WO2025201689A1

WO2025201689A1 - Conditional handover

Info

Publication number: WO2025201689A1
Application number: PCT/EP2025/051240
Authority: WO
Inventors: Rathi GANESHAN; Halit Murat Gürsu; Krzysztof Kordybach
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2024-03-28
Filing date: 2025-01-20
Publication date: 2025-10-02
Anticipated expiration: 2026-09-28
Also published as: GB2639914A; GB202404439D0

Abstract

Examples of the disclosure relate to indirect data forwarding during conditional handover. In examples of the disclosure a target secondary node receives a secondary node addition request from a target master node. The target secondary node determines whether the target master node is to be used for data forwarding and sends an acknowledgment to the secondary node addition request. The acknowledgement comprises data forwarding information and identifies whether the target master node is to be used for data forwarding.

Description

TITLE

Conditional Handover

TECHNOLOGICAL FIELD

Examples of the disclosure relate to conditional handover. Some relate to indirect data forwarding during conditional handover.

BACKGROUND

A conditional handover (CHO) is a handover that is executed by a user equipment (UE) when one or more handover execution conditions are met. CHO can be performed by UEs configured with dual connectivity. In such examples the source master node (MN) (controlling primary cell, (PCell)) sends a handover request to the target MN (controlling target PCell). In addition to preparing a candidate PCell the target MN selects a secondary node (controlling target primary secondary cell (PSCell)) and prepares it as part of the CHO preparation. When the CHO execution condition is met, the UE performs or initiates access procedure to the target PCell and PSCell.

BRIEF SUMMARY

According to various, but not necessarily all, examples of the disclosure there is provided a target secondary node comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the target secondary node to perform at least: receiving a secondary node addition request from a target master node; determining whether the target master node is to be used for data forwarding; sending acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding.

The data forwarding information can comprise tunnelling endpoint identification, TEID, details. Determining whether the target master node is to be used for data forwarding can comprise determining whether data forwarding information has previously been sent to the target master node or to another target master node.

The processor and at least one memory can be arranged to cause the target secondary node to perform: determining that the data forwarding information has not been sent to the target master node already; and based on determining that the data forwarding information has not been sent to the target master node already, including in the acknowledgement an indication that the target master node is to be used for data forwarding.

The processor and at least one memory can be arranged to cause the target secondary node to perform: determining that the data forwarding information has been sent to the another target master node already; and based on determining that the data forwarding information has been sent to the another target master node already, sending the acknowledgement without an indication that the target master node is to be used for data forwarding

The processor and at least one memory can be arranged to cause the target secondary node to perform: receiving a release request from a target master node that is used for data forwarding; and based on the release request, sending a modification request to a target master node that is not used for data forwarding, wherein the modification request comprises an indication that the target master node is to be used for data forwarding.

According to various, but not necessarily all, examples of the disclosure there may be provided a method comprising: receiving a secondary node addition request from a target master node; determining whether the target master node is to be used for data forwarding; sending acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding. According to various, but not necessarily all, examples of the disclosure there may be provided a computer program comprising instructions which, when executed by a target secondary node, cause the target secondary node to perform at least: receiving a secondary node addition request from a target master node; determining whether the target master node is to be used for data forwarding; sending acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding.

According to various, but not necessarily all, examples of the disclosure there may be provided a target master node comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the target master node to perform at least: sending a secondary node addition request to a target secondary node; receiving an acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding.

The data forwarding information can comprise tunnelling endpoint identification details.

The acknowledgement can include an indication that the target master node is to be used for data forwarding; and wherein the processor and at least one memory are arranged to cause the target master node to perform: performing, based on the indication included in the acknowledgement, data forwarding.

The secondary node addition request can be sent following receipt of a handover request from a source master node.

The processor and at least one memory can be arranged to cause the target master node to perform: sending a handover request acknowledgement to the source master node wherein the handover request acknowledgement identifies whether the target master node is to be used for data forwarding. The processor and at least one memory can be arranged to cause the target master node to perform: when the target master node is not used for data forwarding, receiving a modification request from the target secondary node, wherein the modification request comprises an indication that the target master node is to be used for data forwarding.

The processor and at least one memory can be arranged to cause the target master node to perform: sending, to the source master node, an indication of a new data forwarding path via the target master node to be used for data forwarding.

According to various, but not necessarily all, examples of the disclosure there may be provided a method comprising: sending a secondary node addition request to a target secondary node; receiving an acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding.

According to various, but not necessarily all, examples of the disclosure there may be provided a computer program comprising instructions which, when executed by a target secondary node, cause the target secondary node to perform at least: sending a secondary node addition request to a target secondary node; receiving an acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding.

According to various, but not necessarily all, examples of the disclosure there may be provided a source master node comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the source master node to perform at least: sending a handover request to multiple target master nodes; receiving a handover request acknowledgement from a target master node among the multiple target master nodes, wherein the handover request acknowledgement identifies whether the target master node among the multiple target master nodes is to be used for data forwarding. The acknowledgement can include an indication that the target master node among the multiple target master nodes is to be used for data forwarding; and wherein the processor and at least one memory are arranged to cause the source master node to perform: performing, based on the indication included in the acknowledgement, data forwarding via the target master node among the multiple target master nodes.

The processor and at least one memory can be arranged to cause the target master node to perform: receiving, from a target master node among the multiple target master nodes, an indication of a new data forwarding path and changing the data forwarding path to the new data forwarding path.

According to various, but not necessarily all, examples of the disclosure there may be provided a method comprising: sending a handover request to multiple target master nodes; receiving a handover request acknowledgement from a target master node among the multiple target master nodes, wherein the handover request acknowledgement identifies whether the target master node among the multiple target master nodes is to be used for data forwarding.

