WO2020197454A1

WO2020197454A1 - Paging of idle state wireless communication devices

Info

Publication number: WO2020197454A1
Application number: PCT/SE2019/050280
Authority: WO
Inventors: Göran HALL; Göran RUNE; Gunnar Mildh; Jari Vikberg; Ulf Mattsson
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2019-03-28
Filing date: 2019-03-28
Publication date: 2020-10-01

Abstract

In an aspect, a method of a node (228) configured to provide core network user plane functionality in a communications network (200) to enable paging of a wireless communication device (210) being in an idle state is provided. The method comprises receiving (S101) an indication that data is to be transmitted in downlink to the wireless communication device (210), identifying (S102), in response to the received downlink data indication, a radio access network control plane function (225) to which the wireless communication device (210) was connected before entering the idle state, and sending (S103), to the identified radio access network control plane function (225), a downlink data notification comprising an identifier of the wireless communication device (210), thereby enabling for the identified radio access network control plane function (225) to trigger paging of the wireless communication device (210).

Description

PAGING OF IDLE STATE WIRELESS COMMUNICATION DEVICES

TECHNICAL FIELD

The disclosure relates to methods and devices of enabling paging of a wireless communication device. BACKGROUND

Now, 3rd Generation Partnership Project (3GPP) is standardizing a fifth generation (5G) Core Network (CN), being referred to as 5GC, and Next Generation Radio Access Network (NG-RAN).

Figure 1 shows a 5G wireless communication network 100 as depicted in 3GPP TS 23.501 comprising a User Equipment (UE, 110) in the form of for instance a mobile phone, tablet, smart phone, Internet-of-Things (IoT) sensor, etc., connecting to a (Radio) Access Network ((R)AN, 111), and to a Data Network (DN, 113) via a User Plane Function (UPF, 112). The UPF is a service function that processes user plane packets; processing may include altering the packet’s payload and/or header, interconnection to data network(s), packet routing and forwarding, etc.

Further, the network is shown to comprise a Network Slice Selection

Function (NSSF, 114) for handling network slicing, a Network Exposure Function (NEF, 115) for exposing capabilities and events, an NF (Network Function) Repository Function (NRF, 116) for providing discovery and registration functionality for NFs, a Policy Control Function (PCF, 117), Unified Data Management (UDM, 118) for storing subscriber data and profiles, and an Application Function (AF, 119) for supporting specific applications and optionally application influence on traffic routing. Moreover, the network is shown to comprise an Authentication Server Function (AUSF, 120) for storing data for authentication of UE, a core network control plane function configured to provide mobility management in the form of an Access and Mobility Function (AMF, 121) for providing UE- based authentication, authorization, mobility management, etc., and a core network control plane function configured to provide session management in the form of a Session Management Function (SMF, 122) configured to perform session management, e.g. session establishment, modify and release, etc. Figure 2 illustrates a prior art 5G wireless communication network 100 in a different view illustrating a radio base station 124, a so called Next

Generation NodeB (gNB), supporting New Radio (NR) radio access technology and forming part of the NG-RAN. The gNB 124 comprises a radio access network control plane function in the form of a Central Unit Control Plane (CU-CP, 125), a radio access network user plane function in the form of a Central Unit User Plane (CU-UP, 126) and a Distributed Unit (DU, 127) for connecting the NG UE 110 to the control plane and the user plane,

respectively, which is referred to as a Higher Layer Split (HLS). The gNB provides NR control and user plane terminations towards the UE, and is connected via NG-C/N2 and NG-U/N3 interfaces to the 5GC. Further, the NG-RAN may comprise evolved Long Term Evolution (eLTE) base stations, referred to as ng-eNBs.

The CU-CP 125 hosts the Radio Resource Control (RRC) protocol and the Packet Data Convergence Protocol (PDCP) protocol used for control plane, while the CU-UP 126 hosts the Service Data Adaptation Protocol (SDAP) protocol and the PDCP protocol used for user plane. The CU-CP 125 is controlling the CU-UP 126 via an El interface.

As shown in Figure 2, the CU-CP 125 is the function that terminates an N2 interface from the AMF 121 in the 5GC, and the CU-UP 126 is the function terminating an N3 interface from the UPF 112b in the 5GC. Logically, the NG UE no has one CU-UP 126 configured per Packet Data Unit (PDU) session.

The SMF 122 connects to UPFs 112a, 112b via the N4 interface and to the AMF 121 via the Nil interface. The Nil interface can alternatively be realized using service-based interfaces utilized by the AMF 121 and SMF 122, i.e.

Namf and Nsmf, respectively. Figure 2 illustrates that the network 100 comprises a plurality of UPFs 112a, 112b, but it is also envisaged that the UPF 112b connecting the NG UE 110 to a local service network 123 via local breakout is omitted, in which case the interface N3 extends between the CU-UP 126 and the UPF 112a. A problem with this structure is that it results in inefficient user plane handling with multiple different user plane related functions, i.e. DU, CU-UP and one or more UPFs being controlled by separate control plane entities over various interfaces.

SUMMARY

An objective of the present disclosure is to solve or at least mitigate this problem in the art and thus to provide an improved method of connecting a wireless communication device to a user plane in a wireless communication network.

This object is attained in a first aspect by a method of a node configured to provide core network user plane functionality in a communications network to enable paging of a wireless communication device being in an idle state. The method comprising receiving an indication that data is to be transmitted in downlink to the wireless communication device, identifying, in response to the received downlink data indication, a radio access network control plane function to which the wireless communication device was connected before entering the idle state, and sending, to the identified radio access network control plane function, a downlink data notification comprising an identifier of the wireless communication device, thereby enabling for the identified radio access network control plane function to trigger paging of the wireless communication device.

This object is attained in a second aspect by a node configured to provide core network user plane functionality in a communications network to enable paging of a wireless communication device being in an idle state, the network node comprising a processing unit and a memory, said memory containing instructions executable by said processing unit, whereby the network node is operative to receive an indication that data is to be transmitted in downlink to the wireless communication device, identify, in response to the received downlink data indication, a radio access network control plane function to which the wireless communication device was connected before entering the idle state, send, to the identified radio access network control plane function, a downlink data notification comprising an identifier of the wireless communication device, thereby enabling for the identified radio access network control plane function to trigger paging of the wireless

communication device. This object is attained in a third aspect by a method of a node configured to provide radio access network control plane functionality in a

communications network to enable paging of a wireless communication device being in an idle state. The method comprises receiving, from a node configured to provide core network user plane functionality, a downlink data notification comprising an identifier of the wireless communication device to be paged, and triggering paging of the wireless communication device identified in the downlink data notification.

This object is attained in a fourth aspect by a method of a node configured to provide radio access network control plane functionality in a

communications network to enable paging of a wireless communication device being in an idle state, the radio access control network control plane function comprising a processing unit and a memory, said memory containing instructions executable by said processing unit, whereby the radio access control network control plane function is operative to receive, from a node configured to provide core network user plane functionality, a downlink data notification comprising an identifier of the wireless communication device to be paged, and trigger paging of the wireless communication device identified in the downlink data notification.

Hence, in some aspects, a network node referred to herein as a Combined RAN and CN User Plane Function (CRC-UPF) is introduced in which UPF functionality and CU-UP functionality are integrated. The CRC-UPF advantageously enables removal of the user plane tunnel between 5GC and NG-RAN as the N3 interface becomes an internal interface in the CRC-UPF. Further, with the CRC-UPF user plane latency is reduced.

Advantageously, the disclosure provides support for paging of, and downlink data delivery to, a UE in an RRC IDLE state when a NG-RAN controlled CRC- UPF is used. A UPF part of the CRC-UPF 228 maintains information needed to forward a downlink data notification to the correct CU-CP for the CU-CP 225 to trigger paging of the UE and further to identify the UE context in the AMF. In an embodiment, the identifier of the wireless communication device comprises a 5G S-Temporary Mobile Subscription Identity (5G-S-TMSI).

In an embodiment the downlink data notification further comprises paging information related to the wireless communication device including one or more of a tracking area list, a current registration area of the wireless communication device, 5G Globally Unique Temporary UE Identity (5G- GUTI), paging Discontinuous Reception (DRX) length, UE paging identity index parameter, UE paging capability, paging assistance information, paging origin information and paging priority indication.

