1. OSI Layers Protocol Functions
Presented by
K.GAYATHRI

2. OSI Model
 Introduction
The Open Systems Interconnection (OSI) model is a
reference tool for understanding data communications
between any two networked systems.
 Some Benefits of OSI Model
1.Less complex,More quality
2.Easier to learn and Develop
3.Multivendor interoperability
4.Standard interface
5.Troubleshooting.

3. OSI Model 7 Layers With Protocols

4. Physical Layer
Purpose
Deals with the transmission of 0s and 1s over the physical media
Translation of bits into signals(Electrical,
Mechanical)
The Physical layer provides specifications for a variety of hardware:
• Cabling
• Connectors
• Network interface cards (NICs)
• Wireless radios
• Hubs

5. Ethernet
Ethernet is a family of technologies that provides datalink and physical specifications for controlling access to a
shared network medium.
Ethernet has several benefits over other LAN
technologies:
• Simple to install and manage
• Inexpensive
• Flexible and scalable
• Easy to interoperate between vendors

6. Cabling the LAN
Cabling is an integral part of building any network.
●
Cabling standards are a set of specifications for the installation
and testing of cables.
●
Standards specify types of cables to use in specific
environments, conductor materials, pin outs, wire sizes,
shielding, cable lengths, connector types and performance limits.
●
Media Characteristics:
Cable length
●
Ethernet Cabling Types
Coaxial
●
Fiber Optic
●
Cost
●
Ease of installation
●
Susceptibility to interference
●
Space
●
Category 5 unshielded twisted-pair
cable (Cat 5 UTP)
●

7. Twisted Pair Cable
●
Twisted pair cable is most
in network installations
commonly used
●
The TIA/EIA organization defines two different patterns, or
wiring schemes, called T568A and T568B.
●
Each wiring scheme defines the pin out, or order of wire
connections, on the end of the cable.
●
There are two types of twisted pair cable STP,UTP
●
(Cat 5 UTP) is mainly used in network installations.

8. Unshielded Twisted Pair (UTP)
Unshielded twisted-pair cable (UTP) is a four-pair wire medium
used in a variety of networks.
●
TIA/EIA-568-A contains specifications governing cable
performance.
●
RJ-45 connector
●
UTP Cable Types
Straight-Through
●
Crossover
●
Rollover
●
RJ-45 Connector
RJ-45 Connector

9. Straight-through Cable
A Straight-through cable is the most common cable type.
●
It maps a wire to the same pins on both ends of the cable.
●
Straight-through cables used for following connections,
Switch to router
●
Switch to PC or server
●
Hub to PC or server
●

10. Crossover Cable
A crossover cable uses both wiring schemes.
●
The wires on the cable are crossed over so that the receive
signal pins on the RJ-45 connector on one end are connected to
the transmit signal pins on the RJ-45 connector on the other end.
●
Crossover cables used for following connections,
Switch to switch
●
Switch to hub
●
Hub to hub
●
Router to router
●
PC to PC
●
Router to PC
●

11. Rollover Cable
Rollover cable (also known as Cisco console cable) is a type of
null-modem cable that is most commonly used to connect a
computer terminal to a router's console port.
●
Cisco routers and switches are normally configured over their
console ports.
●
The pin outs on one end are reversed from the other, as if the
wire had been rolled over and you were viewing it from the other
side.
●
Rollover cables used for following connections
Connect a terminal to a console port.
●

12. Wireless Network
802.11 standard specifies the operating parameters of
wireless local area networks (WLAN)
●
The 802.11 wireless networks operate in two basic modes:
1.Infrastructure mode
2.Ad-hoc mode
Infrastructure Mode
Infrastructure Mode

