Computer networks

Computer networksComputer networks

What is a network?What is a network? A A computer networkcomputer network is a group is a group

of interconnected computers. of interconnected computers. Networks may be classified Networks may be classified according to a wide variety of according to a wide variety of characteristics. This article characteristics. This article provides a general overview of provides a general overview of some types and categories and some types and categories and also presents the basic also presents the basic components of a network. components of a network.

The main objective of connecting The main objective of connecting these computers is to share these computers is to share resources and information with resources and information with each othereach other

LANLAN WANWAN MANMAN

Is a computer Is a computer network covering a network covering a small physical small physical area, like a home, area, like a home, office, or small office, or small group of buildings, group of buildings, such as a school, such as a school, or an airport or an airport

Is a network that Is a network that connects two or connects two or more Local Area more Local Area Networks or Networks or Campus Area Campus Area Networks Networks together but together but does not extend does not extend beyond the beyond the boundaries of boundaries of the immediate the immediate town/city. town/city.

Is a computer Is a computer network that network that covers a broad covers a broad area (i.e., any area (i.e., any network whose network whose communications communications links cross links cross metropolitan, metropolitan, regional, or regional, or national national boundaries boundaries

Local Area networkLocal Area network Local Area Network (LAN)Local Area Network (LAN) is a computer network covering a small is a computer network covering a small

physical area, like a home, office, or small group of buildings, such 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 as a school, or an airport. This is a network covering a small geographic area, like a home, office, or building. Current LANs are geographic area, like a home, office, or building. Current LANs are most likely to be based on Ethernet technology. most likely to be based on Ethernet technology.

The defining characteristics of LANs, in contrast to WANs (wide The defining characteristics of LANs, in contrast to WANs (wide area networks), include their higher data transfer rates, smaller area networks), include their higher data transfer rates, smaller geographic range, and lack of a need for leased telecommunication geographic range, and lack of a need for leased telecommunication lines. lines.

LAN networks are also primarily used in call centers as well as LAN networks are also primarily used in call centers as well as BPOSBPOS

An example of a LAN network of a An example of a LAN network of a LibraryLibrary

WANWAN A A Wide Area Network (WAN)Wide Area Network (WAN) is a computer network that covers a is a computer network that covers a

broad area Less formallybroad area Less formally

A WAN is a network that uses routers and public communications A WAN is a network that uses routers and public communications links links

Contrast with personal area networks (PANs), local area networks Contrast with personal area networks (PANs), local area networks (LANs), campus area networks (Cams), or metropolitan area (LANs), campus area networks (Cams), or metropolitan area networks (MANs) which are usually limited to a room, building, networks (MANs) which are usually limited to a room, building, campus or specific metropolitan area.campus or specific metropolitan area.

The largest and most well-known example of a WAN is the Internet. The largest and most well-known example of a WAN is the Internet.

A WAN is a data communications network that covers a relatively A WAN is a data communications network that covers a relatively broad geographic area (i.e. one city to another and one country to broad geographic area (i.e. one city to another and one country to another country) and that often uses transmission facilities provided another country) and that often uses transmission facilities provided by common carriers, such as telephone companiesby common carriers, such as telephone companies

Example of a WANExample of a WAN

MAN (metropolitan area network)MAN (metropolitan area network) A Metropolitan Area Network (MAN) is one of a number of types of networks (see 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 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. similar to an ISP, but for corporate users with large LANs.

There are three important features which discriminate MANs from LANs or WANs:There are three important features which discriminate MANs from LANs or WANs:

The network size falls intermediate between LANs and WANs. A MAN typically 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 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 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. large as the North of Scotland.

A MAN (like a WAN) is not generally owned by a single organization. The MAN, its 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 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 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, service provided to each user must therefore be negotiated with the MAN operator, and some performance guarantees are normally specified. and some performance guarantees are normally specified.

A MAN often acts as a high speed network to allow sharing of regional resources 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 (similar to a large LAN). It is also frequently used to provide a shared connection to other networks using a link to a WAN.other networks using a link to a WAN.

Example of a MAN ( Metropolitan Example of a MAN ( Metropolitan area network)area network)

Star NetworkStar Network Star networksStar networks are one of the most common are one of the most common

computer network topologies. In its simplest computer network topologies. In its simplest form, a star network consists of one central form, a star network consists of one central switch, hub or computer, which acts as a switch, hub or computer, which acts as a conduit to transmit messages. Thus, the hub conduit to transmit messages. Thus, the hub and leaf nodes, and the transmission lines and leaf nodes, and the transmission lines between them, form a graph with the topology between them, form a graph with the topology of a star. of a star.

An An activeactive star network has an active central star network has an active central node that usually has the means to prevent node that usually has the means to prevent echo-related problems.echo-related problems.

The star topology reduces the chance of The star topology reduces the chance of network failure by connecting all of the network failure by connecting all of the systems to a central node. systems to a central node. When applied to a bus-based network, this When applied to a bus-based network, this central hub rebroadcasts all transmissions central hub rebroadcasts all transmissions received from any peripheral node to all received from any peripheral node to all peripheral nodes on the network, sometimes peripheral nodes on the network, sometimes including the originating node. All peripheral including the originating node. All peripheral nodes may thus communicate with all others nodes may thus communicate with all others by transmitting to, and receiving from, the by transmitting to, and receiving from, the central node only.central node only.

The failure of a transmission line linking any The failure of a transmission line linking any peripheral node to the central node will result peripheral node to the central node will result in the isolation of that peripheral node from all in the isolation of that peripheral node from all others, but the rest of the systems will be others, but the rest of the systems will be unaffected.unaffected.

