WO2020154855A1

WO2020154855A1 - Mobility enhancement of terminal device

Info

Publication number: WO2020154855A1
Application number: PCT/CN2019/073456
Authority: WO
Inventors: Haitao Li; Srinivasan Selvaganapathy; Jussi-Pekka Koskinen
Original assignee: Nokia Shanghai Bell Co Ltd; Nokia Solutions and Networks Oy; Nokia Technologies Oy
Current assignee: Nokia Shanghai Bell Co Ltd; Nokia Solutions and Networks Oy; Nokia Technologies Oy
Priority date: 2019-01-28
Filing date: 2019-01-28
Publication date: 2020-08-06
Anticipated expiration: 2021-07-28
Also published as: CN113348698A; CN113348698B

Abstract

Example embodiments of the present disclosure relate to methods, devices, apparatuses and computer readable storage media for mobility enhancement of a terminal device. In example embodiments, a terminal device is served by a source access network device connected to a source core network device and determines cell reselection from a source cell of the source access network device to a target cell of a target access network device connected to a target core network device. If a connectivity indication is received from the target access network device to enable a connection resume procedure for data forwarding through a source backhaul link between the source access network device and the source core network device, the terminal device sends to the target access network device a connection resume request for initiating a connection resume procedure. The terminal device receives, from the target access network device, a connection resume response for indicating whether a connection setup procedure is to be initiated.

Description

MOBILITY ENHANCEMENT OF TERMINAL DEVICE

FIELD

Example embodiments of the present disclosure generally relate to the field of communications, and in particular, to methods, devices, apparatuses and computer readable storage media for mobility enhancement of a terminal device.

BACKGROUND

The Long Term Evolution (LTE) connectivity to the fifth generation Core Network (5G-CN) technology allows radio access network (RAN) level interworking and provides a migration path between the LTE access network and the 5G-CN. Machine-type communication (MTC) and Narrow Band Internet of thing (NB-IoT) have not been allowed to use this technology due to the tighter scheduling and the narrower frequency band. For the third generation Partnership Project (3GPP) Release 16 (Rel-16) , to further enhance the NB-IoT, inter-radio access technology (inter-RAT) mobility in an IDLE mode is proposed, and various inter-RAT mobility scenarios are discussed.

Conventionally, MTC or NB-IoT user equipment (UE) , which is served by an evolved LTE (eLTE) eNodeB (eNB) connected to the 5G-CN, may enter an INACTIVE state after data transmission. If the UE wants to access the eLTE cell or a different eLTE cell, the UE may trigger a radio resource control (RRC) resume procedure. Similarly, for a UE which is served by a LTE eNB connected to an evolved packet core (EPC) , the UE may enter a suspended or IDLE state after data transmission, and a RRC resume procedure may be triggered when the UE intends to access a LTE cell which may or may not be the same as the currently serving LTE cell. The detailed processes of the two RRC resume procedures are different, for example, which may include different security related information elements (IEs) in the RRC messages.

When a UE moves from an eLTE coverage to a LTE coverage, a tracking area update (TAU) procedure conventionally needs to be triggered so that a device or entity such as a Mobile Management Entity (MME) in the EPC is aware of the UE and will page the UE when Network Attached Storage (NAS) downlink (DL) data or signaling arrives. The TAU procedure involves both Attached Storage (AS) message exchange and NAS message exchange. Accordingly, signaling overhead and UE power consumption would be significant high when UE is moving between the eLTE coverage and the LTE coverage.

SUMMARY

In general, example embodiments of the present disclosure provide methods, devices, apparatuses and computer readable storage media for mobility enhancement of a terminal device.

In a first aspect, a method is provided. In the method, a terminal device is served by a source access network device connected to a source core network device and determines cell reselection from a source cell of the source access network device to a target cell of a target access network device connected to a target core network device. If a connectivity indication is received from the target access network device to enable a connection resume procedure for data forwarding through a source backhaul link between the source access network device and the source core network device, the terminal device sends to the target access network device a connection resume request for initiating a connection resume procedure. The terminal device receives, from the target access network device, a connection resume response for indicating whether a connection setup procedure is to be initiated.

In a second aspect, a method is provided. In the method, a target access network device receives, from a terminal device served by a source access network device connected to a source core network device, a connection resume request for initiating a connection resume procedure. The target access network device sends, to the source access network device, a handover request for retrieving context of the terminal device. The target access network device receives, from the source access network device, a handover response for indicating whether backhaul switching from a source backhaul link between the source access network device and the source core network device to a target backhaul link between the target access network device and the target core network device is required. The target access network device sends, to the terminal device, a connection resume response based on the handover response.

In a third aspect, a method is provided. In the method, a source access network device is connected to a source core network device and is serving a terminal device. The source access network device receives, from a target access network device connected to a target core network device, a handover request for retrieving context of the terminal device. The source access network device determines whether backhaul switching from a source backhaul link between the source access network device and the source core network device to a target backhaul link between the target access network device and the target core network device is required. The source access network device sends, to the target access network device, a handover response based on the determining.

In a fourth aspect, a device is provided comprising at least one processor and at least one memory including computer program code. The at least one memory and the computer program code are configured to, with the at least one processor, cause the device to the method according to the first, second or third aspect.

In a fifth aspect, there is provided an apparatus comprising means for performing the method according to the first, second or third aspect.

In a sixth aspect, there is provided a computer readable storage medium that stores a computer program thereon. The computer program, when executed by a processor of a device, causes the device to perform the method according to the first, second or third aspect.

