tnk108 introduction lecture 1a
DESCRIPTION
Computer NetworksTRANSCRIPT
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TNK108 TNK108 Datornt/Computer Networks 2010p
Scott Fowler
Lecture 1
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Book for the courseBook for the course
Computer Networking: A Top-Down Approach: International Version, 5/E
James F. Kurose, University of Massachusetts, AmherstJa es u ose, U e s y o assac use s, e sKeith W. Ross, Polytechnic University, Brooklyn
Publisher: Pearson Higher Education
Sid 2
ISBN-10: 0131365487ISBN-13:9780131365483
Scott Fowler, ITN
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Course Information (contd)Course Information (cont d) Literature Literature
Lecture notes
Textbook: J Kurose and K Ross Computer Textbook: J. Kurose and K. Ross, Computer Networking A Top Down Approach, 5th edition
Lecture notes and lab assignments: Lecture notes and lab assignments: http://webstaff.itn.liu.se/~scofo47/TNK108/tnk108.html(password = )
Supplement material, if needed, will be specified or handed out
Course Staff
Me -> Scott Fowler
Arash Matinrad
Scott Fowler, ITNSid 3
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Course Information (contd)Course Information (cont d) Examination and grading
2 closed book written exams (3 credits)
90% -100% = 5 (ECTS A)
75% 89% = 4 (ECTS B) 75% -89% = 4 (ECTS B)
60% -74% = 3 (ECTS C)
0 -59% = fail (ECTS F)0 59% a ( C S )
Overall grade = exam, if the result of the lab assignments is pass
Lab assignments (3 credits)g ( ) Pass / fail
Show your work and results to the course staff during lab hours
Re-examination Re-examination periods, not responsible for the times
A single written exam covering the entire scope of the course
Scott Fowler, ITNSid 4
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Chapter 1: roadmapChapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge end systems, access networks, links
1.3 Network core circuit switching, packet switching, network structure
1 4 Delay loss and throughput in packet-switched1.4 Delay, loss and throughput in packet switched networks
1 5 Protocol layers service models1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 HistoryIntroduction 1-5
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Whats the Internet: nuts and bolts view
millions of connected Mobile networkPCcomputing devices: hosts = end systems
Global ISPserver
wirelesslaptop running network apps
Home networkRegional ISP
laptopcellular handheld
i ti li k
I tit ti l t k
Regional ISP
access points
communication links fiber, copper,
radio satellite Institutional networkwiredlinks
p radio, satellite transmission
rate = bandwidth
router
rate = bandwidthrouters: forward
packets (chunks of packets (chunks of data)
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Whats the Internet: nuts and bolts view
protocols control sending, Mobile networkp otoco s co t o se d g,receiving of msgs e.g., TCP, IP, HTTP, Skype,
Mobile network
Global ISPg , , , , yp ,
Ethernet
Internet: network of Home networkR i l ISPnetworks
loosely hierarchicalRegional ISP
public Internet versus private intranet
I d d
Institutional network
Internet standards RFC: Request for comments IETF: Internet Engineering
Task Force Introduction 1-7
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Whats the Internet: a service view
communication infrastructure enables distributed applications:
Web, VoIP, email, games, e-commerce, file sharing
communication services provided to apps:
reliable data delivery from source to destination
best effort (unreliable) data delivery
Introduction 1-8
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Whats a protocol?What s a protocol?human protocols: network protocols:u a p otoco s
whats the time?I h ti
et o p otoco s
machines rather than humans I have a question
introductions
humans
all communication activity in Internet
specific msgs sent
activity in Internet governed by protocols
protocols define format, specific actions taken
when msgs received,
protocols define format, order of msgs sent and received among network
or other events entities, and actions taken on msgtransmission receipttransmission, receipt
Introduction 1-9
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Whats a protocol?What s a protocol?a human protocol and a computer network protocol:a u a p otoco a d a co pute et o p otoco
Hi
Hi TCP ti
TCP connectionrequest
HiGot thetime?
