Ch 1 Chapter 1 Introduction Introduction Computer Networking: A T D A h A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously A Top Down Approach , 5 th edition. Jim Kurose, Keith Ross Addis W sl A il represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!) If you post any slides in substantially unaltered form on a www site that Addison-Wesley, April 2009. If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Thanks and enjoy! JFK/KWR Introduction 1-1 All material copyright 1996-2009 J.F Kurose and K.W. Ross, All Rights Reserved
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Ch 1Chapter 1IntroductionIntroduction
Computer Networking: A T D A h
A note on the use of these ppt slides:We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously
A Top Down Approach ,5th edition. Jim Kurose, Keith RossAddis W sl A il
( g ) y y yrepresent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!) If you post any slides in substantially unaltered form on a www site that Addison-Wesley, April
2009. If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material.
Thanks and enjoy! JFK/KWR
Introduction 1-1
All material copyright 1996-2009J.F Kurose and K.W. Ross, All Rights Reserved
Chapter 1: IntroductionChapter 1: IntroductionOur goal: Overview:Our goal get “feel” and
terminology
Overview: what’s the Internet? what’s a protocol?
more depth, detail later in course
pp h:
what s a protocol? network edge; hosts, access
net physical media approach: use Internet as
example
net, physical media network core: packet/circuit
switching, Internet structureexample g, performance: loss, delay,
throughputg p security protocol layers, service models
Introduction 1-2
p y history
Chapter 1: roadmapChapter 1: roadmap
1 1 Wh i h I1.1 What is the Internet?1.2 Network edge
d k li k end systems, access networks, links1.3 Network core
circuit switchin packet switchin network structure circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched
networksnetworks1.5 Protocol layers, service models1 6 Networks under attack: security1.6 Networks under attack: security1.7 History
Introduction 1-3
What’s the Internet: “nuts and bolts” view
millions of connected Mobile networkPC
computing devices: hosts = end systems
k
Global ISPserver
wirelesslaptop
running network apps Home network
Regional 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 = bandwidth routers: forward
packets (chunks of
Introduction 1-4
packets (chunks of data)
“Cool” internet appliancesCool internet appliances
Web-enabled toaster +weather forecaster
IP picture framehttp://www.ceiva.com/
World’s smallest web serverhttp://www-ccs.cs.umass.edu/~shri/iPic.html Internet phones
Introduction 1-5
p Internet phones
What’s the Internet: “nuts and bolts” viewWhat s the Internet: nuts and bolts view
protocols control sending, Mobile networkprotoco s contro s n ng, receiving of msgs e.g., TCP, IP, HTTP, Skype,
E h
Global ISP
Ethernet Internet: “network of
networks”Home network
Regional ISPnetworks loosely hierarchical public Internet versus I tit ti l t k
Regional ISP
public Internet versus private intranet
Internet standards
Institutional network
RFC: Request for comments IETF: Internet Engineering
Task Force
Introduction 1-6
Task Force
What’s the Internet: a service viewWhat s the Internet: a service view communication
i f bl infrastructure enables distributed applications:
W b V IP il s Web, VoIP, email, games, e-commerce, file sharing
communication services communication services provided to apps: reliable data delivery reliable data delivery
from source to destination
“best effort” (unreliable) data delivery
Introduction 1-7
What’s a protocol?What s a protocol?human protocols: network protocols:human protoco s “what’s the time?” “I have a question”
n twor protoco s machines rather than
humans I have a question introductions all communication
activity in Internet … specific msgs sent… specific actions taken
governed by protocols
protocols define format, p fwhen msgs received, or other events
protocols define format, order of msgs sent and received among network
entities, and actions taken on msg
transmission receiptIntroduction 1-8
transmission, receipt
What’s a protocol?What s a protocol?a human protocol and a computer network protocol:a human protoco an a comput r n twor protoco
1 1 Wh i h I1.1 What is the Internet?1.2 Network edge
d k li k end systems, access networks, links1.3 Network core
circuit switchin packet switchin network structure circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched
networksnetworks1.5 Protocol layers, service models1 6 Networks under attack: security1.6 Networks under attack: security1.7 History
Introduction 1-10
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 Introduction 1-11
network of networks
The network edge:The network edge: end systems (hosts): end systems (hosts):
run application programs e.g. Web, emailg at “edge of network” peer-peer
client/server model
client/server
client host requests, receives service from always-on server
e g Web browser/server; e.g. Web browser/server; email client/server
peer-peer model:p p minimal (or no) use of
dedicated servers e g Skype BitTorrent
Introduction 1-12
e.g. Skype, BitTorrent
Access networks and physical mediaAccess networks and physical media
Q: How to connect end Q How to conn ct n systems to edge router?
