Data Communication notes

1. Unit - V

5. Transmission Medium
In data communication,
 Transmission media is a pathway that carries the
information from sender to receiver.
 We use different types of cables or waves to transmit
data.
 Data is transmitted normally through electrical or
electromagnetic signals.

6. Characteristics
 A good transmission medium should provide
communication with good quality at long distance.
 For voice communication, quality of communication is
determined by the voice quality.
 For data communication, however, the quality of
communication is mainly determined by the effective
data rate of communication.
6

7. Factors Affecting Data
Communication of a Medium
 Communication bandwidth of the medium
 Interference
 The transmission impairments
7

8.  The bandwidth of a medium determines the
signal frequencies that can be carried in the
medium.
 A wide bandwidth, or broadband, usually
allows communication at a higher data rate.
8

9. Reasons For Transmission Impairence
Attenuation
Distortion during signal propagation
 Noises
9

10. TYPES
of
TRANSMISSION MEDIA
10

11. Transmission
Media
Guided
Media
Twisted
Pair
Cable
Coaxial
Cable
Fiber-
Optic
Cable
Unguided
Media
Radio Microwave Satellite
11

12. Twisted-pair cable
 A twisted pair consists of two conductors
 Basically copper based
 With its own plastic insulation, twisted together.
12

13. Twisted Pair Description
 Provide protection against cross talk or interference(noise)
 One wire use to carry signals to the receiver
 Second wire used as a ground reference
 For twisting, after receiving the signal remains same.
 Therefore number of twists per unit length, determines the
quality of cable.
13

14. Twisted Pair
Advantages:
 Cheap
 Easy to work with
Disadvantages:
 Low data rate
 Short range
14

15. Twisted Pair - Applications
 Very common medium
 Can be use in telephone network
 Connection Within the buildings
 For local area networks (LAN)
15

16. Twisted Pair Cables
Twisted Pair cables
Unshielded
Twisted Pair
(UTP)
Shielded
Twisted pair
(STP)
16

17. Unshielded Twisted Pair (UTP):
Description
 Pair of unshielded wires
wound around each
other
 Easiest to install
17

18. Applications
UTP :
 Telephone subscribers connect to the central
telephone office
 DSL lines
 LAN – 10Mbps or 100Mbps
18

19. UTP Cable Types
Cat 7
Cat 6
Cat 5e
Cat 5
Cat 4
Cat 3
Cat 2
Cat 1
UTP
Cat means category according to IEEE standards.
19

20. Advantages of UTP:
 Affordable
 Most compatible cabling
 Major networking system
Disadvantages of UTP:
 Suffers from external Electromagnetic interference
20

21. Shielded Twisted Pair (STP)
 Pair of wires wound
around each other
placed inside a protective
foil wrap
 Metal braid or sheath foil
that reduces interference
 Harder to handle (thick,
heavy)
21

22. STP Application
• STP is used in IBM token ring networks.
• Higher transmission rates over longer distances.
22

23. Advantages of STP:
 Shielded
 Faster than UTP
Disadvantages of STP:
 More expensive than UTP
 High attenuation rate
23

24. Co-axial cable carries signal of higher frequency ranges than twisted pair
cable
Co-axial Cable
• Inner conductor is a solid wire
• Outer conductor serves as a shield against noise and a second conductor
24

25. Coaxial Cable Applications
 Most versatile medium
 Television distribution
 Long distance telephone transmission
 Can carry 10,000 voice calls simultaneously
 Short distance computer systems links
 Local area networks
25

26. ADVANTAGES
 Easy to wire
 Easy to expand
 Moderate level of Electro Magnetic Interference
DISADVANTAGE
 Single cable failure can take down an entire network
 Cost of installation of a coaxial cable is high due to its thickness and
stiffness
 Cost of maintenance is also high
COAXIAL CABLE
26

27. Fiber-Optic Cable
A fiber optic cable is made of glass or plastic and transmit signals in the
form of light.
Nature of light:
 Light travels in a straight line
 If light goes from one substance to another then the ray of light changes
direction
 Ray of light changes direction when goes from more dense to a lessdence
substance
27

