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What to configure• IPaddress• Netmask(specifies network id)• DefaultGateway (atleast one)• DNSserver(atleast one)– Server’s IPaddress
• Other stuff– TFTPserver– Configuration file– Executable imagedownload
ETSF05/ETSF10- InternetProtocols 3
DynamicHostConfiguration Protocol(DHCP)• BOOTP– Notdynamic!– Servercannot reclaim IPaddress
• DHCP– IPaddress
• Allocationfrompoolorstatic (mapping toe.g.MACaddr)– Networkmask– Defaultgateway– DNSserver(s)– Leasetime
5ETSF05/ETSF10- InternetProtocols
DynamicHostConfigurationProtocol(DHCP)
Internetprotocolthat
enablesdynamic
allocationofIPaddressestohosts
DefinedinRFC2131
WasdevelopedtodealwiththeshortageofIPaddresses
EnablesalocalnetworktoassignIPaddressesfromapoolofavailableIPaddressestohostscurrentlyinuse• Whenahostisnotinuse,itsIPaddressisreturnedtothepoolmanagedbyaDHCPserver
Canalsoassign
permanentIPaddressesto
somesystems,suchasservers,so
thattheaddress
remainsthesamewhenthesystemisrebooted
ETSF05/ETSF10- InternetProtocols 6
ETSF05/ETSF10- InternetProtocols 7
EnterpriseNetwork
DNSDatabase
Request IPaddress
Respond with IP
address, parameters
Figure 21.14 DHCP Role
DHCPDatabase
DHCPServer
DNSServer
ThefollowingDHCPmessagesareusedforprotocoloperation:(referenceonly)
DHCPDISCOVER•Clientbroadcasttolocateavailableservers
DHCPOFFER•ServertoclientinresponsetoDHCPDISCOVERwithofferofconfigurationparameters
DHCPREQUEST•Clientmessagetoserverseither(a)requestingofferedparametersfromoneserverandimplicitlydecliningoffersfromallothers,(b)confirmingcorrectnessofpreviouslyallocatedaddressafter,forexample,systemreboot,or(c)extendingtheleaseonaparticularnetworkaddress
DHCPACK•Servertoclientwithconfigurationparameters,includingcommittednetworkaddress
DHCPNACK•Servertoclientindicatingclient’snotionofnetworkaddressisincorrect(e.g.,clienthasmovedtonewsubnet)orclient’sleasehasexpired
DHCPDECLINE•Clienttoserverindicatingnetworkaddressisalreadyinuse.DHCPservershouldthennotifysysadmin
DHCPRELEASE•Clienttoserverrelinquishingnetworkaddressandcancelingremaininglease
DHCPINFORM•Clienttoserver,askingonlyforlocalconfigurationparametersclientalreadyhasexternallyconfigurednetworkaddress
ETSF05/ETSF10- InternetProtocols 8
InternetDirectoryServiceDomainNameSystem(DNS)• AdirectorylookupservicethatprovidesamappingbetweenthenameofahostontheInternetanditsnumericaladdress
• EssentialtothefunctioningoftheInternet• DefinedinRFCs 1034and1035• FourelementscomprisetheDNS:
Domainnamespace
DNSdatabase
Nameservers Resolvers
ETSF05/ETSF10- InternetProtocols 12
ETSF05/ETSF10- InternetProtocols 13
Figure 24.4 Portion of Internet Domain Tree
com
ibm apple
info
mil
mit
edu
treas
gov net
shore ieee acm
org us cn br
raleigh
itso
(root)
csail lcs
DNSDatabase
• Basedonahierarchicaldatabasecontainingresourcerecords(RR)thatincludethename,IPaddress,andotherinformationabouthosts
• Keyfeatures:– Variable-depthhierarchyfornames– Distributeddatabase– Distributioncontrolledbythedatabase
ETSF05/ETSF10- InternetProtocols 14
DNSresource records
ETSF05/ETSF10- InternetProtocols 15
See also Table 24.5 Resource Record TypesFigure 24.5 for record format
Domainnameresolution
• Actionofaddressmapping– Client=resolver– Server=DNS
• Oneservercannothavealltheanswers!– Howtoaskothers?–Whattodowiththeanswer?
