【5G核心网】free5GC 注册请求流程源码分析

最新推荐文章于 2022-09-19 16:59:06 发布

张忠琳

最新推荐文章于 2022-09-19 16:59:06 发布

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本文链接：https://blog.csdn.net/zhonglinzhang/article/details/107808404

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本文分析 Free5GC Registration request procedure 注册请求流程

1. UE 发起注册请求

NAS Message 结构体，包括安全头部，移动管理以及会话管理消息

// Message TODO：description
type Message struct {
	SecurityHeader
	*GmmMessage
	*GsmMessage
}

根据 NAS N1 MM 消息定义

Table 8.2.6.1.1: REGISTRATION REQUEST message content

注册请求设置移动管理类型为 MsgTypeRegistrationRequest，NAS 消息需包裹在 NGAP 消息中，包括的参数为：

ExtendedProtocolDiscriminator
Security header type
Spare half octet
Message Type
ngksi
5GS mobile identity 9.11.3.4
5GMM capability 9.11.3.1
UE security capability 9.11.3.54
NSSAI 9.11.3.37
Uplink data status 9.11.3.57

registrationRequest.MobileIdentity5GS = mobileIdentity
registrationRequest.Capability5GMM = &nasType.Capability5GMM{
	Iei:   nasMessage.RegistrationRequestCapability5GMMType,
	Len:   1,
	Octet: [13]uint8{0x07, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},
}
registrationRequest.UESecurityCapability = ueSecurityCapability
registrationRequest.RequestedNSSAI = requestedNSSAI
registrationRequest.UplinkDataStatus = uplinkDataStatus

设置的 NGAP 消息 Present 为 NGAPPDUPresentInitiatingMessage，初始消息 ProcedureCode 为 ProcedureCodeInitialUEMessage，包括一些 IE 信息：

- RAN UE NGAP ID，

- NAS-PDU，

- User Location Information，

- RRC Establishment Cause，

- 5G-S-TSMI (optional)，

- AMF Set ID (optional)，

- UE Context Request (optional)，

- Allowed NSSAI (optional)

2 AMF 处理注册请求

根据 NGAPPDUPresentInitiatingMessage 和 ProcedureCodeInitialUEMessage 定位到 HandleInitialUEMessage 函数

请求的 IE 包括：

id-RAN- UE-NGAP-ID
id-NAS-PDU
id-UserLocationInformation
id-RRCEStablishmentCause
id-UEContextRequest

func HandleInitialUEMessage(ran *context.AmfRan, message *ngapType.NGAPPDU) {

	amfSelf := context.AMF_Self()

	var rANUENGAPID *ngapType.RANUENGAPID
	var nASPDU *ngapType.NASPDU
	var userLocationInformation *ngapType.UserLocationInformation
	var rRCEstablishmentCause *ngapType.RRCEstablishmentCause
	var fiveGSTMSI *ngapType.FiveGSTMSI
	// var aMFSetID *ngapType.AMFSetID
	var uEContextRequest *ngapType.UEContextRequest
	// var allowedNSSAI *ngapType.AllowedNSSAI

<5G-S-TMSI> := <AMF Set ID><AMF Pointer><5G-TMSI>

GUAMI := <MCC><MNC><AMF Region ID><AMF Set ID><AMF Pointer>

5G-GUTI := <GUAMI><5G-TMSI>

2.1 场景对应无 UDSF 部署情况

无 UDSF 部署情况：如果 UE 的 5G-GUTI （全局唯一的临时 UE 标识）包含在注册请求，且从上次注册过程服务的 AMF 已更改，新的 AMF 向旧的 AMF 调用 Namf_Communication_UEContextTransfer 服务，包括完成注册服务 NAS 消息，可以是完整性保护，也可以是接入类型，来请求 UE 的 SUPI 和 UE 上下文。旧的 AMF 即使用 5G-GUTI 和完成性保护完成注册请求 NAS 消息，或者 SUPI，以及 UE 从新 AMF 验证的指示。旧 AMF 还将每个 NF消费者（UE）的事件订阅信息传给新 AMF。

if ranUe == nil {
	ranUe = ran.NewRanUe()
	ranUe.RanUeNgapId = rANUENGAPID.Value
	Ngaplog.Debugf("New RanUe [RanUeNgapID: %d]", ranUe.RanUeNgapId)

	if fiveGSTMSI != nil {
		Ngaplog.Debug("Receive 5G-S-TMSI")

		servedGuami := amfSelf.ServedGuamiList[0]

