The document discusses the OSI reference model, which defines seven layers for network communication between devices. It describes each layer and its functions, with a focus on the application, presentation, and network layers. The OSI model provides standardization for network communication and troubleshooting by dividing the communication process into these defined layers.

1. Created and Presented By:
Anis Mizi
Student of CSE (Stamford University Bangladesh)
49th Batch
Email:fulsuccess9@gamil.com
Facebook: https://www.facebook.com/mizianis

2. OSI REFERENCE MODEL
• OSI-Open Systems Interconnection
• OSI was developed by the International
Organization for Standardization (ISO) and
introduced around 1980.
• The main intention of OSI model is defining
how the communication happens between
two or more network devices
• It is a layered architecture (consists of seven
layers) which defines and explains how the
communication happens in between two or
more network devices within the organization
or internet.
• Each layer defines a set of functions in data
communication.

3. OSI REFERENCE MODEL(continues)
• OSI tells how the communication happens
between two or more devices
• It provides Standardization
• Example=Pc>Switch>Router>Isp>Internet>yah
oo.com server
• Internet is biggest public network where
everyone is network
• The reply comes back to pc. This process
happens in milliseconds
• There are lot of devices and processes in this
reply which ensures the communication is
perfect.

4. OSI REFERENCE MODEL(continues)
• Pc is my source and yahoo.com is my destination
• How OSI defines standardization- example with
each device of the process(router,
switch,computer(web application-
IE,mozilla,chorome))
• This entire process is divided into layers which is
called layered architecture
• Total 7 layers. Each and every layers defines a set
of functions
• Advantages of OSI model
 Troubleshooting
 Standardization(router, switch,motherboard
example)- everything should be standardized
 Different routers problem without
standardized(compatibility issues)

5. OSI REFERENCE MODEL(continues)
• Advantages of OSI model
 Troubleshooting
 Standardization(router, switch,motherboard
example)- everything should be standardized
 Different routers problem without
standardized(compatibility issues)
• OSI model basics for CCNA exam
• 7 layers example
• Top 3 layers happens inside our pc, inside
application in general.
• First three layers hardware layers because of
hardware devices are involved here
• Example, router(layer 3),switch(layer
2),cables,hubs(layer 1) are involved
• There are no devices involved in top 3 layers

6. OSI REFERENCE MODEL(continues)
• Transport layer is core layer of OSI which
interconnects the hardware layers and
software layers
• We should remember the layer number for
CCNA exam. Example layer 5(Session layer)
• You may be asked which device works on
which layer or layer number. Example, router
on Layer 3(Network layer)

7. Application Layer(Layer 7)
• Application Layer is responsible for providing
an interface for the users to interact with
application services or Networking Services.
Ex: Web browser etc.
• Identification of Services is done using Port
Numbers.
• Port is a logical communication Channel
• Port number is a 16 bit identifier.
• Total No. Ports 0 – 65535
• Reserved Ports 1 - 1023
• Unreserved Ports 1024 – 65535

8. Application Layer(Layer 7)(continues)
• Example of internet
• Whenever we try to access a website we need to
initiate the application
• Initiation means typing the url on web browser
application not in notepad or other documents
• We can use any browsing program like mozilla,
chrome, safari, opera etc
• These browsing programs will allow us to access
web pages
• Generally we see the browsing programs but
internally http will do the job for accessing
website

9. Application Layer(Layer 7)(continues)
• We generally see http://www.xyz.com
• http is inbuilt protocol inside TCP/IP
• Similarly ftp, smtp/pop3 etc protocols
• Application layer is going to provide an user
interface
• These browsing programs are providing the
interface. But the backend protocol is http,
ftp, smtp etc
• So this is the job of Application layer which
provides an user interface

10. Application Layer(Layer 7)(continues)
• We can change the port numbers
• Web server administrator can change the port
number
Service Port No.
HTTP 80
FTP 21
SMTP 25
TELNET 23
TFTP 69

11. Presentation Layer(Layer 6)
• After application layer provides the interface, the
next step is presentation layer
• Presentation layer defines specific format of data
to be sent
• If we type www.google.com the http:// is
automatically added
• If we visit a banking website and we log in, it
should be more secured, then we will see https://
added
• Both are http protocol but https is more secured
• For https, the entire content will be encrypted
format. So no one can see or read the
information
• The format depends on the type of the service. It
can be clear text, encrypted text etc

12. Presentation Layer(Layer 6)
• The major function presentation layer defines
in which format your data should go
• This format is defined by source and
destination application
• Compression – Decompression . It works on
Wan links like PPP/HDLC. PPP supports
Compression and HDLC doesn’t
• Depending on the type of links, data can go in
a compressed format or normal format
• These are decided by Presentation layer. It
decides which format the data has to be sent

13. Presentation Layer(Layer 6)(continues)
• Presentation Layer is responsible for defining a
standard format for the data.
• The major functions described at this layer are..
• Encoding– Decoding
Ex: ASCII, EBCDIC (Text)
JPEG,GIF,TIFF (Graphics)
MIDI,WAV (Voice)
MPEG,DAT,AVI (Video)
• Encryption – Decryption
Ex: DES, 3-DES, AES
• Compression – Decompression
Ex: Predictor, Stacker, MPPC