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This paper develops simple cost models for provisioning content distribution networks that use the simple and highly scalable bandwidth skimming protocol for streaming. New insight is obtained into: (1) how cost-effective proxy servers are in multicast streaming systems; (2) the most effective streaming protocol; and (3) the optimal proxy content, as a function of the system configuration and workload. A key result is that proxy servers are only cost effective if: (a) the origin server does not have a multicast capability; or (b) the file request rate is low, and thus multicast is not highly effective; or (c) the cost of a proxy server stream is a very small fraction (i.e., approximately 1/P) of the cost of an origin server stream, where P is the number of proxy servers and the cost of either type of stream includes both the server and network resource costs. For cases where proxy servers are cost effective, results in the paper provide the optimal proxy content and the most effective streaming protocol, as a function of a wide range of system configuration and workload parameters. In contrast to previous work, full file caching outperforms prefix caching over a significant region of this system design space, due to more efficient multicast streaming protocols as well as a more complete exploration of the practical system configuration space.