28. Optical fiber
 Uses reflection to guide
light through a channel
 Core is of glass or plastic
surrounded by Cladding
 Cladding is of less dense
glass or plastic
An optical fiber cable has a cylindrical shape
and consists of three concentric sections:
the core, the cladding, and the jacket(outer
part of the cable).
Jacket
28

29. Fiber Construction
29

30. Fiber – Optic cable Connectors
30
Subscriber Channel (SC) Connecter
Straight-Tip (ST) Connecter
Same szie as RJ45 connector

31. Areas of Application
 Telecommunications
 Local Area Networks
 Cable TV
 CCTV
 Medical Education
31

32. Optical Fiber Advantages
 Greater capacity
Example: Data rates at 100 Gbps
 Smaller size & light weight
 Lower attenuation
 Electromagnetic isolation
 More resistance to corrosive materials
 Greater repeater spacing facility
Example: After every 10s of km at least
32

33. Optical Fiber Disadvantages
 Installation and maintenance need expertise
 Only Unidirectional light propagation
 Much more expensive
33

34. Unguided Media
Wireless transmission waves
34

35.  Omnidirectional Antenna
 Frequencies between 3 KHz
and 1 GHz.
 Used for multicasts(multiple
way) communications, such as
radio and television, and
paging system.
 Radio waves can penetrate
buildings easily, so that widely
use for indoors & outdoors
communication.
Unguided Media – Radio Waves
35

36. An Antenna is a structure that is generally a metallic object may be a wire
or group of wires, used to convert high frequency current into
electromagnetic waves.
Antenna are two types:
 Transmission antenna
 Transmit radio frequency from transmitter
 Radio frequency then
Convert to electromagnetic energy by antenna
 Then, radiate into surrounding environment
 Reception antenna
 Electromagnetic energy get in antenna
 Then Antenna convert radio frequency to electrical energy
 Then, Goes to receiver
same antenna can be used for both purposes
Antennas
36

37. Microwaves are ideal when large areas need to be covered
and there are no obstacles in the path
37
Microwaves

38. Micro waves Transmission
 Microwaves are unidirectional
 Micro waves electromagnetic waves having frequency between 1 GHZ and
300 GHZ.
 There are two types of micro waves data communication system :
terrestrial and satellite
 Micro waves are widely used for one to one communication between
sender and receiver,
example: cellular phone, satellite networks and in wireless
LANs(wifi), WiMAX,GPS
38

39. Infrared
 Frequencies between 300 GHz to 400 THz.
 Used for short-range communication
 Example: Night Vision Camera, Remote control, File
sharing between two phones,
Communication between a PC and peripheral device,
39

41. Multiplexing
 Method of dividing physical channels into many
logical channels so that a number of independent
signals may be simultaneously transmitted
 Electronic device that performs multiplexing is known
as a multiplexer.
 Multiplexing enables a single transmission medium to
concurrently transmit data between several
transmitters and receivers.

42. Multiplexing
T1 T2 T3 T4
Multiplexer
Modem
Modem
Multiplexer
computer

43. Types of multiplexing
 Frequency division multiplexing(FDM) is a
networking technique in which multiple data signals
are combined for simultaneous transmission via a
shared communication medium.
 Time division multiplexing(TDM)is a technique
used for transmitting several message signals over a
single communication channel by dividing the time
slots, one slot for message channel.

44. Frequency Division Multiplexing

45. Time Division Multiplexing


46. Network switching techniques
 Data is always transmitted from source to destination
through a network of intermediate nodes.
 Switching techniques deal with the methods of
establishing communication links between the sender
and receiver in a communication network.
 Three commonly used switching techniques are
 Circuit switching: Dedicated physical path is
established between sending and receiving stations
through nodes of the network for the duration of
communication.

47. Network switching techniques
Message switching:
Sender appends receivers destination address
to the message and it is transmitted from
source to destination either by
 Store-and-forward method and
 Broadcast method.

48. Message switching
D
C
5
4
2
1
B
A
Store- and - forward is a telecommunications technique
in which information is sent to an intermediate station
where it is kept and sent at a later time to the final
destination or to another intermediate station

49. Message Switching
 Broadcast Method– A method of sending information
over a network.
 Data comes from one source and goes to all other
connected sources.
 This has the side effect of congesting a medium or large
network segment very quickly.
Message
1 2 3 n
Broadcast channel
Nodes

50. Packet Switching
 Packet Switching refers to technologies in which
messages are divided into packets before they are sent.
 Each packet is then transmitted individually and can
even follow different routes to its destination.
 Once all the packets forming a message arrive at the
destination, they are recompiled into their original
form.
 Either store-and-forward or broadcast method is used
for transmitting the packets.

