Data communications and networking may be the fastest growing technologies in our culture today. One ofthe ramifications of that growth is a dramatic increase in the number of professions where an understanding of these technologies is essential for successand a proportionate increase in the number and types of students taking courses to learn about them.
The text book is written in simple and easily understandable language. I made sincere attempts to analyse every important topic completely and put before the reader of this book in the best presentable form.The book covers all the major syllabus topic of the subject "Data Communication and Networks" for BCA, BCACS,B.Tech and MCA,Comuter Science & Information Technology students from the basic to the advance points.
An attempt has been made by me to write this book in a simple and lucid language with neat and self-explanatory programs and diagrams, whic could be easily understood by an average student.
The subject matters is divided in Seven Chapters. All the chapters are providing a complete course coverage in a simple and understandable language. The brief content of the book is as follows :
Chapter 1 : Unfolds the introduction of Data Communication. The text also covers the concepts of communication models.
Chapter 2: Provides the concepts of Computer Networking. The text also covers the concept of Distributed processing and NIU.
Chapter 3: Unfolds the concept of basic types of networks
Chapter 4 : Unfolds introduction of Physical Structure/topologies.
Chapter 5 : Unfolds diffrent Network Models(OSI,TCP/IP), layers and their functionalities.
Chapter 6: Explore the concepts of Analog and Digital Signals and cover the all aspects related to the Signals.
Chapter 7 : Unfolds the introduction of Ethernet evolutions, different types of LAN Technologies.
Chapter 8 : Provide the concepts of Network Security and Cryptography.
All the topic have been illustrated with suitable diagram for easy understanding. All the efforts have been made to bring out a very good and useful book. Nevertheless,the author does not lay and claim to perfection,there is always scope for improvement in a book of this kind.
All suggestions for improvement will therefore be welcomed.
Dr. Prakash Kumar
HOD - Computer Science and Cyber Security
JRSU,Ranchi
1
DATA COMMUNICATIONS
---------------------------------------------------------------------------------------------------------------------------------
The term communication means sending or receiving information. When we communicate, we share information or data.
A communication system can be defined as the collection of hardware and software that facilitates intersystem exchange of
information between different devices.
1.1 DATA & INFORMATION
1.2 Data Communication
It is the exchange of data between two devices using some form of transmission media or medium. It includes the transfer of data
or information and the method of preservation of data during the transfer process. Data is transferred from one place to another in
the form of signals.
In Data Communications, data generally are defined as information that is stored in digital form. Information is defined as the
knowledge or intelligence. Data communications can be summarized as the transmission, reception, and processing of
digital information. Communication or transmission channels refer to the direction of signal flow between two linked devices.
For data communications to occur, the communicating devices must be part of a communication system made up of a combination
of hardware (physical equipment) and software (programs).
The effectiveness of a data communications system depends on four fundamental characteristics: delivery, accuracy, timeliness,
and jitter.
1.2.1 Data Representation
Information today comes in different forms such as text, numbers, images, audio, and video.
Text: In data communications, text is represented as a bit pattern, a sequence of bits (Os or Is). Different sets of bit patterns have
been designed to represent text symbols. Each set is called a code, and the process of representing symbols is called coding. Today,
the prevalent coding system is called Unicode, which uses 32 bits to represent a symbol or character used in any language in
the world. The American Standard Code for Information Interchange (ASCII), developed some decades ago in the United States,
now constitutes the first 127 characters in Unicode and is also referred to as Basic Latin.
Numbers: Numbers are also represented by bit patterns. However, a code such as ASCII is not used to represent numbers; the
number is directly converted to a binary number to simplify mathematical operations. Appendix B discusses several different
numbering systems.
