Jingping Bi

On Characterizing PPStream: Measurement and Analysis of P2P IPTV under Large-Scale Broadcasting

Despite the recent and remarkable popularity of P2P IPTV systems, the study of their characteristics on largescale broadcasting is rare. In this paper, we have undertaken a measurement study on one of the most popular P2P IPTV systems, PPStream, during the 29th Olympics broadcasting. We deployed our dedicated measurement tool, PPS-Sniffer, under different network environments, and collected extensive data during a large number of events. We evaluate the playback delay, and the peering strategies towards local cluster. We also investigate the data scheduling, and its impact on the playback quality and the control overhead. To the best of our knowledge, results obtained in our study are unique and new as compared with existing work. Specifically, our study demonstrates that: 1.) The playback delay is notable in Olympic channels, even for close peers. 2.) Peering strategies of PPStream target mainly on the ISP level, and should exploit peers of local clusters to reduce the playback lag among close peers. 3.) We unveil an overhead-quality tradeoff that sheds light on the design of future systems that can achieve a good balance. Our study aids the understanding of significant performance and design issues of PPStream, and is also useful for optimizing, modeling and the future design of P2P IPTV systems.

On estimating clock skew for one-way measurements

Owning to the asymmetry of Internet paths, more and more studies have turned to the measurement of one-way metrics. Since the clocks at end systems often behave diversely, the synchronization between end hosts is what we care about all along. In this paper, we firstly propose a general model for clock skew estimation in one-way measurements, which turns the problem of clock skew estimation to the solution of n-dimension equation group, and give the equation group needed based on different presumptions. We then present Piece-wise Reliable Clock Skew Estimation Algorithm (PRCSEA), which introduces reliability test to estimation results and eliminates the extra presumptions needed by other algorithms, such as only one clock adjustment in the measurements. PRCSEA solves the skew estimation problem in a heuristic way, and it can handle many special cases affecting the estimation of clock skew, such as routing change, clock hiccup and network congestion. PRCSEA is the only algorithm that can handle clock drift to the best of our knowledge.

Adaptive nodes scheduling approach for clustered sensor networks

Energy efficiency is an important issue in wireless sensor networks. One available power saving strategy is having only a portion of nodes work, but this would always compromise data quality as a result. In this paper, we propose an adaptive nodes scheduling approach (ADNS) to conserve energy while maintaining the overall data quality. ADNS selects a subset of nodes to be active and puts the others into sleep mode to save energy. An efficient active node selection (ANS) algorithm is presented. Using the spatial correlation among sensor readings as the prediction model, the values of sleep nodes are predicted by data collected from active nodes to ensure the data quality. In order to maintain the data quality throughout network operation, the prediction errors are validated timely and prediction models are adaptively reconstructed if necessary. We evaluate ADNS on a real-world sensor network data set and validate its effectiveness.

Packet delay and packet loss in the Internet

The distribution characteristic of RTT (round-trip time) is an important part of Internet end-to-end behavior characteristics. People have made lots of studies of it, but many conclusions only adapt to the cases of small packet loss rate. We study the RTT characteristics on nearly 40 end-to-end paths in CSTNET and CERNET in China, and draw the following conclusions: (1) the distribution characteristics of RTT and loss rate are dependable; (2) when loss rate is small, RTT distribution is usually unimodal, but with the increase of loss rate, RTT distribution is no longer unimodal and it becomes more and more decentralized; (3) with the increase of loss rate, the occurring times of inherent RTT tend to decrease.

Data-Coverage Sleep Scheduling in Wireless Sensor Networks

Data samples sensed from a densely deployed sensor network often exhibit strong spatial and temporal correlation. Sampling and transmitting these highly correlated data through wireless channel would result in excessive energy consumption. One way to conserve energy is to set a portion of sensors into sleep mode provided their missing data can be well recovered by sensors that remain active. Different from traditional full area coverage sleep scheduling schemes, we propose a data-coverage scheme based on the ability of active nodes to recover the missing data of sleeping nodes. For this purpose, we present the scheme to extract correlation among sensing data of nodes. We also propose the greedy reduction algorithm (GRA) to select the set of active sensors. The missing data of sleeping nodes is recovered using active nodespsila sensing data as well as the correlation among data of nodes. Using a publicly released sensing data set, we analyze how to implement this data-coverage sleep scheduling scheme. We also evaluate its performance and conduct comparison experiments with the full area coverage scheme. Experimental results indicate that the data-coverage sleep scheduling scheme offers superior performance.

