Informing of discarded data unit

Abstract

Example embodiments of the present disclosure are directed to informing of a discarded data unit. A method for wireless communication includes determining that at least one data unit of a plurality of downlink data units has been discarded by a second apparatus; and sending, to a third apparatus, an indication of the at least one discarded downlink data unit, during termination point change of at least one bearer of a first apparatus from the second apparatus to the third apparatus.

Description

INFORMING OF DISCARDED DATA UNITFIELDS

[0001] Various example embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to apparatuses, methods and computer readable storage medium for informing of a discarded data unit.BACKGROUND

[0002] A packet data convergence protocol sequence number (PDCP SN) gap report is introduced for extended reality (XR) enhancements of New Radio (NR) in the third-generation partnership project (3GPP) Release 18 (Rel-18). The PDCP SN gap report is a PDCP control protocol data unit (PDU) with which a transmitting PDCP entity may inform a receiving PDCP entity of PDCP COUNT values of discarded PDCP service data units (SDUs). The PDCP COUNT is a 32-bit running sequence number assigned to PDCP SDUs. With the PDCP SN gap report, the receiving PDCP entity may know which PDCP SDUs it should not expect to receive, thereby expediting delivery of received PDCP SDUs to upper layers when the receiving PDCP entity delivers the received PDCP SDUs to the upper layers in an increasing order of PDCP COUNT values.SUMMARY

[0003] In a first aspect of the present disclosure, there is provided a second apparatus for wireless communication. The second apparatus includes at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus at least to: determine that at least one data unit of a plurality of downlink data units has been discarded by the second apparatus; and send, to a third apparatus, an indication of the at least one discarded downlink data unit, during termination point change of at least one bearer of a first apparatus from the second apparatus to the third apparatus.

[0004] In a second aspect of the present disclosure, there is provided a third apparatus for wireless communication. The third apparatus includes at least one processor; and at least onememory storing instructions that, when executed by the at least one processor, cause the third apparatus at least to: receive, from a second apparatus, a request for a termination point change of at least one bearer of a first apparatus from the second apparatus to the third apparatus; and receive, from the second apparatus, during the termination point change, an indication of at least one discarded data unit of a plurality of downlink data units.

[0005] In a third aspect of the present disclosure, there is provided a second apparatus for wireless communication. The second apparatus includes means for determining that at least one data unit of a plurality of downlink data units has been discarded by the second apparatus; and means for sending, to a third apparatus, an indication of the at least one discarded downlink data unit, during termination point change of at least one bearer of a first apparatus from the second apparatus to the third apparatus.

[0006] In a fourth aspect of the present disclosure, there is provided a third apparatus for wireless communication. The third apparatus includes means for receiving, from a second apparatus, a request for termination point change of at least one bearer of a first apparatus from the second apparatus to the third apparatus; and means for receiving, from the second apparatus, during the termination point change, a first indication of at least one discarded data unit of a plurality of downlink data units.

[0007] In a fifth aspect of the present disclosure, there is provided a first apparatus for wireless communication. The first apparatus for wireless communication includes: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus at least to: determine to trigger at least one report on at least one discarded data unit of a plurality of data units, during a termination point change of at least one bearer of the first apparatus from a second apparatus to a third apparatus; and send, in response to the determining to trigger the at least one report, the at least one report to at least one of the second apparatus or the third apparatus.

[0008] In a sixth aspect of the present disclosure, there is provided a second apparatus for wireless communication. The second apparatus for wireless communication includes at leastone processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus at least to: initiate a termination point change of at least one bearer of a first apparatus from the second apparatus to a third apparatus; and receive, from the first apparatus, during the termination point change, at least one report on at least one discarded data unit of a plurality of data units.

[0009] In a seventh aspect of the present disclosure, there is provided a third apparatus for wireless communication. The third apparatus for wireless communication includes at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the third apparatus at least to: receive, from a second apparatus, a request for a termination point change of at least one bearer of a first apparatus from the second apparatus to the third apparatus; and receive, from the first apparatus, during the termination point change, at least one report on discarding at least one data unit of a plurality of data units by the first apparatus.

[0010] In an eighth aspect of the present disclosure, there is provided a first apparatus for wireless communication. The first apparatus includes means for determining to trigger at least one report on at least one discarded data unit of a plurality of data units during a termination point change of at least one bearer of the first apparatus from a second apparatus to a third apparatus; and means for sending, in response to the determining to trigger the at least one report, the at least one report to at least one of the second apparatus or the third apparatus.

[0011] In a ninth aspect of the present disclosure, there is provided a second apparatus for wireless communication. The second apparatus includes means for initiating a termination point change of at least one bearer of a first apparatus from the second apparatus to a third apparatus; and means for receiving, from the first apparatus, during the termination point change, at least one report on at least one discarded data unit of a plurality of data units.

