【5G核心网】free5GC 会话建立流程源码分析

- 日理万妓 2022-11-24 12:58 1019阅读 0赞

本文分析 Free5GC PDU Session Establishment procedure 会话建立流程

# 1. UE 发起的 PDU 会话建立请求 （RAN -> AMF）  #

GetPduSessionEstablishmentRequest 创建 NAS-PDU，填充 NAS 消息中的 SM 消息，设置 SM 头消息类型为 *MsgTypePDUSessionEstablishmentRequest *PDUSessionEstablishmentRequestPDUSessionTypeType，SM 头格式为：

type GsmHeader struct {
    	Octet [4]uint8
    }

PDUSessionEstablishmentRequest 结构体

type PDUSessionEstablishmentRequest struct {
    	nasType.ExtendedProtocolDiscriminator
    	nasType.PDUSessionID
    	nasType.PTI
    	nasType.PDUSESSIONESTABLISHMENTREQUESTMessageIdentity
    	nasType.IntegrityProtectionMaximumDataRate
    	*nasType.PDUSessionType
    	*nasType.SSCMode
    	*nasType.Capability5GSM
    	*nasType.MaximumNumberOfSupportedPacketFilters
    	*nasType.AlwaysonPDUSessionRequested
    	*nasType.SMPDUDNRequestContainer
    	*nasType.ExtendedProtocolConfigurationOptions
    }

NAS 消息中的 MM 消息头部类型为 *MsgTypeULNASTransport*，设置的内容 ULNASTransport，类型为 *MsgTypeULNASTransport*，*PayloadContainerTypeN1SMInfo*

添加 DNN，SNSSAI，PayloadContainer（上面创建的 NAS 携带 SM 消息）

type ULNASTransport struct {
    	nasType.ExtendedProtocolDiscriminator
    	nasType.SpareHalfOctetAndSecurityHeaderType
    	nasType.ULNASTRANSPORTMessageIdentity
    	nasType.SpareHalfOctetAndPayloadContainerType
    	nasType.PayloadContainer
    	*nasType.PduSessionID2Value
    	*nasType.OldPDUSessionID
    	*nasType.RequestType
    	*nasType.SNSSAI
    	*nasType.DNN
    	*nasType.AdditionalInformation
    }

### **   1.1 BuildUplinkNasTransport 函数创建 NGAP 消息** ###

NGAP 消息了类型为 ***NGAPPDUPresentInitiatingMessage***，数据结构体为 InitiatingMessage，ProcedureCode 设置为 *ProcedureCodeUplinkNASTransport*，携带 IE 有

>     // AMF UE NGAP ID
> 
>        ProtocolIEIDAMFUENGAPID     UplinkNASTransportIEsPresentAMFUENGAPID
> 
>     // RAN UE NGAP ID
> 
>        ProtocolIEIDRANUENGAPID      UplinkNASTransportIEsPresentRANUENGAPID
> 
>     // NAS-PDU
> 
>         ProtocolIEIDNASPDU                 UplinkNASTransportIEsPresentNASPDU
> 
>     // User Location Information
> 
>         ProtocolIEIDUserLocationInformation      UplinkNASTransportIEsPresentUserLocationInformation

**     UPLINK NAS TRANSPORT**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 1][] UplinkNASTransport，UL NAS transport，PDU session establishment request

# 2. AMF 收到 RAN 发送的 NGAP **UPLINK NAS TRANSPORT 消息** #

根据 NGAP 消息类型为 *NGAPPDUPresentInitiatingMessage*，ProcedureCode 设置为 *ProcedureCodeUplinkNASTransport*，*InitiatingMessagePresentUplinkNASTransport，定位到 *HandleUplinkNasTransport

提取出 IE 包括 AMFUENGAPID RANUENGAPID NASPDU UserLocationInformation

func HandleUplinkNasTransport(ran *context.AmfRan, message *ngapType.NGAPPDU) {
    
    	var aMFUENGAPID *ngapType.AMFUENGAPID
    	var rANUENGAPID *ngapType.RANUENGAPID
    	var nASPDU *ngapType.NASPDU
    	var userLocationInformation *ngapType.UserLocationInformation

HandleNAS

-->  Dispatch

-->  SendEvent GmmMessageEvent

-->  Registered

-->  HandleULNASTransport

根据 3GPP 接入类型，以及 MM 消息类 *MsgTypeULNASTransport，目前状态已经未 REGISTED，定位到函数 * HandleULNASTransport

提取出 PDU session ID，Snssai，DNN，requestType（*ULNASTransportRequestTypeInitialRequest*）设置为 *RequestType\_INITIAL\_REQUEST*

func HandleULNASTransport(ue *context.AmfUe, anType models.AccessType, procedureCode int64, ulNasTransport *nasMessage.ULNASTransport, securityHeaderType uint8) error {
    	logger.GmmLog.Infoln("Handle UL NAS Transport")
    
    	if ue.MacFailed {
    		return fmt.Errorf("NAS message integrity check failed")
    	}
    
    	switch ulNasTransport.GetPayloadContainerType() {
    	case nasMessage.PayloadContainerTypeN1SMInfo:

在处理 SM 消息根据类型为 *MsgTypePDUSessionEstablishmentRequest *根据初始请求 ULNASTransportRequestTypeInitialRequest 设置为：*RequestType\_INITIAL\_REQUEST*

func HandlePDUSessionEstablishmentRequest(ue *context.AmfUe, anType models.AccessType, payload []byte, pduSessionID int32, requestType models.RequestType, sNssai *models.Snssai, dnn string) error {
    	// TODO Request Type Emergency requset
    	var pduSession models.PduSessionContext
    	pduSession.PduSessionId = pduSessionID
    	pduSession.AccessType = anType
    	amfSelf := context.AMF_Self()
    	if requestType == models.RequestType_INITIAL_REQUEST {

