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1: Characteristics of Data – Communication
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This sharing can be local or remote
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The term
telecommunication, which includes telephony, telegraphy, and television, means communication at a distance
(tele is Greek for "far")
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Data communications are the exchange of data between two devices via some
form of transmission medium such as a wire cable
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The effectiveness of a data communications system depends on four fundamental
characteristics: delivery, accuracy, timeliness, and jitter
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II
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IV
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The system must deliver data to the correct destination
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Accuracy
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Data that have been altered in transmission and
left uncorrected are unusable
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The system must deliver data in a timely manner
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In the case
of video and audio, timely delivery means delivering data as they are produced, in the same order that
they are produced, and without significant delay
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Jitter
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It is the uneven delay in the delivery of
audio or video packets
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If some of
the packets arrive with 3D-ms delay and others with 4D-ms delay, an uneven quality in the video is the
result
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Five components of data communication
I
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The message is the information (data) to be communicated
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2
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The sender is the device that sends the data message
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3
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The receiver is the device that receives the message
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4
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The transmission medium is the physical path by which a message travels from sender to
receiver
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5
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A protocol is a set of rules that govern data communications
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Without a protocol, two devices may be connected but not communicating, just as a
person speaking French cannot be understood by a person who speaks only Japanese

CN –I UNIT I

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Data Flow
Communication between two devices can be simplex, half-duplex, or full-duplex
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Only one of the two devices on a
link can transmit; the other can only receive
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The keyboard can only introduce input; the monitor can only accept output
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Half-Duplex
In half-duplex mode, each station can both transmit and receive, but not at the same time
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When cars are traveling in one direction, cars going the other way must wait
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Walkietalkies and CB (citizens band) radios are both half-duplex systems
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Full-Duplex
In full-duplex, 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
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This sharing can occur in two ways: Either the link
must contain two physically separate transmission paths, one for sending and the other for receiving; or the
capacity of the channel is divided between signals traveling in both directions
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When two people are communicating by a telephone line, both can talk
and listen at the same time
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The capacity of the channel, however, must be divided between the two
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4
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A node can be a
computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the
network
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Instead of one
single large machine being responsible for all aspects of process, separate computers (usually a personal computer
or workstation) handle a subset
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The most important of these are performance,
reliability, and security
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Transit time is the amount
of time required for a message to travel from one device to another
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The performance of a network depends on a number of factors, including the number
of users, the type of transmission medium, the capabilities of the connected hardware, and the efficiency of the
software
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We often need more
through put and less delay
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If we try to send more data to the
network, we may increase throughput but we increase the delay because of traffic congestion in the network
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Security
Network security issues include protecting data from unauthorized access, protecting data from damage and
development, and implementing policies and procedures for recovery from breaches and data losses
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Type of Connection
A network is two or more devices connected through links
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For visualization purposes, it is simplest to imagine any link as a line drawn between
two points
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There are two possible types of connections:
Point-to-point and multipoint
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The entire capacity of
the link is reserved for transmission between those two devices
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When you change television channels by infrared remote control, you are establishing a point-to-point
connection between the remote control and the television's control system
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In a multipoint environment, the capacity of the channel is shared, either spatially or temporally
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If users must take turns, it is a
timeshared connection
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Physical Topology
The term physical topology refers to the way in which a network is laid out physically
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The topology of a network is the geometric representation of
the relationship of all the links and linking devices (usually called nodes) to one another
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INTERNET
The Internet is a communication system that has brought a wealth of information to our fingertips and organized it
for our use
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An internet (note the
lowercase letter i) is two or more networks that can communicate with each other
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Private individuals as well as various organizations such as government agencies, schools, research
facilities, corporations, and libraries in more than 100 countries
use the Internet
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Yet this extraordinary communication system only came into being
in 1969
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Computers from different manufacturers were unable to communicate with one another
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In 1967, at an Association for Computing Machinery (ACM) meeting, ARPA presented its ideas
for ARPANET, a small network of connected computers
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The IMPs, in tum, would be connected to one another
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By 1969, ARPANET was a reality
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California at Los Angeles (UCLA), the University of California at Santa Barbara (UCSB), Stanford Research Institute
(SRI), and the University of Utah, were connected via the IMPs to form a network
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In 1972, Vint Cerf and Bob Kahn, both of
whom were part of the core ARPANET group, collaborated on what they called the Internetting Projec1
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This paper on
Transmission Control Protocol (TCP) included concepts such as encapsulation, the datagram, and the functions of a
gateway
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IP would handle datagram routing while TCP would be
responsible for higher-level functions such as segmentation, reassembly, and error detection
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8
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An entity is anything capable
of sending or receiving information
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For communication to occur, the entities must agree on a protocol
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A protocol defines what is communicated, how it is communicated, and
when it is communicated
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Syntax
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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
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The word semantics refers to the meaning of each section of bits
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The term timing refers to two characteristics: when data should be sent and how fast they can be sent
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Standards
Standards are essential in creating and maintaining an open and competitive market for equipment manufacturers
and in guaranteeing national and international interoperability of data and telecommunications technology and
processes
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Data communication standards fall into two categories: de facto (meaning "by fact" or "by
convention") and de jure (meaning "by law" or "by regulation")
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De facto
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De facto standards are often established originally by
manufacturers who seek to define the functionality of a new product or technology
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Those standards that have been legislated by an officially recognized body are de jure standards
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Standards Creation Committees
While many organizations are dedicated to the establishment of standards, data telecommunications
in North America rely primarily on those published by the following:
International Organization for Standardization (ISO)
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The ISO is active in
developing cooperation in the realms of scientific, technological, and economic activity
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By the early 1970s, a
number of countries were defining national standards for telecommunications, but there was still little
international compatibility
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This committee was devoted
to the research and establishment of standards for telecommunications in general and for phone and data systems
in particular
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American National Standards Institute (ANSI)
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S
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However, all ANSI
activities are undertaken with the welfare of the United States and its citizens occupying primary importance
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The Institute of Electrical and Electronics Engineers is the
largest professional engineering society in the world
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As one of its goals, the IEEE oversees the development and adoption of international standards for
computing and communications
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Aligned with ANSI, the Electronic Industries Association is a nonprofit
organization devoted to the promotion of electronics manufacturing concerns
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In the field of information
technology, the EIA has made significant contributions by defining physical connection interfaces and electronic
signaling specifications for data communication
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Types of Network Topology
Network Topology is the schematic description of a network arrangement, connecting various nodes (sender and
receiver) through lines of connection
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Features of Bus Topology
1
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2
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It is cost effective
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Cable required is least
compared to other
network topology
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Used in small networks
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It
is
easy
to
understand
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Easy to expand joining
two cables together
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Cables fails then whole
network fails
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If network traffic is
heavy or nodes are
more the performance
of
the
network
decreases
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Cable has a limited
length
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It is slower than the ring
topology
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Exactly two neighbours for each device
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A number of
repeaters are used and the
transmission
is
unidirectional
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Date
is
transferred in a sequential
manner that is bit by bit
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Transmitting
network is not affected by
high traffic or by adding
more nodes, as only the
nodes having tokens can
transmit data
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Cheap to install
and expand

