CS204:AdvancedComputerNetworks
Jiasi ChenLectures:MWF12:10-1pm
HumanitiesandSocialSciences1403
http://www.cs.ucr.edu/~jiasi/teaching/cs204_spring17/
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WhyNetworks?
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Videostreaming
NumberofInternetusers• 97%ofAmericansbetween18-29• 40%oftheworldpopulationà
scopeformoreusers
http://www.pewinternet.org/data-trend/internet-use/latest-stats/https://en.wikipedia.org/wiki/List_of_countries_by_number_of_internet_users
Supportstheapplicationsthatweusetoday…
Socialmedia
WhyNetworks?
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Butalsoasourceofconflict.
NetworkneutralityCybersecurity
http://www.huffingtonpost.com/eric-dezenhall/a-look-back-at-the-target_b_7000816.htmlhttp://www.nytimes.com/2015/11/12/technology/t-mobile-video-plan-could-test-fccs-new-net-neutrality-rules.html
Whatisnetworking?
• Bunchofacronyms?
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TCP
OSPF
IP
BGP
DNS
ABR
UMTS
DDoS
HTTP
REST
SPDY
MCS
MACRED
NAT
VLAN
DHCP
Whatisnetworking?
• Bunchofheaders?
5Source:https://nmap.org/book/tcpip-ref.html
Networkingis…
Thesearchforgeneralprinciplestoguidecommunication
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SomeResearchTopicsinNetworking
• Layering• Whatfunctionalitytoplacewithineachlayer?• Howmanylayersshouldtherebe?
• Protocols• Howtocommunicatewithineachlayer,andtalktootherlayers?
• Resourceallocation• Howtosharelimitedresourcesbetweencompetingusers?
• Wireless• Howtoprovideaone-to-onecommunicationinaninherentlybroadcastenvironment
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Application(e.g.videostreaming)
Transport(e.g.TCP,UDP)
Network(e.g.routing)
Link(e.g.scheduling)
Physical(e.g.OFDM)
WhatYouWillLearninthisCourse
• Knowledge• 1/3:Linklayerthroughapplicationlayer• 2/3:currenttopicsinnetworking(wireless,multimedia,datacenters,etc.)
• Skills• Howtoread• Howtopresent• Howtodiscuss• Howtousecommonnetworkingtools
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CourseStructure
• Paperreading• 2-3papersperweek
• Classroomtime• Lecture• Paperdiscussion
• Programmingassignments• Multipath-TCP• Mininet +OpenFlow
• Project• Proposal,presentation,andfinalreport• Canworkindividuallyinoringroups• Canbeanextensionofexistingworkorresearch(subjecttoapproval)
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CalendarWeek Topic Assignment1 Introduction +MAClayer2 Networklayer3 Transport layer MPTCPassignment4 Applicationlayer5 Contentdistribution Projectproposal6 Datacenters7 Wireless8 Security SDNassignment9 FutureInternet(SDN,IoT)10 Project presentations
Finals week Finalreportdue
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Grading
• Papersummaries(20%)• Writeaone-paragraphreviewforeachpaper
• Classparticipation(20%)• Speakupduringdiscussion!
• Assignments(20%)• 2programmingassignments
• Project(40%)
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Review1.1whatis theInternet?1.2 networkedge
§ end systems, access networks, links1.3networkcore
§ packet switching, circuit switching, network structure1.4 protocollayers,servicemodels
AdaptedfromComputerNetworking:ATop-DownApproach,Kurose&Ross
What’stheInternet:“nutsandbolts” view
• millionsofconnectedcomputingdevices:
• hosts= endsystems• runningnetworkapps
vcommunication links§ fiber, copper, radio,
satellite§ transmission rate:
bandwidth
vPacket switches: forward packets (chunks of data)§ routers and switches
wiredlinks
wirelesslinks
router
mobile network
global ISP
regional ISP
home network
institutionalnetwork
smartphone
PC
server
wirelesslaptop
• Internet:“networkofnetworks”• InterconnectedISPs
• protocols controlsending,receivingofmsgs
• e.g.,TCP,IP,HTTP,Skype,802.11
• Internetstandards• IETF:InternetEngineeringTaskForce
What’s the Internet: “nuts and bolts” view
mobile network
global ISP
regional ISP
home network
institutionalnetwork
What’stheInternet:aserviceview
• Infrastructurethatprovidesservicestoapplications:
• Web,VoIP,email,games,e-commerce,socialnets,…
• providesprogramminginterfacetoapps
• hooksthatallowsendingandreceivingappprogramsto“connect” toInternet
• providesserviceoptions,analogoustopostalservice
mobile network
global ISP
regional ISP
home network
institutionalnetwork
What’saprotocol?
humanprotocols:• “what’sthetime?”• “Ihaveaquestion”• introductions
…specificmsgssent…specificactionstakenwhenmsgsreceived,orotherevents
networkprotocols:• machinesratherthanhumans
• allcommunicationactivityinInternetgovernedbyprotocols
protocols define format, orderof msgs sent and receivedamong network entities,
and actions taken on msg transmission, receipt
ahumanprotocolandacomputernetworkprotocol:
Hi
Hi
Got thetime?2:00
TCP connectionresponse
Get http://www.awl.com/kurose-ross
<file>time
TCP connectionrequest
What’s a protocol?
