This paper studies a globally-aware optimization algorithm for the allocation of limited bandwidth during multipath routing inside a MANET. When allocating the limited bandwidth, this algorithm not only considers the current transmission at a crowded node, but also globally takes into account any other transmissions converging there in the network through the use of Flow Cost. An objective function is formulated in terms of the Flow Cost (capturing the effect of each flow on others) and the utilization factor (capturing queueing performance) so that an optimization can be carried out to allocate the bandwidth for the multiple routing paths. A 20-node network is used to illustrate the performance of our algorithm and its capability to support multiple paths.

This paper provides a network flow allocation algorithm that can be used for multipath routing in the wireless ad hoc networks. Called GANFA (Globally Aware Network Flow Allocation), this algorithm assigns a FC (Flow Cost) to every routing path in the network. The FC is a function of end-to-end delay, power consumption and hop distance, and is used to choose multiple routing paths. An optimization is executed at a node by taking into account the influence of any flows converging there, with the purpose of choosing the best bandwidth allocation scheme for multipath routing. Some allocation evaluation by AIMMS-CPLEX is provided to demonstrate the capability of this algorithm.

This paper proposes an SU controller based on the H2/H∞norm formulation to address the data traffic control issues in the Transport Layer of the AQM Network. The SU controller arises from the incorporation of the S (Sensitivity) function and the U (Input Sensitivity) function along with their associated weight functions. It keeps the robust steady-state performance of the H∞controller, but uses H2formulation in addition to improve the transient performance. We have evaluated the robustness and transient performances of this controller to show the improvement over the same controller with the H∞formulation only. We have also compared it with the PI-controller.

The OFEX (Optimal and Fully EXplicit) rate controller is able to provide not only the optimal bandwidth allocation but also the fully explicit congestion signal to sources. It feeds back the congestion signal from the most congested link along a flow path, instead of the summation of congestion signals. The OFEX controller overcomes the drawbacks of the relatively explicit controllers that (1) bias the multi-bottlenecked users in terms of the source sending rate and convergence speed, (2) are not adaptable to varying link bandwidth and (3) can potentially incur large queue sizes upon congestion. In this paper, we would like to investigate the convergence property of the OFEX controller which is of particular concern and interests to researchers, and point out how the OFEX controller can quickly converge to equilibrium even under bandwidth variations. Furthermore, our OPNET simulation experimentally demonstrates the superior convergence capability of the OFEX controller when compared with other schemes.

We have designed and investigated a new congestion control scheme, called the OFEX (Optimal and Fully EXplicit) controller. Different from the existing relatively explicit controllers, this new scheme is able to provide not only optimal bandwidth allocation but also fully explicit congestion signal to sources. It overcomes the drawback of the relatively explicit controllers that “bias” the multi-bottlenecked users, and improves their convergence speed and source throughput performance. Furthermore, the OFEX controller design considers a dynamic model by proposing a remedial measure against the unpredictable bandwidth changes in contention-based networks (such as shared Ethernet and IEEE 802.11). Compared with the former works/controllers, such a remedy also effectively reduces the instantaneous queue size in a link, and thus significantly improving the queueing delay and system stability performance. We have evaluated the effectiveness of the OFEX controller in OPNET. The experimental comparison verifies the superiority of the OFEX controller.

In view of the fast-growing Internet traffic, this paper propose a distributed traffic management framework, in which routers are deployed with intelligent data rate controllers to tackle the traffic mass. Unlike other explicit traffic control protocols that have to estimate network parameters (e.g., link latency, bottleneck bandwidth, packet loss rate, or the number of flows) in order to compute the allowed source sending rate, our fuzzy-logic-based controller can measure the router queue size directly; hence it avoids various potential performance problems arising from parameter estimations while reducing much consumption of computation and memory resources in routers. As a network parameter, the queue size can be accurately monitored and used to proactively decide if action should be taken to regulate the source sending rate, thus increasing the resilience of the network to traffic congestion. The communication QoS (Quality of Service) is assured by the good performances of our scheme such as max-min fairness, low queueing delay and good robustness to network dynamics. Simulation results and comparisons have verified the effectiveness and showed that our new traffic management scheme can achieve better performances than the existing protocols that rely on the estimation of network parameters.

The IntelRate controller does not require to evaluate some critical network parameters (such as the bottleneck bandwidth and the number of flows in the link) while performing well to the sudden changes in traffic load or bandwidth. This paper demonstrates theoretically that the IntelRate control system is globally asymptotically stable. Opnet simulations verify that the IntelRate controller can maintain stable operations regardless of the traffic conditions. Finally, comparison demonstrates that the IntelRate controller can have more stable performance than other exiting controllers upon network changes.

The most important goal in event-driven wireless sensor networks(EWSNs) is to transmit the event information to users timely. One of the most important factors that would make it possible to reach this goal is the design of efficient detecting protocols. In this paper we present an efficient event detecting protocol(EEDP) designed for event monitoring applications based on geographical routing. In the event area, each node broadcasts its primary detection result to make a decision corporately. And then nodes will choose the nearest node to destination as forwarder to reduce the delivery time. To improve the event detection probability, EEDP makes final decisions combing with other single decisions. EEDP is a highly efficient and accurate protocol for the event detection applications where the constraints of end-to-end delay and reliability are stringent.

When a node is not abiding by the rules of the protocol of a wireless network for its own benefit, it can cause severe degradation to network performance. Therefore it is important to detect such selfish behaviour. However, this is not an easy task. The main difficulty comes from the random operation of the carrier-sense multiple-access with collision avoidance (CSMA/CA) protocol, and is exacerbated by the nature of the wireless medium itself. The authors propose in this study a simple and quick algorithm, called sliding window non-parametric cumulative sum (SWN-CUSUM), to detect selfish nodes that deliberately modify its backoff window to gain unfair access to the network resources. SWN-CUSUM uses a sliding window to prevent unlimited build-up of the cumulating sum used in the protocol. The efficiency of this detection algorithm has been validated by extensive simulations using a Qualnet simulator. Comparative analysis of the proposed algorithm with a traditional CUSUM method demonstrates its superior performance with high detection accuracy and low false alarm rate. In addition, the authors compared SWN-CUSUM with other detection techniques, such as sequential probability ratio test and exponentially weighted moving average, the results show that our algorithm has a good performance in detection delay.

TCP is an important communication protocol as more and more multimedia technologies are deployed in the Internet nowadays. However, existing TCP control mechanism has some shortcomings in supporting real-time streaming traffic. Although UDP can be used as an alternative to transmit real-time application data, it lacks congestion control. Introducing a new TCP-friendly protocol that supports the multimedia applications as well as congestion control has been the aim for many researchers for a long time. The transport layer protocol DCCP was designed to reach this goal recently. Another challenge in high bandwidth-delay product networks is to achieve a fair bandwidth allocation with efficiency, while minimizing packet loss and bottleneck queue. As a simple and low-complexity protocol, VCP can meet this challenge by leveraging the two ECN bits in network congestion feedback. In this paper, we study and implement the VCP controller in a bottleneck network with DCCP traffic. We use VCP to analyze the traffic load into different congestion states in order to effect congestion avoidance and control in the presence of huge DCCP-CCID2 traffic. We perform mathematical analysis and run OPNET simulation to validate our DCCP/VCP controller. We compare the performance of DCCP/VCP with TCP/RED, DCCP/RED and TCP/VCP in a bottleneck network. Our simulation results show that VCP controller can provide DCCP flows with a smooth throughput, a small queue size and a low packet drop rate.

In this paper we model the data traffic congestion scenario in a vehicular ad-hoc network, and we apply the Adaptive PI Rate Controller (APIRATE) to deal with the congestion. Derived from classical control theory, the APIRATE controller performs AQM (Active Queue Management) by controlling the source rate based on the instantaneous queue length of the congested node. We then study the performance of this controller in a mobile rural scenario, and show that it has better performance for streaming traffic when compared with other existing controller.