In an embodiment, the node configured to provide core network user plane functionality receives, from the radio access network control plane function, the identifier of the wireless communication device and the paging

information for enabling sending of the downlink data notification to the radio access network control plane function, and stores the received identifier of the wireless communication device and the paging information, and information about the radio access network control plane function sending the received identifier of the wireless communication device and the paging information.

In an embodiment, the node configured to provide core network user plane functionality receives, from the radio access network control plane function, a confirmation that the paging of the wireless communication device was successful, and if so sending data which is indicated with the downlink data indication to the wireless communication device.

In an embodiment, the node configured to provide core network user plane functionality verifies whether or not the paging is successful within a time period from the downlink data notification being sent, wherein a new attempt to trigger paging is made if the paging was not successful.

In an embodiment, the node configured to provide radio access network control plane functionality receives a service request message from the wireless communication device in case of successful paging and forwarding the service request message to a core network control plane function configured to provide mobility management.

In an embodiment, the node configured to provide radio access network control plane functionality receives, from the core network control plane function configured to provide mobility management, a message triggering creation of UE context for the wireless communication device.

In an embodiment, the node configured to provide radio access network control plane functionality locates the node configured to provide core network user plane functionality and instructs the node configured to provide core network user plane functionality to transmit the downlink data to the wireless communication device.

In an embodiment, the node configured to provide radio access network control plane functionality, upon triggering the paging of the identified wireless communication device, sends a paging message directly to the identified wireless communication device. In an embodiment, the node configured to provide radio access network control plane functionality, upon triggering the paging of the identified wireless communication device, triggers paging of the identified wireless communication device via one or more further nodes configured to provide radio access network control plane functionality in the communications network.

In an embodiment, the node configured to provide radio access network control plane functionality sends, to said one or more further nodes configured to provide radio access network control plane functionality, the received data downlink data notification, and a current registration area of the wireless communication device, thereby enabling for said one or more further nodes configured to provide radio access network control plane functionality to perform the paging if the wireless communication device is in an area served by the one or more further nodes configured to provide radio access network control plane functionality.

In an embodiment, the node configured to provide radio access network control plane functionality determines which of said one or more further nodes configured to provide radio access network control plane functionality serves the current registration area of the wireless communication device, where the sending is performed only to those of one or more further nodes configured to provide radio access network control plane functionality which serves said current registration area.

In an embodiment, the node configured to provide radio access network control plane functionality verifies whether or not the paging is successful within a time period from the downlink data notification being sent, wherein a new attempt to trigger paging is made if the paging was not successful.

In an embodiment, the node configured to provide radio access network control plane functionality selects a core network control plane function configured to provide mobility management, and sends the downlink data notification to the selected core network control plane function configured to provide mobility management, thereby enabling the core network control plane function (221) configured to provide mobility management to page the identified wireless communication device. The steps of selecting and sending may be preceded by a step of determining that paging failure has occurred, In an embodiment, the node configured to provide radio access network control plane functionality receives, upon the core network control plane function configured to provide mobility management having paged the identified wireless communication device, a message triggering creation of UE context.

In an embodiment, the node configured to provide radio access network control plane functionality locates the node configured to provide core network user plane functionality, and instructs the node configured to provide core network user plane functionality to transmit the downlink data to the wireless communication device.

In an embodiment, the node configured to provide radio access network control plane functionality triggers paging of the identified wireless communication device via one or more further nodes configured to provide radio access network control plane functionality in the communications network is performed upon a paging failure having occurred.

Further embodiments will be described in the following.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are now described, by way of example, with reference to the accompanying drawings, in which:

Figure l shows a prior art 5G wireless communication network; Figure 2 illustrates a prior art 5G wireless communication network in a different view;

Figures 3a and 3b illustrate a 5G communication network implementing a network node configured to connect a wireless communication device to a user plane in the network according to an embodiment;

Figure 4 shows a signalling diagram illustrating paging of a wireless communication device being in an idle state in 5G communication network of Figures 3a or 3b in an embodiment;

Figure 5 shows a signalling diagram illustrating paging of a wireless communication device being in an idle state in 5G communication network in an embodiment where paging control is provided;

Figure 6 shows a signalling diagram illustrating paging of a wireless communication device being in an idle state in 5G communication network in another embodiment where paging control is provided; Figure 7 shows a signalling diagram illustrating paging of a wireless communication device being in an idle state in 5G communication network in yet another embodiment where paging control is provided;

Figure 8 shows a signalling diagram illustrating paging of a wireless communication device being in an idle state in 5G communication network in an embodiment where a fallback mechanism is implemented involving paging by the AMF;

Figure 9 shows a high-level view of a scenario where extended paging of a wireless communication device being in an idle state in 5G communication network is utilized in an embodiment; Figure 10 shows a CRC-UPF according to an embodiment; and

Figure 11 shows a CU-CP according to an embodiment. DETAILED DESCRIPTION

Embodiments will now be described more fully hereinafter with reference to the accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers refer to like elements throughout the description.

Figure l shows a prior art 5G wireless communication network having been previously discussed.

Figure 2 illustrates a prior art 5G wireless communication network in a different view, also having been previously discussed.

Figure 3a illustrates a 5G communication network 200 implementing a network node 228 configured to connect a wireless communication device 210 (i.e. the NG UE) to a user plane in the network 200 according to an embodiment.

In the following, the network node 228 according to the embodiment will be referred to as a Combined RAN and CN User Plane Function (CRC-UPF).

As is shown in Figure 3a, the NG-RAN comprises a CU-CP 225 hosting the RRC protocol and the PDCP protocol used for control plane. The CU-CP 225 connects to an AMF 221 via the N2 interface, and to a DU 227 via an Fi-C interface, which DU 227 is responsible for connecting the NG UE 210 to the control plane via interface Fi-C and to the user plane via interface Fi-U.

In this embodiment, the UPF functionality and CU-UP functionality are integrated within the CRC-UPF 228. Hence, the CRC-UPF 228 hosts the

SDAP protocol and the PDCP protocol used for user plane. The CU-CP 225 is controlling the CU-UP functionality of the CRC-UPF via an El interface. The CRC-UPF 228 connects to data network 213 via an N6 interface (and possibly also via an N9 interface in case multiple UPFs are used, as discussed hereinabove).

Further, the CRC-UPF 228 is arranged with a tunnelled interface - replacing the former N4 interface illustrated with reference to Figure 2 between the prior art UPF 112a and the SMF 122 - passing over the CU-CP 225 and the AMF 221 to the SMF 222 via which the SMF 222 is controlling the UPF functionality of the CRC-UPF 228. Hence, the tunnelled interface of the CRC- UPF 228 passes over the El, N2 and Nil interfaces. The Nil interface can alternatively be realized using service-based interfaces utilized by the AMF 221 and SMF 222, i.e. Namf and Nsmf, respectively.

This interface passing over E1-N2-N11 is“tunnelled” in the sense that a so called transparent data container is prepared at the SMF 222 and sent over the tunnelled interface via the AMF 221 and the CU-CP 225 which just forward the data container to the CRC-UPF 228 being the final destination. Thus, the AMF 221 and the CU-CP 225 do not process the data included in the container, but merely relay the data container to the CRC-UPF 228 (which principle also applies in the opposite direction; from the CRC-UPF to the SMF). In other words, the interface is configured to carry transparent data containers comprising configuration data for configuring the core network user plane functionality of the CRC-UPF 228.

Advantageously, with the CRC-UPF 228 user plane latency as well as number of signalling interfaces in the network is reduced. Further, the CRC-UPF 228 advantageously also enables removal of the user plane tunnel between 5GC and NG-RAN as the N3 interface becomes an internal interface in the CRC- UPF 228.

Figure 3b illustrates an alternative embodiment of the CRC-UPF 228, where the functionality of the CU-UP 228a and the UPF 228b is not combined into one single functional entity as depicted in Figure 3a, but as two separate functional entities with an N3 interface interconnecting the two thereby forming a CRC-UPF 228. In this case, the UPF 228b could either be arranged in the NG-RAN or in the 5GC, but connects to the SMF 222 via the tunnelled N4 interface. Hence, the tunnelled interface is also extended over the N3 interface and therefore passes over the N3, El, N2 and Nil interfaces.

Alternatively, a new interface is introduced between the CU-CP 225 and the UPF 228b such that data can be sent directly between the CU-CP 225 and the UPF 228b.

