WO2024094479A1

WO2024094479A1 - Method, apparatus and computer program

Info

Publication number: WO2024094479A1
Application number: PCT/EP2023/079579
Authority: WO
Inventors: Rathi GANESHAN; Srinivasan Selvaganapathy; Ahmad AWADA; Halit Murat Gürsu; Umur KARABULUT; Krzysztof Kordybach; Panagiotis SPAPIS
Original assignee: Nokia Technologies Oy
Priority date: 2022-11-04
Filing date: 2023-10-24
Publication date: 2024-05-10

Abstract

There is provided an apparatus comprising: means for communicating with a user equipment, wherein the user equipment is served by a serving cell, the serving cell provided by a source node, and means for receiving an indication that the user equipment is moving from the serving cell to a target cell. The apparatus also comprising means for, based on the received indication: i) retaining configuration information associated with a configuration for the user equipment, and ii) resetting information related to at least one protocol layer associated with the configuration for the user equipment.

Description

METHOD, APPARATUS AND COMPUTER PROGRAM

Field

The present application relates to a method, apparatus, and computer program for a wireless communication system.

Background

A communication system may be a facility that enables communication sessions between two or more entities such as user terminals, base stations/access points and/or other nodes by providing carriers between the various entities involved in the communications path. A communication system may be provided, for example, by means of a communication network and one or more compatible communication devices. The communication sessions may comprise, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia and/or content data and so on. Non-limiting examples of services provided comprise two-way or multi-way calls, data communication or multimedia services and access to a data network system, such as the Internet.

Summary

According to an aspect, there is provided an apparatus comprising: means for communicating with a user equipment, wherein the user equipment is served by a serving cell, the serving cell provided by a source node; means for receiving an indication that the user equipment is moving from the serving cell to a target cell; and means for, based on the received indication: i) retaining configuration information associated with a configuration for the user equipment, and ii) resetting information related to at least one protocol layer associated with the configuration for the user equipment.

In an example, the configuration for the user equipment is a user equipment context.

In an example, the apparatus comprises: means for reconnecting with the user equipment using the configuration information associated with the user equipment, such that the user equipment is served by the cell of the source node. In an example, the configuration information associated with configuration for the user equipment to be retained is received in a user equipment context setup request message,

In an example, the configuration information comprises user-plane transport network layer information associated with the user equipment.

In an example, the means for resetting information related to at least one protocol layer comprises: means for resetting resources associated with the configuration for the user equipment.

In an example, the indication comprises a further indication to maintain transport layer resources associated with the configuration for the user equipment.

In an example, the means for resetting information related to at least one protocol layer comprises at least one of: means for resetting signalling transport resources associated with the configuration for the user equipment; means for resetting user data transport resources associated with the configuration for the user equipment; means for performing a radio link control re-establishment associated with the configuration for the user equipment; means for performing a medium access control reset associated with the configuration for the user equipment; means for creating at least one tunnel endpoint identifier for at least one data radio bearer associated with the configuration for the user equipment; means for maintaining at least one existing tunnel endpoint identifier associated with the configuration for the user equipment.

In an example, the means for maintaining at least one existing tunnel endpoint identifier comprises: means for flushing an existing tunnel associated with the tunnel endpoint identifier.

In an example, the means for flushing comprises means for discarding data comprised within the existing tunnel.

In an example, the means for creating at least one tunnel endpoint identifier comprises: means for determining resources for a tunnel associated with the at least one tunnel endpoint identifier.

In an example, the means for creating tunnel endpoint identifiers for at least one data radio bearer associated with the user equipment comprises: means for receiving, from the centralised unit, uplink user-plane transport network layer information with the indication; and means for applying the uplink user-plane transport network layer information after the user equipment has moved from the serving cell to the target cell.

In an example, the uplink user-plane transport network layer information is comprised in a data radio bearer to be modified list.

In an example, the indication is received in one of: an F1 application protocol message, and an Xn application protocol message.

In an example, the F1 application protocol message is one of: a user equipment context modification request message, a user equipment context release command message, and a user equipment context reset request message.

In an example, the indication is received from a second node.

In an example, the second node is one of: a centralised unit, a master node, a target node, a gNodeB-centralised unit.

In an example, wherein one of: the apparatus is for the source node, the apparatus is comprised in the source node, and the apparatus is the source node.

In an example, the source node is one of: a gNodeB, a source distributed unit, and a source gNodeB.

According to an aspect, there is provided an apparatus comprising: means for communicating with a user equipment via a source node, wherein the user equipment is served by a serving cell, the serving cell provided by the source node; and means for providing, to the source node, an indication that the user equipment is moving from the serving cell to a target cell, wherein the indication is for the source node to: i) retain configuration information associated with a configuration for the user equipment, and ii) reset information related to at least one protocol layer associated with the configuration for the user equipment.

In an example, the apparatus comprises: means for receiving signalling, from the source node, to reconnect with the user equipment using the configuration information associated with the user equipment, such that the user equipment is served by the cell of the source node.

In an example, apparatus comprises: means for providing, to the source node, the configuration for the user equipment to be retained in a user equipment context setup request message, In an example, the configuration information comprises user-plane transport network layer information associated with the user equipment.

In an example, apparatus comprises: means for providing, to the source node, uplink user-plane transport network layer information with the indication, wherein the source node is indicated to apply the uplink user-plane transport network layer information after the user equipment has moved from the serving cell to the target cell.

In an example, the indication is provided in one of: an F1 application protocol message, and an Xn application protocol message.

In an example, one of: the apparatus is for a second node, the apparatus is comprised in the second node, and the apparatus is the second node.

In an example, the second node is one of: a centralised unit, a master node, a gNodeB-centralised unit.

According to an aspect, there is provided a method comprising: communicating with a user equipment, wherein the user equipment is served by a serving cell, the serving cell provided by a source node; receiving an indication that the user equipment is moving from the serving cell to a target cell; and based on the received indication: i) retaining configuration information associated with a configuration for the user equipment, and ii) resetting information related to at least one protocol layer associated with the configuration for the user equipment.

In an example, the method comprises: reconnecting with the user equipment using the configuration information associated with the user equipment, such that the user equipment is served by the cell of the source node.

In an example, the configuration information associated with configuration for the user equipment to be retained is received in a user equipment context setup request message.

In an example, the configuration information comprises user-plane transport network layer information associated with the user equipment. In an example, the resetting information related to at least one protocol layer comprises: resetting resources associated with the configuration for the user equipment.

In an example, the resetting information related to at least one protocol layer comprises at least one of: resetting signalling transport resources associated with the configuration for the user equipment; resetting user data transport resources associated with the configuration for the user equipment; performing a radio link control re-establishment associated with the configuration for the user equipment; performing a medium access control reset associated with the configuration for the user equipment; creating at least one tunnel endpoint identifier for at least one data radio bearer associated with the configuration for the user equipment; maintaining at least one existing tunnel endpoint identifier associated with the configuration for the user equipment.

In an example, the maintaining at least one existing tunnel endpoint identifier comprises: flushing an existing tunnel associated with the tunnel endpoint identifier.

In an example, the flushing comprises discarding data comprised within the existing tunnel.

In an example, the creating at least one tunnel endpoint identifier comprises: determining resources for a tunnel associated with the at least one tunnel endpoint identifier.

In an example, the creating tunnel endpoint identifiers for at least one data radio bearer associated with the user equipment comprises: receiving, from the centralised unit, uplink user-plane transport network layer information with the indication; and applying the uplink user-plane transport network layer information after the user equipment has moved from the serving cell to the target cell.

In an example, the F1 application protocol message is one of: a user equipment context modification request message, a user equipment context release command message, and a user equipment context reset request message. In an example, the indication is received from a second node.

In an example, the method is performed by the source node.

According to an aspect, there is provided a method comprising: communicating with a user equipment via a source node, wherein the user equipment is served by a serving cell, the serving cell provided by the source node; and providing, to the source node, an indication that the user equipment is moving from the serving cell to a target cell, wherein the indication is for the source node to: i) retain configuration information associated with a configuration for the user equipment, and ii) reset information related to at least one protocol layer associated with the configuration for the user equipment.

In an example, the method comprises: receiving signalling, from the source node, to reconnect with the user equipment using the configuration information associated with the user equipment, such that the user equipment is served by the cell of the source node.

