mation exchange are classified as logical O&M forming an integral part of NBAP [6]. Management Platform(s) Node B Node B Co-located Management Management Management equipment Model Model Model Management Model Co-located equipment Node B Node B Implementation O&M specific specific O&M RNC O&M Implementation Node B Logical Logical Logical interface interface Traffic Traffic Traffic Functions Functions Functions Figure 3.11 RNS architecture with O&M interfaces [6]. The UMTS Network and Radio Access Technology Figure 3.11, with representative logical connections, shows the concept of an interface from the RNC to the management system and O&M functions within the management system for clarity only. The specifications of these functional connections do not corre- spond to the scope of the radio network specification. UTRAN INTERFACES 3.7.1 General Protocol Model for UTRAN Interfaces Figure 3.12 presents the general UTRAN interfaces protocol model. The structure as- sumes that layers and planes are logically independent of each other, and if needed, the whole structure may evolve later with standardization work. Radio Network Layer Control Plane User Plane Application Protocol Stream(s) 'Transport Network Transport Network Transport Network Plane Control Plane Plane ALCAP(s) Signalling Signalling Bearer(s) Bearer(s) Bearer(s) Physical Layer Transport Network Layer Figure 3.12 General protocol model for UTRAN Interfaces. 3.7.2 Horizontal Layers The radio network and transport network layers constitute the main components of the protocol structure. The first layer contains all visible UTRAN related issues, and the second layer represents standard UTRAN transport technology for selection without any specific requirements. 3.7.3 Vertical Planes 3.7.3.1 Control Plane The control plane includes the application protocol, i.e. RANAP, RNSAP or NBAP, and the signalling bearer for transporting the application protocol messages. The UMTS Development Platform Among other things, the application protocol is used for setting up beare