ppt_dcn.pptx networks networks security of networks

19CAB09 – DATA COMMUNICATION
AND NETWORKS
Prepared by
S.NITHYANANTH, ASP
DEPARTMENT OF MCA
MUTHAYAMMAL ENGINEERING
COLLEGE,RASIPURAM.

OBJECTIVES
• To
understand
and
basic
• To
understand
components
communication.
and
data
required for
• To analyze the function and
• To Acquire knowledge of various
developed for internet.

UNIT I NETWORK FUNDAMENTALS
Introduction to Networks – Categories of
Networks -Communication model –Data
transmission concepts and terminology –
Protocol architecture – Protocols – OSI –
TCP/IP – LAN Topology - Transmission
media.

UNIT II DATA LINK LAYER
Data link control – Error Detection – VRC
– LRC – CRC – Checksum – Error
Correction – Hamming Codes – MAC –
Ethernet, Token ring , Token Bus –
Wireless LAN - Bluetooth – Bridges.

UNIT III
NETWORK LAYER
Network layer – Switching concepts –
Circuit switching – Packet switching – IP
Addressing –IPV4, IPV6 – Routing
Protocols – Distance Vector – Link State.

UNIT IV
TRANSPORT LAYER
Transport layer – service – Connection
establishment – Flow control –
Transmission control protocol –
Congestion control and avoidance – User
datagram protocol - Transport for Real
Time Applications (RTP).

UNIT V APPLICATIONS
Applications - DNS – E-Mail Protocols –
WWW – SNMP – SMTP - Security –
Threats and Services- Cryptography -DES-
RSA- Web security -SSL .

OUTCOMES
• Able to trace the flow of information from one node
to another node in the network.
• Able to Identify the components required to
build different types of networks.
• Able to understand the functionalities needed for data
communication into layers.
• Able to choose the required functionality at
each layer for given application.
• Able to understand the working principles of various
application protocols.
• Acquire knowledge about security issues and services
available.

REFERENCES
1.Forouzan, “ Data Communication and Networking”, Fifth
Edition , TMH 2012
2. Larry L. Peterson & Bruce S. Davie, “Computer
Networks – A systems Approach”, Fourth
Edition, Harcourt Asia / Morgan Kaufmann, 2010.
3.William Stallings, “Data and Computer
Communications”, Nineth Edition, Prentice Hall 2011.
David J.
Edition
,
Wetherall,
Pearson
4. Andrew S.Tannenbaum
“Computer
Networks”Fifth Education
2011
5.James F. Kurose, Keith W. Ross, “Computer
Networking: A Top-down Approach, Pearson
Education, Limited, sixth edition,2012.
6. John Cowley, “Communications and Networking :
An Introduction”, Springer Indian Reprint, 2010.

UNIT – I
NETWORK FUNDAMENTALS

OVERVIEW
• Introduction to Networks
• Categories of Networks
• Communication Model
• Data Transmission Concepts and Terminology
• Protocol Architecture
• Protocols
• OSI
• TCP/IP
• LAN Topology
• Transmission Media

Introduction to Networks
• A Network: A group of devices that
can communicate with each other over links.
• Each device is called a host. Each host has
a unique address.

• Network is a connection between two or
more devices.
• Which is connected by a communication
links.
• A node can be computer, printer or any
other devices which is capable of sending
and receiving information at each other.

INTERNET
• An internet:
each host has an
address of the form n/h where n is the
network number and h is the number of the
host on network n.

Uses of Network
• It is Used for
i) Business Application
ii) Home Application
iii) Mobile Users
iv) E-Mail

Categories or Types of Network
• There are Three Types:
1. LAN - Local Area Network
2. MAN - Metropolitan Area Network
3. WAN – Wide Area Network

1. LAN - Local Area Network
A LAN is Designed by Local Area Connections such
as:
i) within Building
ii) within office
iii) within Campus
iv) within Specific Place

Advantages :
1) Sharing of Files.
2) Sharing of Programs.
3) Communication Exchange.
Disadvantages :
1) Reliability.
2) Capacity.
3) High Cost.

2. MAN - Metropolitan Area Network
A Metropolitan Area Network (MAN) is a
network that interconnects users with
computer resources in a geographic area or
region larger than that covered by even a
large local area network (LAN) but smaller
than the area covered by a wide area
network (WAN).

• MAN supports up to 150 Kilometers Distance.
• Example:
 Telephone Network
 Cable TV

Advantages :
1) High Bandwidth.
2) It support Large number of
Clients.
3) Reduce the Errors.
Disadvantages :
1) Large Space Requirements.
2) Slower Data Access.
3) High Cost.

3. WAN – Wide Area Network
• WAN Provide a Long Distance Transmission of Data.
• By Using WAN Exchange the Information from
one country to another country.

Components of Network
- Which gives the Request.
- Which gives the Response.
- It Indicates Modulator / Demodulator.
- Which identifies the Path between Client
& Server.
- Which
overcomes the Traffic
problems.

Communication Model
• Data communications are exchange of
data between two devices via some
transmission medium.
• It should be done in two ways
i) Local - It takes LAN Connection.
ii)Remote - It takes Long distance
like MAN & WAN.
• Data should be Transferred in the form of
0’s and 1’s

1) Delivery - The System must deliver the data
to the correct Destination.
2) Accuracy - The System must deliver the data
at Accurate way.
Source
Transmission
Medium Destination

3)Timeline - The System must deliver the data at
Exact Time.
4) Jitter - It refers to the variable in the
i) Sender
ii) Receiver
iii) Medium
iv) Message
v) Protocol

1. Sender 2.
Receiver
3. Medium
5. Protocol
Step : 1
Step : 2
4.
Message
5.
Protocol
Step : 1
Step : 2

: It is a device ,
that Sends the information to the
Receiver.
: It is a device , that Receives the
information from the Sender.
: It is the physical path between
Sender to Receiver.
: This is the passing
Informations.
: It is a set of rules and regulations
that “ Governed “ from data communication.

• Data Transmission occurs between sender and
receiver over some Transmission Medium
or Transmission Media.
• Transmission Media may be classified into Two
Types :
i) Guided Media [Wired Technology]
ii) Unguided Media [Wireless Technology]

i) Guided Media (Wired Network)
• In Guided Media Signals are Passed in a “
same physical path”
• Example:
i) Twisted pair Cable
ii) Coaxial Cable
iii) Fiber Optic Cable

ii) Unguided Media (Wireless Network)
• In Unguided Media Signals are Passed in
the form of “ Electromagnetic Waves”
• Example :
i) Mobile phones
ii) Satellite microwave
iii) Infrared

It Provides
a dedicated links between two devices.
• For example, a wired system that connects two
computers together can be thought of a
point- to-point link.

It is a link between
two or more devices. It is also known as Multi-
Point configuration. The networks having
multipoint configuration are called

Transmission Mode
 It refers to the direction of information
flow between two devices.
 Data flow is the flow of data
between 2 points.

The direction of the data flow can
be described as

Simplex Mode

Half-Duplex Mode

Full-Duplex Mode

 Simplex: Data flows in only one direction
on the data communication line (medium).
Examples are Radio and Television
broadcasts.
 Half-Duplex: Data flows in both
directions but only one direction at a
time on the data communication line.
Ex. Conversation on walkie-talkies.
 Full-Duplex: Data flows in both
directions simultaneously. Modems are
configured to flow data in both directions.
Ex. Phone Conversation

Figure 1.2 Data flow (simplex, half-duplex, and full-
Data Flow

Protocol Architecture
• It is a layered structure of H/W and S/W
that
supports exchange of data b/w systems
• It supports distributed applications(E-
Mail,
File Transfer)
• Each layer of protocol architecture
provides some set of rules
• There are 2 widely used
protocol architecture
TCP/IP Architecture
OSI Model

Protocol
• Protocol is a set of rules that govern
data communication
• It represents what is communicated, when
it is communicated and how it is
communicated.
• There are 3 key elements
Syntax
Semantics
Timing

Syntax
• It represents structure, Format of data
the order in which it is presented
Data may contain:
• First 8 bit -> Sender Address
• Second 8 bit -> Receiver Address
• Remaining bits-> message stream

SEMANTICS
• It refers the meaning of each section of bit
TIMING
• It refers when data sent and how fast it is
sent (Says Characteristics)
• Ex:100Mbps

• It provides model for the development
of product regardless of individual
manufacturer
• It falls in 2 categories

ppt_dcn.pptx networks networks security of networks

De Facto standard
• Not officially adopted but used
widespread
• It has 2 categories
• Proprietary->Wholly owned by company
• Non-Proprietary->Group or communiy
developed for public

De Jure Standard
• A Standard Legislated by an
officially recognized body
Standard Organizations:
• International Standard Organization
• ANSI
• IEEE

The OSI Model
• An ISO (International standard Organization) that
covers all aspects of network communications is
the Open System Interconnection (OSI) model.
• An open system is a model that allows any two
different systems to communicate regardless of
their underlying architecture (hardware or
software).
• The OSI model is not a protocol; it is model for
understanding and designing a network
architecture that is flexible, robust and
interoperable.

• The OSI model is a layered framework for the
design of network systems that allows
for communication across all types of
computer systems.
• The OSI model is built of seven ordered layers:
1. (Layer 1) Physical layer
2. (Layer 2) Data link layer
3. (Layer 3) Network layer
4. (Layer 4) Transport layer
5. (Layer 5) Session layer
6. (Layer 6) Presentation layer
7. (Layer 7) Application layer

Peer-to-Peer Process
• Within a single machine, each layer calls upon services of
the layer just below it.
• Layer 3, for example, uses the services provided by layer
2 and provides services for layer 4.
• Between machines, layer x on one machine communicates
with layer x on another machine, by using a protocol
(this is Peer-to-Peer Process).
• Communication between machines is therefore a peer-to-
peer process using protocols appropriate to a given
layer.

Interfaces between
Layers
• There is an interface between each pair
of adjacentlayers. This interface defines
what provide
information and services a layer must
for the layer above it.

Functions of Layers
1. Physical Layer
The physical layer is responsible for transmitting
individual bits from one node to the next.

