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 …

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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

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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

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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

15

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

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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)

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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

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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

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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 +++==