Evaluation of Joint Admission Control and VoIP Codec Selection Policies in Generic Multirate Wireless Networks
Multirate wireless networks in general share a common problem for the transmission of VoIP traffic, since the rate changes of some of the flows affect the transmission of all others, which causes an unacceptable voice quality degradation. In this work, an admission control algorithm is combined with a codec selection block to mitigate this negative effect. This centralized admission control is able to block or drop calls in order to maintain the system stability despite rate changes. Moreover, the integrated codec selection block is able to select the most adequate VoIP codec for each incoming or already active call based on the channel rate used and according to a number of optimization policies. Several such policies are designed and evaluated in this paper. Results show that this combined adaptive solution provides a beneficial trade-off among the performances of the different codecs in terms of MOS, blocking and dropping probability and cell resource usage. Furthermore, a number of interesting singularities deriving from the multirate nature of the network are identified.
KeywordsVoIP codecs Mobile Networks Multiple channel transmission rates WLANs
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