The OSI reference model outlines 7 layers of network functions: physical, data link, network, transport, session, presentation, and application. The top 4 layers provide program-to-program communication between hosts while the bottom 3 layers control physical delivery of data over the network.

1. OSI Reference Model
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2. Тойм
• The Layered Model
• Layers 1 & 2: Physical &
Data Link Layers
• Layer 3: Network Layer
• Layers 4–7: Transport,
Session, Presentation,
and Application Layers

4. Хэрхэн цээжлэх вэ?
All - Application
People - Presentation
Seems - Session
To - Transport
Need of - Network
Data - Data Link
Processing - Physical

5. The Layered Model
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6. Why a Layered Network Model?
7 Application • Нарийн төвөгтэй байдлыг
багасгасан (нэг гол асуудал
6 Presentation нь 7-н жижиг one big problem
5 Session to seven smaller ones)
• Интерфейсийг стандартад
4 Transport
оруулсан
3 Network • Заах ба суралцахад хялбар
2 Data Link болсон
1 Physical

7. Давхарга бүр дэхь
төхөөрөмжүүдийн үүрэг
7 Application
6 Presentation
NIC Card
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
Hub

8. Эзэмшигч давхаргууд
}
7 Application
6 Presentation Host layers: Өгөгдлийг
компьютераас компьютер
5 Session
лүү алдаагүй дамжуулалтыг
4 Transport хангаж өгнө.
3 Network
2 Data Link
1 Physical

9. Зөөврийн давхаргууд
}
7 Application
6 Presentation Host layers: Өгөгдлийг
5 Session компьютераас компьютер
лүү алдаагүй дамжуулалтыг
4 Transport хангаж өгнө.
}
3 Network
2 Data Link Media layers: Мэдээг
сүлжээнд дамжуулахад
1 Physical физик хяналт тавина.

10. Application Layer
7 Application Хэрэглээний програмуудын
сүлжээний орчинд найдвартай
ажиллагааг хангаж өгнө. (жнь:е-майл,
файл дамжуулалт ба терминалд
хувилгах )

11. Presentation Layer
7 Application Хэрэглээний програмын сүлжээн
дэхь үйлчилгээ
6 Presentation Өгөгдлийн илэрхийлэл
• Системээр хүлээн авсан
өгөгдлийг ойлгомжтой
байлгах баталгаагаар хангах
• Өгөгдлийг форматлах
• Өгөгдөл дамжуулахад
холбоотой систем болох
хэрэглээний давхаргатай
тохиролцоно.

12. Session Layer
7 Application Хэрэглээний програмын сүлжээн
дэхь үйлчилгээ
6 Presentation Өгөгдлийн илэрхийлэл
5 Session Дундын эзэмшигчийн харилцан
холбоо
• Establishes, manages, and
terminates sessions between
applications

13. Transport Layer
7 Application Network services to applications
6 Presentation Data representation
5 Session Inter-host communication
4 Transport End-to-end connection reliability
• Concerned with data transport
issues between hosts
• Data transport reliability
• Establishes, maintains, and
terminates virtual circuits
• Fault detection and recovery
• Information flow control

14. Network Layer
7 Application Network services to applications
6 Presentation Data representation
5 Session Inter-host communication
4 Transport End-to-end connection reliability
3 Network Addresses and best path
• Provides connectivity and path
selection between two end
systems
• Domain of routing

15. Data Link Layer
7 Application Network services to applications
6 Presentation Data representation
5 Session Inter-host communication
4 Transport End-to-end connection reliability
3 Network Addresses and best path
2 Data Link Access to media
• Provides reliable transfer of data
across media
• Physical addressing, network
topology, error notification, flow
control

16. Physical Layer
7 Application Network services to applications
6 Presentation Data representation
5 Session Inter-host communication
4 Transport End-to-end connection reliability
3 Network Addresses and best path
2 Data Link Access to media
1 Physical Binary transmission
• Wires, connectors, data rates

17. Communications
Host A Host B
7 Application Application
6 Presentation Presentation
5 Session Session
Segments
4 Transport Transport
Packets
3 Network Network
Frames
2 Data Link Data Link
Bits
1 Physical Physical

