Establishment of tunnel in core network prior to UE handover

Abstract

One aspect of the disclosure provides a method performed by a RAN entity in a communication system comprising a RAN and a core network (CN). The method comprises, during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, transmitting a request message to a CN entity. The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node.

Description

[0001] ESTABLISHMENT OF TUNNEL IN CORE NETWORK PRIOR TO UE HANDOVER

[0002] Technical field

[0003] Embodiments of the disclosure relate to handover in wireless networks, and particularly to methods, apparatus and computer-readable media for configuring tunnels to carry data packets for a user equipment after handover.

[0004] Figure 1 depicts the 5G reference architecture 100 as defined by 3GPP TS 23.501 V17.1.1.

[0005] The following functions may be relevant to embodiments of the disclosure:

[0006] • UE (User Equipment) 112: the terminal device receiving network services.

[0007] • (R)AN (Radio Access Network) 113: part of the network that connects to the UE via a certain radio technology and interconnects it to a Core Network.

[0008] • AMF (Access and Mobility Management Function) 109: this function manages the registration, connection and mobility management between the network and the UE. It also mediates communication between the UE and the SMF.

[0009] • SMF (Session Management Function) 110: this function is responsible for session establishment, modification and release, including selection and control of the UPF entities, maintaining the topology of the involved PDU (protocol data unit) session anchor (PSA) UPFs, establishing and releasing the tunnel between the access network and the UPF, and between UPFs. It also configures traffic forwarding at the UPF. The SMF interacts with the UPF over N4 Reference point using Packet Forwarding Control Protocol (PFCP) procedures.

[0010] • UPF (User Plane Function) 114: This function handles the user data traffic. Among other things, it provides the external PDU Session point of interconnect to Data Network (i.e. , the PSA), and performs packet routing and forwarding (e.g. support of uplink classifier (UL CL) to route traffic flows to an instance of a data network, support of branching point to support multi-homed PDU Session, etc).

[0011] Thus, as relevant for embodiments of the disclosure, the network architecture 100 comprise a UE 112, a RAN (more particularly, a RAN node) 113, an AMF 109, an SMF 110 and a UPF 114. The UE 112 has an interface to the RAN 113 (known as the Uu interface) and an interface to the AMF 109 (known as the N1 interface). The RAN 113 has an interface to the AMF 109 (known as the N2 interface) and an interface to the UPF (the N3 interface). The AMF 109 has an interface to the SMF 110 (the N11 interface - not explicitly shown in Figure 1). The SMF 110 has an interface to the UPF 114 (the N4 interface). Different UPF instances 114 have interfaces with each other (the N9 interface).

[0012] The network architecture 100 further comprises a Network Slice Selection Function (NSSF) 102, a Network Exposure Function (NEF) 103, a Network Repository Function (NRF) 104, a Policy Control Function (PCF) 105, a Unified Data Management function (UDM) 106, an Application Function (AF) 107, an Authentication Server Function (AUSF) 108, a Service Communication Proxy (SCP) 117 and a Data Network (DN) 115. One network function specified in 3GPP TS 23.501 v17.1.1 is not shown in Figure 1 : the Network Slice-specific and SNPN (standalone non-public network) Authentication and Authorization Function (NSSAAF). These functions are not relevant to embodiments of the disclosure and will not be described further herein.

[0013] Embodiments of the disclosure relate to handover. Mobility in connected mode - which is when a terminal device is active - is controlled by the network, assisted by the terminal device. The terminal device transmits measurement reports if the cellular link to the serving cell is degraded and / or a neighboring cell in the same frequency has better performance than the serving cell.

[0014] Based on these measurement reports, the network may possibly move (i.e., handover) the terminal device connection from the serving cell to that neighbor cell, so the terminal device experiences better radio conditions and consequently a better user experience.

[0015] The handover preparation and execution phases in RAN are performed as specified in TS 38.300 v16.6.0 clause 9.2.3, while the connected mode handover procedures are described in TS 23.502 v17.1 .0, clause 4.9. A brief description of the concept is set out below, and illustrated in Figure 2; for a detailed description please refer directly to the references cited above.

[0016] The signalling involves a UE 202, a source RAN node 204, a target RAN node 206, an AMF 208, an SMF 210 and a UPF 212. In step 220, handover preparation is performed between the UE 202, the source RAN node 204 and the target RAN node 206. In step 222, the handover of the UE 202 from the source RAN node 204 to the target RAN node 206 is executed. As part of the handover procedure, the Source RAN node 204 is configured to forward all DL data 224 received for the given UE PDU session(s) towards the Target RAN node 206. UL data is sent from the UE 202 directly to the Target RAN node 206, which sends it to the UPF 212 using an UL tunnel identifier received from the Source RAN node 204 (e.g., during handover preparation 220).

[0017] In step 226, the Target RAN nod 206 issues a Path Switch Request to the AMF 208, targeting the SMF 210 (in more generic terms, the control plane), with the aim of informing it that the UE 202 has moved to the Target RAN node 206 and so the PDU session(s) user plane (UP), i.e. , the N3 tunnels to / from the UPF 212, is to be switched. The request includes the AN tunnel info (i.e., tunnel identifiers for the DL traffic) for the PDU session to be switched.

[0018] In step 228, the request is forwarded by the AMF 208 to the serving SMF 210. The SMF 210 determines whether the existing UPF 212 can continue to serve the UE 202. If the existing UPF(s) cannot continue to serve the UE, then intermediate UPF(s) (e.g., UPFs acting as UL CLs and local PSAs) may need to be selected and inserted via an N4 Session Establishment Request message. However, in the illustrated example, the existing UPF(s) 212 can continue to serve the UE 202, and in step 230 the SMF 210 sends an N4 Session Modification Request message to the UPF 212 including the AN tunnel info. In step 232, the UPF(s) 212 returns an N4 Session Modification Response message to the SMF 210 after the requested PDU sessions are switched. Tunnel identifiers are provided for those PDU sessions that could be switched.

[0019] In order to assist the reordering function in the Target RAN node 206, the UPF 212 sends one or more "end marker" packets for each N3 tunnel on the old path (e.g., to the Source RAN node 204 in step 234, and then to the Target RAN node 206 in step 236) immediately after switching the path. The UPF 212 starts sending downlink packets to the Target RAN node 206 in step 238.

[0020] In step 240, the SMF 210 triggers (through a transmission to the AMF 208, which is forwarded by the AMF 208 in step 242) a Path Switch Request Ack message to the Target RAN node 206. The Path Switch Request Ack message may include a list of PDU sessions that failed to be switched, as well as core network (CN) tunnel identifiers for the PDU sessions that were switched. Based on this, the Target RAN node 206 may switch the UL tunnel.

[0021] In step 244, the Target RAN node 206 confirms success of the handover by sending a Release Resources message to the Source RAN node 204. This triggers the release of resources associated with the connection to the UE 202 within the Source RAN node 204.

[0022] As part of 3GPP’s Release 16, conditional handover (CHO) was specified with the aim of improving the robustness of handover. The main concept behind conditional handover is depicted in Figure 3, which shows signalling between a UE 302, a source RAN node 304 and a potential target RAN node 306. Note that, in this context, the latter node only becomes a target RAN node once handover of the UE is initiated.

