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LTE Integration of P25 ISSI for Colorado
June 2015
Prepared by:
Signals Analytics, LLC
Disclaimer:ThiswhitepaperwascreatedaspartofthedeliverablesduetotheFirstNetColoradocontractwithSignalsAnalytics,LLC.ThiswhitepaperwaspreparedfortheStateofColorado-Governor’sOfficeofInformationTechnologyusingfundsunderaward08-10-S13008fromtheNationalTelecommunicationsandInformationAdministration(NTIA),U.S.DepartmentofCommerce(DOC). Thestatements,findings,conclusions,andrecommendationsarethoseoftheauthor(s)anddonotnecessarilyreflecttheviewsoftheNTIA,DOCorFirstNet.
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Contents
ExecutiveOverview......................................................................................................................................2
OverviewofP25ISSIInterface.....................................................................................................................3
OverviewofStateandFrontRangeRadioNetworks...................................................................................4
OptionsforLTEInteroperability..................................................................................................................6
OTTApplications......................................................................................................................................7
MCPTT....................................................................................................................................................10
PSBNandCommercialIntegration.............................................................................................................13
SuggestedStateActions.........................................................................................................................15
Executive Overview TheStateofColoradoGovernor’sOfficeofInformationTechnology(OIT)hasbeenplanningfortheimplementationofastatewideLongTermEvolution(LTE)networkthatwillbepartoftheNationalPublicSafetyBroadbandNetwork(NPSBN).Theintentisthat,overtime,thisLTEnetworkwillprovidesignificantterrestrialanddeployablebroadbandcoverageforalllocal,tribal,stateandfederalfirstrespondersinColorado.ItisunknownwhenthisvisionwillbefullyrealizedandthereforethesupportofexistingLandMobileRadio(LMR)systemswillberequiredfortheforeseeablefuture.Additionally,manyindividualjurisdictionswithinthestateofColoradohaveprocuredorareupgradingandexpandingtheirLMRcapabilities.ThesesignificantinvestmentsinLMRwillbeutilizedformanyyearsandprovidethebasisofcurrentwirelessmissioncriticalvoicecommunicationsfortheState.ThesedrivingfactorsarethemainforcewithdevelopingaplannedapproachofhowtointegrateLMRandLTEnetworksacrossthestateinawaythatiscompatiblewiththeNPSBN,technicallyfeasibleandcosteffective.
TheColoradostatewideDigitalTrunkedRadioSystemorDTRSisanAssociationofPublic-SafetyOfficialsProject25(P25)networkthatinterconnectstootherP25networksviatheInterSub-SystemInterface(ISSI).SeveraloptionsexistandwillsoonbedevelopedforconnectingnativelyfromaLTEnetworktotheISSI.LTENetworksareinherentlyIPbasedandtheintroductionofmissioncriticalpush-to-talk(MCPTT)inLTERelease13promisesdirectconnectivitybetweenP25andLTE.DeployingthisMCPTToverLTEinteroperabilitywillincreasethefunctionalityoftheP25networktoLTEdevicesandpotentiallyreducecongestionontheP25channels.ThiswhitepaperwillwalkthroughthedefinitionoftheISSIinterface,ISSIinteroperabilityinthestateofColorado,differentimplementationsofISSIintoLTEandsuggestedactionstohelpensureISSIandLTEintegration.ColoradohastheopportunitytosetacourseofdirectiontoensurebothtypesnetworkscanworkcooperativelyforthenextgenerationofPublicSafetycommunications.
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Overview of P25 ISSI Interface ThecurrentstandardforpublicsafetyLMRwascreatedbytheAPCOProject25ProgramandisknownsimplyasP25.P25hasitsownstandardsprocessthatismanagedindependentlybytheTelecommunicationsIndustryAssociation(TIA)andtheyhavedevelopedover75maindocuments1thatspecifytheentirenetworkend-to-end.TheTIATSB-102-Bdocumentationsuitecoversthemethodologyofhowvendorsandusersutilizethenetwork.Themajorityofthedocumentsarecenteredontheradiofrequency(RF)orCommonAirInterface(CAI),asthiswasonetheprimaryreasonsforthefragmentationintheLMRmarket.However,itwasquicklynotedthatinteroperabilitybetweennetworkinterfaceswasnecessaryandcreationofanewinterfacewouldberequired.SpecificallytheTIA-102.BACA-A2documentdefineshowRadioFrequencySubsystems(RFSS)canbeconnectedviaanIPinterfacetoallowwirelineinteroperability.TheInterSub-SystemInterface(ISSI)isanIPbasedconnectionbasedontheSessionInitiationProtocol3(SIP)forcallcontrolandmediaishandledviatheReal-timeTransportProtocol4(RTP).UsingIPinsteadofTDMbasedtechnologyandopeninterfaceswasanewdirectionforPublicSafetyLMR.TheuseofinternationallystandardizedinterfacesallowedforinteroperabilitybetweendifferentvendorsRFSS,whichbeforetheISSIwasonlypossibleviabasebandvoicegateways.
