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To perform an Optical Burst Switching (OBS) network, a lot of challenges are faced that have to be solved. The edge node has to manage burst offset time and burst assembly technique. The core node has to reserve resources to send the data burst, schedule the control packet and data burst and contention resolution strategy. In this paper, we discuss the burst assembly mechanisms and their disadvantages which we will overcome using a new and simple algorithm for data burst generation which relies on changing some characteristics in queuing model in OBS network by taking into consideration the presences of Quality of Service (QoS) for multiple data priorities. The OBS network simulation using our algorithm shows that it adaptively changes the data burst size according to the offered load. So, it can offer high data burst utilization, limits the maximum end to end delay and reduces burst drop rate for high priority packets.

In this paper, we propose a scheme for partially dynamic lane control for energy saving in multilane-based high-speed Ethernet. In this scheme, among the given transmission lanes, at least one lane is always operating, and the remaining lanes are dynamically activated to alleviate the network performance in terms of queuing delay and packet loss in the range of acceptance. The number of active lanes is determined by the decision algorithm based on the information regarding traffic and queue status. The reconciliation sublayer adjusts the transmission lane with the updated number of lanes received from the algorithm, which guarantees no processing delay in the media access control layer, no overhead, and minimal delay of the exchanging control frames. The proposed scheme is simulated in terms of queuing delay, packet loss rate, lane changes, and energy saving using an OPNET simulator. Our results indicate that energy savings of around 55% (or, when the offered load is less than 0.25, a significant additional savings of up to 75%) can be obtained with a queuing delay of less than 1 ms, a packet loss of less than 10 –4 , and a control packet exchange time of less than 0.5 μs in random traffic.

Fibre delay lines (FDLs) can substantially reduce the burst loss in Optical Burst Switching (OBS) networks and share-per-node FDL configurations can provide a more cost-efficient solution compared to architectures where delay lines are shared per port. Nevertheless, mathematical performance analysis of this configuration is more difficult due to traffic correlations arising from the shared resource. In this paper, an approximate two-moment traffic model is developed for quantifying end-to-end burst blocking probability in networks of OBS switches with share-per-node FDLs. The two-moment approach can improve model accuracy over more usual Poisson network analysis methods and additionally allows the characteristics of offered load to be taken into account. The accuracy of the proposed method is shown to be favourable, when compared to discrete-event simulations of an OBS network.

In this study, the authors provide an analytical framework to assess network-level quality of service (QoS) measures for differentiated, non-saturated traffic in infrastructure-mode 802.11 wireless local area networks using the distributed coordination function access mechanism. The authors build on a general analytical framework that takes into account the medium access control (MAC) access mechanism, the MAC layer packet buffer and the characteristics of the offered load to obtain the probability of a collision with M classes of traffic. The authors then derive analytical expressions for the throughput, the end-to-end packet delay and the packet delay outage probability for differentiated traffic. A case study of voice-over-IP (VoIP) traffic in 802.11b/g networks is used to validate the theoretical framework. The analytical results are in good agreement with the simulation results, showing that although the collision probability for packets transmitted at the access point (AP) is lower than for packets transmitted from the clients, the end-to-end delay in the downlink is much longer than that in the uplink because of the large queuing delay because of the multiplexing of several VoIP connections at the AP. The authors also compare the maximum number of VoIP connections that can be admitted in an 802.11 network while respecting their QoS constraints; these were computed with the proposed theoretical model, an ns-2 simulation model and other schemes previously proposed in the literature. The results indicate that their approach is more accurate over a wide range of parameter values, thus demonstrating the validity, the flexibility and the robustness of the proposed theoretical framework.

In this letter, a reservation scheme with contention resolution diversity slotted ALOHA (CRDSA), called R-CRDSA, is proposed. Although CRDSA promises excellent performance compared to slotted ALOHA (SA), there are two barriers to be overcome for its use in satellite networks. The first is a low critical point of an offered load; i.e., at this point, as the offered load increases, the throughput will decrease. CRDSA has a lower critical point than that of SA. The second barrier is that CRDSA has a lower capacity efficiency compared to SA; i.e., on average, CRDSA requires more power or bandwidth than SA for transmission. R-CRDSA can overcome these barriers at the same cost as CRDSA, especially for multi-packet messages. The analytic performances are derived by the observation of the transition between two successive frames, and the average number of packets in a message. The simulation results show that the analytic derivations are valid, and they confirm that the barriers are resolved by R-CRDSA.

In multi-hop ad hoc networks, sources may pump more traffic into the networks than that can be supported, resulting in high end-to-end delay and packet-loss rate. Controlling the offered load at the sources can eliminate this problem. To conduct traffic control, the throughput of the network is necessary. In addition, the authors propose a concept of bandwidth mapping to analyse how much traffic in application can be injected to make the network supporting the maximum throughput. A multi-dimensional Markov model is built to analyse the performance of IEEE 802.11 DCF in unsaturated condition, in which M/G/1/K queuing model is used to analyse the service condition of the packet queue inside the node. The effects of carrier sensing property, hidden-node problem and signal capture property are considered together to analyse the contention experienced by the nodes in the network. Furthermore, the bandwidth mapping situation of voice and video traffic is analysed in string topology of a multi-hop ad hoc network. This analysis can provide a theoretical guide for the traffic admission control.

