【5G核心网】free5GC 业务请求流程源码分析

àì夳堔傛蜴生んèń 2022-11-24 14:22 671阅读 0赞

本文分析 Free5GC Service request procedure 业务请求流程

# 1. UE Context Release Request (NG-RAN node initiated) #

UE上下文释放请求过程的目的是由于 NG-RAN 节点的原因，请求 AMF 释放与 UE 相关的逻辑 NG 连接。该过程使用 UE 相关的信令。UE 上下文释放请求消息应指示释放的适当原因值，例如“ TXnRELOCOverall Expiry”，“ Redirection”。

![20201117103343483.png][] Figure 8.3.2.2-1: UE context release request

NGAP 消息， Present：***NGAPPDUPresentInitiatingMessage***，Procedure： ***ProcedureCodeUEContextReleaseRequest***

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70][] UEContextReleaseRequest

###    1.1 AMF 处理 UE Context Release Request  ###

NGAP.Dispatch

-->  HandleUEContextReleaseRequest

如果 ue 在 AMF 状态是已经注册的， PDU 会话资源列表不空，则 SendUpdateSmContextDeactivateUpCnxState 更新上下文 Deactivate 状态

if amfUe.State[ran.AnType].Is(context.Registered) {
    	Ngaplog.Info("[NGAP] Ue Context in GMM-Registered")
    	if pDUSessionResourceList != nil {
    		for _, pduSessionReourceItem := range pDUSessionResourceList.List {
    			pduSessionID := int32(pduSessionReourceItem.PDUSessionID.Value)
    			response, _, _, err := consumer.SendUpdateSmContextDeactivateUpCnxState(amfUe, pduSessionID, causeAll)
    			if err != nil {
    				logger.NgapLog.Errorf("Send Update SmContextDeactivate UpCnxState Error[%s]", err.Error())
    			} else if response == nil {
    				logger.NgapLog.Errorln("Send Update SmContextDeactivate UpCnxState Error")
    			}
    		}
    	}

如果 ue 在 AMF 是未注册，则释放上下文

Ngaplog.Info("[NGAP] Ue Context in Non GMM-Registered")
    for pduSessionId := range amfUe.SmContextList {
    	releaseData := consumer.BuildReleaseSmContextRequest(amfUe, &causeAll, "", nil)
    	detail, err := consumer.SendReleaseSmContextRequest(amfUe, pduSessionId, releaseData)
    	if err != nil {
    		logger.NgapLog.Errorf("Send ReleaseSmContextRequest Error[%s]", err.Error())
    	} else if detail != nil {
    		logger.NgapLog.Errorf("Send ReleaseSmContextRequeste Error[%s]", detail.Cause)
    	}
    }
    ngap_message.SendUEContextReleaseCommand(ranUe, context.UeContextReleaseUeContext, causeGroup, causeValue)
    return

###    1.2 SendUpdateSmContextDeactivateUpCnxState 函数 ###

BuildUpdateSmContextRequest 函数更新 SmContextUpdateData，SMF API 为 /sm-contexts/\{smContextRef\}/modify

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 1][] AMF->SMF UpdateSmContext 请求

###    1.3 SMF 处理 UpdateSmContextDeactive ###

func HandlePDUSessionSMContextUpdate(smContextRef string, body models.UpdateSmContextRequest) *http_wrapper.Response {
    	//GSM State
    	//PDU Session Modification Reject(Cause Value == 43 || Cause Value != 43)/Complete
    	//PDU Session Release Command/Complete
    	logger.PduSessLog.Infoln("In HandlePDUSessionSMContextUpdate")
    	smContext := smf_context.GetSMContext(smContextRef)

既不包含 N1 也不包含 N2 信息，简单多了，UpCnxState 为 Deactivated

case models.UpCnxState_DEACTIVATED:
    	if smContext.SMContextState != smf_context.Active {
    		//Wait till the state becomes Active again
    		//TODO: implement sleep wait in concurrent architecture
    		logger.PduSessLog.Infoln("The SMContext State should be Active State")
    		logger.PduSessLog.Infoln("SMContext state: ", smContext.SMContextState.String())
    	}
    	smContext.SMContextState = smf_context.ModificationPending
    	logger.CtxLog.Traceln("SMContextState Change State: ", smContext.SMContextState.String())
    	response.JsonData.UpCnxState = models.UpCnxState_DEACTIVATED
    	smContext.UpCnxState = body.JsonData.UpCnxState
    	smContext.UeLocation = body.JsonData.UeLocation

###    1.4 SMF 释放 N3，主要就是 FAR ###

// TODO: Deactivate N2 downlink tunnel
    //Set FAR and An, N3 Release Info
    farList = []*smf_context.FAR{}
    smContext.PendingUPF = make(smf_context.PendingUPF)
    for _, dataPath := range smContext.Tunnel.DataPathPool {
    
