oS scheme, the following QoS structure (Figure 3.13) considered in this thesis for the IP-based UTRAN. In this proposed structure, there are in total six IP DiffServ PHBs: 1 EF PHB for sending signaling, conversational voice and video streaming traffic; 4 AF PHBs for Interactive traffic class with 4 different priorities (AF11, AF21, AF31 and AF41); 1 BE PHB for background traffic class. Each DiffServ PHB has its own dedicated queue. High Priority Flow 1 (Priority Queue) Flow 2 Middle Priority Flow 3 (WF Queues) Flow 4 Egress Flow 5 Flow 6 Flow 7 Low Priority (Best Effort) Flow 8 Figure 3.13: DiffServ-based QoS structure in the IP-based UTRAN 3.4 IP-Based UTRAN Typically in the IP DiffServ architecture, a combination of Priority Queuing (PQ) and Weighted Fair Queuing (WFQ) is often applied to support different service classes, e.g. [FPR00] [TNC*01]. PQ is used to provide premium service (like delay- and jitter- sensitive real time services) for the highest priority; and WFQ is used in addition to serve lower priority service classes with different priorities and fairness. In this thesis, the combined PQ and WFQ scheduling scheme is used in the DiffServ architecture of the IP-based UTRAN. As shown in Figure 3.13, the EF PHB is given the highest priority, therefore between EF and other PHBs is the priority queuing. While all AF PHBs and BE PHBs use the spare bandwidth which is not reserved by the EF PHB. The Weighted Fair (WF) Queues are used for AF and BE PHBs and for different AF PHBs and BE PHBs different weights are assigned which determine their priorities, and WFQ scheduling is used to allocate the bandwidth according to their weights among all AF and BE PHBs. WRED is applied for dropping packets for AF and BE PHBs. It is the probabilistic discard of packets as a function of queue fill before overflow conditions are reached. Random dropping takes place when the algorithm detects signs of congestion. The congestion variable is the average queue size that is calculated from the instantaneous queue size by using 