According to various, but not necessarily all, examples of the disclosure there may be provided a computer program comprising instructions which, when executed by a source secondary node, cause the source secondary node to perform at least: sending a handover request to multiple target master nodes; receiving a handover request acknowledgement from a target master node among the multiple target master nodes, wherein the handover request acknowledgement identifies whether the target master node among the multiple target master nodes is to be used for data forwarding.

According to various, but not necessarily all, examples of the disclosure there may be provided a target secondary node comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the source master node to perform at least: receiving a secondary node addition request from a target master node; determining that data forwarding information has previously been sent to another target master node, wherein the data forwarding information comprises tunnelling endpoint identification details; based on the determining, sending acknowledgment to the secondary node addition request without including the data forwarding information in the acknowledgement.

According to various, but not necessarily all, examples of the disclosure there may be provided a method comprising: receiving a secondary node addition request from a target master node; determining that data forwarding information has previously been sent to another target master node, wherein the data forwarding information comprises tunnelling endpoint identification details; based on the determining, sending acknowledgment to the secondary node addition request without including the data forwarding information in the acknowledgement.

According to various, but not necessarily all, examples of the disclosure there may be provided a computer program comprising instructions which, when executed by a target secondary node, cause the target secondary node to perform at least: receiving a secondary node addition request from a target master node; determining that data forwarding information has previously been sent to another target master node, wherein the data forwarding information comprises tunnelling endpoint identification details; based on the determining, sending acknowledgment to the secondary node addition request without including the data forwarding information in the acknowledgement.

According to various, but not necessarily all, embodiments there is provided an apparatus comprising: at least one processor; and at least one memory including computer program code; the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to perform at least a part of one or more methods described herein.

According to various, but not necessarily all, embodiments there is provided an apparatus comprising means for performing at least part of one or more methods described herein. The description of a function and/or action should additionally be considered to also disclose any means suitable for performing that function and/or action. Functions and/or actions described herein can be performed in any suitable way using any suitable method.

According to various, but not necessarily all, embodiments there is provided examples as claimed in the appended claims.

While the above examples of the disclosure and optional features are described separately, it is to be understood that their provision in all possible combinations and permutations is contained within the disclosure. It is to be understood that various examples of the disclosure can comprise any or all the features described in respect of other examples of the disclosure, and vice versa. Also, it is to be appreciated that any one or more or all the features, in any combination, may be implemented by/comprised in/performable by an apparatus, a method, and/or computer program instructions as desired, and as appropriate. The description of a function should additionally be considered to also disclose any means suitable for performing that function

BRIEF DESCRIPTION

Some examples will now be described with reference to the accompanying drawings in which:

FIG. 1 shows an example network;

FIG. 2 shows an example method;

FIG. 3 shows an example method;

FIG. 4 shows an example method;

FIG. 5 shows an example signal flow;

FIG. 6 shows an example method;

FIG. 7 shows an example signal flow;

FIG. 8 shows an example handover;

FIG. 9 shows an example handover; and

FIG. 10 shows an example controller.

The figures are not necessarily to scale. Certain features and views of the figures can be shown schematically or exaggerated in scale in the interest of clarity and conciseness. For example, the dimensions of some elements in the figures can be exaggerated relative to other elements to aid explication. Corresponding reference numerals are used in the figures to designate corresponding features. For clarity, all reference numerals are not necessarily displayed in all figures. DEFINITIONS gNB gNodeB

MME Mobility Management Entity

MN Master Node

NR New Radio

PCell Primary Cell

PSCell Primary Secondary Cell

QoE Quality of Experience

RAN Radio Access Network

SN Secondary Node

TEID Tunnel Endpoint identifier (ID)

UE User Equipment

DETAILED DESCRIPTION

Fig. 1 illustrates an example of a communications network 100 such as a 5G network or a 6G network or any other suitable type of network. The network 100 comprises a plurality of different types of nodes 110, 120, 130. The different types of nodes 110, 120, 130 can comprise terminal nodes 110, and network nodes 120, 130. The network nodes can comprise access nodes 120 and core network nodes 130 and/or any other suitable type of apparatus or device.

The access nodes 120 can be configured to communicate with the terminal nodes 110. The core network nodes 130 communicate with the access nodes 120. In some examples the core network nodes 130 communicate with the terminal nodes 110.

The core network nodes 130 can, in some examples, communicate with each other. The one or more access nodes 120 can, in some examples, communicate with each other.

The network 100 can be a cellular network comprising a plurality of cells 122. Each of the cells is served by an access node 120. In this example, the interface between the terminal node 110 and an access node 120 providing a cell 122 is a wireless interface 124.

The access nodes 120 can comprise one or more cellular radio transceivers. The terminal nodes 110 can comprise one or more cellular radio transceivers. The terminal nodes 110 can comprise user equipments (UEs) or any other suitable type of devices.

The access nodes 120 can be base stations. The access nodes 120 can be any suitable type of base station. The access node 120 can be a network entity responsible for radio transmission and reception in one or more cells to or from terminal nodes 110. The access node 120 can be a network element in a Radio Access Network (RAN), or any other suitable type of network.

The core network nodes 130 can be part of a core network. The core network nodes 130 can be configured to manage functions relating to connectivity for the terminal nodes 110. For example, the core network nodes 130 can be configured to manage functions such as connectivity, mobility, authentication, authorization and/or other suitable functions.

In the example of Fig. 1 the core network node 130 is shown as a single entity. In some examples the core network node 130 could be distributed across multiple entities. For example, the core network node 130 could be cloud based or distributed in any other suitable manner.