[0023] In step 310, the source RAN node 304 transmits a CHO request message to the potential target RAN node 306. The CHO request message may be transmitted by the source RAN node 304 responsive to a determination that handover of the UE 302 is desirable (e.g., measurements reported by the UE 302 show a degradation of its radio link with the source RAN node 304). In step 312, the potential target RAN node 306 transmits a response message to the source RAN node 304, comprising a configuration (e.g., an RRC configuration) of the potential target RAN node 306.

[0024] In step 314, the source RAN node transmits a CHO configuration message (e.g., a handover command) to the UE 302, comprising the configuration for the potential target RAN node 306 as well as a condition upon the fulfillment of which the UE 302 is to perform handover to that potential target RAN node 306. For example, the condition may relate to radio measurements performed by the UE 302 on signals transmitted by the source RAN node 304 and / or the potential target RAN node 306.

[0025] The configuration is stored by the UE 302, which then monitors the condition (plus the conditions associated with any other potential target RAN node) in step 316. In step 318, once the condition is fulfilled, the UE 302 applies the previously stored handover command, as if the network just sent it, instead of first sending a measurement report to the source RAN node 304 (that may not be successfully received by the source RAN node 304 in view of the poor radio conditions) and then waiting to receive a handover command (which may fail to be received by the UE 302). Thus the UE 302 switches to the potential target RAN node 306, and in step 320 transmits an RRCReconfigurationComplete message to confirm that the UE 302 has executed the handover. In step 322, the target RAN node 306 informs the source RAN node 304 that the UE 302 has handed over to it, and in step 324 the source RAN node 304 transfers the status of any secondary nodes configured for the UE 302 and begins forwarding and DL data packets that have been received for the UE 302. In step 3236, the target RAN node 306 initiates a procedure to switch paths for the UE 302 in the network and to release contexts for the UE stored in network nodes that are no longer required.

[0026] Sending the handover command when the radio conditions are still favorable reduces the risk of handover failure through non-reception of measurement reports by the source RAN node and / or non-reception of the handover command by the UE.

[0027] One problem associated with the procedures in Figures 2 and 3 is that the UP path between the RAN and the UPF (e.g., N3 tunnel) is longer during handovers until the Path Switch Request Ack is received, for both downlink and uplink traffic. The DL UP path is anchored at the source RAN node because of the existing N3 tunnel, with data forwarding being configured from the Source RAN node to the Target RAN node. The UL UP path is anchored at the old UPF, but there may be a need to add or change UPFs, e.g., a new local UL CL could be added to break out latency sensitive traffic.

[0028] This suboptimal UP path may cause service degradation for latency critical flows. In this case, a PDU session may fail or become degraded during or after the handover, due to the SMF or UPF being unable to reserve the required resources on the new N3 tunnel. For example, a PDU session may have one or more Quality-of-Service (QoS) flows, and there is a need for transport resource re-allocation on the new N3 tunnel, coupled with admission control. This may be required in distributed RAN and distributed anchor scenarios needed to support e.g., edge computing, where statistical multiplexing is low and thus over-provisioning would not be sufficient for transport network dimensioning. Similarly, in the case of ultra-reliable, low-latency communications (URLLC), e.g., Time- Sensitive Networking (TSN) traffic, there are flows that require extreme low delays and thus there will be a need for transport resource re-allocation after handover that may or may not be successful. In the case of handovers that require insertion or change of an Intermediate UPF (l-LIPF), e.g., breakout of traffic that requires edge computing, the selected l-LIPF may not have the necessary resources to handle the PDU session.

[0029] Conditional handover can reduce the risk of RAN handover failure, but it cannot handle PDU session failures and degradation related to N3 tunnel switch after handover.

[0030] Embodiments of the disclosure seek to address these and other issues. For example, according to embodiments of the disclosure improve the robustness of UE mobility by provisioning resources on the new tunnel for downlink packets from the core network to a target RAN node prior to execution of the handover of the UE from a source RAN node to the target RAN node. The handover may be conditional or non-conditional.

[0031] A first aspect of the disclosure thus provides a method performed by a RAN entity in a communication system comprising a RAN and a core network (CN). The method comprises, during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, transmitting a request message to a CN entity. The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node.

[0032] A second aspect of the disclosure provides a method performed by a network entity in a communication system comprising a RAN and a CN. The method comprises, during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, receiving a request message from a RAN entity. The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node. The method further comprises configuring a tunnel between one or more user plane CN entities and the target RAN node (e.g., in response to receiving the request message). The network entity in this context may comprise a control plane entity such as a SMF. Alternatively, the method may be performed by a user plane entity (e.g., a RAN node such as the source RAN node or the target RAN node). A third aspect of the disclosure provides a method performed by a user plane core network entity in a communication system comprising a RAN and a CN. The method comprises, during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, receiving a request message from a control plane CN entity. The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the user plane CN entity to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node. The method further comprises reserving resources for the tunnel to the target RAN node (e.g., responsive to receiving the request message).

[0033] Apparatus for performing the methods set out above is also provided. For example, the method according to the first aspect may be performed by a RAN node comprising processing circuitry configured to cause the RAN node to: during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, transmit a request message to a CN entity. The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node.

[0034] The method according to the second aspect may be performed by a network entity comprising processing circuitry configured to cause the network entity to: during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, receive a request message from a RAN entity. The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node. The processing circuitry is further configured to cause the network entity to configure a tunnel between one or more user plane CN entities and the target RAN node (e.g., in response to receiving the request message).

[0035] The method according to the third aspect may be performed by a user plane core network entity comprising processing circuitry configured to cause the user plane core network entity to: during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, receive a request message from a control plane CN entity. The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the user plane CN entity to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node. The processing circuitry is further to cause the user plane core network entity to reserve resources for the tunnel to the target RAN node (e.g., responsive to receiving the request message).

[0036] While the disclosure as a whole relates both to conditional handover and “regular” (i.e., non-conditional) handover, certain embodiments relate particularly to conditional handover. Such methods may comprise additional signaling relative to that shown in Figure 3:

[0037] Upon deciding on CHO, the Target RAN node issues a Conditional Path Switch (CPS) request towards the CN control plane, based on which the CN (e.g., SMF) configures the new N3 tunnel from Target RAN to UPF.

[0038] After handover execution, the Target RAN and / or the UPF sends a handover confirmation message to the CN about the handover event, based on which the CN (SMF) removes the old N3 tunnel, i.e., those UPF states that are no longer needed.

[0039] Embodiments of the present disclosure have the technical advantages of reducing or eliminating the transient period during handover in which paths between the RAN and the core network are longer than necessary. This in turn reduces the latency associated with handover, and reduces the likelihood of failed or degraded PDU sessions during handover, particularly for PDU sessions requiring low latency.

