1 Kyung Hee University Introduction

2 1.1 Data Communications  Data communication is the process of communicating information of binary form between two or more points.  Data communication is the exchange of data (in the form of 0s and 1s) between two devices via some form of transmission medium(such as a wire cable)

3 Kyung Hee University Fundamental Characteristics ( 기본 특성 )  The effectiveness of a data communication system depends on three fundamental characteristics 전달 (Delivery) ~ must deliver data to the correct destination (the intended device or user) 정확성 (Accuracy) ~ must deliver data accurately 적시성 (Timeliness) ~ must deliver data in a timely manner

4 Kyung Hee University Data communication system components

5 Kyung Hee University Data communication system components (cont’d)  메시지 (Message) ~ is the information(data) to be communicated. (text, numbers, pictures, sound, video or any combination of these)  송신자 (Sender) ~ is the device that sends the data message. (computer, workstation, telephone handset, video camera)  수신자 (Receiver) ~ is the device that receives the message. (computer, workstation, telephone handset, video camera)

6 Kyung Hee University Data communication system components (cont’d)  전송매체 (Medium) ~ is the physically path by which a message travels from sender to receiver. (twisted pair wire, coaxial cable, fiber- optic cable, laser, or radio waves(terrestrial or satellite microwave))  프로토콜 (Protocol) ~ is a set of rules that govern data communication.

7 Kyung Hee University Data Presentation  Text  ASCII : by ANSI, 7bits  Extended ASCII, 8bits  Unicode : 16 bits  ISO : 32bits  Numbers : see Appendix B  Images  Audio : continuous  Video

8 Kyung Hee University

9 Direction of Data Flow ~ is used to define the direction of signal flow between two link devices  단방향 (Simplex) is unidirectional, as on a one-way street (keyboard, monitor)  반이중 (Half-Duplex) each station can both transmit and receive, but not at the same time  전이중 (Full-Duplex) both stations can transmit and receive simultaneously

10 Kyung Hee University Direction of Data Flow  Simplex

11 Kyung Hee University Direction of Data Flow  Half-Duplex

12 Kyung Hee University Direction of Data Flow  Full-Duplex

13 Kyung Hee University 1.2 네트워크 (Networks) ~ is a set of devices(nodes) connected by media links.  장치 (Device or Node) - computer, printer, any other device capable of sending and/or receiving data generated by other nodes on the network.  링크 (Link) - communication channel

14 Kyung Hee University 분산처리 (Distributed processing)  In which a task is divided among multiple computers.  Advantage 1. Security/encapsulation - A system designer can limit the kinds of interactions that a given user can have with the entire system. For example, ATM (Automated Teller Machine) 2. Distributed databases - No one system needs to provide storage capacity for the entire database.

15 Kyung Hee University Distributed processing (cont’d) 3. Faster problem solving - Multiple computers working on parts of a problem concurrently can often solve the problem faster than a single machine working alone. 4. Security through redundancy - Multiple computers running the same program at the same time can provide security through redundancy (ex: space shuttle) 5. Collaborative processing - Both multiple computers and multiple users may interact on a task (ex: multiuser network games)

16 Kyung Hee University 네트워크 평가기준 (Network Criteria) Performance Reliability Security Data communication network criteria Data communication network criteria

17 Kyung Hee University Performance ( 성능 )  Depends on a number of factors. number of users type of transmission medium(data rate) hardware software : error-free delivery

18 Kyung Hee University Reliability ( 신뢰성 )  Frequency of failure  Recovery time of a network after a failure  Catastrophe Networks must be protected from catastrophic events such as fire, earthquake, or theft.

19 Kyung Hee University 보안 (Security)  Unauthorized access  Viruses and Worms

20 Kyung Hee University Physical Structures  Type of Network Connection 점 - 대 - 점 (Point-to-point) l ~ provides a dedicated link between two devices. 다중 점 (Multipoint) : multidrop l ~ is configuration in which more than two specific devices share a single link

21 Kyung Hee University Type of Network Connection  point-to-point

22 Kyung Hee University Type of Network Connection  Multipoint

23 Kyung Hee University Physical Topology 

24 Kyung Hee University Physical Topology  Mesh Every device has a dedicated point-to-point link to every other device. A fully connected mesh network therefore has n(n- 1)/2 physical channels to link n devices.

25 Kyung Hee University Physical Topology  Mesh

26 Kyung Hee University Mesh (cont’d)  Advantages The use of dedicated links guarantees that each connection can carry its data load. Mesh topology is robust. Privacy and security. Point-to-point links make fault identification and fault isolation easy.

