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Transcript of Tlc p01 network_services_2012
Telecomunicazioni
Docente: Andrea BaiocchiDIET - Stanza 35, 1° piano palazzina “P. Piga”
Sede Facoltà S. Pietro in Vincoli
E-mail: [email protected]
University of Roma
“La Sapienza”
Corso di Laurea in Ingegneria Gestionale
A.A. 2011/2012
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Programma
1. SERVIZI E RETI DI TELECOMUNICAZIONE (KR-Cap. 1; GW-Cap. 1)
2. FONDAMENTI DI COMUNICAZIONI
3. ARCHITETTURE DI COMUNICAZIONE
4. SERVIZI DI RETE E MODI DI TRASFERIMENTO
5. STRATO DI COLLEGAMENTO E ACCESSOMULTIPLO
6. TECNOLOGIE DI STRATO DI COLLEGAMENTO
7. LO STRATO DI RETE IN INTERNET
8. LO STRATO DI TRASPORTO IN INTERNET
9. CENNI SUI PROTOCOLLI APPLICATIVI
Communication Networks andServices
Basic terminology and concepts
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Communication
Network
The big picture
Communication
Network
Users
Users run applications and interact via acommunication network
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Applications
• Client-server
– Few host (servers) have got information content,processing power or any needed facility and are ready toanswer to service requests from a much larger number ofhosts (clients)
• Peer-to-peer
– Many hosts (peers) cooperate to create service, withpossibly small help from some centralized servers
• Also:
– Uni/bi-directional
– Interactive or not
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Examples: client-server apps
• FTP
• SSH, Telnet
• WWW
• E-commerce
• Audio & video streaming
• Web 2.0
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Examples: p2p apps
• Telephony, Voice/Telephony-over-Internet
• Instant messaging: messenger, SMS
• File sharing: eMule, BitTorrent,…
• Real-time P2P: Skype, IPTV
• Network interactive games
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What is a communication network?
• The equipment (hardware & software) and facilitiesthat provide the basic communication service
• Virtually invisible to the user; represented by acloud
Communication
Network
• Equipment
– Routers, servers,switches, multiplexers,hubs, modems, …
• Facilities
– Copper wires, coaxialcables, optical fiber, radio
– Ducts, conduits,telephone poles …
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Analogies
• A communication network provides services
– This is like utilities, e.g. water supply, electric supply,…
• Flexible connectivity
– This is like transportation systems
Goods / people
information
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Approaches to long-distancecommunications
• Transfer of messages made up of
– parseable sequence of symbols (digital information)
– continuously variable physical quantities (analoginformation)
• Courier: physical transport of the message
– Messenger pigeons, pony express, FedEx,…
• Messages can be transferred by means oftransmission and reception of signals
– Drums, beacons, mirrors, smoke, flags, semaphores,…
– Electromagnetic field
• We focus on electrical communications
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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• Morse code converts text message into sequenceof dots and dashes
• Use transmission system designed to convey dotsand dashes
— — — — —0! — — — —1! — !R! !I
— — — — !9— — ! !Z— — ! —Q! ! ! !H
— — — ! !8— ! — —Y! — — !P— — !G
— — ! ! !7— ! ! —X— — —O! ! — !F
— ! ! ! !6! — —W— !N!E
! ! ! ! !5! ! ! —V— —M— ! !D
! ! ! ! —4! ! —U! — ! !L— ! — !C
! ! ! — —3—T— ! —K— ! ! !B
! ! — — —2! ! !S! — — —J! —A
MorseCode
MorseCode
MorseCode
MorseCode
Example of digital communications
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Digital Transmission Evolution
1.0E+00
1.0E+02
1.0E+04
1.0E+06
1.0E+08
1.0E+10
1.0E+12
1.0E+14
1850 1875 1900 1925 1950 1975 2000
Morse
T-1 Carrier
SONET
Optical
Carrier
Info
rma
tio
n t
ran
sfe
r
pe
r se
co
nd
Wavelength
Division
Multiplexing
Baudot
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Multiplexing
• Point-to-point communication systems:
– tx + communication link + rx
• Usually much more capacity available thanuseful/affordable for single user pair
• Natural approach: put multiple information flowsof different user pairs onto the same sharedcommunication system
• Generalizable to point-to-multipointcommunications
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The N2 Problem
• For N users to be fullyconnected directly
– Requires N(N – 1)/2connections, i.e. scaleswith square of number ofusers
– Requires too muchcommunication resources,often underutilized:inefficient & costly
• Basic idea to improve:resource sharing
N = 1000
N(N – 1)/2 = 499500
1
2
34
N
. . .
