COPACC: An Architecture of Cooperative

Proxy caching is a key technique to reduce transmission cost for on-demand multimedia streaming. The
effectiveness of current caching schemes, however, is limited by the insufcient storage space and weak cooperations
among proxies and their clients, particularly considering the high bandwidth demands from media objects. In this
paper, we propose COPACC, a cooperative proxy-and-client caching system that addresses the above deciencies.
This innovative approach combines the advantages of both proxy caching and peer-to-peer client communications.
It leverages the client-side caching to amplify the aggregated cache space and rely on dedicated proxies to
effectively coordinate the communications. We propose a comprehensive suite of distributed protocols to facilitate
the interactions among different network entities in COPACC. It also realizes a smart and cost-effective cache
indexing, searching, and verifying scheme. Furthermore, we develop an efcient cache allocation algorithm for
distributing video segments among the proxies and clients. The algorithm not only minimizes the aggregated
transmission cost of the whole system, but also accommodates heterogeneous computation and storage constraints
of proxies and clients. We have extensively evaluated the performance of COPACC under various network and endsystem
congurations. The results demonstrate that it achieves remarkably lower transmission cost as compared to
pure proxy-based caching with limited storage space. On the other hand, it is much more robust than a pure peerto-
peer communication system in the presence of node failures. Meanwhile, its computation and control overheads
are both kept in low levels.
Keywords: Media Streaming, Proxy caching, Peer-to-Peer caching, Media segmentat ion and Resource allocation
I. Introduction
For the past few years, we have witnessed the increasingly used streaming multimedia trafc on the
Internet, and on-demand streaming for clients of asynchronous playback requests is amongst the most
popular networked media services. Given its broad spectrum of applications, like NetTV and distance

Alan