In an example, method comprises: providing, to the source node, the configuration for the user equipment to be retained in a user equipment context setup request message,

In an example, method comprises: providing, to the source node, uplink userplane transport network layer information with the indication, wherein the source node is indicated to apply the uplink user-plane transport network layer information after the user equipment has moved from the serving cell to the target cell.

In an example, the indication is provided in one of: an F1 application protocol message, and an Xn application protocol message. In an example, the F1 application protocol message is one of: a user equipment context modification request message, a user equipment context release command message, and a user equipment context reset request message.

In an example, method is performed by a second node.

According to an aspect, there is provided an apparatus comprising: at least one processor, and at least one memory storing instructions that, when executed by the one or more processors, cause the apparatus to perform: communicating with a user equipment, wherein the user equipment is served by a serving cell, the serving cell provided by a source node; receiving an indication that the user equipment is moving from the serving cell to a target cell; and based on the received indication: i) retaining configuration information associated with a configuration for the user equipment, and ii) resetting information related to at least one protocol layer associated with the configuration for the user equipment.

In an example, the apparatus is caused is perform: reconnecting with the user equipment using the configuration information associated with the user equipment, such that the user equipment is served by the cell of the source node.

In an example, the configuration information associated with configuration for the user equipment to be retained is received in a user equipment context setup request message,

In an example, the resetting information related to at least one protocol layer comprises: resetting resources associated with the configuration for the user equipment.

In an example, the indication is received from a second node.

In an example, one of: the apparatus is for the source node, the apparatus is comprised in the source node, and the apparatus is the source node.

In an example, the source node is one of: a source distributed unit, and a source gNodeB.

According to an aspect, there is provided an apparatus comprising: at least one processor, and at least one memory storing instructions that, when executed by the one or more processors, cause the apparatus to perform: communicating with a user equipment via a source node, wherein the user equipment is served by a serving cell, the serving cell provided by the source node; and providing, to the source node, an indication that the user equipment is moving from the serving cell to a target cell, wherein the indication is for the source node to: i) retain configuration information associated with a configuration for the user equipment, and ii) reset information related to at least one protocol layer associated with the configuration for the user equipment.

In an example, method is performed by a second node.

According to an aspect, there is provided a computer program comprising instructions, which when executed by an apparatus, cause the apparatus to perform at least the following: communicating with a user equipment, wherein the user equipment is served by a serving cell, the serving cell provided by a source node; receiving an indication that the user equipment is moving from the serving cell to a target cell; and based on the received indication: i) retaining configuration information associated with a configuration for the user equipment, and ii) resetting information related to at least one protocol layer associated with the configuration for the user equipment.

According to an aspect, there is provided a computer program comprising instructions, which when executed by an apparatus, cause the apparatus to perform at least the following: communicating with a user equipment via a source node, wherein the user equipment is served by a serving cell, the serving cell provided by the source node; and providing, to the source node, an indication that the user equipment is moving from the serving cell to a target cell, wherein the indication is for the source node to: i) retain configuration information associated with a configuration for the user equipment, and ii) reset information related to at least one protocol layer associated with the configuration for the user equipment. According to an aspect, there is provided a computer program comprising instructions stored thereon to perform the methods as described herein:

A computer product stored on a medium may cause an apparatus to perform the methods as described herein.

A non-transitory computer readable medium comprising program instructions, that, when executed by an apparatus, cause the apparatus to perform the methods as described herein.

An electronic device may comprise apparatus as described herein.

In the above, various aspects have been described. It should be appreciated that further aspects may be provided by the combination of any two or more of the various aspects described above.

Various other aspects and further embodiments are also described in the following detailed description and in the attached claims.

According to some aspects, there is provided the subject matter of the independent claims. Some further aspects are defined in the dependent claims. The embodiments that do not fall under the scope of the claims are to be interpreted as examples useful for understanding the disclosure.

List of abbreviations:

AF: Application Function AMF: Access Management Function

AN: Access Network

BS: Base Station

CN: Core Network

CPA: Conditional PSCell Addition

CPC: Conditional PSCell Change

DL: Downlink eNB: eNodeB gNB: gNodeB

HoT: Industrial Internet of Things

LTE: Long Term Evolution

NEF: Network Exposure Function

NG-RAN: Next Generation Radio Access Network

NF: Network Function

NR: New Radio

NRF: Network Repository Function

NW: Network

MS: Mobile Station

PCF Policy Control Function

PDCP: Packet data convergence protocol

PLMN: Public Land Mobile Network

PSCell: Primary Serving Cell

RAN: Radio Access Network

RF: Radio Frequency

SMF: Session Management Function

UE: User Equipment

UDR: Unified Data Repository

UDM: Unified Data Management

UL: Uplink

UPF: User Plane Function

3GPP: 3^rd Generation Partnership Project

5G: 5^th Generation

5GC: 5G Core network

5G-AN: 5G Radio Access Network 5GS: 5G System

Description of Figures

Embodiments will now be described, by way of example only, with reference to the accompanying Figures in which:

Figure 1 shows a schematic representation of a 5G system;

Figure 2 shows a schematic representation of a control apparatus;

Figure 3 shows a schematic representation of a terminal;

Figure 4 shows a schematic representation of a user equipment moving from a source cell to a target cell;

Figure 5 shows a signalling diagram between a user equipment and network entities for a conditional PSCell change;

Figure 6 shows a signalling diagram between a user equipment and network entities for a serving cell change according to a first example;

Figure 7 shows a signalling diagram between a user equipment and network entities for a serving cell change according to a second example;

Figure 8 shows a signalling diagram between a user equipment and network entities for a serving cell change according to a third example;

Figure 9 shows a method flow diagram performed by an apparatus;

Figure 10 shows a method flow diagram performed by a further apparatus; and

Figure 11 shows a schematic representation of a non-volatile memory medium storing instructions which when executed by a processor allow a processor to perform one or more of the steps of the method of Figures 9 and 10.

Detailed description

Before explaining in detail some examples of the present disclosure, certain general principles of a wireless communication system and mobile communication devices are briefly explained with reference to Figures 1 to 3 to assist in understanding the technology underlying the described examples.

In a wireless communication system 100, such as that shown in Figure 1 , mobile communication devices/terminals or user apparatuses, and/or user equipments (UE), and/or machine-type communication devices 102 are provided wireless access via at least one base station (not shown) or similar wireless transmitting and/or receiving node or point. A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling access to a communication network or communications directly with other devices. The communication device may access a carrier provided by a station or access point, and transmit and/or receive communications on the carrier.

In the following certain examples are explained with reference to mobile communication devices capable of communication via a wireless cellular system and mobile communication systems serving such mobile communication devices. Before explaining in detail the examples of the disclosure, certain general principles of a wireless communication system, access systems thereof, and mobile communication devices are briefly explained with reference to Figures 1 , 2 and 3 to assist in understanding the technology underlying the described examples.

Figure 1 shows a schematic representation of a wireless communication system 100. The wireless communication system 100 may comprise one more devices 102 such as user equipments (UEs), or terminals. The wireless communication system 100 may also comprise a 5G system (5GS), as shown in Figure. The 5GS comprises a 5G radio access network (5G-RAN) 106, a 5G core network (5GC) 104 comprising one or more network functions (NF), one or more application functions (AFs) 108, and one or more data networks (DNs) 110.

The 5G-RAN 106 may comprise one or more gNodeB (gNB) distributed unit (DU) functions connected to one or more gNodeB (gNB) centralized unit (CU) functions.

The 5GC 104 may comprise an access management function (AMF) 112, a session management function (SMF) 114, an authentication server function (AUSF) 116, a user data management (UDM) 118, a user plane function (UPF) 120, a network exposure function (NEF) 122 and/or other NFs. Some of the examples as shown below may be applicable to 3GPP 5G standards. However, some examples may also be applicable to 5G-advanced, 4G, 3G and other 3GPP standards.

In a wireless communication system 100, such as that shown in Figure 1 , mobile communication devices/terminals or user apparatuses, and/or user equipments (UE), and/or machine-type communication devices are provided with wireless access via at least one base station or similar wireless transmitting and/or receiving node or point. The terminal is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling access to a communication network or communications directly with other devices. The communication device may access a carrier provided by a base station or access point, and transmit and/or receive communications on the carrier.