It is to be understood that the summary section is not intended to identify key or essential features of example embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Some example embodiments will now be described with reference to the accompanying drawings, where:

FIG. 1 illustrates an example environment in which example embodiments of the present disclosure can be implemented;

FIG. 2 illustrates an example signaling procedure in the mobility of a terminal device from a source access network device to a target access network device according to some example embodiments of the present disclosure;

FIG. 3 illustrates an example signaling procedure where a connection setup procedure is not initiated in accordance with some example embodiments of the present disclosure;

FIG. 4 illustrates an example signaling procedure where a connection setup procedure is initiated in accordance with some example embodiments of the present disclosure;

FIG. 5 illustrates a flowchart of an example method in accordance with some example embodiments of the present disclosure;

FIG. 6 illustrates a flowchart of an example method in accordance with some other example embodiments of the present disclosure;

FIG. 7 illustrates a flowchart of an example method in accordance with yet other example embodiments of the present disclosure;

FIG. 8 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these example embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

As used herein, the term “access network device” refers to a device via which a terminal device or UE can access a communication network. Examples of the BS include a relay, an access point (AP) , a transmission point (TRP) , a node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a gigabit NodeB (gNB) , a Remote Radio Module (RRU) , a radio header (RH) , a remote radio head (RRH) , a low power node such as a femto, a pico, and the like.

As used herein, the term “source access network device” refers to an access network device currently serving a terminal device when the terminal device is moving towards another access network device. As used herein, the term “target access network device” refers to an access network device to which the terminal device is moving and thus will be handed over.

As used herein, the term “core network device” refers to a device capable of communicating with the access network device and providing services to the terminal device in a core network. Examples of the core network device may include Mobile Switching Centers (MSCs) , MMEs, Operation and Management (O&M) nodes, Operation Support System (OSS) nodes, Self-Organization Network (SON) nodes, positioning nodes, such as Enhanced Serving Mobile Location Centers (E-SMLCs) , and/or Mobile Data Terminals (MDTs) .

As used herein, the term “source core network device” refers to a core network device currently serving a terminal device when the terminal device is moving towards another core network device. As used herein, the term “target core network device” refers to a core network device to which the terminal device is moving and thus will be handed over.

As used herein, the term “terminal device” or “user equipment” (UE) refers to any terminal device capable of wireless communications with each other or with the base station. The communications may involve transmitting and/or receiving wireless signals using electromagnetic signals, radio waves, infrared signals, and/or other types of signals suitable for conveying information over air. In some example embodiments, the UE may be configured to transmit and/or receive information without direct human interaction. For example, the UE may transmit information to the network device on predetermined schedules, when triggered by an internal or external event, or in response to requests from the network side.

Examples of the UE include, but are not limited to, user equipment (UE) such as smart phones, wireless-enabled tablet computers, laptop-embedded equipment (LEE) , laptop-mounted equipment (LME) , and/or wireless customer-premises equipment (CPE) . For the purpose of discussion, some example embodiments will be described with reference to UEs as examples of the terminal devices, and the terms “terminal device” and “user equipment” (UE) may be used interchangeably in the context of the present disclosure.

As used herein, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable) : (i) a combination of analog and/or digital hardware circuit (s) with software/firmware and (ii) any portions of hardware processor (s) with software (including digital signal processor (s) ) , software, and memory (ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(c) hardware circuit (s) and or processor (s) , such as a microprocessor (s) or a portion of a microprocessor (s) , that requires software (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 and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in a server, a cellular network device, or other computing or network device.

As used herein, the singular forms “a” , “an” , and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term “includes” and its variants are to be read as open terms that mean “includes, but is not limited to” . The term “based on” is to be read as “based at least in part on” . The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment” . The term “another embodiment” is to be read as “at least one other embodiment” . Other definitions, explicit and implicit, may be included below.

As used herein, the terms “first” , “second” and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be referred to as a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the listed terms.

Example embodiments of the present disclosure provide a modified signaling scheme for inter-cell and inter-core network mobility of a terminal device. With this procedure, a terminal device is currently served by a source access network device which is connected to a source core network device and determines cell reselection to a target cell of a target access network device connected to a target core network device as the terminal device moves. The terminal device sends a connection resume request to the target access network device to initiate a connection resume procedure.

Then, the target access network device sends a handover request to the source access network device. In response to the handover request, the source access network device determines whether to switch a source backhaul link between the source access network device and the source core network device to a target backhaul link between the target access network device and the target core network device. The source access network device sends a handover response to the target access network device based on the determining of the backhaul switching. Further, the target access network device sends a connection resume response based on the handover response. Accordingly, the terminal device determines whether to initiate a connection setup procedure.

With such a signaling procedure, when the terminal device is moving from a source cell of the source access network device to a target cell of the target access network device, the terminal device may establish connection with the target access network device in a more flexible and efficient way. As such, the mobility of the terminal device in particular between different core networks may be enhanced.

FIG. 1 shows an example environment 100 in which example embodiments of the present disclosure can be implemented. The environment 100, which is a part of a communication network, includes a terminal device 105 which is currently served by a source access network device 110 connected to a source core network device 115. As shown, the terminal device 105 is moving from a source cell 120 of the source access network device 110 to a target cell 125 of a target access network device 130 connected to a target core network device 135.

The access network devices and the core network devices may be implemented by any suitable devices and may comply with any suitable communication standards or protocols. In some example embodiments, the source access network device 110 may be implemented by an eLTE eNB, and the source core network device 130 may be implemented by a device or entity in the 5G-CN. Moreover, the target access network device 130 may be implemented by a LTE eNB, and the target core network device 135 may be implemented by a MME in the EPC.

It is to be understood that the numbers of terminal devices, access network devices, and core network devices are shown in FIG. 1 only for the purpose of illustration, without suggesting any limitation to the scope of the present disclosure. The environment 100 may include any suitable number of terminal devices, access network devices, and core network devices.

