WO2024110057A1

WO2024110057A1 - Extensions related to upf buffering

Info

Publication number: WO2024110057A1
Application number: PCT/EP2022/087994
Authority: WO
Inventors: Yong Yang; Maria Luisa Mas Rosique; Miguel Angel MUÑOZ DE LA TORRE ALONSO
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2022-11-24
Filing date: 2022-12-29
Publication date: 2024-05-30
Anticipated expiration: 2025-05-24

Abstract

An aspect provides a method of operating a user plane network node (114) in a communication network. The user plane network node (114) has a buffer for storing user plane traffic. The method comprises sending (601), to another network node (104; 110) in the communication network, a first message (202; 206; 502) comprising information about a size of the buffer and/or a status of the buffer.

Description

Extensions related to UPF buffering

Technical Field

This disclosure relates to user plane functions in a communication network, and in particular to a status of a buffer of a user plane function.

In 5^th Generation (5G) cellular networks, a service-based architecture is used for the 5G core (5GC) network, which is broken down into communicating services known as Network Functions (NFs). Fig. 1 illustrates a 5G system reference architecture 101 showing service-based interfaces used within the Control Plane (CP). It will be appreciated that not all NFs are depicted. Service-based interfaces are represented in the format Nxyz and point to point interfaces in the format Nx. The reference architecture 101 comprises a Network Slice Selection Function (NSSF) 102 that has a Nnssf interface, a Network Exposure Function (NEF) 103 that has a Nnef interface, a Network Repository Function (NRF) 104 that has a Nnrf interface, a Policy Control Function (PCF) 105 that has a Npcf interface, a Unified Data Management (UDM) 106 that has a Nudm interface, an Application Function (AF) 107 that has a Naf interface, an Authentication Server Function (AUSF) 108 that has a Nausf interface, an Access and Mobility Management Function (AMF) 109 that has a Namf interface, and a SMF 110 that has a Nsmf interface.

The AMF 109 has an N1 interface to a user equipment (UE) 112, and an N2 interface to an access network (AN) 113 (which can be a radio AN, RAN). The SMF 110 has an N4 interface to a User Plane Function (UPF) 114. The interface between the R(AN) 113 and the UPF 114 is the N3 interface, and the interface between the UPF 114 and a Data Network 115 is the N6 interface.

The relevant architectural aspects for the present disclosure are the NRF 104, the SMF 110 and the UPF 114.

The NRF 104 provides registration and discovery capabilities among the different NFs within the 5GC. The NRF 104 supports service discovery function, i.e. the NRF 104 receives NF Discovery Requests from NF instances, and provides information about the discovered NF instances. The NRF 104 also maintains the NF profiles of available NF instances and their supported services.

The SMF 110 supports different functionality, e.g. session establishment, modify and release, and policy related functionalities like termination of interfaces towards policy control functions, charging data collection, support of charging interfaces and control and coordination of charging data collection at a UPF 114. As a particular example, the SMF 110 receives Policy Charging and Control (PCC) rules from a PCF 105 and configures the UPF 114 accordingly through N4 reference point (a packet flow control protocol (PFCP)).

The UPF 114 supports the handling of user plane traffic based on the rules received from the SMF 110, for example packet inspection and different enforcement actions such as Quality of Service (QoS) handling.

A UPF 114 will be selected for a Protocol Data Unit (PDU) session. According to the Third Generation Partnership Project (3GPP) Technical Standard (TS) 23.501 v17.6.0 (sections 6.3.3.2 and 6.3.3.3), UPF selection for a PDU session can be based on the following information:

The following parameter(s) and information may be considered by the SMF 110 for UPF selection and reselection:

• UPF's dynamic load.

• UPF's relative static capacity among UPFs supporting the same Data Network Name (DNN).

• UPF location available at the SMF.

• UE location information.

• Capability of the UPF and the functionality required for the particular UE session: an appropriate UPF can be selected by matching the functionality and features required for an UE.

• Data Network Name (DNN).

• PDU Session Type (i.e. IPv4, IPv6, 1 Pv4v6, Ethernet Type or Unstructured Type) and if applicable, the static Internet Protocol (IP) address/prefix.

• Session and Service Continuity (SSC) mode selected for the PDU Session.

• UE subscription profile in UDM.

• Data Network Access Identifier (DNAI) as included in the PCC Rules

• Local operator policies.

• Single - Network Slice Selection Assistance Information (S-NSSAI).

• Access technology being used by the UE.

• Information related to user plane topology and user plane terminations, that may be deduced from: o Access Network (AN)-provided identities (e.g. CelllD, Tracking Area Identity (TAI)), available UPF(s) and DNAI (s);

• Information regarding the user plane interfaces of UPF(s). This information may be acquired by the SMF using N4;

• Information regarding the N3 User Plane termination(s) of the AN serving the UE. This may be deduced from AN-provided identities (e.g. CelllD, TAI);

• Information regarding the N9 User Plane term! nation (s) of UPF(s) if needed;

• Information regarding the User plane termination(s) corresponding to DNAI(s).

In 3GPP TS 29.510 v17.6.0, section 6.1.6.2.2, the NF profile is defined as being composed of several attributes like IP address and/or Fully Qualified Domain Name (FQDN) of the NF, name of the NF and specific information depending on each NF. For example, upfinfo is defined in 3GPP TS 29.510 v17.6.0 at section 6.1.6.2.13.

Summary

There currently exist certain challenge(s).

Firstly, the UPF supports downlink (DL) buffering for user traffic (e.g. when UE is in idle mode). Recently, as part of Release 17 (Rel17) enhancements for Edge Computing, it has been proposed to add UPF support for uplink (UL) buffering. This applies mostly to edge computing scenarios during Edge Application Server (EAS) relocation. These new UPF buffering scenarios imply that more UPF resources (in terms of memory) need to be allocated, and there is a higher probability of a UPF running out of space/resources.

Secondly, there is no current control mechanism defined by 3GPP for scenarios where the UPF is running out (or about to run out) of buffering space, either to prevent that from happening, or to react to that if that happens.

Certain aspects of the disclosure and their embodiments may provide solutions to these or other challenges. In short, the techniques described herein provide a mechanism which allows the network operator to be aware of, and control, scenarios when a UPF is running out of, or is about to run out of, buffering space.