The network 100 can be any suitable type of network, for example it can be a New Radio (NR) network that uses gNB as access nodes. New Radio is the 3GPP name for 5G technology. In such cases the access nodes 120 can comprise gNBs configured to provide user plane and control plane protocol terminations towards the terminal nodes 110 and/or to perform any other suitable functions. The gNBs are interconnected with each other by means of an X2/Xn interface 126. The gNBs are also connected by means of the N2 interface 128 to the core network nodes 130. Other types of networks and interfaces could be used in other examples. Other types of networks could comprise next-generation mobile and communication network, for example, a 6G network.

A UE 110 or other terminal node can perform a conditional handover (CHO) from a first access node 120 to a second access node 120. CHO is designed so that the UE 110 can initiate the handover autonomously without the need for the serving access node 120 to trigger the handover execution. To enable CHO the UE 110 is configured with a CHO command containing the target cell configuration and a condition to execute the handover for one or multiple target cells. The condition can be based on, for example, radio measurements of the neighboring cells or any other suitable factors. CHO can be performed by UEs 110 configured with dual connectivity. In such examples the source master node (MN) (controlling primary cell, (PCell)) sends a Handover Request to the target MN (controlling target PCell). In addition to preparing a candidate PCell the target MN selects a secondary node (controlling target primary secondary cell (PSCell)) and prepares it as part of the CHO preparation. When the CHO execution condition is met, the UE 110 performs access to the target PCell and PSCell.

Multiple secondary nodes may be prepared for the handover. In case of multiple preparations, each target MN can prepare its own target secondary node (SN). A target MN may prepare multiple SNs. It is possible for multiple target MNs to select the same target SN because each of the target MNs will receive the same measurements. A target SN can determine that SN addition requests received from different target MNs are related to the same UE 110. A target SN can compare the Secondary Cell Group (SCG) configurations to determine that multiple target MNs have provided the same configuration for SN terminated bearers.

Duplicate data forwarding can occur if the bearer is SN terminated and there are multiple target MNs that have selected the same target SN. In a scenario, wherein multiple target MNs have selected the same target SN, data forwarding from the source MN to the target SN can occur via a first target MN and a second target MN. The duplication of this data or duplicate data forwarding can cause an overload to the system.

Examples of the disclosure address these issues and reduce unnecessary data forwarding in such systems.

Fig. 2 shows an example method that may be implemented in examples of the disclosure. The method of Fig. 2 may be implemented by a target SN or an apparatus such as a controller within a target SN.

The method of Fig. 2 comprises, at block 200, receiving an SN addition request from a target MN.

At block 202 the method comprises determining whether the target MN that has sent the request is to be used for data forwarding.

In examples of the disclosure the target MN can be used for data forwarding if data forwarding information has not been sent previously to another target MN (or to the target MN). For example, if the target MN is the first target MN to send the SN addition request to the target SN then no data forwarding will have been sent to any target nodes yet. Determining whether the target MN is to be used for data forwarding can therefore comprise determining whether data forwarding information has previously been sent to another target MN (or to the target MN).

At block 204 the method comprises sending acknowledgment to the SN addition request. The acknowledgement comprises data forwarding information. The acknowledgement identifies whether the target MN is to be used for data forwarding.

In some use cases, the target SN will determine that the data forwarding information has not been sent to the target MN already. In such cases the target MN will be used for data forwarding. Therefore, based on determining that the data forwarding information has not been sent to the target MN already the target SN will include an indication that the target MN is to be used for data forwarding in the acknowledgement.

In some use cases, the target SN will determine that the data forwarding information has been sent to the target MN or to another target MN already. In such cases the target MN that has sent the request will not be used for data forwarding. Therefore, based on determining that the data forwarding information has been sent to a target MN already the target SN will include, in the acknowledgement, an indication that the target MN is not to be used for data forwarding. Another option may be that the information element reserved for the data forwarding information is left empty. A further option may be that the information element reserved for the data forwarding information is absent from the acknowledgement.

Any suitable means can be used to identify if the target MN is to be used for data forwarding. For instance, the acknowledgement can comprise an information element (IE) that is used to identify whether the target MN is to be used for data forwarding. In such cases if the IE is present in the acknowledgement then the target MN is to be used for data forwarding. If the IE is not present in the acknowledgement then target MN is not to be used for data forwarding.

The data forwarding information that is included in the acknowledgement comprises information that enables data to be forwarded to the target SN. The data forwarding information comprises tunnel endpoint identifier (TEID) details or any other suitable data. TEID details may be referred to as tunnelling endpoint identification details. In some examples the method performed by the target SN can comprise additional blocks that are not shown in Fig. 2. For example if a target MN cancels the handover request then additional blocks to the method can be performed to change the target MN that is used for data forwarding. For example, the target SN can receive a release request from a target MN that is used for data forwarding. Based on the release request, the target MN sends a modification request to a target MN that is not used for data forwarding. This can be a target MN that has previously been sent an indication that it is not to be used for data forwarding. The modification request comprises an indication that the target MN is now to be used for data forwarding.

Fig. 3 shows another example method that may be implemented in examples of the disclosure. The method of Fig. 3 may be implemented by a target MN or an apparatus such as a controller within a target MN. The target MN that performs the method of Fig. 3 can be a corresponding target MN to the target SN that performs the method of Fig. 2.

The method of Fig. 3 comprises, at block 300, sending an SN addition request to a target SN. The SN addition request can be sent following receipt of a handover request from a source MN or following any other suitable trigger event.

At block 302 the method comprises receiving an acknowledgment to the SN addition request. The acknowledgement comprises data forwarding information. The acknowledgement identifies whether the target MN is to be used for data forwarding.

The data forwarding information comprises information that enables data to be forwarded to the target SN. The data forwarding information can comprise TEID details.