如果 UE 未提供 Snssai，则根据 UE 订阅的切片信息选择，如果 DNN 未提供，选择切片默认 DNN

如果以上情况没有，则使用 UE Allow 切片信息

if sNssai == nil {
    	if ue.SmfSelectionData != nil {
    		for snssai, sNssaiInfo := range ue.SmfSelectionData.SubscribedSnssaiInfos {
    			var err error
    			sNssai, err = util.SnssaiHexToModels(snssai)
    			if err != nil {
    				return err
    			}
    			if dnn == "" {
    				for _, dnnInfo := range sNssaiInfo.DnnInfos {
    					if dnnInfo.DefaultDnnIndicator {
    						dnn = dnnInfo.Dnn
    						break
    					}
    				}
    			}
    
    		}
    	}
    	if sNssai == nil {
    		allowedNssai := ue.AllowedNssai[anType]
    		if len(allowedNssai) > 0 {
    			sNssai = allowedNssai[0].AllowedSnssai
    		} else {
    			err := fmt.Errorf("Ue[%s] doesn't have allowedNssai\n", ue.Supi)
    			logger.GmmLog.Errorf(err.Error())
    			return err
    		}
    	}
    
    }

### **   2.1 selectSmf 函数** ###

![20200728114858612.png][]

>     AMF 根据切片信息，DNN 等为 PDU 会话选择 SMF
> 
>     AMF->SMF：  Nnssf\_NSSelection\_Get 返回了网络切片 ID，AMF 根据 NSI 找到 S-NAASI 选择 SMF

GetNsiInformationFromSnssai 函数根据请求的 SNssai 是否存在允许的列表中，如果不存在则选择一个，NSSelectionGetForPduSession 则选择一个切片信息

通过 NRF 的 Nnrf\_NFDiscovery 服务发现 /nf-instances。AMF 根据切片信息，DNN 等为 PDU 会话选择 SMF

param := Nnrf_NFDiscovery.SearchNFInstancesParamOpts{
    	ServiceNames: optional.NewInterface([]models.ServiceName{models.ServiceName_NSMF_PDUSESSION}),
    	Dnn:          optional.NewString(pduSession.Dnn),
    	Snssais:      optional.NewInterface(util.MarshToJsonString([]models.Snssai{*pduSession.SNssai})),
    }

### **   2.2 如果 UE 的会话上下文存在** ###

则调用 SendUpdateSmContextRequest 向 SMF 发送* Nsmf\_PDUSession /sm-contexts/\{smContextRef\}/modify* 请求

// Store PduSessionContext For duplicated PDU Session Id
    if smContext, ok := ue.SmContextList[pduSessionID]; ok {
    	ue.StoredSmContext[pduSessionID] = &context.StoredSmContext{
    		SmfId:             smfID,
    		SmfUri:            smfUri,
    		PduSessionContext: &pduSession,
    		AnType:            anType,
    		Payload:           payload,
    	}

###    2.3 如果 UE 的会话上下文不存在 ###

BuildCreateSmContextRequest 创建会话上下文请求，其包括：

>     - supi
> 
>     - UnauthenticatedSupi
> 
>     - pei
> 
>     - gpsi
> 
>     - pdusessionId
> 
>     - sNssai
> 
>     - DNN
> 
>     - servingNfId
> 
>     - guami
> 
>     - servingNetwork
> 
>     - requestType
> 
>     - N1Smmsg
> 
>     - Antype
> 
>     - RatType
> 
>     - \[ UeLocation \] 
> 
>     - SmContextStatusUri

smContextCreateData.Supi = ue.Supi
    smContextCreateData.UnauthenticatedSupi = ue.UnauthenticatedSupi
    smContextCreateData.Pei = ue.Pei
    smContextCreateData.Gpsi = ue.Gpsi
    smContextCreateData.PduSessionId = pduSessionContext.PduSessionId
    smContextCreateData.SNssai = pduSessionContext.SNssai
    smContextCreateData.Dnn = pduSessionContext.Dnn
    smContextCreateData.ServingNfId = context.NfId
    smContextCreateData.Guami = &context.ServedGuamiList[0]
    smContextCreateData.ServingNetwork = context.ServedGuamiList[0].PlmnId

**      2.3.1 SendCreateSmContextRequest**

向 SMF 发送 *Nsmf\_PDUSession /sm-contexts* 请求

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 2][] AMF->SMF，sm-context 请求，Nsmf\_PDUSession\_CreateSMContext

# 3. SMF Nsmf\_PDUSession\_CreateSMContext #

SMF 从 AMF 接收 *Nsmf\_PDUSession\_CreateSMContext* 请求，*/sm-contexts，则进入 *PostSmContexts 函数处理，设置为 *PDUSessionSMContextCreate* 类型消息，丢进 channel 进行集中处理

###     HandlePDUSessionSMContextCreate 函数 ###

SMF 创建会话管理上下文，实例化 SMContext

>     - supi
> 
>     - pduSessionID
> 
>     - gpsi
> 
>     - DNn
> 
>     - SNssai
> 
>     - HplmnSnssai
> 
>     - ServingNetwork
> 
>     - AnType
> 
>     - RatType
> 
>     - UeLocation
> 
>     - OldPduSessionId
> 
>     - ServingNfId
> 
>     - SmContextStatusUri

createData := request.JsonData
    smContext := smf_context.NewSMContext(createData.Supi, createData.PduSessionId)
    smContext.SMContextState = smf_context.ActivePending
    logger.CtxLog.Traceln("SMContextState Change State: ", smContext.SMContextState.String())
    smContext.SetCreateData(createData)
    smContext.SmStatusNotifyUri = createData.SmContextStatusUri

