1
Overview 1-1
Lec 1: Internet Overview
Overview 1-2
IntroductionOur goal:
get “feel” and terminologymore depth, detail later in courseapproach:
use Internet as example
Overview:what’s the Internetwhat’s a protocol?network edgenetwork coreaccess net, physical mediaInternet/ISP structureperformance: loss, delayprotocol layers, service modelsnetwork modeling
2
Overview 1-3
Outline
1.1 What is the Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs1.6 Delay & loss in packet-switched networks1.7 Protocol layers, service models1.8 History
Overview 1-4
What’s the Internet: “nuts and bolts” viewmillions of connected computing devices: hosts = end systemsrunning network apps
communication linksfiber, copper, radio, satellitetransmission rate = bandwidth
routers: forward packets (chunks of data)
local ISP
companynetwork
regional ISP
router workstationserver
mobile
3
Overview 1-5
“Cool” internet appliances
World’s smallest web serverhttp://www-ccs.cs.umass.edu/~shri/iPic.html
IP picture framehttp://www.ceiva.com/
Web-enabled toaster +weather forecaster
Internet phones
Overview 1-6
What’s the Internet: hardware view
Internet: “network of networks”
loosely hierarchicalpublic
Intranet: private networksInternet standards
RFC: Request for commentsIETF: Internet Engineering Task Force
local ISP
companynetwork
regional ISP
router workstationserver
mobile
4
Overview 1-7
What’s the Internet: a service viewDistributed applications:
Web, email, games, e-commerce, file sharing
Network protocols: used by applications to control sending, receiving of msgs:
TCP, IP, HTTP, FTP, PPPCommunication services provided to apps:
Connectionless unreliableconnection-oriented reliable
Overview 1-8
What’s a protocol?human protocols:
“what’s the time?”“I have a question”introductions
network protocols:machines rather than humansall communication activity in Internet governed by protocols
protocols define:- msg format- order of msgs sent & received- actions taken on msg transmission
& receipt
5
Overview 1-9
Outline
1.1 What is the Internet?1.2 Network edge 1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks1.7 Protocol layers, service models1.8 History
Overview 1-10
A closer look at network structure:
network edge:applications and hostsnetwork core:
routersnetwork of networks
access networks, physical media:communication links
6
Overview 1-11
The network edge:end systems (hosts):
run application programse.g. Web, emailat “edge of network”
client/server modelclient host requests, receives service from always-on servere.g. Web browser/server; email client/server
peer-peer model:minimal (or no) use of
dedicated serverse.g. Gnutella, KaZaA, Skype
Overview 1-12
Outline
1.1 What is the Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs1.6 Delay & loss in packet-switched networks1.7 Protocol layers, service models1.8 History
7
Overview 1-13
The Network Core
mesh of interconnected routersthe fundamental question: how is data transferred through net?
circuit switching:dedicated circuit per call: telephone netpacket-switching: data sent thru net in discrete “chunks”
Overview 1-14
Network Core: Circuit Switching
End-end resources reserved for “call”link bandwidth and switch capacity pre-determineddedicated resources with no sharing of bandwidthguaranteed performancecall setup required
8
Overview 1-15
Network Core: Circuit Switchingnetwork resources
(e.g., bandwidth) divided into “pieces”pieces allocated to callsresource piece idle if not used by owning call (no sharing)
dividing link bandwidth into “pieces”
frequency divisiontime division
Overview 1-16
Circuit Switching: FDM and TDM
Frequency Domain Mux (FDM)
bandwidth/frequencyof the link
time
Time Domain Mux (TDM)Transmission rate of single circuit = frame rate in frames/sec * #bits in a slot
bandwidth/frequency of the link
time
4 users/slots
Example:
Slot4 slots/frame
Note: Circuit is analogous to connection
9
Overview 1-17
Numerical example
How long does it take to send a file of 640,000 bits (1 byte=8bits) from host A to host B over a circuit-switched network?
All links are 1.536 Mbps (Mega Bits Per Second)Each link uses TDM with 24 slots/sec500 msec to establish end-to-end circuit (setup time including propagation delay)
Single circuit speed = 1.536 Mbps / 24 = 64kbpsFile transmission time = 500 msec + file size/speed
= 0.5 sec + 640,000 bits / 64 kbps= 10.5 sec
Overview 1-18
Network Core: Packet Switchingeach end-end data stream
divided into packetsuser A, B packets sharenetwork resourceseach packet uses full link bandwidth resources used as needed
resource contention:flow-control needed as aggregate resource demand can exceed amount availablecongestion control needed as packets queued and wait for link usestore and forward: packets move one hop at a time
Bandwidth division into “pieces”Dedicated allocationResource reservation
10
Overview 1-19
Packet Switching: Statistical Multiplexing
Sequence of A & B packets does not have fixed pattern, on demand sharing of resources (statistical multiplexing).
