Route selection based on the traditional Erlang B formula is not efficient because of the unique features of OBS networks such as streamline effect. We analyze the streamline effect and propose a more accurate loss estimation formula which takes the streamline effect into consideration. Based on this formula, we develop a mixed integer linear programming (MILP) formulation for the problem. Since the MILP-based solution is computationally intensive, we develop a heuristic algorithm. We evaluate the effectiveness of the proposed algorithms through the numerical results obtained from CPLEX and simulation results.

In this paper, we investigate the problem of multipath dynamic traffic routing in optical burst switching (OBS) networks. In this work, traffic is split among the multiple link-disjoint paths between each source and destination pair. Taking into consideration the packet reordering problem, we propose a new adaptive proportional routing scheme that operates on flow level. The objective of the proposed scheme is to reduce the overall burst loss in the network and at the same time avoid the packet out-of-sequence arrival problem. This is achieved by adaptively adjusting the traffic flow proportions assigned to the multiple paths between a source and destination pair based on the measurement of the impact of the offered traffic load on each of them in the past. When a new flow arrives, an appropriate path is chosen for it based on the calculated flow proportions. In addition, burst assembly time between different paths can also be adjusted to further enhance the performance. Through extensive simulations, we show that the proposed flow-based multi-path traffic routing approach not only provides significantly better burst loss performance than the basic equal-proportion and hop-length based traffic routing algorithms, but is also void of any packet re-orderings.

Target tracking and localization are important applications in wireless sensor networks. Although the coverage problem for target detection has been intensively studied, few consider the coverage problem from the perspective of target localization. In this paper, we propose two methods to estimate the necessary sensor density which can guarantee a localization error bound over the sensing field. In the first method, we convert the coverage problem for localization to a conventional disk coverage problem, where the sensing area is a disk centered around the sensor. Our results show that the disk coverage model requires 4 times more sensors for tracking compared to detection applications. We then introduce the idea of sector coverage, which can satisfy the same coverage conditions with 2 times less sensors over the disk coverage approach. This shows that conventional disk coverage model is insufficient for tracking applications, since it overestimates the sensor density by two times. Simulation results show that the network density requirements derived through sector coverage are close to the actual need for target tracking applications.

Optical burst switching (OBS) is a promising technology to transmit bursty data traffic over optical networks. For QoS routing, an accurate estimation of the amount of residual capacity on a link is necessary. In IP or ATM networks, the residual bandwidth of a link can be computed as the total bandwidth subtracted by the effective bandwidth of each flow. However, this method is based on the assumption that each node has a large buffer. This method is not applicable to OBS networks, where there is no buffer at the core nodes. We propose a new metric, called residual admission capacity (RAC), to determine the amount of residual capacity on the links in OBS networks. To show the effectiveness of the new metric, we propose a routing algorithm called RAC-WSP, which is a widest shortest path (WSP) algorithm with RAC as the measurement of the residual capacity on a link. Experimental results show that RAC-WSP can admit more loss-guaranteed flows than other routing schemes, including the shortest path algorithm and other WSP algorithms where the residual capacity is evaluated by other metrics

In a 802.11 based mobile ad hoc network (MANET), the routing protocol may wrongly assume that a route is broken due to temporal packet loss in connectivity arising from multiple packet collisions, which we term as a false route breakage. In this paper, we investigate the impact of false route breakages in MANETs. It is found that false route breakage is dependent on the size of packets transmitted in a network and the path length of a source-destination pair. We present a protocol enhancement to the IEEE 802.11 MAC protocol which increases the reliability of wireless links by reducing false route breakages. We achieve the goal of alleviating false route breakages by initiating a HELLO message to the sender whenever the number of RTS received by a receiver exceeds a threshold. The simulation results show that the proposed modification substantially reduces the false route breakages and improves throughput by up to 35%

The capacity of a multi-time-hopping (MTH) binary pulse position modulation (PPM) ultra-wideband (UWB) system with Rake receivers and Gaussian monocycles supporting variable bit rate (VBR) multiclass services is presented. The analytical framework is formulated for the general case in which different traffic classes have different varying bit rates. The indoor channel model used is based on IEEE 802.15.3a. The analytical work leads to the determination of the system capacity of an MTH binary PPM UWB system with VBR traffic in an indoor multipath environment. Numerical results of the system capacity region are also presented.