The paper analyses forwarding performance of IPsec gateway over the rage of offered loads. It focuses on the forwarding rate and packet loss particularly at the gateway's performance peak and at the state of gateway's overload. It explains possible performance degradation when the gateway is overloaded by excessive offered load. The paper further evaluates different approaches for obtaining forwarding performance parameters - a widely used throughput described in RFC 1242, maximum forwarding rate with zero packet loss and us proposed equilibrium throughput. According to our observations equilibrium throughput might be the most universal parameter for benchmarking security gateways as the others may be dependent on the duration of test trials. Employing equilibrium throughput would also greatly shorten the time required for benchmarking. Lastly, the paper presents methodology and a hybrid step/binary search algorithm for obtaining value of equilibrium throughput.

Recently, as the interest in Green IT is exponentially increased, EPON with sleep mode has been studied to reduce energy consumption in access network. In oder to guarantee cyclic sleep for ONU(Optical Network Units), EPON with sleep mode transmits upstream and downstream data at the same time. However, since conventional algorithms for sleep mode in EPON allocate bandwidth to each ONU according to upstream bandwidth request, the QoS of downstream data is not guaranteed when the offered load of OLT is larger than that of ONU. In this paper, we propose a bandwidth allocation algorithm for improving QoS in EPON with sleep mode. The proposed algorithm compares its size with an upstream request of ONU when a downstream buffer in the OLT exceeds a QoS threshold. And then it allocates selectively a bandwidth that satisfies the required QoS between the bandwidth request of ONU and OLT. Therefore, the proposed algorithm can save energy through cyclic sleep of ONUs while guaranteeing the QoS of up/downstream data. In order to evaluate the proposed algorithm, we perform simulation in terms of total sleep time of ONUs, queueing delay between OLT and ONU, and the utilization of allocated bandwidth at OLT through OPNET.

WFQ(Weighted Fair Queuing) is the most popular fair queuing algorithm to guarantee the Quality-of-Service(QoS), but it has the inherent drawback of a poor resource utilization, particularly under the low rate traffic requiring a tight delay bound. It was recently identified that the poor utilization is mainly due to non-optimized latency of a traffic flow and then LOFQ(Latency-Optimized Fair Queuing) to overcome the drawback was introduced. The LOFQ algorithm, however, renews their optimal latencies for all flows whenever a new flow arrives, which results in the high implementation complexity of O().This paper is to reduce thecomplexity to O(1). The proposed method is first to derive the optimal latency index function from the statistical QoS characteristics of the offered load, and then to simply calculate the optimal latency index of the arriving flow using the function.

For many applications, it is desirable for a node to be able to identify the neighbor nodes currently within range. However, the identification procedures for terrestrial communication networks TCNs are inefficient when implemented in long-delay networks LDNs such as underwater acoustic networks or satellite networks, where the propagation time of a packet cannot be neglected. Here, we propose a time-efficient and power-efficient procedure, which is insensitive to propagation delay, for identifying neighbors in an LDN by optimizing the network offered load using either unslotted or slotted protocols. The procedure is adapted to the scenario when node cardinality and distribution are either known or unknown in advance. We achieve improvements as high as 80% in time and 45% in power consumption for our proposed approach compared with approaches developed previously for TCN. Furthermore, we analyze our proposed approach with the inclusion of the capture effect and packet receive time variations. We also provide a closed form formula for finding the optimum guard time and a procedure to estimate the packet receive time variations. Copyright © 2012 John Wiley & Sons, Ltd.

IEEE 802.15.6 standard technology is proposed for low-power wireless communication in, on and around body, where vital signs such as pulse, blood pressure, ECG, and EEG signals are transmitted as a type of data packet. Especially, these vital signs should be delivered in real time, so that the latency from slave node to hub node can be one of the pivotal performance requirements. However, in the case of IEEE 802.15.6 technology data retransmission caused by transmission failure can be done in the next superframe. In order to overcome this limitation, we propose an adaptive polling algorithm for IEEE 802.15.6 technology. The proposing algorithm makes the hub to look for an appropriate time period in order to make data retransmission within the superframe. Through the performance evaluation, the proposing algorithm achieves a 61% and a 73% latency reduction compared to those of IEEE 802.15.6 technology in the environment of 70% traffic offered load with 10ms and 100ms superframe period. In addition, the proposing algorithm prevents bursty traffic transmission condition caused by mixing retransmission traffic with the traffic reserved for transmission. Through the proposing adaptive polling algorithm, it will be possible to transmit time-sensitive vital signs without severe traffic delay.

