1 3 장 OSI 기본 참조 모델 zOSI : Open System Interconnection zBasic Reference Model : ISO-7498 zPurpose of OSI Model y~ 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 zOSI Model ~ is layered framework for the design of network systems that allows for communication across all types of computer systems zLayered Architecture ~ shows the layers involved when a message is sent from device A to device B

4 Model(cont’d) zOSI Model

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

7 Model(cont’d) zOrganization of the Layers yLayer 1, 2, 3(network support layers) ~ deal with the physical aspects of moving data from one device to another yLayer 5, 6, 7(user support layers) ~ allow interoperability among unrelated software systems yLayer 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) zOSI 모델을 이용한 교환 T2H2 H3 H4 H5 H6 H5 H4 H3 H2T2

9 3.2 각 계층의 기능 z 물리 층 (Physical Layer) z 데이터 링크 층 (Data Link Layer) z 네트워크 층 (Network Layer) z 전송 층 (Transport Layer) z 세션 층 (Session Layer) z 표현 층 (Presentation Layer) z 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) zPhysical Layer

12 물리 층 (cont’d) z 고려사항 y 회성 구성 (Line configuration) y 데이터 전송 모드 (Data transmission mode) y 토폴로지 (Topology) y 신호방식 (Signals): 신호유형 y 부호화 (Encoding) y 인터페이스 (Interface) y 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) zData Link Layer

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

16 데이터 링크 층 (cont’d) zData 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. ySwitching yRouting

18 네트워크 층 (cont’d) zSwitching ~ refer to temporary connections between physical links, resulting in longer links for network transmission.(ex: telephone conversation) zrouting ~ 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) zNetwork Layer

20 네트워크 층 (cont’d) zSpecific responsibilities ySource-to-destination delivery(packet) yLogical addressing yRouting yAddress transformation yMultiplexing

21 네트워크 층 (cont’d) z 예 3.2

22 네트워크 층 (cont’d) z 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) zTransport Layer

25 전송 층 (cont’d) zSpecific responsibility yEnd-to-end message delivery yService-point(port) addressing ySegmentation and reassembly yConnection control

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

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

28 세션 층 (cont’d) zSpecific responsibility ySession management ySynchronization yDialog control yGraceful 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) zPresentation Layer

31 표현 층 (cont’d) zSpecific responsibility yTranslation yEncryption yCompression ySecurity

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) zApplication Layer

34 응용 층 (cont’d) zSpecific services yNetwork virtual terminal yFile access, transfer, and management yMail services yDirectory services

35 각 계층의 기능 요약