    	ANUPF := dataPath.FirstDPNode
    	DLPDR := ANUPF.DownLinkTunnel.PDR
    	if DLPDR == nil {
    		logger.PduSessLog.Errorf("AN Release Error")
    	} else {
    		DLPDR.FAR.State = smf_context.RULE_UPDATE
    		DLPDR.FAR.ApplyAction.Forw = false
    		DLPDR.FAR.ApplyAction.Buff = true
    		DLPDR.FAR.ApplyAction.Nocp = true
    		smContext.PendingUPF[ANUPF.GetNodeIP()] = true
    	}
    
    	farList = append(farList, DLPDR.FAR)
    }
    
    sendPFCPModification = true
    smContext.SMContextState = smf_context.PFCPModification
    logger.CtxLog.Traceln("SMContextState Change State: ", smContext.SMContextState.String())

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 2][] PFCP Session Modification Request

###    1.5 AMF 发送 UE Context Release Command  ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 3][] UEContextReleaseCommand

###    1.6 发送 NGAP UE Context Release Complete ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 4][] UEContextReleaseComplete

###    1.7 HandleUEContextReleaseComplete 函数 ###

删除 UE 上下文

# 2. UE 发送 Service Request #

Gmm 消息类型设置为 ***MsgTypeServiceRequest***

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 5][] NAS Table 8.2.16.1.1: SERVICE REQUEST message content

***    ***NGAP 消息设置 Present 为 ***NGAPPDUPresentInitiatingMessage***，ProcedureCode 为 ***ProcedureCodeInitialUEMessage***

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 6][] InitialUEMEssage， Service request

# 3. AMF 处理 Service Request  #

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

###    3.1 UE 上下文在 AMF 已经被清除 ###

if ranUe == nil {
    	var err error
    	ranUe, err = ran.NewRanUe(rANUENGAPID.Value)
    	if err != nil {
    		logger.NgapLog.Errorf("NewRanUe Error: %+v", err)
    	}
    	Ngaplog.Debugf("New RanUe [RanUeNgapID: %d]", ranUe.RanUeNgapId)
    
    	if fiveGSTMSI != nil {
    		Ngaplog.Debug("Receive 5G-S-TMSI")
    
    		servedGuami := amfSelf.ServedGuamiList[0]

## ##

# 4. HandleServiceRequest 函数 #

// TS 24501 5.6.1
    func HandleServiceRequest(ue *context.AmfUe, anType models.AccessType,
    	serviceRequest *nasMessage.ServiceRequest) error {
    	logger.GmmLog.Info("Handle Service Reqeust")
    
    	if ue == nil {
    		return fmt.Errorf("AmfUe is nil")
    	}
    
    	util.StopT3513(ue)
    	util.StopT3565(ue)

###    4.1 处理 UplinkDataStatus  ###

SendUpdateSmContextActivateUpCnState 函数向 SMF 发送激活会话上下文请求

if serviceRequest.UplinkDataStatus != nil {
    	uplinkDataPsi := nasConvert.PSIToBooleanArray(serviceRequest.UplinkDataStatus.Buffer)
    	reactivationResult = new([16]bool)
    	for pduSessionId, smContext := range ue.SmContextList {
    		if pduSessionId == targetPduSessionId {
    			continue
    		}
    		if uplinkDataPsi[pduSessionId] && smContext.PduSessionContext.AccessType == models.AccessType__3_GPP_ACCESS {
    			response, errRes, _, err := consumer.SendUpdateSmContextActivateUpCnxState(
    				ue, pduSessionId, models.AccessType__3_GPP_ACCESS)

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 7][] AMF-SMF UpdateSmContextActivateUpCnState

# 5. SMF 处理函数 HandlePDUSessionSMContextUpdate #

根据 N2 会话信息类型为 N2SmInfoType\_PDU\_RES\_SETUP\_RSP

switch smContextUpdateData.N2SmInfoType {
    case models.N2SmInfoType_PDU_RES_SETUP_RSP:
    	if smContext.SMContextState != smf_context.Active {
    		//Wait till the state becomes Active again
    		//TODO: implement sleep wait in concurrent architecture
    		logger.PduSessLog.Infoln("The SMContext State should be Active State")
    		logger.PduSessLog.Infoln("SMContext state: ", smContext.SMContextState.String())
    	}
    	smContext.SMContextState = smf_context.ModificationPending
    	logger.CtxLog.Traceln("SMContextState Change State: ", smContext.SMContextState.String())
    	pdrList = []*smf_context.PDR{}
    	farList = []*smf_context.FAR{}

SMF 向 UPF 发送 PFCP Session Modification Request 将 N3 RAN 与 UPF 建立 GTP 隧道

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 8][] PFCP Session Modification Request

###    5.1 SMF response AMF  ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 9][] SMF->AMF response UpdateSmContextActivateUpCnState

# 6. AMF 发送 Service Accept #

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 10][] InitialContextSetupRequest，Service request

# 7. NGAP InitialContextSetupResponse #

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 11][] NGAP InitialContextSetupResponse

# 8. AMF 函数 HandleInitialContextSetupResponse #

根据 PDU 会话资源列表更新发向 SMF，这里不分析了，还有 SMF 向 UPF 更新

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,
    		_, _, _, 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
    		// }
    	}
    }

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