Computer networks

What is a network? A computer network is a group of interconnected computers. Networks may be classified according to a wide variety of characteristics. This article provides a general overview of some types and categories and also presents the basic components of a network. The main objective of connecting these computers is to share resources and information with each other LAN WAN MAN Is a computer network covering a small physical area, like a home, office, or small group of buildings, such as a school, or an airport Is a network that connects two or more Local Area Networks or Campus Area Networks together but does not extend beyond the boundaries of the immediate town/city. Is a computer network that covers a broad area (i.e., any network whose communications links cross metropolitan, regional, or national boundaries

Local Area network Local Area Network (LAN) is a computer network covering a small physical area, like a home, office, or small group of buildings, such as a school, or an airport. This is a network covering a small geographic area, like a home, office, or building. Current LANs are most likely to be based on Ethernet technology. The defining characteristics of LANs, in contrast to WANs (wide area networks), include their higher data transfer rates, smaller geographic range, and lack of a need for leased telecommunication lines. LAN networks are also primarily used in call centers as well as BPOS

An example of a LAN network of a Library

WAN A Wide Area Network (WAN) is a computer network that covers a broad area Less formally A WAN is a network that uses routers and public communications links Contrast with personal area networks (PANs), local area networks (LANs), campus area networks (Cams), or metropolitan area networks (MANs) which are usually limited to a room, building, campus or specific metropolitan area. The largest and most well-known example of a WAN is the Internet. A WAN is a data communications network that covers a relatively broad geographic area (i.e. one city to another and one country to another country) and that often uses transmission facilities provided by common carriers, such as telephone companies

MAN (metropolitan area network) A Metropolitan Area Network (MAN) is one of a number of types of networks (see also LAN and WAN). A MAN is a relatively new class of network, it serves a role similar to an ISP, but for corporate users with large LANs. There are three important features which discriminate MANs from LANs or WANs: The network size falls intermediate between LANs and WANs. A MAN typically covers an area of between 5 and 50 km diameter. Many MANs cover an area the size of a city, although in some cases MANs may be as small as a group of buildings or as large as the North of Scotland. A MAN (like a WAN) is not generally owned by a single organization. The MAN, its communications links and equipment are generally owned by either a consortium of users or by a single network provider who sells the service to the users. This level of service provided to each user must therefore be negotiated with the MAN operator, and some performance guarantees are normally specified. A MAN often acts as a high speed network to allow sharing of regional resources (similar to a large LAN). It is also frequently used to provide a shared connection to other networks using a link to a WAN.

Example of a MAN ( Metropolitan area network)

Star Network Star networks are one of the most common computer network topologies. In its simplest form, a star network consists of one central switch, hub or computer, which acts as a conduit to transmit messages. Thus, the hub and leaf nodes, and the transmission lines between them, form a graph with the topology of a star. An active star network has an active central node that usually has the means to prevent echo-related problems. The star topology reduces the chance of network failure by connecting all of the systems to a central node. When applied to a bus-based network, this central hub rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, sometimes including the originating node. All peripheral nodes may thus communicate with all others by transmitting to, and receiving from, the central node only. The failure of a transmission line linking any peripheral node to the central node will result in the isolation of that peripheral node from all others, but the rest of the systems will be unaffected.

Advantages and Disadvantages of a Star Network Advantages Better performance Isolation of devices Benefits from centralization: Simplicity Disadvantages Limited Network Size Dependency Complex Wiring System

Ring Network A ring network is a network topology in which each node connects to exactly two other nodes, forming a circular pathway for signals - a ring. Data travels from node to node, with each node handling every packet. Because a ring topology provides only one pathway between any two nodes, ring networks may be disrupted by the failure of a single link. A node failure or cable break might isolate every node attached to the ring.

Advantages and Disadvantages Advantages Very orderly network where every device has access to the token and the opportunity to transmit Performs better than a star topology under heavy network load Can create much larger network using Token Ring Does not require network server to manage the connectivity between the computers Disadvantages One malfunctioning workstation or bad port in the MAU can create problems for the entire network Moves, adds and changes of devices can affect the network Network adapter cards and MAU's are much more expensive than Ethernet cards and hubs Much slower than an Ethernet network under normal load

Bus Network A bus network topology is a network architecture in which a set of clients are connected via a shared communications line, called a bus. There are several common instances of the bus architecture, including one in the motherboard of most computers, and those in some versions of Ethernet networks. Bus networks are the simplest way to connect multiple clients, but may have problems when two clients want to transmit at the same time on the same bus. A true bus network is passive – the computers on the bus simply listen for a signal; they are not responsible for moving the signal along. However, many active architectures can also be described as a "bus", as they provide the same logical functions as a passive bus.

Advantages and Disadvantages of a Bus Network Advantages Easy to implement and extend Well suited for temporary or small networks not requiring high speeds (quick setup) Cheaper than other topologies. Cost effective as only a single cable is used Cable faults are easily identified Disadvantages Limited cable length and number of stations. If there is a problem with the cable, the entire network goes down. Maintenance costs may be higher in the long run. Performance degrades as additional computers are added or on heavy traffic. Proper termination is required (loop must be in closed path). Significant Capacitive Load (each bus transaction must be able to stretch to most distant link). It works best with limited number of nodes. It is slower than the other topologies.

Tree Network telecommunication networks, a tree network is a combination of two or more star networks connected together. Each star network is a local area network (LAN) in which there is a central computer or server to which all the workstation nodes are directly linked. The central computers of the star networks are connected to a main cable called the bus. Thus, a tree network is a bus network of star networks. The tree network topology is ideal when the workstations are located in groups, with each group occupying a relatively small physical region. An example is a university campus in which each building has its own star network, and all the central computers are linked in a campus-wide system. It is easy to add or remove workstations from each star network. Entire star networks can be added to, or removed from, the bus. If the bus has low loss and/or is equipped with repeaters, this topology can be used in a wide area network (WAN) configuration.

Acknowledgements Wikipedia.org Google.com MsnEncarta.com

Computer networks

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Computer networks