This paper proposes an intelligent rate controller for the Internet traffic. Called the IntelRate (Intelligent Rate), it is a router-based controller and uses the fuzzy logic control approach to adjust the source sending rate based on the instantaneous queue size of the router. Unlike other explicit congestion control protocols, the IntelRate controller need not evaluate the link states (such as bottleneck bandwidth or the number of flows in the link) while performing well to the sudden changes in traffic load or bandwidth. Simulation results and comparisons have verified the effectiveness of our scheme, and showed the IntelRate controller is more stable and robust upon large network changes than other existing protocols that rely on the estimation of available bandwidth in order to compute the admissible source sending rate.

Admission and rate control are key components for providing QoS (Quality of Service) flows in multi- rate wireless ad hoc networks where transmission rate at the physical layer is adapted dynamically according to the channel condition. Key to these controls is the formulation of a rate constraint that can regulate the flow rate passing through each node. This paper formulates a cross-layer rate constraint to serve this purpose. Although node- based, the new rate constraint captures the interference level at the receiver side as well as the contention at the sender side, which is more accurate than that of existed work. Simulation results on DSR incorporated with such constraint show that the QoS routing algorithm can admit feasible flows and make full use of the bandwidth resource based on the rate constraint, moreover it outperforms the other algorithms in the scenarios we tested.

As an explicit congestion control protocol, API-RCP (Adaptive PI rate control protocol) was originally proposed for best-effort traffic control in the IP networks with high bandwidth-delay product. The original API-RCP adopts a truncated network model for IP router in order to simplify the control system design while still achieving various designed performance measures at steady-state. A further benefit can be realized if one can specify a desirable transient system response (e.g., a shorter settling time). We have achieved this by using a pole-placement technique on a non-truncated closed-loop network model along with proper assignments of the damping ratio and the undamped natural frequency. Our OPNET simulations demonstrate a satisfactory transient network performance as designed. We also make performance comparison between API-RCP and TCP/RED. In the sequel, we can verify the effectiveness of the original truncated model using theoretical analysis instead of numerous simulations.

TCP becomes inefficient and prone to instability when its bandwidth-delay product increases. By sending explicit congestion information from routers to end hosts, both XCP and API-RCP have been proposed to solve the stability issue of TCP in high bandwidth-delay product networks. Since the estimation errors of the network parameters are unavoidable, we would like to design a robust controller to address this type of model uncertainty in the explicit congestion control system. We employ the H∞optimal criterion in our design, and select a proper weight function to solve the H∞sensitivity problem. By using the maximum modulus theorem from the robust control theory, we obtain an optimal internal model controller from which a robust H∞controller can be derived. OPNET simulations demonstrate that our H∞controller exhibits a good robustness to varying network parameters. Performance comparison between our robust explicit congestion controller and TCP/RED is provided.

Intra- and Inter-flow interferences are the principal causes of network utilization degradation in MR-MC (Multi-Radio Multi-Channel) wireless mesh networks. To minimize these interferences, we propose in this paper a channel assignment algorithm and incorporate it in an on-demand routing protocol called the HCARP (Hybrid Channel Assignment Routing Protocol). In addition, HCARP uses load balancing in route discovery to avoid "hot-spots" with severe interference and to find a route satisfying QoS requirements of the incoming flows. Simulation results and test bed experiments demonstrate that intra- and interflow interferences can be mitigated significantly and the overall network throughput is improved considerably. In addition, our algorithm outperforms the one based on superimposed code if the strength of the superimposed code is less than the interferer number of a node. Our simulation results show that HCARP has the capability of circumventing congested areas in the network and enhancing the QoS support for bandwidth-intensive traffic.

In this paper, we propose an improved gradient-based micro sensor routing protocol (GMSRP) using a node sleep scheduling mechanism, to save energy for sensor nodes, called the GMSRP-SLE. This algorithm takes into account the characteristic of most applications in WSNs, i.e.,the sensor nodes are deployed randomly with some areas covered by many sensor nodes at same time. During network initialization, each sensor node in GMSRP-SLE can learn its gradient information, which is the minimal number of hops away from the sink node. Sensor nodes with the same gradients in the same layer can form a cluster according to the requirement of minimal sensing coverage ratio. One sensor node in the cluster is selected to be a cluster head, and the rest will go to sleep. Additionally, in order to balance the energy consumption and the lifetime of sensor nodes in a cluster, each sensor node will take turn to become the cluster head. Our NS-2 simulation results show that the GMSRP-SLE algorithm can work efficiently to keep some nodes sleeping in order to save more energy.

Video and image communications can assist in highway traffic control, accident avoidance and management as well as road congestion control and coordination. This paper studies video streaming over wireless medium among a cluster of vehicles in an ad-hoc network. Through intense tradeoff study, we investigate the issues encountered in building a robust system that would allow automobiles to effectively transmit multimedia information in an ad-hoc network with constantly changing wireless environments. Based on our OPNET simulation results, we offer some design guidelines for transmitting streaming video over a vehicular adhoc network.

Selfish behavior at the MAC (medium access control) layer can have devastating side effects on the performance of wireless ad hoc networks. In this work, we consider the problem of detecting selfish behavior at the MAC layer in IEEE 802.11 wireless networks when a selfish node can manipulate the backoff operation. We propose a simple and robust mechanism based on CUSUM (cumulative sum) test by tracing the statistics characteristic in real time to detect the selfish behavior. This method can be used with any random access MAC protocols and it does not require any modification on the existing protocols. The efficacy of this detection mechanism has been validated by a Qualnet simulator. Our simulation results show that the detection mechanism has short detection time and high detection accuracy.

Vehicle traffic congestion is reflected as delays while traveling. Traffic congestion has a number of negative effects and is a major problem in today's society. Several techniques have been deployed to deal with this problem. In this paper, we have proposed an innovative approach to deal with the problem of traffic congestion using the characteristics of vehicular ad-hoc networks (VANET). We have used the adaptive proportional integral rate controller, a congestion control algorithm designed for the Internet, to deal with the problem of vehicle traffic congestion in vehicular networks. The adaptive PI rate controller is a rate based controller that employs control theory to manage the problem of data traffic congestion in computer networks. Using simulations we have demonstrated the applicability of the algorithm in the domain of vehicle traffic congestion in a VANET.

This paper studies and evaluates a WiMAX relay architecture and its protocols to support multicasting/ broadcasting service and to address several related design issues. Performance of a video application is evaluated in term of different QoS measures. Our results demonstrate that the proposed architecture is feasible for real implementation and in line with the PMP characteristics of WiMAX.

Security is a fundamental prerequisite for the survivability and reliability of wireless networks. In a network where limited wireless resources have to be shared, selfish nodes can manipulate relevant network parameters to gain more access to the resources, and hence obtain a higher performance than their fair share, while the performance of well-behaved nodes will be significantly degraded. This paper considers the environment of an IEEE802.11 WLAN, and proposes a solution from the prospective of a principal-agent system. Our solution uses an incentive and a constraint mechanism to encourage the selfish agent to perform normally. Our method does not modify the IEEE 802.11 protocol, but requires an additional principal node only. Simulation results show that our method can overcome the influence of selfish nodes improve the network fairness performance while maintaining the throughput performance.

Research on the effect of selfish node in wireless ad hoc networks has received considerable attention recently. However, most work concentrates on simulation study, but lacks an analytical study to accurately predict the throughput. This paper investigates the saturated and non-saturated load throughputs of IEEE 802.11 DCF (distributed coordinated function) in the presence of a selfish node. Using a modified Markov model, we have derived the throughput of a node under various traffic loads in the PHY (PHYsical) layer using DSSS (direct sequence spread spectrum) and the wireless MAC (medium access layer). The analytical model and throughput results have been validated by simulations.

Among the many different bandwidth access schemes used in optical packet switched networks nowadays, the issue of transmitting optical packets (called slots in this paper) smoothly to an egress switch appears to be overlooked. Here, we explain the benefits of providing an even (smooth) slot transmission, and propose three methods to achieve an even transmission from an ingress switch of a multi-wavelength/fiber network. An index parameter is introduced in each method, and a formulation is provided to gauge how even a transmission is among different combinations of frame periods, wavelengths, and fibers. These formulations provide us with a new approach to compare different bandwidth access schemes. An example is provided for the comparison of the distributed bandwidth access, and the timer-based plus threshold-based bandwidth access schemes.

