Abstract Contention free bursting (CFB) and block acknowledgement (BACK) are two innovative burst transmission schemes specified in the IEEE 802.11e standard for reducing the contention overheads and further improving the channel utilization of wireless local area networks (WLANs). Existing studies on performance analysis of the CFB and BACK schemes have been primarily focused on the system throughput and have not taken into account the realistic factors, such as unsaturated traffic loads and finite buffer capacity. To fill this gap, this paper proposes a new and comprehensive analytical model for evaluating the Quality‐of‐Service (QoS) metrics including throughput, end‐to‐end delay, and frame loss probability of both burst transmission schemes under unsaturated traffic conditions. The proposed model is validated through extensive simulation experiments and then is used to conduct performance analysis and comparison of the burst transmission schemes under various working conditions. The analytical results reveal that (1) both CFB and BACK schemes can substantially improve the QoS performance; (2) BACK scheme outperforms the CFB scheme when the transmission opportunity (TXOP) limit exceeds a threshold; (3) the analytical model can be used to identify the optimal configuration of system parameters for the burst transmission schemes subject to QoS constraints. Copyright © 2010 John Wiley & Sons, Ltd.

The explosive growth in advanced multimedia applications poses great challenges for design and deployment of wireless communication networks. Transmission Opportunity (TXOP) is a promising MAC protocol extension for provisioning of differentiated Quality-of-Service (QoS) in multimedia WLANs. However, for analytical tractability and simplicity, most existing performance models of TXOP have been restricted to unrealistic working scenarios where the traffic is saturated or follows a Poisson process, which is unable to capture the heterogeneous characteristics of multimedia traffic. To fill this gap, this paper proposes an original analytical model for TXOP in WLANs with heterogeneous stations in the presence of multimedia applications. Specifically, the traffic generated by heterogeneous stations with background, voice and video applications is modelled by the non-bursty Poisson, bursty Markov-Modulated Poisson Process, and fractal self-similar process, respectively. QoS measures including throughput, end-to-end delay, and frame loss probability are derived. The extensive comparison between the analytical results and those obtained from simulation experiments subject to the traffic parameters of real-world voice and video sources validates the accuracy of the developed model for WLANs with practical multimedia applications. The performance results reveal the importance of taking into account the heterogeneous stations for the accurate evaluation of TXOP in wireless multimedia networks.

In this paper we present a formal specification of a queueing network performance evaluation model for database designs. The purpose of the model is to provide what if comparisons of database designs before database system implementation. The performance model is applied to the performance evaluation of three database designs of an implementation of the TPC-C benchmark. Experimental evaluation showed that the database design queueing network model was able to give an upper bound of system response time in the steady state for the measured system.

Localized Quality of Service (QoS) routing has been recently proposed for supporting the requirements of multimedia applications and satisfying QoS constraints. Localized algorithms avoid the problems associated with the maintenance of global network state by using statistics of flow blocking probabilities. Using local information for routing avoids the overheads of global information with other nodes. However, localized QoS routing algorithms perform routing decisions based on information updated from path request to path request. This paper proposes to tackle a combined localized routing and admission control in order to avoid congestion. We introduce a new Congestion Avoidance Routing algorithm (CAR) in localized QoS routing which make a decision of routing in each connection request using an admission control to route traffic away from congestion. Simulations of various network topologies are used to illustrate the performance of the CAR. We compare the performance of the CAR algorithm against the Credit Based Routing (CBR) algorithm and the Quality Based Routing (QBR) under various ranges of traffic loads.

Heterogeneous error protection (HEP) of H.264/AVC coded video is investigated using hierarchical quadrature amplitude modulation (HQAM), which takes into consideration the non- uniformly distributed importance of intracoded frame (I-frame) and predictive coded frame (P-frame) as well as the sensitivity of the coded bitsream against transmission errors. The HQAM constellation are used to give different degrees of error protection of the most important information of the video content. The performance of the transmission system is evaluated under additive Gaussion Noise (AWGN). The simulation results indicate that the strategy produces a high quality of the reconstructed video data compared with uniform protection.

