(C) Ho-Won Jung, Korea University 1 Business Data Communications Ho-Won Jung, office A514 ( ) College of Business Administration Korea University College of Business Administration Korea University Fall, 2001

(C) Ho-Won Jung, Korea University 2 Course information m Exam: Two examinations (mid, final) m Reports: Two reports ê One group presentation m Office hour: 10:00 (A.M.) – 6:00 (P.M.) ê From Monday – Wednesday m Slide copy: ê course\ 경영정보통신

(C) Ho-Won Jung, Korea University 3 Contents of the Business Data Communications (1)  Part I: Media and Physical Layer  Chapter 1: Physical Aspects of Data Communications (DC): Media  Chapter 2: Physical Aspects of DC: Data Transmission  Part II: Local Area Networks  Chapter 3: Introduction to Networks  Chapter 4: LAN Hardware  Chapter 5: LAN Topologies and Media Access Control  Chapter 6: LAN System Software  Chapter 7: LAN Considerations

(C) Ho-Won Jung, Korea University 4 Contents of the Business Data Communications (2)  Part III: Wide Area Networks  Chapter 8: WAN Hardware  Chapter 9: WAN Topologies and Transmission Services  Chapter 10: WAN System Software  Chapter 11: WAN Implementation  Part IV: Network Inter-connections and Management  Chapter 12: Network Inter-connections  Chapter 13: Network Management Objectives  Chapter 14: Network Management Systems  Chapter 15: Security, Recovery, and Network Applications  Chapter 16: Systems Analysis  Chapter 17: Distributed Systems

(C) Ho-Won Jung, Korea University 5 DC at Business school  Business data communications  Managerial issues and technical knowledge  Combination of elements of business, information systems, network engineering  Hybrid area  Data Communications 의 study  용어의 이해  기술의 이해  적용 (= 응용 ) 대한 감각  장래의 방향 및 동향  새로운 서비스 : 예 ; 초고속망, IMT-2000, Internet  정보통신관련 국내외 환경 변화 : 예 ; 규제완화, 자유화, 국제화

(C) Ho-Won Jung, Korea University 6 참조 : Data and Information m Data ê A representation of facts, concepts, or instructions in a formalized manner suitable for communication, interpretation, or processing by human beings or by automatic means. m Information ê The meaning that is currently assigned to data by means of the conventions applied to those data.

(C) Ho-Won Jung, Korea University 7 Data Communication 의 변화  Data Communications 변화  급속한 기술 발전  국내외 경쟁의 심화  장비 가격의 하락 및 저렴한 이용료  DP (computer) 와 DC (transmission & switching equipment) 차이가 없어짐  Data, voice, video 이 차이가 없어짐  국내외 Standardization 활동의 강화 (WTO 협정 참조 )  Incorrect concepts  정보통신 ( 정보 + 통신 = information + communications )  예 ) 정보통신부 (Ministry of Information & Communications)  Lower 에 대한 관심 ==> Applications ( 응용 ) 이 더 중요

(C) Ho-Won Jung, Korea University 8 Telecommunications 및 Data communications 의 정의  Telecommunications: 한 sender(agent) 가 하나 이상의 receiver (agent) 에게 electromagnetic system (electrical transmission by wire, radio, optical transmission, guided waves, etc) 를 통해 정보 (printed copy, fixed or moving pictures, visual or audible signals, etc.) 를 전달하는 프로세스. 예 ) FAX, 전신, 이미지, 동화상, 전화 등  Data communications: Transmission of data to and from computers and components of computer systems through a conducted medium (wires, coaxial cables, or fiber optic cables) or by the use of radiated electromagnetic waves (broadcast radio, microwaves).  차이점 ) Data Communication : 전송되는 것에 제한이 있음  유사점 ) audio, video, graphical data -> 0/1 representation

(C) Ho-Won Jung, Korea University 9 Scope of Data communications Input device Transmission medium TransmitterReceiver Output device Source systemDestination system (1) (2) (3) (4)(5)(6) Data communications : (2) 와 (5) 사이 Data transmission: (3) 와 (4) 사이 Agent Input information Output information Input data or signal Transmitted signal Transmitted signal Output data or signal

(C) Ho-Won Jung, Korea University 10 Essential features of communication (message, sender, receiver, medium)(1) 1) Message · file: 예 ; remote job entry · Request ( 예 ; on-line) - display information, update the DB, login, logoff · Response (return message) - requested information, error message · Status - functional status of the system · Control - transmission between system components eg) Don't send me any more data · Correspondences - message sent from user to user eg)

(C) Ho-Won Jung, Korea University 11 Essential features of communication (message, sender, receiver, medium)(2) 2) Sender Transmitter (computers, terminals) of the message 3) Receiver Computers, terminals, remote printers, people 4) Medium Wires, radio waves, light pulses 5) Understandability ASCII, EBCDIC 6) Error detection

(C) Ho-Won Jung, Korea University 12 Data communications applications 1) Batch applications (including RJE): large data transfers in two directions 2) Data entry applications: lengthy inputs with short responses 3) Distributed applications: data or the processing or both are distributed among a number of processing units. 4) Inquiry/response applications: inputs generally have only a few characters and output responses have many. 5) Interactive applications: applications characterized by relatively short inputs and outputs 6) Sensor-based applications

(C) Ho-Won Jung, Korea University 13 Requirements of an online system(1) 1) Performance · Response time: the time elapsed between the user pressing the Enter key to send the request and the return of the first character of the response. · Throughput: the amount of work performed by a system per unit of time 2) Consistency: A consistent system is one that works predictably with respect both to the people who use the system and to response time.