A two-level fractional guard channels (TLFGC) scheme to efficiently provide priority access for handoff calls over new calls in cellular systems is proposed. The switching between the levels is controlled by a dropped call. The first level has a small number of guard channels like the fixed guard channel (FGC) scheme, while the second level has a larger number of guard channels and a smaller number of fractional guard channels. An analytical formulation of the steady state probabilities, new call blocking probability, handoff call blocking probability, system utilization, probabilities in each level and the equivalent number of guard channels is presented. Numerical results show that the performance of TLFGC is almost the same as a fixed guard channels (FGC) scheme under light load. However, the advantage of the TLFGC scheme is demonstrated under heavy load where the handoff call blocking probability is much better than that of a FGC scheme, giving more priority and protection to handoff calls over new calls.

An important application of wireless sensor networks is to perform the monitoring missions, for example, to monitor some targets of interests at all times. Sensors are often equipped with non-rechargeable batteries with limited energy and energy saving is a critical aspect for wireless sensor networks. If a target is monitored simultaneously by serval sensors, some of them can be switched off to save energy without causing mission failure and by which their operational times as well as the network lifetime can be prolonged. In this paper, we study the problem of scheduling sensor activity to cover a set of targets with known locations such that all targets can be monitored all the time and the network can operate as long as possible. A solution to this scheduling problem is to partition all sensors into sensor covers such that each cover can monitor all targets and the covers are activated successively. In this paper, we propose to use the notion of information coverage which is based on the estimation theory to exploit the collaborative nature of wireless sensor networks, instead of using the conventional definition of coverage. Due to the use of information coverage, a target that is not within the sensing disk of any single sensor can still be considered to be monitored (information covered) by the cooperation of more than one sensor.

In this paper, we describe and study a phenomenon unique to bufferless optical burst switched (OBS) networks called the streamline effect. This is the phenomenon wherein bursts within an input stream to a core node only contend with those from other input streams but not among themselves. It causes the burst loss probability at a link to depend strongly on the number of input streams to the link and their relative burst rates. We analyse the streamline effect and provide a burst loss probability formula that is more accurate than the traditionally used Erlang B formula. The formula is then used in a load balancing scheme for reservation-based quality of service (QoS) traffic to give a better link cost function. Through extensive simulation experiments for different traffic scenarios, we show that the proposed load balancing scheme utilising the streamline effect performs better than the shortest path routing scheme and the load balancing scheme without considering the streamline effect.

Researchers have used extensive simulation and experimental studies to understand TCP performance in adhoc wireless networks. In contrast, the objective of this paper is to theoretically analyze TCP performance in this environment. By examining the case of running one TCP session over a string topology, a system model for analyzing TCP performance in adhoc wireless networks is proposed, which considers packet buffering, nodes' contention for access to the wireless channel, and spatial reuse of the wireless channel. Markov chain modelling is applied to analyze this system model. Analytical results show that when the number of hops that the TCP session crosses is fixed, the TCP throughput is independent of the TCP congestion window size. When the number of hops increases from one, the TCP throughput decreases first, and then stabilizes when the number of hops becomes large. The analysis is validated by comparing the numerical and simulation results

An analytical formulation of the outage probability in terms of bit error rate specification for variable bit rate (VBR) multiclass services in a multi-code direct-sequence ultra-wideband (DS-UWB) system is presented. The analytical framework is formulated for the general case in which different traffic classes have different varying bit rates. Multiple spreading codes are used by each user to achieve variable bit rate (VBR). Closed-form expressions for the signal at the correlator's output during a frame interval and the power of the interference resulting from one of the active spreading codes from the interfering users on one pulse are explicitly derived. The analytical work leads to the determination of the capacity region of a multi-code DS-UWB system supporting VBR services. Numerical results of the capacity region are also presented.

This paper analyzes the TCP performance in an 802.11 based multi-hop ad hoc network. The analysis is unique because it tries to quantify the throughput of a TCP flow after considering the interaction between TCP's congestion window size and 802.11's MAC (medium access control) contention window size. The analysis results in formulae to compute the throughput of a single TCP flow for an n-hop string topology under the ideal situation where there is no packet loss in the network. The analytical results have been validated by benchmarking against simulation results from ns-2. The outcome of the analysis is useful when ad hoc networks are adopted as an extension to the Internet because TCP is the prevalent transport protocol for reliable data transmissions in the Internet.

