A rate-controlled VoIP system based on Wireless Mesh Network infrastructure: Design issues and performance analysis

Wireless Mesh Networks (WMNs) are increasingly proposed as an economic and effective solution to easily delivering a large variety of services anytime anywhere. However, wireless communications suffer from some shortcomings which limit the use of real-time applications, especially VoIP applications. In fact, the effective available bandwidth can be, sometimes, too low to accept new calls, in addition to the ongoing ones, without the call quality becoming unacceptable. Moreover large delay variations and packet loss dramatically affect speech quality and speakers interactivity. This paper refers to a wireless mesh network scenario used to provide VoIP services to a group of buildings. Application of Automatic Repeat-reQuest (ARQ) to reduce losses due to the wireless link however causes high variability on the output transmission rate of the buffer in the multiplexer located in each building. So, to avoid buffer congestion, in this paper we propose an architecture where VoIP sources use Adaptive MultiRate encoder (AMR), in such a way that they can be controlled according to the state of the buffer queue in the multiplexer. To this end a new rate controller scheme is defined, and its performance is evaluated in order to achieve some hint to design its parameters.