###    3.1 SendNFDiscoveryUDM ###

服务发现 UDM，向 NRF 查找 Nnrf\_NFDiscovery /nf-instances

###    3.2 向 UDM 发起 Nudm\_SubscriberDataManagement.请求 */\{supi\}/sm-data 步骤 4* ###

smPlmnID := createData.Guami.PlmnId
    
    smDataParams := &Nudm_SubscriberDataManagement.GetSmDataParamOpts{
    	Dnn:         optional.NewString(createData.Dnn),
    	PlmnId:      optional.NewInterface(smPlmnID.Mcc + smPlmnID.Mnc),
    	SingleNssai: optional.NewInterface(openapi.MarshToJsonString(smContext.Snssai)),
    }
    
    SubscriberDataManagementClient := smf_context.SMF_Self().SubscriberDataManagementClient
    
    sessSubData, _, err := SubscriberDataManagementClient.SessionManagementSubscriptionDataRetrievalApi.GetSmData(context.Background(), smContext.Supi, smDataParams)

> \{  
>     "\_id": ObjectId("5ef0907d29ad99a43c018d2d"),  
>     "smPolicySnssaiData": \{  
>         "01010203": \{  
>             "snssai": \{  
>                 "sst": 1,  
>                 "sd": "010203"  
>             \},  
>             "smPolicyDnnData": \{  
>                 "internet": \{  
>                     "dnn": "internet"  
>                 \}  
>             \}  
>         \},  
>         "01112233": \{  
>             "snssai": \{  
>                 "sst": 1,  
>                 "sd": "112233"  
>             \},  
>             "smPolicyDnnData": \{  
>                 "internet": \{  
>                     "dnn": "internet"  
>                 \}  
>             \}  
>         \}  
>     \},  
>     "ueId": "imsi-2089300007487"  
> \}

###    3.3 为 UE 分配 IP 地址 ###

func (smContext *SMContext) HandlePDUSessionEstablishmentRequest(req *nasMessage.PDUSessionEstablishmentRequest) {
    	// Retrieve PDUSessionID
    	smContext.PDUSessionID = int32(req.PDUSessionID.GetPDUSessionID())
    	logger.GsmLog.Infoln("In HandlePDUSessionEstablishmentRequest")
    	// Handle PDUSessionType
    
    	smContext.PDUAddress = AllocUEIP()
    }

###    3.4 PCF Selection （步骤 7a） ###

###    3.5 SM Policy Association Establisment (步骤 7b) ###

实例化 SmPolicyContextData 并填充 Supi，PDUSessionID，Dnn，Snssai 等等。调用 /sm-policies 更新 PCF 策略配置

smPolicyData := models.SmPolicyContextData{}
    
    smPolicyData.Supi = smContext.Supi
    smPolicyData.PduSessionId = smContext.PDUSessionID
    smPolicyData.NotificationUri = fmt.Sprintf("%s://%s:%d/nsmf-callback/sm-policies/%s", smf_context.SMF_Self().URIScheme, smf_context.SMF_Self().HTTPAddress, smf_context.SMF_Self().HTTPPort, smContext.Ref)
    smPolicyData.Dnn = smContext.Dnn
    smPolicyData.PduSessionType = nasConvert.PDUSessionTypeToModels(smContext.SelectedPDUSessionType)
    smPolicyData.AccessType = smContext.AnType
    smPolicyData.RatType = smContext.RatType
    smPolicyData.Ipv4Address = smContext.PDUAddress.To4().String()
    smPolicyData.SubsSessAmbr = smContext.DnnConfiguration.SessionAmbr
    smPolicyData.SubsDefQos = smContext.DnnConfiguration.Var5gQosProfile
    smPolicyData.SliceInfo = smContext.Snssai
    smPolicyData.ServingNetwork = &models.NetworkId{
    	Mcc: smContext.ServingNetwork.Mcc,
    	Mnc: smContext.ServingNetwork.Mnc,
    }
    smPolicyData.SuppFeat = "F"
    
    smPolicyDecision, _, err := smContext.SMPolicyClient.DefaultApi.SmPoliciesPost(context.Background(), smPolicyData)

> \{  
>     "\_id": ObjectId("5f0290d83fbd30af88df2945"),  
>     "singleNssai": \{  
>         "sst": 1,  
>         "sd": "010203"  
>     \},  
>     "dnnConfigurations": \{  
>         "internet": \{  
>             "pduSessionTypes": \{  
>                 "defaultSessionType": "IPV4",  
>                 "allowedSessionTypes": \["IPV4"\]  
>             \},  
>             "sscModes": \{  
>                 "defaultSscMode": "SSC\_MODE\_1",  
>                 "allowedSscModes": \["SSC\_MODE\_1", "SSC\_MODE\_2", "SSC\_MODE\_3"\]  
>             \},  
>             "5gQosProfile": \{  
>                 "5qi": 0,  
>                 "arp": \{  
>                     "priorityLevel": 8,  
>                     "preemptCap": "",  
>                     "preemptVuln": ""  
>                 \},  
>                 "priorityLevel": 8  
>             \},  
>             "sessionAmbr": \{  
>                 "uplink": "1000 Kbps",  
>                 "downlink": "1000 Kbps"  
>             \}  
>         \}  
>     \},  
>     "ueId": "imsi-208930000000003",  
>     "servingPlmnId": "20893"  
> \}

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 3][] PCF-AMF ApplySmPolicy response

### **   3.6 **ApplySmPolicyFromDecision **函数** ###

应用 session rule

func ApplySmPolicyFromDecision(smContext *smf_context.SMContext, decision *models.SmPolicyDecision) error {
    	logger.PduSessLog.Traceln("In ApplySmPolicyFromDecision")
    	smContext.SMContextState = smf_context.ModificationPending
    	selectedSessionRule := smContext.SelectedSessionRule()
    	if selectedSessionRule == nil { //No active session rule
    		//Update session rules from decision
    		for id, sessRuleModel := range decision.SessRules {
    			handleSessionRule(smContext, id, &sessRuleModel)
    		}
    		for id := range smContext.SessionRules {
    			// Randomly choose a session rule to activate
    			smf_context.SetSessionRuleActivateState(smContext.SessionRules[id], true)
    			break
    		}
    	}