In this paper we investigate the benefits of a heterogeneous architecture for wireless sensor networks composed of a few resource rich mobile nodes and a large number of simple static nodes. These mobile nodes can either act as mobile relays or mobile sinks. To investigate the performance of these two options and the trade-offs associated with these two options, we first consider a finite network. We then compute the lifetime for different routing algorithms for three cases (i) when the network is all static (ii) when there is one mobile sink and (iii) when there is one mobile relay. We find that using the mobile node as a sink results in the maximum improvement in lifetime. We contend however that in hostile terrains, it might not always be possible for the sink to be mobile. We then investigate the performance of a large dense network with one mobile relay and show that the improvement in network lifetime over an all static network is upper bounded by a factor of four. Also, the proof implies that the mobile relay needs to stay only within a two hop radius of the sink. We then construct a joint mobility and routing algorithm which comes close to the upper bound. However this algorithm requires all the nodes in the network to be aware of the location of the mobile node. We then proposed an alternative algorithm, which achieves the same performance, but requires only a limited number of nodes in the network to be aware of the location of the mobile. We finally compare the performance of the mobile relay and mobile sink and show that for a densely deployed sensor field of radius R hops, we require O(R) mobile relays to achieve the same performance as the mobile sink.

An analytical formulation of the outage probability in terms of bit error rate specification for variable bit rate (VBR) multiclass services in a multi-code direct-sequence ultra-wideband (DS-UWB) system with Rayleigh monocycles is derived via an outage probability analysis. The analytical framework is formulated for the general case in which different traffic classes have different varying bit rates. Multiple spreading codes are used by each user to achieve variable bit rate (VBR). Closed-form expressions for the signal at the correlator's output during a frame interval and the power of the interference resulting from one of the active spreading codes from the interfering users on one pulse are explicitly derived for Rayleigh monocycles. The analytical work leads to the determination of the capacity region of a multi-code DS-UWB system supporting VBR services. Numerical results of the capacity region are also presented.

In this paper, we develop analytical models for a single persistent TCP flow in the presence of channel error-induced packet loss over IEEE 802.11 based multi-hop networks. Two analytical models are proposed, based on different packet loss models: periodic packet loss model and i.i.d. random packet loss model. For the latter, we develop a stochastic model using the Markov renewal reward approach. The analytical results are validated against results using the ns simulator. The results show that the impact of the channel errors is reduced significantly with packet retransmissions on a per-hop basis and the two models are valid for a packet error rate ranging from 0 to /spl sim/0.05.

An analytical formulation of the outage probability in terms of bit error rate specification for variable bit rate (VBR) multiclass services in a multi-time-hopping (MTH) binary pulse position modulation (PPM) ultra-wideband (UWB) system is presented. The analytical framework is formulated for the general case in which different traffic classes have different varying bit rates. Multiple time hopping sequences are used by each user to achieve variable bit rate (VBR). Closed-form expressions for the signal at the correlator's output during a frame interval and the power of the interference resulting from one of the active time hopping sequences from the interfering users on one pulse are explicitly derived. The analytical work leads to the determination of the capacity region of an MTH binary PPM UWB system with VBR traffic. Numerical results of the capacity region corresponding to typical parameter values are also presented.

Multicode-code division multiple access (CDMA) supports a variety of transmission rates within a wireless network. However, providing packet-delay guarantees in a multicode-CDMA network is difficult because its transmission capacity is time varying even in an error-free wireless channel. In this paper, we develop a packet-scheduling algorithm called multicode-deficit round robin (DRR) as a solution to the problem. The basic idea of multicode-DRR is to separate the time-varying capacity into a deterministic component and a variable component, and to use these components to serve time-sensitive and non-time-sensitive traffic, respectively. With the proposed scheduling algorithm, simulation results have confirmed that the maximum packet delays for time-sensitive traffic never exceed their target upper bounds.

