cbc-ip

7/29/2019 cbc-ip

1/14

CBCTECHNOLOGYREVIEWJuly2007 1/14

IPBased

Radio

Production

and

Networking:

A

Path

to

the

Future

IPBASEDRADIOPRODUCTIONANDNETWORKING:A

PATHTOTHEFUTURE

PierreRobidoux,Eng.

SeniorEngineer

NewBroadcastTechnologies

ABSTRACT

Analogradiosystemsuseacentralizedsignalbasedworkflow.Whendigitizationcamealong,theworkflowstayedunchangedformostradiostations.Digitalaudiorecordersreplacedanalogones,signalprocessingandswitchingbecamealldigital,andsignaltransportbecameAES/EBU(AudioEngineeringSociety/EuropeanBroadcastingUnion).

Oneofthemainremainingproblemsatnewdigitalradiositesisallthewiringstillneededtotransport theaudio signal,mainlybecauseof the routing topology.AES/EBUwillonlycarry

twochannelsinonedirection.Countlesscablesarestillcarryingtheaudiosignalfromsourcestodestinationsviaamastercontrolroom,aswasdoneintheformeranalogworld.

InanIPvirtualtopology,Ethernetswitchessendaudiostreamsfromporttoport,routingthesignalinrealtimedirectlyfromanysourcetoanysingleoranymultipledestinations.ThisarticleforradiobroadcasterspresentstechnologicalelementsformigratingtoacompletelynetworkedIPaudioinfrastructure.

INTRODUCTION

Theuseofcomputertechnologiesissharplyontheincreaseinbroadcasting,especiallyinradio.

Many operators are already using DTR (Desktop Radio) and DAW (Desktop AudioWorkstation) and havebeen doing so for several years now. Almost all DTR systems arenetworkbased. Metadata management is done by an SQL (Structured Query Language)databaseserver,andaudioitemsarestoredononeormorefileservers.Ontheaudioplaybackandrecordside,manyDTRinstallationsuseAES/EBUorevenanaloginputs/outputs.

Issue4 Jul 2007 www.cbc.radiocanada.ca

CBCTECHNOLOGYREVIEW

7/29/2019 cbc-ip

2/14


IPBased

Radio

Production

and

Networking:

A

Path

to

the

Future

Currently,radiobroadcastingismovingtowardsITordatacentricarchitectureonalargescale,usingatapelessenvironment,filebasedworkflow,metadatamanagement,contentIPtransportandnetworks.WearenowfamiliarwithVoiceoverIP(VoIP).Thistechnologyisusedbymanyphone services and in corporations and is replacing the traditional PBX (Private BrancheXchange).

The

concept

of

using

an

Ethernet

network

to

transport

audio

can

be

applied,

with

considerable

benefit, to radiobroadcastingandmanymanufacturersarealreadyofferingnetworkedaudiosystems.AxiaTMandDigigramTMareamongthekeyplayersinaudioIPnetworktechnologyforradiobroadcasting.

Thispaperdoesnotsupportorpromoteanyparticulartechnology.ItsimplyshowssomeofthepracticalaspectsofrealworldAudiooverEthernet(AoE)forradiostations.

ADVANTAGESFORARADIOSTATIONTOMIGRATETOIP

Atfirstsight,IPnetworkpacketizedtransportdoesnotseemtobetheeasiestsolutionforaudio.IP was not designed to transport realtime data. However, this technology is gaining an

increasinglylargemarketshareinradiobroadcasting,mainlyforthefollowingreasons:

Transport:Computercablecan transporttheaudiosignaltoadistanceofupto80kmusingopticalfiber(singlemode)andupto100metersusingcopper.

Distribution:The receivingdevicesjustlisten to the feed from thesourcedevices inmulticastmode.Distributionamplifiersarenolongernecessary.

Routing: There is no centralized crosspoint audio router. Audio routing is donebystandardcomputerswitches.

Convergence:Theaudionetworkusestheexistingcomputer infrastructureastheDTRworkstations,serversandofficecomputers.

Cost:Mainlybecause of thewidespread availability of computer technologies, an IPsystemischeapertoinstall,supportandoperate. Flexibility: Compared to a traditional fixed studio installation, a modular IP audionetworkcanbeconfigured,modifiedandupgradedmuchmoreeasily.