Physical layer
The physical layer is concerned with the following:
• Physical characteristics of interfaces and
media: It define the type of transmission
media
• Representation of the bits: the physical layer
data consist of a stream of bits(0,1).
The transmitted bits must be encoded into
signals – electrical or optical. The physical
layer defines the type of encoding.
• Data rate: The physical layer defines the
transmission rate, the number of bits sent
each second.

Physical Layer
• Line configuration: the physical layer is
concerned with the connection of
devices to the medium.
• Physical topology – Ring, star
• Transmission Mode - Simplex,
Half duplex Full Duplex

2. Data Link
Layer
• It is responsible for node-to-node delivery of
data.

Functions of the Data Link
Layer:
• Framing. The data link layer divides the stream of bits
received from the network layer into data units called
frames.
• Physical addressing. If frames are to be distributed to
different systems on the network, the data link layer
adds a header to the frame to define the physical
address of the sender (source address) and/or receiver
(destination address) of the frame.
• If the frame is intended for a system outside the
sender’s network, the receiver address is the address of
the device that connects one network to the next.

• Flow Control. If the rate at which the data are absorbed by
the receiver is less than the rate produced in the sender,
the data link layer imposes a flow control
mechanism to prevent overwhelming the receiver.
• Error control. The data link layer adds reliability to the
physical layer by adding mechanisms to
retransmit damaged or lost frames. Error
detect and
control
is
normally achieved through a trailer to the end of the frame.
• Access Control. When two or more devices are connected
to the same link, data link layer protocols are necessary
to determine which device has control over the link
at any time.

3. Network Layer
• The Network layer is responsible for the source-
to- destination
delivery of a packet possible across
multiple networks.
•It converts Frames into packets.
•If two systems are connected to the same link,
there is usually no need for a network layer.
However, if the two systems are attached to different
networks, there is often a need for the network layer
to accomplish source-to-destination delivery.

Network Layer
Functions:
•Logical addressing-Physical addressing (May change) handle
addressing problem locally
•If packet pass the network boundary, we need another
addressing
called logical addressing (Never change)
•Routing - Route the packet to final destination
The network layer is responsible for the delivery of packets from the
original
source to the final destination.

4. Transport Layer
• The transport layer is responsible for process-to-process
or end-end delivery of the entire message.
• The network layer oversees host-to-destination delivery of
individual packets, it does not recognize any relationship
between those packets.
• The transport layer ensures that the whole message arrives
intact and in order, overseeing both error control and flow
control at the process-to-process level.

Transport layer
The transport layer is responsible for delivery of a message
from one process to another.

Functions of the Transport layer
Service point addressing:
Computer often run several processes (running programs)
at the same time. Process-to-process delivery means
delivery from a specific process on one computer to a
specific process on the other.
• The transport layer header include a type of address
called port address.
• The network layer gets each packet to the correct
computer; the transport layer gets the entire message to
the correct process on that computer.

Cont..
,
• Segmentation and reassembly: a message is divided
into transmittable segments, each having a
sequence number. These numbers enable the
transport layer to reassemble the message correctly
upon arrival at the destination.
• Connection control: The transport layer can be either
connectionless or connection-oriented.
• A connectionless transport layer treats each segment as an
independent packet and delivers it to the transport layer
at the destination machine.
• A connection-oriented transport layer makes a connection
with the transport layer at the destination machine
first before delivering the packets. After all the
data are transferred, the connection is terminated.

Functions of the transport layer
• Flow control: the transport layer performs a flow control
end to end. The data link layer performs flow control
across a single link.
• Error control: the transport layer performs error control
end to end. The data link layer performs control across a
single link.
• Congestion control concerns controlling traffic entry into
a telecommunication networks so as to avoid congestive
collapse by attempting to avoid oversubscription of any of
the processing or link capabilities of the intermediate
nodes and networks and taking resource reducing steps,
such as reducing the rate of sending packets. It should not
be confused with flow control, which prevents the sender
from overwhelming the receiver.

5. Session Layer
• The session layer is responsible for dialog
control and synchronization.

Functions of Session Layer
• Decision Control:- Half duplex,
Full Duplex
• Synchronization: Adding checkpoints
to stream data.
• Ex: System sending 2000 pages.
• Add check point after each 100th page.
• So in case of failure no need to sent whole
page.

6. Presentation Layer
• It is concerned with the syntax and
semantics of the information exchanged
b/w 2 devices.

Functions of Presentation Layer
• Translation: Interoperability b/w
different encoding formats.
• Encryption: Converting plain to cipher
text and vice versa.
• Compression: Reducing number of bits
in multimedia data when transmitting.

7. Application layer
The application layer is responsible for
providing services to the user.

Functions of Application Layer
• It provides user access to
network.
• X.500-Directory service.
• X.400-Message handling service.
• FTAM- File
Transfer management.
• Network Virtual Terminal.
Access and

•
Transmission Control Protocol
/ Internetworking Protocol is used in
the internet and is developed prior to the
OSI model.
• It would not match exactly with OSI
model
• It is divided into layers.

• It contains relatively independent protocols
that can mixed and matched with depend
on needs of the system.

• It defines the Physical (or)
Logical arrangement of Links in a Network.
• Topology refers to the layout of connected
devices in a network.
• The Topology of the Network is
Geometric Representation of the
relationship between all Communication
links.

Types of Topology
i) Mesh Topology
ii) Star Topology
iii) Tree Topology
iv) Bus Topology
v) Ring Topology
vi) Hybrid Topology

Types of Topology
• Here every device has a direct point to
point link between every other device.
• A fully connected mesh can have n(n-
1)/2 physical channels to link n devices.
if n=5 (Number of Nodes)
5(5-1)/2 = 10 ( Communication Links)
• 5 Nodes are Connected by using
10 Communication Links

Mesh Topology
Advantages:
• It eliminate the traffic problem.
• It is robustness.
• It has privacy and security.
• Fault can be easily found.

Mesh Topology
Disadvantages:
• More number of cables to be used.
• Every devices must be connected to some
other devices. So installation process is
very difficult.

Types of Topology
• Each device has a dedicated point-to-point link
between only a central controller or “HUB”.
• The devices are not directly linked to some
other devices.
• If one device wants to send data to another
device, it sends to the central controller
and the Central controller send to other
device.

Star Topology
Star Topology Diagram:
Central controller
(or)
HUB
D
A
C
B

Star Topology
Advantages :
• Less expensive than Mess topology.
• Less number of cables to be used.
• It is robustness.

Star Topology
Disadvantages:
• Each device must connected
to controller.
• It require more installation
process.
• If central controller failure
means devices should be failed.
central
all the

Types of Topology
• Tree topology has some variation from
star topology.
• The nodes in the tree are linked to the
central controller.
• The primary HUB in the tree is represented
by “Active Hub”.
• The secondary HUB in the tree is represented
by “Passive Hub”.

Tree Topology
Advantages:
• It allows more devices to be attached in
a single central controller.
• It allows the network to prioritize
the communication.

Tree Topology
Disadvantages:
• Each device must be linked
to controller.
• It require more installation processes.
• If central controller failure
means system should fail down.
central
entire

Types of Topology
• A Bustopology describes the
multipoint configuration.
• One long cable act as a backbone to link all the
devices in a network.
• Devices are connected in a bus topology
with the help of “Drop lines” and “Tapes”.

Bus Topology
Bus Topology Diagram:
Back bone
bone
Drop line Drop line Tape Back
A D
C
B

Bus Topology
Advantages:
• Installation process is very easy.
• Redundancy can be eliminated.
• Less number of cables to be used.

Bus Topology
Disadvantages:
• Reconfiguration is very difficult.
• Very difficult to adding (or) deleting
of a devices

Types of Topology
• InRing Topology each device has
dedicated point-to-point link between other
devices.
• The signals are passed along the “ring” in only
one direction from device to device.
• Each devices in a ring should have
a “Repeater”.

Ring Topology
Ring Topology Diagram:
Ring
A
C
D B

Advantages:
• Easy to install and reconfigure.
• Fault can be easily identified.
Ring Topology

Ring Topology
Disadvantages:
• It is unidirectional traffic.
• In rings if one device gets failure then the
entire system should be failed.

VI. Hybrid Topology
 Combination of all topology is
called hybrid topology.

The physical path between transmitter
and receiver.
• Repeaters or amplifiers may be used
to extend the length of the medium.
• Communication of electromagnetic
waves is guided or unguided.

BNC
connectors
•To connect coaxial cable to devices, it is necessary to use coaxial
connectors. The most common type of connector is the Bayone-Neill-
Concelman, or BNC, connectors.
Applications include cable TV networks, and some traditional
Ethernet LANs like 10Base-2, or 10-Base5.

Propagation Modes (Types of Optical Fiber )

OVERVIEW
• Data Link Control
• Error Detection
• VRC
• LRC
• CRC
• Checksum
• Error Correction
• Hamming Codes
• MAC
• Ethernet
• Token ring
• Token Bus
• Wireless LAN
• Bluetooth
• Bridges

Data Link Control
Communication
Minimum 2 devices are needed for data
communication. So line discipline is
necessary for co-operation b/w 2 devices.
The 2 important functions of data link
layer is flow control and error
control.This functions are otherwise
called as Data link control.

Line Discipline
It coordinates the link system
It is done in 2 ways
◦ ENQ (Enquiry)
 Used in peer – peer communication
 Enquire whether there is a required link b/w
two devices
 Check whether the intended device is capable to
receive
◦ ACK (Acknowledgment)
 Used in Primary secondary communication
 The intended device will acknowledge about its status to
the
receiver

There are 2 categories in
line discipline

Select
It is a line discipline used in
topologies
with primary secondary relationship.
Select
It is uses whenever the primary
device
has something to send.ie)Primary
controls the link.

Pol
l
The polling function is used by the
primary device to Select
transmissions from the secondary
devices.
If the primary device is ready to
receive data , It ask each device in
turn if it has anything to send.

Flow Control
It is a set of procedures to tell the sender
how much data it can transmit before it
must
wait for an
acknowledgement
from
the
receiver.
Two categories of flow control:
◦ Stop-and-wait
Send one frame at a
time.
◦ Sliding window
Send several frames at a
time.

Stop-and-
wait
Sender sends one frame and waits for an
acknowledgement before sending the next
frame.

