Bandwidth is the amount of data that can be passed along a communications channel in a given period of time. Bandwidth is limited. Regardless of transmitting medium the rate of data transfer is limited by partly the laws of physics, and partly the technologies used for forwarding the information. Bandwidth isn’t free. It is possible to buy appliances for LAN that can provide nearly unlimited bandwidth for long time. In case of WAN we can buy bandwidth from a provider. In every case we may refer, companies and individuals can save a lot of money, if they know the term of bandwidth, and that how their needs would change. The meaning of bandwidth can be represented as pipeline system. A pipe network delivers the water to homes and companies. The network use different diameters of pipes. Some of the main lines in a major city can be 2 metres in diameter, but the pipe that takes the water to the kitchen tap is only 2 cm. in this example the water is the data, the diameter of the pipe is the bandwidth. Another way to represent is the roads and streets. Every city and town connected with the road-system. Leaving the highway we reach wide streets, that lead us to narrow ones, and they end up in homes, companies, etc. when a few numbers of vehicles use the roads, the traffic is fast. But with the rise of the number of vehicles traffic gets slower, even on highways we can see traffic jams. Data network is very similar to this system. If we look at the data network as a road-system it is easy to admit that slower data transfer systems results slower traffic.