27 Kyung Hee University 그물형 (cont’d)  Disadvantages ~ are related to the amount of cabling and the number of I/O ports because every device must be connected to every other device, installation and reconfiguration are difficult the sheer bulk of the wiring can be greater than the available space(in walls, ceiling, or floors) can accommodate the hardware required to connect each link (I/O port and cable) can be prohibitively expensive

28 Kyung Hee University 스타형 (Star : 성형 )  Each device has a dedicated point-to-point link only to a central controller, usually called a hub  스타형 (Star : 성형 )

29 Kyung Hee University Star (cont’d)  Advantage Each device needs only one link and one I/O port to connect it to any number of others (easy to install and reconfigure) Robustness l if one link fails, only that link is affected

30 Kyung Hee University 트리형 (Tree)  is a variation of a star active hub(central hub) ~ contains a repeater, which is a hardware device that generates the received bit patterns before sending them out passive hub ~ provides a simple physical connection between the attached devices

31 Kyung Hee University 버스형 (Bus)  is multipoint. One long cable acts as a backbone to link all the devices in the network  Nodes are connected to the bus cable by drop lines and taps drop line ~ is a connection running between the device and the main cable tap ~ is a connector either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core

32 Kyung Hee University Bus 형

33 Kyung Hee University Bus (cont’d)  Advantages ~ include ease of installation  Disadvantages ~ include difficult reconfiguration and fault isolation

34 Kyung Hee University 링형 (Ring)  Each device has a dedicated point-to-point line configuration only with the two devices on either side of it  Advantage ~ is relatively easy to install and reconfigure ~ fault isolation is simplified  Disadvantage unidirectional traffic l break in the ring can disable the entire network --> needs dual ring

35 Kyung Hee University 네트워크 분류 (Categories of Networks)  three primary categories 근거리 통신망 (LAN) 도시 통신망 (MAN) 광역 통신망 (WAN)  size, ownership, distance it cover, physical architecture

36 Kyung Hee University Categories of Networks (cont’d) Metropolitan area network (MAN) Metropolitan area network (MAN) Local area networks (LAN) Local area networks (LAN) Wide area network (WAN) Wide area network (WAN) Network

37 Kyung Hee University Categories of Networks (cont’d)  LAN(Local Area Networks) ~ is usually privately owned and links the devices in a single office, building or campus

38 Kyung Hee University Categories of Networks (cont’d)

39 Kyung Hee University Categories of Networks (cont’d)  MAN(Metropolitan Area Networks) ~ is designed to extend over an entire city

40 Kyung Hee University Categories of Networks (cont’d)  WAN(Wide Area networks) ~ provides long-distance transmission of data, voice, image, and video information over large geographical areas that may comprise a country, a continent, or even the whole world

41 Kyung Hee University Categories of Networks (cont’d)  WAN

42 Kyung Hee University 1.3 Internet  A Brief History Internet (not internet) ARPANET (Advanced Research Projects Agency: ARPA) – mid-1960s l Advanced Research Projects Agency (ARPA) in the DOD : presented ideas of ARPANET, 1967 l Reality : 1969 (UCLA, UCSB, SRI, U of Utah) Birth of Internet : in 1972 l Vint Cerf and Bob Kahn : Internetting Project TCP/IP : A paper by Cerf and Kahn in 1973 l In 1983, TCP/IP became to official protocol for the ARPANET MILNET : in 1983 CSNET, NSFNET, ANSNET, …

43 Kyung Hee University Internet Today  Four-node ARPANET established.  ARPA hosts implement NCP.  Development of TCP/IP suite begins.  An internet tested using TCP/IP.  UNIX distributed to academic sites.  CSNET established.  TCP/IP becomes the official protocol  MILNET was born.  NSFNET established.  ARPANET replaced by NSFNET.  NSFNET became a research network.  ISPs started.

44 Kyung Hee University Internet Today

45 Kyung Hee University 1.4 Protocols and Standard  Communication in computer networks ~ occurs between entities in different systems  Entity ~ is anything capable of sending or receiving information  프로토콜 (Protocol) ~ is a set of rules that govern data communication

46 Kyung Hee University Protocol & Standards (cont’d)  Protocol 의 주요 요소 문법 (Syntax) ~ refers to the structure or format of the data, meaning the order in which they are presented. 의미론 (Semantics) ~ refers to the meaning of each section of bits. 타이밍 (Timing) ~ refers to two characteristics (when data should be sent and how fast it can be sent)

47 Kyung Hee University Standards  표준안 (Standards) ~ are essential in creating and maintaining an open and competitive market for equipment manufactures and in guaranteeing national and international interoperability of data and communications technology and processes. Standards De facto (by fact) De facto (by fact) De jure (by law) De jure (by law)

48 Kyung Hee University Standards Organizations ( 표준화 기구 )  Standard Creation Committees ISO (The International Standard Organization) ~ created in 1947 ~ voluntary organization ~ is an organization dedicated to worldwide agreement on international standards in a variety of fields (scientific, technological, economic activity)

