Computer IX Chapter#4 Data Communication

Complete guide and notes of Data Communication Transmission Medium and much more exciting topics;

4.1 BASICS OF DATA COMMUNICATION

Communication is the process (Data Communication Transmission Medium)  of sharing a message. A conversation between two people is an example of communication. Data communications refers to the sharing of a virtual message. Electronic communications, like emails and instant messages and phone calls are
examples of data communications. Data communication is the exchange of digital messages between two devices. It involves a sender and a receiver which communicate via some form of transmission medium such as a cable.

4.1.1 Basic Terminologies of Data Communication
In order to understand the data communication, it is good to know some basic terms related to it.

(i) Data
Collection of raw facts and figures is called data. The word data is derived from Latin language and it is plural of Datum. The text, numbers, symbols, images, voice and video which are processed by computers and digital devices are called data. Data can be considered as unprocessed information.

(ii) Data Communication
Data Communication is the process of transferring data electrically from one place to another. It is the process of exchange of data and information between two parties such as human and electronic or computing device.

(iii) Data Transmission

(Data Communication Transmission Medium)
The data transmission means emission of data in any direction via wireless or wired medium. Transmission may occur between source and destination.

(iv) Analog Signals
Analog signals are a continuously varying signals or waves that change with time period and used to represent data. An analog signal can be used to measure changes in some physical quantities such as light, sound, pressure or temperature.

(vi) Data Rate / Bit Rate
Data rate is the rate at which data is transferred. It is normally measured in bits per second. Bit is the actual binary digit which is the basic unit of data transmission. Bit can hold either 0 or 1. Data rate can be ranging from bps (bits per second) for smaller values to kbps (kilo bits per second) and mbps (megabits per second). It is also called bit rate. Data rate becomes faster when more bits are transferred in one second.

(vii) Baud Rate
The baud rate is the number of signals transmitted per second and one signal can represent one or more bits. It is used to describe the maximum change in an electronic signal. For example, if a signal changes 1200 times in one second, it would be measured at 1200 baud.

Data Communication Transmission Medium

4.1.2 Components of a Communication System
A Communication system has following five components.

(i) Message
It is the information or data to be communicated. Common forms of information include text, numbers, pictures, audio and video.
(ii) Sender
It is the device that generates and sends a message. It can be a computer, telephone handset, etc.
(iii) Receiver
Any particular digital electronic device which has capability to receive data in form of message. The location of receiving computer is generally different from the sending computer. Like sender, it can also be a computer, telephone handset, etc.
(iv) Medium
It is the channel or path through which the message is carried from sender to the receiver. Some examples include twisted-pair cable, coaxial cable, radio waves, etc.
(v) Protocol
Protocols are the rules and procedures on which computers exchange data on network. Sender and receiver follow same protocols to communicate with each other. In other words, a protocol is an agreement between two parties or venders, using communication devices.

4.2 TRANSMISSION MEDIUM
Transmission Medium or Communication Channel is a wireless or physical path between the sender and receiver through which data is sent and received from one place to another. Data is transmitted normally by electromagnetic or electrical signals through different types of wires, atmosphere or vacuum. Transmission media is broadly classied into two
groups; guided and unguided.

4.2.1 Guided Media
In guided media signals are transmitted in a narrow pathway by using physical links. It is also called Wired or Bounded transmission media. The physical links are the cables that are tangible or have physical existence. There are three common types of guided media used for the networks. Each of them has its own characteristics like transmission speed, effect of noise, physical appearance, cost, etc. 

Data Communication Transmission Medium

(i) Twisted Pair Cable 

As name suggests, this cable is made by two separate wires twisted together. A twisted pair cable is made up of insulated copper wires. The insulation and twisting of wires prevent external interference. Each pair of wires has unique color code. This type of cable is widely used in different kinds of data and voice infrastructures. There are two types of twisted pair cables: 

(a) Unshielded Twisted Pair (UTP) 

(b) Shielded Twisted Pair (STP)

Unshielded Twisted Pair (UTP) 

This type of cable can block interference but it is vulnerable to external interference. It is mostly used for telephonic applications. It is less expensive and easy to install. 

(b) Shielded Twisted Pair (STP) 

This type of cable consists of a special coating to block external interference. It is used in fast-data-rate ethernet and also in voice and data channels of telephone lines. 

(ii) Coaxial Cable 

Coaxial cable is also known as coax. It has an outer plastic covering containing two parallel conductors each having a separate insulated protection cover. Cable TVs and analog television networks widely use coaxial cables. 

