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Wednesday, 22 May 2013

0 Networking, Wide Area Networking (WAN)

Networking, Wide Area Networking (WAN)

Network Basics: LAN, WAN, VPN

A network is a system of hardware and software, put together for the purpose of communication and resource sharing. A network includes transmission hardware, devices to interconnect transmission media and to control transmissions, and software to decode and format data, as well as to detect and correct problems. There are several types of networks in use today. This chapter will focus on three of them:
LAN - Local Area Network
WAN - Wide Area Network
VPN - Virtual Private Network

The most widely deployed type of network, LANs were designed as an alternative to the more expensive point-to-point connection. A LAN has high throughput for relatively low cost. LANs often rely on shared media, usually a cable, for connecting many computers. This reduces cost. The computers take turns using the cable to send data.

Repeaters and Bridges
LANs typically connect computers located in close physical proximity, i.e., all the computers in a building. Repeaters are used to join network segments when the distance spanned causes electrical signals to weaken. Repeaters are basically amplifiers that work at the bit level; they do not actively modify data that is amplified and sent to the next segment. Like repeaters, bridges are used to connect two LANs together. Unlike repeaters, bridges work at the frame level. This is useful, allowing bridges to detect and discard corrupted frames. They can also perform frame filtering, only forwarding a frame when necessary. Both of these capabilities decrease network congestion. Bridged LANs can span arbitrary distances when using a satellite channel for the bridge. The resulting network is still considered a LAN and not a WAN.


To be considered a WAN, a network must be able to connect an arbitrary number of sites across an arbitrary distance, with an arbitrary number of computers at each site. In addition, it must have reasonable performance (no long delays) and allow all of the computers connected to it to communicate simultaneously. This is accomplished with packet switches. 


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