Colorado’sstatewideLMRsystemknownastheDigitalTrunkedRadioSystemorDTRS5utilizesP25technologyforPush-To-Talk(PTT)voiceservices.TheDTRSP25networkcananddoesconnecttootherP25networksviaISSI.TheuseofISSIallowsdisparateP25systemslikeFrontRangeCommunicationsConsortium(FRCC)andCityofWestminstertobeconnectedviaastandardizedSIPbasedinterface.MuchlikeANSI-41inCodeDivisionMultipleAccess(CDMA)andGlobalSystemMobile(GSM)MobileApplicationPart(MAP)interfacesthatareusedforcellularroaming,theISSIcanalsoallownon-P25systemstobeinterconnectedtoforeignP25networkstoenableinteroperabilityandthatistheprimarypremiseofthiswhitepaper.
FS FS
ISSI
RFSSRFSS
SU SU
RFSS–RFSubsystemFS–FixedStationSU–SubscriberUnitISSI–InterSubsystemInterface
Figure1:ISSINetworkDiagram
1http://www.pscr.gov/about/highlights/citig_2011/citig_p25_standards_process_122011.pdf2https://global.ihs.com/doc_detail.cfm?document_name=TIA-102.BACA3https://www.ietf.org/rfc/rfc3261.txt4https://www.ietf.org/rfc/rfc3550.txt5Seehttp://www.oit.state.co.us/cto/dtrsformoreinformationonDTRS
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TheISSIsupportstraditionalgrouporone-to-manyvoicecommunicationsanditalsosupportsdirectsubscriberunit(SU)voicecommunications.SomeofthebasicfeaturesthattheISSIprovidesarethefollowing:
• GroupCallSetup/Teardown• SUCallSetup/Teardown• PTTVoiceservicesforGroupandSUCalls• RoamingServices
o SubscriberManagemento SUAuthentication
FunctionallytheISSIprovidessomeofthebasiccallconnectivitythatmostpeopleareusedtoinmoderncellularnetworks.Ifnetwork‘A’andnetwork‘B’areconnectedviatheISSI,thenSUsinnetwork‘A’cancallSUsinnetwork‘B’.Regardlessiftheradiosareprogrammedfordifferentfrequencies,aslongastheSUIDorgroupIDisavailablethenPTTvoicecommunicationscanbeestablished.AsimilarusecasewouldbeaT-MobilecellphonecallingaSprintcellphone.Thisisanexampleofinteroperabilityacrossnetworks.
ISSIprovidessimilarcapabilityforP25roamingasseeninacellularroamingscenariowhereanAT&TcellphoneisphysicallyinaTelefonicanetworkandcanmake/receivecalls.Ifnetwork‘A’SUscansupportthesamechannels,frequencies,numberingplanandtalkgroupsofnetwork“B”,thenroamingcanbeaccomplished.Network‘B’SUswillbeabletoauthenticateandmakecallswhileinnetwork‘A’coverage.Capabilitieslikethisarecrucialformutualaidsituationsonborderingjurisdictionswherecoordinatedeffortsarerequiredbymultipleagencies.
However,itshouldbenotedthatwhentheP25ISSIwascreated,LTEwasnotevendeployedoravailableasastandardandthusitwasneverenvisionedasaninterfaceintoP25networks.TheISSIinterfacewasinitiallymeantandstilldefinedasaninterfacebetweentwoP25RFSSs–notanRFSSandLTEIMScoreorMCPTTserver.DuetotheflexibilityofLTEapplicationserversandIMScorenetworkinfrastructure,theinfrastructurecanemulatethesignalingandmediaofaP25RFSSessentially“looking”likeaP25RFSS.