Now, the UE 210 may enter three different RRC states: CONNECTED, INACTIVE or IDLE, of which the RRC IDLE state in particular will affect the CRC-UPF 228 communicating over the tunnelled N4 interface. When the UE 210 is in the IDLE state and downlink data is pending for delivery to the UE

210, the UE must be paged such that it can enter the CONNECTED state.

With reference to Figures 3a and 3b, in the IDLE state, UE context is only maintained in the network on non-access stratum (NAS) level. This means that the UE is known in the AMF 221 and the SMF 222 which maintain their UE context when the UE enters the IDLE state.

The UE context is a block of information containing the necessary

information required to page idle UEs, maintain services towards the active UE, such as UE state information, security information, UE capability information, etc. The UE context is also maintained in the UPF part of the CRC-UPF 228

(regardless of whether or not the CRC-UPF is implemented as in Figure 3a or 3b) to have the UE anchor point available in the CRC-UPF 228.

This is needed for example for UE-terminated traffic (i.e. to have the UE anchor point or local breakout point available for the UE 210 terminating traffic).

The problem with the CRC-UPF 228 for UEs in IDLE state is that there is no N4 interface from the CRC-UPF 228 to the SMF 222 or any other interface to the SMF 222 or the AMF 221 to trigger a downlink data notification upon the downlink data arriving at the CRC-UPF 228 over the N6 or N9 interfaces. Further, there is no UE-specific signalling association maintained over the El N2 and N3 interfaces, i.e. the interfaces carrying the transparent data containers enabling the“tunnelled N4” connection between the CRC-UPF 228 and the AMF 221 (and the SMF 222). Therefore, the tunnelled interface does not exist for UEs in IDLE state.

To conclude, again with reference to Figure 3a (the following description is equally applicable to Figure 3b), the information maintained in the network for a UE in RRC IDLE state (CM-IDLE state in the 5GC) will be discussed in the following. This assumes that the UE has previously been in RRC

CONNECTED state. a. The UE 210 is in RRC IDLE state. b. There is no UE control plane context in the CU-CP 225 in NG-RAN. c. There is no UE user plane context in the CU-UP part of the CRC- UPF 228 in NG-RAN. d. There are one or more UE context(s) in the UPF part of the CRC- UPF 228 for one or more UE PDU Sessions (i.e. each UE PDU Session has a separate UE context in a corresponding UPF in the same CRC-UPF or in different CRC-UPFs). e. There is UE control plane context in the AMF 221 in 5GC. The UE control plane context in the AMF 221 is mainly related to

Registration Management (RM) and Connection Management (CM). f. There is UE control plane context in at least one SMF 222 in 5GC.

The UE control plane context in the SMF 222 is mainly related to Session Management (SM), e.g. UE PDU session(s). Further, the UE related control plane contexts in the AMF 221 and the SMF 222 are associated. This association can be realized in different ways. The interface between the AMF 221 and the SMF 222 maybe realized using service-based interfaces exhibited by AMFs and SMFs, i.e. Namf and Nsmf, respectively. In this case the association is created by the AMF 221 and the SMF 222 providing identifiers of the relevant UE related control plane contexts to each other. These identifiers are then used to create the association. The actual UE related control plane contexts may also be stored outside the AMF 221 and the SMF 222, e.g. in an Unstructured Data Storage Function (UDSF). In this case, the identifiers provided by the AMF 221 and the SMF 222 to each other are actually identifying the UE related control plane context stored in the UDSF.

The Nil interface association may also be based on a UE specific signalling association between the AMF 221 and the SMF 222.

The Ei interface between the CU-CP 225 and the CRC-UPF 228 is established with a Stream Control Transmission Protocol (SCTP) association but there is no UE related signalling association over this interface.

The N2 interface between the CU-CP 225 and the AMF 221 is established with an SCTP association but there is no UE related signalling association over this interface.

Now, in the prior art network 100 described with reference to Figure 2, the paging procedure is straightforward; upon a UPF 112a receiving downlink data to be delivered to the UE 110, the UPF 112a will inform the SMF 122 over the N4 interface accordingly, which in its turn will inform that AMF 121 that the UPF 112a has downlink data pending for the UE 110 being in IDLE state. As a result, the AMF 121 will page the UE 110 via the CU-CP 125, and after successful paging of the UE, the UPF 112a can deliver downlink data to the UE 110 via the CU-UP 126 and the DU 127. With a CRC-UPF 228 as shown in Figures 3a and 3b, combining a CU-UP with one or more UPFs, this paging procedure is not possible.

Examples of embodiments will be described herein in the context of 5GC and NG-RAN. However, it is also possible to apply the embodiments to other standards, such as previous-generation 3GPP networks, e.g. 4G E- UTRAN/EPC (“Evolved Universal Terrestrial Radio Access Network/Evolved Packet Core”).

Figure 4 shows a signalling diagram illustrating a method of enabling paging of a UE 210 being in RRC IDLE state according to an embodiment in a network 200 of the type illustrated in Figure 3a. Similar signalling would be applied in a network 200 of the type illustrated in Figure 3b with the exception that communication between the CU-UP part 228a and the UPF part 228b of the CRC-UPF 228 occurs over the N3 interface.

In the embodiment illustrated with reference to Figure 4, the CRC-UPF 228 (i.e. the UPF part 228b of the CRC-UPF 228) initiates and controls the paging of the UE 210 being in RRC IDLE when downlink data is received.

The CU-CP 225 performing the first paging attempt of the UE 210 is the last known CU-CP where the UE 210 was last connected to and with which an interface to the CRC-UPF 228 consequently was established at RRC

CONNECTED state. The CRC-UPF 228 thus needs to inform the CU-CP 225 that it has downlink data pending for the UE 210 and thus that the UE 210 must be paged.

Therefore, the CRC-UPF 228 must have access to information identifying the last CU-CP to which the UE 210 was connected and further access to information to be used by the CU-CP 225 to identify and page the UE 210, i.e. a UE paging identifier (which identifier may be represented by the previously discussed UE context stored in the AMF 221, the SMF 222 and the CRC-UPF 228). It is noted that the AMF 221, CRC-UPF 228 and/or SMF 222 may handle multiple PDU sessions (and a corresponding number of UE contexts) for the UE 210 over which downlink data may be transmitted, and each UE context session should in such case be identified.

An example of such an identifier is the 5G-GUTI (“5G Globally Unique Temporary UE Identity”) which is a global unique UE identifier identifying the AMF 221 currently serving the UE 210 and the UE context of this particular UE in the AMF 221; it is noted that the AMF 221 typically serves a great number of UEs. In addition, the CU-CP 225 needs to maintain information about how to reach the AMF 221 as will be described in the following. A further example of a UE identifier is a 5G-S-TMSI (“5G-S Temporary Mobile Subscriber Identity”) comprised in the 5G-GUTL The 5G-GUTI comprises a 5G-S Temporary Mobile Subscriber Identity (5G- S-TMSI) identifying the UE 210 and a Globally Unique AMF Identifier (GUAMI) identifying the AMF 221.

Further, paging information provided to the CRC-UPF 228 may optionally comprise information used for the paging performed by the CU-CP 225 including a current registration area of the UE 210 (to indicate in which area the UE 210 is registered) or even a registration area list indicating a plurality of tracking areas at which the UE 210 is registered, paging Discontinuous Reception (DRX) length (to help the CU-CP 225 determine which paging slot to use), UE paging identity index parameter (used in RAN to calculate paging slot / paging group), UE paging capability (to facilitate paging within the bandwidth supported by UE 210), paging assistance information (e.g. last known cell to facilitate paging optimization), paging origin information (in case paging can be triggered from multiple domains), paging priority indication (important at congestion in order for RAN to only page high priority UEs) and access associated to the PDU Session. Some part of this information might be locally configured in the UPF part 228b of the CRC- UPF 228 (or in the CU-CP 225) or sent via N4 tunnelling at session set-up. A registration area list is interesting in case it can be used by the CU-CP 225 to broaden the paging to multiple CU-CPs, or to any AMF, by utilizing a fallback mechanisms to be described in the following.