If the acknowledgement that is received includes an indication that the target MN is to be used for data forwarding then the target MN will use the indication included in the acknowledgement to perform data forwarding.

Conversely, if the acknowledgement that is received includes an indication that the target MN is not to be used for data forwarding then the target MN will not perform data forwarding.

Any suitable means can be used to indicate whether the target MN is to be used for data forwarding. In some examples the acknowledgement can comprise an information element (IE) that is used to identify whether the target MN is to be used for data forwarding. In such cases if the IE is present in the acknowledgement then the target MN is to be used for data forwarding. If the IE is not present in the acknowledgement then target MN is not to be used for data forwarding.

In some examples the method can comprise additional blocks that are not shown in Fig. 3. For example the method can comprise sending a handover request acknowledgement to the source MN that triggered the method of Fig. 3. The handover request acknowledgement can identify whether the target MN is to be used for data forwarding.

Also in some examples the target MN that is to be used for data forwarding can change. For example, the target MN that is to be used for data forwarding may cancel the request. In such cases if the target MN is an MN that is not to be used for data forwarding it can receive a modification request from the target SN. The modification request comprises an indication that the target MN is to be used for data forwarding. In such cases the target MN can send an indication of a new data forwarding path to the source MN. The data forwarding path can be used for data forwarding via the target MN.

Fig. 4 shows another example method that may be implemented in examples of the disclosure. The method of Fig. 4 may be implemented by a source MN or an apparatus such as a controller within a source MN. The source MN that performs the method of Fig. 4 can be a corresponding source MN to the target SN that performs the method of Fig. 2 and the target MN that performs the method of Fig. 3.

The method comprises, at block 400, sending a handover request to multiple target MNs.

At block 402 the method comprises receiving a handover request acknowledgement from a target MN among the multiple target MNs. The handover request acknowledgement identifies whether the target MN among the multiple target MNs is to be used for data forwarding.

If the handover request acknowledgement includes an indication that the target MN among the multiple target MNs is to be used for data forwarding then the method comprises performing data forwarding via the target MN among the multiple target MNs. The data forwarding can be performed based on the indication included in the handover request acknowledgement. In an example, the data forwarding can be performed based on detected absence of the indication in the handover request acknowledgement. Any suitable means can be used to indicate whether the target MN is to be used for data forwarding. In some examples the handover request acknowledgement can comprise an information element (IE) that is used to identify whether the target MN (sender of the handover request acknowledgement) is to be used for data forwarding. In such cases if the IE is present in the handover request acknowledgement then the target MN is to be used for data forwarding. If the IE is not present in the handover request acknowledgement then target MN (sender of the handover request acknowledgement) is not to be used for data forwarding. The handover request acknowledgement may identify whether the target MN is to be used for data forwarding.

The method performed by the source MN can also comprise blocks that are not shown in Fig. 4. For example, if a target MN cancels the handover request then the method can comprise additional blocks that are not shown in Fig. 4. The additional blocks could comprise receiving, from a target MN among the multiple target MNs, an indication of a new data forwarding path and changing the data forwarding path to the new data forwarding path.

Fig. 5 shows an example signal flow that can be used in some examples. In the example of Fig. 5 multiple data forwarding paths are provided to the source MN but only one of these data forwarding paths is indicated as the main data forwarding path. In this example an IE is added to the acknowledgements (SN addition request acknowledgement (Ack) and handover request Ack) and used to indicate whether the target MN is to be used for data forwarding. The presence or absence of an IE in the acknowledgements can be used to distinguish between a target MN that is to be used for data forwarding and a target MN that is not to be used for data forwarding.

Fig. 5 also shows signaling that can be used if the main data forwarding path is released. The example signal flow of Fig. 5 can be used to enable a different data path to be indicated as the main data forwarding path.

In blocks 500 to 506 a source MN prepares multiple target MNs for CHO of the UE 110. In this case a first target MN and a second target MN are prepared. More than two target MNs could be prepared in other examples.

At block 500 the UE sends a measurement report to the source MN. At block 502 the source MN makes a decision whether to trigger CHO. The decision can be based on the measurement report. Following the decision to trigger CHO the source MN sends a handover request to multiple target MNs. At block 504 the source MN sends a handover request to a first target MN1 and at block 506 the source MN sends a handover request to a second target MN2.

When the target MNs receive the handover request the target MNs will prepare a target SN for the CHO of the UE. The target MNs can each prepare a target SN for the CHO independently of the other target MNs.

At block 508 the first target MN1 sends an SN addition request to a target SN. At block 510 the target SN determines if the first target MN1 is to be used for data forwarding.

In this example, to determine if the first target MN1 is to be used for data forwarding the target SN checks if the first target MN1 has previously been sent TEID details. In this case the TEID details have not already been sent to the first target MN1.

The target SN will reserve resources for the UE for the CHO and at block 512 the target SN sends an acknowledgement (SN addition request Ack) to the first target MN1. The acknowledgement comprises TEID and an IE indicating that the first target MN1 is to be used as the main data forwarding path.

The first target MN1 receives the acknowledgement from the target SN. At block 514 the first target MN1 sends a handover request acknowledgement to the source MN. The handover request acknowledgement comprises an IE indicating that the first target MN1 is to be used as the main data forwarding path.

The second target MN2 also follows a similar procedure to prepare a target SN for the CHO of the UE. In this case the second target MN2 can prepare the same target SN as the first target MN1. This circumstance can arise during CHO because the respective target MNs (the first target MN1 and the second target MN2) receive the same measurement results from the UE.

At block 516 the second target MN2 sends an SN addition request to the target SN. At block 518 the target SN determines if the second target MN2 is to be used for data forwarding. In this example, to determine if the second target MN2 is to be used for data forwarding the target SN checks if the TEID details have previously been sent to a target MN. In this case the TEID details have already been sent to the first target MN1.

