A scalable scheme to access multimedia documents with quality of service guarantees

Abstract

This paper describes a scalable scheme, we call SAS, that allows users to access multimedia documents in a distributed system. SAS assumes a system which consists of a set of client machines, a set of server machines, and networks connecting these machines. Popular documents are replicated and stored on the servers; this replication is realistic and required since popular documents are accessed by most users. A user can ask to play a document with the desired quality of service (QoS) from any server; SAS allows to select the best server which is able to deliver the document to the user. This means that (1) this server stores the requested document; (2) has enough available resources to deliver the document with the desired QoS; preferably it is the least loaded server; and (3) there are enough network resources to support the transfer of the document from the server to the user. SAS consists of high level interactions between some management entities and thus may be applied to an arbitrary system with different types of commercial and research multimedia-on-demand servers; it is essentially independent of the technologies used to deliver multimedia data. SAS allows to minimize the blocking probability as much as possible; a user request is rejected only if all servers (storing the requested document) are loaded at maximum or the communication system is overloaded; it also allows to recover automatically, if this is possible, from QoS degradations during the presentation of the document. Last and not least, SAS allows to mask server failures.