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We compare the performance of different backoff functions for the multiple access protocol in an IEEE 802.11 wireless LAN (WLAN). We provide a unified analytical model with explicit expressions for the mean and standard deviation of the access delay for generalized exponential, polynomial and linear backoff functions. Using our model, we show that linear and polynomial backoffs with appropriate parameter settings can improve upon binary exponential backoff specified in the 802.11 WLAN standards, in terms of throughput, access delay statistics and packet drop rate.

We analyze the MAC access delay of the IEEE 802.11e enhanced distributed channel access (EDCA) mechanism under saturation. We develop a detailed analytical model to evaluate the influence of all EDCA differentiation parameters, namely AIFS, CWmin, CWmax, and TXOP limit, as well as the backoff multiplier. Explicit expressions for the mean, standard deviation, and generating function of the access delay distribution are derived. By applying numerical inversion on the generating function, we are able to efficiently compute values of the distribution. Comparison with simulation confirms the accuracy of our analytical model over a wide range of operating conditions. We derive simple asymptotics and approximations for the mean and standard deviation of the access delay, which reveal the salient model parameters for performance under different differentiation mechanisms. We also use the model to numerically study the differentiation performance and find that differentiation, though rejected during the standardization process, is an effective differentiation mechanism that has some advantages over the other mechanisms.

In this paper, we analyse the MAC access delay of the IEEE 802.11e EDCA mechanism under saturation. We develop a detailed analytical model to evaluate the influence of all EDCA differentiation parameters, namely AIFS, CWmin, CWmax and TXOP limit, as well as the backoff multiplier β. We derive explicit expressions for the mean, standard deviation and generating function of the access delay distribution. By applying numerical inversion on the generating function, we are able to efficiently compute values of the distribution. Through comparison with simulation, we confirm the accuracy of our analytical model over a wide range of operating conditions. Using the model, we derive simple asymptotics and approximations for the mean and standard deviation of the access delay, which reveal the salient model parameters for performance under different differentiation mechanisms. We also use the model to study the characteristics of CWmin, AIFS, TXOP, and β differentiation. We find that, though rejected during the standardization process, β differentiation is an effective differentiation mechanism that has some advantages over the other mechanisms.

Although the IEEE 802.11e standard including Quality of Service support in WiFi networks was recently approved, it does not increase wireless capacity. In order to optimize wireless resources, it is necessary to model the behavior of the system to assist network planning and deployment. In this article, we propose a Markov chain model for the EDCA access scheme described in IEEE 802.11e. Contrary to existing IEEE 802.11 models, our contribution studies more realistic assumptions since we consider a non-ideal channel moreover in unsaturated mode. The benefits of our model are manifold: we calculate the throughput more precisely, we can study various traffic loads, and finally we can examine various transmission environments.

The paper presents a preliminary study of a revised analysis of IEEE 802.11e performance. One of many possible topologies is analyzed in order to emphasize the severe problem of the incapability to prioritize traffic in networks with hidden nodes. The article also provides some innovative conclusions.

This paper investigates rate configuration of the Expedited Forwarding (EF) class of Differentiated Services (DiffServ) when used with 802.11e EDCA. The rate configuration problem is presented, and several approaches are tested and evaluated in order to solve the problem. Results reveal that the contention window makes rate configuration very hard for the highest priority class (AC_VO) in 802.11e EDCA. Our evaluations show that 802.11e EDCA is not able to conform to DiffServ's EF PHB specifications.

Up to the present, several studies have been performed in order to provide priorization of stations or classes of service for WLAN IEEE 802.11. The IEEE 802.11e draft specification aims to extend the original IEEE 802.11 MAC protocol to support QoS. One of the mechanisms for priorizing traffic is the assignment of different AIFS times to each priority level. Nevertheless, the AIFSs employed are separated by values that are multiples of the slot time. Therefore, due to the fact that the backoff time counter is slotted, the different priority levels can attempt for transmission simultaneously.

An analytical model is proposed to describe the priority schemes of the Enhanced Distributed Channel Access (EDCA) mechanism of the IEEE 802.11e standard. EDCA provides class-based differentiated Quality of Service (QoS) to IEEE 802.11 WLANs. The main contribution of this paper opposed to other works is that the model predicts the full delay distribution through its z-transform. Furthermore, the mean delay, throughput and frame dropping probabilities of the different traffic classes are found in the whole range from a lightly loaded, non-saturated channel to a heavily congested, saturated medium. Moreover, the model describes differentiation based on different Arbitration Inter-Frame Space (AIFS) values, in addition to the other adjustable parameters (i.e. window-sizes, retransmission limits, transmission opportunity (TXOP) lengths etc.) also encompassed by previous models. AIFS differentiation is described by a simple equation that enables access points to predict at which traffic loads starvation of a traffic class will occur. The model is calculated numerically and validated against simulation results. We observed a good match between the analytical model and simulations.

The EDCA mechanism of the 802.11e standard provides QoS support through service differentiation, by using different MAC parameters for different stations. The configuration of these parameters, however, is still an open research challenge, as the standard provides only a set of fixed recommended values which do not take into account the current WLAN conditions and therefore lead to suboptimal performance. In this paper we propose a novel algorithm for EDCA that, given the throughput and delay requirements of the stations present in the WLAN, computes the optimal configuration of the EDCA parameters. We first present a throughput and delay analysis that provides the mathematical foundation upon which our algorithm is based. This analysis is validated through simulations of different traffic sources (both data and real-time) and EDCA configurations. We then propose a mechanism to derive the optimal configuration of the EDCA parameters given a set of performance criteria for throughput and delay. We assess the effectiveness of the configuration provided by our algorithm by comparing it against i) the recommended values by the standard, ii) the results from an exhaustive search over the parameter space, and iii) previous configuration proposals, both standard and non-standard compliant. Results show that our configuration outperforms all other approaches.