Overview of State and Front Range Radio Networks Startingin2001theStateanditagainin2008OITbeganupgradingtheirLMRnetworktoP25andestablishingtheDTRSacrosstheState.The220radiositesandfiveZoneControllersprovideserviceforover1,000state,local,county,federalandtribalagencieswith82,000+subscriberradios.6InadditiontotheDTRSP25network,severalotherP25networksresidewithindividualagenciesoperatingthroughouttheState.Operationalneeds,fundingandtechnicalchallengeshavepreventedinterconnectionofallthesenetworks.ForintegrationintoaLTEMCPTTsystemtherewillbeadesiretoconnectthroughacommonorcentralrouterbywhichalltheseLMRnetworksareconnectedto.MinimizingconnectionpointsandIPhopswillhelpensurethattheSIPandRTPpacketsbetween6http://www.oit.state.co.us/cto/dtrsN
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networkscanbedeliveredwithminimumlatencyandappropriatesecurity.WithintheNorthCentralRegion(NCR),whichincludesDenverandits9surroundingcounties,thevariousP25networksthathavebeenworkingtointerconnecttheirISSIandcreatecommonchannelnamingconventionsforcrossnetworkuseandroaming.ThePublicSafetyCommunicationsSubcommittee(PSCS)thatmanagesthisprocesshasalsobeenworkingtodefineEMStalkgroupsandEOCtalkgroups.TheproposedcommonhubapproachtheyaredeployingenvisionsthefollowingentitiestobepartofthenetworktheirISSIsharingagreement:
• FrontRangeCommunicationsConsortium(FRCC)–IntergovernmentalAgreementbetweenAdcom911andWeldCounty
• DenverInternationalAirport(DIA)• FederalBureauofInvestigation(FBI)• CityofWestminster,CO• CityofAurora,CO• MetropolitanAreaRadioCooperative(MARC)–CooperativebetweencitiesofDenver,
Lakewood&Arvada• ColoradoStatePatrol(CSP)-future
EachoneoftheseP25networkshasISSIcapabilitythatisprovidedbyvendorssuchasMotorolaSolutions,Cassidian(AirbusDefense)andHarrisCorporation.ThesevendorsandjurisdictionshavebeenworkingcollaborativelyonISSIinteroperability.EventhoughtheISSIisstandardized,theimplementationoftheISSIisleftuptoeachvendor,whichrequiressignificantintegrationefforttoensureinteroperability.HarrishastakenacentralroleinimplementinginteroperabilityfortheregionwithISSIconnectionstoMotorolaSolutionsandEADSsystemslocatedintheMARC,DTRSandbetweentheWestminsternetworkandFRCC.Additionally,theDTRSsystemhasanISSIconnectiontoFRCCandDTRS.WiththeISSI,usersontheDTRScannowcommunicatetotheWestminsterusersgoingthroughtheFRCCconnection.Although,thisisnotanidealorleastcostroute,itprovidesameansforestablishingcallsacrossmultiplenetworks.
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FBI
DIA
Aurora
DTRS
MARC
FRCC Westminster
ExistingConnection
FutureConnection
HarrisISSI
Figure2:FrontRangeISSIInterconnection Source:RenderedfromHarrisCorp.Info
OneoftheissuesthePSCSisdealingwithistheaspectofinteroperabilityversusencryption.Duetothemultiplicityofvendors,eachnetworkhasestablisheddifferentmodesofencryption;somevendorsuseAES256andotheruse3DES.EncryptionoptionsforP25networksrequiresignificantlicensingcostsandthedifferentencryptiontechniquesarenotcompatiblewitheachother.Intheoryencryptionkeyscouldeasilybesharedacrossnetworks,asthereisnocommonP25keymanagementfunctionbetweenallthenetworks.
Withinthestate,theNCRisoneoftheonlyconsortiaworkingoninterconnectingISSIandcreatingthisabilityforborderingregionstointerconnect.ThenecessityforconnectiontootherP25andnon-P25systemsinotherpartsofthestatearenotdeemedasoperationallynecessaryatthispoint.Manyjurisdictionsthataregeographicallyseparateddonotoperationallyinteractwitheachother.Theamountofresourcesnecessarytoplan,design,implement,manageandmaintainISSIinterconnectstonon-collaboratingjurisdictionsissomethingthatwouldbenearlyimpossibletofund.However,interoperabilitybetweensurroundingstatessuchasUtahandWyomingintotheColoradoDTRSandbordercounties/citiesiscrucialformutualaidoperations.
Options for LTE Interoperability TheintegrationofP25PTTvoiceservicesintoLTEnetworkscanbeaccomplishedintwogeneralways.ThefirstoptionistouseanOver-The-Top(OTT)serviceandthesecondoptionistoimplement3GPPMissionCriticalPTT(MCPTT).WewillevaluatethebenefitsandchallengesofeachimplementationforColorado.
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OTT Applications UtilizingOTTapplicationsissomethingthatcanbeaccomplishedtodaywithavastarrayofoptions.OnGooglePlaythereareover150applicationsavailablefordownloadthatpurporttoofferPTTfunctionality,twoyearsagotherewereonly16apps.Theseappsthoughcanbesplitintotwomajorcategories,thefirstofthosethatareenterprisegradeandsecondtierofappsthatareforrecreationaluse.Forthefocusofthispaperwewillconsiderapplicationsthatareconsideredenterprisegrade.AsampleofsomeoftheapplicationsthatfitintothiscategorywouldbeBeOn,Zello,VoxerWalkieTalkie,BroadNet,ClearSAPTT,MotoTalkandWaveMobileCommunications7.