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Switching
• Since information flows share same link, there is aneed of intermediate dispatching
– Analogous to railway or bus stations
• A system where more links converge (input) andfrom which more links depart (output) is definedas a switching node if it has the task of decidingand actuating the correct output for each piece ofinformation coming from an input
– In Internet context known as router;
– in telephone circtui networks known as exchange;
– in LAN or ATM contexts known as switch.
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Switching: telephony example
• Patchcord panel switch invented in 1877
• Operators connect users on demand
– Establish circuit to allow electrical current to flow frominlet to outlet
• Only N connections required to central office
1
23
N – 1
N
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Circuit switching0
1
62
0
1
31
2
2
0
1
62
0
1
31
0
1
62
0
1
31
0
1
62
0
1
31
3161
0
1
62 31
0
1
0
1
31
0
1
62
A1
B1C1
A2
B2C2
0
1
62
C261
B
C
AA3
B3
C3
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Telephone subscribers connected to local CO (central office)
Tandem & Toll switches connect COs
Hierarchical Network Structure
Tandem
CO
Toll
CO COCO
CO
Tandem
CO = central office
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1
2
3
Routing
Store&Forward
Input
lines
Output
lines
Packet switching
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Communications modes
• With connection
– Two or more parties
– Stateful
– Three phases: Set up, Data transfer, Tear down
• Connectionless
– Two or more parties
– Stateless
– Single phase: Data transfer
Network selects route;
Sets up connection;
Called party alerted
Telephone
network
Pick up phone
Dial tone.
Dial number
Exchange voice
signals
1.
2.
3.
4.
5.
Telephone
network
Telephone
network
Telephone
network
Telephone
network
Hang up.6.
Connection
set up
Information
transfer
Connection
release
Telephone
network
Example: telephone call
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Communication Network Architecture
• Network architecture: the plan that specifieshow the network is built and operated
– Architecture is driven by network services and relieson available technology
• Overall communication process is complex:therefore network architecture partitions overallcommunication process into separate functionalareas called layers
– E.g. physical layer, end-to-end layer,…
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Architecture layer view
• Given a layer of the network architecture, thecommunication network can be modeled by a graph
– Vertices are nodes that cooperate with neighboring nodes tosupport upper layer service
– Edges define (logical) direct communication links used bynodes to cooperate
• Network topology
• Interface (node-to-node)
• Protocol (layer)
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Network topology
• Refers to a givenarchitecture layer viewof the system
• Specifies connectivity,i.e. capability of directinteraction betweenpeer entities
• Topology model: agraph
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Connections of all Internetsub-networks in the world
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What is an interface?• Contact point between two entities at a given level of
abstraction (layer)
– In the graph model of the layer, an edge between two nodescorresponds to an interface
• Entity: piece of sw/hw able to perform a task by co-operating with other remote, peer entities
• An interface is defined by specification of thefollowing aspects:
– Mechanical (only for physical interfaces)
– Electrical (only for physical interfaces)
– Functional (role played by any part of the interface)
– Procedural (sequence of events that involve one or morefunctions of the i/f: protocol)
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Example: ITU-T V.24
!
!
