Introduction

Unit 1

Unit 2

 

 

 

  

4. Transfer Of Data In An ICT System

Key Concepts Content and Amplification
Students should be aware of current and emerging communication technologies.
1. Basic elements of an ICT
network.		 Students should be aware of what is available in order to
create and use an ICT network:
• communication devices
• networking software
• data transfer media
• standards and procedures
• ICT networks for different geographical scales and uses should be considered.
2. Characteristics of networks. The World Wide Web and the Internet and the ability to
distinguish between them.
The characteristics of intranets and extranets.
3. Uses of communication
technologies.		 Candidates should be able to comment on the
appropriate and inappropriate use of networks and other
technologies for a range of activities.
4. Standards The need for standards when transferring data.


1. The basic elements of an ICT network. A network is made up of computers that are linked together and share common resources. To create a network there has to be the following present:

  • the devices to be used for the communication;
  • the media in which communicated data will travel; (Media: the cabling [wire or fibre optic] or wireless connections - there are Ethernet cables, copper wire, coaxial cable, fibre optic cables, leased telephone lines and ever air is also a communication medium for the satellite communication.);
  • the software that instructs the devices to send and receive the data;
  • the standards and procedures to which all communication devices and software must adhere to.

The Communication Devices required for a Local Area Network (LAN), will be computers or devices with a Network Interface Card (NIC), hubs, switches, network adapters, cables, routers, internal/external modems, and connectors.

The communication devices required for a Wide Area Network (WAN), will be routers, switches, and dedicated or leased telephone lines such as ISDN lines.

A Network Interface Card, NIC, is a device that allows computers to be joined together in a LAN. The most common protocol for LANs is Ethernet. An Ethernet network interface card is installed in an expansion slot inside the computer. The NIC assigns a unique address called a MAC (media access control) to the machine. The MACs on the network are used to direct traffic between the computers. The network interface card has a port that is slightly larger than the telephone socket. This port accommodates an Ethernet cable, which resembles a thicker version of a standard telephone line. Ethernet cable must run from each network interface card to a central hub or switch. The hub or switch acts like a relay, passing information between computers using the MAC addresses and allowing resources like printers and scanners to be shared along with data.

A Hub is a device in a network where every device connected to it is able to communicate with any other device, any signal being sent to machine D is sent to all machines.

A Switch does essentially what a hub does but more efficiently. Each time data comes into the switch, it saves the physical address (MAC address) and the port it came from in its MAC address table. It then checks the destination MAC address in the table, and if it recognises it it sends the frame to the appropriate port. This means a signal for machine D is only sent to that machine. This ensures that most of the network traffic only goes where it needs to rather than to every port. On busy networks this can make the network significantly faster.

A Router will join more than one wired or wirelass networks together. They use software to identify ports and addresses of data signals. Small computer networks in business or at home use a router to connect computers allowing sharing of files and devices as well as access to the Internet.

The Data Transfer Media is the material that connects computers and devices together. This is mainly wire but more networks are now being connected wirelessly. The three main methods for connection are:

  • Metal wires - usually copper:
    • UTP (Unsheilded Twisted Pair) - This type of cable is very cheap to purchase and is flexible and easy to install. This isthe most common type of cabling used commonly for many purposes with easy installation and management. Some types of twisted pair cables can be used for communications up to 10 Gbps. The wires are twisted around each other which helps to lessen the effect of interference, (any interference is equal to both lines). When electrical current flows through a wire, it creates a small, circular magnetic field around the wire. When two wires in an electrical circuit are placed close together, their magnetic fields are the exact opposite of each other and cancel each other out. They also cancel out any outside magnetic fields. The UTP cabling system uses a RJ-45 connector and 100 Ohm unshielded twisted pair cabling. The maximum distance of a UTP link is 100 m. It is normally used to connect work groups of users, sometimes by wiring an entire floor with outlets to each work area.

  •  

    • STP (Shielded Twisted Pair) - are similar to UTP in their design but have an extra insulation sleeve of foil or copper braiding similar to the outer design of the coaxial cable. This makes it more expensive than UTP but less prone to interference.

    Shielded Twisted Pair

 

  • Coaxial Cable - This type of cable has a central copper conductor. Surrounding this is a layer of flexible insulation, over which is a woven copper braid or metallic foil that acts both as the second wire in the circuit and as a shield for the inner conductor. This second layer, or shield, can help reduce the amount of outside interference. Coaxial cable supports 10 to 100 Mbps and is relatively inexpensive, although it is more costly than UTP. Coaxial cable can be cheaper for a physical bus topology because less cable will be needed. Coaxial cable can be cabled over longer distances than twisted-pair cable. UTP maximum is 100 meters compared to 500m for coaxial cable.