(C) Ho-Won Jung, Korea University 14 Requirements of an online system(2) 3) Flexibility: The ability to have both growth and change having minimal impact on existing applications and users. 4) Availability: A system is available when all components a user needs to satisfy the request are usable. 5) Reliability: The probability that the system will continue to function over a given time period. 6) Security · Physical security is intended to deny access to a facility · Typical security measures include identification and authentication, data encryption, and user profiles.

(C) Ho-Won Jung, Korea University 15 Reliability attributes ( 참조 ) · MTBF (Mean Time Between Failures): A measure of the average amount of time a given component may be expect to operate before failing · MTTR (Mean Time To Repair): The average time required to fix a failed component · Fault tolerance: A combination of H/W and S/W techniques that improve the reliability of a system · Recovery: The act of restoring a system to operational status following a failure

(C) Ho-Won Jung, Korea University 16 Terminology m File server ê A computer that allows microcomputers on a network to share resources such as data, programs, and printers. The file server's software controls access to shared files, as opposed to the OS of the microcomputer. m Enterprise network ê A network of two or more LANs connected to each other, or one or more LANs connected to a WAN. m Common carrier ê telephone (satellite) companies

(C) Ho-Won Jung, Korea University 17 Introduction to networks Data Communications 은 network 을 사용 ( 예 : 전화망 ) Computer 의 증가 -> Network 의 필요성 증대 가격, 성능 Circuit: actual communication between devices.

(C) Ho-Won Jung, Korea University 18 Data communication networking  Switched networks  Circuit-switched networks  Packet-switched networks  Broadcast networks  Packet radio networks  Satellite networks  Local networks

(C) Ho-Won Jung, Korea University 19 Computer networks m One host computer network [Fig 4, P.16] ê Host (computer) ê Communication circuits ê Communication equipments ê Terminals m A network of computers (nodes) [Fig 5, P.17] ê defined as two or more computers connected via a communication medium, together with associated communications links, terminals, and communications equipment. m Interconnected networks [Fig 6, P.18] ê Interconnections of LANs and WAN ê Internet

(C) Ho-Won Jung, Korea University 20 Data communication applications and configurations  Company A : A LAN of law firm [Fig 7, P.19]  Company B : Trucking company [Fig 8, P.20]  Company C : Service company [Fig 9, P.21]  Company D : Computer manufacturer[Fig 10, P.22]  Decision point: Effective and cost-efficient network for business !  Note : coaxial cable vs. fiber optic cable

(C) Ho-Won Jung, Korea University 21 DC 관련 주요 Standards Organization  ANSI(900 개의 기업체 ): American national Standards Institute  ISO(100 개국 ): International Organization for Standardization  CCITT(150 개국 ): Consultative Committee on International Telegraph and Telephone  IEEE: Institute of Electrical and Electronics Engineers  EIA: Electronic Industries Association

(C) Ho-Won Jung, Korea University 22 Computer communications architecture  Computer communications : cooperative action 을 위하여 컴퓨터간에 정 보교환 m Computer network : 두개 이상의 컴퓨터가 communication network 을 통 해 연결되었을 경우, 이들 컴퓨터들의 총칭 m 핵심 ê protocol : 두 개체간의 데이터 교환을 관리하는 규약들의 집합 ( 개체 (entity): 정보를 송수신할 수 있는 것 ) Þ Syntax : data type and signal level Þ Semantics : control information for coordination & error handling Þ Timing : speed matching and sequencing ê computer-communications architecture

(C) Ho-Won Jung, Korea University 23 Open architecture m Open architecture: Architecture whose network specifications are available to any company ê 구매자 우선주의 개념 ê Vendor 의 경쟁 유도 ê Interface 가 중요 ê 표준화의 중요성 m OSI (Open Systems Interconnection) 7 layers (OSI Reference model) m Reference model : 추상화 (abstract) 단계에서 나온 model ê ( 추상적 시스템 (abstract system) : 상호의존적인 생각이나 개념 구성물의 질 서정연한 배열 ) ê a framework or an architecture which standards can be developed, compared, and understood ê not a standard, nor a collection of standard ê logical group of functions required to connect two computers

(C) Ho-Won Jung, Korea University 24 - 응용 프로세스 : 상호간에 정보교환 및 사무처리 주체 ( 예 ; 단말기, 응용프로그램 ) - 개방형시스템 : 응용프로세스간에 통신할 수 있도록 통신기능 제공장치 ( 예 ; Host computer, 통신제어장치, 단말제어장치 ) - 물리매체 : 전기적 매체 OSI 7 layers

