Computer Networks. Introduc)on to Computer Networks. Week 01. College of Information Science and Engineering Ritsumeikan University

Transcription

1 Computer Networks Introduc)on to Computer Networks Week 01 College of Information Science and Engineering Ritsumeikan University

2 Today s lecture outline l Introduction to the instructor and course l Short history of networks - Historical networks - Telegraph - Broadcast networks - Public Switched Telephone Networks - Very brief background of the Internet l Reading: Lesson 1 of the course material Except when otherwise noted, photo images on these slides are from Wikimedia Commons under the GNU license, for educational purposes only not for redistribution 2

3 Important Information l Name of this course: Computer Networks l Course language: English l Instructor s name: (Prof. Dr.) PIUMARTA ( ピュマータ ) l piumarta@cs.ritsumei.ac.jp l Instructor s office: CC 301 l Office hours: Thursdays, 14:30-16:00 l Course web site: 3

4 Course Grading l Short tests (50%) Usually at the beginning or end of class, about the previous week s topic One longer test, approximately mid-term Hand-written notes may be allowed in tests, so take notes! l Final exam (50%) 4

5 Grading l Grading is by university standards with no exceptions l The final grade combines tests and a final exam l Tests will be used as reference for attendance records l Students who copy or cheat will be reported to the academic office 5

6 Course Materials l Reading will be provided each week l Students must keep a notebook for the course and must write lecture notes l Check the course site each week for practice exercises and other materials l Use a dictionary and other study tools l Slides are only to illustrate lectures, not a substitute for listening or reading! l Students will be asked to investigate some topics on their own in reports 6

7 Course Overview 1. History of networks 2. OSI Communication Reference Models 3. Basic Communication Concepts 4. Media and Devices 5. Architectures and Topologies 6. Standards and Protocols 7. Mid-term test 8. Data Encapsulation 9. Naming, Addressing and Routing 10. Common Protocols and Standards 11. Application Layer Elements 12. Client-Side Programming 13. Web-Based Applications 14. Network Security and Ethics 15. Course Review 7

8 Types of Networks l The study of networks, their structure and behavior, is a growing topic of interest for all science, especially biology, sociology, and anthropology l Relationships between various things can often be described as a network: organisms, proteins, human interaction l It is important to note these networks share some common representations and mathematical properties l This class focuses on computer networks 8

9 Computer Networks: a Definition l Computer network: any system that allows communication of information between devices that perform algorithms on data l Communication is considered to be by digital and analog signals, including electrical, optical, and radio signals l In practice, computational devices are digital but some devices on a network may be non-computational (eg. a refrigerator) l The objectives of communication are as various as all of human activity 9

10 10 l Before communication by electrical signal, various forms of signaling devices were in use, including the semaphore device shown here Before the Telegraph Optical telegraph in Germany

11 11 Beginnings the Telegraph Telegraph key for input Telegraph ticker for output l For our purposes, communication by devices using electrical signals begins with the telegraph l The first long-distance line was between Washington DC and Baltimore, in 1844

12 Telegraph Network Concepts l Repeating was essential for sending messages over long distances l Repeating first done by human operators but devices such as the relay became cheaper, faster, and more reliable l Later, the task could be done with vacuum tubes (or valves), which were mostly replaced by the solid-state transistor l The basic concepts of signals and codes for information processing were developed for telegraphy 12

13 Repeaters A telegraph relay is an amplifier to receive signals and retransmit them. Photo from edisongallery.com for educational purposes only do not redistribute l The distance a signal be sent is limited by degradation so human repeaters were needed to increase the distance l When attenuation and noise become too great, the signal becomes useless l Mechanical repeaters became cheaper, faster, and more reliable than humans 13

14 14 Relays, tubes, transistors l A relay can be used as a repeater for telegraphy l Vacuum tubes (also known as valves) took their place and were also the basis of some of the first computers l Transistors were smaller, cooler, more efficient and reliable, and were later put on integrated circuits (ICs) Tube Relay Transistors

15 15 Telegraph Codes l Transmission codes were first for human sending and receiving l For these human-read codes, on devices that could not yet transmit voice, binary codes of variable length were convenient, such as Morse code l Later codes were automatically interpreted by machine, often binary codes of regular length, such as Baudot code

16 16 l Developed by Émile Baudot Baudot Code l 5-bit code for telegraphy of alphabetic characters and a few other special symbols, predecessor of ASCII l Speeds of early networks were described as Baud rate instead of bits per second or bytes per second Table of Baudot codes, with the top of each square showing the hex code and the bottom the character or figure represented

