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.

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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..

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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ReadingReading

Chapter 6, Basic Communication Chapter 7, The Local Area Network Arrives

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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.

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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.

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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ModulationModulation

Amplitude Modulation Frequency Modulation Phase Modulation

Modulation means imposing information on an electrical signal (called the carrier)

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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Source: Yale Universityhttp://www.yale.edu/ee100/class18/sld018.gif

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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..

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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…

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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 …

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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.

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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.

January 10, 2002 CE80N -- Winter 2002 -- Lecture #3

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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.