CE80N Introduction to Networks

1. CE80NIntroduction to Networks Dr. Chane L. Fullmer UCSC Winter 2002

2. CE80N - Course Information • Class Web Page (http://www.cse.ucsc.edu/classes/cmpe080n/) • Syllabus (Reading, Assignments, Exams) • Assignments • Due BY dates shown, not ON those dates • Section is available to turn in work on Fridays • Lecture notes • On-line in Power Point format (today?) CE80N -- Winter 2002 -- Lecture #3

3. Course Schedule • 4. Jan 15 (T) A Brief History Of The Internet • Read • Chapter 8, Internet: The Early Years; • Chapter 9, Two Decades of Incredible Growth; • Chapter 10, The Global Internet; • Chapter 11, A Global Information Infrastructure. • 5. Jan 17 (Th) How Does The Network Work? • Read • Chapter 12, Packet Switching; • Chapter 13, Internet: A Network of Networks; • Chapter 14, ISPs and Network Connections • Due by Jan 29: Web Search Engine Evaluation

4. Search Engine Comparison Assignment (#2) Conduct a compound search using a subject that is of use to you in this or another class. Use four different search engines and evaluate the results. CE80N -- Winter 2002 -- Lecture #3

5. Assignment #2 Information • Web Search Engine comparison • 1 page written report • What search engines you used • Results based on the four criteria: • Ease of use • Accuracy of the search • Advanced Search Capabilities • Extra Features/Functions • Due by – January 29, 2002 CE80N -- Winter 2002 -- Lecture #3

6. Introduction to Networks • Review from lecture #2 • Telephone system • Pervasive, ubiquitous • Provides uniform service • Underlying technology transparent to users • The analog world • Analog sources – music, voice, etc.. • Analog reproduction distortion prone CE80N -- Winter 2002 -- Lecture #3

7. Introduction to Networks • Review – lecture #2 • Sampling • Sample at twice the signal frequency • Quantization • Sampling across time • Lossy – round-off error • True reproduction of stored information • No distortion – all or nothing  • Although… there is bit rot.. CE80N -- Winter 2002 -- Lecture #3

8. Introduction to Networks • Review – Lecture #2 • The digital telephone network • Circuit switched • Must connect end-to-end • Guaranteed bandwidth • Wasteful during idle periods CE80N -- Winter 2002 -- Lecture #3

9. Reading • Chapter 6, Basic Communication • Chapter 7, The Local Area Network Arrives CE80N -- Winter 2002 -- Lecture #3

10. Communication Using Electricity • Digital communication resulted in three historical stages that: • Focused on the properties of signals on wires. • Focused on how to use signals to send bits. • Focused on how to detect and correct errors. CE80N -- Winter 2002 -- Lecture #3

11. Signals on Wires • An electrical signal reflects from the end of a metal wire the same way that light reflects from a mirror. • Signals: • Lose strength as they pass across the wire. • Emit electromagnetic radiation that interferes with nearby wires. CE80N -- Winter 2002 -- Lecture #3

12. Modulation • Modulation means imposing information on an electrical signal (called the carrier) Amplitude Modulation Frequency Modulation Phase Modulation CE80N -- Winter 2002 -- Lecture #3

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14. Source: Yale University http://www.yale.edu/ee100/class18/sld018.gif CE80N -- Winter 2002 -- Lecture #3

15. Modem: A Modulator And A Demodulator • Principles of modulation exist today. • Requires a modulator at one end and a demodulator at the other end • Requires a set of wires • Uses a modulator/demodulator device called a modem CE80N -- Winter 2002 -- Lecture #3

16. Introduction to Networks • Modems … • Allows two-way communication • Designed to either use two different signals or • Agree to take turns sending data • In either case, data appears to flow simultaneously in both directions. • Dial-up modems • Can dial the phone line and set up call • Talk only to other modems • Newer modems can talk to older slower modems CE80N -- Winter 2002 -- Lecture #3

17. Introduction to Networks • Encoding the data • Voice, music (sounds) are quantized to numeric values represented as bits.. • Text is represented by ASCII.. CE80N -- Winter 2002 -- Lecture #3

18. Binary Number System - Review • We have 10 fingers • Computers have devices with 2 states ... 1000 100 10 1 ... 10^310^210^110^0 10011 the binary number 2^42^32^22^12^0 place values (1 * 2^4) + (0 * 2^3) + (0 * 2^2) + (1 * 2^1) + (1 * 2^0) = 16 + 0 + 0 + 2 + 1 = 19 CE80N -- Winter 2002 -- Lecture #3

19. Encoding Text • Text can be represented in binary • ASCII - American Standard Character Information Interchange Ascii Binary CodeA 01000001 a 01100001B 01000010 b 01100010C 01000011 c 01100011D 01000100 d 011001001 00110001 # 001000112 00110010 $ 001001003 00110011 % 00100101 CE80N -- Winter 2002 -- Lecture #3