The purpose of this paper is to study the performance of voice transportation in wireless ad hoc networks. First we analyze the characteristics of wireless channel and speech coding standard AMR-WB, and then we propose an adaptive source network rate control scheme to battle packet loss. The basic idea is to adapt the voice coding bit rate to the available network bandwidth in order to maximize the quality of voice. The PESQ MOS value is used as the evaluation criteria for the adaptive rate control scheme. Moreover, the discontinuous transmission operation and packet combination are utilized to improve the performance further. The experimental results show the effectiveness of this scheme.

In optical burst switching (OBS) networks, many packets are aggregated into larger bursts, which exhibit different traffic characteristics in the bufferless optical core networks compared to the packet-level traffic in the conventional electronic switching systems. However, many OBS studies often neglect this issue by assuming the inputs to be bursts when analyzing the system-level performance. This paper demonstrates that the loss performances of optical bursts are dramatically different when considering burst assembly process at the edge nodes and the connectivity of the core nodes. We develop some analytical models for the JET and JETseg networks, which can model the loss performance more accurately than the traditional methods. Our performance evaluation reveals that the connectivity and burst assembly process affect the loss performance significantly, particularly for a WDM network with a small node-degree and a large number of wavelength channels. Our model provides an in-depth understanding on the OBS scheme.

We study and evaluate the performance of three potential candidates of resource-sharing algorithms in agile single-hop slotted buffer-less all-optical packet switched metro networks. Both reservation-based (centralized) and collision-based (distributed) schemes are considered. In the centralized scheme, all decisions are made at the core switch and loss can be avoided through reservations. On the other hand, decisions are made at the edge switches in the distributed scheme, and we need to retransmit the dropped traffic. We also implement an integrated architecture that combines the good attributes of both schemes and characterize this architecture by various measures such as delay and loss probabilities at the edge switches.

In this paper we examine multiple failure restorability performance of self-repairing shared trees for local link restoration in unicast mesh networks. We demonstrate how these shared hierarchical protection trees could be utilized to effectively handle multiple consecutive link failures with minimal reconfiguration. We evaluate the restorability performance using simulation of random graphs and present the results of second- and third-failure restorability as well as the required redundancy to achieve various restorability targets.

Protection trees have been used in the past for protecting multicast and unicast traffic in networks in various scenarios. In this paper we focus on shared protection trees for link protection in unicast mesh networks. We present a heuristic algorithm that reduces the redundant capacity required for protection on shared trees, and improves the restorability of the network. We use simulation of random mesh graphs to compute the performance improvement for various network sizes.

It is important to study the traffic in the wireless network control and management. This paper proposes the use of the EVT (extreme value theory) for the analysis of wireless network traffic. The role of EVT is to allow the development of procedures that are scientifically and statistically rational to estimate the extreme behavior of random processes. We have performed extensive simulation experiments by taking traffic data that is greater than a given threshold value. The results of our experiments and analysis show the wireless network traffic model obtained through the EVT fits well with the empirical distribution of traffic. Meanwhile, we can obtain EVT model has the lowest "average deviation" compared with other popular distribution model such as exponential, lognormal, gamma, Weibull. Thus illustrates EVT is more suitable than other distributions to model the traffic and it has a good application foreground in the analysis of wireless network traffic.

Several centralized and distributed algorithms have been recently proposed to maximize the multicast lifetime for directional communications in wireless ad-hoc networks. Their performance has been studied by simulations; however, their theoretical performance in terms of approximation ratio is still unknown. In this paper, we use the graph theoretic approach, by the first time, to derive the upper bound of the approximation ratio in an analytical expression for these algorithms. We have also discovered that these upper bounds are finite numbers. Based on this analysis and some key observations, we present a new distributed constant-factor approximation algorithm in order to achieve a higher performance. This effort is validated by our simulation studies.

The paper proposes a self-tuning active queue management (AQM) controller for Internet protocol (IP) routers supporting transmission control protocol (TCP) traffic in the Internet. Classical control theory is applied in the design to meet the frequency-domain-specification gain margin. The user can assign a proper gain margin to achieve good AQM performance. Simple equations for obtaining the AQM controller are derived. The designed AQM controller self-tunes, only when changes in Internet traffic have drifted the traffic monitoring parameter outside its specified interval, otherwise the self-tuning AQM controller remains unchanged. The OPNET® simulations used by the authors in single and in multiple bottleneck links demonstrate that, with the use of a self-tuning AQM controller in the routers, this AQM control system adapts very well to great fluctuations in the TCP traffic, thus providing the network with good stability robustness.

In this paper, we study the routing and wavelength assignment (RWA) problem in a semi-dynamic scenario where rearrangements are conducted in a series of sessions after traffic demands vary. Unlike pure static RWA problems, each rearrangement scheme must consider established lightpaths in the previous session. A novel formulation of the WDM network rearrangement problem is used to minimize rejected new demands and rerouted lightpaths. This is done by coordinating the re-routing of existing lightpaths with the adaptation to varying demands. The Lagrangean Relaxation and Subgradient Method (LRSM) has been successfully used to solve the problem along with fairness consideration. The superior performance and reduced computation complexity of our algorithm are demonstrated in sample networks. In addition, we evaluate the benefit of using wavelength converters in a WDM network rearrangement. In contrast to previous studies with conclusions that wavelength converters are of little value in the static RWA problem, we show that wavelength converters improve network performance in a WDM network rearrangement.

To explore the advantages of power saving offered by the wireless multicast advantage property, we consider the case of source-initiated multicast traffic. Current research activity for the minimum energy multicast (MEM) problem has been focused on devising efficient centralized greedy algorithms for static ad hoc networks. In this paper, we consider mobile ad hoc networks (MANETs) that use omnidirectional antennas and have limited energy resources. We propose the design and initial evaluation of the distributed minimum energy multicast (DMEM) algorithm for MANETs that attempts to reduce as much as possible the total RF energy required by the multicast communication. Several localized operations are presented for the DMEM algorithm, in which each node requires only the knowledge of and distances to all neighboring tree nodes. Through extensive simulation studies, we show that these operations are very efficient both in terms of energy saving and operation overhead

In this paper, we propose an adaptive PI (proportional-integral) rate controller for the AQM (active queue management) router that would support best-effort traffic in the Internet. Unlike most window-based controllers, our rate-based controller design is derived from the classical control theory and it would allow the users to achieve good stability robustness of the AQM control system by specifying a proper phase margin. We also make our controller adaptive by selecting a simple heuristic parameter to monitor the network environment real-time so that the controller would self-tune only when a dramatic change of the network traffic has drifted the monitoring parameter outside its specified interval. Located in the router, the adaptive PI rate controller calculates desirable source window sizes (i.e., source sending rates) based on the instantaneous queue length of the buffer and advertises it to the sources. Our simulations demonstrate that our AQM control system can adapt very well to sudden changes in network environment, thus providing the network with good transient behavior. By making the source sending rate relatively smooth, our adaptive PI rate controller becomes quite suitable for streaming media traffic control in the Internet

This paper presents a bandwidth management framework for the support of differentiated-service-aware traffic engineering (DS-TE) in multiprotocol label switching (MPLS) networks. Our bandwidth management framework contains both bandwidth allocation and preemption mechanisms in which the link bandwidth is managed in two dimensions: class type (CT) and preemption priority. We put forward a Max-Min bandwidth constraint model in which we propose a novel "use it or lend it" strategy. The new model is able to guarantee a minimum bandwidth for each CT without causing resource fragmentation. Furthermore, we design three new bandwidth preemption algorithms for three bandwidth constraint models, respectively. An extensive simulation study is carried out to evaluate the effectiveness of the bandwidth constraint models and preemption algorithms. When compared with the existing constraint models and preemption rules, the proposed Max-Min constraint model and preemption algorithms improve not only bandwidth efficiency, but also robustness and fairness. They achieve significant performance improvement for the well-behaving traffic classes in terms of bandwidth utilization and bandwidth blocking and preemption probability. We also provide guidelines for selecting different DS-TE bandwidth management mechanisms.

