CS 8591 Computer_Networks Unit - I - Introduction and Physical Layer

1. CS – 8591
COMPUTER NETWORKS
Unit - I
INTRODUCTION AND
PHYSICAL LAYER
Ms. Angayarkanni S A
Assistant Professor, IT, RMKEC

2. Outline of Day 1
 Network? - need
 Data - representation
 Data communication
 Data flow
 Network criteria – P R S
 Network Topology
 Network Types – LAN, MAN, WAN
 History of Internet
1.2

3. Network
 Dictionary meaning
 group of system of interconnected people or
things
 To connect
1.3
Interact with others to exchange
information

4. What is the need for
networking?
 To provide communication
 Access to geographically distant resources
 distributed processing
1.4

5. Data
 Collection of values
 Raw unorganized facts that need to be
processed
 23
 John
 Chennai
1.5

6. Information
 Processed, organized & structured data
 23
 John
 Chennai
1.6
Temp  23oC
Name  John
City  Chennai
Information  formatted data
’data’ in ‘a form’

7. Representation of Data
 Different forms of Information
 Text
 Numbers
 Images
 Audio
 Video
1.7

8. Text
 Sequence of bits  forms code
 7 bit  ASCII (American Standard Code
for Information Interchange)
 32 bits  Unicode
 Multi-language support
1.8

9. Numbers
 Bit pattern
 Binary
 Octal
 Decimal
 Hexadecimal
1.9

10. Images
 Matrix of pixel (picture element)
 Size of pixel  resolution
 1280*720, 2048*1536
 Each pixel  bit pattern
 Black & White (1 bit – B/W)
 Grey scale (00-Black, 01- Dark Grey, 10 Light
grey 11- White)
 RGB (Red Green Blue)
 CMYK (Cyan Magenta Yellow Key (Black))
1.10

11. Audio
 Recording/broadcasting of sound/music
 Natural/artificial
1.11

12. Video
 Sequence of images
 Recording/broadcasting of picture/movie
1.12

13. Data Communication
 Communicate – share information
 Local  face – face
 Remote  tele (far) + communicate
 Telephone, telegram, television
 Data communication - exchange of data
between two devices via some form of
transmission medium such as a wire cable
1.13

14. Effectiveness of data
communication
 Delivery – must be received by correct
destination
 Accuracy – unaltered data
 Timeliness –
 right time delivery
 Delivered late -- useless
 Jitter – variation in arrival time for data
1.14
A/V  same order, timely delivery without
significant delay real time transmission

15. Components of communication
 Message  information/data to be
communicated
 Sender device that sends the message
 Can be a computer, workstation, telephone handset,
video camera
 Receiver  device that receives the message
 Can be a computer, workstation, telephone handset, TV
1.15

16. Components of communication
 Transmission Medium physical path by which
a message travels from sender to receiver
 Twisted pair, Coaxial cable, Fibre optic, Radio
waves
 Protocol set of rules tha govern the data
communication that receives the message
 Agreement between communication parties
 Connecting devices  communicating device1.16

17. Data Flow
Flow of
data
Simplex Duplex
Half
Duplex
Full
Duplex
1.17

18. Simplex
 as on a one-way street.
 the communication is unidirectional
 Only one of the two devices on a link can
only transmit, the other can only receive.
 The simplex mode can use the entire
capacity of the channel to send data in one
direction.
 Eg- traditional TV, radio,
 Keyboard, monitor, remote
1.18

19. Half duplex
 Two lane road
 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.
 Usedwhere there is no need for
communication in both direction at same time.
 The entire capacity of the channel can be
utilized for each direction.
 Eg- Walkie Talkie
1.19

20. Full duplex
 Two lane road
 both stations can transmit and receive
simultaneously
 signals going in one direction share the
capacity of the link with signals going in
other direction
1.20

21. Full duplex…
 Sharing
 Either the link must contain two physically
separate transmission paths, one for sending
and other for receiving.
 Or the capacity is divided between signals
travelling in both directions.
1.21

22. 1.22
Data flow (simplex, half-duplex, and full-duplex)

23.  Communication between a computer and
a keyboard involves ______________
transmission.
a) Automatic
b) Half-duplex
c) Full-duplex
d) Simplex
1.23

24.  Communication between a computer and
a keyboard involves ______________
transmission.
a) Automatic
b) Half-duplex
c) Full-duplex
d) Simplex
1.24

25.  A _______ is the physical path over which
a message travels.
a) Path
b) Medium
c) Protocol
d) Route
1.25

26.  A _______ is the physical path over which
a message travels.
a) Path
b) Medium
c) Protocol
d) Route
1.26

27. 1.27
1-2 NETWORKS
A network is a set of devices (often referred to as nodes)
connected by communication links.
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.
A link can be a cable, air, optical fiber, or any medium
which can transport a signal carrying information.