In this paper, we propose the cooperative transmission scheme (CTS) for system throughput maximization in OFDMA based enterprise femtocell networks. In our scheme, the user equipment (UE) can receive the desired signal from serving femtocell BS (fBS) as well as an adjacent fBS. Thus, UE achieves an improved signal to interference plus and noise ratio (SINR) by the synchronized two signals. The performances of this strategy consider not only the call-level quality of service (QoS) but also the packet-level QoS. We first measure the call blocking probability and utilization for the downlink resources for various offered load in femtocell. Based on that, the outage probability and effective throughput of the system are simulated. Simulation results show that the proposed scheme can reduce the outage probability for enterprise femtocell compared with conventional systems.

This paper describes a methodology for setting long-term care capacity levels over a multiyear planning horizon to achieve target wait time service levels. Our approach integrates demographic and survival analysis, discrete event simulation, and optimization. Based on this methodology, we developed a decision support system for use in practice. We illustrate this approach through two case studies: one for a regional health authority in British Columbia, Canada, and the other for a long-term care facility. We also compare our approach to the fixed ratio approach used in practice and the SIPP (stationary, independent, period by period) and MOL (modified offered load) approaches developed in the call center literature. Our results suggest that our approach is preferable. The fixed ratio approach lacks a rigorous foundation, and the SIPP and MOL approaches do not perform reliably mainly because of long service times. We conclude the paper with policy recommendations.

Rate allocation among a fixed set of end-to-end connections in the Internet is carried out by congestion control, which has a well established model: it optimizes a concave network utility, a particular case of which is the alpha-fair bandwidth allocation. This paper studies the slower dynamics of connections themselves, that arrive randomly in the network and are served at the allocated rate. It has been shown that under the condition that the mean offered load at each link is less than its capacity, the resulting queueing system is stochastically stable, for the case of exponentially distributed file-sizes. The conjecture that the result holds for general file-size distributions has remained open, and is very relevant since heavy-tailed distributions are often the best models of Internet file sizes. In this paper, building on existing fluid models of the system, we use a partial differential equation to characterize the dynamics. The equation keeps track of residual file size and therefore is suitable for general file size distributions. For alpha fair bandwidth allocation, with any positive alpha parameter, a Lyapunov function is constructed with negative drift when the offered load is less than capacity. With this tool we answer the conjecture affirmatively in the fluid sense: we prove asymptotic convergence to zero of the fluid model for general file-size distributions of finite mean, and finite-time convergence for those of finite moment. In the stochastic sense, we build on recent work that relates fluid and stochastic stability subject to a certain light-tailed restriction. We further provide the supplementary fluid stability argument to establish the conjecture for this class that includes phase-type distributions. Results are supplemented by illustrative network simulations at the packet level.

In this paper, we study impacts of TXOP allocation and AIFS parameter on one hop IEEE 802.11e EDCA network under varying offered load. Offered load is modified by changing the parameters of arrival process and node populations. Arrival process is varied by altering burst size distribution, mean burst size, frame size, and arrival rates. We investigate the effects of the offered load parameters on the network stability and non-saturation boundaries of IEEE 802.11e EDCA. Our results show interaction of offered load and MAC parameters. The results suggest the range of network parameters which preserve network stability and still achieve QoS differentiation.

The asymptotic many-server queue with abandonments, G/GI/N + GI, is considered in the quality- and efficiency-driven (QED) regime. Here the number of servers and the offered load are related via the square-root rule, as the number of servers increases indefinitely. QED performance entails short waiting times and scarce abandonments (high quality) jointly with high servers' utilization (high efficiency), which is feasible when many servers cater to a single queue. For the G/GI/N + GI queue, we derive diffusion approximations for both its queue-length and virtual-waiting-time processes. Special cases, for which closed-form analysis is provided, are the G/M/N + GI and G/D/N + GI queues, thus expanding and generalizing existing results.

An all-optical network still remains a long way from realistic deployment. However, all-optical packet switches, in which optical packets are buffered and routed in optical form, are still expected to solve the problems of electronic bottlenecks and large power consumption in electronic routers. An approximation is presented for blocking probabilities and delays of optical buffers, where optical packet arrival process is Poisson and packet-length distribution is general. The approximation aims at providing a simple calculation tool for optical buffer design without requiring computer simulations or extensive iterative computations. An approximation for the cumulative distribution function of the waiting time for general packet-length distributions was obtained that holds when the waiting time is sufficiently large and the traffic load is heavy. The difference in the blocking probabilities between the approximation and the simulation results was found to be less than 10% when the offered load was greater than 0.7. The approximation can be applied to investigate multiclass optical buffers for priority queueing and to design wavelength-division-multiplexing optical packet switches and networks with the maximum throughput.

Resource scheduling in large-scale distributed systems, such as grids and clouds, is difficult due to the size, dynamism, and volatility of resources. These resources are eclectic and autonomous, and may exhibit different usage policies, levels of participation, capabilities, local load, and reliability. Moreover, applications are likely to exhibit various patterns and levels, and distributed resources may organize into various different overlay topologies for information and query dissemination. Researchers have proposed a wide variety of approaches and policies for mapping offered load onto resources and for solving the various component parts of the scheduling problem. However, production clouds and grids may be underutilized, and may not exhibit the load to effectively characterize all of the scheduling system inputs. The composition of large-scale systems is also changing, potentially to include more individual and peer-to-peer resources. These factors will influence the effectiveness of proposed scheduling solutions. Therefore, a simulation environment is necessary to study different approaches under different scenarios, especially those that are expected, but that are not currently characteristic of existing systems. This article describes a general-purpose peer-to-peer simulation environment that allows a wide variety of parameters, protocols, strategies and policies to be varied and studied. To provide a proof of concept, utilization of the simulation environment is presented in a large-scale distributed system problem that includes a core model and related mechanisms. In particular, this article presents a definition and possible peer-to-peer solutions for the large-scale scheduling problem. Moreover, this article describes a general simulation model, some policies that can be varied, an implementation, and some sample results.

