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Computer Networks - Layers in OSI Model
1. LAYERS IN THE OSI
MODEL
Open System Interconnection Layers-
An Interactive Study
2. •The application layer enables the user (human or software) to
access the network by user interfaces and support for services.Application
•The presentation layer is responsible for translation, compression
and encryption.Presentation
•The session layer is responsible for dialog control and
synchronizationSession
•The transport layer is responsible for the delivery for a message
for one process to another.Transport
•The network layer is responsible for the delivery of individual
packets from the source host to the destination host.Network
•The data link layer is responsible for moving frames one hop
(node) to the next.Data Link
•The physical layer is responsible for movements of individual bits
from one hop(node) to the next.Physical
A BRIEF OVERVIEW -
4. LET’S SEE WHAT
HAPPENS WHEN RAJ
SENDS HIS MESSAGE
Let his message be DATA-MESSAGE
DATA-MESSAGE
5. The application layer provides services to the user such as –
■ Network Virtual Terminal – via SSH/ Telnet +Putty/ CygWIN
■ File transfer, access and management –via FTP/SAMBA/AFP/DLNA
■ Mail Services via SMTP, IMAP, POP3
■ Directory Services for accessing global information about objects and services
via HTTP/HTTPS
H7 DATA-MESSAGE
6. The presentation layer handles the semantics and syntax of the information
exchanged between systems.
■ Translation– Encodes/Decodes machine-dependent format of encoded bit-
streams to/from a common format.
■ Encryption & Decryption of sensitive information.
■ Compression
H7 DATA-MESSAGE
H6 DATA
7. The session layer is the network
dialog controller. It establishes,
maintains, and synchronizes the
interaction among communicating
systems.
It’s responsibilities include
■ Dialog Control by allowing
communication between two
processes to take place in either
half-duplex mode or full-duplex
mode.
■ Synchronization by utilization of
synchronization checkpoints.
H6
H5 DATA
H7 DATA-MESSAGE
8. The transport layer is responsible for process-
to-process delivery of the entire message.
■ Service- point addressing ( i.e. port
addressing services to ports e.g. FTP to )
■ Segmentation and reassembly of the
divided message, in form of
transmittable segments, each with a
unique sequence number.
■ Connection Control – Connectionless or
Connection-Oriented
■ Flow Control performed end-to-end.
■ Error Control performed process-to-
process.
Error Correction is usually performed by re-transmission of segments.
H6
H4 DATA
H7 DATA-MESSAGEH5
9. The network layer is responsible for the
source-to-destination delivery of a packet,
possible across multiple links. It ensures that
the packet gets delivered from it’s point of
origin to it’s final destination.
It is not essential when two systems are
connected end-to-end, i.e. to the same link.
■ Logical Addressing – for packets that are
sent outside the network boundary, to
distinguish source and destination
systems. It adds a header that include
logical address of sender and receiver.
■ Routing – to route/switch the packets to
their final destination from a sender.
H6H4
DATA
H7H5 DATA-MESSAGE
H3
10. The data link layer transforms the physical layer
into a reliable link. It makes the physical layer
appear error-free to the upper layers ( network
layer ).
It’s responsibilities include -
■ Framing- Dividing the stream of bits from
network layer into frames.
■ Physical Addressing –Adding headers to a
frame to define sender and/or receiver.
■ Flow Control – To prevent overflow of the
receiving mechanism of receiver.
■ Error Control (Encapsulation)– Detecting and
retransmitting lost frames by adding a tail.
■ Access Control – To determine control over
link.
H6H4
DATA
H7H5 DATA-MESSAGEH3
H2 T
11. The physical layer coordinates the functions required to carry a
bit stream over a physical medium.
It defines the procedures and functions that physical devices
and interfaces have to perform for the transmission to occur.
It is characterized by –
■ Physical characteristics of the medium
■ Representation of bits, i.e. encoding
■ Data Rate/Transmission Rate ( number of bits/sec)
■ Synchronization of bits – by synchronization of sender and
receiver clocks
■ Line Configuration – Connection of device to media
■ Physical Topology
■ Transmission Mode (simplex/full-duplex/half-duplex)
H6H4
DATA
H7H5 DATA-MESSAGEH3
H1
TH2
12. NOW, LET’S SEND THE
MESSAGE TO THE
RECEIVER
Here’s what the message looks like so far -
H6H4 H7H5 DATA-MESSAGEH3H1 TH2
13. The physical layer coordinates the functions required
to carry a bit stream over a physical medium.
H6H4
DATA
H7H5 DATA-MESSAGEH3
H1
TH2
14. The data link layer transforms the physical
layer into a reliable link. It makes the
physical layer appear error-free to the
upper layers ( network layer ).
It checks and decodes now, removing the
tail. ( ERROR CORRECTION IS MAINLY
PERFORMED BY ASKING FOR RE-
TRANSMISSION).
H6H4
DATA
H7H5 DATA-MESSAGEH3
H2 T
15. It get’s the addressing information of the
receiver from from the header H3.
H6H4
DATA
H7H5 DATA-MESSAGE
H3
16. The transport layer is responsible for
process-to-process delivery of the entire
message at the receiving end.
It manages the services and is
responsible for re-assembling packets
according to the sequence id of packets
derived from the H4 HEADER.
Error Correction is usually performed by re-transmission of segments.
H6
H4 DATA
H7 DATA-MESSAGEH5
17. The session layer is the network dialog
controller. It establishes, maintains, and
synchronizes the interaction by use of
information checkpoints contained
according to H5 Header.
It also determines the mode of connection
according to the header.
H6
H5 DATA
H7 DATA-MESSAGE
18. The presentation layer handles the semantics and syntax of the information
exchanged between systems. Based on information from the H6 Header it performs -
■ Translation– Decodes common format encoded bit-streams to machine-
dependent format.
■ Decryption of sensitive information
■ De-Compression
H7 DATA-MESSAGE
H6 DATA
19. The application layer provides services to the recieving user such according to the
application used.
The information about the application to be used is derived from the H7 Header.
H7 DATA-MESSAGE
20. HERE IS THE MESSAGE
TO THE RECIVER-
DATA-MESSAGE
22. THANK YOU FOR WATCHING THE
PRESENTATION!
BIBLIOGRAPHY
• Data Communications and Networking (4TH Edition), McGraw Hill Education, Behrouz A.
Foruzan
OTHER SOURCES OF INFORMATION-
• Dr. Mydhili K. Nair , Department of Information Science and Engineering, M.S. Ramaiah
Institute of Technology, Bangalore, India
Presentation made by –
Shreyash Agarwal,
Student, Information Science and Engineering
M.S. Ramaiah Institute of Technology
