3. LAYER 7: APPLICATION
• The top layer of the OSI model
• The application layer is the OSI layer that is closest to
the user.
• It provides network services to the user’s applications.
• Examples of such applications are spreadsheet
programs, word processing programs, and bank
terminal programs.
4. LAYER 7: APPLICATION
• 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.
• The application layer establishes the availability of
intended communication partners, synchronizes and
establishes agreement on procedures for error recovery
and control of data integrity.
5. LAYER 7: APPLICATION
• Purpose
– User application to network service interface
– The application layer is responsible for
providing services to the user.
• Examples
– File request from server
– E-mail services
– etc.
7. Examples
• Browsers:
– Mozilla Firefox, Internet Explorer, Google Chrome
etc
• Email clients:
– Gmail, Hotmail, Yahoomail and etc.
• FTP clients :
– Filezilla, sFTP, vsFTP
8. Application Layer Protocols
• SNMP (Simple Network Management Protocol):—
Allows control of networked devices.
• TFTP (Trivial File Transfer Protocol):— Simple,
lightweight file transfer.
• DNS (Domain Naming System):— Translates a
website name (easy for people) to an IP address (easy
for computers).
• DHCP (Dynamic Host Configuration Protocol):—
Assigns IP, mask, and DNS server (plus a bunch of
other stuff) to hosts.
9. Application Layer Protocols
• Telnet :— Provides a remote terminal connection to
manage devices, which you are not close enough to use
a console cable.
• HTTP (Hypertext Transfer Protocol):— Browse web
pages.
• FTP (File Transfer Protocol):— Reliably
sends/retrieves all file types.
• SMTP (Simple Mail Transfer Protocol):— Sends
email.
• POP3 (Post Office Protocol v.3):— Retrieves email.
• NTP (Network Time Protocol):— Synchronizes
networked device clocks.
10. LAYER 6: PRESENTATION
• The presentation layer ensures that the information
that the application layer of one system sends out is
readable by the application layer of another system.
• If necessary, the presentation layer translates between
multiple data formats by using a common format.
• Provides encryption and compression of data.
• Examples :- JPEG, MPEG, ASCII, EBCDIC, HTML.
11. LAYER 6: PRESENTATION
• Purpose
– Formats data for exchange between points
of communication
• Ex: Between nodes in a network
• Example:
– Redirector software
• Formats for transmission to the server
13. Presentation Layer Function
• Protocol conversion
• Data translation
• Encryption
• Character set conversion
• Expansion of graphics command
14. LAYER 5: SESSION
• The session layer defines how to start, control and end
conversations (called sessions) between applications.
• This includes the control and management of multiple bi-
directional messages using dialogue control.
• It also synchronizes dialogue between two hosts'
presentation layers and manages their data exchange.
• The session layer offers provisions for efficient data
transfer.
15. LAYER 5: SESSION
• Purpose
– Oversee a communication session
• Establish
• Maintain
• Terminate
• Example
– ASP(AppleTalk Session Protocol)
16. Session Layer Function
• Performs name recognition and related security
• Synchronization between sender and receiver
• Assignment of time for transmission
– Start time
– End time etc.
17. LAYER 4: TRANSPORT
• The transport layer regulates information flow
to ensure end-to-end connectivity between host
applications reliably and accurately.
• The transport layer segments data from the
sending host's system and reassembles the data
into a data stream on the receiving host's
system.
18. LAYER 4: TRANSPORT
• The boundary between the transport layer and the
session layer can be thought of as the boundary
between application protocols and data-flow protocols.
Whereas the application, presentation, and session
layers are concerned with application issues, the lower
four layers are concerned with data transport issues.
• Layer 4 protocols include TCP (Transmission Control
Protocol) and UDP (User Datagram Protocol).
19. LAYER 4: TRANSPORT
• Purpose
– Repackage proper and efficient delivery of
packages
• Error free
• In sequence
• Without duplication
20. Transport Layer Function
• For sending data
– Repackage the message to fit into packets
• Split long messages
• Assemble small messages
• On receiving data
– Perform the reverse
– Send an acknowledgment to the sender
• Solve packet problems
– During transmission and reception
21. Transport Layer Function
• Main functions
– Segmentation
– Connection Management
– Reliable and Unreliable data delivery
– Flow control
– Connection Multiplexing
22. Segmentation
• Segmentation is the process of breaking large data file
into small manageable size that the network can
accommodate. To understand this in easy way, think
about a 700 MB movie that you want to download
from internet. You have 2MBPS internet connection.
How will you download a 700MB movie on 2MBPS
internet connection ?. And the answer is segmentation
process. On server transport layer breaks 700MB
movie in smaller size of segments (less than your
internet connection speed) that your PC can easily
download. Once your browser received all segments
from server, it pop up a message indicating download
completed.
