爱立信：2023年2G与3G网络落幕后的语音和短信转型白皮书（英文版）（22页）.pdf

1、Ericsson White PaperBCSD-23:003115 UenMay 2023With the introduction of 4G and 5G,there is a need to plan for the 2G/3G closure in order to reuse the spectrum and to eliminate the cost of 2G/3G equipment.Most communications service providers(CSPs)will close 2G/3G networks at some point in time,but th

2、e strategies and timelines differ and depend on the starting point,for example,licenses,Voice over Long-Term Evolution(VoLTE)penetration,roaming agreements and installed bases of IoT devices.This white paper provides recommendations on how to prepare in the Circuit Switching(CS)and IP Multimedia Sub

3、system(IMS)domains to close either a 2G/3G network,or both,and how to adapt to 2G/3G sunsets for roaming scenarios.Voice and SMS transformation following 2G/3G SunsetVoice and SMS transformation following 2G/3G SunsetContentMay 20232ContentIntroduction 3The evolution to VoLTE and VoNR 4Modernization

4、 of network interconnect 6Preparing for the migration and scaling down of 2G/3G 8 Modernization of legacy services 9Outbound 2G/3G roaming and SMS in 4G 10Maintaining limited 2G/3G network capacity for specific use cases 12VoLTE S8 Home Routed(S8HR)Roaming 15Conclusion 17Glossary 18References 20Auth

5、ors 21Voice and SMS transformation following 2G/3G SunsetIntroductionMay 20233Introduction4G and 5G have enabled CSPs to gain access to new frequency bands and to re-farm the 2G/3G spectrum,allowing it to be used in a more efficient way.This results in more capacity and lower costs for mobile broadb

6、and.Energy efficiency and security are also improving as the transition from 2G/3G to 4G/5G is progressing.The transition from 2G/3G networks to 4G/5G is globally progressing with more than 50 percent of all mobile voice subscriptions moved to VoLTE or Voice over New Radio(VoNR)by now according to t

7、he latest Ericsson Mobility Report 1.Some CSPs have already closed their 2G and/or 3G networks but most of these legacy networks are still in operation.The transition is expected to continue at a fast pace and many CSPs have already reached a VoLTE penetration exceeding 90 percent where it would be

8、possible to retire both the 2G/3G networks for voice purposes.However,some challenges remain for these CSPs,such as IoT devices and emergency calls from vehicles(eCall)in the European Union(EU),preventing the final closure.Additionally,inbound roaming needs to be considered before closing a CSPs own

9、 2G/3G network,and outbound roaming to 2G/3G networks usually needs to be supported as CSPs around the world have very different timelines for their VoLTE launches and transitions.This white paper covers important areas to be considered during the evolution from CS voice networks to VoLTE and VoNR.T

10、his includes recommendations on how to prepare in the Circuit Switching(CS)and IP Multimedia Subsystem(IMS)domains to close a 2G and/or 3G network and how to adapt to 2G/3G sunsets in roaming scenarios.Voice and SMS transformation following 2G/3G SunsetThe evolution to VoLTE and VoNRMay 20234The evo

11、lution to VoLTE and VoNRPrerequisites for closing 2G/3G and CS coreThe introduction of VoLTE,and later VoNR,to gradually replace 2G/3G is a long process,which can take more than 10 years.In addition to the introduction of IMS,the 4G/5G radio network needs to provide sufficient coverage and have voic

12、e services enabled and tuned.A sufficient base of VoLTE capable phones is also a prerequisite for replacing 2G/3G for voice services,and to achieve this,communication of shut-down plans needs to take place several years in advance.Sometimes,commercial incentives for mobile subscribers also need to b

13、e considered to avoid churn at closure.Mobile virtual network operators(MVNOs)in the network also need to be prepared and aligned with the plans.Figure 1 provides an overview of the prerequisites to close 2G/3G and the CS core.IoT devices,eCall,and roaming aspects will be covered in subsequent chapt

