ComputerNetworksandMobileSystemsShyamGollakota

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TheInternetofThings“Theinternet'snextbigfrontier”

–  1/7/2013

•  AlookathowtheInternetisbecomingimmersedinthephysicalworld,notjustcommunications– Backscatterandsensing

InternetReferenceModel•  Afourlayermodelbasedonexperience;omitssomeOSIlayersandusesIPasthenetworklayer.

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4Application–Programsthatusenetworkservice3Transport–Providesend-to-enddatadelivery2Internet –Sendpacketsovermultiplenetworks

1Link –Sendframesoveralink

InternetReferenceModel(3)•  IPisthe“narrowwaist”oftheInternet

–  Supportsmanydifferentlinksbelowandappsabove

4

4Application3Transport

2Internet

1Link Ethernet802.11

IP

TCP UDP

HTTPSMTP RTP DNS

3GDSLCable

InternetReferenceModel(3)•  IPisthe“narrowwaist”oftheInternet

–  Supportsmanydifferentlinksbelowandappsabove

5

4Application3Transport

2Internet

1Link Ethernet802.11

IP

TCP UDP

HTTPSMTP RTP DNS

3GDSLCable

CoverCuttingEdgeResearch

ComputerNetworks

•  PHYLayer:Backscatter,IOT•  Internet:DataCenter,SDN•  Transport:DCTCP,Multipath-TCP•  Applications:Localization,Gesturerecognition,SPDY,mobilesystemdesign,gamingdesign

ClassStructure

ComputerNetworks

•  Goovereachofthelayer

•  Goovertherequiredbackground

•  Readthelatestpapersoneachtopic

ClassStructure

ComputerNetworks

•  Goovereachofthelayer

•  Goovertherequiredbackground

•  Readthelatestpapersoneachtopic– Questionstobeansweredbeforeeachclass– Wewillcover2-3papers

Evaluation

ComputerNetworks

•  Project1,2,3(10%,10%,10%)–  Createacommunicationsystembetweentwophones(Jan31st)–  Programaraspberrypi(Feb10th)–  Performgesturerecognitiononsmartphone(Feb20th)

•  Project4(40%)–  Defineandexecutearesearchproject(groupsof2)

•  Paperpresentations(30%)

CourseWebpage

ComputerNetworks

Cs.washington.edu/561

CoverCuttingEdgeResearch

ComputerNetworks

•  PhyLayer:Backscatter,passive-wifi•  Internet:DataCenter,SDN•  Transport:DCTCP,Multipath-TCP•  Applications:Localization,Gesturerecognition,SPDY,mobilesystemdesign,gamingdesign

ComputerNetworks 12

ProtocolsandLayers•  Protocolsandlayeringisthemainstructuringmethodusedtodivideupnetworkfunctionality–  Eachinstanceofaprotocoltalksvirtuallytoitspeerusingtheprotocol

–  Eachinstanceofaprotocolusesonlytheservicesofthelowerlayer

ProtocolsandLayers(3)•  Protocolsarehorizontal,layersarevertical

ComputerNetworks 13

X

YY

XInstanceofprotocolX

Peerinstance

Node1 Node2

Lowerlayerinstance(ofprotocolY)

ProtocolX

ServiceprovidedbyProtocolY

ProtocolsandLayers(4)•  Setofprotocolsinuseiscalledaprotocolstack

ComputerNetworks 14

ComputerNetworks 15

ProtocolsandLayers(6)•  Protocolsyou’veprobablyheardof:

–  TCP,IP,802.11,Ethernet,HTTP,SSL,DNS,…andmanymore

•  Anexampleprotocolstack–  UsedbyawebbrowseronahostthatiswirelesslyconnectedtotheInternet

HTTP

TCP

IP

802.11

Browser

ComputerNetworks 16

Encapsulation•  Encapsulationisthemechanismusedtoeffectprotocollayering–  Lowerlayerwrapshigherlayercontent,addingitsowninformationtomakeanewmessagefordelivery

–  Likesendingaletterinanenvelope;postalservicedoesn’tlookinside

Encapsulation(3)•  Message“onthewire”beginstolooklikeanonion

–  Lowerlayersareoutermost

ComputerNetworks 17

HTTP

TCP

IP

802.11

HTTP

TCP HTTP

TCP HTTPIP

TCP HTTPIP802.11

Encapsulation(4)

ComputerNetworks 18

HTTP

TCP

IP

802.11

HTTP

TCP HTTP

TCP HTTPIP

TCP HTTPIP802.11

HTTP

TCP

IP

802.11(wire)