Figure 2 illustrates an example of a control apparatus 200 for controlling a function of the 5G-RAN or the 5GC as illustrated on Figure 1 . The control apparatus may comprise at least one random access memory (RAM) 211a, at least one read only memory (ROM) 211 b, at least one processor 212, 213 and an input/output interface 214. The at least one processor 212, 213 may be coupled to the RAM 211 a and the ROM 211 b. The at least one processor 212, 213 may be configured to execute an appropriate software code 215. The software code 215 may for example allow to perform one or more steps to perform one or more of the present aspects. The software code 215 may be stored in the ROM 211 b. The control apparatus 200 may be interconnected with another control apparatus 200 controlling another function of the 5G-AN or the 5GC. In some examples, each function of the 5G-AN or the 5GC comprises a control apparatus 200. In alternative examples, two or more functions of the 5G-AN or the 5GC may share a control apparatus.

Figure 3 illustrates an example of a terminal 300, such as the terminal illustrated on Figure 1 . The terminal 300 may be provided by any device capable of sending and receiving radio signals. Non-limiting examples comprise a user equipment, a mobile station (MS) or mobile device such as a mobile phone or what is known as a ’smart phone’, a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle), a personal data assistant (PDA) or a tablet provided with wireless communication capabilities, a machine-type communications (MTC) device, a Cellular Internet of things (CloT) device or any combinations of these or the like. The terminal 300 may provide, for example, communication of data for carrying communications. The communications may be one or more of voice, electronic mail (email), text message, multimedia, data, machine data and so on.

The terminal 300 may receive signals over an air or radio interface 307 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 3, a transceiver apparatus is designated schematically by block 306. The transceiver apparatus 306 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device. The terminal 300 may be provided with at least one processor 301 , at least one memory ROM 302a, at least one RAM 302b and other possible components 303 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems and other communication devices. The at least one processor 301 is coupled to the RAM 302b and the ROM 302a. The at least one processor 301 may be configured to execute an appropriate software code 308. The software code 308 may for example allow to perform one or more of the present aspects. The software code 308 may be stored in the ROM 302a.

The processor, storage and other relevant control apparatus may be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 304. The device may optionally have a user interface such as keypad 305, touch sensitive screen or pad, combinations thereof or the like. Optionally one or more of a display, a speaker and a microphone may be provided depending on the type of the device.

One or more of the following examples may be related to cell handovers and serving cell changes. A handover is a process in telecommunications and mobile communications in which a cellular connection is transferred from one cell to another cell, without disconnecting the session.

Up to Rel. 17 of the 3GPP 5G standards, a UE releases all stored conditional reconfiguration information after successfully executing a conditional primary serving cell (PSCell) change (CPC) procedure. However, in a mobility enhancement work item for Rel. 18 (RP-213565) there has been objectives including, i) to specify mechanisms and procedures of New Radio Dual Connectivity (NR-DC) with selective activation of the cell groups (at least for a secondary cell group (SCG)) via L3 enhancements, and ii) to allow subsequent cell group change after changing cell group (CG) without reconfiguration and re-initiation of CPC/conditional PSCell addition (CPA).

Figure 4 shows a schematic representation of a user equipment moving from a source cell to a target cell. In Figure 4, double-ended arrows indicate two-way communication between the two relevant entities.

There is provided a user equipment (UE) 401 , which moves from a first location to a second location. The moving of the UE 401 is illustrated with a block arrow. The first location is within the coverage of a first cell 403. While the UE 401 is located within the area of the first cell 403, the UE 401 is served by the first cell 403. The first cell 403 is provided by a first gNB 405. The first gNB 405 comprises a distributed unit (DU) (not shown), which provides the first cell 403.

As the UE 401 moves (physically) from the first location to the second location, the UE 401 may change cells. This may be referred to as a handover. In some examples, the handover may be a conditional handover (CHO), or a condition primary serving cell change (CPC).

In Figure 4, the serving cell of the UE 401 changes from the first cell 403 to a second cell 407. The second cell 407 is provided by a second gNB 409. The second gNB 409 comprises a distributed unit (DU) (not shown), which provides the second cell 407. In some other examples, the UE 401 may change to a target cell, whereby the source and target cells are provided by the same gNB (with different DUs). In some other examples, the UE 401 may change to a target cell, whereby the source and target cells are provided by the same gNB, and the same DU.

The first gNB 405 and the second gNB 409 are able to communicate with a centralised unit (CU) 411 . The CU 411 may be provided by a further gNB. The CU 411 is used to change the serving cell of the UE 401 from the first cell 403 to the second cell 407.

Once the UE 401 has successfully moved to the second cell 407 and is connected to the second gNB 409, the UE 401 with stop communicating with the first gNB 405. At this point, all uplink and downlink traffic will take place with the second gNB 409.

Figure 5 shows a signalling diagram between a user equipment and network entities for a conditional PSCell change. At the start of the process, the UE is connected to a source gNB-DU, whereby uplink and downlink data is communicated between the UE and the source gNB-DU via a gNB-CU.

At S501 , the UE sends a measurement report to the source gNB-DU.

At S502, the source gNB-DU sends an uplink resource radio control (RRC) message transfer to the gNB-CU.

At S503, the gNB-CU sends a UE context setup request to a target gNB-DU.

At S504, the target gNB-DU sends a UE context setup response message to the gNB-CU.

At S505, the gNB-CU sends a downlink RRC message transfer to the source gNB-DU. At S506, the source gNB-Dll sends an RRC reconfiguration message to the

UE.

At S507, the UE sends an RRC reconfiguration complete message to the source gNB-DU.

At S508, the source gNB-DU sends an uplink RRC message transfer to the gNB-CU.

At S509, the UE determines that a condition for the PSCell change has been fulfilled. This may be referred to as the execution condition being fulfilled.

At S510, the UE and the target gNB-DU perform a random access procedure with each other. Once the random access procedure is successfully completed, the target gNB-DU provides an ‘access success’ indication to the gNB-CU.

At S511 , the UE sends an RRC reconfiguration complete message to the target gNB-DU.

At S512, the target gNB-DU sends an uplink RRC message transfer to the gNB- CU.

At S513, the gNB-CU sends a UE context modification request to the target gNB-DU. Following a modification of the UE context at the target gNB-DU, downlink and uplink data may be communicated between the UE and the target gNB-DU, via the gNB-CU.

At S514, the target gNB-DU sends a UE context modification response message to the gNB-CU.

At S515, the gNB-CU sends a UE context release command to the target gNB- DU.

At S516, the target gNB-DU sends a UE context release complete message to the gNB-CU.

Once steps S501 to S516 have been completed, the UE has successfully changed serving cell from a cell of the source gNB-DU to a cell of the target gNB-DU.

As shown in Figure 5, after a UE executes a random access to the target DU (S510), the CU is informed with an ‘access success’ message. The CU then indicates to modify the UE context (S513). The UE context modification comprises stopping the data radio bearers (DRBs) that transmit data towards the UE and requests for the source DU to send the downlink data delivery status to the CU. Once source DU acknowledges the change of the UE context modification, the CU indicates to release the UE context (S515) and release all related signalling and data transport resources reserved for the UE.

A UE may be configured with selective activation for a conditional handover (CHO), or for CPC with candidate cell(s) in candidate-gNB-DU. Selective activation allows subsequent cell group changes after changing cell group without reconfiguration and re-initiation of CPC/CPA. Said another way, a network configures a UE once, with multiple handover configurations, to allow the UE to execute handovers from one cell to another without requiring any further handover related configurations.

When CHO or CPC handover execution conditions are met to move to the target cell, the UE moves from the source gNB-DU controlling the serving cell to the target gNB-DU.

In these scenarios, a network instructs the UE to travel between the cells freely and seamlessly. Since a UE context in a source cell may be released after handover when selective activation is not used, this requires extra configuration if the UE goes back to the source cell again in a ‘ping-pong’ scenario. A so-called ‘ping-pong’ scenario is when a UE hands over to a target cell and then back to the original source cell, in a short amount of time. On the other hand, when the UE context is not released when selective activation is used, this may lead to problems associated with layers such as, RLC and MAC layers. For example, this may lead to RLC and MAC layers having old protocol data units (PDUs), timeouts, incorrect state variables, incomplete procedures, etc. Thus, when a UE returns back to the source gNB-DU, the UE context is not usable.

One or more of the following examples aims to address one or more of the problems identified above.

In example, a UE is connected to a serving cell provided by a source node. The connection between the UE and source node allows for uplink/downlink communications between these entities. The UE may then handover to a different serving cell. This may be due to, for example, the UE moving location.

