Patent Publication Number: US-2022232369-A1

Title: Mapping a user plane function to a user equipment

Description:
TECHNICAL FIELD 
     This relates to a 5G cellular communication network, and in particular to operation of systems for policy, charging and analytics. 
     BACKGROUND 
     The 5G network architecture defines a Network Data Analytics Function (NWDAF), which collects data from network functions, retrieves information from data repositories, and provides analytics on demand to other network functions of the 5G core network. 
     In general, the NWDAF subscribes to a network function, so that it is notified about the occurrence of certain events. The NWDAF thus collects data from the network functions, based on exposure services that are offered by the network functions. 
     It has been proposed that the User Plane Function (UPF) should implement an event exposure service, but there is no mechanism for a network function, such as the NWDAF, to discover the UPF that is associated to a certain user. Moreover, a user that is initially assigned to one UPF, may be later assigned to another UPF. Thus, even if the UPF implements an event exposure service, there is no way for the NWDAF to ensure that it obtains notifications from the relevant UPF relating to that specific user. 
     SUMMARY 
     According to an aspect of the present disclosure, there is provided a method of operation of a network function in a telecommunications network, the method comprising:
         for a communication session, storing information identifying a User Plane Function associated with said communication session.       

     According to an aspect of the present disclosure, there is provided A method of operation of a network function in a telecommunications network, the method comprising:
         in response to initiation of a data session, sending a User Plane Function discovery request to a Network Repository Function, NRF;   receiving a response from the NRF, said response containing information identifying at least one User Plane Function, UPF, and information indicating that at least one identified UPF supports an event exposure service;   selecting an identified UPF; and   registering the selected UPF in a network function, with information identifying the session, information identifying the selected UPF, and information indicating that the selected UPF supports the event exposure service.       

     According to an aspect of the present disclosure, there is provided a method of operation of a network function in a telecommunications network, the method comprising:
         sending a query to a second network function, wherein the query contains information identifying a user;   receiving a response from the second network function, wherein the response contains information identifying a UPF allocated to the user; and   subscribing to an event exposure service of the UPF.       

     According to an aspect of the present disclosure, there is provided a method of operation of a network function in a telecommunications network, the method comprising: 
     sending a subscription request to a second network function, wherein the subscription request contains information identifying a user, and wherein the subscription request comprises a request to be notified in the event of a change in a UPF allocated to the user. 
     According to an aspect of the present disclosure, there is provided a method of operation of a network function in a telecommunications network, the method comprising: 
     registering with a Network Repository Function, NRF, wherein the step of registering with the NRF comprises sending an indication that the UPF supports the event exposure service, and information identifying at least one event for which the event exposure service is supported. 
     According to an aspect of the present disclosure, there is provided a method of operation of a network function in a telecommunications network, the method comprising:
         receiving a request for registration from a User Plane Function, UPF, wherein the request comprises an indication that the UPF supports the event exposure service, and information identifying at least one event for which the event exposure service is supported.       

