WO2024156415A1

WO2024156415A1 - Data transfer using data radio bearers

Info

Publication number: WO2024156415A1
Application number: PCT/EP2023/084458
Authority: WO
Inventors: Halit Murat Gürsu; Behnam KHODAPANAH; Ahmad AWADA; Umur KARABULUT; Dariusz PALKA; Srinivasan Selvaganapathy; Panagiotis SPAPIS
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2023-01-25
Filing date: 2023-12-06
Publication date: 2024-08-02
Anticipated expiration: 2025-07-25
Also published as: CN120457744A

Abstract

A user equipment, UE, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the UE at least to perform: receiving downlink signaling that provides a first data radio bearer configuration for a cell (DRB), and a second data radio bearer configuration for the cell (DRB); storing the first data radio bearer configuration, for execution of data transfer via the cell using the first data radio bearer and for storing the second data radio bearer configuration, for execution of data transfer via the cell using the second data radio bearer; receiving a trigger; and in response to the received trigger, executing data transfer between user equipment and the cell using the first data radio bearer configuration if the trigger indicates use of the first data radio bearer configuration and executing data transfer between the user equipment and the cell using the second data radio bearer configuration if the trigger indicates use of the second data radio bearer configuration.

Description

TITLE

Data transfer using data radio bearers

TECHNOLOGICAL FIELD

Examples of the disclosure relate to data transfer using data radio bearers.

Examples of the disclosure relate to data transfer using data radio bearers for Third Generation Partnership cellular radio telecommunications networks.

BACKGROUND

A data radio bearer represents a transfer channel for data. Data radio bearers are, for example, used to transfer data via the radio interface in a radio telecommunications network. The radio interface is the interface between user equipment and a base station that serves one or more cells of the cellular radio telecommunications network.

Cellular radio telecommunications networks require that a user equipment can be handed over from one cell to another.

The configuration of a data radio bearer requires signaling and takes time.

BRIEF SUMMARY

The inventors have recognized that the configuration of a data radio bearer in existing systems can use up time and resources in anticipation of handover, during handover and/or after handover, depending upon implementations.

According to various, but not necessarily all, examples there is provided examples as claimed in the independent claims, like e.g.:

And/or a method comprising: receiving downlink signaling that provides a first data radio bearer configuration for a cell (DRB), and a second data radio bearer configuration for the cell (DRB); storing the first data radio bearer configuration, for execution of data transfer via the cell using the first data radio bearer and for storing the second data radio bearer configuration, for execution of data transfer via the cell using the second data radio bearer; receiving a trigger; if the trigger indicates use of the first data radio bearer configuration, then executing data transfer between user equipment and the cell using the first data radio bearer configuration and if the trigger indicates use of the second data radio bearer configuration, executing data transfer between the user equipment and the cell using the second data radio bearer configuration.

And/or a computer program for a user equipment comprising instructions that, when run on a computer, perform: conditionally execute data transfer between user equipment and a cell wherein the if a trigger, indicates use of a previously received and stored first data radio bearer configuration then causing execution of data transfer between the user equipment and the cell using the first data radio bearer configuration and if the trigger indicates use of a previously received and stored second data radio bearer configuration then causing execution of data transfer between the user equipment and the cell using the second data radio bearer configuration.

And/or an apparatus for a radio access network comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: causing transmission towards user equipment of downlink signaling that provides a first data radio bearer configuration for a cell, and a second data radio bearer configuration for the cell; causing transmission towards the user equipment of a trigger configured to indicate use of the first data radio bearer configuration to enable data transfer between the user equipment and the cell using the first data radio bearer or, configured to indicate use of the second data radio bearer configuration to enable data transfer between the user equipment and the cell using the second data radio bearer.

According to various, but not necessarily all, examples there is provided examples as claimed in the appended claims, like e.g.:

An apparatus (user equipment), wherein the control circuitry is configured to switch a data transfer session between transfer using the first data radio bearer configuration or the second data radio bearer configuration based on the trigger or wherein the control circuitry is configured to switch a data transfer session on or off based on the trigger.

An apparatus, wherein the trigger is received as a medium access control (MAC) message. An apparatus, wherein the trigger indicates a mapping to be used as in the received first or second configuration for the cell, between the data radio bearer for the cell and a data transfer session

An apparatus, wherein the first data radio bearer configuration or the second data radio bearer configuration comprises at least one mapping between a usable data transfer session to provide data for transfer and a usable data radio bearer to provide a transfer channel for data.

An apparatus, wherein the at least one mapping maps a data transfer session to a sub-set of a set of multiple preconfigured data radio bearers, wherein the sub-set is indicated by the trigger.

An apparatus, wherein the data transfer session is a pre-existing data transfer session

An apparatus, wherein the first and second data radio bearer configurations configure data radio bearers for a first data transfer session and a second data transfer session wherein executing data transfer with user equipment via the cell using the first data radio bearer configuration if the trigger indicates use of the first data radio bearer configuration comprises executing the second data transfer session with the first data radio bearer configuration and executing data transfer with the user equipment via the cell using the second data radio bearer configuration if the trigger indicates use of the second data radio bearer configuration comprises executing the second data transfer session with the second data radio bearer configuration

An apparatus, wherein there is a state where a data transfer session is mapped to a sub-set of a set of multiple preconfigured data radio bearers and a state where the data transfer session is not mapped to any preconfigured data radio bearers, wherein the state is indicated by the trigger.

An apparatus, wherein the first and second data radio bearer configurations configure data radio bearers for at least a first data transfer session and optionally a second data transfer session wherein executing the second data transfer between user equipment and the cell using the first data radio bearer configuration if the trigger indicates use of the first data radio bearer configuration comprises executing the second data transfer session with the first data radio bearer configuration executing the second data transfer between the user equipment and the cell using the second data radio bearer configuration if the trigger indicates use of the second data radio bearer configuration comprises executing the second data transfer session with the second data radio bearer configuration.

A method, wherein execution of data transfer between the cell and the user equipment requires a mapping between a usable data transfer session to provide data for transfer and a usable data radio bearer to provide a transfer channel for data

A method, wherein at a time of triggering execution of data transfer between the user equipment and the cell using the data radio bearer for the cell, as a consequence of the received trigger, there is a mapping, for the cell, between the data radio bearer for the cell and a data transfer session.

A method, wherein execution of data transfer between the user equipment and the cell requires

- a usable data transfer session to provide data for transfer -a usable data radio bearer to provide a transfer channel for data wherein at a time of triggering, a data radio bearer for the cell is usable for the cell and at a time of the downlink signaling, the data radio bearer for the cell is not usable for the cell and/or wherein at the time of triggering, a data transfer session is usable for the cell and at the time of the signaling, the data transfer session is not usable for the cell.

A method, wherein at the time of triggering, a data transfer session is usable for the cell and the data radio bearer for the cell is usable for the cell; and at time of the downlink signaling, the data transfer session is usable for the cell and the data radio bearer is not usable for the cell or the data transfer session is not usable for the cell and the data radio bearer is usable for the cell.

An apparatus (network node like e.g. gNB and/or supporting central unit and/or distributed unit functionality and/or layer 2 protocol and/or layer 3 protocol processing of a radio access network like LTE, 5G, NR, etc.), configured for receiving and using a configuration of the first data radio bearer configuration for the cell and a configuration of a second data radio bearer configuration for the cell to enable the downlink signaling that provides the first data radio bearer configuration for the cell, and the second data radio bearer configuration for the cell.

An apparatus, configured for receiving and using at least one decision criterion for causing transmission of the trigger to the user equipment and/or setting mapping parameters in the trigger.

An apparatus, wherein the decision criterion specifies at least one of a. an availability of data radio bearers at a current cell b. an availability of data radio bearers at a future cell c. a new data transfer session An apparatus, configured for receiving and using a report that comprises information for the decision criteria for causing transmission of the trigger to the user equipment of the trigger and/or setting mapping parameters in the trigger.

An apparatus, configured for receiving and using a report that comprises information, indicating availability of data radio bearers at the cell, for the decision criteria for causing transmission of the trigger to the user equipment of the trigger and/or setting mapping parameters in the trigger.

An apparatus, wherein the report is a periodic report or an event-based report.

An apparatus, wherein the report indicates lack of resources or existence of resources for one or more data radio bearer configurations.

An apparatus, wherein the trigger is a medium access control (MAC) layer message.

An apparatus, wherein the apparatus determines cell handover according to lower layer triggered mobility processes (LTM).

An apparatus, configured as a distributed unit of a centralized unit-distributed units network architecture.

An apparatus, wherein the apparatus is configured to receive and process an indication from the centralized unit concerning a newly setup data radio bearer.

An apparatus, wherein the centralized unit determines cell handover according to lower layer triggered mobility processes (LTM) and informs the apparatus.

An apparatus, configured for receiving and processing an indication, from the centralized unit, indicating that the first and second data radio bearer configurations have been sent to the user equipment.

An apparatus, configured for receiving and processing a decision criterion for causing transmission of the trigger to the user equipment. An apparatus, wherein the decision criterion specifies at least one of a. an availability of data radio bearers at a current cell b. an availability of data radio bearers at the cell c. a new data transfer session

An apparatus, configured for receiving and using a report that comprises information, indicating availability of data radio bearers at the cell, for comparison to the decision criteria for causing transmission of the trigger to the user equipment of the trigger.

An apparatus, wherein the report is a periodic report or an event-based report and/or wherein the report indicates lack of resources or existence of resources for one or more data radio bearer configurations.

In some but not necessarily all examples, the user equipment is configured to receive (from a first source) first downlink signaling that provides the first data radio bearer configuration and to receive separately (from the first source) second downlink signaling that provides the second data radio bearer configuration. The downlink signaling comprises the first downlink signaling and the second downlink signaling. Downlink signaling can be transmitted using e.g. downlink control channels like PDCCH. Downlink signaling content can be transmitted using e.g. downlink control messages like e.g. layer 3 RRC Reconfiguration message(s), and/or layer 2 MAAC CE message(s).

In some but not necessarily all examples, the user equipment is configured to receive (from a first source) first downlink signaling that provides the first data radio bearer configuration and to receive separately (from a second source, different to the first source) second downlink signaling that provides the second data radio bearer configuration. The downlink signaling comprises the first downlink signaling and the second downlink signaling.

In some but not necessarily all examples, the user equipment is configured to receive the downlink signaling via a first cell and/or the user equipment is configured to receive the trigger via the first cell. In some but not necessarily all examples, the apparatus is configured to transmit the downlink signaling via a first cell and/or the apparatus is configured to transmit the trigger via the first cell.

In some examples, the first cell and the second cell are different cells. In other examples, the first cell and the second cell are the same cell.

In some examples, the first cell a source cell for the UE and the second cell is a target cell of the UE, for example a handover target cell of the UE.

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 of 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 of 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.

BRIEF DESCRIPTION

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

FIG. 1 shows an example triggering use of a pre-configured data radio bearer configuration;

FIGs. 2 & 3 show an example of triggering different uses of a pre-configured data radio bearer configuration;

FIGs. 4 & 5 show an example of triggering different uses of a pre-configured data radio bearer configuration;

FIGs. 6 show an example of lower layer triggered mobility and handover;

FIGs. 7A & 7B show example of centralized unit (CU) - distributed unit (DU architecture;

FIG 8 illustrates an example of triggering data transfer in different cells; FIG 9 illustrates an example of event-base triggering; FIG 10A illustrates an operational mapping, for a first embodiment, created by triggering use of a pre-configured data radio bearer configuration;

FIG 10B illustrates an operational mapping, for a second embodiment, created by triggering use of a pre-configured data radio bearer configuration;

FIG 11 A, 11 B, 11C illustrate examples of the first embodiment.

FIG 12A, 12B, 12C illustrate examples of the second embodiment.

FIG 13A illustrates an example of a controller;

FIG 13B illustrates an example of a computer program;

FIG 14 illustrates a cellular telecommunications network;

FIG 15 illustrates a method;

FIG 16 illustrates an example of a third embodiment.

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. Similar reference numerals are used in the figures to designate similar features. For clarity, all reference numerals are not necessarily displayed in all figures.

In the following description a class (or set) can be referenced using a reference number without a subscript index (e.g. 10) and a specific instance of the class (member of the set) can be referenced using the reference number with a numerical type subscript index (e.g. 10_1) and a non-specific instance of the class (member of the set) can be referenced using the reference number with a variable type subscript index (e.g. 10_i).

DETAILED DESCRIPTION

The following description describes various examples. Consistent reference numerals are used through the drawings for the same or similar features.

The drawings and description relate to examples of user equipment (UE) 110 comprising: means for receiving 2 signaling 11 that provides a first data radio bearer configuration 10_1 for a cell 120_2 (DRB_1), and a second data radio bearer configuration 10_2 for the cell 120_2; means for storing 4 the first data radio bearer configuration 10_1 , for execution of data transfer 15 via the cell 120_2 using the first data radio bearer (DRB_1) and for storing 4 the second data radio bearer configuration 10_2, for execution of data transfer 15 via the cell 120_2 using the second data radio bearer (DRB_2); means for receiving 6 120_1, a trigger 13; and means for, in response to the received trigger 13, executing data transfer 15 between user equipment (UE) 110 and the cell 120_2 using the first data radio bearer configuration 10_1 if the trigger 13 indicates use of the first data radio bearer configuration 10_1 and executing data transfer 15 between the user equipment (UE) 110 and the cell 120_2 using the second data radio bearer configuration 10_2 if the trigger 13 indicates use of the second data radio bearer configuration 10_2.

The drawings and description relate to examples of apparatus 120 (132) for a cellular telecommunication network like a radio access network comprising: means for causing transmission to user equipment (UE) 110 of signaling 11 that provides a first data radio bearer configuration 10_1 for a cell 120_2 (DRB_2), and a second data radio bearer configuration 10_2 for the cell 120_2 (DRB_2); means for causing transmission to the user equipment (UE) 110 of a trigger 13 configured to indicate use of the first data radio bearer configuration 10_1 to enable data transfer 15 between the user equipment (UE) 110 and the cell 120_2 using the first data radio bearer (DRB_1) or, configured to indicate use of the second data radio bearer configuration 10_2 to enable data transfer 15 between the user equipment (UE) 110 and the cell 120_2 using the second data radio bearer (DRB_2).

In some but not necessarily all examples, the user equipment 110 is configured to receive (from a first source) first signaling that provides the first data radio bearer configuration 10_1 and to receive separately (from the first source) second signaling that provides the second data radio bearer configuration 10_2. The signaling 11 comprises the first signaling and the second signaling.

In some but not necessarily all examples, the user equipment 110 is configured to receive (from a first source) first signaling that provides the first data radio bearer configuration 10_1 and to receive separately (from a second source, different to the first source) second signaling that provides the second data radio bearer configuration 10_2. The signaling 11 comprises the first signaling and the second signaling.

In at least some examples, the apparatus 120 is configured to transmit the signaling 11 via a first cell and/or the apparatus 120 is configured to transmit the trigger 13 via a first cell (the first cell). The signaling 11 can, for example, be downlink signaling.

In at least some examples, the user equipment 110 is configured to receive the signaling 11 via a first cell and/or the user equipment is configured to receive the trigger 13 via a first cell (the first cell). The signaling 11 can, for example, be downlink signaling.

