sport Layer. It does not include any Radio Network Layer information. It is responsible for the transport bearer management, which includes the signaling, establishment, maintenance and release of transport bearers for the user plane. The Transport Network Control Plane includes the ALCAP protocol that is needed to set up the transport bearers (Data Bearer) for the User Plane, and also includes the Signaling Bearers needed for the ALCAP. The following sections give a detailed introduction of the UTRAN network structure and protocol stacks of different UMTS releases. It starts from the first UMTS release, i.e. UMTS Rel99, which is considered as the reference model for the evolved UTRAN networks. The introduction of the HSPA (HSDPA/HSUPA) networks is given in Appendix A.9. 3.3 UMTS Release 99 UMTS Release 99 (Re199) is established as the first UMTS version specified by 3GPP. It contains all the basic elements to meet the requirements for IMT-2000 technologies. As 3.3 UMTS Release 99 introduced in section 2.3.1, UMTS Rel99 selected the ATM as the transport technology for the UTRAN transport network. 3.3.1 UTRAN Protocol Stack This subsection introduces the UTRAN protocol stack in the Control Plane and the User Plane respectively. Protocol Stack for the Control Plane Figure 3.3 shows the UTRAN protocol stack in the control plane. MSC or SGSN Node B Node B RANAP RANAP AAL 5 AAL 5 ATM or IP ATM or IP Physical Physical Physical Physical Physical WCDMA L1 WCDMA L1 Layer Layer Layer Layer Layer Figure 3.3: Control plane protocol stack in UTRAN The signaling protocols in the control plane of UTRAN consists of NBAP on the lub interface, RANAP at the Iu interface handling communication between RNC and CN, and RNSAP for the Iur interface in charge of communications between RNCs. NBAP uses ATM together with the AAL5 as the underlying transport network layer to transport signaling messages over the lub interface. While at the Iu interface, the RANAP is conveyed by Signaling Connection Control Part (SCCP) and ATM or optionally I