Theseapplicationseitherworkwithanenterprisegradeserverdeployedinthepublicsafetynetworkoracloudbasedserver.UsingaserverlocatedwithinyourownLTEnetworkofferscontroloverfeatures,additionalsecurityandeasierintegrationintoaP25network.Cloudbasedsolutionscanbeimplementedimmediately,areverycosteffectiveandscalefromsingleusertomassiveenterprisegradewithrelativeease.NearlyallOTTPTTapplicationshavetheabilitytoworkonmultiplebroadbandaccesstechnologiessuchasWi-Fi,LTEandeven3Gdata.SeveraloftheappsalsohaveadesktopapplicationsoPCuserscanutilizePTTandchatwithmobiledeviceusers.ThisaddedfunctionalityacrossmultipleaccesstechnologiesandnetworkscanbeveryattractivebyallowingmultipleauthorizedusersaccesstotheP25networkviatheISSIconnection.Additionally,someofthefeaturerichfunctionalityofferedinOTTappsisnotnecessarilyavailableinMCPTT.Theseoptionsinclude
• Chatortextintegration• Filetransfer• Nearlyunlimitedvirtualtalkgroupcreation• Geo-fencedtalkgroupcreation• Geo-locationtracking• PushtoVideointegration• Presenceindicators(seewho’sinserviceoronline)• PTTtoPC,smartphone,tablet,IPPhoneandLMR• Advancedsecurityattheapplicationlayer
SomesmartphonevendorssuchasSamsungandKyocerahaveworkedtointegratetheirphysicalPTTbuttontotheapplicationsoftbuttonfortrueseamlessinteroperability.ThecosttoimplementandscaleupusersonOTTsystemsmakestheiruseveryattractiveforgovernmentusers.OTTsystemsareinusebymanygovernmentagenciessuchastheUSArmy8andNCR9users.ThetwomajorvendorsofLMRequipmentintoColoradoareHarrisandMotorola.
• SpecifictoHarrisistheBeOnsystem,whichisaPTTapplicationserverplatformandphoneapplicationsoftware.TheBeOnsystemsupportsgeographicredundancyandhasGIScapabilitiestoshowusersonanear-realtimemapandvisuallyselectthemtotalk.ItfullyintegrateswiththeHarrisISSIsolutionandsupportsothervendorISSInetworkswithadvancedfeatureslikeembeddedAMBEvocodersandAESencryption.
7Norecommendationsaretobeinferredwithanyoftheseapplications.Itismerelyarepresentationofsomeoftheavailablechoices.8http://blog.zello.com/?p=6259HarrisBeOnisbeingevaluatedbymultipleagenciesintheNCR
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• MotorolaSolutionsutilizessimilarapplicationserverplatformandphoneapplicationsoftwarecalledWaveMobileCommunications(NOTE:thisistheformerTwistedPairsolution).TheWaveserverandapplicationhavefullinteroperabilityandintegrationwithMotorolaAstro25networks.Advancedfeaturesforfloorcontrolandend-to-endencryptionaresupportedwithinanAstro25networkonly.BasicfeaturesforvoiceinteroperabilitycanbesupportedthroughaseparateISSIgateway.
SincethesesystemssupportP25capabilitiesinAndroidandApplebasedphones,theyusetheP25IMBE/AMBEcodec.Thisallowsoftheconceptofend-to-endfunctionalitywithencryption.However,thisfunctionalitydoesnotscalewelleconomicallyastheAMBE/IMBEcodecisalicensedpieceofsoftware.Inmostcasesthismakestheappcostover$300perdevice–whichcouldbemorethanthecostofalow-tiersmartphone.ThecoststructureisessentiallylinearwithverylittlediscountforthevolumesthatColoradowouldneedandthismakesenablingitsuseforallsmartphoneuserspotentiallycostprohibitive.Additionally,theAMBE/IMBEcodecisnotnativetoLTEdevicesandwillrunontheapplicationprocessorofthedevice.ThisimplementationisnotanoptimizedconfigurationandtypicallyleadstohigherbatterydrainandlesstalktimeonthedevicewhencomparedtoanativevocoderrunningonaDSPchip.AppcompatibilitytestingwouldbenecessarytoensureallLTEdevicesperformnominallywiththeapplication.
