When you talk with someone, you are communicating. When you mail a card to a relative, you are communicating. You probably don‛t think much about the rules of communication when you do these two things. But there are rules, and good communication happens only when all parties know and follow those rules. It is the same with devices on a network. This chapter explains the rules, which are called protocols, of network communication. When you understand the various protocols and how they work with other protocols, you not only will understand how networks and the Internet work but also be able to troubleshoot problems in your own network.