In this paper, we design a self-tuning utility- based controller for end-to-end congestion in the IP (Internet protocol)-based Internet. Multiple controlled sources transmit the packets through a series of AQM (Active Queue Management) routers into their destinations simultaneously and share the limited bandwidth of the Internet. Each AQM router runs the RED (Random Early Detection) algorithm that uses ECN (Explicit Congestion Notification) packet marking strategy to provide the link congestion information through IP packets. A self-tuning utility-based controller is placed in every source node to regulate source transmission rate based on the feedback route congestion information from the AQM routers through ACK packets. The pole placement technique in classical control theory is used to allow the user to achieve good transient network performance. By assigning a proper interval of damping ratio ζ, ach controller self-tunes only when the change of network parameters drifts ζ outside its specified interval. Our simulations demonstrate the stability of the Internet achieved by our self-tuning utility-based congestion controller.

Blocking is an extremely important performance issue in optical burst switching (OBS) networks because of the asynchronous nature of bufferless burst-mode switching. In this paper we revisit the timer-based burst assembly algorithm to generate Poisson-type burst traffic at source edge nodes. We then investigate the influences of burst characteristics on the loss rate of burst flows at the core nodes. Based on the analytical results, we make use of the burst assembly process to devise a feedback control scheme capable of achieving the required loss rate for a burst flow. Compared to other QoS control research on OBS networks, our work is more suitable for bufferless OBS networks because it 1) does not degrade the network throughput, 2) does not require any global network information to control the loss rate of a flow, 3) has a low time and computing complexity. We demonstrate the effectiveness of our method in the Just-In-Time (JIT) OBS network.

This paper studies the total network restorability using only two protection cycles in a mesh optical network with fixed and uniformly distributed working and protection capacities. We present a detailed analysis for the shared case when two cycles share the capacity in a number of edges common between the two cycles, and also for the non-shared case when the capacities are not shared. We study how the restorability changes with respect to different network parameters.

We consider the problem of maximizing the network lifetime for multicast connections in a wireless ad hoc network (WANET) that use omni-directional / directional antennas and have limited energy resources. Unlike most centralized multicast algorithms, we provide a globally optimal solution to this problem in a distributed manner in a WANET with omnidirectional antennas. This graph theoretic approach provides us insights into more general case of using directional antennas, and inspires us to produce a group of distributed algorithms. Simulation results show that our distributed algorithms outperform other centralized multicast algorithms significantly in terms of network lifetime.

Reconfigurable optical add/drop multiplexers (ROADMs) manufactured with different designs and technologies are soon going to be available in the market. Unfortunately, the latest available ROADM architectures are either suffering from high insertion losses or high manufacturing costs that prevent their rapid deployment in the network. In this paper, we propose a low-loss hybrid architecture for a ROADM subsystem that combines the best features of the latest available ROADM designs. A metro network testbed has been designed and simulated in order to compare the performance of different ROADM modules. The obtained results indicate that our proposed hybrid-ROADM module performs better than the latest available ROADM subsystems and would reduce the overall network operating costs.

In this paper, we consider the queueing performance of periodic polling services for VoIP in an IEEE802.16 system, which is modeled by an MIGIC type queue with periodic batch service. We carry out an analysis for this system, using a generating function approach with supplementary variable technique. As a service discipline, the size of batch, the transmission duration in units of frames, i.e., contiguous frames, and the vacation period correspond to the bandwidth assigned to a subscriber station and the period to poll other subscriber stations, respectively. In numerical examples, the mean queue lengths are given, according to various system parameters.

We propose a novel link-based formulation of the WDM network reconfiguration problem for the semi-dynamic scenario, where reconfigurations are required in a series of sessions as traffic demands vary. Each reconfiguration session must consider existing connections obtained from the previous reconfiguration session. We coordinate the reconfiguration of existing connections with the new traffic demands by minimizing the rejected demands and reconfigured connections. With a much more complicated formulation, we are also able to incorporate the fairness consideration. The Lagrangean Relaxation and Subgradient Methods (LRSM) are successfully used to solve the WDM network reconfiguration problem. We demonstrate superior algorithm performance and reduced computation complexity in sample networks. In addition, we demonstrate that there is a benefit of using wavelength converters in WDM network reconfiguration problem, in contrast to the conclusion of the previous studies that wavelength converters are of little value in the static RWA problem.

Optical time division multiplexing can be deployed in an all-optical network to provide a finer granularity and improve the bandwidth usage. In contention-based slotted all-optical networks, transmitted traffic (referred to as slot in this paper) on the same wavelength and time-slot from different ingress switches may collide at the optical switches and therefore a number of slots will be lost. In this paper, we study various software techniques to reduce the slot loss rate at an optical switch. We prove some lemmas related to the contention avoidance issue. We show that the ingress switches can have an important role in the loss rate reduction issue in the slotted all-optical networks by balancing the traffic on the wavelength channels and the symmetric traffic transmission. We analyze for the first time the lower-bound on the slot loss rate. We show how to achieve the lower-bound on the loss rate in practice.

Traffic demands in the metro market are rapidly increasing due to different service applications like broadband access and video on demand. Unfortunately service providers are still using costly optical-electrical-optical (O-E-O) regenerators for ring-to-ring interconnections. This paper presents detailed features for ring-to-ring interconnections in an optical domain by using Planner Lightwave Circuit (PLC) based Reconfigurable Optical Add/Drop Multiplexers (ROADMs). A small modification is also proposed to the PLC-based ROADM's architecture and extensive simulations are run to optimize their performance in the metro ring network in terms of fibre span and cascadability.

In a typical installation of an 802.11 based WLAN (Wireless Local Area Network), mobile hosts would access the network through Access Points, even when two mobile stations can communicate within the same WLAN. Effectively, all the packets in a WLAN are required to forward through the AP (Access Point) according to the MAC (Medium Access Control) layer protocol. Since the AP has the same priority as the other mobile stations to access the channel, the AP usually becomes a bottleneck in WLANs and the network performance degrades significantly. In this paper, we propose a new MAC layer protocol for WLANs in order to improve the throughput performance. Theoretical analysis and simulation results show that our new protocol works much better in WLAN than the standard DCF.

We consider the problem of maximizing the multicast lifetime in multihop wireless networks in which each node is static and has limited energy, bandwidth, memory, and computation capabilities. Unlike most multicast algorithms that use centralized greedy algorithms, our algorithm can construct a global optimal maximum lifetime multicast tree in a distributed manner. It has a low complexity of O(λu) for both memory and computation requirements at each node u, where λu is the degree of node u. The simulation results have shown that it has an expected linear communication complexity under different network sizes and multicast group sizes. This means that our distributed algorithm is also scalable in terms of communication overhead and it is very useful for large-scale energy and bandwidth constrained multihop wireless networks like sensor networks.

Ordinary congestion control methods based on queueing models are not suitable for the bufferless Optical Burst Switching (OBS) networks. This paper designs a novel heuristic congestion control scheme in order to achieve desired QoS for optical burst flows through the adjustment of burst assembly intervals. Our method is simple and easy to implement. The simulation results demonstrate that our system can maintain a stable network throughput.

A new framework, called distributed TDM (DTDM), is proposed to access a slotted all-optical packet switching network within the DiffServ domain. In DTDM, each ingress switch measures the bandwidth (in slots per frame) of the traffic torrents (a torrent is the traffic between each pair of ingress and egress switches) at each frame time. Then the slots assigned to each torrent are distributed throughout the frame and among the output wavelengths and fibers. A schedule is determined so that each torrent knows in which wavelength/fiber and time-slot can transmit its traffic. DTDM uses packet schedulers to provide packet differentiation

We consider the problem of minimizing the energy consumptions of a given multicast connection in mobile ad hoc networks (MANETs) that use omnidirectional antennas and have limited energy resources. Unlike most multicast algorithms that use centralized greedy algorithms to achieve energy-efficiency in static ad hoc networks, our distributed algorithms explore the localized operations to take the advantages of power saving offered by the wireless multicast advantage property in mobile networks. The extensive simulation results have shown that our DMEM (distributed minimum energy multicast) algorithm is very efficient in terms of energy saving under different node motilities.