• Caching– Rememberwhatyouhavelearned
18ETSF05/ETSF10- InternetProtocols
Domain
• Referstoagroupofhoststhatareundertheadministrativecontrolofasingleentity
• Organizedhierarchically,sothatagivendomainmayconsistofanumberofsubordinatedomains
• Namesareassignedandreflectthehierarchicalorganization
ETSF05/ETSF10- InternetProtocols 22
Domains,subdomains,zones
Domain• SubtreeofDNS
Zone• Servers’controlarea
ETSF05/ETSF10- InternetProtocols 23
ETSF05/ETSF10- InternetProtocols 29
UserProgram
UserSystem
Internetuser
query query
query
userresponse
response
response
NameResolver
Cache
NameServer
Cache
Database
Figure 24.6 DNS Name Resolution
Database
ForeignNameServer
Cache
www.root-servers.org
ETSF05/ETSF10- InternetProtocols 31
• 13rootservers:A,B,C,D,E,F,G,H,I,JK,L,M• Implementedbytotal641servers
NameResolution• Eachquerybeginsatanameresolverlocatedintheuser
hostsystem• Iftheresolverdoesnothavetherequestednameinits
cache,itsendsaDNSquerytothelocalDNSserver• ResolversuseUDPforsinglequeriesandTCPforgroup
queries
• Queryanothernameserverforthedesiredresultandthensendtheresultback
• Usedforrequestssentbyanameresolver
Recursivetechnique
• ReturntheaddressofthenextservertowhomtherequestshouldbesentthensendoutanewDNSrequesttothatserver
Iterativetechnique
ETSF05/ETSF10- InternetProtocols 32
The image part with relationship ID rId3 was not found in the file.
Iterativeresolution
34ETSF05/ETSF10- InternetProtocols
Manuallookup(onUNIXlike)##Lookup>hostlu.selu.se hasaddress130.235.52.5lu.se hasIPv6address2001:6b0:16:1:5ee:bad:c0de:1002lu.se mailishandledby10mx.lu.se.
>host–tAlu.selu.se hasaddress130.235.52.5
##Reverse>host130.235.52.55.52.235.130.in-addr.arpadomainnamepointerlb3v1.net.lu.se.
ETSF05/ETSF10- InternetProtocols 35
DynamicDNS
• Hostmaymovearound– ChangeofIPaddress
• Newdomainsmayemerge– Binding(IPaddress↔Name)– DHCPupdatesprimaryDNSserver– Primaryserverupdateszone– Secondaryserversnotified
37ETSF05/ETSF10- InternetProtocols
DNSsec
• Provides–Message authentication
• Protect against– Forged ormanipulated data
• Noconfidentiality
• Digitalsignature
ETSF05/ETSF10- InternetProtocols 38
Real-timeaudio/video
• One-waycommunication– IPTV,InternetRadio– OverTheTop(OTT)
• Two-waycommunication(interactive)– IPtelephony– VoiceoverIP(VoIP)– Videoconferencing
39ETSF05/ETSF10- InternetProtocols
Compare OnDemand Services
• Audio/Video• Notreal-time• TCPandbuffering• Example:– Youtube– Spotify– PlayChannels
ETSF05/ETSF10- InternetProtocols 40
ETSF05/ETSF10- InternetProtocols 41
Internet
Source:Multimedia Server
DestinationMultimedia PC
constant flow of packets(160 data octets every 20 ms)
packets arrive unevenly spaced
packets delivered with original spacing(some may be missing)
Time delaybuffer
Figure 25.1 Real-Time Traffic
ETSF05/ETSF10- InternetProtocols 42
T
t
(a) Continuous data source
T
t
(c) Compressed video source
T
t
(b) Voice sourcewith silent intervals
Figure 25.2 Real-Time Packet Transmission (based on [ARAS94])
RequirementsforReal-TimeCommunication• Lowjitter(delayvariations)• Lowlatency• Abilitytoaggregatenon-real-timeandreal-timeservices• Adaptabletodynamicallychangingnetworkandtraffic
conditions• Goodperformanceforlargenetworksandlargenumbersof
connections• Modestbufferrequirementswithinthenetwork• Effectivecapacityutilization• Lowoverheadinheaderbitsperpacket• Lowprocessingoverheadperpacketwithinthenetworkand
attheendsystem
ETSF05/ETSF10- InternetProtocols 43
HardVersusSoftReal-TimeApplicationsSoft
• Cantoleratelossofsomeportionofdata
• Imposefewerrequirementsonthenetwork,thereforepermissibletofocusonmaximizingnetworkutilization,evenatthecostofsomelostormisorderedpackets
Hard
• Zerolosstolerance• Adeterministicupper
boundonjitterandhighreliabilitytakesprecedenceovernetworkutilizationconsiderations
ETSF05/ETSF10- InternetProtocols 44
Stillnotgoodenough!
