A IEEE 802.11e HCCA Scheduler with a Reclaiming Mechanism for Multimedia Applications

The QoS offered by the IEEE 802.11e reference scheduler is satisfactory in the case of Constant Bit Rate traffic streams, but not yet in the case of Variable Bit Rate traffic streams, whose variations stress its scheduling behavior. Despite the numerous proposed alternative schedulers with QoS, multimedia applications are looking for refined methods suitable to ensure service differentiation and dynamic update of protocol parameters. In this paper a scheduling algorithm,Unused Time Shifting Scheduler(UTSS), is deeply analyzed. It is designed to cooperate with a HCCA centralized real-time scheduler through the integration of a bandwidth reclaiming scheme, suitable to recover nonexhausted transmission time and assign that to the next polled stations. UTSS dynamically computes with anO(1)complexity transmission time providing an instantaneous resource overprovisioning. The theoretical analysis and the simulation results highlight that this injection of resources does not affect the admission control nor the centralized scheduler but is suitable to improve the performance of the centralized scheduler in terms of mean access delay, transmission queues length, bursts of traffic management, and packets drop rate. These positive effects are more relevant for highly variable bit rate traffic

An admission control scheme for IEEE 802.11e wireless local area networks

Includes bibliographical references (leaves 80-84).Recent times has seen a tremendous increase in the deployment and use of 802.11 Wireless Local Area Networks (WLANs). These networks are easy to deploy and maintain, while providing reasonably high data rates at a low cost. In the paradigm of Next-Generation-Networks (NGNs), WLANs can be seen as an important access network technology to support IP multimedia services. However a traditional WLAN does not provide Quality of Service (QoS) support since it was originally designed for best effort operation. The IEEE 802. 11e standard was introduced to overcome the lack of QoS support for the legacy IEEE 802 .11 WLANs. It enhances the Media Access Control (MAC) layer operations to incorporate service differentiation. However, there is a need to prevent overloading of wireless channels, since the QoS experienced by traffic flows is degraded with heavily loaded channels. An admission control scheme for IEEE 802.11e WLANs would be the best solution to limit the amount of multimedia traffic so that channel overloading can be prevented. Some of the work in the literature proposes admission control solutions to protect the QoS of real-time traffic for IEEE 802.11e Enhanced Distributed Channel Access (EDCA). However, these solutions often under-utilize the resources of the wireless channels. A measurement-aided model-based admission control scheme for IEEE 802.11e EDCA WLANs is proposed to provide reasonable bandwidth guarantees to all existing flows. The admission control scheme makes use of bandwidth estimations that allows the bandwidth guarantees of all the flows that are admitted into the network to be protected. The bandwidth estimations are obtained using a developed analytical model of IEEE 802.11e EDCA channels. The admission control scheme also aims to accept the maximum amount of flows that can be accommodated by the network's resources. Through simulations, the performance of the proposed admission control scheme is evaluated using NS-2. Results show that accurate bandwidth estimations can be obtained when comparing the estimated achievable bandwidth to actual simulated bandwidth. The results also validate that the bandwidth needs of all admitted traffic are always satisfied when the admission control scheme is applied. It was also found that the admission control scheme allows the maximum amount of flows to be admitted into the network, according the network's capacity

Real-time support for HCCA function in IEEE 802.11e networks: a performance evaluation

The IEEE 802.11 standard for wireless networks has been recently enhanced with the IEEE 802.11e amendment which introduces Quality of Service support. It provides differentiation mechanisms at the Medium Access Control layer, using two additional access functions: the Enhanced Distributed Channel Access (EDCA) function and the HCF Controlled Channel Access (HCCA) function. Only the HCCA mechanism is suitable for serving traffic streams with real-time requirements such as multimedia applications and Voice Over IP. The IEEE 802.11e standard does not specify a mandatory HCCA scheduling algorithm, but it offers a reference scheduler as the guideline in the resources scheduling design.In this paper we analyze four HCCA alternative schedulers to the reference one. They offer real-time guarantees proposing different solutions to the request of QoS and real-time support expressed by the increasing diffusion of multimedia applications. A performance evaluation is conducted to show the main differences between the considered schedulers, including the reference one.The results show that under several scenarios there is not a unique best scheduler, but there exists a variety of solutions depending on the specified requirements. The conclusions of the paper offer some guidelines in the choice of the scheduler tailored for a particular scenario of interest

Supporting Real-Time Communication in CSMA-Based Networks : the VTP-CSMA Virtual Token Passing Approach

Tese de doutoramento. Engenharia Electrotécnica e de Computadores. Faculdade de Engenharia. Universidade do Porto. 200