In this paper, we consider wireless ad hoc networks that use adaptive antennas and have limited energy resources. To explore the advantages of power saving offered by the use of adaptive antennas, we consider the case of source initiated multicast traffic. We present a constraint formulation for the MEM (Minimum-Energy Multicast) problem in terms of MILP (Mixed Integer Linear Programming) for wireless ad hoc networks. An optimal solution to the MEM problem using our MILP model can always be obtained in a timely manner for moderately sized networks. In addition to the theoretical effort, we also present two polynomial-time heuristic algorithms called RB-MIDP and D-MIDP to handle larger networks for which the MILP model may not be computationally efficient. The experimental results show that our algorithms compare well with other proposals discussed in this paper.

To explore the energy saving advantage offered by the use of directional antennas, we consider the case of source initiated multicast traffic in static ad hoc wireless networks that use switched antennas and have limited energy resources. We present a constraint formulation for the joint optimization problem MEM-AO (minimum-energy multicast and antenna orientation) in terms of MTLP (mixed integer linear programming). The optimal solution can be obtained using an MILP solver in a timely manner for moderately sized networks with switched antennas. In addition to the theoretical effort, we also provide two heuristic algorithms and a general post-process operation TR (tree reconstruction) for handling larger networks. The experimental results show that our TR operation significantly improves the performance of both heuristic algorithms.

In this paper, we propose a new scheduling technique, called output-controlled round robin (OCRR), for the support of class-based IP networks with variable packet sizes. This technique can be used in edge switches of an optical network to assemble traffic from aggregated flows into bursts/slots. Traffic flows from different classes are scheduled in logical frames. In each logical frame, a flow obtains a grant quantum with respect to its average rate and bandwidth usage in order to pass its traffic. The round robin technique is extended to include smaller cycles to send packets from aggregate flows one by one, thus, eliminating bursty effect from the same flow on the output bandwidth. The amount of the output traffic from each flow is also controlled. Our performance evaluation demonstrated that this output-controlled technique has better performance results than the deficit round robin algorithm in reduction of queuing delay and burst size from the same flow.

This paper designs a robust AQM controller for IP routers based on the robust mu-analysis technique. Specifically, by modeling the uncertainties of the TCP/AQM system in terms of the uncertainty weight, we synthesize the controller by approximating the mu-optimal control problem with the HinfinS/T/U mixed sensitivity problem (MSP). We also analyze the NP (nominal performance), the RS (robust stability) and the RP (robust performance) of the system under the synthesized controller using the mu-analysis technique. Extensive simulations are performed on the OPNET platform to verify the effectiveness of the designed controller

We design an adaptive multiloop PI (proportional-integral) rate-based controller for the MIMO (multiple-input multiple-output) AQM (active queue management) router to support best-effort streaming media traffic in the Internet. Our controller design employs the DNA (direct Nyquist array) method by shaping the Gershgorin band analytically, thus allowing users to achieve good stability robustness of the MIMO AQM control system through specifying a proper phase margin.

This paper presents two bandwidth preemption algorithms for two widely deployed bandwidth constraint models supporting differentiated service aware traffic engineering: the maximum allocation model and the Russian doll model. Our designs aim at achieving preemption fairness and performance robustness, in addition to the objectives of minimizing the preemption disruption to the existing connections. We propose that the preemption decision be made not only on the basis of priority level, but also on the basis of the bandwidth reservation status and bandwidth constraint model characteristics. Simulation results show that the proposed preemption algorithms achieve significant performance improvement in terms of both bandwidth blocking and preemption rate and bandwidth utilization.

This paper proposes an AQM controller design procedure for IP routers using the recently developed H/sub /spl infin// optimal control theory. We apply the H/sub /spl infin// loop-shaping technique to solve the S/U Mixed Sensitivity Problem (MSP) in the controller design. Different weight functions and their impacts on the system performance are evaluated and discussed. Extensive OPNET simulations are performed to verify the effectiveness of our designed controller.

We consider the problem of maximizing the lifetime of a given multicast connection in wireless networks that use directional antennas and have limited energy resources. We present a constraint formulation for the MLM (multicast lifetime maximization) problem in terms of MILP (mixed integer linear programming) for wireless ad hoc networks, which we can use to evaluate and compare the realistic performance of different heuristic algorithms.

In this paper, we propose a self-tuning PI (proportional-integral) rate controller for an AQM (active queue management) router that would support best-effort traffic in the Internet. Our design employs classical control theory that allows the users to achieve good stability robustness of AQM control system by assigning a proper interval of gain and phase margins. Our self-tuning PI controller will self-tune only when the gain margin or phase margin drifts outside the specified interval. Every controlled source node always sends the data to the network at the maximum allowed transmission rate, thus maximizing the utilization of network resources. The self-tuning PI controller located in the router can calculate the advertised transmission rate for source nodes based on the instantaneous queue length of the buffer. Our simulations demonstrate good stability robustness of AQM control system with our self-tuning PI controller.

We consider the problem of maximizing the lifetime of a given multicast connection in wireless networks that use omni-directional antennas and have limited energy resources. In this paper, we first explore the upper bound of the multicast lifetime using dynamic routing. We then provide a set of heuristic algorithms. Experimental results show that minimum total power consumption does not guarantee maximum lifetime for either broadcasting or multicasting, and our algorithms outperform other energy-aware multicast algorithms significantly in terms of multicast lifetime.

The 802.11 standard supports multiple data transmission rates. To achieve a high performance under varying conditions, wireless stations need to adapt their transmission rate dynamically. Typically, stations with 802.11b products would reduce their bit rate from 11 Mbps to 5.5, 2, or 1 Mbps if they are far away from an access point (AP) and subject to significant signal fading and interference. This leads to considerable rate diversity, particularly when the network is congested. Under such conditions, aggregate throughput of WLANs will be degraded drastically (M. Heusse et al., 2003) because the basic CSMA/CA channel access method would guarantee an equal long term CAP (channel access probability) to all hosts. The main contribution of this paper is the proposal of an algorithm that can be implemented at both the AP and the wireless stations (WSs) with the purpose of guaranteeing fairness and improving the aggregate throughput of 802.11b multi-rate WLANs, We use COT (channel occupancy time) as fairness index instead of the CAP to analyze the fairness of WLANs. With our algorithm, the AP and wireless stations in the WLAN can achieve COT-based fairness by adjusting their packet length, sending the multiple back-to-back packets at one time, or giving up an opportunity to access the channel. Through exclusive simulations, we show that our algorithm leads to significant improvements in aggregate throughput and provides COT-fairness under multi-rate condition

We consider the performance of various algorithms to maximize the lifetime of a given multicast connection in wireless networks that use directional antennas and have limited energy resources. Based on the IMILP (mixed integer linear programming) formulation [S. Guo et al, 2005], which provides a globally optimal solution to this problem for a small or medium network, we can evaluate the realistic performance of different heuristic algorithms. Experimental results show that minimum total power consumption does not guarantee maximum lifetime for either broadcasting or multicasting, and the algorithms S-DPMT and D-DPMT [S. Guo et al, 2004] outperform other energy-aware multicast algorithms significantly in terms of multicast lifetime.

In this paper, we propose a novel on-demand routing protocol called backup source routing (BSR) to establish and maintain backup routes that can be utilized after the primary path breaks. The key advantage of BSR is the reduction of the frequency of route discovery flooding, which is recognized as a major overhead in on-demand protocols. We define a new routing metric, called the route reliability, and use it to provide the basis for the backup path selection. We use a heuristic cost function to develop an analytical model and an approximation method to measure this metric. Various algorithms for our BSR protocol in the route discovery phase and route maintenance phase have been designed based on this cost function. Extensive simulations demonstrated that our routing strategy has two interesting features: 1) in less stressful situations of lower mobility, BSR has similar performance to DSR, 2) in more challenging situations of high mobility, BSR can improve the performance significantly.

We consider the problem of maximizing the lifetime of a given multicast connection in wireless networks that use directional antennas and have limited energy resources. We first provide a globally optimal solution to this problem for the special case of using omnidirectional antennas. This graph theoretic approach provides insights into the more general case of using directional antennas, and inspires us to produce two heuristic algorithms. Experimental results show that minimum total power consumption does not guarantee maximum lifetime for either broadcasting or multicasting, and our algorithms outperform the group of minimum-energy multicast algorithms significantly.