The target SN will determine that resources are already reserved for the UE for the CHO. In this case the resources are reserved at the first target MN1. At block 520 the target SN sends an acknowledgement to the second target MN2. The acknowledgement comprises TEID but does not comprise an IE indicating that the second target MN2 is to be used as the main data forwarding path. In this case the absence of the IE in the acknowledgement indicates that the second target MN2 is not to be used as the main data forwarding path.

The second target MN2 receives the acknowledgement from the target SN. At block 522 the second target MN2 sends a handover request acknowledgement to the source MN. The handover request acknowledgement does not comprise an IE indicating that the second target MN2 is to be used as the main data forwarding path. The absence of the IE in the acknowledgement indicates that the second target MN2 is not to be used as the main data forwarding path. This therefore informs the source MN that the UE context exists and that resources are reserved for the target SN and also for the target MN1.

At block 524 the source MN sends an RRC reconfiguration message to the UE. The RRC reconfiguration message can comprise a CHO command.

At block 526 the UE evaluates the CHO condition. If one of the CHO conditions is met for a prepared target cell then UE can apply the corresponding CHO configuration and execute the handover. At block 528 user data is transmitted between the UE and the source MN.

At block 530 early data forwarding is performed via the first target MN1. Data forwarding is not performed via the second target MN2. The data forwarding is performed in accordance with the indications provided in the acknowledgement.

In the example of Fig. 5 an overload scenario or some other similar scenario is detected in the first target MN1 which causes the first target MN1 to decide to cancel the CHO. At block 532 the first target MN1 sends a CHO handover cancel message to the source MN and at block 534 the first target MN1 also sends an SN release request to the target SN.

The target SN can determine that the target MN1 that has been designated for data forwarding has cancelled CHO. The main data forwarding path is therefore no longer to be used and the target SN now has to determine another data forwarding path. The target MN that is used to replace the cancelled data forwarding path can be selected based on channel conditions, based on the order in which the target SN has received requests or based on any other suitable factors.

At block 536 the target SN sends a modification request to the target MN that is to replace the first target MN1 as the main data forwarding path. In this example there is only one alternative target MN and so the modification request is sent to the second target MN2. The second target MN2 sends a confirmation to the modification request at block 538.

At block 540 the second target MN2 sends an Xn-ll address indication to the source MN. This can comprise an IE indicating that the second target MN2 is now to be used for data forwarding. This is used by the source MN to update data forwarding TEID details. At block 542 early data forwarding is performed via the second target MN2.

At block 544 the UE determines that a CHO condition is (or conditions are) fulfilled for a prepared cell and executes the handover. At block 546 the PRACH preamble is sent from the UE to second target MN2 and at block 548 the second target MN2 sends a RACH response to the UE. At block 550 an RRC reconfiguration complete message is sent from the UE to the second target MN2. At block 552 the source MN stops transmitting to the UE and starts data forwarding. At block 554 an SN status transfer message is sent from the source MN to the second target MN2. At block 556 data forwarding is performed via the second target MN2. At block 558 the path switch from the source MN to the target MN is performed.

Fig. 6 shows another example method that may be implemented in examples of the disclosure. The method of Fig. 6 may be implemented by a target SN or an apparatus such as a controller within a target SN.

The method of Fig. 6 comprises, at block 600, receiving an SN addition request from a target MN. At block 602 the method comprises determining whether data forwarding information has previously been sent to another target MN. The data forwarding information comprises TEID details.

At block 604 the method comprises based on the determining, sending acknowledgment to the secondary node addition request without including the data forwarding information in the acknowledgement. The data forwarding information is included in the acknowledgement if the target MN is to be used for data forwarding and the data forwarding information is not included in the acknowledgement if the target MN is not to be used for data forwarding.

Fig. 7 shows an example signal flow that can implement the method of Fig. 6. In the example of Fig. 7 multiple data forwarding paths are provided to the source MN but only one of these data forwarding paths is indicated as the main data forwarding path. In this example an IE is added to the acknowledgements and used to indicate whether the target MN is to be used for data forwarding. The presence or absence of an IE in the acknowledgements can be used to distinguish between a target MN that is to be used for data forwarding and a target MN that is not to be used for data forwarding.

Fig. 7 also shows signaling that can be used if the main data forwarding path is released. The example signal flow of Fig. 7 can be used to enable a different data path to be indicated as the main data forwarding path.

In blocks 700 to 706 a source MN prepares multiple target MNs for CHO of the UE 110. In this case a first target MN and a second target MN are prepared. More than two target MNs could be prepared in other examples.

At block 700 the UE sends a measurement report to the source MN. At block 702 the source MN makes a decision whether to perform CHO. The decision can be based on the measurement report.

Following the decision to perform CHO the source MN sends a handover request to multiple target MNs. At block 704 the source MN sends a handover request to a first target MN1 and at block 706 the source MN sends a handover request to a second target MN2. When the target MNs receive the handover request the target MNs will prepare a target SN for the CHO of the UE. The target MNs can each prepare a target SN for the CHO independently of the other target MNs.

At block 708 the first target MN1 sends an SN addition request to a target SN. At block 510 the target SN determines if the first target MN1 is to be used for data forwarding.

In this example, to determine if the first target MN1 is to be used for data forwarding the target SN checks if the first target MN1 has previously been sent TEID details. In this case the TEID details have not already been sent to the first target MN1 .

The target SN will reserve resources for the UE for the CHO and at block 712 the target SN sends an acknowledgement to the first target MN1. The acknowledgement comprises TEID details. The presence of the TEID details in the acknowledgement indicates that the first target MN1 is to be used as the main data forwarding path.

