Ten most important ideas/concepts to take away 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, as well as 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 and wireless.
A computer network enables distributed applications. A
distributed application runs on end systems and exchanges data via the computer
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.
When one end system sends data to another the 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 on a packet by packet basis.
Also, packet switches typically “store and forward” packets – that is, before a switch
begins to forward a packet on an outgoing link, if first receives and stores the entire
As defined on Page 8, a protocol defines the format and order of messages
exchanged between two or more communication entities, as well as the actions taken on
the transmission and/or receipt of a message or other event. Computer networks make
extensive use of protocols. Figure 1.2 provides an analogy between a human protocol
and a computer network protocol for messages exchanged between a Web browser and
a Web server. In this example, the Web browser first sends an introductory message to
the server; the server responds with its own introductory message; the browser then
sends another message, requesting a specific Web page; finally, the server sends a last
message, which includes the requested Web page.
Computer networks constitute one major class of computer networks.
Another major class of communication networks is traditional digital telephone networks.
Traditional digital telephone networks do not use packet switching to move data from