We study the performance of contention based medium access control (MAC) protocols. In particular, we provide a simple and accurate method for estimating the throughput of IEEE 802.11 DCF and IEEE 802.11e EDCA. Our method is based on a rigorous analysis of the Markov chain associated with the back-off process at the contending nodes. Our results provide new insights into the operation of the IEEE 802.11 DCF and IEEE 802.11e EDCA. Although we focus on the IEEE 802.11 MAC protocol in this paper, the techniques developed are applicable to a wide variety of contention based MAC protocols. † In order to avoid confusion arising from the superficially similar terminology, we emphasize that the fixed points we talk of in this work are different from the fixed points in [3], [7], . Their fixed points are for the 1dimensional coupling parameter p; our fixed points are for the n-dimensional state descriptor in a joint Markovian representation of the back-off stages at all n stations. The details are provided in the next section.

We study the performance of contention based medium access control (MAC) protocols. In particular, we provide a simple and accurate method for estimating the throughput of IEEE 802.11 DCF and IEEE 802.11e EDCA. Our method is based on a rigorous analysis of the Markov chain associated with the back-off process at the contending nodes. Our results provide new insights into the operation of the IEEE 802.11 DCF and IEEE 802.11e EDCA. Although we focus on the IEEE 802.11 MAC protocol in this paper, the techniques developed are applicable to a wide variety of contention based MAC protocols. † In order to avoid confusion arising from the superficially similar terminology, we emphasize that the fixed points we talk of in this work are different from the fixed points in [3], [7], . Their fixed points are for the 1dimensional coupling parameter p; our fixed points are for the n-dimensional state descriptor in a joint Markovian representation of the back-off stages at all n stations. The details are provided in the next section.

A modification to the access policy for ETHERNET" Version 1.0 is proposed. By placing additional restrictions (compared with Paper approved by the Editor for Communication Theory of the IEEE Communications Society for publication without oral presentation. Manuscript

The paper proposes a simulation model which enables the evaluation of IEEE 802.11e EDCA networks, focusing in the behavior of the Enhanced Distributed Channel Access (EDCA) function associated to Quality of Service (QoS) stations. When compared with currently used simulation models, the proposed model provides a more accurate implementation of some aspects (timeouts, EIFS), a flexible implementation, and an easiness of use. Besides, a large number of different types of performance measures can be obtained. The model is based on a high level Stochastic Petri Net formalism referred as Stochastic Activity Networks (SAN), able to produce very compact and efficient models, and which is supported by the Möbius tool.

In this paper, we analyse the MAC access delay of the IEEE 802.11e EDCA mechanism under saturation. We develop a detailed analytical model to evaluate the influence of all EDCA differentiation parameters, namely AIFS, CWmin, CWmax and TXOP limit, as well as the backoff multiplier β. We derive explicit expressions for the mean, standard deviation and generating function of the access delay distribution. By applying numerical inversion on the generating function, we are able to efficiently compute values of the distribution. Through comparison with simulation, we confirm the accuracy of our analytical model over a wide range of operating conditions. Using the model, we derive simple asymptotics and approximations for the mean and standard deviation of the access delay, which reveal the salient model parameters for performance under different differentiation mechanisms. We also use the model to study the characteristics of CWmin, AIFS, TXOP, and β differentiation. We find that, though rejected during the standardization process, β differentiation is an effective differentiation mechanism that has some advantages over the other mechanisms.

This paper investigates Enhanced Distributed Coordination Function (EDCF) differentiation functionality and effectiveness in the emerging standard IEEE 802.11e via numerical and simulation results. An analytical model is proposed to derive saturation throughputs, saturation delays, and frame dropping probabilities for EDCF differentiation services. Effects of different parameters on the EDCF differentiation mechanism are obtained to provide some insights on the protocol.

In this paper, we analyse the MAC access delay of the IEEE 802.11e EDCA mechanism under saturation. We develop a detailed analytical model to evaluate the influence of all EDCA differentiation parameters, namely AIFS, CWmin, CWmax and TXOP limit, as well as the backoff multiplier β. We derive explicit expressions for the mean, standard deviation and generating function of the access delay distribution. By applying numerical inversion on the generating function, we are able to efficiently compute values of the distribution. Through comparison with simulation, we confirm the accuracy of our analytical model over a wide range of operating conditions. Using the model, we derive simple asymptotics and approximations for the mean and standard deviation of the access delay, which reveal the salient model parameters for performance under different differentiation mechanisms. We also use the model to study the characteristics of CWmin, AIFS, TXOP, and β differentiation. We find that, though rejected during the standardization process, β differentiation is an effective differentiation mechanism that has some advantages over the other mechanisms.

Abstract Transmission opportunity (TXOP) is a channel control mechanism introduced in the IEEE802. 11e wireless LAN standard to improve channel utilization. In a previous paper, we have proposed a novel scheme to effectively predict the throughput of various TXOP classes based on a common threshold. In this paper, we extend this solution to incorporate the impact of the contention window (CW) size.

ABSTRACT The emerging multimedia wireless networking environment is pushing the research to optimize the wireless network performance. In this work there is a study about the impact of MAC functionality on some relevant network parameters, namely throughput, idle time and collision time. Obtained results are presented and discussed, comparing several distributed channel access proposals, for different channel loads.

Abstract The enhanced distributed channel access (EDCA) mechanism of the IEEE 802.11 e standard provides quality-of-service (QoS) support through service differentiation by using different medium-access-control (MAC) parameters for different stations. The configuration of these parameters, however, is still an open research challenge, as the standard provides only a set of fixed recommended values that do not take into account the current wireless local area network (WLAN) conditions and, therefore, lead to suboptimal performance.