We propose a self-tuning proportional-integral (PI) controller for active queue management (AQM) in the Internet. Classical control theory is applied in the controller design. We assign a proper interval of gain and phase margins to achieve good AQM performance while adapting the AQM control system to great traffic load changes very well. Based on the knowledge of the queue size, our PI controller can regulate the TCP source window size to clamp the steady value of queue size to specified target buffer occupancy. OPNET simulations demonstrate that, with our self-tuning PI controller applied, the network shows good stability robustness.

The paper studies the concept of restoration paths (RP) matrix for analysis and performance evaluation of link restoration schemes. The RP matrix provides a very useful tool for computing single, double and multiple failure analysis of network restorability. It can be constructed for any link restoration scheme, regardless of unique scheme architecture or pattern. For this reason, the RP matrix can be used to compare various link restoration schemes. We present a description of the RP matrix, provide examples of it for well-known network architectures, and compute mathematical formulas to calculate various performance parameters of the network from network topology info and the RP matrix.

In this paper, we make use of the distributed utility-based congestion controller to study the stabilization problem under a general network topology. The network allows multiple users to simultaneously share the limited availability of network resources and to control their transmission rates by delayed feedback signals. We establish a sufficient condition for global stability for the controlled network with delays in both data paths and control paths. This condition for testing global stability is very simple and does not need the assumptions that the congestion marking function is differentiable and converges to an equilibrium point.

This paper revisits the simple pole placement technique in the classical control theory, and exploits this technique to propose a controller for the active queue management (AQM) in IP routers. Our self-tuning proportional-plus-integral controller based on pole placement (ST-PI-PP controller) can assign proper intervals of the damping ratio /spl xi/ and the undamped natural frequency /spl omega//sub n/ to guarantee the system stability, to achieve good AQM performance and thereby to make the system adapt to significant load changes very well. We verify the effectiveness of the controller via OPNET simulation. Our simulation results show that: a) choosing appropriate /spl xi/ and /spl omega//sub n/ can successfully satisfy the transient response of the system; and b) when the network load changes, the ST-PI-PP controller can still stabilize the queue size at the reference value.

We have designed a proportional and integral rate (PIR) controller based on the continuous-time fluid flow control theory to solve both of the traffic control performance problems observed in RED, i.e. the unnecessary packet loss and the queue size oscillation in the router. We prove the controller's stability by the Second Method of Lyapunov's Stability Theorem and provide an implementation method. Our simulation results demonstrated that the PIR controller outperforms other common traffic and congestion control schemes significantly.

The packet-level traffic characteristics in the Internet are so complex that it is natural to do traffic engineering (TE) and control at the flow level. The emerging multi-protocol label switching (MPLS) has introduced an attractive solution to TE in IP networks. The main objective of this paper is to balance traffic at the flow level among the parallel label switched paths (LSPs) in MPLS networks. We first introduce a multipath load-balancing model at the flow level. In this model, each LSP is modeled as an M/G/1 processor-sharing queue. Based on the analysis of the model, we propose a heuristic but efficient mechanism that is implemented only at the ingress label switched routers (LSRs) and egress LSRs in the network. Extensive simulations using NS2 are performed with MPLS modules. The simulation results show that the load through the network is well balanced so that the network throughput is improved and the delay is decreased significantly.

Energy conservation is a critical issue in wireless multihop ad-hoc networks, which have nodes powered by batteries only. One major metric for energy conservation is to route a communication session along the routes that require the lowest total energy consumption. We consider wireless ad hoc networks that use adaptive antennas and have limited energy resources. To explore the advantages of power saving offered by the use of adaptive antennas, we consider the case of source initiated multicast traffic. We present a constraint formulation for the MEM (minimum-energy multicast) problem in terms of MILP (mixed integer linear programming) for wireless ad hoc networks. Experiment results show that an optimal solution of the MEM problem using our MILP model can always be obtained in a timely manner for moderately sized network, and it also provides a way to evaluate the realistic performance of different heuristic algorithms.

In wireless ad hoc networks a crucial problem is to minimize energy consumption, as in most cases the nodes are battery operated. In this paper, we consider wireless ad hoc networks that use omni-directional antennas and have limited energy resources. We focus on the problem of minimum-energy multicast, for which it is well known that the broadcast nature of the radio transmission can be exploited to optimize energy consumption. In order to handle larger networks, we present a dynamic multicast tree reconstruction heuristic algorithm called MIDP (multicast incremental-decremental power), which provides a near optimal solution in polynomial-time. The experiment results show that our algorithm compares well with other proposals.

This paper presents an analytical study of preplanned protection cycles (p-cycles) in mesh optical networks. We mathematically define and calculate the total network restorability for a Hamiltonian p-cycle in the case where the working and protection capacities of a network are fixed and uniformly distributed. The dependency of the total network restorability on various network parameters such as network size and the ratio of maximum to minimum link capacity in the network are discussed in detail. We present analytical and simulation results for random and real networks to show the remarkable accuracy of our analysis.

Energy conservation is a critical issue in wireless ad hoc networks since batteries are the only limited-life energy source to power the nodes. The introduction of real-time applications has posed additional challenges. Transmission of video and imaging data requires both energy and QoS aware routing in order to ensure efficient usage of the networks. We only consider "bandwidth" as the QoS in TDMA-based wireless ad hoc networks that use omni-directional antennas and have limited energy resources. We present a constraint formulation model for the QoS-MEM (QoS-aware minimum energy multicast) problem in terms of mixed integer linear programming (MILP). It can be used for an optimal solution of the QoS-MEM problem, and it also provides a way to evaluate the realistic performance of different heuristic algorithms.

Energy conservation is a critical issue in wireless ad hoc networks since batteries are the only energy source to power the nodes. One major metric for energy conservation is to route a communication session along the routes which require the lowest total.

This paper revisits the simple pole placement technique in the classical control theory, and exploits this technique to propose two kinds of controllers for active queue management (AQM) in Internet protocol (IP) routers: the self-tuning proportional controller based on pole placement (ST/spl I.bar/P/spl I.bar/PP) and the self-tuning proportional-plus-integral controller based on pole placement (ST/spl I.bar/PI/spl I.bar/PP). The damping ratio /spl xi/ and undamped natural frequency /spl omega//sub n/ can be appropriately chosen such that: 1) the transient response performance of the system is satisfied and 2) all the poles would lie in the left-half s-plane to guarantee the stability of the control system. The self-tuning controllers can assign proper intervals of /spl xi/ and /spl omega//sub n/ to achieve good AQM performance and thereby adapting the system to significant load changes very well. Furthermore, the ST/spl I.bar/PI/spl I.bar/PP controller can regulate the packet drop probability based on the knowledge of the instantaneous queue size, and clamp the steady value of the queue length to a specified reference value. We verify the effectiveness of these two controllers via OPNET simulation. Our simulation results show the following: 1) choosing appropriate /spl xi/ and /spl omega//sub n/ can successfully satisfy the transient response of the system and 2) when the network load changes, the ST/spl I.bar/P/spl I.bar/PP controller and the ST/spl I.bar/PI/spl I.bar/PP controller exhibit extremely short settling time.

Unlike traditional heuristics, we provide in this paper an optimization framework for the routing and wavelength assignment (RWA) problems with the objective of minimizing the rejection penalty of the connection demands in an all-optical wavelength-division-multiplexing (WDM) network. Our new link-based formulation takes the fairness issue and the limited wavelength conversion into consideration. The framework employs a decomposition approach to decide on the rejection/selection of the route and wavelength assignment for a semilightpath, by appropriately relaxing some of the constraints in the Lagrangean relaxation (LR) method. At the higher level, we update Lagrange multipliers iteratively with the subgradient method. At the lower level, we propose the modified minimum cost semilightpath (MMCSLP) algorithm to solve all the subproblems. A heuristic algorithm is also proposed to generate a feasible RWA scheme based on the solution to the dual problem. When compared with some latest methodology in the literature, we demonstrate that our framework can achieve better performance in terms of the computation time and the number of connection demands rejected. The much shorter computation time is due to the polynomial time complexity of our framework. In addition to achieving a very good (near-optimal) solution, the influence from the change of the number of converters is studied. Finally, we demonstrate that our framework produces fairer routing decisions by adjusting some design parameters in our framework.