The terminal device 105 may communicate with the source access network device 110 and the target access network device 130 or with another terminal device (not shown) directly or via the source access network device 110 or the target access network device 130. The communication may follow any suitable communication standards or protocols such as Universal Mobile Telecommunications System (UMTS) , Long Term Evolution (LTE) , LTE-Advanced (LTE-A) , evolved Long Term Evolution (eLTE) , the fifth generation (5G) NR, Wireless Fidelity (Wi-Fi) and Worldwide Interoperability for Microwave Access (WiMAX) standards, and employs any suitable communication technologies, including, for example, Multiple-Input Multiple-Output (MIMO) , Orthogonal Frequency Division Multiplexing (OFDM) , time division multiplexing (TDM) , frequency division multiplexing (FDM) , code division multiplexing (CDM) , Bluetooth, ZigBee, and machine type communication (MTC) , enhanced mobile broadband (eMBB) , massive machine type communication (mMTC) , Narrow Band Internet of thing (NB-IoT) , and ultra-reliable low latency communication (URLLC) technologies.

The access network device can communicate with the corresponding core network device in a wired or wireless way. The access network devices may communicate with each other via a communication interface such as an X2 interface. The core network devices may communicate with each other via a dedicated interface. These communications may use any suitable communication technologies that are already known or to be developed in the future.

In the environment 100, when the terminal device 105 is moving into the target cell 125 of the target access network device 130, the terminal device 105 can reselect to the target access network device 130 by cell reselection, for example. In various example embodiments of the present disclosure, the terminal device 105 sends a connection resume request (for example, a RRC-Connection-Resume-Request message) to the target access network device 130 to initiate a connection resume request. Upon the reception of the connection resume request, the target access network device 130 sends a handover request to the source access network device 110 to cause the source access network device 110 to determine whether a source backhaul link between the source access network device 110 and the source core network device 115 is to be switched to a target backhaul link between the target access network device 130 and the target core network device 135.

If the backhaul switching is required or determined to be performed, the source access network device 110 may release context of the terminal device 105. If the backhaul switching is unrequired or determined not to be performed, the source access network device 110 may continue to communicate with the terminal device 105 using the source backhaul link by forwarding of the target access network device 130.

FIG. 2 shows an example signaling procedure 200 in the mobility of the terminal device 105 from the source access network device 110 to the target access network device 130 according to some example embodiments of the present disclosure.

In the procedure 200, the terminal device 105 determines (205) cell reselection to the target cell 125 of the target access network device 130. For example, when moving from the source cell 120 to the target cell 125, the terminal device 105 may reselect to the target access network device 130 by cell reselection. In some example embodiments, the cell reselection may be performed from the 5G-CN to the EPC. For example, the terminal device 105 in an INACTIVE state is currently served by the 5G-CN, and reselects a LTE cell in the EPC. The terminal device 105 may obtain the information about the target CN connectivity from system information broadcasted by the target access network device 130.

The terminal device 105 receives (210) , from the target access network device, a connectivity indication to enable a connection resume procedure for data forwarding through a source backhaul link between the source access network device 110 and the source core network device 115, that is, backhaul switching from the source backhaul link to a target backhaul link between the target access network device 130 and the target core network device 135 is not required. As such, the terminal device 105 may determine whether the data forwarding is enabled by the target access network device 130.

For example, the target access network device 130 may broadcast the connectivity indication in a system information block (SIB) to indicate the connection resume procedure to be enabled for the data forwarding. If the target access network device 130 does not enable the use of the connection resume procedure for the data forwarding, the terminal device 105 enters an IDLE state and triggers the connection setup procedure. If the use of the connection resume procedure is allowed, the terminal device 105 may send the connection resume request to the target access network device 130.

The terminal device 105 sends (215) a connection resume request to the target access network device 130 to initiate a connection resume procedure. The connection resume procedure may comprises any suitable suspend or resume procedure that is already known or to be developed in the future. As an example, the connection resume procedure may be implemented by a RRC Resume procedure. In this case, the connection resume request may be implemented by a RRC-Connection-Resume-Request message.

In some example embodiments, in order to save power consumption, the terminal device 105 may defer the sending of the connection resume request until a paging time window (PTW) if extended discontinuous reception (eDRX) is activated.

To save the power consumption, in some other example embodiments, the connection resume request may be sent by the terminal device 105 upon arrival of uplink (UL) data, so as to save power consumption of the terminal device 105. For example, if a power saving mode (PSM) is activated, the terminal device 105 may defer the sending of the connection resume request until the arrival of the UL data.

In some example embodiments, the terminal device 105 may determine whether to initiate the connection resume procedure based on a time from the arrival of the UL data to triggering opportunity of a connection setup procedure, to further reduce the UL transmission latency. For example, if UL data (for example, NAS data) arrives, the terminal device 105 may determine whether a time from arriving of the UL data to an available triggering opportunity of a connection setup procedure (for example, a TAU procedure) is greater than a predetermined threshold. The threshold may be predefined based on actual service requirements such as latency requirements. If the time is greater than the predetermined threshold, which means that the triggering opportunity is relatively late, the terminal device 105 may send the connection resume request to the target access network device 130. Otherwise, the terminal device 105 may enter an IDLE state and initiate a connection setup procedure in the triggering opportunity.

The connection resume request may contain information about the source access network device 110. For example, in the example embodiments where the source access network device 110 is an eLTE eNB, the connection resume request may contain resume identification (ID) and a security ID based on the context of the terminal device 105 in the source eLTE cell. In addition, the connection resume request may contain an indication to indicate the mobility of the terminal device 105 from the source cell 120. In the case that the source access network device 110 is an eLTE eNB, the indication may be implemented by a flag to indicate the mobility from the 5GC.

