ESSENTIAL BACKGROUND
ON-DEMAND SERVICE TYPES
1. Pay-Per-View (PPV) Service
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simplest type, analogous to existing PPV channels
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time of access for multimedia documents is decided by the
server rather than the client
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the server multicasts the program at fixed times and any
interested clients tune in to the server at these fixed times
2. Near Video-on-Demand (NVD)
(fig. 10-4)
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sometimes called: Shared Viewing with
Constraints
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motivation: observation that for certain applications, such
as on-demand movies, request arrivals exhibit significant temporal and
spatial locality
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the client accesses the multimedia documents at any time
it decides by sending a request to the MOD server. The server processes
and accepts these requests in groups to exploit any clustering properties
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the client can face admission latency after which it becomes
part of a group, all members of which are using the same connection
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advantage: the client can access data at any time
instance
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disadvantage: difficult to implement for applications
that
don't exhibit clustering properties
3. True Multimedia-On-Demand
(TMOD)
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each access request from clients is treated independently
at the server
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advantage: personalized, interactive multimedia
delivery
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disadvantage: serious implications in
throughput