[0040] Brief description of the drawings

[0041] For a better understanding of examples of the present disclosure, and to show more clearly how the examples may be carried into effect, reference will now be made, by way of example only, to the following drawings in which:

[0042] Figure 1 shows the 5G network architecture;

[0043] Figure 2 is a signalling diagram showing handover;

[0044] Figure 3 is a signalling diagram showing conditional handover;

[0045] Figure 4 is a flowchart of a method performed by a RAN node according to embodiments of the disclosure; Figure 5 is a flowchart of a method performed by a network entity according to embodiments of the disclosure;

[0046] Figure 6 is a flowchart of a method performed by a user plane core network entity according to embodiments of the disclosure;

[0047] Figure 7 is a signalling diagram showing handover preparation according to embodiments of the disclosure;

[0048] Figure 8 is a signalling diagram showing handover execution according to some embodiments of the disclosure;

[0049] Figure 9 is a signalling diagram showing handover execution according to other embodiments of the disclosure;

[0050] Figure 10 shows an example of a RAN node according to embodiments of the disclosure;

[0051] Figure 11 shows an example of a network entity according to embodiments of the disclosure; and

[0052] Figure 12 shows an example of a user plane core network entity according to embodiments of the disclosure.

[0053] Detailed

[0054] 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.

[0055] Embodiments of the disclosure seek to address the problems associated with conventional handover procedures (whether conditional or not), and particularly seek to reduce the latency and / or increase the robustness associated with switching of paths between the core network (CN) and the radio access network (RAN), e.g., from a path to the source RAN node to a path to the target RAN node.

[0056] For example, in one embodiment a RAN entity (such as the source RAN node or the target RAN node), during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, transmits a request message to a network entity (e.g., in the CN). The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node. The network entity receiving this request message (e.g., a SMF, UPF, etc) configures a tunnel between one or more user plane CN entities and the target RAN node. For example, the network entity may request a user plane network entity (e.g., UPF) to configure the tunnel, e.g., by reserving resources for the tunnel, prior to handover. Thus the tunnel for downlink packets can be pre-configured for the UE, prior to handover, between the core network and the target RAN node. Upon execution of handover of the UE to the target RAN node, the tunnel can be activated. Latency associated with the path switch, whereby downlink packets for the UE are redirected via the source RAN node, can be substantially reduced.

[0057] Figures 4 to 6 below are flow charts of complementary methods in a RAN node (e.g., source or target RAN node), a network entity (e.g., SMF, UPF) and a user plane entity (e.g., UPF) respectively. Figures 7 to 9 are signalling diagrams showing aspects of the signalling described with respect to Figures 4 to 6.

[0058] Figure 4 depicts a method in accordance with particular embodiments, related to handover of a user equipment (UE) from a source RAN node or a target RAN node. The handover may be conditional or non-conditional. In the former case, the target RAN node may also be referred to as a “potential target RAN node” or, equivalently, a “candidate target RAN node”, particularly during preparation of the conditional handover. Once the conditional handover is initiated, the potential target RAN node becomes the target RAN node. The method may be performed by a RAN node (e.g. the source RAN node or the target RAN node). Complementary methods performed by a network entity (e.g., a SMF, UPF) and a user plane network entity (e.g., UPF) are described with respect to Figures 5 and 6 respectively.

[0059] The method begins at step 402, which is performed during a procedure to prepare handover of a UE from a source RAN node to a target RAN node. As noted above, the handover may be conditional or non-conditional. In the former case, the target RAN node may also be referred to as a “potential target RAN node” or, equivalently, a “candidate target RAN node”, particularly during preparation of the conditional handover. Once the conditional handover is initiated, the potential target RAN node becomes the target RAN node.

[0060] Accordingly, step 402 is performed prior to handover of the UE. For example, where the handover is conditional and the method is performed by the potential target RAN node, step 402 may be performed responsive to reception of a conditional handover (CHO) request message from the source RAN node. Where the handover is conditional and the method is performed by the source RAN node, step 402 may be performed responsive to reception of a CHO request acknowledgement message from the potential target RAN node. Where the handover is non-conditional, step 402 may be performed prior to initiation of the handover by the source RAN node, e.g., prior to transmission of a handover reconfiguration message (e.g., a RRCReconfiguration message containing a HO command) from the source RAN node to the UE, but after a handover decision has been taken by the source RAN node. For example, the source RAN node may have received reports of radio measurements from the UE, based on reference signal transmissions by the source RAN node and one or more neighbouring RAN nodes. The decision to handover the UE from the source RAN node to one of those neighbouring RAN nodes (which then becomes the target RAN node) is taken based on those measurements.

[0061] In step 402, the RAN node transmits a request message to a CN entity (e.g., a SMF, UPF, etc). In one embodiment, the request message is transmitted to the CN entity via one or more intermediate network entities, such as the AMF.

[0062] The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node. The request message may comprise a conditional path switch (CPS) request message where the handover is conditional, or a path switch request message where the handover is nonconditional.

[0063] The request to configure a tunnel for downlink packets for a connection for the UE from the core network to the target RAN node may be explicit or implicit. For example, the request may comprise a flag, field or information element within the request message which is set or included to indicate that the message is a request to configure a tunnel for downlink packets for the UE. Alternatively, the type of the request message itself may be interpreted by the network entity as relating to requests for configuration of such a tunnel. The tunnel may be an N3 tunnel, e.g., a tunnel over the N3 interface between the core network (e.g., the UPF) and the radio access network (e.g., the target RAN node). The tunnel may carry all user plane traffic for the UE, or only a subset of the user plane traffic for the UE (e.g., the user plane traffic for certain protocol data unit (PDU) sessions). The request message may further comprise information that enables the tunnel to be set up. For example, the request message may comprise addressing information for the target RAN node (e.g., one or more of: an identity or identifier for the target RAN node; an address (e.g., IP address) for the target RAN node). The request message may further contain indications of an identity and / or addressing information for other network entities involved in the connection for the UE, such as the AMF, UPF, etc.

[0064] The indication that configuration of the tunnel is being requested prior to execution of the handover of the UE may be explicit or implicit. For example, the indication may comprise a flag, field or information element within the request message which is set or included to indicate that the request is prior to execution of the handover of the UE. Alternatively, the indication may comprise the type of request message. That is, the type of the request message itself may be interpreted by the network entity as relating to requests prior to execution of the handover of the UE.

[0065] The network entity that receives the request message transmitted in step 402 is thus enabled to configure a tunnel for the UE between the core network and the target RAN node. Further detail regarding this process is set out below in Figures 5 and 6.

[0066] In step 404, the RAN node receives a request message acknowledgement message from the network entity, confirming the outcome of the request message (e.g., that the tunnel has been configured as requested), and comprising information enabling use of the tunnel by the target RAN node. For example, the information may comprise one or more of: an identifier for the tunnel; an identifier for the core network entity (e.g., UPF) to which the tunnel is connected. Where the method is performed by the source RAN node, this information is forwarded by the source RAN node to the target RAN node in a subsequent step (not illustrated).

[0067] Thus the tunnel is configured and set up for use by the target RAN node once handover from the source RAN node to the target RAN node is executed.