residential access nets institutional access
networks (school, company)
mobile access networks
Keep in mind: bandwidth (bits per ( p
second) of access network?
Introduction 1-13
shared or dedicated?
Dial-up Modemcentral office
p
telephonenetwork Internet
office
homedial-upmodem
ISPmodem(e.g., AOL)
homePC
Uses existing telephony infrastructure Home is connected to central office
up to 56Kbps direct access to router (often less) Can’t surf and phone at same time: not “always on”p y
Digital Subscriber Line (DSL)InternetExisting phone line:
0-4KHz phone; 4-50KHz
g
homephone
0 4KHz phone; 4 50KHz upstream data; 50KHz-1MHz downstream data
telephonenetwork
DSLAM
splitter
DSLmodem
home
p
centraloffice
PC
Also uses existing telephone infrastruture up to 1 Mbps upstream (today typically < 256 kbps) up to 8 Mbps downstream (today typically < 1 Mbps)p p y yp y p dedicated physical line to telephone central office
Cable and Wireless), national/international coverageCable and W reless), nat onal/ nternat onal coverage treat each other as equals
Tier 1 ISPTier-1 providers
Ti 1 ISP
providers interconnect (peer) privately
Tier 1 ISP Tier 1 ISPpr vately
Introduction 1-40
Tier-1 ISP: e g SprintTier-1 ISP: e.g., Sprint
to/from backbone
POP: point-of-presence
…peering
….
………
to/from customers
Introduction 1-41
Internet structure: network of networksInternet structure: network of networks
“Tier-2” ISPs: smaller (often regional) ISPs Tier 2 ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
Tier-2 ISPs l
Tier 1 ISPTier-2 ISPTier-2 ISPTier-2 ISP pays
tier-1 ISP for connectivity to
also peer privately with each other.
Ti 1 ISP
rest of Internet tier-2 ISP is customer of
1 d Tier 1 ISP Tier 1 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISPtier-1 provider
Introduction 1-42
Internet structure: network of networksInternet structure: network of networks
“Tier-3” ISPs and local ISPs Tier 3 ISPs and local ISPs last hop (“access”) network (closest to end systems)
localISPlocal
ISPlocalISP
localISP Tier 3
ISPL l d i
Tier 1 ISPTier-2 ISPTier-2 ISPLocal and tier-
3 ISPs are customers ofhi h ti
Ti 1 ISP
higher tier ISPsconnecting them to rest Tier 1 ISP Tier 1 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
l llocalISP
them to rest of Internet
Introduction 1-43
localISP
localISP
localISP
ISP
Internet structure: network of networksInternet structure: network of networks
a packet passes through many networks! a packet passes through many networks!
