6-OSI Model - ISO - Organization for Standardization.

OSI layers - Application
Presentation
Session
Transport
Network
Data Link
Physical

1. 1

2. 2

3. 3
OSI means Open System Interconnect model.

Developed by the International Organization for
Standardization in 1974.

It consists of seven layers.

Each layer has a different but specific processing
function.
OSI Model

4. ISO - Organization for Standardization.
International standards organisation is responsible
for a wide range of standards, including many that
are relevant to computer networking.
In 1984 , the Open Systems Interconnection (OSI)
Reference Model was approved as an international
standard for communications architecture.

5. Figure. Tasks involved in sending a letter

6. 6
Advice
Person
Sales
Take
Not
Do
Please
OSI Model Layers
Application
Presentation
Session
Transport
Network
Data Link
Physical
Layer - 7
Layer - 6
Layer - 5
Layer - 4
Layer - 3
Layer - 2
Layer - 1
Upper Layer
or
Software Layer
Lower Layer
or
Hardware Layer
Heart of OSI

7. 7
Application Layer
Application Layer is
responsible for providing
Networking Services to user.
It also known as Desktop Layer.
Identification of Services is
done using Port Numbers.
e.g. HTTP,FTP, SMTP,
SIP,IMAP,DNS

Ports are nothing but Socket i.e.
Entry and Exit Point to the Layer

Total No. Ports 0 – 65535
Reserved Ports 0 – 1023
Open Ports 1024 – 65535
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application

8. 8
Examples of Networking Services
Service Port No.
HTTP 80
FTP 21
SMTP 25
TELNET 23
TFTP 69

9. 9
Example of FTP request
Client FTP Server
ftp://ftp.microsoft.com

10. 10
Example of FTP request
FTP Request
ftp://ftp.microsoft.com
FTP Request
Listen on
Port 21
Sending FTP Reply

Received FTP Reply
ftp://ftp.microsoft.com

Client FTP Server

11. 11
Application
21 80 25 67 53 69
How data flows from Application Layer
Data
Presentation
Session
Transport
Network
Data Link
Physical

12. 12
Presentation Layer
Presentation Layer is
responsible for converting data
into standard format.

Examples : ASCII, EBCDIC, JPEG,
MPEG, BMP, MIDI, WAV, MP3

Following tasks are perform at
Presentation layer :

Encoding – Decoding
Encryption – Decryption
Compression – Decompression
Application
Presentation
Session
Transport
Network
Data Link
Physical
Presentation

13. 13
How data flows from Presentation Layer
Data
Data Application
Presentation
Session
Transport
Network
Data Link
Physical

14. 14
Session Layer
Session Layer is responsible
establishing, maintaining and
terminating session.
Session ID also works at Session
Layer.


Application
Presentation
Session
Transport
Network
Data Link
Physical
Session

15. 15
How data flows from Session Layer
Data
Data
Data
Application
Presentation
Session
Transport
Network
Data Link
Physical

16. 16
Transport Layer
Transport Layer is
responsible for end-to-end
connectivity. It is also known as
heart of OSI Layers. Following
task are performed at Transport
Layer : -

•Identifying Service
•Multiplexing & De-multiplexing
•Segmentation
•Sequencing & Reassembling
•Flow Control
•Error Detection
Application
Presentation
Session
Transport
Network
Data Link
Physical
Transport

17. 17
Identifying Service
•Transmission Control
Protocol
•Connection Oriented
•Acknowledgement
•Reliable
•Slower
•Port No. 6
•e.g. HTTP, FTP, SMTP
•User Datagram
Protocol
•Connection Less
•No Acknowledgement
•Unreliable
•Faster
•Port No. 17
•e.g. DNS, DHCP,
TFTP,SNMP
TCP UDP

18. 18
Application
Presentation
Session
Multiplexing & De-multiplexing
21 80 25 67 53 69
Transport
TCP - 6 UDP - 17
Network
Data Link
Physical

19. 19
Segmentation
Hello! How are you ?
Hello! How Are You ?

Hello!
How are
you ?

A B

20. 20
Sequencing & Reassembling
Hello! How are you ?
Hello!
1/5
How
2/5
Are
3/5
You
4/5
?
5/5

Hello!
How are
you ?

A B
Hello! How are you ?
Hello!
1/5
How
2/5
Are
3/5
You
4/5
?
5/5
Hello!
1/5
How
2/5
Are
3/5
You
4/5
?
5/5

Hello!
How are
you ?

21. 21
Error Detection
Hello! How are you ?
Hello!
1/5
How
2/5
Are
3/5
You
4/5
?
5/5

Hello!
How are
you ?

Hello!
1/5
Are
3/5
You
4/5
?
5/5
Hello!
1/5
Are
3/5
You
4/5
?
5/5
Segment Missing
Hello!
1/5
Are
3/5
You
4/5
?
5/5
How
2/5
How
2/5
Hello! How are you ?

Hello!
How are
you ?

A B

22. 22
Flow Control - Windowing
Sending
3-window
Received
3-window
Ack-Rec-
3
Sending
5-window
Received
4-window
A B
Ack.
Received-
4
PC-A
can send 4 Segment
at a time to
PC-B

23. 23
How data flows from Transport Layer
Data
Data
Data
Data TH Segment
Application
Presentation
Session
Transport
Network
Data Link
Physical

24. 24
Network Layer
Network Layer is
responsible for providing best
path to data to reach destination.
Logical Addressing sits on this
layer. Device working on Network
Layer is Router.