[0068] In step 406, handover of the UE is initiated or executed. Execution of the handover may be largely conventional and the operations thereof familiar to the skilled person. For example, where the handover is conditional, the UE may trigger handover upon fulfilment of a condition associated with the handover, e.g., radio measurements with respect to reference signals transmitted by the source RAN node and a potential target RAN node meet one or more criteria. Where the handover is non-conditional, handover may be initiated by the source RAN node transmitting a configuration message to the UE (e.g., RRCReconfiguration) comprising a handover command and identifying the target RAN node. In either case, the UE disconnects from the source RAN node and connects to the target RAN node, e.g., through random-access or pre-configured resources. After the UE has connected to it, the target RAN node receives uplink transmissions from the UE and forwards the user plane data in those transmissions on a newly configured UL tunnel to the UPF(s). In some examples, the target RAN node may transmit a dummy UL packet (e.g., containing no user plane data) on the newly configured UL tunnel. See Figure 8 and steps 824a and 824b for further discussion of this feature.

[0069] Figure 5 depicts a method in accordance with particular embodiments, related to handover of a UE from a source RAN node or a target RAN node. The method may be performed by a network entity, such as a control plane entity (e.g. a CN node such as SMF) or a user plane entity (e.g., UPF). Complementary methods performed by a RAN node (e.g., the source RAN node or the target RAN node) and a user plane network entity (e.g., UPF) are described with respect to Figures 4 and 6 respectively.

[0070] The method begins at step 502, in which the network entity receives, during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, a request message from a RAN entity. The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node. Step 502 may correspond to step 402, but from the network entity’s perspective, and the detail set out above is not repeated for brevity.

[0071] In step 504, responsive to reception of the request message in step 502, the network entity configures a tunnel between one or more user plane CN entities and the target RAN node. The tunnel may be an N3 tunnel, e.g., a tunnel over the N3 interface between the core network (e.g., the UPF) and the radio access network (e.g., the target RAN node). The tunnel may carry all user plane traffic for the UE, or only a subset of the user plane traffic for the UE (e.g., the user plane traffic for certain protocol data unit (PDU) sessions). Step 504 may comprise one or more sub-steps. For example, the network entity may check the policy settings associated with the UE and / or the current session of the UE (e.g., PDU session), to see whether pre-configuration of tunnels is permitted for the UE and / or the current session. If pre-configuration of tunnels is not permitted, the network entity may transmit a negative response message to the RAN node confirming that the pre-configuration of the tunnel has not taken place (step not illustrated). If preconfiguration of tunnels is permitted, the method proceeds.

[0072] In another sub-step, the network entity determines whether the existing UPF(s) (e.g., the UPF serving the UE session via the source RAN node) can continue to serve the UE once handover has taken place to the target RAN node. For example, this sub-step may comprise the network entity determining whether the existing UPF(s) has a connection or interface to the target RAN node. If the existing UPF(s) has a connection to the target RAN node, the existing UPF(s) can continue to serve the UE after handover. If the existing UPF(s) cannot continue to serve the UE, then intermediate UPF(s) are selected. UPF selection in this sub-step may utilize existing mechanisms, such as those set out in 3GPP TS 23.501 v 17.8.0.

[0073] Sub-step 506 comprises the network entity transmitting one or more messages to the one or more user plane CN entities (e.g., selected UPFs) comprising addressing information for the target RAN node and an instruction to reserve resources for the transmission of downlink packets for the connection to the target RAN node.

[0074] That is, the network entity configures the current anchor UPF and any newly selected intermediate UMF(s). Such messages may comprise partial N4 Session Establishment / Modification Request messages. These messages may comprise an indication for those UPFs that currently hold a session (e.g., an N4 session) for this UE and / or the current session (PDU session) to indicate that the messages relate to a preconfiguration of a tunnel; that is, the request to reserve resources is being made in advance of handover, so the settings for the current session (via the source RAN node) are still needed, and that tunnel switch will be required when UL traffic starts to flow on the new tunnel.

[0075] The messages transmitted to the one or more user plane CN entities may further comprise a validity timer for the configuration, upon the expiry of which the settings for the new tunnel are released, discarded or deleted if no traffic has flowed on the new tunnel (i.e. , HO to the target RAN node has not been executed or completed). Where the handover is conditional, the validity timer may be aligned with (i.e. take the same value as) validity timers used in RAN nodes for the potential Target RAN settings. Thus, when the conditional handover settings expire in the RAN node, the pre-configuration of the tunnel also expires.

[0076] In a further embodiment, the network entity may also subscribe (e.g., via a subscription request in the one or more messages or additional messages transmitted to the user plane CN entities) to receive notification messages from one or more of the user plane CN entities when they receive UL packets on any tunnel pre-configured by virtue of the messages transmitted in step 506.

[0077] If the UPF is not changed (i.e., a UPF which serves the connection via the source RAN node continues to serve the connection via the target RAN node), then after the configuration in step 506, the UPF will have two DL tunnel endpoints for the session: one active DL tunnel endpoint towards the source RAN node, through which the DL packets for the session continue to be sent until handover, and one stand-by (pre-configured) DL tunnel endpoint towards the target RAN node, corresponding to the new tunnel.

[0078] Once the UPF(s) are pre-configured for the new N3 tunnel, the SMF initiates (through the AMF) a CPS request Ack message to the Source RAN (Step 6a, further conveyed from Source RAN to Target RAN) or to the Target RAN (Step 6b), informing about the N6 tunnel setup outcome and specifying the UL tunnel identifiers for the established N3 tunnel received from the UPF (this message is also novel, as it is a response to the CPS request, so it is a new message compared to the state of art, although the current QoS Flow mobility Confirm or Path Switch Response messages could be reused.)

[0079] In step 508, the network entity transmits a request message acknowledgement message to the RAN node, confirming the outcome of the request message (e.g., that the tunnel has been configured as requested), and comprising information enabling use of the tunnel by the target RAN node. For example, the information may comprise one or more of: an identifier for the tunnel; an identifier for the core network entity (e.g., UPF) to which the tunnel is connected. Where the RAN node is the source RAN node, this information may be forwarded by the source RAN node to the target RAN node subsequently. In step 510, the network entity stores an indication that the tunnel was configured prior to execution of the handover of the UE from the source RAN node to the target RAN node. The indication may be stored in storage that is local to the network entity, or storage to which the network entity has access (e.g., in another network entity). The indication may comprise an identifier for the UE and / or the session (PDU session), as well as one or more of: an identifier for the pre-configured tunnel; an identifier for user plane network entities serving the UE and / or the session via the source RAN node.

[0080] In step 512, the network entity receives a notification that handover of the UE is being or has been executed. For example, the network entity may receive a notification from a user plane network entity serving the UE and / or the session via the target RAN node, responsive to that user plane network entity detecting a flow of traffic on the preconfigured tunnel (see Figure 7 below). See the previous step 504, in which the network entity subscribes to receive such notifications from one or more of the user plane network entities serving the session and / or the UE via the target RAN node. Alternatively, the network entity may receive such a notification from the source RAN node, the target RAN node and / or a mobility management entity (such as an AMF) upon execution of the handover (see Figure 8 below).