A
B
C10 Mb/sEthernet
1.5 Mb/s
D E
statistical multiplexing
queue of packetswaiting for output
link
Overview 1-20
Packet switching versus circuit switching
Problem: 1 Mbps link and each user needs 100 kbps when “active” and is active 10% of time.circuit-switching FDM:
Max #users = (1,000,000 b/s)/(100,000 b/s) = 10
packet switching: Min #users = 10Max is > 10 due to the probability that users are inactive 90% of time
Packet switching allows more users to use network!
N users1 Mbps link
11
Overview 1-21
Packet switching versus circuit switching
Great for bursty dataresource sharingsimpler, no call setup
Excessive congestion: packet delay and lossprotocols needed for reliable data transfer, congestion control
Q: How to provide circuit-like behavior?bandwidth guarantees needed for audio/video appsstill an unsolved problem
Is packet switching a “slam dunk winner?”
Overview 1-22
Packet-switching: store-and-forward
Takes L/R seconds to transmit (push out) packet of L bits on to link or R bpsEntire packet must arrive at router before it can be transmitted on next link: store and forwarddelay = 3L/R (assuming zero propagation delay)
Example:L = 7.5 Mbits (size)R = 1.5 Mbps (speed)delay = 3*7.5/1.5=15 sec
R R RL
more on delay shortly …
12
Overview 1-23
Packet-switched networks: forwarding
Goal: move packets through routers from source to destinationPacket-switched datagram network:
destination address in packet determines next hoproutes may change during sessionanalogy: driving, asking directions
Packet-switched virtual circuit network:each packet carries tag (VC ID), tag determines next hopfixed path determined at call setup time, remains fixed thru callrouters maintain per-call state
Overview 1-24
Network TaxonomyTelecommunication
networks
Circuit-switchednetworks
FDM TDM
Packet-switchednetworks
Networkswith VCs
DatagramNetworks
(Internet)(X.25,Frame relay, ATM)
Course Subject
13
Overview 1-25
Part I summary Internet/Intranet definition:
Public loosely hierarchical Network of Networks Intranet definition:
Private NetworkNetwork Protocol defines:
msg format, order of msgs sent & received and actions taken on msg transmission & receipt
Network edge and core:Hosts or end-systems and routers in the core
Circuit-switching vs Packet-switchingFDM and TDM circuits: guaranteed constant speed, not-shared and requires call setup.VCs and Datagram Networks: variable speed, shared and need resource contention management.
Overview 1-26
Outline
1.1 What is the Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs1.6 Delay & loss in packet-switched networks1.7 Protocol layers, service models
14
Overview 1-27
Access networks and physical media
Q: How to connect end systems to edge router?residential access netsinstitutional access networks (school, company)mobile access networks
Keep in mind: bandwidth (bits per second) of access network?shared or dedicated?
Overview 1-28
Residential access: point to point access
Dialup via modemup to 56Kbps direct access to router (often less)Can’t surf and phone at same time: can’t be “always on”
ADSL: asymmetric digital subscriber lineup to 1 Mbps upstream (today typically < 256 kbps)up to 8 Mbps downstream (today typically < 1 Mbps)FDM: 50 kHz - 1 MHz for downstream
4 kHz - 50 kHz for upstream0 kHz - 4 kHz for ordinary telephone
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Overview 1-29
Residential access: cable modems
HFC: hybrid fiber coaxasymmetric: up to 30Mbps downstream, 2 Mbps upstream
network of cable and fiber attaches homes to ISP router
homes share access to router so communication activity is visible to each other.