Improving the QoS of IEEE 802.11e networks through imprecise computation

IEEE 802.11e HCCA reference scheduler is based on fixed value parameters that do not adapt to traffic changes, thus quality of service (QoS) for multimedia applications is a challenge, especially in the case of variable bit rate (VBR) streams, that requires dynamic resource assignment. This paper is focused on immediate dynamic TXOP HCCA (IDTH) scheduling algorithm and its new evolution immediate dynamic TXOP HCCA plus (IDTH+). Their reclaiming mechanisms, refined by the monitoring of transmission duration, aim at overcoming the limits of fixed preallocation of resources by varying the stations transmission time and avoiding waste of resources. Simulations and theoretical analysis based on the imprecise computation model show that the integration of IDTH and IDTH+ can achieve improved network performance in terms of transmission queues length, mean access delay and packets drop rate, and to efficiently manage bursty traffic. Moreover, the performance improvements of IDTH+ with respect to IDTH are highlighted

Contributions to QoS and energy efficiency in wi-fi networks

The Wi-Fi technology has been in the recent years fostering the proliferation of attractive mobile computing devices with broadband capabilities. Current Wi-Fi radios though severely impact the battery duration of these devices thus limiting their potential applications. In this thesis we present a set of contributions that address the challenge of increasing energy efficiency in Wi-Fi networks. In particular, we consider the problem of how to optimize the trade-off between performance and energy effciency in a wide variety of use cases and applications. In this context, we introduce novel energy effcient algorithms for real-time and data applications, for distributed and centralized Wi-Fi QoS and power saving protocols and for Wi-Fi stations and Access Points. In addition, the di¿erent algorithms presented in this thesis adhere to the following design guidelines: i) they are implemented entirely at layer two, and can hence be easily re-used in any device with a Wi-Fi interface, ii) they do not require modi¿cations to current 802.11 standards, and can hence be readily deployed in existing Wi-Fi devices, and iii) whenever possible they favor client side solutions, and hence mobile computing devices implementing them can benefit from an increased energy efficiency regardless of the Access Point they connect to. Each of our proposed algorithms is thoroughly evaluated by means of both theoretical analysis and packet level simulations. Thus, the contributions presented in this thesis provide a realistic set of tools to improve energy efficiency in current Wi-Fi networks

Towards the Quality of Service for VoIP traffic in IEEE 802.11 Wireless Networks

The usage of voice over IP (VoIP) traffic in IEEE 802.11 wireless networks is expected to increase in the near future due to widely deployed 802.11 wireless networks and VoIP services on fixed lines. However, the quality of service (QoS) of VoIP traffic in wireless networks is still unsatisfactory. In this thesis, I identify several sources for the QoS problems of VoIP traffic in IEEE 802.11 wireless networks and propose solutions for these problems. The QoS problems discussed can be divided into three categories, namely, user mobility, VoIP capacity, and call admission control. User mobility causes network disruptions during handoffs. In order to reduce the handoff time between Access Points (APs), I propose a new handoff algorithm, Selective Scanning and Caching, which finds available APs by scanning a minimum number of channels and furthermore allows clients to perform handoffs without scanning, by caching AP information. I also describe a new architecture for the client and server side for seamless IP layer handoffs, which are caused when mobile clients change the subnet due to layer 2 handoffs. I also present two methods to improve VoIP capacity for 802.11 networks, Adaptive Priority Control (APC) and Dynamic Point Coordination Function (DPCF). APC is a new packet scheduling algorithm at the AP and improves the capacity by balancing the uplink and downlink delay of VoIP traffic, and DPCF uses a polling based protocol and minimizes the bandwidth wasted from unnecessary polling, using a dynamic polling list. Additionally, I estimated the capacity for VoIP traffic in IEEE 802.11 wireless networks via theoretical analysis, simulations, and experiments in a wireless test-bed and show how to avoid mistakes in the measurements and comparisons. Finally, to protect the QoS for existing VoIP calls while maximizing the channel utilization, I propose a novel admission control algorithm called QP-CAT (Queue size Prediction using Computation of Additional Transmission), which accurately predicts the impact of new voice calls by virtually transmitting virtual new VoIP traffic

A quality of service architecture for WLAN-wired networks to enhance multimedia support

Includes abstract.Includes bibliographical references (leaves 77-84).The use of WLAN for the provision of IP multimedia services faces a number of challenges which include quality of service (QoS). Because WLAN users access multimedia services usually over a wired backbone, attention must be paid to QoS over the integrated WLAN-wired network. This research focuses on the provision of QoS to WLAN users accessing multimedia services over a wired backbone. In this thesis, the IEEE 802.11-2007 enhanced data channel access (EDCA) mechanism is used to provide prioritized QoS on the WLAN media access control (MAC) layer, while weighted round robin (WRR) queue scheduling is used to provide prioritized QoS at the IP layer. The inter-working of the EDCA scheme in the WLAN and the WRR scheduling scheme in the wired network provides end-to-end QoS on a WLAN-wired IP network. A mapping module is introduced to enable the inter-working of the EDCA and WRR mechanisms