1. © 2003, Cisco Systems, Inc. All rights reserved.

2. OSI Reference Model

3. ISO / OSI / IOS ISO : International Organization for Standardization
OSI : Open System Interconnect
　　　（Reference Model）
IOS : Internetwork Operating System

4. The OSI Reference Model
The ISO created and released the OSI reference model in 1984 to provide vendors with a set of standards to ensure greater compatibility and interoperability between various types of network technologies.
The OSI reference model reduces complexity, standardizes interfaces, facilitates modular engineering, ensures interoperable technology, accelerates evolution, and simplifies teaching and learning.

5. The OSI Reference Model
Application 7
Presentation 6
Reduces complexity
Standardizes interfaces
Facilitates modular engineering
Ensures interoperable technology
Accelerates evolution
Simplifies teaching and learning
Session 5
Transport 4
Lesson Aim
<Enter lesson aim here.>
Network 3
Data Link 2
Physical 1

6. The Seven Layers of the OSI Model
Network Processes to Applications
Provides network services to application processes (such as electronic mail, file transfer, and terminal emulation)
Application 7
Presentation 6
Session 5
Transport 4
Lesson Aim
<Enter lesson aim here.>
Network 3
Data Link 2
Physical 1

7. The Seven Layers of the OSI Model
Network Process to Applications
Application 7
Data Representation
Ensures data is readable by receiving system
Formats data
Structures data
Negotiates data transfer syntax for application layer
Presentation 6
Session 5
Transport 4
Lesson Aim
<Enter lesson aim here.>
Network 3
Data Link 2
Physical 1

8. The Seven Layers of the OSI Model
Application 7
Network Process to Applications
Presentation 6
Data Representation
Interhost Communication
Establishes, manages, and terminates sessions between applications
Session 5
Transport 4
Lesson Aim
<Enter lesson aim here.>
Network 3
Data Link 2
Physical 1

9. The Seven Layers of the OSI Model
Application 7
Network Process to Applications
Presentation 6
Data Representation
Session 5
Interhost Communication
End-to-End Connections
Handles transportation issues between hosts
Ensures data transport reliability
Establishes, maintains and terminates virtual circuits
Provides reliability through fault detection and recovery information flow control
Transport 4
Lesson Aim
<Enter lesson aim here.>
Network 3
Data Link 2
Physical 1

10. The Seven Layers of the OSI Model
Application 7
Network Process to Applications
Presentation 6
Data Representation
Session 5
Interhost Communication
Transport
End-to-End Connections 4
Data Delivery
Provides connectivity and path selection between two host systems
Routes data packets
Selects best path to deliver data
Lesson Aim
<Enter lesson aim here.>
Network 3
Data Link 2
Physical 1

11. The Seven Layers of the OSI Model
Application 7
Network Process to Applications
Presentation 6
Data Representation
Session 5
Interhost Communication
Transport
End-to-End Connections 4
Lesson Aim
<Enter lesson aim here.>
Network
Data Delivery 3
Access to Media
Defines how data is formatted for transmission and how access to the network is controlled
Data Link 2
Physical 1

12. The Seven Layers of the OSI Model
Application 7
Network Process to Applications
Presentation 6
Data Representation
Session 5
Interhost Communication
Transport
End-to-End Connections 4
Lesson Aim
<Enter lesson aim here.>
Network
Data Delivery 3
Data Link
Access to Media 2
Binary Transmission
Defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link.
Physical 1

13. Data Encapsulation Sender Application Presentation Session Transport
User Data
Application L7
HDR 7
User Data
Presentation L6
HDR L7
HDR 6
User Data
Lesson Aim
<Enter lesson aim here.>
Session L6
HDR L7
HDR 5 L5
HDR
User Data
Transport L4
HDR L5
HDR L6
HDR L7
HDR 4
User Data
Network L3
HDR L4
HDR L5
HDR L6
HDR L7
HDR 3
User Data
Data Link L2
HDR L3
HDR L4
HDR L5
HDR L6
HDR L7
HDR 2
User Data
FCS
Physical
Bits 1
HDR = header

14. Data De-Encapsulation
Receiver
User Data
Application L7
HDR 7
User Data
Presentation L6
HDR L7
HDR 6
User Data
Lesson Aim
<Enter lesson aim here.>
Session L6
HDR L7
HDR 5 L5
HDR
User Data
Transport L4
HDR L5
HDR L6
HDR L7
HDR 4
User Data
Network L3
HDR L4
HDR L5
HDR L6
HDR L7
HDR 3
User Data
Data Link L2
HDR L3
HDR L4
HDR L5
HDR L6
HDR L7
HDR 2
User Data
FCS
Physical
Bits 1
HDR = header

15. Peer-to-Peer Communication
Sender
Receiver
Application
Application
Presentation
Presentation
Session
Session
Lesson Aim
<Enter lesson aim here.>
Segments
Transport
Transport
Packets
Network
Network
Frames
Data Link
Data Link
Bits
Physical
Physical
Network

16. TCP/IP Model Application Transport Network Data Link Physical
Lesson Aim
<Enter lesson aim here.>
Data Link
Physical

17. TCP/IP Protocol Stack vs. OSI Model
Application
Layers
Application
Application
Presentation
Session
Data Flow
Layers
Transport
Transport
Lesson Aim
<Enter lesson aim here.>
Internet
Networks
Network
Network
Access
Data Link
Physical

18. Summary
The OSI reference model reduces complexity, standardizes interfaces, facilitates modular engineering, ensures interoperable technology, accelerates evolution, and simplifies teaching and learning.
Each layer of the OSI model has a set of unique functions. The seven layers of the OSI model are the application, presentation, session, transport, network, data-link, and physical layers.
Encapsulation is the process in which data is wrapped in a particular protocol header before network transit.