Stop-and-wait
Advantages:
◦ Simplicity.
◦ Each frame is checked and
acknowledged before the next frame is
sent.
Disadvantages:
◦ Slow.
Can add significantly to the total transmission
time if the distance between devices is long.
◦ Inefficiency
Each frame is alone on the line.

SlidingWindow
Sender can send several frames
before
needing an
acknowledgement.
Advantages:
◦ The link can carry several frames at
once.
◦ Its capacity can be used
efficiently.

Can detect all single-bit errors. Can detect burst errors only if the
total
Even number of
ones
–add 0
Odd number of
ones
– add 1

•Increases the likelihood of detecting burst
errors.
•n bits LRC can detect a burst error of n bits.
•Errors may be undetected if:
•Have even number of errors in that
position.

You will experience a painful
sharpening from time to time,
but this is required if you are to
become a better pencil.

You have
the ability
to correct
any
mistakes
you might
make.

Hamming Codes-Error correction
Hamming codes, like polynomial codes,
are appended to the transmitted
message
Hamming codes, unlike polynomial
codes, contain the information
necessary to locate a single bit error

Calculating the Hamming
Code
The key to the Hamming Code is the use of extra parity bits to allow
the
identification of a single error. Create the code word as follows:
◦ Mark all bit positions that are powers of two as parity bits. (positions 1, 2, 4,
8, 16,
32, 64,etc.)
◦ All other bit positions are for the data to be encoded. (positions 3, 5, 6, 7,
9, 10, 11, 12, 13, 14, 15, 17, etc.)
◦ Each parity bit calculates the parity for some of the bits in the code
word.The
position of the parity bit determines the sequence of bits that it
alternately
checks and skips.
Position 1: check 1 bit, skip 1 bit, check 1 bit, skip 1 bit, etc.
(1,3,5,7,9,11,13,15,...)
Position 2: check 2 bits, skip 2 bits, check 2 bits, skip 2 bits,etc.
(2,3,6,7,10,11,14,15,...)
Position 4: check 4 bits, skip 4 bits, check 4 bits, skip 4 bits,etc.
(4,5,6,7,12,13,14,15,20,21,22,23,...)
Position 8: check 8 bits, skip 8 bits, check 8 bits, skip 8bits, etc. (8-15,24-
31,40-
47,...)
Position 16: check 16 bits,skip 16 bits,check 16 bits, skip 16 bits, etc.(16-
31,48-
63,80-95,...)
Position 32: check 32 bits,skip 32 bits,check 32 bits, skip 32 bits,etc.(32-
63,96-

Position of Redundancy bit
in Hamming code

MAC
IEEE has subdivided(Project 802) the
data link layer into two sub layers:
◦ Logical Link Control
◦ Medium access control
Functions of MAC
It resolves the contention of shared media
It contains all information to move
information from one place to another
It contains the physical address of next
station to route packet.
MAC protocol are specific to LAN

The project 802 which governs internet working. Here
each
subdivision is identified by a number
802.1(internetworking)
802.2(LLC)
and MAC modules
802.3(CSMA/CD)
802.4(Tokenbus)
802.5(Tokenring)

Figure 13.1 IEEE standard for
LANs

MAC protocol are specific to
LANLAN is a Local Area Network used
for communication inside building
Protocols for LAN are,
◦ Ethernet
◦ Token Ring
◦ Token bus
◦ FDDI

IEEE STANDARDS
Ethernet: It is a LAN protocol that is used in Bus and Star
topologiesand
implements CSMA/CD as the medium access method
Original (traditional) Ethernet developed in 1980 by
three companies: Digital, Intel, Xerox (DIX).
In 1985, the Computer Society of the IEEE started a
project, called Project 802, to set standards to enable
intercommunication among equipment from a variety of
manufacturers.
 Current version is called IEEE Ethernet

◦ IEEE 802.3 supports LAN standard
Ethernet
◦ IEEE802.3 defines two categories
Baseband
Broadband
◦ Base band has five different category
10Base5
10Base2
10BaseT
1Base5
etc.,
◦ Broad band
has a
category

Access Method:CSMA/CD
When multiple user access the single line ,there is
a danger of signals overlapping and destroying
each other(Traffic) .such an overlap is called
Collisions.
T
o avoid this the access method used in Ethernet
is carrier sense multiple access/collision
detection
In CSMA any workstation wishing to transmit
must listen to existing traffic on the line
If no voltage is detected ,line is considered idle
CSMA cuts down the number of collisions, but
cant eliminate. Collisions still occur if both station
try to listen at a time.

IEEE Ethernet
In IEEE 802.3 Ethernet Data link layer is split into two
sublayers:
◦ Bottom part: MAC
The frame is called IEEE 802.3
Handles framing, MAC addressing, MediumAccess
control
Specific implementation for each LAN
protocol
Defines CSMA/CD as the access method for Ethernet
LANs
and Token passing
method for Token
Ring.
Implemented in hardware
◦ Top part: LLC (Logical Link Control)
The subframe is called IEEE 802.2
Provides error and flow control if
needed
It makes the MAC sublayer
transparent
Allows interconnectivity between different LANs data link
layers
Used to multiplex multiple network layer protocols in the data
link
laye
r
frame
Implemented in

Ethernet Provides Unreliable, connectionless
Service
◦ Ethernet data link layer protocol provides
connectionless service to the network layer
No handshaking between sending and
receiving adapter.
◦ Ethernet protocol provides Unreliable service
to the
network layer :
Receiving adapter doesn’t send ACK or NAK
to
sending adapter
This means stream of datagrams passed to
network layer can have gaps (missing data)
Gaps will be filled if application is using reliable transport
layer
protocol
Otherwise, application will see the gaps

Ethernet
FCS
Frame formats. (a) DIX Ethernet ,(b) IEEE
802.3.
FCS
 Ethernet Frame
format

Ethernet
Frame
PREAMBLE
◦ 8 bytes with pattern 10101010 used to synchronize receiver, sender clock rates.
◦ In IEEE 802.3, eighth byte is start of frame (10101011)
Addresses: 6 bytes (explained latter)
Type (DIX)
◦ Indicates the type of the Network layer protocol being carried in the payload
(data) field, mostly IP but others may be supported such as IP (0800), Novell
IPX (8137) and AppleTalk (809B), ARP (0806) )
◦ Allow multiple network layer protocols to be supported on a single machine
(multiplexing)
◦ Its value starts at 0600h (=1536 in decimal)
Length (IEEE 802.3): number of bytes in the data field.
◦ Maximum 1500 bytes (= 05DCh)
CRC: checked at receiver, if error is detected, the frame is discarded
◦ CRC-32
Data: carries data encapsulated from the upper-layer protocols
Pad: Zeros are added to the data field to make the minimum data length = 46 bytes

Ethernet
address
 Six bytes = 48 bits
 Flat address not hierarchical
 Burned into the NIC ROM
First three bytes from left specify the vendor. Cisco 00-
00- 0C, 3Com 02-60-8C and the last 24 bit should be
created uniquely by the company
 Destination Address can be:
 Unicast: second digit from left is even (one
recipient)
 Multicast: Second digit from left is odd (group of
stations
to receive the frame – conferencing applications)
 Broadcast (ALL ones) (all stations receive the
frame)
 Source address is always Unicast

Figure 13.3 Ethernet evolution through four
generations

Categories of traditional Ethernet
•<data rate><Signaling method><Max segment length or cable
type>

IEEE 802.3 Cable Types
Name Cable Max. Max
Cable
Segment
Length
Nodes
/segment Toplogy
10Base5 thick coax 500 meters 100
Bus
10Base2 thin coax 185 meters 30
Bus
10BaseT twisted pair 100 meters 1
Star
10BaseF Fiber Optic 2Km 1
Star

Figure 13.10 10Base5 implementation

Connection of stations to the medium using
10Base2

10BaseT
• Uses twisted pair Cat3 cable
 Star-wire topology
• A hub functions as a repeater with additional functions
• Fewer cable problems, easier to troubleshoot than
coax
• Cable length at most 100 meters

Figure 13.12 10Base-T implementation

Figure 13.13 10Base-F implementation

Fast Ethernet
100 Mbps transmission rate
same frame format, media access, and
collision detection rules as 10 Mbps Ethernet
can combine 10 Mbps Ethernet and Fast
Ethernet on same network using a switch
media: twisted pair (CAT 5) or fiber optic cable
(no coax)
Star-wire topology
◦ Similar to 10BASE-T
CAT 3
CAT 5

Figure 13.19 Fast Ethernet
topology

Figure 13.20 Fast Ethernet implementations

Gigabit Ethernet
Speed 1Gpbs
Minimum frame length is 512 bytes
Operates in fu l/half duplex modes
mostly full duplex

In the full-duplex mode of Gigabit
Ethernet, there is no collision;
the maximum length of the cable
is determined by the signal
attenuation in the cable.

Figure 13.23 Gigabit Ethernet implementations

10Gbps
Ethernet
 Maximum link distances cover 300 m to 40
km
 Full-duplex mode only
 No CSMA/CD
 Uses optical fiber only

Token
Ring
It allows each station to sent one frame
.
The access control mechanism used by
Ethernet is inefficient sometimes
because of collision.
It solves the collision problem by
passing token
Initially a station waits for token, if a
token is free the station may send a
data frame

Cont..
,
This frame proceeds around the ring ,being
regenerated by each station .Each station
examines the destination address finds the
frame is addressed to another station and
relays it to its neighbor.
The intended recipient recognizes its own
address and copies the message and set
the address bit
The token finally reach the sender and it
recognizes that the data is delivered
through address bit
Token is passed from NIC to NIC

Token
Bus
It combines the feature of token ring
and Ethernet

FDDI
• Fiber Distributed Data Interface
• local area network protocol standardized by
ANSI
• 100-Mbps token passing
• Dual-ring LAN
• A high-speed backbone technology
• High bandwidth
• Optical fiber transmission
• Allows up to 1000 stations

Components of FDDI
• Fiber optic cable
• A concentrator (ring)
• Stations: 2 types
• DAS (Dual Attachment Station) or
Class A:
• Connected to both the rings
• SAS (Single Attachment Station) or
Class B:
• Connected to primary ring

FDDI Frame Format
Similar to token
ring frame

Networking and
internetworking
devices:
An internet is a interconnection of
individual network. So to create a
internet we need a internetworking
devices. ie) Linking a number of LAN’s
Internet - WWW
internet-Interconnection of LAN

Why
Interconnect?
• To separate / connect one corporate division with another.
• To connect two LANs with differentprotocols.
• To connect a LAN to the Internet.
• To break a LAN into segments to relieve traffic congestion.
• To provide a security wall between two different types
ofusers.

