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History of Computer NetworkingWILLIAM W. MCMILLAN

The Telegraph1

Printing Telegraph

u 1840s, R. E. House

u Keypresses trans lated into telegraphic codes

u … and then to printed characters at the receiving end

u 28 keys

u With shift key, 56 characters

u Early ones were unreliable

u Not as fast as a skilled telegrapher

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Stock Ticker

u Specialized printing telegraph for reporting s tock prices

u 1863, E. A. Callahan

u T. A. Edison improved, 1871: Universal Stock Ticker

u Better synchronization

u Reduced tape friction

u Better tape feeding

u Reduced power (battery) consumption

u Tickers used until the 1960s

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Teletype

u Used for news wire services, commercial communication, military

u Several inventors worked on the idea starting in 1903

u Patented in 1915

u 5-bit Murray character code, based on Baudet code of 1870

u Included control codes for LF, CR

u Context shift codes: digits ↔ letters

u International and U.S s tandards in 1920s

u Superseded by 7-bit ASCII code in 1963

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Telephone System

u Telephone patented by A. G. Bell, 1876

u Based on harmonic or acoustic transmiss ion (“harmonic telegraph”)

u Multiple s ignals at same time, different frequencies or pitches

u If can send more than one pitch, then can transmit voice

u By 1880, there were 48,000 telephones in the U.S.

u Connected by various regional phone systems for a time

u Switchboard patented by Leroy Firman, 1882, for flexible point-to-point switching by human operators

u By 1910, Bell Telephone connected 5.8 million phones

u Long-dis tance calls required a sequence of operators to establish connections, from city to city

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Telephone System

u Automatic, electromechanical telephone switch patented by A. B. Stowger, 1891

u Depending on the number of pulses sent by the phone for each digit, a switch s teps through a series of contacts to establish connections

u There was a (temporary) dedicated, physical wire connecting two parties in a phone call

u Telephone exchange (switching center) established for each area (the second group of 3 digits in a 10-digit number, e.g., the 995 in 734-995-730 0 )

u Trunk lines carry calls between exchanges, with many calls sharing the same path, each getting a s lice of time in success ion

u Leased lines can provide permanent, direct connections between points

u Used to connect, say, two mainframe computers , pre-Internet

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Cellular Phone Systems

u Radio transmiss ion between phone and tower

u Small area (cell) handled by a cell tower

u Calls are handed off across cells as phone moves

u Mobile Telephone Switching Office is the intermediary to the whole phone system

u Unreliable transmiss ion, a lot of error handling needed

u Digital voice s ignals are compressed to reduce bits sent

u Many calls on one channel us ing time-divis ion multiple access or frequency-based schemes

u Generations go from from analog (1G) through digitization, more sophis ticated encryption, error handling, ways to share bandwidth, use of packets , etc.

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First Remote Use of a “Computer”

u In 1939 George Stibitz of Bell Labs completed the Complex Number Computer, a relay-based, complex-number calculator

u In a 1940 demonstration at a mathematics conference in Dartmouth, New Hampshire, Stibitz used a teletype to send commands to his CNC in New York over telegraph wires

u … and Steve Jobs thought he was something …

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1951: First Business Computer, LEO I

u J. Lyons was a British tea shop and bakery company with outlets across the country

u Sales and inventory data were phoned in to headquarters every day by every outlet

u LEO I (Lyons Electronic Office) computer developed in 1951 to handle all the data streams, produce reports , plan production and delivery

u Innovations in multiple input buffers and data storage us ing magnetic drums

u LEO computation services were sold to other firms

u Later LEO computers were developed and sold

u Networking via humans on the phone, but truly a large-scale, networked, computer application

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Early 1950s: Keyboard Input to Computer

u Whirlwind I computer, s tarted late 1940s

u MIT and U.S. Navy

u Intended for flight s imulation

u Magnetic core memory

u Stored program (program in memory)

u Computed resuts with bits of word in parallel rather than in sequence

u SAGE (see later) prototype Project Charles , 1951

u Radar s tations networked to Whirlwind I

u Keyboards, light pens

u 1956: Direct input to Whirlwind I from keyboard

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SAGE, 1958

u Semi-Autonomous Ground Environment provided networking of radar s tations across the U.S. for air defense

u MIT’s Lincoln Labs and IBM developed AN/FSQ-7 computers to support, based on Whirlwind II