13. Wireless Network Security
Wired Equivalent Privacy (WEP): The original encryption protocol developed
for wireless networks.
WEP encryption is based on the RC4 stream cipher–operation
●
Wi-Fi Protected Access (WPA):Most current WPA implementations use a
preshared key (PSK), commonly referred to as WPA Personal, and the Temporal
Key Integrity Protocol (TKIP, pronounced tee-kip) for encryption.
WPA Enterprise uses an authentication server to generate keys or certificates
●
Wi-Fi Protected Access version 2 (WPA2): Based on the 802.11i wireless
security standard.
The most significant enhancement to WPA2 over WPA is the use of the
Advanced Encryption Standard (AES) for encryption
●

14. WEP vs WPA vs WPA2
WEP WPA WPA2
ENCRYPTION
RC4
RC4
AES
KEY ROTATION
NONE
Dynamic
Session Keys
Dynamic
Session Keys
KEY
DISTRIBUTION
Manually typed
into each device
Automatic
distribution
available
Automatic
distribution
available
AUTHENTICATIO Uses WEP key as Can use 802.1x Can use 802.1x
Authentication
& EAP
& EAP
N

15. Data Link Layer
Switching-Providing MAC address
●
Framing-Send blocks of data (frames) between
physical devices
●
Dealing with transmission errors(Node-Node
Error Control)
●
Regulating data flow(Flow control)
●
It mainly uses the hardware device Switches.
●

16. Switches
Switches do following functions,
• Hardware address learning
• Intelligent forwarding of frames
• Loop avoidance
Switches support three methods of forwarding frames.
Store-and-Forward method
Cut-Through (Real Time) method
Fragment-Free (Modified Cut-Through) method

17. Spanning Tree Protocol(STP)
Switches (and bridges) needed a mechanism to prevent loops from forming.

Switches utilize the Spanning Tree Protocol (STP) to maintain a loop-free
environment.

STP Process
To maintain a loop-free environment, STP performs the following functions:
• A Root Bridge is elected
• Root Ports are identified
• Designated Ports are identified
• If a loop exists, a port is placed in Blocking state. If the loop is
removed the blocked port is activated again.

18. STP Process

19. Point to Point protocol
PPP is a data-link layer protocol, PPP uses a stack of
other protocols to establish the link, to authenticate
the parties involved, and to carry the network layer
data.
Three sets of protocols are used by PPP:
●
Link control protocol
Authentication protocol
●
Network control protocol
●

20. Link Control Protocol (LCP)
It is responsible for establishing, maintaining, configuring, and
terminating links.
●
It also provides negotiation mechanisms to set options between
endpoints.
●
Both endpoints of the link must reach an agreement about the
options before the link can be established.
●
When PPP is carrying an LCP packet, it is either in the
establishing state or in the terminating state.
●
All LCP packets are carried in the data field of the PPP frame.
●

21. Authentication Protocols
Authentication plays a very important role in PPP
because PPP is designed for use over dial-up links
where verification of user identity is necessary.
●
Authentication means validating the identity of a
user who needs to access a set of resources.
●
PPP uses two protocols for authentication: Password
Authentication Protocol (PAP)
●
Challenge Handshake Authentication Protocol
(CHAP)
●

22. Password Authentication Protocol (PAP)
The user who wants to access a system sends an ID
(identification) and a password.
The system checks the validity of the identification and
password and either accepts or denies a connection.

23. Challenge Handshake Authentication Protocol (CHAP)
The CHAP protocol is a three-way handshaking
authentication protocol that provides greater security than
PAP.
In this method, the password is kept secret; it is never sent
on-line.

24. Network Control Protocol (NCP)
After the link is established and authentication (if
any) is successful, the connection goes on the
networking state.
●
NCP is a set of control protocols to allow the
encapsulation of data coming from network layer
protocols into the PPP frame.
●
The set of packets that establish and terminate a
network layer connection is called Internetwork
Protocol Control Protocol (IPCP).
●

25. NCP Example

26. Network Layer
Routing and Forwarding
●
Logical addressing
●
Transport packet from sending to receiving hosts
●
A logical address contains two components:
• Network ID – identifies which network a host belongs to.
• Host ID – uniquely identifies the host on that network.
Logical addressing protocols include
Internetwork Packet Exchange (IPX)
●
Internet Protocol (IP).
●