51. Packet Switching

53. INDEX
 Applications
 Types of networks
 Network components
 Network Topology
 Protocols
 Types
 ISO/OSI Model
 Broadband communication
 Mobile communication

54. Computer Network
 “A computer network is interconnection of various
computer systems located at different places”.
 In computer network two or more computers are
linked together with a medium and data
communication devices for the purpose of
communicating data and sharing resources.
 The computer that provides resources to other
computers on a network is known as server.
 In the network the individual computers, which access
shared network resources, are known as nodes.

55. APPLICATIONS:
 Sharing of resources such as printers
 Sharing of expensive software's and database
 Communication from one computer to another
computer
 Exchange of data and information among users via
network
 Sharing of information over geographically wide
areas.

56. Types of network
 Local Area Network(LAN)
 Wide Area Network(WAN)
 Metropolitan Area Network(MAN)

57. Local Area Networks
 A LAN is a network that is used for communicating
among computer devices, usually within an office
building or home.
 LAN’s enable the sharing of resources which are
needed by multiple users .
 Is limited in size, typically spanning a few 100 meters,
and no more than a mile .
 Is fast, with speeds from 10 Mbps to 10 Gbps.
 Requires little wiring, typically a single cable
connecting to each device.
 Has lower cost compared to MAN’s or WAN’s

59. LAN

60. Types of LAN
 PEER-TO-PEER LAN, in this communication
is carried out from one computer to another,
without a central computer, and where each
computer has the same role.
 CLIENT/SERVER LAN, in this a central
computer provides network services to users.
It has servers and clients
 The Server is a computer that manages shared
resources (hardware, software, data). It is a
powerful computer with large RAM and
secondary storage capacity.
 LAN has number of micro computers called
clients, request the server for services.

61. Metropolitan Area Network (MAN)
 A metropolitan area network (MAN) is a large
computer network that usually spans a city or a large
campus.
 A MAN is optimized for a larger geographical area
than a LAN, ranging from several blocks of buildings
to entire cities.
 A MAN might be owned and operated by a single
organization, but it usually will be used by many
individuals and organizations.

62. Metropolitan Area Network
 A MAN often acts as a high speed network to allow
sharing of regional resources.
 A MAN typically covers an area of between 5 and 50
km diameter.
 Examples of MAN: Telephone company network that
provides a high speed DSL to customers and cable TV
network

64. Wide Area Network
 WAN covers a large geographic area such as country,
continent or even whole of the world.
 A WAN is two or more LANs connected together. The
LANs can be many miles apart.
 To cover great distances, WANs may transmit data over
leased high-speed phone lines or wireless links such as
satellites.

65. Wide Area Network
 Multiple LANs can be connected together using
devices such as bridges, routers, or gateways, which
enable them to share data.
 The world's most popular WAN is the Internet.

67. CAN
PAN

68. Network Components
 Workstations
 Network operating
station
 Network interface card
 LAN cable
 Application software
 HUB
 Fileserver
 Printer server
 Bridges
 Routers
 Gateway
 Repeaters

69. Workstations
 A workstation is a computer intended for individual
use that is faster and more capable than a personal
computer.
 It's intended for business or professional use
 Workstation can of two types user work station and
server workstation.

70. WORKSTATIONS

71. Network operating system
 Network operating system refers to software that
implements an operating system of some kind that is
oriented to computer networking

72. Network Interface card(NIC)
 Network cards also known as Network Interface Cards
(NICs) are hardware devices that connect a computer
with the network. They are installed on the mother
board. They are responsible for developing a physical
connection between the network and the computer.
Computer data is translated into electrical signals send
to the network via Network Interface Cards.

73. LAN Cable
 LAN requires superior cable capable of transferring
data at high speed, coaxial cables or fiber optic cables
may be used for networking computer.

