admission

Admission Control

A compressed stream may require variable bandwidth or variable bit rate (VBR). Two different types of approaches may be used to tackle this problem:

	Allocate the maximum required bit rate. This approach is sometimes wasteful of available resources.
	Allocate the average bit rate. Partial data must be prefetched and put in buffers to absorb the variations in bit rate.

We choose the second approach in the design of our system. We design an admission phase during which an average bit rate for retrieving the stream will be allocated. To exploit the periodic nature of media streams, the service time is divided into rounds of fixed size.

Without loss of generality, let the duration of each round be fixed at t. The bandwidth allocation for disk resources uses the round-robin fashion. Consider a server s_i is servicing l_i client requests. Each round is thus dynamically divided into l_i slots for the l_i requests. Let b_mj be the average bandwidth rate required for stream m_j to be retrieved, h _kij be the allocation of the duration of a disk retrieval slot for stream m_j from server s_i in round r_k, and B^d_i be the total available disk bandwidth with server s_i. We must then have

and a new request for m_li+1 from s_i can then be admitted by server s_i to round r_h+1 for p rounds if, for all rounds r_k, where h+1 <= k <= h+p,

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