localISPlocal
ISPlocalISP
localISP Tier 3
ISP
Tier 1 ISPTier-2 ISPTier-2 ISP
Ti 1 ISPTier 1 ISP Tier 1 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
l llocalISP
Introduction 1-44
localISP
localISP
localISP
ISP
Chapter 1: roadmapChapter 1: roadmap
1 1 Wh i h I1.1 What is the Internet?1.2 Network edge
d k li k end systems, access networks, links1.3 Network core
circuit switchin packet switchin network structure circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched
networksnetworks1.5 Protocol layers, service models1 6 Networks under attack: security1.6 Networks under attack: security1.7 History
Introduction 1-45
How do loss and delay occur?How do loss and delay occur?packets queue in router bufferspackets queue in router buffers packet arrival rate to link exceeds output link
capacitycapacity packets queue, wait for turn
k t b i t itt d (d l )packet being transmitted (delay)
A
Bpackets queueing (delay)
Introduction 1-46
free (available) buffers: arriving packets dropped (loss) if no free buffers
Four sources of packet delayFour sources of packet delay
1. nodal processing: check bit errors d t mi t t li k
2. queueing time waiting at output
link for transmission determine output link link for transmission depends on congestion
level of router
transmissionA propagation
Bnodal
processing queueing
Introduction 1-47
processing queueing
Delay in packet-switched networksDelay in packet-switched networks3. Transmission delay: 4. Propagation delay:. ransm ss on ay R=link bandwidth (bps) L=packet length (bits)
p g y d = length of physical link s = propagation speed in L packet length (bits)
time to send bits into link = L/R
s propagation speed in medium (~2x108 m/sec)
propagation delay = d/sp p g y
Note: s and R are very diff t titi !
A propagation
transmissiondifferent quantities!
B
p p g
Introduction 1-48
nodalprocessing queueing
Caravan analogygy100 km 100 km
toll booth
toll booth
ten-car caravan
cars “propagate” at 100 km/hr
Time to “push” entire caravan through toll
toll booth takes 12 sec to service car (transmission
booth onto highway = 12*10 = 120 secTi f l time)
car~bit; caravan ~ packet Time for last car to
propagate from 1st to 2nd toll both:
Q: How long until caravan is lined up before 2nd toll b th?
2nd toll both: 100km/(100km/hr)= 1 hr
A: 62 minutes
Introduction 1-49
booth? A: 62 minutes
Caravan analogy (more)gy100 km 100 km
toll booth
toll booth
ten-car caravan
Cars now “propagate” at 1000 k /h
Yes! After 7 min, 1st car at 2nd booth and 3 cars
1000 km/hr Toll booth now takes 1
min to service a car
still at 1st booth. 1st bit of packet can
i 2 d min to service a car Q: Will cars arrive to
2nd booth before all
arrive at 2nd router before packet is fully transmitted at 1st router!2nd booth before all
cars serviced at 1st booth?
transmitted at 1st router! See Ethernet applet at AWL
Web site
Introduction 1-50
Nodal delayNodal delayd l ddddd proptransqueueprocnodal ddddd
dproc = processing delay typically a few microsecs or less
dqueue = queuing delay depends on congestion
d t i i d l dtrans = transmission delay = L/R, significant for low-speed links
d propa ation delay dprop = propagation delay a few microsecs to hundreds of msecs
La/R ~ 0: average queueing delay small La/R -> 1: delays become large La/R -> 1: delays become large La/R > 1: more “work” arriving than can be
serviced average delay infinite!
Introduction 1-52
serviced, average delay infinite!
“Real” Internet delays and routesReal Internet delays and routes
Wh d “ l” I d l & l l k lik What do “real” Internet delay & loss look like? Traceroute program: provides delay
s t f s t t l d d 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 sends three packets that will reach router i on path
towards destination router i will return packets to sender sender times interval between transmission and reply.