u 23 hardened radar s ites across the U.S. and Canada, to detect enemy aircraft (78 s ites by 1961)

u Stations networked via telephone lines and microwave transmiss ion to two AN/FSQ-7 computers

u Initially two Direction Centers with computers , connected to a Combat Center

u Operated into the 1980s

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12SAGEArchitecture SABRE, 1960

u American Airlines reservation system: “Semi-Automated Bus iness Research Environment”

u American Airlines couldn’t keep up with passenger reservations us ing manual and teletype system

u In 1946 developed “Reservisor,” but not up to the task

u IBM was contractor for SABRE, used skills acquired in SAGE project

u Transmiss ion via thousands of miles of telephone lines

u Used switches called Mulcoms (Multiplexor Communications)

u Store and forward of data controlled by central computers

u Agents used special-purpose terminal, included card input and printed output

u Agent requested reservation, central computer confirmed

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Reserv i sor

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Time-Sharing

u Multiple users access a computer system interactively via computer terminals or teletypes connected through hardware multiplexers

u Need to control terminal interfaces, “line discipline,” buffering

u Requires multitasking operating system

u 1961: John McCarthy pioneers at MIT

u Compatible Time-Sharing System (CTSS)

u 1964: GE and Dartmouth develop Dartmouth Time-Sharing System

u Kemeny and Kurtz of Dartmouth create BASIC programming language

u 1964-67: GE carries out many demos and trials of remote connections to time-sharing systems, even having employees connect from home

u GE is a major player in commercial time-sharing systems from then on

u 1967: Michigan Terminal System (MTS) – used until the 1990s

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Computer Terminal

u “Dumb” terminal

u About like a teletype, but a CRT display instead of a roll of paper

u The dumbest didn’t even allow movement of the cursor to a given pos ition

u Fixed character set, of course

u Could be connected to nearby computer via terminal multiplexer

u Or could connect over a phone line (see next)

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DEC VT52

Acoustic Modem/Coupler

u Remote connection to computer over phone line

u Modem (modulator/demodulator) connected to computer

u Dial in to computing facility, if hear tone, insert phone handset

u Get login screen on terminal – and proceed

u Need digital → analog convers ion

u Computer s ignal to acoustic wave form

u And analog → digital convers ion

u Acoustic s ignal to computer’s digital codes

u Baud rate (bits per second): mostly 150 to 1200

u In use into the 1980s

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Licklider’s Vision

u J. C. R. Licklider, b. 1915, Ph.D. in experimental psychology, 1942

u At MIT, became involved in SAGE, human factors , and then other IT-related subjects into the 1960s

u Went to Bolt, Beranek, and Newman, government contractor

u Then headed DARPA Information Process ing Techniques Office

u Proposed “Man-Computer Symbios is”

u Conceived of "Intergalactic Computer Network” in 1960s

u Essentially the Internet, WWW, and Cloud computing

u Supported networking research

u Approved funding for ARPANET

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Marill and Roberts Connect Computers, 1965

u Thomas Marill, a psychologis t, and Lawrence Roberts of MIT’s Lincoln Lab connect computers , Marill in Santa Monica, CA, and Roberts in Lexington, MA

u Leased a line from Western Union

u Ins tead of terminal-like interaction, M & R built a defined message protocol into the operating system

u They present a paper in 1966, "Toward a Cooperative Network of Time-Shared Computers”

u DoD Advanced Research Projects Agency (ARPA, later DARPA) funded the research

u Precursor to ARPANET

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Lawrence Roberts

Packet Switching

u Ins tead of a large file being sent in a s ingle s tream, it is divided into s tandard-s ized packets for transmiss ion, typically hundreds of bytes

u Paul Baran, an engineer at Rand Corp., worked on “survivable” communications systems in early 1960s

u If nodes or central computer are disabled, how do you transmit information?

