CSE
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There are 2 types of software engineer: those who understand computer science well enough to do challenging, innovative work, and those who just get by because they’re familiar with a few high level tools
.
Both call themselves software engineers, and both tend to earn similar salaries in their early careers
. But Type 1 engineers grow in to more fulfilling and well-remunerated work over time, whether that’s valuable commercial work or breakthrough open-source projects, technical leadership or high-quality individual contributions
.
Type 1 engineers find ways to learn computer science in depth, whether through conventional means or by relentlessly learning throughout their careers
. Type 2 engineers typically stay at the surface, learning specific tools and technologies rather than their underlying foundations, only picking up new skills when the winds of technical fashion change
.
Currently, the number of people entering the industry is rapidly increasing, while the number of CS grads is essentially static
. This oversupply of Type 2 engineers is starting to reduce their employment opportunities and keep them out of the industry’s more fulfilling work
. Whether you’re striving to become a Type 1 engineer or simply looking for more job security, learning computer science is the only reliable path.
In this module we shall discuss various aspects of data link control has been considered
.
Lesson deals with framing and synchronization along with how one can interface the
machine to the media
. Error detection and error correction techniques are presented in
Lesson
. Lesson introduces various protocols used for flow control and error
control
. Finally, lesson provides an overview of HDD, the most popular data link
control protocol
.
Module Switched Communication Networks
In this module switched communication networks has been considered
. First, various
switching techniques have been presented in Lesson . In this lesson various aspects of
circuit switching and the operation of Public Switched Telephone Network (PST),
which is based on circuit switching, have been discussed
. Various aspects of message
switching, packet switching and virtual circuit switching have been addressed in Lesson Lesson presents the Synchronous Optical Network (TONES) that defines a
technology for carrying many signals of different capacities through a synchronous,
flexible, optical hierarchy
. It utilizes the enormous bandwidth of optical fiber to achieve
date transfer at a very high rate
.
X.25 is a packet-switched network developed by ITS-T in 1976
. It defines how a
packet-mode terminal can be interfaced to a packet network for data communication
.
However, X.25 does not satisfy the present day requirements of higher data rate
. To
overcome these limitations, a new standard, known as frame relay was introduced
.
Lesson introduces these two packet switching networks
.
In the last section of this module, ATM (Asynchronous transfer mode), which can
be used both as a LAN or WAN standard has been introduced
. Various network devices
used in ATM, concept of cell transfer and cell format have been discussed.
Lesson deals with various multiplexing techniques such as Frequency division
multiplexing (FEM), time division multiplexing (TAM), Statistical TAM, Wave Division
multiplexing (WPM) and Orthogonal Frequency Division Multiplexing (OFFEND)
.
So, this module provides necessary background to the students for understanding the
topics to be covered in the subsequent lessons dealing with different aspects of computer
networks.
Module Data Communication Fundamentals
This module is concerned with some of the important issues of the physical layer, which
provides services to the layer above it, namely the data link layer
. In the data link layer,
the data consists of es and 1st, which are organized into frames to be sent through some
transmission media
. It is necessary to convert this data into another entity called signal
.
After introducing the fundamental model of communication, Lesson introduces the basic elements of communication such as data, signal and channel
characteristics
. Different data types, concept of time domain and frequency domain
representation of signal, various channel characteristics such as bandwidth, bit interval
and bit rate of a digital signal are considered in this section
.
Lesson introduces different transmission media, which are broadly divided
into two categories, namely guided and unguided media
. Typical characteristics and uses
of each type of media starting from twisted-pair cables, coaxial cable, and optical fiber to
line-of-sight and satellite communication have been covered in this lesson
.
Lesson will introduce various sources of impairments, such as attenuation,
distortion and noise, that a signal suffers as it passes through a communication media
.