A Fixed Point Approximation (FPA) method has recently been suggested for non-stationary analysis of loss queues and networks of loss queues with Exponential service times. Deriving exact equations relating time-dependent mean numbers of busy servers to blocking probabilities, we generalize the FPA method to loss systems with general service time distributions. These equations are combined with associated formulae for stationary analysis of loss systems in steady state through a carried load to offered load transformation. The accuracy and speed of the generalized methods are illustrated through a wide set of examples.\ud Highlights\ud \ud ► We proposed a method for performance evaluation of non-stationary loss systems. ► Our method works for single-class, multi-class and network of loss queues. ► Non-homogeneous Poisson arrivals and general service time distributions are assumed. ► The accuracy of our algorithms are shown to be close to exact. ► Our algorithms are much faster than simulation and numerical methods.

For analysis of the delay characteristics of the IEEE 802.11-based networks under nonsaturated condition, one of the key assumptions commonly accepted is that given the offered load, the queue utilizations of contending nodes are the same for all transmitted packets. In practice, however, this assumption is not valid due to coupled queues effect. In this paper, we investigate the influence brought by coupled queues and propose an accurate delay model for IEEE 802.11-based networks under nonsaturated condition. The simulations show the accuracy of the analytical model.

This paper presents a novel mathematical model of the IEEE 802.11 Enhanced Distributed Channel Access (EDCA) function. The main advantage of the model is that it combines accurate probability of counting down backoff slots with proper handling of frames. Furthermore, it allows for traffic differentiation with the use of traffic priority-dependent access parameters, i.e., AIFSN, and CW. Additionally, a new method of modelling AIFS differentiation between traffic classes is proposed. Finally, the model is kept reasonably simple and constructed in such a way that taking into account the four-way-handshake mechanism is uncomplicated. The proposed model is compared with simulations as well as numerical results obtained for two other models presented in the literature. The comparison gives satisfactory results regardless of the offered load, number of nodes, or network configuration.

Scheduling in large scale dynamic grids comprising eclectic collections of resources is increasingly difficult. Autonomous resource neighborhoods may wish to determine the level of grid offered load that they can or will accept; different sites may wish to attract different amounts of load, to satisfy some desired property within a grid economy. This changes the traditional notion of load sharing, which generally assumes that the desired equilibrium should be an equal distribution of load across all participating machines, because they are under the jurisdiction of a single site, and therefore more likely to implement one common policy. In large-scale grids, nodes and neighborhoods should instead get a portion of the load that best matches their local policies for supporting and admitting grid jobs. This article describes information dissemination protocols that can distribute load in this way, without using load rebalancing through job migration, which is more difficult and costly in large-scale heterogeneous grids. Essentially, nodes adjust their advertising rates and aggressiveness to influence where jobs get scheduled. We report experimental results with example resource configurations in which each resource neighborhood determines its ideal grid load and disseminates accordingly. In turn, each neighborhood attracts the requisite amount of resource requests from the grid. Moreover, performance does not degrade: overall query satisfaction rates are within 9% of both adaptive dissemination protocols that use static adaptation policies, and static dissemination protocols that may be custom-tailored to specific resource and load distributions.

In the new era of Ambient Intelligence, wireless sensor networks (WSNs) are seen to bridge the gap between physical world and the Internet, making a large amount of information accessible anywhere, anytime. Over the last few years, WSNs are being developed towards a large number of multimedia streaming applications, e.g. video surveillance, traffic control systems, health monitoring, and industrial process control. WSNs consist of small sensor devices (nodes) that are capable of working unattended, without centralized control, under dynamically changing conditions. However, these devices face important limitations in terms of energy, memory and computational power. The uncontrolled use of limited resources in conjunction with the unpredictable nature of WSNs in terms of traffic load injection, wireless link capacity fluctuations and topology modifications may lead to congestion. Congestion can cause increased packet loss and delay. This paper proposes a bio-inspired congestion control approach for WSNs streaming applications that necessitate controlled performance with graceful degradation. In the proposed approach, congestion in WSNs is prevented (or at least minimized) by regulating the rate of each traffic flow based on the Lotka-Volterra competition model. Performance evaluations reveal that the proposed approach achieves adaptability to changing traffic loads, scalability and fairness among flows, while providing graceful performance degradation as the offered load increases. © 2010 Elsevier B.V. All rights reserved. 33 17 2039 2047 Cited By :20

We consider queueing systems in which customers arrive according to a Poisson process and have exponentially distributed service requirements. The customers are impatient and may abandon the system while waiting for service after a generally distributed amount of time. The system incurs customer-related costs that consist of waiting and abandonment penalty costs. We study capacity sizing in such systems to minimize the sum of the long-term average customer-related costs and capacity costs. We use fluid models to derive prescriptions that are asymptotically optimal for large customer arrival rates. Although these prescriptions are easy to characterize, they depend intricately upon the distribution of the customers' time to abandon and may prescribe operating in a regime with offered load (the ratio of the arrival rate to the capacity) greater than 1. In such cases, we demonstrate that the fluid prescription is optimal up to O(1). That is, as the customer arrival rate increases, the optimality gap of the prescription remains bounded.

