AN2 in Figure 2.21, are managed by people responsible for network operation inside a company. Introduction to Telecommunications Network Engineering Corporate network manager LAN 1 LAN 2 Public network operator Figure 2.21 Management responsibility of a corporate network. Network management responsibility is often divided hierarchically. Local or site managers only take care of LAN networks at each office. A cen- tralized organization of the company manages the usage and availability of wide-area network (WAN) connections between sites. A centralized organiza- tion offers service to business units at various sites and optimizes the utiliza- tion of expensive long-distance or even international WAN connections. The main concerns of network managers of a company include these: Network change management (hardware updates); The location and repair of malfunctions; Software updates and version control; Network security. Most network elements of LANs provide network management func- tions via a standardized management interface. This open standard is known as the Simple Network Management Protocol (SNMP). Software packages for centralized management workstations for LANs are commercially available. The public network operator manages the public network in order to be able to provide reliable service to customers. Network optimization to avoid unnecessary investments as well as quick repairs in the case of faults is important. Short delivery times of leased-line circuits are an important com- petitive advantage today, and a network operator can make delivery time shorter with the help of sophisticated network management tools. In addition to private network management needs, accounting func- tions are needed in a public network for switched circuits. For example, in The Telecommunications Network: An Overview the case of packet-switched service, the amount of transferred data is recorded to generate bills to customers. Accounting functions of the Internet are very limited but in packet-switched cellular networks, such a