twork management system, and it remains in place until the user reconfigures the network. Its use is analogous to the use of a dedicated pri- vate line because it provides an always-on condition between two locations or two devices. In contrast to PVCs, SVCs are set up on demand. They are provisioned dynamically by using signaling techniques. An SVC must be reestablished each time data is to be sent; after the data has been sent, the SVC disappears. An SVC is therefore anal- ogous to a dialup connection in the PSTN. The main benefit of an SVC is that you can use it to access the network from anyplace. The predominant application for SVCs is to accommodate people who are working at home, in a hotel, at an airport, or otherwise outside the physical location of the enterprise network. The Electromagnetic Spectrum and Bandwidth Types of Network Connections Three major types of networks connections can be made: Switched network connections-A switched connection is referred to as a dialup connection. This implies that it uses a series of network switches to establish the connection between the parties. Leased-line network connections-A leased line is also referred to as a pri- vate line. With a leased line, the same locations or the same devices are always connected, and transmission between those locations or devices always occurs on the same path. Dedicated network connections-In essence, a dedicated line works exactly like a leased line. It is always connected, and it always uses the same path for transmission. However, the end user may own the transmission facility (rather than lease it) such that it is exclusive to that user. The Electromagnetic Spectrum and Bandwidth The following sections talk about bandwidth and about where the various trans- mission media lie within the electromagnetic spectrum. The Electromagnetic Spectrum When electrons move, they create electromagnetic waves that can propagate through free space. James Maxwell first predicted the existence of this phenome- non in 1865, and Heinrich Hertz fi