Upon reception of the connection resume request, the target access network device 130 sends (220) to the source access network device 110 a handover request for retrieving context of the terminal device 105. The handover request may be sent via an X2 interface between the two access network devices. In the example embodiments where the source access network device 110 is an eLTE eNB and the target access network device 130 is a LTE eNB, the handover request may be carried in an X2 Application Protocol (X2AP) message. Using this X2AP message, the target access network device 130 may indicate to the source access network device 110 that terminal device 105 has moved out to the EPC area.

The source access network device 110 determines (225) whether to perform the backhaul switching from the source backhaul link between the source access network device 110 and the source core network device 115 to the target backhaul link between the target access network device 130 and the target core network device 135. For example, the source access network device 110 may validate the security of the handover request and make a decision of whether to enable the backhaul switching based on the validation. If the backhaul switching is determined, the source access network device 110 may move a session of the terminal device 105 out.

In some example embodiments, the source access network device 110 may inform the source core network device 115 of the mobility of the terminal device 105. For example, the source access network device 110 may send an indication to the source core network device 115 to indicate that the terminal device 105 has moved out of the source cell 120. The source core network device 115 may further send an indication to the target core network device 135 to inform that the terminal device 105 is moving into the target cell 125.

Based on the determining (225) , the source access network device 110 sends (230) a handover response to the target access network device 130 to indicate whether the backhaul switching is required. Similar to the handover request, the handover response may be sent via the X2 interface between the two access network devices. In the case that the source access network device 110 is an eLTE eNB and the target access network device 130 is a LTE eNB, the handover response may be carried in an X2AP message.

In some example embodiments, if the backhaul switching is required, the source access network device 110 may release the context of the terminal device 105. In addition, the source access network device 110 may inform the source core network device 115 that the terminal device 105 has moved out of the source coverage are 115 and is unreachable for paging. If the backhaul switching is unrequired, the source access network device 110 will continue to communicate with the terminal device 105 by forwarding of the target access network device 130.

As shown in FIG. 2, based on the handover response, the target access network device 130 sends (235) a connection resume response to the terminal device 110 such that the terminal device 105 may determine whether a connection setup procedure is to be initiated. The connection setup procedure may be any suitable setup procedure that is already known or to be developed in the future. As an example, the connection setup procedure may be implemented by a TAU procedure.

For example, if the handover response indicates that the backhaul switching is required, the connection resume response may indicate that the connection resume request is rejected. Accordingly, the terminal device 105 may determine that the connection setup procedure is to be initiated. In this case, the terminal device 105 may first enter an IDLE state and then initiate a connection setup procedure for setup of new context in the target cell 125. In some example embodiments, the target access network device 130 may inform the target core network device 135 of the CN change.

If the handover response indicates that the switching from the source backhaul link to the target backhaul link is determined not to be done, the target access network device 130 may send the connection resume response to indicate that the connection resume request is allowed. In this case, the target access network device 130 may determine to forward communications between the terminal device 105 and the source access network device 110.

By the forwarding of the target access network device 130, the functions on higher layers in the source cell 120 can still be used by the terminal device 105. Accordingly, the target access network device 130 may configure the terminal device 110 to switch only the functions on lower layers such as Radio Link Control (RLC) , Media Access Control (MAC) and Physical (PHY) layers to the target cell 125.

In the example embodiments where the source access network device 110 is an eLTE eNB and the target access network device 130 is a LTE eNB, 5G security and Packet Data Convergence Protocol (PDCP) functions can still be used by the terminal device 105 and the related context of 5G is maintained. Upon the completion of the connection resume procedure, User-Plane (UP) data transmission continues via 5G User-Plane Gateway (UPGW) of the source eLTE eNB by the forwarding of the target eNB.

If the terminal device 105 has UL data to be transmitted, the terminal device 105 may send the UL data to the target access network device 130. Then, the target access network device 130 forwards the UL data to the source access network device 110. Upon the completion of the UL data transmission, the UE enters an IDLE state and will trigger a further connection resume procedure or a connection setup procedure (for example, the TAU procedure or a service request procedure) for a future service request.

With the signaling scheme provided herein, in the case that the source access network device 110 is an eLTE eNB and the target access network device 130 is a LTE eNB, the terminal device 105 may trigger a RRC Connection Resume procedure upon reselecting a LTE cell connecting to the EPC to enable the source eLTE eNB to decide whether to release the context of the terminal device 105 or to enable data forwarding via the target cell while maintaining the 5GC connectivity. The terminal device 105 may have new configurations for RLC, MAC and PHY layers of the target LTE cell and old configurations for PDCP and security of the source eLTE cell.

Accordingly, data of a 5GC cell may be forwarded via an EPC cell, and 5G PDCP and security may still be used for the data transmission. Moreover, the 5GC may be informed about the UE mobility to the EPC when the source eLTE eNB decides to release the context and the UE enters an IDLE state in the new cell.

As an alternative example, in the example embodiments where the source access network device 110 is an eLTE eNB and the target access network device 130 is a LTE eNB, the terminal device 105 may initiate a connection setup procedure upon UL data available for transmission. Two example signaling procedures in the mobility of the terminal device 105 will be discussed with reference to FIGS. 3 and 4. In these examples, the source access network device 110 and the source core network device 115 are 5G (or eLTE) devices, and the target access network device 130 and the target core network device 135 are LTE devices.

FIG. 3 shows an example signaling procedure 300 where the connection setup procedure is not initiated in accordance with some example embodiments of the present disclosure.

In the procedure 300, the target access network device 130 (for example, a LTE eNB) broadcasts (305) support of a connection resume procedure for data forwarding through a source backhaul link between the source access network device 110 and the source core network device 115 (that is, no backhaul switching) . The terminal device 105 (for example, a UE) served by the source access network device 110 (for example, an eLTE eNB) reselects (310) the target cell 125 (for example, a target cell) upon UL NAS data arrival. The terminal device 105 sends (315) a connection resume request (for example, a RRC-Connection-Resume-Request message) to the target access network device 130 to indicate the mobility from 5GC, for example. The target access network device 130 sends (320) a handover request to the source access network device 110 to indicate the mobility from 5GC.