TCP connectionresponse
Get http://www.awl.com/kurose-rosstime?2:00
Get http://www.awl.com/kurose ross
timetime
Q: Other human protocols? Introduction 1-10
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A closer look at network structure:A closer look at network structure:
network edge: network edge:applications and hostshosts
access networks, physical media:physical media:wired, wireless communication linkscommunication links
network core:i t t d interconnected routers
network of network of networks
Introduction 1-11
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The network edge:The network edge: end systems (hosts): end systems (hosts): run application programs e g Web email e.g. Web, email at edge of network
client/server model client/server model client host requests, receives
service from always-on server e.g. Web browser/server;
email client/server peer-peer model: peer-peer model:
minimal (or no) use of dedicated servers
e.g. Skype, BitTorrent
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Access networks and physical media
Q: How to connect end Q o to co ect e dsystems to edge router?
residential access nets residential access nets institutional access
networks (schoolnetworks (school, company)
mobile access networks mobile access networksKeep in mind:
b d idth (bit bandwidth (bits per second) of access network?network?
shared or dedicated?
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Physical MediaPhysical MediaTwisted Pair (TP)
bit: propagates betweentransmitter/rcvr pairs two insulated copper wires
physical link: what lies between transmitter & receiver
Category 3: traditional phone wires, 10 Mbps Eth treceiver
guided media:Ethernet
Category 5: 100Mbps Ethernet signals propagate in solid
media: copper, fiber, coax
id d di
100Mbps Ethernet
unguided media: signals propagate freely, e.g.,
radioradio
Introduction 1-14
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Physical Media: coax, fiber
Coaxial cable: Fiber optic cable:Coaxial cable: two concentric copper
conductors
glass fiber carrying light pulses, each pulse a bit
bidirectional baseband:
high-speed operation: high-speed point-to-point
transmission (e g 10s baseband: single channel on cable legacy Ethernet
transmission (e.g., 10 s-100s Gps)
low error rate: repeaters legacy Ethernet broadband: multiple channels on cable
pspaced far apart ; immune to electromagnetic noise
multiple channels on cable HFC (Hybrid fibre-coaxial)
Introduction 1-15
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Physical media: radio
signal carried in Radio link types:s g a ca edelectromagnetic spectrum
yp terrestrial microwave
e.g. up to 45 Mbps channels no physical wire bidirectional
LAN (e.g., Wifi) 11Mbps, 54 Mbps
bidirectional propagation environment
effects:
wide-area (e.g., cellular) 3G cellular: ~ 1 Mbps
t lliteffects: reflection obstruction by objects
satellite Kbps to 45Mbps channel (or
multiple smaller channels) obstruction by objects interference
multiple smaller channels) 270 msec end-end delay geosynchronous versus low
altitude
Introduction 1-16
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Internet structure: network of networks
roughly hierarchical at center: small # of well-connected large networks at center: small # of well connected large networks tier-1 commercial ISPs (e.g., Verizon, Sprint, AT&T, Qwest,
Level3), national & international coverage) g
large content distributors (Google, Akamai, Microsoft) treat each other as equals (no charges)q ( g )
IXP IXP
Ti 1 ISP & Large Content Distributor (e.g., Google)
Large Content Distributor
(e.g., Akamai)Tier 1 ISPTier-1 ISPs &Content
Distributors, interconnect
Tier 1 ISP Tier 1 ISP
interconnect (peer) privately or at Internet Exchange Points
Introduction 1-17
Exchange Points IXPs
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Tier-1 ISP: e.g., Sprint
to/from backbone
POP: point-of-presence
peering.