**    3.6.1 handleSessionRule 函数**

smContext 加入会话规则，包括 AuthSessAmbr AuthDefQos SessRuleId

## ##

# **4. UPF Selection（步骤 8）** #

###     UPTunnel 结构体 ###

type UPTunnel struct {
    	PathIDGenerator *idgenerator.IDGenerator
    	DataPathPool    DataPathPool
    }

###     DataPath 结构体 ###

type DataPath struct {
    	//meta data
    	Activated         bool
    	IsDefaultPath     bool
    	Destination       Destination
    	HasBranchingPoint bool
    	//Data Path Double Link List
    	FirstDPNode *DataPathNode
    }

###     DataPathNode 结构体 ###

type DataPathNode struct {
    	UPF *UPF
    	//DataPathToAN *DataPathDownLink
    	//DataPathToDN map[string]*DataPathUpLink //uuid to DataPathLink
    
    	UpLinkTunnel   *GTPTunnel
    	DownLinkTunnel *GTPTunnel
    	//for UE Routing Topology
    	//for special case:
    	//branching & leafnode
    
    	//InUse                bool
    	IsBranchingPoint bool
    	//DLDataPathLinkForPSA *DataPathUpLink
    	//BPUpLinkPDRs         map[string]*DataPathDownLink // uuid to UpLink
    
    	HaveSession bool
    }

例如官方例子：

> userplane\_information:
> 
>  *  up\_nodes:
>     
>      *  gNB1:
>         
>          *  type: AN
>          *  an\_ip: 192.188.2.3
>      *  BranchingUPF:
>         
>          *  type: UPF
>          *  node\_id: 10.200.200.102
>          *  up\_resource\_ip: 192.188.2.2
>      *  AnchorUPF1:
>         
>          *  type: UPF
>          *  node\_id: 10.200.200.101
>          *  up\_resource\_ip: 192.188.2.23
>      *  AnchorUPF2:
>         
>          *  type: UPF
>          *  node\_id: 10.200.200.103
>          *  up\_resource\_ip: 192.188.2.24
>      *  links:
>         
>          *  A: gNB1 B: BranchingUPF
>          *  A: BranchingUPF B: AnchorUPF1
>          *  A: BranchingUPF B: AnchorUPF2

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 4][]

在这里区分预先配置和未预先配置 UE SUPI 路径

###    4.1 支持 ULCL 且预先配置路由情况 ###

if smf_context.SMF_Self().ULCLSupport && smf_context.CheckUEHasPreConfig(createData.Supi) {
    	//TODO: change UPFRoot => ULCL UserPlane Refactor
    	logger.PduSessLog.Infof("SUPI[%s] has pre-config route", createData.Supi)
    	uePreConfigPaths := smf_context.GetUEPreConfigPaths(createData.Supi)
    	smContext.Tunnel.DataPathPool = uePreConfigPaths.DataPathPool
    	smContext.Tunnel.PathIDGenerator = uePreConfigPaths.PathIDGenerator
    	defaultPath = smContext.Tunnel.DataPathPool.GetDefaultPath()
    	smContext.AllocateLocalSEIDForDataPath(defaultPath)
    	defaultPath.ActivateTunnelAndPDR(smContext)
    	// TODO: Maybe we don't need this
    	smContext.BPManager = smf_context.NewBPManager(createData.Supi)
    }

###    4.2 没有预先配置路由情况 ###

} else {
    	logger.PduSessLog.Infof("SUPI[%s] has no pre-config route", createData.Supi)
    	defaultUPPath := smf_context.GetUserPlaneInformation().GetDefaultUserPlanePathByDNN(createData.Dnn)
    	smContext.AllocateLocalSEIDForUPPath(defaultUPPath)
    	defaultPath = smf_context.GenerateDataPath(defaultUPPath, smContext)
    	defaultPath.IsDefaultPath = true
    	smContext.Tunnel.AddDataPath(defaultPath)
    	defaultPath.ActivateTunnelAndPDR(smContext)
    }

GetDefaultUserPlanePathByDNN 返回 AN 和 DNN 的路径

AllocateLocalSEIDForUPPath 为 path 分配 Local Seid

GenerateDataPath 函数建立一个链表

###    4.3 ActivateTunnelAndPDR 函数 ###

func (dataPath *DataPath) ActivateTunnelAndPDR(smContext *SMContext) {
    
    	firstDPNode := dataPath.FirstDPNode
    	logger.PduSessLog.Traceln("In ActivateTunnelAndPDR")
    	logger.PduSessLog.Traceln(dataPath.ToString())

Activate Tunnels

Activate PDR

# 5. SendPFCPRule #

对于首次没有 session 的情况，上行链路和下行链路 PDR （包检测规则）和 FAR （转发行为规则）

func SendPFCPRule(smContext *smf_context.SMContext, dataPath *smf_context.DataPath) {
    
    	logger.PduSessLog.Infof("Send PFCP Rule")
    	logger.PduSessLog.Infof("DataPath: ", dataPath)
    	for curDataPathNode := dataPath.FirstDPNode; curDataPathNode != nil; curDataPathNode = curDataPathNode.Next() {
    		pdrList := make([]*smf_context.PDR, 0, 2)
    		farList := make([]*smf_context.FAR, 0, 2)
    		if !curDataPathNode.HaveSession {
    			if curDataPathNode.UpLinkTunnel != nil && curDataPathNode.UpLinkTunnel.PDR != nil {
    				pdrList = append(pdrList, curDataPathNode.UpLinkTunnel.PDR)
    				farList = append(farList, curDataPathNode.UpLinkTunnel.PDR.FAR)
    			}
    			if curDataPathNode.DownLinkTunnel != nil && curDataPathNode.DownLinkTunnel.PDR != nil {
    				pdrList = append(pdrList, curDataPathNode.DownLinkTunnel.PDR)
    				farList = append(farList, curDataPathNode.DownLinkTunnel.PDR.FAR)
    			}
    
    			pfcp_message.SendPfcpSessionEstablishmentRequest(curDataPathNode.UPF.NodeID, smContext, pdrList, farList, nil)
    			curDataPathNode.HaveSession = true