49 Kyung Hee University Standards Organizations (cont’d) ITU-T(International Telecommunications Union - Telecommunications Standards Sector) ~ is an international standards organization related to the United Nations that develops standards for telecommunications. l Two popular standards developed by ITU-T are the V series (data transmission over phone lines) and the X series (transmission over public digital networks)

50 Kyung Hee University Standards Organizations (cont’d) ANSI (American National Standard Institute) ~ is a nonprofit organization and is the U.S. voting representative to be both the ISO and the ITU-T IEEE (Institute of Electrical and Electronic Engineers) ~ is the largest national professional group involved in developing standards for computing, communication, electrical engineering, and electronics) EIA (Electronic Industries Association) ~ is an association of electronics manufactures in the United States. (EIA-232-D, EIA-530 standards)

51 Kyung Hee University Standards Organizations (cont’d)  Forums ~ consist of representatives from corporation that test, evaluate and standardize new technologies. l Frame Relay Forum l ATM Forum and ATM consortium  Regulatory agencies FCC (Federal Communications Commission) MIC (Ministry of Communication)

52 Kyung Hee University Internet Standards  Internet standard is a thoroughly tested specification that is useful to and adhered by those who work with the Internet  A specification begins as an Internet draft Working document with no official status and six-month life- time  RFC (Request for Comment) Recommendation from Internet authorities

53 Kyung Hee University Standards (cont’d)  by law standard ~ are those that have been legislated by an officially recognized body.  by fact standard ~ are often established originally by manufactures seeking to define the functionality of a new product or technology. proprietary(closed) ~ are those originally invented by a commercial organization as a basis for the operation of its products. nonproprietary(open) ~ are those originally developed by group or committees that have passed them into the public domain.

54 Kyung Hee University Standards Organizations ( 표준화 기구 )  Standard Creation Committees ISO (The International Standard Organization) ~ created in 1947 ~ voluntary organization ~ is an organization dedicated to worldwide agreement on international standards in a variety of fields (scientific, technological, economic activity)

55 Kyung Hee University Standards Organizations (cont’d) ITU-T(International Telecommunications Union - Telecommunications Standards Sector) ~ is an international standards organization related to the United Nations that develops standards for telecommunications. l Two popular standards developed by ITU-T are the V series(data transmission over phone lines) and the X series (transmission over public digital networks)

56 Kyung Hee University Standards Organizations (cont’d) ANSI (American National Standard Institute) ~ is a nonprofit organization and is the U.S. voting representative to be both the ISO and the ITU-T IEEE (Institute of Electrical and Electronic Engineers) ~ is the largest national professional group involved in developing standards for computing, communication, electrical engineering, and electronics) EIA (Electronic Industries Association) ~ is an association of electronics manufactures in the United States. (EIA-232-D, EIA-530 standards)

57 Kyung Hee University Standards Organizations (cont’d) Bellcore (now, Telcordia Technologies) ~ provides research and development resources for the advancement of telecommunications technology. Forums ~ consist of representatives from corporation that test, evaluate and standardize new technologies. l Frame Relay Forum l ATM Forum and ATM consortium l IETF(Internet Society and Internet Engineering Task Force) l TINA (Telecommunications Information Networking Architecture)  Regulatory agencies FCC

58 Kyung Hee University Standards Organizations (cont’d)  한국정보통신기술협회 (TTA) 년 12 월 설립 통신 사업자, 산업체, 학계, 연구기관 및 단체 등의 상호 협력과 유대 강화 국내외 정보통신분야의 최신기술 및 표준에 관한 각종 정보 수집, 조사 연구 및 보급 활용 정보통신 산업 및 기술 진흥과 국민 경제 발전에 기여

59 Kyung Hee University Standards Organizations (cont’d)  한국산업표준원 (KISI) 산업표준 연구 개발 표준화 국제 협력 및 진흥 북한 표준 연구 정보산업 표준화 자본재 표준화 KSSN( 한국 표준 정보망 ) 운영

60 Kyung Hee University Standards Organizations (cont’d)  한국전자통신연구소 표준연구센터 년 ETRI 내 설립 초고속 정보통신 기반을 위한 표준 / 규격 / 기준 관련 기술의 연구 개발 주도 정보통신 산업체 중심의 표준화 활동 기반 조성 핵심 표준 기술의 산업체 이전 및 제공 국내 표준 활동 강화를 통한정보통신 시장의 균형적인 발전 및 활성화

61 Kyung Hee University Standards Organizations (cont’d)  한국전자거래진흥원 (KEB) Korea EDI/EC Board 한국 표준 전자문서 (KEDIfact) 제정, 고시 세계 전자문서 표준인 UN/EDIFACT 보급과 제정 활동 참여 전자 거래 실현에 필요한 표준 연구 개발