14、ers.Figure 1:Prerequisites for closing 2G/3G and CS coreVoLTE UE base(90+%)2G/3G Emergency calls(eCall)no longer needed from carsMVNOs ready for 2G and 3G closure4G and 5G coverage equal to 2G and 3G2G and 3G IoT devices phased out2G and 3G inbound and outbound roaming no longer profitableVoice and

15、SMS transformation following 2G/3G SunsetThe evolution to VoLTE and VoNRMay 20235The transition from a pure CS voice network to VoLTE and VoNR consists of many steps.The steps vary between CSPs,and some are optional.The order of the steps may also vary between CSPs.An overview is provided in Figure

16、2,and many of the steps are covered in detail in subsequent chapters.Figure 2:Example of Voice transformation2G and 3GCS network4G and 5GVoLTE andVoNR networkModernize CS for remaining period until 2G/3G phase-outIntroduce VoLTE RoamingIntroduce ICSStart scale-down of CS.Re-farmradio spectrumIntrodu

17、ce 5G VoiceDeploy shared network modelsSunset CS VoiceIntroduce IMS and VoLTEVoLTE Emergency callsIntroduce SMSoIPModernize InterconnectReplace IN services with new interfacesSunset 3GSunset 2GVoice and SMS transformation following 2G/3G SunsetModernization of network interconnectMay 20236Modernizat

18、ion of network interconnectMany mobile networks today still rely on circuit switched technology,including TDM interfaces,for interconnecting to other networks.The Session Initiation Protocol(SIP)is gradually being introduced,enabling transcoder free operations for calls between networks,resulting in

19、 better voice quality,reduced HW cost and better bandwidth utilization.Interworking with new services like video is also becoming possible.After SIP is utilized on the interface to other CSPs,the CS domain is still in many networks the solution for distributing incoming traffic.This type of solution

20、 makes sense when most of the subscribers are still using 2G/3G but is not efficient in the long run,when users are moving to VoLTE as it means unnecessary usage of HW and an extra delay during call establishment and on the media plane.Therefore,an IMS-based solution is the only distribution functio

21、n needed in the future.The figures below show a typical setup where the CS domain distributes the incoming traffic and a recommended setup at a time when most of the subscribers are using VoLTE.As an alternative,the IBCF can also be used to distribute traffic to the right domain based on ENUM querie

22、s.Voice and SMS transformation following 2G/3G SunsetModernization of network interconnectMay 20237Figure 3:Incoming call from foreign networkHLRsdGMSC MGCFsgMSCsI-CSCF VoLTEsI-CSCF WirelinesIBCFgHSSsdI-CSCF VoLTEsI-CSCF WirelinesGMSCsg Old setup Recommended setupVoice and SMS transformation followi

23、ng 2G/3G SunsetPreparing for the migration and scaling down of 2G/3GMay 20238Preparing for the migration and scaling down of 2G/3G Sunsetting of 2G/3G and migration of related services can take many years.To remain fully operational during this period,the HW and SW need to be maintained and supporte

24、d.It is important to also consider new regulatory and security requirements that may necessitate new SW updates.As the 2G/3G traffic is migrated to 4G/5G,there is an opportunity to save costs by consolidating the legacy network.Scaling down of the 2G/3G network with mobile switching center(MSC)in po

25、ol makes it possible to seamlessly remove and decommission pool members.Another way of consolidation is the modernization of the MSCs through virtualization.This allows synergies with other virtual network functions(VNFs)utilizing the same virtualization infrastructure.Furthermore,modernization mean

26、s that fewer nodes can manage the remaining traffic,hence simplifying the scaling down of the 2G/3G network.2G/3G radio network sharing with other national service providers can also be considered through the usage of the Multi-Operator Core Network(MOCN)functionality.This will free up the 2G/3G spe