### **   5.1 **SendPfcpSessionEstablishmentRequest 步骤 10a ###

建立 PFCP 会话建立请求到 UPF，包括 SM 上下文，PDR，FAR，BAR（目前空）

BuildPfcpSessionEstablishmentRequestForULCL 函数主要用来实例化 *PFCPSessionEstablishmentRequest*，并填充 CP NodeID，CreatePDR，CreateFAR 等，

创建的 PFCP 消息头，消息类型为 *PFCP\_SESSION\_ESTABLISHMENT\_REQUEST*

func SendPfcpSessionEstablishmentRequest(upNodeID pfcpType.NodeID, ctx *context.SMContext, pdrList []*context.PDR, farList []*context.FAR, barList []*context.BAR) {
    	pfcpMsg, err := BuildPfcpSessionEstablishmentRequest(upNodeID, ctx, pdrList, farList, barList)
    	if err != nil {
    		logger.PfcpLog.Errorf("Build PFCP Session Establishment Request failed: %v", err)
    		return
    	}
    
    	message := pfcp.Message{
    		Header: pfcp.Header{
    			Version:         pfcp.PfcpVersion,
    			MP:              1,
    			S:               pfcp.SEID_PRESENT,
    			MessageType:     pfcp.PFCP_SESSION_ESTABLISHMENT_REQUEST,
    			SEID:            0,
    			SequenceNumber:  getSeqNumber(),
    			MessagePriority: 0,
    		},
    		Body: pfcpMsg,
    	}
    
    	upaddr := &net.UDPAddr{
    		IP:   upNodeID.ResolveNodeIdToIp(),
    		Port: pfcpUdp.PFCP_PORT,
    	}

# 6.  UPF 处理 PFCP 建立请求 #

消息类型为： ***PFCP\_SESSION\_ESTABLISHMENT\_REQUEST***，body 结构为： PFCPSessionEstablishmentRequest，处理函数为 UpfN4HandleSessionEstablishmentRequest

Status UpfN4HandleSessionEstablishmentRequest(UpfSession *session, PfcpXact *pfcpXact,
                                                  PFCPSessionEstablishmentRequest *request) {
        Status status;
        uint8_t cause = PFCP_CAUSE_REQUEST_ACCEPTED;
    
        UTLT_Assert(session, return STATUS_ERROR, "Upf Session error");
        UTLT_Assert(pfcpXact, return STATUS_ERROR, "pfcpXact error");

###    6.1 UpfN4HandleCreateFar 处理 FAR 转发行为规则 ###

gtp5g\_far\_alloc 实例化 gtp5g\_far 对象

struct gtp5g_far {
        struct hlist_node    hlist_id;
    
        u32 id;
    
    //    u8 dest_iface;
        u8 action;                              // apply action
    
        struct forwarding_parameter *fwd_param;
    
        struct net_device   *dev;
        struct rcu_head     rcu_head;
    };

***    CreateFAR 结构体***

typedef struct _CreateFAR {
        unsigned long presence;
        FARID fARID;
        ApplyAction applyAction;
        ForwardingParameters forwardingParameters;
        DuplicatingParameters duplicatingParameters;
        BARID bARID;
    } __attribute__((packed)) CreateFAR;

根据 3GPP 定义的 Create FAR IE within PFCP Session Establishment Request

<table> 
 <tbody> 
 <tr> 
 <td> FAR ID </td> 
 <td> M </td> 
 <td> This IE shall uniquely identify the FAR among all the FARs configured for that PFCP session. </td> 
 </tr> 
 <tr> 
 <td> Apply Action </td> 
 <td> M </td> 
 <td> This IE shall&nbsp;indicate the action to apply to the packets, See clauses 5.2.1 and 5.2.3. </td> 
 </tr> 
 <tr> 
 <td> Forwarding Parameters </td> 
 <td> C </td> 
 <td> This IE shall be present when the Apply Action requests the packets to be forwarded. It may be present otherwise. &nbsp; When present, this IE shall contain the forwarding instructions to be applied by the UP function when the Apply Action requests the packets to be forwarded. See table 7.5.2.3-2. </td> 
 </tr> 
 <tr> 
 <td> Duplicating Parameters </td> 
 <td> C </td> 
 <td> This IE shall be present when the Apply Action requests the packets to be duplicated. It may be present otherwise. &nbsp; When present, this IE shall contain the forwarding instructions to be applied by the UP function for the traffic to be duplicated, when the Apply Action requests the packets to be duplicated. &nbsp; Several IEs with the same IE type may be present to represent to duplicate the packets to different destinations. See NOTE 1. &nbsp; See table 7.5.2.3-3. </td> 
 </tr> 
 <tr> 
 <td> BAR ID </td> 
 <td> O </td> 
 <td> When present, this IE shall contain the BAR ID of the BAR defining the buffering instructions to be applied by the UP function when the Apply Action requests the packets to be buffered. </td> 
 </tr> 
 </tbody> 
</table>