CSMA/CA is a common access mechanism for contention based wireless channels. One of the ways in which quality of service in contention based wireless networks is achieved is by service differentiation. This can be realised by prioritising packets based on their importance while taking into account the network load. p-persistent CSMA is a form of CSMA/CA and in this paper an analytical model for the throughput and delay of a p-persistent CSMA system is developed where the system contains a finite number of non-saturated stations with both heterogeneous loads and priorities. Results based on this new model show how the throughput and delay for the traffic flows on the network are affected by the relative p-persistence and offered load values for all of the stations in the network.

In this work, we study the problem of minimizing the total power consumption in a multihop wireless network subject to a given offered load. It is well-known that the total power consumption of multihop wireless networks can be substantially reduced by jointly optimizing power control, link scheduling, and routing. However, the known optimal cross-layer solution to this problem is centralized and with high computational complexity. In this paper, we develop a low-complexity and distributed algorithm that is provably power-efficient. In particular, under the node-exclusive interference model and with suitable assumptions on the power-rate function, we can show that the total power consumption of our algorithm is at most (2+?) times as large as the power consumption of the optimal (but centralized and complex) algorithm, where ? is an arbitrarily small positive constant. Our algorithm is not only the first such distributed solution with provable performance bound, but its power-efficiency ratio is also tighter than that of another suboptimal centralized algorithm in the literature.

In the future intervehicle communication will make driving safer, easier, and more comfortable. As a cornerstone of the system, vehicles need to be aware of other vehicles in the vicinity. This cooperative awareness is achieved by beaconing, the exchange of periodic single-hop broadcast messages that include data on the status of a vehicle. While the concept of beaconing has been developed in the first phase of research on VANETs, recent studies have revealed limitations with respect to network performance. Obviously, the frequency of beacon messages directly translates into accuracy of cooperative awareness and thus traffic safety. There is an indisputable trade-off between required bandwidth and achieved accuracy. In this work we analyze this trade-off from different perspectives considering the consequences for safety applications. As a solution to the problem of overloading the channel, we propose to control the offered load by adjusting the beacon frequency dynamically to the current traffic situation while maintaining appropriate accuracy. To find an optimal adaptation, we elaborate on several options that arise when determining the beacon frequency. As a result, we propose situation-adaptive beaconing. It depends on the vehicle's own movement and the movement of surrounding vehicles, macroscopic aspects like the current vehicle density, or microscopic aspects.

Optical burst switching (OBS) is a switching technique that occupies the middle of the spectrum between the well-known circuit switching and packet switching paradigms. OBS has advantages in terms of switching efficiency for bursty IP traffic and optical hardware feasibility. Especially, the advantages of buffer less operation and low setup time promote the use of OBS to applications like grid computing. However, its reliability and scalability are low since OBS generally uses a one-way reservation protocol, where the bursts are transmitted without confirming their reservation. The paradigm shift of applications on the Internet requires the characteristic Quality of service (QoS) e. g. multiple bursts transmission. This paper addresses the issue of providing QoS for Optical Burst Switching (OBS) systems. In this paper, a novel QoS oriented integrated scheme based on Optical Burst /Circuit Switching network architecture has been proposed. The proposed scheme utilizes the modified Just-Enough-Time (JET) protocol and advanced reservation based on Linear Predictive Filter (LPF), which can provide differentiated services for optical burst switching (OBS) network. Simulation results show that the proposed scheme is averagely 60 % better than a First Come First Served (FCFS) protocol in guaranteeing QoS of real-time traffic when the offered load ratio of real-time to non-real-time is set at 1:9. Also, the results yield significant delay reduction for time-critical traffic, while maintaining the bandwidth overhead within limits. As a result, the proposed scheme has achieved QoS differentiation in terms of burst loss probability and flow loss probability.

This paper proposes a stabilized multichannel random access protocol based on slotted ALOHA for relay deployed cellular networks. To ensure the stability of random access, the proposed protocol dynamically controls the number of random access channels in a BS and a RS and the retransmission probability of the random access packets under heavy load conditions. A mathematical formula is also developed that derives an optimal partition ratio of the shared random access channels between a base station and a relay station without and with capture effect. Numerical results show that the proposed protocol can guarantee the required utilization and delay even in high offered load, which otherwise can cause bistable problem of slotted ALOHA.

