1 3 장 osi 기본 참조 모델 zosi : open system interconnection zbasic reference model :...

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3 장 OSI 기본 참조 모델

OSI : Open System InterconnectionBasic Reference Model : ISO-7498Purpose of OSI Model

~ is to open communication between different systems without requiring changes to the logic of the underlying hardware and software.

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목차

3.1 모델3.2 각 계층의 기능3.3 요약

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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

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Model(cont’d)

OSI Model

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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)

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6

5

4

3

2

1

7

6

5

4

3

2

12-1 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

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Model(cont’d)

Peer-to-peer process

~ process on each machine that communicate at a gi

ven layer

Interfaces between Layers

~ defines what information and services a layer muc

h provide for the layer above it

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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

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Model(cont’d)OSI 모델을 이용한 교환

T2 H2

H3

H4

H5

H6 H6

H5

H4

H3

H2T2

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3.2 각 계층의 기능

물리 층 (Physical Layer)

데이터 링크 층 (Data Link Layer)

네트워크 층 (Network Layer)

전송 층 (Transport Layer)

세션 층 (Session Layer)

표현 층 (Presentation Layer)

응용 층 (Application Layer)

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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)

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물리 층 (cont’d)

Physical Layer

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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)

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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

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데이터 링크 층 (cont’d)

Data Link Layer

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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)

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데이터 링크 층 (cont’d)

Data Link Layer( 예 3.1)

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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

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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

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네트워크 층 (cont’d)

Network Layer

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네트워크 층 (cont’d)

Specific responsibilities Source-to-destination delivery(packet)

Logical addressing

Routing

Address transformation

Multiplexing

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네트워크 층 (cont’d)

예 3.2

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네트워크 층 (cont’d)

예 3.2(cont’d)

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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.

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전송 층 (cont’d)

Transport Layer

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전송 층 (cont’d)

Specific responsibility End-to-end message delivery

Service-point(port) addressing

Segmentation and reassembly

Connection control

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전송 층 (cont’d)

예 3.3

Physical link

T2

T2

H2

H2

T2

T2

H2

H2

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세션 층 (Session Layer)

~ is the network dialog controller

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세션 층 (cont’d)

Specific responsibility Session management

Synchronization

Dialog control

Graceful close

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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.

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표현 층 (cont’d)

Presentation Layer

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표현 층 (cont’d)

Specific responsibility Translation Encryption Compression Security

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응용 층 (Application Layer)

~ enables the user, whether human or software, to access the network.

~ provides user interfaces and support for services.

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응용 층 (cont’d)

Application Layer

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응용 층 (cont’d)

Specific services Network virtual terminal

File access, transfer, and management

Mail services

Directory services

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각 계층의 기능 요약