Selective Packet Prioritization forWireless Voice over IP

Abstract

Voice over IP (VoIP) has the potential to be integrated with other Internet applications to provide interactive multimedia communication services that are impossible (or at least very difficult) to deploy over the traditional circuit-switched wired and wireless networks. To fully exploit the benefit of service integration, it is necessary that VoIP services can be seamlessly provided with a good Quality-of-Service over several different network technologies. Due to their wide availability and significant user interest in mobile voice communications, particularly wireless network technologies will be crucial for the success of VoIP (and vice versa).
However, the legacy Internet architecture is based on the ”best effort” principle which does not guarantee a minimum amount of packet loss and a minimum delay of packet transmission required for voice communication. Considering a wireless access network to the Internet, QoS assurance is even more difficult. This is due to the inherently shared nature of the medium as well as its high medium error rate which add to the effect of congestion at routers known from wireline networks. In this paper we first analyze the concealment performance of the G.729 decoder as one prominent example of the CELP coder family which are typically employed for VoIP. Using this result, we then develop QoS support schemes which selectively mark packets to a higher (DiffServ) network priority at the sender dependent on the properties of the speech signal and the expected concealment performance. On the wireless access link the priorities are then mapped to a simple ARQ scheme. This layered approach is in full conformance with existing standards. Objective quality measures (ITU-T P.861A and EMBSD) show that almost the same speech quality as if all packets of the data stream would have been marked as eligible for retransmission can be achieved while significantly reducing the number of actual retransmissions.