• Packetscanbedeliveredoutoforder.• Packetscanbedroppedontheirway.• Timestampsdonotdetectlostpackets.
• Moresupport:–Multicast?Translation?Mixing?
49ETSF05/ETSF10- InternetProtocols
Sequencenumbers
Summaryandcomparison
RealTime PerformanceRequirements• Sensitiveto:– Delay– Jitter
• Notsosensitiveto:– Packetloss– Corruptedpackets
vs.CharacteristicsofTCP• Sensitiveto:– Lostorcorruptedpackets
• Notsosensitiveto:– Delay
• Nomulticasting!
ETSF05/ETSF10- InternetProtocols 50
So,whataboutUDP?
UDPheader format
• Checksumoptional• Nonumbering– Norelationbetweendatagrams
ETSF05/ETSF10- InternetProtocols 52
Real-TimeTransportProtocol(RTP)
• DefinedinRFC3550• Bestsuitedtosoftreal-timecommunication• Lacksthenecessarymechanismstosupporthardreal-timetraffic
• TwoprotocolsthatmakeupRTPare:
RTP• Datatransferprotocol RTCP
• Controlprotocol
ETSF05/ETSF10- InternetProtocols 53
Real-timeTransportProtocol
54ETSF05/ETSF10- InternetProtocols
See• Fig 25.7 RTP Header
Table 25.1 Payload types
ETSF05/ETSF10- InternetProtocols 55
Network Access
IP
UDPRTP
MPEGJPEG
H.261
Figure 25.6 RTP Protocol Architecture [THOM96]
RTPConcepts
• RTPsupportsthetransferofreal-timedataamonganumberofparticipantsinasession– AsessionisalogicalassociationamongtwoormoreRTPentitiesthatismaintainedforthedurationofthedatatransfer• Definedby:
– RTPportnumber– RTCPportnumber– ParticipantIPaddresses
ETSF05/ETSF10- InternetProtocols 56
Real-time TransportProtocol
• RTPhandles real-time traffic• Nodeliverymechanism– UsesUDP/IP
• Contributions– Time-stamping– Sequencing–Mixing
57ETSF05/ETSF10- InternetProtocols
RTPRelays
• Arelayoperatingatagivenprotocollayerisanintermediatesystemthatactsasbothadestinationandasourceinadatatransfer
• Twokinds:–Mixer– Translator
ETSF05/ETSF10- InternetProtocols 58
Mixer• RTPrelaythatreceivesstreamsofRTPpackets
fromoneormoresources,combines thesestreams,andforwardsanewRTPpacketstreamtooneormoredestinations
• Maychangethedataformatorsimplyperformthemixingfunction
• Providesthetiminginformationinthecombinedpacketstreamandidentifiesitselfasthesourceofsynchronization
• Example:Audio/videosessionwithseveralparticipants
ETSF05/ETSF10- InternetProtocols 61
Translator
• AsimpledevicethatproducesoneormoreoutgoingRTPpacketsforeachincomingRTPpacket
• Maychange theformatofthedatainthepacketoruseadifferentlower-levelprotocolsuitetotransferfromonedomaintoanother
• Examplesoftranslatoruseinclude:– Convertavideotoalowerqualityformat– Ifanapplication-levelfirewallpreventstheforwardingofRTPpackets,twotranslatorscansetuptunnel
– ReplicateanincomingmulticastRTPpacketandsendittoanumberofunicast destinations
ETSF05/ETSF10- InternetProtocols 62
Real-time TransportControlProtocol(RTCP)• RTPonlycarriesdata– SessionsinitialisedbySIP(SessionInitiationProtocol)
• RTCPcarries control messages– Flowcontrol– Servicequality– Feedbacktosource
67ETSF05/ETSF10- InternetProtocols
Senderreport
• Sentbyactivesenders– Periodical
• Statistics– Transmission– Reception
• Absolutetimestamp– ReceiverscansynchRTPmessages• Important foraudioandvideo
68ETSF05/ETSF10- InternetProtocols
Receiverreport
• Sentbylisteners– Notsending RTPpackets– FeedbackaboutQoS
69
Andothers...
ETSF05/ETSF10- InternetProtocols
Some multimediaapplications
Two-way
• Skype• Webex• AdobeConnect• Zoom• …
One-way
• Youtube• Netflix• Spotify• Playchannels
– Free orsubscribed
• …
ETSF05/ETSF10- InternetProtocols 71
Many of these use TCP!