When the offered load ρ is 1, we investigate the asymptotic behavior of the stationary measure for the MAP/G/1 queue and the asymptotic behavior of the loss probability for the finite buffer MAP/G/1/K + 1 queue. Unlike Baiocchi [Stochastic Models 10(1994):867–893], we assume neither the time reversibility of the MAP nor the exponential moment condition for the service time distribution. Our result generalizes the result of Baiocchi for the critical case ρ = 1 and solves the problem conjectured by Kim et al. [Operations Research Letters 36(2008):127–132].

The capacity of ad hoc wireless networks can be substantially increased by equipping each network node with multiple radio interfaces that can operate on multiple nonoverlapping channels. However, new scheduling, channel-assignment, and routing algorithms are required to fully utilize the increased bandwidth in multichannel multiradio ad hoc networks. In this paper, we develop fully distributed algorithms that jointly solve the channel-assignment, scheduling, and routing problem. Our algorithms are online algorithms, i.e., they do not require prior information on the offered load to the network, and can adapt automatically to the changes in the network topology and offered load. We show that our algorithms are provably efficient. That is, even compared with the optimal centralized and offline algorithm, our proposed distributed algorithms can achieve a provable fraction of the maximum system capacity. Furthermore, the achievable fraction that we can guarantee is larger than that of some other comparable algorithms in the literature.

We propose an approximate model for a nonsaturated IEEE 802.11 DCF network that is simpler than others that have appeared in the literature. Our key simplification is that the attempt rate in the nonsaturated setting can be approximated by scaling the attempt rate of the saturated setting with an appropriate factor. Use of different scaling factors leads to variants of the model for a small buffer and an infinite buffer. We develop a general fixed-point analysis that we demonstrate can have nonunique solutions for the infinite buffer model variant under moderate traffic. Nevertheless, in an asymptotic regime that applies to light traffic, we are able to prove uniqueness of the fixed point and predict the offered load at which the maximum throughput is achieved. We verify our model using ns-2 simulation and show that our MAC access delay results are the most accurate among related work, while our collision probability and throughput results achieve comparable accuracy to (D. Malone et al., 2007), (K. Duffy et al., 2007).

In this article we propose the Minimization of Probability and Size of scheduling Latency (MinPSL) protocol for remarkably efficient load balancing and scheduling of variable length messages in WDM star networks. Our EMPS protocol has been shown to noticeably increase the performance of practical networks with non-uniform destinations and non-negligible transceiver tuning latencies, while other well-known schemes like EATS and MSL seem to suffer under these realistic conditions. EMPS tries to balance the offered load by only considering the heads of the message queues maintained by the source nodes. As a result, its performance is degraded, especially for medium to high offered loads and for rather slowly tunable transceivers. The proposed MinPSL scheme, on the other hand, examines each source node’s message queue up to a certain depth and assigns higher priorities to messages intended for the least used destinations. In this way, MinPSL perfectly minimizes the probability of having to schedule two or more messages intended for the same destination simultaneously or at close times. Furthermore, it also minimizes the actual performance penalty incurred, when scheduling of consecutive messages with the same destination cannot be avoided. Extensive simulations are carried out in order to study the performance of MinPSL and compare it to the EMPS scheme under various conditions. The simulation results ascertain the fact that the proposed MinPSL protocol always brings about a considerable performance improvement.

Prior investigations on the Aloha network have primarily focused on its system throughput. Good system throughput, however, does not automatically translate to good delay performance for the end users. Neither is fairness guaranteed: Some users may starve, while others hog the system. This paper establishes the conditions for bounded mean queuing delay and nonstarved operation of the slotted Aloha network. We focus on the performance when collisions of packets are resolved using an exponential backoff protocol. For a nonsaturated network, we find that bounded mean delay and nonstarved operation can be guaranteed only if the offered load is limited to below a quantity called "safe bounded mean-delay (SBMD) throughput." The SBMD throughput can be much lower than the saturation system throughput if the backoff factor r in the exponential backoff algorithm is not properly set. For example, it is well known that the maximum throughput of the Aloha network is e -1 = 0.3679. However, for r = 2, a value assumed in many prior investigations, the SBMD throughput is only 0.2158, a drastic penalty of 41% relative to 0.3679. Fortunately, using r = 1.3757 allows us to obtain an SBMD throughput of 0.3545, less than 4% away from 0.3679. A general conclusion is that the system parameters can significantly affect the delay and fairness performance of the Aloha network. This paper provides the analytical framework and expressions for tuning r and other system parameters to achieve good delay and nonstarved operation.

We consider a network control problem for wireless networks with flow level dynamics under the general k-hop interference model. In particular, we investigate the control problem in low load and high load regimes. In the low load regime, we show that the network can be stabilized by a regulated maximal scheduling policy considering flow level dynamics if the offered load satisfies a constraining bound condition. Because maximal scheduling is a general scheduling rule whose implementation is not specified, we propose a constant-time and distributed scheduling algorithm for a general k-hop interference model which can approximate the maximal scheduling policy within an arbitrarily small error. Under the stability condition, we show how to calculate transmission rates for different user classes such that the long-term (time average) network utility is maximized. This long-term network utility captures the real network performance due to the fact that under flow level dynamics, the number of users randomly change so instantaneous network utility maximization does not result in useful network performance. Our results imply that congestion control is unnecessary when the offered load is low and optimal user rates can be determined to maximize users' long-term satisfaction. In the high load regime where the network can be unstable under the regulated maximal scheduling policy, we propose a cross-layer congestion control and scheduling algorithm which can stabilize the network under arbitrary network load. Through extensive numerical analysis for some typical networks, we show that the proposed scheduling algorithm has much lower overhead than other existing queue-length-based constant-time scheduling schemes in the literature, and it achieves performance much better than the guaranteed bound.

