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1. A sender (source), which creates the message to be transmitted.
2. A medium which caries the message.
3. A receiver (sink), which receives the message.
For example, when you speak to your friend on the telephone, you are the sender. The telephone line through which your voice is transmitted is the medium and your friend is the receiver. This is the simple example of voice communication. The same concept holds good for data communications also. Data Communication is the function of transporting data from one point to another. In this case the sender and the receiver are normally machines, in particular, computer devices (computers, terminals, peripheral devices like line printers, teletypes, disks, etc) and the transmission medium may be telephone lines, microwave links, satellite links, etc.
How ever, the messages that are transmitted are data, not voice conversation. Thus, the electronics system that transfers data from one point to other point is called data communication system. Un like computers that process and rearrange data, data communication systems transmit data from one point to another point with out any change.
What is a Network?
This is a difficult question to answer. A network can consist of two computers connected together on a desk or it can consist of many Local Area Networks (LANs) connected together to form a Wide Area Network (WAN) across a continent. The key is that two or more computers are connected together by a medium and are sharing resources. These resources can be files, printers, hard drives, or CPU number-crunching power.
Communication Channels
If channel is considered as the highway, then the bandwidth is like the number of lane in the high way. More lanes mean more traffic at a time and high speed transportation. Bandwidth also refers to as grade, tells us the rate, or speed at which data can be transmitted over the channel. There are three brands for communication channel:
1. Narrow Band Channel
Narrow band channel or the low speed channel is the slowest band, transmits the data from 40 bit per second to 1200 bits per seconds. Telegraph lines are the example of narrow band channel.
2. Voice Band Channel
Voice band channel or the medium speed channel is faster than narrow band channel, and transmit data from 110 bits per second to 9600 bits per second. Telephone lines are the example of voice band channel.
3. Broad Band Channel
Broad band channel or the high speed channel is the fastest channel which transmits data up to several million bits per second and in special cases, goes up to billions of bits per seconds. Coaxial cable, fiber optics, and Microwave are the examples of broadband channels.
Network Trends
Many individuals have asked to see the "Big Picture" of networking: How does everything. Where does Microsoft NT fit in with routers and the OSI layers? What about UNIX, Linux and Novell? The following page has a graphic showing The Big Picture. It attempts to show all areas of networking and how they tie into each other. The following key describes the graphical symbols used:
Local Area Network (LAN)
LANs (local area networks) are networks that connect computers and resources together in a building or buildings that are close together.
This is the most widely used network in organizations. A local area network is a digital communication system capable of inter connecting a large number of computer, terminal and other peripheral devices with in a limited geographical area, typically under 1KM across. LANs normally operates with in a compact area such as an office building or a campus and is owned by the using organization. The popular Netware are Window Anti, Novell, and lantastic.