[0012] In a tenth aspect of the present disclosure, there is provided a third apparatus for wireless communication. The third apparatus includes means for receiving, from a second apparatus, a request for a termination point change of a first apparatus from the secondapparatus to the third apparatus; and means for receiving, from the first apparatus, during the termination point change, at least one report on discarding at least one data unit of a plurality of data units by the first apparatus.

[0013] In an eleventh aspect of the present disclosure, there is provided a second apparatus for wireless communication. The second apparatus includes at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus at least to: determine that at least one data unit of a plurality of uplink data units has been discarded by a first apparatus; and send, to a third apparatus, an indication of the at least one discarded uplink data unit, during a termination point change of at least one bearer of the first apparatus from the second apparatus to the third apparatus.

[0014] In a twelfth aspect of the present disclosure, there is provided a third apparatus for wireless communication. The third apparatus includes at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the third apparatus at least to: receive, from a second apparatus, a request for termination point change of at least one bearer of a first apparatus from the second apparatus to the third apparatus; and receive, from the second apparatus, during the termination point change, an indication of at least one discarded data unit of a plurality of uplink data units.

[0015] In a thirteenth aspect of the present disclosure, there is provided a second apparatus for wireless communication. The second apparatus includes means for determining that at least one data unit of a plurality of uplink data units has been discarded by a first apparatus; and means for sending, to a third apparatus, an indication of the at least one discarded uplink data unit, during a termination point change of at least one bearer of the first apparatus from the second apparatus to the third apparatus.

[0016] In a fourteenth aspect of the present disclosure, there is provided a third apparatus. The third apparatus includes means for receiving, from a second apparatus, a request for termination point change of at least one bearer of a first apparatus from the second apparatus to the third apparatus; and means for receiving, from the second apparatus, during thetermination point change, an indication of at least one discarded data unit of a plurality of uplink data units.

[0017] It is to be understood that the Summary section is not intended to identify key or essential features of 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

[0018] Some example embodiments will now be described with reference to the accompanying drawings, where:

[0019] FIG. 1 illustrates an example communication environment in which example embodiments of the present disclosure may be implemented;

[0020] FIG. 2 illustrates a signaling diagram for informing of a discarded data unit according to some example embodiments of the present disclosure;

[0021] FIG. 3 illustrates a signaling diagram for sequence number (SN) Status Transfer procedure according to some example embodiments of the present disclosure;

[0022] FIG. 4 illustrates a signaling diagram for informing of a discarded data unit according to some example embodiments of the present disclosure;

[0023] FIG. 5 illustrates a flowchart of a method implemented at a first apparatus according to some example embodiments of the present disclosure;

[0024] FIG. 6 illustrates a flowchart of a method implemented at a second apparatus according to some example embodiments of the present disclosure;

[0025] FIG. 7 illustrates a flowchart of a method implemented at a third apparatus according to some example embodiments of the present disclosure;

[0026] FIG. 8 illustrates a flowchart of a method implemented at a second apparatus according to some other example embodiments of the present disclosure;

[0027] FIG. 9 illustrates a flowchart of a method implemented at a third apparatus according to some other example embodiments of the present disclosure;

[0028] FIG. 10 illustrates a flowchart of a method implemented at a second apparatus according to some other example embodiments of the present disclosure;

[0029] FIG. 11 illustrates a flowchart of a method implemented at a third apparatus according to some other example embodiments of the present disclosure;

[0030] FIG. 12 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

[0031] FIG. 13 illustrates a block diagram of an example computer readable medium in accordance with some example embodiments of the present disclosure.

[0032] Throughout the drawings, the same or similar reference numerals represent the same or similar element.DETAILED DESCRIPTION

[0033] Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these 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. Embodiments described herein may be implemented in various manners other than the ones described below. Multiple figures may be used to illustrate the described embodiments.

[0034] 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.

[0035] References in the present disclosure to “one embodiment,” “an embodiment,” “an example embodiment,” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodimentincludes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0036] It shall be understood that although 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 termed 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.

[0037] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0038] As used herein, unless stated explicitly, performing a step “in response to A” does not indicate that the step has to be performed immediately after “A” occurs and one or more intervening steps may be included.

[0039] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. 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. It will be further understood that the terms “comprises”, “comprising”, “has”, “having”, “includes” and / or “including”, when used herein, specify the presence of stated features, elements, and / or components etc., but do not preclude the presence or addition of one or more other features, elements, components and / or combinations thereof.

[0040] 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 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.

[0041] 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 server, a cellular network device, or other computing or network device.

[0042] As used herein, the term “communication network” refers to a network following any suitable communication standards, such as New Radio (NR), Long Term Evolution (LTE), LTE-Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), High-Speed Packet Access (HSPA), Narrow Band Internet of Things (NB-IoT) and so on. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should notbe seen as limiting the scope of the present disclosure to only the aforementioned system.

[0043] As used herein, the term “network device” or “network access device” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP), for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio head (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node such as a femto, a pico, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, an aircraft network device, and so forth, depending on the applied terminology and technology. In some example embodiments, radio access network (RAN) split architecture includes a Centralized Unit (CU) and a Distributed Unit (DU) at an IAB donor node. An IAB node includes a Mobile Terminal (IAB -MT) part that behaves like a UE toward the parent node, and a DU part of an IAB node behaves like a base station toward the next-hop IAB node.

