ts previously occupied bandwidth shall be released. Thus, the TNL CAC needs update the Total Reserved Bandwidth by decreasing the occupied bandwidth by this released connection. Another factor which is taken into account by the TNL CAC is the maximum number of transport connections supported by the ATM VCs or VPs. That means the TNL CAC also needs to make sure that each AAL2 PVC allows only up to 248 active connections simultaneously. 3.4 IP-Based UTRAN 3.4 IP-Based UTRAN ATM was selected as the underlying transport technology in the UTRAN transport network since UMTS Rel99. At present, there is a strong trend of replacing the current ATM with IP as the transport technologies in the UTRAN, as stated in section 2.3.4 and 2.3.4.1. 3GPP Release 5 firstly introduces the IP-based UTRAN transport network. 3.4.1 IP-Based UTRAN User Plane Protocol Architecture The user plane protocol architecture of the IP-based UTRAN is shown in Figure 3.11. By comparing the ATM-based UTRAN (as shown in Figure 3.4 and Figure 3.5) and following the IP-based UTRAN protocol architecture, it can be seen that the radio network layer protocols, i.e. RLC, MAC and FP are kept unchanged, while the underlying transport network layer protocols replace the AAL2/ATM by UDP/IP layers (as highlighted in Figure 3.11). The UDP layer is responsible to establish/release the transport connections for each user flow. The IP layer is in charge of routing, addressing and QoS support. IP can either be IPv4 or IPv6. In the 3GPP standard for the IP-based UTRAN, the technology to be used in the layer 2 and layer 1 of the Node B and RNC is not specified. This provides the network provider freedom to choose a suitable implementation on the MAC and physical layer. Usually Ethernet is preferred to be used for commercial consideration due to its low cost, flexibility and scalability. In this thesis, Ethernet (see Appendix A.4) is considered to be the layer 2 transport technique on the IP-based lub link. UDP/IP UDP/IP WCDMA L1 WCDMA L1 Layer 2 Layer 2 Physical Physical