Connecting Devices
Networking
Devices
Repeater
s
Bridge
s
Internetworki
ng
Devices
Router
s
Gateway
s

Introductio
n
•Many times it is necessary to connect a local area network to another
local
area network or to a wide area network.
•Local area network to local area network connections are usually
performed
with a bridge.
•Local area network to wide area network connections are usually
performed
with a router.
•A third device, the switch, can be used to interconnect segments of a
local
area network.

98/
25
Connecting Devices
Hu
b

Repeater:
A repeater is a regenerator, not
an amplifier
A repeater installed on a link receives
the signal before it becomes too weak
or corrupted ,regenerates the original
bit pattern, and put the refreshed copy
back onto the link.

Gateways:
A gateway is a protocol convertor.
It accepts a packet format for one
protocol(e.g., Apple Talk) and
convertsit into a packet format for
another protocol(e.g.,TCP/IP).

104
/ 25
A gateway
SNA network (IBM)
Netware network
(Novell)

105
/ 25
Bridge
s
Divide a large network into smaller segment
It filters the traffic . It contains
logic(Bridge table) that allows them to keep
the traffic for each segment separate.
Ie) Isolating and controlling the link
problems (e.g.congestion)
Bridges have look-up table that contains
physical address of every station connected to
it.

When aframe enters abridge ,itchecks the address of
the destination and forward the new copy only to
the segment to which the address which belongs

Types
Simple
Multiport
Transparent
Remote
Source
routing

Simple
Bridge
It is a less expensive type of bridge
It links 2 segments (LANS) and lists
the address of all the stations in
table included in each of them.
Here address must be entered
manually. The table is modified when
stations are added and removed.

Multiport
Bridge
It is used to connect more than two
LANS. So the bridge has 3 tables.
Here address must be entered manually
Transparent Bridge:
• A transparent or learning bridge builds its table of
station on its own (automatically).
• The table is empty when it is installed, it builds its
table when it encounters the packet for
transmission. It uses the source address for building
table.
• It identifies the changes and update the table
when system moved from one station to another

Cont.
,
Bridges are normally installed
redundantly,that is two LANS may
be connected by more than one
bridge.in this cases they may create
a loop.
So packet may go round and round,It
can be avoided by algorithms like
◦ Spannig tree algorithm
◦ Source routing

Data Communications and Computer Networks
Remote
Bridges
•A remote bridge is capable of passing a data
frame from one local area network to another
when the two LANs are separated by a long
distance and there is a wide area network
connecting the two LANs.
•A remote bridge takes the frame before it leaves
the first LAN and encapsulates the WAN
headers and trailers.
•When the packet arrives at the destination
remote bridge, that bridge removes the WAN
headers and trailers leaving the original frame.

Data Communications and Computer Networks
Switche
s
•A switch is a combination of a hub and a bridge
(multiport bridge).
•It can interconnect two or more workstations, but
like a bridge, it observes traffic flow and learns.
•When a frame arrives at a switch, the switch examines
the destination address and forwards the frame out the
one necessary connection.
•Workstations that connect to a hub are on a shared
segment.
•Workstations that connect to a switch are on a
switched segment.

LAN/WLAN World
 LANs provide connectivity for
interconnecting computing resources at the
local levels of an organization
 Wired LANs
Limitations because of
physical,hard- wired infrastructure
 Wireless LANs provide
Flexibility
Portability
Mobility
Ease of

Wireless LAN
Applications
Medical
Professionals
Education
Temporary
Situations
Airlines
Security Staff
Emergency Centers

IEEE 802.11 Wireless LAN
Standard
In response to lacking standards, IEEE
developed the first internationally
recognized wireless LAN standard –
IEEE 802.11
IEEE published 802.11 in 1997, after
seven years of work
Scope of IEEE 802.11 is limited to
Physical and Data Link Layers.

Benefits of 802.11
Standard
Appliance Interoperability
Fast Product Development
Stable Future Migration
Price Reductions
The 802.11 standard takes into account
the following significant differences
between wireless and wired LANs:
Power Management
Security
Bandwidth

WLAN Topology
Ad-Hoc Network
The BSS without an AP is a stand-alone network and cannot send data to other
BSSs. they can locate one another and agree to be part of a BSS.

WLAN Topology
Infrastructure
EX: cellular network if we consider each BSS to be a cell
and
each AP to be a basestation.

StationTypes
IEEE 802.11 defines three types of
stations based on their mobility in a
wireless LAN:
◦ no-transition
A station is either stationary (not moving) or moving only inside a
BSS
◦ BSS-transition
station can move from one BSS to another
, but the movement is
confined inside one ESS.
◦ and ESS-transition mobility.
A station can move from one ESS to another

collision avoidanceCSMAICA
network allocation vector (NAV) used
to avoid collision.
◦ RTS frame includes the duration of time that it needs to
occupy
the channel.
◦ stations affected by this transmission create a timer called
(NAV)
◦ the network allocation vector (NAV) shows the time must
pass before these stations allowed to check the channel for
idleness.
there is no mechanism for collision detection, if the
sender has not received a CTS frame from the
receiver, assumes there has been a collision ,the
sender tries again.

BLUETOOTH
Bluetooth is a wireless LAN
technology designed to connect devices of
different functions
such as telephones, notebooks, computers,
and so on.
A
cameras, printers, coffee makers,
Bluetooth LAN is an ad hoc network,
which
means that the network is formed
spontaneously.
Bluetooth defines two types of networks:
piconet and scatternet.

Picone
tA Bluetooth network is called a piconet, or a small net.
It can have up to eight stations, one of which is called the master;
the rest
are called slaves.
Maximum of seven slaves. Only one master.
Slaves synchronize their clocks and hopping sequence with the
master. But an additional eight slaves can stay in parked state,
which means they
can be synchronized with the master but cannot take part in
communication until it is moved from the parked state.

Scatternet
Piconets can be combined to form what is called
a scatternet.
A slave station in one piconet can become
the master in
• another piconet.
Bluetooth devices has a built-in short-range
radio transmitter.

Bluetooth
layers
Radio Layer: Roughly equivalent to physical layer of the Internet
model.
Physical links can be synchronous or asynchronous.
◦ Uses Frequency-hopping spread spectrum [Changing frequency of usage].
Changes it modulation frequency 1600 times per second.
◦ Uses frequency shift keying (FSK )with Gaussian bandwidth filtering
to transform bits to a signal.
Baseband layer: Roughly equivalent to MAC sublayer in LANs.
Access is using Time Division (Time slots).
◦ Length of time slot = dwell time = 625 microsec. So, during one
frequency
, a sender sends a frame to a slave, or a slave sends a frame to
the master.
Time division duplexing TDMA (TDD-TDMA) is a kind of half-duplex
communication in which the slave and receiver send and receive data,
but not at the same time (half-duplex). However
, the communication
for each direction uses different hops, like walkie-talkies.

Physical
Links
Synchronous connection-oriented (SCO)
◦ Latency is important than integrity.
◦ Transmission using slots.
◦ No retransmission.
Asynchronous connectionless link (ACL)
◦ Integrity is important than latency.
◦ Does like multiple-slave communication.
◦ Retransmission is done.
L2CAP (Logical Link Control and Adaptation Protocol)
◦ Equivalent to LLC sublayer in LANs.
◦ Used for data exchange on ACL Link. SCO channels do not use L2CAP
.
◦ Frame format has 16-bit length [Size of data coming from upper layer in
bytes],
channel ID, data and control.
◦ Can do Multiplexing, segmentation and Reassembly, QoS [with no QoS, best-
effort delivery is provided] and Group mangement [Can do like multicast
group, using some kind of logical addresses].

• Network Layer
OVERVIEW
• Switching Concepts
• Circuit Switching
• Packet Switching
• Message Switching
• IP Addressing
• IPV4
• IPV6
• Routing Protocols
• Distance Vector Routing
• Link State Routing

Network Layer
•The Network layer is responsible for
the source-to-destination delivery of a
packet possible across multiple
networks.
• It converts Frames into packets.

• Source-to-Destination delivery of a
packet
• Logical addressing
• Routing
• Internetworking

Switching Concepts
Switches are hardware or software devices used
for temporary connection b/w 2 or more
devices linked to the switch in network but not
to each another
Switches are needed to connect multiple
devices for making one-one communication
TYPES:
•
•
•

Circuit switching
It creates direct physical
connection b/w two devices such as
phone or computers.
Any computer can be connected to
any other using Levers.
N-by-N folded switches can connect
n lines in full duplex mode.
2 types:
◦
◦

Space Division
Switch
Path in the circuit are separated from each other
It is used both in analog and
digital communication
2 Types:
◦ Crossbar switch
◦ Multistage switch
• Crossbar Switch:
It connects n inputs to moutputs using
cross
points
• Limitation:

Multistage switch
Devices are linked to switches ,that are in
turn linked to another switches(Hierarchy
of switches)

Blocking:
The reduction in a number of
cross points causes a phenomena
called Blocking.
During heavy traffic one input cannot
be connected to output because no
path available

Time Division
Switches
It uses time division multiplexing
2 methods:
Time slot
interchange TDM
bus
Time slot interchange:
It changesthe ordering of the slot based on
the desired connection
It uses RAM to store time
slot Ex:
1->3 2->4 3->1 4-
>2

TDM Bus-Time Division
Multiplexing Here each input and output
lines are connected to high speed bus
Each bus is closed during one of the four time
slots

Limitations of Circuit
Switching
• It is specially designed for
voice suitable
communication(telephone). Not
for data communication.
• Once a circuit is
established, it remains
for
duration of the session. It
creates
dialed(temporary)and
leased(Permanent).
• Less data rate because of point
to connection.
poin
t

Packet
switching
• Packet switching is better for
data transmission.
• Here data are transmittedthrough unit
of variable length blocks called packets.
• Longer transmission are
divided multiple packets.
• Packet length is decided by
network.
int
o

DatagramApproach
• In this approach a message is divided
into multiple packets.
• All packets choose various routes
and reaches the destination.
• Ordering of packets in destination is done
by transport layer.

