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Long Duration Continuous Media Retrieval

servers server msrs service

Definition: Pool of servers can be used to retrieve very long duration movies.

A central issue in the design networked/distributed multimedia services or DMMS is in addressing how to retrieve and transmit compressed-format videos (e.g., movies) from the server sites to the clients using the underlying network without under-utilizing the resources (e.g., storage of disk and memory, bandwidth of disk and network, etc.). Single-server systems fail obviously with an increase in the user access rates and also the network bandwidth becomes a natural bottleneck, especially for a DMMS type. A decentralized (or distributed) approach would rather handle this increased access rates more elegantly, a typical of a requirement on Internet like networks. As opposed to the idea of employing a single server, multiple servers can be employed for retrieval. This strategy is referred to as Multiple Server Retrieval Strategy (MSRS). In MSRS, several servers retrieve disjoint portions of a movie (taking into account the server and link bandwidths) in a particular sequence to form one complete continuous stream for the user. This novel idea of employing a pool of servers to retrieve is more meaningful for very long duration movies (110 to 140 minutes).

Some inherent advantages of MSRS: on a DMMS environment, if a single server system, however sophisticated it may be (in terms of speed and capacity) is used there is a continuous “work pressure” that is enforced on the system. For instance, when there is a continuous demand for a long duration video retrieval by several clients, more than 80% of the time is spent in servicing these requests, while some small number of requests demanding short services may undergo long waiting times. By employing MSRS, the work pressure can be balanced among the servers. Secondly, even low-bandwidth servers, that may not be efficient to utilize, can now be a part of several servers in retrieving the movie. Thirdly, considering fault-tolerance aspects, even under server/link failures, the workload imbalance can be gracefully accounted by the remaining servers. Also, failure of one or more servers, will allow the service to continue without any interruption so long as there is at least one server to cater. In fact, with a clever design of a retrieval strategy, the clients will continue to view the presentation while certain number of servers may “die” and come back to “life” after some time. Also, as shown in some feasible studies, scalability and heterogeneity of the system can be easily accounted in the design. Fourthly, the service providers can use a mix of heterogeneous servers to offer this service, as server bandwidths are inherently considered in servicing a request. Finally, from SP’s perspective, since each server, on the whole, is engaged only for a short while in retrieving a portion of the media document, the number of clients that can be entertained simultaneously can be maximized. Thus MSRS offers a clear win-win situation for both the customers and the service providers.

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