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

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

Adaptive TXOP assignment for QoS support of video traffic in IEEE 802.11e networks

Quality of Service (QoS) is provided in IEEE 802.11eprotocol by means of HCF Controlled Channel Access (HCCA) scheduler which is efficient for supporting Constant Bit Rate (CBR) applications. Numerous researches have been carried out to enhance the HCCA scheduler attempting to accommodate the needs of Variable Bit Rate (VBR) video traffics which probably demonstrates a non-deterministic profile during the time. This paper presents an adaptive TXOP assignment mechanism for supporting the transmission of the prerecorded video traffics over IEEE 802.11e wireless networks. The proposed mechanism uses a feedback about the size of the subsequent video frames of the uplink traffic to assist the Hybrid Coordinator (HC) accurately assign TXOP according to the fast changes in the VBR profile. The simulation results show that our mechanism 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 data transmission

Review on QoS provisioning approaches for supporting video traffic in IEEE802.11e: challenges and issues

Recently, the demand for multimedia applications is dramatically increased, which in turn increases the portion of video traffic on the Internet. The video streams, which require stringent Quality of Service (QoS), are expected to occupy more than two-thirds of web traffic by 2019. IEEE802.11e has introduced HCF Controlled Channel Access (HCCA) to provide QoS for delay-sensitive applications including highly compressed video streams. However, IEEE802.11e performance is hindered by the dynamic nature of Variable Bit Rate (VBR) video streams in which packet size and interval time are rapidly fluctuating during the traffic lifetime. In order to make IEEE802.11e able to accommodate with the irregularity of VBR video traffic, many approaches have been used in the literature. In this article, we highlight and discuss the QoS challenges in IEEE802.11e. Then, we classify the existing QoS approaches in IEEE802.11e and we also discuss the selection of recent promising and interesting enhancements of HCCA. Eventually, a set of open research issues and potential future directions is presented

Adaptive multi-polling scheduler for QoS support of video transmission in IEEE 802.11e WLANs

The 802.11E Task Group has been established to enhance quality of service (QoS) provision for time-bounded services in the current IEEE 802.11 medium access control protocol. The QoS is introduced throughout hybrid coordination function controlled channel access (HCCA) for the rigorous QoS provision. In HCCA, the station is allocated a fixed transmission opportunity (TXOP) based on its TSPEC parameters so that it is efficient for constant bit rate streams. However, as the profile of variable bit rate traffics is inconstant, they are liable to experience a higher delay especially in bursty traffic case. In this paper, we present a dynamic TXOP assignment algorithm called adaptive multi-polling TXOP scheduling algorithm (AMTXOP) for supporting the video traffics transmission over IEEE 802.11e wireless networks. This scheme invests a piggybacked information about the size of the subsequent video frames of the uplink streams to assist the hybrid coordinator accurately assign the TXOP according to actual change in the traffic profile. The proposed scheduler is powered by integrating multi-polling scheme to further reduce the delay and polling overhead. Extensive simulation experiments have been carried out to show the efficiency of the AMTXOP over the existing schemes in terms of the packet delay and the channel utilization

Syndrome d’ogilvie chez le brule (a propos de 2 cas)

La pseudo-occlusion colique aigue ou syndrome d’Ogilvie est une dilatation aigue du colon antérieurement sain, survenant en l’absence de lésion obstructive. Des circonstances pathologiques comme les brûlures, une médication neuroleptique ont été reconnues comme prédisposantes. En réanimation des brûlés, l’incidence de cette complication digestive varie de 0,5 à 1%. Le but de notre travail est de rappeler à travers deux cas de pseudo-obstruction aiguë du côlon (syndrôme d'Ogilvie) chez des patients atteints de brûlures étendues, les données cliniques et paracliniques de ce syndrome, ses bases physiopathologiques, ainsi que sa prise en charge thérapeutique. Le tableau clinique était caractéristique chez nos deux patients : météorisme abdominal important. Le scanner abdominal a montré une énorme dilatation colique sans obstacles mécaniques L'évolution a été défavorable chez notre premier patient et favorable chez le deuxième patient après une exsufflation colonoscopique. Le syndrome d'OGILVIE est une éventualité rare, qui peut conduire, sans traitement efficace, à la perforation cæcale au pronostic péjoratif. Il est donc nécessaire d'établir le diagnostic précocement et surtout de réaliser une surveillance radiologique stricte après la mise en place d'un traitement médical, dans lequel la colonoscopie constitue un apport précieux