74. Application Software
 The primary purpose of having a LAN is to allow
several application programs to talk to each other. It
has to be ensured that application software works in
the multiuser environment

75. Hub
 A hub is a common connection point for devices in a
network. Hubs are commonly used to connect
segments of a LAN.

76. Bridges
 A bridge is a computer networking device that builds
the connection with the other bridge networks which
use the same protocol

77. Switches
 A switch is a Network Device that
connects many other Ethernet devices
together.
 Switching is, more advanced than hub
because it only sends a message to the
device that needs the message and not
broadcast to the entire segment or local
area network.

78. Routers
 Router is used to create larger complex networks by
complex traffic routing.

79. Brouter
 Brouters are the combination of both the bridge and
routers. They take up the functionality of the both
networking devices serving as a bridge when
forwarding data between networks, and serving as
a router when routing data to individual systems

80. Gateways
 Gateway is a device which is used to connect multiple
networks and passes packets from one packet to the
other network.

81. Repeaters
 are equipments that are used expansion of a LANs by
boosting the signals to accommodate long distances

82. Printer Server
 A print server, or printer
server, is a device that
connects printers to client
computers over a network.
 A print server usually allows
users in a computer network
to perform a printing job
without having to move files
to the computer connected
directly to the printer

83. File Server
 In computing, a file server is a computer attached to a
network that has the primary purpose of providing a
location for shared disk access

84. Network topology

85. Topology
 Topology refers to the layout of connected
devices on a network.
 Here, some logical layout of topology.
 Bus
 Ring
 Star
 Tree and Hybrid
 Mesh

86. Network Topology

87. Bus Topology
 All the nodes on a bus topology are connected by
one single cable.
 A bus topology consists of a main run of cable with
a terminator at each end. All nodes are connected
to the linear cable.
 Popular on LANs because they are inexpensive and
easy to install

88. Bus Topology

89. Bus Topology

90. Bus Topology

91. Bus Topology
 Advantages:
1. Ease of installation
2. Less cabling
Disadvantages:
1. Difficult reconfiguration and fault isolation.
2. Difficult to add new devices.
3. Signal reflection at top can degradation in quality.
4. If any fault in backbone can stops all transmission.

92. Star Topology
 Here each device has a dedicated point-to-point link to
the central controller called “Hub”(Act as a
Exchange).
 There is no direct traffic between devices.
 The transmission are occurred only through the
central “hub”.
 When device 1 wants to send data to device 2; First
sends the data to hub. Which then relays the data to
the other connected device.

93. Star Topology

94. Star Topology
Advantages Disadvantages
• Easy to manage
• Easy to locate problems
(cable/workstations)
• Easier to expand than a bus or
ring topology.
• Easy to install and wire.
• Easy to detect faults and to
remove parts.
• Requires more cable length
than a linear topology.
• If the hub or concentrator fails,
nodes attached are disabled.
• More expensive because of the
cost of the concentrators.

95. Ring Topology
 Here each device has a dedicated connection with two
devices on either side.
 The signal is passed in one direction from device to
device until it reaches the destination and each device
have repeater.
 When one device received signals instead of intended
another device, its repeater then regenerates the data
and passes them along.
 To add or delete a device requires changing only two
connections.

96. Applications
 Star topology used in Local Area Networks(LANs).
 High speed LAN often used STAR.

97. Ring Topology

98. Ring Topology

99. Ring Topology
 Advantages:
1. Easy to install.
2. Easy to reconfigure.
3. Fault identification is easy.
Disadvantages:
1. Unidirectional traffic.
2. Break in a single ring can break entire network.

100. Ring Topology
 Applications:
 Ring topologies are found in some office buildings or
school campuses.
 Today high speed LANs made this topology less
popular.

101. Tree Topology
 Alternatively referred to as a star bus topology.
 Tree topology is one of the most common network
setups that is similar to a bus topology and a star
topology.
 A tree topology connects multiple star networks to
other star networks. Below is a visual example of a
simple computer setup on a network using the star
topology.

102. Tree Topology

103. Tree Topology
Advantages Disadvantages
• Point-to-point wiring for individual
segments.
• Supported by several hardware and
software vendors.
• All the computers have access to
the larger and their immediate
• Overall length of each segment is limited
by the type of cabling used.
• If the backbone line breaks, the entire
segment goes down.
• More difficult to configure and wire than
other topologies.