deployment: available via cable TV companies
Overview 1-30
Residential access: cable modems
Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
16
Overview 1-31
Cable Network Architecture: Overview
home
cable headend
cable distributionnetwork (simplified)
Typically 500 to 5,000 homes
Overview 1-32
Cable Network Architecture: Overview
home
cable headend
cable distributionnetwork (simplified)
17
Overview 1-33
Cable Network Architecture: Overview
home
cable headend
cable distributionnetwork
server(s)
Overview 1-34
Cable Network Architecture: Overview
home
cable headend
cable distributionnetwork
Channels
VIDEO
VIDEO
VIDEO
VIDEO
VIDEO
VIDEO
DATA
DATA
CONTROL
1 2 3 4 5 6 7 8 9
FDM:
18
Overview 1-35
Company access: local area networks
company/univ local area network (LAN) connects end system to edge routerEthernet:
shared or dedicated link connects end system and router10 Mbs, 100Mbps, Gigabit Ethernet
LANs: chapter 5
Overview 1-36
Wireless access networksshared wireless access network connects end system to router
via base station aka “access point”
wireless LANs:802.11b (WiFi): 11 Mbps
wider-area wireless accessprovided by telco operator3G ~ 384 kbps
• Will it happen??WAP/GPRS in Europe
basestation
mobilehosts
router
19
Overview 1-37
Physical Media
Bit: propagates betweentransmitter/rcvr pairsphysical link: what lies between transmitter & receiverguided media:
signals propagate in solid media: copper, fiber, coax
unguided media:signals propagate freely, e.g., radio
Twisted Pair (TP)two insulated copper wires
Category 3: traditional phone wires, 10 Mbps EthernetCategory 5: 100Mbps Ethernet
Overview 1-38
Physical Media: coax, fiber
Coaxial cable:two concentric copper conductorsbidirectionalbaseband:
single channel on cablelegacy Ethernet
broadband:multiple channels on
cableHFC
Fiber optic cable:glass fiber carrying light pulses, each pulse a bithigh-speed operation:
high-speed point-to-point transmission (e.g., 10’s-100’s Gps)
low error rate: repeaters spaced far apart ; immune to electromagnetic noise
20
Overview 1-39
Physical media: radio
signal carried in electromagnetic spectrumno physical “wire”bidirectionalpropagation environment effects:
reflection obstruction by objectsinterference
Radio link types:terrestrial microwave
e.g. up to 45 Mbps channelsLAN (e.g., Wifi)
2Mbps, 11Mbps, 54 Mbpswide-area (e.g., cellular)
e.g. 3G: hundreds of kbpssatellite
Kbps to 45Mbps channel (or multiple smaller channels)270 msec end-end delaygeosynchronous versus low altitude
Overview 1-40
Outline
1.1 What is the Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs1.6 Delay & loss in packet-switched networks1.7 Protocol layers, service models1.8 History
21
Overview 1-41
Internet structure: network of networks
roughly hierarchicalat center: “tier-1” ISPs or Internet backbone networks (e.g., MCI, Sprint, AT&T, Cable and Wireless), national/international coverage, connect to large tier-2 ISPs and to all tier-1 ISPs and many customer networks.
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-1 providers interconnect (peer) privately
NAP
Tier-1 providers also interconnect at public Network Access Points (NAPs).
Overview 1-42
Tier-1 ISP: e.g., SprintSprint US backbone network
Seattle
Atlanta
Chicago
Roachdale
Stockton
San Jose
Anaheim
Fort Worth
Orlando
Kansas City
CheyenneNew York
PennsaukenRelayWash. DC
Tacoma
DS3 (45 Mbps)OC3 (155 Mbps)OC12 (622 Mbps)OC48 (2.4 Gbps)
22
Overview 1-43
Internet structure: network of networks
“Tier-2” ISPs: smaller (often regional) ISPsConnect to one or more tier-1 ISPs, possibly other tier-2 ISPs
NAPs (Network Access Points) are complex high-speed switching networks often concentrated at a single building. Operated by 3rd party telecom or Internet backbone ISP-1. PoPs (Points of Presence) are private group of routers within each ISP and used to connect it (peer it) with other up/down/equal ISPs and is the new trend in connectivity.
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
NAP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet, tier-2 ISP is customer oftier-1 provider
Tier-2 ISPs also peer privately with each other, interconnect at public NAPs or private POPs.
Overview 1-44
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
NAP
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 are customers ofhigher tier ISPsconnecting them to rest of Internet
23
Overview 1-45
Internet structure: network of networks
a packet passes through many networks!