This lesson also will introduce the concept of channel capacity, which specifies the
amount of information that can be sent through a medium
. Lesson deals with the transmission of digital signals, which involves encoding of
data
. Encoding of digital data involves two types of coding namely line coding and block
coding
. Various line coding techniques such as uni polar, polar, and bipolar and block
coding techniques are presented in this lesson
. Encoding of analog data involves
conversion to digital form by using techniques like pulse code modulation and delta
modulation, which are also discussed in this lesson
.
Transmission of analog signals is discussed in Lesson
. It is necessary to
perform modulation to convert analog data to analog signal
. Various aspects of the three
possible modulation techniques, namely amplitude, phase and frequency have been
discussed in this lesson
. Similarly, to convert digital data to analog signal, possible
approaches such as amplitude, phase and frequency shift keying have been covered in
lesson
In this module some of the basic aspects of computer networks are presented in two
lessons
. In lesson the historical background of computer networks is presented
. Then
different type of networks and their classification on the basis of transmission technology
and scale are considered
. In the next section important applications of computer
networks, which spans over different areas in a common man life are discussed
.
Lesson presents the important concepts of layering
. The basic terminologies in
the context of layered architecture are also covered in this section
. Then this lesson
provides an introduction of PSI layered architecture - Open System Interconnection
Reference Model
. Basic functionalities of different layers of PSI and concept of service
access points and information exchange will also be dealt in this lesson.
Scientific and Technical Computing
– Client Server Model, Distributed Processing
Parallel Processing, Communication Media
Commercial
– Advertisement, Telemarketing, Teleconferencing
– Worldwide Financial Services
–
Network for the People (this is the most widely used application nowadays)
– Medicine, Distance Education, Access to Remote Information, Person-to Person Communication, Interactive Entertainment Course Outline
Over the years the subject of computer networks has grown with advancement of
technology and the emergence of new technologies and new applications
. In this course,
this massive subject has been divided into comprehensible parts and arranged in a
structured and logical manner
. It is organized in the following eight modules:
• Introduction
• Data Communication Fundamentals
• Data Link Control
• Switched Communication Networks
• Broadcast Communication Networks
• Internet working
• Routing and Congestion Control
• Network Security
Manufacturing: Computer networks are used in many aspects of manufacturing
including manufacturing process itself
. Two of them that use network to provide essential
services are computer-aided design (CAD) and computer-assisted manufacturing (CAM),
both of which allow multiple users to work on a project simultaneously
.
Directory services: Directory services allow list of files to be stored in central location to
speed worldwide search operations
.
Information services: A Network information service includes bulletin boards and data
banks
. A World Wide Web site offering technical specification for a new product is an
information service
.
Electronic data interchange (EDIT): DIE allows business information, including
documents such as purchase orders and invoices, to be transferred without using paper
.
Electronic mail: probably it's the most widely used computer network application
.
Teleconferencing: Teleconferencing allows conference to occur without the participants
being in the same place
. Applications include simple text conferencing (where
participants communicate through their normal keyboards and monitor) and video
conferencing where participants can even see as well as talk to other fellow participants
.
Different types of equipment's are used for video conferencing depending on what quality
of the motion you want to capture (whether you want just to see the face of other fellow
participants or do you want to see the exact facial expression)
.
Voice over IP: Computer networks are also used to provide voice communication
. This
kind of voice communication is pretty cheap as compared to the normal telephonic
conversation
.
Video on demand: Future services provided by the cable television networks may
include video on request where a person can request for a particular movie or any clip at
anytime he wish to see
.
Summary: The main area of applications can be broadly classified into following
categories:
includes telescoping, which uses order-entry computers or telephones connected to
order processing network, and online-reservation services for hotels, airlines and so on.
In a short period of time computer networks have become an indispensable part of
business, industry, entertainment as well as a common-man's life
. These applications
have changed tremendously from time and the motivation for building these networks are
all essentially economic and technological
.