		// <5G-S-TMSI> := <AMF Set ID><AMF Pointer><5G-TMSI>
		// GUAMI := <MCC><MNC><AMF Region ID><AMF Set ID><AMF Pointer>
		// 5G-GUTI := <GUAMI><5G-TMSI>
		tmpReginID, _, _ := ngapConvert.AmfIdToNgap(servedGuami.AmfId)
		amfID := ngapConvert.AmfIdToModels(tmpReginID, fiveGSTMSI.AMFSetID.Value, fiveGSTMSI.AMFPointer.Value)

		tmsi := hex.EncodeToString(fiveGSTMSI.FiveGTMSI.Value)

		guti := servedGuami.PlmnId.Mcc + servedGuami.PlmnId.Mnc + amfID + tmsi

		// TODO: invoke Namf_Communication_UEContextTransfer if serving AMF has changed since last Registration Request procedure
		// Described in TS 23.502 4.2.2.2.2 step 4 (without UDSF deployment)

进入核心函数 nas.HandleNAS 处理的类型为 ProcedureCodeInitialUEMessage

HandleNAS

--> Dispatch 设置类型为 EVENT_GMM_MESSAGE，根据初始 ue 状态为 Deregistered

func Dispatch(ue *context.AmfUe, accessType models.AccessType, procedureCode int64, msg *nas.Message) error {

	return gmm.GmmFSM.SendEvent(ue.State[accessType], gmm.GmmMessageEvent, fsm.ArgsType{
		gmm.ArgAmfUe:         ue,
		gmm.ArgAccessType:    accessType,
		gmm.ArgNASMessage:    msg.GmmMessage,
		gmm.ArgProcedureCode: procedureCode,
	})
}

根据 DeRegistered 函数中，事件类型为 EVENT_GMM_MESSAGE 和 gmm 类型为 MsgTypeRegistrationRequest 定位到函数HandleRegistrationRequest，如果成功状态由事务 AuthRestartEvent DeRegistered --> Authentication

2.2 HandleRegistrationRequest 函数

根据前提为 3GPP，根据 EVENT_GMM_MESSAGE 和 MsgTypeRegistrationRequest 定位到 HandleRegistrationRequest 函数

func HandleRegistrationRequest(ue *context.AmfUe, anType models.AccessType, procedureCode int64, registrationRequest *nasMessage.RegistrationRequest) error {

	logger.GmmLog.Info("[AMF] Handle Registration Request")

	util.ClearT3513(ue)
	util.ClearT3565(ue)

	var guamiFromUeGuti models.Guami
	amfSelf := context.AMF_Self()

根据 nasType.MobileIdentity5GS 中第一个字节类型为 0x01 类型为 suci

根据 suci(imsi) = "suci-0-${mcc}-${mnc}-${routingIndentifier}-${protectionScheme}-${homeNetworkPublicKeyIdentifier}-${schemeOutput}"

suci -0 -460-03 -0 -0 -0 -0000007487

如果 NAS 消息为 RegistrationType5GSInitialRegistration 则传输设置为 “INIT_REG”

根觉 NAS 消息类型为 MobileIdentity5GSTypeSuci

mobileIdentity5GSContents := registrationRequest.MobileIdentity5GS.GetMobileIdentity5GSContents()
ue.IdentityTypeUsedForRegistration = nasConvert.GetTypeOfIdentity(mobileIdentity5GSContents[0])
switch ue.IdentityTypeUsedForRegistration { // get type of identity
case nasMessage.MobileIdentity5GSTypeNoIdentity:
	logger.GmmLog.Debugf("No Identity")
case nasMessage.MobileIdentity5GSTypeSuci:
	var plmnId string
	ue.Suci, plmnId = nasConvert.SuciToString(mobileIdentity5GSContents)
	ue.PlmnId = util.PlmnIdStringToModels(plmnId)
	logger.GmmLog.Debugf("SUCI: %s", ue.Suci)
	ue.IsCleartext = true

