The document describes the seven layers of the OSI model. It explains each layer from the physical layer at the bottom to the application layer at the top. The physical layer deals with electrical signals and hardware transmission. The data link layer handles encoding and decoding data into bits. The network layer provides routing and addressing. The transport layer ensures reliable data transfer. The session layer organizes data exchange. The presentation layer resolves syntax differences. And the application layer provides user services like file transfer.

2. Seven Layer of OSI Model

3. OSI reference model
 Open System Interconnection (OSI)
represents a generalization of concept
of inter-process communication so
that any open system may be
technically able to communicate with
another open system.
 In the OSI reference model, the
communication functions are divided
into a hierarchy of seven layers. It
also referred to as 7-layer model.
 The transmission medium is not
included in the seven layers and it
can be regarded as 0th layer.

4. Layer Architecture of the OSI Reference Model

5.  The Application Layer the seventh layer in
OSI network model.
 Application Layer is the top-most layer of
the seven layered Open Systems
Interconnection (OSI) network model.
 As the highest layer in the OSI model, the
application layer provides services to the
user of the OSI environment.

6. Application Layer
•Login , password checking, file transfer
are some of the functions of the
application layer.
•. Real traffic data will be often
generated from the Application Layer.
This may be a web request generated
from HTTP protocol, a command from
telnet protocol, a file download request
from FTP protocol etc.

7.  The purpose of the presentation layer is
to present the information to
communicating application entities in a
way that preserves the meaning while
resolving the syntax differences.
 There are three syntactic version of data
being transferred, the syntax used by the
application entity of the originator of the
data, the syntax used by the recipient of
the data, and the “transfer” syntax used
to transfer the data between presentation
entities.

8. Application layer
Presentation layer
Transfer syntax
Local syntaxLocal syntax
Local and transfer syntax of the presentation layer

9.  The purpose of the session layer is to
provide the means necessary for the
cooperating presentation entities to
organize and synchronize their data
exchange.
 The session layer provides two-way
simulaneous, two-way alernate, and
one-way communication services.

10.  Transport layer provides transparent
transfer of data between end systems,
or hosts, and is responsible for end-to-
end error recovery and flow control. It
ensures complete data transfer.
 Layer 4 Transport examples include
SPX, TCP, UDP.

11. Network layer
 Network layer
provides switching and routing technolo
gies, creating logical paths, known
as virtual circuits, for transmitting data
from node to node. Routing and
forwarding are functions of this layer, as
well as addressing,internetworking, error
handling, congestion control and packet
sequencing.
 Layer 3 Network examples include
AppleTalk DDP, IP, IPX.

12. Data link layer
 At this layer, data packets
are encoded and decoded into bits.
 The data link layer is divided into two
sub layers: The Media Access Control
(MAC) layer and the Logical Link
Control (LLC) layer
 Layer 2 Data Link examples include
PPP, FDDI, ATM, IEEE 802.5/ 802.2,
IEEE 802.3/802.2, HDLC, Frame
Relay.

13. Physical layer
 Physical layer conveys the bit stream -
electrical impulse, light or radio
signal — through the network at the
electrical and mechanical level.
 It provides the hardware means of
sending and receiving data on a
carrier, including defining cables,
cards and physical aspects.

14. Physical layer

15. Physical layer
 The bottom-most layer of the Seven
Layers of Open Systems
Interconnection (OSI) Model is
Physical Layer.
 Fast Ethernet,RS232,
and ATM are protocols with physical
layer components.