[0044] The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), a Portable Subscriber Station, a Mobile Station (MS), or an Access Terminal (AT). The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE), an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chaincontexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like. The terminal device may also correspond to a Mobile Termination (MT) part of an IAB node (e.g., a relay node). In the following description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

[0045] As described above, a PDCP SN gap report is introduced in 3GPP Rel-18 for XR enhancements. For example, transmitting and receiving operations of the PDCP SN gap report are specified in the 3GPP standards. Regarding the transmitting operation, for Unacknowledged mode (UM) data radio bearers (DRBs) and Acknowledged mode (AM) DRBs configured by upper layers to send the PDCP SN gap report in uplink, the transmitting PDCP entity may trigger the PDCP SN gap report when some conditions are met. For example, if the PDCP SDU(s) are discarded, there is at least one stored PDCP SDU(s) which is associated with a COUNT value larger than the COUNT value associated to the discarded PDCP SDU(s), and the discarded PDCP SDU(s) have not been submitted by radio link control (RFC) to lower layers, then the PDCP SN gap report may be sent.

[0046] If a PDCP SN gap report is triggered, the transmitting PDCP entity may compile the PDCP SN gap report and submit the PDCP SN gap report to lower layers for Uu interface. Furthermore, the transmitting PDCP entity may compile the PDCP SN gap report. For example, the transmitting PDCP entity may set the first discarded COUNT (FDC) field to the smallest COUNT value among those associated with the discarded PDCP SDUs. If more than one PDCP SDUs is discarded, the transmitting PDCP entity may allocate a Discard Bitmap field of length in bits equal to the number of COUNT values from and not including the first discarded PDCP SDU up to and including the last discarded PDCP SDU. This length may be rounded up to the next multiple of 8, or up to and including a PDCP SDU for which the resulting PDCP Control PDU size is equal to 9000 bytes, whichever comes first. For example, the transmitting PDCP entity may set in the discard bitmap field as ‘0’ for all PDCP SDUs that have not been discarded and set in the discard bitmap field as ‘1’ for all PDCP SDUs that have been discarded. It is to be noted that it is up to UE implementation how to limit the frequency of the PDCP SN gapreporting.

[0047] Upon reception of a PDCP SN gap report from lower layers, the receiving PDCP entity may consider each PDCP SDU with the bit in the discard bitmap set to ‘ U or with the associated COUNT value equal to the value FDC field as discarded. If RX_DELIV is less than or equal to the largest COUNT value associated with the discarded PDCP SDUs, and if RX_NEXT is less than or equal to COUNT value associated with the last discarded PDCP SDU indicated in the PDCP SN gap report, the receiving PDCP entity may update the RX_NEXT to the largest COUNT value associated with the discarded PDCP SDU plus one. RX_DELIV represents the COUNT value of the first PDCP SDU that has not been delivered to the upper layers but is still awaited. RX_NEXT represents the COUNT value of the next PDCP SDU that the receiving PDCP entity expects to receive.

[0048] If RX_DELIV is equal to any COUNT value associated with the discarded PDCP SDU(s), then after performing header decompression if not decompressed before, the receiving PDCP entity may deliver all stored PDCP SDUs with consecutively associated COUNT values starting from RX_DELIV + 1 to upper layers in an ascending order of the associated COUNT value. Consecutively associated COUNT value(s) include COUNT value(s) of both the stored PDCP SDU(s) and PDCP SDU(s) which are considered as discarded. Then, the receiving PDCP entity may update the RX_DELIV to the COUNT value of the first PDCP SDU which has not been delivered to upper layers and is not considered as discarded, with COUNT value greater than RX_DELIV.

[0049] If a reordering timer, referring to the t-Reordering, is running and if RX_DELIV is greater than or equal to RX_REORD, the receiving PDCP entity may stop and reset the t- Reordering. If the t-Reordering is not running and RX_DELIV is less than RX_NEXT, the receiving PDCP entity may update RX_REORD to be RX_NEXT and start t-Reordering. RX_REORD represents the COUNT value following the COUNT value associated with the PDCP SDU which triggered the t-Reordering.

[0050] In the 3GPP Release 19 (Rel-19) continuation, REC AM may be improved to bebetter suited for XR applications. On radio bearers mapped on RLC AM, the PDCP COUNT may not be reset as part of a PDCP re-establishment procedure. The PDCP re-establishment procedure may be executed by the UE whenever a network-side PDCP-termination point changes and a PDCP security key needs to be changed, such as during handover from a source gNB to a target gNB. At such a termination-point change, an Xn application protocol (XnAP) SN Status Transfer procedure may be used to transfer from a source network node to a target network node records of which uplink PDCP SDUs have been successfully received from the UE and which uplink PDCP SDUs are not successfully received. The status may include at least the lowest COUNT value of an unreceived PDCP SDU whose reception is still expected, and optionally (if PDCP SDUs with higher COUNT values have been received) a bitmap indicating for immediately following higher COUNT values whether or not the PDCP SDU has been received.