20. Introduction to Networks • Errors • Transmission errors can (and do) occur • Bits can get reversed: 01, 10… • Error detection • Parity bits -- odd, even • Bits in a message are summed • Parity bit is set to complete sum for either odd or even total (0 is even, 1 is odd) • Parity bits alone are not sufficient • Checksum • Bytes are summed to total • Total is included with message and the sums “checked” • Corrupted messages are dropped CE80N -- Winter 2002 -- Lecture #3

21. Introduction to Networks • The Local Are Network (LAN) • Early data transfers were accomplished by physically “moving the data” around • Magnetic tapes, disk packs • “Never underestimate the bandwidth of a station wagon loaded full of mag tapes headed for LA” --- anonymous • Interconnecting computers was becoming necessary to facilitate the information flow… CE80N -- Winter 2002 -- Lecture #3

22. Introduction to Networks • Interconnecting the computers • Circuit boards • Specific to hardware platform • IBM, DEC, CDC, NCR…. • Today it is better standardized – ISA, PCI, PCMCIA • Specific to physical medium and protocol • Wire -- Ethernet, X.25… • Wireless – 802.11, HIPERLAN… • Physical layers are standardized • A Sun running Ethernet can talk to an IBM running Ethernet or a Windows PC running Ethernet or anything running Ethernet … CE80N -- Winter 2002 -- Lecture #3

23. Circuit Boards Plug Into A Computer • Computers are built such that they contain a set of sockets. • Using wires to connect sockets together • Using wires to carry power and data • Plugging circuit boards into sockets to control external devices CE80N -- Winter 2002 -- Lecture #3

24. Figure 7.1 Illustrations of the components visible in a computer when the cover has been removed. A circuit board can plug into each socket; wires connect the sockets to other components.

25. NIC (Network Interface Card) • A computer needs network interface hardware and a cable that connects to the LAN. • A computer uses the network interface card (NIC) to send and receive data.

26. Introduction to Networks • Connecting Computers • A minimum network – two nodes Computer A Computer B CE80N -- Winter 2002 -- Lecture #3

27. Introduction to Networks • Connecting Computers • Adding a new computer to the network… Computer C Computer A Computer B CE80N -- Winter 2002 -- Lecture #3

28. Early Systems • Advantage of early LANs were speed. • Disadvantages of early LANs were inconvenience and cost. Requiring effort to: • Add a new computer • Connect incompatible hardware CE80N -- Winter 2002 -- Lecture #3

29. Introduction to Networks • Connecting Computers • Example: Thin Net (Ethernet) Computer B Computer C Computer A Terminator LAN Hub CE80N -- Winter 2002 -- Lecture #3

30. Introduction to Networks • Connecting Computers • Example: 10BaseT (Ethernet) Computer C LAN Hub Computer A Computer B CE80N -- Winter 2002 -- Lecture #3

31. Introduction to Networks • LANs A computer communication technology is classified as a Local Area Network (LAN) if it provides a way to interconnect multiple computers across short distances. • Modern day LANs are inexpensive, reliable and convenient to install and manage CE80N -- Winter 2002 -- Lecture #3

32. Introduction to Networks • LAN technology is standardized • The LAN is isolated from the computers that use it (via the circuit cards – aka network interface card (NIC) ) • LAN parameters are independent of user machines – speed, distance, etc.. CE80N -- Winter 2002 -- Lecture #3

33. Introduction to Networks • LANs have changed the economies of computing • LANs allow the sharing of resources • Use of inexpensive computers to access expensive resources • Printers, disks… • Remote printing is common • LANs came along just in time.. • Internet design assumed many LANs would be interconnected via the Internet… CE80N -- Winter 2002 -- Lecture #3

34. Relationship To The Internet • Xerox gave universities a prototype of a new LAN technology from their Palo Alto Research Center (Xerox PARC). • Beginning of Ethernet • Developing the idea of inexpensive and widely available LANs CE80N -- Winter 2002 -- Lecture #3

35. Introduction to Networks • Summary – Lecture #3 • Modulation of signals • Modulator/Demodulator -- Modem • Encoding of data to binary • Error detection • LAN Technology • Easy, cheap, reliable CE80N -- Winter 2002 -- Lecture #3

36. Glossary • ASCII • Abbreviation for American Standard Code for Information Interchange. • Carrier • A steady electrical signal or tone that is used by a modem to encode information for transmission across a communication line or a telephone connection. CE80N -- Winter 2002 -- Lecture #3

37. Glossary • Demodulator • The electronic device in a modem that decodes an incoming signal and extracts data. • Modulator • The electronic device in a modem that encodes data for transmission. • Modem • a device used to transmit digital data a long distance across an analog transmission path. CE80N -- Winter 2002 -- Lecture #3

38. Glossary • Computer network • A hardware mechanism that computers use to communicate. • Ethernet • A popular LAN technology invented at Xerox Corporation (Xerox PARC). • Hub • An electronic device connecting several computers; serving as the center of a LAN CE80N -- Winter 2002 -- Lecture #3

39. Glossary • Local Area Network (LAN) • A computer network technology designed to connect computers across a short distance. • Network of Networks • A phrase used to describe the Internet. CE80N -- Winter 2002 -- Lecture #3