Chapter 2

1HANNAM UNIVERSITYHttp://netwk.hannam.ac.kr

Chapter 2Chapter 2

Upon completion you will be able to:

The OSI Model andThe OSI Model andthe TCP/IP Protocol Suitethe TCP/IP Protocol Suite

• Understand the architecture of the OSI model• Understand the layers of the OSI model and their functions• Understand the architecture of the TCP/IP Protocol Suite• Differentiate between the OSI model and the TCP/IP Suite• Differentiate between the three types of Internet addresses

Objectives


CONTENTSCONTENTS• THE OSI MODEL• LAYERS IN THE OSI MODEL• TCP/IP PROTOCOL SUITE• ADDRESSING• TCP/IP VERSIONS


2.1 The OSI Model

Established in 1947, the Established in 1947, the International Standards Organization (ISO)International Standards Organization (ISO) is a is a multinational body dedicated to worldwide agreement on international multinational body dedicated to worldwide agreement on international standards. An ISO standard that covers all aspects of network standards. An ISO standard that covers all aspects of network communications is the communications is the Open Systems Interconnection (OSI)Open Systems Interconnection (OSI) model. It model. It was first introduced in the late 1970s.was first introduced in the late 1970s.

The topics discussed in this section include:The topics discussed in this section include:

Layered ArchitectureLayered ArchitecturePeer-to-Peer ProcessesPeer-to-Peer ProcessesEncapsulationEncapsulation


Open System Interconnection

ISO 7498 OSI Basic Reference Model

모든 종류의 컴퓨터 시스템간 통신을 가능하게

하는 네트워크 설계를 위한 계층 구조

서로 연관된 7 계층으로 구성

2.1 2.1 OSI OSI 모델모델


ISO is the organization.OSI is the model

Note:Note:


2.1 2.1 OSI OSI 모델모델 (( 계속계속 )) OSI 모델


2.1 2.1 OSI OSI 모델모델 (( 계속계속 )) OSI 계층 구조


Headers are added to the data at layers

6, 5, 4, 3, and 2. Trailers are usually added only at layer 2.


2.1 2.1 OSI OSI 모델모델 (( 계속계속 )) OSI 모델을 이용한 교환


2.2 Layers in the OSI Model

The functions of each layer in the OSI model is briefly described.The functions of each layer in the OSI model is briefly described.


Physical LayerPhysical LayerData Link LayerData Link LayerNetwork LayerNetwork LayerTransport LayerTransport LayerSession LayerSession LayerPresentation LayerPresentation LayerApplication LayerApplication LayerSummary of LayersSummary of Layers


2.2 2.2 OSI OSI 모델의 계층모델의 계층

물리계층 (physical layer)물리적인 매체를 통하여 비트 스트림을 전송하는데

필요한 기능 제공


The physical layer is responsiblefor the movement of individual bits from one hop (node) to the next.

Note:Note:


2.2 2.2 OSI OSI 모델의 계층모델의 계층 (( 계속계속 ))

물리계층의 주요 기능장치와 전송 매체간의 인터페이스 특성과 전송

매체 유형 규정비트 표현 방법 ( 부호화 유형 )

데이터 전송 속도 (bps)

비트의 동기화 ( 송수신자간 클록 )

회선 구성 ( 점대점 , 다중점 )

접속형태 (mesh, star, ring, bus, tree)

전송 모드 (simplex, half-duplex, full-duplex)



데이터링크계층 (data link layer)



데이터링크층의 주요 기능프레임 (frame) 구성

물리 주소 지정 ( 송수신자 주소 )

흐름 제어

오류 제어

접근 제어


The data link layer is responsible for moving frames from one hop (node) to

the next.

Note:Note:


2.2 2.2 OSI OSI 모델의 계층모델의 계층 (( 계속계속 )) 노드 - 대 - 노드 전달



네트워크계층 (network layer)패킷 (packet) 을 네트워크를 통하여 발신지에서

목적지까지 전달 책임


The network layer is responsible for the delivery of individual packets from the source host to the destination host.

Note:Note:



네트워크계층 주요 기능논리 주소 지정

라우팅 패킷이 최종 목적지에 전달될 수 있도록 경로를

지정하거나 교환 기능 제공



종단 - 대 - 종단 전송



전송계층 (transport layer)발신지에서 목적지 ( 종단 - 대 - 종단 ) 까지 전체

메시지 전달기능 제공


The transport layer is responsible for the delivery of a message from one

process to another.

Note:Note:



전송계층 주요 기능서비스 지점 주소지정 ( 포트 주소 )

분할과 재조립 (Segmentation and reassembly)

연결 제어 (Connection Control)

흐름 제어 (Flow Control)

오류 제어 (Error Control)



신뢰성 있는 종단 - 대 - 종단 메시지 전송



세션계층 (session layer)통신 시스템간의 상호 대화 설정 , 유지 , 동기화 기능

제공



세션계층의 주요 기능대화 제어 ( 반이중 , 전이중 )

동기화 ( 검사점 추가 )



표현계층 (presentation layer)



표현계층의 주요 기능변환 (Translation)

암호화 (Encryption)

압축 (Compression)



응용계층 (application layer)사용자나 소프트웨어를 네트워크에 접근 가능하도록

하는 기능 제공



응용계층 주요 기능네트워크 가상 터미널 (Network Virtual Terminal)

파일 접근 , 전송 및 관리 (File Transfer, Access, and

Management)

우편 서비스 (Mail Service)

디렉토리 서비스 (Directory Service)



계층별 요약


2.3 TCP/IP Protocol Suite

The The TCP/IP protocol suiteTCP/IP protocol suite is made of five layers: physical, data link, is made of five layers: physical, data link, network, transport, and application. The first four layers provide network, transport, and application. The first four layers provide physical standards, network interface, internetworking, and transport physical standards, network interface, internetworking, and transport functions that correspond to the first four layers of the OSI model. The functions that correspond to the first four layers of the OSI model. The three topmost layers in the OSI model, however, are represented in three topmost layers in the OSI model, however, are represented in TCP/IP by a single layer called the application layer.TCP/IP by a single layer called the application layer.