[0081] In step 514, responsive to reception of the notification in step 512, and based on the indication stored in step 510, the network entity refrains from establishing a further tunnel for the connection between the core network and the target RAN node. That is, the network entity would ordinarily configure a new tunnel for downlink packets from the core network to the target RAN node in response to a notification that handover to the target RAN node has taken place or has been initiated. As such a tunnel has already been pre-configured, no additional tunnel is required.

[0082] In addition, in step 516, responsive to reception of the notification in step 512, the network entity may instruct one or more user plane CN entities configured for the transmission of downlink packets for the connection from the core network to the source RAN node to release resources for the transmission of downlink packets to the source RAN node. For example, the UPFs serving the session via the source RAN node, which are no longer required to serve the session via the target RAN node, may release resources associated with connections via the source RAN node. Figure 6 depicts a method in accordance with particular embodiments, related to handover of a user equipment (UE) from a source RAN node or a target RAN node. The method may be performed by a user plane network entity (e.g., UPF). Complementary methods performed by a RAN node (e.g. the source RAN node or the target RAN node) and a network entity (e.g., a SMF, UPF) are described with respect to Figures 4 and 5 respectively.

[0083] The method begins at step 602, in which the user plane network entity, during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, receives a request message from a control plane CN entity. The request message comprises: a request to configure a tunnel for downlink packets for the UE from the user plane CN entity to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node. Step 602 may correspond substantially to step 506 described above, but from the user plane network entity’s perspective, and the detail set out above is not repeated for brevity.

[0084] In step 604, responsive to reception of the request message in step 602, the user plane network entity reserves resources for the tunnel to the target RAN node. The tunnel may be an N3 tunnel, e.g., a tunnel over the N3 interface between the core network (e.g., the UPF) and the radio access network (e.g., the target RAN node). The tunnel may carry all user plane traffic for the UE, or only a subset of the user plane traffic for the UE (e.g., the user plane traffic for certain protocol data unit (PDU) sessions).

[0085] That is, the tunnel to the target RAN node may be configured or established, but with an indication that the tunnel is configured or established prior to handover of the UE. Thus the tunnel is not to be used until a path switch is implemented between the core network and the RAN, from the source RAN node to the target RAN node (i.e. , until handover of the UE from the source RAN node to the target RAN node).

[0086] In step 606, the user plane CN entity receives an uplink packet for the UE from the target RAN node, indicating that handover has taken place. That is, the UE has disconnected from the source RAN node and is now connected to the target RAN node (e.g., following random-access or some other mechanism for connecting to the target RAN node). As stated above, the handover may be conditional or non-conditional. In the latter case, the handover may be carried out by the UE upon receipt of a handover command from the source RAN node with an instruction to connect to the target RAN node. In the former case, the handover may be initiated by the UE upon fulfilment of some condition that triggers the handover (e.g., upon radio conditions with respect to the source RAN node and the target RAN node meeting one or more criteria).

[0087] The uplink packet may be received over an UL tunnel newly established between the target RAN node and the user plane CN entity as part of the handover. In one embodiment, the uplink packet carries user plane data, i.e. , “real” data for the session. In another embodiment, the uplink packet is a dummy and contains little or no user plane data, but is instead used as a trigger for the path switch for DL packets from the “old” tunnel (to the source RAN node) to the pre-configured tunnel (to the target RAN node). One advantage of this approach is that the path switch from the old DL tunnel to the preconfigured DL tunnel does not rely upon the user plane CN entity first receiving UL user plane data.

[0088] In step 608, responsive to reception of the uplink packet in step 606, and particularly where the user plane CN entity is first configured for the transmission of DL packets via the source RAN node (i.e., prior to handover), the user plane CN entity switches the transmission of downlink packets for the connection from the tunnel to the source RAN node, to the tunnel configured for the target RAN node (i.e., using the resources reserved in step 604). In step 610, resources for the transmission of downlink packets to the source RAN node are released.

[0089] In step 612, the user plane CN entity transmits a handover complete message, such as a path switch complete message, to the network entity (e.g., the network entity which transmitted the request message in step 602).

[0090] Figure 7 is a signalling diagram showing handover preparation according to embodiments of the disclosure, particularly from the perspective of preparing conditional handover. However, those skilled in the art will appreciate that the signals shown can equally be applied to non-conditional handover. The diagram shows signalling between a UE 702, a source RAN node 704, a potential target RAN node 706, an AMF 708, an SMF 710 and one or more UPFs 712.

[0091] In step 720, the source RAN node 704 transmits a (conditional) handover request message to the potential target RAN node 706, which responds with a CHO response message in step 722. The response message comprises configuration data (RRC Reconfiguration data) for the UE to apply in the event that handover to the potential target RAN node 706 is triggered. Note that the source RAN node 704 continues with CHO configuration towards the UE 702 after receiving the response message in step 722 (not shown in Figure 7).

[0092] Optionally, the response message also includes access network tunnel information, and this enables the source RAN node, in step 724a, to transmit a conditional path switch request message to the AMF 708, which then forwards that information to the SMF 710. In an alternative embodiment, the response message may not include that information, but rather the target RAN node 706 transmits, in step 724b, a conditional path switch request message to the AMF 708, which then forwards that information to the SMF 710. Steps 724a and 724b may correspond to step 402, described above, when performed by the source RAN node and the target RAN node respectively.

[0093] In the illustrated example it is assumed that the CHO request is granted by the target RAN node 706 before the new downlink tunnel is set up. However, it is also possible that the target RAN node 706 may only accept the CHO request after the new downlink tunnel has been set up (either in general or for particular UEs or PDU sessions). In this case, step 722 moves to the end of the signalling sequence.

[0094] The request message transmitted in step 724a or 724b comprises access network tunnel information for the new tunnel to be set up (e.g., identifying the target RAN node, see step 402 above), and also an indication that the tunnel setup is being requested prior to execution of the handover itself (in the illustrated embodiment, conditionally).

[0095] In step 726, the SMF 710 checks its policy settings whether early N3 tunnel setup is allowed for this UE and PDU session and determines whether the existing UPF(s) can continue to serve the UE following handover. If the existing UPF(s) cannot continue to serve the UE, then intermediate UPF(s) may be selected. In step 728 (which may correspond to step 504 described above), the SMF 710 then configures the current anchor UPF and any newly selected intermediate UPF(s) 712, e.g., via partial N4 Session Establishment / Modification Request messages. These messages may be enhanced with an indication (e.g., a flag or other indication) for those UPFs that currently hold an N4 session for this PDU session that this is an early N3 setup, so the settings for the current tunnel to the source RAN node 704 are still needed, and tunnel switch will only be required when UL traffic appears on the new N3 tunnel from the target RAN node. These messages may also include a validity timer for the in-advance configuration, after the expiry of which the new settings may be deleted if no UL traffic has appeared on the new N3 tunnel (in other words, that handover has not happened). This timer may be aligned with the validity timers used in the RAN for the potential target RAN node settings. The SMF 710 may also subscribe to one or more of the UPFs 712 for notification messages when they receive UL packets on these new tunnels. Such notifications may be used to trigger removal of the old N3 tunnels after handover.

