cos 461: computer networks · • four assignments (10% each) – 95% 3 hours, 70% 2 days late, 50%...
TRANSCRIPT
COS461:ComputerNetworksSpring2011
Lectures:MW10‐10:50aminBowen222
Prof.MikeFreedman
Precepts:F10‐10:50am,11‐11:50am
Preceptors:MatveyArye,JacopoCesareo,PremGopalan
hNp://www.cs.princeton.edu/courses/archive/spr11/cos461/
WhatYouLearninThisCourse• Knowledge:howtheInternetworks
– IPprotocolsuite– Internetarchitecture– ApplicaTons(Web,DNS,P2P,…)
• Insight:keyconceptsinnetworking– Protocols,layering,resourceallocaTon,naming
• Skill:networkprogramming– Manynodesaregeneral‐purposecomputers
• Andincreasingly,evenspecial‐purposeswitchesareprogrammable!
– Youcanprogramthenodes– Veryeasytoinnovateanddevelopnewusesofnetwork– Contrast:MaBellownedthetelecomnetwork,noinnovaTon
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LearningtheMaterial:People• Lecture(Prof.MikeFreedman)
– SlidesavailableonlineatcourseWebsite
– Officehours:Immediatelyfollowinglectures
• TeachingAssistantsofficehoursTBD
• Mainemail:cos461‐staffatlists.cs.princeton.edu– EmailtoindividualTAswillnotbeanswered
• MainQ&Aform:www.piazzza.com– Wewilladdallyouremailaddressestothecourse
– GradedonclassparTcipaTon:soask*and*answer!3
LearningtheMaterial:Books• Requiredtextbook
– ComputerNetworks:ASystemsApproach(4thedi9on),byPetersonandDavie[Okaytousethe3rdediTon]
• Booksonreserve– Networkingtextbooks
• ComputerNetworking:ATop‐DownApproachFeaturingtheInternet(3rdedi9on),byKuroseandRoss
• ComputerNetworks(4thedi9on),byTanenbaum
– Networkprogrammingreferences• TCP/IPIllustrated,Volume1:TheProtocols,byStevens
• UnixNetworkProgramming,Volume1:TheSocketsNetworkingAPI(3rdEdi9on),byStevens,Fenner,&Rudolf
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GradingandSchedule• Fourassignments(10%each)
– 95%3hours,70%2dayslate,50%>3dayslate– Onefreelatedayduringsemester– Mustcompleteallassignmentstopass
• Twoexams(50%total)– Midtermexambeforespringbreak(25%)– Finalexamduringexamperiod(25%)
• ClassparTcipaTon(10%)– Inlectureandprecept– Intheforums
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GraduateStudents:TwoChoices• PickoneoftwoopTons
– Dothefourprogrammingassignments
– Or,firsttwoassignments,plusresearchproject
• Researchprojects– Networking‐relatedresearchproblem
– Musthaveasystemsprogrammingcomponent– Talktome
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Policies:WriteYourOwnCodeProgramminginanindividualcreaTveprocess.Whilethinkingaboutaproblem,discussionswithfriendsareencouraged.However,whentheTmecomestowritecodethatsolvestheproblem,theprogrammustbeyourownwork.
IfyouhaveaquesTonabouthowtousesomefeatureofC,UNIX,etc.,youcancertainlyaskyourfriendsortheTA,butdonot,underanycircumstances,copyanotherperson'sprogram.
Lerngsomeonecopyyourprogramorusingsomeoneelse'scodeinanyformisaviola7onofacademicregula7ons.
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NetworkingisRelevant
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Informa7onwants to be free because it has becomesocheaptodistribute,copy,andrecombine...Itwantsto be expensive because it can be immeasurablyvaluabletotherecipient. (1985)
http://www.google.com/transparencyreport/traffic/
Themonolithicview
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1
2
3 4
5
6 7
Client Browser
Web server
THEINTERNET
!!!!
Why“Internet”• Networkofnetworks• StandardizedformatandprotocolsforspeakingbetweenHETEROGENOUSnetworks
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Why“Internet”• Networkofnetworks• StandardizedformatandprotocolsforspeakingbetweenHETEROGENOUSnetworks
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Themonolithicview
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1
2
3 4
5
6 7
Client Browser
Web server
THEINTERNET
!!!!
