Communication Network

Steven Low

CS & EE Depts, CaltechOct 1, 2001

Outline

• Information revolution– 3 circles of impact

• Network growth– 4 driving forces

Technological Revolutions

1780s - 1840s Steam power

1840s - 1890s Railway

1890s - 1930s Electricity

1930s - 1980s Car

1980s - Information Technology (IT)

IT : processing, storage & communication of info

(flight reservation, ID database, telephone, ...)

Circles of Impact

Core IT

IT-using Industries

Economic & Social life

Core IT: computer, communication technologiesIT-using Industries: corporations, governments, institutionsEconomic & Social life: how we live, work, play & interact

1st Circle: Core IT

Moore’s Law

Computing power doubles every 18 months

logscale

time

Computing power 1972 - 97: 1,000 times

Computing cost: -30%/yr 1995 cost = 0.01% of 1970s

Advances in Computer

1945 Computer (US)

1947 Transister (Bell Labs)

1971 Microprocessor (Intel)

1982 PC (IBM)

1970s: 5,000 computers worldwide

1996: 140M (US: 35 comp / 100 people

AU: 27 comp / 100 people)

28,000 times / 25 years

Advances in Communication

1876 Telephone (Alexander G. Bell)

1890 Telephone network

1920s Fax, movie transmission (BL)

1940s Mobile phone (1983 cellular, BL)

1958 Laser (BL)

1969 Internet

1980s Digital transmission, optical fiber

1990s WWW

Advances in Communication

Telephone Network:

1960s Undersea cable carries 138 calls

1996 Fiber optic cable carries 1.5M calls

10,000 times / 35 yreas

Data Network:

1969 4 hosts on Internet

1983 500 hosts

1995 4.5M hosts, 30M users

10,000 times / 12 years

Analogy: Car

If car technology has been advancing as fast:

• US$ 5 /car [US$ 25,000 /car]

• 100 km / lt [8 km / lt]

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 USBy late 1990s, Bell Labs in Netherland, China, etc

• Networking allows organizations to coordinate their decisions & activities globally.

Fig. 5, Economist, survey 28/9/1996

Trade & Investment

• Globalization1986 - 96 Int’l trade grew twice as fast as output

Foreign direct investment 3 times

1996 Foreign exchange trading US$1.3 tr/day

Global cross-border transactions in bond & equity:

1970: 3% US GDP

1995: 136% US GDP

“Little Productivity Gain”

• Productivity gain (output/worker, big-7 avg)

1960 - 73 : 4.5%

1973 - 95 : 1.5%

Two reasons:

• measurement error

• time to learn and change

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”

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

1925 Different city planning conceptualized

1960s Large shopping malls along highway

50 yrs of learning & diffusion

40 yrs of reorganizing

Learning & Diffusion Time

Example : Electricity

1880s Electro dynamo

1899 Electricity < 5% of power in US

1919 Electricity ~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

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

Summary

• IT : processing, storage & communication of information

• Information Revolution– Core IT industries– IT-using industries– Social & economic life

• Communication networks : key sector of IT

Outline

• Information revolution– 3 circles of impact

• Network growth– 4 driving forces

Networks Industry

US Communications Industry (1994)

TelephoneUS$ 200 B/yrComputer 80Newspaper 60Broadcasting 50Books 15

US$ 400 B/yr

Networks : 70% of communications industry

Communication Services

Voice

Telephone (wired & mobile), Pager, Radio

Image

Fax, WWW

Data

Fax, Email, WWW

Multimedia

TV, Tele-conferencing, Video-conferencing, VoD

Network Growth

Factors promoting network growth

• Digitization

• Economy of scale

• Network externalities

• Service integration

Analog Transmission

S -> E E -> S

Telephone

Transmitted signal Received signal

t t

Digital Transmission• Digitization (Analog -> Digital)• Digital transmission• Reconstruction (Digital -> Analog)