Composizione
numero
telefonico
DTR ON
RI ON
RTS ON
CTS ON
Tono
Audio
Cifre di
selezione
T x D
RTS OFF
CTS OFF
Toni Audio
(Dati)
Toni Audio
(OFF)
Toni Audio
(Dati)R x D
RTS OFF
CTS OFF
CD OFFCD OFF
CTS OFF
RTS OFF
T x D
CTS ON
Breve
Ritardo
Breve
Ritardo
RTS ON
CD OFF
R x D
DSR ON
DTR ON
Modalità
Dati
CD ON
Fase d
i
trasfe
rim
ento
dati
Fase d
i
Insta
ura
zio
ne
Fase d
i
abbattim
ento
Toni Audio
(OFF)
DCE
(Modem)
DTE
(Terminale)
DCE
(Modem)
DTE
(Terminale)
Interfaccia
DTE/DCE
Interfaccia
DTE/DCE
Linea
telefonica
commutata
! Spia luminosa accesa Spia luminosa spenta
DCE
Ring Indication
Data Terminal Ready
Carrier Detect
Signal Ground
Data Set Ready
Clear To Send
Request To Send
Receive Data
Transmit Data
Shield Ground
22
20
8
7
6
5
4
3
2
1
DTE
Connettore 25 pinISO 2110
RI
DTR
CD
SIG
DSR
CTS
RTS
RxD
TxD
SHG
25 24 23 22 21 20 19 18 17 16 15 14
47.17 mm
13 12 11 10 9 8 7 6 5 2 134
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Example: Ethernet
• Specification of electrical quantities (current, voltage) andwaveforms (sync pulse trains, pulse shape)
• Specification of access procedures: Medium Access Control (MAC)protocol
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What’s a protocol?
a human protocol and a computer network protocol:
Hi
Hi
Got thetime?
2:00
TCP connection request
TCP connectionresponse
Get http://net.infocom.uniroma1.it
<file>
time
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Protocol elements
• A protocol is a set of rules that governs how two ormore parties communicating over an interface areto interact
• Examples
– Internet Protocol (IP), Transmission Control Protocol(TCP), HyperText Transfer Protocol (HTTP), Simple MailTransfer Protocol (SMTP)
• Key elements of a protocol
– Syntax
– Semanthics
– Timing
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Protocols• A protocol can be described by means of state
machines
• State is the set of variables whose value issufficient to decide next transition given input andinternal events
– E.g. message receipts, timer expiration
• Given state at time t, X(t)=a, any event occurringin the interface at a subsequent time t+h makesthe state evolve to b
• Actions are associated to transition a->b.
Protocols define format, order of msgs sent and receivedamong network entities, and actions taken on msg send/rcv
Communication Networks andServices
Internet at large
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Packet Switching
• Internet is but one example of a packet switchednetwork
• Basic ideas:
– Information is segmented into “small”, self-containedchunks (smaller than typical amount of information to betransferred) -> PACKETS
– Packets hop from one node to another until they find theirway to the destination -> STORE & FORWARD
– Hop can be realized by ANY underlying communicationtechnology -> INTERNETWORKING
– Improvement of QoS demanded to end-to-end protocols(e.g. error recovery, flow/congestion control)
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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High-level view of Internet• Hosts, routers and inter-networking
G
G
G
G
G
G
Net 1
Net 5
Net 3
Net 4Net 2
H
HH
H
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First packet switching ideasPaul Baran, 1964
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A closer look at network structure:
• network edge
– applications and hosts
• access networks
– wired/wirelesscommunication links
– large number of “small”routers
• network core
– interconnected routers
– network of networks
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Q: How to connect end systems to edge router?
• residential access nets
• institutional access networks (school, company)
• mobile access networks
Dialup modem
xDSL - Digital Subscriber Line
wirelessaccess point
wirelesslaptops
router/firewall
modemto/from
CO
Access networks
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Q: How to connect end systems to edge router?