27、ctrum for 4G/5G usage and reduce costs for the remaining 2G/3G radio network.This possibility is further elaborated on later in this white paper.Voice and SMS transformation following 2G/3G SunsetModernization of legacy servicesMay 20239Modernization of legacy servicesAn evolution from CS to IMS is

28、an opportunity to modernize or phase out several legacy services as this involves a major network update.Traditional supplementary services,like call forwarding or call hold,are generally supported in IMS.IMS Centralized Services(ICS)provides the means to utilize a single service engine in IMS durin

29、g the transition from CS voice to VoLTE/VoNR.However,all roaming partners are not likely to support ICS,meaning that a limited set of supplementary services needs to be supported for inbound roamers and a service profile for outbound roamers also needs to be defined in the HLR.ICS still provides a w

30、ay to offload the CS domain and is an important step towards the centralization of services that S8HR introduces.Value added services(VAS)provided by Customized Applications for Mobile network Enhanced Logic(CAMEL)have been widely deployed in CS networks.Although these mechanisms are also supported

31、in IMS deployments,alternatives are recommended.For prepaid services,the 3GPP specified Ro interface is an attractive alternative if the prepaid systems require modernization.Representational State Transfer(REST)-based exposure interfaces,like the Open Mobile Alliance(OMA)OneAPI,is an alternative fo

32、r many new and existing VAS services.If the CSP supports services utilizing Unstructured Supplementary Service Data(USSD),the IMS equivalent USSD using IMS(that is,USSI)can be deployed as a long-term replacement.USSI is carried over SIP,and a USSI Gateway is used to interwork with the legacy USSD in

33、frastructure.However,the recommended strategy is to replace USSD services with more modern alternatives and utilize USSD through Circuit-Switched Fallback(CSFB)for the migration period.An example of a more modern alternative is to provide a smartphone app utilizing a REST interface for managing prep

34、aid accounts.Voice and SMS transformation following 2G/3G SunsetOutbound 2G/3G roaming and SMS in 4GMay 202310Outbound 2G/3G roaming and SMS in 4GWhen the 2G/3G service has been phased out in the home network,there is still a continued need to support outbound roaming in many networks that will only

35、 or partly offer 2G/3G capabilities for voice,SMS,and emergency calls.Even if VoLTE has been deployed in most countries today there will still be large areas that are only covered by 2G/3G services for the foreseeable future.Some CSPs are still expanding their 2G/3G capacity and modernizing their ne

36、tworks through virtualization to support users beyond 2030.Figure 4:Outbound voice roaming in 2G/3G and 4G/5G coverageCountry 1MAPHLRsdDiameterHSSsdIMSsgGMSCsgHPLMNVPLMNs2G/3GCountry 24G/5GCountry 34G/5G2G/3GBBBBBAVoice and SMS transformation following 2G/3G SunsetOutbound 2G/3G roaming and SMS in 4

37、GMay 202311Besides support for outbound roaming in 2G/3G networks,there is also a continued need to support SMS over non-access stratum(NAS)2 in the 4G access.Today,this is provided by the MSC through the SGs-interface to the 4G MME.SMS over NAS is typically used for initial over-the-air(OTA)device

38、configuration and for low-cost IoT devices for which the SMS over IP solution is neither feasible nor cost-effective.CSPs may use the alternative to the MSC and SGs-interface which is the Diameter-based SGd-interface between the SMSC and MME.These CSPs will however still need a GMSC if they want to

39、offer outbound roaming in 2G/3G networks.Figure 5:SMSoNAS options for the 4G accessNAS(SMS)SGs(SMS)SGd(SMS)MAPMAP/S6cMAP(SMS)HSSsdHLRsdMMEsgSMSoNAS MSCsSMSCsdS6a4GTo continue supporting both outbound roaming in 2G/3G networks and SMS over NAS in the 4G home network,it is recommended to keep at least