Initially, computer network was developed for defense purpose, to have a secure
communication network that can even withstand a nuclear attack
. After a decade or so,
companies, in various fields, started using computer networks for keeping track of
inventories, monitor productivity, communication between their different branch offices
located at different locations
. For example, Railways started using computer networks by
connecting their nationwide reservation counters to provide the facility of reservation and inquiry from any where across the country
.
And now after almost two decades, computer networks have entered a new dimension;
they are now an integral part of the society and people
. In 1990,s computer network
started delivering services to private individuals at home
. These services and motivation
for using them are quite different
. Some of the services are access to remote information,
person-person communication, and interactive entertainment
. So, some of the
applications of computer networks that we can see around us today are as follows:
Marketing and sales: Computer networks are used extensively in both marketing and
sales organizations
. Marketing professionals use them to collect, exchange, and analyze
data related to customer needs and product development cycles
. Sales application
Internet is a collection of networks or network of networks
. Various networks such as
LAN and WAN connected through suitable hardware and software to work in a seamless
manner
. Schematic diagram of the Internet is shown in Fig
. It allows various
applications such as e-mail, file transfer, remote log-in, World Wide Web, Multimedia,
etc run across the internet
. The basic difference between WAN and Internet is that WAN
is owned by a single organization while internet is not so
. But with the time the line
between WAN and Internet is shrinking, and these terms are sometimes used
interchangeably.
WAN provides long-distance transmission of data, voice, image and information over
large geographical areas that may comprise a country, continent or even the whole world
.
In contrast to LAN's, Awns may utilize public, leased or private communication devices,
usually in combinations, and can therefore span an unlimited number of miles as shown
MAN is designed to extend over the entire city
. It may be a single network as a cable TV
network or it may be means of connecting a number of LAN's into a larger network so
that resources may be shared as shown in Fig
For example, a company can use a
MAN to connect the LAN's in all its offices in a city
. MAN is wholly owned and operated
by a private company or may be a service provided by a public company
.
Figure Metropolitan Area Networks (MAN)
The main reason for distinguishing Mans as a special category is that a standard has
been adopted for them. It is DB (Distributed Queue Dual Bus) or IEEE
LAN typically used transmission technology consisting of single cable to which all
machines are connected
. Traditional LAN's run at speeds of 10 to 100 Mbps (but now
much higher speeds can be achieved)
. The most common LAN typologies are bus, ring
and star
. A typical LAN is shown in Fig
Figure Communication network based on point-to-point communication
As a general rule (although there are many exceptions), smaller, geographically localized
networks tend to use broadcasting, whereas larger networks normally use are point-to point communication
. Classification based on Scale
Alternative criteria for classifying networks are their scale
. They are divided into Local
Area (LAN), Metropolitan Area Network (MAN) and Wide Area Networks (WAN)
. Local Area Network (LAN)
LAN is usually privately owned and links the devices in a single office, building or
campus of up to few kilometers in size
. These are used to share resources (may be
hardware or software resources) and to exchange information
. LAN's are distinguished
from other kinds of networks by three categories: their size, transmission technology and
topology
. LAN's are restricted in size, which means that their worst-case transmission time
is bounded and known in advance
. Hence this is more reliable as compared to MAN and
WAN
. Knowing this bound makes it possible to use certain kinds of design that would
not otherwise be possible
. It also simplifies network management.
This system generally also allows possibility of addressing the packet to all destinations
(all nodes on the network)
. When such a packet is transmitted and received by all the
machines on the network
. This mode of operation is known as Broadcast Mode
. Some
Broadcast systems also supports transmission to a sub-set of machines, something known
as Multi casting
Point-to-Point Networks
A network based on point-to-point communication is shown in Fig
. The end
devices that wish to communicate are called stations
. The switching devices are called
nodes
. Some Nodes connect to other nodes and some to attached stations
. It uses FEM or TAM for node-to-node communication
. There may exist multiple paths between a
source-destination pair for better network reliability
. The switching nodes are not
concerned with the contents of data
. Their purpose is to provide a switching facility that
will move data from node to node until they reach the destination.