cs 204: advanced computer networksjiasi/teaching/cs204_spring16/slides/lec1_overview.pdf · why...

CS204:AdvancedComputerNetworks

Jiasi ChenLectures:MWF12:10-1pminWCH139

http://www.cs.ucr.edu/~jiasi/teaching/cs204_spring16/

1

WhyNetworks?

2

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?

3

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?

4

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

6

SomeResearchTopicsinNetworking

• Layering• Whatfunctionality toplacewithineach layer?• Howmanylayersshouldtherebe?

• Protocols• Howtocommunicate withineach layer,andtalktoother layers?

• Resourceallocation• Howtoshare limited resourcesbetweencompeting users?

• Wireless• Howtoprovideaone-to-onecommunication inaninherently broadcastenvironment

7

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:Linklayerthroughapplication layer• 2/3:currenttopics innetworking(wireless,multimedia, datacenters,etc.)

• Skills• Howtoread• Howtopresent• Howtodiscuss• Howtousecommonnetworkingtools

8

CourseStructure

• Paperreading• Onepapertoreviewbeforeeachclass

• Classroom time• Lecture• Paperdiscussion

• Programmingassignments• Mininet +OpenFlow

• Project• Proposal,presentation,andfinalreport• Canwork individuallyinoringroups• Canoverlapwithexistingindependent workorresearchproject

9

CalendarWeek Topic AssignmentDue1 Introduction+MAClayer2 Networklayer3 Transport layer4 Applicationlayer Assignment15 Contentdistribution6 Datacenters Projectproposal7 Wireless8 Security Assignment29 FutureInternet(SDN,IoT)10 Projectpresentations

Finals week Finalreportdue

10

Grading

• Papersummaries(20%)• Writeaone-paragraphreviewforeachpaper

• Classparticipation(20%)• Speakupduringdiscussion!

• Assignments(20%)• 2programmingassignments

• Project(40%)

11

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


What’stheInternet:aserviceview

• Infrastructurethatprovidesservicestoapplications:

• Web,VoIP,email, games,e-commerce,socialnets,…

• providesprogramminginterfacetoapps

• hooksthatallowsendingandreceiving appprogramsto“connect” toInternet

• providesserviceoptions,analogoustopostalservice

mobile network

global ISP

regional ISP

home network


What’saprotocol?

humanprotocols:• “what’sthetime?”• “Ihaveaquestion”• introductions

…specificmsgssent…specific actionstakenwhenmsgsreceived,orotherevents

networkprotocols:• machines ratherthanhumans

• allcommunication activityinInternetgovernedbyprotocols

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



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


Accessnetworksandphysicalmedia

Q:Howtoconnectendsystemstoedgerouter?

• residential access nets• institutional accessnetworks(school,company)

• mobile accessnetworks

keepinmind:• bandwidth(bitspersecond)ofaccess network?

• 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)

• typicallyused incompanies, universities, etcv 10Mbps,100Mbps,1Gbps,10Gbpstransmission ratesv today,endsystems typicallyconnect intoEthernet switch

Ethernet switch

institutional mail,web servers

institutional router

institutional link to ISP (Internet)

Wirelessaccessnetworks

• sharedwireless access networkconnects endsystemtorouter• 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

12

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

• eachpackettransmitted atfulllinkcapacity

Thenetworkcore

Packet-switching:store-and-forward

• takesL/R secondstotransmit(pushout)L-bitpacket intolinkatR bps

• storeandforward: entirepacketmust arriveatrouterbeforeitcanbetransmittedonnextlink

one-hopnumericalexample:

§ L =7.5Mbits§ R =1.5Mbps§ one-hoptransmissiondelay=5sec

sourceR bps destination

123

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 ofaccess ISPs,howtoconnectthemtogether?

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnet

accessnetaccess

net

accessnet


Option:connecteachaccess ISPtoeveryotheraccessISP?

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.


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


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


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


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


• atcenter:small#ofwell-connected largenetworks• “tier-1” commercialISPs (e.g.,Level3,Sprint,AT&T,NTT),national&internationalcoverage

• contentprovidernetwork(e.g,Google):privatenetworkthatconnects itdatacenterstoInternet,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


§ 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

• changeofimplementation oflayer’sservice transparenttorestofsystem

• e.g.,changeinletter languagedoesn’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 X 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



ForNextTime

• Reading• TheDesignPhilosophyoftheDARPAInternetProtocols• HowtoReadaPaper

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