Data Communication And Networking Computer Science Essay

Published Date: 02 Nov 2017

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INDIVIDUAL ASSIGNMENT

DATA COMMUNICATION AND NETWORKING

IT 703A(08)

Name : Vincent Vinoth A/L James Manimaran

IC : 910126-02-5629

Index No : PP102374

Batch No : 1101

CAMPUS : PENANG

WORD COUNT :

Question

You are now working in the IT department in an organization and responsible to design a network system for the organization. Do a research on the types of network topology available and identify the network topology that you would recommend to the management. Give the reasons to support your recommendation.

The transmission media that are used to convey information can be classified as guided or unguided. Guided media provide a physical path along which signal is propagated. Unguided media employs and antenna for transmitting through air, vacuum or water. Discuss the both transmission media in detail with examples.

Table of Content

Content

Pages

Introduction

question 1

question 2

Conclusion

BIBLIOGRAPHY

Introduction

Network topology, refers to the arrangement or physical layout of computers, cables, and other components on the network. "Topology" is the standard term that most network professionals use when they refer to the network's basic design. In addition to the term "topology," there are several other terms that are used to define a network's design: Physical layout, Design, Diagram, and Map. This report will set a whole gamut of information and work that went into the search for a suitable topology to be used by the consumer.

This report will also explain transmission medium through its two main group which is guided media, electromagnetic waves are guided along a solid medium, such as copper twisted pair, copper coaxial cable, and optical fibre. And unguided media, the wireless media that simply transports electromagnetic waves without using any physical conductor

Question 1

Network topology is the arrangement of the various elements of a computer or biological network. Essentially, it is the topological structure of a network, and may be depicted physically or logically. Physical topology refers to the placement of the network's various components, including device location and cable installation, while logical topology shows how data flows within a network, regardless of its physical design. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ between two networks, yet their topologies may be identical.

A good example is a local area network (LAN). Any given node in the LAN has one or more physical links to other devices in the network, graphically mapping these links results in a geometric shape that can be used to describe the physical topology of the network. Conversely, mapping the data flow between the components determines the logical topology of the network.

The study of network topology recognizes three basic topologies:

Bus

Star

Ring

Bus network

In local area networks where bus topology is used, each node is connected to a single cable. Each computer or server is connected to the single bus cable. A signal from the source travels in both directions to all machines connected on the bus cable until it finds the intended recipient. If the machine address does not match the intended address for the data, the machine ignores the data. Alternatively, if the data matches the machine address, the data is accepted. Since the bus topology consists of only one wire, it is rather inexpensive to implement when compared to other topologies. However, the low cost of implementing the technology is offset by the high cost of managing the network. Additionally, since only one cable is utilized, it can be the single point of failure. If the network cable is terminated on both ends and when without termination data transfer stop and when cable breaks, the entire network will be down.

http://members.tripod.com/barhoush_2/images/lin_bus.gif

Fig 1: bus network

Star network

In local area networks with a star topology, each network host is connected to a central hub with a point-to-point connection. In Star topology every node is connected to central node called hub or switch. The switch is the server and the peripherals are the clients. The network does not necessarily have to resemble a star to be classified as a star network, but all of the nodes on the network must be connected to one central device. All traffic that traverses the network passes through the central hub. The hub acts as a signal repeater. The star topology is considered the easiest topology to design and implement. An advantage of the star topology is the simplicity of adding additional nodes. The primary disadvantage of the star topology is that the hub represents a single point of failure.

http://www.klbict.co.uk/gcse/theory/images/star_network_topology_ani.gif

Fig 2: star network

Ring network

A network topology that is set up in a circular fashion in which data travels around the ring in one direction and each device on the right acts as a repeater to keep the signal strong as it travels. Each device incorporates a receiver for the incoming signal and a transmitter to send the data on to the next device in the ring. The network is dependent on the ability of the signal to travel around the ring. When a device sends data, it must travel through each device on the ring until it reaches its destination. Every node is a critical link.

http://homepages.uel.ac.uk/u0330814/images/ring.gif

Fig 3: ring network

Tree network

The type of network topology in which a central 'root' node is connected to one or more other nodes that are one level lower in the hierarchy with a point-to-point link between each of the second level nodes and the top level central 'root' node, while each of the second level nodes that are connected to the top level central 'root' node will also have one or more other nodes that are one level lower in the hierarchy connected to it, also with a point-to-point link, the top level central 'root' node being the only node that has no other node above it in the hierarchy. Each node in the network having a specific fixed number, of nodes connected to it at the next lower level in the hierarchy, the number, being referred to as the 'branching factor' of the hierarchical tree. This tree has individual peripheral nodes.