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
NAP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
Overview 1-46
MichNet: Statewide Backbone
Nation’s longest-running regional networkAn 2.5 Gigabit (OC48c) backbone, with 24 backbone nodesTwo diverse 2.5 gigabit (2x OC48) to chicagowww.merit.edu/mn
24
Overview 1-47
Outline
1.1 What is the Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs1.6 Delay & loss in packet-switched networks1.7 Protocol layers, service models1.8 History
Overview 1-48
How do loss and delay occur?packets queue in router buffers
packet arrival rate to link exceeds output link capacitypackets queue, wait for turn
A
B
packet being transmitted (delay)
packets queueing (delay)free (available) buffers: arriving packets dropped (loss) if no free buffers
25
Overview 1-49
Four sources of packet delay
1. Processing delay at router:
check bit errorsdetermine output link
A
B
propagation
transmission
nodalprocessing queueing
2. Queueing delay at router
time waiting at output link for transmission depends on congestion level of router
Overview 1-50
Delay in packet-switched networks3. Transmission delay of
link:R=link bandwidth (bps)L=packet length (bits)time to send bits into link = L/R
4. Propagation delay of medium:d = length of physical links = propagation speed in medium (~2x108 m/sec)propagation delay = d/s
A
B
propagation
transmission
nodalprocessing queueing
Note: s and R are very different quantities!
26
Overview 1-51
Total End-End Delay
N = #links between source and destination = #routers + 1dproc = processing delay at router (task 1)
typically a few microsecs or lessdqueue = queuing delay at router (task 2)
depends on congestion (neglect if light traffic)dtrans = transmission delay for router to put data on medium (task 3)
= L/R, significant for low-speed linksdprop = propagation delay at medium (task 4)
a few microsecs to hundreds of msecs
)()( proptransqueueproc nodalend-end ddddNdNd +++==
∑=
+++=− ⎥⎦⎤
⎢⎣⎡N
q
qpropdq
transdqqueuedq
procdendend
d1
homogeneous links
heterogeneous links
Overview 1-52
The cause of Queueing delay
R=link bandwidth (bps)L=packet length (bits)a=average packet arrival rate (requests/sec)
traffic intensity (link utilization) = La/R
La/R ~ 0: average queueing delay smallLa/R -> 1: delays become largeLa/R > 1: more “work” arriving than can be serviced, average delay infinite!
27
Overview 1-53
“Real” Internet delays and routes
What do “real” Internet delay & loss look like? Traceroute program (in Unix) or Tracert (MS-DOS): 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 destinationrouter i will return packets to sendersender times interval between transmission and reply.3 probes
3 probes
3 probes
Overview 1-54
“Real” Internet delays and routes
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms2 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 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 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 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 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
traceroute: gaia.cs.umass.edu to www.eurecom.frThree delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu
* means no response (probe lost, router not replying at any one of the 3 msgs)
trans-oceaniclink
28
Overview 1-55
“Real” Internet delays and routes
Tracing route to www.yahoo.akadns.net [216.109.118.67]over a maximum of 30 hops:
1 1 ms 1 ms 1 ms 192.168.0.12 11 ms 9 ms 8 ms 64.230.197.2413 7 ms 7 ms 7 ms 64.230.235.854 7 ms 7 ms 7 ms 64.230.235.975 12 ms 12 ms 12 ms rtp627197rts [64.230.220.254]6 13 ms 13 ms 12 ms 64.230.242.2057 12 ms 12 ms 12 ms bx3-toronto12-pos5-0.in.bellnexxia.net [206.108.107.234]8 13 ms 13 ms 13 ms if-7-0.core1.TTT-Scarborough.teleglobe.net [209.58.25.69]9 31 ms 32 ms 31 ms if-3-3.mcore3.NJY-Newark.teleglobe.net [216.6.57.33]
10 36 ms 36 ms 36 ms if-13-0.core1.AEQ-Ashburn.teleglobe.net [216.6.57.42]11 37 ms 36 ms 36 ms ix-14-2.core1.AEQ-Ashburn.teleglobe.net [63.243.149.110]12 36 ms 36 ms 36 ms vlan200-msr1.dcn.yahoo.com [216.115.96.161]13 35 ms 36 ms 36 ms ge3-1.bas2-m.dcn.yahoo.com [216.109.120.146]14 36 ms 36 ms 37 ms p4.www.dcn.yahoo.com [216.109.118.67]
Trace complete.It took 13 routers to get from my house to www.yahoo.com
3 delay (end-end) measurements for each of the 3 msgs
Note: an * in one of the routers result means no response (probe lost, router did not reply for at least one of the 3 msgs)
tracert www.yahoo.com
Overview 1-56
“Real” Internet delays and routes
Ping program: checks if a host is live or not and provides RTT delay measurement from source to destination along end-end Internet path.