In this paper, we developed a proportional rate control for the high-speed data networks subject to varying round-trip delays and packet loss. Given that data can be lost and round-trip delays can be varied, we showed that the proposed rate control could stabilize the network and overcome the oscillation problem that exists in most of current existing traffic controllers. It is also shown that the proposed rate control is not sensitive to the packet loss and achieves the fairness.

A fundamental issue in packet switching is contention resolution, because distinct packets from different input ports can be destined to the same output port at the same time. Optical packet switching is no exception. In this paper, we perform throughput analysis on large optical packet switches under heavy traffic load. We also run simulations to validate our analysis. Results from our performance evaluation indicate that throughput of large optical packet switches is not satisfactory under heavy traffic load. Both analysis and simulations reveal that optical packet switching in core networks would not be practical without a breakthrough in the research area of optical buffering technology.

We present two algorithms for transmitting the jittered constant bit rate (CBR) traffic on the upstream channel in broadband wireless access (BWA) systems: a calibration algorithm and a scheduling algorithm. The high priority CBR service class is used to transmit the voice traffic because of its stringent QoS requirements. Our design is aimed at supporting stringent QoS requirements and obtaining high utilization of the upstream bandwidth. Simulation results are presented to demonstrate the effectiveness of our algorithms in achieving high bandwidth utilization and the good traffic performance in terms of both cell loss ratio and mean queuing delay.

Seasonal ARIMA model is a good traffic model capable of capturing the behavior of a network traffic stream. In this paper, we give a general expression of seasonal ARIMA models with two periodicities and provide procedures to model and to predict traffic using seasonal ARIMA models. Our feasibility study experiments showed that seasonal ARIMA models could be used to model and predict actual wireless traffic such as GSM traffic in China.

The emergence of DWDM (dense wavelength-division multiplexing) technology has provided the network designer great convenience in constructing a wavelength routing optical network. In this paper, we study the problem of routing and wavelength assignment (RWA) in an all-optical DWDM network. We formulated the problem into a constrained integer linear problem (ILP) and the objective is to minimize the overall cost of the routing scheme over the DWDM network. Considering the complexity of the RWA problem, a decomposition approach using Lagrangean relaxation is proposed to simplify the solution procedure. The overall problem is decomposed into semi-lightpath level subproblems for the wavelength and route selection from the source to the destination. The multipliers are then updated at high level. To optimize the dual function, subgradient approach is used. Also, a heuristics algorithm is proposed to generate a feasible RWA scheme based on the dual solution. The performance evaluation for the optimization result of one network example indicates that the algorithm we used can achieve very good near-optimum solution, and the influence from the changing of the number of resources is also studied.

Energy conservation is a critical issue in wireless multi-hop networks since the nodes are powered by batteries only. One major metric for energy conservation is to route a communication session along the routes which requires the lowest total energy consumption. In this paper, based on the concepts of virtual relay, we present a constraint formulation for the minimum-energy broadcast routing problem in terms of mixed integer linear programming (MIP). Moreover the model extends its analytical capability into more general scenarios in asymmetric networks, where few studies have addressed the broadcast routing problem before. The experiment results show that in a typical multi-hop network with node less than 50, optimal solution can be always solved in a timely manner, and save up to 30% power consumption compared to the most efficient heuristic algorithm BIP known so far.

Energy conservation is a critical issue in wireless multi-hop networks since the nodes are powered by batteries only. In the previous work in minimum-energy routing, the optimal routing of data flows is formulated essentially as a shortest directed path problem based on various power cost function. In this paper, we study the minimum-energy QoS routing problem using a capacitated multi-commodity flow model for the data flows in the network. Experiment results show that when the network bandwidth is very limited, it can offer a higher success rate to find a satisfactory QoS route than those protocols that only try to find a unipath.

This paper proposes a novel bandwidth reservation mechanism called the multipath bandwidth splitting reservation (MBSR) for ad hoc networks. In MBSR, an overall bandwidth B-quest is split into several smaller bandwidth requests, and these requests will be reserved on multiple disjoint paths respectively. Both theoretical analysis and simulation results prove that the probability of successful reservation of MBSR is higher than that of single-path reservation, In addition, simulation results show that the MBSR can improve the reserved packet ratio of QoS traffic, the packet delivery ratio and the end-to-end delay of both best-effort traffic and QoS traffic.

With the rising popularity of delay-sensitive real-time multimedia applications (video, voice, data) in wireless local area networks (WLANs), it is becoming important to study the delay performance of WLANs. When the medium access control (MAC) protocol is taken into consideration, the access contention delay is a key problem. In this paper, based on a Markov model, we analyze delay performance of the IEEE 802.11 distributed coordination function (DCF). In addition, through extensive simulations, we calculate the delay performance of both basic access and RTS/CTS access mechanism of the 802.11 protocol.

In this paper, we propose a new adaptive load balancing mechanism for MPLS networks in that core LSRs are not required to perform traffic engineering. Based on measurements, we obtain the average one-way delay between a pair of label switched routers (LSR), and dynamically distribute traffic load among multiple label switched paths (LSP) according to this average. Simulation results indicate that our approach improves end-to-end throughput and decreases packet loss probability. Our work demonstrates that our algorithm is robust and simple to use.

We present a bandwidth management algorithm for supporting differentiated-service-aware traffic engineering. The algorithm contains both bandwidth allocation and preemption schemes, in which the link bandwidth is managed in two dimensions: class type and preemption priority. For the purpose of achieving simple, effective and non-fragmentation bandwidth allocation, we establish a novel "use it or lend it" bandwidth management model, which is implemented by an innovative technique of separating the reserved bandwidth information into three colored matrices. A new bandwidth preemption rule is proposed by extending the basic preemption rule in the standard. Our algorithm has been prototyped in the C programming language, and experimental results are presented to demonstrate the effectiveness of our algorithm.

We introduce the problem of mesh optical network protection based on multiple logical ring/cycles. A two-staged problem formulation as well as classical ring finding algorithms are first discussed. A state-of-art protection cycle (p-cycle) finding algorithm is then proposed. This algorithm is scalable and especially suitable for sparse mesh networks. Finally, the performance of the algorithm is gauged by running on some real world network topologies.

A load-balancing scheme has a significant effect on the performance of the multipath routing protocol, especially in an ad hoc network environment. In order to analyze the effect on the distribution of input traffic among multiple paths in MSR (multipath source routing), we first established a network queuing model that would incorporate the cross-traffic among these paths. We then considered the load balancing as an optimization problem. The solution to the optimization problem is interestingly in accordance with the heuristic equation proposed by Wang ICC'2001 (2001). Our simulation results show that MSR with load balancing is so effective that the end-to-end delay is decreased significantly while the network resource can be utilized more efficiently than that in DSR (dynamic source routing).

High-speed optical networks need efficient protection/restoration schemes. A heuristic distributed MST algorithm, called the token tree (TT) algorithm, is proposed in this paper. The TT algorithm consists of four subalgorithms, Namely the upward root selection (URS) algorithm, the star token polling (STP) algorithm, the passive state (PS) algorithm and the active state (AS) algorithm cooperate together to form a logical spanning tree for network protection. Tokens are polled between the PS and AS algorithm and thus decide the node sequence in a spanning tree. The restoration strategy lies in two points: using tree links to protect non-tree links, and seeking a shortest path from a node to its parent in order to protect the corresponding tree link. Performance analysis of the algorithms is performed in some topologies based on existing networks.

We propose a novel routing algorithm, called backup source routing (BSR) to establish and maintain backup paths based on the concepts of similar path. The BSR algorithm selects a backup path that is piggybacked with the primary path in the header of data packets in order to achieve the most durable routes between any pair of communicating mobile nodes. We define a new routing metric, called the route durability, to provide the criterion for the backup path selection. We have developed a mathematical model from which the new routing metric can be defined in order to allow the evaluation of our algorithm. Extensive simulations demonstrated that such routing strategy has two interesting futures: (1) in less stressful situations of lower load and mobility, BSR has similar performance to DSR; (2) in more challenging situations of high mobility, BSR can improve the performance significantly.