Virtual Circuit approach
It uses single route to send all packets of
the message
Two formats:
◦ Switched virtual circuit
◦ Permanent virtual circuit
SVC
• Connection is temporary
• Dial-up lines
DuringTransmission.
A connection is established-all packets
proper ACK- Connection is terminated
are sent –

PVC
• Connection is permanent.
• Circuit is dedicated for two users, No one else
can use the line when
communication takes place.
• It always gets the same route.
• Leased lines.
During Transmission.
No connection establishment or termination

Circuit switchedVs Virtual
Circuit
Path Vs
Route:
Circuit switched-
>Path Virtual Circuit-
>route

Message Switching
• It uses a mechanism called store and
forward
• Here a message is received and stored
until a appropriate route is free, then sends
along.
• Message switching- uses
secondary storage(Disk)
• Packet switching – uses
primary storage(RAM)

Routers
• The routers decide which route is best
among many routes in a particular
transmission.
• Routers are like stations on the network
Routing concepts:
Least cost
routing:
Cheaper
Shortest path(using small number of relays or
hops. Hop-count ->Number of relays

Non - Adaptive
Routing
In some routing protocols , once a
pathway to a destination is selected ,the
router sends all packets in that way.
Adaptive Routing:
The router may select new route for each
packet.
Packet Life Time (or)Time to Live:
The problem created by looping or
bouncing is avoided by destroying the
packet without looping, New
packet is retransmitted

• To route the packet with optimal cost
many routing algorithms are used to
Calculating the shortest path between 2
routers
1. Distance Vector Routing
2. Link State Routing

Distance vector
Routing
Def:
• Each router periodically shares its knowledge
about the entire network with its neighbor.
• It is represented by graph.
Key Works:
• Each router shares its knowledge about the
entire network to neighbors.
• Routing only to the directly linked routers.
• Information sharing at regular interval(each
30 seconds).

The Concept of Distance Vector Routing

Distance Vector Routing
Table
12/28/202 Unit-3 : Network
2
8
1

Link State
Routing
Def:
Each router shares its knowledge of it neighborhood
with all routers in the internetwork.
It is represented by directed graph with weight.
Key work:
Each router shares its knowledge about
the neighborhood
Each router sends its knowledge to all router.
Flooding -> Each router share info to neighbor,
The neighbor to its own neighbor and so on.,
Information sharing when there is a change.

Link State
Packet
2
8
6

Link State Database
2
8
7

TCP/
IP
calle
d
• It was developed before OSI
• This project was funded by ARPA of
U.S ARPANET which is turned into
TCP/IP networ
k
• In internet it acts like a
single connection many of any size
and type.
• TCP and UDP creates a data unit
called
Segment or datagram.

What is an IP address?
An Internet Protocol address is a numerical
label assigned to each device connected to a
computer network that uses the Internet
Protocol for communication.
An IP address serves two principal functions:
host or network interface identification
location addressing.

IP (Internet Proocol)
Network layer of TCP/IP supports IP in turn
four other supporting protocol
◦ ICMP
◦ IGMP
◦ ARP
◦ RARP
It is a transmission mechanism used by
TCP/IP protocols

C ont.,
IP Is a unreliable and connection
less datagram protocol.
No error checking or tracking.
Data transmitted to destination but
no guarantees.
IP must be paired with TCP.

IP
Addressing
In addition to physical address (NIC) ,to
identify each device in the network it requires
IP address.
Address that identify host of its network.
An IP address is a 32-bit
address. The IP addresses are
unique and universal.
It Represented in a Dotted-decimal
Notation.

Example 1
Change the following IP addresses from binary notation to
dotted- decimal notation.
a. 10000001
00001011
b. 11111001
10011011
00001011 11101111
11111011 00001111
Solution
We replace each group of 8 bits with its equivalent
decimal number and add dots for separation:
a.
b.
129.11.11.239
249.155.251.15

Example 2
Change the following IP addresses from dotted-decimal notation
to binary notation.
a.
b.
111.56.45.78
75.45.34.78
Solution
We replace each decimal number with its binary
equivalent (see Appendix B):
a. 01101111
b.
00111000 00101101 01001110
01001011 00101101 00100010 01001110

Figure 19.10 Finding the class in binary notation

Finding the class in decimal notation (changes from 0 to 255)

Class Starting IPAddress Ending IPAddress # of Hosts
A 10.0.0.0 10.255.255.255 16,777,216
B 172.16.0.0 172.31.255.255 1,048,576
C 192.168.0.0 192.168.255.255 65,536
Private and Public IP
Address

Types of IP address
Static address
Dynamic
address
Static IP
address
◦ manually input
by network
administrator.
◦ manageable for

Types of IP address
Dynamic IP address
examples - BOOTP, DHCP
◦ Assigned by server
when host boots
◦ Derived automatically from a range
of addresses
◦ Duration of ‘lease’ negotiated, then
address released back to server

Subnetting
Dividing the network into several smaller
groups (subnets) with each group having its
own subnet IP address.
Site looks to rest of internet like single
network and routers outside the organization
route the packet based on the main Network
address.
Local routers route within subnetted
network using subnet address.

Subnettin
g
Host portion of address partitioned into subnet
number (most significant part) and host number
(least significant part)
In this case, IP address will have 3 levels
(Main network, subnet, host)
Subnet mask is a 32-bit consists of zeros and ones
that indicates which bits of the IP address are
subnet number and which are host number
Subnet mask when AND ed with the IP address
it gives the subnetwork address

Masking
.
Masking is a process that extracts the
address of the physical network from an IP
address.
Boundary level masking: Here the
mask numbers are either 255 or 0,
finding the subnetwork address is very
easy.
Non-boundary level masking.
If mask numbers are not just 255 or 0,
finding the subnetwork address

Supernetting:
• Supernetting combines several networks
into one lager one (Because of Address
reduction)

IP Network Addressing
INTERNET  world’s largest public data
network, doubling in size every nine
months
IPv4, defines a 32-bit address - 232
(4,294,967,296) IPv4 addresses available
The first problem is concerned with the
eventual depletion of the IP address space.
Traditional model of classful addressing does not
allow the address space to be used to its
maximum potential.

ClassfulAddressing
When IP was first standardized in Sep 1981,
each system attached to the IP based
Internet had to be assigned a unique 32-bit
address
The 32-bit IP addressing scheme involves a
two level addressing hierarchy
Network
Number/Prefix
Host Number

Internet Protocol (IP)
What is Internet Protocol?
◦ Internet Protocol is a set of technical
rules that defines how computers
communicate over a network.
◦ Currently, There are two versions of IP
IP version 4 (IPv4)
IP version 6
(IPv6).

What is IPv4?
◦ IPv4 was the first version of Internet
Protocol to be widely used, and
accounts for most of today’s Internet
traffic.
◦ There are just over 4 billion IPv4
addresses. While that is a lot of IP
addresses, it is not enough to last
forever.

What is IPv6?
◦ IPv6 is a newer numbering system that
provides a much larger address pool
than IPv4. It was deployed in 1999 and
should meet the world’s IP
addressing needs well into the
future.

What is the major difference?
◦ The major difference between IPv4
and IPv6 is the number of IP
addresses.
◦ There are 4,294,967,296 IPv4
addresses.
◦ while, there are
340,282,366,920,938,463,463,374,607,431
,
768,211,456 IPv6 addresses.

128-bit IPv6
Address
3FFE:085B:1F1F:0000:0000:0000:00A9:1234
8 groups of 16-bit hexadecimal numbers separated
by “:”
Leading zeros can
be removed
3FFE:85B:1F1F::A9:1234
:: = all zeros in one or more group of 16-bit
hexadecimal numbers

IPv4 vs. IPv6
IPv6
IPv4 addresses are 32
bit length.
IPv6 addressesare 128
bit length.
IPv4 addresses are binaryIPv6 addresses are
binary
numbersrepresented innumbers
decimals.
represented
in
hexadecimals.
IPSec support is
only
optional.
Inbuilt IPSec
support.
Fragmentation is done by
Fragmentation is done
only
sender and forwarding
by sender.

No packet flow identification.
Packet flow identification is
available within the IPv6
header using the Flow Label
field.
Checksum field is
available
in IPv4
header
No checksum field
in IPv6
header.
Options fields are
available
in IPv4
header.
No option fields, but IPv6
Extension
headers
are available.
Address Resolution Protocol

Internet Group
Management Protocol
(IGMP) is used to manage
multicast group
membership.
IGMP is replaced with
Multicast Listener
Discovery (MLD) messages.
Broadcast messages
are available.
Broadcast messages are
not available. Instead a
link- local scope "All
nodes" multicast IPv6
address(FF02::1) is used
for broadcast similar
functionality.
Manual configuration
(Static) of IPv4 addresses or
DHCP (Dynamic
Host configuration Protocol)
Auto-configuration
of addresses is
available.