Specific embodiments propose one or more of the following:

• Extensions in the NF profile(s) for a UPF in the NRF, e.g. to extend the upflnfo attribute, which includes: o A new feature flag indicating UPF support buffering control and reporting. o Buffering capacity, including both uplink capacity and downlink capacity. o Buffering status (reflecting the current available buffering capacity for both uplink and downlink). o In addition, the NF profile of UPF may be updated with current available buffering status.

• At or during a PFCP Association Setup procedure, the UPF indicates its support of a new capability (i.e. a feature) indicating UPF support for buffering control and reporting, with this feature including: o To report the UPF configured buffer size (capacity) per Network Instance and/or S-NSSAI, e.g. during a PFCP Association Setup procedure. o The SMF instructs the UPF to report its buffering status via provisioning the thresholds to report, and/or the frequency to report. o A PFCP protocol extension to the PFCP Node procedure or PFCP Session related signalling to report the buffer size and status from UPF to SMF.

It should be noted that although such reporting of buffering status is suitable for node level reporting, reporting may be simplified by using PFCP Association Update request signalling or by being 'piggybacked' on PFCP session level signalling.

• Such buffering capacity (either reported at or during a PFCP Association Setup procedure, or retrieved from the NRF) and buffering status (current available buffering size) can be used to support UPF selection and reselection.

Certain embodiments may provide one or more of the following technical advantages. For example, the solutions can allow the network operator to control UPF buffering, minimising a number of lost packets, resulting in an improved user experience. As another example, the solution can allow the network operator to support UPF selection and reselection based on UPF buffer size and status.

According to a first aspect, there is provided a method of operating a user plane network node in a communication network. The user plane network node has a buffer for storing user plane traffic. The method comprises sending, to another network node in the communication network, a first message comprising information about a size of the buffer and/or a status of the buffer.

According to a second aspect, there is provided a method of operating a profile storage network node in a communication network. The method comprises sending, to a session management network node in the communication network, a discovery response message identifying one or more user plane network nodes in the communication network. The user plane network nodes have a respective buffer for storing user plane traffic, and the discovery response message further comprises respective information on a size of the buffer and/or a status of the buffer for said user plane network nodes.

According to a third aspect, there is provided a method of operating a session management network node in a communication network. The method comprises selecting a user plane network node to use for handling user plane traffic in the communication network. The user plane network node has a buffer for storing user plane traffic, and the user plane network node is selected based on information about a size of the buffer of the user plane network node and/or a status of the buffer of the user plane network node.

According to a fourth aspect, there is provided a computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method according to the first aspect, the second aspect, the third aspect, or any embodiment thereof.

According to a fifth aspect, there is provided a network node configured to perform the method according to the first aspect, the second aspect, the third aspect, or any embodiment thereof.

According to a sixth aspect, there is provided a network node comprising a processor and a memory, said memory containing instructions executable by said processor whereby said network node is operative to perform the method according to the first aspect, the second aspect, the third aspect, or any embodiment thereof.

According to a seventh aspect, there is provided a network node, the network node comprising processing circuitry configured to cause the network node to perform the method according to the first aspect, the second aspect, the third aspect, or any embodiment thereof, and power supply circuitry configured to supply power to the processing circuitry.

Brief Description of the Drawings

Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings, in which:

Fig. 1 illustrates a 5G system reference architecture showing service-based interfaces used within the control plane;

Fig. 2 is a signalling diagram illustrating an embodiment of UPF registration in a NRF;

Fig. 3 is a signalling diagram illustrating an embodiment of UPF discovery assisted by a NRF;

Fig. 4 is a signalling diagram illustrating an embodiment of a PFCP Associated Setup procedure; Fig. 5 is a signalling diagram illustrating an embodiment of a PFCP Node Report procedure;

Fig. 6 is a flow chart illustrating an exemplary method of operating a user plane network node;

Fig. 7 is a flow chart illustrating an exemplary method of operating a profile storage network node;

Fig. 8 is a flow chart illustrating an exemplary method of operating a session management network node;

Fig. 9 is a block diagram of a network node in accordance with some embodiments; and

Fig. 10 is a block diagram illustrating a virtualization environment in which functions implemented by some embodiments may be virtualized.

Detailed Description

Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

The signalling diagrams in Figs. 2-5 illustrate various embodiments of the techniques described herein. Fig. 2 shows the signalling between a UPF 114 and a NRF 104 for UPF registration. Fig. 3 shows the signalling between a SMF 110 and a NRF 104 for UPF discovery. Fig. 4 shows the signalling between a UPF 114 and a SMF 110 in a PFCP Association Setup procedure. Fig. 5 shows the signalling between a UPF 114 and a SMF 110 in a PFCP Node Report procedure.

While the technique of extending UPF buffering capabilities is described in detail with reference to a 5G network architecture, it will be appreciated that the technique can also be used in other types of network architecture, including a 4^th Generation (4G) network, which is also known as Long Term Evolution (LTE) network (although it will be appreciated that in 4G there is no equivalent of the NRF registration and discovery procedure). The flow of operations and signalling/messaging between nodes is generally the same in 5G as it is in 4G, but the 4G network architecture is different to the 5G service-based architecture. The correspondence between the operations of the NFs in the 5G service-based architecture according to the techniques described herein and the operations of the nodes in a 4G network in implementing the techniques described herein is as follows: the SMF 109 corresponds to a Packet Data Network Gateway-Control Plane (PGW-C) or Traffic Detection Function-Control Plane (TDF-C) in 4G, and the UPF 114 corresponds to a PGW-User Plane (PG -U) or TDF-User Plane (TDF-U).

As noted above, the techniques described herein provide a mechanism which allows the network operator to control the scenarios when a UPF 114 is running out of, or is about to run out of, buffering space.

Optionally, the UPF NF profile stored in the NRF 104 is extended, e.g. in upflnfo, with one or more of: a new feature flag; a buffer size (i.e. buffering capacity); and status (e.g. current available buffering size). According to this information, the SMF 110 can select and/or reselect the UPF instance. 3GPP TS 29.510 v17.6.0 defines procedures for registering and updating NFs in the NRF 104. In the techniques described herein, new parameters are proposed in the existing procedures:

• UPF NF profile in NRF 104 during initial configuration/registration, for example registering buffer size and status.

• UPF update to NRF 104, for example updating information on buffer status (available buffering capacity).