[0051] Moreover, if a radio bearer, mapped on RLC AM, experiences a change in its network-side PDCP-termination point, the UE may execute the related PDCP re-establishment procedure shortly after the UE has sent a PDCP SN gap report to the network or the source PDCP network node has sent a PDCP SN gap report to the UE. There may be the following three scenarios associated with the PDCP re-establishment procedure, for example, including Scenario A, Scenario B and Scenario C.

[0052] In Scenario A, the previously sent PDCP SN gap report was not received. RLC or medium access control (MAC) transmissions of the PDCP SN gap report do not complete in time before the RLC memory is flushed (because the underlying RLC entities are released or re-established). In this case, the receiving PDCP entity, such as at the target network node or the UE, may wait to receive PDCP SDUs that the transmitting PDCP entity has actually discarded, and delay delivery of received PDCP SDUs with higher COUNT values to upper layers.

[0053] In Scenario B, the previously sent PDCP SN gap report was received by the source PDCP network node. For the PDCP SDUs indicated in the PDCP SN gap report as discarded,the source network node indicates “has been received correctly” in the XnAP SN Status Transfer sent to the target network node. In this case, given this XnAP SN Status Transfer indication, the target network node may wait to receive those PDCP SDUs to be forwarded by the source network node, and delay delivery of received PDCP SDUs with higher COUNT values to upper layers.

[0054] In Scenario C, the previously sent PDCP SN gap report was received by the source PDCP network node. For the PDCP SDUs indicated in the PDCP SN gap report as discarded, the source network node indicates “has not been received” in the XnAP SN Status Transfer sent to the target network node. In this case, given this XnAP SN Status Transfer indication the target network node may wait to receive those PDCP SDUs from the UE, and delay delivery of received PDCP SDUs with higher COUNT values to upper layers.

[0055] Example embodiments of the present disclosure propose a solution for informing of a discarded data unit. In some example embodiments, a first apparatus (such as a UE) may determine to trigger a report on a discarded data unit of a plurality of data units during a termination point change of at least one bearer of the first apparatus from a second apparatus (such as a source network device) to a third apparatus (such as a target network device). Correspondingly, the second apparatus and / or the third apparatus may receive the report on the discarded data unit, during the termination point change.

[0056] In some other example embodiments, if the second apparatus determines that a data unit of a plurality of data units has been discarded by the first apparatus or by the second apparatus, the second apparatus may send, to the third apparatus, an indication of the discarded data unit, during a termination point change of at least one bearer of the first apparatus from the second apparatus to the third apparatus. Correspondingly, the third apparatus may receive the indication of the discarded data unit.

[0057] With the report on a discarded data unit, the second apparatus and / or the third apparatus may determine that some data units are not expected. In this way, transmission delay of data units may be reduced.

[0058] FIG. 1 illustrates an example communication environment 100 in which example embodiments of the present disclosure may be implemented. As shown in FIG. 1, the communication network 100 may include a first apparatus 110 which may be, for example, a terminal device such as a UE. The communication network 100 may further include a second apparatus 120 and a third apparatus 130. The second apparatus 120 may operate as a network device such as a BS, a gNB and an eNB, and provide at least one cell, for example, including a cell 125. The third apparatus 130 may also operate as a network device such as a BS, a gNB and an eNB, and provide at least one cell including a cell 135. Either or both of the cells 125 and 135 may serve the first apparatus 110.

[0059] It is to be understood that the numbers and types of apparatuses are illustrated in FIG. 1 only for the purpose of illustration without suggesting any limitations. The communication environment 100 may include any suitable numbers and types of apparatuses for implementing embodiments of the present disclosure.

[0060] In the example embodiments where the first apparatus 110 operates as a terminal device and the second apparatus 120 or the third apparatus 130 operates a network device, a transmission direction from the second apparatus 120 or the third apparatus 130 to the first apparatus 110 may be referred to as a downlink (DL), and a transmission direction from the first apparatus 110 to the second apparatus 120 or the third apparatus 130 may be referred to as an uplink (UL). In DL, the second apparatus 120 or the third apparatus 130 is a transmitting (TX) device (or a transmitter) and the first apparatus 110 is a receiving (RX) device (or a receiver). In UL, the first apparatus 110 is a TX device and the second apparatus 120 or the third apparatus 130 is an RX device. In the example embodiments where both the first apparatus 110 and the second apparatus 120 or the third apparatus 130 operates as terminal devices, a link between the first apparatus 110 and the second apparatus 120 or the third apparatus 130 may be referred to as a sidelink (SL). In SL, one of the first apparatus 110 and the second apparatus 120 (or the third apparatus 130) is a Tx device, and the other of the first apparatus 110 and the second apparatus 120 or the third apparatus 130 is a Rx device.