**     6.1.1  \_pushFarToKernel**

-->  GtpTunnelAddFar

-->  NetlinkSockOpen

-->  gtp5g\_add\_far

-->  genl\_nlmsg\_build\_hdr

-->  gtp5g\_build\_far\_payload

-->  genl\_socket\_talk

###    struct nlmsghdr ###

Netlink 的报文由消息头和消息体构成，struct nlmsghdr 为消息头：

> struct nlmsghdr
> 
> \{
> 
>     \_\_u32 nlmsg\_len; /\* Length of message including header \*/
> 
>     \_\_u16 nlmsg\_type; /\* Message content \*/
> 
>     \_\_u16 nlmsg\_flags; /\* Additional flags \*/
> 
>     \_\_u32 nlmsg\_seq; /\* Sequence number \*/
> 
>     \_\_u32 nlmsg\_pid; /\* Sending process PID \*/
> 
> \};
> 
>    -  nlmsg\_len：消息的长度，按字节计算。包括了Netlink消息头
> 
>    -  nlmsg\_type：消息类型，数据/控制消息。如下：
> 
>         a) NLMSG\_NOOP，空消息
> 
>         b) NLMSG\_ERROR，指明该消息中包含一个错误
> 
>         c) NLMSG\_DONE，如果内核通过Netlink队列返回了多个消息，那么队列的最后一条消息的类型为NLMSG\_DONE，其余所有消息的 nlmsg\_flags 属性都被设置NLM\_F\_MULTI位有效。
> 
>         d) NLMSG\_OVERRUN，暂时没用到
> 
>    -  nlmsg\_flags：附加在消息上的额外说明信息，如上面提到的 NLM\_F\_MULTI

###    6.2 UpfN4HandleCreatePdr 处理 PDR 包检测规则 ###

gtp5g\_pdr\_alloc 实例化 gtp5g\_pdr 对象，

struct gtp5g_pdr {
        uint16_t id;
        uint32_t *precedence;
        struct gtp5g_pdi *pdi;
    
        uint8_t *outer_hdr_removal;
        uint32_t *far_id;
    
        /* Not in 3GPP spec, just used for routing */
        struct in_addr *role_addr_ipv4;
    
        /* Not in 3GPP spec, just used for buffering */
        char *unix_sock_path;
    };

\_CreatePDR 结构体

typedef struct _CreatePDR {
        unsigned long presence;
        PacketDetectionRuleID pDRID;
        Precedence precedence;
        PDI pDI;
        OuterHeaderRemoval outerHeaderRemoval;
        FARID fARID;
        URRID uRRID;
        QERID qERID;
        ActivatePredefinedRules activatePredefinedRules;
    } __attribute__((packed)) CreatePDR;

PDI SDF 过滤器 很多未实现

###    6.3 UpfN4BuildSessionEstablishmentResponse 函数 ###

响应请求设置类型为 *PFCP\_SESSION\_ESTABLISHMENT\_RESPONSE*，设置 seid。body 结构体为 *pFCPSessionEstablishmentResponse*

**    6.3.2 SendPfcpSessionModificationRequest 函数**

对于已经存在的会话，修改的情况

### 7. HandlePfcpSessionEstablishmentResponse 函数 ###

从 UPF 收到回复请求，类型为 *PFCP\_SESSION\_ESTABLISHMENT\_RESPONSE*

func HandlePfcpSessionEstablishmentResponse(msg *pfcpUdp.Message) {
    	rsp := msg.PfcpMessage.Body.(pfcp.PFCPSessionEstablishmentResponse)
    	logger.PfcpLog.Infoln("In HandlePfcpSessionEstablishmentResponse")
    
    	SEID := msg.PfcpMessage.Header.SEID
    	smContext := smf_context.GetSMContextBySEID(SEID)

###    7.1 BuildGSMPDUSessionEstablishmentAccept 函数 ###

实例化 NAS 消息，填充 GSM 消息，设置类型为 *MsgTypePDUSessionEstablishmentAccept*，PDUSessionEstablishmentAccept 结构体如下

type PDUSessionEstablishmentAccept struct {
    	nasType.ExtendedProtocolDiscriminator
    	nasType.PDUSessionID
    	nasType.PTI
    	nasType.PDUSESSIONESTABLISHMENTACCEPTMessageIdentity
    	nasType.SelectedSSCModeAndSelectedPDUSessionType
    	nasType.AuthorizedQosRules
    	nasType.SessionAMBR
    	*nasType.Cause5GSM
    	*nasType.PDUAddress
    	*nasType.RQTimerValue
    	*nasType.SNSSAI
    	*nasType.AlwaysonPDUSessionIndication
    	*nasType.MappedEPSBearerContexts
    	*nasType.EAPMessage
    	*nasType.AuthorizedQosFlowDescriptions
    	*nasType.ExtendedProtocolConfigurationOptions
    	*nasType.DNN
    }

**     7.1.1 填充 PDUSessionEstablishmentAccept 结构体**

>  *       PDUSessionID
>  *       消息类型 MsgTypePDUSessionEstablishmentAccept
>  *       PTI：0x00
>  *       PDU 会话类型：这里实现为 IPv4
>  *       SSC 模式，这里设置为 1
>  *       SessionAMBR
>  *       QOS 规则
>  *      【PDU Address】

pDUSessionEstablishmentAccept.SetPDUSessionID(uint8(smContext.PDUSessionID))
    pDUSessionEstablishmentAccept.SetMessageType(nas.MsgTypePDUSessionEstablishmentAccept)
    pDUSessionEstablishmentAccept.SetExtendedProtocolDiscriminator(nasMessage.Epd5GSSessionManagementMessage)
    pDUSessionEstablishmentAccept.SetPTI(0x00)
    pDUSessionEstablishmentAccept.SetPDUSessionType(smContext.SelectedPDUSessionType)
    pDUSessionEstablishmentAccept.SetSSCMode(1)
    pDUSessionEstablishmentAccept.SessionAMBR = nasConvert.ModelsToSessionAMBR(smContext.SessionRule.AuthSessAmbr)
    pDUSessionEstablishmentAccept.SessionAMBR.SetLen(uint8(len(pDUSessionEstablishmentAccept.SessionAMBR.Octet)))