The first target MN1 receives the acknowledgement from the target SN. At block 714 the first target MN1 sends a handover request acknowledgement to the source MN. The handover request acknowledgement comprises an IE indicating that the first target MN1 is to be used as the main data forwarding path.

The second target MN2 also follows a similar procedure to prepare a target SN for the CHO of the UE. In this case the second target MN2 can prepare the same target SN and the first target MN1. This circumstance can arise during CHO because the respective target MNs receive the same measurement results from the UE.

At block 716 the second target MN2 sends an SN addition request to the target SN. At block 718 the target SN determines if the second target MN2 is to be used for data forwarding.

In this example, to determine if the second target MN2 is to be used for data forwarding the target SN checks if the TEID details have previously been sent to a target MN. In this case the TEID details have already been sent to the first target MN1.

The target SN will determine that resources are already reserved for the UE for the CHO. In this case the resources are reserved at the first target MN1. At block 720 the target SN sends an acknowledgement to the second target MN2. The acknowledgement does not comprise the TEID details. The absence of the TEID details in the acknowledgement indicates that the second target MN2 is not to be used as the main data forwarding path.

The second target MN2 receives the acknowledgement from the target SN. At block 722 the second target MN2 sends a handover request acknowledgement to the source MN. The handover request acknowledgement does not comprise an IE indicating that the second target MN2 is to be used as the main data forwarding path. The absence of the IE in the acknowledgement indicates that the second target MN2 is not to be used as the main data forwarding path. This therefore informs the source MN that the UE context exists and that resources are reserved for the target SN and also for the target MN1.

At block 724 the source MN sends an RRC reconfiguration message to the UE. The RRC reconfiguration message can comprise a CHO command.

At block 726 the UE evaluates the CHO condition. If one of the CHO conditions is met for a prepared target cell then UE can apply the corresponding CHO configuration and execute the handover. At block 728 user data is transmitted between the UE and the source MN.

At block 730 early data forwarding is performed via the first target MN1. Data forwarding is not performed via the second target MN2. The data forwarding is performed in accordance with the indications provided in the acknowledgement.

In the example of Fig. 7 an overload scenario or some other similar scenario is detected in the first target MN1 which causes the first target MN1 to decide to cancel the CHO.

At block 732 the first target MN1 sends a CHO handover cancel message to the source MN and at block 734 the first target MN1 also sends an SN release request to the target SN.

The target SN can determine that the target MN1 that has been designated for data forwarding has cancelled CHO. The main data forwarding path is therefore no longer to be used and the target SN now has to determine another data forwarding path. The target MN that is used to replace the cancelled data forwarding path can be selected based on channel conditions, based on the order in which the target SN has received requests or based on any other suitable factors. At block 736 the target SN sends a modification request to the target MN that is to replace the first target MN1 as the main data forwarding path. In this example there is only one alternative target MN and so the modification request is sent to the second target MN2. The modification request comprises the TEID details that can be used for data forwarding.

The second target MN2 sends a confirmation to the modification request at block 738.

At block 740 the second target MN2 sends an Xn-ll address indication to the source MN. This can comprise an IE indicating that the second target MN2 is now to be used for data forwarding. This is used by the source MN to update data forwarding TEID details. At block 742 early data forwarding is performed via the second target MN2.

At block 744 the UE determines that a CHO is fulfilled for a prepared cell and executes the handover. At block 746 the PRACH preamble is sent from the UE to second target MN2 and at block 748 the second target MN2 sends a RACH response to the UE. At block 750 an RRC reconfiguration complete message is sent from the UE to the second target MN2. At block 752 the source MN stops transmitting to the UE and starts data forwarding. At block 754 an SN status transfer message is sent from the source MN to the second target MN2. At block 756 data forwarding is performed via the second target MN2. At block 758 the path switch from the source MN to the target MN is performed.

Fig. 8 shows an example handover scenario for which examples of the disclosure can be used. In the examples of Fig. 8 indirect data forwarding is used. In the examples of Fig. 8 data is terminated in the source SN. In the first case 800 data is forwarded from the source SN 804, to the Source MN 806 then to the candidate MNs 808 and then to the target SN 810.

In the second case 802 data is forwarded from the source SN 804 to the candidate MNs 808 and then to the target SN 810.

Fig. 9 shows an example handover scenario for which examples of the disclosure can be used. In the example of Fig. 9 indirect data forwarding is used. In the example of Fig. 9 data is terminated in the source MN. In this case 900 data is forwarded from the Source MN 806 then to the candidate MNs 808 and then to the target SN 810. Fig. 10 shows an example controller 1000. The controller 1000 could be provided within an entity such as a target secondary node, a target master node, a source master node or any other suitable entity. Implementation of the controller 1000 may be as controller circuitry. The controller 1000 may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware).

As illustrated in Fig. 10 the controller 1000 can be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program 1006 in a general-purpose or special-purpose processor 1002 that may be stored on a computer readable storage medium (disk, memory etc.) to be executed by such a processor 1002.

The processor 1002 is configured to read from and write to the memory 1004. The processor 1002 may also comprise an output interface via which data and/or commands are output by the processor 1002 and an input interface via which data and/or commands are input to the processor 1002.

The memory 1004 stores a computer program 1006 comprising computer program instructions (computer program code) that controls the operation of the apparatus when loaded into the processor 1002. The computer program instructions, of the computer program 1006, provide the logic and routines that enables the apparatus to perform the methods illustrated in the Figs. The processor 1002 by reading the memory 1004 is able to load and execute the computer program 1006.

The controller 1000 therefore comprises means for: receiving 200 a secondary node addition request from a target master node; determining 202 whether the target master node is to be used for data forwarding; sending 204 acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding.