[0061] In the following, for the purpose of illustration, some example embodiments are described with the first apparatus 110 operating as a terminal device and the second apparatus 120 (or the third apparatus 130) operating as a network device. However, in some example embodiments, operations described with respect to a terminal device may be implemented at a network device or other devices, and operations described with respect to a network device may be implemented at a terminal device or other devices.

[0062] Communications in the communication environment 100 may be implemented according to any proper communication protocol(s), including, but not limited to, cellular communication protocols of the first generation (1G), the second generation (2G), the third generation (3G), the fourth generation (4G), the fifth generation (5G), the sixth generation (6G), and the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and / or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, including but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple- Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), Discrete Fourier Transform spread OFDM (DFT-s-OFDM) and / or any other technologies currently known or to be developed in the future.

[0063] Multi-radio access technology (Multi-RAT) Dual Connectivity (MR-DC) may be allowed in the communication environment 100. In MR-DC, various bearer type changes may be supported, for example, including a master cell group (MCG) bearer to / from a split bearer, an MCG bearer to / from a secondary cell group (SCG) bearer, and an SCG bearer to / from a split bearer. A bearer termination point change may be supported for the various bearer types, and may be performed with or without a bearer type change. An example of the bearer termination point change may be a master node (MN) terminated bearer to / from a secondary node (SN) terminated bearer.

[0064] In the communication environment 100, a radio bearer has been established between the first apparatus 110 and the second apparatus 120 for transmission of data units (for example, PDCP SDUs). When the first apparatus 110 is moving, for example, the first apparatus 110 may move from cell 125 towards the cell 135, a bearer termination point change of the first apparatus 110 may be performed from the second apparatus 120 to the third apparatus 130. Examples of the bearer termination point change include a change of a Primary Cell (Pcell), also called handover, and bearer-type changes between an MN-terminated and an SN- terminated bearer when the UE is configured with Dual Connectivity (DC). In various example embodiments, information about a discarded data unit may be transferred among the first apparatus 110, the second apparatus 120 and the third apparatus 130 during the bearer termination point change of the first apparatus 110. Some example implementations for informing of a discarded data unit will be described below with reference to FIGS. 2 to 4.

[0065] FIG. 2 shows a signaling diagram for communications between the first apparatus 110, the second apparatus 120 and the third apparatus 130 for informing of a discarded data unit according to some example embodiments of the present disclosure.

[0066] As shown in FIG. 2, the second apparatus 120 (such as a source network device) may initiate (205) a termination point change of at least one bearer of the first apparatus 110 (such as a terminal device) from the second apparatus 120 to the third apparatus 130 (such as a target network device). Correspondingly, the third apparatus 130 may receive (210), from the second apparatus 120, a request (206) for the termination point change.

[0067] The second apparatus 120 may initiate (205) the termination point change based on any suitable rule. In some example embodiments, the second apparatus 120 may receive a measurement report (423) from the first apparatus 110. Based on the measurement report, the second apparatus 120 may determine whether to change a termination point for one or more bearers of the first apparatus 110 to the third apparatus 130. If the second apparatus 120 determines to change the termination point, the second apparatus 120 may transmit a handover request (427) or a secondary node modification request to the third apparatus 130 to initiate thetermination point change of at least one bearer of the first apparatus 110 from the second apparatus 120 to the third apparatus 130.

[0068] According to some example embodiments of the present disclosure, illustrated to as Option 1 in FIG. 2, the first apparatus 110 may trigger at least one report (220-1 or 220-2, 445 or 459) on a discarded data unit (425-1) during the termination point change. As shown, the first apparatus 110 may determine (215) to trigger at least one report (220-1 or 220-2, 445 or 459) on the discarded data unit (425-1) of a plurality of data units (425) during a termination point change of at least one bearer of the first apparatus from the second apparatus 120 to the third apparatus 130.

[0069] The plurality of data units (425) may be in any suitable format or structure. In some example embodiments, the plurality of data units (425) may include PDCP SDUs. The report (220-1 or 220-2, 445 or 459) on the discarded data unit (425-1) may be implemented in any suitable message. In some example embodiments, the report (220-1 or 220-2, 445 or 459) may include a PDCP SN gap report (458) for the discarded data unit (425-1).

[0070] The first apparatus 110 may determine to trigger the report ((220-1 or 220-2, 445 or 459) on the discarded data unit in any suitable ways. In some example embodiments, the first apparatus 110 may determine to trigger the report (220-1 or 220-2, 445 or 459) based on the discarded data unit (425-1) having satisfied at least one condition. In some example embodiments, the at least one condition may include a condition that no confirmation of successful delivery of a previous report (431) for the discarded data unit (425-1) is received by the first apparatus 110. For example, the first apparatus 110 may trigger a PDCP SN gap report (445 or 459) if there is an outstanding PDCP SN gap report (431) sent by the first apparatus 110 for which no confirmation of successful delivery of the previous report (431) for the discarded data unit (425-1) was received from lower layers (e.g., a RLC layer) before the PDCP re-establishment.