###    7.2 BuildPDUSessionResourceSetupRequestTransfer 函数 ###

实例化 PDUSessionResourceSetupRequestTransfer 对象，主要包含的是 IE 信息元素

func BuildPDUSessionResourceSetupRequestTransfer(ctx *SMContext) (buf []byte, err error) {
    	var UpNode = ctx.Tunnel.UpfRoot.UPF
    	var teidOct = make([]byte, 4)
    	binary.BigEndian.PutUint32(teidOct, ctx.Tunnel.UpfRoot.UpLinkTunnel.TEID)
    
    	resourceSetupRequestTransfer := ngapType.PDUSessionResourceSetupRequestTransfer{}

PDUSessionResourceSetupRequestTransferIEs 结构定义如下：

>     type PDUSessionResourceSetupRequestTransferIEs struct {
>        Id          ProtocolIEID
>        Criticality Criticality
>        Value       PDUSessionResourceSetupRequestTransferIEsValue `aper:"openType,referenceFieldName:Id"`
>     }

-  UL NG-U UP TNL Information

-   PDU Session Type

-   QoS Flow Setup Request List，use Default 5qi, arp

###    7.3 实例化 N1N2MessageTransferRequest ###

官方 3GPP 提供的 openapi 生成，包括 PDU 会话 ID，包括 N1，N2 消息，N2 信息包括 Snssai

n1n2Request := models.N1N2MessageTransferRequest{}
    n1n2Request.JsonData = &models.N1N2MessageTransferReqData{
    	PduSessionId: smContext.PDUSessionID,
    	N1MessageContainer: &models.N1MessageContainer{
    		N1MessageClass:   "SM",
    		N1MessageContent: &models.RefToBinaryData{ContentId: "GSM_NAS"},
    	},
    	N2InfoContainer: &models.N2InfoContainer{
    		N2InformationClass: models.N2InformationClass_SM,
    		SmInfo: &models.N2SmInformation{
    			PduSessionId: smContext.PDUSessionID,
    			N2InfoContent: &models.N2InfoContent{
    				NgapIeType: models.NgapIeType_PDU_RES_SETUP_REQ,
    				NgapData: &models.RefToBinaryData{
    					ContentId: "N2SmInformation",
    				},
    			},
    			SNssai: smContext.Snssai,
    		},
    	},
    }
    n1n2Request.BinaryDataN1Message = smNasBuf
    n1n2Request.BinaryDataN2Information = n2Pdu

###     7.4 SMF 发送消息到 AMF ###

/ue-contexts/\{ueContextId\}/n1-n2-messages

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 5][] SMF->AMF， N1N2MessageTransfer

# 8. N1N2MessageTransfer（SMF->AMF）步骤 11 #

包裹 N1N2MessageTransfer，设置类型为 *EventN1N2MessageTransfer*，丢进 channel 进行处理

###    HandleN1N2MessageTransferRequest 函数 ###

由 SMF 向 AMF 发送的 N2 信息 ngap 类型为 *NgapIeType\_PDU\_RES\_SETUP\_REQ*

// TS23502 4.2.3.3, 4.2.4.3, 4.3.2.2, 4.3.2.3, 4.3.3.2, 4.3.7
    func HandleN1N2MessageTransferRequest(request *http_wrapper.Request) *http_wrapper.Response {
    
    	logger.ProducerLog.Infof("Handle N1N2 Message Transfer Request")
    
    	n1n2MessageTransferRequest := request.Body.(models.N1N2MessageTransferRequest)
    	ueContextID := request.Params["ueContextId"]
    	reqUri := request.Params["reqUri"]

###    8.1 N1N2MessageTransferProcedure 函数 ###

根据 N1 N2 消息进行处理

// There are 4 possible return value for this function:
    //   - n1n2MessageTransferRspData: if AMF handle N1N2MessageTransfer Request successfully.
    //   - locationHeader: if response status code is 202, then it will return a non-empty string location header for
    //     response
    //   - problemDetails: if AMF reject the request due to application error, e.g. UE context not found.
    //   - TransferErr: if AMF reject the request due to procedure error, e.g. UE has an ongoing procedure.
    // see TS 29.518 6.1.3.5.3.1 for more details.
    func N1N2MessageTransferProcedure(ueContextID string, reqUri string,
    	n1n2MessageTransferRequest models.N1N2MessageTransferRequest) (
    	n1n2MessageTransferRspData *models.N1N2MessageTransferRspData,
    	locationHeader string, problemDetails *models.ProblemDetails,
    	transferErr *models.N1N2MessageTransferError)

###    8.2 N2 信息类型为 NgapIeType\_PDU\_RES\_SETUP\_REQ ###

AMF 将透传 N1 N2 消息，如果存在 N1 消息，BuildDLNASTransport 函数将创建 gmm 消息，类型为 ***MsgTypeDLNASTransport***，SendPDUSessionResourceSetupRequest 函数构建 NGAP 消息

case models.NgapIeType_PDU_RES_SETUP_REQ:
    	logger.ProducerLog.Debugln("AMF Transfer NGAP PDU Resource Setup Req from SMF")
    	var nasPdu []byte
    	var err error
    	if n1Msg != nil {
    		pduSessionId := uint8(smInfo.PduSessionId)
    		nasPdu, err = gmm_message.BuildDLNASTransport(ue, nasMessage.PayloadContainerTypeN1SMInfo, n1Msg,
    			pduSessionId, nil, nil, 0)
    		if err != nil {
    			logger.HttpLog.Errorln(err.Error())
    		}
    	}
    
    	if ue.RanUe[anType].SentInitialContextSetupRequest {
    		list := ngapType.PDUSessionResourceSetupListSUReq{}
    		ngap_message.AppendPDUSessionResourceSetupListSUReq(&list, smInfo.PduSessionId, *smInfo.SNssai, nasPdu, n2Info)
    		ngap_message.SendPDUSessionResourceSetupRequest(ue.RanUe[anType], nil, list)
    	} else {
    		list := ngapType.PDUSessionResourceSetupListCxtReq{}
    		ngap_message.AppendPDUSessionResourceSetupListCxtReq(&list, smInfo.PduSessionId, *smInfo.SNssai, nil, n2Info)
    		ngap_message.SendInitialContextSetupRequest(ue, anType, nasPdu, &list, nil, nil, nil)
    		ue.RanUe[anType].SentInitialContextSetupRequest = true
    	}