     According to further aspects of the present disclosure, there are provided network nodes, comprising a processor configured for performing a method according to any of the other aspects. 
     According to further aspects of the present disclosure, there are provided computer program products, comprising code configured for causing a suitably programmed processor to perform a method according to any of the other aspects. 
     Thus, there is provided a mechanism and a node that provide the means for a network function to subscribe to event exposure for a specific user and/or session, when that user is assigned to a UPF. The mechanism allows the SMF to provide information about which user/session is assigned to each UPF. 
     This has the advantage that it allows a network function to subscribe to an Event Exposure service in a UPF, generally using existing subscription mechanisms, and therefore allows greater functionality in a network function such as a NWDAF or NEF. 
     Further, embodiments have the advantage that event exposure can be continued, even in the event of re-assignment of the subscriber/session to a different UPF. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a part of a network architecture. 
         FIG. 2  illustrates a part of a network architecture. 
         FIG. 3  illustrates a connection between network functions. 
         FIG. 4  is a signalling diagram illustrating operation of an event exposure service. 
         FIG. 5  is a flow chart, illustrating methods in accordance with the disclosure. 
         FIG. 6  is a signalling diagram, illustrating a first method as shown in  FIG. 5 . 
         FIG. 7  is a signalling diagram, illustrating a second method as shown in  FIG. 5 . 
         FIG. 8  is a signalling diagram, illustrating a third method as shown in  FIG. 5 . 
         FIG. 9  is a signalling diagram, illustrating a fourth method as shown in  FIG. 5 . 
         FIG. 10  is a block schematic diagram, illustrating a form of a network node in accordance with the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a reference architecture  100  for a 5G network, as proposed by 3GPP, and in particular as disclosed in 3GPP TS 23.501 v16.0.2. 
     A User Equipment device (UE)  102  connects to a (Radio) Access Network ((R)AN)  104 . The (R)AN  104  connects to a User Plane Function (UPF)  106 , and hence to a Data Network (DN)  108 . 
     Other network nodes shown in  FIG. 1  are the Network Slice Selection Function (NSSF)  110 , Network Exposure Function (NEF)  112 , Network Repository Function (NRF)  114 , Policy Control Function (PCF)  116 , Unified Data Management (UDM)  118 , Application Function(s) (AF)  120 , Authentication Server Function (AUSF)  122 , Access and Mobility Management Function (AMF)  124 , and Session Management Function (SMF)  126 . 
     The network shown in  FIG. 1  operates in a generally conventional way, except as described in more detail below. 
       FIG. 2  shows an architecture  200  policy, charging and analytics in a 5G network, in accordance with the present invention. The architecture  200  shown in  FIG. 2  is generally as defined by 3GPP, except as described in more detail below. 
     In particular, this includes a Network Data Analytics Function (NWDAF)  202 , the operation of which is described in more detail below. Other network nodes shown in  FIG. 2  are the User Data Repository (UDR)  204 , the Network Exposure Function (NEF)  112 , Application Function(s) (AF)  120 , Policy Control Function (PCF)  116 , CHarging Function (CHF)  206 , Access and Mobility Management Function (AMF)  124 , and Session Management Function (SMF)  126 . 
     The User Plane Function (UPF)  106  connects to the other nodes through the Session Management Function (SMF)  126 . 
       FIG. 2  also shows a node not previously specified by 3GPP, referred to herein for the purposes of this disclosure only as a UE-UPF Binding Function (UBF)  222 . 
     The UE-UPF Binding Function (UBF)  222  is described herein, by way of illustration only, as a standalone node, but it can also be collocated with existing network functions (for example the SMF, or the UDM, or any other convenient node). The UBF may be a centralized node. Alternatively, the UBF can be distributed, in which case it may provide a single point of access. The UBF may be provided as a 3GPP network function. Alternatively, the UBF may be provided as an independent Service-Based Architecture (SBA) service. 
     As mentioned above, the Network Data Analytics Function (NWDAF)  202  is part of the architecture specified in TS 23.501 and uses the mechanisms and interfaces specified for the 5G core network and for Operations, Administration and Maintenance (OAM). 
     The NWDAF interacts with different entities for different purposes. As one example, the NWDAF performs data collection based on event subscription, provided by network functions (NFs) of the 5G core network (for example the AMF, SMF, PCF, UDR, and NEF), by other application functions (AFs), and by OAM. As another example, the NWDAF retrieves information from data repositories, for example the UDR for subscriber-related information, the NRF for NF-related information, and the NSSF for slice-related information. As another example, the NWDAF provides, on demand, analytics to NFs of the 5G core network, AFs and OAM. 
       FIG. 3  shows the NWDAF  202  connected to a Network Function  302 , which may be any NF, for example one of the NFs mentioned above, in order to collect data from the NF. The NWDAF  202  belongs to the same Public Land Mobile Network (PLMN) where the network function  302  that notifies the data is located. 
       FIG. 3  shows the NWDAF  202  connected to the NF  302  by means of the Nnf interface, and this refers to the Event Exposure service of each NF. The Event Exposure service is invoked by the NWDAF in order to collect data for a particular context (based on notifications received for subscribed events), to cancel a subscription for data collection, and to get a specific report of data for a particular context. 
     The NWDAF subscribes to a NF or an AF to be notified at certain events, and then the NWADF receives a notification, with the relevant information, when the event occurs. 
     The NWDAF collects data from NFs/AFs based on the exposure services (specifically the Event Exposure Service) offered by network functions such as the AMF, SMF, UDM, PCF, NRF and AF via the NEF. 
     This exposure service is used directly by the NWDAF in order to retrieve data for individual UEs or UE groups (for example based on UE location) from each NF (or AF). 
       FIG. 4  is a signalling diagram, taken from 3GPP TS 23.288 v0.4.0, illustrating a procedure used by the NWDAF to subscribe to, or unsubscribe from, the Event Exposure service at an NF or AF, in order to manage notifications for data collection on one or more relevant event. 
     Specifically, as shown in message  401  in  FIG. 4 , the NWDAF may subscribe (or unsubscribe) message to the Event Exposure service in any NF(s) or AF(s). 
     The message  401  may use the framework defined in 3GPP TS 23.502 clause 4.15. This framework supports the possibility for the NWDAF to use the subscription message to indicate:
         one or multiple Event ID(s),as defined in TS 23.502 clause 4.15.1;   the objects targeted by the Events, as defined in TS 23.502 clause 4.15.1 (within a subscription, all Event IDs are associated with the same target of event reporting, and in the case of the NWDAF, the objects can be one or more UE, one or more UE group, or any UE);   Event Filter Information, as defined in TS 23.502 clause 4.15.1, providing Event Parameter Types and Event Parameter Value(s) to be matched against;   a Notification Target Address and a Notification Correlation ID, as defined in TS 23.502 clause 4.15.1, allowing the NWDAF to correlate notifications received from the NF with this subscription;   Event Reporting Information, as described in TS 23.502 Table 4.15.1-1; and/or   an Expiry time as defined in TS 23.502 clause 4.15.1.       