[0071] In some other example embodiments, the at least one condition may include a condition that a first count value (VI) of the at least one discarded data unit (425-1) is greaterthan a second count value (V2) of a reference discarded data unit (425-2) but less than a third count value (V3) of a non-discarded data unit (425-3), where a confirmation of successful delivery of the reference discarded data unit (425-2) to the second apparatus (120, 410) has been received by the first apparatus 110. In some example embodiments, the second count value (V2) of the reference discarded data unit (425-2) may be a maximum count value (Vmax) of at least one reference discarded data units (425-2, 425-x), where a confirmation of successful delivery of the at least one reference discarded data unit (425-2, 425-x) has been received by the first apparatus 110. For example, the first apparatus 110 may trigger a PDCP SN gap report (459) if one or more uplink PDCP SDUs (e.g., 425-1) have been discarded whose first COUNT values (VI) are greater than a highest COUNT value (V2) of one or more PDCP SDUs (425-2, 425-x) discarded after the successful delivery of the one or more PDCP SDUs (425-2, 425-x), but are less than the third COUNT value (V3) of at least one non-discarded SDU (425-3).

[0072] In response to the determining to trigger the report (220-1 or 220-2, 445 or 459), as shown in FIGS. 2 and 4, the first apparatus 110 may send (220), the one or more report (220-1 or 220-2, 445 or 459) on the one or more discarded data unit (425-1) to at least one of the second apparatus 120 or the third apparatus 130. Correspondingly, during the termination point change, the second apparatus 120 and / or the third apparatus 130 may receive (225, 230), from the first apparatus 110, the report (220-1 or 220-2, 445 or 459) for the discarded data unit (425- 1).

[0073] In some example embodiments, based on the report, the second apparatus 120 and / or the third apparatus 130 may determine that the discarded data unit (425-1) is unexpected to be received. Accordingly, transmission efficiency and processing efficiency of the plurality of data units (425) may be improved.

[0074] In some example embodiments, the determining (215) to trigger the report (220-1 or 220-2, 445 or 459) for the discarded data unit (425-1) may be executed during PDCP reestablishment (442). For example, the first apparatus 110 may trigger a PDCP SN gap report (445 or 459) as part of the PDCP re-establishment procedure. Then, the sending (220) of thereport (220-1 or 220-2, 445 or 459) may be executed as part of the termination point change.

[0075] An example implementation of triggering the report (220-1 or 220-2, 445 or 459) on the discarded data unit (425-1) will be discussed below by taking 3GPP TS 38.323 as an example.

[0076] According to some other example embodiments of the present disclosure, illustrated as Option 2 in FIGS. 2 and 4, the second apparatus 120, 410 may send to the third apparatus 130 an indication (241, 449) of a data unit (one or more of 242, 425-1) that has been discarded by the first apparatus 110, 405, during a termination point change of at least one bearer of the first apparatus 110 from the second apparatus (120, 410) to the third apparatus 130, 415.

[0077] In Option 2, as shown in FIGS. 2 and 4, after the second apparatus 120 initiates (205) the termination point change, the second apparatus 120 may determine (in step 235, 446) that at least one data unit (one or more of 242, 425-1) of a plurality of uplink data units (425) has been discarded by the first apparatus 110. Then, the second apparatus 120, 410 may send (240, 448), to the third apparatus (130, 415), an indication (241, 449) of the at least one discarded uplink data unit (one or more of 242, 425-1), during the termination point change. For example,the second apparatus 120 may send an indication (241) of the first COUNT values (VI) of first uplink PDCP SDUs (242, 425-1) discarded by the first apparatus (110, 405) to the third apparatus (130, 415).

[0078] Correspondingly, the third apparatus 130 may receive (in step 245) the indication (241, 449) of the discarded uplink data unit (242, 425-1) from the second apparatus 120 during the termination point change. In some example embodiments, based on such an indication (241, 449), the third apparatus 130 may determine (452) that the discarded uplink data unit (242, 425-1) is unexpected to be received by the third apparatus (130, 415). Accordingly, transmission delay and processing delay of the plurality of uplink data units (425) may be reduced. Moreover, in the example embodiments where both the second apparatus (120, 410) and the third apparatus (130, 415) operate as network devices, the messaging between the second apparatus 120 and the third apparatus 130 may further save radio resources.

[0079] The second apparatus 120 may determine (235) the discarding of the data unit (one or more of 242, 425-1) in any suitable way. In some example embodiments, the second apparatus 120 may receive (225, 444), from the first apparatus 110, a report (220-1, 445) for the discarded data unit (one or more of 242, 425-1). In some example embodiments, the report (220-1, 445) for the discarded data unit may include a PDCP SN gap report (431). Based on this report (220-1, 445), the second apparatus 120 may determine (235) that the data unit (one or more of 242, 425-1) has been discarded by the first apparatus 110.