Anothersolutiontohelpreduceindividualdevicelicensingcostsistoutilizeamorecentralizedapproachinthenetworkcalledtranscoding.Transcodinghasbeenusedfordecadesincellularnetworksandvideoformattingwithgreatsuccess.Theprocessinvolvesperformingadigital-to-digitalformatconversiontosomethingthetargetnetworkordevicecaninterpret.SystemssuchastheCiscoInstantConnectUMSserversupporton-demandtranscodingofP25AMBE/IMBEvocoderstocommonformatssuchasG.711.OpensourceorlicensefreecodecssuchasAMR10andG.711areverypopularandofferexcellentvoicequality.Bytranscodingcentrally,licensecostscanbemanagedacrossthenetworkmoreeffectivelythanperdevice.Transcodingcanincursomelossanddelaybutpacketsmustbedecryptedbeforebeingtranscoded.Ifend-to-endencryptionisnecessarythetranscodedpacketsneedtobere-encryptedbeforebeingdeliveredtotheenddevice.Itisessentialthatthefunctionneedstoresideinasecurenetworktoensureend-to-endsecurity.
TheotheraspecttoconsiderwithOTTPTTisthatonceavendorisselectedfortheapplication,youarelockedintothatecosystem.ForinstanceaZelloPTTsystemcannotdirectlycommunicatetoaVoxerPTTsystem.Asstatedaboveyoucantranscodeoruseavoicegatewaybutyouloseallthekeyfunctionalityandhaveonlyavoicepath.Foreigndeviceauthenticationandinteroperabilitytypicallybreaksunderthismodelorbecomesalargescalemanagementproblem.FormutualaidusersacrossstatebordersorfromtheNPSBNmaybeusinganotherapporMCPTTthatisdifferentfromthestateandthiswouldcreateinteroperabilityissues.TheotherveryimportantaspectisthatOTTapplicationsarenotdirectlyintegratedintotheLTEUE,RadioAccessNetwork(RAN)orEvolvedPacketCore(EPC).Theuseoffeaturestoenablequalityofserviceandpriority(e.g.QCIsettings)wouldneedtobemanuallyimplementedinthenetwork–whichistheoreticallypossiblebutwouldrequireconsiderableefforttoimplementandmaintain.AdvancedfeaturesinVoLTEandMCPTTtoenhancecelledgeperformancemayalsonotbeavailableforOTTapplicationspotentiallycausingperformanceissues.
10AMRisusedintheGSMfamilyofcellphonedeviceswhichnumberinthemultipleofbillionsglobally
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ItshouldbenotedthatOTTappshavebeenveryadepttoimplementingadvancedfeatureslikeimmediateperilandmandownbuttonfunctionality.TheirabilitytointegrateISSI,implementchangesandadaptdynamicallytothemarketdemandsmakestheiruseveryattractive.
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MCPTT MCPTT11iscurrentlybeingdevelopedin3GPPSA6forRelease13.ThestudyonApplicationArchitecture&ArchitectureEnhancementstotheEPSandIMSwascompletedinSept2015.Completingthefunctionalarchitectureandinformationflowsforthe3GPPRelease13March2016freezedatewillallowvendorstostartdevelopingMCPTTsystems.CurrentlyvendorsfromEricsson12andSamsung13arealreadydemoingpre-Release13MCPTTthatcanbeupgradedbysoftwaretobecomplianttoR13.AttheendofMarch2016Release13contentwasfrozenwithamajorityofthefeaturesnecessaryforMCPTT.ManyofthefeaturesinP25willberepresentedinMCPTTforLTEincluding:
Security Codecs&MediaHandlingCallControl–On/OffNetwork FloorControl–On/OffNetworkBroadcastControl–On/OffNetwork GroupManagementIdentityManagement ConfigurationManagement
ThereareseveralkeyfeaturesthatMCPTTcanofferwhichwillbedifficultforOTTproviderstocompetewith.ThefirstandforemostisthatMCPTTisalsopartofRelease14anddevicesthatareRelease14compliantwillhaveundergonesignificantperformanceandfunctionaltesting.AnexampleofthisistheinclusionofOffNetworkfeaturestosupportLTE-Direct(LTE-D)orProximityServices(ProSe).TheintentofLTE-Distoprovidedirectdevice-to-devicecommunicationsoffnetworkforoperationalsupportofpublicsafetyusersthatareoutofLTEnetworkcoverage.ThefunctionalityissimilartooperatinginP25simplexordirectmode.Operationallythough,theperformanceofLTE-DdevicesmayvaryfromP25subscriberssinceLTEsmartphonepowerwilllikelybelimitedto23dBm.
Secondly,inRelease13wasthecreationofnewQualityofServiceClassIdentifiers(QCI)tosupportMCPTTforusercontrolandplanetraffic.NotablyQCI65,whichisaGuaranteedBitRateBearerandQCI69whichisintendedforMCPTTsignalinghavebeenspecifiedtoprovideguaranteedpacketdeliveryintheshortestpossibletimeforLTE.Developingalloftheauthenticationprocedures,callmanagementfeaturesandQCIissomethingthatOTTvendorswillnotbeabletotakeadvantageofeasily.UtilizingQoSiscrucialforMCPTTtoensureguaranteedvoicedeliveryinloadedconditions.TheNPSBNmayresultinsharedspectrumwithcommercialservice.DuringpeaktimesofPublicSafetyandcommercialnetworkuse,theabilitytodifferentiatePublicSafetyMCPTTtrafficfromcommercialtrafficwillbeanoperationalnecessity.