Scalability: Inamultilevel topology, IP isveryscalable.Thebandwidthwould restrictthesizeofanIPradiosite,butGigabitEthernethaspushedthislimitsignificantly.

7/29/2019 cbc-ip

3/14


IPBased

Radio

Production

and

Networking:

A

Path

to

the

Future

Figure1illustratesaclientserverDTRsystem.ConventionalworkstationAhasaprofessionalbroadcastAES/EBUaudiocard(3stereo inputsand3stereooutputs). IPbasedworkstationBonlyneedsanetworkcardtoaccess(audiostreams)upto16stereoinputsand16stereooutputs

viaswitchB.BothswitchesarelinkedtoenableworkstationBtoaccesstherestofthenetwork.

AFIRSTSTEP

IP audio technologies offer awide range of possibilities for audio projects, from a simpleEthernetPCsoundcardtoacompletemultiplestudioradiobroadcastsite.Asafirstexample,a16pairaudiocableisreplacedbyasinglecomputercable.

Figure2showsanexampleofanIPaudioprojectusingRaveTMdigitalaudiorouters.

ThefirstaudioIPunit(left)has16analogaudioinputs.TheotheraudioIPunit(right)has16analog outputs.This Ethernet snake canuse aCat5 crossover cable,without a switch, at

lengthsup to100meters (328 feet).Witha switch, thismaximumdoubles.A coppertofibermediaconvertercanalsobeusedtosignificantlyextendthismaximumlength.

7/29/2019 cbc-ip

4/14


IPBased

Radio

Production

and

Networking:

A

Path

to

the

Future

STUDIOCOMPONENTS

ExampleofastudiocontrolsurfacefromAxiaTMandStuderTMfornetworkedaudio

IntheIPworld,theconsolebecomesacontrolboardonly.Mixing,processingandotheraudiofunctions,suchasmixminus,EQandauxiliaryfeeds,areprovidedbyaseparatehardwareunitcalledthecoreorstudioengine.Thefaders,buttonsandothercontrolscanbemappedintopagestoservedifferentpurposes(assignedtoseveralfunctions).

AstandaloneI/OIPnodeandaninput/outputrackwithIPcapability

OneoftheIPsystemsusesseparate(fromthestudioengine)IPdevicesforaudiosignalinputandoutput(analoganddigital).AnothersystemusesanIPaudiocard,whichisinstalledinitsI/Oroutingracktoenableupto128audiochannelstobetransportedviaasingleCAT5cable

INTERNETPROTOCOL(IP)

TheInternetProtocol is layerstructuredtoprovideefficientcommunicationbetweendifferentkindsofcomputers.Severalversionsofthislayeringmodelaredocumented.Theyhavefourorfive layers,anddifferentnamesareused for the layers. IP isbasedon theoriginalDoD (U.S.Department ofDefence)ARPANET layeredmodel created in the 1970s. Today, IP is used,amongmanyothers,bythelargestworldwidepubliccomputernetwork:theInternet.

Indepthcomputingexpertiseisnotmandatory,butbasicIPknowledgeisessentialforbuildingandsupportinganetworkedaudiofacility.

7/29/2019 cbc-ip

5/14


IPBased

Radio

Production

and

Networking:

A

Path

to

the

Future

Figure3presentsa5layerconceptforIPaudionetworking(overEthernet):

Physical(ElectricalInterface)Hardware communication for PCs and IP devices is providedby anNIC (NetworkInterfaceController,orNetworkInterfaceCard).ThestandardforaudioistheEthernet,using100BaseT(100Mbps)and1000BaseT(1000Mbps)cables.Thesecablesaremadeof eight conductors, four UTP (Unshielded Twisted Pairs), and RJ45 8pin plugs.Category5e(enhancedCat5)cablemaybeacceptable,butCat6cableisrecommended.MediatwistTM Cat6 is often suggested. Cable pinout should be TIA/EIA(Telecommunications Industry Association/Electronic Industries Alliance) T568 Bcompliant, a standard commonly used for data applications. 1000BASET GigabitEthernet(GbE)isalsoknownastheIEEE802.3abstandard.