[0096] Once the UPF(s) 712 are pre-configured for the new N3 tunnel, the SMF 710 initiates (through the AMF 708) a CPS request Ack message to the source RAN node (step 730a, further conveyed from the source RAN node 704 to the target RAN node 706) or to the target RAN node (step 730b). The CPS request Ack message may inform the RAN node about the N3 tunnel setup outcome and specifying the UL tunnel identifiers for the established N3 tunnel received from the UPF(s) 712. The reception of this acknowledgment message by the RAN node may correspond to step 404 described above.

[0097] Figure 7 is a signalling diagram showing handover preparation according to embodiments of the disclosure. Figure 8 is a signalling diagram showing handover execution according to embodiments of the disclosure. Those skilled in the art will appreciate that the signals shown can equally be applied to conditional and nonconditional handover. The diagram shows signalling between a UE 802, a source RAN node 804, a target RAN node 806, an AMF 808, an SMF 810 and one or more UPFs 812. These entities may correspond to the equivalent entities shown in Figure 7.

[0098] In step 820, handover completion of the UE 802 from the source RAN node 804 to the target RAN node 806 takes place in the radio access network. Thus, the UE 802 disconnects from the source RAN node 804 and establishes a connection to the target RAN node 806. As part of this, the source RAN node 804 may forward downlink data packets to the target RAN node 806 for onward transmission to the UE 802 (step 822).

[0099] In step 824a, the target RAN node 806 sends a dummy packet on the new UL tunnel configured in the CHO preparation phase to the UPF 812. The dummy packet reaches the UPF 812 and triggers the UPF to switch (in step 826, corresponding to step 608) to the pre-configured tunnel settings for use after HO (e.g., as pre-configured in the signalling of Figure 7). If the UPF 812 is not changed after HO, then the UPF will switch from the currently active DL tunnel towards the source RAN node 804 to the DL tunnel whose identifier was sent by either RAN node in step 724a or 724b in the preparation procedure. If the UPF 812 is changed after HO, then the UPF 812 simply starts to use the pre-configured DL tunnel towards the target RAN node.

[0100] Alternatively, in step 824b, the first UL packet from the UE 802 (e.g., containing user plane data) is used as a trigger for the UPF 812 to switch to or start using the preconfigured DL tunnel to the target RAN node (in step 826, corresponding to 608). Both steps 824a and 824b may correspond to step 606 described above.

[0101] In either case, the UPF 812 transmits a handover completion notification to SMF (step 828, corresponding to step 612). In parallel, the UPF 812 may send an end marker (e.g., an N3 end marker) to the source RAN node (step 834), based on which the source RAN node also removes its states and resources related to the old N3 tunnel.

[0102] Upon reception of the handover complete message (which may correspond to step 512 above), and based on the internal states installed at the CHO preparation phase, in step 830 the SMF 810 determines that this is a PDU session with pre-setup N3 tunnel towards the target RAN node 806, and therefore the N4 reconfiguration should accomplish in this case only a removal of states related to the old tunnel towards the source RAN node 804 (see step 514 above). Accordingly, in step 832 (which may correspond to step 516 above), partial N4 reconfiguration message(s) is performed between the SMF 810 and the UPF(s) 812 configured as part of the connection to the source RAN node 804.

[0103] Figure 9 is a signalling diagram showing handover execution according to embodiments of the disclosure. Those skilled in the art will appreciate that the signals shown can equally be applied to conditional and non-conditional handover. The diagram shows signalling between a UE 902, a source RAN node 904, a target RAN node 906, an AMF 908, an SMF 910 and one or more UPFs 912. These entities may correspond to the equivalent entities shown in Figure 7.

[0104] The signalling illustrated in Figure 9 shows an alternative embodiment by which the SMF 910 may be notified about the requirement for path change during HO execution. Instead of using UP signaling as shown in steps 824 and 828, in this embodiment, the target RAN node 906 transmits a handover completion message to the AMF 908 on the control plane via a Path Switch message (to be forwarded on to the SMF 910).

[0105] Thus in step 920, handover completion of the UE 902 from the source RAN node 904 to the target RAN node 906 takes place in the radio access network. Thus, the UE 902 disconnects from the source RAN node 904 and establishes a connection to the target RAN node 906. As part of this, the source RAN node 904 may forward downlink data packets to the target RAN node 906 for onward transmission to the UE 902 (step 922).

[0106] In step 924, for example responsive to reception of the DL packets from the source RAN node 904 in step 922, the target RAN node 906 transmits a path switch request message to the AMF 908. This message is forwarded on to the SMF 910 in step 926.

[0107] Upon reception of the path switch request message (which may correspond to step 512 above), and based on the internal states installed at the CHO preparation phase, in step 928 the SMF 910 determines that this is a PDU session with pre-setup N3 tunnel towards the target RAN node 906, and therefore the N4 reconfiguration should accomplish in this case only a removal of states related to the old tunnel towards the source RAN node 904 (corresponding to step 514 above). Accordingly, in step 930, partial N4 reconfiguration message(s) is performed between the SMF 910 and the UPF(s) 912 configured as part of the connection to the source RAN node 904 (corresponding to step 516 above).

[0108] In step 932, potentially in parallel to steps 924 to 930 discussed above, the target RAN node 906 sends the first UL packet from the UE 902 (e.g., containing user plane data) on the new UL tunnel configured in the CHO preparation phase to the UPF 912. The UL packet reaches the UPF 912 and triggers the UPF to switch (in step 934) to the preconfigured tunnel settings for use after HO (e.g., as pre-configured in the signalling of Figure 7). If the UPF 912 is not changed after HO, then the UPF will switch from the currently active DL tunnel towards the source RAN node 904 to the DL tunnel whose identifier was sent by either RAN node in step 724a or 724b in the preparation procedure. If the UPF 912 is changed after HO, then the UPF 912 simply starts to use the preconfigured DL tunnel towards the target RAN node 906.

[0109] In parallel, the UPF 912 may send an end marker (e.g., an N3 end marker) to the source RAN node (step 936), based on which the source RAN node also removes its states and resources related to the old N3 tunnel. Figure 10 illustrates a schematic block diagram of a radio access network node 1000. The RAN node 1000 is operable to carry out the example method described with reference to Figure 4 and possibly any other processes or methods disclosed herein (such as the signalling of the source RAN node or target RAN node described with respect to any of Figures 7 to 9). It is also to be understood that the method of Figure 4 is not necessarily carried out solely by the RAN node 1000. At least some operations of the method can be performed by one or more other entities.

[0110] The RAN node 1000 comprises processing circuitry 1004, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include digital signal processors (DSPs), special-purpose digital logic, and the like. The processing circuitry 1004 may be configured to execute program code stored in memory 1002, which may include one or several types of memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory 1002 includes program instructions for executing one or more telecommunications and / or data communications protocols as well as instructions for carrying out one or more of the techniques described herein, in several embodiments. In some implementations, the processing circuitry 1004 may cause the RAN node 1000 to perform corresponding functions according one or more embodiments of the present disclosure.

[0111] According to embodiments of the disclosure, the processing circuitry 1004 is configured to cause the RAN node 1000 to: during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, transmit a request message to a CN entity. The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node.

