networs and telecommunication - de l200

NETWORKS AND TELECOMMUNICATION

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IT Networks

IT network is a co-ordinated group of IT components (computers linked with equipment and systems) that support many people working together by using and sharing data/info.. IT networks therefore consists of combinations of PC’s, storage devices and communication equipment.

IT networks vary according to:

– Span of control: centralised, distributed.

– Ownerships: Private Network (for an organizational use only) or Public Network (no restrictions and use of its resources).

– Geographical location: LAN (Local Area Network), MAN (Metropolitan Area Network) , WAN (Wide Area Network)

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Centralised and Distributed IT Network systems

Centralized IT network

Usually have a central/one computing processing, storage and communication device centre.

It usually support single tasks at a time. All terminals and interfaces are centralized or in one area and have only one operating system.

The main advantage is that they are easy to maintain.

But when part of the system breaks down, the whole system is affected. e.g. 3-in-1 machines like printer, fax, scanner.

It may not support additional devices.

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Distributed network systems– Spread over wider areas

– multi-user systems. They

– Support multiple Operating systems communication links and processing systems.

– A mainframe computer is an example connected with several workstations.

Centralised and distributed IT network systems

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Types of networks

LAN: – Is an IT network system that serves users within a confined

geographical area or a “local area”. It spans a distance of about 1km, an office, a building or groups of buildings in one location.

– They connect nearby IT devices usually with visible direct and short cables.

– Owned and operated by individuals or organizations.

– Economy and flexibility.

– when part of the system breaks down, the whole system is affected.

– They may be client-server or peer-to-peer.

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MAN – Networks that link office buildings within a city or a metropolis.

It may span several kilometers.

– Involve the use of invisible cables, radio waves or satellite dishes to link the various IT devices.

– Normally own by organizations.

– When a part of the system breaks down, the others system may not be affected.

– Cost and the administration of MAN may be high and difficult.

Types of networks

WAN: – is an IT network that span wide geographical area for example a

whole country.

– They are the largest type of network available. eg the Internet is the largest WAN in the world.

– Owned by multinational companies, with worldwide branches.

– Uses radio or microwave links as well as satellite dishes to connect the various IT systems usually servers.

– The initial cost may be expensive, but the long cost is shared by the users.

Types of networks

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Network topology

The physical arrangement or layout of IT networks. Network architecture-describes how IT networks

are configured and the strategies employed to optimize its use or resources. Types of topology:

–Star – connected to a central hub.–Ring -connected in a continuous loop.–Bus – connected to a common channel–Hybrid – combination of star, bus and ring.

Network topology

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Advantages of Networks

Sharing of peripheral devices

Better communication - email

Security of information –through administrator

Access to databases – private and organizational

Sharing of program and data – (Hutchinson and Sawyer, 2000)

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Services on IT networks

Fax messagesVoice mailElectronic mailVideo conferencingElectronic data exchange – exchange of standard

business documents.Virtual office – offices devoid of physical

structuresIntranets and extranetsTelecommuting – work b/n office and home

(Hutchinson and Sawyer, 2000).

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Telecommunications

Basic Concepts:

– Telecommunications or communications in IT refers to the electronic transfer of data/information across distances or from one location to another (Hutchinson & Sawyer, 2000).

– Communication systems are electronic systems that transmit data/info. from one location to another.

– The elements of communication systems therefore include – sending and receiving devices, communication channels, connecting devices, and transmission specifications (O’Leary & O’Leary, 2004).

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Sending and receiving devices – theses include all devices can be used to send and/or receive data/info./instructions on IT networks. These are the source & receiver devices included but not limited to computers, mobile phones, TV, radio set, etc.

Communication channels – these are the actual connecting or transmission medium, devices or links which can be physical (wired - cable) or non-physical (wireless connections).These include telephone lines, coaxial cables and fiber-optic cable; and infrared, broadcast radio, microwave and satellite (O’Leary & O’Leary, 2004).

Telecommunications

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Connecting devices – these devices – act as an interface/link between the sending and receiving devices and

the communication channel

– convert incoming and/or outgoing messages/signals into a form and format so that they can travel across the communication channel (O’Leary & O’Leary, 2004). e.g. Modem a device that converts digital signals into analog (modulation) and then from analog to digital (demodulation) form for transmission over telephone lines (Hutchinson & Sawyer, 2001).

Data transmission specifications (protocols) – these are rules and procedures that coordinate the sending and receiving devices by precisely defining the how the messages/signals will be sent across the communication channel. eg email, fax, text messages, etc.