EthernetorDataLink(orSwitching)EachNIChasaunique48bit IDassignedbymanufacturers: theMAC (MediaAccessControl) address. The Layer 2 header contains this address,which is used for local(intrasite)communications.TheMACaddresshasthefollowingformat:001124EB28DG.The IEEE802.3groupofstandardsdefines thephysical layer (1)andtheMACpartof

thedatalinklayer(2)(wiredEthernet).

IP(NetworkorRouting)

ThetaskofIP istogetpacketsofdatafromthesourcetothedestination.Thedotteddecimalnotationofthe32bitIPaddressconsistsoffouroctetsofeightbitsseparatedbythreedots.AnexampleofanIPaddressis192.15.121.10.Theleftmostbitsindicatethenetworkaddress.Theothersindicatethehost(PCorIPdevice)address.

7/29/2019 cbc-ip

6/14


IPBased

Radio

Production

and

Networking:

A

Path

to

the

Future

The number of bits assigned to each is determined by the class. For a mediumsizedorganization,aclassBwillbeneeded,butaclassCwillsufficeforasmallorganization.

Class AddressRange Max.Hosts

A 1.0.0.0to126.0.0.0 167772142B 128.1.0.0to191.254.0.0 65534

C

192.0.1.0

to

223.255.254.0

254

D 224.0.0.0to239.255.255.255 MulticastGroups

E 240.0.0.0to254.255.255.255 Experimental

Between theDataLink and the network layers is theARP (AddressResolution Protocol), aserviceforfindingthecorrespondencebetweentheMACaddressandtheIPaddress.

Foraudionetworkdesign,bothIPandMACaddressesforeachhostmayberequired.OnaPC(usingthecommandline),ipconfigallwillprovideboththeMACandIPaddressesofthePC.

TodisplaytheARPtable,enterarpa,usingthecommandline.ThecommandpingisusedtotestwhetheraspecificsystemisvisibleonanIPnetwork.PingsendsanICMP(InternetControlMessageProtocol)echorequest.Example:ping1.126.23.12

UDP/RTP(Transport)UDP(UserDatagramProtocol)ismainlyusedforapplicationssuchasstreamingaudioandvideo,whereontimedeliveryismoreimportantthanreliability.UDPusesasendandforgetstrategywithnoacknowledgmentprocess,asisthecaseforTCP.TherearefourfieldsinaUDPheader.Oneofthemisthesourceport,anotherthedestinationport.RTP (RealTimeProtocol),a layerbuilton topofUDP,hasa timestampandsequencenumberfieldsinitsheaderforsynchronizationandjitterprocesses.RTPwasoriginally

designed as a multicast protocol for delivering realtime media over an Ethernetnetwork.

AoE(AudiooverEthernet)Application.

Inthislayer,wefindprotocolssuchasHTTP,FTPandSMTP.InAoE,theprotocolusedwillbe,forexample,LivewireTMorEtherSoundTM.Thesearerealtimeaudiostreamingapplicationsthatincludesomeformofcontrolandidentificationdialog.

The14fieldsofanIPpacket(13header+1data)forIPv4areshowninthetablebelow.

Version IHL ToS TotalLengthIdentification Flags Frag.OffsetTTL Protocol HeaderChecksum

SourceAddress

DestinationAddress

IPOptionsData

7/29/2019 cbc-ip

7/14


IPBased

Radio

Production

and

Networking:

A

Path

to

the

Future

ThespecificfieldsthatrequirespecialattentionforAoEare: ToS(TypeofService):Thisisforassigningdifferentlevelsofimportancetodatagrams.Informationon setting this fieldcanbe found in the sectionentitledNetworking inthispaper.

TTL(TimeToLive):Thecounter,setatthesource,whichdecrementsateveryhop.Ifthisfieldreachesthevalueofzerobeforethedataarrivesatitsdestination,thedatawill

be

discarded.