HTTP

TCP HTTP

TCP HTTPIP

TCP HTTPIP802.11

TCP HTTPIP802.11

AdvantageofLayering•  Informationhidingandreuse

ComputerNetworks 19

HTTP

Browser

HTTP

Server

HTTP

Browser

HTTP

Server

or

AdvantageofLayering(2)•  Informationhidingandreuse

ComputerNetworks 20

HTTP

TCP

IP

802.11

Browser

HTTP

TCP

IP

802.11

Server

HTTP

TCP

IP

Ethernet

Browser

HTTP

TCP

IP

Ethernet

Server

or

AdvantageofLayering(3)•  Usinginformationhidingtoconnectdifferentsystems

ComputerNetworks 21

HTTP

TCP

IP

802.11

Browser

HTTP

TCP

IPEthernet

Server

AdvantageofLayering(4)•  Usinginformationhidingtoconnectdifferentsystems

ComputerNetworks 22

HTTP

TCP

IP

802.11

Browser

IP

802.11

IP

Ethernet

HTTP

TCP

IPEthernet

Server

IP TCP HTTP

802.11 IP TCP HTTP Ethernet IP TCP HTTP

ComputerNetworks 23

DisadvantageofLayering•  ??

InternetReferenceModel•  Afourlayermodelbasedonexperience;omitssomeOSIlayersandusesIPasthenetworklayer.

ComputerNetworks 24

4Application–Programsthatusenetworkservice3Transport–Providesend-to-enddatadelivery2Internet –Sendpacketsovermultiplenetworks

1Link –Sendframesoveralink

InternetReferenceModel(3)•  IPisthe“narrowwaist”oftheInternet

–  Supportsmanydifferentlinksbelowandappsabove

ComputerNetworks 25

4Application3Transport

2Internet

1Link Ethernet802.11

IP

TCP UDP

HTTPSMTP RTP DNS

3GDSLCable

ComputerNetworks 26

Layer-basedNames(2)•  Fordevicesinthenetwork:

NetworkLink

NetworkLink

Link Link

Physical PhysicalRepeater(orhub)

Switch(orbridge)

Router

ComputerNetworks 27

Layer-basedNames(3)•  Fordevicesinthenetwork:

Proxyormiddleboxorgateway

NetworkLink

NetworkLink

AppTransport

AppTransport

Buttheyalllooklikethis!

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ScopeofthePhysicalLayer•  Concernshowsignalsareusedtotransfermessagebitsoveralink– Wiresetc.carryanalogsignals– Wewanttosenddigitalbits

…1011010110…

Signal

SimpleLinkModel•  We’llendwithanabstractionofaphysicalchannel

–  Rate(orbandwidth,capacity,speed)inbits/second–  Delayinseconds,relatedtolength

•  Otherimportantproperties:– Whetherthechannelisbroadcast,anditserrorrate

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DelayD,RateR

Message

MessageLatency•  Latencyisthedelaytosendamessageoveralink

–  Transmissiondelay:timetoputM-bitmessage“onthewire”

–  Propagationdelay:timeforbitstopropagateacrossthewire

–  Combiningthetwotermswehave:

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MessageLatency(2)•  Latencyisthedelaytosendamessageoveralink

–  Transmissiondelay:timetoputM-bitmessage“onthewire”

T-delay=M(bits)/Rate(bits/sec)=M/Rseconds

–  Propagationdelay:timeforbitstopropagateacrossthewire

P-delay=Length/speedofsignals=Length/⅔c=Dseconds

–  Combiningthetwotermswehave:L=M/R+D

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MetricUnits•  Themainprefixesweuse:

•  Usepowersof10forrates,2forstorage–  1Mbps=1,000,000bps,1KB=210bytes

•  “B”isforbytes,“b”isforbits

Prefix Exp. prefix exp. K(ilo) 103 m(illi) 10-3

M(ega) 106 µ(micro) 10-6

G(iga) 109 n(ano) 10-9

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LatencyExamples(2)•  “Dialup”withatelephonemodem:

D=5ms,R=56kbps,M=1250bytes

L=5ms+(1250x8)/(56x103)sec=184ms!

•  Broadbandcross-countrylink:D=50ms,R=10Mbps,M=1250bytes

L=50ms+(1250x8)/(10x106)sec=51ms

•  Alonglinkoraslowratemeanshighlatency–  Often,onedelaycomponentdominates

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Bandwidth-DelayProduct•  Messagestakespaceonthewire!

•  Theamountofdatainflightisthebandwidth-delay(BD)product

BD=RxD– Measureinbits,orinmessages–  SmallforLANs,bigfor“longfat”pipes

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Bandwidth-DelayExample(2)•  Fiberathome,cross-country

R=40Mbps,D=50msBD=40x106x50x10-3bits

=2000Kbit=250KB

•  That’squitealotofdata“inthenetwork”!

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