1 Kyung Hee University Chapter 2 The OSI Model and the TCP/IP Protocol Suite

2 Kyung Hee University OSI Reference Model oOSI : Open System Interconnection by ISO oBasic Reference Model : ISO-7498 oPurpose of OSI Model ~ is to open communication between different systems without requiring changes to the logic of the underlying hardware and software.

3 Kyung Hee University 2.1 The OSI Model oOSI Model ~ is layered framework for the design of network systems that allows for communication across all types of computer systems oLayered Architecture ~ shows the layers involved when a message is sent from device A to device B

4 Kyung Hee University OSI Model (cont’d) oThe OSI Model

5 Kyung Hee University OSI Layers

6 Kyung Hee University OSI Model (cont’d) oPeer-to-peer process ~ process on each machine that communicates at a given layer oInterfaces between Layers ~ defines what information and services a layer must provide for the layer above it

7 Kyung Hee University OSI Model (cont’d) oOrganization 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

8 Kyung Hee University OSI Model (cont’d) oOSI 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.

9 Kyung Hee University 2.2 Layers in the OSI Model o 물리 계층 (Physical Layer) o 데이터 링크 계층 (Data Link Layer) o 네트워크 계층 (Network Layer) o 전송 계층 (Transport Layer) o 세션 계층 (Session Layer) o 표현 계층 (Presentation Layer) o 응용 계층 (Application Layer)

10 Kyung Hee University Physical Layer o 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 Kyung Hee University Physical Layer (cont’d) oPhysical Layer

12 Kyung Hee University Physical Layer (cont’d) o 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

13 Kyung Hee University Data Link Layer ois responsible for delivering data units(group of bits) from one station to the next without errors. oIt 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 Kyung Hee University Data Link Layer oData Link Layer

15 Kyung Hee University Node-to-Node Delivery

16 Kyung Hee University Data Link Layer (cont’d) oSpecific 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

17 Kyung Hee University Network Layer ois responsible for the source-to-destination delivery of a packet across multiple network link oprovides two related services. Switching Routing

18 Kyung Hee University Network Layer (cont’d) oSwitching ~ refer to temporary connections between physical links, resulting in longer links for network transmission.(ex: telephone conversation) orouting ~ means selecting the best path for sending a packet from one point to another when more than one path is available

19 Kyung Hee University Network Layer (cont’d)

20 Kyung Hee University Network Layer (cont’d) End-to-End Delivery

21 Kyung Hee University Network Layer (cont’d) oSpecific responsibilities Source-to-destination delivery(packet) Logical addressing Routing

22 Kyung Hee University Transport Layer ois 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.

23 Kyung Hee University Transport Layer (cont’d) oSpecific responsibility Reliable End-to-end message delivery Service-point(port) addressing l delivery of a message to the appropriate application on a computer running multiple applications Segmentation and reassembly Connection control Flow Control Error Control

24 Kyung Hee University Transport Layer (cont’d) o Reliable End-to-end delivery of a message

25 Kyung Hee University Transport Layer (cont’d) oTransport Layer

26 Kyung Hee University Session Layer ois the network dialog controller Dialog unit

27 Kyung Hee University Session Layer (cont’d) oSpecific responsibility Session management Synchronization Dialog control : Deciding who sends, and when

28 Kyung Hee University Presentation Layer oensures interoperability among communicating devices. ois 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 Kyung Hee University Presentation Layer (cont’d)

30 Kyung Hee University Presentation Layer (cont’d) oSpecific responsibility Translation Encryption Compression

31 Kyung Hee University Application Layer oenables the user, whether human or software, to access the network. oprovides user interfaces and support for services. , remote file access and transfer, shared database management

32 Kyung Hee University Application Layer (cont’d) oApplication Layer

33 Kyung Hee University Application Layer (cont’d) oSpecific services Network virtual terminal File access, transfer, and management Mail services Directory services

34 Kyung Hee University 2.3 TCP/IP Protocol Suite ~ is made of five layers : physical, data link, network, transport, and application

35 Kyung Hee University Internetworking Protocol (IP) oTransmission mechanism by the TCP/IP oAn unreliable and connectionless datagram protocol – best-effort delivery service; IP provides no error checking or tracking

36 Kyung Hee University UDP and TCP oUser Datagram Protocol (UDP) A process-to-process protocol that add only port addresses, checksum error control, length information oTransmission Control Protocol (TCP) Reliable stream (connection-oriented) transport protocol Dividing a stream of data into smaller units called segments

37 Kyung Hee University 2.4 Addressing oAddresses in TCP/IP

38 Kyung Hee University 2.4 Addressing (cont’d) oRelationship of layers and addresses in TCP/IP

39 Kyung Hee University Physical address (example 1)

40 Kyung Hee University Physical address (example 2) oMost local area networks use a 48-bit (6 bytes) physical address written as 12 hexadecimal digits, with every 2 bytes separated by a hyphen as shown below: o C-4B A 6-byte (12 hexadecimal digits) physical address

41 Kyung Hee University IP Addresses (example 3)

42 Kyung Hee University IP Addresses (example 4) oAs 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 o

43 Kyung Hee University Port Addresses (example 5)

44 Kyung Hee University Port Addresses (example 6) oAs we will see in Chapters 11 and 12, a port address is a 16-bit address represented by one decimal number as shown below. o753 : A 16-bit port address

45 Kyung Hee University 2.5 TCP/IP Versions oVersion 4 (IPv4) 32 bits address length oVersion 6 (IPv6 or IPng) 128 bits address length