3 장 OSI 기본 참조 모델

1. 3 장 OSI 기본 참조 모델 • OSI : Open System Interconnection • Basic Reference Model : ISO-7498 • Purpose of OSI Model • ~ is to open communication between different systems without requiring changes to the logic of the underlying hardware and software.

2. 목차 3.1 모델 3.2 각 계층의 기능 3.3 요약

3. 3.1 Model • OSI Model ~ is layered framework for the design of network systems that allows for communication across all types of computer systems • Layered Architecture ~ shows the layers involved when a message is sent from device A to device B

4. Model(cont’d) • OSI Model

5. Model(cont’d) Peer-to-peer protocol(7th layer) 7 7 Application Application 7-6 interface Peer-to-peer protocol(6th layer) 7-6 interface 6 6 Presentation Presentation Peer-to-peer protocol(5th layer) 6-5 interface 6-5 interface 5 5 Session Session 5-4 interface Peer-to-peer protocol(4th layer) 5-4 interface 4 Transport Transport 4 4-3 interface 4-3 interface 3rd 3rd 3rd 3 3 Network Network Network Network 3-2 interface 3-2 interface 2nd 2nd 2nd 2 2 Data Link Data Link Data Link Data Link 2-1 interface 2-1 interface 1st 1st 1 1st 1 Physical Physical Physical Physical

6. Model(cont’d) • Peer-to-peer process ~ process on each machine that communicate at a given layer • Interfaces between Layers ~ defines what information and services a layer much provide for the layer above it

7. Model(cont’d) • Organization of the Layers • Layer 1, 2, 3(network support layers) ~ deal with the physical aspects of moving data from one device to another • Layer 5, 6, 7(user support layers) ~ allow interoperability among unrelated software systems • Layer 4(transport layer) ~ links the two subgroups and ensures that what the lower layers have transmitted is in a form that the upper layers can use

8. Model(cont’d) • OSI 모델을 이용한 교환 H6 H6 H5 H5 H4 H4 H3 H3 T2 H2 T2 H2

9. 3.2 각 계층의 기능 • 물리 층(Physical Layer) • 데이터 링크 층(Data LinkLayer) • 네트워크 층(Network Layer) • 전송 층(Transport Layer) • 세션 층(Session Layer) • 표현 층(Presentation Layer) • 응용 층(Application Layer)

10. 물리 층(Physical Layer) ~ coordinates the functions required to transmit a bit stream over a physical medium. (deal with the mechanical and electrical specification of the primary connections: cable, connector)

11. 물리 층(cont’d) • Physical Layer

12. 물리 층(cont’d) • 고려사항 • 회성 구성(Line configuration) • 데이터 전송 모드(Data transmission mode) • 토폴로지(Topology) • 신호방식(Signals): 신호유형 • 부호화(Encoding) • 인터페이스(Interface) • 전송매체(Medium)

13. 데이터 링크 층(Data Link Layer) ~ is responsible for delivering data units(group of bits) from one station to the next without errors. ~ It accepts a data unit from the third layer and adds meaningful bits to the beginning(header) and end(trailer) that contain addresses and other control information: Frame

14. 데이터 링크 층(cont’d) • Data Link Layer

15. 데이터 링크 층(cont’d) • Specific responsibilities • node-to-node 전달(delivery): station-to-station • 주소지정(Addressing) • 액세스 제어(Access control) • 흐름 제어(Flow control) • 에러 처리(Error handling) • 동기화(Synchronization)

16. 데이터 링크 층(cont’d) • Data Link Layer(예 3.1)

17. 네트워크 층(Network Layer) ~ is responsible for the source-to-destination delivery of a packet across multiple network link. cf: the data link oversees station-to-station(node-to-node) delivery. ~ provides two related services. • Switching • Routing

18. 네트워크 층(cont’d) • Switching ~ refer to temporary connections between physical links, resulting in longer links for network transmission.(ex: telephone conversation) • routing ~ means selecting the best path for sending a packet from one point another when more than one path is available

19. 네트워크 층(cont’d) • Network Layer

20. 네트워크 층(cont’d) • Specific responsibilities • Source-to-destination delivery(packet) • Logical addressing • Routing • Address transformation • Multiplexing

21. 네트워크 층(cont’d) • 예 3.2

22. 네트워크 층(cont’d) • 예 3.2(cont’d)

23. 전송 층(Transport layer) ~ is responsible for source-to destination (end-to-end) delivery of the entire message. cf: the network layer oversees end-to-end delivery of individual packet.

24. 전송 층(cont’d) • Transport Layer

25. 전송 층(cont’d) • Specific responsibility • End-to-end message delivery • Service-point(port) addressing • Segmentation and reassembly • Connection control

26. 전송 층(cont’d) • 예 3.3 T2 T2 H2 H2 T2 H2 T2 H2 Physical link

27. 세션 층(Session Layer) ~ is the network dialog controller

28. 세션 층(cont’d) • Specific responsibility • Session management • Synchronization • Dialog control • Graceful close

29. 표현 층(Presentation Layer) ~ ensures interoperability among communicating devices. ~ is responsible for the encryption and decryption of data for security purpose and for the compression and expansion of data when necessary for transmission efficiency.

30. 표현 층(cont’d) • Presentation Layer

31. 표현 층(cont’d) • Specific responsibility • Translation • Encryption • Compression • Security

32. 응용 층(Application Layer) ~ enables the user, whether human or software, to access the network. ~ provides user interfaces and support for services.

33. 응용 층(cont’d) • Application Layer

34. 응용 층(cont’d) • Specific services • Network virtual terminal • File access, transfer, and management • Mail services • Directory services

35. 각 계층의 기능 요약