23. Connection Management
• Transport layer setup, maintain and tear down
connections for session layer. Actual mechanic
of connection is controlled by transport layer.
Transport layer use two protocols for
connection management UDP and TCP.
24. UDP
• UDP is connection less protocols. Connection-
less transmission is said to be unreliable. Now,
don't get worried about the term "unreliable"
this doesn't mean that the data isn't going to get
its destination; it only means that it isn't
guaranteed to get its destination.
25. TCP
• TCP is connection oriented protocols.
Connection-oriented transmission is said to be
reliable.
27. Reliability
Once connection established data transmission is
initiated. To provide maximum reliability it cover
these items :
• Detect lost packets and resend them
• Detect packets that arrived out of order and reorder
them
• Recognize duplicate packets and drop extra packet
• Avoid congestion by implementing flow control
28. Flow Control
The transport layer can implement two
flow control methods:
• Ready/not ready signals
• Windowing
29. Ready/not ready signals
• In this method sender sends data according to
its buffer size. Receiver receives data in its
buffer. When receivers buffer get filled, it send
a not ready signal to sender, so sender can stop
transmitting more segments. Receivers send
ready signal when it become ready to receive
next segment. There are two problems with the
use of ready/not ready signals to implement
flow control.
30. Windowing
• In windowing a window size is defined between sender
and receiver. Sender host will wait for an
acknowledgement signal after sending the segments
equal to window size. If any packet lost in way
receiver will respond with acknowledgement for lost
packet. And sender will send lost packet again.
Window size is automatically set during the three step
handshake process. It can be adjust anytime throughout
the lifetime of connection.
31. Connection Multiplexing/
Application Mapping
• Connection multiplexing features allow multiple
applications to connect at once. For example a server
performs a number of functions like email, FTP, DNS,
Web service, file service, data service etc. Suppose
server has a single IP address, still it can perform all
these different functions for all the hosts that want to
connect with it. To make this possible transport layer
assigns a unique set of numbers for each connection.
These numbers are called port or socket numbers.
These port number allows multiple applications to
simultaneously send and receive data.
32. Port
Port numbers are divided into ranges. Following are the
current port ranges:
• 0–1023
– Well-Known—For common TCP/IP functions and
applications
• 1024–49151
– Registered—For applications built by companies
• 49152–65535
– Dynamic/Private—For dynamic connections or
unregistered applications
34. Remember
• A convenient aid for
remembering the OSI layer
names is to use the first letter of
each word in the phrase:
• All People Seem To Need
Data Processing
35. SUMMARY
• There was no standard for networks in the early days
and as a result it was difficult for networks to
communicate with each other.
• The International Organisation for Standardisation
(ISO) recognised this. and researched various network
schemes, and in 1984 introduced the Open Systems
Interconnection (OSI) reference model.
• The OSI reference model has standards which ensure
vendors greater compatibility and interoperability
between various types of network technologies.
36. SUMMARY
• The OSI reference model organizes network functions
into seven numbered layers.
• Each layer provides a service to the layer above it in the
protocol specification and communicates with the same
layer’s software or hardware on other computers.
• Layers 1-4 are concerned with the flow of data from
end to end through the network and Layers 5-7 are
concerned with services to the applications.
37. Definition of terms
• SNMP (Simple Network Management Protocol):— Allows control of
networked devices.
• TFTP (Trivial File Transfer Protocol):— Simple, lightweight file
transfer.
• DNS (Domain Naming System):— Translates a website name (easy for
people) to an IP address (easy for computers).
• DHCP (Dynamic Host Configuration Protocol):— Assigns IP, mask,
and DNS server (plus a bunch of other stuff) to hosts.
• Telnet :— Provides a remote terminal connection to manage devices,
which you are not close enough to use a console cable.
• HTTP (Hypertext Transfer Protocol):— Browse web pages.
38. Definition of terms
• FTP (File Transfer Protocol):— Reliably sends/retrieves all file types.
• SMTP (Simple Mail Transfer Protocol):— Sends email.
• POP3 (Post Office Protocol v.3):— Retrieves email.
• NTP (Network Time Protocol):— Synchronizes networked device
clocks.
• UDP - is connection less protocols.
• Connection-less transmission - is said to be unreliable.
• TCP - is connection oriented protocols.
• Connection-oriented transmission - is said to be reliable.
• Segmentation - is the process of breaking large data file into small
manageable size that the network can accommodate
39. Definition of terms
• Encryption - is the most effective way to achieve data security.
• Decryption - is the process of converting encrypted data back into its
original form, so it can be understood
• Packet - A packet is the unit of data that is routed between an origin and
a destination on the Internet or any other packet-switched network.
• APS - (AppleTalk Session Protocol)
• Redirector - A special software facility called a “redirector” operates at
this layer to determine if a request is network related on not and forward
network-related requests to an appropriate network resource