Protocol:Indicatestheupperlayerprotocol(UDPforaudiooverIP). SourceAddress:Thesendinghostaddress. DestinationAddress:Thereceivinghostaddress. Data:Containsupperlayerinformation(from/totheTransportlayer)

7/29/2019 cbc-ip

8/14


IPBased

Radio

Production

and

Networking:

A

Path

to

the

Future

BUILDING A COMPLETE BROADCAST STUDIO

Figure4showsasimplebutcompletemodular(networked)IPbasedradiostudio.

The audioworkstation, the audio I/Omodules and the control surface are connected to theswitchat100Mbps.Themixingandprocessingmoduleand the linktootherstudio(s)or themastercontrolroomareconnectedtotheswitchat1000Mbps.TheaudiomodulesandaudioworkstationswillbeassignedtwoIPaddresses,oneforcontrol,theother(aClassD)foraudiostreaming.Thevirtualaudioroutingamongthemodulesandtheaudioworkstationisdonebymanagementandmonitoringsoftware.

7/29/2019 cbc-ip

9/14


IPBased

Radio

Production

and

Networking:

A

Path

to

the

Future

QoE,QoSandINSTRUMENTS

Quality is the evaluation of the degree of excellence. Quality of Experience (QoE) is theconsumers perception of how good a service is.QoE shouldbe planned, and it shouldbepredicted. It cannotbebased on afterthefact consumer complaints alone. QoE is directlyrelatedtothetechnicalQualityofService(QoS).

QoS, thebroadcasters evaluation of the service has to be measured and it needs tobemonitoredusingproperinstrumentation.Itcannotbepresumedgoodwithoutbeingtested.

AudioPrecisionTMATS2 FlukeTMcabletester CiscoTMSAA(ServiceAssuranceAgent)

A tone generator and an oscilloscope used tobe enough formostmaintenance tasks in ananalog onlyenvironment.Thearrivalofdigitalaudiochanged this.There isaneednow formoresophisticated test equipment. Families of products from firms likeAudio PrecisionTMperform simple and advanced generation (including FFT [Fast Fourier Transform]) andmeasurements of analog audio signal and AES/EBU digital audio data to ensure contentintegrity.

IPnetworkQoSforrealtimeaudioisbasedmainlyonfourelements: The Bandwidth has tobe secured. For each stream, there is aminimumbandwidth

requirement.

For

example,

an

uncompressed

standard

stream

would

have

a

bitrate

of

2.3

Mbps.AGigabitEthernetlinkwouldcarryupto430audiochannels. Packet Loss can be caused by several factors, such as signal degradation, anoversaturatednetwork,corruptedpackets, faultynetworkinghardware,or theroutingconfiguration.

Jitteristhevariationinpacketarrivaltime.AudioIPdevicesrequireajitterbuffer. Latencyisafixeddelayinarrivaltime.Lessthan3msissaidtobeacceptable.

Oneofthemajormanufacturersofswitchesandroutersofferstools,oneofthembeingarouterprobe,formeasuringdelay,jitterandpacketloss.

Cablesand connectorsareblamed 70 to80%of the timewhenproblemsoccur inanetworkenvironment. In addition to conductivity testing, proper troubleshooting instruments andmethodsshouldbeavailable,especiallyfor100/1000BaseTsignalcarryingwiring.

USINGCOMPUTERSINIPRADIO

In amixed clientserver/peertopeer topology for an IPbased radio stationproject,PCs andservershaveatendencytomultiplyveryrapidly.ANIPradiositewouldhaveDTRclientandserver software, several control software programs, administrative software programs, and

7/29/2019 cbc-ip

10/14


IPBased

Radio

Production

and

Networking:

A

Path

to

the

Future

automationsoftware.Furthermore,clusteringand/or redundancywouldaddonsystems.Foraudioworkstations,PCswouldbe kept inplace,mainly forDSP (Digital SignalProcessing)functions.Forallothertypesofwork,fromofficetosystemmanagement,therearesolutionsforgettingjobsdoneefficiently.

BSITM DTR system Thin client 16-blade servers (10 U rack)

Herearesomeitemstoconsiderforareliablemissioncriticalsystemand,atthesametime,for

minimizingthetotalcostofownership(TCO)ofanIPbasedradiostationproject.