40、 a redundant pair of MSCs in service even after the 2G/3G service has been discontinued in the home network.The MSCs will then continue working as combined Gateway MSCs(GMSCs)for call routing toward the outbound 2G/3G roaming networks,and as SGs-MSCs for SMS over NAS in the 4G home network.Later whe

41、n the very last outbound 2G/3G roaming agreement has been discontinued,the GMSC and home location register(HLR)can be removed,and the SMS over SGs(SMSoSGs)solution can be replaced by the SMSoSGd solution.Figure 6:Combined GMSC and SMSoSGS-MSCNAS(SMS)SGs(SMS)AGMSC SMSoNAS MSCsgHLRsdMAPHPLMNVPLMNMMEsg

42、2G/3GB4GVoice and SMS transformation following 2G/3G SunsetMaintaining limited 2G/3G network capacity for specific use casesMay 202312Maintaining limited 2G/3G network capacity for specific use cases Emergency services When VoLTE networks were introduced,emergency calls were initially handled by 2G/

43、3G through CSFB.To reduce capacity and coverage in the 2G/3G networks,VoLTE emergency calls need to be deployed.Automatic emergency calls from vehicles,for example,eCall in Europe,is a special case as the modems in cars are not easy to upgrade to support Next Generation-eCall(NG-eCall).It remains an

44、 open question how regulators will act to secure these types of emergency calls in the long term as the number of vehicles with 2G/3G eCall will be significant for at least the next 10-15 years.Therefore,guidelines are needed by regulators to allow CSPs to plan their network evolution.The EU also ne

45、eds to regulate NG-eCall,that is,eCall on VoLTE/VoNR,before national regulators can proceed with their planning.Authorities are also impacted as NG-eCall requires upgrades of the public safety answering points(PSAPs).Voice and SMS transformation following 2G/3G SunsetMaintaining limited 2G/3G networ

46、k capacity for specific use casesMay 202313IoTUpdating existing 2G/3G-based IoT devices is a big and costly task for many companies and consumers.However,an update also means future-proofing devices,better data throughput,reduced power consumption,and in some cases better coverage.Early planning is

47、key to a successful transition,that is,CSPs need to give notice to their customers years in advance before closure.As most of these early IoT devices utilize 2G,this is a contributing reason why in some cases 3G networks are often closed first.Cooperation between CSPs is also an option in the later

48、phases,for example,through shared network concepts like MOCN.From a commercial perspective,the question of how to phase out early IoT devices for a CSP also has to be considered,that is,in some cases sharing the upgrade cost with customers,for example,an electricity company which can be justified by

49、 the benefits of 2G/3G closure.On the other hand,some CSPs may see a business opportunity in supporting old IoT devices while competitors close their 2G/3G networks.More information about what 2G/3G sunset means for IoT can be found in 3.Inbound CS voice roamingInbound CS voice roaming is often a go

50、od source of revenue for CSPs which is at risk when sunsetting the 2G/3G network.All inbound roaming revenues from users that have not yet upgraded to VoLTE-capable devices will then be given to competing CSPs that continue supporting 2G/3G for a longer period.LaggardsThe CSPs subscribers that insis

51、t on keeping their old 2G/3G phones until they no longer work may still provide good profitability from their monthly payments and virtually no retention and acquisition costs for subsidized devices.As for CS inbound roamers,the revenue from this group is also at risk when sunsetting the 2G/3G netwo

52、rk.This is because competing CSPs may either continue supporting 2G/3G for a longer period or offer attractive 4G/VoLTE packages that drive customers to change CSP.MOCN sharing for cost-effective 2G/3G extension An alternative to completely stop offering 2G/3G services for eCalls,IoT devices,inbound

53、 CS roamers,and laggard subscribers that havent upgraded to VoLTE capable devices,is to deploy a nationwide 2G and/or 3G MOCN.MOCN can be used as a cost-efficient tool for two or more CSPs for sharing a common radio access network including the radio spectrum.The CSPs can then gradually migrate as m