27. IPv4 address Classes
Class First
Octet Range
Default Subnet Mask
Class A
1 – 126
255.0.0.0
Class B
128 – 191
255.255.0.0
Class C
192 – 223
255.255.255.0
Class D
224 – 239
-
Class E
240 – 255
-
Ranges 127.x.x.x are reserved for the loopback or localhost.
●
127.0.0.1 is a comman Loopback address.
●

28. Routing And Forwarding
Routing algorithm determines
end-end-path through network
routing algorithm
Forwarding table determines
local forwarding at this router
local forwarding table
header value output link
0100
0101
0111
1001
3
2
2
1
value in arriving
packet’s header
0111
Routing-Determine
route taken by
packets from source
to destination
1
3 2
ForwardingMove packets from
router’s input to
appropriate router
output

29. Transport Layer
This layer is responsible for the reliable transfer of data, by ensuring that
data arrives at its destination error-free and in order.
It provides Port number to specifies the Application.
It is Host-to-Host layer.
Transport layer communication falls under two categories:
• Connection-oriented – requires that a connection with specific agreedupon parameters be established before data is sent.(TCP)
• Connectionless – requires no connection before data is sent.(UDP)

30. Some common Port numbers
Port Number
Transport Protocol
Application
20, 21
TCP
FTP
22
TCP
SSH
23
TCP
Telnet
25
TCP
SMTP
53
TCP/UDP
DNS
80
TCP
HTTP
110
TCP
POP3
443
TCP
SSL
666
TCP
Doom

31. Transmission Control Protocol(TCP)
Connection establishment – connections are established,
maintained, and ultimately terminated between devices.
●
Segmentation and sequencing – data is segmented into
smaller pieces for transport. Each segment is assigned a
sequence number, so that the receiving device can reassemble
the data on arrival.
●
Acknowledgments – receipt of data is confirmed through the
use of acknowledgments. If a segment is lost, data can be
retransmitted to guarantee delivery.
●
Flow control (or windowing) – data transfer rate is negotiated
to prevent congestion.
●
Connection Termination.
●

32. TCP Process
Segment N
H
Segment 1
H

33. User Datagram Protocol(UDP)
The User Datagram Protocol (UDP) is a
connectionless,unreliable transport protocol.
●
UDP experiences less latency(High speed transmission)
●
It provides no three-way handshake, no flow-control, no
sequencing, and no acknowledgment of data receipt.
●
UDP essentially forwards the segment
●
UDP ideal for applications that require speed over
reliability. For example, DNS primarily uses UDP as its
transport protocol
●

34. Session Layer
The session layer is responsible for dialog
control and synchronization.
●
The session layer defines how to start, control and end
conversations (called sessions) between applications.
●
This includes starting, stopping, and re-synchronizing
communications between applications on two computers.
●
The session layer offers provisions for efficient data transfer.
●
Session layer Protocols,
Structured Query Language (SQL)
●
Remote Procedure Call (RPC)
●
Network File system(NFS)
●

35. Basic Functions for the Session Layer
Managing multiple sessions
A computer can establish multiple sessions with several other
computers
e.g., session 1: exchanging information over the World Wide Web with
www.yahoo.com
session 2: exchanging information over the World Wide Web with www.google.com
session 3: exchanging information over the World Wide Web with www.espn.com
Two computers can also establish multiple sessions,
e.g., function 1: exchanging information over the World Wide Web;
function 2: exchanging information over the FTP;
function 3: exchanging information over the email

36. Session layer Examples
Software
news
music

37. Presentation Layer
The presentation layer is responsible for translation, compression,
and encryption.
This layer controls the formatting and syntax of user data for the
application layer.
 This ensures that data from the sending application can be
understood by the receiving application.
Examples of Presentation layer formats include:
• Text - RTF, ASCII, EBCDIC
• Images - GIF, JPG, TIF
• Audio - MIDI, MP3, WAV
• Movies - MPEG, AVI, MOV

38. Presentation Layer Protocols
●This layer has two protocols for secure purpose of transmission
1.Transport layer Security Protocols(TLS)
●The primary goal of the TLS protocol is to provide privacy and
data integrity between two communicating applications”
●In practice, used to protect information transmitted between
browsers and Web servers
2.Secured Socket Layer protocols(SSL)
●SSL is an Internet security protocol used by Internet browsers
and Web servers to transmit sensitive information.
●Both protocols works on three features like Confidentiality,
integrity, and Availability.