Lastly,theuseofenhancedmulticastbroadcast(eMBMS)allowsforefficientgroupcommunications.HistoricallyandoperationallymostPublicSafetyPTTvoiceusehasbeenaone-to-manyimplementationwiththeuseoftalkgroups.However,LTEoperatesnativelyinauni-castmethodofcommunication,e.g.,user-to-userforvoicecommunications.Theconceptofone-to-manycommunicationswasoriginallyenvisionedforbroadcastTVservicesonLTEandthusthestandardforeMBMSwascreated.TheadoptionofeMBMShasbeenhamperedintheUS,bymostcarriers,duetotheusecasesnotjustifyingthecostoffullyimplementingit,(i.e.viewinghabitshavechangedtoondemandvideofromNetflix,YouTube…etc.).CurrenteMBMSimplementationsrequireaminimumof10%oftheresourceblocks(RB)toutilizeit;futurereleasesmayallowfordynamicusethough.ForBand14thatwould11http://www.3gpp.org/DynaReport/23179.htm12http://www.ericsson.com/news/189840813http://www.whowired.com/407675.htm
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mean5resourceblocksor900kHzofspectrumwouldbeneedtobededicatedforsupportingeMBMSMCPTT.Thiswouldallowforinstantaneousmulti-castcommunicationsovertheentireeMBMScoverageareaforMCPTTandcouldbeutilizedforcommonmutualaidchannelsoralerts.OTTapplicationscouldpotentiallytakeadvantageofeMBMSbutitwillrequireanadditionalintegrationeffortwhencomparedtoMCPTT.ItshouldbenotedthatrecentlyAustraliancarrierTelstra14,hasimplementedeMBMSononeofitsthree20MHzLTEbandsandpotentiallywillbeevaluatingMCPTTforuseonthenetworktosupportAustralianGovernmentForces.
Identitymanagement
client
MCPTT-1
CSC-1
CSC-2
CSC-3
Commonservicescore
Floorcontrolserver
Floorparticipant
MCPTT-4
Groupmanagement
client
Identitymanagement
server
Groupmanagement
server
CSC-4 Configurationmanagement
client
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Interworkingfunctionto
legacysystem
IWF-1
MCPTT-3OtherMCPTTserver
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MCPTTclientMCPTT-5
Mediadistributionfunction
MCPTTUE
Mediamixer
MCPTT-7
MCPTT-8
MCPTT-6
EPS
MCPTTuserdatabase
MCPTT-2MB2C
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CSC-5
Othergroupmanagement
serverCSC-7
MCPTT-9
CSC-6
Keymanagement
client
CSC-8Keymanagement
server
CSC-10
CSC-9
CSC-13
Figure3:MCPTTOn-NetworkFunctionalDiagram Source:3GPPTS23.179
TheinitialintentforMCPTTwastofullyusetheIMScorefunctionalitybut3GPPhasallowedsomeflexibilityhereinanticipationofPublicSafety.3GPPhasallowedfornon-IMSMCPTTapplicationserverstobepartofthestandardaslongastheirexternalinterfacesareinteroperablewithIMSnetworks,EPSnetworksandtheMCPTTsubsystems.ForOTTvendorsthismeansthatanOTTserverthathasmanyoftheaforementionedrichfeaturesnotinherenttoMCPTT(e.g.chatcapabilities)couldprovideMCPPTservicestoanLTEnetwork.
TheMCPTTfunctionnetworkincludestheIWF-1interface(seeFigure3)whichistheinterworkingfunctioninterfacetolegacynetworks.TheinclusionoftheIWF-1meansthatP25networkswillbeabletonativelyintegratewithLTEMCPTT.TheP25ISSIinterfacewouldoperateasthefunctionalconnection14http://www.ericsson.com/news/1898408
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andterminateSIP/RTPtrafficattheIWF.ThecurrentMCPTTstandarddoesnotmandatetheuseofAMBE/IMBEvocodersbutallowsfortranscodingtotheapprovedAMR-WBcodec.P25SUexclusivelyusetheAMBE/IMBEcodecandthesearequiteexpensivetolicenseinLTEdevices.SincetranscodingwilllikelybeutilizedforMCPTTcallstonon-LTEdevices,thesecurityimpacts,latencyimpactsandscalingforusersintheStatewillneedtobeevaluated.TheIWF-1interfaceconnectstoamediafunction,whichwilldeterminewhethertopassthetrafficthroughortranscodethevoicepackets.MCPTTisalsointendedtoscaletosupportinexcessof500,000MCPTTgroupsandupto150simultaneousgroupcallsinaLTEsector.15ThistypeofscalabilitywillprovideenoughgrowthwithintheMCPTTsystemforalluserswithintheState.
