TOPIC 10: DATA COMMUNICATION & NETWORKING Sub-topic 10.1: Data Communication


DATA COMMUNICATION

This refers to the electronic transfer of data, instructions, and information from one device to another via a transmission media.

ELEMENTS FOR DATA COMMUNICATION

Sender: The computer or device that generates and sends data is called the sender, source or transmitter. It can be a computer, workstation (node), telephone handset, video camera. Etc

Message: This is the information or data to be communicated. It consists of text, numbers, pictures, sound or video.

Transmission Medium: is the physical pathway by which a message travels from sender to receiver.

Receiver: The device or computer that receives the message is called receiver. The receiver can be a computer, printer, a fax machine, etc.

Protocol: This is a set of rules that allow devices to exchange information

A protocol defines the format for communication between systems. For example the Hyper Text Transfer Protocol (HTTP) defines the format for communication between Web browsers and Web servers on the internet

Other examples of communication protocols include: Internet Protocol (IP) Transmission Control Protocol (TCP), Trivial File Transfer Protocol (TFTP), Wireless Application Protocol (WAP), and Simple Mail Transfer Protocol (SMTP) for emails

Data communication tools

Data communication tools are devices that enable the users to send and receive messages. Etc. Data communication tools can be categorized into two: electronic and manual data communication tools.
Electronic data communication tools use electric power. Examples include Computers, Mobile phones and internet.
Manual data communication tools don’t use electricity. Examples include drums, bells and messengers.

d) Types of electronic data communication tools

As technology progresses, new communications are born and old fade away. When you’re trying to connect with employees, colleagues, bosses, clients, customers or suppliers electronic media are critical to getting business done efficiently and cost- effectively.


Examples of data communications tools include

Computers, Fax machines, Radio and Television, Mobile Devices like phones and PDAs, internet services (Email, Websites, Social networking, chartrooms Forums, etc)

Data transmission media

The term transmission media refers to any physical or non-physical link / pathway between two or more devices and in which a signal can be made to flow from source to destination. A data signal cannot be sent from one place to another without a medium of communication.

Data communication media can be divided into two:

  1. Physical /Wired / Bounded/ Guided transmission media
  2. Wireless / Unbounded / Unguided transmission media

Physical /Wired / Bounded/ Guided transmission media

Physical transmission media use wire, cable, and other physical materials to send communications signals. Physical media transmits data signals from the source to the destination through a restricted pathway such as a cable.

Examples of physical transmission media

  • Unshielded Twisted Pair (UTP) Cable
  • Shielded Twisted Pair (STP) Cable
  • Coaxial Cable
  • Fiber Optic Cable

Twisted pair cable: Twisted pair cable is made up of solid copper wire strands wound in pairs within a single media. The winding of the wires is meant to avoid the development of an electromagnetic field around the two wires as they transmit data. TP is commonly used to interconnect devices on a Local Area Network

There are two common types of twisted pair cabling, STP and UTP. The S stands for Shielded, the U stands for Unshielded.

The extra covering in shielded twisted pair wiring protects the transmission line from electromagnetic interference leaking into or out of the cable, but makes it more expensive.

Coaxial cables

The Coaxial cable has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield . The metal shield helps to block any outside magnetic interference from fluorescent lights, motors, and other

Coaxial cables have bandwidths in Gigabits per second. Hence, they are installed in a network to form the network backbone.

Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable. The two types of coaxial cabling are thick coaxial and thin coaxial.

Fiber Optic Cable

The fiber optic cable consists of a center glass core surrounded by several layers of protective materials. It transmits light rather than electronic signals eliminating the problem of electrical interference.

This makes it ideal for certain environments that contain a large amount of electrical interference.

It has also made it the standard for connecting networks between buildings, due to its immunity to the effects of moisture and lighting.

Fibre optic cable utilizes light to transmit data from one point to another on the network. The electrical signal from the source are converted to light signals, and then propagated along the fiber optic cable.

Advantages of physical transmission media

  • It is fast and supports high bandwidth
  • Can be used in hazardous places (high flammable) because they do not generate electrical signal
  • They can carry voice, data and video signal simultaneously.
  • They are more resistant to radio and electromagnetic interference.
  • Installation equipment are cheap and readily available.

Disadvantages of physical transmission media

  • Connectivity devices and media are expensive.
  • Installation is difficult because the cable must be carefully handled.
  • It is relatively complex to configure
  • It covers short distance since they use the physical wires
  • Inconvenience due to inflexibility of restrictive cables.

Wireless / Unbounded / Unguided transmission media

Wireless or unbounded media is that is where data signals flow through the air

In this case transmitting antenna and receivers aerial facilitates the communication

Example of wireless transmission media include:

The major wireless transmission media include radio waves, microwaves, and infrared which is part of the   electromagnetic spectrum, which is the range of all possible frequencies of electromagnetic radiation.

Wireless media send communications signals through the air or space using radio, microwave, and infrared signals (electromagnetic waves).

Examples of wireless transmission media

  • Microwaves
  • Radio waves
  • Infrared

MICROWAVES: Microwaves are high-frequency electromagnetic radiations that are sent through space to deliver telecommunications services. Microwaves are dependent on line of sight. Microwave communication systems are mainly classified into satellite and terrestrial.

Terrestrial microwave signals are sent from one ground-based antenna to another.

Satellite microwave signals travel from Earth to a satellite in space and then back to a station on the earth.

RADIO WAVES: Radio waves frequencies are easy to generate and are widely used for communication, both indoors and outdoors. Examples of communication technologies using radio waves include Bluetooth, Wireless Fidelity (Wifi)

Bluetooth is a short range wireless based information transmission system which works on the basis of microchips embedded in the digital devices like mobile phones, speakers and laptops.

