 the delay. However, with careful design of the system, RT services can be efficiently trans- ported over time-shared channels as well. A potential advantage of transmission speech on a channel previously designed for data traffic is the improved efficiency in terms of resource sharing, spectrum usage, provision of multimedia services, and network architecture. The challenge is to port VoIP services on wireless networks while retaining the QoS of circuit-switched networks and the inherent flexibility of IP-based services. Long term evolution of 3GPP work targeting to release 8 is defining a new packet-only wideband radio-access technology with flat architecture aiming to develop a framework toward a high-data-rate, low-latency, and packet-optimized radio access technology called E-UTRAN (evolved universal terrestrial radio access network). Its air interface is based on OFDMA for downlink (DL) and SC-FDMA for uplink (UL). Because E-UTRAN is purely packet-switched radio access tech- nology, it does not support CS voice at all, stressing the importance of efficient VoIP traffic support in E-UTRAN. However, supporting VoIP in E-UTRAN faces the very same challenges as those for any other radio access technology: (1) the tight delay requirement and intolerable scheduling overhead combined with the frequent arrival of small VoIP packets and (2) the scarcity of radio resources along with control channel restriction. Thus, designing effective solutions to meet the stringent QoS requirements such as packet delay and packet loss rate (PLR) of VoIP in E-UTRAN is crucial. Chapter 10 ("Radio Access Network VoIP Optimization and Performance on 3GPP HSPA/LTE") aims to give an overview of the challenges faced in implement- ing VoIP service over PS cellular networks, in particular 3GPP HSPA and LTE. © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology Generally accepted solutions leading to an efficient overall VoIP concept are out- lined, and the performance impact of various aspects o