2. Definition
• CN is a collection of two or more
computers, which are connected to
share information and resources.
• Computers in a network are
interconnected by telephone lines,
coaxial cables, satellite links, radio
or some other communication
technique.
• The computers can be
geographically located anywhere.
3. Applications of Networks
Resource Sharing
Hardware (computing resources, disks, printers)
Software (application software)
Information Sharing
Easy accessibility from anywhere (files, databases)
Search Capability (WWW)
Communication
Email
Message broadcast -prerecorded message to people
Remote computing
- Access thru network
Distributed processing (GRID Computing)
-Combination of several computers to process large
amount of data.
4. Types / categories:
1. Local Area Network (LAN) -Network in
small geographical Area (Room,
Building or a Campus) is called LAN
(Local Area Network)
2. Metropolitan Area Network (MAN) -
Network in a City is call MAN
(Metropolitan Area Network)
3. Wide Area Network (WAN) -Network
spread geographically (Country or
across Globe) is called WAN (Wide
Area Network)
5. Network Topology
The network topology defines the way in which
computers, printers, and other devices are
connected. A network topology describes the
layout of the wire and devices as well as the
paths used by data transmissions.
7. Star & Tree Topology
Star topology resembles spokes
in a bicycle wheel.
Larger networks use the
extended star topology also
called tree topology. When used
with network devices that filter
frames or packets, like bridges,
switches, and routers, this
topology significantly reduces
the traffic on the wires by
sending packets only to the
wires of the destination host.
8. Ring Topology
A frame travels around the ring,
stopping at each node. If a node
wants to transmit data, it adds the
data as well as the destination
address to the frame.
The frame then continues around
the ring until it finds the
destination node, which takes the
data out of the frame.
Single ring – All the devices on the
network share a single cable
Dual ring – The dual ring topology
allows data to be sent in both
directions.
9. Mesh Topology
The mesh topology
connects all devices
(nodes) to each other
for redundancy and
fault tolerance.
It is used in WANs to
interconnect LANs and
for mission critical
networks like those
used by banks and
financial institutions.
Implementing the mesh
topology is expensive
and difficult.
10. OSI Model Overview
The Open Systems
Interconnection (OSI)
reference model is an
industry standard
framework that is used to
divide the functions of
networking into seven
distinct layers.
Each layer provides specific
services to the layers above
and below it in order for the
network to work effectively.
11. Functions of the Layers
1. Physical
• transmit a bit stream over a physical medium.
2. Data-Link
• Organizes bits into logical units called frames.
• Node-to-node delivery
3. Network
• Source-to-destination delivery of a packet.
4. Transport
• Source-to-destination delivery of the entire message.
5. Session
• Establishes, maintains, and synchronizes
the dialog between communicating systems.
6. Presentation
• Deals with the fact that different systems use
different coding methods.
7. Application
• Enables the user to access the network.
12. Physical Layer
It defines the physical and electrical characteristics
of the N/W.
This layer also defines what kind of network
interface card must be installed in each computer
and what kinds of hubs to be used.
In other words the physical layer is a conduit
(connection) between the computers networking
hardware and its networking software.
This layer communicates with the data link layer and
regulates the transmission of a stream of bits over a
physical medium.
This layer also defines which transmission technique
is used to send data over the cable.
13. Data Link Layer
The function of data link layer is to transform the
data into a line that is free of transmission errors
and is responsible for node-to-node delivery
On the sender side the data link layer divides the
layer divides the stream of bits fro the N/W layer
into a manageable form known as frames.
These data frames are then transmitted
sequentially to the receiver.
On the receiver end the data link layer detects and
corrects any errors in the transmitted data which
it gets from the physical layer.
14. Network Layer
The network layer provides the physical routing of
the data that is it determines the path between
the sender and receiver.
The outbound data is passed down from the
transport layer is encapsulated in the networks
layers protocol and then sent to the data link layer
for segmentation and transmission.