A network that is based upon the physical hierarchical topology must have at least three levels in the hierarchy of the tree, since a network with a central 'root' node and only one hierarchical level below it would exhibit the physical topology of a star.

A network that is based upon the physical hierarchical topology and with a branching factor of 1 would be classified as a physical linear topology.

The branching factor, f, is independent of the total number of nodes in the network and, therefore, if the nodes in the network require ports for connection to other nodes the total number of ports per node may be kept low even though the total number of nodes is large – this makes the effect of the cost of adding ports to each node totally dependent upon the branching factor and may therefore be kept as low as required without any effect upon the total number of nodes that are possible.

The total number of point-to-point links in a network that is based upon the physical hierarchical topology will be one less than the total number of nodes in the network.

If the nodes in a network that is based upon the physical hierarchical topology are required to perform any processing upon the data that is transmitted between nodes in the network, the nodes that are at higher levels in the hierarchy will be required to perform more processing operations on behalf of other nodes than the nodes that are lower in the hierarchy. Such a type of network topology is very useful and highly recommended.

tree topology image diagram wikipedia, tree network topology

Fig 4: tree network

Advantages

It is scalable. Secondary nodes allow more devices to be connected to a central node.

Point to point connection of devices.

Having different levels of the network makes it more manageable hence easier fault identification and isolation.

It is an extension of Star and bus Topologies, so in networks where these topologies can't be implemented individually for reasons related to scalability, tree topology is the best alternative.

Expansion of Network is possible and easy.

Here, we divide the whole network into segments (star networks), which can be easily managed and maintained. 

Error detection and correction is easy.

Each segment is provided with dedicated point-to-point wiring to the central hub.

If one segment is damaged, other segments are not affected.

Disadvantages

Maintenance of the network may be an issue when the network spans a great area.

Since it is a variation of bus topology, if the backbone fails, the entire network is crippled.

Because of its basic structure, tree topology, relies heavily on the main bus cable, if it breaks whole network is crippled.

As more and more nodes and segments are added, the maintenance becomes difficult.

Scalability of the network depends on the type of cable used.

Question 2

Guided media, electromagnetic waves are guided along a solid medium, such as copper twisted pair, copper coaxial cable, and optical fibre. In the case of guided media, the medium itself is more important in determining the limitations of transmission. Table 1.0 indicates the characteristics typical for the common guided media for long-distance point-to-point applications.

http://www.engineersblogsite.com/wp-content/uploads/2010/05/Point-to-point-transmission-characteristics-of-guided-media.jpg

Table 1.0: characteristics of common guided media

For guided transmission media, the transmission capacity, in terms of either data rate or bandwidth, depends critically on the distance and on whether the medium is point-to-point or multipoint.

Twisted Pair:

The least-expensive and most widely-used guided transmission medium is twisted pairs. A twister pair consists of two conductors (normally copper) .Each with its own plastic insulation, twisted together as shown in figure 1.0.

http://www.engineersblogsite.com/wp-content/uploads/2010/05/15.jpg

Fig 1: twisted pair cable

A twisted pair consists of two insulated copper wires arranged in a regular spiral pattern. A wire pair acts as a single communication link. Typically, a number of these pairs are bundled together into a cable by wrapping them in a tough protective sheath. Over longer distances, cables may contain hundreds of pairs. The twisting tends to decrease the crosstalk interference between adjacent pairs in a cable. Neighbouring pairs in a bundle typically have somewhat different twist lengths to reduce the crosstalk interference. On long-distance links, the twist length typically varies from two to six inches. The wires in a pair have thicknesses of from 0.016 to 0.036 inches.

