OSI Reference Model

1. DCCN PPT
ON
OSI REFERNCE(7
LAYER)MODEL
BY
Bhargavi and group
DECE

2. An open system is a set of protocols that allow two
different systems to communicate regardless of their
Open Systems Interconnection Open Systems
Interconnection (OSI) it is a networking model which
is fundamental to all communications between network
devices
It is now the theoretical model for how communication
takes place between network devices.

3. The OSI reference model is an arbitrary hierarchical
stratification (layering) of computer networking
functions. The stratification consists of seven layers.

4. The OSI Reference Model
The OSI reference model consists of seven layers, not including layer 8, the
end user’s application, and layer 0 the physical transmission media.
8. O/S or User Application
0. Physical Transmission Media

5. THE SEVEN OSI
REFERENCE MODEL
LAYERS

6. LAYER 1: PHYSICAL
 The physical layer deals with the physical
characteristics of the transmission medium. and it
sends the data in the form
of raw bits
 It defines the electrical, mechanical, procedural,
and functional specifications for activating,
maintaining, and deactivating the physical link
between end systems.
 .

7. FUNCTIONS
It controls the define voltages and bit rates needed for
transmission
 This layer manages the interface between the computer and
the network medium (coaxial cable, twisted pair)
 It is the bottom layer of the OSI model

8.  1.Signal encoding
 2.Bit synchronization
 3.transmission type
 4.topology
 5.Transmission media
 Multiplexing
 Interface 6. Bandwidth 7.Signal type

9. Layer 2 : DATA LAYER
This layer takes the data frames (or) messages from the
layer and provides their actual transmission
A message is a block statement such as ok (or) yes,
which denotes positive (or) negative
acknowledgement (or) request for repeating such as
“come again” (or) pardon me .
At the sending end this layer handles conversion of
data into raw formats that can be handled by the
Physical Layer

10. Data Link Layer
 synchronization
 To take packets from the upper layer and converting
them into frames
 To take bits from lower and converting them into packet
 Error detection and control
 Framing
 0
10110110101 10110000001
0110001011

11. DATA LINK LAYER

12. LAYER 3: NETWORK
 Defines end-to-end delivery of packets.
 It receives the packets from transport layer
and converts them into frames
 Defines how routing works and how routes are
learned so that the packets can be delivered.
 It is responsible for sending the data to
destination node by choosing the data

13. NETWORK LAYER

14.  Establishing the connection
 Releasing the connections
 Sending the data
 This layer also handles packet switching and network
congestion control

15. LAYER 4: TRANSPORT
 If once it receives the data from session layer
it splits the data into packets
 After dividing it adds sequence to the packets
 It is responsible for error control and flow
control

16. The Transport Layer
DIAGRAM

17.  ERROR CONTROL: while transmitting the data if
they are errors in the data which is been sent to the
destination node it detects and controls the error and
resends the data to the node
 FLOW CNTROL: when the data is sent . The form of
data sending should be maintained currently for
acknowledgement

18. LAYER 5: SESSION LAYER
 When once the data is received from the presentation layer it
is converted in the form of sessions
 Again this sessions are divided into sub sessions
 It avoids the retransmission by adding the checking point
feature if the system craches (or) power failures last checking
point substation re-trasnmitts the left data but not the entire
data again
 At destination side it receives the data from the transport layer
and handovers the data to the presentation layer
 Whenever it is divided into substations it adds the sequence
number

20. The Session Layer
 Responsibilities:
 establishes, manages, and terminates
sessions between applications.
 service location lookup

21.  Responsible for security and access control to
session information (via session participant
identification)
 Responsible for synchronization services
(checkpoints)

22. LAYER 6: PRESENTATION
 It provides compression of data
 It is concerned with Semantics and syntax of
the information
 Provides compression of data
 It is responsible for
 Data Encoding
 Data Compression
 Data conversion

23. The Presentation Layer
 Responsibilities:
 data encryption
 data compression
 data conversion

24. PRESENTATION LAYER

25.  Data Encoding: The data is encoded i.e if one node
(source node) supports ASCII format, Destination
node may support UNICODE format and at this time
the data is transmitted in the form of UNCODE even
the source node supports ASCII format
 Compression: The data is compressed before sending
it to the destination node, here the data is compressed
in the destination layer
 This layer is also responsible for certain protocol
conversions, data encryption/decryption, or data
compression/decompression.

26. LAYER 7: APPLICATION
The top layer of the OSI model
The container which contains various types of protocols i.e
www, http is called application layer
If once it is connected to the protocol it handovers to the
presentation layer

27. APPLICATION LAYER

28. The application layer is the closest to the user.
 It provides network access to the user.
 It differs from the other layers in that it does not
provide services to any other OSI layer, but rather,
only to applications outside the OSI model.
 Examples of such applications are spreadsheet
programs, word processing programs, and bank
terminal programs.

29. Sending Computer Receiving Computer
User User
Application Application
7 Application 7 Application
6 Presentation 6 Presentation
5 Session 5 Session
Transmission Media
4 Transport 4 Transport
3 Network 3 Network
2 Data Link 2 Data Link
1 Physical 1 Physical

30. EXAMPLE FOR OSI
REFERENCE MODEL
FUNCTIONING