153GPPTS23.179–AppendixC
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PSBN and Commercial Integration AunifiedsolutionthatencompassesinteroperabilitybetweenP25,LTEandIPnetworksshouldbesomethingthattheNPSBNaccomplishes.WiththeintegrationofP25ISSIvoicecommunicationstherearemultipleconsiderationsthatshouldbeaccountedfortoensureinteroperabilityandusabilitywhenconnectingtoaLTEnetwork.
1. ThePublicSafetyLTEnetworkthatwillbedeployedinColoradowillbeastatewidenetworkregardlessofwhetheritisbuiltbyFirstNetorColorado.
2. ManyagencieshaveexistingcommercialLTEdevicesandservicecontractswhichtheywillcontinuetoutilize.
3. TheDTRSandotherP25networksthroughoutthestatewillalsocontinuetooperateintotheforeseeablefuturetosupportPublicSafetyoperations.
4. ManyPSAPshaveupgradedtoIPbasedphonesystems(e.g.CiscoandAvaya)ashavemanygovernmentoffices.
ThetechnologyandtestingexiststodaytoprovideP25ISSIconnectivitytocommercialLTEandPublicSafetyLTEnetworks.Theabilitytointegratethemultiplevendors’ISSIsolutionsintoLTEandotheraccesstechnologiesisbeingdoneintheNCRwiththeHarrisBeOnnetworkandsmartphonesoperatingonvariouscommercialcarriers.JurisdictionsevaluatingPTTsolutionsshouldavoidproprietarysolutionsthatdonotinteroperatewithP25andMCPTT.InvestinginaPTTsolutionfromavendorwillrequirethoroughlyevaluatingasolutionthatcanscalecosteffectively,integrateintoexistingpublicsafetynetworksandbeeasilyupgradedtoMCPTT.
ColoradoisalsofortunatetohavetheAdcom911LTEnetworkasoneofonly5PSBNearlybuilderprojectsintheentirecountry.ThenetworkiscurrentlyLTEonlyanditdoesnothaveMCPTTorVoLTEdeployed,sotherearenonativevoiceservicesavailable;onlyVoIPserviceslikeSkypeorOTTPTTapplicationscanbeused.ItisunknownifthecurrentGeneralDynamicsEPCcansupportMCPTTandtheydonothaveanIMScoredeployedlocally.Additionally,thePCRFhasnotbeenenabledtodeployQCIdifferentiationfordifferentbearers.IfthesetechnicalissuescanbeaddressedbythevendorthentheAdcom911networkcouldbeusedasatestbedforOTTandMCPTTsystems.MostofthisintegrationcouldtakeplacewithoutIMS,evenforpre-Release13MCPTTandsimplechangestothePCRF.TheapplicationserverscouldresideinvendorlocationspendingIPconnectivity.WithaccesstoFRCCandDTRSISSI,thesystemcouldbeusedtotestmultipleinteroperabilityscenariosandproveoutsystemconfigurations.
OTTPTTintegrationintoacommercialcarrierisassimpleasdownloadingtheapplicationonmultiplephonesandhavingtrafficgoovertheinternet.However,forintegrationoftheISSI,theISSIgatewayneedstobeaddressablefromtheinternetorhavearoutableIPaddress.AnyOTTapplicationthatisbeingconsideredshouldhavedirectsupportforISSI.IfaparticularappdoesnotsupportISSIinteroperability;itshouldbedisqualifiedfromconsideration.Additionally,anyOTTPTTappshouldbesoftwareupgradeabletoMCPTT.Strongconsiderationshouldbegiventoevaluatingpre-Release13MCPTTsystemsfromthevariousLTEinfrastructurevendorsthatarecurrentlyofferingthisfeature.IntheeventofintegrationintoanLTEnetwork,theP25systemitisinterconnectingtoshouldactasthe“homeRFSS”;theLTEnetworkshouldlooklikethe“servingRFSS”.
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Lastly,developingaStatewideISSIhuborclearinghousewouldbeidealtoensureinteroperabilitybetweenallP25networks.WiththeappropriateamountofIPredundancy,thiswouldcreateasingleentrypointforcommercialandPublicSafetyLTEnetworkstointerfacewith.ItmaytakeasignificantamountoftimetoimplementthisbutsystemssimilartoNCR’sproposalareproposingareagoodstarttobeginintegration.