Admission control is an important mechanism for the provisioning of the user-perceived Quality-of-Service (QoS) in the IEEE 802.11e Wireless Local Area Networks (WLANs). In this paper, we present an efficient admission control scheme based on analytical modelling and non-cooperative game theory where the Access Point (AP) and new users are the players. The decision of admission control is made by virtue of the strategies to maximize the utilities of the players, which are determined by the QoS performance metrics in terms of the end-to-end delay and frame loss probability. To obtain these required performance metrics, we develop a new analytical model incorporating the Contention Window (CW) and Transmission Opportunity (TXOP) differentiation schemes in the IEEE 802.11e protocol under unsaturated working conditions. The efficiency of the proposed admission control scheme is validated via NS-2 simulation experiments. The numerical results demonstrate that the proposed admission control scheme can maintain the system operation at an optimal point where the utility of the AP is maximized subject to the QoS constraints of both the real-time and non-real-time users.

To support the differentiated Quality-of-Service (QoS) and improve the utilization of the scarce wireless bandwidth, the IEEE 802.11e standard specifies an efficient burst transmission scheme referred to as the transmission opportunity (TXOP). Recently, analytical models have been reported to evaluate the performance of the TXOP scheme. However, most of these models were developed under the assumptions of the ideal channels or uniform error channels which fail to capture the characteristics of bursty and correlated channel errors in the practical wireless environment. In this paper, we propose an analytical model for the TXOP scheme in WLANs in the presence of bursty error channels. To this end, the transmission queue of each station is modelled by a two-state continuous time Markov chain. This model can be adopted to obtain the performance metrics including the throughput and buffer overflow probability. The accuracy of the analytical model is validated via NS-2 simulation experiments. Utilizing the proposed model, we investigate the impact of traffic loads, TXOP limit, and the number of stations on the performance of the TXOP scheme under various channel conditions.

In mobile ad hoc networks (MANET), broadcasting is widely used in route discovery and many other network services. The efficiency of broadcasting protocol can affect the performance of the entire network. As such, the simple flooding algorithm aggravates a high number of unnecessary packet rebroadcasts, causing contention and packet collisions. Proper use of probabilistic method can reduce the number of rebroadcasting, therefore reduce the chance of contention and collision among neighboring nodes. A good probabilistic broadcast protocol can achieve high save rebroadcast and low collision. In this paper, we propose a dynamic probabilistic approach when nodes move according to way point mobility model and compare it with simple flooding AODV and fixed probabilistic scheme. Our approach dynamically set the rebroadcasting probability according to the number of neighbours nodes distributed in the ad hoc network. Simulation results show our approach performs better than both simple flooding and fixed probabilistic flooding.

The enhanced distributed channel access (EDCA) protocol has been proposed to support differentiated quality-of-service (QoS) of wireless local area networks (WLANs). edca introduces a promising scheme, transmission opportunity (TXOP), which enables a station to transmit multiple frames consecutively in a burst upon winning the contention of the channel. The analytical models of the TXOP scheme have been mainly developed under the assumptions that the traffic generated by the stations is saturated or follows a non-bursty Poisson arrival process. These assumptions are unable to capture the characteristics of heterogeneous multimedia traffic. This paper proposes a new analytical model for the TXOP scheme in WLANs comprising heterogeneous classes of stations with multimedia applications. The traffic of such applications is modelled by the non-bursty Poisson, bursty Markov-modulated Poisson process (MMPP), and fractal self-similar traffic. The accuracy of the proposed model is validated through extensive NS-2 simulation experiments.

Arbitrary inter-frame space (AIFS), contention window (CW) and transmission opportunity (TXOP) are three important quality-of-service (QoS) differentiation schemes specified in the IEEE 802.11e enhanced distributed channel access (EDCA) protocol for wireless local area networks (WLANs). Analytical models of EDCA in the current literature have been mainly developed for the AIFS, CW, and TXOP schemes, separately. This study proposes a comprehensive analytical model to accommodate the combination of these three QoS schemes in WLANs under unsaturated traffic loads. We derive the performance metrics in terms of throughput, end-to- end delay, and frame loss probability. Extensive simulation experiments are conducted to validate the accuracy of the model.

