detail description anout osi model

1. © N. Ganesan, Ph.D. , All rights reserved.
Chapter
OSI Reference Model

2. ISO and OSI Defined
• ISO
– International Standards Organization
• OSI
– Open Systems Interconnect/interface

3. OSI Model Background
• OSI model Introduced in 1978 and
revised in 1984 by ISO
• It is first standardization of protocol of
N/W.
• It is also called OSI because it connect
open system.
• Open system means a system that is
open for communication with other
system.

4. OSI Model Background
• It give set of rules , how to different
n/w communicate with each other.
• It used layered approach because it
divide work and assign work to each
layer.
• Protocol is used to implement specific
task.
• Protocol is set of rules.

5. OSI Model Background
• OSI model is called reference model
because it provide reference to
implement network communication.
• It tell just what each layer should do.
• OSI is not a physical model, it is set of
guideline that application developer
can use to create and implement
applications that can run on network.

6. The Layered Approach to
Communication
7. Application
6. Presentation
5. Session
4. Transport
3. Network
2. Data Link
1. Physical

7. Division of Layers
Upper Layers
Lower Layers
Middle Layer
7. Application
6. Presentation
5. Session
4. Transport
3. Network
2. Data Link
1. Physical

8. The Function of a Layer
• Each layer deals with one aspect of
networking
– Ex. Layer 1 deals with the communication media
• Each layer communicates with the adjacent
layers
– In both directions
– Ex: Network layer communicates with:
• Transport layer
• Data Link layer
• Each layer formats the data packet
– Ex: Adds or remove header

9. Role of Layers
7. Application
6. Presentation
1. Physical
Node A
Data Out
Data In
To/from
Node B

10. The Role of Layers in Point-to-
point Communication
7. Application
1. Physical
7. Application
1.Physical
Node a Node b

11. 7. Application Layer function
• This layer provide user interface and
support services.
• It allow user to direct access to
application and n/w services.
• Services include web service(HTTP),
mail service(SMTP,POP3, IMAP), telnet
services(remote login), file service(FTP,
TFTP)

12. 6. Presentation Layer function
• Data formatting is done by this layer
• Presentation layer is responsible for
data encoding/decoding,
encryption/decryption,
compression/decompression
• It is also responsible for user
authentication
• It is also responsible for translation
services

13. 5. Session Layer Function
• Session layer is dialog controller.
• Session layer establish, maintain, and
terminate session between two systems.
• It is also provide synchronization
service.
• Session layer decide transmission type
like.. Simplex, half-duplex, full duplex.

14. 4. Transport Layer Function
• It provide transport( transport
provider).
• It provide end to end connection via
virtual circuit.
• It is responsible for connection less and
connection oriented communication.
• It is also responsible for error detection,
error correction(data recovery), flow
control.

15. 4. Transport Layer Function
• Message is divided into transmittable
segment and reassemble.
• Connection oriented communication is
reliable, secure and provide ack.
Ex. TCP
• Connection less communication is not
reliable, secure and does not provide
ack.
Ex.UDP

16. 3. Network Layer Function
• This layer is responsible for routing.
• Routing means communication
between different network.
• It provide logical addressing which
router use for path determination.
• Using IP, it manage device addressing,
track the address of the devices on the
network and determine the best path to
data transfer.
• It is also responsible for IP to MAC and
Mac to IP Mapping.

17. 2. Data Link Layer Function
• Data link layer is responsible for taking
packet from network layer and put it on
network media .
• It convert packet into frame and vise
versa.
• Data link layer has two sub layers.
1). Logic link control.(LLC)
2). Media access layer(MAC).

18. Data Link Layer Subdivision
• Logical Link Control (LLC) work on IP
– It identify network layer protocol and tells
what to do once frame received.
– Error and flow control
• Media Access Control (MAC) work on
MAC
– It provide access to media using Mac
address.
– It define how to put frame on the media.
– Error detection and error correction , flow
control.

19. 1. Physical Layer Function
• It is responsible for transmit bits over
media.
– Carry data from the h higher layers
• It define following characteristics.
– Electrical
– Mechanical
– Functional
– Example: specify voltage, pin out of cable.

20. Media Access Control
Application
• Network Interface Card driver
NETWORK
SOFTWARE
NETWORK
CARD
NIC Driver
facilitates data
transfer

21. Summary of layers

22. Layer Operations
• At each layer, additional information is
added to the data packet
• An example would be information
related to the IP protocol that is added
at Layer 3

23. Formatting of Data Through the
Layers
Application Header Presentation Header Session Header
Transport HeaderNetwork Header
Data Link Header and Trailer Physical Frame Preamble

24. Data formatting

25. Packet : General Format
Header Trailer
Data
A general concept of packets serves as a prerequisite to
the understanding of the ISO-OSI model.

26. Some Header Information Added at
Various Layers
• Packet arrival information
• Receiver’s address
• Sender’s address
• Synchronization character

27. Data
• Actual data
• May contain error correction code
– Performed on individual characters of the data
– Example: Parity
• Size may vary
– Depending on the protocol
– Example
• 802.3 specifies range of data packet length

28. Tasks involved in sending letter

29. 7 Layers
7. Application Layer
6. Presentation Layer
5. Session Layer
4. Transport Layer
3. Network Layer
2. Data Link Layer
1. Physical Layer
All
People
Seem
To
Need
Data
Processing

30. How Does It All Work Together
• Each layer contains a Protocol Data Unit
(PDU)
– PDU’s are used for peer-to-peer contact
between corresponding layers.
– Data is handled by the top three layers, then
Segmented by the Transport layer.
– The Network layer places it into packets and
the Data Link frames the packets for
transmission.
– Physical layer converts it to bits and sends it
out over the media.
– The receiving computer reverses the process
using the information contained in the PDU.
2

31. Layer 7 Application All user access and net services
Layer 6 Presentation People data formatting
Layer 5 Session Seem Dialogues controller
Layer 4 Transport To Computer Segment TCP and UDP,IPX end to end transport ation and Quality of Servic
Layer 3 Network Need
Router, brouter,
layer 3 switch
Packet
Routable Protocols. (IP,
IPX, AppleTalk) routing
protocol(rip, igrp) IGMP
ICMP, ARP, RARP
ip addressind Path Selection, routing
Data Protocols Words to Remember
OSI
Model
Layer
Pneumonic devices
OSI Model
layer and
har
Layer 1 Physical Processing
Repeater, Hub
(Multi-port),
Cabling
Bit
Layer 2 Data
Bridge (2 Ports) or
Switch and NIC,
intelligent hub
Frame
Data Link
-MAC
-LLC
protocol defined by
underlying network
bit transmission over media
Computer Data
FTP, Telnet, SMTP,
SNMP, DNS
making bits to frame and host to host delievery
protocol defined by
underlying network