Optionally, the UPF discovery assisted by NRF procedure can be based on the extended profile information for the UPF 114 (e.g. upflnfo) including buffer size and/or status. According to this information, the SMF 110 can select and/or reselect the UPF instance. According to the techniques described herein, the discovery mechanism (Nnrf_NFDiscovery service) can be extended by including, for example, the (minimum) buffer size and/or the (maximum) buffer occupancy in the request.

In the PFCP Association procedure (which is a procedure to create an association between a UPF and a SMF instance and which allows the UPF to indicate its capabilities to the SMF), the UPF 114 reports a capability to report the UPF buffer size and/or buffer status to the SMF 110.

The UPF 114 can report the buffer size and/or status (e.g. on a per UL/DL basis) to the SMF 110 by extending the PFCP Node Report procedure (which is a procedure used to report information from a UPF to SMF on a per node basis).

At PDU session establishment/modification, the SMF 110 can select (and/or re-select) the UPF instance based on the UPF buffer size and/or status.

As an example, the frequency of the buffer status updates to the NRF 104/SMF 110 can be done periodically or based on thresholds. The frequency of the buffer status updates could be negotiated or locally configured in the UPF 114.

Fig. 2 is a sequence diagram showing exemplary mechanisms for UPF 114 registration and registration update in a NRF 104. That is, Fig. 2 illustrates how profile information for a UPF 114 is registered, stored and (optionally) updated in a NRF 104. It will be appreciated that the procedure in Fig. 2 is optional as UPF selection by the SMF 110 does not need to be based on the information stored by the NRF 104.

In step 201 , performed by the UPF 104, the UPF 114 registers its NF profile (NFProfile) in the NRF 104. To register its profile, the UPF 114 triggers/sends a registration request message 202 (e.g. a Nnrf_NFManagement NFRegister Request message) to the NRF 104. The registration request message includes information about the UPF 104, and can include one or more of the following parameters: an indication of the type of NF making the registration request (e.g. NFType=UPF), an identifier of the UPF 104 (e.g. NFInstanceld), and profile information (e.g. NFProfile comprising upflnfo) for the UPF 104. The profile information can comprise any of an indication that the UPF 104 supports buffering, an indication of the size of the buffer (‘bufferSize’), and the buffer status (‘bufferstatus').

Table 1 below provides an example of the implementation of the additional UPF profile information in upflnfo. The definition of upflnfo is found in 3GPP TS 29.510 v17.6.0 Table 6.1.6.2.13-1 (changes in bold and highlight).

Table 6.1.6.2.13-1 : Definition of type Upflnfo

Table 1

At step 203 the NRF 104 stores the received profile information for the UPF 104 (e.g. NFProfile including upflnfo extended with the above information), and responds to the UPF 104 with response message 204, e.g. a Nnrf_NFManagement NFRegister Response message, indicating successful operation (i.e. the profile information has been stored).

If the stored profile information for the UPF 114 needs to be updated, for example to indicate a changed buffer status, a profile update procedure can be performed. Thus, in step 205, the UPF 114 updates its NFProfile in the NRF 104. To do this, the UPF 114 triggers/sends an update request message 206 (e.g. a Nnrf_NFManagement NFUpdate Request message) to the NRF 104. The update request message includes information about the UPF 104, and can include one or more of the following parameters: an indication of the type of NF making the registration request (e.g. NFType=UPF), an identifier of the UPF 104 (e.g. NFInstanceld), and the updated profile information. The updated profile information can be an updated NFProfile comprising an updated upflnfo (i.e. that indicates all information for the UPF 104, not just the information that has changed), or an updated NFProfile that just indicates the information that has changed. Thus, in some embodiments the updated NFProfile only includes the delta changes (HTTPS PATCH), e.g. upflnfo including an updated bufferstatus. The UPF 114 may update the stored profile information periodically, when any of the stored information has changed (e.g. if bufferSize or bufferstatus, etc. has changed) or when the stored information has changed by a sufficient amount, e.g. more than a threshold. The threshold may be locally configured in the UPF 114.

At step 207 the NRF 104 updates the stored profile information for the UPF 104 according to the received update request, and responds to the UPF 104 with response message 208, e.g. a Nnrf_NFManagement NFUpdate Response message, indicating successful operation (i.e. the profile information has been updated).

Fig. 3 is a sequence diagram showing exemplary mechanisms for NRF-assisted UPF selection in the SMF 110.

That is, Fig. 3 illustrates how a SMF 110 uses the information stored in a NRF 104 to identify a suitable UPF 114 for a session. It will be appreciated that the procedure in Fig. 3 is optional as UPF selection by the SMF 110 does not need to be based on information stored in the NRF 104.

In step 301 , the SMF 110 triggers the UPF discovery procedure assisted by the NRF 104. To do this, the SMF 110 triggers/sends a discovery request message 302 (e.g. a Nnrf_NFDiscovery Request message) to the NRF 104. It will be appreciated that if at the start of the UPF discovery procedure the SMF 110 has information from a previous discovery request available and the information is still valid, the SMF 110 can use that information rather than sending a new discovery request message. The discovery request message includes information about the desired UPF 104, and can include one or more of the following parameters: an indication of the type of NF that is to be discovered (e.g. NFType=UPF), and profile information (e.g. NFProfile) for the desired UPF 104. The profile information can comprise an indication of a requested buffer size (‘bufferSize’) and/or an indication of a requested buffer status (‘bufferstatus'). Alternatively, a single indication for minimum buffering capacity available may be provided instead of requested profile information (i.e. instead of upflnfo). This single indication can be a new condition in the UPF Discovery request message related to the required buffering capacity. As an alternative approach, the SMF 110 may not add conditions or adjust the request to the NRF 104, and the SMF 110 may not indicate a required buffering capacity.

In step 303, the NRF 104 determines a list of UPF instances 114 matching the criteria in the discovery request message 302, and sends a discovery response message 304 (e.g. a Nnrf_NFDiscovery Response message) to the SMF 110 containing the list or otherwise indicating the UPF instances 114 that match the criteria. The discovery response message 304 can indicate the UPFs 114 that match the criteria by including the UPF identifier (e.g. NFInstanceld), and profile information (e.g. NFProfile) indicating the buffer size and buffer status. As an example of step 303, when the discovery request message 301 indicates a bufferSize and a bufferstatus, any UPF 114 with the requested buffering capacity available may be considered to match the request. In the alternative example above where the SMF 110 does not include buffer size and/or buffer status conditions in the request 302 to the NRF 104, the NRF 104 can respond to the SMF 110 with a list of available UPFs 114, and indicate in the response 304 the respective buffer sizes and statuses of those UPFs 114 as part of the profile information (e.g. NFProfile), and the SMF 110 can take that information into account when selecting a UPF 114.