Transmission opportunity (TXOP) is a new scheme specified in the IEEE 802.11e standard which enables a station to transmit multiple frames consecutively within a burst after it gains the channel. Realistic traffic loads in wireless local area networks (WLANs) with multimedia applications often exhibit the bursty and self-similar properties which imply the frequent occurrence of the large bursts of frame arrivals and thus require the TXOP scheme to be dynamically adapted to the traffic characteristics. This paper presents a dynamic TXOP scheme which adjusts the TXOP limits of mobile stations according to the current status of their transmission queues. We further develop an analytical model to evaluate the performance of this scheme under self-similar traffic. QoS performance metrics in terms of throughput, end-to-end delay, and frame loss probability are derived and validated via NS2 simulation experiments. The numerical results reveal that the dynamic TXOP scheme achieves the better QoS than the original one under self-similar traffic.

Contention free bursting (CFB) and block acknowledgement (BACK) are two efficient burst transmission schemes specified in the IEEE 802.11e standard for improving the utilization of scarce wireless bandwidth. Most existing performance models of the CFB and BACK schemes have focused on the analysis of system throughput and have not taken the realistic factors, such as unsaturated traffic loads and finite buffer capacity, into account. In this paper, we propose a comprehensive analytical model for evaluating the throughput, end-to-end delay, and loss probability of burst transmission schemes in wireless local area networks (WLANs) under unsaturated traffic conditions. The accuracy of the proposed model is validated through extensive ns2 simulation experiments. Performance results obtained from the model demonstrate that both schemes can substantially improve network performance. Moreover, the BACK scheme outperforms the CFB scheme when the transmission opportunity (TXOP) limit exceeds a certain threshold.

A congestion control mechanism is proposed, correlation based random early detection, or CRED that exploits the fact that Internet traffic is often long range dependent and self similar. It thus has a past history that can be used to estimate the mean queue length in the not too distant future. This enables CRED to detect the congestion degree status, either increasing or decreasing, and react accordingly. It is demonstrated that this can result in substantial performance gain when compared with existing versions of RED. CRED shows lower delay with the same loss rate and throughput and the mean queue length profile is more stable with light or heavier congestion.

In mobile ad hoc networks (MANET), broadcasting is widely used in route discovery and many other network services. The efficiency of broadcasting protocol can affect the performance of the entire network. As such, the simple flooding algorithm aggravates a high number of unnecessary packet rebroadcasts, causing contention and packet collisions. Proper use of probabilistic method can reduce the number of rebroadcasting, therefore reduce the chance of contention and collision among neighbouring nodes. A good probabilistic broadcast protocol can achieve high save rebroadcast and low collision. In this paper, we propose a dynamic probabilistic approach when nodes move according to different mobility models and compare it with simple flooding AODV and fixed probabilistic scheme. Our approach dynamically set the rebroadcast probability according to the number of neighbour nodes distributed in the ad hoc network. Simulation results show our approach performs better than both simple flooding and fixed probabilistic flooding.

As the access point (AP) is responsible for forwarding all the frames to and from the infrastructure-based WLANs, the network performance is significantly degraded by the unbalanced traffic loads. A potential solution is to assign different transmission opportunities (TXOPs) to AP and other mobile stations, respectively. This study develops an analytical model to investigate the performance of infrastructure-based WLANs with the TXOP differentiation under the unbalanced traffic loads. The analytical model is validated through extensive ns2 simulation experiments.

Contention free bursting (CFB) is an innovative quality-of-service (QoS) scheme specified in the IEEE 802.11e standard. To reduce the contention overheads, this scheme enables the stations that gain the channel to transmit multiple frames back-to-back in a burst. Most existing analytical models of the CFB scheme have been developed under the assumption of identical stations with saturated traffic loads. In this paper, we present an analytical model for investigating the performance metrics of throughput, end-to-end delay, loss probability, and energy consumption of the CFB scheme in the presence of nonidentical stations with different traffic generation rates. The model is validated against extensive ns2 simulation experiments. Numerical performance results demonstrate the efficiency of the CFB scheme for improving the network performance.