IPv4 companion protocols (1)
ARP: Address Resolution Protocol
◦ Mapping from IP address to MAC address
ICMP: Internet Control Message
Protocol
◦ Error reporting & Query
IGMP: Internet Group Management
Protocol
◦ Multicast member join/leave
Unicast Routing Protocols (Intra-AS)
◦ Maintaining Unicast Routing Table
◦ E.g. RIP, OSPF (Open Shortest Path

IPv4 companion protocols (2)
Multicast Routing Protocols
◦ Maintaining Multicast Routing Table
◦ E.g. DVMRP, MOSPF, CBT, PIM
Exterior Routing Protocols (Inter-
AS)
◦ E.g. BGP (Border Gateway Protocol)
Quality-of-Service Frameworks
◦ Integrated Service (ISA, IntServ)
◦ Differentiated Service (DiffServ)

Why IPv6?
Deficiency of IPv4
Address space
exhaustion
New types of service 
Integration
◦ Multicast
◦ Quality of Service
◦ Security
◦ Mobility (MIPv6)
Header and format

Advantages of IPv6 over IPv4
Larger address
space Better
header format New
options
Allowance for extension
Support for resource
allocation Support for more
security Support for mobility

OVERVIEW
• Transport Layer
• Service
• Connection Establishment
• Flow Control
• Congestion Control and Avoidance
• Transmission Control Protocol
• User Datagram Protocol
• Transport for Real Time Applications

• The Transport layer is responsible for process-
to-process or end-end delivery of the
entire message.
• The transport layer ensures that the whole
message arrives intact and overseeing
both

 Service point addressing(Process-
Process delivery)
 Segmentation and reassembly
 Connection control
 Flow control(QoS) – MUX & Demux
 Error control – error checking
and recovery
 Congestion control

– Transport Layer Provides :
• Efficient
• Reliable and
• Cost-effective services
– Another TWO Kinds of Services are :
•Connection oriented -
TCP
•Connectionless - UDP

Simple Service: Primitives
• Simple primitives:
– Connect
– Send
– Receive
– Disconnect
• How to handle incoming connection request in
server process?
Wait for connection request from client!
– listen

Connection Establishment
• Once a connection is established, both client and
server may exachnge data using several
system calls.
client-server
• A connection is typically used for
interaction.
• A server advertizes a particular server at a well-
known address and clients establish connections
to that socket to avail of the offered service.
• Thus the connection estblishment procedure is
asymmetric.

–Problems to solve
•Selection of the initial
sequence number for a new
connection.
•Wrap around of sequence
numbers for an active connection.
•It Handle host crashes.

Releasing a connection
– Asymmetric
• Connection broken when one party hangs
up
• Abrupt!  may result in data loss
– Symmetric
• Both parties should agree to release connection
• How to reach agreement? Two-army
problem
• Solution: three-way-handshake
– Pragmatic approach
• Connection = 2 unidirectional connections
• Sender can close unidirectional connection

Flow Control
It is a set of procedures to tell the sender how
much
data it can transmit before it must wait for
an
acknowledgementfrom the
receiver.
Two categories of flow control:
◦ Stop-and-wait
Send one frame at a time.
◦ Sliding window
Send several frames at a
time.

Congestion Control and Avoidance
• Congestion Control is
concerned
with
efficiently using a network at high load.
techniques can be employed. These
• Several
include:
• –
Warnin
g bit
– Chok
e
packe
ts
– Load
shedd
Detection
Avoidance

Principles of Congestion Control
Congestion:
 informally: “too many sources sending too much
data too fast for network to handle”
different from flow control!
= end-to-end issue!
–lost packets (buffer overflow at routers)
–long delays (queue-ing in router buffers)

Causes of Congestion
 Two senders, Two receivers
One router, Infinite buffers
No retransmission

Approaches towards congestion control
End-to-End congestion
control:
 no explicit feedback from
network
 congestion inferred from
end-system observed loss,
delay
 approach taken by TCP
Network-assisted
congestion control:
 routers provide feedback to
end systems
– single bit indicating
congestion (SNA, ATM)
– explicit rate sender should
send it.
Two broad approaches towards congestion control:

Congestion Detection and Control
The following 3 Methods are used to Detect &
Control the Congestions :
1. Warning bit
2. Choke packets
3. Load shedding

Warning Bit
6
• A special bit in the packet header is set by
the router to warn the source when
congestion is detected.
• The bit is copied and piggy-backed on the
ACK and sent to the sender.
• The sender monitors the number of ACK
packets it receives with the warning bit set
and adjusts its transmission rate accordingly.

Choke Packets
• A more direct way of telling the source to
slow down.
• A choke packet is a control packet
generated at a congested node and
transmitted to restrict traffic flow.
• The source, on receiving the choke packet
must reduce its transmission rate by a
certain percentage.
• An example of a choke packet is the
ICMP Source Quench Packet.
3
4
7

Load Shedding
3
4
8
• When buffers become full, routers simply discard
packets.
• Which packet is chosen to be the victim depends
on the application and on the error strategy usedin
the data link layer.
• For a file transfer, for, e.g. cannot discard older
packets since this will cause a gap in thereceived
data.
• For real-time voice or video it is probably better
to
throw away old data and keep new packets.
• Get the application to mark packets with
discard priority.

Congestion Avoidance
The following 2 Methods are used to Avoid the
Congestions :
1. Random Early Discard
2. Traffic Shaping

Random Early Discard (RED)
• This is a proactive approach in which the
router discards one or more packets before the
buffer becomes completely full.
3
5
0
• Each time a packet
algorithm computes
length, avg.
arrives,
the the
average
RED
queue
• If avg is lower than some lower threshold,
congestion is assumed to be minimal or non-
existent and the packet is queued.

RED, cont.
• If avg is greater than some upper threshold,
congestion is assumed to be serious and the
packet is discarded.
• If avg is between the two thresholds, this
might indicate the onset of congestion. The
probability of congestion is then calculated.
3
5
1

Traffic Shaping
• Another method of congestion Avoidance is to
“shape” the traffic before it enters the
network.
• Traffic shaping controls the rate at which
packets are sent (not just how many). Used in
ATM and Integrated Services networks.
• At connection set-up time, the sender and
carrier negotiate a traffic pattern (shape).
• Two traffic shaping algorithms are:
– Leaky Bucket
– Token Bucket

The Leaky Bucket Algorithm
• The Leaky Bucket Algorithm used to control
rate in a network. It is implemented as a
single- server queue with constant service
time. If the bucket (buffer) overflows then
packets are discarded.

The Leaky Bucket Algorithm
(a)A leaky bucket with water. (b) a leaky bucket with packets.

Token Bucket Algorithm
• In contrast to the LB, the Token Bucket
Algorithm, allows the output rate to vary,
depending on the size of the burst.
• In the TB algorithm, the bucket holds tokens. To
transmit a packet, the host must capture and destroy
one token.
• Tokens are generated by a clock at the rate of one
token every sec.
• Idle hosts can capture and save up tokens (up to the
max. size of the bucket) in order to sendlarger bursts
later.

The Token B5-u34cket
Algorithm
(a) Before. (b) After.

Transmission Control Protocol
 TCP
is
receive
r
reliable
protocol. always
sends
either
positive
That is,
the
or
negative acknowledgementabout the
data packet to the sender
 It ensures the data packet is reached
the destination or it needs to resend it.
 TCP provides end-to-end communication.
 TCP provides full duplex server
T C P
I P I n t e r n e t w o r
k
By
teSt
r
e
a
m
By
teS
tr
e
a
m
T C P

TCP
Header
 The length of TCP header is minimum
20 bytes long and maximum 60 bytes.
 Source Port (16-bits) - It identifies
source port of the application process on
the sending device.
 Destination Port (16-bits) - It identifies
destination port of the application process
on the receiving device.
 Sequence Number (32-bits) -
Sequence number of data bytes of
a segment in a session.

 Acknowledgement Number (32-
bits) - When ACK flag is set, this number
contains the next sequence number of the
data byte expected and works as
acknowledgement of the previous data
received.
 Data Offset (4-bits) - This field implies
both, the size of TCP header (32-bit
words) and the offset of data in current
packet in the whole TCP segment.
 Reserved (3-bits) - Reserved for future use
and all are set zero by default.

 Flags (1-bit each)
 NS - Nonce Sum bit is used by
Explicit Congestion Notification signaling
process.
 CWR - When a host receives packet with
ECE bit set, it sets Congestion Windows
Reduced to acknowledge that ECE
received.
 ECE - If SYN bit is clear to 0, then ECE means
that
the IP packet has its CE (congestion experience)
bit set.

 URG - It indicates that Urgent
Pointer field has significant data and
should be processed.
 ACK - It indicates that
Acknowledgement field has significance. If
ACK is cleared to 0, it indicates that packet
does not contain any acknowledgement.
 PSH - When set, it is a request to the
receiving station to PUSH data (as soon as
it comes) to the receiving application
without buffering it.

 RST - Reset flag has the
following features:

It is used to refuse an incoming
connection.

It is used to reject a segment.

It is used to restart a connection.
 SYN - This flag is used to set up
a connection between hosts.
 FIN - This flag is used to release a
connection and no more data is
exchanged thereafter. Because packets
with SYN and FIN flags have sequence

 Windows Size - This field is used for flow
control between two stations and
indicates the amount of buffer (in bytes)
the receiver has allocated for a
segment,
i.e. how much data is the
receiver expecting.
 Checksum - This field contains
the checksum of Header, Data and
Pseudo Headers.
 Urgent Pointer - It points to the
urgent data byte if URG flag is set to 1.

 Options - It facilitates additional
options regula
r
which are not covered by
the header.
 Option field is always
described in
32-
bit
words. If this field contains data less
than 32-bit, padding is used to cover
the remaining bits to reach 32-bit
boundary.

Connection Management in
TCP
 Opening a TCP Connection
 Closing a TCP Connection
 Special Scenarios
 State Diagram

TCP Connection
Establishment
 TCP uses a three-way handshake to open a
connection:
(1) ACTIVE OPEN: Client sends a segment with
 SYN bit set *

port number of client

initial sequence number (ISN) of client
(2) PASSIVE OPEN: Server responds with a segment
with
 SYN bit set *
 initial sequence number of server

ACK for ISN of client
(3) Client acknowledges by sending a segment with:

ACK ISN of server(* counts as one byte)

Figure : Connection establishment using three-way
handshaking

Figure : Connection termination using three-way handshaking

The User Datagram Protocol (UDP) is called a
connectionless, unreliable transport protocol. It
does not add anything to the services of IP
except to provide process-to-process
communication instead of host-to- host
communication.
•provide unreliable service

Table : Well-known ports used with
UDP

UDP Format
 Source and destination port : 16,
16 identify applications at ends
of the connection
 length: 16 - length of datagram
including header and data
 checksum :16 -one’s complement
of header and data including
pseudo data

UDP for Application
 TFTP
 DNS
 RPC,
NFS
 SNMP

Figure :Pseudo header for checksum
calculation

TCP UDP
Transmission Control Protocol User Datagram Protocol
Connection Oriented Connection Less
Slow Fast
Highly Reliable Unreliable
20 Bytes 8 Bytes
It takes acknowledgement of data
and has the ability to retransmit if
the user requests.
It neither takes acknowledgement,
nor it retransmits the lost data.
TCP is heavy-weight. UDP is lightweight.