As previously discussed with reference to Figures 3a and 3b, the CRC-UPF 228 consists of both UPF and CU-UP parts. The actual signalling from the UPF part of the CRC-UPF 228 to the CU-CP can be handled in different ways and depends on the internal implementation of the CRC-UPF 228. In the alternative of Figure 3b, this signalling occurs via the CU-UP 228a in the CRC-UPF 228 using the N3 interface between the UPF part 228b and the CU-UP part 228a. In this alternative, the CU-UP part 228a forwards the information over the El interface to the CU-CP 225 identified by the UPF part 228b.

In the alternative of Figure 3a, this signalling may occur directly from the UPF to the CU-CP 225, i.e. if the UPF part of the CRC-UPF 228 can access the El interface directly.

With reference to Figure 4, in the following the signalling will be illustrated in the context of the CRC-UPF 228 illustrated with reference to Figure 3a, i.e. there is no internal N3 interface in the CRC-UPF 228.

As there is no UE context in the CU-CP 225 and neither any established El association for the specific UE 210 over El, the initial signalling over the Ei- interface is based on non-UE associated signalling. Similar to what has been described with reference to Figure 3a, the following condition prevails in the network 200. a. The UE 210 is in RRC IDLE state. b. There is no UE control plane context in the CU-CP 225 (nor in the DU 227) in NG-RAN. c. There is no UE user plane context in the CU-UP part of the CRC-

UPF 228. d. There are one or more UE contexts in the UPF part of the CRC-UPF 228 (for one or more corresponding UE PDU Sessions). However, in contrast to what is described in Figure 3a, this UE context is configured to contain information identifying the last CU-CP 225 to which the UE 210 was connected, which in the following will be referred to as the“CU-CP identifier”. In an embodiment, the CRC- UPF 228 stores a CU-CP identifier when the UE 210 is in RRC CONNECTED or RRC INACTIVE state for subsequently identifying the CU-CP 225 when the UE 210 has entered RRC IDLE state and needs to be paged.

The CU-CP identifier may be represented by an Internet Protocol (IP) address or other Transport Network Layer (TNL) address, or by a logical address which can be mapped to an TNL address, e.g. by a Domain Name System (DNS) server.

Further, the UE context comprises the UE paging identifier identifying the current UE 210, for instance in the form of the 5G- GUTI, and optionally the previously discussed paging information. e. There is UE control plane context in the AMF 221 in 5GC. f. There is UE control plane context in at least one SMF 222 in 5GC.

The UE related control plane contexts in AMF and SMF are associated. g. The N2 interface between the CU-CP 225 and the AMF 221 is

established but there is no UE related signalling association over the N2 interface. h. The Ei interface between the CU-CP 225 and the CRC-UPF 228 is established but there is no UE related signalling association over the Eiinterface.

In a first step S101, the UPF part of the CRC-UPF 228 receives an indication over the N6 interface (or over N9 interface) that data is to be transmitted in downlink to the UE 210 using a specific PDU session. The received indication may comprise the actual downlink data to be forwarded to the UE and associated with a specific UE address (e.g. IPv4 or IPv6 address) identifying the specific PDU session of the UE.

In response thereto, the CRC-UPF 228 identifies a need to trigger paging of the UE 210. This maybe based on internal knowledge in the CRC-UPF 228 that there is no UE user plane context in the CU-UP part of the CRC-UPF 228 for the corresponding UE PDU session, as the UE is in RRC IDLE state, or that there is no downlink path established from the CRC-UPF 228 towards the DU 227 for the corresponding UE PDU session. The CRC-UPF 228 identifies in step S102 the CU-CP 225 by means of the CU- CP identifier to which it has access.

In step S103, the CRC-UPF 228 sends, to the identified CU-CP 225, a downlink data notification, referred to as an EiAP paging message, comprising the UE paging identifier in the form of e.g. the 5G-S-TMSI identifying the UE 210, thereby enabling for the identified CU-CP 225 to identify the UE 210.

The UE paging identifier in the form of the 5G-S-TMSI (and the optional paging information) maybe provided to the CRC-UPF 228 in different ways, typically either from the AMF 221 or from the SMF 222, before the UE 210 enters the RRC IDLE state, via the N2 and El (and Nil) interfaces. The message(s) may be related either to UE context or UE PDU sessions. In one example, the AMF 221 provides the 5G-S-TMSI to the SMF 222 that further provides the 5G-S-TMSI to the CRC-UPF 228 using the tunneled interface. In another example, the AMF 221 provides the 5G-S-TMSI to the CU-CP 225 over the N2 interface and the CU-CP 225 provides the 5G-S-TMSI to the CRC-UPF 228 over the El interface. In both examples, the 5G-S-TMSI is forwarded to the UPF part of the CRC-UPF 228 within the CRC-UPF 228.

The UE paging identifier and the optional paging information may also be known by the CRC-UPF 228 by other means, such as local policies. In an embodiment, the CRC-UPF 228 includes in step S103 an identifier configured to identify the UE PDU session over which the downlink data is received.

Upon receiving the 5G-S-TMSI over the El interface, the CU-CP 225 selects in step S104 the UE 210 to be paged as identified by the 5G-S-TMSI comprised in the ElAP paging message received from the CRC-UPF 228 over the Ei interface.

Thereafter, in step S105, the CU-CP 225 triggers paging by itself directly paging the UE 210, thereby notifying the UE 210 that the downlink data previously received in step S101 is available, whereby the UE 210 responses to the paging by performing a conventional Service Request procedure in step S106. The CU-CP used for the UE-triggered Service Request maybe different from that via which the UE 210 was paged in step S105.

Once the UE 210 has responded to the paging, the AMF 221 triggers creation of UE context in the CU-CP 225 in step S107, e.g.by having the AMF 221 send a UE context setup message to the UE 210. The AMF may also provide information about UE PDU Sessions to the CU-CP 225 (in case of multiple PDU sessions being setup).

Further, in step S108, the CU-CP 225 needs to locate the CRC-UPF(s) 228 that were previously selected for the UE 210, before the UE entered the RRC IDLE state, since the UPF part of the CRC-UPF 228 is maintained also in the RRC IDLE state and the CU-CP 225 needs to select the correct CRC-UPF 228 for each PDU session. In the current case, the mobile-terminated downlink data traffic for the UE 210 is waiting for delivery in one of the CRC-UPF(s) 228.

This can be achieved in different ways, as will be exemplified in the following. a. When a UE enters RRC IDLE state, the CU-CP sends a message indicating current UE RAN configuration to the AMF. This message would thus comprise information identifying the CRC- UPF(s) used for the UE PDU sessions, for example in the form of a

CRC-UPF identifier for each PDU session. Another alternative is to include El interface information for each PDU Session. The AMF stores this information and sends it to the CU-CP in step S107. In one embodiment the AMF only provides the CRC-UPF identifier or the El interface information only for the UE PDU session over which the downlink data is received. b. The CRC-UPF 228 includes a CRC-UPF identifier in the ElAP

paging message of step S103. In step S108, the CU-CP 225 thus locates the CRC-UPF(s) 228, configures the CU-UP part 228a of the CRC-UPF 228, and instructs the CU-UP part 228a of the CRC-UPF 228 in step S109 to forward the downlink data which is pending to the UE 210. In addition, the CU-CP 225 may further configure both the UE 210 and the RAN as needed, e.g. the DU 227. In step S109, the CRC-UPF 228 may again receive the paging identifier of the UE 210 and the paging information and stores the received identifier of the UE 210 and the paging information.

Finally, the CRC-UPF 228 sends the data to the UE 210 via the DU 227 in step S110, after which the UE 210 again may enter the RRC IDLE state. Hence, the CRC-UPF 228 will in an embodiment store a CU-CP identifier designating the CU-CP 225 via which the UE 210 is connected to the control plane of the network 200 before entering the RRC IDLE state, and a UE paging identifier and paging information for enabling direct paging of the UE 210 from the CU-CP 225. Advantageously, the disclosure provides support for paging of, and downlink data delivery to, a UE 210 in an RRC IDLE state when a NG-RAN controlled CRC-UPF 228 is used, being connected to the SMF via the“tunnelled N4” interface. The UPF part 228b of the CRC-UPF 228 maintains information needed to forward a downlink data notification to the correct CU-CP 225 for the CU-CP 225 to directly page the UE 210 and further to identify the UE context in the AMF 221.

