Quick Tech Tips: Wide Area Networks - WAN

Wide Area Networks, or WAN, span a large geographical area. A WAN contains a collection of machines intended for running user programs. Transmission rates are typically 2 Mbps, 34 Mbps, 45 Mbps, 155 Mbps, 625 Mbps, etc.
The machines are connected by a subnet whose job is to carry messages from machine to machine. The subnet consists of two distinct components : transmission lines and switching elements. Transmission lines move bits between machines. The switching elements are specialized computers used to connect two or more transmission lines. It is the job of the switching element to decide which outgoing line to choose to forward the data on incoming line.
In WANs, the network contains numerous cables or telephone lines, each one connecting a pair of routers. When a packet is sent from one router to another via one or more intermediate routers, the packet is received at each intermediate router in its entirety, stored there until the required output line is free, and then forwarded. A subnet using this principle is called a point-to-point, store and forward, or packet switched network.
Second option for a WAN is satellite or ground radio system. Each router has an antenna through which it can send and receive. All routers can hear the output from the satellite, and in some cases they can also hear the upward transmissions of their fellow routers to the satellite as well.

Quick Tech Tip : Metropolitan Area Networks - MANs

A metropolitan area network, or MAN is basically a bigger version of LAN. MAN is a computer networks usually spanning a campus or a city, which typically connect a few local area networks using high speed backbone technologies. A MAN supports both data and voice. A MAN just has one or two cables and does not contain switching elements.
A MAN is optimized for a larger geographical area than a LAN, ranging from several blocks of buildings to entire cities. MANs can also depend on communications channels of moderate-to-high data rates. A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations. MANs might also be owned and operated as public utilities. They will often provide means for internetworking of local networks. Metropolitan area networks can span up to 50km, with the devices being used such as modem and wire/cable devices.
The standard that has been adopted for MANs is called DQDB (Distributed Queue Dual Bus). DQDB consists of two unidirectional cables or buses to which all other computers are connected. Each bus has a head-end which initiates transmission activity.
There are three important features which discriminate MANs from LANs or WANs:
1. The network size falls intermediate between LANs and WANs. A MAN typically covers an area of between 5 and 50 km range. Many MANs cover an area the size of a city, although in some cases MANs may be as small as a group of buildings.
2. A MAN, its communications links and equipment are generally owned by either a consortium of users or by a network service provider who sells the service to the users.
3. A MAN often acts as a high speed network to allow sharing of regional resources. It is also frequently used to provide a shared connection to other networks using a link to a WAN.

Quick Tech Explanation: Local Area Networks - LANs

Local Area networks, generally called LANs, are privately owned networks within a single building or campus of up to a few kilometers in size. Most local area networks are built with relatively inexpensive hardware such as Ethernet cables, network adapters, and hubs. Wireless LAN and other more advanced LAN hardware options also exist as a part of modern LANs.
The most common type of local area network is an Ethernet LAN. If you look at size of LAN's, the smallest home LAN can have exactly two computers; a large LAN can accommodate many thousands of computers. Many of the larger LANs are divided into logical groups called subnets.

LANs are distinguished from other kinds of networks by three characteristics:
1. Size: LANs have a size limit and cannot expand beyond this size, essentially meaning that it is possible to plan and design for the worst case transmission time.
2. Topology: This is the geometric arrangement of devices on the network. For example, devices can be arranged in a ring or in a straight line. In a bus network, one machine is master and is allowed to transmit. An arbitration mechanism is needed to resolve conflicts when two or more machines want to transmit simultaneously.
In ring network, each bit propgates around on its own, not waiting for the rest of the packet to which it belongs.
3. Protocols: The rules and encoding specifications for sending data. The protocols also determine whether the network uses a peer-to-peer or client/server architecture.
4. Media: Devices can be connected by twisted-pair wire, coaxial cables, or fiber optic cables. Some networks do without connecting media altogether, communicating instead via radio waves.

Most LANs connect workstations and personal computers. Each node (individual computer) in a LAN has its own CPU with which it executes programs, but it also is able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as laser printers, as well as data. Users can also use the LAN to communicate with each other, by sending e-mail or engaging in chat sessions.

LANs are capable of transmitting data at very fast rates, much faster than data can be transmitted over a telephone line; but the distances are limited, and there is also a limit on the number of computers that can be attached to a single LAN.