• residential access nets
• institutional access networks (school, company)
• mobile access networks
LAN - Local Area NetworkWireless
basestation
mobilehosts
router
Access networks
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Internet structure: network of networks
• roughly hierarchical
• at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cableand Wireless), national/international coverage
– treat each other as equals
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-1providersinterconnect(peer)privately
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Tier-1 ISP: e.g., Sprint
…
to/from customers
peering
to/from backbone
…
.
………
POP: point-of-presence
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Internet structure: network of networks
• “Tier-2” ISPs: smaller (often regional) ISPs
– Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
Tier-2 ISP paystier-1 ISP forconnectivity torest of Internet! tier-2 ISP iscustomer oftier-1 provider
Tier-2 ISPsalso peerprivately witheach other.
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Internet structure: network of networks
• “Tier-3” ISPs and local ISPs
– last hop (“access”) network (closest to end systems)
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
Local and tier-3 ISPs arecustomers ofhigher tierISPsconnectingthem to restof Internet
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Internet structure: network of networks
• a packet passes through many networks!
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Hourglass model (H. Schulzrinne)
Communication Networks andServices
Outlook
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Trends in Network Evolution
• It’s all about services
– Building networks involves huge investment
– Services that generate revenues drive the networkarchitecture
• Current trends and issues
– Multimedia applications
– Info-centric communications
– End of trust
– Legal issues (laws are local, network is global)
– Overlay networks
– Nano-networks
– E-government, e-business, e-commerce
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Declination on Internet
• Internet of Communities: organization of people activitiesthrough the Internet, on the basis of common interests andlikings.
• Internet of Services: interconnection of providers andconsumers of any type of service that can be accessedthrough the Internet.
• Internet of Media: network supporting media search,delivery, and integration, regardless their format, providingsuitable storage and quick access.
• Internet of Things: pervasive network, capable ofconnecting all devices that can generate, transmit, or receivecontents, including sensors, cameras, wearable devices.
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Evolution of services
Yesterday,call switching…
…today,call center
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Network models:intelligent vs dumb
Source: M. Dècina, 2006
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Network models: flat• Mesh, ad hoc networks
– IEEE 802.11 e 802.16
• Pervasive andubiquitous computing
– Domotics,embedded/wearablecomputing
– event-driven, context-aware, communicating,networked smart objects
• Wireless sensornetworks
– ZigBee, RFID Source: M. Dècina, 2006
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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End of Trust
• Security Attacks
– Spam, Phishing, Pharming
– Denial of Service, DDoS
– Viruses
– Impersonators
• Firewalls & Filtering
– Control flow of traffic/data from/to Internet
• Confidentiality, integrity and authentication;authorization; traffic monitoring
• Anonymity, privacy
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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ICT security attributes
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TCP/IP stack & security
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Operations, Administration,Maintenance, and Billing
• Communication like transportation networks
– Traffic flows need to be monitored and controlled, QoSand security must be guaranteed, possibly at differentlevels
– Tolls have to be collected
– Roads have to be maintained
– Need to forecast traffic and plan network growth
• Highly-developed in telephone network
– Entire organizations address OAM & Billing
– Becoming automated for flexibility & reduced cost
• Under development for IP networks
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Success Factors for New Services
• Technology not only factor in success of a newservice
• Three factors considered in new telecom services
TechnologyMarket
Regulation
Can it be
implemented cost-
effectively?
Can there be
demand for the
service?
Is the service
allowed/somehow
constrained?
