The document discusses the OSI model and its seven layers, detailing how different protocols work together to facilitate network communication. It explains the roles and responsibilities of each layer, ranging from the physical layer that handles raw bit transmission to the application layer that provides services to end-user applications. The content emphasizes the importance of layered architecture in simplifying communication processes and interoperability between different systems.

1. OSI MODEL
MS(CS)
IIUI

2. PROTOCOL STACK
• Protocol Stack is a combination of different protocol.
• All these protocols works together to perform specific task.
• Every Layer Hs different protocol.
• We discuss aboouut layer
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3. LAYERED TASK
•We use the concept of layers in our daily life.
•As an example would two friends who communicate
through postal email.
•The process of sending a letter to a friend would be
complex if there are no service available from the post
office
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4. LAYERED TASK
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Sender Receiver
The letter is written put in an
envelope, and dropped in a
mailbox
The letter is delivered to
carrier by the post office
The letter is carried from the
mailbox to a post office
The letter is picked up,
removed from the envelop,
and read
The letter is delivered to
carrier by the post office
The letter is carried from the
mailbox to a post officeMiddle Layer
Lower Layer
Higher Layer
Parcel is Carried from the source to the destination

5. THE OSI MODEL
• ISO is an organization which is established in 1947.
• AN ISO standard that covers all aspects of network
communication.
• Network communication model is defined in OSI.
• It was first introduced in the late 1970s, 1983
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6. ISO is the organization.
OSI is the model.
Note
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7. WHY OSI MODEL
• OSI model decide how different equipment from different
vendors can communicate with one another
• Communication process is divided into different subtasks.
• Using OSI model NETWORK HARDWARE and SOFTWARE
can easily communicate with one another.
• If any kind of change is required then it occurs only in
required layer.
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8. 7 LAYERS OF OSI MODEL
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Application
Network process to Application
Presentation
Data Representation and Encryption
Session
Interhost Communication
Transport
End to End Connection and Reliability
Network
Path Determination and IP(Logical) Add.
DataLink
MAC and LLC(Physical Addr)
Physical
Media, Signal and Binary Transmission Send Packet in the form of BITS
Error Checking and Physical Connection
Sequencing and Address Information
Errors Control
Traffic Flow Information
Formatting and Encryption of Packets data
Accept request to Communicate
DATA
DATA
DATA
Segment
Packets
Frames
Bits

9. MNEMONICS
•The following mnemonics may help you remember
the layers sequence and names.
•All People Seems To Need Data Processing.
•Please Do Not Take Sales People’s Advice.
•People Design Networks To Send packets
Accurately
•Always Put Some Thoughts Into Designing
Programs.
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10. LAYERING AND INTERNETWORKING
•Communication environments separate the
networking functions and application processing
are called LAYERING.
• OSI divides the big task of host-to-host
networking called INTERNETWORKING in to a
vertical stack.
• This OSI stack contains the seven numbered layers
,these indicate distinct functions.
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11. CLIENT AND SERVER
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Application
Presentation
Session
Transport
Network
Datalink
Physical
Client Server
Application
Presentation
Session
Transport
Network
Datalink
PhysicalPhysical Link
Logical Link

12. SK Ahsan Figure:The interaction between layers in the OSI model
OSI Layers Interaction

13. SK Ahsan
Transmission Medium
Figure: An exchange using the OSI model

14. ARCHITECTURE DESCRIPTION
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15. PHYSICAL LAYER
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16. PHYSICAL LAYER
• It transmits data over physical medium or on network like
hardware like cables, cards, electrical, optical, mechanical
and functional interface to the medium.
• It handles the transmission of raw bits over a
communication link.
• It is responsible for transmitting bit(ZERO and ONE) by
providing signaling of the message and the interface
between the sender or receiver and the medium.
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17. PHYSICAL LAYER
• Physical Layer must decide the following
• Characteristics of Media
• Representation of Bits
• Data Rate
• Synchronization
• Line Configuration
• Transmission Mode
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18. The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
Note

19. DATALINK LAYER
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20. DATA LINK LAYER
• Frames not raw bits are actually delivered to the host.
• The data link layer is responsible for moving frames from
one hop (node) to the next.
• Manage physical layer communication between
connecting systems.
• It is responsible for providing node to node
communication on a single, local network.
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21. HOP TO HOP DELIVERY
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22. FUNCTIONS OF DATA LINK LAYER
• It must provide an address mechanism that enable messages to be delivered
to the correct nodes.
• Data units at the Data Link layer are most commonly called frames, although
the term packets is used with some protocols.
• The single layer actually incorporates two sub-layers as IEEE Logical Link
Control Model.
• The Lower of the two sub-layers is called the MAC and the upper sub-layer is
the LLC.
• The MAC layer provides local addressing. Error correction and in some
cases includes a field to distinguish the frame type from the other types.
• Example of Data Link Standards include frame relay, ETHERNET, Token Ring
and FDDI.
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23. DATA LINK LAYER
•Datalink layer must decide the following
•Framing
•Flow control
•Error Control
•Access Control
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24. The data link layer is responsible for moving
frames from one hop (node) to the next.
Note