In an alternative embodiment, the 5G-GUTI is used to identify and locate a CU-CP by the CRC-UPF 228. The principle in this embodiment is that the CRC-UPF 228 performs a CU-CP lookup based on the AMF identifier (i.e. the GUAMI) in the 5G-GUTI and the result is a list of CU-CPs that are able to connect to the AMF 221 identified by the AMF identifier. The UPF part of the CRC-UPF 228 may then select one of the CU-CPs received via the lookup and send the downlink data notification to the selected CU-CP 225. The UPF part of the CRC-UPF 225 may also select more than one CU-CP and forward the notification to these CU-CPs.

Figure 4 describes an embodiment implemented in the network 200 of the type illustrated in Figure 3a. Figure 3b illustrates an alternative embodiment of the CRC-UPF 228, where the functionality of the CU-UP 228a and the UPF 228b is not combined into one single functional entity as depicted in Figure

3a, but as two separate functional entities with an N3 interface

interconnecting the two, thereby forming the CRC-UPF 228. The description given in relation to Figure 4 also applies in a network 200 of the type illustrated in Figure 3b with the additions that the UPF 228b also needs to select an CU-UP 228a for the downlink data notification (in relation to step S102), and that the CU-CP 225 needs to locate both a CU-UP 228a and the UPF 228b (in relation to step S108).

Figure 5 illustrates an embodiment based on that previously described with reference to Figure 4. In Figure 5, all steps performed up until step S103 are identical to those performed in Figure 4.

However, when sending the ElAP paging message to the CU-CP 225 in step S103, the CRC-UPF 228 initiates a paging control procedure in step Si03a in order to detect if the paging attempt fails. The CRC-UPF 228 may for instance start a timer for supervision of the paging, where the paging attempt is considered to have failed if the time period set by the timer elapses before a confirmation has been received that the paging indeed is successful.

Thereafter, steps S104-S105 are identical to those already described in Figure 4. However, in this embodiment, a paging failure occurs (and steps S106- S109 of Figure 4 are thus not performed) and the CRC-UPF 228 concludes in step Si05a after the time period set in step Si03a has expired accordingly that no configuration data has been received from the CU-CP 225 for configuring the CU-UP part 228a of the CRC-UPF 228 (cf. step S109 of Figure 4, which would have acted as confirmation of successful paging), which serves as detection of the paging failure. As a consequence, the downlink data which is pending for the UE 210 is not delivered (cf. step S110 of Figure 4), and the paging procedure is repeated from step S103, or a fallback mechanism to be discussed hereinbelow is applied.

Figure 6 illustrates an embodiment based on that previously described with reference to Figure 5. In Figure 6, all steps performed up until step S103 are identical to those performed in Figure 5.

However, upon receiving the 5G-S-TMSI over the El interface in step S104, the CU-CP 225 further initiates a paging control procedure in order to detect if the paging attempt fails (i.e. similar to the procedure initiated by the CRC- UPF 228 in step Si03a of Figure 5). The CU-CP 225 may for instance start a timer for supervision of the paging, where the paging attempt is considered to have failed if the time period set by the timer elapses before a confirmation has been received that the paging indeed is successful.

Thereafter, the CU-CP 225 triggers paging by performing a direct paging of the UE 210 in step S105. However, in this embodiment, if the CU-CP 225 concludes in step Siosb that no service request procedure is initiated by the UE 210 (cf. step S106 of Figure 4) within the time period set in step S104, then a paging failure has occurred.

As a consequence, the downlink data which is pending for the UE 210 is not delivered (cf. step S110 of Figure 4), and the paging procedure is repeated from step S103, or a fallback mechanism to be discussed hereinbelow is applied. Figure 7 illustrates an embodiment based on that previously described with reference to Figure 6. In Figure 7, all steps performed up until step S106 are identical to those performed in Figure 6.

It should further be noted that the teachings of step Si07a discussed with reference to Figure 6 again is applied in this embodiment, i.e. the CU-CP 225 concludes in step Si07a as to whether a confirmation is received that the UE 210 has been paged (in the form of the service request received in step S106) within the time period set in step S104. In this particular exemplifying embodiment, a confirmation is received. After having received the service request message from the UE 210 in step S106 - i.e. a confirmation that the UE 210 is responding to the paging- the AMF 221 may optionally in step Si07b be informed about the successful paging of the UE 210. Step Si07b maybe performed as non UE-associated signaling over the N2 interface but may also be used to trigger establishment of UE association over the N2 interface (for example for the purpose of performing any NAS signaling between the UE 210 and the AMF 221 or the SMF 222, or to enable the establishment of the tunneled N4 communication between the SMF 222 and the CRC-UPF 228.

As previously described, in step S108, the CU-CP 225 needs to locate the CRC-UPF(s) 228 that were previously selected for the UE 210, i.e. the CRC- UPF 228 where the pending downlink data is waiting for delivery to the UE 210.

Figure 7 illustrates two embodiments, where in alternative 1, the CU-CP 225 informs the CRC-UPF 228 that paging was successful in step Si09a and that the pending downlink data thus can be delivered. In this case, the downlink data is delivered to the CU-CP 225 in step Snoa, which in its turn delivers the downlink data to the UE 210 via the DU 227 on an RRC signalling

connection, i.e. using any Signalling Radio Bearer (SRB). If so, there is no need to configure the CU-UP part of the CRC-UPF 228. Alternative 2 is similar to what previously has been described, the CU-CP 225 configures the CU-UP part of the CRC-UPF 228 in step S109, and the pending downlink data is delivered to the UE 210 directly via the DU 227 in step S110 using a Data Radio Bearer (DRB). The CU-CP 225 may also trigger signalling towards the UE 210 for the DRB (not shown). As the AMF involvement is optional in this case, the CU-CP 225 may use local

configuration for the DRB configuration. In still another variant, the DRB configuration is also stored in the CRC-UPF and received in the CU-CP in step 4. As has been mentioned hereinabove, should paging of the UE 210 fail, a couple of fallback mechanisms are envisaged, wherein a first fallback mechanism will be described with reference to Figure 8. In this embodiment, the AMF 221 will perform the paging of the UE 210.

In accordance with previously described embodiments, paging control for detecting if the paging attempt fails is initiated either by the CU-CP 225 or by the CRC-UPF 228.

In a first scenario where the CU-CP 225 performs the paging control, the CU- CP 225 contacts the AMF 221 for paging assistance upon detecting that paging of the UE has failed. In a second scenario where the CRC-UPF 228 performs the paging control, the CRC-UPF 228 will need to inform the CU-CP 225 that paging indeed has failed, such that the CU-CP 225 may contact the AMF 221 for paging assistance.

Hence, with reference to Figure 8, either the CRC-UPF 228 informs the CU- CP 225 in step S2oia that paging has failed, or the CU-CP 225 alternatively itself detects in step S20ib that paging has failed.

Thereafter, in step S202 - based on the previously received 5G-GUTI

(received with the EiAP paging message of step S104 of previously described embodiments) - the CU-CP 225 identifies the AMF 221 where the UE 210 currently is registered and the UE context in that AMF 221, thereby enabling for the identified CU-CP 225 to subsequently forward the downlink data notification to the identified AMF 221 in order to enable the AMF 221 to page the UE 210. Hence, in step S202 the CU-CP 225 triggers paging of the UE 210 via the AMF 221.

It may further be envisaged that the AMF that the downlink data notification is forwarded to not necessarily is the AMF where the UE currently is registered at (in this particular example the AMF 221). The CU-CP 225 may select an AMF for example based on the current registration area of the UE, i.e. the downlink data notification is only forwarded to AMF(s) being capable to page the UE 210 in its current registration area. The CU-CP 225 provides both the received UE paging identity, e.g. 5G-S-TMSI, and the paging information to the selected AMF, after which the selected AMF pages the UE based on the received information as will be discussed in the following. Hence, in step S203, the CU-CP 225 sends the downlink data notification to the selected AMF 221 over the N2 interface, thereby enabling the AMF 221 to page the UE 210 identified by the 5G-S-TMSI included in the downlink data notification.

In an embodiment, the CU-UP 225 includes in step S203 the identifier previously received from CRC-UPF configured to identify the UE PDU session over which the downlink data is received.

