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.
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
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
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
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
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
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
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