FS FS
ISSI
DTRSFRCC
SU SUISSI
Gateway
ISSI
eNodeB PSLTEUe
Internet
MCPTTServer
AdcomLTEEPC
ISSIISSI
CommercialLTEEPC
eNodeBUe
OTTServer
Figure4:ProposedLogicalISSIGateway&MCPTTDiagram
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Suggested State Actions UponexaminationofthefuturegrowthofLTEforpublicsafetythereareseveralareaswhereColoradocanprovideaframeworktoensuresuccessfulintegrationofISSIandLTE.
Table1:Issues&Solutions
Issue SuggestedSolutionLimitedcoordinationacrossmultipleagenciesP25networksacrosstheNCRhascreatedtheissueofdevelopingaconnectionhubandgovernancestructureforroaming.
ThePSCSefforthasspearheadedthiseffortfortheNCR.SupportingthisgroupwiththeappropriateresourcesandexpandingthescopetoincludetheentirestateandborderingStates(e.g.Wyoming,Kansas,Utah)wouldhelpleadtodevelopingacommonISSIinterconnectionscheme.
CurrentlythereislimitedefforttointerconnectalltheP25networkswithintheStateasthereisnooperationalneedtodothisforgeographicallyseparateareas.ForastatewideornationwideLTEnetworkalogicallycentralconnection(router)shouldbecreatedasanISSIclearinghousetoallowconnectionacrossallagencies.Definitionofauthorizedusersandsharingofencryptionkeyscouldbewithinscope.
ThefewerinterconnectionpointsthatthePSBNhastoISSItheeasieritwillbetomanageoverallanditwillincreasenetworkperformancebyhavinglessrouterhopstonegotiate.HostingandmanaginganISSIgateway(s)withthisscaletakessignificantresources.LTEisanallIPnetworkandallinterconnectionswillneedtobeIPbased,noTDMconnectionswouldbeallowed.LeveragingexistingsystemsintheNCR/FRCCwouldbelogicalsteptowardsdesigningacentralconnectionhub.
Commonlistsofservices,talk/callgroupnamingconventions,numberingplansandalloweduserequipmentwillbenecessaryforimplementingvirtualtalkgroupsinaMCPTTLTEnetwork.
ThecoordinationeffortacrossallISSIchannelsandnon-ISSIchannelsneedstotakeplacetointegrateintoMCPTT.Theaforementionedgroupcouldhelpmanagethiseffortlocallythroughoutthestateandcreateacommonservicelevelagreement.
SIPandRTP(theprotocolsusedinISSI)donottraverseacrossfirewallsandmultipleprivaterouterswithoutsignificantdesignengineering.NearlyalljurisdictionsareontheirownprivateandpublicIPaddressingschemes,whichwillmakeimplementingISSILTEintegrationverydifficulttoachieve.
RoutableIPaddressesshouldbeusedforallISSIsubscribersandLTEMCPTTsubscribers.Thismaynotbepracticalwithexistingimplementations.Thenewlyformedtaskgroupshouldinvestigatedualstack(IPv4/IPv6)usabilityinthenetwork.IPv6allocationsandcoordinationshouldbeconsideredforallISSInetworksacrosstheState.
SeveraltrialsaregoingoninvariousjurisdictionswithOTTPTTsystems.MCPTTwillnotbefullycommerciallyavailableuntil2017ininternationalmarketsandlikelyinthe2018-2019timeframeforFirstNet.HowcanColoradoensureISSIinteroperability,futurecapabilitiesandcosttargetscanbeachievedifmultipleOTTsystemsaredeployed?
AnyOTTPTTsystemthatisbeingconsideredforprocurementshouldbesoftwareupgradeabletoMCPTT,supportISSInativelyandoffermultiplecodecs.AfullyresourcedandfunctionaltestbedcouldbecreatedinconjunctionwiththeAdcomLTEnetwork,NCRISSInetworkandcommercialcarriers.ThegoalwouldbetoevaluateavailableOTTandMCPTTsolutionsandintegratethemintothenetwork,andhelpcreatedesigncriteriaforastatewideimplementation.
CostconsiderationsrelatedtoISSIsustainability,e.g.,ISSIlicensesperportanddevicearecostlytomaintainpersystem.AnISSIhubmaybecostprohibitivetomaintain.
ThecurrentFirstNetRFPrequiresPublicSafetyEnterpriseNetworks(PSEN)tobecomplianttoFirstNetinterfaces.ItisunknownwhatthecoststosupportandmaintaintheseinterfacesareandwhowouldbeartheongoingcostofISSIinteroperability.FurtherinvestigationisrequiredonthisonceanOfferorhasbeenselected.ThetechnicalteamcanalsoinvestigateusingMC-PTTastheinteroperabilitysolutionbetweenjurisdictionsasopposedtoanISSIhub,orlookatnon-ISSIsolutionsforMC-PTTintegration.
