一、什么是NAS NAS(Non-Access Stratum)是无线网络中非接入层及包括移动性管理(MM)和会话管理(SM)协议 。5G(NR)系统中NAS(非接入层)是一组协议,用于用户(UE)和移动管理实体(AMF)之间传送非无线信令消息和进行5G/RAN接入和会话管理。它位于NR网络最高层(L3)层; 图1.5G(NR)系统中NAS位置图 二、NAS层移动性管理(MM) 在5G网络中NAS(非接入层)做为终端(UE)和核心网单元AM之间控制面的最高层除负责3GPP和non 3GPP网络的接入外,负责终端(UE)的移动性管理(Mobility Management),具体负责:
三、NAS层会话管理 在5G网络中终端(UE)通过N1接口的NAS消息执行5GS会话(5GSM)管理流程。也就是5GSM子层支持UE和SMF中的PDU会话处理(经AMF传输)的实体。5GSM包括以下流程:
每个PDU会话代表一个在UE和SMF之间建立的PDU会话;即使构成UE和 SMF之间相应PDU会话的无线和网络资源被临时释放,PDU会话也可以保持建立。只有在UE和AMF之间建立了5GMM 上下文,并且AMF使用5GMM流程启动NAS消息安全交换后才能执行5GSM流程。会话管理具体包括:
四、移动性和会话管理网络 通过NAS进行终端移动性管理和会话网络中包括RRC、PDCP、RLC、MAC和PHY层。其中网络单元中AMF只有NAS层,没有传输层。相关管理和传输层结构如下图所示: 图2.5G(NR)系统移动性和会话管理结构图 N1上的NAS协议包括:NAS移动性管理和NAS会话管理组件,其中:
五、NAS消息解析 在无线网络中NAS消息可通过RRC SetupComplete、DL Information Transfer、UL InformationTransfer、initiating Message 、 Initial Context Setup Request等消息传递。 5.1 RRC SetupComplete UuMsg message t = c1 rrcSetupComplete t = rrcSetupComplete tOptFlags registeredAMFPresent = 1 guami_TypePresent = 1 selectedPLMN_Identity = 1 registeredAMF tOptFlags plmn_IdentityPresent = 0 amf_Identifier numbits = 24 data = 08 00 08(HEX) guami_Type = 0 : RRCSetupComplete_IEs_guami_Type_Root_native dedicatedNAS_Message nocts = 78 data = ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff(HEX) 5.2 dlInformationTransfer UuMsg message t = c1 t = dlInformationTransfer dlInformationTransfer rrc_TransactionIdentifier = 2 criticalExtensions dlInformationTransfer tOptFlags dedicatedNAS_MessagePresent = 1 lateNonCriticalExtensionPresent = 0 nonCriticalExtensionPresent = 0 dedicatedNAS_Message nocts = 4 data = ff ff ff ff(HEX) 5.3 ulInformationTransfer UuMsg message t = ulInformationTransfer criticalExtensions ulInformationTransfer tOptFlags dedicatedNAS_MessagePresent = 1 lateNonCriticalExtensionPresent = 0 nonCriticalExtensionPresent = 0 dedicatedNAS_Message nocts = 25 data = ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff(HEX) 5.4 initiatingMessage NgapMsg t = initiatingMessage procedureCode = pDownlinkNASTransport union_value pDownlinkNASTransport protocolIEs tOptFlags ....... aMF_UE_NGAP_ID = 446628041 rAN_UE_NGAP_ID = 98956 nAS_PDU nocts = 4 data = ff ff ff ff(HEX) 5.5 InitialContextSetupRequest NgapMsg t = initiatingMessage procedureCode = pInitialContextSetupRequest union_value pInitialContextSetupRequest protocolIEs tOptFlags oldAMFPresent = 0 uEAggregateMaximumBitRatePresent = 0 coreNetworkAssistanceInformationForInactivePresent = 1 pDUSessionResourceSetupListCxtReqPresent = 0 traceActivationPresent = 1 ...... nAS_PDUPresent = 1 ...... aMF_UE_NGAP_ID = 446628041 rAN_UE_NGAP_ID = 98956 coreNetworkAssistanceInformationForInactive tOptFlags ...... uEIdentityIndexValue t = indexLength10 numbits = 10 data = 10110110 00(BIT) periodicRegistrationUpdateTimer numbits = 8 data = 05(HEX) tAIListForInactive n = 1 elem[0] tOptFlags iE_ExtensionsPresent = 0 tAI tOptFlags iE_ExtensionsPresent = 0 pLMNIdentity nocts = 3 data = 64 f0 00(HEX) tAC nocts = 3 data = 12 70 c0(HEX) gUAMI tOptFlags iE_ExtensionsPresent = 0 pLMNIdentity nocts = 3 data = 64 f0 00(HEX) aMFRegionID numbits = 8 data = 08(HEX) aMFSetID numbits = 10 data = 00000000 00(BIT) aMFPointer numbits = 6 data = 001000(BIT) allowedNSSAI n = 1 elem[0] tOptFlags iE_ExtensionsPresent = 0 s_NSSAI tOptFlags sDPresent = 0 iE_ExtensionsPresent = 0 sST nocts = 1 data = 01(HEX) uESecurityCapabilities tOptFlags iE_ExtensionsPresent = 0 nRencryptionAlgorithms numbits = 16 data = e0 00(HEX) nRintegrityProtectionAlgorithms numbits = 16 data = e0 00(HEX) eUTRAencryptionAlgorithms numbits = 16 data = e0 00(HEX) eUTRAintegrityProtectionAlgorithms numbits = 16 data = e0 00(HEX) securityKey numbits = 256 data = ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff(HEX) traceActivation tOptFlags iE_ExtensionsPresent = 0 nGRANTraceID nocts = 8 data = 64 f0 00 76 08 64 00 00(HEX) interfacesToTrace numbits = 8 data = f8(HEX) traceDepth = 0 : Ngap_TraceDepth_Root_minimum traceCollectionEntityIPAddress numbits = 32 data = 00 00 00 00(HEX) nAS_PDU nocts = 50 data = ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff(HEX) |
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