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Communication Network Steven Low CS & EE Depts, Caltech Oct 1, 2001.

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Presentation on theme: "Communication Network Steven Low CS & EE Depts, Caltech Oct 1, 2001."— Presentation transcript:

1 Communication Network Steven Low CS & EE Depts, Caltech Oct 1, 2001

2 Outline Information revolution –3 circles of impact Network growth –4 driving forces

3 Technological Revolutions 1780s sSteam power 1840s sRailway 1890s sElectricity 1930s sCar 1980s - Information Technology (IT) IT :processing, storage & communication of info (flight reservation, ID database, telephone,...)

4 Circles of Impact Core IT IT-using Industries Economic & Social life Core IT: computer, communication technologies IT-using Industries:corporations, governments, institutions Economic & Social life: how we live, work, play & interact

5 1st Circle: Core IT Moore’s Law Computing power doubles every 18 months log scale time Computing power : 1,000 times Computing cost: -30%/yr 1995 cost = 0.01% of 1970s

6 Advances in Computer 1945Computer (US) 1947 Transister (Bell Labs) 1971Microprocessor (Intel) 1982PC (IBM) 1970s:5,000 computers worldwide 1996:140M (US: 35 comp / 100 people AU: 27 comp / 100 people) 28,000 times / 25 years

7 Advances in Communication 1876Telephone (Alexander G. Bell) 1890Telephone network 1920sFax, movie transmission (BL) 1940sMobile phone (1983 cellular, BL) 1958Laser (BL) 1969Internet 1980sDigital transmission, optical fiber 1990sWWW

8 Advances in Communication Telephone Network: 1960sUndersea cable carries 138 calls 1996Fiber optic cable carries 1.5M calls 10,000 times / 35 yreas Data Network: hosts on Internet hosts M hosts, 30M users 10,000 times / 12 years

9 Analogy: Car If car technology has been advancing as fast: US$ 5 /car[US$ 25,000 /car] 100 km / lt[8 km / lt]

10 2nd Circle: IT-using Diffusion of IT technology in industry –US investment in computers rising at 20-30%/year –1970: 7%, 1996: 40% Before early 1980s, AT&T has little presence outside US By late 1990s, Bell Labs in Netherland, China, etc Networking allows organizations to coordinate their decisions & activities globally. Fig. 5, Economist, survey 28/9/1996

11 Trade & Investment Globalization Int’l trade grew twice as fast as output Foreign direct investment 3 times 1996Foreign exchange trading US$1.3 tr/day Global cross-border transactions in bond & equity: 1970: 3% US GDP 1995:136% US GDP

12 “Little Productivity Gain” Productivity gain (output/worker, big-7 avg) :4.5% : 1.5% Two reasons: measurement error time to learn and change

13 Measurement Error Service industry exceeds agricultural & mining industries –US workers in agriculture 1820: 75% 1996: 3% Easy to measure agriculture & manufacturing outputs –Productivity gain has been quite significant Difficult to measure service “output”

14 Learning & Diffusion Time Time to learn to use technology Time to reorganize economic & societal activities Time for technology to mature & diffuse Example: Car 1877 Internal-combustion engine patented 1925Different city planning conceptualized 1960sLarge shopping malls along highway 50 yrs of learning & diffusion 40 yrs of reorganizing

15 Learning & Diffusion Time Example : Electricity 1880sElectro dynamo 1899Electricity < 5% of power in US 1919Electricity ~50% of power in US 40 yrs to mature and diffuse Before:machines around water wheels & steam engines After:assembly lines to optimize work flow

16 3rd Circle: Social Life Social & Economic Life –Globalization of culture –More intrusive government –Breakdown of monopoly of propaganda –Cultural islands 30M users on Internet in 1995 USENET: 10M news articles/month 3M Web pages in 18 months to 7/95 March 97: of 220M people >16 in US & Canada 23% (50M) use Internet 17% (37M) on Web

17 Summary IT : processing, storage & communication of information Information Revolution –Core IT industries –IT-using industries –Social & economic life Communication networks : key sector of IT

18 Outline Information revolution –3 circles of impact Network growth –4 driving forces

19 Networks Industry US Communications Industry (1994) TelephoneUS$ 200 B/yr Computer 80 Newspaper 60 Broadcasting 50 Books 15 US$ 400 B/yr Networks : 70% of communications industry

20 Communication Services Voice Telephone (wired & mobile), Pager, Radio Image Fax, WWW Data Fax, , WWW Multimedia TV, Tele-conferencing, Video-conferencing, VoD

21 Network Growth Factors promoting network growth Digitization Economy of scale Network externalities Service integration

22 Analog Transmission S -> EE -> S Telephone Transmitted signal Received signal t t

23 Digital Transmission Digitization (Analog -> Digital) Digital transmission Reconstruction (Digital -> Analog) t A/DD/A t

24 Digitization Nyquist’s Samplilng Theorem Sampling rate  2 x max frequency e.g. Sinusoidal signal of freq w ==> sampling rate = 2w samples/sec Voice max freq = 4 kHz ==> sampling rate = 8 samples/sec

25 Digitization Quantization Error SNR due to quantization ~ 6N dB (SNR = N, N = bits/sample) e.g.Telephone voice48 dB Low quality cassette55 High quality cassette68 CD96

26 Digital Data Voice Max freq = sample/sec Req SNR = 48 dB==>N = 48/6 = 8 bits/sample Uncompressed digital voice: 8k x 8 = 64 kbps CD Max freq = 20 40,000 samples/sec Req SNR = 96 dB==>N = 96/6 = 16 bits/sample Uncompressed stereo CD: 40k x 16 x 2 = 1.3 Mbps 70-min CD stores 1.3M x 70 x 60 / 8 = MB NTSC TV Max freq = M sample/sec Req SNR = 48 dB==>N = 48/6 = 8 bits/sample Uncompressed NTSC TV: 9M x 8 = 72 Mbps