In this example, the source access network device 110 decides (325) not to perform the backhaul switching. The source access network device 110 indicates (330) to the source core network device 115 (for example, in 5GC) that the terminal device 105 is moving out of 5GC, for example. The source core network device 115 indicates (335) to the target core network device 135 (for example, in EPC) that the terminal device 105 is moving into the EPC, for example. The source access network device 110 sends (340) a handover response to the target access network device 130 to require forwarding of 5G-PDCP packets via LTE RLC/MAC/PHY layers. The target access network device 120 sends (345) a connection resume response (for example, RRC-Connection-Resume message) to the terminal device 105 to switch only the functions on the RLC/MAC/PHY layers while maintaining the PDCP and security context of 5G.

The target access network device 130 forwards (350) the data transmission between the terminal device 105 and the source access network device 110. After the data transmission is completed, the target access network device 130 sends (355) a connection release message (for example, a RRC-Connection-Release message) to the terminal device 105.

FIG. 4 shows an example signaling procedure 400 where the connection setup procedure is initiated in accordance with some example embodiments of the present disclosure.

In the procedure 400, the actions (or operations) 405 to 420 in the procedure 400 are the same as the actions (or operations) 305-320, and the details thereof will be omitted. In this example, upon the reception of the handover request from target access network device 130, the source access network device 110 decides (425) to perform the backhaul switching. Then, the

actions

430 and 435, same as the

actions

330 and 335, are performed such that the source and target core network devices can be aware of the mobility of the terminal device 105. The source access network device 110 sends (440) a handover response to the target access network device 130 to indicate the release of the UE context. The terminal device 105 sends (450) a connection setup request (for example, a RRC-Connection-Request) to the target access network device 130 to initiate a connection setup procedure (for example, the TAU procedure) .

FIG. 5 shows a flowchart of an example method 500 in accordance with some example embodiments of the present disclosure. The method 500 can be implemented at the terminal device 105 as shown in FIG. 1. For the purpose of discussion, the method 500 will be described with reference to FIG. 1.

At block 505, the terminal device 105 determines cell reselection from the source cell 120 of the source access network device 110 to the target cell 125 of the target access network device 130. At block 510, the terminal device 105 receives, from the target access network device 130, a connectivity indication to enable a connection resume procedure for data forwarding through a source backhaul link between the source access network device and the source core network device. At block 515, the terminal device 105 sends to the target access network device 130 a connection resume request for initiating a connection resume procedure. At block 520, the terminal device 105 receives, from the target access network device 130, a connection resume response for indicating whether a connection setup procedure is to be initiated.

In some example embodiments, the connectivity indication may be broadcast from the target access network device 130.

In some example embodiments, the terminal device 105 may send the connection resume request in response to arrival of uplink data. In some example embodiments, the terminal device 105 may defer the sending of the connection resume request until the arrival of the uplink data if a power saving mode is activated.

In some example embodiments, the terminal device 105 may determine whether a time from the arrival of the uplink data to an available triggering opportunity of a connection setup procedure is greater than a predetermined threshold. If it is determine that the time is greater than the predetermined threshold, the terminal device 105 may send the connection resume request to the target access network device 130.

In some example embodiments, the terminal device 105 may defer the sending of the connection resume request until a paging time window if extended discontinuous reception is activated.

In some example embodiments, the terminal device 105 may determine that the connection setup procedure is unrequired if the connection resume response indicates that the connection resume request is allowed. The terminal device 105 may further transmit uplink data to the target access network device.

In some example embodiments, the terminal device 105 may determine that the connection setup procedure is to be initiated if the connection resume response indicates that the connection resume request is rejected. The terminal device 105 may send, to the target access network device 130, a connection setup request to initiate the connection setup procedure.

In some example embodiments, the terminal device 105 may enter an idle state. The terminal device 105 may send the connection setup request in the idle state. In some example embodiments, the terminal device 105 may send the connection setup request to initiate the connection setup procedure in response to uplink data to be transmitted.

In some example embodiments, the connection resume request contains an indication for mobility of the terminal device from the source cell 120 of the source access network device 110. In some example embodiments, the connection resume procedure may comprise a radio resource control connection resume procedure. In some example embodiments, the connection setup procedure may comprise a tracking area update procedure. In some example embodiments, the source core network device may comprise a fifth generation core network device, and the target core network device may comprise an evolved packet core network device.

FIG. 6 shows a flowchart of an example method 600 in accordance with some other example embodiments of the present disclosure. The method 600 can be implemented at the target access network device 130 as shown in FIG. 1. For the purpose of discussion, the method 600 will be described with reference to FIG. 1.

At block 605, the target access network device 130 receives, from the terminal device 105, a connection resume request for initiating a connection resume procedure. At block 610, the target access network device 130 sends, to the source access network device 110, a handover request for retrieving context of the terminal device 105. At block 615, the target access network device 130 receives, from the source access network device 110, a handover response for indicating whether backhaul switching from a source backhaul link between the source access network device 110 and the source core network device 115 to a target backhaul link between the target access network device 130 and the target core network device 135 is required. At block 620, the target access network device 130 sends, to the terminal device 105, a connection resume response based on the handover response.

In some example embodiments, the target access network device 130 may broadcast a connectivity indication to enable a connection resume procedure for data forwarding through the source backhaul link (that is, no backhaul switching) .

In some example embodiments, the target access network device 130 may send the connection resume response to indicate that that the connection resume request is allowed if the handover response indicates that the backhaul switching is unrequired.

In some example embodiments, the target access network device 130 may receive uplink data from the terminal device 105.

In some example embodiments, the target access network device 130 may defer the sending of the connection resume request until a paging time window if extended discontinuous reception is activated. The target access network device 130 may further forward the uplink data to the source access network device 110.