     As shown by message  402 , and NF/AF receiving a subscription message  401  may then provide notifications to the NWDAF. The notification message  402  may contain, in addition to the Event being reported, some dedicated information being reported for this event, such as:
         the Notification Correlation Information provided by the NWDAF in its request;   the Target ID, for example the ID (such as a SUbscription Permanent Identifier (SUPI)) of a UE, when applicable to the event, and, if available, a Generic Public Subscription Identifier (GPSI); and/or   a time-stamp.       

     The document 3GPP TS 23.288 v0.4.0 defines that the NWDAF collects data from NFs using their Event Exposure services. The same document also defines some data that is produced by the UPF (for example bit rates, delays, packet retransmissions, etc.). It has also been proposed that the UPF should implement an Event Exposure service. 
     Implementation of the Event Exposure service in the UPF entails certain problems. For example, the events that are exposed by the UPF can be per user (that is, associated to a specific user-ID), but there is no procedure for a NF (for example the NWDAF) that wants to consume the Event Exposure service in the UPF to discover the UPF that is associated to a certain user for a certain Event-ID. As another example, when a certain user is initially assigned to a UPF, it may be later assigned to another UPF. This means that, if the UPF implements an Event Exposure service, there is no mechanism for a NF (for example the NWDAF) that has subscribed to the Event Exposure service for a specific user to ensure the persistence of the subscription if the user is assigned to a different UPF. 
       FIG. 5  is a flow chart, illustrating methods in accordance with the present disclosure. 
     At step  502  of the method, the UPF  106  registers with the Network Repository Function (NRF)  114 . 
     The UPF registration process in the NRF is shown in more detail in  FIG. 6 . 
     Specifically, the existing NRF registration operation from the UPF is extended to allow the Event Exposure service, and the Event-IDs supported by that service, to be registered. One or more Event Exposure services could be registered by a single UPF, with each Event Exposure service supporting one or multiple Event-IDs. 
     Thus, in message  601 , the UPF invokes the Nnrf_NFManagement NFRegister Request, and this request includes the NF profile, an indication that the UPF supports the Event Exposure service, and the list of Event-IDs that are supported by the Event Exposure service for this UPF. 
     In message  602 , the NRF acknowledges the registration to the UPF. 
     Returning to  FIG. 5 , at step  504 , the SMF discovers the supported Event Exposure service, and registers this in the new UBF network function. 
     The SMF discovery of the supported Event Exposure service, and its registration in the UBF, is shown in more detail in  FIG. 7 . 
     Thus, in message  701 , a network function, for example the AMF, invokes Nsmf_PDUSession_CreateSMContext Request at the SMF, including the SUbscription Permanent Identifier (SUPI). 
     At step,  702 , the SMF performs its conventional subscription data retrieval, Protocol Data Unit (PDU) session, and SMF registration procedures. 
     At step  703 , the SMF performs its conventional PDU session authentication and Policy association procedures. 
     Then, in message  704 , the SMF sends a UPF discovery request to the NRF invoking the Nnrf_NFDiscovery Request (with NF Type=UPF). 
     In message  705 , the NRF responds to the SMF including a list of tuples. As is conventional, each tuple includes the UPF-ID, and the UPF IP address. 
     However, in the case illustrated here, where the UPF registration process in the NRF has stored the information that the UPF supports the Event Exposure service, message  705  also contains an explicit or implicit indication that the UPF supports the Event Exposure service, and may also contain a list of supported Event-IDs. 
     At step  706 , the SMF selects the UPF from among the list received from the NRF. 
     Then, in message  707 , the SMF registers the user-UPF binding in the new network function, the UBF  222 , invoking Nubf_Register. This registration includes a user ID (for example the SUPI) and/or a PDU Session ID, and also includes a list of tuples. Each tuple may include some or all of: the UPF ID; the UPF IP address; and a list of Event-IDs that are supported by the Event Exposure service for this UPF. The list of supported Event-IDs may be specific to a certain PDU session and/or to a certain user. 