  • Coaxial cable

  • Fibre optic cable - glass or plastic hollow tubes: A fibre optic cable will allow a pulse of light signal propagate along the hollow tube. (Propagate - send). A fibre optic cable is made from a glass or plastic core that carries light surrounded by glass cladding that (due to its lower refractive index) reflects "escaping" light back into the core, resulting in the light being guided along the fibre. The outside of the fibre is protected by cladding. It is intended that the Light pulses are always sent at angles, so that they are refracted along the core. Fiber optic networks operate at high speeds - up into the gigabits with. Signals can be transmitted further without needing to be "refreshed" or strengthened.
    With no wires to pick up interference ther is a much greater resistance to electromagnetic noise such as radios, motors or other nearby cables, and much less oportunity for signals being listened to by unauthorised methods..
    Although fibre optic networks are more expensive to create they cost much less to maintain.

Fibre optic cable.

  • Wireless - no medium:
    • Network - Wireless communication uses radio frequencies (RF) or infrared (IR) waves to transmit data between computer devices on a LAN. For wireless LANs, a key component is the wireless hub, or access point for signal distribution. To receive the signals from the access point, a PC or laptop must install a wireless adapter card (wireless NIC). Wireless signals are electromagnetic waves that can travel through the vacuum of outer space and through a medium such as air. Therefore, no physical medium is necessary for wireless signals resulting in a very versatile network. Wireless signals use portions of the RF spectrum to transmit voice, video, and data. Wireless frequencies range from 3 kilohertz (kHz) to 300 gigahertz (GHz). The data-transmission rates range from 9 kilobits per second (kbps) to as high as 54 Mbps.
    • Wireless communication also allows people to connect with the Internet from more and more places. For example you can use your laptop in an airport, coffee shop, library or a hotel, as these places are running a wireless network. All people need is a WiFi capability on their computers. Many people also use wireless networking, to connect their computers at home, and an increasing number of cities are also using the technology to provide free or low-cost Internet access to residents. In the near future, wireless networking may become so widespread that you can access the Internet just about anywhere at any time, providing that you live in a populated area.
    • A wireless network can include, with modern equipment: wireless printers, scanners, mp3 players, games console etc.

The equipment necessary for a WiFi connection include:

  • A router connected to the Internet by way of broadband,
  • It sends and receives data to and from the Internet to a computer by way of radio signals,
  • Each computer that is connected has a wireless adapter that converts the radio signal into computer binary.

Check out the Network Hardware slides!

Network Software: all networked devices need a special operating system so that they can all communicate with each other.

  • Network Operating systems: are used to run computers that act as servers. They provide the capabilities required for network operation. Network operating systems are also designed for client computers to provide certain functions. Network operating systems provide the following functions:
    • File and print sharing.
    • Account administration for users.
    • Security.
    • Client functionality.
    • Server functionality.
    • Account Administration for users.
    • Backing up data.
  • Examples of Network Operating Systems are:
    • Windows NT , and Windows XP,
    • Unix,
    • Linux,
    • Novell Netware
    • Mac OS X
  • Network Management Software: is used to assist the network manager keep control of all the computers and other devices in the network.
    • Controlling all the software used on the network, whose user name is using it, and what it is being used for,
    • Controlling the software for the licences and ensuring the manager is informed of when licences need renewing,
    • Controlling the software for the latest security programs to prevent destructive programs from causing any loss of data,
    • Keeping a log of user's activities on the network, and what the user's are doing during work time, ensuring that users are not installing personal software onto the network,
    • Controlling access onto the network and prevention of unauthorised access by use of user names and passwords,
    • Keeping a check on the hardware performance of computers to check that the memory and processor speed is sufficient for the tasks.

Network Standards and Procedures: For all network devices to be able to communicate there has to be an industry world wide standard.

  • Manufacturers of all devices agree to these standards (if they didnt the use would be very limited),
  • Procedures (ways of doing things) also have to be standard across the world.
  • Communication may be slow or impossible if different computers have different ways of sending data and different ways of collecting data and presenting it for people to understand.

Local Area Network (LAN) - computers connected over a small geographical area; a building or a group of buildings using localised cabling or wireless communication.