This layer organizes frames from data link layer
into packets and is passed to the transport layer
Network layer provides uniform addressing
mechanism so that more than one networks can be
interconnected.
15. Transport Layer
The basic function of the transport layer is to
handle error recognition and recovery of the data
packets.
The T L establishes, maintains, and terminates
communication between the sender and the
receiver.
At the receiving end transport layer rebuilds
packets into the original message, and to ensure
that the packets arrived correctly, the receiving
transport layer sends receipt acknowledgments.
16. Session Layer
The session layer organizes and synchronizes the
exchange of data between the sending and
receiving applications.
The session layer lets each application at one end
know the status of the other at the other end.
An error in the sending application is handled by
the session layer in such a manner so that the
receiving application may know that the error has
occurred.
The SL can resynchronize applications that are
currently connected to each other.
This may be necessary when communications are
temporarily interrupted or when an error has
occurred that results in loss of data.
17. Presentation Layer
The basic function of the presentation layer is to
ensure that information sent from the application
layer of one system would be readable by the
application layer of another system.
This is where application data is packed or
unpacked ready for use by the running application.
This layer also manages security issues by
providing services such as data encryption and
compresses data so that fewer bits need to be
transferred on the N/W .
18. Application Layer
The A L is the entrance point that programs use to
access OSI model and utilize network resources.
This layer represents the services that directly
support applications.
This OSI layer is closest to the end user.
Application layer includes network software that
directly serves the user , providing such things as
the user interface and application featurs such as
electronic Mail.
19. NETWORK STRUCTURE
The subnet interconnects hosts.
Subnet
◦ Carries messages from host to host. It is made
up of telecommunication lines (i.e. circuits,
channels, trunks) and switching elements (i.e.
Interface Message Processor’s, routers).
Hosts
◦ End user machines or computers.
20. Services
Connection-Oriented and Connectionless
◦ Connection-Oriented – before data is sent, the
service from the sending computer must
establish a connection with the receiving
computer.
◦ Connectionless – data can be sent at any time by
the service from the sending computer.
21. Service Primitives
Request – entity wants the service to do some work
Indicate – entity is to be informed about an event
Response – entity responds to an event
Confirm – entity is to be informed about its request
Sending Computer Receiving Computer
4 Transport 4 Transport
1. request 4. confirm 2. indicate 3. response
3 Network 3 Network
24. Introduction to Computer Networks
Networking Devices
HUB, Switches, Routers,
Wireless Access Points,
Modems etc.
25. Network Devices
• These devices interconnect individual computers
and ensure that they communicate efficiently.
• Some network devices are as below
1. Network Interface Card
2. Hub
3. Repeater
4. Switch
5. Bridge
6. Router
7. Gateway
26. Network Devices
Network Interface Card
• Interface between the machine and the N/W.
• It connects the clients, servers and peripherals
to the network via a port.
• Most network interfaces come as small circuit
board that can be inserted onto one of the
computers motherboard slots.
• Each network interface is associated with a
unique address called its media access control
(MAC) address.
• The MAC address helps in sending information to
its intended destination.
27. Network Devices
Hub
• Is a small box that connects individual devices on
a network so that they can communicate with one
another.
• The hub operates by gathering the signals from
individual network devices, optionally amplifying
the signals and then sending them onto all other
connected devices.
• Amplification of the signal ensures that devices
on the network receive reliable information.
• Also known as concentrator, a hub works on
physical layer of the OSI model.
28. Network Devices
Repeater
• Is an electronic device that operates on the
physical layer of the OSI model.
• Signals that carry information within a network
can travel a fixed distance.
• A repeater installed on the link receives signal ,
regenerates it and sends the refreshed copy back
to the link.
• Nowadays the terms repeater and hub are used
synonymously, but they are actually not the same
• Although at its very basic level, a hub can be
thought of as a multiport repeater.
29. Network Devices
Switch
• Like a hub a switch too connects individual
devices on a network so that they can
communicate with one another.