Enhancements on hybrid coordination function controlled channel access for video transmission in IEEE 802.11E network

The rapid advancement in wireless technologies and the reduced cost in electronic hardware has stimulated the vast deployment of Wireless Local Area Networks (WLANs) in public and residential places. Nowadays, a wide range of multimedia traffics emerge in WLANs with different Quality of Service (QoS) requirements. In order to support multimedia traffics with stringent requirements, IEEE 802.11e introduced HCF Controlled Channel Access (HCCA). In HCCA, Transmission Opportunity (TXOP) duration is allocated to the QoSenabled Station (QSTA) based on the mean characteristics of its Traffic Stream (TS) described by a TS Specification (TSPEC). Although HCCA operates well for the Constant Bit Rate (CBR) traffics, it is inadequate for Variable Bit Rate (VBR) traffic, where the instantaneous sending rate and the packet size are usually different from its mean values. The aim of this research is to address the deficiency of HCCA in supporting VBR video transmission over wireless networks. Accordingly, a novel polling scheme called Feasible Polling (F-Poll) is proposed to minimize the delay imposed by overpolling stations in the HCCA function. The actual arrival time of the next frame of the uplink TS is obtained and reported to the central scheduler called Hybrid Coordinator (HC). Upon the reception of the data frame at the HC, a decision will be made to poll the corresponding station in the next Service Interval (SI) or not to prevent stations that are not ready to transmit from receiving unnecessary polls. Consequently, the packet access delay and the channel utilization will be enhanced. The TXOP in HCCA scheduler is allocated to the QSTA based on its TSPEC by estimating the amount of data expected to be transmitted by the QSTA during the service interval. Yet, this estimation is not accurate for VBR traffics. Thus, a novel TXOP assignment scheme is proposed which is referred to as Adaptive TXOP Scheme (ATXOP). In this scheme, the TXOP duration is adopted based on the feedback of the actual next frame size reported by QSTAs. So, an accurate TXOP is allocated to the station to ensure that the end-to-end delay is minimized without jeopardizing the channel bandwidth. To leverage the benefit of the ATXOP, a multi-polling scheme has been integrated and named Adaptive Multipolling TXOP Scheme (AMTXOP). Moreover, a new approach incorporating the polling scheme and the TXOP assignment of HCCA scheduler has been presented called Adaptive Feedbackbased HCCA Scheduler (AF-HCCA). The AF-HCCA accommodates to the video applications that show variability in both frame inter-arrival time and frame size, such as H.263 streams. The proposed scheme, accurately assigns TXOP duration time for each traffic stream which is just enough to send their data. Moreover, it only polls QSTAs when needed to minimize the delay and conserve the bandwidth channel. The findings demonstrate that F-Poll is a promising scheme for supporting video streams with a different variability level of frame inter-arrival time while ATXOP scheme and its enhanced version, namely AMTXOP is beneficial for video streams that show variability in packet sizes such as H.264 streams. The integrated scheme shows further improvements for VBR video streams. The results show that F-Poll, ATXOP and AMTXOP schemes outperform the HCCA polling and TXOP assignment schemes in terms of the end-to-end delay and the channel bandwidth utilization while maintaining the system throughput. Moreover, the AF-HCCA shows superior improving in the packet end-to-end delay and remarkably minimize the polling overhead compared to not only the HCCA scheduler, but also to one of the recent enhancement of HCCA scheduler called Enhanced Earliest Due Date (EDD) scheduler