3 b 3 b3 probes
3 probes
3 probes
Introduction 1-53
“Real” Internet delays and routesReal Internet delays and routestraceroute: gaia.cs.umass.edu to www.eurecom.fr
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms
gThree 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)
Introduction 1-54
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
Packet lossPacket loss
( k b ff ) di li k i b ff h queue (aka buffer) preceding link in buffer has finite capacity
packet arriving to full queue dropped (aka lost) lost packet may be retransmitted by previous p y y p
node, by source end system, or not at allbuffer
Apacket being transmitted
buffer (waiting area)
Bpacket arriving to
Introduction 1-55
full buffer is lost
ThroughputThroughput throughput: rate (bits/time unit) at which throughput: rate (bits/time unit) at which
bits transferred between sender/receiver instantaneous: rate at given point in time instantaneous: rate at given point in time average: rate over longer period of time
h link capacity link capacityi h server, withfile of F bits
to send to client
link capacityRs bits/sec
link capacityRc bits/sec
pipe that can carryfluid at rateRs bits/sec)
pipe that can carryfluid at rateRc bits/sec)
server sends bits (fluid) into pipe
Introduction 1-56
s c )
Throughput (more)Throughput (more) R < R What is average end end throughput? Rs < Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
Rs > Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
link on end-end path that constrains end-end throughputbottleneck link
Introduction 1-57
link on end end path that constrains end end throughput
Throughput: Internet scenarioThroughput: Internet scenario
RRs
per-connection Rs Rspend-end throughput:
R R
Rg p
min(Rc,Rs,R/10) in practice: R or Rc
Rc
Rc in practice: Rc or Rs is often bottleneck
10 connections (fairly) share
bottleneck
Introduction 1-58
( y)backbone bottleneck link R bits/sec
Chapter 1: roadmapChapter 1: roadmap
1 1 Wh i h I1.1 What is the Internet?1.2 Network edge
d k li k end systems, access networks, links1.3 Network core
circuit switchin packet switchin network structure circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched
networksnetworks1.5 Protocol layers, service models1 6 Networks under attack: security1.6 Networks under attack: security1.7 History
Introduction 1-59
Protocol “Layers”Protocol LayersNetworks are complex! N twor s ar comp ! many “pieces”:
hosts Question: hosts routers links of various
Question:Is there any hope of organizing structure of links of various
media applications
organizing structure of network?
pp protocols hardware,
Or at least our discussion of networks? hardware,
software
Introduction 1-60
Organization of air travelOrganization of air travel
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 1-62
Why layering?Why layering?Dealing with complex systems:Dealing with complex systems explicit structure allows identification,
relationship of complex system’s piecesp p y p layered reference model for discussion
modularization eases maintenance, updating of modular zat on eases ma ntenance, updat ng of system change of implementation of layer’s service g p y
transparent to rest of system e.g., change in gate procedure doesn’t affect
physical link: data transfer between neighboring network elements PPP, Ethernet
physical
Introduction 1-64
PPP, Ethernet physical: bits “on the wire”
ISO/OSI reference modelISO/OSI reference model presentation: allow applications to presentation: allow applications to
interpret meaning of data, e.g., encryption, compression, machine-
applicationpresentationyp p
specific conventions session: synchronization,
h k f d
presentationsession
checkpointing, recovery of data exchange
I t t t k “ i i ” th
transportnetwork
Internet stack “missing” these layers! these services if needed must
linkphysical these services, if needed, must
be implemented in application needed?
physical
Introduction 1-65
needed?
sourceapplication
Encapsulationmessage M application
transportnetwork
li kHtHn M
segment Ht
datagram
pmessage M
Ht 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
router
Introduction 1-66
physical
Chapter 1: roadmapChapter 1: roadmap
1 1 Wh i h I1.1 What is the Internet?1.2 Network edge
d k li k end systems, access networks, links1.3 Network core
circuit switchin packet switchin network structure circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched
networksnetworks1.5 Protocol layers, service models1 6 Networks under attack: security1.6 Networks under attack: security1.7 History
Introduction 1-67
Network SecurityNetwork Security The field of network security is about: The field of network security is about:
how bad guys can attack computer networks how we can defend networks against attacks how we can defend networks against attacks how to design architectures that are immune to
attacksattacks Internet not originally designed with
(much) security in mind(much) security in mind original vision: “a group of mutually trusting
users attached to a transparent network” users attached to a transparent network Internet protocol designers playing “catch-up” Security considerations in all layers!
Introduction 1-68
Security considerations in all layers!
Bad guys can put malware into hosts via Internet Malware can get in host from a virus worm or 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.p
Infected host can be enrolled in a botnet, used for spam and DDoS attacks.