In some examples, the first cell is a source cell for the UE and the second cell is a target cell of the UE, for example a handover target cell of the UE.

The drawings and description relate to some examples.

FIG 1 illustrates a part of a cellular telecommunications network comprising cells served by apparatus 120. The apparatus 120 are radio access apparatus that communicate using radio waves with user equipment 110. In FIG 1, the first cell (Cell_1) is served by a first apparatus 120_1. The second cell (Cell_2) is served by a second apparatus 120_2.

The user equipment (UE) is initially within the first cell (cell_1 ) and is initially being served by the first apparatus 120_1. In the following description the first cell may be referenced using the text reference ‘Cell_1 ’ or using the numerical reference ’ 120_1 ’ which is a reference for the first apparatus 120_1 serving the first cell. In the following description the second cell may be referenced using the text reference ‘Cel l_2’ or using the numerical reference ’120_2’ which is a reference for the second apparatus 120_2 serving the second cell.

As will be described later, the user equipment 110 comprises circuitry or other means for receiving 2 downlink signaling 11 , circuitry or other means for storing 4 information including data radio bearer configurations 10, circuitry or other means for receiving 6 a trigger 13, circuitry or other means for executing data transfer 15 between user equipment (UE) 110 and the second cell 120_2 conditionally using one or more data radio bearer configurations 10 in dependence upon the received trigger 13. The described circuitry can be configured for the described purposes.

The user equipment 110 comprises means for receiving 2, via the first cell 120_1, downlink signaling 11 that provides a first data radio bearer configuration 10_1 for a second cell 120_2, and a second data radio bearer configuration 10_2 for a second cell 120_2.

The user equipment 110 comprises means for storing 4 the first data radio bearer configuration 10_1 , for execution of data transfer 15 via the second cell 120_2 using the first data radio bearer (DRB_1) and for storing 4 the second data radio bearer configuration 10_2, for execution of data transfer 15 via the second cell 120_2 using the second data radio bearer (DRB_2).

The user equipment 110 comprises means for receiving 6, via the first cell 120_1, a trigger 13.

The user equipment 110 comprises means for, in response to the received trigger 13, i) executing data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the first data radio bearer configuration 10_1 , if the trigger 13 indicates use of the first data radio bearer configuration 10_1 and ii) executing data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer configuration 10_2, if the trigger 13 indicates use of the second data radio bearer configuration 10_2.

The downlink signaling 11 is transmitted by the first apparatus 120_1 of the first cell (Cell_1) and received 2 by the user equipment 110. The trigger 13 is transmitted by the first apparatus 120_1 of the first cell (Cell_1) and received 2 by the user equipment 110.

The data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 can be an uplink transfer, that is, a transmission from the user equipment 110 to the first apparatus 120_1 of the first cell (Cel l_1 ) and /or a downlink transfer, that is, reception at the user equipment 110 of transmissions from the first apparatus 120_1 of the first cell (Cell_1).

A data radio bearer configuration 10 is a collection of information that can be used to set-up and use one or more data radio bearers (DRB). A data radio bearer (DRB) is a transport channel for data. The first data radio bearer configuration 10_1 can relate to a set of first data radio bearers DRB_1 that can comprise one or more data radio bearers. The second data radio bearer configuration 10_2 can relate to a set of second data radio bearers DRB_2 that can comprise one or more data radio bearers.

In at least some examples, the user equipment 110 comprises means for, in response to receiving the trigger 13, determining at least if the received trigger 13 indicates use of the first data radio bearer configuration 10_1 or if the received trigger 13 indicates use of the second data radio bearer configuration 10_2 in relation to a Qos Flow. Indicating that a radio bearer is not to be used in relation to a QoS Flow that a radio bearer is not to be used by the UE at all. In this example, the user equipment also comprises means for executing data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the first data radio bearer configuration 10_1 , as a consequence of a determination that the received trigger 13 indicates use of the first data radio bearer configuration 10_1. The user equipment also comprises means for executing data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer configuration 10_2, as a consequence of a determination that the received trigger 13 indicates use of the second data radio bearer configuration 10_2.

The downlink signaling 11 and the trigger 13 are distinct messages, sent independently. The cause of sending the downlink signaling 11 to set-up appropriate data radio bearers (DRBs) is separate and distinct from the cause of sending the trigger 13 to execute use of one or more of the previously set-up data radio bearers.

In some but not necessarily all examples, the trigger 13 is sent as a consequence of an event and the trigger comprises at least an indication of the event.

The downlink signaling 11 enables future execution of data transfer 15 (in response to the trigger 13) without additional downlink signaling being required to provide configuration information for a data radio bearer.

The downlink signaling 11 is received 2 via the first cell and the trigger 13 is received via the first cell. However, the data transfer executed in response to (or independence upon) the trigger 13 is received via the second cell.

In at least some examples, the trigger 13 can be used to trigger a preconfigured configuration, the pre-configuration can happen before the trigger is sent to the UE. In some but not necessarily all examples, the trigger 13 is not a data radio bearer configuration message and does not enable transfer of a data radio bearer configuration message. In some but not necessarily all examples, it is therefore possible to avoid messaging for the purpose of configuring a data radio bearer at the user equipment 110 in the time period between the trigger 13 and the data transfer 15 initiation. The trigger 13 triggers a pre-stored data radio bearer configuration 10.

In at least some examples, the user equipment 110 does not send a message confirming reception of the trigger 13, although there can be reporting of a consequence of the trigger 13.

The separation of the downlink signaling 11 and the trigger 13 therefore can improve speed of operation and reduce radio signaling. The speed of the operation can be improved as the trigger is a small message that may only indicate the use of data radio bearer of the UE that has been pre-configured.

The trigger 13 enables future execution of the data radio bearer (DRB) for data transfer 15 in the second cell 120_2, whether future means time-separated from the downlink signaling 11.

In some examples, the trigger 13 indicates use of the first data radio bearer configuration 10_1 explicitly, for example, using a predetermined flag, for example. In some examples, the trigger 13 indicates use of the first data radio bearer configuration 10_1 implicitly, for example, providing information which because of a shared context is interpreted by the user equipment 110 as an Indication to use the first data radio bearer configuration 10_1.

In some but not necessarily all examples, the trigger 13 indicates the first data radio bearer configuration 10_1. In some examples, the trigger 13 indicates the first data radio bearer configuration 10_1 explicitly using a predetermined flag, for example. In some examples, the trigger 13 indicates the first data radio bearer configuration 10_1 implicitly, for example, providing information which because of a shared context is interpreted by the user equipment 110 as an Indication of the first data radio bearer configuration 10_1.

In some but not necessarily all examples, the trigger indicates which part of an optional RRCconfiguration a user equipment should use.

In at least some examples, execution 8 of data transfer 15 between the user equipment 110 and the second cell 120_2 requires an operational mapping 14 between a usable data transfer session (DTS) 12 and a usable data radio bearer (DRB). The usable data transfer session (DTS) 12 routes data for transfer. The usable data radio bearer (DRB) provides a transfer channel for data.

FIG 2 illustrates putative mappings between data transfer sessions (DTS) 12 and data radio bearers (DRB). Execution of data transfer 15 becomes possible when at least some of the mappings are usable. There is a putative mapping between a first data transfer session (DTS_1) 12_1 and, a first data radio bearer (DRB_1) defined by the first data radio bearer configuration 10_1 or a second data radio bearer (DRB_2) defined by the second data radio bearer configuration 10_2. There is a putative mapping between a second data transfer session (DTS_2) 12_2 and, a third data radio bearer (DRB_3) defined by third data radio bearer configuration 10_3.

As will be explained later the mapping is putative but not operational at a specific cell because until the trigger 13 is received one or both of the data radio bearers or data transfer sessions may have a different data radio bearer at a specific cell. The different radio bearer may also be no data radio bearer. UE can use the data transfer sessions at the target with a mapping to data radio bearers. The mapping is indicated by the trigger. However, in case the trigger doesn’t indicate a mapping, the multiple configuration of mappings can include a default mapping that is used in case there is a lack of explicit mapping of data transfer session to data radio bearers.

A usable data transfer session (DTS) 12 routes data for transfer. A usable data radio bearer (DRB) 10 provides an operational transfer channel for data.

FIG 3 illustrates how the trigger 13 causes the putative mappings of FIG 2 to become an operational mapping 14.

In one scenario (illustrated to the left), the trigger 13 indicates use of the first data radio bearer configuration 10_1 and causes creation of an operational mapping 14_1 between the first data transfer session (DTS_1) 12_1 and the first data radio bearer (DRB_1) defined by the first data radio bearer configuration 10_1. Optionally, there is also an operational mapping 14_2 between the second data transfer session (DTS_2) 12_2 and, the third data radio bearer (DRB_3) defined by third data radio bearer configuration 10_3.

The operational mapping 14_1 is between the first data transfer session (DTS_1) 12_1 and the first data radio bearer (DRB_1) but not between the first data transfer session (DTS_1) 12_1 and the second data radio bearer (DRB_2). In this example, but not necessarily all examples, the operational mapping 14_1 is between the first data transfer session (DTS_1) 12_1 and only the first data radio bearer (DRB_1). The operational mapping 14_1 is used to execute data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the first data radio bearer configuration 10_1.

In another scenario (illustrated to the right), the trigger 13 indicates use of the second data radio bearer configuration 10_2 and causes creation of an operational mapping 14_3 between the first data transfer session (DTS_1) 12_1 and, the second data radio bearer (DRB_2) defined by the second data radio bearer configuration 10_2. Optionally, there is also an operational mapping 14_4 between the second data transfer session (DTS_2) 12_2 and the third data radio bearer (DRB_3) defined by the third data radio bearer configuration 10_3.

The operational mapping 14_3 is between the first data transfer session (DTS_1) 12_1 and the second data radio bearer (DRB_2) but not between the first data transfer session (DTS_1) 12_1 and the first data radio bearer (DRB_1). In this example, but not necessarily all examples, the operational mapping 14_3 is between the first data transfer session (DTS_1) 12_1 and only the second data radio bearer (DRB_2).

The operational mapping 14_3 is used to execute data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer configuration 10_2.

In some but not necessarily all examples, the first data radio bearer and the second data radio bearer have different characteristics such as bandwidth, latency, reliability and/or quality of service.

In some examples, the first data radio bearer has a lower bandwidth, greater latency, worse reliability and/or lower quality of service than second data radio bearer.

In some but not necessarily all example, the first data radio bearer is a default data radio bearer.

The user equipment 110 therefore comprises: means for receiving 2, via the first cell 120_1, downlink signaling 11 that provides a first data radio bearer configuration 10_1 for a second cell 120_2, and a second data radio bearer configuration 10_2 for the second cell 120_2; means for storing 4 the first data radio bearer configuration 10_1 , for execution of data transfer 15 via the second cell 120_2 using the first data radio bearer (DRB_1) and for storing 4 the second data radio bearer configuration 10_2, for execution of data transfer 15 via the second cell 120_2 using the second data radio bearer (DRB_2); means for receiving 6, via the first cell 120_1 , a trigger 13; means for, in response to the received trigger 13, i) executing data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the first data radio bearer (DRB_1) defined by the first data radio configuration 10_1 , if the trigger 13 indicates use of the first data radio bearer configuration (DRB_1) 10_1 and ii) executing data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer (DRB_2) defined by the second data radio bearer configuration 10_2, if the trigger 13 indicates use of the second data radio bearer configuration (DRB_2) 10_2.

FIG 4 illustrates putative mappings between data transfer sessions (DTS) 12 and data radio bearers (DRB). Execution of data transfer 15 becomes possible when at least some of the mappings are usable.

There is a putative mapping between a first data transfer session (DTS_1) 12_1 and a first data radio bearer (DRB_1) defined by the first data radio bearer configuration 10_1 or nothing. There is a putative mapping between a second data transfer session (DTS_2) 12_2 and a second data radio bearer (DRB_2) defined by the second data radio bearer configuration 10_2

As will be explained later the mapping is putative but not operational because until the trigger 13 is received one or both of the data radio bearers or data transfer sessions is not usable. A usable data transfer session (DTS) 12 routes data for transfer. A usable data radio bearer (DRB) 10 provides an operational transfer channel for data.

FIG 5 illustrates how the trigger 13 causes the putative mappings of FIG 4 to become operational mappings 14.

In one scenario (illustrated to the left), the trigger 13 indicates use of the first data radio bearer configuration 10_1 and causes creation of an operational mapping 14_1 between the first data transfer session (DTS_1) 12_1 and the first data radio bearer (DRB_1) defined by the first data radio bearer configuration 10_1. Optionally, there is also an operational mapping 14_2 between the second data transfer session (DTS_2) 12_2 and the second data radio bearer (DRB_2) defined by the second data radio bearer configuration 10_2.

In another scenario (illustrated to the right), the trigger 13 indicates use of the second data radio bearer configuration 10_2 and causes creation of an operational mapping 14_3 between the second data transfer session (DTS_2) 12_2 and, the second data radio bearer (DRB_2) defined by the second data radio bearer configuration 10_2. The operational mapping 14_3 is between the second data transfer session (DTS_2) 12_2 and the second data radio bearer (DRB_2) but not between the second data transfer session (DTS_2) 12_2 and the first data radio bearer (DRB_1). In this example, but not necessarily all examples, the operational mapping 14_3 is between the second data transfer session (DTS_2) 12_2 and only the second data radio bearer (DRB_2). The operational mapping 14_3 is used to execute data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer configuration 10_2.

In some but not necessarily all examples, the first data radio bearer DRB_1 and the second data radio bearer DRB_2 have different characteristics such as bandwidth, latency, reliability and/or quality of service.

Thus in FIG 3 there is use of the first data radio bearer configuration 10_1 for data transfer 15 if the trigger 13 indicates a use of the first data radio bearer configuration 10_1 or use of the second data radio bearer configuration 10_2 for data transfer 15 if the trigger 13 indicates a use of the second data radio bearer configuration 10_2. Thus in FIG 5 there is use of the second data radio bearer configuration 10_2, not the first data radio bearer configuration 10_1 , for data transfer 15 if the trigger 13 indicates a use of the second data radio bearer configuration 10_2 then there is use of the second data radio bearer configuration 10_2. Or there is use of not the second data radio bearer configuration 10_2, but the first data radio bearer configuration 10_1 , for data transfer 15 if the trigger 13 indicates the first data radio bearer configuration 10_1 , for data transfer 15 if the trigger 13 indicates a use of the first data radio bearer configuration 10_1.

FIG 6 illustrates an example of handover.

In this example, before handover (also referred to as hand-off) there is data communication between the user equipment 110 and the radio access apparatus 120_1 of the first cell (Cell_1). After handover 26 there is data communication 20 between the user equipment 110 and the radio access apparatus 120_2 of the second cell (Cell_2). The handover decision is based on a measurement report 22 provided by the user equipment.

Optionally lower layer triggered mobility (LTM) can be set-up 24 in advance of handover 26 and the handover decision can then be taken at a lower layer, for example at the radio access apparatus.

The decision to set-up LTM can be based on a measurement report 22 provided by the user equipment 110.

Lower layer triggered mobility (LTM) results in the decision to perform handover 26 being made at a lower layer. The decision is made at layer 2 or layer 1 (e.g. Medium Access Control) rather than layer 3 (Radio Resource Control RRC).