New
Service
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Role of regulation
• Public regulation is fundamental as communicationservices become a commodity
• Minimum service access to be guaranteed
– Universal service
• Digital divide
• Also fundamental for
– unique resources (radio spectrum)
– protection of public interests (e.g. health)
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Standards
• New technologies very costly and risky
• Standards allow players to share risk and benefitsof a new market
– Reduced cost of entry
– Interoperability and network effect
– Compete on innovation
– Completing the value chain
• Chips, systems, equipment vendors, service providers
• Example
– 802.11 wireless LAN products
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Standards Bodies• Internet Engineering Task Force (IETF)
– Internet standards development
– Request for Comments (RFCs): www.ietf.org
• International Telecommunications Union (ITU)
– International telecom standards
• International Standardization Organization (ISO)
• IEEE 802 Committee
– Local area and metropolitan area network standards
• Regional bodies (ETSI, ANSI)
• Industry Organizations and Fora
– 3GPP, MPLS Forum, WiFi Alliance, World Wide Web Consortium,Bluetooth
Communication Networks andServices
History
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Computer Network Evolution Overview
• 1950s: Telegraph technology adapted to computers
• 1960s: Dumb terminals access shared host computer
– SABRE airline reservation system
• 1970s & 1980s: Computers connect directly to each other
– ARPANET packet switching network
– TCP/IP based internetworking
– Ethernet local area network
• 1990s & 2000s: New applications and Internet growth
– Commercialization of Internet
– E-mail, file transfer, web, P2P, streaming . . .
– Internet traffic surpasses voice traffic
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Internet History (1/5)
• 1961: Kleinrock - queueing theory shows effectiveness ofpacket-switching
• 1964: Baran - packet-switching in military nets
• 1967: ARPAnet conceived by Advanced Research ProjectsAgency
• 1969: first ARPAnet node operational
• 1972:
– ARPAnet public demonstration
– NCP (Network Control Protocol) first host-host protocol
– first e-mail program
– ARPAnet has 15 nodes
1961-1972: Early packet-switching principles
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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ARPANET - September 1971
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Internet History (2/5)
• 1970: ALOHAnet satellite network in Hawaii
• 1974: Cerf and Kahn - architecture for interconnecting nets
• 1976: Ethernet at Xerox PARC
• Late 70’s: proprietary architectures: DECnet, SNA, XNA
• Late 70’s: switching fixed length packets (ATM precursor)
• 1979: ARPAnet has 200 nodes
Cerf and Kahn’s internetworking principles:
– minimalism, autonomy - no internal changes required to interconnect nets
– best effort service model
– stateless routers
– decentralized control
1972-1980: Internetworking, new and proprietary nets
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Internet History (3/5)
• 1983: deployment of TCP/IP
• 1982: smtp e-mail protocol defined
• 1983: DNS defined for name-to-IP-address translation
• 1985: ftp protocol defined
• 1988: TCP congestion control
• new national networks: Csnet, BITnet, NSFnet, Minitel
• 100,000 hosts connected to confederation of networks
1980-1990: new protocols, a proliferation of networks
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Internet History (4/5)
• Early 1990’s: ARPAnet decommissioned
• 1991: NSF lifts restrictions on commercial use of NSFnet(decommissioned, 1995)
• Early 1990s: Web
– hypertext [Bush 1945, Nelson 1960’s]
– HTML, HTTP: Berners-Lee, 1989
– 1993: Mosaic, later Netscape
• Late 1990’s
– commercialization of the Web
– network security to forefront
– estimated 50 million host, 100 million+ users
– backbone links running at Gbps
1990, 2000’s: commercialization, the Web, new apps
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi
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Internet History (5/5)
• 2000’s
– more killer apps:
• instant messaging
• P2P applications (BitTorrent - file sharing; Skype - VoIP;PPLive - video)
• YouTube
• Gaming
• E-commerce
– wireless, mobility
– tens/hundreds Gbps backbone
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The Internet gotha
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Internet statistics
• ~769 million hosts (July 2010)
• ~2 billion users
• As of Feb. 27rd, 2012: 138,143,921 Top Level Domains
• As of Feb. 1st, 2012: 3,479,770,880 IP addresses assigned in 246countries
End of 2009:
• 234 million websites
• 247 billion emails sent daily on the average
• Facebook serves 260 billion page views per month (6 millions permin)
• YouTube serves 1 billion videos per day
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Host count