M l i ft lf li ti f Malware is often self-replicating: from an infected host, seeks entry into other hosts
Introduction 1-69
Bad guys can put malware into hosts via Internet Trojan horse Worm: Trojan horse
Hidden part of some otherwise useful
Worm: infection by passively
receiving object that gets software
Today often on a Web page (Active-X plugin)
g j gitself executed
self- replicating: propagates to other hosts userspage (Active X, plugin)
Virus infection by receiving
to other hosts, usersSapphire Worm: aggregate scans/sec
in first 5 minutes of outbreak (CAIDA, UWisc data) infection by receiving
Bad guys can attack servers and network infrastructure D i l f s i (D S) tt k s k s s Denial of service (DoS): attackers make resources
(server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus trafficy g g
1. select targetb k i h 2. break into hosts around the network (see botnet)(see botnet)
3. send packets toward target from targettarget from compromised hosts
g
Introduction 1-71
The bad guys can sniff packetsThe bad guys can sniff packetsPacket sniffing: Packet sniffing:
broadcast media (shared Ethernet, wireless) promiscuous network interface reads/records all 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
labs is a (free) packet-sniffer
Introduction 1-72
labs is a (free) packet sniffer
The bad guys can use false source addresses
IP fi d k h f l dd IP spoofing: send packet with false source address
A CA C
B d t A l d
Bsrc:B dest:A payload
Introduction 1-73
The bad guys can record and playback
record-and-playback: sniff sensitive info (e.g., password), and use laterp password holder is that user from system point of
view
AC
A
src:B dest:A user: B; password: foo
B
Introduction 1-74
Network SecurityNetwork Securitymore throughout this coursemore throughout this course chapter 8: focus on security hi t h i b i d crypographic techniques: obvious uses and
not so obvious uses
Introduction 1-75
Chapter 1: roadmapChapter 1: roadmap
1 1 Wh i h I1.1 What is the Internet?1.2 Network edge
d k li k end systems, access networks, links1.3 Network core
circuit switchin packet switchin network structure circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched
networksnetworks1.5 Protocol layers, service models1 6 Networks under attack: security1.6 Networks under attack: security1.7 History
Introduction 1-76
Internet Historyy1961-1972: Early packet-switching principles
1961: Kleinrock - queueing theory shows effectiveness of packet
1972: ARPAnet public demonstration
effectiveness of packet-switching
1964: Baran - packet-
NCP (Network Control Protocol) first host-host protocol
first e-mail programpswitching in military nets
1967: ARPAnet conceived by Advanced Research
first e-mail program ARPAnet has 15 nodes
by Advanced Research Projects Agency
1969: first ARPAnet node ti loperational
Introduction 1-77
Internet Historyy1972-1980: Internetworking, new and proprietary nets
1970: ALOHAnet satellite network in Hawaii
1974: Cerf and Kahn -
Cerf and Kahn’s internetworking principles: minimalism, autonomy - no 9 f K
architecture for interconnecting networks
1976: Ethernet at Xerox
minimalism, autonomy no internal changes required to interconnect networks
best effort service model 1976: Ethernet at Xerox PARC
ate70’s: proprietary architectures: DECnet SNA
stateless routers decentralized control
define today’s Internet architectures: DECnet, SNA, XNA
late 70’s: switching fixed length packets (ATM
def ne today s Internet architecture
length packets (ATM precursor)
1979: ARPAnet has 200 nodes
Introduction 1-78
Internet Historyy1980-1990: new protocols, a proliferation of networks
1983: deployment of TCP/IP
new national networks: Csnet, BITnet,
1982: smtp e-mail protocol defined
NSFnet, Minitel 100,000 hosts
1983: DNS defined for name-to-IP-dd t l ti
connected to confederation of networksaddress translation
1985: ftp protocol defined
networks
defined 1988: TCP congestion
control
Introduction 1-79
control
Internet Historyy1990, 2000’s: commercialization, the Web, new apps
Early 1990’s: ARPAnet decommissioned1991 NSF lif i i
Late 1990’s – 2000’s: more killer apps: instant
1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)
ppmessaging, P2P file sharing
network security to forefront
early 1990s: Web hypertext [Bush 1945, Nelson
1960’s]
forefront est. 50 million host, 100
million+ users1960 s]
HTML, HTTP: Berners-Lee 1994: Mosaic, later Netscape
backbone links running at Gbps
, p late 1990’s:
commercialization of the Web
Introduction 1-80
Internet Historyy
2007:2007: ~500 million hosts Voice Video over IP Voice, Video over IP P2P applications: BitTorrent