The Wari Specializes In Star Topology Computer Science Essay

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The Local Area Network is by far the most common type of data network. As the name suggests, a LAN serves a local area typically the area of a floor of a building, but in some cases spanning a distance of several kilometers. Typical installations are in industrial plants, office buildings, college or university campuses, or similar locations.

It is divided into two parts WARI and WAIRLISE.

WARI specializes in Star topology, Bus topology, Ring topology and Mesh topology.

1.2 Introduction

Network is important in computer world each communication does not work without network and it consists of LAN, MAN and WAN.

A LAN is a local area network that means it is diffused over a small area, such as a home, a school, our college, sometime maybe a small group of buildings. A LAN is usually but not always carried-out as a single IP subnet. They are usually controlled by one person and tend to use Ethernet and wireless connectivity systems.

Typically a LAN can withstand up to 1024 computers but practically the boundary, is 256 computers because of the routers and in real life, even less computers are connected in the LAN because of the need.

1.3 Objectives

We made this report to:

To understand many things about networks.

Make this things about LAN easy to understand because we made it in easy way.

Also to get more information about networks and LAN .

To make a user knows which the best topology of networks.

1.4 Method

At first we met for taking a first look on the subject , When I started this report we collect all sources I can found , We search in a Books .. because I need know more details about the subject , I also go to the website in internet and see information and understand and write information by our concept in network course ( By Dr.Asad Tarq ) , also we see a lot of report for people make report before to know how the sheep for this report , and I use the way what ( Dr.Mohamed Elhassan ) learned us in technical report .

CHAPTER2 . NETWORKS

2.1 General network

A computer network is simply two or more computers connected together so they can exchange information. A small network can be as simple as two computers linked together by a single cable

2.2 Network criteria :

He network most has these criteria : To make network more effective and efficient performance, reliability, and security.

2.2.1 Performance

"Performance can be measured in many ways, including transit time and response time. Transit time is the amount of time required for a message to travel from one device to another. Response time is the elapsed time between an enquiry and a response"(2)

This Criteria is important for any network for example at my house network is weak.. Because the box in Neighborhood is old .. but when I go to house for my friend in AL- Khober the network is very Strong ,because the box in Neighborhood is new .

This Criteria is depended for number of users, like if there are a lot of users make response is low .

2.2.2 Reliability

"Reliability: In addition to accuracy of delivery, network reliability is measured frequency of failure, the time it takes a link to recover from a failure, and the network’s robustness in a catastrophe. "(2)

Reliability means when you send a message sure this message go to correct user that is a function for reliability.

2.2.3 Security

"Security: Network security issues include protecting data from unauthorized access and viruses."(2)

This Criteria is very important for any network because if the security is not strong any one can hacked and take all information at this computer connected with this network .

2.3 Network type:

Local area network (LAN) : That mean smallest network can found in small distance such as transferee the data inside the class , small building , a home, school or computer laboratory and it is really important.

Wide Area Network (WAN): That mean largest network can found in large distance such as transferee the data between the countries.

Metropolitan area network (MAN): That mean medium network can found in medium distance such as transferee the data between the cities.

CHAPTER3 . LAN

3.1 LAN

A Local Area Network (LAN) consists of four major components:

-Servers: Which are computers that are organize and manage the network.

They also centralize the information and are responsible for the security of information. Who control and maintain those servers are qualified and authorized personnel.

-Work Stations: Are devices that computer users do their work on, in the network.

-Network Operating system: This is an operating system that is designed especially for the network. It sends and receives information through the network.

-Connection tools and software: Is hardware with its software designed to make the transmission of information easier.

There are non-primary components connected with the network

That varies depending on the need such as: printers, faxes, scanners, etc.

3.2 Topology

The term physical topology refers to the way in which a network is laid out physically

two or more devices connect to a link; two or more links form a topology. 

3.2.1 Star topology

"In the star LAN topology, each station is directly connected to a common central node. Typically, each station attaches to a central node, referred to as the star coupler, via two point-to-point links, one for transmission and one for reception. In general, there are two alternatives for the operation of the central node. One approach is for the central node to operate in a broadcast fashion. A transmission of a frame from one station to the node is retransmitted on all of the outgoing links. In this case, although the arrangement is physically a star, it is logically a bus; a transmission from any station is received by all other stations, and only one station at a time may successfully transmit. Another approach is for the central node to act as a frame switching device. An incoming frame is buffered in the node and then retransmitted on an outgoing link to the destination station." (3) Figure 1. Show how connected star topology

Figure 1. Star topology

That show how every computer connected with hub by one wire.

