To provide application-oriented network services, a variety of overlay networks are deployed over physical IP networks. Since they share and compete for the same physical network resources, their selfish behaviors affect each other and, as a result, their performance deteriorates. In this paper, we propose a mechanism for pureP2P networks of file-sharing applications to cooperate with each other. In our proposal, a cooperative peer first finds another P2P network and establishes a logical link to a cooperative peer in the found network. Both ends of the logical link decide whether they cooperate or not from a viewpoint of the mutualism. When they consider they benefit from the cooperation, messages and files are exchanged among cooperative P2P networks through the logical link. For an efficient and effective cooperation, our mechanism has an algorithm for the selection of cooperative peers and a caching mechanism to avoid putting too much load on cooperative peers and
cooperating networks. Simulation results showed that the number of discovered providing peers and the ratio of search hits increased about twice, while the load by the cooperation among P2P networks was reduced about half by caching.
The proxy mechanism widely used in WWW systems offers low-delay and scalable delivery of data by means of a "proxy server". By applying proxy mechanism to video streaming systems, high-quality and low-delay video distribution can be accomplished without imposing extra load on the system. We have proposed proxy caching mechanisms to accomplish the high-quality and highly-interactive video streaming services. In our proposed mechanisms, proxies communicate with each other, retrieve a missing video data from an appropriate server by taking into account transfer delay and offerable quality. In addition, the quality of cached video data can be adapted appropriately in the proxy to cope with the client-to-client heterogeneity, in terms of the available bandwidth, end-system performance, and user preferences on the perceived video quality. In this paper, to verify the practicality of our mechanisms, we implemented them on a real system for MPEG-4 video streaming services, and conducted experiments. Through evaluations, it was shown that our proxy caching system can provide users with a continuous and high-quality video distribution in accordance with network condition.
In this paper, we investigate mechanisms for the video streaming system where proxies cooperate to provide users with low-latency and high-quality services under heterogeneous and mobile environment where hosts have different capabilities and dynamically change their locations. The proxy is capable of adapting incoming or cached video data to user's demand by means of transcoders and filters. With such proxies, heterogeneous QoS requirements on the delivered stream can be fully satisfied by preparing high-quality video data in the local cache buffer and adjust them to the requirements. On receiving a request from a user, the proxy first checks the cache. If no
appropriate data is available, it retrieves the video data of the satisfactory quality from the video server or proxies nearby. The proxy communicates with the others and finds an appropriate one for data retrieval by taking into account the transfer delay and the video quality. We propose a cooperative video caching mechanism for the video streaming system and evaluate the performance in terms of the delay introduced and the video quality.
The proxy mechanisms widely used in WWW systems offer low-delay data delivery by a means of ``proxy server''. By applying the proxy mechanism to the video transfer, we expect a real-time and interactive video streaming without introducing extra load on the system. In addition, if the proxy appropriately adjusts the quality of cached video data to the user's demand, video streams can be delivered to users considering their heterogeneous QoS requirements. In this paper, we propose proxy caching mechanisms that can achieve a high-quality video transfer considering the user's demand and the available bandwidth. In our system, a video stream is divided into pieces. The proxy caches them in local buffer, adjusts their quality if necessary, transmits them to users, replaces them with cached data, and retrieves them from the video server, considering user's requirement. We evaluate the proposed video caching mechanisms and compare their performance in terms of the required buffer size, the play-out delay and the video quality. Consequently, the validity of the video quality adjustment in the proxy is confirmed.
When both TCP and UDP connections co-exist in the Internet environment, the performance of TCP connections is heavily affected by the behavior of `greedy' UDP connections of real-time multimedia applications. In this paper, we propose a new TCP-friendly rate control protocol for video connections, called MPEG-TFRCP, to fairly share the link with TCP connections. To achieve fairness among TCP and UDP connections while performing high quality video transmission, we argue that (1) the interval of rate control must be appropriately determined, (2) the network condition must be accurately predicted, (3) the TCP throughput must be precisely estimated and (4) the video rate must be effectively adjusted. Although our algorithm is based on the existing proposals which do not satisfy all of those conditions, through careful considerations ont he applicability of TFRCP to the actual video applications ours can achieve the high-quality MPEG-2 video transfer while satisfying the TCP-friendliness. Through simulation experiments, we show that the TCP throughput estimation based on pseudo-TCP feedback collection is acceptable and the rate adjustment base don the quantization control should be performed at the interval of 32 times as long as estimated RTT.