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Description:
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The increasing demand for real -time multimedia applications and the lack
of quality of service (QoS ) support in public best -effort or Internet Protocol (IP )
networks has prompted many researchers to propose improvements on the QoS of such
networks . This research aims to improve the QoS of real -time multimedia applications
in public best -effort networks , without modifying the core network infrastructure or
the existing codecs of the original media applications .
A source buffering control is studied based on a fluid model developed for a single
flow transported over a best -effort network while allowing for flow reversal . It is shown
that this control is effective for QoS improvement only when there is sufficient flow
reversal or packet reordering in the network .
An alternate control strategy based on predictive multi -path switching is studied
where only two paths are considered as alternate options . Initially , an emulation study
is performed , exploring the impact of path loss rate and traffic delay signal frequency
content on the proposed control . The study reveals that this control strategy provides
the best QoS improvement when the average comprehensive loss rates of the two paths
involved are between 5 % and 15 % , and when the delay signal frequency content is
around 0 .5 Hz . Linear and nonlinear predictors are developed using actual network
data for use in predictive multi -path switching control . The control results show
that predictive path switching is better than no path switching , yet no one predictor developed is best for all cases studied . A voting based control strategy is proposed
to overcome this problem . The results show that the voting based control strategy
results in better performance for all cases studied . An actual voice quality test is
performed , proving that predictive path switching is better than no path switching .
Despite the improvements obtained , predictive path switching control has some
scalability problems and other shortcomings that require further investigation . If
there are more paths available to choose from , the increasing overhead in probing
traffic might become unacceptable . Further , if most of the VoIP flows on the Internet
use this control strategy , then the conclusions of this research might be different ,
requiring modifications to the proposed approach . Further studies on these problems
are needed . |