25. NETWORK LAYER
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26. SOURCE TO DESTINATION DELIVERY
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27. NETWORK LAYER
• The network layer handles routing among nodes within a
packet switched network.
• The network layer operates independently of the physical
medium, which is a concern of the physical layers.
• Routers are network layer devices, they can be used to
forward packets between physically different networks.
• It adds a header to the message that includes the source and
destination network address.
• This combination of data plus the network layer is called a
PACKETS
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28. NETWORK LAYER
• It translates logical addresses and names into physical addresses for
Packets Delivery.
• The addressing which makes this delivery can be thought of as a
universal address as compared to the local addressing of the MAC.
• It determines routes for sending, managing network traffic problems,
packet switching, routing, data congestion and reassembling data.
• It control end-to-end flow of segmentation and reassembly functions
of large packets of data which exceed the Maximum Transmission
Units.
• The Internet Protocol(IP) is the most common example.
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29. NETWORK LAYER
•Some responsibilities of the network layer are
as follows
•Logical Addressing
•Routing
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30. The network layer is responsible for the
delivery of individual packets from
the source host to the destination host.
Note

31. TRANSPORT LAYER
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32. RELIABILITY
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33. TRANSPORT LAYER
• It translates system names into addresses.
• The unit of data exchange is commonly called MESSAGE rather than a
packet or frame.
• It divides messages into fragments that fit within the size limitation
established by the network.
• It allows users to segments/reassemble several upper layer application on
to the same transport data stream.
• It ensure host to host session connection.
• This layer is responsible for addressing, determining network traffic
problems, packet switching, routing, congestion and reassembling data at
receiving end to recover the original message.
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34. TRANSPORT LAYER
• It ensures that the segments delivered will be acknowledge back too the
sender.
• It provides retransmission of segments those are not acknowledged.
• Puts segments back into their correct sequence at the destination.
• To enable packets reassemble in their original order, this layer include a
MESSAGE SEQUENCE NUMBER in its header.
• Sometimes it provides a multiplexing between the same two end-points.
• Delivery may be GUARANTEED or CONNECTION-ORIENTED streams like
TCP or UDP
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35. TRANSPORT LAYER
•It is also responsible for delivering message from a
specific process on one computer to the
corresponding process on the destination computer.
•Transport layer assigns a service access point to
each packet. In TCP/IP terms that is called PORT.
•One more responsibility of the transport layer is
DETECTING ERRORS In transmitting data.
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36. TRANSPORT LAYER
•Some responsibilities of the transport layer are as
follows
•Service Point Addressing
•Segmentation and Re-assembly
•Connection Control
•Flow Control
•Error Control
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37. The transport layer is responsible for the delivery
of a message from one process to another.
Note

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39. SESSION LAYER
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40. SESSION LAYER
• It establishes, manages and terminates session between application.
• It provides mechanism for managing end-user, host, process operations
termination and restart procedures.
• It is responsible for dialog control between nodes. Dialog is a formal
conversation in which two nodes agree to exchange data.
• The communication across a network can take place and controlled in one of
three dialog modes are simplex, Half Duplex and Full Duplex.
• Testing for out-of-sequence packet is handles also.
• Session enables communication in organized manner in three phases as
Connection Establishment, Data Transfer and Connection Release.
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41. PRESENTATION LAYER
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42. PRESENTATION LAYER
• This layer provides data communication and code formatting.
• It provides a way for a remote host to inform the local client how to
present the data to the application or client.
• It ensures that the data that arrives from the network can be used by the
application, and information send by the application can be transmitted
on the network.
• It directly translates data from one format to another.
• It provides data encryptioiin, decryption, compression and
decompression.
• It delivers and format information for application layer processing.
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43. PRESENTATION LAYER
•Presentation Layer perform the following
•Data Reformatting
•Encryption
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44. The presentation layer is responsible
for translation, compression, and
encryption.
Note

45. APPLICATION LAYER
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46. APPLICATION LAYER
• The application layer provides different services to user application.
• It interfaces directly to these services and provide conversion between
associated application process.
• It contains a variety of protocols that are commonly needed.
• Another application layer function is file transfer.
• Different file system have different file naming conventions.
• Transferring a file between two different system requires handling all
incompatibilities.
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47. APPLICATION LAYER
•Application Layer provide different information
services as
•File Transfer
•Mail Services
•Directory Services
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48. The application layer is responsible for
providing services to the user.
Note

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50. SUMMARY

51. REFERENCES
• Behroz A Frozen, Textbook Chapter 2, Topic 2.1, 2.2
• Larry and Peterson, Textbook Chapter 1
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52. ABOUT
• Sunawar Khan Ahsan
• Sk_ahsan38@yahoo.com
• +923334892200
• More Slides Find on Slide Share
• facebeek.com/sk.ahsan.ms
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