**    8.2.1 AppendPDUSessionResourceSetupListSUReq 函数**

**PDUSessionResourceSetupListSUReq** 结构填充 PDU 会话 ID，SNSSAI，nasPDU

**    8.2.2 SendPDUSessionResourceSetupRequest 函数 *****N2 PDU Session Request（AMF->RAN） 步骤  12***

为多个 PDU 会话和对应的 Qos 流在 Uu 和 NG-U 分配资源，来给 UE 建立相应的 DRB，这个流程使用 UE 相关的信令，由 AMF 发起 *PDU SESSION RESOURCE SETUP REQUEST *消息到 NG-RAN 节点

BuildPDUSessionResourceSetupRequest 函数实例化 NGAPPDU 对象

Present 设置为 *NGAPPDUPresentInitiatingMessage，填充的为 *initiatingMessage，ProcedureCode 设置为 *ProcedureCodePDUSessionResourceSetup  *InitiatingMessagePresentPDUSessionResourceSetupRequest

type NGAPPDU struct {
    	Present             int
    	InitiatingMessage   *InitiatingMessage
    	SuccessfulOutcome   *SuccessfulOutcome
    	UnsuccessfulOutcome *UnsuccessfulOutcome
    }

-  （IE）AMF UE NGAP ID

ProtocolIEIDAMFUENGAPID -->  PDUSessionResourceSetupRequestIEsPresentAMFUENGAPID

-   （IE）RAN UE NGAP ID

ProtocolIEIDRANUENGAPID -->  PDUSessionResourceSetupRequestIEsPresentRANUENGAPID

-   （IE）Ran Paging Priority (optional)

-   （IE）NAS-PDU (optional)

ProtocolIEIDNASPDU -->  PDUSessionResourceSetupRequestIEsPresentNASPDU

-   （IE）PDU Session Resource Setup Request list

ProtocolIEIDPDUSessionResourceSetupListSUReq -->  PDUSessionResourceSetupRequestIEsPresentPDUSessionResourceSetupListSUReq

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3pob25nbGluemhhbmc_size_16_color_FFFFFF_t_70 6][]

###     ###

### 9. N2 PDU Session Response （RAN -> AMF）步骤 14     ###

NGAP 消息类型为 NGAPPDUPresentSuccessfulOutcome，填充数据结构为 SuccessfulOutcome，设置为 ProcedureCodePDUSessionResourceSetup，SuccessfulOutcomePresentPDUSessionResourceSetupResponse

AMF 收到 N2 PDU Session Response 进行处理，定位函数为 HandlePDUSessionResourceSetupResponse，包括更新到 SMF （步骤 15） Nsmf\_PDUSession\_UpdateSMContextRequest  /sm-contexts/\{smContextRef\}/modify，类型为 *N2SmInfoType\_PDU\_RES\_SETUP\_RSP*

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
    		}
    	}
    }

###    9.1 BuildUpdateSmContextRequset 函数 ###

实例化 SmContextUpdateData

func BuildUpdateSmContextRequset(ue *amf_context.AmfUe, present UpdateSmContextPresent, pduSessionId int32, param updateSmContextRequsetParam) (updateData models.SmContextUpdateData) {
    	smContext := ue.SmContextList[pduSessionId]
    	context := amf_context.AMF_Self()
    	switch present {
    
    	case UpdateSmContextPresentOnlyN2SmInfo:
    		updateData.N2SmInfoType = param.n2SmType
    		updateData.N2SmInfo = new(models.RefToBinaryData)
    		updateData.N2SmInfo.ContentId = "N2SmInfo"
    		updateData.UeLocation = &ue.Location
    	}
    	return
    }

# 10. Nsmf\_PDUSession\_UpdateSMContext request (步骤 15) #

UpdateSmContext 函数设置消息类型为 PDUSessionSMContextUpdate，丢进 channel 处理，定位到函数 HandlePDUSessionSMContextUpdate

switch smContextUpdateData.N2SmInfoType {
    case models.N2SmInfoType_PDU_RES_SETUP_RSP:
    	pdrList = []*smf_context.PDR{}
    	farList = []*smf_context.FAR{}
    
    	for _, dataPath := range tunnel.DataPathPool {
    
    		if dataPath.Activated {
    			ANUPF := dataPath.FirstDPNode
    			DLPDR := ANUPF.DownLinkTunnel.PDR
    
    			DLPDR.FAR.ApplyAction = pfcpType.ApplyAction{Buff: false, Drop: false, Dupl: false, Forw: true, Nocp: false}
    			DLPDR.FAR.ForwardingParameters = &smf_context.ForwardingParameters{
    				DestinationInterface: pfcpType.DestinationInterface{
    					InterfaceValue: pfcpType.DestinationInterfaceAccess,
    				},
    				NetworkInstance: []byte(smContext.Dnn),
    			}
    
    			DLPDR.State = smf_context.RULE_UPDATE
    			DLPDR.FAR.State = smf_context.RULE_UPDATE
    
    			pdrList = append(pdrList, DLPDR)
    			farList = append(farList, DLPDR.FAR)
    		}
    
    	}
    
    	err = smf_context.HandlePDUSessionResourceSetupResponseTransfer(body.BinaryDataN2SmInformation, smContext)

参考:

github free5gc 3.0.4

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