     In message  708 , the UBF acknowledges the registration. 
     At step  709 , the establishment of the PDU session is completed. 
     Returning to  FIG. 5 , the stored indication about the supported Event Exposure service can be used in different ways. 
     For example, a network function can obtain notifications about events. 
     In step  510 , the network function obtains information from the UBF. This is shown in more detail in  FIG. 8 . 
       FIG. 8  depicts the signal flow, by which one particular network function, namely the NWDAF, subscribes to obtain information about events that are relevant to a specific user. The use of the UBF means that the network function is able to identify the relevant UPF.  FIG. 8  shows a process in which the network function is the NWDAF, but a generally similar process may be performed by any suitable network function, for example the NEF. 
     At step  801 , the NWDAF receives a request for an analytic by means of the existing Nnwdaf_EventsSubscription Subscribe or Nnwdaf_Analyticslnfo Request service operations, including the SUPI of the user of interest, and the Analytic-ID. 
     The NWDAF needs to know the UPF associated to the user having that SUPI, and so, in message  802 , it queries the UBF invoking Nubf_Get, including the SUPI and the Event-ID of the desired event. The Event-ID(s) needed for a specific Analytic-ID are known by the NWDAF. 
     In message  803 , the UBF responds to the NWDAF, including the UPF IP address and/or the PDU session ID for the user identified by that SUPI. 
     Thus, the network function obtains information from the UBF, and that information identifies the UPF associated with the user of interest. 
     In step  512  of the process shown in  FIG. 5 , the network function subscribes with the UPF identified in the received information. 
       FIG. 8  shows the subscription step in more detail. 
     Thus, in message  804 , the NWDAF subscribes to the Event Exposure service of the previously identified UPF, by invoking the Nupf_EventExposure Subscribe. This message includes the SUPI and/or a PDU Session ID. In particular, if the UPF does not handle SUPIs, the PDU session ID can be used instead. In addition, the message  804  also includes other information relevant to the subscription, namely the Event-ID of the event(s) that the NWDAF is interested in, and any Event filters. 
     In message  805 , the UPF acknowledges the subscription. 
     Thus, the network function subscribes with the UPF identified in the information that was received in step  510 . 
     In step  514  of the process shown in  FIG. 5 , the UPF notifies the network function of a relevant event. 
       FIG. 8  shows the notification step in more detail. 
     Thus, when a relevant event (as defined in the message  804 ) occurs, in message  806  the UPF reports the event to the NWDAF. Specifically, it invokes Nupf_EventExposure Notify, including the SUPI and/or PDU session ID (depending on the which of these identifies can be handled by the UPF), and information about the Event. 
     The NWDAF is then able to use the received information about the Event in generating the analytic requested in step  801 . 
     Thus,  FIG. 8  shows how the network function, in the illustrated example the NWDAF, retrieves from the UBF the IP address of the UPF that is allocated to a certain user for a certain Event-ID. Using this information, the network function subscribes to the Event Exposure service in the UPF for the or each relevant subscriber, and for one or multiple Event-IDs. 
     Although, in the illustrated example, the network function is the NWDAF, there exists the possibility of having the NEF as an intermediary. In this case, the NWDAF subscribes to the Event Exposure service of the NEF, the NEF interacts with the UBF to find the UPF associated with the user, and in turn the NEF subscribes to the Event Exposure service of the UPF. 
     Returning to  FIG. 5 , this also shows how the stored indication about the UPF that is associated with a UE can be updated in the event of a change of UPF. 
     In step  520  of the process shown in  FIG. 5 , a network function subscribes with the UBF. 
       FIG. 9  shows the subscription step in more detail. 
     Specifically, the NWDAF sends message  901  to the UBF, subscribing to receive UPF allocation changes by invoking Nubf_Subscribe, with the message including the SUPI and/or the PDU Session ID, and also specifying that the Data type, about which it wishes to receive information, is the allocated UPF. 