Stream-based Message-based
Delivery of all data is managed Not performed
Flow control using sliding window
protocol
None
TCP doesn’t supports Broadcasting. UDP supports Broadcasting.
Small to moderate amounts of
data
Small to enormous amounts of the
data
Applications where reliable
transmission of data matters.
Application where data delivery
speed matters.
FTP
, Telnet, SMTP
, IMAP. DNS, BOOTP, DHCP, TFTP.

• A protocol is designed to handle real-time
traffic (like audio and video) of the Internet, is
known as Real Time Transport Protocol
(RTP).
• RTP must be used with UDP.
• It does not have any delivery mechanism
like multicasting or port numbers.
• RTP supports different formats of files
like MPEG and MJPEG.

• It is very sensitive to packet delays and less
sensitive to packet loss.
• RTP is first time published in 1996 and
known as RFC 1889. And next it published
in 2003 with name of RFC 3550.

1. RTP mainly helps in media
mixing, sequencing and time-stamping.
2. Voice over Internet Protocol (VoIP)
3. Video Teleconferencing over Internet.
4. Internet Audio and video streaming.

• Version : This 2-bit field defines version number. The current version is
2.
• P –The length of this field is 1-bit. If value is 1, then it denotes
presence of padding at end of packet and if value is 0, then there is
no padding.
• X –The length of this field is also 1-bit. If value of this field is set to 1,
then its indicates an extra extension header between data and
basic header and if value is 0 then, there is no extra extension.
• Contributor count –This 4-bit field indicates number of contributors.
Here maximum possible number of contributor is 15 as a 4-bit
field can allows number form 0 to 15.
• M –The length of this field is 1-bit and it is used as end marker by
application to indicate end of its data.
• Payload types –This field is of length 7-bit to indicate type of payload.
We list applications of some common types of payload.

• Sequence Number –The length of this field is 16
bits. It is used to give serial numbers to
RTP packets.
• Time Stamp –The length of this field is 32-bit. It is
used to find relationship between times
of different RTP packets.
• Synchronization Source Identifier –This is a 32-bit
field used to identify and define the source.
The value for this source identifier is a random
number that is chosen by source itself.
• Contributor Identifier –This is also a 32-bit field
used for source identification where there is
more than one source present in session.

OVERVIEW
• Applications
• DNS
• E-Mail Protocol
• WWW
• SNMP
• SMTP
• Security
• Threats and Services
• Cryptography
• DES
• RSA
• Web security
• SSL

• An application layer is an abstraction layer that
specifies the shared communications
protocols and interface methods used by
hosts in a communications network.
• The application layer abstraction is used in both
of the standard models of computer
networking.
• The Internet Protocol Suite (TCP/IP) and the OSI
model.
• Although both models use the same term for their
respective highest-level layer.

Services of Application Layers
• File Transfer
• Addressing
• Mail Services
• Directory Services
• Authentication

• (Domain Name
DNS
System) The
Internet's
system for converting alphabetic names
into numeric IP addresses.
• For example, when a Web address (URL) is
typed into a browser, DNS servers return the
IP address of the Web server associated
with that name.
• In this example, the DNS converts the URL
www.company.com into the IP address
204.0.8.51.

A Hierarchy of Servers
• The DNS system is a hierarchy of duplicated
database servers worldwide that begin with
the "root servers" for the top-level domains
(.com,
.net, .org, .gov, .edu, .mil, etc.). The root
servers point to the "authoritative" servers
located in ISPs,
www.yahoo.com
www --------> Host Name
Yahoo--------> Server Name
com ----------> Domain Name

Structure of DNS
• It Consists of Four Elements
1. DNS Name Space
2. DNS Database
3. Name Servers
4. DNS Resolvers

1. DNS Name Space
• The Domain Name Space consists of a tree data
structure.
• Each node or leaf in the tree has a label and zero or
more resource records (RR), which
hold information associated with the domain name.
• The domain name itself consists of the label, parent
node on the right.
• The tree sub-divides into zones beginning at the
A DNS zone may consist of only
one
domain, or may consist of many domains and sub-
domains, depending on the administrative choices

2. DNS Database
• DNS does not only deal with IP addresses of hosts,
but also exchanges information on Name Servers.
• The Key features of the Database are as Follows :
1) Variable-Depth Hierarchy for Names.
2) Distributed Database.
3) Distribution Controlled by Database.

3. Name Servers
• The Domain Name System is maintained by a
distributed database system, which uses
the client–server model.
• The nodes of this database are the name servers.
• Each domain has at least one authoritative DNS
server that publishes information about
that domain and the name servers of any
domains subordinate to it.
• The top of the hierarchy is served by the root
name servers.

4. DNS Resolvers
• The client side of the DNS is called a DNS resolver.
• A resolver is responsible for initiating and
sequencing the queries that ultimately lead to
a full resolution.
• DNS resolvers are classified by a variety of query
methods, such as recursive, non-recursive,
and iterative.

• The DNS protocol uses two types of DNS
messages, queries and replies; both have
the same format.
• Each message consists of a header and four
sections: question, answer, authority, and
an additional space.
• A header field (flags) controls the content of these
four sections.
• The header section consists of the following
fields: Identification, Flags, Number of
questions, Number of answers, Number of
authority resource records (RRs), and
Number of additional RRs. Each field is 16

• Primary website.
• Marketing campaign websites.
• Email servers.
• Customer support websites.
• Online resource libraries.
• Inside sales web portals.
• Multi-tier web applications.
• P2P resources.

• Electronic Mail or E-Mail is a method of sending
and receiving messages (Mail) electronically
over a Computer Network.
• E-Mail is a system allows a person or a group to
electronically communicate to others
through Internet.
• It is method of exchanging message between
people using electronic devices.
• Exchanging message as Text files and non-text
files (images, graphics Image, files so on.,)

Components of Email System
Mail Server
Receive, Store and Deliver the mail
DNS
Find and match the IP Address of the Mail
Server
 Mailbox
It is a Folder contains
Emails and their information.

E-Mail Protocol
The E-Mail communication
is
three protocols in general. They are,
done via
1.SMTP ( Simple Mail Transfer Protocol)
2.POP ( Post Office Protocol)
3.IMAP ( Internet Mail Access Protocol)

 SMTP (Simple Mail Transfer Protocol)
 The SMTP stands for Simple Mail Transfer Protocol.
 Email is sent using this protocol.
 Is an internet standard communication
protocolfor
electronic mail transmission.
 Mail servers and other message transfer
agents use SMTP to send and receive mail messages.

 ADVANTAGES:
 SMTP provides the simplest form of communicating
through email message between various
computers in a particular network.
 Since SMTP is developed from a simple platform ,
email messages may be sent easily and quickly.
 SMTP also offers reliability in terms of outgoing
email messages.
DISADVANTAGES:
 The main drawback of sending through an SMTP
server is that it is insecure, it can be easily
hacked.
 Another disadvantage is the server limitation.

 POP (Post Office Protocol):
 This protocol is also used for incoming emails.
The main difference with the both protocols is that POP
downloads the entire email into the local computer
and deletes the data on the server once it is
downloaded.
This is helpful in a server with less free memory.
Current version of POP is POP3 .

ADVANTAGES:
 Emails are downloaded to the user`s computer.
 opening attachments is quick and easy as they are
already
downloaded.
 Less server storage space required all emails are stored on local
machine.
 Storage capacity of emails limited by the size of your hard disk.
 very popular, easy to configure and use.
DISADVANTAGES:
 Emails cannot be accessed from other machines(unless configured
to do so).
 Exporting the local mail folder to another email client or physical
machine can be difficult.
 Email folders can become corrupted, potentially losing the entire
mailbox at once.

 IMAP(Internet Mail Access Protocol)
 This protocol is used while receiving an email.
 When one uses IMAP, the emails will be present in
the server and not get downloaded to the user`s mail box
and deleted from the server.
 This helps to have less memory used in the
local computer and server memory is increased.

 ADVANTAGES:
 Mail stored on remote server, i.e. accessible
from multiple different location.
 Internet connection needed to access mail.
 Mail is automatically backed up if server is
managed properly.
 DISADVANTAGES:
 The main disadvantage of the IMAP protocols is that
it is mandatory to have an internet connection on
all the time to read/reply and search the message.

WWW
• The World Wide Web is the universe of network-
accessible information.
• In simple terms, The World Wide Web is a way of
exchanging information between computers on
the Internet.
• The World Wide Web is based on several different
Technologies : Web browsers, Hypertext
Markup Language (HTML) and Hypertext
Transfer Protocol (HTTP).

Features of WWW
• HyperText Information System
• Cross-Platform
• Distributed
• Open Standards and Open Source
• Uses Web Browsers to provide a single interface
for many services
• Dynamic, Interactive and Evolving.
• “Web 2.0”

Components of WWW
• There are 5 Components of WWW:
1.Uniform Resource Locator (URL): serves
as system for resources on web.
2.HyperText Transfer Protocol (HTTP):
specifies communication of browser and server.
3.Hyper Text Markup Language (HTML): It
Defines structure, organisation and content of
webpage.
4.Web Server : A web server is computer
software and underlying hardware that accepts
requests via HTTP, the network protocol created
to distribute web pages.

Components of WWW
5.Web Browser : A web browser
(commonly referred to as a browser or internet
browser).
• It is an application software for accessing the
World Wide Web.
• When a user requests a web page from a
particular website, the web browser retrieves
the necessary content from a web server and
then displays the page on the user's device.

Working of WWW
• The World Wide Web is based on several different
technologies :
1. Web browser.
2. Hypertext Markup Language (HTML).
3. Hypertext Transfer Protocol (HTTP).
1. Web browser : It is used to access webpages.
Web browsers can be defined as programs which
display text, data, pictures, animation and video on
the Internet.

2.HTML : Hyperlinked resources on the
World Wide Web can be accessed using
software interface provided by Web browsers.
3.HTTP : It can be used for several
tasks including : searches, mailing, transferring
files, and much more. Some of the commonly
used browsers are Internet Explorer, Opera
Mini, Google Chrome.

• Online Forms
• Shopping Carts
• Word Processors
• Spreadsheets
• Video and Photo Editing
• File Conversion
• File Scanning
• E-mail programs such as Gmail, Yahoo and AOL.
• Popular Applications include Google Apps and
Microsoft 365.