In some example embodiments, the handover response indicates that the backhaul switching is required, the target access network device 130 may send the connection resume response to indicate that that the connection resume request is rejected.

In some example embodiments, the target access network device 130 may receive, from the terminal device 105, a connection setup request to initiate a connection setup procedure. In some example embodiments, the connection setup procedure may comprise a tracking area update procedure.

In some example embodiments, at least one of the connection resume request and the handover request may contain an indication for mobility of the terminal device 105 from a source cell of the source access network device 110.

In some example embodiments, the connection resume procedure may comprise a radio resource control connection resume procedure. In some example embodiments, the source core network device may comprise a fifth generation core network device, and the target core network device comprises an evolved packet core network device.

FIG. 7 shows a flowchart of an example method 700 in accordance with yet other example embodiments of the present disclosure. The method 700 can be implemented at the source access network device 110 as shown in FIG. 1. For the purpose of discussion, the method 700 will be described with reference to FIG. 1.

At block 705, the source access network device 110 receives, from the target access network device 130, a handover request for retrieving context of the terminal device 105. At block 710, the source access network device 110 determines whether backhaul switching from the source backhaul link between the source access network device 110 and the source core network device 115 to the target backhaul link between the target access network device 130 and the target core network device 135 is required. At block 715, the source access network device 110 sends, to the target access network device 130, a handover response based on the determining.

In some example embodiments, the source access network device 110 may receive uplink data from the terminal device 105 via the target access network device 130 in response to the backhaul switching is disabled.

In some example embodiments, the source access network device 110 may send the connection resume response to indicate that that the connection resume request is allowed if the handover response indicates that the backhaul switching is disabled.

In some example embodiments, the source access network device 110 may send, to the source core network device 130, a switching indication to indicate that the source backhaul link is to be switched to the target backhaul link if the backhaul switching is required.

In some example embodiments, the source access network device 110 may release context of the terminal device.

In some example embodiments, the source access network device 110 may send, to the source core network device 115, an indication for mobility of the terminal device 105 from the source cell 120 of the source access network device 115.

In some example embodiments, the handover request contains an indication for mobility of the terminal device 105 from the source cell 120 of the source access network device 115.

In some example embodiments, the source core network device may comprise a fifth generation core network device, and the target core network device comprises an evolved packet core network device.

All operations and features as described above with reference to FIGS. 1-4 are likewise applicable to the methods 500 to 700 and have similar effects. For the purpose of simplification, the details will be omitted.

In some example embodiments, an apparatus capable of performing the

method

500, 600 or 700 may comprise means for performing the respective steps of the

method

500, 600 or 700. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus capable of performing the method 500 comprises: means for determining, at a terminal device served by a source access network device connected to a source core network device, cell reselection from a source cell of the source access network device to a target cell of a target access network device connected to a target core network device; means for receiving, from the target access network device, a connectivity indication to enable a connection resume procedure for data forwarding through a source backhaul link between the source access network device and the source core network device; means for sending, to the target access network device, a connection resume request for initiating a connection resume procedure; and means for receiving, from the target access network device, a connection resume response for indicating whether a connection setup procedure is to be initiated.

In some example embodiments, the connectivity indication may be broadcast by the target access network device.

In some example embodiments, means for sending the connection resume request may comprise: means for sending the connection resume request in response to arrival of uplink data.

In some example embodiments, means for sending the connection resume request in response to the arrival of the uplink data may comprise: means for deferring the sending of the connection resume request until the arrival of the uplink data if a power saving mode is activated.

In some example embodiments, means for sending the connection resume request in response to the arrival of the uplink data may comprise: means for determining whether a time from the arrival of the uplink data to an available triggering opportunity of a connection setup procedure is greater than a predetermined threshold; and means for in response to determining that the time is greater than the predetermined threshold, sending the connection resume request to the target access network device.

In some example embodiments, means for sending the connection resume request may comprise: means for deferring the sending of the connection resume request until a paging time window if extended discontinuous reception is activated.

In some example embodiments, the apparatus may further comprise: means for in response to the connection resume response indicating that the connection resume request is allowed, determining that the connection setup procedure is unrequired; and means for transmitting uplink data to the target access network device.

In some example embodiments, the apparatus may further comprise: means for in response to the connection resume response indicating that the connection resume request is rejected, determining that the connection setup procedure is to be initiated; and means for sending, to the target access network device, a connection setup request to initiate the connection setup procedure.

In some example embodiments, means for sending the connection setup request may comprise: means for entering an idle state; and means for sending the connection setup request in the idle state.

In some example embodiments, means for sending the connection setup request may comprise: means for in response to uplink data to be transmitted, sending the connection setup request to initiate the connection setup procedure.

In some example embodiments, the connection resume request may contain an indication for mobility of the terminal device from a source cell of the source access network device.

In some example embodiments, the connection resume procedure may comprise a radio resource control connection resume procedure.

In some example embodiments, the connection setup procedure may comprise a tracking area update procedure.

In some example embodiments, the source core network device may comprise a fifth generation core network device, and the target core network device may comprise an evolved packet core network device.

In some example embodiments, the apparatus capable of performing the method 600 comprises: means for receiving, at a target access network device connected to a target core network device, a connection resume request for initiating a connection resume procedure from a terminal device served by a source access network device connected to a source core network device; means for sending, to the source access network device, a handover request for retrieving context of the terminal device; means for receiving, from the source access network device, a handover response for indicating whether backhaul switching from a source backhaul link between the source access network device and the source core network device to a target backhaul link between the target access network device and the target core network device is required; and means for sending, to the terminal device, a connection resume response based on the handover response.

In some example embodiments, the apparatus may further comprise: means for broadcasting a connectivity indication to enable a connection resume procedure for data forwarding through the source backhaul link.