104. Hybrid Topology
 A network which contain all type of physical structure
and connected under a single backbone channel.

105. Hybrid Topology
 a

106. Mesh Topology
 In this topology, each node is connected to every
other node in the network.
 In this type of network, each node may send
message to destination through multiple paths.
 Implementing the mesh topology is expensive and
difficult.

107. Mesh Topology
Advantages:
1. They use dedicated links so each link can only
carry its own data load. So traffic problem can be
avoided.
2. It is robust. If any one link get damaged it cannot
affect others.
3. It gives privacy and security.(Message travels
along a dedicated link)
4. Fault identification and fault isolation are easy.

108. Mesh Topology

109. Mesh Topology
 Disadvantages:
1. The amount of cabling and the number of I/O ports
required are very large. Since every device is
connected to each devices through dedicated links.
2. The sheer bulk of wiring is larger then the available
space.
3. Hardware required to connected each device is
highly expensive.

110. Mesh Topology
 Applications:
1. Telephone Regional office.
2. WAN.(Wide Area Network).

111. Considerations for choosing
topology
 Money-Bus n/w may be the least expensive way to
install a n/w.
 Length-of cable needed- the linear bus n/w uses shorter
lengths of cable.
 Future growth-with star topology, expending a n/w is
easily done by adding another devices.
 Cable type-most common used cable in commercial
organization is twisted pair. Which often used with star
topologies.

112.  Full mesh topology is theoretically the best since
every device is connected to every other device.(thus
maximizing speed and security. however, it quite
expensive to install)
 Next best would be tree topology, which is basically a
connection of star.

113. Protocols

114. Moving Data
End
System
End
System

115.  Describes the rules that govern the transmission of
data over the communication Network.
 Provide a method for orderly and efficient exchange of
data between the sender and the receiver.

116. Roles of Communication Protocol
 Data Sequencing – to detect loss or duplicate
packets.
 Data Routing – to find the most efficient path
between source and a destination.
 Data formatting – defines group of bits within a
packet which constitutes data, control, addressing and
other information.
 Flow control – ensures resource sharing and
protection against traffic congestion by regulating the
flow of data on communication lines.

117. Roles of Communication Protocol
 Error control – detect errors in messages. Method for
correcting errors is to retransmit the erroneous message
block.
 Precedence and order of transmission – condition
all nodes about when to transmit their data and when to
receive data from other nodes. Gives equal chance for all
the nodes to use the communication channel.
 Connection establishment and termination –
These rules define how connections are established,
maintained and terminated between two nodes.
 Data security – Prevents access of data by
unauthorized users.

118. Types of protocols
 Ethernet
 Token Ring
 TCP/IP
 FTP
 HTTP
 Mail Protocols(POP, SNMP, IMAP)
 Security Protocols(SSL,SET)
 FDDI

119. Ethernet
 The Ethernet protocol is by far the most widely used.
Ethernet uses an access method called CSMA/CD
(Carrier Sense Multiple Access/Collision Detection).
This is a system where each computer listens to the
cable before sending anything through the network.

120. Token Ring
 The Token Ring protocol was developed by IBM in the
mid-1980s. The access method used involves token-
passing.
 In Token Ring, the computers are connected so that
the signal travels around the network from one
computer to another in a logical ring. A single
electronic token moves around the ring from one
computer to the next.

121. Token Ring

122.  The TCP/IP protocol suite was first defined in 1974
 TCP/IP represents a set of public
standards that satisfy how packets of information are
exchanged between computers over one and more
networks.
TCP/IP Protocol Suite

123.  Ensures a sent message is sent without any loss of
data or any mix up of the order of the data
 Will request re-transmission of lost or damaged
packets
TCP Protocol

125.  IP, which stands for Internet Protocol , is a Network
layer protocol that is responsible for delivering packets
to network devices.
 Each packet is treated as an independent unit of data
without any relation to any other unit of data.
IP Protocol

127. TCP Protocol

128.  It is used to transfer files from a server to a client
computer.
 example of an FTP service is when you visit a site
to download software--you click on download, and
it contacts the FTP server which then downloads
the file to your computer.
FILE TRANSFER PROTOCOL(FTP)

130. Hypertext Transfer Protocol
 Hypertext Transfer Protocol(HTTP) – This protocol is
used to access, send and receive Hypertext Markup
Language(HTML) files on the internet.
 HTTP protocol communicates between an Internet
browser, such as Internet Explorer or Firefox, and a web
server that is hosting a website.