Recently, some absolute QoS schemes have been proposed to offer quantitative loss guarantees at core nodes in OBS networks. By moving the admission control process to core nodes, which have the most updated information about their own traffic conditions, these schemes can provide reliable and robust per-link loss guarantees. However, the issue of how to provide edge-to-edge guarantees for burst flows over the entire edge-to-edge paths have not been investigated in any of the proposals. In this paper, we propose a signalling and reservation scheme to coordinate the reservation and teardown process over the edge-to-edge path in the absolute QoS model. The key idea is to judiciously divide the edge-to-edge loss requirement into a series of small loss probabilities that are allocated to the intermediate links. The performance of the scheme is evaluated through simulation.

Analytical formulations of the outage probability in terms of bit error rate specification using Chernoff bound and central limit Gaussian approximation for variable bit rate (VBR) multiclass services in the downlink of a round-robin carrier-hopping multirate multicarrier (MC) DS-CDMA cellular system is presented The analytical framework is formulated for the general case in which different traffic classes have different data rates in each of the subcarriers. The analytical work leads to the determination of the capacity region of the downlink in a round-robin carrier-hopping multirate MC-DS-CDMA system for VBR traffic. Numerical results of the capacity region corresponding to typical parameter values are also presented.

For power-constrained wireless ad hoc networks, a crucial issue in routing and multicasting is to conserve as much power as possible while still achieving good throughput performance. In this paper, we propose a class of power-efficient multicasting algorithms using a new cost function that jointly optimizes power conservation and path efficiency. Simulation results demonstrate significant performance improvement in terms of power efficiency and interference control, while achieving better path efficiency compared with the algorithms that use pure power as the cost function.

Analytical formulations of the outage probability in terms of bit error rate specification using Chernoff bound and central limit Gaussian approximation for variable bit rate (VBR) multiclass services in the downlink of a dynamic complete partitioning (DCP) round-robin carrier-hopping multirate multi-carrier (MC) DS-CDMA cellular system is presented. The analytical framework is formulated for the general case in which different traffic classes have different spreading gains in each of the subcarriers. The analytical work leads to the determination of the capacity region of a dynamic complete partitioning round-robin carrier-hopping multirate MC-DS-CDMA system for VBR traffic. Numerical results show that the system capacity with DCP can be larger than that with complete sharing (CS) of the subcarriers.

An analytical formulation of the outage probability in terms of bit error rate specification for video services in the uplink of a round-robin carrier-hopping multirate multi-carrier (MC) DS-CDMA cellular system is presented. The video model used in this paper accounts for scene changes. In the model, each video source is modeled by a two-dimensional Markov chain. The analytical framework is formulated for the general case in which different traffic classes have different spreading gains in each of the subcarriers. The analytical work leads to the determination of the capacity region of the uplink in a round-robin carrier-hopping multirate MC-DS-CDMA system for video traffic that accounts for slow and fast motions, numerical results of the capacity region corresponding to typical parameter values are also presented.

In this paper, we consider the problem of fast and efficient dynamic scheduling of bursts that belong to different classes of priority in wavelength-division multiplexing (WDM)-based optical burst switching (OBS) networks with limited optical buffers. In OBS networks, control and data components of a burst are sent separately with a time gap to ensure that resources such as wavelengths and fiber delay lines (FDLs) are reserved at various nodes before the data burst arrives. A scheduling algorithm with attractive features such as computational simplicity and efficient resource utilization is mandatory to quickly handle dynamic burst traffic and reduce burst dropping probability. While void filling algorithms achieve good burst dropping performance they are computationally complex. We propose burst rescheduling as an alternative to void filling which can do fast scheduling without requiring to examine and fill voids and at the same time can achieve good performance. Burst rescheduling uses two mechanisms known as wavelength reassignment and lasthop FDL reassignment. We develop a scheduling algorithm using the above rescheduling mechanisms called burst rescheduling with wavelength and last-hop FDL reassignment (BR-WFR) which is computationally simpler than a void filling algorithm. We then discuss the signalling overhead and feasibility of implementing burst rescheduling. Through simulation experiments we demonstrate the effectiveness of the proposed burst rescheduling algorithm.

An analytical formulation of the outage probability in terms of bit error rate specification for variable bit rate (VBR) multiclass services in the uplink of a wideband CDMA-based cellular system is presented. The analytical framework is formulated for the general case in which different traffic classes have different spreading gains. The analytical work leads to the determination of the capacity region of a wideband CDMA system with VBR traffic. Numerical results of the capacity region corresponding to typical parameter values are also presented.