Fig. 4 is a sequence diagram showing exemplary mechanisms for a PFCP Association procedure between a UPF 114 and a SMF 110. That is, Fig. 4 illustrates how to create an association between a UPF and a SMF instance and which allows the UPF to indicate its capabilities to the SMF.

The UPF 114 initiates the PCFP Association Setup procedure between the UPF 114 and SMF 110 by sending an association setup request (e.g. PFCP Association) 401 to the SMF 110. The association setup request 114 can indicate one or more capabilities of the UPF 114, for example the buffer size and a buffer status report (as indicated by "BURU” in Table 2 below). These capabilities of the UPF 114 can be included in UP Function Features field in the PFCP Association Setup Request message. The SMF 110 may select a UPF instance 114 based on the received capabilities. Table 2 below provides an example of the implementation of the additional UPF capability information in UP Function Features. The definition of UP Function Features is found in 3GPP TS 29.244 v17.6.0 Table 8.2.25-1 (changes in bold and highlight). Table 8.2.25-1 : UP Function Features

Table 2 In response to the association setup request 401 , the SMF 100 responds to the UPF 114 with an association setup response message 402 (e.g. a PFCP Association Setup Response message) indicating successful operation.

In step 403, based on the capabilities of the UPF 114, the SMF 110 may decide to enable reporting of the buffer size (e.g. bufferSize) and/or the status of the buffer (e.g. bufferstatus) by the UPF 114.

Fig. 5 shows the signalling between a UPF 114 and a SMF 110 in a PFCP Node Reporting procedure. The PFCP Node Reporting procedure of Fig. 5 can be performed if the SMF 110 has previously required the UPF 114 to report buffer size and/or buffer status, for example according to the method in Fig. 4, or if the UPF 114 is otherwise configured to report buffer size and/or buffer status to the SMF 110. Thus, at some point in time, which can be periodically, or when, e.g., the UPF 114 is running out of buffer space or is close to running out based on preconfigured thresholds, the UPF 114 is triggered to report buffer size and buffer status to the SMF 110 (step 501), and the UPF 114 sends a node report request 502 to the SMF 110. The node report request 502 can be a PFCP Node Report Request message. This node report request 502 can indicate the buffer size and/or buffer status for the UPF 114. Table 3 below provides an example of the addition of a buffering report indicating the buffer size and/or buffer status information to Information Elements (lEs) in a PFCP Node Report Request. The definition of the IE in a PFCP Node Report Request is found in 3GPP TS 29.244 v17.6.0 Table 7.4.5.1.1-1 (changes in bold and highlight).

Table 7.4.5.1.1-1 : Information Elements in PFCP Node Report Request

Table 3 Table 4 below provides an exemplary definition of the Buffering Report IE in the PFCP Node Report Request message 502. This definition can be added to 3GPP TS 29.244 v17.6.0 as Table 7.4.5.1.x.

Table 7.4.5.1.x: Buffering Report IE within PFCP Node Report Request

Table 4

Table 5 below provides an exemplary definition of the Node Report Type. This definition can be added to 3GPP TS 29.244 V17.6.0 as Table 8.2.69-1. Figure 8.2.69-1 : Node Report Type

Table 5

In response to the node report request 502, the SMF 110 sends node report response 503 to the UPF 114 indicating successful operation. The node report response 503 can be a PFCP Node Report Response message.

In step 504 the SMF 110 stores the information on the buffer size (e.g. bufferSize) and information on the buffer status (e.g. bufferstatus) for this UPF instance 114. The SMF 110 takes this stored information into account to select the UPF instance 114 to use in a PDU session establishment procedure (for new PDU sessions). In addition, the information provided in a node report request message 502 may trigger the SMF 110 to (re-)evaluate and decide whether to change the UPF 114 for one or more existing PDU sessions (i.e. decide whether to perform UPF re- selection).

An SMF instance 110 may use one or more criteria to select a UPF instance for a PDU session. These criteria conventionally relate to the location of the UPF 114, support for Deep Packet Inspection (DPI) capabilities, etc. According to the techniques described herein, the buffer size and/or buffer status of the UPF instances 114 can be considered when selecting a suitable UPF instance 114. For example if a new PDU session corresponds to an edge scenario, the SMF 110 can use the information on the buffer size and/or buffer status to avoid selecting a UPF instance 114 whose buffer is almost full.

Fig. 6 is a flow chart illustrating an exemplary method of operating a user plane network node 114 (e.g. UPF, PGW-U, TDF-U) according to various embodiments. The user plane network node 114 has a buffer for storing user plane traffic. The user plane network node 114 is part of a communication network. The user plane network node 114 may perform the method in response to executing suitably formulated computer readable code. The computer readable code may be embodied or stored on a computer readable medium, such as a memory chip, optical disc, or other storage medium. The computer readable medium may be part of a computer program product.

In step 601 , the user plane network node 114 sends a first message comprising information about a size of the buffer and/or a status of the buffer to another network node in the communication network. The status of the buffer can comprise any of: a remaining capacity of the buffer, a remaining capacity for uplink user plane traffic, a remaining capacity for downlink user plane traffic, a used capacity of the buffer, a used capacity for uplink user plane traffic, and a used capacity for downlink user plane traffic.

The first message can further comprise an identifier for the user plane network node 114.

The information about the size of the buffer and/or the status of the buffer can be comprised in profile information for the user plane network node 114 in the first message.

In some embodiments, the first message is a registration request message 202 or an update request message 206 sent to a profile storage network node 104 (e.g. a NRF 104). In these embodiments, the first message can be a Nnrf_NFManagement NFRegister Request message 202 or a Nnrf_NFManagement NFUpdate Request message 206. It will be appreciated that in some embodiments the user plane network node 114 can be configured to send both a registration request message 202 and an update request message 206 to a profile storage network node 104 as appropriate.

In alternative embodiments, the first message can be a node report request 502 sent to a session management network node 110 (e.g. a SMF). In these embodiments, the first message can be a PFCP Node Report Request message 502.

