CE80N Introduction to Networks Dr. Chane L. Fullmer UCSC Winter 2002

January 10, 2002CE80N -- Winter Lecture #32 CE80N - Course Information Class Web Page ( –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?)

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 Course Schedule

January 10, 2002CE80N -- Winter Lecture #34 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.

January 10, 2002CE80N -- Winter Lecture #35 Assignment #2 Information Web Search Engine comparison –1 page written report –What search engines you used –Results based on the four criteria: 1.Ease of use 2.Accuracy of the search 3.Advanced Search Capabilities 4.Extra Features/Functions Due by – January 29, 2002

January 10, 2002CE80N -- Winter Lecture #36 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

January 10, 2002CE80N -- Winter Lecture #37 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..

January 10, 2002CE80N -- Winter Lecture #38 Introduction to Networks Review – Lecture #2 –The digital telephone network Circuit switched –Must connect end-to-end –Guaranteed bandwidth –Wasteful during idle periods

January 10, 2002CE80N -- Winter Lecture #39 Reading Chapter 6, Basic Communication Chapter 7, The Local Area Network Arrives

January 10, 2002CE80N -- Winter Lecture #310 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.

January 10, 2002CE80N -- Winter Lecture #311 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.

January 10, 2002CE80N -- Winter Lecture #312 Modulation Amplitude Modulation Frequency Modulation Phase Modulation Modulation means imposing information on an electrical signal (called the carrier)

January 10, 2002CE80N -- Winter Lecture #313

January 10, 2002CE80N -- Winter Lecture #314 Source: Yale University

January 10, 2002CE80N -- Winter Lecture #315 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

January 10, 2002CE80N -- Winter Lecture #316 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

January 10, 2002CE80N -- Winter Lecture #317 Introduction to Networks Encoding the data –Voice, music (sounds) are quantized to numeric values represented as bits.. –Text is represented by ASCII..

January 10, 2002CE80N -- Winter Lecture #318 Binary Number System - Review We have 10 fingers Computers have devices with 2 states ^310^210^110^ the binary number 2^42^32^22^12^0place values (1 * 2^4) + (0 * 2^3) + (0 * 2^2) + (1 * 2^1) + (1 * 2^0) = = 19

January 10, 2002CE80N -- Winter Lecture #319 Encoding Text Text can be represented in binary ASCII - American Standard Character Information Interchange Ascii Binary Code A a B b C c D d # $ %

January 10, 2002CE80N -- Winter Lecture #320 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

January 10, 2002CE80N -- Winter Lecture #321 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…

January 10, 2002CE80N -- Winter Lecture #322 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 – , 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 …

January 10, 2002CE80N -- Winter Lecture #323 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

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.

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.

January 10, 2002CE80N -- Winter Lecture #326 Introduction to Networks Connecting Computers –A minimum network – two nodes Computer AComputer B

January 10, 2002CE80N -- Winter Lecture #327 Introduction to Networks Connecting Computers –Adding a new computer to the network… Computer AComputer B Computer C

January 10, 2002CE80N -- Winter Lecture #328 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

January 10, 2002CE80N -- Winter Lecture #329 Introduction to Networks Connecting Computers –Example: Thin Net (Ethernet) Computer A Computer CComputer B LAN Hub Terminator

January 10, 2002CE80N -- Winter Lecture #330 Introduction to Networks Connecting Computers –Example: 10BaseT (Ethernet) Computer AComputer B Computer C LAN Hub

January 10, 2002CE80N -- Winter Lecture #331 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

January 10, 2002CE80N -- Winter Lecture #332 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..

January 10, 2002CE80N -- Winter Lecture #333 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…

January 10, 2002CE80N -- Winter Lecture #334 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

January 10, 2002CE80N -- Winter Lecture #335 Introduction to Networks Summary – Lecture #3 –Modulation of signals –Modulator/Demodulator -- Modem –Encoding of data to binary –Error detection –LAN Technology Easy, cheap, reliable

January 10, 2002CE80N -- Winter Lecture #336 GlossaryGlossary 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.

January 10, 2002CE80N -- Winter Lecture #337 GlossaryGlossary 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.

January 10, 2002CE80N -- Winter Lecture #338 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

January 10, 2002CE80N -- Winter Lecture #339 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.