nclusion of an element-management sys- tem that will allow the customer to manage the device within his or her network. The only problem is that today, most networks are made up of equipment purchased from a variety of vendors. Each vendor develops its own element managers on a device-by-device basis, and they work excep- tionally well for each device. This does not become a problem until it comes time to create a management hierarchy for a large network- shown in Figure 2-15-at which time the network management center begins to look a lot like a Macy's television department. Each device or Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Protocols Protocols DSL/cable-based IP Phones Figure 2-15 Branch telecommuter A large Office managed Switch Firewall network Media PC/laptop with VPN Gateway remote client, IP SoftPhone Internet Media Gateway Firewall Application Servers IP Phones set of devices requires its own display monitor, and when one device in the network fails, causing a waterfall effect, the network manager must reconstruct the entire chain of events to discover what the original causative factor was. This is sometimes called the "Three Mile Island effect." Back in the 1970s when the Three Mile Island nuclear power plant went critical and tried to make Pennsylvania glow in the dark, it became clear to the Monday morning quarterbacks trying to reconstruct the event (and create the "How could this have been prevented" docu- ment) that all the information required to turn the critical failure of the reactor into a nonevent was in fact in the control room; that is, buried somewhere in the hundreds of pages of fanfold paper that came spewing out of the high-speed printers scattered all over the control room. There was no procedure in place to receive the output from the many managed devices and processes involved in the complex task of 