It will be appreciated that in some embodiments the user plane network node 114 can be configured to send a registration request message 202 and/or an update request message 206 to a profile storage network node 104, and configured to send a node report request 502 to a session management network node 110

In some embodiments, the first message is sent periodically. In other embodiments, the first message can be sent when the size and/or status of the buffer changes. In other embodiments, the first message can be sent when the size and/or status of the buffer changes by more than a threshold amount.

In some embodiments, the method further comprises the user plane network node 114 sending an association setup request message 401 to a session management network node 110. This association setup request message 401 can comprises capability information for the user plane network node 114, indicating the size of the buffer and/or status of the buffer. In some embodiments, the association setup request message 401 is a PFCP Association Setup Request message 502.

Fig. 7 is a flow chart illustrating an exemplary method of operating a profile storage network node 104 (e.g. a NRF) according to various embodiments. The profile storage network node 110 is part of a communication network. The profile storage network node 110 may perform the method in response to executing suitably formulated computer readable code. The computer readable code may be embodied or stored on a computer readable medium, such as a memory chip, optical disc, or other storage medium. The computer readable medium may be part of a computer program product.

In step 701 , the profile storage network node 104 sends a discovery response message 304 identifying one or more user plane network nodes 114 in the communication network to a session management network node 110. The user plane network nodes have a respective buffer for storing user plane traffic, and the discovery response message 304 further comprises respective information on a size of the buffer and/or a status of the buffer for the user plane network nodes 114. The status of the buffer can comprise any of: a remaining capacity of the buffer, a remaining capacity for uplink user plane traffic, a remaining capacity for downlink user plane traffic, a used capacity of the buffer, a used capacity for uplink user plane traffic, and a used capacity for downlink user plane traffic

The discovery response message 304 can be a Nnrf_NFDiscovery Response message 304.

The discovery response message can be sent in response to receiving a discovery request message 302 from the session management network node 110. The discovery request message 302 can be a Nnrf_NFDiscovery Request message 302. The discovery request message 302 may comprise one or more criteria to be met by user plane network nodes 114 to be identified in the discovery response message 304. The one or more criteria can comprise a requested size of the buffer and/or a requested status of the buffer.

In some embodiments, the profile storage network node 104 can receive a first message comprising information about a size of the buffer of the user plane network node 114 and/or a status of the buffer from a user plane network node 114. The first message may also comprise an identifier for the user plane network node 114. The first message may be a registration request message 202 or an update request message 206. The first message can be a Nnrf_NFManagement NFRegister Request message 202 or a Nnrf_NFManagement NFUpdate Request message 206. It will be appreciated that in some embodiments the profile storage network node 104 can be configured to receive both a registration request message 202 and an update request message 206 from a user plane network node 114. The information about the size of the buffer and/or the status of the buffer may be comprised in profile information for the user plane network node 114 in the first message. The first message may be received periodically.

In some embodiments, the profile storage network node 104 can store the received information about the size of the buffer of the user plane network node 114 and/or the status of the buffer.

Fig. 8 is a flow chart illustrating an exemplary method of operating a session management network node 110 (e.g. a SMF, PGW-C or TDF-C) according to various embodiments. The session management network node 110 is part of a communication network. The session management network node 110 may perform the method in response to executing suitably formulated computer readable code. The computer readable code may be embodied or stored on a computer readable medium, such as a memory chip, optical disc, or other storage medium. The computer readable medium may be part of a computer program product.

In step 801 , the session management network node 110 selects a user plane network node 114 to use for handling user plane traffic in the communication network. The user plane network node 114 has a buffer for storing user plane traffic, and the user plane network node 114 is selected based on information about a size of the buffer of the user plane network node and/or a status of the buffer of the user plane network node. The status of the buffer may be any of: a remaining capacity of the buffer, a remaining capacity for uplink user plane traffic, a remaining capacity for downlink user plane traffic, a used capacity of the buffer, a used capacity for uplink user plane traffic, and a used capacity for downlink user plane traffic.

In some embodiments, step 801 is performed at or during a PDU Session Establishment procedure.

The session management network node 110 can further receive a discovery response message 304 identifying one or more user plane network nodes 114 from a profile storage network node 104 in the communication network. The discovery response message 304 comprises respective information on a size of the buffer and/or a status of the buffer for the user plane network nodes 114. This discovery response message can be is a Nnrf_NFDiscovery Response message 304. The discovery response message may be received in response to sending a discovery request message 302 to the profile storage network node 104. The discovery request message 302 may be a Nnrf_NFDiscovery Request message 302. The discovery request message 302 may comprise one or more criteria to be met by user plane network nodes 114 to be identified in the discovery response message 304. In some embodiments, the one or more criteria comprise a requested size of the buffer and/or a requested status of the buffer.

In some embodiments, the session management network node 110 receives a first message 502 from a user plane network node 114 that comprises information about a size of the buffer of the user plane network node 114 and/or a status of the buffer. The first message can be a node report request 502. The first message may be a PFCP Node Report Request message 502. The first message may be received periodically.

In some embodiments, the session management network node 1 10 may further receive an association setup request message 401 from the user plane network node 1 14. The association setup request message 401 comprises capability information for the user plane network node 1 14, with the capability information indicating the size of the buffer and/or status of the buffer. In some embodiments, the association setup request message 401 is a PFCP Association Setup Request message 502. Fig. 9 is a simplified block diagram of a network node 900 according to some embodiments that can be used to implement one or more of the techniques described herein. The network node 900 can be or implement any one or more of the user plane network node, profile storage network node and session management network node described herein. In particular embodiments, the network node 900 can be or implement any one or more of the NFs used in the 5G implementation of the techniques described herein, such as the NRF 104, SMF 110 and UPF 114. In other embodiments, the network node 900 can be or implement any one or more of the functions used in the 4G implementation of the techniques described herein, such as the PGW-C/TDF-C and PGW-U/TDF-U.

The network node 900 comprises processing circuitry (or logic) 901. It will be appreciated that the network node 900 may comprise one or more virtual machines running different software and/or processes. The network node 900 may therefore comprise, or be implemented in or as one or more servers, switches and/or storage devices and/or may comprise cloud computing infrastructure that runs the software and/or processes.

The processing circuitry 901 controls the operation of the network node 900 to implement the relevant part of the methods described herein. The processing circuitry 901 can comprise one or more processors, processing units, multi-core processors or modules that are configured or programmed to control the network node 900 in the manner described herein. In particular implementations, the processing circuitry 901 can comprise a plurality of software and/or hardware modules that are each configured to perform, or are for performing, individual or multiple steps of the method described herein in relation to the network node 900.