• Switches work on the data link layer of OSI
model.
• Allows reducing overall network traffic
30. Network Devices
Bridge
• A bridge filters data traffic at a network
boundry.
• It reduces the amount of traffic on a LAN by
dividing it into two segments.
• Bridges operate at the data link layer of the OSI
model.
• It inspects each incoming traffic and decides
whether to forward or discard it .
• When a frame enters a bridge the bridge not
only regenerates the signals but also checks the
address of the destination and forwards the new
copy only to the segment to which the address
belongs
31. Network Devices
Router
• A router is an essential network device for
interconnecting two or more networks.
• Routers aim is to trace the best route for information to
travel .
• As network traffic changes during the day routers can
redirect information to take less congested routes.
• A router creates or maintains a table called a routing
table that stores the best route to certain destinations.
• They can permit or deny network communications with a
particular network.
32. Network Devices
Gateway
• Is internetworking device which joins two different
network protocols together.
• It works on all seven layers of the OSI model
• A gateway accepts the packet formatted for one protocol
and converts the formatted packet into another protocol.
33. Introduction to Computer Networks
Networking Media
Networking media can be
defined simply as the
means by which signals
(data) are sent from one
computer to another
(either by cable or
wireless means).
34. TRANSMISSION MEDIA
1. Guided
Data is sent via a wire or optical cable.
Twisted Pair
Two copper wires are twisted together to reduce the effect of
crosstalk noise.
Baseband Coaxial Cable
A 50-ohm cable used for digital transmission.
Broadband Coaxial Cable
A 75-ohm cable used for analog transmission such as Cable
TV.
35. TRANSMISSION MEDIA
Fiber Optic Cables
Two general types are multimode and single mode.
In multimode, light is reflected internally. Light source is an
LED.
In single mode, the light propagates in a straight line. Light
source come from expensive laser diodes. Faster and longer
distances as compared to multimode.
* Fiber optic cables are difficult to tap (higher security)
and are normally used for backbone cabling.
36. Twisted Pair
Two insulated copper wires in a spiral
Number of pairs are bundled together
Twisting decreases crosstalk
Most common form for analog and digital
Used in telephone system
Subscriber loops
From a person’s home to the local office of the phone
company
LANS
10Mbps with newer at 100Mbps
37. Long Distance
4 Mbps
ISDN –Integrated Services Digital Network
Digital
Repeaters required every 2 –3 kilometers
Analog
Amplifiers required every 5-6 kilometers
Bandwidth of 250KHz, carry a few voice channels
Susceptible to noise, shielded and unshielded
Compared to optical and coax twisted pair is
limited in bandwidth, distance, and data rate
38. Coaxial Cable
• Hollow outer cylindrical conductor
surrounding a single view
• Most versatile of mediums, used for TV,
long distance telephone, and LAN’S
39. Optical fiber
• Thin, flexible light passing material made from glass or
plastic
• Grouped into cables
• Better than coaxial cable or twisted pair
• Data rates of 2Gbps over 10’s of Km
• Light weight –good for buildings
• Lower attenuation than coax or twisted
40. TRANSMISSION MEDIA
2. Unguided
Data is sent through the air.
Line-of-sight
Transmitter and receiver must “see” each other, such as a
terrestrial microwave system.
Communication Satellites
A big microwave repeater in the sky. Data is broadcasted, and
can be “pirated.”
Radio
Term used to include all frequency bands, such as FM, UHF,
and VHF television.
41. • Wireless
• Broadcast Radio
Radio -3kHz to 300Ghz
Broadcast radio –30MHz to 1GHz
• Satellite Microwave 1 –10 GHz
• Infrared
42. Features & Working of the Internet
• Connected by many small networks in the world
using TCP/IP protocol stack
• No specific path between any two hosts that are
communicating
• Path is determined dynamically by Router, that
relays the data from the source host to the
destination host
• Data may need to go thru many routers before they
reach the destination
• When data from different sources need to go thru a
particular router, it will become busy and may delay
or even lost the data
• Hence Internet is NOT a reliable network
43. Performance: Latency and
Bandwidth
• Latency
–How long minimum communication takes in seconds (s)
–Round trip vs. single trip
–More difficult to overcome than bandwidth
• Bandwidth
–Number of bits per time unit usually seconds (bps)
44.