By far the most common transmission medium for both analogue and digital signals is twisted pair. It is the most commonly used medium in the telephone network as well as being the workhorse for communications within buildings. In the telephone system, individual residential telephone sets are connected to the local telephone exchange, or "end office," by twisted-pair wire. These are referred to as subscriber loops.

Within an office building, each telephone is also connected to a twisted pair, which goes to the in-house private branch exchange (PBX) system or to a Centrex facility at the end office. These twisted-pair installations were designed to support voice traffic using analogue signalling. However, by means of a modem, these facilities can handle digital data traffic at modest data rates.

Coaxial Cable:

Coaxial cable, like twisted pair, consists of two conductors, but is constructed differently to permit it to operate over a wider range of frequencies. It consists of a hollow outer cylindrical conductor that surrounds a single inner wire conductor (Figure 2.0). The inner conductor is held in place by either regularly spaced insulating rings or a solid dielectric material. The outer conductor is covered with a jacket or shield. A single coaxial cable has a diameter of from 0.4 to about 1 in. Because of its shielded, concentric construction, coaxial cable is much less susceptible to interference and crosstalk than is twisted pair. Coaxial cable can be used over longer distances and supports more stations on a shared line than twisted pair.

Coaxial cable is perhaps the most versatile transmission medium and is enjoying widespread use in a wide variety of applications; the most important of these are:

Television distribution

Long-distance telephone transmission

Short-run computer system links

Local area networks

http://www.engineersblogsite.com/wp-content/uploads/2010/05/16.jpg

Fig 2: coaxial cable

Coaxial cable is spreading rapidly as a means of distributing TV signals to individual homes-cable TV. From its modest beginnings as Community Antenna Television (CATV), designed to provide service to remote areas, cable TV will eventually reach almost as many homes and offices as the telephone. A cable TV system can carry dozens or even hundreds of TV channels at ranges up to a few tens of miles.

Coaxial cable has traditionally been an important part of the long-distance telephone network. Today, it faces increasing competition from optical fibre, terrestrial microwave, and satellite. Using frequency-division multiplexing a coaxial cable can carry over 10,000 voice channels simultaneously.

Fibre optic communication

An optical fibre is a thin (2 to 125 pm), flexible medium capable of conducting an optical ray. Various glasses and plastics can be used to make optical fibres. The lowest losses have been obtained using fibres of ultra-pure fused silica. Ultra-pure fibre is difficult to manufacture; higher-loss multi component glass fibres are more economical and still provide good performance. Plastic fibre is even less costly and can be used for short-haul links, for which moderately high losses are acceptable.

An optical fibre cable has a cylindrical shape and consists of three concentric sections: the core, the cladding, and the jacket (Figure 3.0). The core is the innermost section and consists of one or more very thin strands, or fibres, made of glass or plastic. Each fibre is surrounded by its own cladding, a glass or plastic coating that has optical properties different from those of the core. The outermost layer, surrounding one or a bundle of cladded fibres, is the jacket. The jacket is composed of plastic and other material layered to protect against moisture, abrasion, crushing, and other environmental dangers

http://www.madehow.com/images/hpm_0000_0001_0_img0138.jpg

Fig 3: optical fibre

One of the most significant technological breakthroughs in data transmission has been the development of practical fibre optic communications systems. Optical fibre already enjoys considerable use in long-distance telecommunications, and its use in military applications is growing. The continuing improvements in performance and decline in prices, together with the inherent advantages of optical fibre, have made it increasingly attractive for local area networking.

The unguided media is the wireless media. It simply transports electromagnetic waves without using any physical conductor. Signals are normally broadcast through the air and thus are available to anyone who has the device capable of receiving them. Unguided signals can be travelled from source to the destination in several ways. These ways include ground propagation, sky propagation and line of sight propagation. 