Roadmap1.1whatis theInternet?1.2networkedge
§ end systems, access networks, links1.3networkcore
§ packet switching, circuit switching, network structure1.4 protocollayers,servicemodels
Acloserlookatnetworkstructure:
• networkedge:• hosts:clientsandservers• serversoftenindatacenters
v access networks, physical media: wired, wireless communication links
v network core: § interconnected routers§network of networks
mobile network
global ISP
regional ISP
home network
institutionalnetwork
Accessnetworksandphysicalmedia
Q:Howtoconnectendsystemstoedgerouter?
• residentialaccessnets• institutionalaccessnetworks(school,company)
• mobileaccessnetworks
keepinmind:• bandwidth(bitspersecond)ofaccessnetwork?
• sharedordedicated?
Access net: home network
to/from headend or central office
cable or DSL modem
router, firewall, NAT
wired Ethernet (100 Mbps)
wireless access point (54 Mbps)
wirelessdevices
often combined in single box
Enterpriseaccessnetworks(Ethernet)
• typicallyusedincompanies,universities,etcv 10Mbps,100Mbps,1Gbps,10Gbpstransmissionratesv today,endsystemstypicallyconnectintoEthernetswitch
Ethernet switch
institutional mail,web servers
institutional router
institutional link to ISP (Internet)
Wirelessaccessnetworks
• sharedwireless accessnetworkconnectsendsystemtorouter• viabasestationaka“accesspoint”
wireless LANs:§ within building (100 ft)§ 802.11b/g (WiFi): 11, 54 Mbps
transmission rate
wide-area wireless access§ provided by telco (cellular)
operator, 10’s km§ between 1 and 10 Mbps § 3G, 4G: LTE
to Internet
to Internet
Host:sendspackets ofdata
hostsendingfunction:vtakesapplicationmessagevbreaksintosmallerchunks,knownaspackets,oflengthLbits
vtransmitspacketintoaccessnetworkattransmissionrateR§ linktransmissionrate,akalinkcapacity,akalinkbandwidth
R: link transmission ratehost
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two packets, L bits each
packettransmission
delay
time needed totransmit L-bit
packet into linkL (bits)R (bits/sec)= =
Review1.1whatis theInternet?1.2 networkedge
§ end systems, access networks, links
1.3networkcore§ packet switching, circuit switching, network structure
1.4 protocollayers,servicemodels
• meshofinterconnectedrouters
• packet-switching:hostsbreakapplication-layermessagesintopackets
• forwardpackets fromoneroutertothenext,acrosslinksonpathfromsourcetodestination
• eachpackettransmittedatfulllinkcapacity
Thenetworkcore
Packet-switching:store-and-forward
• takesL/R secondstotransmit(pushout)L-bitpacketintolinkatR bps
• storeandforward: entirepacketmustarriveatrouterbeforeitcanbetransmittedonnextlink
one-hopnumericalexample:
§ L =7.5Mbits§ R =1.5Mbps§ one-hoptransmissiondelay=5sec
sourceR bps destination
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L bitsperpacket
R bps
v end-end delay = 2L/R (assuming zero propagation delay)
PacketSwitching:queueingdelay,loss
A
B
CR = 100 Mb/s
R = 1.5 Mb/s D
Equeue of packetswaiting for output link
queuing and loss: v If arrival rate (in bits) to link exceeds transmission rate of
link for a period of time:§ packets will queue, wait to be transmitted on link § packets can be dropped (lost) if memory (buffer) fills up
Twokeynetwork-corefunctionsforwarding:movepacketsfromrouter’sinputtoappropriaterouteroutput
routing: determines source-destination route taken by packets
§ routing algorithms
routing algorithm
local forwarding tableheader value output link
0100010101111001
3221
123
dest address in arrivingpacket’s header
Internetstructure:networkofnetworks
Question:givenmillions ofaccessISPs,howtoconnectthemtogether?
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnetaccess
net
accessnet
Internetstructure:networkofnetworks
Option:connecteachaccessISPtoeveryotheraccessISP?