如果 ue 不再 amf 服务小区，则发送注册 reject

// Check TAI
if !context.InTaiList(ue.Tai, amfSelf.SupportTaiLists) {
	gmm_message.SendRegistrationReject(ue.RanUe[anType], nasMessage.Cause5GMMTrackingAreaNotAllowed, "")
	return fmt.Errorf("Registration Reject[Tracking area not allowed]")
}

2.2.1 如果更换 AMF的情况

新的 AMF 向旧的 AMF 调用 Namf_Communication_UEContextTransfer，包括完成的注册请求 NAS 消息，来请求 UE 的 SUPI 和 UE 上下文（对应步骤 4）

// TODO (TS 23.502 4.2.2.2 step 4): if UE's 5g-GUTI is included & serving AMF has changed since last registration procedure,
// new AMF may invoke Namf_Communication_UEContextTransfer to old AMF, including the complete registration request nas
// msg, to request UE's SUPI & UE Context
if ue.ServingAmfChanged {

向旧的 AMF 发起请求 Namf_Communication_UEContextTransfer /ue-contexts/{ueContextId}/transfer，旧的 AMF 处理函数为 UEContextTransfer，将事件设置为 EventUEContextTransfer，发送到待处理的 channel 中，定位到函数 HTTPUEContextTransfer，流转到函数 HandleUEContextTransferRequest

2.2.2 HandleUEContextTransferRequest 函数

旧的 AMF 根据消息中的 imsi / imei / 5g-guti，查找是否存在该 UE，如果存在则根据传输原因 “INIT_REG” 或者 “MOBI_REG”，如果是 “INIT_REG” 则发送 UE 上下文，包括 SUPI；如果是 “MOBI_REG”，看代码也是一样的 UE 上下文

state	event	From	To
Deregistered	GmmMessageEvent	Deregistered	Deregistered
Deregistered -> Authentication	StartAuthEvent	Deregistered	Authentication

func (fsm *FSM) SendEvent(state *State, event EventType, args ArgsType) error {
	key := eventKey{
		From:  state.Current(),
		Event: event,
	}

	if trans, ok := fsm.transitions[key]; ok {
		// exit callback
		if trans.From != trans.To {
			fsm.callbacks[trans.From](state, ExitEvent, args)
		}

		// event callback
		fsm.callbacks[trans.From](state, event, args)

		// entry callback
		if trans.From != trans.To {
			state.Set(trans.To)
			fsm.callbacks[trans.To](state, EntryEvent, args)
		}
		return nil
	} else {
		return fmt.Errorf("Unknown transition[From: %s, Event: %s]", state.Current(), event)
	}
}

根据 SendEvent 函数中，状态转移，由 Deregistered -> Authentication，From -> To（Deregistered, Authenticaion），进入 Authentication

3 Authentication 函数

func Authentication(state *fsm.State, event fsm.EventType, args fsm.ArgsType) {
	logger.GmmLog.Debugln("UE in GMM State [Authentication]")

	switch event {
	case fsm.EntryEvent:
		fallthrough
	case AuthRestartEvent:
		amfUe := args[ArgAmfUe].(*context.AmfUe)
		accessType := args[ArgAccessType].(models.AccessType)

		pass, err := AuthenticationProcedure(amfUe, accessType)
		if err != nil {
			logger.GmmLog.Errorln(err)
		}
		if pass {
			if err := GmmFSM.SendEvent(state, AuthSuccessEvent, fsm.ArgsType{
				ArgAmfUe:      amfUe,
				ArgAccessType: accessType,
			}); err != nil {
				logger.GmmLog.Errorln(err)
			}
		}

3.1 AuthenticationProcedure 函数

如果发起的请求中未包含 SUCI/SUPI，则发起 TS 23.502 步骤6

func AuthenticationProcedure(ue *context.AmfUe, accessType models.AccessType) (bool, error) {
	logger.GmmLog.Info("Authentication procedure")

	// Check whether UE has SUCI and SUPI
	if IdentityVerification(ue) {
		logger.GmmLog.Debugln("UE has SUCI / SUPI")
		if ue.SecurityContextIsValid() {
			logger.GmmLog.Debugln("UE has a valid security context - skip the authentication procedure")
			return true, nil
		}
	} else {
		// Request UE's SUCI by sending identity request
		gmm_message.SendIdentityRequest(ue.RanUe[accessType], nasMessage.MobileIdentity5GSTypeSuci)
		return false, nil
	}

