Networking The Complete Reference, Third Edition

CHAPTER

2 The OSI Reference Model

Network communications take place on many levels and can be difficult to understand, even for the knowledgeable network administrator. The Open Systems Interconnection (OSI) reference model is a theoretical construction that separates network communications into seven distinct layers, as shown in Figure 2-1. Each computer on the network uses a series of protocols to perform the functions assigned to each layer. The layers collectively form what is known as the protocol stack or networking stack. At the top of the stack is the application that makes a request for a resource located elsewhere on the network, and at the bottom is the physical medium that actually connects the computers and forms the network, such ...