The document discusses the OSI model, which defines 7 layers for network communication: Physical, Data Link, Network, Transport, Session, Presentation, and Application. Each layer has a specific function - for example, the Physical layer deals with transmission of raw bits of data, while the Application layer provides services directly to the end user. The OSI model was developed by ISO in the late 1970s and provides a standardized way to understand network communication across different technologies.

1. Lec 2
OSI model

2. LAYERED TASKS
We use the concept of layers in our daily life. As an
example, let us consider two friends who communicate
through postal mail. The process of sending a letter to a
friend would be complex if there were no services
available from the post office.
Sender, Receiver, and Carrier
Hierarchy
Topics discussed in this section:

3. Figure 1 Tasks involved in sending a letter

4. THE OSI MODEL
Established in 1947, the International Standards
Organization (ISO) is a multinational body dedicated to
worldwide agreement on international standards. An ISO
standard that covers all aspects of network
communications is the Open Systems Interconnection (OSI)
model. It was first introduced in the late 1970s.
Layered Architecture
Peer-to-Peer Processes
Encapsulation
Topics discussed in this section:

5. ISO is the organization.
OSI is the model.
Note

6. Figure 2 Seven layers of the OSI model

7. Figure 3 The interaction between layers in the OSI model

8. Figure 4 An exchange using the OSI model

9. LAYERS IN THE OSI MODEL
In this section we briefly describe the functions of each
layer in the OSI model.
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer
Topics discussed in this section:

10. Figure 5 Physical layer

11. The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
Note

12. Physical layer
• The physical layer is also concerned with the following:
1. Physical characteristics of interface and medium
2. Representation of bits
3. Data rate
4. Synchronization of bits
5. Line configuration (point to point-multipoint)
6. Physical topology
7. Transmission mode (simplex-half duplex-full duplex)

13. Figure 6 Data link layer

14. The data link layer is responsible for moving
frames from one hop (node) to the next.
Note

15. Figure 7 Hop-to-hop delivery

16. Data link layer
• The data link layer is also concerned with the following:
1. Framing
2. Physical addressing
3. Flow control
4. Error control
5. Access control

17. Figure 8 Network layer

18. The network layer is responsible for the
delivery of individual packets from
the source host to the destination host.
Note

19. Figure 9 Source-to-destination delivery

20. Network layer
• The network layer is also concerned with the following:
1. Logical addressing
2. Routing

21. Figure 10 Transport layer

22. The transport layer is responsible for the delivery
of a message from one process to another.
Note

23. Figure 11 Reliable process-to-process delivery of a message

24. Transport layer
• The transport layer is also concerned with the following:
1. Service point addressing (port address)
2. Segmentation and reassembly
3. Connection control (connection less or connection oriented)
4. Flow control
5. Error control

25. Figure 12 Session layer

26. The session layer is responsible for dialog
control and synchronization.
Note

27. Session layer
• The session layer is also concerned with the following:
1. Dialog control (half duplex-full duplex)
2. Synchronization (check point)

28. Figure 13 Presentation layer

29. The presentation layer is responsible for translation,
compression, and encryption.
Note

30. Presentation layer
• The presentation layer is also concerned with the following:
1. Translation
2. Encryption
3. Compression

31. Figure 14 Application layer

32. The application layer is responsible for
providing services to the user.
Note

33. Application layer
• The application layer is also concerned with the following:
1. Network virtual terminal
2. File transfer ,access, and management
3. Mail service
4. Directory service

34. Figure 15 Summary of layers