[0112] The RAN node 1000 further comprises one or more interfaces 1006 with which to communicate with one or more other nodes of the communication network. The interface(s) 1006 may therefore comprise hardware and / or software for transmitting and / or receiving one or more of: radio signals; optical signals; and electronic signals. In alternative embodiments, the RAN node 1000 may comprise one or more units or modules configured to perform the steps of the method, for example, as illustrated in Figure 4. In such embodiments, the RAN node 1000 may comprise a transmitting unit. The transmitting unit may be configured to, during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, transmit a request message to a CN entity. The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node.

[0113] Figure 11 illustrates a schematic block diagram of a network entity or node 1100. The network entity 1100 is operable to carry out the example method described with reference to Figure 5 and possibly any other processes or methods disclosed herein (such as the signalling of the SMF described with respect to any of Figures 7 to 9). It is also to be understood that the method of Figure 5 is not necessarily carried out solely by the network entity 1100. At least some operations of the method can be performed by one or more other entities.

[0114] The network entity 1100 comprises processing circuitry 1104, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include digital signal processors (DSPs), special-purpose digital logic, and the like. The processing circuitry 1104 may be configured to execute program code stored in memory 1102, which may include one or several types of memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory 1102 includes program instructions for executing one or more telecommunications and / or data communications protocols as well as instructions for carrying out one or more of the techniques described herein, in several embodiments. In some implementations, the processing circuitry 1104 may cause the network entity 1100 to perform corresponding functions according one or more embodiments of the present disclosure.

[0115] According to embodiments of the disclosure, the processing circuitry 1104 is configured to cause the network entity 1100 to: during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, receive a request message from a RAN entity. The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node. The processing circuitry 1104 is further configured to cause the network entity to configure a tunnel between one or more user plane CN entities and the target RAN node.

[0116] The network entity 1100 further comprises one or more interfaces 1106 with which to communicate with one or more other nodes of the communication network. The interface(s) 1106 may therefore comprise hardware and / or software for transmitting and / or receiving one or more of: radio signals; optical signals; and electronic signals.

[0117] In alternative embodiments, the network entity 1100 may comprise one or more units or modules configured to perform the steps of the method, for example, as illustrated in Figure 5. In such embodiments, the network entity 1100 may comprise a receiving unit and a configuring unit. The receiving unit may be configured to receive, during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, a request message from a RAN entity. The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node. The configuring unit may configure a tunnel between one or more user plane CN entities and the target RAN node.

[0118] Figure 12 illustrates a schematic block diagram of a user plane core network entity 1200. The user plane core network entity 1200 is operable to carry out the example method described with reference to Figure 6 and possibly any other processes or methods disclosed herein (such as the signalling of the UPF described with respect to any of Figures 7 to 9). It is also to be understood that the method of Figure 6 is not necessarily carried out solely by the user plane core network entity 1200. At least some operations of the method can be performed by one or more other entities.

[0119] The user plane core network entity 1200 comprises processing circuitry 1204, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include digital signal processors (DSPs), special-purpose digital logic, and the like. The processing circuitry 1204 may be configured to execute program code stored in memory 1202, which may include one or several types of memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory 1202 includes program instructions for executing one or more telecommunications and / or data communications protocols as well as instructions for carrying out one or more of the techniques described herein, in several embodiments. In some implementations, the processing circuitry 1204 may cause the user plane core network entity 1200 to perform corresponding functions according one or more embodiments of the present disclosure.

[0120] According to embodiments of the disclosure, the processing circuitry 1204 is configured to cause the user plane core network entity 1200 to: during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, receive a request message from a control plane CN entity. The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the user plane CN entity to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node. The processing circuitry is further to cause the user plane core network entity to reserve resources for the tunnel to the target RAN node (e.g., responsive to receiving the request message).

[0121] The user plane core network entity 1200 further comprises one or more interfaces 1206 with which to communicate with one or more other nodes of the communication network. The interface(s) 1206 may therefore comprise hardware and / or software for transmitting and / or receiving one or more of: radio signals; optical signals; and electronic signals.

[0122] In alternative embodiments, the user plane core network entity 1200 may comprise one or more units or modules configured to perform the steps of the method, for example, as illustrated in Figure 6. In such embodiments, the user plane core network entity 1200 may comprise a receiving unit and a reserving unit. The receiving unit may be configured to receive, during a procedure to prepare handover of a UE from a source RAN node to a target RAN node, a request message from a control plane core network entity. The request message comprises: a request to configure a tunnel for downlink packets for a connection for the UE from the user plane CN entity to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node. The reserving unit may be configured to reserve resources for the tunnel to the target RAN node. The term “unit” may have conventional meaning in the field of electronics, electrical devices and / or electronic devices and may include, for example, electrical and / or electronic circuitry, devices, modules, processors, memories, logic solid state and / or discrete devices, computer programs or instructions for carrying out respective tasks, procedures, computations, outputs, and / or displaying functions, and so on, as such as those that are described herein.

[0123] The methods of the present disclosure may be implemented in hardware, or as software modules running on one or more processors. The methods may also be carried out according to the instructions of a computer program, and the present disclosure also provides a computer readable medium having stored thereon a program for carrying out any of the methods described herein. A computer program embodying the disclosure may be stored on a computer readable medium, or it could, for example, be in the form of a signal such as a downloadable data signal provided from an Internet website, or it could be in any other form.

[0124] It should be noted that the above-mentioned examples illustrate rather than limit the disclosure, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended embodiments. The word “comprising” does not exclude the presence of elements or steps other than those listed in an embodiment or claim, “a” or “an” does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the embodiments. Any reference signs in the claims shall not be construed so as to limit their scope.

Claims

CLAIMS1. A method performed by a radio access network, RAN, entity (704, 706, 1000) in a communication system, the communication system comprising a RAN and a core network, CN, the method comprising: during a procedure to prepare handover of a user equipment, UE, (702) from a source RAN node (704) to a target RAN node (706), transmitting (402, 724) a request message to a CN entity (710), the request message comprising: a request to configure a tunnel for downlink packets for a connection for the UE from the core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node.

2. The method according to claim 1 , wherein the request message further comprises addressing information for the target radio access network.

3. The method according to claim 1 or 2, wherein the tunnel is configured to carry all downlink packets for the connection between the UE and the communication system.

4. The method according to any one of the preceding claims, wherein the method is performed by the source RAN node (704) or the target RAN node (706).

5. The method according to any one of the preceding claims, wherein the core network entity (710) is a control plane entity for session management.

6. The method according to any one of the preceding claims, wherein the request message is transmitted to the core network entity via one or more intermediate network entities (708).

7. The method according to any one of the preceding claims, wherein the indication that configuration of the tunnel is being requested prior to execution of the handover of the UE is an indication that configuration of the tunnel is being requested prior to transmission of a handover reconfiguration message from the source RAN node to the UE.

8. The method according to any one of claims 1 to 7, wherein the procedure to prepare handover of the UE is a procedure to configure the UE for conditional handover from the source RAN node (704) to the target RAN node (706).