In some example embodiments, the means for sending the connection resume response may comprise: means for in response to the handover response indicating that the backhaul switching is unrequired, sending the connection resume response to indicate that that the connection resume request is allowed.

In some example embodiments, the apparatus may further comprise: means for receiving uplink data from the terminal device; and means for forwarding the uplink data to the source access network device.

In some example embodiments, means for sending the connection resume response may comprise: means for in response to the handover response indicating that the backhaul switching is required, sending the connection resume response to indicate that that the connection resume request is rejected.

In some example embodiments, the apparatus may further comprise: means for receiving, from the terminal device, a connection setup request to initiate a connection setup procedure.

In some example embodiments, at least one of the connection resume request and the handover request may contain an indication for mobility of the terminal device from a source cell of the source access network device.

In some example embodiments, the apparatus capable of performing the method 700 comprises: means for receiving, at a source access network device connected to a source core network device, from a target access network device connected to a target core network device, a handover request for retrieving context of a terminal device served by the source access network device; means for determining whether backhaul switching from a source backhaul link between the source access network device and the source core network device to a target backhaul link between the target access network device and the target core network device is required; and means for sending, to the target access network device, a handover response based on the determining.

In some example embodiments, the apparatus may further comprise: means for in response to the backhaul switching being unrequired, receiving uplink data from the terminal device via the target access network device.

In some example embodiments, the apparatus may further comprise: means for in response to the backhaul switching being required, sending, to the source core network device, a switching indication to indicate that the source backhaul link is to be switched to the target backhaul link.

In some example embodiments, the apparatus may further comprise: means for releasing context of the terminal device.

In some example embodiments, the apparatus may further comprise: means for sending, to the source core network device, an indication for mobility of the terminal device from a source cell of the source access network device.

In some example embodiments, the handover request may contain an indication for mobility of the terminal device from a source cell of the source access network device.

FIG. 8 is a simplified block diagram of a device 800 that is suitable for implementing example embodiments of the present disclosure. The device 800 can be implemented at or as a part of the terminal device 105, the target access network device 130 or the source access network device as shown in FIG. 1.

As shown, the device 800 includes a processor 810, a memory 820 coupled to the processor 810, a communication module 830 coupled to the processor 810, and a communication interface (not shown) coupled to the communication module 830. The memory 820 stores at least a program 840. The communication module 830 is for bidirectional communications, for example, via multiple antennas. The communication interface may represent any interface that is necessary for communication.

The program 840 is assumed to include program instructions that, when executed by the associated processor 810, enable the device 800 to operate in accordance with the example embodiments of the present disclosure, as discussed herein with reference to FIGS. 1-7. The example embodiments herein may be implemented by computer software executable by the processor 810 of the device 800, or by hardware, or by a combination of software and hardware. The processor 810 may be configured to implement various example embodiments of the present disclosure.

The memory 820 may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology, such as a non-transitory computer readable storage medium, semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. While only one memory 820 is shown in the device 800, there may be several physically distinct memory modules in the device 800. The processor 810 may be of any type suitable to the local technical network, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 800 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

When the device 800 acts as the terminal device 105 or a part of the terminal device 105, the processor 810 and the communication module 830 may cooperate to implement the method 500 as described above with reference to FIG 5. When the device 800 acts as the target access network device 130 or a part of the target access network device 130, the processor 810 and the communication module 830 may cooperate to implement the method 600 as described above with reference to FIG. 6. When the device 800 acts as the source access network device 110 or a part of the source access network device 110, the processor 810 and the communication module 830 may cooperate to implement the method 700 as described above with reference to FIG 7.

All operations and features as described above with reference to FIGS. 1-7 are likewise applicable to the device 800 and have similar effects. For the purpose of simplification, the details will be omitted.

Generally, various example embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. 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. While various aspects of example embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method 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 present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the

method

500, 600 or 700 as described above with reference to FIGS. 1-7. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various example embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

In the context of the present disclosure, the computer program codes or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable media.

The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , Digital Versatile Disc (DVD) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular example embodiments. Certain features that are described in the context of separate example embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple example embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in languages specific to structural features and/or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Various example embodiments of the techniques have been described. In addition to or as an alternative to the above, the following examples are described. The features described in any of the following examples may be utilized with any of the other examples described herein.

Claims

A method comprising:

determining, at a terminal device served by a source access network device connected to a source core network device, cell reselection from a source cell of the source access network device to a target cell of a target access network device connected to a target core network device;

receiving, from the target access network device, a connectivity indication to enable a connection resume procedure for data forwarding through a source backhaul link between the source access network device and the source core network device;

sending, to the target access network device, a connection resume request for initiating a connection resume procedure; and

receiving, from the target access network device, a connection resume response for indicating whether a connection setup procedure is to be initiated.
The method of claim 1, wherein the connectivity indication is broadcast by the target access network device.
The method of claim 1, wherein sending the connection resume request comprises:

sending the connection resume request in response to arrival of uplink data.
The method of claim 3, wherein sending the connection resume request in response to the arrival of the uplink data comprises:

deferring the sending of the connection resume request until the arrival of the uplink data if a power saving mode is activated.
The method of claim 3, wherein sending the connection resume request in response to the arrival of the uplink data comprises:

determining whether a time from the arrival of the uplink data to an available triggering opportunity of a connection setup procedure is greater than a predetermined threshold; and

in response to determining that the time is greater than the predetermined threshold, sending the connection resume request to the target access network device.
The method of claim 1, wherein sending the connection resume request comprises:

deferring the sending of the connection resume request until a paging time window if extended discontinuous reception is activated.
The method of claim 1, further comprising:

in response to the connection resume response indicating that the connection resume request is allowed, determining that the connection setup procedure is unrequired; and

