Computer network basics
Internet business would not exist without a computer network. In fact, it was the ability to network personal computers that made the computer an incredibly powerful tool for business. Imagine having to send someone a floppy disk or Zip disk by mail or courier every time you wanted to send information in digital form. Imagine not being able to submit an order using the Internet. In this section we look at some basic network concepts. A very simple computer network is illustrated in Figure 41. For obvious reasons this is called a star network. The hub at the center of this network is a very simple piece of networking hardware that takes the data from one computer in the network and passes them on to the other computers in the network. The network illustrated in Figure 41 is known as a local area network or LAN. A LAN is a communications network consisting of cables, computers, and network devices confined to a very small geographic region such as a single building, or floor of a building.
Figure 4--1 A basic Local Area Network (LAN).
Packet: When sending a message over a network (e.g., an email), the message is usually broken up into a smaller set of messages called packets.
A very important LAN technology is ethernet. This technology was developed by Robert Metcalfe and David Boggs at Xerox PARC. With ethernet, any computer on the network can send data packets to any other computer on the network. However, no two computers can "talk on the line" at the same time. If two computers send a packet at the same time there is a "collision." Ethernet is a technology for handling these collisions and retransmitting the packets. When a collision occurs the packets are retransmitted after a very small random interval. Ethernet is a very effective protocol and it is easy to connect a computer into the network.
Bandwidth: When talking about computer networks, bandwidth refers to the capacity of a network. Bandwidth is often measured in kilobits per second (Kbps), megabits per second (Mbps), or gigabits per second (Gbps). The terms broadband, narrowband, and midband are often used to describe the bandwidth. These are not precisely defined, except in an ordinal sense, and the actual bandwidth associated with these terms is changing rapidly over time as network capacity increases. We will define broadband as at least 10 Mbps, midband as 1--10 Mbps, and narrowband as less than 1 Mbps.
ALOHAnet was a radio network designed to allow computers in the Hawaiian Islands to communicate with each other. It was developed by Norman Abramson, a professor at the University of Hawaii and a surfing (on real waves, not the Internet) enthusiast. ALOHAnet was built on the idea of retransmitting packets after a small random interval if there is a collision on the network. This is the basic idea used in ethernet.
When an organization's local area networks are connected together over a larger geographical region, perhaps the world, they are called a wide area network or WAN. This is illustrated in Figure 42. A router is a network device used to send or route packets from one LAN to another LAN. The LANs may be connected by dedicated leased phone lines, fiber optic cable, or through various wireless technologies.
Figure 4--2 A basic Wide Area Network (WAN).
If you are planning to install or upgrade your company's network, you should be concerned about the following:
Which kind of data are transmitted3voice, text, video?
What is the network bandwidth? Is it narrowband, midband, or broadband?
How reliable is the network?
Will it provide the bandwidth to meet future needs?
How is speed degraded by traffic load?
How much does it cost to operate?
How secure is it?
What protocols are used? Are they compatible with other networking protocols?
We will touch on a number of these issues throughout the book. The emphasis of this chapter is the Internet and we want to concentrate on TCP/IP, which is the networking protocol used by the Internet.