(iii) Fiber-Optic Cable 

In optical Fiber or Fiber-optic cable data is transferred in the form of light. It uses the concept of reflection of light through a core made up of glass or plastic. The core is surrounded by a less dense glass or plastic covering called the cladding. It is used for transmission of large volumes of data at very high speed.

Data Communication Transmission Medium

4.2.2 Unguided Media 

Unguided media is also termed as wireless or unbounded transmission media. As the name implies, it does not require physical medium such as wire for the transmission of electromagnetic signals. There are three major types of Unguided Media. 

(i) Radio Waves 

R a d i o wa v e s a r e a l s o c a l l e d electromagnetic waves. These are easy to generate and can penetrate through buildings. Radio waves are omnidirectional and propagated in all directions. It means that sending and receiving antennas do not need to be aligned. FM, AM radios, television and cordless phones use radio waves for transmission. 

(ii) Microwaves 

Microwave transmission is a line of sight transmission i.e. the sending and receiving antennas need to be properly aligned with each other. The distance covered by the signal is directly proportional to the height of the antenna. These are mostly used for mobile phone communications tower and television broadcast. Terrestrial and Satellite are two types of microwave transmissions. 

Terrestrial: Terrestrial microwaves have both stations having antennas on earth. 

Satellite: In satellite system (Figure 4.10), some antenna are on satellite in orbit and others are on stations on earth. They work at remote places so it can be used in mobile devices.

(iii) Infrared 

It uses infrared light to transmit signals. LED is used to transmit signals and light-receivers (photodiodes) to receive signals. They use terahertz frequency. It cannot penetrate walls or other objects. Infrared light is transmitted generally line of sight (point to point). Wireless infrared communications can be used to establish short range wireless links or wireless Local Area Network. 

Data Communication Transmission Medium

4.2.3 Transmission Impairments 

Sometimes, signals traveling through transmission media lose their quality. This means that received signal is not same as the signal that was sent. This phenomenon is called transmission impairments. Transmission impairments are those defects that occur when data is transmitted. There are three causes of impairment i.e. attenuation, distortion and noise. 

(i) Attenuation:

Attenuation means loss of energy. A signal loses its energy due to the resistance of medium while it is transmitted. Its strength decreases with increase in distance. Ampliers are used to overcome attenuation and make signal stronger again. It is measured in decibels.

(ii) Distortion

Distortion means change in the shape of the signal. A composite signal has several frequencies. When it travels through a medium different component of signal may reach at different time at destination because each component has different speed in that medium. This is called distortion. They have different phases at sender and receiver ends.

(iii) Noise 

Unwanted signal that mixes up with the original signal during the transmission of data is called noise. It can be induced noise, crosstalk noise, thermal noise and impulse noise which may damage the signal. 

4.3 COMMUNICATION DEVICES 

A communication device is any type of hardware capable of transmitting and receiving data, instructions and information. 

4.3.1 Switch 

A switch or network switch (Figure 4.15) is a networking device that connects computers and other devices like printers, scanners and cameras on a network. Data cables from all computers and other devices of network are plugged into the switch to enable communication between them.

 4.3.2 Router 

A Router (Figure 4.16) is a device that connects two or more networks. Routers are a combination of hardware and software. The main function of a router is to determine the optimal data path and transfer the information through that path, also known as network trafc controller. 

4.3.3 Modem 

Modem is short for Modulator and Demodulator. Modulation is the process of converting digital signals into analog signals. Demodulation is quite opposite; it converts analog signals into digital signals. Modem has the ability of sending and receiving signals that allows computers to share information with each other. This sharing of information is possible over phone lines, cables or satellite connections. 

(i) Dial-up Modem 

Dialup modems (Figure 4.17) use standard telephone lines to transmit and receive information. A dialup modem can be internal or external. It is important to remember that telephone lines carry only analog signals, whereas data packets sent by the computer are in digital form. In order to send these packets across a telephone line, modem converts digital signals into analog. 

(ii) DSL Modem 

D SL s t ands f o r D i g it a l Subscriber Line (Figure 4.18). Like dial-up modem DSL modem also uses telephone lines to transfer digital signals. DSL modem has a built-in network switch which enables use of twisted pair wires to deliver data and voice at high speed as compare to dial-up modem. Some DSL modems also have wireless communication functionality.