The source node then receives an indication that the UE is moving from the serving cell to a target cell. The source node will then, based on the received indication: i) retain configuration information associated with a configuration for the UE; and ii) reset information related to at least one protocol layer associated with the configuration for the user equipment In this way, if the UE is to move/change back to the cell provided by the source node, the UE and the source node can connect more quickly using the retained UE configuration rather than performing a ‘full’ configuration procedure.

In the following examples, a source node may be a source DU. The source DU may be provided in a gNB (i.e. source gNB-DU). A target node may be a target DU. The target DU may be provided in a gNB (i.e. target gNB-DU). In the following, a second node may be a CU. The CU may be provided in a gNB (i.e. gNB-CU).

In some examples, there is mechanism whereby the UE context is partially released at the source DU, after a serving cell change away from the source DU. This enables the UE to go back to the same DU (i.e. the source DU) without any additional re-configuration. In examples, a ‘new’ indication is provided from the CU to the source DU to maintain the transport layer resources related to the UE. The indication also instructing the source DU to release/re-prepare/reset information related to communication layers/protocol layers, such as for example, MAC and RLC layers. This may comprise resetting MAC and RLC layer buffers, in some examples. The re- preparing/resetting of the communication layers/protocol layers may comprise resetting the configurations to zero. Alternatively, the re-preparing or resetting of the other configurations may comprise resetting the configurations to their default value.

Said another way, the UE configuration received for the UE is retained at the source DU/source node, while the MAC and RLC layers are reset or re-established.

In some examples, a MAC reset is performed. The MAC reset may be performed according to the specification of 3GPP 38.321 , 5.12. In some examples, an RLC re-establishment is performed. The RLC re-establishment may be performed according to the specification of 3GPP 38.322, 5.1.2.

In some examples, for a CHO or CPC, once the preparation and execution phases are complete, the completion phase is performed. During the completion phase, the UE configuration in the source gNB is retained in order to enable UE to ‘come back’ to the last serving cell, when selective activation or successive CPC/CHO is configured for this cell. The preparation phase comprises the configuration at the target node being acquired and provided to the UE. The execution phase comprises the UE completing random access and re-configuration towards the target cell. The completion phase comprises stopping transmission at the source DU and doing a path switch towards the target DU for the user plane. The mechanisms described may be applicable to i) inter gNB inter DU CHO or CPC, whereby the UE hands over to different gNB, and thus a different DU, ii) intra gNB inter DU CHO or CPC, whereby the UE hands over to the same gNB, but a new cell from a different DU, and iii) intra gNB intra DU CHO or CPC, whereby the UE hands over to the same gNB and the same DU, but a different cell of the same DU.

In some examples, in order to enable early data forwarding to the source gNB- DU, user-plane (UP) transport network layer (TNL) information is kept at the source DU even after the UE moved to the target DU.

In some examples, the source DU receives a UE context/UE configuration associated with a UE, from a CU. The UE context/UE configuration may be received at the source DU in a UE context setup request message, from the CU (similar to the target DU receiving a message in S503). The UE context/UE configuration is used by the source DU to initially connect with the UE. When the UE moves away from the source DU, the source DU retains at least part of the information of the UE context/UE configuration, while the also resetting information related to at least one protocol layer of the UE context/UE configuration. The resetting t may include at least one of the following steps: i) RLC re-establishment, ii) ‘new’ tunnel endpoint identifiers (TEID) creation for at least one DRB, iii) maintenance of at least one existing TEID, and iv) MAC reset. In some examples, a MAC reset may not be applicable for intra gNB intra DU scenarios.

In this way, the reset of the UE contexts/resources at the source DU, during the completion phase, is triggered by the gNB-CU. The trigger may be the message provided by the CU to the source DU, indicating that the UE is moving cell. In some examples, the reset is triggered by a messaged from the target DU. In some examples, the trigger is implicit. In some examples, the trigger will be the source DU not receiving a message during a predetermined time frame.

In some examples, the CU initiates the re-establishment or reset of the UE context in the source DU by making changes to at least one of the F1 AP messages of the CHO/CPC procedure (as shown in Figure 5). Examples of the F1AP messages to be changed include: the UE context setup request (S503), the UE context modification request (S513), the UE context modification response (S514), and the UE context release request (S515). In other examples, Xn application protocol messages are used (in place of the F1AP messages).

These examples above will be described in more detail below. Figure 6 shows a signalling diagram between a user equipment and network entities for a serving cell change according to a first example.

In Figure 6, there is a trigger to reset resources of a UE context, at a source DU (also referred to as source gNB-DU), comprised in a UE context release command. On receiving the UE context modification command at the source DU, after stopping downlink data transmission to the UE, the following is done in the source DU to receive data from the CU-UP to enable early data forwarding, or to receive DL data once UE moves back to the source DU.

When an existing user-plane (UP) tunnel is reused at the source DU, the existing tunnel is flushed. The tunnel is a protocol that is used to transfer the data between two network entities. The two network entities may be the source DU and the CU, in some examples. For example, the tunnel may comprise a transport layer address, a tunnel endpoint identifier, and QoS mapping information to setup the protocol between the two network entities.

A flushing of the tunnel comprises discarding any data comprised within the reused tunnel.

Alternatively, when an existing UP tunnel is not reused at the source DU, new data tunnel resources are created. On receiving the UE context release command, the source DU shall reset related signalling transport resources and user data transport resources. This is described in more detail below.

Before S601 , it is assumed that the UE is connected to the source DU, whereby uplink and downlink data may be communicated between the UE and the source DU via a CU. The source DU provides the serving cell for the UE.

At S601 , the UE sends a measurement report message to the source DU/source node (which is also referred to as a source gNB-DU).

At S602, the source DU sends an UL RRC message transfer message to the CU (which is also referred to as a gNB-CU, or a second node) to convey the received measurement report message.

At S603, the CU sends a UE context setup request message to a target DU (which is also referred to as a target/candidate gNB-DU) to create a UE context and setup one or more data bearers. The UE context setup request message is sent to each target/candidate DU. The UE context setup request message may comprise ‘HandoverPreparation Information’, for a conditional handover. The UE context setup request message may comprise ‘CG-Configlnfo’ for a conditional PSCell change. At S603.1 , the UE context setup request message comprises an indication that selective activation is enabled. The selective activation is configured by the network (by the CU) so that the UE knows that the provided configuration is for selective activation.

At S604, the target DU responds to the CU with a UE context setup response message.

At S605, the CU sends a DL RRC message transfer message to the source DU. The DL RRC message transfer message includes a generated RRCReconfigu ration message.

At S606, the source DU forwards the received RRCReconfigu ration message to the UE.

At S607, the UE responds by providing, to the source DU, an RRCReconfigurationComplete message.

At S608, the source DU forwards the RRCReconfigurationComplete message to the CU. The RRCReconfigurationComplete message may be provided in an UL RRC message transfer message.

At S609, an execution condition to trigger the initiation of a conditional handover or a conditional PSCell change is fulfilled. For example, the UE measures an A3 event whereby the target becomes an offset better than the serving cell, or the UE measures an A4 event whereby the target becomes better than a threshold.

At S610, a random access procedure is performed between the UE and the target DU. The target DU sends a downlink data delivery status frame to inform the CU. The target DU also sends an ‘ACCESS SUCCESS’ message to the CU, to inform the CU of which cell the UE has successfully accessed.

At S611 , the UE sends, to the target DU, with an RRCReconfigurationComplete message.

At S612, the target DU sends, to the CU, an UL RRC message transfer message. The UL RRC message transfer comprising the RRCReconfigurationComplete message.

At this stage, DL packets may then be sent to the UE from the target DU. Also, uplink packets may be sent from the UE, which are forwarded to the CU through the target DU.

At S613, the CU sends a UE context modification request message to the source DU. The UE context modification request message indicates for the source DU to stop data transmissions with the UE. The source DU sends a DL data delivery status frame to the CU, to inform the CU about any unsuccessfully transmitted DL data to the UE. Any DL packets including, for example, PDCP protocol data units (PDUs) that have not been successfully transmitted from the source DU, are sent from the CU to the target DU. The target DU may then transmit those DL packets to the UE.

In some examples, when an existing UP TNL is not reused at the CU, the CU includes a ‘DRB to Be Modified List’ in the modification request. It may be indicated that the UL UP TNL information included in the UE context modification request message is to be applied after CHO or CPC is complete. In this example, the UP TNL refers to uplink UP TNL information which refers to the CU (i.e. , gNB-CU endpoint of the F1 transport bearer that is used by the DU for delivery of UL PDUs to the CU). When the uplink UP TNL information is being reused at the CU, the source DU will continue using the same UP TNL for delivery of UL data to the CU.