When the AMF 221 receives the downlink data notification in step S203, it identifies the UE 210 to be paged based on the 5G-GUTI (i.e. by means of the 5G-S-TMSI included in the 5G-GUTI) in step S204 and accordingly pages the UE 210 in step S205 via the CU-CP 225 over the N2 interface, whereby the UE 210 responses to the paging by performing a conventional Service Request procedure in step S206. The CU-CP used for the UE-triggered Service Request maybe different from that via which the UE 210 was paged in step S205. Once the UE 210 has responded to the paging, the AMF 221 triggers creation of UE context in the CU-CP 225 in step S207. The AMF 221 also provides information about UE PDU Sessions to the CU-CP 225 (in case of multiple PDU sessions being setup). Further, the CU-CP 225 needs to locate the CRC-UPF(s) 228 that were previously selected for the UE 210, before the UE entered the RRC IDLE state, since the UPF part of the CRC-UPF 228 is maintained also in the RRC IDLE state and the CU-CP 225 needs to select the correct CRC-UPF 228 for each PDU session. In the current case, the mobile-terminated downlink data traffic for the UE 210 is waiting for delivery in one of the CRC-UPF(s) 228.

In step S208, the CU-CP 225 thus locates the CRC-UPF(s) 228 based on the information received from the AMF 221 in step S207 and instructs the CU-UP part of the CRC-UPF in step S209 to forward the downlink data which is pending to the UE 210. Finally, the CRC-UPF 228 sends the data to the UE 210 via the DU 227 in step S210, after which the UE 210 again may enter the RRC IDLE state.

In an alternative, the embodiment of triggering paging of the UE 210 via an AMF as described in Figure 8 is not used as a fallback, but as an option of performing paging of the UE 210 even when a paging failure has not occurred.

In such an alternative embodiment, step S101-S104 are performed as described with reference to Figure 4, but instead of having the CU-CP 225 directly paging the UE 210 (cf. step S105 of Figure 4), the paging process continues with step S202 as described with reference to Figure 8 and continues through steps S203-S210.

Again, the AMF selected in step S202 in this alternative embodiment is not necessarily the AMF 221 where the UE 210 currently is registered at.

Figure 9 illustrates a further embodiment, where the paging is extended to multiple CU-CPs, in this case four CU-CPs denoted 225, 230, 231 and 232. This paging, referred to in the following as extended paging, may be triggered either by local decision in the first CU-CP 225 or it may be triggered by the CRC-UPF 228. As input to the extended paging, the CRC-UPF 228 can provide the first CU-CP 225 with assistance information, e.g. indicating the last known cell of the UE 210 (which typically would constitute a good starting point for paging).

Figure 9 shows a high-level view of a scenario where extended paging is useful. The exemplary RAN consists of four different RAN areas 234-237, where each area comprises a respective CU-CP. In addition, a fifth CU-CP 233 is shown as an example of a further CU-CP located outside the four RAN areas. An Xn interface is established from the first CU-CP 225 to the other CU-CPs 230-233.

The first CU-CP 225 in the first RAN area 234 is the latest CU-CP used for the UE 210. The CRC-UPF 228 where the UE 210 has its UE context is connected to the first CU-CP (it may also be connected to all other CU-CPs, even though not shown in Figure 9).

The registration area (e.g. on NAS level) of the UE 210 consists of the four different RAN areas 234-237. The UE 210 is currently located in the second RAN area 235, implying that any paging triggered locally by the first CU-CP 225 will not be received by the UE 210.

Therefore, it would be highly beneficial if the first CU-CP 225 could extend the paging towards other CU-CPs which are serving the current registration area of the UE 210.

The following information is needed by a CU-CP in order to be made aware of to which other CU-CPs the paging may be extended:

1. the current Registration Area of the UE 210, for example consisting of one or more Tracking Areas identified by Tracking Area

Identities (TAI); and 2. the RAN areas served by the other CU-CPs, for example which TAIs are served by the other CU-CPs.

As to the information under item 1, i.e. the current Registration Area of the UE 210, an indication of the current Registration Area of the UE 210 can be forwarded from the UPF part of the CRC-UPF 228 to the first CU-CP 228 with step S103 as described in any one of Figures 4-7.

As to the information under item 2, the CU-CPs 225, 230-233 may exchange information indicating supported RAN areas when the respective Xn- interface is established, for instance in the form of“supported TAIs” or “supported cells”.

Hence, the information needed to involve other CU-CPs 230-233 in the paging is available at the latest CU-CP 225 where the UE was connected.

Two different embodiments are envisaged for the extended paging depending on where the actual decision of extending the paging is taken, as will be described in the following.

For illustrating a first of the two embodiments involving extended paging, reference is made to the previously described embodiments of Figures 4-7, starting at step S104 where the first CU-CP 225 realizes that paging of the UE 210 is to be triggered based on the EiAP paging message received in step S103.

Hence, in step S104, the first CU-CP 225 further decides to which CU-CP(s) the paging should be extended.

The first CU-CP 225 compares the current Registration Area of the UE 210 (consisting of the four RAN areas 234-237) with the information indicating which RAN areas are served by the three CU-CPs 230-232. The paging is then extended to all CU-CPs 230-232 serving a part of the current Registration Area of the UE 210. In the example shown in Figure 9, the paging is extended the second, third and fourth CU-CPs 230-232, but not to the fifth CU-CP 233. The actual extending of the paging is performed by the first CU-CP 225 creating a (new) XnAP paging message and including the information received in the ElAP paging message received from the CRC-UPF 228 in step S103 and sending the XnAP message to the CU-CPs 230-232. When the CU-CPs 230-232 receive the XnAP paging message, each CU-CP compares the received information indicating the current Registration Area of the UE 210 with the locally configured RAN area information and triggers the paging on all RAN areas that belong to the current Registration Area of the UE 210. In this particular example, the second CU-CP 230 is assumed to be the CU- CP that will page the UE 210 in step S105.

As a result, again with reference to Figures 4-7, after the second CU-CP 230 has paged the UE 201 in step S105, the CU-CP involved in any

communication according to steps S106-S110 will no longer be the first CU- CP 225, but the second CU-CP 230.

For illustrating a second of the two embodiments involving extended paging, reference is again made to the previously described embodiments of Figures 4-7, starting at step S104 where the first CU-CP 225 realizes that paging of the UE 210 is to be triggered based on the ElAP paging message received in step S103.

Again, the actual extending of the paging is performed by the first CU-CP 225 in step S104 by creating a (new) XnAP paging message and including the information received in the ElAP paging message received from the CRC- UPF 228 in step S103. However, in this embodiment, the XnAP message is sent to all the CU-CPs 230-233.

The four CU-CPs 230-233 thus receive information indicating the current Registration Area of the UE 210 and compare it to the information indicating which RAN area(s) are served by each CU-CP. Then, each of the four CU-CPs 230-233 to which the paging is extended triggers paging on all its RAN areas which belong to the current Registration Area of the UE 210.

In this particular example, the second CU-CP 230 is assumed to be the CU- CP that will page the UE 210, and the CU-CP involved in any communication according to steps S106-S110 will no longer be the first CU-CP 225, but the second CU-CP 230.

In both these embodiments, it is also possible that any of the CU-CPs receiving the XnAP Paging message perform the action of the first CU-CP 225 to even further extend the paging to additional CU-CPs. For both embodiments described with reference to Figure 10, paging control can be performed as described in Figures 5-7, i.e. either by the CRC-UPF 228 (cf. Si03a) or by the latest CU-CP that the UE 210 connected, in these exemplifying embodiments being the first CU-CP 225 (cf. S104).

In case the CRC-UPF 228 performs the paging control, said control is performed as in Figure 5 but towards the second CU-CP 230 being

responsible for paging the UE 210.

However, in case the paging control is performed by the first CU-CP 225, a mechanism is needed to indicate successful paging to the first CU-CP 225 such that the paging control is discontinued. This is achieved by the CRC- UPF 228 informing the first CU-CP 225 that the paging indeed has been successful, which maybe indicated upon the second CU-CP 230 configuring the CU-UP part of the CRC-UPF 228 in step S109.

Further, the embodiments described with reference to Figure 10 may be used as an alternative to the first fallback mechanism described with reference, thus providing a second fallback mechanism.

In the embodiment providing the second fallback mechanism, the first CU- CP 225 has made one or more attempts to page the UE 210, and the paging control has concluded that the paging has failed as previously described with reference to any one of Figures 5-7. The first CU-CP 225 has been made aware of the CRC-UPF 228 currently serving UE 210 (i.e. the CRC-UPF 228 where downlink data is pending for delivery to the UE 210) by means of the EiAP paging message S103.