3.2.2 Ring topology

"In the ring topology, the network consists of a set of repeaters joined by point-to point links in a closed loop. By bit, on the other link as fast as they are received, with no buffering at the repeater. The links are unidirectional; that is, data are transmitted in one direction only and all are oriented in the same way. Thus, data circulate around the ring in one direction (clockwise or counterclockwise).

Each station attaches to the network at a repeater and can transmit data onto the network through that repeater. As with the bus and tree, data are transmitted in frames. As a frame circulates past all the other stations, the destination station recognizes its address and copies the frame into a local buffer as it goes by. The frame continues to circulate until it returns to the source station, where it is removed. Because multiple stations share the ring, medium access control is needed to determine at what time each station may insert frames."(4) Figure 2. Show how connected ring topology

Figure 2. Ring topology

That show how one computer connected with other computer by one wire and make it like a ring.

3.2.3 Bus topology

For the bus, all stations attach, through appropriate hardware interfacing known as a tap, directly to a linear transmission medium, or bus. Full-duplex operation between the station and the tap allows data to be transmitted onto the bus and received from the bus. A transmission from any station propagates the length of the medium in both directions and can be received by all other stations. At each end of the bus is a terminator, which absorbs any signal, removing it from the bus. Figure 3. Show how connected bus topology

Figure 3. bus topology

That show how every computer connected with one line and but tap in line to connected with computers .

3.2.4 Mesh topology

Mesh offers several advantages over other network topologies. First, the use of dedicated links guarantees that each connection can carry its own data load, thus eliminating the traffic problems that can occur when links must be shared by multiple devices. Second, a mesh topology is robust. If one link becomes unusable, it does not incapacitate the entire system. Third, there is the advantage of privacy or security. When every message travels along a dedicated line, only the intended recipient sees it. Physical boundaries prevent other users from gaining access to messages. Finally, point-to-point .links make fault identification and fault isolation easy. Traffic can be routed to avoid. links with suspected problems. This facility enables the network manager to discover the precise location of the fault and aids in finding its cause and solution. The main disadvantages of a mesh are related to the amount of cabling and the number of I/O ports required. First, because every device must be connected to every other device, installation and reconnection are difficult. Second, the sheer bulk of the wiring can be greater than the available space (in walls, ceilings, or floors) can accommodate. Finally, the hardware required to connect each link (I/O ports and cable) can be prohibitively expensive. For these reasons a mesh topology is usually implemented in a limited fashion, for example, as a backbone connecting the main computers of a hybrid network that can include several other topologies. One practical example of a mesh topology is the connection of telephone regional offices in which each regional office needs to be connected to every other regional office. Figure 4. Show how connected mesh topology

Figure 4. Mesh topology

That show how every computer connected with others and become like a mesh .

3.3 Compare between Topology

Topology

Contact wires

Setup

Disadvantage

Information Transfer

Cost

Star Bus

Each computer connects to a central connection device.

Each computer must be close to the central device(Hub).

If the connection device(Hub) goes down, then the network is down.

All information passes through the Hub device

More expensive of the simple topologies, it requires costly connection device.

Bus

.

All device are connects single cable .

Connect the cable from one computer to the next and so on to the end. A terminator is placed at each end of the network.

If one computer goes down, the entire network goes down.

One computer at a time sends information. Information goes along the cable and the computer accesses the information off the cable.

It is the cheapest topology because it has one cable.

Ring

Each tow device connects to each other.

Computers are located close to each other.

Setup is easy.

There is no connector.

The ring has no beginning and no end.

If there's a break in the cable or an error in the network, information continues to transfer through the rest of the ring until reaching the point of the break.

Information goes in one direction around the ring and passes along the ring until it reaches the correct computer.

It's one of the expensive topology because the high cable costs.

Mesh

Connect all device to each other .

Connect many different devices each one Connect to the other .

It has a lot of wires and hard to find the break in the cable.

Often used across long distances.

it's depends on the numbers of wires.

Table 1. Compare Between 4 topology

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