cation information in the HLR updated. The MAP-E interface between visited MSC servers is used in handovers where the serving MSC server is also changed. The MAP-E interface is used for delivering short messages between the visited MSC server and the SMS-GMSC server for mobile terminated short messages and the visited MSC server and the SMS-IWMSC (interworking MSC) server for mobile originated short messages. Alternatively, the visited MSC server can be connected directly to the SMSC (short message service centre) if it is part of the SS7 network and the SMSC can make the necessary HLR queries itself. The MAP-F interface is located between the MSC server and the EIR and the MAP-G interface is located between the VLR and the VLR (see Figure 4.22 for the available protocol stacks). Protocols supported are the CAP, INAP and MAP, which can use SIGTRAN or the PCM based SS7 as the transportation layer. 4.5 CS Core Detailed Network Planning As discussed before, the 3GPP release 4 standards introduce the separation of the user plane from the control plane. In release 4 network architecture, the user data are carried on the user plane, while the signalling traffic is carried on the control plane. The user plane is therefore carried independently of the control plane on the Nb, Iu-CS and A interfaces and the external interface to the PSTN. On the Iu-CS and Nb interfaces, the user plane traffic is carried over the IP/ATM networks. 4.5.1 Control Plane Detailed Planning Despite being separate entities, the user plane and the control plane are linked in an indirect and flexible way via the user plane destination (UPD) and user plane destination reference (UPDR) parameters. Signalling Interfaces and Protocols (Figure 4.23) Detailed planning of the control plane requires: signalling point code allocations for MSS, MGW, HLR, RNC, BSC and PSTN POI; GT allocations for MSS, HLR, RNC and MGW. CS Core Detailed Network Planning Services CAP/INAP ATM/IP Server Server Sigtran H.248 H.248 Sigtran RANAP AAL2/AAL5 AAL5/ATM lu-CS BSSAP Figur