18. Data Encapsulation
Host A Host B
Application Application
Presentation
Session
Transport
Network
} { Data Presentation
Session
Transport
Network
Data Link Data Link
Physical Physical

19. Data Encapsulation
Host A Host B
Application Application
Presentation
Session
Transport
Network
} { Data
Network Data
Header
Presentation
Session
Transport
Network
Data Link Data Link
Physical Physical

20. Data Encapsulation
Host A Host B
Application Application
Presentation
Session
Transport
Network
} { Data
Network Data
Header
Presentation
Session
Transport
Network
Frame Network Data Frame
Data Link Data Link
Header Header Trailer
Physical Physical

21. Data Encapsulation
Host A Host B
Application Application
Presentation
Session
Transport
Network
} { Data
Network Data
Header
Presentation
Session
Transport
Network
Frame Network Data Frame
Data Link Data Link
Header Header Trailer
Physical 0101101010110001 Physical

22. Layers 1 & 2:
Physical & Data Link
Layers
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23. MAC Address
24 bits 24 bits
Vendor Code Serial Number
0000.0c12. 3456
ROM
RAM
• MAC address is burned into ROM on a
network interface card

24. Layer 3:
Network Layer
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25. Network Layer: Path Determination
Which Path?
Which Path?
• Layer 3 functions to find the best
path through the internetwork

26. Layers 4–7:
Transport, Session,
Presentation, and
Application Layers
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27. Transport Layer
• Segments upper-layer applications
• Establishes an end-to-end connection
• Sends segments from one end host to another
• Optionally, ensures data reliability

28. Transport Layer—
Establishes Connection
Sender Receiver
Synchronize
Negotiate Connection
Synchronize
Acknowledge
Connection Established
Data Transfer
(Send Segments)

29. Transport Layer—
Sends Segments with Flow Control
Transmit
Sender Receiver
Buffer Full
Not Ready
Stop
Process
Segments
Go Ready
Buffer OK
Resume Transmission

30. Transport Layer—
Reliability with Windowing
• Window Size = 1
Send 1 Receive 1
Ack 2
Sender Send 2 Receive 2 Receiver
Ack 3
• Window Size = 3
Send 1 Receive 1
Send 2 Receive 2
Sender
Send 3 Receive 3 Receiver
Ack 4
Send 4

31. Transport Layer—
An Acknowledgement Technique
Sender Receiver
1 2 3 4 5 6 7 1 2 3 4 5 6 7
Send 1
Send 2
Send 3
Ack 4
Send 4
Send 5
Send 6
Ack 5
Send 5
Ack 7

32. Transport to Network Layer
End-to-End Segments
Routed Packets

33. Session Layer
• Network File System (NFS)
• Structured Query Language (SQL)
• Remote-Procedure Call (RPC)
• AppleTalk Session Protocol (ASP)
• DEC Session Control Protocol (SCP)
Service Request
Service Reply
• Coordinates applications as
they interact on different hosts

34. Presentation Layer
• Text • Graphics
• Data • Visual images
ASCII PICT
login:
EBCDIC TIFF
Encrypted JPEG
• Sound GIF
MIDI
• Video
MPEG
QuickTime
• Provides code formatting and
conversion for applications

35. Application Layer
COMPUTER
APPLICATIONS NETWORK
Word Processor APPLICATIONS INTERNETWORK
Presentation Graphics Electronic Mail
APPLICATIONS
Spreadsheet File Transfer Electronic Data Interchange
Database Remote Access World Wide Web
Design/Manufacturing Client-Server Process E-Mail Gateways
Project Planning Information Location Special-Interest Bulletin Boards
Others Network Management Financial Transaction Services
Others Internet Navigation Utilities
Conferencing (Voice, Video, Data)
• User Interaction Others

36. Summary
• OSI reference model describes building
blocks of functions for program-to-
program communications between
similar or dissimilar hosts
• Layers 4–7 (host layers) provide accurate
data delivery between computers
• Layers 1–3 (media layers) control
physical delivery of data over the network