In the 802.11b networks, the guarantee of an equal long-run channel access probability causes performance anomaly in a multi-rate wireless cell. Much interest has been involved in this issue and many effective mechani...In the 802.11b networks, the guarantee of an equal long-run channel access probability causes performance anomaly in a multi-rate wireless cell. Much interest has been involved in this issue and many effective mechanisms have been proposed. The usual MAC layer solutions include the initial contention window adaptation, the maximum transfer unit size adaptation and the packet bursting. In this paper, we propose a novel approach which introduces a new parameter called the transmission prob- ability pt to the legacy protocol. By adjusting pt according to the transmission rate, the proposed scheme can solve the performance anomaly problem cleanly. Throughput analysis and performance evaluation show that our scheme achieves significant im- provement in the aggregate throughput and the fairness.展开更多
When wireless hosts use different rates to transmit data in IEEE 802.11 networks, it will take on the state of performance anomaly which will severely decrease the throughputs of all the higher rate hosts. Hence, it i...When wireless hosts use different rates to transmit data in IEEE 802.11 networks, it will take on the state of performance anomaly which will severely decrease the throughputs of all the higher rate hosts. Hence, it is bad for video service transmission. Considering that video is very sensitive to packet delivery delay but can tolerate some packet losses, we propose a novel cross-layer scheme which takes these two characteristics into consideration. Firstly, the maximum number of retransmissions for a video Medium Access Control (MAC) frame is computed in MAC layer according to video frame rate requirement of application layer and current access delay of MAC layer. Secondly, within the margin of the tolerant Packet Loss Rate (PLR) of application layer, several video MAC frames are allowed to drop so that we can adaptively select the transmission rate as high as possible for the rest of video MAC frames in terms of current channel quality and the maximum number of retransmissions. Experiment results show that the proposed method can reduce the delay and jitter of video service and improve the throughputs of fast hosts. Therefore, it increases the quality of reconstructed video to a certain extent and relieves the performance anomaly of network effectively.展开更多
The growing scale and complexity of component interactions in cloud computing systems post great challenges for operators to understand the characteristics of system performance. Profiling has long been proved to be a...The growing scale and complexity of component interactions in cloud computing systems post great challenges for operators to understand the characteristics of system performance. Profiling has long been proved to be an effective approach to performance analysis; however, existing approaches confront new challenges that emerge in cloud computing systems. First, the efficiency of the profiling becomes of critical concern; second, service-oriented profiling should be considered to support separation-of-concerns performance analysis. To address the above issues, in this paper, we present P-Tracer, an online performance profiling tool specifically tailored for cloud computing systems. P-Tracer constructs a specific search engine that proactively processes performance logs and generates a particular index for fast queries; second, for each service, P-Tracer retrieves a statistical insight of performance characteristics from multi-dimensions and provides operators with a suite of web-based interfaces to query the critical information. We evaluate P- Tracer in the aspects of tracing overheads, data preprocessing scalability and querying efficiency. Three real-world case studies that happened in Alibaba cloud computing platform demonstrate that P-Tracer can help operators understand soft-ware behaviors and localize the primary causes of performance anomalies effectively and efficiently.展开更多
基金Project supported by the National Mid- and Small-Scale EnterpriseTechnical Innovation Fund of China (No. 06C26225101730)the Sichuan Provincial Key Science and Technology Program, China (No. 05GG021-003-2)
文摘In the 802.11b networks, the guarantee of an equal long-run channel access probability causes performance anomaly in a multi-rate wireless cell. Much interest has been involved in this issue and many effective mechanisms have been proposed. The usual MAC layer solutions include the initial contention window adaptation, the maximum transfer unit size adaptation and the packet bursting. In this paper, we propose a novel approach which introduces a new parameter called the transmission prob- ability pt to the legacy protocol. By adjusting pt according to the transmission rate, the proposed scheme can solve the performance anomaly problem cleanly. Throughput analysis and performance evaluation show that our scheme achieves significant im- provement in the aggregate throughput and the fairness.
基金Supported by the National Natural Science Foundation of China(No.61071091,No.60802021)the Research and Innovation Program for University Postgraduates of Jiangsu Province(CX10B_188Z)
文摘When wireless hosts use different rates to transmit data in IEEE 802.11 networks, it will take on the state of performance anomaly which will severely decrease the throughputs of all the higher rate hosts. Hence, it is bad for video service transmission. Considering that video is very sensitive to packet delivery delay but can tolerate some packet losses, we propose a novel cross-layer scheme which takes these two characteristics into consideration. Firstly, the maximum number of retransmissions for a video Medium Access Control (MAC) frame is computed in MAC layer according to video frame rate requirement of application layer and current access delay of MAC layer. Secondly, within the margin of the tolerant Packet Loss Rate (PLR) of application layer, several video MAC frames are allowed to drop so that we can adaptively select the transmission rate as high as possible for the rest of video MAC frames in terms of current channel quality and the maximum number of retransmissions. Experiment results show that the proposed method can reduce the delay and jitter of video service and improve the throughputs of fast hosts. Therefore, it increases the quality of reconstructed video to a certain extent and relieves the performance anomaly of network effectively.
基金This research was supported by the National Basic Research Program of China （2011CB302600）, the National High Technology Research and Development Program of China （2012AA011201）, the National Natural Science Foundation of China （Grant Nos. 61161160565, 90818028, 91118008, 60903043）, and an NSFC/RGC Joint Research Scheme sponsored by the Research Grants Council of Hong Kong, China and National Natural Science Foundation of China Project （JC201104220300A）.
文摘The growing scale and complexity of component interactions in cloud computing systems post great challenges for operators to understand the characteristics of system performance. Profiling has long been proved to be an effective approach to performance analysis; however, existing approaches confront new challenges that emerge in cloud computing systems. First, the efficiency of the profiling becomes of critical concern; second, service-oriented profiling should be considered to support separation-of-concerns performance analysis. To address the above issues, in this paper, we present P-Tracer, an online performance profiling tool specifically tailored for cloud computing systems. P-Tracer constructs a specific search engine that proactively processes performance logs and generates a particular index for fast queries; second, for each service, P-Tracer retrieves a statistical insight of performance characteristics from multi-dimensions and provides operators with a suite of web-based interfaces to query the critical information. We evaluate P- Tracer in the aspects of tracing overheads, data preprocessing scalability and querying efficiency. Three real-world case studies that happened in Alibaba cloud computing platform demonstrate that P-Tracer can help operators understand soft-ware behaviors and localize the primary causes of performance anomalies effectively and efficiently.