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnetaccess
net
accessnet
connecting each access ISP to each other directly doesn’t
scale: O(N2) connections.
Internetstructure:networkofnetworks
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnetaccess
net
accessnet
Option: connect each access ISP to a global transit ISP? Customerand provider ISPs have economic agreement.
globalISP
Internetstructure:networkofnetworks
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnetaccess
net
accessnet
But if one global ISP is viable business, there will be competitors ….
ISP B
ISP A
ISP C
Internetstructure:networkofnetworks
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnetaccess
net
accessnet
But if one global ISP is viable business, there will be competitors …. which must be interconnected
ISP B
ISP A
ISP C
IXP
IXP
peering link
Internet exchange point
Internetstructure:networkofnetworks
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnet
accessnetaccess
net
accessnet
… and regional networks may arise to connect access nets to ISPS
ISP B
ISP A
ISP C
IXP
IXP
regional net
Internetstructure:networkofnetworks
• atcenter:small#ofwell-connectedlargenetworks• “tier-1” commercialISPs (e.g.,Level3,Sprint,AT&T,NTT),national&internationalcoverage
• contentprovidernetwork(e.g,Google):privatenetworkthatconnectsitdatacenterstoInternet,oftenbypassingtier-1,regionalISPs
accessISP
accessISP
accessISP
accessISP
accessISP
accessISP
accessISP
accessISP
Regional ISP Regional ISP
IXP IXP
Tier 1 ISP Tier 1 ISP Google
IXP
Tier-1ISP:e.g.,Sprint
…
to/from customers
peering
to/from backbone
…
………
POP: point-of-presence
Roadmap1.1whatis theInternet?1.2 networkedge
§ end systems, access networks, links1.3networkcore
§ packet switching, circuit switching, network structure1.4protocollayers,servicemodels
Protocol“layers”Networksarecomplex,withmany“pieces”:
• hosts• routers• linksofvariousmedia
• applications• protocols• hardware,software
Question:isthereanyhopeoforganizing structureof
network?
….oratleastourdiscussionofnetworks?
Internetprotocolstack• application: supportingnetworkapplications
• FTP,SMTP,HTTP• transport: process-processdatatransfer
• TCP,UDP• network: routingofdatagramsfromsourcetodestination
• IP,routingprotocols• link: datatransferbetweenneighboringnetworkelements
• Ethernet,802.111(WiFi),PPP• physical: bits“onthewire”
application
transport
network
link
physical
Whylayering?dealingwithcomplexsystems:• explicitstructureallowsidentification,relationshipofcomplexsystem’spieces
• layeredreferencemodel fordiscussion• modularizationeasesmaintenance,updatingofsystem
• changeofimplementationoflayer’sservicetransparenttorestofsystem
• e.g.,changeinletterlanguagedoesn’taffectrestofsystem
• layeringconsideredharmful?
Sender writes letter
Sender drops off letter at post office
Post office X sends mail to city Y
Sender city X Recipient city Yintermediate air-trafficcontrol centers
airplane routing
Recipient reads letter
Mailman delivers from post office to sender’s home
Post office Y receives mail from city X
Layeringofpostofficefunctionality
layers: eachlayerimplementsaservice• viaitsowninternal-layeractions• relyingonservicesprovidedbylayerbelow
Sender writes letter
Sender drops off letter at post office
Post office X sends mail to city Y
Sender city X Recipient city Yintermediate air-trafficcontrol centers
airplane routing
Recipient reads letter
Mailman delivers from post office to sender’s home
Post office Y receives mail from city X
Layeringofpostofficefunctionality
layers: eachlayerimplementsaservice• viaitsowninternal-layeractions• relyingonservicesprovidedbylayerbelow
PhysicalLink
Network
PhysicalLinkNetwork
Transport:DeliveryviaUPS(signaturerequired)orUSPS(nosignaturerequired)Application:thecontentsoftheletter,e.g.photo,video,novel
sourceapplicationtransportnetwork
linkphysical
HtHn M
segment Ht
datagram
destinationapplicationtransportnetwork
linkphysical
HtHnHl M
HtHn M
Ht M
M
networklink
physical
linkphysical
HtHnHl M
HtHn M
HtHn M
HtHnHl M
router
switch
Encapsulationmessage M
Ht M
Hn
frame
Roadmap1.1whatis theInternet?1.2 networkedge
§ end systems, access networks, links1.3networkcore
§ packet switching, circuit switching, network structure1.4 protocollayers,servicemodels
ForNextTime
• Reading• TheDesignPhilosophyoftheDARPAInternetProtocols• HowtoReadaPaper
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