However, in case of applying extended paging, the second CU-CP 230 must be made aware of the first CU-CP 225 and the CRC-UPF 228 when the UE 210 responds to the paging. This is not possible if the second CU-CP 230 would perform stateless paging (as the UE identity in RRC IDLE has no indication about the latest CU-CP 225 or the CRC-UPF 228).

However, the solution is that the second CU-CP 230 would perform stateful paging when receiving the XnAP Paging message. The UE context for the stateful paging would also store information about the first CU-CP 225.

When the UE 210 responds to the paging performed by the second CU-CP 230, the second CU-CP 230 retrieves information about the current CRC- UPF 228 for the UE 210 from the first CU-CP 225. The second CU-CP 230 then contacts the CRC-UPF 228 and indicates successful paging of the UE 210, for instance in connection to the message being sent in step Si09a and Si09b, respectively, from the second CU-UP 230 to the CRC-UPF 228.

As an alternative, it is envisaged that the first CU-CP 225 includes

information about the current CRC-UPF 228 for the UE 210 in the XnAP paging message, as previously described, which information was received in the EiAP paging message from the CRC-UPF 228 in step S103. This information can be used by the second CU-CP 230 to contact the CRC-UPF 228 directly when the UE 210 responds to the paging.

Figure 10 illustrates a CRC-UPF 228 according to an embodiment. The steps of the method performed by the CRC-UPF 228 of enabling establishment of user plane connectivity for a wireless communication device with a wireless communication network according to embodiments are in practice performed by a processing unit 415 embodied in the form of one or more microprocessors arranged to execute a computer program 416 downloaded to a suitable storage volatile medium 417 associated with the microprocessor, such as a Random Access Memory (RAM), or a non-volatile storage medium such as a Flash memory or a hard disk drive. The processing unit 415 is arranged to cause the CRC-UPF 228 to carry out the method according to embodiments when the appropriate computer program 416 comprising computer-executable instructions is downloaded to the storage medium 417 and executed by the processing unit 415. The storage medium 417 may also be a computer program product comprising the computer program 416. Alternatively, the computer program 416 maybe transferred to the storage medium 417 by means of a suitable computer program product, such as a Digital Versatile Disc (DVD) or a memory stick. As a further alternative, the computer program 416 maybe downloaded to the storage medium 417 over a network. The processing unit 415 may alternatively be embodied in the form of a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a complex programmable logic device (CPLD), etc.

Figure 11 illustrates a radio access network control plane function 225 according to an embodiment in the form of a CU-CP. The steps of the method performed by the CU-CP 225 of enabling establishment of user plane connectivity for a wireless communication device with a wireless

communication network according to embodiments are in practice performed by a processing unit 435 embodied in the form of one or more microprocessors arranged to execute a computer program 436 downloaded to a suitable storage volatile medium 437 associated with the microprocessor, such as a Random Access Memory (RAM), or a non-volatile storage medium such as a Flash memory or a hard disk drive. The processing unit 435 is arranged to cause the CU-CP 225 to carry out the method according to embodiments when the appropriate computer program 436 comprising computer-executable instructions is downloaded to the storage medium 437 and executed by the processing unit 435. The storage medium 437 may also be a computer program product comprising the computer program 436. Alternatively, the computer program 436 maybe transferred to the storage medium 427 by means of a suitable computer program product, such as a Digital Versatile Disc (DVD) or a memory stick. As a further alternative, the computer program 436 maybe downloaded to the storage medium 437 over a network. The processing unit 435 may alternatively be embodied in the form of a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a complex programmable logic device (CPLD), etc.

The disclosure has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the disclosure, as defined by the appended patent claims.

Claims

1. A method of a node (228) configured to provide core network user plane functionality in a communications network (200) to enable paging of a wireless communication device (210) being in an idle state, the method comprising:

receiving (S101) an indication that data is to be transmitted in downlink to the wireless communication device (210);

identifying (S102), in response to the received downlink data indication, a radio access network control plane function (225) to which the wireless communication device (210) was connected before entering the idle state; sending (S103), to the identified radio access network control plane function (225), a downlink data notification comprising an identifier of the wireless communication device (210), thereby enabling for the identified radio access network control plane function (225) to trigger paging of the wireless communication device (210).

2. The method of claim 1, the identifier of the wireless communication device (210) comprising a 5G S-Temporary Mobile Subscription Identity, 5G- S-TMSI.

3. The method of any one of the preceding claims, wherein said downlink data notification further comprises paging information related to the wireless communication device (210) including one or more of a tracking area list, a current registration area of the wireless communication device (210), 5G- GUTI, paging DRX length, UE paging identity index parameter, UE paging capability, paging assistance information, paging origin information and paging priority indication.

4. The method of any one of the preceding claims, further comprising: receiving (S109), from the radio access network control plane function

(225), the identifier of the wireless communication device and the paging information for enabling sending of the downlink data notification to the radio access network control plane function (225); and storing (S109) the received identifier of the wireless communication device and the paging information, and information about the radio access network control plane function sending the received identifier of the wireless communication device and the paging information. 5. The method of any one of the preceding claims, further comprising: receiving (Si09a), from the radio access network control plane function (225), a confirmation that the paging of the wireless communication device (210) was successful; and if so

sending data which is indicated with the downlink data indication to the wireless communication device (210).

6. The method of any one of the preceding claims, further comprising: verifying (Sio8a) whether or not the paging is successful within a time period from the downlink data notification being sent, wherein a new attempt to trigger paging is made if the paging was not successful. 7. A method of a node (225) configured to provide radio access network control plane functionality in a communications network (200) to enable paging of a wireless communication device (210) being in an idle state, the method comprising:

receiving (S103), from a node (228) configured to provide core network user plane functionality, a downlink data notification comprising an identifier of the wireless communication device (210) to be paged; and

triggering (S105) paging of the wireless communication device (210) identified in the downlink data notification.

8. The method of claim 7 , the identifier of the wireless communication device (210) comprising a 5G S-Temporary Mobile Subscription Identity, 5G- S-TMSI.

9. The method of any one of claims 7 or 8, wherein said downlink data notification further comprises paging information related to the wireless communication device (210) including one or more of a tracking area list, a current registration area of the wireless communication device (210), 5G- GUTI, paging Discontinuous Reception, DRX, length, UE paging identity index parameter, UE paging capability, paging assistance information, paging origin information and paging priority indication.

10. The method of any one of claims 7 to 9, further comprising:

receiving (S106) a service request message from the wireless

communication device (210) in case of successful paging and forwarding the service request message to a core network control plane function (221) configured to provide mobility management.

11. The method of claim 10, further comprising:

receiving (S107), from the core network control plane function (221) configured to provide mobility management, a message triggering creation of User Equipment, UE, context for the wireless communication device (210).

12. The method of claims 10 or 11, further comprising:

locating (S108) the node (228) configured to provide core network user plane functionality; and

instructing (S109, Si09a) the node (228) configured to provide core network user plane functionality to transmit the downlink data to the wireless communication device (210).

13. The method of any one of claims 7-12, the triggering (S105) of the paging of the identified wireless communication device (210) comprising: sending a paging message directly to the identified wireless

communication device (210).

14. The method of any one of claims 7-13, the triggering (S105) of the paging of the identified wireless communication device (210) comprising: triggering paging of the identified wireless communication device (210) via one or more further nodes (230-233) configured to provide radio access network control plane functionality in the communications network (200).

15. The method of claim 14, further comprising:

sending, to said one or more further nodes (230-233) configured to provide radio access network control plane functionality, the received data downlink data notification, and the current registration area of the wireless communication device (210), thereby enabling for said one or more further nodes (230-233) configured to provide radio access network control plane functionality to perform the paging if the wireless communication device

(210) is in an area served by the one or more further nodes (230-233) configured to provide radio access network control plane functionality.

16. The method of claim 14, further comprising:

determining which of said one or more further nodes (230-233) configured to provide radio access network control plane functionality serves the current registration area of the wireless communication device (210), where the sending is performed only to those of one or more further nodes (230-233) configured to provide radio access network control plane functionality which serves said current registration area. 17. The method of any one of claims 7-16, further comprising:

verifying (Sio8a) whether or not the paging is successful within a time period from the downlink data notification being sent, wherein a new attempt to trigger paging is made if the paging was not successful.