Wireless Fidelity (WiFi) is used to create a hotspots from where information signals can be easily accessed by Wi-Fi enabled devices, forming a wireless local area network (WLAN).

HOTSPOT

A hotspot is a specific location that provides Internet access via a wireless local area network (WLAN). The term is generally synonymous with a Wi-Fi connection. A network that creates a hotspot primarily includes a modem and wireless router. The radio frequency (RF) waves sent by the wireless network extend in different directions from its centralized location. These signals become weaker as they travel, either further from the central location or due to interference.

Wimax stands for Worldwide Interoperability for Microwave Access. It is a telecommunication technology providing wireless data over long distances in a variety of ways from point to point links to full mobile cellular type access.

Radio-frequency identification (RFID) uses radio waves to automatically identify and track tags attached to objects. The RFID tag can be affixed to an object and used to track and manage inventory, assets, people, etc. For example, it can be affixed to cars, computer equipment, books etc.

INFRARED uses electromagnetic waves with a smaller wavelength than radio. A TV remote control is an example of an Infrared application.

IrDA (Infrared Data Association) ports transmit data via infrared light waves. As long as the devices are within a few feet and nothing obstructs the path of the infrared light wave, data can be transferred without the use of cables

Asynchronous and Synchronous transmissions

With asynchronous transmission, transmission occurs at irregular intervals in small bits (i.e., not synchronized).

Asynchronous transmission is relatively slow.

With synchronous transmission, large blocks of bytes are transmitted at regular intervals without any start/stop signals.

Synchronous transmission requires that both the sending and receiving devices be synchronized before any bytes are transmitted.

Synchronous transmission requires more expensive equipment but provides greater speed and accuracy than asynchronous transmission.

Characteristics of Asynchronous Transfer Mode

  • It is scalable and flexible. It can support megabit-to-gigabit transfer speeds and is not tied to a specific physical medium.
  • It efficiently transmits video, audio, and data through the implementation of several adaptation layers.
  • Bandwidth can be allocated as needed, lessening the impact on and by high-bandwidth users.
  • It transmits data in fixed-length packets, called cells, each of which is 53 bytes long, containing 48 bytes of payload and 5 bytes of header.
  • It is asynchronous in the sense that although cells are relayed synchronously, particular users need not send data at regular intervals.
  • It is connection oriented, using a virtual circuit to transmit cells that share the same source and destination over the same route.

Transmission Direction

The direction in which data flows along transmission media is characterized as  simple,  half-duplex, full-duplex or multiplex

Simplex transmission

Simplex transmission sends data in one direction only. Simplex transmission is used only when the sending device does not require a response from the receiving device. Examples of simplex transmission is television broadcasting and radio broad casting

Half-duplex transmission

Half-duplex transmission allows data transmission in either direction, but only one way at a time. Many fax machines, police radio calls, credit card verification systems and automatic teller machines use half-duplex transmission

Full-duplex transmission

In full-duplex transmission, data can flow in both directions at the same time. A regular telephone line, for example, supports full-duplex transmission, allowing both parties to talk at same time.

Multiplex transmission

In multiplex transmission, several different types of signals can be carried at once through the same line. E.g. During Video calls where Images

PACKET SWITCHING

When a computer sends data over the Internet, the data is divided into small pieces called packets.

Each packet contains the data, as well as the recipient (destination), the origin (sender), and the sequence information used to reassemble the data at the destination.

Each packet travels along the fastest individual available path to the recipient’s computer via communications devices called routers.

This technique of breaking a message into individual packets, sending the packets along the best route available, and then reassembling the data is called packet switching.

Services offered by data communication tools

Data communication tools offer services like Telephone, SMS, E-mail, Skype, Newsgroups and instant messaging.

Telephone voice calls help keep people talking even when they are distant and mobile.

Short Messaging Services SMS facilitate sending and receiving of brief text messages.

Electronic mail and fax : An electronic mail is the message transmitted electronically over the internet, from one user to another. A fax machine is a device that transmits and receives typed or hand written documents over telephone lines.

Skype supports voice and video calls, text, instant messaging and sharing conversation with (someone) over the Internet using the software application Skype, frequently also viewing by webcam.

Newsgroups are organized group of internet users who wish to share ideas and interests through discussion forums and debates.

Instant messaging: This is a more enhanced messaging service that allows two or more people to chat directly in real time.

Social networking e.g. Facebook and Twitter create digital societies through linking people of common interests.

Implications of using data communication services

Positive Implications

  • Have led to faster, simpler communications between people e.g.through electronic-mail, mobile phones, social networks etc
  • Communications costs have become lower e.g. Making cheap internet calls, for example via Google talk and Skype
  • Community mobilization now easier – its now very simple to send a message to many people in one go e.g using Mailing lists and group chats.
  • Data communication tools like the internet have facilitated emergence of the worldwide-web where there is a wealth of information, such as news, weather reports, and airline schedules.
  • Data communication tools like telephones and SMS Have revolutionized the way people transact businesses e.g access to mobile money services using phones.

Negative Implications

  • Security and privacy: data communication services have made it easy access private information e.g. on social networks, hence posing security concern.
  • Spamming is high especially by advertisers who send unwanted e-mails in bulk, such as email adverts.
  • There has been emergency of new kinds of crimes facilitated by data communication services, such as cyber-bullying.
  • Inaccurate information on the internet can be misleading and lead to dire consequences to the users.
  • Data communication services have facilitated the digital divide in society, hence disadvantaging the computer illiterate people when it comes to opportunities like jobs and government services

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