39. SSL/TLS

40. Cryptography
Cryptography is the practice and study of hiding information.
It is the Art or Science of converting a plain intelligible data
into an unintelligible data and again retransforming that
message into its original form.
It provides Confidentiality, Integrity, Accuracy.
Encryption –The process of converting plain text into an
unintelligible format (cipher text) is called Encryption.
Decryption –The process of converting cipher text into a plain
text is called Decryption

41. Symmetric And Asymmetric Key Methods
Symmetric Key
Cryptography (Secret Key
Cryptography)
Asymmetric Key Cryptography
(Public Key Cryptography)
Same Key is used by both
parties
Users get the Key from an
Certificate Authority
Advantages
Advantages
Simpler and Faster
More Secured
Disadvantages
Authentication
Less Secured
2 different keys are used
Disadvantages
Relatively Complex

42. Application Layer
It mainly provides user interface
●
Everything at this layer is application-specific.
●
This layer provides application services for file transfers, email, and other network software services
●
This layer handles issues like network transparency,
resource allocation and problem partitioning.
●

43. Application Layer Protocols
DNS- Domain Name system
HTTP - Hyper Text Transfer Protocol
FTP - File Transfer Protocol
POP 3-Post Office Protocol
IMAP- Internet Message Access protocol
SMTP - Simple Mail Transfer Protocol
Telnet - Remote Access

44. Domain Name system(DNS)
DNS is a host name to IP address translation service.
●
DNS is a distributed database implemented in a hierarchy of
name servers.
●
An application level protocol for message exchange between
clients and servers.
●
Root DNS Servers
com DNS servers
yahoo.com
amazon.com
DNS servers DNS servers
org DNS servers
edu DNS servers
pbs.org
poly.edu
umass.edu
DNS servers
DNS serversDNS servers

45. DNS Process

46. Hyper Text Transfer Protocol(HTTP)
HTTP is the protocol that supports communication between
web browsers and web servers
●
It provides web services.
●
HTTP can support multiple request-reply exchanges over a
single TCP connection.
●
The “well known” TCP port
●
for HTTP servers is port 80.

47. File Transfer Protocol(FTP)
File Transfer Protocol (FTP) is the standard mechanism
provided by TCP/IP for copying a file from one host to
another.
FTP uses the services of TCP. It needs two TCP connections.
The well-known port 21 is used for the control connection
and the well-known port 20 for the data connection.

48. Electronics Mail(SMTP,POP3,IMAP)
SMTP-Uses TCP to reliably transfer email
●
message from client to server, port 25.
It is a push protocol; it pushes the message from the client to
the server.
●
POP- Protocol used to retrieve email from a mail server.
●
It stores and forwards messages
●
IMAP- Keep all messages in one place(The server).
●
Allows user to organize messages in folders.
●

49. Electronics Mailing
Internet
Internet Message
Access Protocol
SMTP
IMAP
Mail Server
IMAP
store
POP
Store
POP
SMTP
Mail
Client
Mail
Client
SMTP

50. Telnet
It is the standard TCP/IP protocol
●
Telnet allows a user to log into a computer across an internet.
●
Telnet establishes a TCP connection and then passes keystrokes
from the users keyboard directly to the remote computer .
●
Telnet offers three basic services .
1. It defines a network virtual terminal that provides a standard
interface to remote systems.
2. Telnet includes a mechanism that allows the client and server to
negotiate options .
3. Telnet treats both ends of the connection symmetrically.

51. TELNET Operation

52. THANK
YOU