The network node 900 also comprises a communications interface 902. The communications interface 902 is for use in enabling communications with other network node, computers, servers, etc. For example, the communications interface 902 can be configured to transmit to and/or receive from other network nodes requests, acknowledgements, information, data, signals, or similar. The communications interface 902 can use any suitable communication technology.

The processing circuitry 901 may be configured to control the communications interface 902 to transmit to and/or receive from other network nodes, etc. requests, acknowledgements, information, data, signals, or similar, according to the methods described herein.

The network node 900 may comprise a memory 903. In some embodiments, the memory 903 can be configured to store program code that can be executed by the processing circuitry 901 to perform the method described herein in relation to the network node 900. Alternatively or in addition, the memory 903 can be configured to store any requests, acknowledgements, information, data, signals, or similar that are described herein. The processing circuitry 901 may be configured to control the memory 903 to store such information therein.

Although the network node may include the illustrated combination of hardware components, other embodiments may comprise computing devices with different combinations of components. It is to be understood that these computing devices may comprise any suitable combination of hardware and/or software needed to perform the tasks, features, functions and methods disclosed herein. Determining, calculating, obtaining or similar operations described herein may be performed by processing circuitry, which may process information by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored in the network node, and/or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination. Moreover, while components are depicted as single boxes located within a larger box, or nested within multiple boxes, in practice, computing devices may comprise multiple different physical components that make up a single illustrated component, and functionality may be partitioned between separate components. For example, a communication interface may be configured to include any of the components described herein, and/or the functionality of the components may be partitioned between the processing circuitry and the communication interface. In another example, non-computationally intensive functions of any of such components may be implemented in software or firmware and computationally intensive functions may be implemented in hardware.

In certain embodiments, some or all of the functionality described herein may be provided by processing circuitry executing instructions stored on in memory, which in certain embodiments may be a computer program product in the form of a non-transitory computer-readable storage medium. In alternative embodiments, some or all of the functionality may be provided by the processing circuitry without executing instructions stored on a separate or discrete device-readable storage medium, such as in a hard-wired manner. In any of those particular embodiments, whether executing instructions stored on a non-transitory computer-readable storage medium or not, the processing circuitry can be configured to perform the described functionality. The benefits provided by such functionality are not limited to the processing circuitry alone or to other components of the computing device, but are enjoyed by the computing device as a whole, and/or by end users and a wireless network generally.

Fig. 10 is a block diagram illustrating a virtualization environment 1000 in which functions implemented by some embodiments may be virtualized.

In the present context, virtualizing means creating virtual versions of network nodes which may include virtualizing hardware platforms, storage devices and networking resources. As used herein, virtualization can be applied to any network node described herein, or components thereof, and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components. Some or all of the functions described herein may be implemented as virtual components executed by one or more virtual machines (VMs) implemented in one or more virtual environments 1000 hosted by one or more of hardware nodes, such as a hardware computing device that operates as a network node. Further, the network node may be entirely virtualized.

Applications 1002 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment 1000 to implement some of the features, functions, and/or benefits of some of the embodiments disclosed herein.

Hardware 1004 includes processing circuitry, memory that stores software and/or instructions executable by hardware processing circuitry, and/or other hardware devices as described herein, such as a network interface, input/output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers 1006 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1008a and 1008b (one or more of which may be generally referred to as VMs 1008), and/or perform any of the functions, features and/or benefits described in relation with some embodiments described herein. The virtualization layer 1006 may present a virtual operating platform that appears like networking hardware to the VMs 1008.

The VMs 1008 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 1006. Different embodiments of the instance of a virtual appliance 1002 may be implemented on one or more of VMs 1008, and the implementations may be made in different ways. Virtualization of the hardware is in some contexts referred to as network function virtualization (NFV). NFV may be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which can be located in data centers, and customer premise equipment.

In the context of NFV, a VM 1008 may be a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each of the VMs 1008, and that part of hardware 1004 that executes that VM, be it hardware dedicated to that VM and/or hardware shared by that VM with others of the VMs, forms separate virtual network elements. Still in the context of NFV, a virtual network function is responsible for handling specific network functions that run in one or more VMs 1008 on top of the hardware 1004 and corresponds to the application 1002.

Hardware 1004 may be implemented in a standalone network node with generic or specific components. Hardware 1004 may implement some functions via virtualization. Alternatively, hardware 1004 may be part of a larger cluster of hardware (e.g. such as in a data center or CPE) where many hardware nodes work together and are managed via management and orchestration 1010, which, among others, oversees lifecycle management of applications 1002. In some embodiments, hardware 1004 is coupled to one or more radio units that each include one or more transmitters and one or more receivers that may be coupled to one or more antennas. Radio units may communicate directly with other hardware nodes via one or more appropriate network interfaces and may be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a radio access node or a base station. In some embodiments, some signalling can be provided with the use of a control system 1012 which may alternatively be used for communication between hardware nodes and radio units.

The foregoing merely illustrates the principles of the disclosure. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements, and procedures that, although not explicitly shown or described herein, embody the principles of the disclosure and can be thus within the scope of the disclosure. Various exemplary embodiments can be used together with one another, as well as interchangeably therewith, as should be understood by those having ordinary skill in the art. Abbreviations

At least some of the following abbreviations may be used in this disclosure. If there is an inconsistency between abbreviations, preference should be given to how it is used above. If listed multiple times below, the first listing should be preferred over any subsequent listing(s).

