DHCP DNS Real time applications RTP - eit.lth.se
Transcript of DHCP DNS Real time applications RTP - eit.lth.se
Higher layer protocols
ETSF05/ETSF10– InternetProtocols
• DHCP
• DNS
• Realtimeapplications
• RTP
Thehenortheegg?
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IPaddr.
DNS
TCPUDP
IP
DHCP
What to configure• IPaddress• Netmask(specifies network id)• DefaultGateway (atleast one)• DNSserver(atleast one)– Server’s ip address
• Other stuff– TFTPserver– Configuration file– Executable imagedownload
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ObtaininganIPaddress (bootp)
• Bootstrap
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DynamicHostConfiguration Protocol(DHCP)• BOOTP– Notdynamic!
• DHCP– IPaddress
• Allocationfrompoolorstatic
– Networkmask– Defaultgateway– DNSserver(s)
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DynamicHostConfigurationProtocol(DHCP)
Internetprotocolthat
enablesdynamic
allocationofIPaddressestohosts
DefinedinRFC2131
WasdevelopedtodealwiththeshortageofIPaddresses
EnablesalocalnetworktoassignIPaddressesfromapoolofavailableIPaddressestohostscurrentlyinuse• Whenahostisnotinuse,itsIPaddressisreturnedtothepoolmanagedbyaDHCPserver
Canalsoassign
permanentIPaddressesto
somesystems,suchasservers,so
thattheaddress
remainsthesamewhenthesystemisrebooted
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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
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DHCPoperation
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DHCPstates
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75%Normallywe’re here
InternetDirectoryService(DNS)
• AdirectorylookupservicethatprovidesamappingbetweenthenameofahostontheInternetanditsnumericaladdress
• EssentialtothefunctioningoftheInternet• DefinedinRFCs 1034and1035• FourelementscomprisetheDNS:
Domainnamespace
DNSdatabase
Nameservers Resolvers
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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
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DNSresource records
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See also Table 24.5 Resource Record TypesFigure 24.5 for record format
Domainnameresolution
• Actionofaddressmapping– Client=resolver– Server=DNS
• Oneservercannothavealltheanswers!– Howtoaskothers?–Whattodowiththeanswer?
• Caching– Rememberwhatyouhavelearned
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UserProgram
UserSystem
Internetuser
query query
query
userresponse
response
response
NameResolver
Cache
NameServer
Cache
Database
Figure 24.6 DNS Name Resolution
Database
ForeignNameServer
Cache
NameResolution• Eachquerybeginsatanameresolverlocatedintheuser
hostsystem• Iftheresolverdoesnothavetherequestednameinits
cache,itsendsaDNSquerytothelocalDNSserver• ResolversuseUDPforsinglequeriesandTCPforgroup
queries
• Queryanothernameserverforthedesiredresultandthensendtheresultback
• Usedforrequestssentbyanameresolver
Recursivetechnique
• ReturntheaddressofthenextservertowhomtherequestshouldbesentthensendoutanewDNSrequesttothatserver
Iterativetechnique
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Recursiveresolution
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The image part with relationship ID rId3 was not found in the file.
Iterativeresolution
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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.
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Domain
• Referstoagroupofhoststhatareundertheadministrativecontrolofasingleentity
• Organizedhierarchically,sothatagivendomainmayconsistofanumberofsubordinatedomains
• Namesareassignedandreflectthehierarchicalorganization
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Domains,subdomains,zones
Domain• SubtreeofDNS
Zone• Servers’controlarea
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Domainnamesandlabels
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Genericdomains
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Compare Table 24.4
eu
se
lth
eit
eit.lth.se
…
Countrydomains
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Hierarchyofdomainnameservers
• 13rootservers
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www.root-servers.org
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• 13rootservers:A,B,C,D,E,F,G,H,I,JK,L,M• Implementedbytotal641servers
DynamicDNS
• Hostmaymovearound– ChangeofIPaddress
• Newdomainsmayemerge– Binding(IPaddress↔Name)– DHCPupdatesprimaryDNSserver– Primaryserverupdateszone– Secondaryserversnotified
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DNSsec
• Provides–Messageauthentication
• Protect against– Forgedormanipulateddata
• Noconfidentiality
• Digitalsignature
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Real-timeaudio/video
• One-waycommunication– IPTV,InternetRadio– OverTheTop(OTT)
• Two-waycommunication(interactive)– IPtelephony– VoiceoverIP(VoIP)– Videoconferencing
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CompareOnDemand Services
• Audio/Video• Notreal-time• TCPandbuffering• Example:– Youtube– Spotify– PlayChannels
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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
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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-time andreal-timeservices• Adaptabletodynamicallychangingnetworkandtraffic
conditions• Goodperformance forlargenetworksandlargenumbersof
connections• Modestbuffer requirementswithin thenetwork• Effective capacityutilization• Lowoverhead inheaderbitsperpacket• Lowprocessingoverhead perpacketwithin thenetwork and
attheendsystem
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HardVersusSoftReal-TimeApplicationsSoft
• Cantoleratethelossofsomeportionofthecommunicateddata
• Imposefewerrequirementsonthenetwork, thereforepermissibletofocusonmaximizingnetworkutilization,evenatthecostofsomelostormisorderedpackets
Hard
• Zerolosstolerance• Adeterministicupper
boundonjitterandhighreliabilitytakesprecedenceovernetworkutilizationconsiderations
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• Justdelay?Noproblem!(?)
