end bidirectional 64- or 128-Kbps digital circuit is available with the help of a network terminal that takes care of the digital bidirectional transmission over the subscriber loop. For active Internet users who require continuous connection or higher data rates, circuit-switched services are expensive because the cost is based on the dura- tion of the call and they do not provide high enough performance. An attrac- tive access method for these types of users is ADSL, which provides data rates up to a few megabits per second with a fixed monthly fee. In Figure 2.20 one office site of a company has high-data-rate access to its ISP. All employees have access to the Internet via the company's private LAN. Leased lines, which interconnect two offices in Figure 2.20, are often the most economical solution for high-data-rate circuits that are needed, for example, for LAN interconnections. Different options for data connections are discussed in Chapter 6. As we have seen, telecommunications networks contain a huge number of different complex systems that are located in multiple sites. In the old days, when the structure of the network was simple, most of the equipment sites had personnel to keep systems operational and they carried out fault location and performed needed maintenance operations. Nowadays systems are SO numerous and SO complicated that this way of network operations and maintenance is not possible anymore and implementation of automated net- work management tools is mandatory for all network operators. The follow- ing section gives an overview of the importance of network management and of the standardized structure of network management. 2.11 Network Management The importance of network management has grown together with the size and complexity of the telecommunications network. The standardization of The Telecommunications Network: An Overview this area is not as advanced as the standardization of telecommunications sys- tems that carry the actual traffic and provide the services. Efficient network man