The handover decision can therefore be made at a radio access apparatus, for example at the control plane of a radio access apparatus. This can, in some examples occur at a distributed unit (DU).

The lower layer triggered mobility (LTM) can, for example, be controlled by a lower layer entity at the radio access apparatus 120_1. In some but not necessarily all example, lower layer triggered mobility (LTM) can, for example, be controlled by a medium access control (MAC) entity at the radio access apparatus 120_1. The trigger 13 originates at the MAC entity in the radio access control apparatus 120 and can, for example, be a MAC message.

There are various different architectures that can be used for the radio access apparatus 120.

The radio access apparatus 120 is a cellular base station. In some but not necessarily all examples, a base station can have a de-centralized architecture. In such cases the base station comprises a centralized unit (CU) and one or more distributed units (DU).

The centralized unit (CU) and the distributed unit(s) (DU) divide the base station into different logical entities, and optionally into different physical entities.

One DU can support one or more cells. Each cell has one or more associated transmission-reception points.

In common architectures, the DUs are physically separated from each other and are located close to the transmission-reception point(s) associated with the DU.

In common architectures there is a single CU per base station and the CU controls one or more DUs.

The CU provides a higher layer interface to the core network (higher layers of the protocol stack). The DU provides a lower layer interface to the UE (lower layers of the protocol stack)

The 3GPP protocol stack comprises:

The MAC entity can be within a DU. Where LTM is in operation, the handover decision can be taken at the DU.

FIG 7A illustrates an example where the first cell (Cell_1) and the second Cell (Cell_2) are controlled by a common CU 134. The first DU 132_1 controlled by CU 134 provides the first radio access apparatus 110_1. The second CU 132_2 controlled by DU 134 provides the second radio access apparatus 110_2.

FIG 7B illustrates an example where the first cell (Cell_1) and the second Cell (Cell_2) are controlled by different DUs 134. The first DU 132_1 controlled by a first CU 134_1 provides the first radio access apparatus 110_1. The second DU 132_2 controlled by a second CU 134_2 provides the second radio access apparatus 110_2.

The CUs 134 can communicate to each other directly or via a core network 129.

A DU 132_1 can send the downlink signaling 11 that provides a first data radio bearer configuration 10_1 for a second cell 120_2, and a second data radio bearer configuration 10_2 for a second cell 120_2, and can transmit, via the first cell 120_1 , a trigger 13.

FIG 8 illustrates an example in which the user equipment 110 comprises: means for receiving, via a first cell 120_1 , downlink signaling 11 that provides at least a first configuration for a first data radio bearer (DRB_1) (DRB) for a first (serving) cell and a second configuration for a second data radio bearer (DRB_2) (DRB) for a second (non-serving) cell; means for storing the first configuration 10_1 of the first data radio bearer (DRB_1) for the first cell 120_2, for execution of data transfer 15_2 via the first cell 120_2 using the first data radio bearer (DRB_2); means for storing the second configuration 10_2 of the second data radio bearer (DRB_2) for the second cell 120_2, for future execution of data transfer 15_2 via the first cell 120_1 using the first data radio bearer (DRB_2); means for execution, in response to a trigger 13_1 , of data transfer 15_1 between the user equipment (UE) 110 and the first cell 120_1 using the first data radio bearer (DRB_1); means for future execution, in response to a trigger 13_2, of data transfer 15_2 between the user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer (DRB_2).

In some examples, the first configuration 10_1 is executed for the first cell 120_1 for a first data transfer session 12_1 , and the second configuration 10_2 is not executed for the first cell 120_1 for a data transfer session 12. After handover from the first cell 120_1 to second cell 120_2, the second DRB configuration 10_2 is executed for the second cell 120_2 for the first data transfer session or a second data transfer session 12_2.

In some examples the second data transfer session 12_2 is a continuation of the first data transfer session 12_1.

In some other examples, the second data transfer session 12_2 is a different data transfer session 12 to the first data transfer session.

FIG 9 illustrates an example of the user equipment (UE) 110 comprising: means for receiving, via a first cell 120_1 , downlink signaling 11 that provides at least a configuration 10 of a data radio bearer (DRB) for a second cell 120_2; means for storing at least the configuration 10 of the data radio bearer (DRB) for the second cell 120_2, for future execution of data transfer 15 via the second cell 120_2 using the data radio bearer (DRB); means for storing, in response to a trigger 13, an operational mapping 14 between the data radio bearer (DRB) and a data transfer session 12, for data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the data radio bearer (DRB) and means for execution, using the operational mapping 14, of transfer 15 of data, of the data transfer session 12, between the user equipment (UE) 110 and the second cell 120_2 using the data radio bearer (DRB).

In some but not necessarily all examples, the trigger 13 is sent as a consequence of an event 30 and the trigger 13 comprises at least an indication of the event. The event can, for example, relate to a data transfer session 12, a data radio bearer (DRB), a data radio bearer configuration 12 or a mapping between a data transfer session 12 and a data radio bearer (DRB) defined by a data radio bearer configuration 12.

In some but not necessarily all examples, the trigger 13 indicates a mapping 14 to be used to map the received first DRB configuration 10_1 for the second cell (Cell_2) or the received second DRB configuration 10_2 for the second cell (Cell_2) and a data transfer session 12.

The user equipment 110 can comprise means for storing, in response to a trigger 13, an operational mapping 14 between a data radio bearer (DRB) and a data transfer session 12, for data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the data radio bearer (DRB) and means for execution, using the operational mapping 14, of transfer 15 of data of the data transfer session 12 between the user equipment (UE) 110 and the second cell 120_2 using the data radio bearer (DRB).

The trigger 13 can make complete an existing mapping and make it operational or make an existing complete mapping operational. The mapping can be stored as part of the DRB configuration. For example, the first DRB configuration 10_1 can comprise data defining a mapping or operational mapping 14 between a usable data transfer session 12 to provide data for transfer and the usable first data radio bearer (DRB) to provide a transfer channel for data.

For example, the second DRB configuration 10_2 can comprise data defining a mapping or operational mapping 14 between a usable data transfer session 12 to provide data for transfer and the usable second data radio bearer (DRB) to provide a transfer channel for data.

In some examples, no operational mapping 14 is possible between a usable data transfer session 12 to provide data for transfer and a usable data radio bearer (DRB) to provide a transfer channel for data.

As illustrated in FIGs 10A & 10B, execution of data transfer 15 between the user equipment (UE) 110 and a cell requires a usable data transfer session 12 to provide data for data transfer, a usable data radio bearer (DRB) to provide a transfer channel for data, and at least in some examples an operational mapping 14 between the usable data transfer session 12 and the usable data radio bearer (DRB).

At time t_1 of the downlink signaling 11 , there is no operational mapping 14, for the second cell 120_2, between the data radio bearer (DRB) for the second cell 120_2 and a data transfer session 12.

At a time t2 of receipt of the trigger 13 triggering execution of data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the data radio bearer (DRB) for the second cell 120_2, as a consequence of the received trigger 13, there is a mapping 14, for the second cell 120_2, between the data radio bearer (DRB) for the second cell 120_2 and a data transfer session 12

Referring to FIG 10A, at a time t_1 of the downlink signaling 11 , the data radio bearer (DRB) for the second cell 120_2 is not usable for the second cell 120_2 and at the time t2 of triggering, the data radio bearer (DRB) for the second cell 120_2 is usable for the second cell 120_2. Additionally or alternatively, referring to FIG 11 B at the time t_1 of the downlink signaling 11 , the data transfer session 12 is not usable for the second cell 120_2 and at the time of triggering t_2, a data transfer session 12 is usable for the second cell 120_2.

Thus at the time of triggering, a data transfer session 12 is usable for the second cell 120_2 and the data radio bearer (DRB) for the second cell 120_2 is usable for the second cell 120_2; and at time t_1 of the downlink signaling 11, the data transfer session 12 is usable for the second cell 120_2 and the data radio bearer (DRB) is not usable for the second cell 120_2 (FIG 10A) or at time t_1 of the downlink signaling 11, the data transfer session 12 is not usable for the second cell 120_2 and the data radio bearer (DRB) is usable for the second cell 120_2 (FIG 10B).

First Embodiment

FIG 11 A, 11 B, 11C illustrate different examples of a first embodiment.

Referring to FIG 11 A, the process optionally comprises set-up of lower layer triggered mobility (LTM) 24 as previously described.

The process comprises a ‘Configuration stage’ downlink signaling 11 that provides a first data radio bearer configuration 10_1 for a second cell 120_2, and a second data radio bearer configuration 10_2 for a second cell 120_2.

The process comprises an ‘event stage’ where an event causes transmission of the trigger 13 to the user equipment 110. In this example, the event is that a state of availability of a data radio bearer (DRB) changes. For example, a data radio bearer becomes available or becomes not available.

The process comprises an ‘trigger stage’ where the trigger is transmitted by the apparatus 120_1 of the first cell (Cell_1) to the user equipment 110. The process, in FIG 11 A, comprises a handover stage 26, followed by a data transfer 15. This comprises, as previously described, executing data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the first data radio bearer configuration 10_1 , if the trigger 13 indicates use of the first data radio bearer configuration 10_1 (first data radio bearer available) or executing data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer configuration 10_2, if the trigger 13 indicates use of the second data radio bearer configuration 10_2 (first data radio bearer not available).

In some but not necessarily all example, the first data radio bearer and the second data radio bearer have different characteristics such as bandwidth, latency, reliability and/or quality of service.

In at least some examples, the trigger 13 enables the user equipment to create an operational mapping 14 as previously described.

The data transfer session 12 is mapped, by an operational mapping 14 used for data transfer, to a sub-set of a set if multiple preconfigured data radio bearers (DRBs), where the sub-set is selected by the trigger 13.

The selected subset is the first data radio bearer if the trigger 13 indicates use of the first data radio bearer configuration 10_1 (for example, indicates that the first data radio bearer)

The selected subset is the second data radio bearer if the trigger 13 indicates use of the second data radio bearer configuration 10_1 (for example, indicates that the first data radio bearer is not available or does not indicate availability of the first data radio bearer). In at least some examples, the data transfer session 12 is a pre-existing data transfer session 12.

In FIG 11 B, the LTM setup stage and the configuration stage are amalgamated. The user equipment transmits a measurement report 41 to the apparatus 120_1 of the first cell (Cell_1)

The apparatus 120_1 of the first serving cell (Cell_1) communicates 51 with the apparatus 120_2 of the second non-serving cell (Cell_2), directly or indirectly, to setup LTM with ‘persistence’ of DRB.

The apparatus 120_2 of the second non-serving cell (Cell_2) communicates 53 with the apparatus 120_1 of the first serving cell (Cell_1), directly or indirectly, to identify available DRBs at the second non-serving cell.

The apparatus 120_1 sends a configuration message 11 to the user equipment 110 that configures persistence of DRB configurations at the LIE110. This causes the storage of first and second DRB configurations 10_1 , 10_2 as previously described.

At least one of the DRB (e.g. the first DRB_1 or second DRB_2) is not usable at present and cannot be used for data transfer but is nevertheless stored for possible future use in response to a received trigger 13. This storage for future use when current use is not possible is ’persistence’. At least one of the DRBs (e.g. the second DRB_2) may be usable at present and can be used for data transfer. The second DRB_2 can for example be a fall back default DRB.

The user equipment 110 sends an acknowledgement 43 for the configuration message 11.

The apparatus 120_2 of the second non-serving cell (Cell_2) informs 55 the apparatus 120_1 of the first serving cell (Cell_1), directly or indirectly, of availability of DRBs at the second non-serving cell. This informing can occur as a result of an event such as expiry of a periodic timer and/or a change in the availability of DRBs at the second non-serving cell (Cell_2).

The user equipment 110 transmits measurement reports 45 to the apparatus 120_1 of the first cell (Cell_1) so that it is informed, inter alia, of the current availability of DRBs at the second non-serving cell.

The apparatus 120_1 of the first cell (Cell_1) determines 60, based on the measurement report 45, to trigger LTM for the second non-serving cell, for example because handover to the non-serving cell (cell_2) is becoming more likely or probable, or for other reasons.

The apparatus 120_1 of the first cell (Cell_1) having determined 60 to trigger LTM for the second non-serving cell, sends a trigger 13 to the user equipment 110. The trigger is used to select a particular DRB for data transfer.

The apparatus 120_1 of the first serving cell (Cell_1) informs 57 the apparatus 120_2 of the second non-serving cell (Cell_2), directly or indirectly, that the particular DRB has been triggered for that data transfer.

Alternatively, in some examples, the user equipment 110 can inform the apparatus 120_2 of the second non-serving cell (Cell_2) that the particular DRB has been triggered for that data transfer.

More detail of an example implementation is illustrated in FIG 11C. The references of previous FIGs are re-used to indicate the same or similar features.

In FIG 11 C, the LTM setup stage and the configuration stage are amalgamated. The apparatus 120_1 of the first cell is a first DU 132_1 which is in communication with a CU 134.

The apparatus 120_2 of the second cell is a second DU 132_2 in communication with the CU 134. The user equipment transmits a measurement report 41 to the first DU 132_1of the first cell (Cell_1).

The first DU 132_1 of the first serving cell (Cell_1) communicates 51 with the second DU 132_2 of the second non-serving cell (Cell_2) indirectly via the CU 134 to set-up LTM with ‘persistence’ of DRB. In this example, the communication 51 comprises sending 71 the measurement report from the first DU 134 to the CU 134. The CU 134 determines 64 to trigger LTM. The CU 134 sends a UE content modification request 73 relating to LTM for cell 2 to the DU 132_2 of the second cell (cell_2). This informs the DU 132_2 of the DRBs for cell 2 (e.g. first data radio bearer DRB_1, second data radio bearer DRB_2. The request 73 has a special format indicating it is requesting LTM with maintenance (persistence) of DRB configurations.

The DU 132_2 of the second non-serving cell (Cell_2) communicates 53 with the DU 132_1 of the first serving cell (Cell_1), indirectly, to identify available DRBs at the second non-serving cell Cell_2. The DU 132_2 determines 62 the resources for the DRBs specified in the request 73. In this example, resources for a first DRB_1 are not available and resources for a second DRB_2 are available. The first DRB DRB_1 will be added/admitted even though resources are not available (persistence). The second DRB DRB_2 will be added as a usable default DRB for fallback. The DU 132_2 sends a UE setup context setup confirmation 81 regarding LTM for the second cell (Cell_2) and specification of the default DRB.

The CU 134 transmits a RRC Reconfiguration Message 11 for LTM for second cell (Cell_2) to the DU 132_1 of the first serving cell (Cell_1). This indicates that the first data radio bearer DRB_1 is to be added/admitted but is not available and that the second data radio bearer DRB_2 is a fallback default and available. The RRC Reconfiguration Message 11 comprises a first DRB configuration 10_1 for the first DRB, DRB_1, and a second DRB configuration 10_2 for the second DRB, DRB_2. The RRC Reconfiguration Message 11 is implicit or explicit instructions to use the default DRB unless a usable alternative DRB is indicated subsequently in a trigger 13. The DU 132_1 sends a configuration message 11 (a RRC Reconfiguration Message 11 ) to the user equipment 110. This configures persistence of DRB configurations at the UE 110. This causes the storage of first and second DRB configurations 10_1, 10_2 as previously described. At least one of the DRB (e.g. the first DRB_1) is not usable at present and cannot be used for data transfer but is nevertheless stored for possible future use in response to a received trigger 13. This storage for future use when current use is not possible is ’persistence’. At least one of the DRBs (e.g. the second DRB_2) is usable at present and can be used for data transfer. The second DRB_2 can for example be a fall back default DRB.