to/from customers
Introduction 1-18
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Internet structure: network of networks
tier-2 ISPs: smaller (often regional) ISPsconnect to one or more tier-1 (provider) ISPsconnect to one or more tier-1 (provider) ISPs
each tier-1 has many tier-2 customer nets tier 2 pays tier 1 providerp y p
tier-2 nets sometimes peer directly with each other (bypassing tier 1) , or at IXP
Tier 2ISPIXP IXPTier 2
ISPTier 2
PLarge Content
Distributor (e.g., Google)
Large Content Distributor
(e.g., Akamai)Tier 1 ISP
ISP ISP
Tier 1 ISP Tier 1 ISP
( g , )
Tier 2P
Introduction 1-19
Tier 1 ISP r STier 2ISP
ISP Tier 2ISP
Tier 2ISP
Tier 2ISP
Tier 2ISP
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Internet structure: network of networks
Tier 3 ISPs local ISPs Tier-3 ISPs, local ISPs customer of tier 1 or tier 2 network
last hop (access) network (closest to end systems)
Tier 2
last hop ( access ) network (closest to end systems)
Tier 2ISP
Large Content Large Content
IXP IXP
Tier 1 ISP
Tier 2ISP
Tier 2ISP
Large Content Distributor (e.g., Google)
Large Content Distributor
(e.g., Akamai)Tier 1 ISP
Tier 1 ISP Tier 1 ISPTier 2
Tier 2ISP Tier 2
ISPTier 2 Tier 2 Tier 2
ISP
Introduction 1-20
ISPISP ISP ISP ISP
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Internet structure: network of networks
a packet passes through many networks from source a packet passes through many networks from source host to destination host
Tier 2Tier 2ISP
Large Content Large Content
IXP IXP
Tier 1 ISP
Tier 2ISP
Tier 2ISP
Large Content Distributor (e.g., Google)
Large Content Distributor
(e.g., Akamai)Tier 1 ISP
Tier 1 ISP Tier 1 ISPTier 2
Tier 2ISP Tier 2
ISPTier 2 Tier 2 Tier 2
ISP
Introduction 1-21
ISPISP ISP ISP ISP
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Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge end systems, access networks, links
1.3 Network core circuit switching, packet switching, network structure
1 4 Delay loss and throughput in packet-switched1.4 Delay, loss and throughput in packet switched networks
1 5 Protocol layers service models1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 HistoryIntroduction 1-22
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How do loss and delay occur?
packets queue in router bufferspackets queue in router buffers packet arrival rate to link exceeds output link capacity packets queue, wait for turn
packet being transmitted (delay)
A
BBpackets queueing (delay)
free (available) buffers: arriving packets d d (l ) f f b ffdropped (loss) if no free buffers
Introduction 1-23
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Four sources of packet delay
Atransmission
A propagation
Bnodal
processing queueing
dnodal = dproc + dqueue + dtrans + dprop
dproc: nodal processing check bit errors
dqueue: queueing delay time waiting at output link check bit errors
determine output link typically < msec
time waiting at output link for transmission
depends on congestion level of routertypically msec of router
Introduction 1-24
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Four sources of packet delay
Atransmission
A propagation
Bnodal
processing queueing
dnodal = dproc + dqueue + dtrans + dprop
dtrans: transmission delay: L: packet length (bits)
dprop: propagation delay: d: length of physical linkL: packet length (bits)
R: link bandwidth (bps) dtrans = L/R
d: length of physical link s: propagation speed in
medium (~2x108 m/sec)/d d d
Introduction 1-25
dprop = d/sdtrans and dpropvery different
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Queueing delay (revisited)
i
n
g
R: link bandwidth (bps) L: packet length (bits)
e
q
u
e
u
e
d
e
l
a
y
a: average packet arrival rate
a
v
e
r
a
g
e
traffic intensity = La/R
a
L /R 0 La/R ~ 0: avg. queueing delay small La/R -> 1: avg. queueing delay large
La/R ~ 0
La/R > 1: more work arriving than can be serviced, average delay infinite!
Introduction 1-26
La/R -> 1
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Real Internet delays and routes
What do real Internet delay & loss look like? Traceroute program: provides delay measurement
from source to router along end-end Internet path towards destination. For all i: sends three packets that will reach router i on path towards
destination
router i will return packets to sender router i will return packets to sender sender times interval between transmission and reply.
3 b 3 b3 probes
3 probes
3 probes
Introduction 1-27
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Real Internet delays and routes
traceroute: gaia.cs.umass.edu to www.eurecom.fr
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms
Three delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu
g ( )2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene vbns abilene ucaid edu (198 32 11 9) 22 ms 18 ms 22 ms6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms
trans-oceaniclink
10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 lb 3t2 ft t (193 48 50 54) 135 128 13315 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17 * * *18 * * *19 f t i f (193 55 113 142) 132 128 136
* means no response (probe lost, router not replying)19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
Introduction 1-28
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Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge end systems, access networks, links
1.3 Network core circuit switching, packet switching, network structure
1 4 Delay loss and throughput in packet-switched1.4 Delay, loss and throughput in packet switched networks
1 5 Protocol layers service models1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 HistoryIntroduction 1-29
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Protocol Layers
Networks are complex,et o s a e co p e ,
with many pieces:
h t Question: hosts routers
Question:Is there any hope of organizing structure of links of various
media
organizing structure of network?
applications protocols Or at least our discussion f t k ? protocols hardware, software
of networks?