Multibeam antennas (MBAs) are capable of supporting concurrent communications with multiple neighboring users in wireless networks and, thus, can improve the throughput over omnidirectional antennas and switched-beam directional antennas. The throughput performance, however, may degrade in the absence of a proper access scheme for user scheduling, and thus, collisions occur. The probability of having such collisions further increases in a multipath propagation environment, which is commonly encountered in a wireless network. Furthermore, there is an increased demand to deliver various types of data with differentiated quality and latency requirements. Thus, it is desirable to incorporate user/packet priority in the medium access control (MAC) protocol. In this paper, priority-based access schemes are proposed for wireless networks exploiting MBAs, respectively, in single-path and multipath environments. An analytical framework is then developed to analyze the node throughput performance when the proposed access scheme is used. The analytical and simulated results clearly show that, in contrast to a random-access scheme, where significant throughput degradation occurs in a multipath propagation environment, when the proposed access scheme is applied, the node throughput becomes a nondecreasing function of the offered load, and the degradation due to multipath is significantly mitigated.

We propose a new and exact method to analyze the throughput of the DS CDMA unslotted ALOHA system with variable number of fixed-length packets. The proposed scheme requires two-dimensional summation while the previous requires four. Thus the proposed analysis scheme is of less computational complexity. The proposed analysis result is also slightly closer to the simulation result than the previous analysis result is, especially in heavier offered load.

We consider a multiserver delay queue with finite additional waiting spaces and time-varying arrival rates, where the customers waiting in the buffer may abandon. These are features that arise naturally from the study of service systems such as call centers. Moreover, we assume rewards for successful service completions and cost rates for service resources. Finally, we consider service-level agreements that constrain both the fractions of callers who abandon and the ones who are blocked.Applying the theory of Lagrangian mechanics to the fluid limit of a related Markovian service network model, we obtain near-profit-optimal staffing and provisioning schedules. The nature of this solution consists of three modes of operation. A key step in deriving this solution is combining the modified offered load approximation for loss systems with our fluid model. We use them to estimate effectively both our service-level agreement metrics and the profit for the original queuing model. Second-order profit improvements are achieved through a modified offered load version of the conventional square root safety rule.

For the Erlang loss system with s servers and offered load a, we show that: (i) the load carried by the last server is strictly increasing in a; (ii) the carried load of the whole system is strictly supermodular on {(s,a)|s=0,1,… and a>0}.

It is well known that the end-to-end throughput in IEEE 802.11-based multihop wireless networks degrades due to the imprecise Extended Inter-Frame Space (EIFS) problem. The paper considers this throughput degradation issue by analyzing the end-to-end throughput in a backhaul-type wireless mesh network. Focusing on a three-node chain topology, we model it as a tandem queueing network with two nodes to derive the end-to-end throughput, and validate the analysis with ns-2 simulation. Numerical results show that the analytical results agree fairly well with simulation for a certain range of the offered load.

The Erlang B formula represents the steady-state blocking probability in the Erlang loss model or $M/M/s/s$ queue. We derive asymptotic expansions for the offered load that matches, for a given number of servers, a certain blocking probability. In addressing this inversion problem we make use of various asymptotic expansions for the incomplete gamma function. A similar inversion problem is investigated for the Erlang C formula.

Field data were collected and simulation experiments based on traffic at an intersection in Virginia were conducted to test the hypothesis that headways increase with long green times and to test the common assumption that throughput increases with longer cycles. The results showed that headways increased with long green times as a result of departing turning vehicles and that this effect could cause a significant increase in overall average approach headways. The results also showed that maximum throughput, defined as the point where additional offered load could not be served, did not increase with longer cycles. With values derived from the field data, increasing the cycle did not increase throughput. In simulation, increasing the cycle caused a reduction in throughput as a result of increasing the effect of departing turning traffic on the average headway.

We consider a first-come first-served multiserver queue in the Quality- and Efficiency-Driven (QED) regime. In this regime, which was first formalized by Halfin and Whitt, the number of servers N is not small, servers' utilization is [Formula: see text] (Efficiency-Driven) while waiting time is [Formula: see text] (Quality-Driven). This is equivalent to having the number of servers N being approximately equal to [Formula: see text], where R is the offered load and β is a positive constant. For the G/DK/N queue in the QED regime, we analyze the virtual waiting time VN(t), as N increases indefinitely. Assuming that the service-time distribution has a finite support (hence the DK in G/DK/N), it is shown that, in the limit, the scaled virtual waiting time [Formula: see text] is representable as a supremum over a random weighted tree (S denotes a service time). Informally, it is then argued that, for large N, [Formula: see text]here [Formula: see text] is the averaging of [Formula: see text] over S, and the process [Formula: see text] is zero-mean Gaussian that summarizes all relevant information about arrivals and service times ([Formula: see text] arises as a limit of an infinite-server (G/DK/∞) process, appropriately scaled). The results are obtained by using both combinatorial and probabilistic arguments. Possible applications of our approximations include fast simulation of queues and estimation/prediction of customer waiting times in the QED regime.