The DU 132_2 of the second non-serving cell (Cell_2) informs 55 the DU 132_1 of the first serving cell (Cell_1), indirectly, of availability of DRBs at the second nonserving cell. This informing can occur as a result of an event such as expiry of a periodic timer and/or a change in the availability of DRBs at the second non-serving cell. In this example, the DU 132_2 sends to the CU 134, a load status report 83 for the first DRB (DRB_1) and/or the second DRB (DRB_2) e.g. DRB_1 not currently usable or DRB_1 currently usable. The CU 134, then sends to the DU 132_1 a load status report 85 for the first DRB (DRB_1) and/or the second DRB (DRB_2) e.g. DRB_1 not currently usable or DRB_1 currently usable.

The user equipment transmits measurement reports 45 to the apparatus 120_1 of the first cell (Cell_1) so that it is informed of the current availability of DRBs at the second non-serving cell. The measurement reports are reports of layer one (L1) measurements made by the user equipment 110.

The DU 132_1 of the first cell (Cell_1) determines 60, based on the measurement report 45, to trigger LTM for the second non-serving cell (Cel_2), for example because handover to the non-serving cell (cell_2) is becoming more likely or probable, or for other reasons The DU 132_1 of the first cell (Cell_1) having determined 60 to trigger LTM for the second non-serving cell (Cell_2), sends a trigger 13 to the user equipment 110. The trigger is used to select a particular DRB for data transfer. The trigger 13 is a MAC control element for LTM to the second cell (Cell_2).

The DU 132_1 of the first serving cell (Cell_1) informs 57 the DU 132_2 of the second non-serving cell (Cell_2), directly or indirectly, that the particular DRB has been triggered for that data transfer. In this example, DU 132_1 of the first serving cell (Cell_1) informs 75 the CU 134 and the CU 134 informs 77 the DU 132_2.

Alternatively, in some examples, the user equipment 110 can inform the DU 132_2 of the second non-serving cell (Cell_2) that the particular DRB has been triggered for that data transfer.

In FIG 12C two different scenarios are illustrated. In scenario 90_1 , the first data radio bearer (DRB_1) is unavailable. The trigger 13 enables execution of data transfer 15 between user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer configuration 10_2.

In scenario 90_2, the first data radio bearer (DRB_1) is available. The trigger 13 enables execution of data transfer 15 between user equipment (UE) 110 and the second cell 120_2 using the first data radio bearer configuration 10_1.

Second Embodiment

FIG 12A, 12B, 12C illustrate different examples of a second embodiment.

Referring to FIG 12A, the process optionally comprises set-up of lower layer triggered mobility (LTM) 24 as previously described.

The process comprises an ‘event stage’ where an event causes transmission of the trigger 13 to the user equipment 110. In this example, the event is that a sate of availability of data transfer session (DTS) changes. For example, a data transfer session becomes available or becomes not available.

The process comprises a ‘trigger stage’ where the trigger is transmitted by the apparatus 120_1 of the first cell (Cell_1) to the user equipment 110.

The process, in FIG 11A, comprises a handover stage 26, followed by a data transfer 15. This comprises, as previously described, executing data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the first data radio bearer configuration 10_1 , if the trigger 13 indicates use of the first data radio bearer configuration 10_1 or executing data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer configuration 10_2, if the trigger 13 indicates use of the second data radio bearer configuration 10_2

A new data transfer session 12 is mapped, by an operational mapping 14 used for data transfer, to a sub-set of a set if multiple preconfigured data radio bearers (DRBs).

In FIG 12B, the LTM setup stage and the configuration stage are amalgamated. The user equipment transmits a measurement report 41 to the apparatus 120_1 of the first cell (Cell_1)

The apparatus 120_1 of the first serving cell (Cell_1) communicates 51 with the apparatus 120_2 of the second non-serving cell (Cell_2), directly or indirectly, to setup LTM with ‘persistence’ of DRB. The apparatus 120_2 of the second non-serving cell (Cell_2) communicates 53 with the apparatus 120_1 of the first serving cell (Cell_1), directly or indirectly, to identify lower layer resources for pre-active DRB provision.

There is currently no usable data transfer session mapped to the at least one of the DRBs (e.g. the first DRB_1). This DRB is not part of a usable mapping for data transfer at present and cannot be used for data transfer but is nevertheless stored for possible future use in response to a received trigger 13. This storage for future use when current use is not possible is ’persistence’.

There are communications 141, 142 to set up a data transfer session (DTS). The UE sends a message 141 requesting setup of a data transfer session, and can indicate a predicted service. The second data radio bearer (DRB_2) is set up, if available, for the new data transfer session (DTS).

The user equipment transmits measurement reports 45 to the apparatus 120_1 of the first cell (Cell_1).

The apparatus 120_1 of the first cell (Cell_1) determines 60, based on the measurement report 45, to trigger LTM for the second non-serving cell, for example because handover to the non-serving cell (cell_2) is becoming more likely or probable, or for other reasons. It also determines to use the proactive lower layer provision (the second DRB configuration) for the new data transfer session in cell 2.

The apparatus 120_1 of the first cell (Cell_1) having determined 60 to trigger LTM for the second non-serving cell, sends a trigger 13 to the user equipment 110. The trigger is used to determine whether or not the new data transfer session is supported.

The apparatus 120_1 of the first serving cell (Cell_1) informs 57 the apparatus 120_2 of the second non-serving cell (Cell_2), directly or indirectly, that the particular DRB (DRB_2) has been triggered for the new data transfer session.

Alternatively, in some examples, the user equipment 110 can inform the apparatus 120_2 of the second non-serving cell (Cell_2) that the particular DRB (DRB_2) has been triggered for the new data transfer session.

More detail of an example implementation is illustrated in FIG 12C. The references of previous FIGs are re-used to indicate the same or similar features.

In FIG 12C, the LTM setup stage and the configuration stage are amalgamated. The apparatus 120_1 of the first cell is a first DU 132_1 which is in communication with a CU 134. The apparatus 120_2 of the second cell is a second DU 132_2 in communication with the CU 134.

The user equipment transmits a measurement report 41 to the first DU 132_1of the first cell (Cell_1)

The first DU 132_1 of the first serving cell (Cell_1) communicates 51 with the second DU 132_2 of the second non-serving cell (Cell_2) indirectly via the CU 134 to set-up LTM with ‘persistence’ of DRB. In this example, the communication 51 comprises sending the measurement report 71 from the first DU 132_1 to the CU 134. The CU 134 determines 64 to trigger LTM. The CU 134 sends a UE content modification request 73 relating to LTM for cell 2 to the DU 132_2 of the second cell (cell_2). This informs the DU 132_2 of the DRBs for cell 2 (e.g. first data radio bearer DRB_1 , second data radio bearer DRB_2). The request 73 has a special format indicating it is requesting LTM with maintenance (persistence) of DRB configurations.

The DU 132_2 of the second non-serving cell (Cell_2) communicates 53 with the DU 132_1 of the first serving cell (Cell_1), indirectly, to identify lower layer resources for pre-active DRB provision. The DU 132_2 determines 62 the resources for the DRBs specified by the request 73. In this example, data radio resources will be added/admitted even though there is no mapped data transfer session. The DU 132_2 sends to the CU 134 a UE setup context setup confirmation 81 regarding LTM for the second cell (Cel l_2).

The CU 134 transmits a RRC Reconfiguration Message 11 for LTM for second cell (Cell_2) to the DU 132_1 of the first serving cell (Cell_1). This indicates that the first data radio bearer DRB_1 is to be added/admitted and that the second data radio bearer DRB_2 is to added/admitted. It will also indicate whether they are currently mapped to usable data transfer sessions. The RRC Reconfiguration Message 11 comprises a first DRB configuration 10_1 for the first DRB, DRB_1, and a second DRB configuration 10_2 for the second DRB, DRB_2.

The DU 132_1 sends a configuration message 11 (a RRC Reconfiguration Message 11 ) to the user equipment 110. This configures persistence of DRB configurations at the UE 110. This causes the storage of first and second DRB configurations 10_1, 10_2 as previously described.

There is currently no usable data transfer session mapped to the at least one of the DRBs (e.g. the second DRB_2). This DRB is not part of a usable mapping for data transfer at present and cannot be used for data transfer but is nevertheless stored for possible future use in response to a received trigger 13. This storage for future use when current use is not possible is ’persistence’.

There follow communications to set up a data transfer session (DTS). The UE sends a message 141 requesting setup of a data transfer session, and can indicate a predicted service. The second data radio bearer (DRB_2) is set up, if available, for the new data transfer session (DTS). The DU 132_1 sends message 141 to the CU 132 as message 151. The CU 134 sets-up 66 a second data radio bearer configuration 10_2 for a second data radio bearer (DRB_2) for new data transfer session. The CU 134 sends a UE content modification request 153 to the DU 132_1 of the serving cell (Cell_1). The request 153 requests use of the proactive DRB (DRB_2) after handover to the second cell for the new data transfer session.

The DU 132_1 of the serving cell (Cell_1) determines 62 whether the requested resources (DRB_2) are available. The DU 132_1 of the serving cell (Cell_1) sends a UE context modification response message 155 for DRB_2 to the CU 134.

The CU 134 sends a RRC Reconfiguration message 143 relating to LTM for the second cell (Cell_2) to the DU 132_1 of the serving cell (Cell_1). The DU 132_1 of the serving cell (Cell_1) sends the received RRC Reconfiguration message 143 relating to LTM for the second cell (Cell_2) to the UE 110.

The UE sends a RRC Reconfiguration Complete message 157 to the DU 132_1 of the serving cell (Cell_1). The DU 132_1 of the serving cell (Cell_1) sends the received RRC Reconfiguration Complete message 157 to the CU 134.

The user equipment transmits measurement reports 45 to the apparatus 120_1 of the first cell (Cell_1). The measurement reports are reports of layer one (L1) measurements made by the user equipment 110.

The DU 132_1 of the first cell (Cell_1) determines 60, based on the measurement report 45, to trigger LTM for the second non-serving cell (Cell_2), for example because handover to the non-serving cell (Cell_2) is becoming more likely or probable, or for other reasons. It also determines to use the proactive lower layer provision (the second DRB configuration) for the new data transfer session in cell 2.

The DU 132_1 of the first cell (Cell_1) having determined 60 to trigger LTM for the second non-serving cell (Cell_2), sends a trigger 13 to the user equipment 110 which can provide (or not proved) a usable mapping 14 for data transfer relating to the new data transfer session. The trigger 13 is a MAC control element for LTM to the second cell (Cell_2). The DU 132_1 of the first serving cell (Cell_1) informs 57 the DU 132_2 of the second non-serving cell (Cell_2), directly or indirectly, that the usable mapping 14 has been triggered for the new data transfer session. In this example, DU 132_1 of the first serving cell (Cell_1) informs 75 the CU 134 and the CU 134 informs 77 the DU 132_2. Alternatively, in some examples, the user equipment 110 can inform the DU 132_2 of the second non-serving cell (Cell_2).

Referring back to FIG 5, there is a state where a data transfer session 12_1 is mapped to a sub-set (DRB_1) of a set of multiple preconfigured data radio bearers (DRB) and a state where that data transfer session 12_1 is not mapped to any preconfigured data radio bearers (DRB), wherein the state is selected by the trigger 13.

There is (or is not) a DRB to data transfer session mapping 14, for data transfer session 12_1 , as a result of the trigger 13.

The data transfer session 12_1 is a new data transfer session 12 that has not, before the trigger 13, been previously used for transfer of data between the UE and first cell 120_1 or second cell 120_2.

The first and second data radio bearer configurations 10 configure data radio bearer (DRB)s for at least a first data transfer session 12_1 and optionally a second data transfer session 12_2. Executing data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the first data radio bearer configuration 10_1 if the trigger 13 indicates use of the first data radio bearer configuration 10_1 comprises not executing the second data transfer session 12_2 with the first data radio bearer configuration 10_1 , and executing data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer configuration 10_2 if the trigger 13 indicates use of the second data radio bearer configuration 10_2 comprises executing the second data transfer session 12_2 with the second data radio bearer configuration 10_2 The examples described, include examples of an apparatus 120 (132) for a cellular telecommunication network comprising: means for causing transmission, via a first cell 120_1 , to user equipment (UE) 110 of downlink signaling 11 that provides a first data radio bearer configuration 10_1 for a second cell 120_2 (DRB_1), and a second data radio bearer configuration 10_2 for a second cell 120_2 (DRB_2); means for causing transmission, via the first cell 120_1 , to the user equipment (UE) 110 of a trigger 13: configured to indicate use of the first data radio bearer configuration 10_1 to enable data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the first data radio bearer (DRB_1) or, configured to indicate use of the second data radio bearer configuration 10_2 to enable data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer (DRB_2).

In some, but not necessarily all examples, the apparatus 120 (132) is configured to receive 53 a configuration of the first data radio bearer configuration 10_1 for a second cell 120_2, and a configuration of a second data radio bearer configuration 10_2 for a second cell 120_2 to enable downlink signaling 11 that provides the first data radio bearer configuration 10_1 for a second cell 120_2 (DRB_1), and the second data radio bearer configuration 10_2 for a second cell 120_2 (DRB_2).

In some, but not necessarily all examples, the apparatus 120 (132) is configured to receive 53 a decision criterion (for decision process 60) for causing transmission, via the first cell 120_1 , to the user equipment (UE) 110 of a trigger 13 and/or setting mapping parameters in the trigger.

The decision criteria to use first or second DRB configuration 10_1 , 10_2 can comprise at least one of a. an availability of data radio bearer (DRB)s at first cell 120_1 b. an availability of data radio bearer (DRB)s at the second cell 120_2 c. a new data transfer session

In some, but not necessarily all examples, the apparatus 120 (132) is configured to receive and use a report 45 that comprises information that is compared to decision criteria, at decision process 60, for causing transmission, via the first cell 120_1, to the user equipment (UE) 110 of the trigger 13 and/or setting mapping parameters in the trigger.

In some, but not necessarily all examples, the apparatus 120 (132) is configured to receive and use a report 55 from the second cell 120_2 indicating availability of DRB at second cell 120_2 for comparison to the decision criterion. The report 55 can be a periodic report or an event-based report indicating the load status with respect to the DRB allocation of the UE.

The report 55 can indicate lack of resources or existence of resources for a DRB configuration.

Fig 13A illustrates an example of a controller 400 suitable for use in an apparatus 110; 120(132). Implementation of a controller 400 may be as controller circuitry. The controller 400 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 13A the controller 400 may be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program 406 in a general-purpose or special-purpose processor 402 that may be stored on a computer readable storage medium (disk, memory etc) to be executed by such a processor 402.

The processor 402 is configured to read from and write to the memory 404. The processor 402 may also comprise an output interface via which data and/or commands are output by the processor 402 and an input interface via which data and/or commands are input to the processor 402.

The memory 404 stores a computer program 406 comprising computer program instructions (computer program code) that controls the operation of the apparatus 110; 120(132) when loaded into the processor 402. The computer program instructions, of the computer program 406, provide the logic and routines that enables the apparatus to perform the methods illustrated in the accompanying Figs. The processor 402 by reading the memory 404 is able to load and execute the computer program 406.

