Introduction

To prepare for the CompTIA Network+ exam, you should begin by reviewing the foundations of networking. Among these, you must understand the logical models on which networks are designed and created, the protocols they use to communicate, the addressing schemes by which they identify individual devices on the network, and the technologies they use to ensure that data reaches its destination. In this chapter, we will cover the OSI (Open Systems Interconnect) model in depth and then begin the discussion on TCP/IP (Transmission Control Protocol/Internet Protocol). Both are covered in great detail on the exam and need to be completely understood before sitting the exam if you want success.

The vast majority of networks today (including the Internet) use TCP/IP to transmit information among computers and networks in a wide area network (WAN). Together, TCP and IP are referred to as a protocol stack or as network/transport protocols because they work together at two different levels (called the Network and Transport layers) to enable computers to communicate with each other. This is important because TCP/IP, like other protocol suites (groupings) such as IPX/SPX (Internet Packet Exchange/Sequenced Packet Exchange), are arranged as suites of protocols that provide different functionality. If you want to send an e-mail to someone today, you will most likely need IP communications to establish communication and complete the transmission of the message. The models and the protocols (as you will see), tie very closely together, and that is why it s hard to discuss one without the...