[0080] After determining (235) the discarded data unit (one or more of 242, 425-1), the second apparatus 120 may determine to send the indication (241, 449) of the at least one discarded uplink data unit (one or more of 242, 425-1) based on some rules. In some example embodiments, the second apparatus 120 may send the indication (241, 449) based on determining that the at least one discarded uplink data unit (one or more of 242, 425-1) has satisfied at least one condition.

[0081] In some example embodiments, the at least one condition may include a condition that a first count value (VI) of a first uplink discarded data unit (425-1) is greater than a fourthcount value (V4) of an unreceived uplink data unit (425-4) that is unreceived but still expected from the first apparatus 110. The count value (V4) of the unreceived uplink data unit (425-4) is to be indicated to the third apparatus 130. In some example embodiments, the count value (V4) of the unreceived uplink data unit (425-4) may be a lowest count value (Vx) of at least one unreceived uplink data unit (425-3, 425-4) that is unreceived but still expected from the first apparatus 110. In some example embodiments, the lowest count (Vx) is to be indicated to the third apparatus 130 in a SN Status Transfer message (315).

[0082] The indication (241, 449) of the at least one discarded uplink data unit (242, 425-1) may be sent by the second apparatus 120 to the third apparatus 130 in any suitable message. In one example, the indication (241, 449) of the at least one discarded uplink data unit (242, 425-1) may be sent in the SN Status Transfer message (315, 447). In another example, the indication (241) of the at least one discarded uplink data unit (242, 425-1) may be sent in a message separate from the SN Status Transfer message (315, 447).

[0083] For example, in the example embodiments where the second apparatus (120, 410) operates as a source network device and the third apparatus (130, 415) operates as a target network device, to transfer from the second apparatus (120, 410) to the target network device (130, 415) the records of which PDCP SDUs (425-2) have been successfully received from the first apparatus 110 (either discarded or not discarded yet by the first apparatus 110) and which uplink PDCP SDUs (one or more of 242, 425-1, 425-4) have not been successfully received from the first apparatus 110 (either discarded or not discarded by the first apparatus 110), the XnAP SN Status Transfer procedure may be used.

[0084] FIG. 3 illustrates a signaling diagram for SN Status Transfer procedure according to some example embodiments of the present disclosure. As shown in FIG. 3, in an SN Status Transfer procedure, a source NG-RAN node 305 (as an example of the second apparatus 120) may send a SN Status Transfer message (315) to a target NG-RAN node 310 (as an example of the third apparatus 130), indicating which PDCP SDU (425-2) may be received or sent based on the PDCP SNs. This SN Status Transfer message (315) includes the PDCP count value tobe assigned to a downlink SDU to be sent to a UE (as an example of the first apparatus 110) (DL Count) and the first (i.e., lowest) PDCP count value of a missing (i.e., unreceived) uplink SDU (one or more of 242, 425-1) to be received from the UE (UL Count). This may help in maintaining the continuity of the data flow and preventing data loss or duplication during the termination-point change.

[0085] According to some other example embodiments of the present disclosure, illustrated as Option 3 in FIGS. 2 and 4, the second apparatus 120 may send to the third apparatus 130 an indication (241, 449) of at least one downlink data unit (258, 433-1) that has been discarded (434) by the second apparatus 120, during a termination point change of at least one bearer of the first apparatus 110 from the second apparatus 120 to the third apparatus 130.

[0086] In Option 3, as shown in FIGS. 2 to 4, the second apparatus 120 may determine (250,446) that a data unit (one or more of 258, 433-1) of a plurality of downlink data units (433) has been discarded by the second apparatus 120. Then, the second apparatus 120 may send (255, 448), to the third apparatus 130, a first indication (256, 449) of the discarded downlink data unit (one or more of 258, 433-1), during the termination point change. For example, the second apparatus 120 may generate and send a first indication (256, 449) of COUNT values (V5) of discarded downlink SDUs (433-1) to the third apparatus 130. Correspondingly, during the termination point change, the third apparatus 130 may receive (see step 260) the first indication (256) of the discarded downlink data unit (258, 433-1) from the second apparatus 120.

[0087] In some example embodiments, the first indication (256, 449) of the discarded downlink data unit (258, 433-1) may be sent in a SN status transfer message (315, 447). Alternatively, the first indication (256) of the discarded downlink data unit (258) may be sent in a message separate from the SN status transfer message (315, 447). For example, as shown in FIG. 3, the source NG-RAN node 305 may also include the count values of the discarded downlink SDUs (one or more of 258, 433-x) in the SN STATUS TRANSFER message (315,447) sent to the target NG-RAN node 310.

[0088] In some example embodiments, the third apparatus (130, 415) may relay thisinformation, about the data unit (258, 433-1) discarded by the second apparatus (120, 410), to the first apparatus 110. For example, the third apparatus (130, 415) may send, to the first apparatus (110, 405), a second indication (455) of the discarded data unit (433-1). In some example embodiments, the second indication (455) of the discarded data unit (433-1), may be sent to the first apparatus (110, 405) in a PDCP SN gap report (453).