Images: Images are also represented by bit patterns. In its simplest form, an image is composed of a matrix of pixels
(picture elements), where each pixel is a small dot. The size of the pixel depends on the resolution. For example, an image can
be divided into 1000 pixels or 10,000 pixels. In the second case, there is a better representation of the image (better resolution),
but more memory is needed to store the image. After an image is divided into pixels, each pixel is assigned a bit pattern. The size
and the value of the pattern depend on the image. For an image made of only black and white dots (e.g., a chessboard), a I-bit
pattern is enough to represent a pixel. If an image is not made of pure white and pure black pixels, you can increase the size of the bit
pattern to include gray scale. For example, to show four levels of gray scale, you can use 2-bit patterns. A black pixel can be
represented by 00, a dark gray pixel by 01, a light gray pixel by 10, and a white pixel by 11. There are several methods to
represent color images. One method is called RGB, so called because each color is made of a combination of three primary colors:
red, green, and blue.
The intensity of each color is measured, and a bit pattern is assigned to it. Another method is called YCM, in which a color is made
of a combination of three other primary colors: yellow, cyan,and magenta.
Audio: Audio refers to the recording or broadcasting of sound or music. Audio is by nature different from text, numbers, or images. It
is continuous, not discrete. Even when we use a microphone to change voice or music to an electric signal, we create a continuous signal.
Video: Video refers to the recording or broadcasting of a picture or movie. Video can either be produced as a continuous entity
(e.g., by a TV camera), or it can be a combination of images,each a discrete entity, arranged to convey the idea of motion. Again we
can change video to a digital or an analog signal.
1.2.2 Data Flow
Communication between two devices can be simplex, half-duplex, or full-duplex.
Simplex
In simplex mode, the communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit; the other can only receive. Keyboards and traditional monitors are examples of simplex devices. The keyboard can only introduce input; the monitor can only accept output. The simplex mode can use the entire capacity of the channel to send data in one direction.
Half-Duplex
In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa. The half-duplex mode is like a one-lane road with traffic allowed in both directions. When cars are traveling in one direction, cars going the other way must wait.
In a half-duplex transmission, the entire capacity of a channel is taken over by whichever of the two devices is transmitting at the time.Walkie-talkies and CB(citizens band) radios are both half-duplex systems.
Full Duplex
In full-duplex mode, both stations can transmit and receive simultaneously. The full-duplex mode is like a two way street with traffic flowing in both directions at the same time. One common example of full-duplex communication is the telephone network. When two people are communicating by a telephone line, both can talk and listen at the same time.
1.3 PROTOCOL
In computer networks, communication occurs between entities in different systems. An entity is anything capable of sending or receiving information. However, two entities cannot simply send bit streams to each other and expect to be understood. For communication to occur, the entities must agree on a protocol. A protocol is a set of rules that govern data communications. A protocol defines what is communicated, how it is communicated, and when it is communicated.
i.e,
1.3.1 Elements of a Protocol
A. Syntax:
The term syntax refers to the structure or format of the data, meaning the order in which they are presented. For example, a simple protocol might expect the first 8 bits of data to be the address of the sender, the second 8 bits to be the address of the receiver, and the rest of the stream to be the message itself.
i.e.,
B. Semantics
The word semantics refers to the meaning of each section of bits. How is a particular pattern to be interpreted, and what action is to be taken based on that interpretation? For example, does an address identify the route to be taken or the final destination of the message?
i.e.,
C. Timing
The term timing refers to two characteristics: when data should be sent and how fast they can be sent. For example, if a sender produces data at 100 Mbps but the receiver can process data at only 1 Mbps, the transmission will overload the receiver and some data will be lost.
i.e.,
1.4 COMMUNICATION SYSTEM
The communication system is a system which describes the information exchange between two points. The process of transmission and reception of information is called communication. The major elements of communication are the Transmitter of information, Channel or medium of communication and the Receiver of information.
Some definitions of communication:
A data communications system has five components:
Verlag: BookRix GmbH & Co. KG
Tag der Veröffentlichung: 02.03.2021
ISBN: 978-3-7487-7635-2
Alle Rechte vorbehalten