In this paper, we study resource allocation policies for data services in a CDMA-based network. We present a detailed packet level resource allocation scheme that consists of different sorting strategies for backlogged flows and an exhaustive data rate allocation algorithm that satisfies the optimal power allocation constraint. The sorting strategies and the rate allocation algorithm determine the order that a user receives resources and the resource share that a user can receive. We present three sorting strategies, which may characterize the relationship between fairness among users and system utilization efficiency. We compare the performance of the sorting strategies via simulations and our investigations include the achievable system capacity, fairness among users and delay performance.

A data user may request different transmission rates during its connection holding time to reduce its resource usage cost but still meeting QoS requirements. In this paper, the procedure of the resource request for a data user is formulated as a Markov decision process in which the user requests different transmission rates based on its buffer occupancy. The objective is to find an optimal policy (if it exists) that minimizes the expected average cost per unit time. We prove that a stationary optimal policy is monotone in the buffer occupancy for our problem. Numerical examples are provided comparing the performance of the optimal policies with some other policies.

An analytical formulation of the outage probability in terms of bit error rate specification for video services in the uplink of a multirate DS-CDMA-based cellular system is presented. The video model used in this paper accounts for scene changes. In the model, each video source is modeled by a two-dimensional Markov chain. The analytical framework is formulated for the general case in which different traffic classes have different low- and/or high-bit-rate spreading gains. Furthermore, each class has a combination of low- and high-bit-rate spreading codes for each user. The analytical work leads to the determination of the capacity region of a multirate DS-CDMA system with video traffic that accounts for slow and fast motions.

A relative bandwidth service differentiation scheme is proposed for mobile ad-hoc networks (MANETs). The service profile for a traffic session is defined as a relative target rate, which is a fraction of the effective link capacity of nodes. To calculate the effective link capacity of nodes in a randomly moving topology MANET, two methods are presented: one is parameter based and the other is measurement based calculations work effectively to estimate the effective link capacity of nodes and the relative service differentiation is consistent. Furthermore, the differentiation is more consistent when nodes use the measurement based calculation of link capacity because it is more accurate.

In the paper, we investigate and evaluate a radio resource allocation strategy for non-realtime data services in a single cell UMTS uplink. We focus on a packet level allocation strategy, which guarantees certain fairness levels. Non-realtime data services normally have average throughput requirement, which can be achieved either by way of continuous transmission with a low instantaneous data rate or by way of a higher instantaneous data rate over a shorter time. We find that it is energy-efficient by transmitting with high instantaneous data rate based on variable spreading factor operation. Furthermore, based on an average throughput based fairness criterion, we propose a fair resource allocation scheme that is easy to implement. Simulations are used to evaluate the proposed scheme.

An approximate analytical formulation of the resource allocation problem for handling variable bit rate multiclass services in a cellular direct sequence code-division multiple-access (DS-CDMA) system is presented. The novelty in this paper is that all grade-of-service (GoS) or quality-of-service (QoS) requirements at the connection level, packet level, and link layer are satisfied simultaneously, instead of being satisfied at the connection level or at the link layer only. The analytical formulation shows how the GoS/QoS in the different layers are intertwined across the layers. A complete sharing (CS) scheme with guard channels is used for the resource sharing policy at the connection level. The CS model is solved using a K-dimensional Markov chain. Numerical results illustrate that significant gain in system utilization is achieved through the joint coupling of connection/packet levels and link layer. This can translate to more revenues for network providers and/or lower charges for mobile users.

A MultiCode-CDMA network that is capable of providing quality-of-service guarantees will find widespread application in future wireless multimedia networks. However, providing delay guarantees to time-sensitive traffic in such a network is challenging because its transmission capacity is variable even in the absence of any channel impairment. We propose and evaluate the performance of a novel transmission scheduling scheme that is capable of providing such a delay guarantee in a MultiCode-CDMA network. The proposed scheme drops packets to ensure that delays for all transmitted packets are within the guaranteed target bounds, but packets are dropped in a controlled manner such that the average dropping ratios of a set of time-sensitive flows can be proportionally differentiated according to the assigned weighting factors or shares. We provide extensive simulation results to show the effectiveness of the proposed scheme as well as to study the effects of various parameters on its performance. In particular, we show that it can simultaneously guarantee a delay upper bound and a proportionally differentiated dropping ratio in a fading wireless channel for different traffic loads, peak transmission rates, and weighting factors of individual flows.