向 NRF 发送服务发现 AUSF 功能，向 AUSF 发送认证 Nausf_UEAuthentication，包括 servingNetworkName，UE 的 SUCI，向 AUSF 发送 POST 请求 /ue-authentications

AMF 向 AUSF 发起认证请求

AUSF 处理的请求：

Location:[https://ausf:29509/nausf-auth/v1/ue-authentications/suci-0-208-93-0-0-0-00007487]] 201 {5G_AKA {391894b3403ae1a7e712067772fdd9a0 eff8a686c72075259d2ab857e788cb11 cc62613e215e8000a8125d9fbd1b18c9} map[link:{https://ausf:29509/nausf-auth/v1/ue-authentications/suci-0-208-93-0-0-0-00007487/5g-aka-confirmation}] 5G:mnc093.mcc208.3gppnetwork.org}

3.2 SendAuthenticationRequest 函数

BuildAuthenticationRequest 函数创建到 UE 的 gmm 消息，BuildDownlinkNasTransport 函数构造 NGAP 消息

STCP 协议连接发送到 RAN

T3560 启动定时器，超过六妙将重发 SendDownlinkNasTransport，超过4次将关闭定时器

3.3 UE 向 AMF 应答 Authentication

NAS 消息类型为 MsgTypeAuthenticationResponse，发送上行数据 NGAP 包裹 NSA 响应消息，类型为 NGAPPDUPresentInitiatingMessage，InitiatingMessage 类型为 ProcedureCodeUplinkNASTransport 和 InitiatingMessagePresentUplinkNASTransport，包括的 IE 有：

- AMF UE NGAP ID，

- RAN UE NGAP ID，

- NAS-PDU，

- User Location Information

3.4 AMF 处理 Authentication Response 消息

根据 NGAPPDUPresentInitiatingMessage 和 ProcedureCodeUplinkNASTransport 定位到 HandleUplinkNasTransport 函数

func HandleUplinkNasTransport(ran *context.AmfRan, message *ngapType.NGAPPDU) {

	var aMFUENGAPID *ngapType.AMFUENGAPID
	var rANUENGAPID *ngapType.RANUENGAPID
	var nASPDU *ngapType.NASPDU
	var userLocationInformation *ngapType.UserLocationInformation

	if ran == nil {
		logger.NgapLog.Error("ran is nil")
		return
	}

核心处理函数 HandleNAS，根据 3GPP 事件，消息设置为 EVENT_GMM_MESSAGE，AUTHENTICATION 函数中定位到 MsgTypeAuthenticationResponse 函数

func HandleAuthenticationResponse(ue *context.AmfUe, anType models.AccessType, authenticationResponse *nasMessage.AuthenticationResponse) error {

	logger.GmmLog.Info("[AMF] Handle Authentication Response")

	util.ClearT3560(ue)

SendAuth5gAkaConfirmRequest 由 AMF 向 AUSF 调用 Nausf_UEAuthentication，/ue-authentications/{authCtxId}/5g-aka-confirmation，由 AUSF 返回 AMF 数据

200 {AUTHENTICATION_SUCCESS imsi-2089300007487 ad15bdad357c72e4d11d9dfb67d84a5a308e594740bef031e4fdf64cecdeeb01}}
[GIN] 2020/07/14 - 07:53:29 | 200 | 46.750921ms | 10.200.200.3 | PUT /nausf-auth/v1/ue-authentications/suci-0-XX-XX-0-0-0-00007487/5g-aka-confirmation

根据返回的数据结果为 AUTHENTICATION_SUCCESS，则状态转移

state	event	From	To
Deregistered -> Authentication	StartAuthEvent	Deregistered	Authentication
Authentication	AuthSuccessEvent	Authentication	SecurityMode

switch response.AuthResult {
case models.AuthResult_SUCCESS:
	ue.UnauthenticatedSupi = false
	ue.Kseaf = response.Kseaf
	ue.Supi = response.Supi
	ue.DerivateKamf()
	logger.GmmLog.Debugln("ue.DerivateKamf()", ue.Kamf)
	return GmmFSM.SendEvent(ue.State[accessType], AuthSuccessEvent, fsm.ArgsType{
		ArgAmfUe:      ue,
		ArgAccessType: accessType,
		ArgEAPSuccess: false,
		ArgEAPMessage: "",
	})