In some examples, S613 may occur before S612. S613 may take place as soon as the CU knows which cell the UE has successfully accessed.

In some examples, when selective activation is enabled, the CU does not initiate a UE context release procedure towards any other signalling connections or other target DUs, if any, to cancel conditional handover or conditional PSCell change for the UE. In some scenarios, the CU may initiate a release procedure for other target cells. However, for selective activation, this should be prevented as the preparations are intended to be preserved and used by the UE afterwards. Therefore, resources in source DU should not be released.

At S613.1 , the UE context modification request message indicates for the source DU to retain configuration information associated with the user equipment, and to reset information related to at least one protocol layer associated with the configuration of the user equipment. The configuration information may be retained by the source DU, so that the source DU can reconnect with the UE more quickly in the future. The UE configuration to be retained may be received at the source DU in a UE context setup request from the CU.

In an example, the resetting comprises: when an existing UP tunnel is reused at the source DU, flushing the existing tunnel to clear any buffered data in the tunnel.

In an example, when new UP TNL is to be created, the CU includes a ‘DRB to Be Modified List’ in the UE context modification request message. DL UP TNL information may also be provided in the UE context modification request message. It may be indicated for the DL UP TNL information to be applied after CHO or CPC is complete. Said another way, when the source DU is to use a new UL UP TNL, the CU sends “UL UP TNL Information” in a “UL UP TNL information to be setup List” which may be comprised in a “DRB to Be Modified List”, to the source DU.

Uplink (UL) UP TNL is the CU endpoint of the F1 transport bearer, and used for delivery of UL protocol data units (PDUs) from the source DU to CU. UL) UP TNL is sent from the CU to the source DU in the UE context modification request.

Downlink (DL) UP TNL is the source DU endpoint of the F1 transport bearer, and used for delivery of DL PDUs. DL UP TNL is sent from the source DU to the CU in a UE context modification response (as discussed below).

On receiving the UE context modification request at the source gNB-DU, when existing UP tunnel is reused, the source DU flushes the existing tunnel to clear any buffered data in the tunnel.

When an existing UP tunnel is not reused: i) the source DU stores the received “DRB to Be Modified List”, and ii) the source DU sends the “DRB Modified List” including new DL UP TNL information in a UE context modification response message (as described in S614 below).

The received UL UP TNL information will be applied by the source DU after CHO or CPC is complete.

At S614, the source DU responds to the CU with a UE context modification response message.

At S614.1 , when a new UP TNL is to be created, a ‘DRB Modified List’ is to include new DL UP TNL information. The DL UP TNL information may be applied after CHO or CPC is complete. The source DU may provide the new “DL UP TNL information” corresponding to the new “UL UP TNL information”, received from the CU.

At S615, the CU sends a UE context release command message to the source DU.

At S615.1 , the UE context release command comprises an indication for selective activation. When the UE context release command indicates selective activation, then information related to at least one protocol layer (e.g. MAC) is reset at the source DU, at S615.2. In this way, the UE configuration/context is not released/deleted in the source DU. At S615.2, the source DU resets information related to at least one protocol layer associated with the configuration for the UE . The source DU resetting may include at least one of the following: RLC re-establishment, new TEID creation for the DRBs, or maintenance of existing TEIDs, MAC reset.

At S616, the source DU responds to the CU with a UE context release complete message.

In some examples, one or more of the steps of Figure 6 above may not be performed, or may be performed in a different order.

Figure 7 shows a signalling diagram between a user equipment and network entities for a serving cell change according to a second example.

In Figure 7, there is a trigger to reset resources of a UE context, at a source DU (also referred to as source gNB-DU), comprised in a UE context modification request. In Figure 7, on receiving the UE context modification request, the source DU shall release signalling transport resources and user data transport resources, and either i) create new data tunnel resources, or ii) flush an existing tunnel. This is described in more detail below.

Before S701 , it is assumed that the UE is connected to the source DU, whereby uplink and downlink data may be communicated between the UE and the source DU via a CU. The source DU provides the serving cell for the UE.

At S701 , the UE sends a measurement report message to the source DU (which is also referred to as a source gNB-DU, or source node).

At 702, the source DU sends an UL RRC message transfer message to the CU (which is also referred to as a gNB-CU, or second node, or master node) to convey the received measurement report message.

At S703, the CU sends a UE context setup request message to a target DU (which is also referred to as a target/candidate gNB-DU, or target node) to create a UE context and setup one or more data bearers. The UE context setup request message is sent to each target/candidate DU. The UE context setup request message may comprise ‘HandoverPreparationlnformation’, for a conditional handover. The UE context setup request message may comprise ‘CG-Configlnfo’ for a conditional PSCell change.

At S703.1 , the UE context setup request message comprises an indication that selective activation is enabled. The selective activation is configured by the network (by the CU) so that the UE knows that the provided configuration is for selective activation.

At S704, the target DU responds to the CU with a UE context setup response message.

At S705, the CU sends a DL RRC message transfer message to the source DU. The DL RRC message transfer message includes a generated RRCReconfiguration message.

At S706, the source DU forwards the received RRCReconfiguration message to the UE.

At S707, the UE responds by providing, to the source DU, an RRCReconfigurationComplete message.

At S708, the source DU forwards the RRCReconfigurationComplete message to the CU. The RRCReconfigurationComplete message may be provided in an UL RRC message transfer message.

At S709, an execution condition to trigger the initiation of a conditional handover or a conditional PSCell change is fulfilled. For example, the UE measures an A3 event whereby the target becomes an offset better than the serving cell, or the UE measures an A4 event whereby the target becomes better than a threshold.

At S710, a random access procedure is performed between the UE and the target DU. The target DU sends a downlink data delivery status frame to inform the CU. The target DU also sends an ‘ACCESS SUCCESS’ message to the CU, to inform the CU of which cell the UE has successfully accessed.

At S711 , the UE sends, to the target DU, with an RRCReconfigurationComplete message.

At S712, the target DU sends, to the CU, an UL RRC message transfer message. The UL RRC message transfer comprising the RRCReconfigurationComplete message.

At S713, the CU sends a UE context modification request message to the source DU. The UE context modification request message indicates for the source DU to stop data transmissions with the UE. The source DU sends a DL data delivery status frame to the CU, to inform the CU about any unsuccessfully transmitted DL data to the UE. Any DL packets including, for example, PDCP protocol data units (PDUs) that have not been successfully transmitted from the source DU, are sent from the CU to the target DU. The target DU may then transmit those DL packets to the UE. 1

At S713.1 , the UE context modification request message indicates for the source DU to retain configuration information associated with the user equipment, and to reset information related to at least one protocol layer associated with the configuration of the user equipment. The configuration information may be retained by the source DU, so that the source DU can reconnect with the UE more quickly in the future.

The CU may include a ‘DRB to Be Modified List’ in the UE context modification request. It may be indicated that the UL UP TNL information included in the UE context modification request message is to be applied after CHO or CPC is complete.

In some examples, S713 may occur before S712. S713 may take place as soon as the CU knows which cell the UE has successfully accessed.

At S713.2, on receiving the UE context modification request, the UE may continue to store configuration information associated with the UE. The UE may reset or re-establish information related to at least one protocol layer associated with the UE configuration.

The source DU resetting may include at least one of the following: RLC reestablishment, new TEID creation for the DRBs, or maintenance of existing TEIDs, MAC reset.

At S714, the source DU responds to the CU with a UE context modification response message.

At S714.1 , the resetting comprises: storing a received ‘DRB to Be Modified List’ (from the UE context modification request), and sending a ‘DRB Modified List’ which includes DL UP TNL information in a UE context modification response message. This may take place after CHO or CPC is complete.

In some examples, one or more of the steps of Figure 7 above may not be performed, or may be performed in a different order.

Figure 8 shows a signalling diagram between a user equipment and network entities for a serving cell change according to a third example. In Figure 8, there is a trigger to reset resources of a UE context, at a source DU (also referred to as source gNB-DU), in a UE context reset request. The UE context reset command is a ‘new’ F1 application protocol (F1AP) message. The UE context reset command is ‘new’ in that it is not found in the signalling shown in Figure 5. On receiving the ‘new’ message that may be called, UE context reset command (or any other suitable name), the source DU shall reset the signalling transport resources and data transport resources, and either i) create new data tunnel resources, or ii) flush an existing tunnel. This will be described in more detail below.