Disadvantages
of
Ring
Topology
1
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2
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3
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STAR Topology
In this type of topology all the computers are connected to a single hub through a cable
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Features of Star Topology
1
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2
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3
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CN –I UNIT I

Advantages of Star Topology
1
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2
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3
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4
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5
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JNEC

Disadvantages
of
Star
Topology
1
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2
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3
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4
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MESH Topology
It is a point-to-point connection to other nodes or devices
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Mesh has n (n-2)/2 physical channels to link hn devices
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Partial
Mesh
Topology : In this topology
some of the systems are
connected in the same
fashion as mesh topology
but some devices are only
connected to two or three
devices
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Full
Mesh
Topology : Each and every
nodes or devices are
connected to each other
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Fully connected
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Robust
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Not flexible
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Each connection
can carry its own data
load
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It is robust
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Fault is diagnosed
easily
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Provides security
and privacy
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Installation and
configuration is difficult
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Cabling cost is
more
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Bulk wiring is
required
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It is also called hierarchical topology
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Advantages
of
Tree Disadvantages of Tree
Features
of
Tree Topology
Topology
Topology
1
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Heavily cabled
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Ideal
if and star topologies
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Costly
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Expansion
of 3
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nodes is possible and are added maintenance
2
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is difficult
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3
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network fails
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Error detection
is easily done
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For example if in an office in
one department ring topology is used and in another star topology is used, connecting these topologies will result
in Hybrid Topology (ring topology and star topology)
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It
is
a
combination of two or
topologies
2
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Reliable as Error
detecting and trouble
shooting is easy
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Effective
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Scalable as size
can be increased easily
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Flexible
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Complex
in
design
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Costly
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com

CN –I UNIT I

JNEC

mandarlokhande@gmail

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