Introduction 1-30
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Organization of air travel
ti k t ( h ) ti k t ( l i )ticket (purchase)
baggage (check)
ticket (complain)
baggage (claim)
gates (load) gates (unload)
runway takeoff
airplane routing
runway landing
airplane routingairplane routing airplane routing
airplane routing
a series of steps
Introduction 1-31
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Layering of airline functionality
ticket (purchase)
baggage (check)
ticket (complain)
baggage (claim
ticket
baggage
gates (load)
runway (takeoff)
airplane routing airplane routing airplane routing
gates (unload)
runway (land)
airplane routing
gate
takeoff/landing
airplane routingairplane routing
departureairport
arrivalairport
intermediate air-trafficcontrol centers
airplane routing airplane routing airplane routing airplane routing
Layers: each layer implements a service
via its own internal layer actions via its own internal-layer actions
relying on services provided by layer below
Introduction 1-32
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Why layering?Why layering?Dealing with complex systems:Dealing with complex systems: explicit structure allows identification, relationship of
complex systems piecescomplex system s pieces
layered reference model for discussion modularization eases maintenance, updating of
system
change of implementation of layers service transparent to rest of system
e.g., change in gate procedure doesnt affect rest of system
layering considered harmful?Introduction 1-33
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Internet protocol stack
application: supporting network applications application: supporting network applications FTP, SMTP, HTTP
transport: process-process data transferapplication
p p p
TCP, UDP network: routing of datagrams from source to
transport
kg g
destination
IP, routing protocolsnetwork
link link: data transfer between neighboring
network elements
Eth t 802 11 (WiFi) PPP
link
physical Ethernet, 802.11 (WiFi), PPP physical: bits on the wire
p y
Introduction 1-34
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ISO/OSI reference model
presentation: allow applications to presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-
applicationpresentation
specific conventions
session: synchronization,
presentationsession
ycheckpointing, recovery of data exchange
transportnetwork
Internet stack missing these layers! these services, if needed, must be
linkphysical, ,
implemented in application
needed?
physical
needed?
Introduction 1-35
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sourceapplication
Encapsulationmessage M application
transportnetwork
li kHtHn M
segment Htdatagram
message MHt M
Hnlink
physicallink
HtHnHl Mframe
linkphysical
switch
d ti tidestinationapplicationtransportHt M
M
networklink
physicalHtHnHl M
HtHn M
HtHn M
transportnetwork
linkphysical
HtHnHl MHtHn M
t
routerphysical
Introduction 1-36
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Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge end systems, access networks, links
1.3 Network core circuit switching, packet switching, network structure
1 4 Delay loss and throughput in packet-switched1.4 Delay, loss and throughput in packet switched networks
1 5 Protocol layers service models1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 HistoryIntroduction 1-37
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Network Security
field of network security: field of network security: how bad guys can attack computer networks how we can defend networks against attacks how to design architectures that are immune to
attacks
Internet not originally designed with (much) g y g ( )security in mind original vision: a group of mutually trusting users original vision: a group of mutually trusting users
attached to a transparent network Internet protocol designers playing catch up Internet protocol designers playing catch-up security considerations in all layers!
Introduction 1-38
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Bad guys: put malware into hosts via Internet
malware can get in host from a virus worm or trojan malware can get in host from a virus, worm, or trojan horse.
spyware malware can record keystrokes, web sites visited, upload info to collection site.visited, upload info to collection site.
infected host can be enrolled in botnet used for infected host can be enrolled in botnet, used for spam and DDoS attacks.
