Haobo Yu

Advances in network simulation

Network researchers must test Internet protocols under varied conditions to determine whether they are robust and reliable. The paper discusses the Virtual Inter Network Testbed (VINT) project which has enhanced its network simulator and related software to provide several practical innovations that broaden the conditions under which researchers can evaluate network protocols.

Multimedia proxy caching mechanism for quality adaptive streaming applications in the Internet

The Internet has witnessed a rapid growth in deployment of Web-based streaming applications during recent years. In these applications, the server should be able to perform end-to-end congestion control and quality adaptation to match the delivered stream quality to the average available bandwidth. Thus the delivered quality is limited by the bottleneck bandwidth on the path to the client. This paper proposes a proxy caching mechanism for layered-encoded multimedia streams in the Internet to maximize the delivered quality of popular streams to interested clients. The main challenge is to replay a quality-variable cached stream while performing quality adaptation effectively in response to the variations in available bandwidth. We present a prefetching mechanism to support higher quality cached streams during subsequent playbacks and improve the quality of the cached stream with its popularity. We exploit inherent properties of multimedia streams to extend the semantics of popularity and capture both level of interest among clients and usefulness of a layer in the cache. We devise a fine-grain replacement algorithm suited for layered-encoded streams. Our simulation results show that the interaction between the replacement algorithm and prefetching mechanism causes the state of the cache to converge to an efficient state such that the quality of a cached stream is proportional to its popularity, and the variations in quality of a cached stream are inversely proportional to its popularity. This implies that after serving several requests for a stream, the proxy can effectively hide low bandwidth paths to the original server from interested clients.

Network visualization with Nam, the VINT network animator

Network protocol designers face many difficult tasks, including simultaneously monitoring state in a potentially large number of nodes, understanding and analyzing complex message exchanges, and characterizing dynamic interactions with competing traffic. Traditionally they have used packet traces to accomplish these tasks, but traces have two major drawbacks: they present an incredible amount of detail, which challenges the designers ability to comprehend the data; and they are static, which hides an important dimension of protocol behavior. As a result, detailed analysis frequently becomes tedious and error-prone. Although network simulators such as the VINT projects ns can easily generate numerous detailed traces, they provide limited help for analyzing and understanding the data. Nam, the network animator that we developed in our work at the VINT project, provides packet-level animation, protocol graphs, traditional time-event plots of protocol actions, and scenario editing capabilities. Nam benefits from a close relationship with ns, which can collect detailed protocol information from a simulation. With some preprocessing. Nam can visualize data taken directly from real network traces.