54、uch 2G and/or 3G spectrum to the 4G or 5G accesses as possible,while keeping just enough spectrum for 2G/3G to serve the remaining tail of eCall,IoT,inbound roamers,and laggards.The MOCN functionality can be seamlessly introduced in the network and existing roaming agreements can be maintained as if

55、 continuing to run separate access networks.The sharing constellation can be kept in service until the number of users reaches such a low level that there is no longer a motivation for the 2G/3G service from a revenue or regulatory point of view.Voice and SMS transformation following 2G/3G SunsetMai

56、ntaining limited 2G/3G network capacity for specific use casesMay 202314The MOCN RAN can be provided by one of the existing 2G/3G CSPs or an independent but co-owned company can be set up to run the MOCN RAN on behalf of the core network operators.2G/3GMOCNRANbsgCNOp.1 sgCNOp.2 sgCNOp.3 sgCNOp.4 Fig

57、ure 7:MOCN sharing for IoT,eCall,inbound roamers and laggardsVoice and SMS transformation following 2G/3G SunsetVoLTE S8 Home Routed(S8HR)RoamingMay 202315VoLTE S8 Home Routed(S8HR)Roaming Inbound VoLTE S8HR roamingWhen eventually sunsetting the 2G/3G accesses,it is important to enable inbound VoLTE

58、 roaming well in advance to not lose out on future roaming revenues to competing CSPs.As the 2G/3G network will no longer be available to handle emergency calls for inbound roamers through fallback from the VoLTE to the CS voice network,it is critical that VoLTE emergency calls are supported by IMS

59、also for inbound roamers.As calls and SMSs 4 to and from inbound roamers are not handled by the local IMS,except for emergency calls,the local packet core network must have the capability to tap all SIP signaling related to inbound roamers to an LI function for analysis.For calls that are associated

60、 with LI targets,the packet core must also be able to tap the actual voice and/or video media to the LI function.Outbound VoLTE S8HR roaming for CS-only CSPs CSPs that today offer outbound roaming with partner CSPs in countries that are about to or have already sunset their 2G/3G networks must prepa

61、re for and launch VoLTE roaming with these partners.Otherwise,they will not be able to roam with them and in the concerned countries anymore.Examples of countries that have progressed far in their 2G/3G sunsets are the US,South Korea,Japan,and Taiwan.Several countries in Europe will also follow over

62、 the coming years.This means that CS-only CSPs must deploy outbound VoLTE roaming Voice and SMS transformation following 2G/3G SunsetVoLTE S8 Home Routed(S8HR)RoamingMay 202316The investment in an IMS for outbound VoLTE roaming can also be used for VoLTE roaming in countries that support both VoLTE

63、and CS voice to offer a better service to more users and to increase the usage and value of the investment.The IMS can later also be used for the VoLTE deployment in the home network if expanding HW capacity and SW licenses.In the short term,it can also be used to offer WiFi Calling for indoor cover

64、age extensions and SIP trunking for a more competitive and future-proof enterprise solution compared to the CS-based PRA/PRI solution.Figure 8:Outbound VoLTE roaming IMS for CS-voice only CSPsVoLTEVoLTEVoLTEVoLTE CS-voice only HPLMN2G/3GMSSsgsgbefore VoLTE has been introduced in the home network.For

65、tunately,in most of these cases,4G data S8HR roaming has already been deployed meaning that the packet core infrastructure and international connectivity are already in place.This drastically simplifies the VoLTE S8HR roaming deployment.However,CSPs that have not yet launched VoLTE in the home netwo

66、rk must spend relatively high efforts on deploying and integrating an IMS and certifying VoLTE devices only for supporting a limited number of outbound VoLTE roaming users.Voice and SMS transformation following 2G/3G SunsetConclusionMay 202317Conclusion4G and 5G allow CSPs to get access to new frequ

