the UTRAN. The next sub-layer provides duplication avoidance functionality [10] and terminates in the CN. It remains part of the access stratum to provide access stratum services to higher layers. However, we assume that higher layer signalling such as Mobility Management (MM) and Call Control (CC) does not belong to the non-access stratum6. In the architecture representation shown by Figure 3.13, each block indicates an in- stance of the respective protocol. At the interface between sub-layers, we mark with ovals Service Access Points (SAP) for peer-to-peer communication. The SAP between MAC and the physical layer provides the transport channels, and SAPs between RLC and the MAC sub-layer provide the logical channels. In the C-plane, the General Con- trol (GC) defines through Notification (Nt) and Dedicated Control (DC) SAPs the inter- face between duplication avoidance and higher L3 sub-layers (CC, MM). Figure 3.13 also illustrates connections between RRC and MAC as well as RRC and L1 affording local inter-layer control services. We have as well, an equivalent interface control between RRC and the RLC sub-layer, between RRC and the PDCP sub-layers and between RRC and the BMC sub-layer. These interfaces enable the RRC to control the configuration of the lower layers. Thus, separate control SAPs defined between RRC and each lower layer (PDCP, RLC, MAC, and L1) exist. 6 Higher level signalling is not in the scope of 3GPP TSG RAN. On the other hand, the UTRA radio interface protocol architecture has similarities to the current ITU-R protocol architecture, ITU-R M. 1035. The UMTS Development Platform The RLC sub-layer provides ARQ functionality in conjunction with the applied radio transmission technique. In this case, we do not see a difference between RLC instances in C and U planes. When the Iu connection-point remains unchanged, the CN may re- quest the UTRAN full data protection. However, when the Iu connection point changes (e.g. SRNS relocation, streamlining, etc.), the UTRAN may not guarantee full data pro- 