Anetworkof“AutonomousSystems”
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3 4
5
7
Client Browser
Web server
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1
2
• Howdoyouname?• Howdoyoufindaname?
Announcingatrafficroute
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3 4
5
7
Client Browser
Web server
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1
2
“EgyptisinthisdirecTon”
“RouTng”traffictoadesTnaTon
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3 4
5
7
Client Browser
Web server
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1
2
Withdrawingatrafficroute
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3 4
5
7
Client Browser
Web server
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1
2
“EgyptisnotinthisdirecTon”
???
KeyConceptsinNetworking• Protocols
– Speakingthesamelanguage– SyntaxandsemanTcs
• Layering– Standingontheshouldersofgiants– Akeytomanagingcomplexity
• ResourceallocaTon– DividingscareresourcesamongcompeTngparTes– Memory,linkbandwidth,wirelessspectrum,paths,
• Naming– Whattocallcomputers,services,protocols,…
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KeyConceptsinNetworking• Protocols
– Speakingthesamelanguage– SyntaxandsemanTcs
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1977 1998 1969
AllspeakIPv4“InternetProtocolversion4”
Protocoldesignisabouttradeoffs• Howshouldhostsandrouterscommunicate?
– Standardprotocol– Fast:Machinereadableinhardwareatlinerates
• Browsers,webservers,andproxies?– Canbeslower:sowwarereadable– Humanreadable– Extensibleandforward‐compaTble– Noteverybodymightbefamiliarwithextensions
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IPv4Packet
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4-bit Version
4-bit Header Length
8-bit Type of Service (TOS) 16-bit Total Length (Bytes)
16-bit Identification 3-bit Flags 13-bit Fragment Offset
8-bit Time to Live (TTL)
8-bit Protocol 16-bit Header Checksum
32-bit Source IP Address
32-bit Destination IP Address
Options (if any)
Payload
Example:HyperTextTransferProtocol
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GET /courses/archive/spr09/cos461/ HTTP/1.1 Host: www.cs.princeton.edu User-Agent: Mozilla/4.03 CRLF
HTTP/1.1 200 OK Date: Mon, 2 Feb 2009 13:09:03 GMT Server: Netscape-Enterprise/3.5.1 Last-Modified: Mon, 42 Feb 2009 11:12:23 GMT Content-Length: 21 CRLF Site under construction
Request
Response
KeyConceptsinNetworking• Protocols
– Speakingthesamelanguage– SyntaxandsemanTcs
• Layering– Standingontheshouldersofgiants– Akeytomanagingcomplexity
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Layering=FuncTonalAbstracTon• Sub‐dividetheproblem
– Eachlayerreliesonservicesfromlayerbelow– Eachlayerexportsservicestolayerabove
• InterfacebetweenlayersdefinesinteracTon– HidesimplementaTondetails– Layerscanchangewithoutdisturbingotherlayers
30 Link hardware
Host-to-host connectivity
Application-to-application channels
Application
TheInternetProtocolSuite
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UDP TCP
Data Link
Physical
Applications
The Hourglass Model
Waist
The waist facilitates interoperability
FTP HTTP TFTP NV
TCP UDP
IP
NET1 NET2 NETn …
LayerEncapsulaToninHTTP
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Get index.html
Connection ID
Source/Destination
Link Address
User A User B
Link hardware
Host-to-host connectivity
App-to-app channels
Application
IPSuite:EndHostsvs.Routers
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HTTP
TCP
IP
Ethernet interface
HTTP
TCP
IP
Ethernet interface
IP IP
Ethernet interface
Ethernet interface
SONET interface
SONET interface
host host
router router
HTTP message
TCP segment
IP packet IP packet IP packet
Conclusions• Internetisanetworkofnetworks
– Howhostsandnetworksnameoneanother,findoneanother,andtalkwithoneanother
• Keyconceptsinnetworking– Protocols,layers,resourceallocaTon,andnaming
• Nextlecture:– HowdoesYouTubeandNeylixserveyouvideos?– E.g.,HTTP,DNS,andcontentdistribuTonnetworks
• Nextweek:– Backtothe1960s
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