sends n requests of size 32 bytes and calculates avg RTTsender times interval between transmission and reply.ping -n <number of requests to send> <hostname>
n probes
29
Overview 1-57
“Real” Internet delays and routes
Pinging www.yahoo.akadns.net [68.142.226.34] with 32 bytes of data:
Reply from 68.142.226.34: bytes=32 time=38ms TTL=51Reply from 68.142.226.34: bytes=32 time=39ms TTL=51Reply from 68.142.226.34: bytes=32 time=38ms TTL=51Reply from 68.142.226.34: bytes=32 time=39ms TTL=51
Ping statistics for 68.142.226.34:Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:Minimum = 38ms, Maximum = 39ms, Average = 38ms
RTTs
ping www.yahoo.com
Overview 1-58
Outline
1.1 What is the Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs1.6 Delay & loss in packet-switched networks1.7 Protocol layers, service models1.8 History
30
Overview 1-59
Protocol “Layers”Networks are complex!
many “pieces”:hostsrouterslinks of various mediaapplicationsprotocolshardware, software
Overview 1-60
Why layering?Dealing with complex systems:
explicit structure allows identification, relationship of complex system’s pieces
layered reference model for discussionmodularization eases maintenance, updating of system
change of implementation of layer’s service transparent to rest of systeme.g., change in gate procedure doesn’t affect rest of system
Layering negatives: duplicate functionality and inter-dependency.
31
Overview 1-61
Internet protocol stackapplication: supporting network applications
FTP, SMTP, HTTPtransport: process-process data transfer
TCP, UDPnetwork: host-host data transfer
IPlink: data transfer between neighboring network elements
PPP, Ethernetphysical: bits “on the wire”
application
transport
network
link
physical
Overview 1-62
messagesegment
datagramframe
sourceapplicationtransportnetwork
linkphysical
HtHnHl MHtHn M
Ht MM
destinationapplicationtransportnetwork
linkphysical
HtHnHl MHtHn M
Ht MM
networklink
physical
linkphysical
HtHnHl M
HtHn M
HtHnHl M
HtHn M
HtHnHl M HtHnHl M
router
switch
Encapsulation
32
Overview 1-63
Overview 1-64
Internet History
1961: Kleinrock - queueing theory shows effectiveness of packet-switching1964: Baran - packet-switching in military nets1967: ARPAnet conceived by Advanced Research Projects Agency1969: first ARPAnet node operational
1972:ARPAnet demonstrated publiclyNCP (Network Control Protocol) first host-host protocol first e-mail programARPAnet has 15 nodes
1961-1972: Early packet-switching principles
33
Overview 1-65
Internet History
1970: ALOHAnet satellite network in Hawaii1973: Metcalfe’s PhD thesis proposes Ethernet1974: Cerf and Kahn -architecture for interconnecting networkslate70’s: proprietary architectures: DECnet, SNA, XNAlate 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 networksbest effort service modelstateless routersdecentralized control
define today’s Internet architecture2005 ACM Turing Award“A protocol for packet network
interconnection”, IEEE Trans. on Communications Technology, vol.22(5), 627-641
1972-1980: Internetworking, new and proprietary nets
Overview 1-66
Internet History
1983: deployment of TCP/IP1982: SMTP e-mail protocol defined 1983: DNS defined for name-to-IP-address translation1985: FTP protocol defined1988: TCP congestion control
new national networks: Csnet, BITnet, NSFnet, Minitel100,000 hosts connected to confederation of networks
1980-1990: new protocols, a proliferation of networks
34
Overview 1-67
Internet History
Early 1990’s: ARPAnet decommissioned1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)early 1990s: Web
hypertext [Bush 1945, Nelson 1960’s]HTML, HTTP: Berners-Lee1994: Mosaic, later Netscapelate 1990’s: commercialization of the Web
Late 1990’s – 2000’s:more killer apps: instant messaging, peer2peer file sharing (e.g., Naptser)network security to forefrontest. 50 million host, 100 million+ usersbackbone links running at Gbps
1990, 2000’s: commercialization, the Web, new apps
Overview 1-68
Part II SummaryInternet Access from Home:
Dialup via modem, ADSL, HFCPhysical medium:
Guided media(TP, optical), Unguided media (Wi-Fi, Radio)Internet Structure:
tier-1,2,3 ISPs connected via NAPs and POPsTotal end-end delay in homogeneous packet networks:
Traceroute/Tracert and Ping programs measure delayslayering and service models:
Internet Protocol Stack (application, transport, network, link, physical)
Four decades history
)()( proptransqueueproc nodalend-end ddddNdNd +++==
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