transmitting uplink data to the target access network device.
The method of claim 1, further comprising:

in response to the connection resume response indicating that the connection resume request is rejected, determining that the connection setup procedure is to be initiated; and

sending, to the target access network device, a connection setup request to initiate the connection setup procedure.
The method of claim 8, wherein sending the connection setup request comprises:

entering an idle state; and

sending the connection setup request in the idle state.
The method of claim 8, wherein sending the connection setup request comprises:

in response to uplink data to be transmitted, sending the connection setup request to initiate the connection setup procedure.
The method of claim 1, wherein the connection resume request contains an indication for mobility of the terminal device from the source cell of the source access network device.
The method of claim 1, wherein the connection resume procedure comprises a radio resource control connection resume procedure.
The method of claim 1, wherein the connection setup procedure comprises a tracking area update procedure.
The method of claim 1, wherein the source core network device comprises a fifth generation core network device, and the target core network device comprises an evolved packet core network device.
A method comprising:

receiving, at a target access network device connected to a target core network device, a connection resume request for initiating a connection resume procedure from a terminal device served by a source access network device connected to a source core network device;

sending, to the source access network device, a handover request for retrieving context of the terminal device;

receiving, from the source access network device, a handover response for indicating whether backhaul switching from a source backhaul link between the source access network device and the source core network device to a target backhaul link between the target access network device and the target core network device is required; and

sending, to the terminal device, a connection resume response based on the handover response.
The method of claim 15, further comprising:

broadcasting a connectivity indication to enable a connection resume procedure for data forwarding through the source backhaul link.
The method of claim 15, wherein sending the connection resume response comprises:

in response to the handover response indicating that the backhaul switching is unrequired, sending the connection resume response to indicate that that the connection resume request is allowed.
The method of claim 17, further comprising:

receiving uplink data from the terminal device; and

forwarding the uplink data to the source access network device.
The method of claim 15, wherein sending the connection resume response comprises:

in response to the handover response indicating that the backhaul switching is required, sending the connection resume response to indicate that that the connection resume request is rejected.
The method of claim 19, further comprising:

receiving, from the terminal device, a connection setup request to initiate a connection setup procedure.
The method of claim 20, wherein the connection setup procedure comprises a tracking area update procedure.
The method of claim 15, wherein at least one of the connection resume request and the handover request contains an indication for mobility of the terminal device from a source cell of the source access network device.
The method of claim 15, wherein the connection resume procedure comprises a radio resource control connection resume procedure.
The method of claim 15, wherein the source core network device comprises a fifth generation core network device, and the target core network device comprises an evolved packet core network device.
A method comprising:

receiving, at a source access network device connected to a source core network device, from a target access network device connected to a target core network device, a handover request for retrieving context of a terminal device served by the source access network device;

determining whether backhaul switching from a source backhaul link between the source access network device and the source core network device to a target backhaul link between the target access network device and the target core network device is required; and

sending, to the target access network device, a handover response based on the determining.
The method of claim 25, further comprising:

in response to the backhaul switching being unrequired, receiving uplink data from the terminal device via the target access network device.
The method of claim 25, further comprising:

in response to the backhaul switching being required, sending, to the source core network device, a switching indication to indicate that the source backhaul link is to be switched to the target backhaul link.
The method of claim 27, further comprising:

releasing context of the terminal device.
The method of claim 25, further comprising:

sending, to the source core network device, an indication for mobility of the terminal device from a source cell of the source access network device.
The method of claim 25, wherein the handover request contains an indication for mobility of the terminal device from a source cell of the source access network device.
The method of claim 25, wherein the source core network device comprises a fifth generation core network device, and the target core network device comprises an evolved packet core network device.
A device comprising:

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the device to perform the method of any of claims 1-14.
A device comprising:

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the device to perform the method of any of claims 15-24.
A device comprising:

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the device to perform the method of any of claims 25-31.
A network comprising the device of claim 32, the device of claim 33 and device of claim 34.
An apparatus comprising:

means for determining, at a terminal device served by a source access network device connected to a source core network device, cell reselection from a source cell of the source access network device to a target cell of a target access network device connected to a target core network device;

means for receiving, from the target access network device, a connectivity indication to enable a connection resume procedure for data forwarding through a source backhaul link between the source access network device and the source core network device;

means for sending, to the target access network device, a connection resume request for initiating a connection resume procedure, the connection resume request indicating the handover; and

means for receiving, from the target access network device, a connection resume response for indicating whether a connection setup procedure is to be initiated.
An apparatus comprising:

means for receiving, at a target access network device connected to a target core network device, a connection resume request for initiating a connection resume procedure from a terminal device served by a source access network device connected to a source core network device;

means for sending, to the source access network device, a handover request for retrieving context of the terminal device;

means for receiving, from the source access network device, a handover response for indicating whether backhaul switching from a source backhaul link between the source access network device and the source core network device to a target backhaul link between the target access network device and the target core network device is required; and

means for sending, to the terminal device, a connection resume response based on the handover response.
An apparatus comprising:

means for receiving, at a source access network device connected to a source core network device, from a target access network device connected to a target core network device, a handover request for retrieving context of a terminal device served by the source access network device;

means for determining whether backhaul switching from a source backhaul link between the source access network device and the source core network device to a target backhaul link between the target access network device and the target core network device is required; and

means for sending, to the target access network device, a handover response based on the determining.
A computer readable storage medium comprising program instructions stored thereon, the instructions, when executed by a processor of a device, causing the device to perform the method of any of claims 1-14.
A computer readable storage medium comprising program instructions stored thereon, the instructions, when executed by a processor of a device, causing the device to perform the method of any of claims 15-24.
A computer readable storage medium comprising program instructions stored thereon, the instructions, when executed by a processor of a device, causing the device to perform the method of any of claims 25-31.