NB: Above all you need a comm. s/w to bring IT networks to life.

Telecommunications

Direction of transmission

Data flow

Transmission rate

Protocols

Transmission mode

Factors affecting communication on IT networks

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– Simplex : where data can travel in only one direction, without a return signal). Eg from TV transmitter to antennae, POS devices, seismograph measures earthquakes, etc).

– Half duplex : where data travels in both directions but only in one direction at a time, eg marine radio, linking PC’s by telephones.

– Full duplex : data is transmitted back and forth at the same time. Its thus considered the fastest and the most efficient form of two way communication. Used for mainframe communications.

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(Serial and parallel) – data on IT network is transmitted either serially or parallel. – Serial data transmission: data signals or bits are

transmitted sequentially on IT networks. They are usually “single lane” data transmission devices. Can transmit data over long distances, but can be very slow. eg telephone lines, modems, mouse, etc.

– Parallel data transmission – data signals or bits travels in separate lines simultaneously. They are faster but limited to short distances (to abt 15 meters). Commonly used to transmit data from systems unit to printer, (O’Leary & O’Leary, 2004; Hutchinson and Sawyer, 2001).

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This refers to the frequency and bandwidth of the data. Frequency :

– is a measure of the amount of data that can be transmitted on a channel per second. It describes the wave frequency or the no. of cycle of waves per second. It is measured in hertz ( 1cycle/1 second). The more the cycles per second the more data that can be transferred.

Bandwidth : – is a measure of the difference between the highest and the lowest frequencies ( the

range of frequencies). Data may be sent on several frequencies within a bandwidth. The greater the bandwidth, the more frequencies and the more data can be sent through the channel. It is usually measured in bits per second (bps; klbs; mbps) (Hutchinson and Sawyer, 2001). There are three categories of bandwidth-• Voice band (used for standard telephone lines, good for text transmission but not

high quality video/voice), • Medium band (special leased lines typically used to connect PC’s and mainframe

and for long distance data transmissions. Mostly used by organizations).• Broadband (used for high capacity transmissions. Pc’s with cable, satellite and

high speed connecting devices use it. Good for high quality audio and video transmission) (O’Leary & O’Leary, 2004).

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It is a set of conventions or communication rules governing the the exchange of data between hardware and/or software components in a communication network. Protocols are built into the h/w and s/w. The standard protocol used now by most developers is the OSI (Open System Interconnection) , which defines 7-layers of protocols for worldwide communications (namely physical, data link, network, transport, session, presentation, and application) (Hutchinson and Sawyer, 2001). The standard protocol for the Internet - TCP/IP(transmission control protocol/Internet protocol). It identifies the sending and recipients devices using IP addresses and DNS domain name servers, and reformatting information for transmission across the Internet.

– Other protocols include • HTTP (hypertext transfer protocol) -connect to websites and download

web pages.• HTTPS (hypertext transfer protocol secure)- supports secured web

communications• FTP (file transfer protocol) supports uploading and downloading of files

from the Internet)• WAP (wireless application protocol) – supports wireless access to the

Internet. (O’Leary & O’Leary, 2004).

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There are two main modes of data transmission on IT networks-the asynchronous and synchronous.

Asynchronous: – data is sent one byte or character at a time. Each string of bits making

up a byte is marked off with special control bits; the “start” bit to indicate the beginning of a character and the “stop” bit to indicate its end. This makes it slow and unable to handle large volumes of data. Advantage is sending data at the convenience of the sender.

Synchronous: – data is sent in blocks of characters (a block of character or words )

rather than as byte (character). Though they are also characterized by start and stop bits, these are used to synchronize internal clocks of the receiving and sending devices so that they are in time with each other. It is complicated and expensive but good for large networks for large data transmission and also faster.

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Communication channel/links/media

A communication channel is the path or the physical medium over which data travels in a telecommunications system from its source to its destination. The types include:

The wired namely • Twisted pair wire

• Coaxial cable

• Fiber optic cable

The wireless • Radio/Microwave systems

• Satellite systems

• Infra red

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Twisted pair cable– consists of two strands of insulated copper wire twisted around

each other. Each strand is made up of hundreds of copper wires. They are then covered in another layer of plastic insulation. A single twisted pair usually culminate in a wall jack into which you can plug your phone and computer.

