  A VoIP based call has stringent QoS requirements with respect to delay,
jitter, loss, MOS and R-Factor. Various QoS mechanisms implemented to satisfy
these requirements must be adaptive under diverse network scenarios and applied
in proper sequence, otherwise they may conflict with each other. The objective
of this paper is to address the problem of adaptive QoS maintenance and
sequential execution of available QoS implementation mechanisms with respect to
VoIP under varying network conditions. In this paper, we generalize this
problem as state-space problem and solve it. Firstly, we map the problem of QoS
optimization into state-space domain and apply incremental heuristic search. We
implement the proposed algorithm under various network and user scenarios in a
VoIP test-bed for QoS enhancement. Then learning strategy is implemented for
refinement of knowledge base to improve the performance of call quality over
time. Finally, we discuss the advantages and uniqueness of our approach.