9. The method according to claim 8, wherein the request message comprises a conditional path switch message.

10. A method performed by a network entity (710, 1100) in a communication system, the communication system comprising a RAN and a core network, CN, the method comprising: during a procedure to prepare handover of a user equipment, UE, (702) from a source RAN node to a target RAN node, receiving (502) a request message from a RAN entity (704, 706), the request message comprising: a request to configure a tunnel for downlink packets for a connection for the UE from the core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node; and configuring (504) a tunnel between one or more user plane CN entities (712) and the target RAN node (706).

11. The method according to claim 10, wherein configuring a tunnel between one or more user plane CN entities (712) and the target RAN node (706) comprises transmitting (506, 728) one or more messages to the one or more user plane CN entities (712) comprising addressing information for the target RAN node and an instruction to reserve resources for the transmission of downlink packets for the connection to the target RAN node.

12. The method according to claim 11 , wherein at least one of the one or more messages further comprises an indication that configuration of the tunnel is being requested prior to execution of the handover to the UE from the source RAN to the target RAN node.

13. The method according to claim 12, wherein the at least one of the one or more messages is transmitted to one or more user plane CN entities (712) configured for the transmission of downlink packets for the connection from the core network to the source RAN node (704).

14. The method according to any one of claims 11 to 13, wherein the one or more messages further comprise an indication of a timer, upon expiry of which without the tunnel being used, the one or more user plane CN entities (712) are permitted to release the resources.

15. The method according to any one of claims 10 to 14, further comprising transmitting (508) a response message to the RAN entity (704, 706), confirming that the tunnel has been configured.

16. The method according to any one of claims 10 to 15, further comprising: storing (510) an indication that the tunnel was configured prior to execution of the handover of the UE from the source RAN node to the target RAN node; receiving (512, 828, 926) a notification that handover of the UE is being or has been executed; and responsive to reception of the notification, and based on the stored indication, refraining (514, 830, 928) from establishing a further tunnel for the connection between the core network and the target RAN node.

17. The method according to claim 16, further comprising, responsive to reception of the notification, instructing (516, 832, 930) one or more user plane CN entities configured for the transmission of downlink packets for the connection from the core network to the source RAN node (704) to release resources for the transmission of downlink packets to the source RAN node (704).

18. The method according to claim 16 or 17, wherein the notification that handover of the UE is being or has been executed comprises one of: a handover completion message (828) from at least one of the one or more user plane CN entities; and a path switch request (926) received from a mobility management CN entity.

19. The method according to any one of claims 10 to 18, wherein the tunnel is configured to carry all downlink packets for the connection between the UE and the communication system.

20. The method according to any one of claims 10 to 19, wherein the RAN entity is the source RAN node (704) or the target RAN node (706).

21. The method according to any one of claims 10 to 20, wherein the network entity is a control plane entity.

22. The method according to any one of claims 10 to 21 , wherein the request message is received from the RAN entity via one or more intermediate network entities (708).

23. The method according to any one of claims 10 to 22, wherein the indication that configuration of the tunnel is being requested prior to execution of the handover of the UE is an indication that configuration of the tunnel is being requested prior to transmission of a handover reconfiguration message from the source RAN node to the UE.

24. The method according to any one of claims 10 to 22, wherein the procedure to prepare handover of the UE is a procedure to configure the UE for conditional handover from the source RAN node (704) to the target RAN node (706).

25. A method performed by a user plane core network entity (712, 812, 912, 1200) in a communication system, the communication system comprising a RAN and a CN, the method comprising: during a procedure to prepare handover of a user equipment, UE, (702) from a source RAN node (704) to a target RAN node (706), receiving (602, 728) a request message from a control plane CN entity (710), the request message comprising: a request to configure a tunnel for downlink packets for a connection for the UE from the user plane CN entity to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node; and reserving (604) resources for the tunnel to the target RAN node.

26. The method according to claim 25, wherein the user plane CN entity is further configured for the transmission of downlink packets for the connection to the source RAN node (704) prior to execution of the handover.

27. The method according to claim 26, further comprising, responsive to reception (606) of an uplink packet for the connection from the target RAN node, switching (608) the transmission of downlink packets for the connection from the source RAN node to the target RAN node.

28. The method according to claim 27, wherein the uplink packet is a dummy packet or wherein the uplink packet comprises user plane data.

29. The method according to claim 27 or 28, further comprising, responsive to reception of the uplink packet for the connection from the target RAN node, releasing resources for the transmission of downlink packets for the connection to the source RAN node.

30. The method according to any one of claims 25 to 29, further comprising, responsive to reception (606) of the uplink packet for the connection from the target RAN node, transmitting (612, 828) a handover complete message to a control plane CN entity (810).

31. The method according to any one of claims 25 to 30, wherein the tunnel is configured to carry all downlink packets for the connection between the UE and the communication system.

32. The method according to any one of claims 25 to 31 , wherein the request message further comprises an indication of a timer, the method further comprising, upon expiry of the timer without the tunnel being used, releasing the resources.

33. The method according to any one of claims 25 to 31 , wherein the indication that configuration of the tunnel is being requested prior to execution of the handover of the UE is an indication that configuration of the tunnel is being requested prior to transmission of a handover reconfiguration message from the source RAN node to the UE.

34. The method according to any one of claims 25 to 31 , wherein the procedure to prepare handover of the UE is a procedure to configure the UE for conditional handover from the source RAN node to the target RAN node.

35. A RAN entity (1000), comprising processing circuitry (1002) configured to cause the RAN entity to: during a procedure to prepare handover of a user equipment, UE, from a source RAN node to a target RAN node, transmit a request message to a core network, CN, entity, the request message comprising: a request to configure a tunnel for downlink packets for a connection for the UE from a core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node36. The RAN entity of claim 35, wherein the processing circuitry (1002) is further configured to cause the RAN entity to perform the method according to any one of claims 2 to 9.

37. A network entity (1100), comprising processing circuitry (1102) configured to cause the network entity to: during a procedure to prepare handover of a user equipment, UE, from a source RAN node to a target RAN node, receive a request message from a RAN entity, the request message comprising: a request to configure a tunnel for downlink packets for a connection for the UE from a core network to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node; and configure a tunnel between one or more user plane CN entities and the target RAN node.

38. The network entity of claim 37, wherein the processing circuitry (1102) is further configured to cause the network entity to perform the method according to any one of claims 11 to 24.

39. A user plane core network entity (1200), comprising processing circuitry (1202) configured to cause the user plane core network entity to: during a procedure to prepare handover of a user equipment, UE, from a source RAN node to a target RAN node, receive a request message from a control plane core network, CN, entity, the request message comprising:a request to configure a tunnel for downlink packets for a connection for the UE from the user plane CN entity to the target RAN node; and an indication that configuration of the tunnel is being requested prior to execution of the handover of the UE from the source RAN node to the target RAN node; and reserve resources for the tunnel to the target RAN node.

40. The user plane core network entity of claim 39, wherein the processing circuitry (1202) is further configured to cause the user plane core network entity to perform the method according to any one of claims 26 to 34.

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