The apparatus 110; 120(132) comprises: at least one processor 402; and at least one memory 404 including computer program code the at least one memory 404 and the computer program code configured to, with the at least one processor 402, cause the apparatus 110; 120(132) at least to perform: conditionally execute data transfer 15 between user equipment (UE) 110 and a second cell 120_2 wherein the if a trigger 13, received from a first cell 120_1, indicates use of a previously received and stored first data radio bearer configuration 10_1 then causing execution of data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the first data radio bearer configuration 10_1 and if the trigger 13, received from the first cell 120_1 , indicates use of a previously received and stored second data radio bearer configuration 10_2 then causing execution of data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer configuration 10_2.

The apparatus 110; 120(132) comprises: at least one processor 402; and at least one memory 404 including computer program code, the at least one memory storing instructions that, when executed by the at least one processor 402, cause the apparatus at least to: conditionally execute data transfer 15 between user equipment (UE) 110 and a second cell 120_2 wherein the if a trigger 13, received from a first cell 120_1, indicates use of a previously received and stored first data radio bearer configuration 10_1 then causing execution of data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the first data radio bearer configuration 10_1 and if the trigger 13, received from the first cell 120_1 , indicates use of a previously received and stored second data radio bearer configuration 10_2 then causing execution of data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer configuration 10_2. As illustrated in Fig 13B, the computer program 406 may arrive at the apparatus 110; 120(132) via any suitable delivery mechanism 408. The delivery mechanism 408 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 406. The delivery mechanism may be a signal configured to reliably transfer the computer program 406. The apparatus 110; 120(132) may propagate or transmit the computer program 406 as a computer data signal.

Computer program instructions for causing an apparatus to perform at least the following or for performing at least the following: conditionally execute data transfer 15 between user equipment (UE) 110 and a second cell 120_2 wherein the if a trigger 13, received from a first cell 120_1, indicates use of a previously received and stored first data radio bearer configuration 10_1 then causing execution of data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the first data radio bearer configuration 10_1 and if the trigger 13, received from the first cell 120_1 , indicates use of a previously received and stored second data radio bearer configuration 10_2 then causing execution of data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer configuration 10_2.

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 404 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. A memory may include e.g. ROM, and/or RAM, and/or EEPROM, and/or DRAM, and/or SRAM, and the like.

A memory may be a computer memory, a device that is used to store data or programs (sequences of instructions) on a temporary or permanent basis for use in an electronic digital computer. Computers represent information in binary code, written as sequences of Os and 1s. Each binary digit (or “bit”) may be stored by any physical system that can be in either of two stable states, to represent 0 and 1.

Computer memory is divided into main (or primary) memory and auxiliary (or secondary) memory. Main memory holds instructions and data when a program is executing, while auxiliary memory holds data and programs not currently in use and provides long-term storage.

Although the main/auxiliary memory distinction is broadly useful, memory organization in a computer forms a hierarchy of levels, arranged from very small, fast, and expensive registers in the CPU to small, fast cache memory; larger DRAM; very large hard disks; and slow and inexpensive nonvolatile backup storage. Memory usage by modern computer operating systems spans these levels with virtual memory, a system that provides programs with large address spaces (addressable memory), which may exceed the actual RAM in the computer. Virtual memory gives each program a portion of main memory and stores the rest of its code and data on a hard disk, automatically copying blocks of addresses to and from main memory as needed. The speed of modern hard disks together with the same locality of reference property that lets caches work well makes virtual memory feasible.

Although the processor 402 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 402 may be a single core or multi-core processor.

FIG 14 illustrates an example of a network 100 comprising a plurality of network nodes including terminal nodes 110, access nodes 120 and one or more core nodes 129. The terminal nodes 110 and access nodes 120 communicate with each other. The one or more core nodes 129 communicate with the access nodes 120. The network 100 is in this example a radio telecommunications network, in which at least some of the terminal nodes 110 and access nodes 120 communicate with each other using transmission/reception of radio waves.

The one or more core nodes 129 may, in some examples, communicate with each other. The one or more access nodes 120 may, in some examples, communicate with each other.

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

The access node 120 is a cellular radio transceiver. The terminal nodes 110 are cellular radio transceivers.

In the example illustrated the cellular network 100 is a third generation Partnership Project (3GPP) network in which the terminal nodes 110 are user equipment (UE) and the access nodes 120 are base stations.

In the particular example illustrated the network 100 is an Evolved Universal Terrestrial Radio Access network (E-UTRAN). The E-UTRAN consists of E-UTRAN NodeBs (eNBs) 120, providing the E-UTRA user plane and control plane (RRC) protocol terminations towards the UE 110. The eNBs 120 are interconnected with each other by means of an X2 interface 126. The eNBs are also connected by means of the S1 interface 128 to the Mobility Management Entity (MME) 129.

In other example the network 100 is a Next Generation (or New Radio, NR) Radio Access network (NG-RAN). The NG-RAN consists of gNodeBs (gNBs) 120, providing the user plane and control plane (RRC) protocol terminations towards the UE 110. The gNBs 120 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 Access and Mobility management Function (AMF). A user equipment comprises a mobile equipment. Where reference is made to user equipment that reference includes and encompasses, wherever possible, a reference to mobile equipment.

FIG 15 illustrates an example of a method 500. The method 500 can be performed by a user equipment 110.

The method comprises, at block 502, receiving, via a first cell 120_1 , downlink signaling 11 that provides a first data radio bearer configuration 10_1 for a second cell 120_2 (DRB_1), and a second data radio bearer configuration 10_2 for a second cell 120_2 (DRB_2).

The method comprises, at block 504, storing the first data radio bearer configuration 10_1 , for execution of data transfer 15 via the second cell 120_2 using the first data radio bearer (DRB_1) and for storing the second data radio bearer configuration 10_2, for execution of data transfer 15 via the second cell 120_2 using the second data radio bearer (DRB_2).

The method comprises, at block 506, receiving via the first cell 120_1 a trigger 13; The method comprises, at block 502, conditionally executing data transfer 15 between user equipment (UE) 110 and the second cell 120_2 using a data radio bearer configuration 10.

If the trigger 13 indicates use of the first data radio bearer configuration 10_1 then, the method 500 executes data transfer 15 between user equipment (UE) 110 and the second cell 120_2 using the first data radio bearer configuration 10_1.

If the trigger 13 indicates use of the second data radio bearer configuration 10_2, then the method 500 comprises executing data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer configuration 10_2.

In some but not necessarily all examples, execution of data transfer 15 between the user equipment (UE) 110 and the second cell requires an operational mapping 14 between a usable data transfer session 12 to provide data for transfer and a usable data radio bearer (DRB) to provide a transfer channel for data.

At a time of the downlink signaling 11, there is no mapping 14, for the second cell 120_2, between the data radio bearer (DRB) for the second cell 120_2 and a data transfer session 12. At a time of triggering execution of data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the data radio bearer (DRB) for the second cell 120_2, as a consequence of the received trigger 13, there is an operational mapping 14, for the second cell 120_2, between the data radio bearer (DRB) for the second cell 120_2 and a data transfer session 12.

In some examples, at a time of the downlink signaling 11 , the data radio bearer (DRB) for the second cell 120_2 is not usable for the second cell 120_2 and at the time of triggering, the data radio bearer (DRB) for the second cell 120_2 is usable for the second cell 120_2 e.g. the data transfer session 12 is usable for the second cell 120_2 and the data radio bearer (DRB) is not usable for the second cell 120_2).

In some examples, at the time of triggering, a data transfer session 12 is usable for the second cell 120_2 and at the time of the signaling, the data transfer session 12 is not usable for the second cell 120_2 e.g. the data transfer session 12 is not usable for the second cell 120_2 and the data radio bearer (DRB) is usable for the second cell 120_2.

The preceding paragraphs describe user equipment (UE) 110 comprising: at least one processor 402; and at least one memory 404 including computer program code, the at least one memory storing instructions that, when executed by the at least one processor 402, cause the apparatus at least to: cause execution of data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the first data radio bearer configuration 10_1 , if a received trigger 13 from a first cell 120_1 indicates use of a previously received and stored first data radio bearer configuration 10_1 and cause execution of data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 using the second data radio bearer configuration 10_2 if the received trigger 13 from the first cell 120_1 , indicates use of a previously received and stored second data radio bearer configuration 10_2.

The preceding paragraphs describe user equipment (UE) 110 comprising: receiver circuitry configured to receive, via a first cell 120_1 , separately: downlink signaling 11 that provides a first data radio bearer configuration 10_1 for a second cell 120_2 (DRB_1) and a second data radio bearer configuration 10_2 for a second cell 120_2 (DRB_2), a trigger 13; memory circuitry configured to store the first data radio bearer configuration 10_1 , for execution of data transfer 15 via the second cell 120_2 using the first data radio bearer (DRB_1) and to store the second data radio bearer configuration 10_2, for execution of data transfer 15 via the second cell 120_2 using the second data radio bearer (DRB_2); control circuitry, configured to execute data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 in dependence upon the received trigger 13, wherein the control circuitry is configured to use the first data radio bearer configuration 10_1 for data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 if the trigger 13 indicates use of the first data radio bearer configuration 10_1 and is configured to use the second data radio bearer configuration 10_2 for data transfer 15 between the user equipment (UE) 110 and the second cell 120_2 if the trigger 13 indicates use of the second data radio bearer configuration 10_2.

Lower Layer triggered Mobility (LTM), (also known as L1/2 inter-cell mobility) is one of the objectives for mobility enhancement in Rel. 18 of 3GPP. In LTM the decision about the cell change is based on L1 measurements and is made in the MAC layer in the Distributed Unit (DU).

In LTM, the target node can generate either a full or a delta configuration for the candidate target PCell or PSCell, respectively. In case of delta configuration, the configuration of the candidate target cell contains only the parameters that need to be modified compared to the current source cell (that is subject for the change). As such, the size of the delta configuration can be much smaller than that of full configuration which reduces substantially the overhead over the radio interface.

Where radio bearer configuration is provided as delta configuration, any update to the radio bearer configuration of the UE needs to be propagated to all prepared target cells to provide an update delta configuration of their corresponding radio bearer configurations.

When new bearers are configured or QoS Flows (data transfer sessions) are created for an RRC connection, the RRC reconfiguration message containing the modified DRB configuration is provided to UE. The delay for activating the new bearers depends on the time it takes to reconfigure the UE. In case of LTM scenario, if the DRB configuration of the serving cell is updated the LTM configurations of the target cells (stored by the UE) need also to be modified to reflect the changes in the radio bearer configurations. This is necessary so that after LTM execution the configurations are aligned between UE and target node.

In an overload situation, the DRBs may be rejected at the time of LTM preparation. The examples provided above (Embodiment 1) mitigate adverse consequences of this.

Issue 2: The signaling latency and internal signaling overhead arising rom creating a new data transfer session are mitigated by examples provided above (Embodiment 2)

The examples provided enhance the low layer resource provisioning on target DU (non-serving cell) side during LTM preparation.

Embodiment 1 : In case of overload situation at the time of LTM preparation, the target DU provides low layer resources for a DRB that it doesn’t have at that moment of LTM preparation. As a fallback, it also allocates a default DRB. The load situation at the target DU is indicated to the source DU, to inform the source DU if it can provide the pro-active low layer resources at the time of the LTM execution. If the overload situation is remedied at the target DU, the source DU indicates UE to use the low layer resource for the DRBs, otherwise, the source DU indicates UE to use the default DRB for the QoS flow (data transfer session). In Figure 11 C, initially the UE is in RRC connected state with source DU in Cell_1 , with 3 DRBs mapping to different QoS flows (data transfer sessions). UE 110 is configured with measurement reports to report potential target cells to the CU. The QoS requirements of the QoS flows is known to the CU 134. The QoS requirements indicate that a minimal interruption time for each QoS flow should be preserved. The CU 134 can determine that the interruption for the DRBs mapping to these QoS flows (data transfer sessions) should be minimized or completely avoided if possible.

The CU 134 determines 64 to prepare LTM for the UE 110 in Cell_1. The CU 134 indicates 73 the LTM preparation to the target DU 1 for Cell_2, while indicating that it wants to use the feature of “maintain RB config”. This indication triggers the maintenance of the DRB configuration even in an overload situation at the target DU 132_2. (The target DU and source DU can be the same node). Target DU also includes a default DRB in the configuration.

UE 110 is configured with the LTM configuration 11 and reports the target cell L1 measurements. Source DU 132_1 monitors 60 L1 measurements and triggers the cell change to Cell_2 with a MAC CE command (trigger 13).

In option 1 (90_1): If there are no available radio resources to admit DRB 2 and 3, the source cell (Cell_1) will indicate the UE 110 to use default DRB, instead of DRB 2 and DRB3 - this will update the DRB to QoS flow mapping at the UE side. In other words, the QoS Flows mapped to DRB2 and DRB3 will be mapped to default DRB.

In option 2 (90_2): If there are available radio resources, the source cell will indicate UE to use DRB2 and DRB3. The available radio resources can appear via a UE 110 finishing a session and releasing the use of existing radio resources. At this point the target DU 132_2 may prioritize allocation and reserving radio resources for the UE 110 with LTM configuration and indicated the resource status to the CU.

The radio resource availability indication 83,85 can be sent on a periodic basis or on an event triggered basis such as disappearing of a UE from a cell that enables the availability of new radio resources. Similarly, a high priority UE may pre-empt radio resource reservation for an LTM UE, which may result in indication of not available radio resources to the CU 134.

Following either option, the source DU 132_1 will indicate 75 the selected DRB to QoS flow mapping to the CU 134 which in turn will inform 77 the target DU about the final UE configuration.

Alternative to these steps, the UE 110 can also report the latest DRB configuration to the target node 132_2.

Alternative to the above, the UE 110 can also report the latest DRB configuration to the CU 134, which can then in turn will inform the target DU 132_2 about the final UE configuration.

In another alternative, the Message 8 and 9 or 15 and 16 dictates the serving DU behavior, i.e., if not ok is reported serving DU has to map QoS flow to default DRB. In that case, the target DU can use the last sent DRB load status to infer the DRB configuration of the UE. However, this case might create racing condition which can be avoided with the above alternatives.

Embodiment 2: At the time of LTM preparation, the target DU may provide pro-active low layer resources for a DRB that doesn’t map to any specific QoS flow at that moment. The LTM configuration is configured to the UE with the pro-active low layer resources for a DRB that doesn’t map to any specific QoS flow. The UE might add a new QoS flow while the LTM configuration is maintained at the UE side. The new QoS flow, results in new DRBs at the serving cell but the candidate LTM configurations stay the same. The LTM configuration is not updated if a new LTM configuration. At the time of LTM execution, the source DU indicates UE to map the new QoS flow to the proactive DRB at the target cell.

In Figure 12C, the UE is in RRC connected state with source DU in Cell_1 , with 1 DRB mapping to a QoS flows. UE 110 is configured with measurement reports to report potential target cells to the CU 134. The service requirements and related QoS requirements of the UE 110 is known to the CU 134. The QoS requirements indicate that a minimal interruption time for each QoS flow should be preserved. The CU 134 can determine that the interruption for the DRBs mapping to these QoS flows should be minimized or completely avoided if possible.