AF Application Function QoS Quality of Service

AMF Access and Mobility Function 40 SDF Service Data Flow

AS Application Server SMF Session Management Function

CP Control Plane SNI Server Name Indication

CUPS Control User Plane Separation S-NSSAI Single - Network Slice Selection Assistance

DM Data Management Information

DNN Data Network Name 45 SPR Subscriber Profile Repository

DNS Domain Name System SUPI Subscription Permanent Identifier

DPI Deep Packet Inspection TLS T ransport Layer Security

EAS Edge Application Server UDP User Datagram Protocol

FAR Forwarding Action Rule UDR Unified Data Repository

FQDN Fully Qualified Domain Name 50 UP User Plane

HTTP Hypertext T ransport Protocol UPF User Plane Function

HTTPS Hypertext T ransport Protocol Secure URR Usage Reporting Rule

IE Information Element

I MEI International Mobile Equipment Identifier 3GPP 3rd Generation Partnership Project

IMSI International Mobile Subscriber Identifier 55 5G 5th Generation

IP Internet Protocol 6G 6th Generation

MBB Mobile Broadband ABS Almost Blank Subframe

MNO Mobile Network Operator ARQ Automatic Repeat Request

NRF Network Repository Function AWGN Additive White Gaussian Noise

QAM Operation Administration and Maintenance 60 BCCH Broadcast Control Channel

PCC Policy Charging and Control BCH Broadcast Channel

PCEF Policy and Charging Enforcement Function CA Carrier Aggregation

PCF Policy Control Function CC Carrier Component

PCRF Policy Control Rules Function CCCH SDU Common Control Channel SDU

PDN Packet Data Network 65 CDMA Code Division Multiplexing Access

PDR Packet Detection Rule CGI Cell Global Identifier

PEI Permanent Equipment Identity CIR Channel Impulse Response

PFCP Packet Flow Control Protocol CP Cyclic Prefix

PFD Packet Flow Description CPICH Common Pilot Channel

PGW-CPDN Gateway Control plane function 70 CPICH Ec/No CPICH Received energy per chip PGW-UPDN Gateway User plane function divided by the power density in the band PUI Public User Identity CQI Channel Quality information C-RNTI Cell RNTI 40 MME Mobility Management Entity

CSI Channel State Information MSC Mobile Switching Center

DCCH Dedicated Control Channel NPDCCH Narrowband Physical Downlink Control

DL Downlink Channel

DM Demodulation NR Next Generation Radio/New Radio

DMRS Demodulation Reference Signal 45 OCNG OFDMA Channel Noise Generator

DRX Discontinuous Reception OFDM Orthogonal Frequency Division Multiplexing

DTX Discontinuous Transmission OFDMA Orthogonal Frequency Division Multiple

DTCH Dedicated Traffic Channel Access

DUT Device Under Test OSS Operations Support System

E-CID Enhanced Cell-1 D (positioning method) 50 OTDOA Observed Time Difference of Arrival eMBMS evolved Multimedia Broadcast Multicast O&M Operation and Maintenance

Services PBCH Physical Broadcast Channel

E-SMLC Evolved-Serving Mobile Location Centre P-CCPCH Primary Common Control Physical Channel ECGI Evolved CGI PCell Primary Cell eNB E-UTRAN NodeB 55 PCFICH Physical Control Format Indicator Channel ePDCCH Enhanced Physical Downlink Control PDCCH Physical Downlink Control Channel

Channel PDCP Packet Data Convergence Protocol

E-SMLC Evolved Serving Mobile Location Center PDP Profile Delay Profile

E-UTRA Evolved UTRA PDSCH Physical Downlink Shared Channel

E-UTRAN Evolved UTRAN 60 PGW Packet Gateway

FDD Frequency Division Duplex PHICH Physical Hybrid-ARQ Indicator Channel

FFS For Further Study PLMN Public Land Mobile Network gNB Base station in NR PMI Precoder Matrix Indicator GNSS Global Navigation Satellite System PRACH Physical Random Access Channel

HARQ Hybrid Automatic Repeat Request 65 PRS Positioning Reference Signal

HO Handover PSS Primary Synchronization Signal

HSPA High Speed Packet Access PUCCH Physical Uplink Control Channel

HRPD High Rate Packet Data PUSCH Physical Uplink Shared Channel

LOS Line of Sight RACH Random Access Channel

LPP LTE Positioning Protocol 70 QAM Quadrature Amplitude Modulation

LTE Long-Term Evolution RAN Radio Access Network

MAC Medium Access Control RAT Radio Access Technology

MAC Message Authentication Code RLC Radio Link Control

MBSFN Multimedia Broadcast multicast service RLM Radio Link Management

Single Frequency Network 75 RNC Radio Network Controller

MBSFN ABS MBSFN Almost Blank Subframe RNTI Radio Network Temporary Identifier MDT Minimization of Drive Tests RRC Radio Resource Control MIB Master Information Block RRM Radio Resource Management RS Reference Signal SS Synchronization Signal

RSCP Received Signal Code Power 20 SSS Secondary Synchronization Signal

RSRP Reference Symbol Received Power OR TDD Time Division Duplex

Reference Signal Received Power TDOA Time Difference of Arrival RSRQ Reference Signal Received Quality OR TOA Time of Arrival

Reference Symbol Received Quality TSS Tertiary Synchronization Signal

RSSI Received Signal Strength Indicator 25 TTI Transmission Time Interval

RSTD Reference Signal Time Difference UE User Equipment

SCH Synchronization Channel UL Uplink SCell Secondary Cell UMTS Universal Mobile Telecommunications

SDAP Service Data Adaptation Protocol System

SDU Service Data Unit

USIM Universal Subscriber Identity Module

SFN System Frame Number UTDOA Uplink Time Difference of Arrival

SGW Serving Gateway UTRA UMTS Terrestrial Radio Access SI System Information UTRAN UTRA Network

SIB System Information Block WCDMA Wide CDMA

SNR Signal to Noise Ratio 35 WLAN Wide Local Area Network

SON Self Optimized Network

Claims

1. A method of operating a user plane network node (114) in a communication network, wherein the user plane network node has a buffer for storing user plane traffic, the method comprising: sending (601), to another network node (104; 110) in the communication network, a first message (202; 206; 502) comprising information about a size of the buffer and/or a status of the buffer.

2. A method as claimed in claim 1 , wherein the first message (202; 206) further comprises an identifier for the user plane network node (114).

3. A method as claimed in claim 1 or 2, wherein the first message is a registration request message (202) or an update request message (206) sent to a profile storage network node (104).

4. A method as claimed in claim 3, wherein the first message is a Nnrf_NFManagement NFRegister Request message (202) or a Nnrf_NFManagement NFUpdate Request message (206).

5. A method as claimed in any of claims 1-4, wherein the information about the size of the buffer and/or the status of the buffer is comprised in profile information for the user plane network node (114) in the first message.

6. A method as claimed in claims 1 or 2, wherein the first message is a node report request (502) sent to a session management network node (110).

7. A method as claimed in claim 6, wherein the first message is a Packet Flow Control Protocol, PFCP, Node Report Request message (502).

