Thus, at the bottom of this hierarchy, (networkelement, element, network) management is applied with variables and parameters, while at the top of this hierarchy (service, business), management is applied in more abstract terms, using policies. This is common to all architectural components, and we will find that policies can be used for each component. NetworkElement Element Network Service Business Policies Variables FIGURE 7.1 Network Management Hierarchy 302 CHAPTER 7 Network Management Architecture NM Infrastructure Element Management NM Information Transport Device Element Management System Switch IP Router Switch Device IP Router FIGURE 7.2 Network Management Is Composed of Managing Elements and Transporting Management Data Network management can be divided into two basic functions: the transport of management information across the system, and the management of NM information elements (Figure 7.2). These functions, as shown in Figure 7.2, consist of a variety of tasks- monitoring, configuring, troubleshooting, and planning-that are performed by users, administrators, and network personnel. One of the first challenges in developing a network management architecture is to define what network management really means to the organizations that will be performing the tasks and receiving the end services-namely, the users, or customers, of the system. There are four categories of network management tasks that we consider here, corresponding to the four tasks mentioned above: • Monitoring for event notification • Monitoring for trend analysis and planning • Configuration of network parameters • Troubleshooting the network 7.3.1 Network Devices and Characteristics A network device is an individual component of the network that participates at one or more of the protocol layers. This includes end devices, routers, switches, DSUs, hubs, and NICs. Network devices have characteristics that can be measured. They are grouped into endtoend, perlink, pernetwork or perelement characteristics, as shown in Figure 7.3. Endtoend characteristics are those that can be measured across multiple network devices in the path of one or more traffic flows, and may be extended across Network Management Mechanisms 303 EndtoEnd Network Network PerElement PerLinkPerNetwork PerElement FIGURE 7.3 Network Characteristics Can Be perElement, perLink, perNetwork, or EndtoEnd the entire network or between devices. Examples of endtoend characteristics for network devices are availability, capacity, delay, delay variation (jitter), throughput, error rates, and network utilization. These characteristics may be modified or added to, depending on the types of traffic on the network. Perlinknetwork and perelement characteristics are those that are specific to the type of element or connection between elements being monitored. These characteristics may be used individually, or may be combined to form an endtoend characteristic.