Traditional Ethernet based local area networks are increasingly visible in the access arena. Fast Ethernet (FE) and Gigabit Ethernet (GE) switches for standard enterprise LAN lack admission control, bandwidth monitoring, rate shaping and access control mechanisms making them unsuitable for widespread access deployments. This paper presents the industry's first, configurable Ethernet 'switch-on-a-chip' from Infineon Technologies (PLB2800), which offers advanced configurability, bandwidth management, security and an on-chip RISC CPU for switch management. PLB2800 can operate in 8GE, 32GE+4FE and 48FE+2GE modes to fit into a variety of access networks.

Existing multicode-CDMA MAC protocols do only single dimensional access control either in the code or time domain, and thus result in a complex optimisation problem. In this paper, we propose a MAC protocol which can do simultaneous code-time access control to avoid the optimisation problem, and to achieve better system utilisation. In order to do that, the proposed protocol decouples the function of transmission ordering from the function of packing all the scheduled transmissions in the resource space. As such, different transmission scheduling algorithms can be adopted without altering the protocol. A water filling approach is used for efficient transmission packing where each of the scheduled transmissions is treated as a rectangular capsule with an arbitrary size and the resource space is viewed as a water container. Simulation results indicate that the proposed protocol can achieve higher throughput compared to single dimensional access control protocols. Therefore, the proposed MAC protocol is a more efficient one.

IP overheads are large and need to be compressed when used in UMTS to save radio resources. A robust header compression (ROHC) scheme has been proposed to provide high compression efficiency and high robustness. We study the performance of ROHC and investigate how to adjust some compression parameters that are recommended as implementation-dependent according to the ROHC specification. Based on our study, we propose to employ the power control mechanism already in the UMTS architecture to prevent additional packet losses in the worst cases of consecutive packet losses exceeding the sliding window width. The proposed augmentation can be seen as a network assisted feedback mechanism for ROHC.

The delay jitter performance of voice traffic, modeled using an exponential on/off source, in a cellular wireless ATM network is analyzed. The uplink MAC (medium access control) protocol is implemented by a P-TDMA/DR (prioritized time division multiple access with dynamic reservation) MAC protocol. Voice, compressed video and data are used as test traffic. The delay jitter (or cell delay variation) of an exponential on/off voice is evaluated using approximate analysis and computer simulation. Numerical results indicate that, with very high probability of 0.92 (simulation) or 0.96 (analysis), the voice delay jitter is practically zero and, with very low probability, it is at other values. 99.1% of the voice delay jitter are within /spl plusmn/10 TDMA frame intervals. This shows that the voice delay jitter is well-behaved due to the excellent design of the P-TDMA/DR MAC protocol for voice traffic.

An approximate analytical formulation of the resource allocation problem for handling multiclass services in a cellular system is presented. Complete partitioning (CP) and complete sharing (CS) schemes with guard channels are used for the resource sharing policies at the call level. The CP model is solved explicitly using a one-dimensional Markov chain while the CS model is solved using a K-dimensional Markov chain. Call and packet level qualities of service (QoS) are considered. The performance of fast and slow mobile users and the effect of cell size are evaluated. The agreements between the analytical and simulation results for the CP and CS cases are good for low blocking probabilities. Numerical results illustrate that higher gain in system utilization is achieved through the joint optimization of call/packet levels.

Multicode-CDMA is a good choice for wireless networking because it can support devices with different peak transmission rates within one network and hence, enables cost scalability. However, delivering delay guarantee in a multicode-CDMA network is difficult because its capacity is variable even in a perfect wireless channel. We develop a scheme called multicode-DRR as a solution to the problem. The basic idea of multicode-DRR is to separate the variable capacity into a deterministic component and a variable component, and to use these components to serve time-sensitive traffic and non-time-sensitive traffic, respectively. Simulation results confirm that the maximum time-sensitive packet delay never exceeds the theoretical upper bound when the devices are served using the proposed scheme. In short, multicode-DRR is significant because it enables a multicode-CDMA network to deliver deterministic upper delay guarantee.

