1. Computer Network

2. Part 1 : 데이터 통신과 네트워킹 개요

3. Chapter 1. Introduction (서론)

4. 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)

5. 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

6. Data communication system components

7. 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.

8. 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.

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

10. 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

11. Direction of Data Flow
Simplex

12. Direction of Data Flow
Half-Duplex

13. Direction of Data Flow
Full-Duplex

14. 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

15. 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.

16. 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)

17. 네트워크 평가기준(Network Criteria)
Data communication
network criteria
Performance
Reliability
Security

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

19. 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.

20. 보안 (Security)
Unauthorized access
Viruses and Worms

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

22. Type of Network Connection
point-to-point

23. Type of Network Connection
Multipoint

24. Physical Topology

25. 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.

26. Physical Topology
Mesh

27. 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.

28. 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

29. 스타형 (Star : 성형)
Each device has a dedicated point-to-point link only to a central controller, usually called a hub
스타형 (Star : 성형)

30. 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
if one link fails, only that link is affected

31. 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

32. 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

33. Bus 형

34. Bus (cont’d) Advantages ~ include ease of installation Disadvantages
~ include difficult reconfiguration and fault isolation

35. 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
break in the ring can disable the entire network
--> needs dual ring

36. 네트워크 분류 (Categories of Networks)
three primary categories
근거리 통신망 (LAN)
도시 통신망 (MAN)
광역 통신망 (WAN)
size, ownership, distance it cover, physical architecture

37. Categories of Networks (cont’d)
Local area networks
(LAN)
Metropolitan area network
(MAN)
Wide area network
(WAN)

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

39. Categories of Networks (cont’d)

40. Categories of Networks (cont’d)
MAN(Metropolitan Area Networks)
~ is designed to extend over an entire city

41. 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

42. Categories of Networks (cont’d)
WAN

43. 1.3 Internet A Brief History Internet (not internet)
ARPANET (Advanced Research Projects Agency: ARPA) – mid-1960s
Advanced Research Projects Agency (ARPA) in the DOD : presented ideas of ARPANET, 1967
Reality : 1969 (UCLA, UCSB, SRI, U of Utah)
Birth of Internet : in 1972
Vint Cerf and Bob Kahn : Internetting Project
TCP/IP : A paper by Cerf and Kahn in 1973
In 1983, TCP/IP became to official protocol for the ARPANET
MILNET : in 1983
CSNET, NSFNET, ANSNET, …

44. Internet Today 1969. Four-node ARPANET established.
1970. ARPA hosts implement NCP.
1973. Development of TCP/IP suite begins.
1977. An internet tested using TCP/IP.
1978. UNIX distributed to academic sites.
1983. TCP/IP becomes the official protocol
1983. MILNET was born.
1986. NSFNET established.
1990. ARPANET replaced by NSFNET.
1991. WWW by CERN
1995. NSFNET became a research network.
1995. ISPs started.

45. Internet Today

46. 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

47. Protocol & Standards (cont’d)
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)

48. Standards Standards De facto De jure (by fact) (by law)
~ 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 jure
(by law)

49. 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)

50. 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.
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)

51. 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)

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

53. 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

54. 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.

55. Standards Organizations (cont’d)
한국정보통신기술협회(TTA) : 정보통신부관련
1988년 12월 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

56. Standards Organizations (cont’d)
한국산업표준원(KISI) : 산업자원부 관련
산업표준 연구 개발
표준화 국제 협력 및 진흥
북한 표준 연구
정보산업 표준화
자본재 표준화
KSSN(한국 표준 정보망)운영

57. 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