Computer Networks

6.829 Fall 2005September 8, 2005

nms.csail.mit.edu/6.829

Muscle-Powered Communications

• Human messengers on foot or horseback• “Command and Control” between capital

and the field

• 14 AD: Roman relays—50 miles per day for regular mail, 100 miles per day for express mail

• 1280 AD: Kublai Khan—200-250 mi per day“Poste Haste”— “Fast Post” —riders signal by horns

“Let us turn now to the system of post-horses by which the Great Khan sends his dispatches. You must know that the city of Khan-balik is a centre from which many roads radiate to many provinces, one to each, and every road bears the name of the province to which it runs. ... When one of the Great Khan's messengers sets out along any of these roads, he has only to go twenty-five miles and there he finds a posting station, which in their language is called yamb and in our language may be rendered as 'horse post'. … Here the messengers find no less that 400 horses, stationed here by the Great Khan's orders and always kept in readiness for his messengers …

"By this means the Great Khan's messengers travel throughout his dominions and have lodgings and horses fully accoutred for every stage. … The whole organization is so stupendous and so costly that it baffles speech and writing.”

-- Marco Polo (1290)

The Pony Express

1861 AD: The Pony Express• 150-200 mi/day, 1966 mi from

Missouri to California, 10-13 days

• Longest ride: 14 year old “Buffalo Bill” Cody, 384 mi

• Record time: 7 days 17 hours with President Lincoln’s Inaugural Address, March 4, 1861

Western Union’s line puts it out of business, October 1861

• Chappe (1763-1805), a “defense contractor”; 1st message successfully sent in 1794• 1799: Napoleon seizes power; sends “Paris is quiet, and the good citizens are content.”• 1814: Extends from Paris to Belgium & Italy • 1840: 4000 miles, 556 stations, 8 main lines, 11 sublines, each hop ~10 km• Many “advanced” techniques: switching, framing, codes, redundant relays, message acks, priority messages, error notification, primitive encryption!

Pics: Proc. Symp. on the Optical Telegraph,Stockholm, June ’94

Visual communications: The optical telegraph

Scientific Advances

• Late 18th—Early 19th Century• Increasing evidence of the close relationship

between electricity and magnetism• Oersted (Copenhagen): demonstrated

electricity’s ability to deflect a needle• Sturgeon (London), 1825: electromagnet demo• Joseph Henry, 1830: 1-mile demo: current

through long wires, causing bell to ring!• Faraday (London), 1831: EM induction

experiments (induction ring), basis for motors

The Electric Telegraph• Cooke and Wheatstone,

Railroad Telegraph, 1837

• 14 mi installed by 1838• 4000 mi by 1852

The Electric Telegraph (Samuel Morse)

Morse Code (1835-1837)• 1838: demo’d over 2

miles• 1844: US- sponsored

demonstration between Baltimore and Washington DC

Dots and Dashes Span the Globe

• 1852: First international telegram

• Reuters establishes “Telegraph News Network”

• 1858: Cyrus Field lays first transatlantic cable

• US President & Queen Victoria exchange telegrams

• Line fails in a few months

• 1866: New cable & technology developed by William Thompson (Lord Kelvin)

Dots and Dashes Span The Globe

• Communications “arms” race in the Imperial Age• No nation could trust its messages to a foreign power

• 1893: British-owned Eastern Telegraph Company and the French crisis in Southeast Asia

• 1914: British cut the German overseas cables within hours of the start of WW I; Germany retaliates by cutting England’s Baltic cables and the overland lines to the Middle East through Turkey

• Strategic necessity: circumventing the tyranny of the telegraph lines owned by nation states

Wireless!

James Clerk Maxwell (1831-1879)"... we have strong reason to conclude that light itself -- including radiant heat, and other radiations if any -- is an electromagnetic disturbance in the form of waves propagated through the electromagnetic field according to electromagnetic laws." Dynamical Theory of the Electromagnetic Field, 1864.

Heinrich Hertz (1857 - 1894)• Mid-1880s: Demonstrated

experimentally the wave character of electrical transmission in space

Wireless TelegraphyGuglielmo Marconi• 1895: 21 year-old

demonstrates communication at distances much greater than thought possible

• Offers invention to Italian government, but they refuse

• 1897: Demonstrates system on Salisbury Plain to British Royal Navy, who becomes an early customer

• 1901: First wireless transmission across the Atlantic

• 1907: Regular commercial service commenced

Wireless in Warfare

“Portable” radio, circa 1915 Airborne radio telephone,post WW I

The Telegraph Learns to Talk

• Morse telegraph: no multiplexing• Only one message sent/received at a time

• Second half of 19th century: many researchers work on improving capacity

• One idea: sending messages at different pitches (Graham Bell)

The TelephoneAlexander Graham Bell

• 1876: Demonstrates the telephone at US Centenary Exhibition in Philadelphia

• Bell and Elisha Gray rush patents to USPTO, Bell first by a few hours

• Bell offers to sell patents to Western Union for $100,000, who refuse. Bell Telephone Company founded 9 July 1877.