28. 1.28
Network Criteria
 Performance
 Depends on Network Elements
 Measured in terms of Delay and Throughput
 Reliability
 Failure rate of network components
 Measured in terms of availability/robustness
 Security
 Data protection against corruption/loss of data due to:
 Errors
 Malicious users

29. Performance
 How much better a network does a piece of
work indicates its performance.
 Performance of a network is affected by the
number of users, transmission medium, and
hardware or software limitations.
 It is measured in terms of:
 Transit time
 Response time
 Throughput
 Delay
1.29

30. Performance
 Transit time
 Amount of time required for a message to
travel from node to node is called Transit
Time.
 Response time
 The time taken by a device to reply to a
message received is called the response time
(inquiry and response).
1.30

31. Performance
 Throughput
 Practical measure of data actually trasnmited
through a channel
 Unit  bps (bits per second).
 Delay
 Time taken to reach (ms).
 Throughput  Delay  contradictory
1.31

32. Physical structure
 Type of Connection
 Point to Point - single transmitter and
receiver
 Multipoint - multiple recipients of single
transmission
1.32

33. 1.33
Types of connections: point-to-point and multipoint

34. Types of connections: point-to-
point and multipoint
 Point to Point – shared link
 1 Tx, 1 Rx
 Secure & private
 Multipoint – dedicated link
 1 Tx , Many Rx
 Lack of security and privacy
1.34

35. Network Topology
 The arrangement of a network which
comprises of nodes and connecting lines
via sender and receiver is referred as
network topology
 Geometric representation of network
1.35

36. 1.36
Categories of topology

37. Mesh Topology
 All the network nodes are connected to
each other.
 Mesh has n(n-1)/2 physical channels to
link n devices.
1.37

38. Mesh Topology
 Pros
 It is robust.
 Fault can easily be detected.
 Very secure
 Cons
 Very costly.
 Installation and configuration are hard.
1.38

39. Star Topology
 all the computers are connected to a
single hub through a cable.
 This hub is the central node and all
others nodes are connected to the central
node.
1.39

40. Star Topology
 Pros
 Fast performance with few nodes and low network traffi
 Hub can be upgraded easily.
 Easy to troubleshoot, to setup and modify.
 Only that node is affected which has failed, rest of the
nodes can work smoothly.
 Cons
 Cost of installation is high.
 Expensive to use.
 If the hub fails -- whole network is stopped because all
the nodes depend on the hub.
 Performance is based on the hub - on its capacity
1.40

41. Bus topology
 A bus topology connecting three stations
 A bus topology connecting three stations
 Every device is connected to a single cable
 One long cable acts as a backbone to
link all the devices in a
 network
1.41

42. Bus Topology
 Pros
 It is cost effective.
 Cable required is least compared to other network topology
 Used in small networks.
 It is easy to understand.
 Easy to expand joining two cables together.
 Cons
 Cables fails then whole network fails.
 If network traffic is heavy or nodes are more the
performance of the network decreases.
 Cable has a limited length.
 It is slower than the ring topology.
1.42

43. Ring topology
 It forms a ring as each computer is connected to
another computer, with the last one connected to the
first
 Exactly two neighbours for each device
1.43

44. Ring Topology
 Pros
 Transmitting network is not affected by high traffic or by
adding more nodes, as only the nodes having tokens can
transmit data.
 Cheap to install and expand
 Cons
 Troubleshooting is difficult in ring topology.
 Adding or deleting the computers disturbs the network
activity.
 Failure of one computer disturbs the whole network.
1.44

45. Tree topology (hierarchical)
 It has a root node and all other nodes are
connected to it forming a hierarchy.
 It should at least have three levels to the
hierarchy.
 Ideal if workstations are located in groups.
 Used in Wide Area Network.
1.45

46. Tree Topology
 Pros
 Extension of bus and star topologies.
 Expansion of nodes is possible and easy.
 Easily managed and maintained.
 Error detection is easily done.
 Cons
 Heavily cabled.
 Costly.
 If more nodes are added maintenance is difficult.
 Central hub fails, network fails.

1.46

47. 1.47
A hybrid topology: a star backbone with three bus networks

48. 1.48
Categories of Networks
 Local Area Networks (LANs)
 Short distances
 Designed to provide local interconnectivity
 Wide Area Networks (WANs)
 Long distances
 Provide connectivity over large areas
 Metropolitan Area Networks (MANs)
 Provide connectivity over areas such as a city, a campus

49. LAN
 Local Area Network
 Offices
 share the hardware and software
resources like printers, FAX, drivers and
hard-disk
 client-server model,
1.49

50. MAN
 Metropolitan Area Network
 Cover bigger geographical area than LAN
Network E.g. cities and districts
 50-60 km
 Fiber optical cable and twisted pair cable
1.50

51. WAN
 Wide Area Network
 It covers bigger areas i.e right from a
state to a country.
 geographical area it covers is from 100 to
several 1000 km.
 complex in nature, however, they are
widely used in mobile communications as
they cover up long distances.
1.51

52. LAN MAN WAN
1.52

53. 1.53
Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet

54. 1.54
Figure 1.11 WANs: a switched WAN and a point-to-point WAN

55. 1.55
Figure 1.12 A heterogeneous network made of four WANs and two LANs

56. 1.56
1-3 THE INTERNET
The Internet has revolutionized many aspects of our daily
lives. It has affected the way we do business as well as the
way we spend our leisure time. The Internet is a
communication system that has brought a wealth of
information to our fingertips and organized it for our use.
Organization of the Internet
Internet Service Providers (ISPs)
Topics discussed in this section:

57.  2. Two devices are in network if
__________
a) a process in one device is able to
exchange information with a process
in another device
b) a process is running on both devices
c) PIDs of the processes running of
different devices are same
d) a process is active and another is
inactive
1.57

58.  4. In computer network nodes are
_________
a) the computer that originates the data
b) the computer that routes the data
c) the computer that terminates the data
d) all of the mentioned
1.58

59.  4. In computer network nodes are
_________
a) the computer that originates the data
b) the computer that routes the data
c) the computer that terminates the data
d) all of the mentioned
1.59