u Divide into packets and have redundant routes , with no central control

u Each node connected to three or more neighbors

u Ideas developed independently by L. Kleinrock and D. Davies

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Paul Baran

ARPANET

u Funded bt DARPA

u 1968: Bas ic ideas for ARPANET defined

u Based on packet switching (see previous ly)

u Interface Message Processors (IMPs) were critical

u “Gateways” or “routers”

u Interfaces between local computers and the network

u Were packet-switching nodes

u By 1973, dozens of univers ities , research centers , and military facilities connected

u TCP/IP protocols created for ARPANET by V. Cerf and R. Kahn

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IBM’s System Network Architecture, 1974

u SNA was motivated by increas ing transaction process ing

u Entering data via terminals for database access , ordering, bank operations , …

u Started as hierachical – tree s tructure – then interconnected trees

u Used leased lines , then extended to dial-in

u Token ring protocol for local connections

u Allowed point-to-point and even direct memory access

u Communication controllers between hosts and peripheral systems

u Establishment controllers connect multiple end points

u Includes path control, datagram creation, routing, reassembly

u Complex s tructure of heterogenous entities – all OSI layers

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DECnet, 1975

u Digital Equipment Corporation

u Developed to connect PDP-11 minicomputers , RSTS operating system

u Firs t peer-to-peer network

u Eventually could support 64K nodes and multiple DEC OSes

u At firs t: Digital Data Communications Message Protocol (DDCMP)

u Serial controller lines used

u Synch or asynch, full or half duplex

u Packets (max 512 bytes), acknowledgements , error detection, retransmiss ion

u Buffered transmiss ion

u All OSI layers

u Later, used Ethernet

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ARCNET, 1976

u Datapoint Corp., Chief Architect John Murphy

u Claim to firs t LAN, was platform agnostic

u Grew out of Datapoint’s disk controller technology

u Bus protocol was token pass ing

u Packets were 253 – 508 bytes (disk blocks were 256 bytes)

u Used coaxial cable, allowing connections over greater dis tances than twis ted-pair (“phone wire”) connections

u Competed with Ethernet, DECnet, and IBM technologies

u Advantages over Ethernet for load balancing and flow control

The typical response was something like, “Why would anyone want to have computers connected together?”

[ John Murphy , http://arcnet.cc/resour ces /Hi st oryA TA. pdf ]

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John Murphy

X.25 Protocol, 1970s

u For WANs

u Packet switched

u Phone companies developed as data traffic grew

u Covers bottom three OSI layers

u Handles various families of devices

u Data terminal equipment (DTE), e.g., user terminals , local hosts

u Data circuit-terminating equipment (DCE), e.g., intermediate modems, switches

u Packet-switching exchange (PSE), in carriers ’ facilities

u Multiplexed virtual c ircuits, i.e., a virtual bidirectional wire between points , many sharing one phys ical connection

u Defines packet formation, assembly, error handling, flow control

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Usenet, 1979

u Decentralized store-and-forward network

u Built on UUCP: Unix-to-Unix Copy protocol

u Created by U. North Carolina and Duke U.

u Tom Truscott, Jim Ellis , Steve Bellovin

u Connected to ARPANET via U. C. Berkeley

u Users post artic les , others respond

u Implemented via shell scripts

u Hierarchically organized by topic (newsgroups)

u E.g., rec.arts .poems, sci.optics , comp.lang.python, alt.tv.s impsons

u Some newsgroups moderated

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Bulletin Board Systems

u Community Memory project by Homebrew Computer Club, 1973

u Terminals in record s tore, laundromats , community centers

u Permanent lines to timesharing system

u Whole Earth 'Lectronic Link (The WELL), 1985

u Dial-up

u “…a dialog between the fiercely independent writers and readers of the Whole Earth Review.” [ https://www. wel l .com /ab out wel l .html ]

u Cleveland Free-Net, 1986, Case Western Reserve Univers ity

u Public Electronic Network (PEN), 1989

u City of Santa Monica, for res idents to dialog with government

u City info, email, conferencing

u … many others during1970s – 1980s

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American Online, 1983

u Commercial system, charged user fees

u Hourly at firs t, then monthly

u “All-inclus ive” environment, restricted to just AOL

u Email, chats , bulletin boards for various interest groups, clubs, news

u Started as s ingle-purpose s ite for Atari 2600 game console

u User had to have computer and modem

u Ins talled AOL software from phys ical disk

u Dial-in connection, 300 or more bits per second

u “You’ve got mail!” voice became cultural meme

u Beat out CompuServe , which s till charged by the hour

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Ethernet, 1974

u Developed at Xerox for LANs

u Robert Metcalfe, David Boggs, Chuck Thacker, Butler Lampson

u Is at heart a bus topology, but can be adapted for s tar

u Competed with token-based arbitration

u Uses packets , including error-detection bits

u Originally coaxial cable, later twis ted-pair and fiber-optic

u Carrier-sense multiple access : all nodes “lis ten” to carrier to determine if it is c lear to send