45. Addressing in TCP/IP
• Each TCP/IP address includes:
– Internet Address
– Protocol (TCP)
– Port Number
46. What is an IP Address?
• Internet identifier including information about how to reach
a network location (via the Internet routing system)
• IPv4: 32-bit* number. Written in Dotted Decimal Notation
205.150.58.7
• 4 billion different host addresses
• IPv6: 128-bit* number. Written in Hex Decimal Notation
2001:0503:0C27:0000:0000:0000:0000:0000
• 16 billion billion network addresses
• Each Network I.D. on the Internet needs to be registered to
the Internet Assigned number Authority (IANA)
47. Address
• Way to identify people / computers
• On the Internet, the term “address” is used loosely
• –Can mean many different things from an email address to
a URL (Uniform resource locator)
• More specifically, 2 types:
• –Internet protocol (IP) address(or network address): 4-part
numeric address
• e.g. 158.132.148.28
• –Domain name system (DNS) address
• e.g. LMS
48. The four formats of IP Addresses
Class
A 0 NetID HostID
B 10 NetID HostID
C 110 NetID HostID
D 1110 Multicast Address
8 bits 8 bits 8 bits 8 bits
49. Hardware vs. Software Firewalls
• Hardware Firewalls
–Protect an entire network
–Implemented on the router level
–Usually more expensive, harder to configure
• Software Firewalls
–Protect a single computer
–Usually less expensive, easier to configure
50. Firewall Rules
• Allow –traffic that flows automatically
because it has been deemed as “safe” (Ex.
Meeting Maker, Eudora, etc.)
• Block –traffic that is blocked because it has
been deemed dangerous to your computer
• Ask –asks the user whether or not the traffic
is allowed to pass through
53. • SCADA refers to a system that collects data from
various sensors at a factory, plant or in other
remote locations and then sends this data to a
central computer which then manages and controls
the data.
• Data acquisition is the process of retrieving
control information from the equipment which is
out of order or may lead to some problem or when
decisions are need to be taken according to the
situation in the equipment. So this acquisition is
done by continuous monitoring of the equipment
to which it is employed. The data accessed are
then forwarded onto a telemetry system ready for
transfer to the different sites.
54. • Components of SCADA System
1. Field Instrumentation 2. Remote Stations 3.
Communications Network 4. Central
Monitoring Station
55. BENEFITS OF SCADA
• Long distance monitoring
• Long distance training
• Protection against terrorism/vandalism-
alarm
• Data management (engineering and
operations)
• Automated operations with real time control
56. What is Internet & Web?
Internet is a world wide, noncommercial, freely
accessible Network of Computer Networks.
World Wide Web (WWW) is a vast, ever-
expanding collection of online documents and
information formatted in HTML and
distributed over the Internet.
57. Working of the Web
• Web documents live on Computers that run
HTTP servers.
• HTTP servers can be hosted on UNIX ,
Macintosh or PC’s.
• Browser requests the Web page from the Web
server.
• Server sends the HTML pages over the
Internet to your computer.
• Browser interprets the data and displays it on
your screen.
59. Web Page & Home Page
• Web Page : Document written in Web
formatting language, HTML
• Home Page : This is the first page or the
opening page of any web document.
60. Elements of Web Page
• Text : This is simple 7-bit ASCII , which can be
easily represented by using the keys available on a
standard keyboard.
• Graphics : Graphics add life to the web pages and
makes them interesting to browse.
• Links and URL’s : Links are transporters of the
Web. Links contain addresses of the Web files that
they are referencing.
Web address / site address is also known as URL
(Uniform Resource Locator)