3.5 SecurityMode 函数

func SecurityMode(state *fsm.State, event fsm.EventType, args fsm.ArgsType) {
	logger.GmmLog.Debugln("UE in GMM State[SecurityMode]")

	switch event {
	case fsm.EntryEvent:
		amfUe := args[ArgAmfUe].(*context.AmfUe)
		accessType := args[ArgAccessType].(models.AccessType)
		if amfUe.SecurityContextIsValid() {

		} else {
			eapSuccess := args[ArgEAPSuccess].(bool)
			eapMessage := args[ArgEAPMessage].(string)
			// Select enc/int algorithm based on ue security capability & amf's policy,
			amfSelf := context.AMF_Self()
			amfUe.SelectSecurityAlg(amfSelf.SecurityAlgorithm.IntegrityOrder, amfSelf.SecurityAlgorithm.CipheringOrder)
			// Generate KnasEnc, KnasInt
			amfUe.DerivateAlgKey()
			gmm_message.SendSecurityModeCommand(amfUe.RanUe[accessType], eapSuccess, eapMessage)
		}

SendSecurityModeCommand 函数发送安全模式命令，NAS 消息中 MM 类型为 MsgTypeSecurityModeCommand，SendDownlinkNasTransport 函数建立 NGAP 消息包裹 NAS 消息，类型为 NGAPPDUPresentInitiatingMessage，ProcedureCodeDownlinkNASTransport，InitiatingMessagePresentDownlinkNASTransport 发送到 (R)AN

DownlinkNASTransport，Security mode command

3.6 (R)AN 发送安全模式完成消息

NAS 消息类型为 MsgTypeSecurityModeComplete，NGAP 消息类型为 NGAPPDUPresentInitiatingMessage，ProcedureCodeUplinkNASTransport，InitiatingMessagePresentUplinkNASTransport

UplinkNASTransport，Security mode complete，Registration request

3.7 AMF 处理收到的 Security mode complete

HandleSecurityModeComplete，最后到 SendEvent 函数将状态转移，事件 SecurityModeSuccessEvent

state	event	From	To
Deregistered -> Authentication	StartAuthEvent	Deregistered	Authentication
Authentication	AuthSuccessEvent	Authentication	SecurityMode
SecurityMode	SecurityModeSuccessEvent	SecurityMode	ContextSetup

func SecurityMode(state *fsm.State, event fsm.EventType, args fsm.ArgsType) {
	logger.GmmLog.Debugln("UE in GMM State[SecurityMode]")

	switch event {

	case GmmMessageEvent:
		amfUe := args[ArgAmfUe].(*context.AmfUe)
		procedureCode := args[ArgProcedureCode].(int64)
		gmmMessage := args[ArgNASMessage].(*nas.GmmMessage)
		accessType := args[ArgAccessType].(models.AccessType)
		switch gmmMessage.GetMessageType() {
		case nas.MsgTypeSecurityModeComplete:
			if err := HandleSecurityModeComplete(amfUe, accessType, procedureCode, gmmMessage.SecurityModeComplete); err != nil {
				logger.GmmLog.Errorln(err)
			}

3.8 HandleInitialRegistration 函数，继续以下的其他流程

func HandleInitialRegistration(ue *context.AmfUe, anType models.AccessType) error {
	logger.GmmLog.Infoln("[AMF] Handle InitialRegistration")

	amfSelf := context.AMF_Self()

	// update Kgnb/Kn3iwf
	ue.UpdateSecurityContext(anType)

3.8.1 getSubscribedNssai 函数

SearchUdmSdmInstace 从 nrf 查找 UDM 实例，SDMGetSliceSelectionSubscriptionData 函数从 UDM 根据 plmnId查找 NSSAI 信息，包含 DefaultSingleNssais 和 SingleNssais

func getSubscribedNssai(ue *context.AmfUe) {
			err := consumer.SearchUdmSdmInstance(ue, amfSelf.NrfUri, models.NfType_UDM, models.NfType_AMF, &param)

	problemDetails, err := consumer.SDMGetSliceSelectionSubscriptionData(ue)

