DHCP DNS Real time applications RTP - eit.lth.se

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Higher layer protocols

ETSF05/ETSF10– InternetProtocols

• DHCP

• DNS

• Realtimeapplications

• RTP

Thehenortheegg?

ETSF05/ETSF10- InternetProtocols 2

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

ETSF05/ETSF10- InternetProtocols 3

ObtaininganIPaddress (bootp)

• Bootstrap

ETSF05/ETSF10- InternetProtocols 4

DynamicHostConfiguration Protocol(DHCP)• BOOTP– Notdynamic!

• DHCP– IPaddress

• Allocationfrompoolorstatic

– Networkmask– Defaultgateway– DNSserver(s)

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

DHCPoperation

10ETSF05/ETSF10- InternetProtocols

DHCPstates

ETSF05/ETSF10- InternetProtocols 11

75%Normallywe’re here

InternetDirectoryService(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

ETSF05/ETSF10- InternetProtocols 19

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

ETSF05/ETSF10- InternetProtocols 20

Recursiveresolution

21ETSF05/ETSF10- InternetProtocols

The image part with relationship ID rId3 was not found in the file.

Iterativeresolution

22ETSF05/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 23

Domain

• Referstoagroupofhoststhatareundertheadministrativecontrolofasingleentity

• Organizedhierarchically,sothatagivendomainmayconsistofanumberofsubordinatedomains

• Namesareassignedandreflectthehierarchicalorganization

ETSF05/ETSF10- InternetProtocols 27

Domains,subdomains,zones

Domain• SubtreeofDNS

Zone• Servers’controlarea

ETSF05/ETSF10- InternetProtocols 28

Domainnamesandlabels

29ETSF05/ETSF10- InternetProtocols

Genericdomains

31ETSF05/ETSF10- InternetProtocols

Compare Table 24.4

eu

se

lth

eit

eit.lth.se

Countrydomains

32ETSF05/ETSF10- InternetProtocols

Hierarchyofdomainnameservers

• 13rootservers

ETSF05/ETSF10- InternetProtocols 34

www.root-servers.org

ETSF05/ETSF10- InternetProtocols 35

• 13rootservers:A,B,C,D,E,F,G,H,I,JK,L,M• Implementedbytotal641servers

DynamicDNS

• Hostmaymovearound– ChangeofIPaddress

• Newdomainsmayemerge– Binding(IPaddress↔Name)– DHCPupdatesprimaryDNSserver– Primaryserverupdateszone– Secondaryserversnotified

37ETSF05/ETSF10- InternetProtocols

DNSsec

• Provides–Messageauthentication

• Protect against– Forgedormanipulateddata

• 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

CompareOnDemand 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-time andreal-timeservices• Adaptabletodynamicallychangingnetworkandtraffic

conditions• Goodperformance forlargenetworksandlargenumbersof

connections• Modestbuffer requirementswithin thenetwork• Effective capacityutilization• Lowoverhead inheaderbitsperpacket• Lowprocessingoverhead perpacketwithin thenetwork and

attheendsystem

ETSF05/ETSF10- InternetProtocols 43

HardVersusSoftReal-TimeApplicationsSoft

• Cantoleratethelossofsomeportionofthecommunicateddata

• Imposefewerrequirementsonthenetwork, thereforepermissibletofocusonmaximizingnetworkutilization,evenatthecostofsomelostormisorderedpackets

Hard

• Zerolosstolerance• Adeterministicupper

boundonjitterandhighreliabilitytakesprecedenceovernetworkutilizationconsiderations

ETSF05/ETSF10- InternetProtocols 44

• Justdelay?Noproblem!(?)

Timerelationship

ETSF05/ETSF10- InternetProtocols 45

PacketDelayVariation(PDV)/Jitter

• Undesiredvariationindelay

ETSF05/ETSF10- InternetProtocols 46

Timestamps

• Separationofarrivaltimefromplaybacktime

ETSF05/ETSF10- InternetProtocols 47

Playbackbuffer

48ETSF05/ETSF10- InternetProtocols

Playout delay – permissable network delay

Stillnotgoodenough!

• Packetscanbedeliveredoutoforder.• Packetscanbedroppedontheirway.• Timestampsdonotdetectlostpackets.

• Moresupport:–Multicast?Translation?Mixing?

49ETSF05/ETSF10- InternetProtocols

Sequencenumbers

Summaryandcomparison

RealTime PerformanceRequirements• Sensitiveto:

– Delay– Jitter

• Notsosensitiveto:– Packet loss– 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

ETSF05/ETSF10- InternetProtocols 54

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 55

Real-time TransportProtocol

• RTPhandles real-time traffic• Nodeliverymechanism– UsesUDP/IP

• Contributions– Time-stamping– Sequencing–Mixing

56ETSF05/ETSF10- InternetProtocols

Real-timeTransportProtocol

57ETSF05/ETSF10- InternetProtocols

See• Fig 25.7 RTP Header

Table 25.1 Payload types

RTPRelays

• Arelayoperatingatagivenprotocollayerisanintermediatesystemthatactsasbothadestinationandasourceinadatatransfer

• Twokinds:–Mixer– Translator

ETSF05/ETSF10- InternetProtocols 58

Mixer

• RTPrelaythatreceivesstreamsofRTPpacketsfromoneormoresources,combinesthesestreams,andforwardsanewRTPpacketstreamtooneormoredestinations

• Maychangethedataformatorsimplyperformthemixingfunction

• Providesthetiminginformationinthecombinedpacketstreamandidentifiesitselfasthesourceofsynchronization

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

Somemultimediaapplications

Two-way

• Skype• Lync• AdobeConnect• …

One-way

• Netflix• Spotify• HBO• Playchannels

– Free orsubscribed

• …

ETSF05/ETSF10- InternetProtocols 71

Many of these use TCP!

Problem• WeexpectthesameorbetterQoE thanterrestrialbroadcast

• Internetbasedapplicationshastocopewith– Besteffort– Crampedaccessnetworks– Badchannels

• DSL• WiFI• Mobile

ETSF05/ETSF10- InternetProtocols 72

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