erged LDP (MPLS) Command (PVC) (Leased lines) or IP or combinations such as MPLS Figure 3.47 By means of H.248 call and connect functions can be split. A horizontal inter- face appears Target network: Whole network controlled by a few server pairs Connectivity network plane Figure 3.48 Physical separation of call and connect nodes Communication control can comprise both peer-to-peer and master/slave elements, with each type of approach used where it is optimal. (Peer-to-peer models are SIP, H.323 and master/slave models are H.248/Megaco, MGCP. Compare the IN model, which is also kind of master/slave.) Call control is contained in the functional control servers (master), which also have peer-level protocols to interact with other functional elements in the system, and drive a large number of slave devices. H.248 is developed jointly by IETF and ITU, based on simplicity, flexibility and cost effectiveness. See also Chapter 11 on edge nodes. H.248 uses a simple, powerful connection/resource model to describe the logical entities or objects within the media gateway that can be controlled by the MGC. It is fundamentally Networks and Technologies based on two key concepts: termination and context. Terminations identify media flows or resources, implement signals, generate events, have properties and maintain statistics. All signals, events, properties and statistics are defined in packages, which are associated with the individual terminations. Controlled terminations are for example PSTN trunking gateways, ATM interface, analogue line, Internet telephones and announcement servers. 3.14.2 IPv6 The initial IPv4 numbering design for IP networks did not anticipate the following: The recent exponential growth of the Internet and the impending exhaustion of the IPv4 address space. The growth of the Internet and the ability of Internet backbone routers to maintain large routing tables. The need for simpler configuration. The requirement for security at the IP level. To address these concerns, the Internet Engineering Task Fo