}

3.8.2 Namf_Communication_RegistrationCompleteNotify 对应步骤 10

如果 AMF 已经更改，新的 AMF 调用 Namf_Communication_RegistrationCompleteNotify 服务操作来通知旧的 AMF， UE 在新的 AMF 注册完成

Namf_Communication_RegistrationCompleteNotify，/ue-contexts/{ueContextId}/transfer-update

// TODO (step 10 optional): send Namf_Communication_RegistrationCompleteNotify to old AMF if need
if ue.ServingAmfChanged {
	// If the AMF has changed the new AMF notifies the old AMF that the registration of the UE in the new AMF is completed
	req := models.UeRegStatusUpdateReqData{
		TransferStatus: models.UeContextTransferStatus_TRANSFERRED,
	}
	// TODO: based on locol policy, decide if need to change serving PCF for UE
	regStatusTransferComplete, problemDetails, err := consumer.RegistrationStatusUpdate(ue, req)
	if problemDetails != nil {
		logger.GmmLog.Errorf("Registration Status Update Failed Problem[%+v]", problemDetails)
	} else if err != nil {
		logger.GmmLog.Errorf("Registration Status Update Error[%+v]", err)
	} else {
		if regStatusTransferComplete {
			logger.GmmLog.Infof("[AMF] Registration Status Transfer complete")
		}
	}
}

3.8.3 SendIdentityRequest 对应步骤 11

如果 UE 未提供 PEI 也未从旧 AMF 取到 PEI，则 AMF 向 UE 发送身份请求消息以获取 PEI。

除非 UE 执行紧急注册且无法进行身份验证，否则 PEI 应加密传输

NAS MM 消息类型为 MsgTypeIdentityRequest

if len(ue.Pei) == 0 {
	gmm_message.SendIdentityRequest(ue.RanUe[anType], nasMessage.MobileIdentity5GSTypeImei)
	return nil
}

3.8.4 UDM Selection 对应步骤 13

if ue.ServingAmfChanged || ue.State[models.AccessType_NON_3_GPP_ACCESS].Is(context.Registered) ||
	!ue.ContextValid {
	if err := communicateWithUDM(ue, anType); err != nil {
		return err
	}
}

如果要执行步骤 14，基于 SUPI 的新 AMF 选择 UDM，然后 UDM 可以选择 UDR 实例，TS 23.501 [2], clause 6.3.9

AMF 选择 UDM TS 23.501 [2], clause 6.3.8

NRF 向 AMF 回应 UDM 信息

3.8.5 Nudm_UECM_Registration 对应步骤 14

如果自从上次注册程序，AMF 已经更改。新 AMF 使用 Nudm_UECM_Registration 向 UDM 注册，如果 AMF 没有 UE 的订阅数据， AMF 使用 Nudm_SDM_Get 检索 AM 订阅数据，SMF 选择订阅数据，在 SMF 中的 UE 上下文。UDM 可以通过 Nudr_DM_Query 从 UDR 检索此信息。

problemDetails, err := consumer.UeCmRegistration(ue, anType, true)
if problemDetails != nil {
	logger.GmmLog.Errorf("UECM_Registration Failed Problem[%+v]", problemDetails)
} else if err != nil {
	logger.GmmLog.Errorf("UECM_Registration Error[%+v]", err)
}

problemDetails, err = consumer.SDMGetAmData(ue)
if problemDetails != nil {
	logger.GmmLog.Errorf("SDM_Get AmData Failed Problem[%+v]", problemDetails)
} else if err != nil {
	logger.GmmLog.Errorf("SDM_Get AmData Error[%+v]", err)
}

problemDetails, err = consumer.SDMGetSmfSelectData(ue)
if problemDetails != nil {
	logger.GmmLog.Errorf("SDM_Get SmfSelectData Failed Problem[%+v]", problemDetails)
} else if err != nil {
	logger.GmmLog.Errorf("SDM_Get SmfSelectData Error[%+v]", err)
}

problemDetails, err = consumer.SDMGetUeContextInSmfData(ue)
if problemDetails != nil {
	logger.GmmLog.Errorf("SDM_Get UeContextInSmfData Failed Problem[%+v]", problemDetails)
} else if err != nil {
	logger.GmmLog.Errorf("SDM_Get UeContextInSmfData Error[%+v]", err)
}

