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U. Glaeser

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CAC<br />

Schemes have been proposed to address the problem of resource allocation for multimedia traffic support<br />

in microcellular networks. In these schemes, real-time traffic being more delay sensitive, is given priority<br />

over non-real-time traffic.<br />

In these schemes, the central approach used is call admission control (CAC). CAC imposes a limit on<br />

the number of calls accepted into the network. Each cell site only supports a predetermined number of<br />

call connections. This call threshold is periodically calculated depending on the number of existing calls<br />

in the cell in which the call arrives and its adjoining cells and the resources utilized by all calls in the<br />

cell. Once the threshold is reached, all subsequent requests for new call connections are refused.<br />

AT<br />

In an admission threshold (AT)-based scheme, resource management is done by periodically calculating<br />

the admission threshold and by blocking all new call connection requests once the threshold is reached.<br />

The call admission decision is made in a distributed manner whereby each cell site makes a decision by<br />

exchanging state information with adjoining cells periodically. A cell with a base station and a control<br />

unit is referred to as cell site.<br />

RS<br />

In a resource sharing (RS)-based scheme to support traffic classes with different delay and error requirements,<br />

resource sharing provides a mechanism to ensure a different grade of service to each class of<br />

traffic. This scheme employs a resource sharing mechanism that reacts to rapidly changing traffic conditions<br />

in a cell. An adaptive call admission control policy that reacts to changing new call arrival rates<br />

can be used to keep the handoff dropping rate and forced call termination rate acceptably low.<br />

The call admission control scheme differentiates the new call on the basis of its traffic class and a<br />

decision is based on traffic class of the new call connection request and number of call connections of<br />

each class already being serviced in the cell cluster.<br />

For real-time call connections, a new call is blocked if no bandwidth is available to service the request.<br />

A similar algorithm is used to service a handoff request. The QoS metrics for real time calls are handoff<br />

dropping probability and forced call termination probability. For non-real-time calls, the available bandwidth<br />

is shared equally among all non-real-time call connections in the cell. Handoff queuing or delaying<br />

is not used in this scheme. CAC keeps the probability of a call being terminated before its lifetime<br />

acceptably low. Resource sharing algorithms provide better performance for a particular class of traffic.<br />

RRN<br />

Resource reservation and renegotiation (RRN) scheme provides QoS guarantee to real-time traffic and<br />

at the same time guarantees a better performance to non-real-time traffic. The resource allocation scheme<br />

uses resource reservation in surrounding cells for real-time calls and renegotiation of bandwidth assigned<br />

to non-real-time calls. The resource allocation scheme is simple enough and can be implemented in a<br />

distributed manner to ensure fast decision making.<br />

In RRN scheme, for service applications requiring smaller bandwidths, a shared pool of bandwidth is<br />

used for reservation. For applications requiring greater bandwidth, the largest of requested bandwidth<br />

is reserved. This helps in keeping the call blocking rate low and does not affect the handoff dropping rate.<br />

In microcellular networks, calls require handoffs at much faster rates in comparison to networks with<br />

larger cells. On the other hand, microcellular networks provide a higher system capacity. The RRN scheme<br />

supports real-time calls and non-real-time calls along with a variety of service type for each class. Realtime<br />

calls are delay sensitive and hence cannot be queued or delayed. Resources must be available when<br />

a handoff is requested. In order to guarantee that real-time calls are not forced to terminate at the time<br />

of handoff, a resource reservation mechanism is used. Resource reservation guarantees acceptably low<br />

handoff dropping rate and forced call termination rate for real-time traffic.<br />

For a real-time call, bandwidth is reserved in all cells adjacent to the cell in which the call arrives.<br />

When a call hands-off to another cell, if enough bandwidth is not available to service the handoff, it uses<br />

© 2002 by CRC Press LLC

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