67、ency bands and to re-farm the 2G/3G spectrum to be used in a more efficient way.This modernization means more capacity,better energy efficiency,and improved security.Voice,SMS,IoT,and emergency services need to be ensured when sunsetting 2G/3G.Voice remains a key service for CSPs and will be complem

68、ented by new communication services running on IMS.A part of the existing HLRs and CS core should be modernized to handle SMS and outbound roaming in 2G/3G networks.These network elements may also be needed to handle the remaining 2G/3G voice traffic,IoT,eCall and inbound roaming in the home network

69、.A MOCN is a cost efficient way of providing the 2G/3G services for the last year before complete sunsetting.The network transformation is an opportunity to modernize many legacy services,ensuring user satisfaction and a future-proof network.A smooth transformation requires careful planning and time

70、ly communication.Consumers and enterprises,need time to adapt and hence phase-out plans need to be communicated several years before closure.Voice and SMS transformation following 2G/3G SunsetGlossaryMay 202318GlossaryCAMEL Customized Applications for Mobile network Enhanced LogicCN Core NetworkCSFB

71、 Circuit-Switched FallbackCS Circuit Switching CSPs Communications Service Providers eCall emergency Calls from vehiclesEU European UnionGMSCs Gateway MSCs HLR Home Location RegisterHPLMN Home Public Land Mobile NetworkHSS Home Subscriber ServerHW HardwareIBCF Interconnect Border Control FunctionICS

72、 IMS Centralized ServicesI-CSCF Interrogating Call Session Control FunctionIMS IP Multimedia SubsystemIoT Internet of ThingsLI Lawful InterceptMAP Mobile Application PartMGCF Media Gateway Control FunctionMME Mobile Management EntityMOCN Multi-Operator Core NetworkVoice and SMS transformation follow

73、ing 2G/3G SunsetGlossaryMay 202319MSC Mobile Switching CenterMVNOs Mobile virtual network operatorsNAS Non-access stratumOBR Outbound roamingOMA Open Mobile AllianceOTA Over-the-airPRA Primary Rate AccessPRI Primary Rate InterfacePSAPs Public Safety Answering PointsRAN Radio Access NetworkREST Repre

74、sentational State TransferSIP Session Initiation ProtocolSMSC Short Message Service CenterSMSoSGs SMS over SGsSW SoftwareS8HR S8 Home RoutedTDM Time Division MultiplexingUSSD Unstructured Supplementary Service DataVAS Value added ServicesVNFs Virtual Network FunctionsVPLMN Visited Public Land Mobile

75、 NetworkVoLTE Voice over Long-Term EvolutionVoNR Voice over New RadioVoice and SMS transformation following 2G/3G SunsetReferencesMay 202320References1.Mobility report November 2022 report https:/ here means signaling between the UE and the core network 3.2G/3G Switch-off:What network evolution mean

76、s for IoT https:/ here refer to IMS-based SMS over IP and not native SMS over NAS for which LI is handled by the local MMEVoice and SMS transformation following 2G/3G SunsetAuthorsMay 202321AuthorsJohan Lundstrm works as Strategic Product Manager for VoLTE.He joined Ericsson in 1991 and since then h

77、e has worked primarily with mobile voice networks.He has held various positions in R&D,pre-sales,solution and product management.Johan has an MSc in Telecommunications and Software Science from the Helsinki University of Technology.Johan Or is Strategic Product Manager for the Mobile Softswitch Solu

78、tion(MSS).He joined Ericsson in 1989 and has since worked within R&D and product management.Johan has a Master of Science in Electrical Engineering and Applied Physics from the Linkping University.Voice and SMS transformation following 2G/3G SunsetAuthorsMay 202322Sven Gemski joined Ericsson in 1991 and he is a Strategic Product Manager for the IP Multimedia Subsystem(IMS).He has had various positions in market units and product management and worked with mobile networks from the late era of 1G to early strategies for voice in 6G.His focus today is on VoLTE roaming and voice in 5G.