Chapter 5. Network Protocols: Real and Imagined

In this chapter

• Network protocols and data communication

• Understanding the OSI Conceptual Model

• The roles of the OSI layers

• Understanding real-world protocol stacks

• Exploring the TCP/IP stack

• Understanding Novell's IPX/SPX network protocol stack

• Using NetBEUI on small networks

• Understanding the AppleTalk protocol stack

So far, we've taken a look at the types of networking, the hardware considerations for building a network, and the different aspects of network architectures and network connectivity media. In this chapter we will concentrate on issues related to how computers actually communicate on the network. We'll cover the theoretical side of network communication and then take a look at the different protocols that are actually being used to transfer data on a network.

"What is a protocol," you ask? Well, think about the word protocol itself. A protocol is really a set of rules or guidelines dictating behavior. One communication protocol that is often followed in the business world is the handshake. It typically means that a nonthreatening exchange of information can take place.

Also, everyone has heard of diplomatic protocol, which defines the rules of communication used when two diplomats meet to discuss various issues. In the computer world, a protocol provides the rules for how computers communicate. Network protocols are actually hard-wired into the programming used by the networking software you find on client and server computers.

Because data is created and saved on a computer in a particular format, that data will actually undergo some translation and modification before it can be sent out over the network to another computer. Again, think about diplomatic protocol; if two diplomats don't speak the same language, they use interpreters. Well, you will find that sometimes data must be translated before it can be sent over the network so that the original data arrives at the receiving computer in a format that is understandable.

So, just as communication between diplomats might have to move through several layers (in this case, translators) before a message is received, computer data must move through several intermediary layers before the data can actually be placed on the network media and then travel out over the network. This means that a number of small protocols actually are used as the data moves through these layers. A group of small protocols that work together to prepare data for the communication process is called a protocol stack .

A number of different protocol stacks, such as TCP/IP and IPX/SPX, can be used to communicate over the network. To understand how the protocols in the stack work together, we will look at a theoretical model that has been created to explain network communication and data transfer. The OSI model is used by network administrators, software programmers, and other Information Technology professionals to discuss the way network protocols manage the communication between computers on the network. Programmers also use this layered model to develop new protocols and tools for network communication.

Note

Although everyone seems comfortable with the handshake as a greeting (except for perhaps Donald Trump, who has a phobia related to shaking hands), you will also find that the term handshake pops up a lot in the networking world. It is often used as a term associated with different data communications strategies and refers to an agreement made between two computers to exchange data. For example, we'll talk about the three-way handshake when we discuss the Transmission Control Protocol (TCP) later in this chapter.