Timerelationship
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PacketDelayVariation(PDV)/Jitter
• Undesiredvariationindelay
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Timestamps
• Separationofarrivaltimefromplaybacktime
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Playbackbuffer
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Playout delay – permissable network delay
Stillnotgoodenough!
• Packetscanbedeliveredoutoforder.• Packetscanbedroppedontheirway.• Timestampsdonotdetectlostpackets.
• Moresupport:–Multicast?Translation?Mixing?
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Sequencenumbers
Summaryandcomparison
RealTime PerformanceRequirements• Sensitiveto:
– Delay– Jitter
• Notsosensitiveto:– Packet loss– Corruptedpackets
vs.CharacteristicsofTCP• Sensitiveto:
– Lostorcorruptedpackets
• Notsosensitiveto:– Delay
• Nomulticasting!
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So,whataboutUDP?
UDPheader format
• Checksumoptional• Nonumbering– Norelationbetweendatagrams
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Real-TimeTransportProtocol(RTP)
• DefinedinRFC3550• Bestsuitedtosoftreal-timecommunication• Lacksthenecessarymechanismstosupporthardreal-timetraffic
• TwoprotocolsthatmakeupRTPare:
RTP• Datatransferprotocol RTCP
• Controlprotocol
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Network Access
IP
UDPRTP
MPEGJPEG
H.261
Figure 25.6 RTP Protocol Architecture [THOM96]
RTPConcepts
• RTPsupportsthetransferofreal-timedataamonganumberofparticipantsinasession– AsessionisalogicalassociationamongtwoormoreRTPentitiesthatismaintainedforthedurationofthedatatransfer• Definedby:
– RTPportnumber– RTCPportnumber– ParticipantIPaddresses
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Real-time TransportProtocol
• RTPhandles real-time traffic• Nodeliverymechanism– UsesUDP/IP
• Contributions– Time-stamping– Sequencing–Mixing
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Real-timeTransportProtocol
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See• Fig 25.7 RTP Header
Table 25.1 Payload types
RTPRelays
• Arelayoperatingatagivenprotocollayerisanintermediatesystemthatactsasbothadestinationandasourceinadatatransfer
• Twokinds:–Mixer– Translator
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Mixer
• RTPrelaythatreceivesstreamsofRTPpacketsfromoneormoresources,combinesthesestreams,andforwardsanewRTPpacketstreamtooneormoredestinations
• Maychangethedataformatorsimplyperformthemixingfunction
• Providesthetiminginformationinthecombinedpacketstreamandidentifiesitselfasthesourceofsynchronization
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Translator
• AsimpledevicethatproducesoneormoreoutgoingRTPpacketsforeachincomingRTPpacket
• Maychange theformatofthedatainthepacketoruseadifferentlower-levelprotocolsuitetotransferfromonedomaintoanother
• Examplesoftranslatoruseinclude:– Convertavideotoalowerqualityformat– Ifanapplication-levelfirewallpreventstheforwardingofRTPpackets,twotranslatorscansetuptunnel
– ReplicateanincomingmulticastRTPpacketandsendittoanumberofunicast destinations
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Real-time TransportControlProtocol(RTCP)• RTPonlycarriesdata– SessionsinitialisedbySIP(SessionInitiationProtocol)
• RTCPcarries control messages– Flowcontrol– Servicequality– Feedbacktosource
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Senderreport
• Sentbyactivesenders– Periodical
• Statistics– Transmission– Reception
• Absolutetimestamp– ReceiverscansynchRTPmessages
• Important foraudioandvideo
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Receiverreport
• Sentbylisteners– Notsending RTPpackets– FeedbackaboutQoS
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Andothers...
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Somemultimediaapplications
Two-way
• Skype• Lync• AdobeConnect• …
One-way
• Netflix• Spotify• HBO• Playchannels
– Free orsubscribed
• …
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Many of these use TCP!
Problem• WeexpectthesameorbetterQoE thanterrestrialbroadcast
• Internetbasedapplicationshastocopewith– Besteffort– Crampedaccessnetworks– Badchannels
• DSL• WiFI• Mobile
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