Lec 2-2 Network Security Definition:

Network Security Definition:
Network security address questions such as how to efficiently control access to computer networks and distributed systems, and how to securely transmit data between them.
1.2 Computing Systems:
The term of computing system is referring to a single main processor, its peripheral devices, its data, and its software. Such a system has a single operating system and one set of users, as shown in figure (1). All blocks of the computing system are located within a small distance of rest of the system.
While the term of computing network is a collection of two or more independent computing systems. The user accesses the network only indirectly through a computing system. The computing network defines to be a computing environment with more than one independent processor, as shown in figure (2).
1.3 ISO-OSI Reference Model:
The ISO (International Standards Organization) has developed OSI (Open
System Interconnect) model in 1982 for computer network connection. The
OSI reference model specifies the seven layers of functionality, as shown in
Figure (3).