In this paper, we propose a new multipath routing protocol for ad hoc wireless networks-multipath source routing (MSR), which is an extension of DSR (dynamic source routing). Based on the measurement of RTT, we propose a scheme to distribute load among multiple paths. The simulation results show that our approach improves the packet delivery ratio and the throughput of TCP and UDP, and reduces the end-to-end delay and the average queue size, while adding little overhead. As a result, MSR decreases the network congestion and increases the path fault tolerance quite well.

The FARIMA (p,d,q) model is a good traffic model capable of capturing both the long-range and short-range behavior of a network traffic stream in time. In this paper, we propose a prediction-based admission control algorithm for an integrated service packet network. We suggest a method to simplify the FARIMA model fitting procedure and hence to reduce the time of traffic modeling and prediction. Our feasibility-study experiments showed that FARIMA models which have number of parameters could be used to model and predict actual traffic on quite a large time scale.

We propose an approach to design a distributed rate-based traffic controller to flow-regulate the best-effort service (e.g., ABR) traffic and guaranteed service traffic through a high-speed switch. The controller is distributed among the source nodes and has a very simple structure. Its local controller at each source node is open-loop stable and only requires the knowledge of the queue length at the bottleneck switch. We show that the proposed controller is fair and can stabilize the network with long variable delays. This controller does not have oscillation and can achieve high utilization.

We demonstrate in this paper how to improve the resource utilization in the context of a network based on the rate-controlled service (RCS) discipline. We propose to allow a small loss probability at the traffic shaper, and analyze the impact of various traffic shaping schemes on the network resource utilization. Our analysis establishes that there exists conditions under which our proposed statistical traffic shaping is more beneficial than lossless shaping for improving the network resource utilization. Several design criteria are also obtained from the analysis. Performance evaluation shows that our proposed statistical traffic shaping can achieve a higher level of network resource utilization than lossless traffic shaping in previous works.

Previous traffic measurements have found the coexistence of both long-range and short-range dependence in network traffic. Therefore, models are required to predict traffic that has both long-range and short-range dependence. This paper provides a procedure to model and predict traffic using FARIMA (p,d,q) models. Our experiments illustrate that the FARIMA model is a good model and is capable of capturing the property of actual traffic. We provide guidelines to simplify the FARIMA model fitting procedure and thus to reduce the time of traffic modeling and prediction.

This paper presents our insights to the issue of achieving scalability and providing QoS guarantee in IP networks. The key idea is to use marking at the edge and aggregation in the core of a network. We propose a traffic classification scheme to facilitate marking and aggregation, a queueing architecture to implement marking in the access routers and aggregation in the core routers, and a scheduling algorithm to provide throughput guarantee. Performance analysis is conducted to evaluate our proposed schemes.

We present an admission control scheme for real-time VBR traffic. The deterministic guarantee on the end-to-end delay bound is adopted as the measure of quality-of-service (QoS). The network environment of our admission control algorithm is the connection-oriented network, in which every network node uses the rate-controlled service (RCS) discipline based on the earliest deadline first (EDF) scheduling policy. Unlike the previous studies, this paper focuses on designing an efficient bandwidth allocation scheme, in which the service curve and the spare capacity curve are two important terminologies employed. Experiments using the parameters derived from some real video traces show that our algorithm performs better than previous ones in terms of both the network bandwidth utilization and the computational time needed.

We argue in this paper that ATM switches should be traffic flow oriented and switches should handle each traffic flow separately. We propose a design of per-VC queueing ATM switches which exert precise traffic management on each virtual connection. We introduce a shared-memory based switching architecture which integrates routing and buffering functionalities in the ATM switch. All ATM cells are stored statically in the buffer. It is different from other common approaches which require cells to move through various sorting and routing stages inside the switch. The proposed switching architecture can easily support multicast/broadcast and priority scheduling. No cells will be duplicated in the buffer for multicasting/broadcasting. This paper also presents performance evaluation of the proposed ATM switching architecture in terms of the throughput, queue size distribution, and cell loss probability.

We propose a new operating mechanism for the rate-controller in the ATM network. This mechanism can fulfill the same function as the "traditional" leaky bucket scheme, but it allows a simple queuing analysis. An analysis is developed to study the statistical performance of the proposed rate-controller, including the cell delay distribution, the cell loss ratio, and the characterization of the output. Numerical experiments are conducted to illustrate the analysis results and to provide insights into the system design.

This paper presents a framework of traffic control in high-speed ATM networks on both connection level and cell level. On the connection level, we consider traffic classification, bandwidth allocation, call admission control, and billing method. On the cell level we examine a queueing architecture, flow control, and scheduling. We also capture the interdependencies among various traffic control aspects to ensure a proper network operation. The key contribution of this paper is an integrated methodology to handle bursty data traffic. Based on the per-VC queueing architecture, we introduce (1) a simple bandwidth allocation mechanism which requires no complex computation for call admission control, (2) an improved credit-based flow control scheme which ensures lossless and congestion-free cell transport, (3) an innovative scheduling algorithm with throughput guarantee, and (4) an easy billing method which imposes tariff on bursty data flows without real-time measurement and processing.

We propose an approach to design a rate-based proportional traffic controller in order to flow-regulate the best-effort service (e.g., ABR traffic) and guaranteed service traffic through an ATM switch. The controller is distributed and it has a very simple structure. Its local controller at each source node is open-loop stable and only requires the knowledge of the buffer occupancy at the bottleneck switch. We show that this controller is fair and is not sensitive to the change of virtual connections (VCs) over time. It does not have oscillations and can achieve a high utilization.

We use simulations to evaluate the performance of an RCP ring network for network interconnection. The RCP (Rotation Counter Protocol) is a token ring protocol that has in its token a special field for counting down of the number of packets transmitted in one cycle. By correlating the queuing performance of each station through the counter, the delay of the high-priority data can be made almost independent and the delay jitters made small, Thus, RCP can be utilized in real-time control environment or integrated services environment. The performance of the backbone networks is investigated, using voice and data integration; the performance measures are mean voice delay, delay jitters, and mean data delay. Various buffering schemes for voice packets are compared. The effect of asymmetric data load is examined, and RCP is found to be capable of minimizing the loading effect of one station to the other.

A protocol for use in fiber optic rings is proposed. The rotation counter protocol (RCP) is a token-ring protocol which includes a counter in the token. The counter counts down on the number of packets accessing the network per cycle, and it is shared and modified by each station. Synchronous traffic is allowed to access the network as the token visits each station, while asynchronous traffic is allowed in only if the counter value is nonzero when the token revisits the station. It is very easy to implement. An integrated voice/data system using this protocol is evaluated in terms of voice and data delay performance. The results show that this protocol can support both synchronous and asynchronous traffic.

The authors consider the network modeling and performance analysis of multimedia file transfer between workstations connected to remotely located local area networks (LANs). The LANs are linked by a satellite wide-area network (SWAN) with a high bandwidth and high path delay. Four areas are addressed: (1) development of a fairly accurate interconnection network model using measured delay values for different network elements; (2) derivation of tight upper and lower bounds for the network throughput for both error-free and error-prone channels using mean value analysis; (3) validation of the model using computer simulation; and (4) analysis of the SWAN performance using numerical results for a wide range of parameters (file sizes, window size, link speed, number of workstations, etc.) for the case of a multimedia SWAN. Based on the analyses, performance bottlenecks for different operating conditions that could be used to evolve design criteria for better overall system performance are identified.>

A matrix-analytic method is used to analyze the queueing behavior of small time division multiplexing (TDM) integrated services systems. Such systems have priority services for time-critical traffics in which adjacent packets exhibit a strong interdependency. The TDM frame with a capacity of M packets is used to transmit the high-priority packets at every time step. Any unused capacity is utilized to transmit low-priority packets. The system can be modeled as a discrete-time system with a fluctuating number of servers for the low-priority packets. Because the number of servers is small and adjacent packets are dependent, the birth-and-death analysis is not appropriate. An algorithm, based on a modification of Neuts' method, is used to determine the boundary points required in the queuing analysis. Numerical results for two integrated services systems, each with different characteristics, are presented to demonstrate the feasibility of the analysis method and the computational algorithm.>