17 International Networks 17

18 18 l Originally telegraph and telephone were single lines PSTN l More than one possible receiver requires either broadcasting (inconvenient for telephony) or switching l Switching was first performed by human operators before electromechanical exchanges were introduced l The telephone network is the Public Switched Telephone Network PSTN

19 19 Telephone exchange Human operated telephone exchange at the beginning of the 20 th century

20 Network Concepts in PSTN l The medium for what are now called landlines was electricity over twisted-pair copper wires l Automatic switching over multiple networks required a hierarchical numbering system l Switching and hierarchical numbering (later called addressing) allow complex segmentation and easy point-to-point access l The PSTN was mostly controlled by large monopolies but legal rulings began to break these monopolies in the 1970 s and 1980 s 20

21 21 Hierarchical Numbering l A phone number is a set of numbers, each set of digits representing an area or segment of the PSTN l The switch has to have a specific algorithm for sending the call so the numbering has to follow specific rules, called a telephone numbering plan (example only) tells the switch to expect a country code 81 is the country code for Japan 77 is the area code for the Shiga area 566 is a local exchange code and 1111 is the BKC number

22 22 PSTN in Early Computer Networks l Telephone and telegraph monopolies resisted the use of unapproved devices and machines on the network but legal rulings changed and opened the way for users to attach their own devices l Users could connect to the telephone network via modems, to contact other users or mainframe computers l A modem is a modulator-demodulator, which converts a digital signal to an analog one and vice versa

23 Broadcast Network Concepts l Radio and television are the most familiar types of broadcasting l Radio communication was at first by telegraph codes, such as Morse code l Voice transmissions allowed broadcasts to ordinary people and homes l Television and radio have been through many changes but the underlying broadcast concept is still in use: each sender sends a signal on one allocated band of the electromagnetic spectrum 23

24 24 Broadcast Networks l Broadcast networks share one electromagnetic spectrum so they introduce government regulation of the electromagnetic bands l Bands are allocated, and potential interference between broadcast devices is regulated l l USA: FCC (Federal Communications Commission) JP: VCCI (Voluntary Control Council for Interference) l The properties of electromagnetic transmission vary greatly depending on the part of the spectrum used, from extremely small X-rays and Gamma rays through radio waves that can be many kilometers

25 Electromagnetic Spectrum Much of this side is internationally and locally regulated for communication 25

26 Early Computer Networks l Many early networks developed in the 1950's and 60's l Militaries developed networks for defense information systems, such as SAGE Semi Automatic Ground Environment l Some people who had developed these military networks also began work on networks for businesses, such as Semi- Automated Business Research Environment (SABRE), for airline reservation systems 26

27 27 ARPANET l The ARPANET introduced the foundation of what would become the Internet l ARPANET stands for Advanced Research Projects Agency Network l ARPANET was a research project for the US military but soon involved other agencies and civilian institutions l A major concept introduced by the ARPANET as it grew was internetworking with packet switching

28 28 ARPANET advances ( ) l The term internetworking was shortened to internet (as an adjective first) l Internet Protocol (TCP-IP, as we ll discuss in a later class) became the only protocols used on ARPANET on the 1 st of January 1983 l The major advances applied that were essential to the Internet were: packet switching, addressing and routing, and best-effort services

29 ARPANET advances ( ) 29

30 30 The Early Internet ( ) l The Internet (now a proper noun) grew exponentially as more educational institutions and other groups joined l OS distributions, such as BSD Unix, made it easier for universities to participate l The National Science Foundation formed NSFNET, linking a handful of universities l In 1991, the NSF opened the Internet to commercial uses and the exponential growth has continued

31 31 Conclusions l Today's lesson is a too short introduction to just a tiny fraction of network history l The history of networks informs us about why networks are the way they are l Many concepts and problems we have today are from the way networks formed l As we discuss computer networks, we will return to these historical networks and familiar networks to get a better picture

32 32 Mini-Test (just for fun) 1) Complete the following statements by choosing the appropriate letter: Broadcast Repeater Telephone Modem a) lets any transmitter communicate with any receiver b) delivers the same message or content to many receivers c) repairs signals that degrade as they travel d) carries analogue, not digital, signals Exchange (switch) e) converts signals between analogue and digital forms

33 33 Important Information l Instructor s name: (Prof. Dr.) Piumarta l piumarta@cs.ritsumei.ac.jp l Instructor s office: CC301 (turn right from 3F elevator) l Name of this course: Computer Networks (QR) Homework: read the course site and follow the instructions given.