ETSF05/ETSF10 –Internet Protocols - eit.lth.se · Hard Versus Soft Real-Time Applications Soft...

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 IPaddress

• Other stuff– TFTPserver– Configuration file– Executable imagedownload


ObtaininganIPaddress(bootp – Bootstrap protocol)


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



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


DHCPoperation


DHCPstates


75%Normallywe’re here

InternetDirectoryServiceDomainNameSystem(DNS)• AdirectorylookupservicethatprovidesamappingbetweenthenameofahostontheInternetanditsnumericaladdress

• EssentialtothefunctioningoftheInternet• DefinedinRFCs 1034and1035• FourelementscomprisetheDNS:

Domainnamespace

DNSdatabase

Nameservers Resolvers



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


DNSresource records


See also Table 24.5 Resource Record TypesFigure 24.5 for record format

Domainnameresolution

• Actionofaddressmapping– Client=resolver– Server=DNS

• Oneservercannothavealltheanswers!– Howtoaskothers?–Whattodowiththeanswer?

• Caching– Rememberwhatyouhavelearned


Domain

• Referstoagroupofhoststhatareundertheadministrativecontrolofasingleentity

• Organizedhierarchically,sothatagivendomainmayconsistofanumberofsubordinatedomains

• Namesareassignedandreflectthehierarchicalorganization


Domains,subdomains,zones

Domain• SubtreeofDNS

Zone• Servers’controlarea


Domainnamesandlabels


Genericdomains


Compare Table 24.4

eu

se

lth

eit

eit.lth.se

…

Countrydomains



UserProgram

UserSystem

Internetuser

query query

query

userresponse

response

response

NameResolver

Cache

NameServer

Cache

Database

Figure 24.6 DNS Name Resolution

Database

ForeignNameServer

Cache

Hierarchyofdomainnameservers

• 13rootservers


www.root-servers.org


• 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


Recursiveresolution


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

Iterativeresolution


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.


DynamicDNS

• Hostmaymovearound– ChangeofIPaddress

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


DNSsec

• Provides–Message authentication

• Protect against– Forged ormanipulated data

• Noconfidentiality

• Digitalsignature


Real-timeaudio/video

• One-waycommunication– IPTV,InternetRadio– OverTheTop(OTT)

• Two-waycommunication(interactive)– IPtelephony– VoiceoverIP(VoIP)– Videoconferencing


Compare OnDemand Services

• Audio/Video• Notreal-time• TCPandbuffering• Example:– Youtube– Spotify– PlayChannels



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


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


HardVersusSoftReal-TimeApplicationsSoft

• Cantoleratelossofsomeportionofdata

• Imposefewerrequirementsonthenetwork,thereforepermissibletofocusonmaximizingnetworkutilization,evenatthecostofsomelostormisorderedpackets

Hard

• Zerolosstolerance• Adeterministicupper

boundonjitterandhighreliabilitytakesprecedenceovernetworkutilizationconsiderations


• Justdelay?Noproblem!(?)

Timerelationship


PacketDelayVariation(PDV)/Jitter

• Undesiredvariationindelay


Timestamps

• Separationofarrivaltimefromplaybacktime


Playbackbuffer


Playout delay – permissable network delay

Stillnotgoodenough!

• Packetscanbedeliveredoutoforder.• Packetscanbedroppedontheirway.• Timestampsdonotdetectlostpackets.

• Moresupport:–Multicast?Translation?Mixing?


Sequencenumbers

Summaryandcomparison

RealTime PerformanceRequirements• Sensitiveto:– Delay– Jitter

• Notsosensitiveto:– Packetloss– Corruptedpackets

vs.CharacteristicsofTCP• Sensitiveto:– Lostorcorruptedpackets

• Notsosensitiveto:– Delay

• Nomulticasting!


So,whataboutUDP?

UDPheader format

• Checksumoptional• Nonumbering– Norelationbetweendatagrams


Real-TimeTransportProtocol(RTP)

• DefinedinRFC3550• Bestsuitedtosoftreal-timecommunication• Lacksthenecessarymechanismstosupporthardreal-timetraffic

• TwoprotocolsthatmakeupRTPare:

RTP• Datatransferprotocol RTCP

• Controlprotocol


Real-timeTransportProtocol


See• Fig 25.7 RTP Header

Table 25.1 Payload types


Network Access

IP

UDPRTP

MPEGJPEG

H.261

Figure 25.6 RTP Protocol Architecture [THOM96]

RTPConcepts

• RTPsupportsthetransferofreal-timedataamonganumberofparticipantsinasession– AsessionisalogicalassociationamongtwoormoreRTPentitiesthatismaintainedforthedurationofthedatatransfer• Definedby:

– RTPportnumber– RTCPportnumber– ParticipantIPaddresses


Real-time TransportProtocol

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

• Contributions– Time-stamping– Sequencing–Mixing


RTPRelays

• Arelayoperatingatagivenprotocollayerisanintermediatesystemthatactsasbothadestinationandasourceinadatatransfer

• Twokinds:–Mixer– Translator


Mixer• RTPrelaythatreceivesstreamsofRTPpackets

fromoneormoresources,combines thesestreams,andforwardsanewRTPpacketstreamtooneormoredestinations

• Maychangethedataformatorsimplyperformthemixingfunction

• Providesthetiminginformationinthecombinedpacketstreamandidentifiesitselfasthesourceofsynchronization

• Example:Audio/videosessionwithseveralparticipants


Translator

• AsimpledevicethatproducesoneormoreoutgoingRTPpacketsforeachincomingRTPpacket

• Maychange theformatofthedatainthepacketoruseadifferentlower-levelprotocolsuitetotransferfromonedomaintoanother

• Examplesoftranslatoruseinclude:– Convertavideotoalowerqualityformat– Ifanapplication-levelfirewallpreventstheforwardingofRTPpackets,twotranslatorscansetuptunnel

– ReplicateanincomingmulticastRTPpacketandsendittoanumberofunicast destinations


Real-time TransportControlProtocol(RTCP)• RTPonlycarriesdata– SessionsinitialisedbySIP(SessionInitiationProtocol)

• RTCPcarries control messages– Flowcontrol– Servicequality– Feedbacktosource


Senderreport

• Sentbyactivesenders– Periodical

• Statistics– Transmission– Reception

• Absolutetimestamp– ReceiverscansynchRTPmessages• Important foraudioandvideo


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

• …


Many of these use TCP!

Problem• Theuseroftenexpectsthesame,orbetter,QoE thanterrestrialbroadcast

• Internetbasedapplicationshastocopewith– Besteffort– Crampedaccessnetworks– Badchannels

• DSL• WiFi• Mobile


ETSF05/ETSF10 –Internet Protocols - eit.lth.se · Hard Versus Soft Real-Time Applications Soft...

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