Advantages and Disadvantages of Advantages and Disadvantages of a Star Networka Star Network

AdvantagesAdvantages Better performanceBetter performance Isolation of devicesIsolation of devices Benefits from centralization:Benefits from centralization: SimplicitySimplicity

DisadvantagesDisadvantages Limited Network SizeLimited Network Size DependencyDependency Complex Wiring SystemComplex Wiring System

Ring NetworkRing Network A A ring networkring network is a network is a network

topology in which each node topology in which each node connects to exactly two other connects to exactly two other nodes, forming a circular nodes, forming a circular pathway for signals - a ring. pathway for signals - a ring. Data travels from node to Data travels from node to node, with each node handling node, with each node handling every packet.every packet.

Because a ring topology Because a ring topology provides only one pathway provides only one pathway between any two nodes, ring between any two nodes, ring networks may be disrupted by networks may be disrupted by the failure of a single link. A the failure of a single link. A node failure or cable break node failure or cable break might isolate every node might isolate every node attached to the ring.attached to the ring.

Advantages and DisadvantagesAdvantages and Disadvantages AdvantagesAdvantages Very orderly network where every device has access to the token and the Very orderly network where every device has access to the token and the

opportunity to transmit opportunity to transmit Performs better than a star topology under heavy network load Performs better than a star topology under heavy network load Can create much larger network using Token Ring Can create much larger network using Token Ring Does not require network server to manage the connectivity between the Does not require network server to manage the connectivity between the

computers computers DisadvantagesDisadvantages

One malfunctioning workstation or bad port in the MAU can create problems One malfunctioning workstation or bad port in the MAU can create problems for the entire network for the entire network

Moves, adds and changes of devices can affect the network Moves, adds and changes of devices can affect the network Network adapter cards and MAU's are much more expensive than Ethernet Network adapter cards and MAU's are much more expensive than Ethernet

cards and hubs cards and hubs Much slower than an Ethernet network under normal load Much slower than an Ethernet network under normal load

Bus NetworkBus Network A A bus network topologybus network topology is a network is a network

architecture in which a set of clients architecture in which a set of clients are connected via a shared are connected via a shared communications line, called a bus. communications line, called a bus.

There are several common instances There are several common instances of the bus architecture, including one of the bus architecture, including one in the motherboard of most computers, in the motherboard of most computers, and those in some versions of and those in some versions of Ethernet networks.Ethernet networks.

Bus networks are the simplest way to Bus networks are the simplest way to connect multiple clients, but may have connect multiple clients, but may have problems when two clients want to problems when two clients want to transmit at the same time on the same transmit at the same time on the same bus.bus.

A true bus network is passive – the A true bus network is passive – the computers on the bus simply listen for computers on the bus simply listen for a signal; they are not responsible for a signal; they are not responsible for moving the signal along. However, moving the signal along. However, many active architectures can also be many active architectures can also be described as a "bus", as they provide described as a "bus", as they provide the same logical functions as a the same logical functions as a passive bus.passive bus.

Advantages and Disadvantages of Advantages and Disadvantages of a Bus Networka Bus Network

AdvantagesAdvantages Easy to implement and extend Easy to implement and extend Well suited for temporary or small networks not requiring high speeds (quick setup) Well suited for temporary or small networks not requiring high speeds (quick setup) Cheaper than other topologies. Cheaper than other topologies. Cost effective as only a single cable is used Cost effective as only a single cable is used Cable faults are easily identified Cable faults are easily identified

DisadvantagesDisadvantages Limited cable length and number of stations. Limited cable length and number of stations. If there is a problem with the cable, the entire network goes down. If there is a problem with the cable, the entire network goes down. Maintenance costs may be higher in the long run. Maintenance costs may be higher in the long run. Performance degrades as additional computers are added or on heavy traffic. Performance degrades as additional computers are added or on heavy traffic. Proper termination is required (loop must be in closed path). Proper termination is required (loop must be in closed path). Significant Capacitive Load (each bus transaction must be able to stretch to most Significant Capacitive Load (each bus transaction must be able to stretch to most

distant link). distant link). It works best with limited number of nodes. It works best with limited number of nodes. It is slower than the other topologies. It is slower than the other topologies.

Tree NetworkTree Network telecommunication networks, a tree network telecommunication networks, a tree network

is a combination of two or more star is a combination of two or more star networks connected together. Each star networks connected together. Each star network is a local area network (LAN) in network is a local area network (LAN) in which there is a central computer or server which there is a central computer or server to which all the workstation nodes are to which all the workstation nodes are directly linked. The central computers of the directly linked. The central computers of the star networks are connected to a main cable star networks are connected to a main cable called the bus. Thus, a tree network is a bus called the bus. Thus, a tree network is a bus network of star networks. network of star networks.

The tree network topology is ideal when the The tree network topology is ideal when the workstations are located in groups, with workstations are located in groups, with each group occupying a relatively small each group occupying a relatively small physical region. An example is a university physical region. An example is a university campus in which each building has its own campus in which each building has its own star network, and all the central computers star network, and all the central computers are linked in a campus-wide system. It is are linked in a campus-wide system. It is easy to add or remove workstations from easy to add or remove workstations from each star network. Entire star networks can each star network. Entire star networks can be added to, or removed from, the bus. If be added to, or removed from, the bus. If the bus has low loss and/or is equipped with the bus has low loss and/or is equipped with repeaters, this topology can be used in a repeaters, this topology can be used in a wide area network (WAN) configuration. wide area network (WAN) configuration.

AcknowledgementsAcknowledgements

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