Ground propagation

Ground wave propagation is particularly important on the LF and MF portion of the radio spectrum. Ground wave radio propagation is used to provide relatively local radio communications coverage, especially by radio broadcast stations that require covering a particular locality.

http://www.ustudy.in/imagebrowser/view/image/5138/_original

Fig 4: ground propagation

Ground wave radio signal propagation is ideal for relatively short distance propagation on these frequencies during the daytime. Sky-wave ionosphere propagation is not possible during the day because of the attenuation of the signals on these frequencies caused by the D region in the ionosphere. In view of this, radio communications stations need to rely on the ground-wave propagation to achieve their coverage.

A ground wave radio signal is made up from a number of constituents. If the antennas are in the line of sight then there will be a direct wave as well as a reflected signal. As the names suggest the direct signal is one that travels directly between the two antenna and is not affected by the locality. There will also be a reflected signal as the transmission will be reflected by a number of objects including the earth's surface and any hills, or large buildings. That may be present.

In addition to this there is surface wave. This tends to follow the curvature of the Earth and enables coverage to be achieved beyond the horizon. It is the sum of all these components that is known as the ground wave. Beyond the horizon the direct and reflected waves are blocked by the curvature of the Earth, and the signal is purely made up from the diffracted surface wave. It is for this reason that surface wave is commonly called ground wave propagation.

Sky propagation

Sky wave refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of the Earth, sky wave propagation can be used to communicate beyond the horizon, at intercontinental distances. It is mostly used in the shortwave frequency bands.

http://www.fas.org/man/dod-101/navy/docs/es310/propagat/IMG00023.GIF

Fig 5: sky propagation

As a result of sky wave propagation, a signal from a distant AM broadcasting station, a shortwave station, or during sporadic E propagation conditions a low frequency television station can sometimes be received as clearly as local stations. Sky wave propagation is distinct from ground wave propagation, where radio waves travel near Earth's surface without being reflected or refracted by the atmosphere the dominant propagation mode at lower frequencies, and line-of-sight propagation, in which radio waves travel in a straight line, the dominant mode at higher frequencies. Most long-distance shortwave (high frequency) radio communication is a result of sky wave propagation. Since the early 1920s amateur radio operators, limited to lower transmitter power than broadcast stations, have taken advantage of sky wave for long distance communication.

Line-of-sight propagation

Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line. The rays or waves may be diffracted, refracted, reflected, or absorbed by atmosphere and obstructions with material and generally cannot travel over the horizon or behind obstacles.

At low frequencies (below approximately 2 MHz or so) radio signals travel as ground waves, which follow the Earth's curvature due to diffraction with the layers of atmosphere. This enables AM radio signals in low-noise environments to be received well after the transmitting antenna has dropped below the horizon. Additionally, frequencies between approximately 1 and 30 MHz can be reflected by the F1/F2 Layer, thus giving radio transmissions in this range a potentially global reach (see shortwave radio), again along multiple deflected straight lines. The effects of multiple diffraction or reflection lead to macroscopically "quasi-curved paths".

http://www.d.umn.edu/~tkwon/course/1001/NetworkECE1001_files/slide0047_image025.jpg

Fig 6: line-of-sight propagation

However, at higher frequencies and in lower levels of the atmosphere, neither of these effects is significant. Thus any obstruction between the transmitting antenna and the receiving antenna will block the signal, just like the light that the eye may sense. Therefore, since the ability to visually see a transmitting roughly corresponds to the ability to receive a radio signal from it, the propagation characteristic of high-frequency radio is called "line-of-sight". The farthest possible point of propagation is referred to as the "radio horizon". In practice, the propagation characteristics of these radio waves vary substantially depending on the exact frequency and the strength of the transmitted signal.

Conclusion

This report elaborates the various network topology that are arrangement of the various elements of a computer or biological network. Essentially, it is the topological structure of a network, and may be depicted physically or logically. This report also want ascertains that a company wants to know which topology is best suit their need. This report shows through careful consideration that the tree network topology is best suited.

In this report, question 2 discusses about transmission medium, A transmission medium (plural transmission media) is a material substance (solid, liquid, gas, or plasma) that can propagate energy waves. For example, the transmission medium for sound received by the ears is usually air, but solids and liquids may also act as transmission media for sound. Electromagnetic radiation can be transmitted through an optical media, such as optical fibre, or through twisted pair wires and coaxial cable.