Wide Area Network (WAN) - computers connected over a large geographical area; a country or across the world using the public telephone networks of cabling and satellite communication.

Topology - the way that computers are connected in a LAN.

Client - Server - the network has a main server computer with the programs and files stored centrally, and other workstations which use the server temporarily downloading from the server the files that are needed..

Peer - to -Peer - the network has programs and files stored on all the workstations, some programs and files are downloaded from another workstation, some programs and files are shared from a workstation..

Check out the Network Structure slides!

The Internet is the physical part of the network and The World Wide Web is the information part of the network.

Check out the Communications Systems slides!

Advantages of Networks:

  • Speed: - Sharing and transferring files within Networks are fast saving time, while maintaining the integrity of the file.
  • Cost: - Individually licensed copies of many popular software programs can be costly. Networkable versions are available at considerable savings. Shared programs, on a network allows for easier upgrading of the program on one single file server, instead of upgrading individual workstations.
  • Security: - Sensitive files and programs on a network are passwords protected allowing only access to authorized users or read only, or "copy inhibit," so that you do not have to worry about illegal copying of programs.
  • Centralized Software Management: - Software can be loaded on one computer (the file server) eliminating that need to spend time installing updates on independent workstation computers throughout the network.
  • Resource Sharing: - Resources such as, printers, scanners, fax machines and modems can be shared.
  • Electronic Mail: - E-mail aids in personal and professional communication. Electronic mail on a LAN can enable staff to communicate within the building network without having to leave their desk.
  • Flexible Access: - Access their files from any workstation computer throughout the network.
  • Workgroup Computing: - Workgroup software (such as Microsoft BackOffice) allows many users to work on a document or project concurrently.

Disadvantages of Networks:

 

• Server faults stop applications being available
• Network faults can cause loss of data.
• Network fault could lead to loss of resources
• User work dependent upon network
• System open to hackers
• Decisions tend to become centralised
• Could degrade in performance due to over use
• Network management can become weak.

 

Protocols:

  • Ethernet: This is the most widely used protocol. This protocol uses an access method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection). Each computer on this network listens to the cable for any transmitting node before sending anything through the network. If the network is clear, the computer will transmit. Else wait and try again when the line is clear. Sometimes, two computers attempt to transmit at the same instant (causing a collision). Each computer then backs off and waits a random amount of time before attempting to retransmit. The delay by collisions and retransmitting is very small and does not normally affect the speed of transmission on the network.
    Topologies are bus, star, or tree and transmission is via twisted pair, coaxial, or fibre optic cable at a speed of 10 Mbps. There is also Fast Ethernet using more expensive exuipment which gcan obtain speeds of 100Mbps. There is a similar system for AppleMac networks which is known as Local Talk.
  • Token Ring: - This protocolused involves token-passing. Computers are connected so that the signal travels around the network from one computer to another in a logical ring. A single electronic token moves around the ring from one computer to the next. If a computer does not have information to transmit, it simply passes the token on to the next workstation. If a computer wishes to transmit, it receives an empty token, and attaches data to the token. The token then proceeds around the ring until it comes to the computer for which the data is meant. At this point, the receiving computer captures the data. All computers read the sender and destination addresses before deciding whether to accept or pass on the token with data. Fibre Data Distributed Interface (FDDI) is a similar protocol but there are two different directional paths, this improves efficiency. Transmison speed is100 Mbps over a fibre optic cable, but it is an expensive alternative.
  • Asynchrous Transfer Mode (ATM): - Transmits data in small packets of a fixed size at a speed of 155 Mbps and higher. ATM supports a variety of media such as video, CD-quality audio, and imaging. ATM employs a star topology with fibre optic or twisted pair cabling.
  • Wireless LANs use high frequency radio signals, infrared light beams, or lasers to communicate between the workstations and the file server or hubs. Each workstation and file server on a wireless network will have a transceiver/antenna to send and receive the data.
    Wireless Networks are ideal for allowing laptop computers or remote computers to connect to the LAN. Wireless networks are also beneficial in older buildings where it may be difficult or impossible to install cables. Printers, scanners and other equipment needed to perform data processing and communications within the network can all be linked wirelessly.

Homework: 

Read text book: p 152-159.

Question 1 & 2 & 3 & 4: p160

Activity 1: p162

Activities:

Use the Learning Gateway for the self marking test!

Slides: Network Hardware

Slides: Network Structure

Slides: Communications Systems

 

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