BladeServersarenotthesolutiontoeverysituation,butwhenthereisaneedformanyserversinasmallspace,itisoneoptiontoconsider.Abladeenclosure(rack)providespower,cooling,networking, interconnectionsandsystemmanagement.Eachblade isacomplete hotswappable server (including a hard drive). Blade storage units,bladeswitchesandotheraccessoriesarecommerciallyavailableaswell.

AnApplicationServerisasoftwareservice(layer)thatrunsontopofaWindowsserverand thatdeliversapplications toclient computersor thinclients.MicrosoftTMuses theRemoteDesktopProtocol(RDP)for itsgraphic terminalservices.CitrixTMalsoofferan

application delivery system that runs on a Windows server which uses ICA(IndependentComputingArchitecture)protocol. AThinClientisagraphicterminalthatworksinaclient/serverarchitecture.Theserverprocessesalltheactivities,andthethinclientdisplaystheminaWindowsenvironment.Itsadvantagesaremainly lowerITadministrativecosts,lowerhardwarecosts,thefactthat itprovidesamoresecure infrastructure,andeasierupgradecapability.Most thinclientscomewithRDPandICAprotocols.

AUPSshouldbeusedtoensureacontinuoussupplyofelectricalpowerwhenutilitysupplied power poses problems, such as transients, interruptions, undervoltages,overvoltages,voltagefluctuations,waveformdistortions,andfrequencyvariations.

ThePCsselectedforradiocontentproduction(DTR)shouldbereliableanddependable,asshouldtheotheraudiobroadcastequipment.ConsumerhomePCsarenotanoption.

NETWORKING

BuildinganIPradiositeismoreelaboratethansimplyhavingtoconnectafewPCsconfiguredas aworkgroup on a hub.One of themain aspects is, of course, networking. If no trainedprofessionalisavailableonsite,itwouldbeagoodideatogetoutsidesupport.

7/29/2019 cbc-ip

11/14


IPBased

Radio

Production

and

Networking:

A

Path

to

the

Future

Figure5showsamulticastsession.Asourcehasstreamingaudioavailableatasinglemulticastaddress(ClassDaddress,from224.0.0.0to239.255.255.255).Hosts(PCsorIPdevices)mayjoin(in order to receive the audio stream) or leave themulticast group. IGMP (InternetGroupManagementProtocol),aLayer3function,isusedtomanagethepresenceofmembers(hosts)inthemulticastgroup.Thisisdonetominimizetrafficonthenetwork.

Alargepartofnetworkengineeringhastodowithswitchinstallationandconfiguration.HerearesomebasicconceptstolookatwhenbuildinganIPstudio:

IP audio network firms recommend specific families of switches for reliable operations.Switchesnormallyoperateonly inLayer2, theDataLink.Theonlyaddressprocessed in thislayer is theMAC. Because of the need to read and process the IP header (in Layer 3, theNetwork), the switches suggested by IP audio manufacturers offer additional Layer 3functionalities at the IP level.Ethernet switches have tobe transparent to IEEE (Institute ofElectricalandElectronicsEngineers)802.1p/QEthernetpacketsandalsobeIGMPcompliant.

TheDiffServ,aLayer3ToS(TypeofService),usesoneoftheIPheaderfieldsinIPv4(theToSByte).TheIETF(InternetEngineeringTaskForce)agreedtoreusetheToSbyteastheDSfieldforDiffServnetworks.Therefore,DiffServarchitecturenowsupersedestheToSfield.

The sixmost significantbitsof theDiffServ fieldare called theDSCP (DifferentiatedServiceCodePoint).

DS5 DS4 DS3 DS2 DS1 DS01 0 1 1 1 0

7/29/2019 cbc-ip

12/14


IPBased

Radio

Production

and

Networking:

A

Path

to

the

Future

TheQoSconfigurationshouldbeset(101110)inExpeditedForwarding(EFPHB)modetobuilda lowloss, lowlatency, lowjitter assured bandwidth service. PHB stands for PerHopBehaviour.

IEEE802.1p/Qusesaninternaltaggingschemetoinserta4fieldtagintotheoriginalEthernetframebetweentheSA(SourceAddress)andtheT/L(Type/Length)fields.