00

11

10

01

00 10 11 10 01 01 10 11

tA/D D/A

t10111001011011

DigitizationNyquist’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

Digitization

Quantization Error

SNR due to quantization ~ 6N dB

(SNR = 100.6N, N = bits/sample)

e.g. Telephone voice 48 dB

Low quality cassette 55

High quality cassette 68

CD 96

Digital DataVoice

Max freq = 4 kHz ==> sample @ 8000 sample/sec

Req SNR = 48 dB ==> N = 48/6 = 8 bits/sample

Uncompressed digital voice: 8k x 8 = 64 kbps

CD

Max freq = 20 kHz ==> sample @ 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 = 682.5 MB

NTSC TV

Max freq = 4.5 MHz ==> sample @ 9 M sample/sec

Req SNR = 48 dB ==> N = 48/6 = 8 bits/sample

Uncompressed NTSC TV: 9M x 8 = 72 Mbps

Advantages of Digitization

• Low transmission error (esp long distance)

• Compression, error correction, signal processingUncompressed Compressed

Voice 64 kbps 16 kbps (GSM IS54), 8 kbpsNTSC TV 72 Mbps 1.5 Mbps

• Same fidelity over time• Ease of storage, manipulation, and distribution

t1 0 1 1 10

t1 0 1 1 10

“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 externalitiese.g. Telephone network, Internet (137 countries

reachable by Email), inter-networking,

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 usersCritical size

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

Outline

• Information revolution– 3 circles of impact

• Network growth– 4 driving forces

• Network basics

Network Basics

• ApplicationsTraffic characterization, quality requirement

• Network typesSwitched, broadcast

• Network elements Switches, links

• Network mechanismsMultiplexing, switching, switches, routing, flow control, error control, medium access control, protocol layering

Applications

• Applications– Telephone, Email, WWW, Video-conferencing, ...

• Traffic characterization– Constant bit rate (Telephone, Video-conferencing)– Variable bit rate (Video-conferencing)– Messages (Email, WWW)

• Quality requirement– Small delay (Telephone, Video-conferencing)– Small loss (Email, WWW)

Applications Traffic Quality

Telephone CBR Small delay, moderate loss

Email Message Large delay, no loss

WWW Message Small delay, small loss

Video (uncomp) CBR Small delay, moderate loss

Video (comp) VBR Small delay, small loss

Examples

Network Types

CommunicationNetworks

Switched Networks Broadcast Networks

Wired(LAN)

Circuit Switching Wireless(radio, satellite, optical)

Packet Switching

Virtual Circuit Datagram

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

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

Multiplexing

• Allows many bit streams to share same transmission link• Frequency division multiplexing (FDM)

• Time division multiplexing (TDM)

• Code division multiplexing (CDM)

1 2 n...frequency

1 2 n...time

Radio, TV, cellular

Telephone, internet, cellular

Total spectrum

time

collision

Mobile network

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

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

• 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

Switching• 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

TCP/IP Protocol Stack

Applications (e.g. Telnet, HTTP)

TCP UDP ICMPARPIP

Link Layer (e.g. Ethernet, ATM)

Physical Layer (e.g. Ethernet, SONET)

Packet Terminology

Application Message

TCP dataTCP hdr

MSSTCP Segment

IP dataIP hdrIP Packet

Ethernet dataEthernet

Ethernet Frame

20 bytes

20 bytes

14 bytes 4 bytesMTU 1500 bytes

IP Header

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 10 1 2 3

Vers(4)

Flags

H len Type of Service Total Length (16 bits)

Fragment OffsetIdentification

Header ChecksumProtocol (TCP=6)Time to Live

Source IP Address

Destination IP Address

Options Padding

IP data

TCP Header

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 10 1 2 3

Source Port Destination Port

Sequence Number (32 bits)

Checksum

Options Padding

Acknowledgement Number (32 bits)

Urgent Pointer

URG

ACK

PSH

RST

SYN

FIN

Data Offse

tReserved Receive Window (16

bits)

TCP data

Window Flow Control

• ~ W packets per RTT

• Lost packet detected by missing ACK

RTT

time

time

Source

Destination

1 2 W

1 2 W

1 2 W

data ACKs

1 2 W

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

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

CS/145 b: Flow Control

• Basic tools– Optimization theory– Linear control theory– Lyapunov stability

• Internet congestion control– TCP– Queue management