(C) Ho-Won Jung, Korea University 25 ISO 의 OSI 7 layers (1) Layer 7: Application layer ( 응용 계층 ) · 전송되는 data 의 결정 · 예 ) Build a record - transaction identifier - the number of accounts to be updated - the date and time of the transaction - the amount to be deducted or added Layer 6: Presentation layer ( 표현 계층 ) · Encryption, compression, terminal screen formatting, code conversion

(C) Ho-Won Jung, Korea University 26 ISO 의 OSI 7 layers (2) Layer 5: Session layer ( 세션 계층 ) · Establish the connection between applications · Enforce rules for carrying on the dialogue - Simplex - Half duplex - Full duplex · Reestablish the connection if a failure occurs

(C) Ho-Won Jung, Korea University 27 ISO 의 OSI 7 layers (3) Layer 4: Transport layer ( 전송 계층 ) · Responsible for generating the end user's address and for the integrity of the receipt of message blocks Layer 3: Network layer ( 망 계층 ) · Responsible for accounting, addressing, and routing functions · Packetizing

(C) Ho-Won Jung, Korea University 28 ISO 의 OSI 7 layers (4) Layer 2: Data link layer ( 데이터 링크 계층 ) · Establish & control the physical path of communication to the next node - Error detection and correction - Flow control Protocol - HDLC (High-level Data Link Control) - LAPB (Balanced Link Access Procedure) - BSC (Binary Synchronous Communications) - X.3 - IEEE 802 logical link control · Note that - Session flow control: End-to-end flow control (between source and destination application) - Data link flow control: for a link

(C) Ho-Won Jung, Korea University 29 Layer 1: Physical layer ( 물리 계층 ) · Electrical connection · Mechanical · Procedure · Protocol - 전화선 : V.10, V11, V21, V22, V23, V24, V.26, V.27, V.28, V.29, V.32 - packet & circuit networks: X.20, X.20bis, X21, X24, X.26, x.27 ISO 의 OSI 7 layers (5)

(C) Ho-Won Jung, Korea University 30 미국의 telecommunications 의 History  AT&T 독점 : data and voice H/W, service, local services (Local BELL), indoor wiring. ê Major source of profits ê metropolitan areas ê businesses ê long-distance service  Universal (affordable) services : 모든 사람에게 저렴한 요금으로 공평하게 기본적인 전화서비스 제공 ê 전국적인 PSTN 구축하여 전화 서비스 제용 ê 전화가입과 이용 촉진을 위한 저렴한 기본료와 시내 통화료 ê 전국 평균요금에 의해 지역에 따른 요금차별 금지와 이용자간 평균 요금 에 의해 이용자간 요금차별 금지

(C) Ho-Won Jung, Korea University 31 Divestiture and Deregulation  Divestiture : AT&T 업무 영역을 분리  AT&T : long-distance services  Local Bell : local telecommunication services  (RBOCs : Regional Bell Operating Companies; US West, Pacific Telesis Group, Southern Bell, Bell South, Bell Atlantic, NYNEX, Ameritech  Deregulation ( 규제완화 )  전화 회사가 타업종 진출을 허용  모든 것이 자유화된 것은 아님 (regulated and deregulated portion)  Gain and loose through the divestiture and deregulation

(C) Ho-Won Jung, Korea University 32 Common carrier  북미에 1,200 개 이상의 Common Carrier  Local Phone Call  LATAs(Local Access Transport Areas)  Long-Distance Calls - AT&T(62.2%) - MCI(15%) - Sprint(9.5%) - All others(13.3%)

(C) Ho-Won Jung, Korea University 33 Regulatory Agencies  규제 가능  FCC (Federal Communications Commission)  Interstate & Foreign telecomm 의 규제  PUCs (Public Utility Commissions)

(C) Ho-Won Jung, Korea University 34 Telecommunications 의 발전 ( 한국 )  1902 년 전화 서비스  통신망에 전화기만 연결 ( 전화국에서 전화기 지급 )  전기통신법 (1961)  단말 접속 허용  단말자유화 조치 (1981)  회선 개방 조치  전기통신 사업법 전기통신사업자  기간통신사업자 : 전기통신회선 설비 설치 + 전기통신 서비스 제공  별정통신사업자 ( 등록제 ): 전기통신설비 이용 ( 또는 임차 ) + 음성 재판매, 인터넷 전 화, 국제 콜백, 구내통신 사업  부가통신사업자 : 전기통신설비를 빌려 부가가치가 높은 통신 서비스 제공

(C) Ho-Won Jung, Korea University 35 국내 정보통신관련 법규 체계  정보화기본법  전기통신관계 법령 : 전기통신기본법, 전파법, 전기통신사업법, 전기통신공사업법, 군용전기통신법  전산망관계 법령 : 전산망보급확장 이용촉진에 관한 법률  방송관계법령 : 유선방송관리법, 종합유선방송법  정보보호관계 법령 : 통신비밀보호법, 컴퓨터프로그램보호법, 공공기관의 개인정보보호에 관한 법률  기타 : 정보통신연구개발에관한법률, 한국전기통신공사법, 통 신개발연구원법