SNMP
• Simple Network Management Protocol
(SNMP)
is an application–layer protocol defined by the
• It is a part
Protocol⁄Internet
suite.
of Transmission Control
Protocol (TCP⁄IP) protocol
• SNMP is one of the widely accepted network
protocols to manage and monitor
network elements.

• GET: The GET operation is a request sent by the manager to
the managed device.
• GET NEXT: The significant difference is that the GET
NEXT operation retrieves the value of the next MIB tree.
• GET BULK: The GETBULK operation is used to
retrieve voluminous data from large MIB table.
• SET: This operation is used by the managers to modify
or assign the value of the Managed device.
• TRAPS: TRAPS are initiated by the Agents. It is a signal to the
SNMP Manager by the Agent on the occurrence of an event.
• INFORM: It includes confirmation from the SNMP
manager on receiving the message.
• RESPONSE: It is the command used to carry back the value(s)
or signal of actions directed by the SNMP Manager.

• SMTP stands for Simple Mail Transfer
Protocol.
• SMTP is a set of communication guidelines
that allow software to transmit an
electronic mail over the internet is called
Simple Mail Transfer Protocol.
• It is a program used for sending messages to
other computer users based on e-mail
addresses.

• It provides a mail exchange between users on the
same or different computers, and it
also supports:
1. It can send a single message to one or more
recipients.
2. Sending message can include text, voice, video
or graphics.
3. It can also send the messages on networks
outside the internet.
4. The main purpose of SMTP is used to set up
communication rules between servers.

• It have the following Working Functionalities
:
1. Composition of Mail
2. Submission of Mail
3. Delivery of Mail
4. Receipt and Processing of Mail
5. Access and Retrieval of Mail

• Network Security deals with all aspects related to
the protection of the sensitive information
assets existing on the network.
• It covers various mechanisms developed
to provide fundamental security services for
data communication.
• It describes the functioning of most common
security protocols employed at
different networking layers right from
application to data link layer.

Goals of Network Security
of network security are
• The primary
goal
Confidentiality,
three pillars of Network Security are
Integrity, and Availability. These
often
represented as CIA triangle.
1.Confidentiality − The function of confidentiality
is to protect precious business data from
unauthorized persons.
2.Integrity − It means maintaining and assuring
the accuracy and consistency of data.
The function of integrity is to make sure that the data
is reliable and is not changed by unauthorized
persons.

3. Availability − The function of availability in
Network Security is to make sure that the data,
network resources/services are continuously
available to the users, whenever they require it.

Security Services
fundamental security services as the following −
1.Confidentiality − E-mail message should not
be read by anyone but the intended recipient.
2.Authentication − E-mail recipient can be sure
of the identity of the sender.
3.Integrity − Assurance to the recipient that the
e- mail message has not been altered since it
was transmitted by the sender.
4.Non-repudiation − E-mail recipient is able
to prove to a third party that the sender really did
send the message.

5. Proof of submission − E-mail sender gets the
confirmation that the message is handed to the mail
delivery system.
6. Proof of delivery − Sender gets a confirmation
that the recipient received the message.

Threats and Services
A Computer System Threat is anything that
leads to loss or corruption of data or physical
damage to the hardware or infrastructure.
• Security Threats can be many like Software
attacks, theft of intellectual property,
identity theft, theft of equipment or
information.
• Threat is any activity that can lead to data
loss/corruption through to delay of normal
business operations.

Types of Threats
• There are physical and non-physical threats.
• Physical Threats : cause damage to computer
systems hardware and infrastructure.
Examples include theft, vandalism through
to natural disasters.
• Non-physical Threats : Target the software
and data on the computer systems.

• A physical threat is a potential cause of an incident
that may result in loss or physical damage to
the computer systems.
• The following list classifies the physical threats
into three main categories
• Internal: The threats include fire, unstable power
supply, humidity in the rooms housing
the hardware, etc.
• External: These threats include Lightning, floods,
earthquakes, etc.
• Human: These threats include theft, vandalism of
the infrastructure and hardware, accidental
or intentional errors.

The following list is the common types of non-physical threats;
• Virus
• Trojans
• Worms
• Spyware
• Key loggers
• Adware
• Denial of Service Attacks
• Distributed Denial of Service Attacks
• Unauthorized access to computer systems resources such as
data
• Phishing
• Other Computer Security Risks

Cryptography
• Cryptography is a method of protecting information
and communications through the use of codes.
• The information is intended can read and process
it.
• The prefix "crypt-" means "hidden" or "vault" --
and the suffix "-graphy" stands for "writing."
• Cryptography refers to secure information and
communication techniques derived
from mathematical concepts and a set of rule-
based calculations called algorithms.

Cryptography Techniques
• Cryptography is closely related to the disciplines of
• It includes techniques such as microdots, merging
words with images, and other ways to
hide information in storage or transit.
• Cryptography is used to convert Plaintext into
Ciphertext is known as Encryption. then
back again
• Encryption : Known to Unknown
• Decryption : Unknown to Known

• Cryptography concerns with the following
Four objectives:
the information cannot be
understood by anyone for whom it was
unintended.
the information cannot be altered
in storage or transit between sender and
intended receiver without the alteration
being detected.

the creator/sender of the
information cannot deny at a later stage his
or her intentions in the creation or
transmission of the information.
the sender and receiver can
confirm each other's identity and the
origin/destination of the information.

1. Single-key or Symmetric-key Cryptography.
2. Public-key or Asymmetric-key Cryptography.
1. Single-key or Symmetric-key Cryptography :
Symmetric cryptography is based on the use of just
is used to both Encrypt and Decrypt the
messages ( only Private Key or Secret Key )
2. Public-key or Asymmetric-key Cryptography :
Asymmetric cryptography, also known as public-key
cryptography, Here Two keys are used to Encrypt and
Decrypt the messages (Both Private and Public Key)

Single-key or Symmetric-key
Cryptography

Public-key or Asymmetric-key
Cryptography

• The
Data
Encryption Standard is a symmetric-key
algorithm for the encryption of digital data.
• The DES (Data Encryption Standard) algorithm is a
symmetric-key block cipher created in the early 1970s
by an IBM team and adopted by the National
Institute of Standards and Technology (NIST).
• DES is an implementation of a Feistel Cipher. It uses 16
round Feistel structure.
• Key length is 64-bit.
• Since DES is based on the Feistel Cipher.
1. Round function.
2. Key schedule.
3. Any additional processing − Initial and
final permutation.

• The algorithm process breaks down into the following steps:
1.The process begins with the 64-bit plain text block
getting handed over to an initial permutation (IP) function.
2.The initial permutation (IP) is then performed on the
plain text.
3.Next, the initial permutation (IP) creates two halves of
the permuted block, referred to as Left Plain Text (LPT) and
Right Plain Text (RPT).
4.Each LPT and RPT goes through 16 rounds of the
encryption process.
5.Finally, the LPT and RPT are rejoined, and a Final
Permutation (FP) is performed on the newly combined block.
6.The result of this process
produces the desired 64-bit ciphertext.

• The DES satisfies both the desired properties of
block cipher. These two properties make
cipher very strong.
• Avalanche effect − A small change in plaintext
results in the very great change in the
ciphertext.
• Completeness − Each bit of ciphertext depends on
many bits of plaintext.

• You must choose a security provider to implement
your data encryption algorithm.
• There are many available providers to choose
from, but selecting one is the essential initial
step in implementation.
• Your selection may depend on the language you
are using,

• RSA (Rivest–Shamir–Adleman) is a public-key
cryptosystem that is widely used for secure
data transmission.
• In a public-key cryptosystem, the encryption key is
public and distinct from the decryption key,
which is kept secret (private).
• RSA algorithm is asymmetric cryptography
algorithm. Asymmetric actually means that it
works on two different keys i.e. Public Key and
Private Key. As the name describes that the
Public Key is given to everyone and Private key
is kept private.

Example
:
• A client (for example browser) sends its
public key to the server and requests for
some data.
• The server encrypts the data using client’s
public key and sends the encrypted data.
• Client receives this data and decrypts it.

The RSA algorithm holds the following features −
• RSA algorithm is a popular exponentiation in
a finite field over integers including prime
numbers.
• The integers used by this method are
sufficiently large making it difficult to solve.
• There are two sets of keys in this
algorithm:
private key and public key.

• The following steps to work on RSA algorithm :
The initial procedure begins with selection of two
prime numbers namely p and q, and then calculating
their product N,
N=p*q
Consider number e as a derived number which should
be greater than 1 and less than (p-1) and (q-1).
The specified pair of numbers n and e forms the RSA
public key and it is made public.

Private Key d is calculated from the numbers p, q
and e. The mathematical relationship between the
numbers is as follows :

Encryption Formula
Consider a sender who sends the plain text message
to someone whose public key is (n,e). To encrypt the
plain text message in the given scenario, use the
following syntax −
Decryption Formula
• The decryption process is very straightforward and
includes analytics for calculation in a
systematic approach. Considering receiver C has
the private key d, the result modulus will be
calculated as −

known as
• Web
security
“Cybersecurity”.
is
also It
basically means
protecting a website or web application by
detecting, preventing and responding to
cyber threats.
• web security is easy to install and it also
helps the business people to make their
website safe and secure.
• A web application firewall prevents
automated attacks that usually target small
or lesser-known websites.

• Secure Sockets Layer (SSL) is a
security
protocol that
authentication, and
provides
privacy, integrity to
Internet
communications.
• SSL eventually evolved into Transport Layer
Security (TLS).
• SSL, or Secure Sockets Layer, is an
encryption-based Internet security
protocol. It was first developed by Netscape
in 1995.

• SSL encrypts data that is transmitted across
the web.
• SSL initiates an authentication process called
a handshake between two communicating
devices to ensure that both devices are
really who they claim to be.
• SSL also digitally signs
data provide data integrity.
in order to

• SSL
supports
the following information
security principles:
1. Encryption: protect data transmissions
(e.g. browser to server, server to server,
application to server, etc.)
2.Authentication: ensure the server
you’re connected to is actually the correct
server.
3.Data integrity: ensure that the data that
is requested or submitted is what is
actually delivered.

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