(iii) ISDN Modem 

Integrated Services Digital Network (ISDN: Figure 4.19) is a digital phone connection that can transmit data, voice and video over a normal telephone line at the same time which was not done before. It is faster and expensive technology. Since ISDN work on digital transmission it converts analog voice to digital signals before transmission. 4.3.4 Network Interface Card (NIC) Network cards also known as Network Interface Cards (NICs: Figure 4.20) are hardware devices that connect a computer with the network. They are installed on the mother board. They are responsible for establishing a physical connection between the network and the computer. Computer data is translated into electrical signals and sent to the network via Network Interface Cards. Modern motherboards have built-in NICs.

Data Communication Transmission Medium

4.4 BASICS OF COMPUTER NETWORKS 

Computer networks are just like a highway on which data can travel. A computer network connects parts of distributed system including hardware and software. It shares common functions and features like data and devices which is very important nowadays. 4.4.1 Computer Network and Networking 

(i) Computer Network 

A computer network is a group of computers and related equipment connected by a communication links to share data and other resources. The related equipment may be printer, scanners, fax machines, server, etc. The resources may include a le server, internet connection, etc. 

(ii) Networking 

Networking is the act of joining computers and its accessories so that exchange of information and sharing of resources take place. In today’s world, networking plays a vital role in computers and telecommunication elds. Modern organizations create a networking environment and device connectivity for fast, inexpensive and reliable communication. 

Data Communication Transmission Medium

4.4.2 Types of Computer Networks 

Computer networks can be categorized by their size as well as their purpose. The size of a network can be expressed by the geographical area they occupy and the number of computers that are part of the network. Networks can cover anything from a handful of devices within a single room to millions of devices spread across the entire globe. There are three types of computer networks: 

• Local Area Network (LAN) 
• Metropolitan Area Network (MAN) 
• Wide Area Network (WAN) 

(i) Local Area Network (LAN) 

LAN is a group of computer and peripheral devices which are connected in a limited area such as school, laboratory, home and ofce building. Useful resources like internet access, storage space and printers can be shared through LAN. It can be built with inexpensive hardware such as hubs, switches, network adapters and network cables. Data and software are also shared through LAN.

(ii) Metropolitan Area Network (MAN)

In MAN, computer network can spread across an entire city, college campus, or a small region. It can cover the area of several miles and may include multiple small networks or LANs. MANs offer very fast communication but they are expensive to establish. Therefore, only large business organization or universities set up MAN. It also requires security measures to prevent unauthorized access.

(iii) Wide Area Network (WAN)

A Wide Area Network is used for long distance transmission of data. WAN helps to cover a larger geographical area and connect cities, provinces or even countries. Using WAN technology, computers may be linked together in different countries using satellites, microwaves or telecommunication links. Therefore, large business, research and educational organizations situated at longer distances use WAN. A WAN
may include multiple MANs and LANS. WANs are set up with expensive
devices and need some dedicated connections.

4.5 Fundamental of Topologies 

The physical layout in which computers are connected is called topology. The topology of network describes the way computers are connected. Topology is a major design consideration for computer networking. 

4.5.1 Bus Topology 

As name suggests, in Bus Topology computers and other devices are connected with a single cable. The central cable is the backbone of the network and every device communicates with the other device through this bus. The advantages of Bus Topology are simplicity, low cost and easy expansion of the network. The disadvantage of the Bus Topology is that a breakdown in the bus cable brings the entire network down.

4.5.2 Ring Topology
In Ring Topology, computers are connected in a ring or circle shape. The signal travels around the loop in one direction and passes through each computer. The recipient of the message receives the message while another computer acts like a repeater to send it to the next computer. The failure of a link or a computer can make the entire network nonfunctional. 

4.5.3 Star Topology
In a star topology, all the computers are connected to a central device called hub or switch. To communicate with any computer, the sender must send information to the hub. Then the hub transmits that information to the destination. The advantages of star topology are easy to set up and easy expansion of the network. Another feature of Star Topology is that if one link to the hub breaks, only the station using that link is affected not the whole network.

4.6 STANDARD ORGANIZATIONS 

Standards are rules that define the appearance, functionality, or protocols of some equipment. They are essential for network communication. Network standards dene rules of communications among computing devices. This ensures that companies (i.e. Cisco and IBM) that manufacture computing and networking products follow these uniform standards. By following standards, all hardware become compatible in the network, allowing efficient networking to take place. Standard Organization develops, coordinates, revises, amends and reissues technical standards. These standards are intended to address the requirements of a group of concerned devices. There are several organizations working on standardization of computing equipment to enable the interoperability among different devices manufactured by different companies in different regions. IEEE, IETF, ITU and ANSI are the examples of standard organizations. 

