ABSTRACT
Networks are built from communication links and devices that connect them. The concepts are analogous to those of roads and a road network. Software to operate communication links, and to route messages to and from applications, is built into all modern operating systems (OSs). It performs two OS functions: managing a shared resource and providing shared services. The mobile (cell) phone network can be used for data communications. Early mobile phone data rates were too low for effective use, but are more than adequate and phones take advantage of this capability. Wi-Fi networks use routers which send and receive radio signals. People try to access information systems without permission for many reasons. Organizations that use networks try to protect their networks and computers from unauthorized access. Network security and database security differ in the methods people use to try to break in and in the defenses that can be used against break-ins.
