e WFQ can be also combined with other scheduling such as priority queuing. For example, the real time traffic mapped to the EF PHB, e.g. voice or video streaming traffic, is given the highest priority. While the interactive data traffic mapped to different AF PHBs are the middle priority, and among them WFQ is used. The lowest priority is assigned to the BE PHB, which utilizes the spare capacity which is not utilized by EF and AF PHBs. 3 UMTS Terrestrial Radio Access Network (UTRAN) 3.4.2.2 Mapping of UMTS QoS to DiffServ PHBs As introduced in section 3.3.4.1, UMTS defines four QoS classes: conversational, streaming, interactive and background class. Both the conversational and streaming class require a certain reservation of resources in the network, mainly intended for carrying Real Time (RT) traffic flows, such as video telephony and audio/video streams. The Interactive and Background class are so-called Non Real Time (NRT) traffic. They are mainly for carrying elastic Internet applications like web, email, and ftp. For example, both the conversational class and streaming class are mapped to EF PHBs as they require low loss, low latency, low jitter, assured bandwidth, end-to-end service through IP transport domains. The interactive class is mapped to AF PHBs, e.g. web traffic. As mentioned in the last section, there are four AF Service classes and each of these classes can also have three levels of dropping precedence: low, medium, and high. In practice, different AF PHBs can be used for different RAB types which provide various QoS for the end users. The background class is mapped to BE PHB as it belongs to Best Effort traffic, which has low requirements on the QoS and utilizes the resources that the network is able provide. For example, best effort HSPA traffic can be set to BE PHB. It should be noted that there can be other alternative mappings of UMTS QoS classes to DiffServ PHBs, depending on system requirements and traffic. 3.4.2.3 DiffServ-Based QoS Architecture in IP-Based UTRAN Based on the DiffServ Q