– There are two types namely UTP (unshielded twisted pair) and the STP (shielded twisted pair). Its currently the most common cable used in the world, and its ideal for both data and voice transmission, on LAN or for short distances. They are being phased out by reliable cables. It can be slow and does not protect well against electrical interference (noise).


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Coaxial cable– it’s a high-frequency transmission cable, replaces the multiple

wires of the twisted pair cable with a single solid-copper core. Thus, it consist of an insulated copper wire wrapped in a solid or braided metal shield, then in an external cover.

– The extra insulation makes coaxial cables much more resistant to electrical interferences than the twisted pair wires. Used mostly for cable television and to connect parts of a LAN over long distances.

– In terms of the number of connections, a coaxial cable has over 80 times the transmission capacity of twisted pair. It can also transmits both data and voice at faster rates than twisted pair wires.


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Fiber optic cable– transmit data as pulses of light instead of electrical

pulses, through tiny tubes of fiber optic glass. In terms of the number of connections, it can support over 26,000 times the transmission capacity of twisted pair wires, eg can support a quarter to a half-million voice conversations at the same time.

– They are not affected by electrical interferences, are lighter, and more durable than twisted and coaxial cables. The disadvantage is, however, cost and inability to bend around tight corners, making it suitable for short distances data transmissions.


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Micro wave– This communication media uses high frequency radio waves to

provide line of sight communication since the microwaves travels in straight lines.

– They waves cannot bend around the curvatures of the earth, hence they can only transmit over short distances eg between buildings within sights.

– For longer distance microwave dishes or antennae are installed on top of buildings, mountains and towers so that signals can be beamed over uneven terrain. Transmits both voce and data.

– Note that the airwaves are getting saturated prompting a shift to satellite systems.


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Satellites : – These are microwaves relay stations in orbit around the earth. They

orbit about 22,000 miles above the earth, rotating at precise speeds, usually at the speed of the earth, and they amplify and relay

– microwave signals from one transmitter on the ground to another. They are can handle (send and receive large volumes of data). Uplink is the term that refers to the sending of data to satellites and down link – the receiving data from satellites.

– They are, however, affected by weather instability. One of the application of satellite communication is GPS (Global Positioning System) – where sets of devices are used to determine the unique geographical positions of objects

( O’Leary & O’Leary, 2004).


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Infrared– uses infrared light waves to communicate over short

distances (line of sight communication). This is because light waves can only travel in straight lines, hence the sending and the receiving device must be in clear view of one another without any obstruction.

– It is common with new PC’s and laptops, and also infrared mouse, printers, etc. Eliminates cabling but limited by distance and affected by obstructions. Transfers both data and voice files.


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The Internet is a global network connecting millions of computers.

The World Wide Web (WWW) is a system of Internet servers that

support specially formatted documents.

Most formatted documents on the web are formatted in HTML –

HyperText Markup Language) that supports links to other

documents, as well as graphics, audio, and video files.

A group of documents accessed from the same web address is

known as a website (ACCA Business Information System, 2005).

Uses of the Internet

• Dissemination of information

• Product/service development

• Recruitment and job search

• Entertainment

• Transaction processing – B2B, B2C

• Relationship enhancement (ACCA Business Information System, 2005).

Other issues to be covered:

Services on the Internet

Problems with the Internet

E-commerce

Intranet, Extranet, Internet

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– The Internet in actual fact is just a technology that allows any computer with a telecoms links to send and receive information from another equipped computer system.

– TCP/IP – Transmission Control Protocol/ Internet Protocol: is a standardized set of computer protocols that allow different computers on different networks, using different operating systems, to communicate with each other (Hutchinson and Sawyer, 2000). It breaks messages into packets and sends them via the shortest possible route (1,500 characters each).

– Browsers – are the programs used to access/view the Internet.Micky 31

Internet Address

are used to identify an individual or resource on the Internet. The Internet’s address scheme is called the Domain Name System (DNS).

Web addresses: – to access a web site, you need to specify an address or a URL (Uniform

Resource Locator): eg.

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First part : http stands for Hypertext Transfer Protocol: the protocol for transferring web files. This tells the browser to use this protocol when retrieving documents from the Internet server (NB: // - introduces a host name)

Second part : www. ug.edu.gh is the domain name ( where www stands for world wide web)

Third part : infostudies ( in ‘2’) is the directory path (location) which identifies where the document is stored on the computer.

Fourth part : course.html ( in ‘2’) is the document name ( specific document on the computer

http://www.ug.edu.gh/

http://www.ug.edu.gh/infostudies/courses.html