1. 정보 시스템 보안 3-1 장. 네트워크 기초 최미정mjchoi@kangwon.ac.kr 강원대학교 컴퓨터과학전공

2.  이 장에서 다룰 내용  OSI 7 계층의 세부 동작을 이해한다. 11

3. OSI : Open System Interconnection by ISO Purpose of OSI Model ~ is to open communication between different systems without requiring changes to the logic of the underlying hardware and software.

4. 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

7. Peer-to-peer process ~ process on each machine that communicates at a given layer Interfaces between Layers ~ defines what information and services a layer must provide for the layer above it

8. 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

9. OSI 모델을 이용한 교환 o Headers are added to the data at layers 6, 5, 4, 3, and 2. Trailers are usually added only at layer 2.

10. 물리 계층 (Physical Layer) 데이터 링크 계층 (Data Link Layer) 네트워크 계층 (Network Layer) 전송 계층 (Transport Layer) 세션 계층 (Session Layer) 표현 계층 (Presentation Layer) 응용 계층 (Application Layer)

11. 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)

12. Physical Layer

13. 특징  인터페이스 및 매체의 물리적 특성  Representation of bits : 부호화 (Encoding); 신호에 의한 data 표현  Data rate : 전송속도  비트의 동기화 (Synchronization of bits)  회선구성 (Line configuration) : point-to-point, multipoint  물리적 접속형태 (Topology) : mesh, star, ring, bus  데이터 전송 모드 (Data transmission mode) : simplex, half-duplex, full- duplex

14. 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

15. Data Link Layer

17. Specific responsibilities  Framing : dividing into Frames  물리주소지정 (Addressing) : 프레임 수신 주소지정  흐름 제어 (Flow control) : for avoiding overwhelming the receiver  에러 제어 (Error Control) : retransmission  액세스 제어 (Access control) : for avoiding collision

18. is responsible for the source-to-destination delivery of a packet across multiple network link provides two related services.  Switching  Routing

19. 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 to another when more than one path is available

21. End-to-End Delivery

22. Specific responsibilities  Source-to-destination delivery(packet)  Logical addressing  Routing

23. 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. Specific responsibility  Reliable End-to-end message delivery  Service-point(port) addressing  delivery of a message to the appropriate application on a computer running multiple applications  Segmentation and reassembly  Connection control  Flow Control  Error Control

25. Reliable End-to-end delivery of a message

26. Transport Layer

27. Specific responsibility  Session management  Synchronization  Dialog control : Deciding who sends, and when

28. 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.

29. Specific responsibility  Translation  Encryption  Compression

30. enables the user, whether human or software, to access the network. provides user interfaces and support for services.  Email, remote file access and transfer, shared database management

31. Application Layer

32. Specific services  Network virtual terminal  File access, transfer, and management  Mail services  Directory services