Before S801 , it is assumed that the UE is connected to the source DU, whereby uplink and downlink data may be communicated between the UE and the source DU via a CU. The source DU provides the serving cell for the UE.

At S801 , the UE sends a measurement report message to the source DU (which is also referred to as a source gNB-DU, or source node).

At S802, the source DU sends an UL RRC message transfer message to the CU (which is also referred to as a gNB-CU, or second node, or master node) to convey the received measurement report message.

At S803, the CU sends a UE context setup request message to a target DU (which is also referred to as a target/candidate gNB-DU, or target node) to create a UE context and setup one or more data bearers. The UE context setup request message is sent to each target/candidate DU. The UE context setup request message may comprise ‘HandoverPreparationlnformation’, for a conditional handover. The UE context setup request message may comprise ‘CG-Configlnfo’ for a conditional PSCell change.

At S803.1 , the UE context setup request message comprises an indication that selective activation is enabled. The selective activation is configured by the network (by the CU) so that the UE knows that the provided configuration is for selective activation.

At S804, the target DU responds to the CU with a UE context setup response message.

At S805, the CU sends a DL RRC message transfer message to the source DU. The DL RRC message transfer message includes a generated RRCReconfigu ration message.

At S806, the source DU forwards the received RRCReconfigu ration message to the UE. At S807, the UE responds by providing, to the source DU, an RRCReconfigurationComplete message.

At S808, the source DU forwards the RRCReconfigurationComplete message to the CU. The RRCReconfigurationComplete message may be provided in an UL RRC message transfer message.

At S809, an execution condition to trigger the initiation of a conditional handover or a conditional PSCell change is fulfilled. For example, the UE measures an A3 event whereby the target becomes an offset better than the serving cell, or the UE measures an A4 event whereby the target becomes better than a threshold.

At S810, a random access procedure is performed between the UE and the target DU. The target DU sends a downlink data delivery status frame to inform the CU. The target DU also sends an ‘ACCESS SUCCESS’ message to the CU, to inform the CU of which cell the UE has successfully accessed.

At S811 , the UE sends, to the target DU, with an RRCReconfigurationComplete message.

At S812, the target DU sends, to the CU, an UL RRC message transfer message. The UL RRC message transfer comprising the RRCReconfigurationComplete message.

At S813, the CU sends a UE context modification request message to the source DU. The UE context modification request message indicates for the source DU to stop data transmissions with the UE. The source DU sends a DL data delivery status frame to the CU, to inform the CU about any unsuccessfully transmitted DL data to the UE. Any DL packets including, for example, PDCP protocol data units (PDUs) that have not been successfully transmitted from the source DU, are sent from the CU to the target DU. The target DU may then transmit those DL packets to the UE.

At S814, the source DU responds to the CU with a UE context modification response message.

At S815, the CU sends a UE context reset command message to the source DU. It should be understood that in other examples, other suitable names for the ‘UE context reset command’ message are used. The UE context reset command is an F1AP message. The UE context reset command message may indicate for the source DU to retain configuration information associated with the user equipment, and to reset information related to at least one protocol layer associated with the user equipment. The configuration information may be retained by the source DU, so that the source DU can reconnect with the UE more quickly in the future.

At S815.1 , the CU indicates that a ‘DRB Modified List’ is to include DL UP TNL information. It may be indicated that the DL UP TNL information included in the UE context reset command message is to be applied after CHO or CPC is complete.

At S815.2, the source DU retains configuration information associated with the UE. The source DU resets information related to at least one protocol layer associated with the UE configuration.

In some examples, on receiving the UE context reset command message, the source DU shall reset signalling transport resources and data transport resources, and/or either i) create new data tunnel resources, or ii) flush an existing tunnel.

On receiving the UE context reset command at the source DU, when an existing UP tunnel is reused, the source DU flushes the existing tunnel to clear any buffered data in the tunnel.

When an existing UP tunnel is not reused: i) the source DU stores the received “DRB to Be Modified List”, and ii) the source DU sends the “DRB Modified List” including new DL UP TNL information in a UE context reset complete message (as described in S816 below).

At S816, the source DU sends a UE context reset complete message to the CU.

At S816.1 , the source DU also sends the ‘DRB Modified List’, to the CU, which includes DL UP TNL information associated with the UE, to be applied after CHO or CPC is complete. The ‘DRB Modified List’ may be included in the UE context reset complete message.

In some examples, one or more of the steps of Figure 8 above may not be performed, or may be performed in a different order. Even though the examples of Figures 6 to 8 are shown with conditional handovers and serving cell changes, the mechanisms are equally applicable to nonconditional handovers and serving cell changes.

In a fourth example for a serving cell change, there is provided a trigger to reset resources of a UE context, at a source DU, with TNL modification using a UE context release command. On receiving a UE context release command, at the source DU, the following is performed: either i) create new data tunnel resources, or ii) flush an existing tunnel. Furthermore, on receiving the UE context release command, the source DU shall reset related signalling transport resources and user data transport resources (while retaining configuration information associated with the UE). The source DU may send a ‘DRB Modified List’, to the CU, which includes DL UP TNL information associated with the UE. The ‘DRB Modified List’ may be included in a UE context release complete message.

As previously mentioned, when a handover or serving cell change takes place, a UE moves from a source cell to target cell. When the UE has successfully moved to the target cell, information related to the UE stored at the DU provided the source cell is typically deleted (or similar). Therefore, if the UE is to move back to the source cell, a further configuration procedure will have to take place in order to connect the UE to the source cell, which takes times. One or more of the examples above show a partial release of the UE context at the source DU after a serving cell change execution. This enables the UE to go back to the same DU without any extra re-configuration. This is achieved via the indication from the CU to the source DU to maintain the configuration information such as transport layer resources related to the UE, but release and re- prepare/reset other configurations of the UE, such as, for example, MAC and RLC buffers. In this way, the UE is able to reconnect to the same DU (source DU) more quickly.

Figure 9 shows an example method flow performed by an apparatus. The apparatus may be for a source node, in some examples. The apparatus may be comprised in the source node, in some examples. The apparatus may be the source node, in some examples. In some examples, the source node is one of: a gNB, a source distributed unit, and a source gNB. In S901 , the method comprises communicating with a user equipment, wherein the user equipment is served by a serving cell, the serving cell provided by a source node.

In S903, the method comprises receiving an indication that the user equipment is moving from the serving cell to a target cell.

In S905, the method comprises, based on the received indication: i) retaining configuration information associated with a configuration for the user equipment, and ii) resetting information related to at least one protocol layer associated with the configuration for the user equipment.

Figure 10 shows an example method flow performed by a further apparatus. The further apparatus may be for a second node, in some examples. The further apparatus may be comprised in the second node, in some examples. The further apparatus may be the second node, in some examples. In some examples, the second node is one of: a centralised unit, a master node, a gNB-centralised unit

In S1001 , the method comprises communicating with a user equipment via a source node, wherein the user equipment is served by a serving cell, the serving cell provided by the source node.

In S1003, the method comprises providing, to the source node, an indication that the user equipment is moving from the serving cell to a target cell, wherein the indication is for the source node to: i) retain configuration information associated with a configuration for the user equipment, and ii) reset information related to at least one protocol layer associated with the configuration for the user equipment.

Figure 11 shows a schematic representation of non-volatile memory media 1100a (e.g. blu-ray disk (BD), computer disc (CD) or digital versatile disc (DVD)) and 1100b (e.g. solid state drive (SSD), universal serial bus (USB) memory stick) storing instructions and/or parameters 1102 which when executed by a processor allow the processor to perform one or more of the steps of the methods of Figure 9 and Figure 10.

It is noted that while the above describes example embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention.

The examples may thus vary within the scope of the attached claims. In general, some embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although embodiments are not limited thereto. While various embodiments may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The examples may be implemented by computer software stored in a memory and executable by at least one data processor of the involved entities or by hardware, or by a combination of software and hardware. Further in this regard it should be noted that any procedures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD.

The term “non-transitory”, as used herein, is a limitation of the medium itself (i.e. tangible, not a signal) as opposed to a limitation on data storage persistency (e.g. RAM vs ROM).