DSRelay: A scheme of cooperative downloading based on dynamic slot

Peoples growing dependency on the Internet makes them want to access the network anytime and anywhere, even while driving cars. Although 3G or 4G networks can be used to achieve this goal, roadside APs have the advantages of low cost and high bandwidth. At present, however, APs cannot cover all the areas, which cause intermittent connectivity. In this paper, we propose the DSRelay, a scheme of cooperative downloading. Unlike some studies that multiple cars download files from the Internet and different cars deliver different blocks of files like a P2P network, our work concentrates on the request of downloading respectively. Making use of the characters of the limited communication range of WIFI network, DSRelay schedules the Dark Areas (DA) out of AP coverage areas. If a mobile client leaves an AP coverage area without finishing its downloading, using the proposed scheme, APs calculate meeting time and communication duration between client car and other registered cars, and choose a series of cars to carry data client needed so that the data can be transmitted to it at different slot in DA. Also, we analyze the influence of change of car speed and a corresponding solution is presented. This scheme utilizes DAs for extending the downloading areas of the client as much as possible. Simulation results indicate the benefits of the proposed scheme in terms of increasing throughput and reducing delay.

A compensation model of cooperative downloading for vehicular network

The ever growing dependence on the Internet makes people keen on accessing the network anytime and anywhere, even while driving cars. Cooperative downloading among vehicles could help the clients obtain more data when running out of access point coverage area. One of the methods is that the access point predicts communication duration between the helper and the client according to the registered speed of vehicles to decide how many packets should be carried by the helper. However, it is possible that cooperative vehicles cannot always transmit all of the carried data to the client due to the changing speed. A key challenge that lies at the heart of this problem is how to increase the packet transmitting rate of cooperative vehicles. Towards the end, this paper proposes a novel compensation model that exploits nodes own regulatory function to mitigate the packet transmission loss. By analysing a real speed dataset collected from a test car with global positioning system running from May 2011 to July 2012 on the No. G15 highway in China, we derive a strong spatiotemporal regularity in vehicle speeds. Impending speed can be predicted, therefore, using Markov chain. On the basis of the aforementioned quantitative prediction, the compensation schemes is presented to increase received data amount by using the characteristics of encountering, overtaking and being overtaken among vehicles. Simulation results indicate the benefits of the proposed model in terms of increasing throughput and reducing delay. Copyright

PPStream characterization: Measurement of P2P live streaming during Olympics

P2P streaming technique is spreading widely and the study of its characteristics on large-scale broadcasting is meaningful and important. In this paper, we have undertaken a measurement on one of the most popular P2P IPTV systems, PPStream, during the 29th Beijing Olympics. We collected extensive data traces under different network environments. New and unique observations are presented in our study as compared with existing measurements. Specifically, our results show that 1.) The playback delay is more remarkable in Olympics channels; 2.) Parent overlap is extremely small even for peers very nearby; 3.) The change of buffering fluctuates periodically in both Olympic and ordinary channels; 4.) Smaller scheduling unit is employed in Olympic channels with potential inefficiency. Measurement results obtained in our study bring to light significant performance and design issues of P2P live streaming systems during large-scale broadcasting, and are valuable in better understanding, optimizing and modeling of such systems.

Experiment and analysis of active measurement for packet delay dynamics

Active measurements have formed the basis for much of our empirical efforts to understand Internet packet delay dynamics. Packet-average performance of user flow is getting more and more important for users, and especially for network service providers. But in network active measurement area, there are not empirical efforts to investigate the performance of active measurement for packet performance from users standpoint. We quantitatively assess and compare the one-way delay statistics experienced by user flow and active probe flow based on simulation experiments, and find that: (1) Active measurement systematically underestimates statistics of packet delay experienced by user flow and the estimation error is far severe than can be ignored. (2) Increasing sampling frequency is almost helpless for the reducing of the estimation error. (3)The estimation error degrees of active measurement decrease as the increasing of the queue utilization. The above conclusions are based on active measurements using Poisson sampling and Periodic sampling. As they are mainly used sampling methods in active measurement area, so our conclusions indicate that current active method for measuring Internet packet delay suffer from system errors from users standpoint.

Reliable Clock Skew Estimation Algorithm for one-way measurements

Owing to the asymmetry of Internet paths, more and more studies have turned to the measurement for one-way metrics. However, since the clocks at end systems often behave diversely, the synchronization between the end hosts is what we care about all along. In this paper, we firstly propose a general model for clock skew estimation in one-way measurements, which turns the problem of clock skew estimation to the solution of n-dimension equation group, and give the equation group what it needs based on different presumptions. We then present a Piece-wise Reliable Clock Skew Estimation Algorithm (PRCSEA), which introduces the reliability test of estimation results and eliminates the extra presumptions needed by other algorithms, such as only one clock adjustment in the measurements. PRCSEA solves the skew estimation problem in a heuristic way, and it can handle many special cases affecting the estimation of clock skew, such as routing change, clock hiccup and network congestion. PRCSEA is the only algorithm that can handle non-constant clock skew to the best of our knowledge. The time complexity of PRCSEA is O(n*logn), which is the same as that of Paxsons algorithm.