     In message  902  to the NWDAF, the UBF acknowledges the subscription. 
     Thus, the NWDAF has subscribed with the UBF, identifying a user and/or a session, and requesting to be notified when there is any change to the UPF allocated to that user or session. 
     Then, in step  522  of the process shown in  FIG. 5 , a SMF updates the UBF. 
       FIG. 9  shows the update step in more detail. 
     Specifically, when there is a change in the UPF that is allocated to the user and/or session identified by the NWDAF in message  901 , the SMF invokes the Nubf_Update message  903 , including the SUPI and/or the PDU Session ID. The message also includes information about the newly allocated UPF. For example, the message may include the UPF ID of the newly allocated UPF, and its IP address. 
     Thus, the UBF is updated with the new information. 
     In step  524  of the process shown in  FIG. 5 , the UBF notifies the network function about the newly allocated UPF. 
       FIG. 9  shows the notification step in more detail. 
     Specifically, when the UBF is notified that there has been a change in the UPF that is allocated to the user and/or session identified by the NWDAF in message  901 , the UBF sends a notification  904  to the NWDAF, invoking the Nubf_Notification message. This includes the SUPI and/or the PDU Session ID. The message also includes some or all of the information received from the SMF about the newly allocated UPF. For example, the message  904  may include the UPF ID of the newly allocated UPF, and its IP address. 
     Thus, the network function is notified about the change of UPF allocated to a user of interest. 
     In step  526  of the process shown in  FIG. 5 , the NF reacts to this change. 
       FIG. 9  shows the reaction step in more detail. 
     Specifically, in this illustrated example, the NWDAF unsubscribes to the old UPF invoking the Nupf_EventExposure_UnSubscribe message  905 . The old UPF acknowledges the un-subscription in message  906 . 
     Then, the NWDAF subscribes to the new UPF invoking the Nupf_EventExposure Subscribe message  907 . This message includes the SUPI and/or a PDU Session ID. In particular, if the UPF does not handle SUPIs, the PDU session ID can be used instead. In addition, the message  804  also includes other information relevant to the subscription, namely the Event-ID of the event(s) that the NWDAF is interested in, and any Event filters. 
     In message  908 , the new UPF acknowledges the subscription. 
     Thus, this allows the persistence of the subscriptions to the Event Exposure service of the UPF, in the event of UPF re-selection. Specifically, the network function subscribes to the UBF to receive notifications about UPF reselection, and, when the UBF is updated by the SMF, the network function receives a notification, and is then able to update its subscriptions to the event exposure functionality when the UPF is reselected for the user. 
       FIG. 10  is a block schematic diagram, illustrating a form of a network node  1000  in accordance with the disclosure. 
     The network node  1000  may implement any of the network functions described herein, such as the Network Slice Selection Function (NSSF)  110 , Network Exposure Function (NEF)  112 , Network Repository Function (NRF)  114 , Policy Control Function (PCF)  116 , Unified Data Management (UDM)  118 , Application Function(s) (AF)  120 , Authentication Server Function (AUSF)  122 , Access and Mobility Management Function (AMF)  124 , Session Management Function (SMF)  126 , Network Data Analytics Function (NWDAF)  202 , User Data Repository (UDR)  204 , CHarging Function (CHF)  206 , and/or the UE-UPF Binding Function (UBF)  222 . 
     The network node  1000  has a communications module  1002 , allowing communication with any other network node, for example in the Radio Access Network or in the Core Network, over any suitable wired or wireless interface. 
     The network node  1000  also has a data processing and control unit  1004 , which includes one or more processor  1006  and one or more memory  1008 . The memory  1008  may store data and/or programs, and the processor  1006  may operate under the control of the stored program(s) to perform any of the methods described herein. 
     There is thus provided a mechanism to allow a network function to take advantage of event exposure in a UPF network function. 
     ABBREVIATIONS 
     The following abbreviations and acronyms are used in this document. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Abbreviation 
                 Explanation 
               