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

The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), gate level circuits and processors based on multi core processor architecture, as non-limiting examples. Alternatively, or additionally some examples may be implemented using circuitry. The circuitry may be configured to perform one or more of the functions and/or method steps previously described. That circuitry may be provided in the base station and/or in the communications device.

As used in this application, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit implementations (such as implementations in only analogue and/or digital circuitry); (b) combinations of hardware circuits and software, such as: (i) a combination of analogue 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(ies) that work together to cause an apparatus, such as the communications device or base station to perform the various functions previously described; and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., 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 also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example integrated device.

The foregoing description has provided by way of exemplary and non-limiting examples a full and informative description of some embodiments. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings will still fall within the scope as defined in the appended claims.

Claims

Claims:

1 . An apparatus comprising: means for communicating with a user equipment, wherein the user equipment is served by a serving cell, the serving cell provided by a source node; means for receiving an indication that the user equipment is moving from the serving cell to a target cell; and means for, based on the received indication: i) retaining configuration information associated with a configuration for the user equipment, and ii) resetting information related to at least one protocol layer associated with the configuration for the user equipment.

2. The apparatus according to claim 1 , wherein the apparatus comprises: means for reconnecting with the user equipment using the configuration information associated with the user equipment, such that the user equipment is served by the cell of the source node.

3. The apparatus according to claim 1 or claim 2, wherein the configuration information associated with configuration for the user equipment to be retained is received in a user equipment context setup request message.

4. The apparatus according to any of claims 1 to 3, wherein the configuration information comprises user-plane transport network layer information associated with the user equipment.

5. The apparatus according to any of claims 1 to 4, wherein the means for resetting information related to at least one protocol layer comprises: means for resetting resources associated with the configuration for the user equipment.

6. The apparatus according to any of claims 1 to 5, wherein the indication comprises a further indication to maintain transport layer resources associated with the configuration for the user equipment.

7. The apparatus according to any of claims 1 to 6, wherein the means for resetting information related to at least one protocol layer comprises at least one of: means for resetting signalling transport resources associated with the configuration for the user equipment; means for resetting user data transport resources associated with the configuration for the user equipment; means for performing a radio link control re-establishment associated with the configuration for the user equipment; means for performing a medium access control reset associated with the configuration for the user equipment; means for creating at least one tunnel endpoint identifier for at least one data radio bearer associated with the configuration for the user equipment; means for maintaining at least one existing tunnel endpoint identifier associated with the configuration for the user equipment.

8. The apparatus according to claim 7, wherein the means for maintaining at least one existing tunnel endpoint identifier comprises: means for flushing an existing tunnel associated with the tunnel endpoint identifier.

9. The apparatus according to claim 7, wherein the means for creating at least one tunnel endpoint identifier comprises: means for determining resources for a tunnel associated with the at least one tunnel endpoint identifier.

10. The apparatus according to claim 7, wherein the means for creating tunnel endpoint identifiers for at least one data radio bearer associated with the user equipment comprises: means for receiving, from the centralised unit, uplink user-plane transport network layer information with the indication; and means for applying the uplink user-plane transport network layer information after the user equipment has moved from the serving cell to the target cell.

11. The apparatus according to claim 10, wherein the uplink user-plane transport network layer information is comprised in a data radio bearer to be modified list.

12. The apparatus according to any of claims 1 to 11 , wherein the indication is received in one of: an F1 application protocol message, and an Xn application protocol message.

13. The apparatus according to claim 12, wherein the F1 application protocol message is one of: a user equipment context modification request message, a user equipment context release command message, and a user equipment context reset request message.

14. The apparatus according to any of claims 1 to 13, wherein the indication is received from a second node.

15. The apparatus according to claim 14, wherein the second node is one of: a centralised unit, a master node, a target node, a gNodeB-centralised unit.

16. The apparatus according to any of claims 1 to 15, wherein one of: the apparatus is for the source node, the apparatus is comprised in the source node, and the apparatus is the source node.

17. The apparatus according to claim 16, wherein the source node is one of: a gNodeB, a source distributed unit, and a source gNodeB.

18. An apparatus comprising: means for communicating with a user equipment via a source node, wherein the user equipment is served by a serving cell, the serving cell provided by the source node; and means for providing, to the source node, an indication that the user equipment is moving from the serving cell to a target cell, wherein the indication is for the source node to: i) retain configuration information associated with a configuration for the user equipment, and ii) reset information related to at least one protocol layer associated with the configuration for the user equipment.

19. The apparatus according to claim 18, wherein the apparatus comprises: means for receiving signalling, from the source node, to reconnect with the user equipment using the configuration information associated with the user equipment, such that the user equipment is served by the cell of the source node.

20. The apparatus according to claim 18 or claim 19, wherein apparatus comprises: means for providing, to the source node, the configuration for the user equipment to be retained in a user equipment context setup request message.

21. The apparatus according to any of claims 18 to 20, wherein the configuration information comprises user-plane transport network layer information associated with the user equipment.

22. The apparatus according to any of claims 18 to 21 , wherein the indication comprises a further indication to maintain transport layer resources associated with the configuration for the user equipment.

23. The apparatus according to any of claims 18 to 22, wherein apparatus comprises: means for providing, to the source node, uplink user-plane transport network layer information with the indication, wherein the source node is indicated to apply the uplink user-plane transport network layer information after the user equipment has moved from the serving cell to the target cell.

24. The apparatus according to claim 23, wherein the uplink user-plane transport network layer information is comprised in a data radio bearer to be modified list.

25. The apparatus according to any of claims 18 to 24, wherein the indication is provided in one of: an F1 application protocol message, and an Xn application protocol message.

26. The apparatus according to claim 25, wherein the F1 application protocol message is one of: a user equipment context modification request message, a user equipment context release command message, and a user equipment context reset request message.

27. The apparatus according to any of claims 18 to 26, wherein one of: the apparatus is for a second node, the apparatus is comprised in the second node, and the apparatus is the second node.

28. The apparatus according to claim 27, wherein the second node is one of: a centralised unit, a master node, a gNodeB-centralised unit.

29. A method comprising: communicating with a user equipment, wherein the user equipment is served by a serving cell, the serving cell provided by a source node; receiving an indication that the user equipment is moving from the serving cell to a target cell; and based on the received indication: i) retaining configuration information associated with a configuration for the user equipment, and ii) resetting information related to at least one protocol layer associated with the configuration for the user equipment.

30. The method according to claim 29, wherein the method comprises: reconnecting with the user equipment using the configuration information associated with the user equipment, such that the user equipment is served by the cell of the source node.

31. The method according to claim 29 or claim 30, wherein the configuration information associated with configuration for the user equipment to be retained is received in a user equipment context setup request message,

32. The method according to any of claims 29 to 31 , wherein the configuration information comprises user-plane transport network layer information associated with the user equipment.

33. The method according to any of claims 29 to 32, wherein the resetting information related to at least one protocol layer comprises: resetting resources associated with the configuration for the user equipment.

34. The method according to any of claims 29 to 33, wherein the indication comprises a further indication to maintain transport layer resources associated with the configuration for the user equipment.

35. The method according to any of claims 29 to 34, wherein the resetting information related to at least one protocol layer comprises at least one of: resetting signalling transport resources associated with the configuration for the user equipment; resetting user data transport resources associated with the configuration for the user equipment; performing a radio link control re-establishment associated with the configuration for the user equipment; performing a medium access control reset associated with the configuration for the user equipment; creating at least one tunnel endpoint identifier for at least one data radio bearer associated with the configuration for the user equipment; maintaining at least one existing tunnel endpoint identifier associated with the configuration for the user equipment.

36. The method according to claim 35, wherein the maintaining at least one existing tunnel endpoint identifier comprises: flushing an existing tunnel associated with the tunnel endpoint identifier.

37. The method according to claim 35, wherein the creating at least one tunnel endpoint identifier comprises: determining resources for a tunnel associated with the at least one tunnel endpoint identifier.

38. The method according to claim 35, wherein the creating tunnel endpoint identifiers for at least one data radio bearer associated with the user equipment comprises: receiving, from the centralised unit, uplink user-plane transport network layer information with the indication; and applying the uplink user-plane transport network layer information after the user equipment has moved from the serving cell to the target cell.

39. The method according to claim 38, wherein the uplink user-plane transport network layer information is comprised in a data radio bearer to be modified list.

40. The method according to any of claims 29 to 39, wherein the indication is received in one of: an F1 application protocol message, and an Xn application protocol message.

