 access point name. Routing and switching - Chosen routing protocols; point-to-multipoint routing. QoS - Diffserv, intserv, choice of radio access bearer, policing with SLA, AAL1, AAL2, AAL5; PDP context with QoS. Security - Encryption; tunnelling (IPsec or L2TP); packet filtering against intrusion and denial of service attacks. Signalling - SIP; H.323; SDP (session description protocol, see Section 8.8.2 and 14.4.2); bearer control signalling; control layer signalling. Synchronization - Synchronization of packets, header marks a beginning. Transmission quality - Design of transmission network. Charging plan - See Chapter 5. Interworking - Address translation. See chapter 15. Mobility - Mobile IP; mobility management. 8.8.2 SIGNALLING PLAN The signalling plan is to a considerable extent inherited from telephony networks. From IETF/Internet the SIP/SDP protocols are a very important contribution. Signalling is mainly used for setting up and tearing down conversational calls. Voice services develop into multimedia services. Chapter 14 contains more about signalling. The core of the plan lies within the control layer, but some protocols are used in the connectivity layer. The reason is that the control plane controls the edge nodes, only, according to Figure 8.26. Further, the service layer might be used for some advanced control. A related protocol is called CAP, CAMEL Application Part. See Figure 8.6. This gives us strictly speaking three control planes according to Figure 8.27. ATM Connectivity There are three main signalling protocols used in the ATM connectivity layer (see Figure 8.28). They are the user network interface (UNI), private network-to-network interface (PNNI) and B-ISDN inter-carrier interface (B-ICI). Some more protocols are mentioned in Chapter 12. The main ones have roughly the following function: UNI - Allows subscribers access to an ATM network, UNI subscriber recognition through ATM addressing, and recognition of the QoS contract and characteristics of the data to be sent across the connectio