132. MAIL PROTOCOLS
 Post Office Protocol is the primary protocol behind email
communication. POP works through a supporting email software client
that integrates POP for connecting to the remote email server and
downloading email messages to the recipient’s computer machine.
 Interactive Mail Access Protocol is a standard protocol for accessing
e-mail from your local server. IMAP is a client/server protocol in which
e-mail is received and held for you by your Internet server
 Simple Mail Transfer Protocol is a communication protocol for mail
servers to transmit email over the Internet. Most e-mail systems that
send mail over the Internet use SMTP to send messages from one
server to another; the messages can then be retrieved with an e-mail
client using either POP or IMAP. In addition, SMTP is generally used to
send messages from a mail client to a mail server.

133. Security Protocols
 Security protocols are sequence of operations that
ensure protection of data.
 Used with a communications protocol, it provides
secure delivery of data between two parties.
 The Secure Sockets Layer (SSL) and Transport Layer
Security (TLS) is the most widely deployed
security protocol used today. It is essentially
a protocol that provides a secure channel between
two machines operating over the Internet or an
internal network.

134. Security Protocols
 .Secure Electronic Transaction (SET) was a
communications protocol standard for securing
credit card transactions over insecure networks,
specifically, the Internet.
 HTTPS (also called HTTP over TLS, HTTP over SSL,
andHTTP Secure) is a protocol for secure
communication over a computer network which is
widely used on the Internet.

135. Point-to-Point Protocol
 In computer networking, Point-to-Point
Protocol (PPP) is a data link (layer 2) protocol used to
establish a direct connection between two nodes.
 It connects two routers directly without any host or
any other networking device in between. It can provide
connection authentication, transmission encryption
and compression.

136. FDDI
 Fiber Distributed Data Interface (FDDI) is a network
protocol that is used primarily to interconnect two or more
local area networks, often over large distances. The access
method used by FDDI involves token-passing. FDDI uses a
dual ring physical topology.

137. • OSI is short for Open Systems Interconnection.
• OSI model was first introduced by the
International Organization for Standardization
(ISO) in 1984
– Outlines WHAT needs to be done to send data from
one computer to another.
– Protocols stacks handle how data is prepared for
transmittal
• Contains specifications in 7 different layers that
interact with each other.

138. What is “THE MODEL?”
 Commonly referred to as the OSI reference model.
 Open system interconnection (OSI) model is a
framework for defining standards for linking
heterogeneous computer systems, located anywhere.
 The OSI model is a theoretical blueprint that helps us
understand how data gets from one user’s computer to
another.
 It is also a model that helps develop standards so that
all of our hardware and software talks nicely to each
other.

139. 7 Layer OSI Model
 Why use a reference model?
 Serves as an outline of rules for how protocols can be
used to allow communication between computers.
 Each layer has its own function and provides support to
other layers.
 Other reference models are in use.
 Most well known is the TCP/IP reference model.

140. 7 Layer OSI Model
 Open system interconnection (OSI) model is a
framework for defining standards for linking
heterogeneous computer systems, located
anywhere.

141. What Each Layer Does
2
All People Seem To Need Data Processing
A mnemonic:

142. Layer7 – Application Layer

143. Application Layer
 The top or seventh layer of the OSI Model is the
Application layer.
 The Application provides interfaces to the software
that enable programs to use network services.

144. Application Layer
 The term “Application Layer” does not refer to a
particular software application, such as Microsoft
Word, running on the network.
 Instead, some of the services provided by the
Application layer include file transfer, file
management, and message handling for electronic
mail.

145. Application Layer
 Examples of common functions include:
 Protocols for providing remote file services, such as
open, close, read, write, and shared access to files
 File transfer services and remote database access
 Message handling services for electronic mail
applications
 Global directory services to locate resources on a
network
 A uniform way of handling a variety of system monitors
and devices
 Remote job execution

146. Layer 6

147. Presentation Layer
 The Presentation Layer serves as a translator between
the application and the network.
 At the Presentation layer, data become formatted in a
schema that the network can understand; this format
varies with the type of network used.
 The Presentation Layer manages data encryption and
decryption, such as the scrambling of system
passwords.