               
                   
                   
               
             
            
               
                   
                 ABR 
                 Adaptive Bit Rate 
               
               
                   
                 AMF 
                 Access and Mobility Management Function 
               
               
                   
                 AP 
                 Access Point 
               
               
                   
                 ARR 
                 Analytics Reporting Rule 
               
               
                   
                 BAR 
                 Buffering Action Rule 
               
               
                   
                 CP 
                 Control Plane 
               
               
                   
                 CUPS 
                 Control User Plane Separation 
               
               
                   
                 eNB 
                 enhanced Node B 
               
               
                   
                 FAR 
                 Forwarding Action Rule 
               
               
                   
                 KPI 
                 Key Performance Indicator 
               
               
                   
                 MBR 
                 Maximum Bit Rate 
               
               
                   
                 NEF 
                 Network Exposure Function 
               
               
                   
                 NSSF 
                 Network Slice Selection Function 
               
               
                   
                 NWDAF 
                 Network Data Analytics Function 
               
               
                   
                 ONAP 
                 Open Network Automation Protocol 
               
               
                   
                 OTT 
                 Over the Top 
               
               
                   
                 PCF 
                 Policy Control Function 
               
               
                   
                 PDR 
                 Packet Detection Rule 
               
               
                   
                 PFCP 
                 Packet Forwarding Control Protocol 
               
               
                   
                 QER 
                 QoS Enforcement Rule 
               
               
                   
                 QoE 
                 Quality of Experience 
               
               
                   
                 RL 
                 Reinforcement Learning 
               
               
                   
                 SMF 
                 Session Management Function 
               
               
                   
                 UDM 
                 Unified Data Management 
               
               
                   
                 UE 
                 User Equipment 
               
               
                   
                 UPF 
                 User Plane Function 
               
               
                   
                 URR 
                 Usage Reporting Rule