3.8.6 PCF selection

param := Nnrf_NFDiscovery.SearchNFInstancesParamOpts{
	Supi: optional.NewString(ue.Supi),
}
for {
	resp, err := consumer.SendSearchNFInstances(amfSelf.NrfUri, models.NfType_PCF, models.NfType_AMF, &param)
	if err != nil {
		logger.GmmLog.Error("AMF can not select an PCF by NRF")
	}

3.9 AMPolicyControlCreate （对应步骤 16）

新的 AMF 执行一个 AM Policy Association Establishment/Modification，对于紧急注册将忽略

policyAssociationRequest := models.PolicyAssociationRequest{
	NotificationUri: amfSelf.GetIPv4Uri() + "/namf-callback/v1/am-policy/",
	Supi:            ue.Supi,
	Pei:             ue.Pei,
	Gpsi:            ue.Gpsi,
	AccessType:      anType,
	ServingPlmn: &models.NetworkId{
		Mcc: ue.PlmnId.Mcc,
		Mnc: ue.PlmnId.Mnc,
	},
	Guami: &amfSelf.ServedGuamiList[0],
}

步骤 17，未体现：

对于紧急请求的 UE，当注册类型为移动性注册更新，该步骤才应用。AMF 在以下场景调用 Nsmf_PDUSession_UpdateSMContext

3.10 步骤 18，19 UE Context Modification Request N3IWF/TNGFW-AGF

对于非 3GPP 未支持

// TODO (step 18 optional):
// If the AMF has changed and the old AMF has indicated an existing NGAP UE association towards a N3IWF, the new AMF
// creates an NGAP UE association towards the N3IWF to which the UE is connectedsend N2 AMF mobility request to N3IWF
// if anType == models.AccessType_NON_3_GPP_ACCESS && ue.ServingAmfChanged {
// 	TODO: send N2 AMF Mobility Request
// }

3.11 AMF 向 UE 发送 “Registration Accept”（步骤 21）

BuildRegistrationAccept 函数，NAS 消息类型为 MsgTypeRegistrationAccept

BuildInitialContextSetupRequest，NGAP 类型为 NGAPPDUPresentInitiatingMessage，ProcedureCodeInitialContextSetup，包括 IE 有：

- AMF UE NGAP ID

- RAN UE NGAP ID

- Old AMF (optional)

- UE Aggregate Maximum Bit Rate (conditional: if pdu session resource setup)

- Core Network Assistance Information (optional)

- GUAMI

- PDU Session Resource Setup Request List

- Allowed NSSAI

- UE Security Capabilities

- Security Key

- Trace Activation (optional)

- Mobility Restriction List (optional)

- UE Radio Capability (optional)

- Index to RAT/Frequency Selection Priority (optional)

- Masked IMEISV (optional)

- NAS-PDU (optional)

- RRC Inactive Transition Report Request (optional)

- UE Radio Capability for Paging (optional)

600

InitialContextSetupRequest，Registration accept

4. send ngap Initial Context Setup Response Msg

NGAP 消息类型为 NGAPPDUPresentSuccessfulOutcome，ProcedureCodeInitialContextSetup

4.1 AMF 处理 Registration Response 消息

func HandleInitialContextSetupResponse(ran *context.AmfRan, message *ngapType.NGAPPDU) {

	var aMFUENGAPID *ngapType.AMFUENGAPID
	var rANUENGAPID *ngapType.RANUENGAPID
	var pDUSessionResourceSetupResponseList *ngapType.PDUSessionResourceSetupListCxtRes
	var pDUSessionResourceFailedToSetupList *ngapType.PDUSessionResourceFailedToSetupListCxtRes
	var criticalityDiagnostics *ngapType.CriticalityDiagnostics