148. Layer 5

149. Session Layer
 The Session Layer is responsible for establishing and
maintaining communication between two nodes on the
network.
 The term session refers to a connection for data exchange
between two parties; it is most often used in the context
of terminal and mainframe communications, in which
the terminal is a device with little (if any) of its own
processing or disk capacity that depends on a host to
supply it with applications and data processing services.

150. Session Layer
 Often, this layer also helps the upper layers identify and
connect to the services that are available on the network.
 If a communication session is broken, is the session layer
that determines where to restart the transmission once the
session has been reconnected
 This layer is also responsible for determining the terms of
the communication session – it will determine which
computer or node can communicate first and for how long
 It is sometimes known as the ‘traffic cop’ of the network

151. Layer 4

152. Transport Layer
 The transport layer provides enhancements to the
services of the network layer.
 Its main tasks is to ensure that data sent form one
computer arrives reliably, in the correct sequence and
without errors at the receiving computer.
 To ensure reliable delivery, the transport layer builds
on the error control mechanism provided by the lower
layer

153. Transport Layer
 This layer is the last chance for error recovery. The
transport layer is also responsible for flow control.
 It s here that there rate of transmission is determined,
based on how fast the receiving computer can accept
the data packets being sent to it.
 Data on the sending computer is broken down into
packets that are the maximum size that the type of
network can handle.

154. Layer 3

155. Network Layer
 The primary function of the Network Layer, the third
layer in the OSI Model has the main objective of
moving data to specific network locations.
 It does this by translating logical addresses into the
appropriate physical address and then decides on the
best route for the data to take from sender to receiver.
 This appears similar to what the data link layer
accomplishes through physical decide addressing.

156. Network Layer
 However, data link layer addressing only operates on a
single network
 The network layer describes methods for moving
information between multiple independent networks,
called internetworks.

157. Layer 2

158. Data Link Layer
 The second layer of the OSI Model, the Data Link
Layer, controls communications between the Network
layer and the Physical layer.
 Its primary function is to divide data it receives from
the Network layer into distinct frames that can be
transmitted by the Physical layer.

159. Data Link Layer
 The basic purposes of the data link layer protocol
implementations are:
 Organise the physical layer’s bits into logical groups of
information called frames
 Detect and correct errors
 Control data flow
 Identify computers on the network

160. LAYER-1

161. Physical Layer
 The Physical layer is the lowest or first layer of the OSI
Model. This layer contains the physical networking
medium, such as cabling, connectors, and repeaters.
 The Physical Layer defines:
 Physical network structures
 Mechanical and electrical specifications for using the
transmission medium
 Bit transmission encoding and timing rules

162. Physical Layer
 The physical layer does not include a description of the
medium and does not provide any sort of error
correction.
 However, implementations of physical protocols are
transmission-media-specific

163. Physical Layer
 The following network connectivity hardware are
normally associated with the OSI physical layer:
 Network interface boards (NIC, adaptors, and so on)
 Hubs, and repeaters that regenerate electrical signals
 Transmission media connectors, which provide the
mechanical interface to interconnect devices to the
transmission media (cables, BNC connectors, etc)
 Modems and codec's, which perform digital analogue
conversions.

168. Broadband Communication
 Broadband is high-speed Internet access that is always
on and faster than the traditional dial-up access.
 Broadband is easier and faster to use than the
traditional telephone and modem as information can
be sent and downloaded much quicker.
 Broadband speed is measured in megabits per
second(Mbps)

169. Types of broadband
 DSL provide internet access using the wires of a local
telephone network.
 Wireless: Wireless broadband connects to the Internet
using a radio link between the customer’s location and the
location of the service provider.
 Satellite: Just as satellites orbiting the earth provide
necessary links for telephone and television service, they
can also provide links for broadband.
 Cable: Cable modem service provides broadband using
coaxial cables (like the ones for your TV).

170. Technological options available
Satellite Dongle
Hotspot Wireless
DSL