Employing effective buffer management schemes at Internet routers has been an increasing important issue in order to guarantee quality of service (QoS) to diverse Internet services. One of its primary goals is to control jitter and latency required by real-time and interactive traffic. Therefore, effectively constraining delay to a specified value is a key QoS requirement. This paper presents a new approach for bounding delay through a buffer at a specified level using dynamic queue thresholds as the arrival rate changes with time. A discrete-time control strategy is presented that operates on a buffer (queue) which incorporates a moveable threshold. An algorithm is developed that controls the delay by dynamically adjusting the threshold which, in turn, controls the arrival rate. The feasibility of the system is examined using both theoretical analysis and simulation

The computer society has not yet agreed on a standard method to measure data security and consequently to date no specific security metric has been defined for routing purposes. This paper used access control, authentication and cryptography to define routing metrics. These metrics are believed to be good, reasonable and practical. Since authentication is regarded as the first line of defense, cryptography is the key tool that ensures secure transmission of data across a network and access control systems help in guaranteeing the availability of services delivered by the information system. Each metric thus demonstrates the level of achievement in preserving the three goals of security.

One of the challenging issues in the environment of large networks with routing algorithms, including quality of service (QoS) routing algorithms is scalability network. This paper studies partitioning as a technique towards scaling QoS routing algorithms. We develop method to create partitions based on probabilities that reflect the frequency of connection requests between nodes across a network. Our evaluation methodology quantifies the reduction of computational effort to find suitable path between a source and destination. The proposed approach is called stochastic partitioning which is a probabilistic method. The performance is measured in terms of reduction in computational effort.

The paper studies the issue of scaling quality of service (QoS) routing algorithms to large-scale networks using partitioning. In particular, the paper focuses on a new approach which we call stochastic partitioning. We investigate the performance of this technique and develop an intelligent partitioning strategy that reduces the computational effort in routing, usually by orders of magnitude. The trade-off is an increase in QoS blocking probability (probability of failure to find a path that satisfies the QoS constraints). Finally, simulation results are produced which demonstrate the benefits and some practical limitations of stochastic partitioning.

Quality of service (QoS) is of extreme importance to accommodate the increasingly diverse ranges of services and types of traffic in the Internet, and maintaining the delay at a specified value is a key QoS requirement. In this paper, a two-state Markov-modulated Bernoulli process (MMBP) is set up as our source model. To satisfy some specified delay, we present an analytical model for a discrete-time finite capacity queue, which incorporates two thresholds (L/sub 1/ in state-one and L/sub 2/ in state-two) in the system so that the source can be blocked. If the number of packets in the system reaches the threshold, then the source stops sending the packets, otherwise the source operates normally. That can be considered as an implicit feedback from the queue to the arrival process. In addition, when the arrival process is in a specific state, this information is used to adjust the thresholds L/sub 1/ and L/sub 2/ so that the mean delay through the queue is maintained at some specified value to satisfy QoS requirements.

The architecture of an IP-based integrated terrestrial/satellite mobile communications network is proposed. This model, which adopts technologies such as mobile-IP, intelligent network and dual-mode mobile terminal, is built on the infusion of mobile communications and Internet technologies, and has two major features: Internet has been chosen as the backbone of the mobile communications network, and the mobile user can access Internet in both satellite and terrestrial environments. By this means, the users can access information anywhere, at any time, and realise the aim of global personal communications. Following the introduction of the proposed network architecture, its protocol stacks are presented. A suite of signalling protocols, including registration, call setup and inter-segment handover protocols, are then derived and discussed.

The orthogonal frequency division multiplexed (OFDM) modulation scheme has been proposed by the digital video broadcasting (DVB) project to facilitate the implementation of single frequency networks (SFN). In this paper, the performance of the DVB-T (2k mode) based SFN system is analysed. The effects on performance due to timing offset errors, carrier frequency offsets and sampling frequency offsets due to the lack of synchronisation between the transmitter and the receiver clocks are considered.

Existing models for product-form closed discrete-time queueing networks with batch movement of customers implicitly assume that batch sizes are unrestricted. In many practical modelling situations however, it is necessary to impose restrictions on the batch sizes, and this paper examines the repercushions of such restrictions on the product-form properties of the networks. It is shown that when batch sizes are restricted independently then, in general, the resulting networks cannot have a product-form equilibrium distribution. Sufficient conditions to retain a product-form are derived in the cases when batch sizes are either correlated or depend on the state of the network. Examples of applying the results to obtain product-form networks with both correlated and state dependent batch movement are given.