 Layer Layer Node B Figure 3.11: Protocol stack of the IP-based UTRAN In addition, according to 3GPP TR 25.933 [3GP04a], the IP-based UTRAN can also apply multiplexing schemes in order to improve the transport efficiency by multiplexing several FP 3 UMTS Terrestrial Radio Access Network (UTRAN) PDU frames into one transport UDP/IP packet. The detailed introduction of these multiplexing schemes has been introduced in Chapter 2.3.4.1. 3.4.2 QoS Support in the IP-Based UTRAN Despite prominent technique advantages and low costs of deploying IP and Ethernet for the transport, the most important challenge of an IP-based UTRAN network is how to provide and differentiate the QoS for a wide range of diverse services with various QoS requirements. The QoS challenge is mainly associated with the fact that IP is designed for the "best effort" Internet where there is no guarantee for the QoS. To provide appropriate QoS support in the IP-based UTRAN, an efficient IP QoS mechanism should be applied to differentiate different service flows and provide the desired level of service. The Internet Engineering Task Force (IETF) has developed a number of IP QoS schemes to support multi-services, like Integrated Services (IntServ) [BCS94] with the Resource Reservation Protocol (RSVP) [BZB+97], Differentiated Services (DiffServ) [BBC*98], Multi- Protocol Label Switching (MPLS) [RVC01], etc. Among them, DiffServ is regarded as the most popular and notable one. It is considered as a practical and promising QoS scheme to be deployed in UMTS networks [AL02a]. Therefore, in this thesis DiffServ QoS scheme is considered for the IP-based UTRAN. The following sections give a detailed introduction of a DiffServ-based QoS structure to be deployed in the IP-based UTRAN network. 3.4.2.1 Introduction of the DiffServ QoS Scheme DiffServ is an IP-based QoS support framework. It provides different treatment of flows or aggregates flows by mapping multiple flows into a finite set of service levels, namely Per Hop Behavior (PHB) groups. Each PHB is ident