The CU 134 determines 64 to prepare LTM for the UE in Cell_1. The CU 134 indicates the LTM preparation to the target DU 2 for Cell_2, while indicating that it wants to use feature of “pro-active RB config”. The target DU_2 adds a DRB configuration that is not mapped to any QoS flow. This indication triggers the addition of low layer resources for the pro-active DRB configuration at the target DU. The source DU 132_1 knows that these DRBs shouldn’t used by the UE 110 unless a QoS flow is later added to be attached to these DRBs.

UE 110 is configured 11 with the LTM configuration and reports 45 the target cell L1 measurements. Source DU 132_1 monitors 60 L1 measurements 45.

Meanwhile, UE 110 requests 141 , 151 a new PDU session (data transfer session) to be setup and the network sets up 66 the DRB configuration for the QoS flow 1 (QoS Flow related to the newly setup PDU Session); PDU = Packet Data Unit. The CU 134 indicates to the source DU 132_1 that the new QoS flow should be mapped to DRB configuration that is provided by the target DU 132_2 (in the example DRB 2 and 3) for the UE 110 in case of a switch to Cell_2. However, LTM configuration is not updated.

Later on, the UE measurements 45 are used to trigger 13 the cell change with a MAC CE command 13 to UE 110. With the MAC CE command 13, the source cell (Cell_1) will indicate the UE 110 to update the DRB to QoS flow mapping 14 at the UE side, i.e. , mapping the QoS Flow 1 to pro-active DRB.

The source DU 132_1 will indicate 75 the selected DRB to QoS flow mapping to the CU 134 which in turn will inform 77 the target DU about the final UE configuration. Alternative to these steps, the UE 110 can also report the latest DRB configuration to the target node 132_2. Alternative to the above, the UE 110 can also report the latest DRB configuration to the CU 134, which can then in turn will inform the target DU 132_2 about the final UE configuration. In another alternative, the CU 134 indicates the DRB mapping 14 QoS flow to the target DU after the addition of the new DRBs for the UE (after 153), but the UE 110 is not updated with a new LTM configuration. For this reason, the latest DRB configuration does not need to be indicated to the target DU.

The examples avoid modifications of the conditional configurations in case of the configuration of the UE 110 in the serving cell is changed.

The examples are expected to result in specification change in specifications TS 38.331 , TS 38.423.

The above embodiments have been described as exemplary embodiments. Features thereof are broadly applicable, e.g. as will be apparent by the description of a further exemplary embodiment. A particular feature of an embodiment might also be used in another embodiment.

Fig. 16 in general shows an exemplary embodiment related to the configuration and use of DRB in a radio access network.

It is further related to a user equipment, UE, configured to connect to a first cell of a first network node that supports distributed unit, DU, functionality and/or a layer 2 protocol processing of a radio access network, RAN, the UE comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the UE at least to: establish a connection towards the first cell, transmit data towards the first cell using at least a first data radio bearer, perform L3 measurements for at least one of a plurality of candidate target cells to potentially switch to, transmit a L3 measurement report related to performed measurements towards a second network node that supports a central unit, CU, functionality and/or a layer 3 protocol processing of the radio access network, RAN, and which is connected to the first node, receive a L3 configuration message including configuration information related to at least one of said plurality of candidate target cells for L1 L2-triggered mobility, LTM, wherein the configuration information includes a pre-configuration to potentially use a second data radio bearer different from the first data radio bearer for transmitting data towards a target cell to switch to; and receive a L2 message including a trigger to switch from the first cell to a target cell, and an implicit or explicit indication whether the pre-configured data radio bearer is to be used for transmitting data towards the target cell and/or whether the currently used first data radio bearer is to be retained and used for transmitting data towards the target cell, establish a connection towards the indicated target cell, transmit data towards the target cell using at least the indicated data radio bearer.

Such user equipment may also cover one or more features of other described embodiments so far.

Coming back to Fig. 16 the user equipment, UE, may be configured to be connected to a radio access network, wherein the indicated target cell is a cell of a third network node that supports distributed unit, DU, functionality and/or a layer 2 protocol processing of the radio access network, RAN.

The user equipment, UE, may further be configured to be connected to the radio access network, wherein the third network node is connected to the second network node.

The user equipment, UE, may further be configured to be connected to the radio access network, wherein the L3 configuration message is an RRCConfiguration message or an RRCReconfiguration message.

The user equipment, UE, may further be configured to be connected to the radio access network, wherein the L2 message is a MAC CE message. The user equipment, UE, may further configured to: transmit data towards the first cell using a third data radio bearer, and wherein the configuration information includes a configuration to maintain using the third data radio bearer for transmitting data towards the target cell to switch to.

The user equipment, UE, may further be configured to be connected to the radio access network, wherein the implicit or explicit indication whether the pre-configured data radio bearer is to be used is received as part of the received L2 message.

The user equipment, UE, may further be configured to be connected to the radio access network, wherein the implicit or explicit indication whether the pre-configured data radio bearer is to be used or not is indicated in at least one of the following ways:

No indication indicating the pre-configured data radio bearer is to be used, A flag or specific instruction to use the pre-configured data radio bearer, A flag or specific instruction to retain the first data radio bearer,

A flag or specific instruction to use both the pre-configured data radio bearer and to retain the first data radio bearer.

The user equipment, UE, may further be configured to be connected to the radio access network, wherein the configuration information further includes an instruction to use the pre-configured second data radio bearer instead of the first data radio bearer for transmitting data towards the target cell to switch to in case no further instruction is received to retain the first data radio bearer for transmitting data towards the target cell to switch to.

The user equipment, UE, may further be configured to be connected to the radio access network, wherein the configuration information includes a pre-configuration to potentially use a second data radio bearer with a specific QoS level, and the implicit or explicit indication indicates to use the pre-configured data radio bearer with its specific QoS level for transmitting data towards the target cell and to retain the first data radio bearer and its assigned QoS for transmitting data towards the target cell. The user equipment, UE, may further be configured to be connected to the radio access network, wherein the specific QoS level and the assigned QoS level are different.

The user equipment, UE, may further be configured to be connected to the radio access network, wherein the implicit or explicit indication indicates to use the pre-configured data radio bearer for transmitting data towards the target cell in a first PDU session and to retain the first data radio bearer and is QoS mapping for a second PDU session, wherein first and second PDU session are different sessions.

Fig. 16 further shows an illustrative example of a user equipment and a radio access network. The radio access network may e.g. be an LTE, 5G, NR (New Radio) network or parts thereof or a mixed network, sometimes referred to as multi-RAT.

The radio access network may include at least one gNBs supporting e.g. L2 and L3 protocol functionalities or a split architecture with separate network nodes, e.g. at least one network node supporting distributed unit (DU) and/or in particular layer 2 (L2) protocol functionalities, and at least one other network node supporting central unit (CU) functionalities and/or in particular layer 3 (L3) protocol functionalities.

The UE of Fig. 16 is already connected to serving cell 1 controlled I supported by serving DU 0.

In order to be in this operational mode, UE first (in step 0 not shown) establishes a connection towards the first cell 1. This cell then becomes the source cell and/or serving cell which transmits data and control signals towards the UE and which receives data and control signals towards the UE.

When connected to cell 1 UE e.g. transmits data towards the first cell using at least a first data radio bearer, e.g. DRB1 , DRB2, and DRB3; DRB = Data Radio Bearer. Which DRBs are in use has been configured during connections etup or updated afterwards depending on the needs of the UE, e.g which services are requested, which Quality of Service, etc; e.g. UE wishing to transmit a phone call may need other DRBs than a UE wishing to transmit e.g. gaming signals, video calls, internet access, sms, mms, etc.

UE may also be configured to transit and/or receive control/signaling signals, e.g. using a least one SRB; SRB = Signalling Radio Bearer.

UE typically performs L3 measurements for at least one of a plurality of candidate target cells to potentially switch to. Such measurements are e.g. performed on a regular/periodic basis, or e.g. event driven. In particular when connections conditions with respect to the serving cell are degrading these measurements are helpful to prepare and support handover towards another cell with expected better connection conditions. UE measurement is e.g. related to reference signals of cells (e.g. neighbor cells, target cells). In LTE, those reference signal for the measurement are e.g. synchronization signal and/or CRS(Cell Specific Reference signal). In NR, the types of reference signal is e.g. synchronization signal/PBCH Reference Signal and CSI-RS

UE generates a measurement report indicating e.g. cells IDs and related measurement results, and in step 1 transmits a related L3 measurement report related to performed measurements towards a second network node that supports a central unit, CU, functionality and/or a layer 3 protocol processing of the radio access network, RAN, and which is connected to the first node, like e.g. serving CU.

The measurement report may be transmitted using an RRC message.

Serving CU receives and analyzes the measurement report. The analysis may lead to different actions, e.g. no action regarding potential handover or preparation of potential handover for UE is taken as connection conditions to cell 1 are still good. And e.g. wait for the next measurement report. If conditions to cell 2 are e.g. (much) better than conditions to cell 1 , serving CU may decide to prepare handover or conditional handover. His may be a L3 handover or a L2 handover. In step 2 serving CU exemplarily determines to initiate preparation of a a L2 handover, e.g. to trigger an LTM (L1 L2 Trigger Mobility).

In step 3 serving CU sends a UE context modification request to target DU1 supporting cell 2. Cell 2 is a potential target cell to switch to, e.g. UE to perform handover from cell 1 to cell 2. Cell 2 has been identified by the received L3 measurements. Serving CU is connected to and controls target DU1 and thus knows that cell 2 is supported by DU1. The measurement report may identify not only one potential cell to switch to, but e.g. multiple, e.g. a cell 3 (not shown) also supported by DU1, and/or a cell 4 (not shown) supported by a DU2 (not shown). The serving CU may then send respective UE context modification request(s) to e.g. DU2 and/or DU1 (including cell 1 and cell 2).

The UE context modification request of step 3 may include a request or instruction to setup or configure LTM for cell 2 (and the UE) and an indication which DRBs are currently used by the UE (connected to cell 1), e.g. DRB1 , DRB2, DRB3, and an instruction to assign the same DRBs if they are available. Assigning the same DRBs for both UE-cell1 connection and UE-cell2 connection has several advantages in the configuration of the UE, the handover process, etc. and thus is preferred.

The UE context modification request of step 3 may further include a request or instruction not to reject the request. This is different from the situation where the DU can always reject when CU asks for UE context, e.g. if there is no resource for a DRB available it is normally rejected. So this is what is changed: To not reject, but to provide some alternative DRBs, e.g. that will not fulfil QoS, will be a new behavior to be triggered by the CU.

In other words the request or instruction not to reject the request may be an instruction for the DU1 to check whether the requested DRBs are currently available and assign the same if available and if not available intermediately (pre-)assign others, but continue monitoring if the requested DRBs become available at a later point in time.

Different cases could thus be distinguished: e.g. DU1 is requested to assign DRB1, DRB2, DRB3 to potential cell 2 - UE connection, DU1 determines: a) all DRBs are available and could be assigned and assigns them and informs serving CU of the assignment, serving CU could then configure UE respectively and in case of LTM UE switches to cell2 using the assigned DRBs, or b) none of the requested DRBs are available, e.g. due to load conditions, potential interferences, or other, and thus DU1 assigns at least one other DRB, e.g. DRB4 (not shown) to enable/support/maintain a minimum connection, or best 3 other DRBs. Serving CU could then configure UE respectively and in case of LTM UE switches to cell2 using the other assigned DRBs, or c) some of the requested DRBs are available, e.g. DRB1, while others like DRB2 and DRB3 are not available, and thus DU1 assigns DRB1 and potentially at least one other DRB, e.g. DRBm and DRBn. Serving CU could then configure UE respectively and in case of LTM UE switches to cell2 using the assigned DRBs.

When DU1 is enabled to continue monitoring if the requested DRBs become available at a later point in time it could indicate this to the serving cell, such that serving CU is enabled to update the newly available DRBs to the serving DU.

For the different cases a), b), c) this may have different effects: a) no effect as the same DRBs have already been assigned, b) depending on when and how many DRBs become available this could have different effects: e.g. before LLM execution DRB1 and DRB2 become available and DRB3 not, resulting in for LTM UE could maintain DRB1 and DRB2 also for the connection to cell2, and use another DRB, if assigned, as a substitute for DRB3. This is beneficial as at least 2 DRBs could be kept and only 1 needed o eb reassigned. c) depending on when and how many DRBs become available this could have different effects: e.g. before LLM execution DRB2 and DRB3 become available, resulting in for LTM UE could maintain DRB1 , DRB2 and DRB3 also for the connection to cell2, and does not have to use DRBm as a substitute for DRB2 or DRMn as a substitute for DRB3. This is beneficial as all 3 DRBs could be kept.

Therefore, configuring or enabling DU1 to continue monitoring if requested DRBs which could not be assigned become available at a later point in time can have benefits.

Coming back to Fig. 16 example. In step 4 DU1 determines which of the requested DRBs are available and determines that DRB1 is available and DRB2 and DRB3 are not available. It then assigns DRB1 and DRB m (as substitute for DRB2) and DRB3 (as substitute for DRB3) and configures LTM for cell2 (for the UE). In step 5 uses a UE context setup confirm message to inform the serving CU about the LTM configuration and the assigned DRBs. The fig. shows default DRB as an abbreviation for the assigned DRBs. In the example default DRB includes DRB1, DRBm, and DRBn.

DU1 further starts monitoring the availability of DRB2 and DRB3.

In step 6 serving CU generates and transmits an RRCReconfiguration message to the UE. The RRCReconfiguration message includes the LTM configuration for cell2 and the default DRB information (for handover to cell2 if such handover is triggered). The RRCReconfiguration message further includes a measurement configuration to perform L1 measurements on cell2 and to report these measurements to serving DUO. Based on the L1 measurements DUO may decide to trigger handover.

LTM configuration for more than one cell potentially being supported by more than one target DU may be included in step 6 message. A respective UE context modification request and setup confirm processing may therefore be performed upfront.

In general UE receives in step 6 a L3 configuration message including configuration information related to at least one of said plurality of candidate target cells for L1L2- triggered mobility, LTM, wherein the configuration information includes a preconfiguration to potentially use a second data radio bearer different from the first data radio bearer for transmitting data towards a target cell to switch to.

A candidate target cell may be cell2. A second DRB may be DRBm which s different from DRB2 and potentially used to substitute DRB2 in case handover.

The L3 configuration message, e.g. RRCReconfiguration message, may further include an indication to use at least the second DRB for handover unless a report/message/trigger indicates to use a different DRB instead. E.g. if second DRB = DRBm, then use DRBm when switching to cell2, or if at a later point in time indicated to use DRB2 instead, use DRB2. The UE may need to be configured/enabled to support monitoring, detection and processing of such further unless indication and related operations, e.g. when receiving an RRCReconfiguration message with LLM configuration, check whether it further includes the unless trigger, and if trigger is received act accordingly. A UE supporting such functionality may store it in its UE capability information and transmit it to the serving CU during establishment of the connection or at a later point in time. Alternatively, such support may be mandatory for a UE supporting a more recent release of a 3GPP standard, e.g. 3GPP TS38.300 and related specs, Release 18 upwards. Then indication f Rel. 18 support during connection setup may already implicitly indicate to the serving CU support of the processing of such further unless indication. Such support may also be implemented as an optional feature. In any case this may need only small amendments to 3GPP as a conventional UE may continue as usual (not checking for further unless indication), while a more advanced UE may do so.

