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”。

    NGAP 消息， Present：NGAPPDUPresentInitiatingMessage，Procedure： ProcedureCodeUEContextReleaseRequest 

   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

   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())

   1.5 AMF 发送 UE Context Release Command 

 

   1.6 发送 NGAP UE Context Release Complete

   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

    NGAP 消息设置 Present 为 NGAPPDUPresentInitiatingMessage，ProcedureCode 为 ProcedureCodeInitialUEMessage

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)

 

5. SMF 处理函数 HandlePDUSessionSMContextUpdate

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)

    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

   5.1 SMF response AMF 

 

6. AMF 发送 Service Accept

 

7. 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
		// }
	}
}