ified by a DiffServ Code Point (DSCP) in the IP header which provides information about the QoS requested for a packet, and defines specific forwarding treatment that the packet will receive at each node. DSCPs are defined in IETF RFC 2474 [NBBB98]. It is specified in the 8-bit Type of Service (TOS) field in the IPv4 header (or in traffic class field in IPv6). The DSCP enables network routers to handle IP packets differently depending on the code point and hence their relative priority. A DiffServ network is partitioned into domains, each having two types of routers: edge or core. A DiffServ domain is completely identified by its set of supported PHB, its edge and core routers, its policy in mapping QoS of an incoming packet to a pre-defined PHB, and the level of QoS associated with each PHB. Each packet belonging to a QoS class is marked with a DSCP in the IP header, and then each node in that domain forwards packet according to its DSCP. 3.4 IP-Based UTRAN DiffServ PHBs The DiffServ working Group of the IETF has defined a number of different PHB groups for different applications. There are three most common PHBs defined in the IETF, Best Effort (BE) PHB, Expedited Forwarding (EF) PHB and Assured Forwarding (AF) PHB. BE PHB is for the traditional Internet traffic and its usage implies that the nodes in the path will do their best to forward the packet in a fair manner, however, there is no guarantee on its delivery or its level of service. Everybody gets the service that the network is able to provide. Its recommended code point (DSCP) is 000000. EF PHB is aimed for a low loss, low latency, low jitter, assured bandwidth edge-to-edge service through IP DiffServ domains. It can be understood as a virtual leased line service. Therefore, the bandwidth cannot be exceeded but the user can leave it idle or use it to the full extent of its capacity. The holder of this pipe should not be affected by the presence or absence of other users. An example of EF service is voice telephony. The DSCP of EF PHB is 101110. AF PHB d