OSS (operation support system) platform. It has a hierarchical structure based on two nodes levels, the OMC (operation and maintenance centre) and the NMC (network maintenance centre). The OMC takes care of the direct management of the network nodes, called network elements (NEs), while network configuration, performance data, alarm and traffic statistics are managed by the NMC. Several OMCs may exist in large networks to regionally distribute the NE management. There is usually one single NMC. Additional centres have lately been introduced for service management and enterprise management. The ITU-T defined the Q3 interface based on the SMI model (structure of management information) and a group of ISO standards like CMIP (common management information protocol) for manager-agent communication, and FTAM (file transfer access and man- agement). The NE agents and the central manager communicate by means of a network called DCN (data communication network). For DCN the fairly secure X.25 technology was proposed. TMN is a detailed model that has not become fully implemented. This is partly due to the strong advance of IP technology and the progressive obsolescence of X.25 networks, Telecom Management - Operations making IP a better solution (but less secure) for the DCN communication. The telecom- munication management communication normally utilizes a specific telecommunication management network. This could be illustrated by means of the telecommunication man- agement network model in Figure 16.5. Datacom: Within the IP environment a flat management structure was used, based on the SNMP protocol for agent-manager communication. No intermediate hierarchical levels were devised. The communication was based on the TCP/IP protocol suite with FTP (file transfer protocol) for file transfer. IP standards based on inherent network topology learning capabilities became a main tool that gave relief to the network administrators. Much of the traffic routing activi- ties then became autonomously handled by the network elements