In step 7 UE confirm having applied the requested configuration successfully by transmitting a respective RRCReconfigurationComplete message to the serving CU.

In the following 2 options will be described showing 2 case scenarios.

Option 1: No available radio resources

DU1 continues to monitor if DRB2 and DRB3 become available. At the same time UE performs L1 measurements and transmits respective L1 measurement report to the serving DU (step 10).

Each target DU, e.g. DU1 may transmit from time to time, or on a regular or periodic basis a status update of the DRB load regarding DRB2 and DRB 3 towards the serving CU (step 8), e.g. DRB2 and DRB 3 are still not available. The serving DU may transmit the status to the serving DUO (step9) informing DUO that nothing has changed, e.g. DRB2 and DRB 3 still available, please use the default DRB in case of LLM to cell2. As nothing has changed steps 8 and/or 9 might be optionally implemented. Regarding timing: UE is configured with DRB n and m and with available DRB1. Target DU1 continues to monitor availability of DRB 2 and 3, e.g. until it receives a RACH from UE or receives a RACHIess connection request or until a respective timer expires. This timing requirement might be implemented as an optional feature in 3GPP Rel. 18 onwards.

Option 1: DRB 2 and 3 remain unavailable

In step 11 DUO determines based on received L1 measurements to trigger LTM, e.g. LLM towards cell2 or another potential target cell/DU which has be preconfigured and to which the UE shall switch if this cell becomes the best cell to switch to, due to decreasing connection conditions regarding celU and better conditions of new target cell. In case 2 cells have good conditions for handover a selection has to be done. The selection may be based on the available resources/DRBs, e.g. if cell2 has DRB1 available and DRB2 and DRB3 not, but another potential target cell has DRB1, DRB2, DRB3 available, then the decision might be to use the other potential target cell for LLM handover, even may be if cell2 has better conditions than the other cell. The reasoning behind is that a sustainable handover can be performed and it is easier to handle as more DRBs are equal (compared to celU connection).

In step 11 DUO determines that cell2 is the cell to switch to and determines further that DRB2 and DRB3 are still not available, and thus triggers with step 12 LTM to cell2. The trigger may be included in a MAC CE message.

The MAC CE message may further include an indication to use the target configuration, e.g. “use default DRB”, or “use DRB1 , DRBm and DRBn”. As there is no change this indication may also not be send. The UE uses the preconfigured configuration incase an LTM trigger is received, and establishes connection towards cell2, e.g. using RACH, RACHIess connection, sending random access request message, or the like (not shown).

DUO sends a message to the target DU1 that LTM to cell2 has been triggered and may include the information which DRBs will be used, e.g. DRB1, DRBm and DRBn. The message may be send directly toDU1 if interface available, or indirectly via serving DU, which will forward the message to DU1 (steps 13, 14). Receiving the message in DU1 may be another trigger to stop monitoring availability of DRB2 and DRB3. Alternatively, the forwarding may not be performed or not trigger stopping, and then, or in parallel, DU1 stops monitoring once a connection request is received from the UE, e.g. random access request.

Option 2: available radio resource(s), e.g. DRB 2 and 3 become available before LTM trigger (no RACH or else from UE received at DU1

DU1 continues to monitor if DRB2 and DRB3 become available. At the same time UE performs L1 measurements and transmits respective L1 measurement report to the serving DU (step 17).

Each target DU, e.g. DU1 may transmit from time to time, or on a regular or periodic basis, or event based a status update of the DRB load regarding DRB2 and DRB 3 towards the serving CU (step 15), e.g. DRB2 and DRB 3 became available. Event based may be configured as: as soon as one of the monitored unavailable DRBs becomes available, a respective status update is sent. The serving DU may transmit the status to the serving DUO (step16) informing DUO that DRB2 and DRB 3 became available, potentially together with an indication or instruction to use the available DRB in case of LLM to cell2. Either the serving CU or the serving DU may be configured to determine if available resources may be used, e.g. UE reconfigured , or not.

Regarding timing: UE is configured with DRB n and m and with available DRB1. Target DU1 continues to monitor availability of DRB 2 and 3, e.g. until it receives a RACH from UE or receives a RACHIess connection request or until a respective timer expires. This timing requirement might be implemented as an optional feature in 3GPP Rel. 18 onwards.

In step 18 DUO determines that cell2 is the cell to switch to and determines further that DRB2 and DRB3 are now available and shall be used, and thus triggers with step 19 LTM to cell2. The trigger may be included in a MAC CE message.

The MAC CE message further includes an indication to use the source configuration e.g. DRB1 , DRB2, DRB3. The UE cancels the preconfigured configuration in case a corresponding LTM trigger is received, and uses the source configuration nsteaad, and establishes connection towards cell2, e.g. using RACH, RACHIess connection, sending random access request message, or the like (not shown).

DUO sends a message to the target DU1 that LTM to cell2 has been triggered and may include the information which DRBs will be used, e.g. DRB1, DRB2 and DRB3. The message may be send directly to DU1 if interface available, or indirectly via serving DU, which will forward the message to DU1 (steps 20, 21).

In case DUO decides to stay with the pre-configuration and not to use DBB2 and DRB3, then DUO sends a message to the target DU1 that LTM to cell2 has been triggered and may include the information which DRBs will be used, e.g. DRB1, DRBm and DRBn, or alternatively DRB1 , DRB2, DRBn if e.g. partly accepted.

In step 12 and/or step 19 the MAC trigger may get a new optional flag/indication field (e.g. in 3GPP Rel.18 onwards) indicating to maintain RB config and/or DRB 2 and 3 are available and thus should be used by UE when connecting to target DU (in addition to DRB1), UE already knows and uses DRB 2 and 3 and thus is able to maintain RB config.

A similar procedure may be applied in e.g. Option 3: DRB 2 becomes available before LTM trigger (but DRB 3 not), e.g. step 12 the MAC trigger in Rel 18 gets a new optional flag/indication field indicating DRB 2 is available and thus should be used by UE when connecting to target DU (in addition to DRB1 and DRB m), UE already knows and uses DRB 2 and thus is able to maintain RB config (for DRB1 and 2).

This may also be beneficial for all UEs, e.g. “older/conventional” ones: UE Rel17 and newer ones: UE Rel 18 onwards, e.g.

UE Rel 17 can operate as in prior art

UE Rel 18 will also operate like in prior art, but in addition monitors and checks whether MAC trigger has an additional field (new optional flag/indication field indicating DRB 2/3 is available), and if so, adapts access to target DU; serving DU knows whether UE is supporting Rel 17 or 18 e.g. from UE capability and thus adds new optional field only for Rel 18 UE; CU may/will inform targert DU if UE is Rel 17 or 18, such that target DU knows whether to operate according new process, e.g. continue to monitor availability of DRB 2 and 3 (e.g. until it receives a RACH from UE) for UE Rel 18, or not (UE Rel 17).

In general UE receive a L2 message including a trigger to switch from the first cell to a target cell (step 12, step 19), and an implicit or explicit indication whether the preconfigured data radio bearer (e.g. DRBm) is to be used for transmitting data towards the target cell and/or whether the currently used first data radio bearer (e.g. DRB2) is to be retained and used for transmitting data towards the target cell.

The ‘or’-combination is e.g. used as described above, e.g. DRBm substitutes DRB2 in case DRB2 is not available. The ‘and’-combination is used e.g. when additional resources are required and/or requested by the UE in the meantime or e.g. determined by serving CU for downlink traffic. As UE knows both source DRB config (e.g. DRB1 , DRB2, DRB3) and target DRB config (e.g. DRB1, DRBm, DRBn) there is no need to reconfigure DRBs as sufficient are known to UE, e.g. DRB1 , DRB2, DRB3, DRBm, DRBn, to select from to use as additional resources when needed. The ‘and’-combination may also refet o the second embodiment described above. A mixture of second and thid might also be possible, e.g. be assigning DRB with different Quality of Service also in the third embodiment.

UE then establishes a connection towards the indicated target cell, and transmit data towards the target cell using at least the indicated data radio bearer(s).

Coming back to Fig. 16 the user equipment, UE, may be configured to be connected to a radio access network, wherein the indicated target cell is a cell of a third network node that supports distributed unit, DU1, functionality and/or a layer 2 protocol processing of the radio access network, RAN. DUO, DU1 , CU may be implemented physically co-located or separate using one or more hardware equipment, e.g. processor 1 and memory 1 for CU at location X, and processor 2 and memory 2 for DUO at location Y, and processor 3 and memory 3 for DU1 at location Z.

The user equipment, UE, may further be configured to be connected to the radio access network, wherein the third network node is connected to the second network node. Du1 may be connected to serving CU, or may be connected to another CU, e.g. CU1. Then communication between serving CU and DU1 takes place via CU1 and corresponding messages are to be added.

The user equipment, UE, may further be configured to be connected to the radio access network, wherein the L3 configuration message is an RRCConfiguration message or an RRCReconfiguration message. One or more messages might be used to transmit one or more different information; RRC = Radio Ressource Control.

The user equipment, UE, may further be configured to be connected to the radio access network, wherein the L2 message is a MAC CE message; MAC = Medium Access Control - Control Element. It is advantageous to use a MAC CE as small changes are needed (indication of radio resources to use, e.g. DRBs) in order to enable a fast handover, e.g. based on L1 measurements an without the need to reconfigure DRBs if they become available, thus e.g. reducing signaling effort enabling a more efficient communication and saving power. Free-up signaling can be used for other purposes, e.g. serving other UEs, etc.

The user equipment, UE, may further be configured to: transmit data towards the first cell using a third data radio bearer, and wherein the configuration information includes a configuration to maintain using the third data radio bearer for transmitting data towards the target cell to switch to.

The solution provides the flexibility to adapt to different situations, whenever resources become available which could help to distribute the resources better among UEs or within a DU, then they can be reallocated easily. E.g. UE will be preconfigured (target config) with other available resources if the actually used source resources are currently not available; but as UE is knowing and using the actual source configuration and related resources it is in a way double configured and using the one or the other configuration or a mix of both becomes easily an option, e.g. in case one or more source DRB(s) get available, they can be used for fast LLM switching. Potentially a DU might be configured to wait till source config becomes available before LLM is triggered as long as source connection is still stable. This way an additional criterion for triggering might be which resources are available. In addition, a DU might be configured to reallocate DRBs which the DU is monitoring to become available, e.g. with a higher priority, thus enabling smoother handovers, e.g. making DRBs available where they are needed to enable an fient distribution of resources and use of resources in UEs and in case of handovers.

The user equipment, UE, may further be configured to be connected to the radio access network, wherein the implicit or explicit indication whether the pre-configured data radio bearer is to be used is received as part of the received L2 message. As described previously, depending on the circumstances it might be sufficient to send a L2 message with an LTM trigger to indicate which resources/DRBs to use as they have been pre-configured and are known in the UE. This may be considered an implicit indication. Or a code may be used to used the pre-configured DRBs or the source DRBs to achieve such implicit indication. An explicit indication may be achieved by indicating which DRB to be used, e.g. DRB1, DBR2, DRBn.

No indication indicating the pre-configured data radio bearer is to be used, A flag or specific instruction to use the pre-configured data radio bearer, A flag or specific instruction to retain the first data radio bearer, A flag or specific instruction to use both the pre-configured data radio bearer and to retain the first data radio bearer.

The user equipment, UE, may further be configured to be connected to the radio access network, wherein the configuration information includes a pre-configuration to potentially use a second data radio bearer with a specific QoS level, and the implicit or explicit indication indicates to use the pre-configured data radio bearer with its specific QoS level for transmitting data towards the target cell and to retain the first data radio bearer and its assigned QoS for transmitting data towards the target cell.

The user equipment, UE, may further be configured to be connected to the radio access network, wherein the specific QoS level and the assigned QoS level are different.

The user equipment, UE, may further be configured to be connected to the radio access network, wherein the implicit or explicit indication indicates to use the preconfigured data radio bearer for transmitting data towards the target cell in a first PDU session and to retain the first data radio bearer and is QoS mapping for a second PDU session, wherein first and second PDU session are different sessions.

References to ‘computer-readable storage medium’, ‘computer program product’, ‘tangibly embodied computer program’ etc. or a ‘controller’, ‘computer’, ‘processor’ etc. should be understood to encompass not only computers having different architectures such as single /multi- processor architectures and sequential (Von Neumann)/parallel architectures but also specialized circuits such as field- programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc.

As used in this application, the term ‘circuitry’ and/or ‘means’ and/or ‘processor’ may refer to one or more or all of the following: (a) hardware-only circuitry implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable):

(i) a combination of analog and/or digital hardware circuit(s) with software/firmware and

(ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory or memories that work together to cause an apparatus, such as a mobile phone or server, to perform various functions and

(c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (for example, firmware) for operation, but the software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry and/or ‘means’ and/or ‘processor’ also covers an implementation of merely a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry and/or ‘means’ and/or ‘processor’ also covers, for example and if applicable to the particular claim element, a baseband integrated circuit for a mobile device or a similar integrated circuit in a server, a cellular network device, or other computing or network device.

The blocks illustrated in the accompanying Figs may represent steps in a method and/or sections of code in the computer program 406. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted.

Operationally coupled and any number or combination of intervening elements can exist (including no intervening elements).

Specific means like receiving means may be programmed to support a specific application and/or operation like receiving radio signals and/or processing of received radio signals, etc. Storing means may include a memory with specific data and/or configurations and/or instructions stored thereon to support specific operational and/or processing tasks. Applications

The above-described examples find application as enabling components of: automotive systems; telecommunication systems; electronic systems including consumer electronic products; distributed computing systems; media systems for generating or rendering media content including audio, visual and audio visual content and mixed, mediated, virtual and/or augmented reality; personal systems including personal health systems or personal fitness systems; navigation systems; user interfaces also known as human machine interfaces; networks including cellular, non-cellular, and optical networks; ad-hoc networks; the internet; the internet of things; virtualized networks; and related software and services.

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 like smartphones, other types of electronic devices, such as, but not limited to: apparatus supporting and/or preparing transmission and/or supporting reception of and/or processing of received of radio signals or parts thereof, 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 following description may provide further details of alternatives, modifications and variances: a gNB comprises e.g., a node providing NR user plane and control plane protocol terminations towards the UE, and connected via the NG interface to the 5GC, e.g., according to 3GPP TS 38.300 V16.6.0 (2021-06) section 3.2 incorporated by reference. A gNB Central Unit (gNB-CU) comprises e.g., a logical node hosting e.g., RRC, SDAP and PDCP protocols of the gNB or RRC and PDCP protocols of the en-gNB that controls the operation of one or more gNB-DUs. The gNB-CU terminates the F1 interface connected with the gNB-DU.

[0056] A gNB Distributed Unit (gNB-DU) comprises e.g., a logical node hosting e.g., RLC, MAC and PHY layers of the gNB or en-gNB, and its operation is partly controlled by the gNB-CU. One gNB-DU supports one or multiple cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the F1 interface connected with the gNB-CU.

