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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u Superseded by 7-bit ASCII code in 1963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