It is divided into two parts
•Routed Protocols
e.g. IP, IPX, Apple Talk.
•Routing Protocols
e.g. RIP, IGRP, OSPF, EIGRP
Application
Presentation
Session
Transport
Network
Data Link
Physical
Network

25. 25
Routed Protocols
192.168.1.1


192.168.1.2
A B
Segment
Segment
Source IP
192.168.1.1

Destination IP
192.168.1.2
Source IP
192.168.1.1

Destination IP
192.168.1.2
Segment

Hello!
How are
you ?


Hello!
How are
you ?

26. 26
How data flows from Network Layer
Data
Data
Data
Segment
Segment
NH
e.g. Router
Packet
Application
Presentation
Session
Transport
Network
Data Link
Physical

27. 27
Datalink Layer
Data link Layer is
divided into two Sub Layers :

•LLC – Logical Link Control
It talks about Wan protocols e.g.
PPP, HDLC, Frame -relay

•MAC – Media Access Control
It talks about Physical Address.
It is 48 bit Addressing
i.e. 12 digit Hexadecimal No.
It is also responsible for Error
Detection
Device working on Data Link
Layer is Switch, Bridge, NIC.

Application
Presentation
Session
Transport
Network
Data Link
Physical
Data Link

28. 28
Error Detection – CRC Check

Hello!
How are
you ?

Packet
Packet
Source MAC
00-20-18-C0-07-71

Destination MAC
00-20-18-C0-07-72
00000 32434 22222 89696 55434 99323 43434 99434 46323 11114 33333 00000 32434 22222 89696 55434 99323 43434 99434 46323 11114 Error Detected
192.168.1.1
00-20-18-C0-07-71
192.168.1.2
00-20-18-C0-07-72
A B
PC-A
CRC No. 33333
PC-B
CRC No. 11114
Error Detected
For Error Correction
Contact Source Transport layer

29. 29
e.g. Switch
How data flows from Data Link Layer
Data
Data
Data
Segment
DH
Packet
DT
Application
Presentation
Session
Transport
Network
Data Link
Physical
Packet Packet Frame

30. 30
Physical Layer
Physical Layer is
responsible for electrical,
mechanical or procedural checks.
Data will be converted in Binary
that is 0’s & 1’s. Data will be in the
form of electrical pulses if it is
Coaxial or Twisted Pair cable and in
the form of Light if it is Fiber Optic
Cable.

Devices working at Physical Layer
are Hubs, Repeaters, Cables,
Modems etc.
Application
Presentation
Session
Transport
Network
Data Link
Physical Physical

31. 31
Physical Layer Example
Frame
Frame
1010101010101010 1010101010101010

Hello!
How are
you ?

A B 0101011010101010101010101 1010101101010101010101010 0101011010101010101010101 1010101101010101010101010 0101011010101010101010101
Frame

32. 32
How data flows from Physical Layer
Data
Data
Data
Segment
Packet
Frame
Bits
e.g. Hub
Application
Presentation
Session
Transport
Network
Data Link
Physical

33. Encapsulation.

34. Layers of OSI Reference Model.

35. 35
Segment
Packet
Frame
A B
Packet
Data
Data
Data
Bits
Data
Segment
Data Encapsulation & De -capsulation
Packet
Data
Data
Data
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical Bits
DH DT
NH
TH
Segment
Packet
DT Packet DH DT DH
NH Segment NH
TH Data
TH
Frame Packet

36. 36
Application
Transport
Internet
Network
Access
Comparing OSI with TCP/IP Layers
OSI Layers TCP/IP Layers
Application
Presentation
Session
Transport
Network
Data Link
Physical

37. OSI Layers (1)
Physical
Bottommost layer
Implements an unreliable bit link
Uses synchronization bits to synchronize the receiver
Specify the modulation scheme
Physical interface between devices
Mechanical
Electrical
Functional
Procedural
For activating, maintaining and deactivating the physical link
between communicating network systems

38. Data Link Layer.
The data link layer is responsible for moving frames from
one hop (node) to the next.
The major duties of the data link layer are:
Framing
Physical addressing:
Physical address is the MAC address, which is hard coded
into NIC and is of 48-bit represented by Hexadecimal
format.
00.27.AB.CC.EE.23
00.27.AB-Vendor
CC.EE.23-User
Cmd Ipconfig/all to show the system details
Flow control
Error Control
Access Control
Data Link layer protocols are CSMA/CD, CSMA/CA, Token passing etc.

39. OSI Layers (2)
Data Link
Supervises transmission of packets by physical layer
Means of activating, maintaining and deactivating a reliable link
Adds sequence number and CRC
Error detection and control
Encapsulation and Decapsulation are performed
Regulates the access to the link
Higher layers may assume error free transmission
A) Medium Access Control
MAC address will be added
B) Logical Link Control
CRC will be added

40. Data Link Layer.

41. Data Link Layer

42. Network Layer.
The network layer is responsible for the source -to-
destination delivery of a packet possibly across
multiple networks.
It 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 with connecting devices between the networks,
there is need for the network layer to accomplish the
delivery.
The major duties performed by the network layer
are:

43. Network Layer.
Logical addressing:
Logical address is also called IP address which is of 32-bits
and represented in decimal format.
192.168.32.97
Routing:
To route the packets from the source to destination in an
internetwork, the router uses network layer information.
The PDU of network layer is packet.
Network layer protocols are IP, IPX, AppleTalk.
Routing protocol-RIP , OSPF, BGP
Routed Protocol - IP, IPX, AppleTalk

44. which layer ?

45. Which Layer ?

46. Example

47. Network Layer.

48. Network Layer