osi refrence model cn

1. Chapter 1
• Reference Model : The OSI reference model
• Network – H/W & S/W
• Layered task
• Ex. Communicate 2 friend by postal mail
• 1 Higher Layer
• 2 Middle Layer
• 3 Lower Layer
Carrier for transmission
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

2. Chapter 1
Network Reference Model
• The OSI model
standard for data communication.
• The TCP/IP Model
protocol suite – commercial Architecture
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

3. Figure 3-1
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OSI Model

4. Figure 3-2
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OSI Layers

5. Figure 3-3
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An Exchange Using the OSI Model

6. Figure 3-4
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Layer 1. Physical Layer

7. Layer 1. Physical Layer
• Carry a bit stream over physical channel
• Physical- devices e.g. NIC
transmission media- cable.
• Bit pattern - (0001101)
must be transmitted- electrical/ optical signal
• Clock synchronization.
• Line configuration
• Physical Topology
• Transmission mode
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

8. Figure 3-5
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Layer 2. Data Link Layer

9. Figure 3-6
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Data Link Layer Example

10. Layer 2. Data link Layer
• Framing- stream , group of bits.
• Physical Addressing
• Flow control
• Error control
• Access control
• node to node delivery.
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

11. Figure 3-7
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Layer 3. Network Layer

12. Figure 3-8
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Network Layer Example

13. Figure 3-8-continued
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Network Layer Example

14. Layer 3. Network layer
(End to End packet delivery)
• The Network Layer Performs
network routing functions
responsible for S to D delivery of packets
fragmentation and reassembly
• Routing- define route
- independent n/w connection create large n/w
• Logical Addressing
Sender’s Address – Receiver’s Address
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

15. Figure 3-9
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Layer 4. Transport Layer
Process to process delivery of message
-Message arrive in order

16. Figure 3-10
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Transport Layer Example

17. Figure 3-10-continued
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Transport Layer Example

18. Layer 4. Transport Layer
• The Transport Layer provides transparent
transfer of data between end users,
providing reliable data transfer services to
the upper layers.
• The Transport Layer controls the reliability
of a given link through flow control,
segmentation/desegmentation, and error
control.
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

19. Layer 4. Transport Layer
• Service Point Addressing (PORT)
• Several programs at same time
process Process
A ------------- B
• Segmentation & reassembly
-Transmittable segments, Seq no.
• Connection Control services.
WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

20. Figure 3-11
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Layer 5. Session Layer

21. Layer 5: Session Layer
• The Session Layer controls the dialogues
(connections) between computers.
• It establishes, manages and terminates
the connections between the local and
remote application.
• It provides for full-duplex, half-duplex,
or simplex operation, and establishes
checkpointing
(e.g. file of 2000 pages & chk point of 100 pages.),
• termination, and restart procedures. 2

22. Figure 3-12
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Layer 6. Presentation Layer

23. Layer 6: Presentation Layer
• Different Syntax & semantic information
• Translation
-encoding
sender dependent format
common format
receiver dependent format
-encryption. –carry sensitive info.
-compression.- reduce the nr. of bits.
(e.g. multimedia, text, audio, video) 2

24. Figure 3-13
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Layer 7. Application Layer

25. Layer 7: Application Layer
• Provide Services
- E-mail
- Remote file access / Transfer
- Shared database management
• Application
-X.400 message handling service.
-X.500 directory service.
-FTAM
2

26. Figure 3-14
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Summary of Layer Functions