41. The method according to claim 40, wherein the F1 application protocol message is one of: a user equipment context modification request message, a user equipment context release command message, and a user equipment context reset request message.

42. The method according to any of claims 29 to 41 , wherein the indication is received from a second node.

43. The method according to claim 42, wherein the second node is one of: a centralised unit, a master node, a target node, a gNodeB-centralised unit.

44. The method according to any of claims 29 to 43, wherein method is performed by the source node.

45. The method according to claim 44, wherein the source node is one of: a gNodeB, a source distributed unit, and a source gNodeB.

46. A method comprising: communicating with a user equipment via a source node, wherein the user equipment is served by a serving cell, the serving cell provided by the source node; and providing, to the source node, an indication that the user equipment is moving from the serving cell to a target cell, wherein the indication is for the source node to: i) retain configuration information associated with a configuration for the user equipment, and ii) reset information related to at least one protocol layer associated with the configuration for the user equipment.

47. The method according to claim 46, wherein the method comprises: receiving signalling, from the source node, to reconnect with the user equipment using the configuration information associated with the user equipment, such that the user equipment is served by the cell of the source node.

48. The method according to claim 46 or claim 47, wherein method comprises: providing, to the source node, the configuration for the user equipment to be retained in a user equipment context setup request message,

49. The method according to any of claims 46 to 48, wherein the configuration information comprises user-plane transport network layer information associated with the user equipment.

50. The method according to any of claims 46 to 49, wherein the indication comprises a further indication to maintain transport layer resources associated with the configuration for the user equipment.

51 . The method according to any of claims 46 to 50, wherein method comprises: providing, to the source node, uplink user-plane transport network layer information with the indication, wherein the source node is indicated to apply the uplink user-plane transport network layer information after the user equipment has moved from the serving cell to the target cell.

52. The method according to claim 51 , wherein the uplink user-plane transport network layer information is comprised in a data radio bearer to be modified list.

53. The method according to any of claims 46 to 52, wherein the indication is provided in one of: an F1 application protocol message, and an Xn application protocol message.

54. The method according to claim 53, wherein the F1 application protocol message is one of: a user equipment context modification request message, a user equipment context release command message, and a user equipment context reset request message.

55. The method according to any of claims 46 to 54, wherein method is performed by a second node.

56. The method according to claim 55, wherein the second node is one of: a centralised unit, a master node, a gNodeB-centralised unit.

57. An apparatus comprising: at least one processor, and at least one memory storing instructions that, when executed by the one or more processors, cause the apparatus to perform: communicating with a user equipment, wherein the user equipment is served by a serving cell, the serving cell provided by a source node; receiving an indication that the user equipment is moving from the serving cell to a target cell; and based on the received indication: i) retaining configuration information associated with a configuration for the user equipment, and ii) resetting information related to at least one protocol layer associated with the configuration for the user equipment.

58. The apparatus according to claim 57, wherein the apparatus is caused is perform: reconnecting with the user equipment using the configuration information associated with the user equipment, such that the user equipment is served by the cell of the source node.

59. The apparatus according to claim 57 or claim 58, wherein the configuration information associated with configuration for the user equipment to be retained is received in a user equipment context setup request message,

60. The apparatus according to any of claims 57 to 59, wherein the configuration information comprises user-plane transport network layer information associated with the user equipment.

61. The apparatus according to any of claims 57 to 60, wherein the resetting information related to at least one protocol layer comprises: resetting resources associated with the configuration for the user equipment.

62. The apparatus according to any of claims 57 to 61 , wherein the indication comprises a further indication to maintain transport layer resources associated with the configuration for the user equipment.

63. The apparatus according to any of claims 57 to 62, wherein the resetting information related to at least one protocol layer comprises at least one of: resetting signalling transport resources associated with the configuration for the user equipment; resetting user data transport resources associated with the configuration for the user equipment; performing a radio link control re-establishment associated with the configuration for the user equipment; performing a medium access control reset associated with the configuration for the user equipment; creating at least one tunnel endpoint identifier for at least one data radio bearer associated with the configuration for the user equipment; maintaining at least one existing tunnel endpoint identifier associated with the configuration for the user equipment.

64. The apparatus according to claim 63, wherein the maintaining at least one existing tunnel endpoint identifier comprises: flushing an existing tunnel associated with the tunnel endpoint identifier.

65. The apparatus according to claim 63, wherein the creating at least one tunnel endpoint identifier comprises: determining resources for a tunnel associated with the at least one tunnel endpoint identifier.

66. The apparatus according to claim 63, wherein the creating tunnel endpoint identifiers for at least one data radio bearer associated with the user equipment comprises: receiving, from the centralised unit, uplink user-plane transport network layer information with the indication; and applying the uplink user-plane transport network layer information after the user equipment has moved from the serving cell to the target cell.

67. The apparatus according to claim 66, wherein the uplink user-plane transport network layer information is comprised in a data radio bearer to be modified list.

68. The apparatus according to any of claims 57 to 67, wherein the indication is received in one of: an F1 application protocol message, and an Xn application protocol message.

69. The apparatus according to claim 68, wherein the F1 application protocol message is one of: a user equipment context modification request message, a user equipment context release command message, and a user equipment context reset request message.

70. The apparatus according to any of claims 57 to 69, wherein the indication is received from a second node.

71. The apparatus according to claim 70, wherein the second node is one of: a centralised unit, a master node, a target node, a gNodeB-centralised unit.

72. The apparatus according to any of claims 57 to 71 , wherein one of: the apparatus is for the source node, the apparatus is comprised in the source node, and the apparatus is the source node.

73. The apparatus according to claim 72, wherein the source node is one of: a source distributed unit, and a source gNodeB.

74. An apparatus comprising: at least one processor, and at least one memory storing instructions that, when executed by the one or more processors, cause the apparatus to perform: communicating with a user equipment via a source node, wherein the user equipment is served by a serving cell, the serving cell provided by the source node; and providing, to the source node, an indication that the user equipment is moving from the serving cell to a target cell, wherein the indication is for the source node to: i) retain configuration information associated with a configuration for the user equipment, and ii) reset information related to at least one protocol layer associated with the configuration for the user equipment.

75. The method according to claim 74, wherein the method comprises: receiving signalling, from the source node, to reconnect with the user equipment using the configuration information associated with the user equipment, such that the user equipment is served by the cell of the source node.

76. The method according to claim 74 or claim 75, wherein method comprises: providing, to the source node, the configuration for the user equipment to be retained in a user equipment context setup request message,

77. The method according to any of claims 74 to 76, wherein the configuration information comprises user-plane transport network layer information associated with the user equipment.

78. The method according to any of claims 74 to 77, wherein the indication comprises a further indication to maintain transport layer resources associated with the configuration for the user equipment.

79. The method according to any of claims 74 to 78, wherein method comprises: providing, to the source node, uplink user-plane transport network layer information with the indication, wherein the source node is indicated to apply the uplink user-plane transport network layer information after the user equipment has moved from the serving cell to the target cell.

80. The method according to claim 7, wherein the uplink user-plane transport network layer information is comprised in a data radio bearer to be modified list.

81. The method according to any of claims 74 to 80, wherein the indication is provided in one of: an F1 application protocol message, and an Xn application protocol message.

82. The method according to claim 81 , wherein the F1 application protocol message is one of: a user equipment context modification request message, a user equipment context release command message, and a user equipment context reset request message.

83. The method according to any of claims 74 to 82, wherein method is performed by a second node.

84. The method according to claim 83, wherein the second node is one of: a centralised unit, a master node, a gNodeB-centralised unit.

85. A computer program comprising instructions, which when executed by an apparatus, cause the apparatus to perform at least the following: communicating with a user equipment, wherein the user equipment is served by a serving cell, the serving cell provided by a source node; receiving an indication that the user equipment is moving from the serving cell to a target cell; and based on the received indication: i) retaining configuration information associated with a configuration for the user equipment, and ii) resetting information related to at least one protocol layer associated with the configuration for the user equipment.

86. A computer program comprising instructions, which when executed by an apparatus, cause the apparatus to perform at least the following: communicating with a user equipment via a source node, wherein the user equipment is served by a serving cell, the serving cell provided by the source node; and providing, to the source node, an indication that the user equipment is moving from the serving cell to a target cell, wherein the indication is for the source node to: i) retain configuration information associated with a configuration for the user equipment, and ii) reset information related to at least one protocol layer associated with the configuration for the user equipment.