The controller 1000 therefore comprises means for: sending 300 a secondary node addition request to a target secondary node; receiving 302 an acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding.

The controller 1000 therefore comprises means for: sending 400 a handover request to multiple target master nodes; receiving 402 a handover request acknowledgement from a target master node among the multiple target master nodes, wherein the handover request acknowledgement identifies whether the target master node among the multiple target master nodes is to be used for data forwarding.

The controller 1000 therefore comprises means for: receiving 600 a secondary node addition request from a target master node; determining 602 that data forwarding information has previously been sent to another target master node, wherein the data forwarding information comprises tunnelling endpoint identification details; based on the determining, sending acknowledgment to the secondary node addition request without including the data forwarding information in the acknowledgement.

The computer program 1006 may arrive at the apparatus via any suitable delivery mechanism 1008. The delivery mechanism 1008 may be, for example, a machine- readable medium, a computer-readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a Compact Disc Read-Only Memory (CD-ROM) or a Digital Versatile Disc (DVD) or a solid-state memory, an article of manufacture that comprises or tangibly embodies the computer program 1006. The delivery mechanism may be a signal configured to reliably transfer the computer program 1006. The apparatus may propagate or transmit the computer program 1006 as a computer data signal.

The computer program 1006 can comprise computer program instructions for causing a target secondary node to perform at least the following or for performing at least the following: receiving 200 a secondary node addition request from a target master node; determining 202 whether the target master node is to be used for data forwarding; sending 204 acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding.

The computer program 1006 can comprise computer program instructions for causing a target master node to perform at least the following or for performing at least the following: sending 300 a secondary node addition request to a target secondary node; receiving 302 an acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding.

The computer program 1006 can comprise computer program instructions for causing a source master node to perform at least the following or for performing at least the following: sending 400 a handover request to multiple target master nodes; receiving 402 a handover request acknowledgement from a target master node among the multiple target master nodes, wherein the handover request acknowledgement identifies whether the target master node among the multiple target master nodes is to be used for data forwarding.

The computer program 1006 can comprise computer program instructions for causing a target secondary node to perform at least the following or for performing at least the following: receiving 600 a secondary node addition request from a target master node; determining 602 that data forwarding information has previously been sent to another target master node, wherein the data forwarding information comprises tunnelling endpoint identification details; based on the determining, sending acknowledgment to the secondary node addition request without including the data forwarding information in the acknowledgement.

The computer program instructions may be comprised in a computer program, a non- transitory computer readable medium, a computer program product, a machine-readable medium. In some but not necessarily all examples, the computer program instructions may be distributed over more than one computer program. Although the memory 1004 is illustrated as a single component/circuitry it may be implemented as one or more separate components/circuitry some or all of which may be integrated/removable and/or may provide permanent/semi-permanent/ dynamic/cached storage.

Although the processor 1002 is illustrated as a single component/circuitry it may be implemented as one or more separate components/circuitry some or all of which may be integrated/removable. The processor 1002 may be a single core or multi-core processor.

The apparatus can be provided in an electronic device, for example, a mobile terminal, according to an example of the present disclosure. It should be understood, however, that a mobile terminal is merely illustrative of an electronic device that would benefit from examples of implementations of the present disclosure and, therefore, should not be taken to limit the scope of the present disclosure to the same. While in certain implementation examples, the apparatus can be provided in a mobile terminal, other types of electronic devices, such as, but not limited to: mobile communication devices, hand portable electronic devices, wearable computing devices, portable digital assistants (PDAs), pagers, mobile computers, desktop computers, televisions, gaming devices, laptop computers, cameras, video recorders, GPS devices and other types of electronic systems, can readily employ examples of the present disclosure. Furthermore, devices can readily employ examples of the present disclosure regardless of their intent to provide mobility.

The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to ‘comprising only one...’ or by using ‘consisting.’

In this description, the wording ‘connect’, ‘couple’ and ‘communication’ and their derivatives mean operationally connected/coupled/in communication. It should be appreciated that any number or combination of intervening components can exist (including no intervening components), i.e., to provide direct or indirect connection/coupling/communication. Any such intervening components can include hardware and/or software components. As used herein, the term "determine/determining" (and grammatical variants thereof) can include, not least: calculating, computing, processing, deriving, measuring, investigating, identifying, looking up (for example, looking up in a table, a database, or another data structure), ascertaining and the like. Also, "determining" can include receiving (for example, receiving information), accessing (for example, accessing data in a memory), obtaining and the like. Also, " determine/determining" can include resolving, selecting, choosing, establishing, and the like.

In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’, or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example.

As used herein, “at least one of the following:” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or” mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims.

Features described in the preceding description may be used in combinations other than the combinations explicitly described above.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. 1

The description of a feature, such as an apparatus or a component of an apparatus, configured to perform a function, or for performing a function, should additionally be considered to also disclose a method of performing that function. For example, description of an apparatus configured to perform one or more actions, or for performing one or more actions, should additionally be considered to disclose a method of performing those one or more actions with or without the apparatus.

Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not.

The term ‘a’, ‘an’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a/an/the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’, ‘an’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning.

The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result.

In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described.

The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative structures and method features which offer equivalent functionality to the specific examples of such structures and features described herein above and which for the sake of brevity and clarity have been omitted from the above description. Nonetheless, the above description should be read as implicitly including reference to such alternative structures and method features which provide equivalent functionality unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure.

Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not emphasis has been placed thereon. l/we claim:

Claims

1 . A target secondary node comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the target secondary node to perform at least: receiving a secondary node addition request from a target master node; determining whether the target master node is to be used for data forwarding; sending acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding.