malware often self-replicating: from one infected host, seeks entry into other hosts
Introduction 1-39
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Bad guys: put malware into hosts via InternetTrojan horse worm:
i f i b i l i i
guy pu m w
hidden part of some otherwise useful software
today often in Web page
infection by passively receiving object that gets itself executed today often in Web page
(Active-X, plugin)
virus
self- replicating: propagates to other hosts, users
virus infection by receiving object
(e.g., e-mail attachment),
Sapphire Worm: aggregate scans/secin first 5 minutes of outbreak (CAIDA, UWisc data)
( g )actively executing
self-replicating: propagate itself to other hosts sersitself to other hosts, users
Introduction 1-40
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Bad guys: attack server, network infrastructureDenial of Dervice (DoS): attackers make resources
(server bandwidth) unavailable to legitimate traffic by
g y ,
(server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic
1. select target2 break into hosts 2. break into hosts
around the network (see botnet)( )
3. send packets to target from compromised h
targethosts
g
Introduction 1-41
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The bad guys can sniff packets
Packet sniffing:Packet sniffing: broadcast media (shared Ethernet, wireless)
promiscuous network interface reads/records all packets (e.g., including passwords!) passing by
A C
Bsrc:B dest:A payload
B
Wireshark software used for end-of-chapter l b i (f ) k t ifflabs is a (free) packet-sniffer
Introduction 1-42
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The bad guys can use false sourceThe bad guys can use false source addresses
IP fiIP spoofing: send packet with false source address
A CA C
Bsrc:B dest:A payload
Introduction 1-43
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The bad guys can record and playback
record-and-playback: sniff sensitive info (e.g., password), and use later
password holder is that user from system point of view
CA
B
src:B dest:A user: B; password: foo
B
l t it (th h t Ch t 8)Introduction 1-44
lots more on security (throughout, Chapter 8)
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Chapter 1: roadmapChapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge end systems, access networks, links
1.3 Network core circuit switching, packet switching, network structure
1 4 Delay loss and throughput in packet-switched1.4 Delay, loss and throughput in packet switched networks
1 5 Protocol layers service models1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 HistoryIntroduction 1-45
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Internet History1961-1972: Early packet-switching principles
1961: Kleinrock - queueing theory shows effectiveness of packet switching
1972: ARPAnet public demonstration
of packet-switching
1964: Baran - packet-switching in military nets
NCP (Network Control Protocol) first host-host protocol
g y
1967: ARPAnet conceived by Advanced Research P j t A
first e-mail program ARPAnet has 15 nodes
Projects Agency
1969: first ARPAnet node operationaloperational
Introduction 1-46
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Internet History1972-1980: Internetworking, new and proprietary nets
1970: ALOHAnet satellite network in Hawaii
1974: Cerf and Kahn -Cerf and Kahns internetworking
principles: 1974: Cerf and Kahn -architecture for interconnecting networks1976 Eth t t X PARC
p p minimalism, autonomy -
no internal changes required to interconnect 1976: Ethernet at Xerox PARC
late70s: proprietary architectures: DECnet, SNA,
required to interconnect networks
best effort service modelXNA
late 70s: switching fixed length packets (ATM precursor)
stateless routers decentralized control
packets (ATM precursor) 1979: ARPAnet has 200 nodes
define todays Internet architecture
Introduction 1-47
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Internet Historyy1980-1990: new protocols, a proliferation of networks
1983: deployment of TCP/IP
new national networks: Csnet, BITnet, NSFnet,
1982: smtp e-mail protocol defined
Minitel
100,000 hosts p 1983: DNS defined for
name-to-IP-address
,connected to confederation of
t ktranslation
1985: ftp protocol
networks
p pdefined
1988: TCP congestion 1988: TCP congestion control
Introduction 1-48
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Internet History1990, 2000s: commercialization, the Web, new apps
early 1990s: ARPAnet decommissioned
late 1990s 2000s: more killer apps: instant
1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)
more killer apps: instant messaging, P2P file sharing
network security to forefront( , ) early 1990s: Web hypertext [Bush 1945, Nelson
est. 50 million host, 100 million+ users
yp [ ,1960s]
HTML, HTTP: Berners-Lee backbone links running at
Gbps
1994: Mosaic, later Netscape late 1990s: commercialization of
th W bthe Web
Introduction 1-49
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Internet Historyy
2010:2010:
~750 million hosts voice, video over IP P2P applications: BitTorrent
(file sharing) Skype (VoIP), PPLive (video)
more applications: YouTube, gaming, Twitter
wireless, mobility
Introduction 1-50
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Introduction: SummaryCovered a ton of material! Internet overview
You now have: context overview Internet overview
whats a protocol? network edge core access
context, overview, feel of networking
more depth, detail to network edge, core, access network packet-switching versus
p ,follow!
packet-switching versus circuit-switching
Internet structureInternet structure performance: loss, delay,
throughputg p layering, service models security security history
Introduction 1-51