u Can tell if there is a collis ion, wait random time to try again

u Data transmiss ion rates have ranged from 3 Mbps to 100 Gbps

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Communication Satellites

u Tels tar 1 made by Bell Labs, launched 1962

u Single transponder, low-earth orbit, operated 7 months

u Many more satellites launched by 1970s , mainly for phone traffic

u Canada began video broadcast in 1973

u Grew to dozens of transponders per satellite

u Iridium: Motorala patent in 1988, system live in 1998, 66+ satellites , cross-linked via microwave, each satellite reads 48 beams, can handle 1000+ phone calls

u Globalstar: Went live 1998, 52 satellites (moving to 24), use ground stations as relays instead of linking between satellites

u MILSTAR and others for military use

u Typical Internet data rates via satellite are 1..1000 Mbps

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Direct Precursors to the Internet

u ARPANET – see earlier

u BITNET

u Univers ities : s tarted with connection from City U. New York and Yale U.

u Used leased lines , IBM protocols

u CSNET

u NSF-funded, computer science departments , Rand, BBN

u For those not on ARPANET

u X.25 packet switching, TCP/IP

u Gateways to ARPANET

u Dial-up available

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Direct Precursors to the Internet

u Minitel: France Telecom, nationwde network

u NSFNET

u Initially to connect supercomputer centers , funded by NSF

u Large centers served as backbones connected to regional networks

u TCP/IP

u Merit

u Started in 1966 to share resources at U Mich, Mich State, Wayne State

u Initially host-to-host and batch oriented

u Through early 1980s , developed interfaces to various hardware

u Telnet connections, dial-up, many educational institutions

u Developed protocols that influenced Internet

u With IBM and others , implemented and managed NSFNET

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Meri t Network

Internet

u Growing commercial activity in regional networking and NSFNET into the 1980s

u 1988-1994: NSF s tudies suggest unified national network

u Leonard Kleinrock presents “Toward a National Research Network,” to U.S. Congress , 1988

u Senator Al Gore introduces bill to support national networking

u High Performance Computing and Communication Act of 1991

u Result is National Information Infrasturcture or “information superhighway”

u Media-rich, end-user interactions employing a wide variety of platforms and resources, integrated into homes, schools , firms, and other organizations (cf. Licklider)

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Al Gore

Internet

u Vint Cerf and Bob Kahn developed TCP/IP in 1970s

u TCP/IP becomes s tandard for ARPANET, early 1980s

u Needed to pass data between different kinds of networks

u Give respons ibility for reliability to the nodes, remove it from the network

u Domain Name Service (DNS) trans lates domain name to IP address

u DNS server can be local for local lookups or, say, at ISP for external lookups

u Border Gateway Protocol (BGP), 1994, defines how to dis tribute routing information in order to dis tribute control and respons ibility for delivery

u A “peer” (say an ISP or univers ity) has routing information that tells it where to send a packet next on its journey, depending on the final destination

u BGP specifies how peers exchange and propagate routing information so that it can be shared and kept up to date

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Vint Cerf

Bob Kahn

Apple’s HyperCard, 1987

u Software development and delivery environment for Macintosh

u Non-programmer can create multimedia applications

u But there is also a powerful scripting language

u Application is a set of windows (called a s tack of cards)

u Developer can eas ily install graphics , sound, text, UI widgets , etc. on cards

u Buttons can be defined to link from one card to another

u … but all on one machine

u If Apple had enhanced to put cards on different machines, it would have been the WWW… had it used Internet protocols

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World Wide Web, 1989

u Tim Berners-Lee: British computing guy at CERN* in Geneva, Switzerland

u Berners-Lee had strong networking background

u Internet was taking off

u Proposed techniques for allowing easy access to files on one machine from another

u Created HTML to format web pages and define links

u Employed Internet technologies : TCP/IP, DNS

u Firs t web page put up 1991

u Development of powerful browsers allowed the masses to use the web

u Mosaic Netscape, Internet Explorer, Opera

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Tim Berners-Lee

*Consei l Européen pour la Recherche Nucléai re