A gNB-CU-Control Plane (gNB-CU-CP) comprises e.g., a logical node hosting e.g., the RRC and the control plane part of the PDCP protocol of the gNB-CU for an en- gNB or a gNB. The gNB-CU-CP terminates the E1 interface connected with the gNB- CU-UP and the F1-C interface connected with the gNB-DU.

A gNB-CU-User Plane (gNB-CU-UP) comprises e.g., a logical node hosting e.g., the user plane part of the PDCP protocol of the gNB-CU for an en-gNB, and the user plane part of the PDCP protocol and the SDAP protocol of the gNB-CU for a gNB. The gNB-CU-UP terminates the E1 interface connected with the gNB-CU-CP and the F1-U interface connected with the gNB-DU, e.g., according to 3GPP TS 38.401 V16.6.0 (2021-07) section 3.1 incorporated by reference.

Different functional splits between the central and distributed unit are possible, e.g., called options:

Option 1 (1 A-like split): o The function split in this option is similar to the 1 A architecture in DC. RRC is in the central unit. PDCP, RLC, MAC, physical layer and RF are in the distributed unit.

Option 2 (3C-like split): o The function split in this option is similar to the 3C architecture in DC. RRC and PDCP are in the central unit. RLC, MAC, physical layer and RF are in the distributed unit.

Option 3 (intra RLC split): o Low RLC (partial function of RLC), MAC, physical layer and RF are in the distributed unit. PDCP and high RLC (the other partial function of RLC) are in the central unit.

Option 4 (RLC-MAC split): o MAC, physical layer and RF are in the distributed unit. PDCP and RLC are in the central unit.

Or else, e.g., according to 3GPP TR 38.801 V14.0.0 (2017-03) section 11 incorporated by reference.

A gNB supports different protocol layers, e.g., Layer 1 (L1) - physical layer.

The layer 2 (L2) of NR is split into the following sublayers: Medium Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP) and Service Data Adaptation Protocol (SDAP), where e.g.: o The physical layer offers to the MAC sublayer transport channels; o The MAC sublayer offers to the RLC sublayer logical channels; o The RLC sublayer offers to the PDCP sublayer RLC channels; o The PDCP sublayer offers to the SDAP sublayer radio bearers; o The SDAP sublayer offers to 5GC QoS flows; o Comp, refers to header compression and Segm. To segmentation; o Control channels include (BCCH, PCCH).

Layer 3 (L3) includes e.g., Radio Resource Control (RRC), e.g., according to 3GPP TS 38.300 V16.6.0 (2021-06) section 6 incorporated by reference.

A RAN (Radio Access Network) node or network node like e.g. a gNB, base station, gNB CU or gNB DU or parts thereof may be implemented using e.g. an apparatus with at least one processor and/or at least one memory (with computer-readable instructions (computer program)) configured to support and/or provision and/or process CU and/or DU related functionality and/or features, and/or at least one protocol (sub-)layer of a RAN (Radio Access Network), e.g. layer 2 and/or layer 3. [0064] The gNB CU and gNB DU parts may e.g., be co-located or physically separated. The gNB DU may even be split further, e.g., into two parts, e.g., one including processing equipment and one including an antenna. A Central Unit (CU) may also be called BBU/REC/RCC/C-RAN/V-RAN, O-RAN, or part thereof. A Distributed Unit (DU) may also be called RRH/RRU/RE/RU, or part thereof. Hereinafter, in various example embodiments of the present disclosure, the CU-CP (or more generically, the CU) may also be referred to as a (first) network node that supports at least one of central unit control plane functionality or a layer 3 protocol of a radio access network; and similarly, the DU may be referred to as a (second) network node that supports at least one of distributed unit functionality or the layer 2 protocol of the radio access network.

A gNB-DU supports one or multiple cells, and could thus serve as e.g., a serving cell for a user equipment (UE).

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. , so as 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 of 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.

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.

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 also 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 it should be understood that 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 user equipment, UE, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the UE at least to perform: receiving downlink signaling that provides a first data radio bearer configuration for a cell (DRB), and a second data radio bearer configuration for the cell (DRB); storing the first data radio bearer configuration, for execution of data transfer via the cell using the first data radio bearer and for storing the second data radio bearer configuration, for execution of data transfer via the cell using the second data radio bearer; receiving a trigger; and in response to the received trigger, executing data transfer between user equipment and the cell using the first data radio bearer configuration if the trigger indicates use of the first data radio bearer configuration and executing data transfer between the user equipment and the cell using the second data radio bearer configuration if the trigger indicates use of the second data radio bearer configuration.

2. An apparatus as claimed in claim 1, wherein the control circuitry is configured to switch a data transfer session between transfer using the first data radio bearer configuration or the second data radio bearer configuration based on the trigger or wherein the control circuitry is configured to switch a data transfer session on or off based on the trigger.

3. An apparatus as claimed in claim 1 or 2, wherein the trigger is received as a medium access control (MAC) message.

4. An apparatus as claimed in any preceding claim, wherein the trigger indicates a mapping to be used as in the received first or second configuration for the cell, between the data radio bearer for the cell and a data transfer session

5. An apparatus as claimed in any preceding claim, wherein the first data radio bearer configuration or the second data radio bearer configuration comprises at least one mapping between a usable data transfer session to provide data for transfer and a usable data radio bearer to provide a transfer channel for data.

6. An apparatus as claimed in claim 5, wherein the at least one mapping maps a data transfer session to a sub-set of a set of multiple preconfigured data radio bearers, wherein the sub-set is indicated by the trigger.

7. An apparatus as claimed in claim 6, wherein the data transfer session is a preexisting data transfer session

8. An apparatus as claimed in any preceding claim, wherein the first and second data radio bearer configurations configure data radio bearers for a first data transfer session and a second data transfer session wherein executing data transfer with user equipment via the cell using the first data radio bearer configuration if the trigger indicates use of the first data radio bearer configuration comprises executing the second data transfer session with the first data radio bearer configuration and executing data transfer with the user equipment via the cell using the second data radio bearer configuration if the trigger indicates use of the second data radio bearer configuration comprises executing the second data transfer session with the second data radio bearer configuration

9. An apparatus as claimed in any preceding claim, wherein there is a state where a data transfer session is mapped to a sub-set of a set of multiple preconfigured data radio bearers and a state where the data transfer session is not mapped to any preconfigured data radio bearers, wherein the state is indicated by the trigger.

10. An apparatus as claimed in any preceding claim, wherein the first and second data radio bearer configurations configure data radio bearers for at least a first data transfer session and optionally a second data transfer session wherein executing the second data transfer between user equipment and the cell using the first data radio bearer configuration if the trigger indicates use of the first data radio bearer configuration comprises executing the second data transfer session with the first data radio bearer configuration executing the second data transfer between the user equipment and the cell using the second data radio bearer configuration if the trigger indicates use of the second data radio bearer configuration comprises executing the second data transfer session with the second data radio bearer configuration.

11. A method comprising: receiving downlink signaling that provides a first data radio bearer configuration for a cell (DRB), and a second data radio bearer configuration for the cell (DRB); storing the first data radio bearer configuration, for execution of data transfer via the cell using the first data radio bearer and for storing the second data radio bearer configuration, for execution of data transfer via the cell using the second data radio bearer; receiving a trigger; if the trigger indicates use of the first data radio bearer configuration, then executing data transfer between user equipment and the cell using the first data radio bearer configuration and if the trigger indicates use of the second data radio bearer configuration, executing data transfer between the user equipment and the cell using the second data radio bearer configuration.

12. A method as claimed in claim 11 , wherein execution of data transfer between the cell and the user equipment requires a mapping between a usable data transfer session to provide data for transfer and a usable data radio bearer to provide a transfer channel for data

13. A method as claimed in claim 12, wherein at a time of triggering execution of data transfer between the user equipment and the cell using the data radio bearer for the cell, as a consequence of the received trigger, there is a mapping, for the cell, between the data radio bearer for the cell and a data transfer session.

14. A method as claimed in any of claims 11 to 13, wherein execution of data transfer between the user equipment and the cell requires

- a usable data transfer session to provide data for transfer

-a usable data radio bearer to provide a transfer channel for data wherein at a time of triggering, a data radio bearer for the cell is usable for the cell and at a time of the downlink signaling, the data radio bearer for the cell is not usable for the cell and/or wherein at the time of triggering, a data transfer session is usable for the cell and at the time of the signaling, the data transfer session is not usable for the cell.

15. A method as claimed in claim 14, wherein at the time of triggering, a data transfer session is usable for the cell and the data radio bearer for the cell is usable for the cell; and at time of the downlink signaling, the data transfer session is usable for the cell and the data radio bearer is not usable for the cell or the data transfer session is not usable for the cell and the data radio bearer is usable for the cell.

16. A computer program for a user equipment comprising instructions that, when run on a computer, perform: conditionally execute data transfer between user equipment and a cell wherein the if a trigger, indicates use of a previously received and stored first data radio bearer configuration then causing execution of data transfer between the user equipment and the cell using the first data radio bearer configuration and if the trigger indicates use of a previously received and stored second data radio bearer configuration then causing execution of data transfer between the user equipment and the cell using the second data radio bearer configuration.

17. An apparatus for a radio access network comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: causing transmission towards user equipment of downlink signaling that provides a first data radio bearer configuration for a cell, and a second data radio bearer configuration for the cell; causing transmission towards the user equipment of a trigger configured to indicate use of the first data radio bearer configuration to enable data transfer between the user equipment and the cell using the first data radio bearer or, configured to indicate use of the second data radio bearer configuration to enable data transfer between the user equipment and the cell using the second data radio bearer.

18. An apparatus as claimed in claim 17, configured for receiving and using a configuration of the first data radio bearer configuration for the cell and a configuration of a second data radio bearer configuration for the cell to enable the downlink signaling that provides the first data radio bearer configuration for the cell, and the second data radio bearer configuration for the cell.

19. An apparatus as claimed in any of claims 17 to 18, configured for receiving and using at least one decision criterion for causing transmission of the trigger to the user equipment and/or setting mapping parameters in the trigger.

20. An apparatus as claimed in claim 19, wherein the decision criterion specifies at least one of d. an availability of data radio bearers at a current cell e. an availability of data radio bearers at a future cell f. a new data transfer session

21. An apparatus as claimed in any of claims 17 to 20, configured for receiving and using a report that comprises information for the decision criteria for causing transmission of the trigger to the user equipment of the trigger and/or setting mapping parameters in the trigger.

22. An apparatus as claimed in claim 21, configured for receiving and using a report that comprises information, indicating availability of data radio bearers at the cell, for the decision criteria for causing transmission of the trigger to the user equipment of the trigger and/or setting mapping parameters in the trigger.

23. An apparatus as claimed in any of claims 21 or 22, wherein the report is a periodic report or an event-based report.

24. An apparatus as claimed in any of claims 21 to 23, wherein the report indicates lack of resources or existence of resources for one or more data radio bearer configurations.

25. An apparatus as claimed in any of claims 17 to 24, wherein the trigger is a medium access control (MAC) layer message.

26. An apparatus as claimed in any of claims 25, wherein the apparatus determines cell handover according to lower layer triggered mobility processes (LTM).

27. An apparatus as claimed in any of claims 17 to 25, configured as a distributed unit of a centralized unit-distributed units network architecture.

28. An apparatus as claimed in claim 27, wherein the apparatus is configured to receive and process an indication from the centralized unit concerning a newly setup data radio bearer.

29. An apparatus as claimed in 27 or 28, wherein the centralized unit determines cell handover according to lower layer triggered mobility processes (LTM) and informs the apparatus.

30. An apparatus as claimed in any of claims 27 to 29, configured for receiving and processing an indication, from the centralized unit, indicating that the first and second data radio bearer configurations have been sent to the user equipment.

31. An apparatus as claimed in any of claims 27 to 29, configured for receiving and processing a decision criterion for causing transmission of the trigger to the user equipment.

32. An apparatus as claimed in claim 31, wherein the decision criterion specifies at least one of d. an availability of data radio bearers at a current cell e. an availability of data radio bearers at the cell f. a new data transfer session

33. An apparatus as claimed in any of claims 21 or 22, wherein the report is a periodic report or an event-based report and/or wherein the report indicates lack of resources or existence of resources for one or more data radio bearer configurations.

34. A user equipment, UE, configured to connect to a first cell of a first network node that supports distributed unit, DU, functionality and/or a layer 2 protocol processing of a radio access network, RAN, the UE comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the UE at least to: establish a connection towards the first cell, transmit data towards the first cell using at least a first data radio bearer, perform L3 measurements for at least one of a plurality of candidate target cells to potentially switch to, transmit a L3 measurement report related to performed measurements towards a second network node that supports a central unit, CU, functionality and/or a layer 3 protocol processing of the radio access network, RAN, and which is connected to the first node, receive a L3 configuration message including configuration information related to at least one of said plurality of candidate target cells for L1 L2-triggered mobility, LTM, wherein the configuration information includes a pre-configuration to potentially use a second data radio bearer different from the first data radio bearer for transmitting data towards a target cell to switch to; and receive a L2 message including a trigger to switch from the first cell to a target cell, and an implicit or explicit indication whether the pre-configured data radio bearer is to be used for transmitting data towards the target cell and/or whether the currently used first data radio bearer is to be retained and used for transmitting data towards the target cell, establish a connection towards the indicated target cell, transmit data towards the target cell using at least the indicated data radio bearer.

35. A user equipment, UE, according to claim 34, wherein the indicated target cell is a cell of a third network node that supports distributed unit, DU, functionality and/or a layer 2 protocol processing of the radio access network, RAN.

36. A user equipment, UE, according to claim 35, wherein the third network node is connected to the second network node.

37. A user equipment, UE, according to claim 34, wherein the L3 configuration message is an RRCConfiguration message or an RRCReconfiguration message.

38. A user equipment, UE, according to claim 34, wherein the L2 message is a MAC CE message.

39. A user equipment, UE, according to claim 34, wherein the UE is further configured to: transmit data towards the first cell using a third data radio bearer, and wherein the configuration information includes a configuration to maintain using the third data radio bearer for transmitting data towards the target cell to switch to.

40. A user equipment, UE, according to claim 34, wherein the implicit or explicit indication whether the pre-configured data radio bearer is to be used is received as part of the received L2 message.

41. A user equipment, UE, according to claim 34, wherein the implicit or explicit indication whether the pre-configured data radio bearer is to be used or not is indicated in at least one of the following ways:

42. A user equipment, UE, according to claim 34, wherein the configuration information further includes an instruction to use the pre-configured second data radio bearer instead of the first data radio bearer for transmitting data towards the target cell to switch to in case no further instruction is received to retain the first data radio bearer for transmitting data towards the target cell to switch to.

43. A user equipment, UE, according to claim 34, wherein the configuration information includes a pre-configuration to potentially use a second data radio bearer with a specific QoS level, and the implicit or explicit indication indicates to use the pre-configured data radio bearer with its specific QoS level for transmitting data towards the target cell and to retain the first data radio bearer and its assigned QoS for transmitting data towards the target cell.

44. A user equipment, UE, according to claim 34, wherein the specific QoS level and the assigned QoS level are different.

45. A user equipment, UE, according to claim 34, wherein the implicit or explicit indication indicates to use the pre-configured data radio bearer for transmitting data towards the target cell in a first PDU session and to retain the first data radio bearer and is QoS mapping for a second PDU session, wherein first and second PDU session are different sessions.