ce80n introduction to networks dr. chane l. fullmer ucsc winter 2002
TRANSCRIPT
CE80NCE80NIntroduction to NetworksIntroduction to Networks
Dr. Chane L. Fullmer
UCSC
Winter 2002
January 10, 2002 CE80N -- Winter 2002 -- Lecture #3
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CE80N - Course InformationCE80N - 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?)
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, 2002 CE80N -- Winter 2002 -- Lecture #3
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Search Engine Comparison Search Engine Comparison Assignment (#2)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.
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Assignment #2 InformationAssignment #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
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Introduction to NetworksIntroduction 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
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Introduction to NetworksIntroduction 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..
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Introduction to NetworksIntroduction to Networks
Review – Lecture #2– The digital telephone network• Circuit switched
– Must connect end-to-end– Guaranteed bandwidth– Wasteful during idle periods
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ReadingReading
Chapter 6, Basic Communication Chapter 7, The Local Area Network Arrives
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Communication Using ElectricityCommunication Using ElectricityCommunication Using ElectricityCommunication 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.
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Signals on WiresSignals on WiresSignals on WiresSignals 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.
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ModulationModulation
Amplitude Modulation Frequency Modulation Phase Modulation
Modulation means imposing information on an electrical signal (called the carrier)
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Source: Yale Universityhttp://www.yale.edu/ee100/class18/sld018.gif
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Modem: A Modulator And A Modem: A Modulator And A DemodulatorDemodulatorModem: A Modulator And A Modem: A Modulator And A DemodulatorDemodulator
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
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Introduction to NetworksIntroduction 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
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Introduction to NetworksIntroduction to Networks
Encoding the data– Voice, music (sounds) are quantized to
numeric values represented as bits..– Text is represented by ASCII..
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Binary Number System - ReviewBinary Number System - ReviewWe have 10 fingers
Computers have devices with 2 states
... 1000 100 10 1
... 10^3 10^2 10^1 10^0
1 0 0 1 1 the binary number
2^4 2^3 2^2 2^1 2^0 place values
(1 * 2^4) + (0 * 2^3) + (0 * 2^2) + (1 * 2^1) + (1 * 2^0)
= 16 + 0 + 0 + 2 + 1 = 19
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Encoding TextEncoding TextText can be represented in binaryASCII - 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
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Introduction to NetworksIntroduction to Networks Errors
– Transmission errors can (and do) occur• Bits can get reversed: 01, 10…• 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
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Introduction to NetworksIntroduction 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…
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Introduction to NetworksIntroduction 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 …
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Circuit Boards Plug Into A Circuit Boards Plug Into A ComputerComputer
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 NIC (Network Interface Card)(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.
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Introduction to NetworksIntroduction to Networks
Connecting Computers– A minimum network – two nodes
Computer A Computer B
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Introduction to NetworksIntroduction to Networks
Connecting Computers– Adding a new computer to the network…
Computer A Computer B
Computer C
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Early SystemsEarly 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
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Introduction to NetworksIntroduction to Networks
Connecting Computers– Example: Thin Net (Ethernet)
Computer A Computer CComputer B
LAN Hub
Terminator
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Introduction to NetworksIntroduction to Networks
Connecting Computers– Example: 10BaseT (Ethernet)
Computer A Computer B
Computer C
LAN Hub
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Introduction to NetworksIntroduction to Networks
LANsA 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
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Introduction to NetworksIntroduction 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..
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Introduction to NetworksIntroduction 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…
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Relationship To The InternetRelationship 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
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Introduction to NetworksIntroduction to Networks
Summary – Lecture #3–Modulation of signals–Modulator/Demodulator -- Modem– Encoding of data to binary– Error detection– LAN Technology• Easy, cheap, reliable
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GlossaryGlossaryGlossaryGlossary
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.
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GlossaryGlossaryGlossaryGlossary
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.
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GlossaryGlossary 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
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GlossaryGlossary
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.