• 1878: Western Union competes using rival system designed by Thomas Edison and Elisha Gray. Bell sues and wins.

Bell’s Early Telephones + “Most Valuable Patent”

US Patent 174,465 (March 7, 1876)

Mechanical Telephone Switch

Almon Brown Strowger (1839 - 1902)• 1889: Invents the “girl-less, cuss-less”

telephone system

“Ma Bell” and the telcos.• Bell’s patents expire in 1890s; over 6000

independent operators spring up• 1910: Bell System controls 50% of local telephone market• 1913: AT&T & U. S. government reach Kingsbury

Agreement: AT&T becomes regulated monopoly while promising "universal" telephone service; Controls “toll” services in U.S.

• Long distance interconnection withheld as a competitive weapon

• 1950: Bell System controls 84% of the local telephone access market

• 1984: Divesture of Ma Bell (Judge Greene)• 1996: Trivesiture of AT&T Bell (AT&T, Lucent, NCR)• Much activitity, mergers, splits, acquisitions over past 10

years

Computer Comms & Packet Switching

ARPA: 1957, in response to SputnikPaul Baran

• Early 1960s: New approaches for survivable comms systems; “hot potato routing” and decentralized architecture, 1964 paper

Donald Davies, early 1960s• Coins the term “packet”

Len Kleinrock (MIT thesis): “Information flow in large communication nets”, 1961

J. Licklider & W. Clark (MIT), On-line Man Computer Communication

L. Roberts (MIT), first ARPANET plan for time-sharing remote computers, SOSP ‘67 paper

ARPANET & Internetworking

BBN team that implementedthe interface message processor

ARPANet• 1967: Connect computers at key

research sites across the US using pt-to-pt telephone lines

• Interface Message Processors (IMP) ARPA contract to BBN

• Ted Kennedy telegram on BBN getting contract

ARPANET Topology in 1969

First inter-site demo, 1969.First crash very soon after!

History, contd.

• 1970, ARPANET hosts start using NCP; first two cross-country lines (BBN-UCLA and MIT-Utah)

History, contd.

• 1972, modified ARPANET email program (BBN), various demos and apps; CYCLADES effort in France; telnet spec

• 1973, APRANET becomes international• 1973-75, internetworking effort (Kahn &

Cerf, et al.)• 1976, UUCP distributed by AT&T• 1978, TCP and IP split (end-to-end

principle)• 1980, ARPANET grinds to halt due to a virus

History, contd.

• 1981, many networks (BITNET, CSNET, Minitel, …)

• 1982, DoD standardizes on TCP/IP• 1984, DNS introduced• 1986, NSFNet started, NNTP, MX

records, big outage in New England• Congestion collapse episodes, Van

Jacobson’s solutions

• Decentralized administration

Some Decentralized Administration (1987)

History, cont.

• 1990, No more ARPANET• 1991, WWW (Berners-Lee)

• 1990s: everyone gets on the web

• mid-1990s: NSFNet gets out of centralized backbone; ISPs take off

• 1996, telcos ask for IP phones to be banned, bubble starts

• 2001, bubble bursts; much progress in between!

• 2000s: net truly international; more non-PC devices than computers on the Internet

Year 2000

Internet hosts (names) with time:

~40% per year

The Big Challenges• Internetworking: interconnecting in the face of

• Heterogeneity• Scale• Generality of uses

• Sharing• Wireless and mobility• Handling and facilitating evolution: expanding

the net toward new uses• Coping with abuses

d(technology)/dt for networks

Moore’s Law2x / 18 months

DRAM Access Time1.1x / 18months

Highest Link Capacity2x / 7 months

Aggregate Internet Traffic2x / 12 months

1

10

100

1,000

10,000

100,000

1,000,000

1980 1983 1986 1989 1992 1995 1998 2001

Norm

alized

Gro

wth

sin

ce 1

98

0

Speed of light0x / 18 months!

Bits/s per dollar2x / 79 months(crude estimate)

# Internet hosts2x / 13.3 months

Thanks to Nick Mckeown @ Stanford for some of these data points

Acknowledgments

• Professor Randy Katz, UC Berkeley, for several of these slides

• Professor Nick McKeown, Stanford, for some data (tech trends)

• Various Web sites, including about.com, zakon.org, isc.org