8. A method as claimed in any of claims 1-7, wherein the first message is sent periodically; sent when the size and/or status of the buffer changes; or sent when the size and/or status of the buffer changes by more than a threshold amount.

9. A method as claimed in any of claims 1-8, wherein the method further comprises: sending, to a session management network node (110) in the communication network, an association setup request message (401) comprising capability information for the user plane network node (114), wherein the capability information indicates the size of the buffer and/or status of the buffer.

10. A method as claimed in claim 9, wherein the association setup request message (401) is a Packet Flow Control

Protocol, PFCP, Association Setup Request message (502).

11. A method as claimed in any of claims 1 -10, wherein the status of the buffer comprises any of: a remaining capacity of the buffer, a remaining capacity for uplink user plane traffic, a remaining capacity for downlink user plane traffic, a used capacity of the buffer, a used capacity for uplink user plane traffic, and a used capacity for downlink user plane traffic.

12. A method of operating a profile storage network node (104) in a communication network, the method comprising: sending (701), to a session management network node (110) in the communication network, a discovery response message (304) identifying one or more user plane network nodes (114) in the communication network, wherein the user plane network nodes have a respective buffer for storing user plane traffic, and wherein the discovery response message (304) further comprises respective information on a size of the buffer and/or a status of the buffer for said user plane network nodes (114).

13. A method as claimed in claim 12, wherein the discovery response message (304) is a Nnrf_NFDiscovery Response message (304).

14. A method as claimed in claim 12 or 13, wherein the discovery response message is sent in response to receiving, from the session management network node (110), a discovery request message (302).

15. A method as claimed in claim 14, wherein the discovery request message (302) is a Nnrf_NFDiscovery Request message (302).

16. A method as claimed in claim 14 or 15, wherein the discovery request message (302) comprises one or more criteria to be met by user plane network nodes (114) to be identified in the discovery response message (304).

17. A method as claimed in claim 16, wherein the one or more criteria comprise a requested size of the buffer and/or a requested status of the buffer.

18. A method as claimed in any of claims 12-17, wherein the method further comprises: receiving, from a user plane network node (114), a first message (202; 206) comprising information about a size of the buffer of the user plane network node (114) and/or a status of the buffer.

19. A method as claimed in claim 18, wherein the first message (202; 206) further comprises an identifier for the user plane network node (114).

20. A method as claimed in claim 18 or 19, wherein the first message is a registration request message (202) or an update request message (206).

21. A method as claimed in claim 20, wherein the first message is a Nnrf_NFManagement NFRegister Request message (202) or a Nnrf_NFManagement NFUpdate Request message (206).

22. A method as claimed in any of claims 18-21 , wherein the information about the size of the buffer and/or the status of the buffer is comprised in profile information for the user plane network node (114) in the first message.

23. A method as claimed in any of claims 18-22, wherein the first message is received periodically.

24. A method as claimed in any of claims 18-23, wherein the method further comprises: storing the received information about the size of the buffer of the user plane network node (114) and/or the status of the buffer.

25. A method as claimed in any of claims 12-24, wherein the status of the buffer comprises any of: a remaining capacity of the buffer, a remaining capacity for uplink user plane traffic, a remaining capacity for downlink user plane traffic, a used capacity of the buffer, a used capacity for uplink user plane traffic, and a used capacity for downlink user plane traffic.

26. A method of operating a session management network node (110) in a communication network, the method comprising: selecting (801) a user plane network node (114) to use for handling user plane traffic in the communication network, wherein the user plane network node (114) has a buffer for storing user plane traffic, and wherein the user plane network node (114) is selected based on information about a size of the buffer of the user plane network node and/or a status of the buffer of the user plane network node.

27. A method as claimed in claim 26, wherein the step of selecting (801) is performed at or during a Protocol Data Unit, PDU, Session Establishment procedure.

28. A method as claimed in claim 26 or 27, wherein the method further comprises: receiving, from a profile storage network node (104) in the communication network, a discovery response message (304) identifying one or more user plane network nodes (114), wherein the discovery response message (304) comprises respective information on a size of the buffer and/or a status of the buffer for said user plane network nodes (114).

29. A method as claimed in claim 28, wherein the discovery response message (304) is a Nnrf_NFDiscovery Response message (304).

30. A method as claimed in claim 28 or 29, wherein the discovery response message is received in response to sending, to the profile storage network node (104), a discovery request message (302).

31 . A method as claimed in claim 30, wherein the discovery request message (302) is a Nnrf_NFDiscovery Request message (302).

32. A method as claimed in claim 30 or 31 , wherein the discovery request message (302) comprises one or more criteria to be met by user plane network nodes (114) to be identified in the discovery response message (304).

33. A method as claimed in claim 32, wherein the one or more criteria comprise a requested size of the buffer and/or a requested status of the buffer.

34. A method as claimed in any of claims 26-33, wherein the method further comprises: receiving, from a user plane network node (114), a first message (502) comprising information about a size of the buffer of the user plane network node (114) and/or a status of the buffer.

35. A method as claimed in claim 34, wherein the first message is a node report request (502).

36. A method as claimed in claim 35, wherein the first message is a Packet Flow Control Protocol, PFCP, Node Report Request message (502).

37. A method as claimed in any of claims 34-36, wherein the first message is received periodically.

38. A method as claimed in any of claims 26-37, wherein the method further comprises: receiving, from the user plane network node (114), an association setup request message (401) comprising capability information for the user plane network node (114), wherein the capability information indicates the size of the buffer and/or status of the buffer.

39. A method as claimed in claim 38, wherein the association setup request message (401) is a Packet Flow Control Protocol, PFCP, Association Setup Request message (502).

40. A method as claimed in any of claims 26-37, wherein the status of the buffer comprises any of: a remaining capacity of the buffer, a remaining capacity for uplink user plane traffic, a remaining capacity for downlink user plane traffic, a used capacity of the buffer, a used capacity for uplink user plane traffic, and a used capacity for downlink user plane traffic.

41. A computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method according to any of claims 1-40.

42. A network node configured to perform the method according to any of claims 1-40.

43. A network node comprising a processor and a memory, said memory containing instructions executable by said processor whereby said network node is operative to perform the method according to any of claims 1-40.

44. A network node, the network node comprising: processing circuitry configured to cause the network node to perform the method according to any of claims 1-

40; and power supply circuitry configured to supply power to the processing circuitry.