Layer2CoS(ClassofService)P S DA SA TAG T/L Data FCS

Thenewtaggedheaderhastwofields,PRIORITYandVID,whichareimportantforIPaudionetworks.

Numberofbits 16 3 1 12FrameField TPID PRIORITY CFI VID

ThePRIORITYfield(3bit)canrepresenteightlevelsofpriority.ItisadvisabletosetAoEtolevel6,asshowninthefollowingtable.

PriorityLevel Assignment7 NetworkControl6 NetworkedAudio(AoE)5 TelephoneAudio(VoIP)4 VideoConferencing3 NetworkedAudioSystemControl2 HighPriorityData1 MediumPriorityData

0 BestEffortData

The VLAN identifier (VID) is a 12bit field. It can have a value of 0 to 4095. VLAN is atechnology that makes it possible to have isolated LANs on the same physical networkinfrastructure.Switchesmayofferportbasedortaggedbased(usingtheVIDfield)operations.

CONCLUSION

ForanIPaudioproject,itisnotadvisabletoadoptadeployandforgetattitude.Informationgathering,discussionswithusers,goodplanning,properarchitecture,andsubsequenttrainingareparamount for ensuringa successful stateofthearthightech IP radio siteproject.Radio

maintenancetechniciansandengineerswouldhavetobeknowledgeableaboutIPnetworking,in addition to analog and digital audio,because of this new convergence of technologies.Computing (mainly networking) and IP audio manufacturers offer extensive practicaldocumentation,goodsupportandtraining.AudiooverEthernetisnolongerafuturisticidea;itissuccessfullybeingdeveloped,inradiobroadcasting.

7/29/2019 cbc-ip

13/14


IPBased

Radio

Production

and

Networking:

A

Path

to

the

Future

REFERENCES

[1]ANetworkEnableRadioConsoleArchitecture,MichaelDosch,AxiaAudio.

[2]AudioRouting,2007,Radiomagazine(beradio).

[3]BridgingBetweenIEEE802.1QVLANs,CiscoSystems.

[4]BuildingEtherSoundNetworks,Digigram.

[5]ConfiguringCiscoCatalystSwitchesforLivewireTM,AxiaAudio.

[6]DIFFSERVTheScalableEndtoEndQoSModel,CiscoSystems.

[7]EthernetforStudioAudioSystems,SteveChurch,Telos.

[8]ExperimentswithMediaTwist,BeldenWebsite.

[9]ImplementingQualityofServicePolicieswithDSCP,CiscoSystems.

[10]InsideTCP/IPthirdedition,NewRidersPublishing.

[11]InterSwitchLinkandIEEE802.1QFrameFormat.CiscoSystems.

[12]IPAudioNetworksintheRealWorld,ClarkNovak,AxiaAudio.

[13]IP,QoSandIGMP.TechnologyDocumentation,CiscoSystems.

[14]MeasuringDelay,Jitter,andPacketLosswithCiscoIOSSAAandRTTMON,Cisco.

[15]NetworkedAudio,2005,WheatstoneCorporation.

[16]OverviewAnIntroductiontotheES100Technology,Digigram.

[17]QualityofExperienceforMediaoverIP,IneoQuest.

[18]SystemDesignReference&Primer,2004,AxiaAudio.

[19]UsingCategory5/5e/6forAudioandVideoApplications,Belden.

7/29/2019 cbc-ip

14/14


Pierre Robidoux hasbeenwith RadioCanada since 1980.He received adegree in electrical engineering from thecolede technologie suprieure(Universit du Qubec) in 1993. Pierre has worked in the VTR,RadioOperationsandRadioMaintenanceDepartments,wherehecreated,amongother things, a system for controlling all the French radio networktransmittersfromtheMontrealnewsroomforthepurposeofairingspecial

newscasts. That project earned him the 2001MICAMAward. PierrejoinedNew BroadcastTechnologiesin2007.Hehasworked,amongotherthings,ontheevaluationofIPaudiocodecsandH.264 (MPEG4AVC) andWM9 (VC1 SMPTE 421M) encoders fordigitalmultimediabroadcasting.PierreismemberoftheAESandtheSMPTE.

cbc-ip

Documents