27 Advantages of Digitization Low transmission error (esp long distance) Compression, error correction, signal processing Uncompressed Compressed Voice 64 kbps16 kbps (GSM IS54), 8 kbps NTSC TV 72 Mbps 1.5 Mbps Same fidelity over time Ease of storage, manipulation, and distribution t t

28 “Large is Good” Economy of scale –Cost increases more slowly than computing or communication capacity ==> multiplexing decreases per-user cost –Fixed costs, e.g. network administration, operation, and maintenance Network externalities e.g. Telephone network, Internet (137 countries reachable by ), inter-networking,

29 Critical Size Below critical size: cost > benefit Above critical size: cost < benefit Positive feedback fuels growth Subsidy needed before critical size is reached e.g. Internet, French Minitel Network, AT&T’s Picturephone Benefit Unit cost Number of users Critical size

30 Economy of Scope Service integration –Cheaper to have one integrated-services network than multiple single-service networks Internet –telephone, data, broadcast TV & radio and CATV, news, magazines, books, digital library –tele-commuting, tele-banking, tele-education Restructuring of industry –Alliances of communications & media giants e.g. US West - Time Warner, Bell Atlantic - Telecommunications, South West Bell - Cox

31 Outline Information revolution –3 circles of impact Network growth –4 driving forces Network basics

32 Network Basics Applications Traffic characterization, quality requirement Network types Switched, broadcast Network elements Switches, links Network mechanisms Multiplexing, switching, switches, routing, flow control, error control, medium access control, protocol layering

33 Applications –Telephone, , WWW, Video-conferencing,... Traffic characterization –Constant bit rate (Telephone, Video-conferencing) –Variable bit rate (Video-conferencing) –Messages ( , WWW) Quality requirement –Small delay (Telephone, Video-conferencing) –Small loss ( , WWW)

34 Applications Traffic Quality Telephone CBRSmall delay, moderate loss MessageLarge delay, no loss WWW MessageSmall delay, small loss Video (uncomp) CBR Small delay, moderate loss Video (comp) VBR Small delay, small loss Examples

35 Network Types Communication Networks Switched Networks Broadcast Networks Wired (LAN) Circuit Switching Wireless (radio, satellite, optical) Packet Switching Virtual CircuitDatagram

36 Network Elements User : telephone, computer, fax, camera, display,... Link : transfers bit stream at a certain rate with a given bit error rate & propagation delay e.g., optical fiber, copper coaxial cable, radio Switch : directs incoming bits to appropriate outgoing link Switch Link User

37 Network Mechanisms Multiplexing & switching –Sharing a link by many users Switches –Space division, time division Routing –Selecting a path end-to-end Flow control –Avoiding congestion Error control –Recovery from error or loss Medium access control –Sharing a broadcast medium

38 Multiplexing Allows many bit streams to share same transmission link Frequency division multiplexing (FDM) Time division multiplexing (TDM) Code division multiplexing (CDM) 12 n... frequency 12 n... time Radio, TV, cellular Telephone, internet, cellular Total spectrum time collision Mobile network

39 Switching Three modes –Circuit Swiching : digital & analog transmission –Virtual Circuit : digital transmission (packet switching) only –Datagram : digital transmission (packet switching) only Increasing simplicity and flexibility Decreasing service quality

40 Switching Circuit Switching –3 Phases: Connection setup, Data transmission, Connection clearing –Packets arrive in order –Dedicated resources, e.g., synchronous TDM slot –No queueing delay, only propagation delay

41 Virtual Circuit –3 Phases: Connection setup, Data transmission, Connection clearing –Packets arrive in order –NO dedicated resources, e.g., statistical multiplexing –Queueing delay, in addition to propagation delay Switching 1 2 3

42 Datagram –No connection setup –Packets may arrive out of order –No dedicated resources, e.g., statistical multiplexing –Queueing delay, in addition to propagation delay –Advantage : simplicity & robustness against network failure 2 1 3

43 TCP/IP Protocol Stack Applications (e.g. Telnet, HTTP) TCPUDP ICMP ARPIP Link Layer (e.g. Ethernet, ATM) Physical Layer (e.g. Ethernet, SONET)

44 Packet Terminology Application Message TCP dataTCP hdr MSS TCP Segment IP dataIP hdr IP Packet Ethernet dataEthernet Ethernet Frame 20 bytes 14 bytes 4 bytes MTU 1500 bytes

45 IP Header Vers(4) Flags H lenType of Service Total Length (16 bits) Fragment OffsetIdentification Header Checksum Protocol (TCP=6) Time to Live Source IP Address Destination IP Address OptionsPadding IP data

46 TCP Header Source PortDestination Port Sequence Number (32 bits) Checksum Options Padding Acknowledgement Number (32 bits) Urgent Pointer URGURG ACKACK PSHPSH RSTRST SYNSYN FINFIN Data Offset Reserved Receive Window (16 bits) TCP data

47 Window Flow Control ~ W packets per RTT Lost packet detected by missing ACK RTT time Source Destination 12W12W12W data ACKs 12W

48 Challenges Distributed control and optimization … –Routing –Flow control –Medium access control … over an uncertain unreliable network –Error control –Fault detection and recovery Real time control using networks –Sensor networks

49 Outline of Course Switch design (0.5 wk) Error control: error detection, ARQ (1 wk) Delay analysis: queueing models (1.5 wk) Medium access control (1 wk) Routing (1.5 wk) Flow control (1.5 wk) Switch Link User

50 CS/145 b: Flow Control Basic tools –Optimization theory –Linear control theory –Lyapunov stability Internet congestion control –TCP –Queue management


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