Redes de computadores

CHAPTER

1
Computer Networks and the Internet

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STUDY COMPANION FOR COMPUTER NETWORKING, THIRD EDITION

Most Important Ideas and Concepts from Chapter 1
Nuts and bolts of computer networks. Computer networks consist of end systems, packet switches, and communication links. End systems—also called hosts—include desktop PCs, laptops, hand-held network devices (including cell phones, PDAs, and BlackBerries), sensors, and servers (such as Web and mail servers). Just as cities are interconnected by a network of roads and intersections, end systems of a computer network are interconnected by a network of communication links and packet switches. Communication links can be wired or wireless. Distributed applications. A computer network enables distributed applications. A distributed application runs on end systems and exchanges data via the computer network. Distributed applications include Web surfing, e-mail, instant messaging, Internet phone, distributed games, peer-to-peer file sharing, television distribution, and video conferencing. New distributed applications continue to be invented and deployed on the Internet. Packet switching. When one end system sends data to another end system, the sending end system breaks the data into chunks, called packets. Similar to the process of delivering post-office mail, the Internet transports each packet separately, routing a packet to its destination using a destination address that is written into the packet. When a packet switch receives a packet, it uses the packet’s destination address to determine on which link it should forward the packet. Thus, a packet switch performs “packet switching,” forwarding incoming packets to outgoing links packet by packet. Also, packet switches typically “store and forward” packets—that is, before a switch begins to forward a packet on an outgoing link, first it receives and stores the entire packet. Protocol. A protocol defines the format and order of messages exchanged