18. The method of claim 17, further comprising:

selecting (S202) a core network control plane function (221) configured to provide mobility management; and

sending (203) the downlink data notification to the selected core network control plane function (221) configured to provide mobility management, thereby enabling the core network control plane function (221) configured to provide mobility management to page the identified wireless communication device (210).

19. The method of claim 18, further comprising:

determining (S20ia, S202b) that paging failure has occurred.

20. The method of claims 18 or 19, further comprising:

receiving (S207), upon the core network control plane function (221) configured to provide mobility management having paged the identified wireless communication device (210), a message triggering creation of User Equipment, UE, context for the wireless communication device (210).

21. The method of claim 20, further comprising:

locating (S208) the node (228) configured to provide core network user plane functionality; and

instructing (S209) the node (228) configured to provide core network user plane functionality to transmit the downlink data to the wireless communication device (210).

22. The method of any one of claims 14-16, wherein the triggering of paging of the identified wireless communication device (210) via one or more further nodes (230-233) configured to provide radio access network control plane functionality in the communications network (200) is performed upon a paging failure having occurred.

23. A computer program (416) comprising computer-executable

instructions for causing a network node (228) to perform steps recited in any one of claims 1-6 when the computer-executable instructions are executed on a processing unit (415) included in the network node (228).

24. A computer program product comprising a computer readable medium (417), the computer readable medium having the computer program (416) according to claim 23 embodied thereon.

25. A computer program (436) comprising computer-executable

instructions for causing a radio access network control plane function (225) to perform steps recited in any one of claims 7-22 when the computer- executable instructions are executed on a processing unit (435) included in the radio access network control plane function (225).

26. A computer program product comprising a computer readable medium (437)_» the computer readable medium having the computer program (436) according to claim 25 embodied thereon.

27. A node (228) configured to provide core network user plane

functionality in a communications network (200) to enable paging of a wireless communication device (210) being in an idle state, the network node (228) comprising a processing unit (415) and a memory (417), said memory containing instructions (416) executable by said processing unit, whereby the network node (228) is operative to:

receive an indication that data is to be transmitted in downlink to the wireless communication device (210);

identify, in response to the received downlink data indication, a radio access network control plane function (225) to which the wireless

communication device (210) was connected before entering the idle state; send, to the identified radio access network control plane function

(225), a downlink data notification comprising an identifier of the wireless communication device (210), thereby enabling for the identified radio access network control plane function (225) to trigger paging of the wireless communication device (210). 28. The node (228) configured to provide core network user plane functionality of claim 27, the identifier of the wireless communication device (210) comprising a 5G S-Temporary Mobile Subscription Identity, 5G-S- TMSI.

29. The node (228) configured to provide core network user plane functionality of claim 27 or 28, wherein said downlink data notification further comprises paging information related to the wireless communication device (210) including one or more of a tracking area list, a current registration area of the wireless communication device (210), 5G-GUTI, paging DRX length, UE paging identity index parameter, UE paging capability, paging assistance information, paging origin information and paging priority indication.

30. The node (228) configured to provide core network user plane functionality of any one of claims 27-29, further being operative to:

receive, from the radio access network control plane function (225), the identifier of the wireless communication device and the paging information for enabling sending of the downlink data notification to the radio access network control plane function (225); and

store the received identifier of the wireless communication device and the paging information, and information about the radio access network control plane function sending the received identifier of the wireless communication device and the paging information.

31. The node (228) configured to provide core network user plane functionality of any one of claims 27-30, further being operative to:

receive, from the radio access network control plane function (225), a confirmation that the paging of the wireless communication device (210) was successful; and if so

send data which is indicated with the downlink data indication to the wireless communication device (210).

32. The node (228) configured to provide core network user plane functionality of any one of claims 27-29, further being operative to:

verify whether or not the paging is successful within a time period from the downlink data notification being sent, wherein a new attempt to trigger paging is made if the paging was not successful.

33. A node (225) configured to provide radio access network control plane functionality in a communications network (200) to enable paging of a wireless communication device (210) being in an idle state, the radio access control network control plane function (225) comprising a processing unit (435) and a memory (437), said memory containing instructions (436) executable by said processing unit, whereby the radio access control network control plane function (225) is operative to:

receive, from a node (228) configured to provide core network user plane functionality, a downlink data notification comprising an identifier of the wireless communication device (210) to be paged; and trigger paging of the wireless communication device (210) identified in the downlink data notification.

34. The node (225) configured to provide radio access network control plane functionality of claim 33, the identifier of the wireless communication device (210) comprising a 5G S-Temporary Mobile Subscription Identity, 5G- S-TMSI.

35. The node (225) configured to provide radio access network control plane functionality of claim 33 or 34, wherein said downlink data notification further comprises paging information related to the wireless communication device (210) including one or more of a tracking area list, a current registration area of the wireless communication device (210), 5G-GUTI, paging Discontinuous Reception, DRX, length, UE paging identity index parameter, UE paging capability, paging assistance information, paging origin information and paging priority indication.

36. The node (225) configured to provide radio access network control plane functionality of any one of claims 33-35, further being operative to: receive a service request message from the wireless communication device (210) in case of successful paging and forwarding the service request message to a core network control plane function (221) configured to provide mobility management.

37. The node (225) configured to provide radio access network control plane functionality of claim 36, further being operative to:

receive, from the core network control plane function (221) configured to provide mobility management, a message triggering creation of User Equipment, UE, context.

38. The node (225) configured to provide radio access network control plane functionality of claims 36 or 37, further being operative to:

locate the node (228) configured to provide core network user plane functionality; and instruct the node (228) configured to provide core network user plane functionality to transmit the downlink data to the wireless communication device (210).

39. The node (225) configured to provide radio access network control plane functionality of any one of claims 33-38, further being operative to, when triggering the paging of the identified wireless communication device (210):

send a paging message directly to the identified wireless communication device (210). 40. The node (225) configured to provide radio access network control plane functionality of any one of claims 33-39, further being operative to, when triggering the paging of the identified wireless communication device (210):

trigger paging of the identified wireless communication device (210) via one or more further nodes (230-233) configured to provide radio access network control plane functionality in the communications network (200).

41. The node (225) configured to provide radio access network control plane functionality of claim 40, further being operative to:

send, to said one or more further nodes (230-233) configured to provide radio access network control plane functionality, the received data downlink data notification, and a current registration area of the wireless

communication device (210), thereby enabling for said one or more further nodes (230-233) configured to provide radio access network control plane functionality to perform the paging if the wireless communication device (210) is in an area served by the one or more further nodes (230-233) configured to provide radio access network control plane functionality.

42. The node (225) configured to provide radio access network control plane functionality of claim 40, further being operative to:

determine which of said one or more further nodes (230-233) configured to provide radio access network control plane functionality serves the current registration area of the wireless communication device (210), where the sending is performed only to those of one or more further nodes (230-233) configured to provide radio access network control plane functionality which serves said current registration area. 43. The node (225) configured to provide radio access network control plane functionality of any one of claims 33-42, further being operative to: verify whether or not the paging is successful within a time period from the downlink data notification being sent, wherein a new attempt to trigger paging is made if the paging was not successful. 44. The node (225) configured to provide radio access network control plane functionality of claim 43, further being operative to: select a core network control plane function (221) configured to provide mobility management; and

send the downlink data notification to the selected core network control plane function (221) configured to provide mobility management, thereby enabling the core network control plane function (221) configured to provide mobility management to page the identified wireless communication device (210). 45. The node (225) configured to provide radio access network control plane functionality of claim 44, further being operative to:

determine that paging failure has occurred.

46. The node (225) configured to provide radio access network control plane functionality of claims 44 or 45, further being operative to:

receive, upon the core network control plane function (221) configured to provide mobility management having paged the identified wireless communication device (210), a message triggering creation of User

Equipment, UE, context.

47. The node (225) configured to provide radio access network control plane functionality of claim 44, further being operative to: locate the node (228) configured to provide core network user plane functionality; and

instruct the node (228) configured to provide core network user plane functionality to transmit the downlink data to the wireless communication device (210).

48. The node (225) configured to provide radio access network control plane functionality of any one of claims 40-42, wherein the triggering of paging of the identified wireless communication device (210) via one or more further nodes (230-233) configured to provide radio access network control plane functionality in the communications network (200) is performed upon a paging failure having occurred.