The aim of service prioritization is to give resource priority to certain traffic types. For example, the voice service can have higher priority than the data service, Web surfing can have higher priority than FTP and e-mail applications, or some users can have higher priority than others. This paper investigates the performance of service prioritization in mobile ad-hoc networks (MANETs). Two schemes, priority buffer management and priority scheduling, are applied to realize service prioritization and three service profiles are discussed as well as simulation results are presented to show that the priority schemes work well with TCP traffic but not with constant bit rate (CBR) traffic. Besides this, the priority scheduling scheme outperforms the priority buffer management scheme in terms of average end-to-end delay of TCP packets and average throughput of TCP sessions.

Future wireless networks need to support different service requirements. Ho-sever, the exiting methods of specifying QoS commitments, namely qualitative commitment and quantitativ e commitment are not perfect for a wireless communication environment. In this paper, we propose a new concept called compound QoS commitment which combines qualitative and quantitative commitments within a single service commitment. As such, the proposed concept can provide a practical approach to deal with the highly variable wireless netw ork capacijr. Since each compound QoS commitment has tw o degrees of freedom, it m\ also increase the fiexibilit y in committing an ahievable QoS. In order to show the feasibility of the proposed concept, we present a scheduling algorithm whic hcan sim ultaneouslypro vide a proportional dropping ratio guarantee and a deterministic upper delay guarantee to a flow. Numerical results confirm that the algorithm is capable of delivering the tw o guarantees simultaneously.

An analytical model of a single TCP session based on a string topology in wireless multihop networks is presented. The model for the communication process also considers buffering, propagation delay and channel access probability. A Markov chain technique is adopted in analyzing the TCP behavior. Full analysis is given for the case where the TCP source and destination are one hop away and the maximum TCP window size is less than the buffer size in each node. Consideration is also given to the case when the maximum TCP window size is larger than the buffer size in each node. The analytical results are validated against results using the NS simulator.

We consider a system configuration consisting of both an uplink MAC (medium access control) protocol and a UPC (usage parameter control) at the base station for supporting heterogeneous services. The MAC is implemented by an enhanced TDMA/DR (time division multiple access with dynamic reservation) MAC protocol while the UPC is implemented by a leaky bucket device. Voice, compressed video and data are used as test traffic. The performance metrics are delay and cell loss. Numerical results based on approximate analysis and simulation are used to draw conclusions regarding the size of input buffers of the leaky bucket needed to yield a prescribed packet loss rate.

Wireless environment properties, such as fading, multipath and interference, mean that the capacity is time-varying and the errors are location dependent. This makes it difficult to directly extend algorithms developed for wire-line networks to wireless networks. In order to support relatively differentiated QoS requirements over a time-varying shared wireless medium with location-dependent errors, we propose in this paper a wireless fair scheduling algorithm which tries both to provide short-term fairness in the rate proportional guarantee sense and to maintain a reasonable system throughput. We present both the numerical and simulation results in this paper to verify that CS-WFQ (channel-state independent wireless fair queueing) has improved the short-term fairness property in error-prone wireless environments.

Future wireless mobile multimedia networks are likely to adopt micro/pico cellular architectures. A consequence of using small cell sizes is the increased rate of call handoffs as mobile terminals move between cells during the holding times of the calls. In a network supporting multimedia services, the increased rate of call handoffs makes it very difficult for the network to guarantee the quality of service (QoS) promised to a call at setup. This paper describes a handoff priority scheme which reduces the probability of call handoff failures in such a mobile multimedia network. The impact of this admission control policy on packet level performance is studied analytically for a homogeneous network supporting a mix of wideband and narrowband calls.

We propose a scheme that provides scalable support of QoS in the Internet by aggregating flows in the backbone networks and using a simple and fast forwarding mechanism to handle aggregated flows in the backbone network routers. Four traffic classes are defined for such aggregated flows, one each for guaranteed, controlled-load, assured and best-effort services. In each router, each class is implemented as a separate queue, served using a priority-based discipline. Aggregated flows are shaped or marked before being inserted into the queues. RED-like buffer management is employed to control the buffer occupancy of conformant and non-conformant packets. A border router placed at the link between an RSVP-capable stub network and an aggregation region, translates the flows into these four classes by tagging the data packets. Simulations have shown that the scheme is able to provide rate and delay guarantees to individual flows even after aggregation.

