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

2. Computer Network Lab. 2 목차 3.1 모델 3.2 각 계층의 기능 3.3 요약

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

4. Computer Network Lab. 4 Model(cont’d) n OSI Model

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

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

7. Computer Network Lab. 7 Model(cont’d) n Organization of the Layers l Layer 1, 2, 3(network support layers) ~ deal with the physical aspects of moving data from one device to another l Layer 5, 6, 7(user support layers) ~ allow interoperability among unrelated software systems l 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. Computer Network Lab. 8 Model(cont’d) n OSI 모델을 이용한 교환 T2H2 H3 H4 H5 H6 H5 H4 H3 H2T2

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

10. Computer Network Lab. 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. Computer Network Lab. 11 물리 층 (cont’d) n Physical Layer

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

13. Computer Network Lab. 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. Computer Network Lab. 14 데이터 링크 층 (cont’d) n Data Link Layer

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

16. Computer Network Lab. 16 데이터 링크 층 (cont’d) n Data Link Layer( 예 3.1)

17. Computer Network Lab. 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. l Switching l Routing

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

19. Computer Network Lab. 19 네트워크 층 (cont’d) n Network Layer

20. Computer Network Lab. 20 네트워크 층 (cont’d) n Specific responsibilities l Source-to-destination delivery(packet) l Logical addressing l Routing l Address transformation l Multiplexing

21. Computer Network Lab. 21 네트워크 층 (cont’d) n 예 3.2

22. Computer Network Lab. 22 네트워크 층 (cont’d) n 예 3.2(cont’d)

23. Computer Network Lab. 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. Computer Network Lab. 24 전송 층 (cont’d) n Transport Layer

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

26. Computer Network Lab. 26 전송 층 (cont’d) n 예 3.3 Physical link T2 H2 T2 H2

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

28. Computer Network Lab. 28 세션 층 (cont’d) n Specific responsibility l Session management l Synchronization l Dialog control l Graceful close

29. Computer Network Lab. 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. Computer Network Lab. 30 표현 층 (cont’d) n Presentation Layer

31. Computer Network Lab. 31 표현 층 (cont’d) n Specific responsibility l Translation l Encryption l Compression l Security

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

33. Computer Network Lab. 33 응용 층 (cont’d) n Application Layer

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

35. Computer Network Lab. 35 각 계층의 기능 요약

36. Computer Network Lab. 36 Figure 3-15 TCP/IP and the OSI Model

37. Computer Network Lab. 37 3.3 요약 n 숙제 2,4,6