This paper proposes an optical broadcast-and-select network architecture with centralized multi-carrier light source (C-MCLS). A large number of optical carriers/wavelengths generated by C-MCLS are distributed to all edge nodes (ENs), which select and modulate wavelengths to realize transmission. To utilize wavelength resources efficiently, we introduce a framework of wavelength allocation and selection (WAS). Wavelength allocation is performed at a wavelength control server, while wavelength selection is done at each EN according to wavelength allocation results. Both static and dynamic schemes are adopted for WAS and their implementations are shown. By using fixed or tunable band pass filter and periodical arrayed waveguide grating demultiplexer, wavelengths are selected and utilized by ENs in a static or dynamic manner. We evaluate network cost and performance of the proposed network. Cost analysis and numerical results show that it offers greatly reduced cost compared to the conventional one when the number of required access wavelengths at EN becomes large. We delineate its applicable areas through cost comparisons. Blocking probabilities of static and dynamic schemes are analyzed to evaluate network performance. Numerical results show that by choosing appropriate design parameters, the dynamic scheme offers about 25% increase in admissible offered load under the specified blocking probability, compared to the static scheme. This indicates that the dynamic scheme makes the proposed network more robust against traffic fluctuations.

In the emerging smart grid technologies, resource utilization is diversified and responsive demand became an important tool in availing various benefits. The informed load curtailment is a popular means of demand response aspect with customers being facilitated by financial incentives for offered load reduction. Therefore, augmentation of such responsive loads with unit commitment process can be effective in resource scheduling of smart grid. This paper attempts to develop a binary fireworks algorithm application solve unit commitment problem along with demand response and wind energy. While the wind energy is considered as non schedulable, load curtailment is modelled as schedulable through demand response aggregator. Further, system and thermal unit constraints applicable for wind energy and DR are modified. The proposed methodology is tested on system with coal fired thermal generation, demand response aggregator and wind energy. Various possible scheduling scenarios are laid out for examination. Simulation results are presented and discussed in detail. Results shows the effectiveness of demand response in reducing the operational cost of system operator. Also, the demand response showed betterment when scheduled along with wind energy. The reduction in cost from from traditional thermal unit scheduling is observed to be 6.5% which is best among all the possible scenarios.

We design a dynamic algorithm for dimensioning and stabilizing a cloud provisioning process. We model the process as a semi-open tandem network consisting of a multi-server queue with host servers that respond to new requests of cloud users and an infinite-server queue that contains the active cloud users. The algorithm matches load predictions by jointly setting the number of host servers and the total available capacity. This dual setting is time-dependent and based on the modified offered load (MOL) method. The algorithm is made to perform in the Quality-and-Efficiency-Driven (QED) regime to achieve economies of scale, and is equipped with the feature of repeated requests, which lets initially blocked users retry to get access to the cloud system after a certain delay. Extensive numerical simulations show that the algorithm stabilizes performance at high QoS-levels, even in face of strongly time-varying loads and repeated requests.

This article proposes a new multi-dimensional Erlang’s Ideal Grading (EIG) model with queues that can service a number of call classes with differentiated access to resources. The model was used to determine delays and packet loss probabilities in the access system composed of a node in the operator’s network and a number of users. The analytical results obtained in the study were then compared with the results of a simulation, which confirmed the essential and required accuracy of the proposed model. The model developed in the study can be used to analyse, design and optimize present-day operator’s networks.

The Random early detection (RED) active queue management (AQM) scheme uses the average queue size to calculate the dropping probability in terms of minimum and maximum thresholds. The effect of heavy load enhances the frequency of crossing the maximum threshold value resulting in frequent dropping of the packets. An adaptive queue management with random dropping (AQMRD) algorithm is proposed which incorporates information not just about the average queue size but also the rate of change of the same. Introducing an adaptively changing threshold level that falls in between lower and upper thresholds, our algorithm demonstrates that these additional features significantly improve the system performance in terms of throughput, average queue size, utilization and queuing delay in relation to the existing AQM algorithms., Comment: 17 pages, 19 figures, and submitted to Telecommunication Systems, Springer

In this paper, we propose the optimal offset-time decision (OOD) algorithm which can effectively reduce the pre-transmission delay compared to the perfect isolation model, and can also be extended to general n priority classes while the target loss probability of each class is guaranteed for the variable offered load. In order to drive the OOD algorithm, we first analyze the loss probability of each priority class through class aggregation and iteration method; the analytic results obtained through the proposed algorithm are then validated with results garnered from extensive simulation tests.