Physical and Data Link LayersPhysical and Data Link LayersNetwork LayerNetwork LayerTransport LayerTransport LayerApplication LayerApplication Layer


2.3 2.3 TCP/IP TCP/IP 프로토콜프로토콜 TCP/IP 와 OSI 모델


2.3 2.3 TCP/IP TCP/IP 프로토콜프로토콜 (( 계속계속 ))

TCP/IP 프로토콜1. 물리계층과 데이터링크계층

기존의 모든 표준과 기술적인 프로토콜 지원

2. 네트워크 계층 인터넷 프로토콜 (IP) : host-to-host protocol

주소변환 프로토콜 (ARP)

역주소변환 프로토콜 (RARP)

인터넷 제어 메시지 프로토콜 (ICMP)

인터넷 그룹 메시지 프로토콜 (IGMP)


2.3 2.3 TCP/IP TCP/IP 프로토콜프로토콜 (( 계속계속 ))

3. 전송계층 사용자 데이터그램 프로토콜 (UDP)

전송 제어 프로토콜 (TCP)

4. 응용계층 OSI 모델의 세션 , 표현 , 응용층을 합친것


2.4 Addressing

Three different levels of addresses are used in an internet using the Three different levels of addresses are used in an internet using the TCP/IP protocols: TCP/IP protocols: physical (link) address, logical (IP) addressphysical (link) address, logical (IP) address, and , and port address.port address.


Physical AddressPhysical AddressLogical AddressLogical AddressPort Address Port Address


2.4 2.4 주소지정주소지정

TCP/IP 에서 사용하는 주소


2.4 2.4 주소지정주소지정 (( 계속계속 )) TCP/IP 에서 주소와 계층간의 관계


2.4 2.4 주소지정주소지정 (( 계속계속 ))

물리 주소링크 주소WAN 이나 LAN 에서 정의된 노드의 주소이더넷 네트워크 인터페이스 카드 (NIC) 6 바이트

(48 비트 ) 주소유니캐스트 (unicast), 멀티캐스트 (multicast),

브로드캐스트 (broadcast)


In Slide 42 a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link. At the data link level this frame contains physical (link) addresses in the header. These are the only addresses needed. The rest of the header contains other information needed at this level. The trailer usually contains extra bits needed for error detection.

Example 1



물리 주소


As we will see in Chapter 3, most local area networks use a 48-bit (6 bytes) physical address written as 12 hexadecimal digits, with every 2 bytes separated by a colon as shown below:

Example 2

07:01:02:01:2C:4B

A 6-byte (12 hexadecimal digits) physical address.



인터넷 주소현재 인터넷에 연결된 호스트 식별 : 32 비트 주소

체계

유니캐스트 ( 단일사용자 ), 멀티캐스트 ( 그룹수신자 ), 브로드캐스트 ( 네트워크 내의 모든 시스템 )


In Slide 47 we want to send data from a node with network address A and physical address 10, located on one LAN, to a node with a network address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use link addresses only; the link addresses have only local jurisdiction. What we need here are universal addresses that can pass through the LAN boundaries. The network (logical) addresses have this characteristic.

Example 3


The packet at the network layer contains the logical addresses, which remain the same from the original source to the final destination (A and P, respectively, in the figure). They will not change when we go from network to network. However, the physical addresses will change as the packet moves from one network to another. The boxes labeled routers are internetworking devices, which we will discuss in Chapter 3.

Example 3 (Continued)


2.4 2.4 주소지정주소지정 (( 계속계속 )) IP 주소


Example 4

As we will see in Chapter 4, an Internet address (in IPv4) is 32 bits in length, normally written as four decimal numbers, with each number representing 1 byte. The numbers are separated by a dot. Below is an example of such an address.

132.24.75.9An internet address in IPv4 in decimal numbers


Slide 51 shows an example of transport layer communication. Data coming from the upperlayers have port addresses j and k ( j is the address of the sending process, and k is the address of the receiving process). Since the data size is larger than the network layer can handle, the data are split into two packets, each packet retaining the service-point addresses ( j and k). Then in the network layer, network addresses (A and P) are added to each packet.

Example 5


The packets can travel on different paths and arrive at the destination either in order or out of order. The two packets are delivered to the destination transport layer, which is responsible for removing the network layer headers and combining the two pieces of data for delivery to the upper layers.

Example 5 (Continued)


2.4 2.4 주소지정주소지정 (( 계속계속 )) 포트 주소


As we will see in Chapters 11, 12, and 13, a port address is a 16-bit address represented by one decimal number as shown below.

Example 6

753A 16-bit port address represented as one single number.


2.5 IP Versions

IP became the official protocol for the Internet in 1983. As the Internet IP became the official protocol for the Internet in 1983. As the Internet has evolved, so has IP. There have been six versions since its inception. has evolved, so has IP. There have been six versions since its inception. We look at the latter three versions here.We look at the latter three versions here.


Version 4Version 4Version 5Version 5Version 6Version 6


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