4.6.1 International Organization for Standardization (ISO) 

It covers a wide range of elds. The ISO has members from the standards committees of various governments across the world. It is even responsible for developing models which provides high level of system compatibility, quality enhancement, improved productivity and reduction in costs. The ISO is also responsible for endorsing and coordinating the functions of the other standards organizations. 

4.6.2 Institute of Electrical and Electronic Engineering (IEEE) 

It is an international professional non-prot organization. Electronics, computer and communication engineers, researchers, scientists and students are the members of IEEE. This organization develops communication and information processing standards for all elds related to electrical and computer engineering. 

4.6.3 International Engineering Task Force (IETF) 

It is a large international community of network designers, operators, vendors and researchers concerned with the development of internet architecture and smooth operation of the internet. 

4.6.4 International Telecommunication Union (ITU) 

This organization is a specialized agency that is responsible for resolving the issues that concern with information and communication technologies.

Data Communication Transmission Medium

4.7 NETWORK ARCHITECTURE 

It is the design of a computer network. It is a framework for the specication of a network’s physical components, their functional organization and conguration, operational procedures and communication protocols used. Just like OSI / TCP layered architecture. 

4.7.1 ISO’s OSI Model 

The Open Systems Interconnection model is a conceptual model developed by ISO. It characterizes and standardizes the communication functions of a telecommunication and computing network. Its goal is the interoperability of different communication systems with standard communication protocols. This model divides a communication system into seven abstraction layers.

4.7.2 TCP/IP Model 

TCP/ IP is a suite of communication protocols used to interconnect
network devices on the internet. These are set of rules and procedures.
TCP/IP species how data is exchanged over the internet by providing
end-to-end communications. It also identies how data should be broken
into packets, addressed, transmitted, routed and received at the
destination. With reference to OSI layers, we can understand the
functions of TCP/IP layers. 

Data Communication Transmission Medium

 4.8 NETWORK ADDRESSING 

Network addresses are like our house addresses. They must be
unique and distinctive. This avoids confusion for the postman. A network
address is any Logical or Physical Address that uniquely identies it from
This layer establishes, maintains and ends a session
or logical connection between applications on two
computers. It manages who can transmit data at a
certain time and for how long. This layer adds
checkpoints. If session fails only data after the most
recent checkpoint need to be transmitted.
Session
It ensures the reliable transmission of data. Transport
layer manages error control, ow control and quality of
the service. If the data is not properly transmitted it
requests to resend.
Transport
The function of this layer is the selection of the shortest
and suitable path from source to destination, from the
number of routes available. It is also responsible to
convert logical address (IP address) to physical address
(MAC address).
Network
This layer is responsible to transmit data using physical
addresses. Data Link Layer ensures error free
transmission of packets. Packet in this layer is referred
as Frame.
Data link
It is responsible for converting electrical signals into bits.
It also denes the cable types to be used as transmission
media, cards, topology and other physical aspects.
Physical
It receives information from the application
layer and converts it to uniform network format
(ASCII or Unicode) which is acceptable by rest of OSI
model and destination. Encryption and decryption
are also the responsibility of this layer. This layer
also reduces number of transfer bits by compression.
Presentation
Application
This layer enables users to access the network with
applications such as email, le transfer, etc. These
applications produce the data, which is
transferred over the network.
7.
6.
5.
4.
3.
2.
1.
No. Layers Functions
Internet
Layer
Network
Access Layer
Transport
Layer
Application
Layer
Using protocols like HTTP and FTP, this
layer allows interaction with applications.
Application layer is also responsible to
encode and decode data and establish
communication between two devices.
Using protocols like UDP and TCP, this
layer establishes a logical connection
between two devices and makes sure the
reliable delivery of data.
It is responsible for packet forwarding by
accessing physical path.
Using the logical addressing this layer
decides how data will be sent across
different networks paths.
OSI Layers TCP/IP Layers Function
Application
Session
Transport
Network
Data link
Physical
Ÿ Dene network address
Ÿ Differentiate between Physical Address and Logical
Address
Ÿ Describe IPV4 address
SLOs
4.8
Presentation
88 89
others. This address is needed to distinguish a network node or device on
a computer network. It is a numeric or symbolic number or address that is
assigned to any device that seeks access to network or is the part of a
network. Remember, Physical and Logical Address are different. 

Computer IX Chapter#4 Data

Computer IX Chapter#4 Data

Computer IX Chapter#4 Data

Computer IX Chapter#4 Data

Computer IX Chapter#4 Data

Computer IX Chapter#4 Data

Computer IX Chapter#4 Data

Computer IX Chapter#4 Data

Computer IX Chapter#4 Data