4.1.1 如果应答消息包含 PDU 会话资源

向 SMF 更新 SM 上下文

if pDUSessionResourceSetupResponseList != nil {
	Ngaplog.Trace("[NGAP] Send PDUSessionResourceSetupResponseTransfer to SMF")

	for _, item := range pDUSessionResourceSetupResponseList.List {
		pduSessionID := int32(item.PDUSessionID.Value)
		transfer := item.PDUSessionResourceSetupResponseTransfer

		response, _, _, err := consumer.SendUpdateSmContextN2Info(amfUe, pduSessionID, models.N2SmInfoType_PDU_RES_SETUP_RSP, transfer)
		if err != nil {
			Ngaplog.Errorf("SendUpdateSmContextN2Info[PDUSessionResourceSetupResponseTransfer] Error:\n%s", err.Error())
		}
		// RAN initiated QoS Flow Mobility in subclause 5.2.2.3.7
		if response != nil && response.BinaryDataN2SmInformation != nil {
			// TODO: n2SmInfo send to RAN
		} else if response == nil {
			// TODO: error handling
		}
	}
}

5. send NAS Registration Complete Msg（步骤22）

NAS 消息类型为 MsgTypeRegistrationComplete

BuildUplinkNasTransport 函数，NGAP 消息类型为 NGAPPDUPresentInitiatingMessage，ProcedureCodeUplinkNASTransport，包括 IE 有：

- AMF UE NGAP ID

- RAN UE NGAP ID

- NAS-PDU

- User Location Information

UplinkNASTransport，Registration complete

5.1 AMF 处理 HandleUplinkNasTransport

定位到函数 HandleUplinkNasTransport

func HandleUplinkNasTransport(ran *context.AmfRan, message *ngapType.NGAPPDU) {

	var aMFUENGAPID *ngapType.AMFUENGAPID
	var rANUENGAPID *ngapType.RANUENGAPID
	var nASPDU *ngapType.NASPDU
	var userLocationInformation *ngapType.UserLocationInformation

5.2 HandleRegistrationComplete 函数

步骤 23 24 未实现，将状态移到 REGISTERED 状态

状态转移

state	event	From	To
Deregistered -> Authentication	StartAuthEvent	Deregistered	Authentication
Authentication	AuthSuccessEvent	Authentication	SecurityMode
SecurityMode	SecurityModeSuccessEvent	SecurityMode	ContextSetup
ContextSetup	GmmMessageEvent	ContextSetup	Registered

func HandleRegistrationComplete(ue *context.AmfUe, accessType models.AccessType,
	registrationComplete *nasMessage.RegistrationComplete) error {

	logger.GmmLog.Info("[AMF] Handle Registration Complete")

	util.StopT3550(ue)

	// if registrationComplete.SORTransparentContainer != nil {
	// 	TODO: if at regsitration procedure 14b, udm provide amf Steering of Roaming info & request an ack,
	// 	AMF provides the UE's ack with Nudm_SDM_Info (SOR not supportted in this stage)
	// }

	// TODO: if
	//	1. AMF has evaluated the support of IMS Voice over PS Sessions (TS 23.501 5.16.3.2)
	//	2. AMF determines that it needs to update the Homogeneous Support of IMS Voice over PS Sessions (TS 23.501 5.16.3.3)
	// Then invoke Nudm_UECM_Update to send "Homogeneous Support of IMS Voice over PS Sessions" indication to udm

	if ue.RegistrationRequest.UplinkDataStatus == nil &&
		ue.RegistrationRequest.GetFOR() == nasMessage.FollowOnRequestNoPending {
		ngap_message.SendUEContextReleaseCommand(ue.RanUe[accessType], context.UeContextN2NormalRelease,
			ngapType.CausePresentNas, ngapType.CauseNasPresentNormalRelease)
	}
	return GmmFSM.SendEvent(ue.State[accessType], ContextSetupSuccessEvent, fsm.ArgsType{
		ArgAmfUe:      ue,
		ArgAccessType: accessType,
	})
}

6. Registered 函数

state	event	From	To
Deregistered -> Authentication	StartAuthEvent	Deregistered	Authentication
Authentication	AuthSuccessEvent	Authentication	SecurityMode
SecurityMode	SecurityModeSuccessEvent	SecurityMode	ContextSetup
ContextSetup	GmmMessageEvent	ContextSetup	Registered
Registered	GmmMessageEvent	Registered	Registered

参考：

github， free5gc 3.0.4

张忠琳

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