Fundamentals of Data Communication in Advanced Computer Networking, Slides of Computer Science

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Advanced Computer Networking

Sep 2021

Chapter One

Data Communication

Basics

Fundamental Characteristics

The effectiveness of a data communications system depends on

four fundamental characteristics:

Delivery : System must deliver data to correct destination.

Accuracy: System must deliver data accurately.

Timelines: System must deliver data in timely manner.

J itter : it is a variation in packet transit delay caused by queuing,

contention and serialization effects on the path through the

network.

Components of Data communication

There are five basic components of data communication.

1. Message
2. Sender
3. Receiver
4. Medium
5. Protocol

Data Representation Techniques

 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 (0s or 1s).
• 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.

Cont’d…

 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.

 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.

Data Transmission

 Signal is electric or electromagnetic representations of data, physically propagates along

medium

 Transmission is the communication of data by the propagation and processing of signals.

 Data transmission occurs between transmitter and receiver over some transmission

medium.

 The successful transmission of data depends principally on two factors: the quality of the

signal being transmitted and the characteristics of the transmission medium.

 Transmission media may be classified as guided or unguided. In both cases, communication

is in the form of electromagnetic waves.

 Guided media : the waves are guided along a physical path;

 Eg. twisted pair , coaxial cable , and optical fiber.

 Unguided media (Wireless) : provide a means for transmitting electromagnetic waves but

do not guide them;

 Eg. propagation through air, vacuum, and seawater.

Analog and Digital Data

The terms analog and digital correspond, roughly, to continuous

and discrete , respectively.

Analog data take on continuous values in some interval. For

example, voice and video are continuously varying patterns of

intensity. Most data collected by sensors, such as temperature and

pressure, are continuous valued.

Digital data take on discrete values; examples are text and

integers.

The most familiar examples of analog data are audio and video.

A familiar example of digital data is text or character strings.

Cont’d…

 The principal advantages of digital signaling are that it is generally

cheaper than analog signaling and is less susceptible to noise

interference.

 The principal disadvantage is that digital signals suffer more from

attenuation than do analog signals.

Cont’d…

 Analog data can be represented by digital signals. The device that

performs this function for voice data is a codec (coder-decoder).

Analog and Digital Transmission

 Analog transmission is a means of transmitting analog signals without regard to their

content; the signals may represent analog data (e.g., voice) or digital data (e.g., binary

data that pass through a modem).

 In either case, the analog signal will become weaker (attenuate) after a certain

distance.

 To achieve longer distances, the analog transmission system includes amplifiers that

boost the energy in the signal.

 Unfortunately, the amplifier also boosts the noise components. With amplifiers

cascaded to achieve long distances, the signal becomes more and more distorted.

 For analog data, such as voice, quite a bit of distortion can be tolerated and the data

remain intelligible.

 However, for digital data, cascaded amplifiers will introduce errors.

Cont’d…

 The question naturally arises as to which is the preferred method of transmission.

 Both long-haul telecommunications facilities and intra-building services have

moved to digital transmission and, where possible, digital signaling techniques.

The most important reasons are as follows:

 Digital technology: The advent of large-scale integration (LSI) and very-large scale integration (VLSI)

technology has caused a continuing drop in the cost and size of digital circuitry. Analog equipment has

not shown a similar drop.

 Data integrity: With the use of repeaters rather than amplifiers, the effects of noise and other signal

impairments are not cumulative. Thus it is possible to transmit data longer distances and over lower

quality lines by digital means while maintaining the integrity of the data.

 Capacity utilization: It has become economical to build transmission links of very high bandwidth,

including satellite channels and optical fiber. A high degree of multiplexing is needed to utilize such

capacity effectively, and this is more easily and cheaply achieved with digital (time division) rather than

analog (frequency division) techniques.

 Security and privacy: Encryption techniques can be readily applied to digital data and to analog data

that have been digitized.

 Integration: By treating both analog and digital data digitally, all signals have the same form and can be

treated similarly. Thus economies of scale and convenience can be achieved by integrating voice, video,

and digital data.

Transmission Impairments

 Signals travel through transmission media, which are not

perfect. The imperfection causes signal impairment.

 This means that the signal at the beginning of the medium

is not the same as the signal at the end of the medium.

 most significant impairments are

• (^) attenuation
• (^) distortion

noise