A virtual connection tree (VCT) concept has been proposed to avoid the need to involve the network call processor for every cell handoff attempt in cellular ATM networks. Acampora and Naghshineh (see IEEE Journal on Selected Areas in Communications, vol.12, no.8, p.1365-75, 1994) propose a model for connection admission control (CAC) to the virtual connection tree is for a homogeneous system. With wireless ATM perceived for supporting multimedia services, it is necessary to consider heterogeneous traffic models. We propose two CAC approaches for admission to the VCT based on equivalent capacity for heterogeneous traffic. We study the performance of one of these approaches by mathematical analysis and the other approach by computer simulation. The quality of service performance are the overload probability in a base station and the % overload period in a base station.

Class based queueing (CBQ) is a link-sharing and resource management mechanism for packet networks. We have ported the CBQ implementation on FreeBSD, also known as alternate queueing (ALTQ), to the Linux platform. This paper investigates the performance of CBQ in terms of latency, bandwidth guarantee and delay. CBQ is found to be able to preserve bandwidth allocated to the classes. However it does not scale well with the number of data flows as it incurs additional delay with each new data flow admitted. Due to this additional delay, the admission control cannot predict the delay experienced by the existing flows after admitting a new flow. Although CBQ is able to provide lower delay to higher priority flows, it also introduces jitter to the traffic owing to its packet scheduling artifact. As such, CBQ is not suitable for fine-grained scheduling of real-time traffic. It is more suited for providing bandwidth guarantee to aggregated data flows.

We construct a finite-state Markov chain model for a Rayleigh fading channel by partitioning the range of the received signal envelope into K intervals. From a simulation of the classic two-way Rayleigh fading model, a Markov transition probability matrix is obtained. Based on this matrix, we introduce an adaptive forward error correction (FEC) coding scheme. Simulation results show that the adaptive FEC coding scheme significantly improves the performance of a wireless communication system.

We describe the architecture design of a wireless cellular ATM access network. A MAC protocol that has been designed to take into consideration the traffic characteristics of different service classes to provide bandwidth efficiency, good QoS for real-time traffic, and reasonable QoS for non-time-critical traffic is also described.

In most current implementations of CT2 telepoint systems, only handset initiated calls are allowed. This paper describes a design to allow two-way calling for the CT2 public telepoint system with minimal modifications to the current CT2 infrastructure and the public switched telephone network (PSTN). The design makes use of centralized databases in the home location register (HLR) and visitor location registers (VLR) to track the location of handsets. This location information is stored in the VLR and HLR, and is used by the PSTN to route incoming calls destined for CT2 handsets to the appropriate CT2 telepoint base station (TBS). The TBS connect to the PSTN local exchanges (LE) through the integrated services digital network (ISDN) basic rate interfaces (BRI) for fast out-of-band signaling. We present simulation results of the system with the objective of determining where congestion might occur within the system and to understand the impact of the new implementation on the PSTN. The results indicate that the performance of the system will be limited by the VLR processing speed and the number of ISDN BRI's connecting the ISDN front end (IFE) to the PSTN.>

The paper presents a new MAC protocol, rate-based headend request control (RHRC), for dual unidirectional bus networks, which overcomes the unfairness of DQDB by allowing each station to generate multiple requests while retaining most of the positive features of DQDB, including 100% bandwidth utilization and low access delay at very low load. In addition, the protocol has two attractive features. Firstly, the transmission mechanism controlling station access to the data channel is able to provide approximately equal opportunity to messages so that they experience almost the same average delay independent of their physical locations and the traffic distribution. Secondly, the bandwidth allocation mechanism can achieve fair bandwidth sharing among stations when the network is overloaded, while maintaining fairness in terms of message delay amongst the underloaded stations. This mechanism also results in a shorter transient period than the bandwidth balancing mechanism of DQDB. Simulation results are included and comparisons are made with DQDB.>

The authors study the performance of an adaptive token-passing bus protocol where only active stations participate in the token passing, and therefore make up the logical ring. A station is active over an interval of time if during that interval data are generated at the station to be sent over the network. The size of the logical ring thus varies randomly according to the traffic intensity of the system. Existing analytical results for token-passing systems assume a fixed number of stations, which will take part in the token passing regardless of whether a station is active or not. An approximate analytical model is provided for a token-passing system where the effective size of the ring changes dynamically according to the network traffic.>