258 research outputs found

    Providing Dynamic TXOP for QoS Support of Video Transmission in IEEE 802.11e WLANs

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    The IEEE 802.11e standard introduced by IEEE 802.11 Task Group E (TGe) enhances the Quality of Service (QoS) by means of HCF Controlled Channel Access (HCCA). The scheduler of HCCA allocates Transmission Opportunities (TXOPs) to QoS-enabled Station (QSTA) based on their TS Specifications (TSPECs) negotiated at the traffic setup time so that it is only efficient for Constant Bit Rate (CBR) applications. However, Variable Bit Rate (VBR) traffics are not efficiently supported as they exhibit nondeterministic profile during the time. In this paper, we present a dynamic TXOP assignment Scheduling Algorithm for supporting the video traffics transmission over IEEE 802.11e wireless networks. This algorithm uses a piggybacked information about the size of the subsequent video frames of the uplink traffic to assist the Hybrid Coordinator accurately assign the TXOP according to the fast changes in the VBR profile. The proposed scheduling algorithm has been evaluated using simulation with different variability level video streams. The simulation results show that the proposed algorithm reduces the delay experienced by VBR traffic streams comparable to HCCA scheduler due to the accurate assignment of the TXOP which preserve the channel time for transmission.Comment: arXiv admin note: substantial text overlap with arXiv:1602.0369

    A Scheduling Algorithm for Providing QoS Guarantees in 802.11e WLANs

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    In this paper we propose a scheduling algorithm for supporting Quality of Service (QoS) in an IEEE 802.11e network using the HCF Controlled Channel Access (HCCA) function. This is derived from Constant Bandwidth Server with Resource Constraints and adapted to wireless medium. It consists of a procedure to actually schedule transmission opportunities to HCCA flows with Quality of Service guarantees, in particular in the case of multimedia applications which present variable bit rate traffic

    Adaptive Segregation-Based MAC Protocol for Real-Time Multimedia Traffic in WLANs

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    Wireless local area networks (WLANs) have become very popular both in private and public sectors. Despite the fast expansion of WLANs in various environments, quality of service (QoS) issues for multimedia applications in WLANs are not yet resolved. Multimedia applications contain traffic that are sensitive to delay and jitter and therefore a best-effort protocol such as the legacy IEEE 802.11 is not suitable. The 802.11e protocol provides prioritization and classification of traffic to offer better QoS for real-time services. However, it leaves the design and implementation of many important optimization features to vendors. In this paper we introduce a mechanism to improve the delay and jitter of real-time traffic in WLAN nodes supporting multimedia applications. In our proposed mechanism, we segregate voice and video traffic from the best-effort traffic. We create a scheduler that schedules the access of real-time traffic and non real-time traffic to the medium with centralized polling and distributed contention respectively. We show that our proposed protocol performs better in terms of delay and jitter than the legacy 802.11 and 802.11e in a scenario where all wireless nodes carry multimedia traffic simultaneously

    Priority-Oriented Adaptive Control With QoS Guarantee for Wireless LANs.

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    In today’s wireless networks there is a great need for QoS, because of the time-bounded voice, audio and video traffic. A new QoS enhanced standard is being standardized by the IEEE 802.11e workgroup. It uses a contention free access mechanism called Hybrid Control Channel Access (HCCA) to guarantee QoS. However, HCCA is not efficient for all types of time-bounded traffic. This work proposes an alternative protocol which could be adapted in HCF (Hybrid Coordination Function). The Priority Oriented Adaptive Control with QoS Guarantee (POAC-QG) is a complete centralized channel access mechanism, it is able to guarantee QoS for all types of multimedia network applications, it enhances the parameterized traffic with priorities, and it supports time division access using slots. Furthermore, it instantly negotiates the quality levels of the traffic streams according to their priorities, supporting multiple streams to the best quality it can achieve. POAC-QG compared to HCCA, provides higher channel utilization, adapts better to the characteristics of the different traffic types, differentiates the traffic streams more efficiently using priorities, and generally exhibits superior performance

    Modeling and performance analysis of an alternative to IEEE 802.11e Hybrid Control Function

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    Modern wireless networks are offering a wide range of applications that require the efficient integration of multimedia and traditional data traffic along with QoS provision. The IEEE 802.11e workgroup has standardized a new QoS enhanced access scheme for wireless LANs, namely Hybrid Control Function (HCF). HCF consists of the Enhanced Distributed Channel Access (EDCA) and the Hybrid Control Channel Access (HCCA) protocols which manage to ensure QoS support. However, they exhibit specific weaknesses that limit network performance. This work analyzes an alternative protocol, called Priority Oriented Adaptive Polling (POAP). POAP is an integrated channel access mechanism, is collision free, it employs priorities to differentiate traffic in a proportional way, it provides fairness, and generally supports QoS for all types of multimedia applications, while efficiently serving background data traffic. POAP is compared to HCF in order to examine the wireless network performance when serving integrated traffic

    Adaptive Control in Wireless Networks

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    A Framework for Enhanced QoS Support in IEEE 802.11e Networks

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    IEEE 802.11 based WLANs have became popular, but they can only provide best effort services and so they are poorly suitable for multimedia applications. Recently IEEE 802.11e standard has been proposed to support quality of service. The new standard introduces a so-called Hybrid Coordination Function containing two medium access mechanisms: contention-based channel access and controlled channel access. In this paper we propose a novel framework to better support QoS guarantees for multimedia applications. It comprises QoS Manager, Admission Control, Enhanced Scheduler, Predictor and Feedback System. The scheduler adopted supports real-time applications, variable packet sizes and variable bit rate traffic streams. We show that this framework is suitable to be used by applications requesting Application Level Contracts which will be translated in Resource Level Contracts to the scheduler subsystem. The QoS manager component is able to dynamically manage available resources under different load conditions
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