2. The target secondary node as claimed in claim 1 wherein the data forwarding information comprises tunnelling endpoint identification, TEID, details.

3. The target secondary node as claimed in any preceding claim wherein determining whether the target master node is to be used for data forwarding comprises determining whether data forwarding information has previously been sent to the target master node or to another target master node.

4. The target secondary node as claimed in claim 3, wherein the processor and at least one memory are arranged to cause the target secondary node to perform: determining that the data forwarding information has not been sent to the target master node already; and based on determining that the data forwarding information has not been sent to the target master node already, including in the acknowledgement an indication that the target master node is to be used for data forwarding.

5. The target secondary node as claimed in claim 3, wherein the processor and at least one memory are arranged to cause the target secondary node to perform: determining that the data forwarding information has been sent to the another target master node already; and based on determining that the data forwarding information has been sent to the another target master node already, sending the acknowledgement without an indication that the target master node is to be used for data forwarding

6. The target secondary node as claimed in any preceding claim wherein the processor and at least one memory are arranged to cause the target secondary node to perform: receiving a release request from a target master node that is used for data forwarding; and based on the release request, sending a modification request to a target master node that is not used for data forwarding, wherein the modification request comprises an indication that the target master node is to be used for data forwarding.

7. A method comprising: receiving a secondary node addition request from a target master node; determining whether the target master node is to be used for data forwarding; sending acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding.

8. A computer program comprising instructions which, when executed by a target secondary node, cause the target secondary node to perform at least: receiving a secondary node addition request from a target master node; determining whether the target master node is to be used for data forwarding; sending acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding.

9. A target master node comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the target master node to perform at least: sending a secondary node addition request to a target secondary node; receiving an acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding.

10. The target master node as claimed in claim 8 wherein the data forwarding information comprises tunnelling endpoint identification details.

11. The target master node as claimed in any of claims 9 to 10 wherein the acknowledgement includes an indication that the target master node is to be used for data forwarding; and wherein the processor and at least one memory are arranged to cause the target master node to perform: performing, based on the indication included in the acknowledgement, data forwarding.

12. The target master node as claimed in any of claims 9 to 11 wherein the secondary node addition request is sent following receipt of a handover request from a source master node.

13. The target master node as claimed in any of claims 9 to 12 wherein the processor and at least one memory are arranged to cause the target master node to perform: sending a handover request acknowledgement to the source master node wherein the handover request acknowledgement identifies whether the target master node is to be used for data forwarding.

14. The target master node as claimed in any of claims 9 to 13 wherein the processor and at least one memory are arranged to cause the target master node to perform: when the target master node is not used for data forwarding, receiving a modification request from the target secondary node, wherein the modification request comprises an indication that the target master node is to be used for data forwarding.

15. The target master node as claimed in claim 14 wherein the processor and at least one memory are arranged to cause the target master node to perform: sending, to the source master node, an indication of a new data forwarding path via the target master node to be used for data forwarding.

16. A method comprising: sending a secondary node addition request to a target secondary node; receiving an acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding.

17. A computer program comprising instructions which, when executed by a target secondary node, cause the target secondary node to perform at least: sending a secondary node addition request to a target secondary node; receiving an acknowledgment to the secondary node addition request wherein the acknowledgement comprises data forwarding information; and wherein the acknowledgement identifies whether the target master node is to be used for data forwarding.

18. A source master node comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the source master node to perform at least: sending a handover request to multiple target master nodes; receiving a handover request acknowledgement from a target master node among the multiple target master nodes, wherein the handover request acknowledgement identifies whether the target master node among the multiple target master nodes is to be used for data forwarding.

19. The source master node as claimed in claim 18 wherein the acknowledgement includes an indication that the target master node among the multiple target master nodes is to be used for data forwarding; and wherein the processor and at least one memory are arranged to cause the source master node to perform: performing, based on the indication included in the acknowledgement, data forwarding via the target master node among the multiple target master nodes.

20. The source master node as claimed in any of claims 18 to 19 wherein the processor and at least one memory are arranged to cause the target master node to perform: receiving, from a target master node among the multiple target master nodes, an indication of a new data forwarding path and changing the data forwarding path to the new data forwarding path.

21. A method comprising: sending a handover request to multiple target master nodes; receiving a handover request acknowledgement from a target master node among the multiple target master nodes, wherein the handover request acknowledgement identifies whether the target master node among the multiple target master nodes is to be used for data forwarding.

22. A computer program comprising instructions which, when executed by a source secondary node, cause the source secondary node to perform at least: sending a handover request to multiple target master nodes; receiving a handover request acknowledgement from a target master node among the multiple target master nodes, wherein the handover request acknowledgement identifies whether the target master node among the multiple target master nodes is to be used for data forwarding.

23. A target secondary node comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the source master node to perform at least: receiving a secondary node addition request from a target master node; determining that data forwarding information has previously been sent to another target master node, wherein the data forwarding information comprises tunnelling endpoint identification details; based on the determining, sending acknowledgment to the secondary node addition request without including the data forwarding information in the acknowledgement.

24. A method comprising: receiving a secondary node addition request from a target master node; determining that data forwarding information has previously been sent to another target master node, wherein the data forwarding information comprises tunnelling endpoint identification details; based on the determining, sending acknowledgment to the secondary node addition request without including the data forwarding information in the acknowledgement.

25. A computer program comprising instructions which, when executed by a target secondary node, cause the target secondary node to perform at least: receiving a secondary node addition request from a target master node; determining that data forwarding information has previously been sent to another target master node, wherein the data forwarding information comprises tunnelling endpoint identification details; based on the determining, sending acknowledgment to the secondary node addition request without including the data forwarding information in the acknowledgement.