[0089] In some example embodiments, the third apparatus 130 may determine (452), based on the first indication (256, 449) of the at least one discarded downlink data unit (258, 433-1), that the at least one discarded downlink data unit (258, 433-1) is unexpected to be received by the third apparatus 130. For example, the third apparatus 130 may not expect the data unit (433-1) indicated as discarded from the second apparatus 120 before transmitting (456) the forwarded SDUs (433, 457) to the first apparatus 110 in an increasing order of their COUNT values.

[0090] An example implementation of sending the indication for the data unit (one or more of 242, 425-1, 433-1) discarded (428) by the first apparatus 110, 405 or (434) the second apparatus 120, 410 will be discussed below by taking 3GPP TS 38.423 as an example.

[0091] Example information elements (IES) of a PDCP SN status transfer message are illustrated below in Table 1 by taking 3GPP TS 38.423 as an example. Table 1 shows a list of DRBs containing information about PDCP SN status.Table 1

[0092] Some example embodiments for informing of a discarded data unit will be described below with reference to FIG. 4. In this example, a UE 405 is an example of the first apparatus 110, a source gNB 410 is an example of the second apparatus 120, and a target gNB 415 is an example of the third apparatus 130.

[0093] As shown in FIG. 4, at 422, the UE 405 may send a measurement report (423) to the source gNB 410. At 424, the UE 405 may send UL PDCP SDUs (425) to the source gNB 410. At 426, the source gNB 410 may send a handover request (427) to the target gNB 415 based on the measurement report (423) from the UE 405. At 428, if a PDCP discard timer has expired at the UE 405, the UE 405 may discard an UL PDCP SDU (425-1). At 430, the UE 405 may send a PDCP SN gap report (431) to the source gNB 410 to indicate the discarded UL SDU(s) (425-1).

[0094] At 440, the UE 405 may receive RRCReconfiguration which causes handover to the target gNB 415. At step 442, the UE 405 may execute the RRC reconfiguration which includesaccessing the target cell and PDCP re-establishment procedure. As part of the PDCP reestablishment procedure, the UE 405 may determine previous discarding of one or more UL PDCP SDUs (one or more of 242, 425-1, ) with COUNT values (Vn) satisfying predefined condition(s). If the predefined condition(s) has been satisfied, at 458, the UE 405 may send a PDCP SN gap report (459) indicating one or more UL PDCP SDUs (one or more of 242, 425- 1) as discarded to the target gNB 415. At 460, the target gNB 415 may not wait for UL SDUs (one or more of 242, 425-1) indicated as discarded.

[0095] In some example embodiments, as shown, at 432, the source gNB 410 may send DL PDCP SDUs (433) to the UE 405. At 434, if a PDCP discard timer has expired at the source gNB 410, the source gNB 410 may discard a DL PDCP SDU (433-1). At 436, the source gNB 410 may send a PDCP SN gap report (437) towards the UE 405. However, the PDCP SN gap report (437) may not be successfully received by the UE 405. At 438, the target gNB 415 may send a handover request acknowledge (439) to the source gNB 410 in response to the handover request (427) sent (426) by the source gNB 410.

[0096] At 443, the source gNB 410 may forward received UL PDCP SDUs (425) and / or undelivered DL PDCP SDUs (433) to the target gNB 415. At 444, as part of the PDCP reestablishment procedure, the UE 405 may send a PDCP SN gap report (445) indicating one or more UL PDCP SDUs (425-1) as discarded to the source gNB 410. At 446, the source gNB 410 may determine discarded UL and / or DL SDUs with COUNT values satisfying respective predefined conditions. At 448, the source gNB 410 may send an SN Status Transfer message (447) including an indication (449) of discarded SDUs (425-1, 433-1) to the target gNB 415. At 450, the UE 405 may send RRCReconfigurationComplete to the target gNB 415. At 452, the target gNB 415 may not wait for UL (425-1) and / or DL SDUs (433-1) indicated as discarded, based on the SN Status Transfer message (447) sent (in step 448) by the source gNB 410. At 454, the target gNB 415 may relay received (448) information regarding discarded DL SDUs (433-1) by sending the PDCP SN gap report (453) indicating (455) the discarded DL SDUs (433-1) to the UE 405. At 456, the target gNB 415 may send undelivered and new DL SDUs(457) to the UE 405.

[0097] In such a process as shown in FIG. 4, the UE 405 may send a PDCP SN gap report (220-2, 459) indicating the one or more UL PDCP SDUs (one or more of 242, 425-1) as discarded to the target gNB 415. Moreover, the source gNB 410 may send an SN Status Transfer message (315, 447) including indication of UL and / or DL discarded SDUs (242, 425- 1, 433-1) to the target gNB 415. Accordingly, the target gNB 415 and / or the UE 405 may not wait for UL and / or DL SDUs (242, 425-1, 433-1) indicated as discarded. In this way, the transmission delay of the data units (425, 433) may be reduced.

[0098] FIG. 5 shows a flowchart of an example method 500 implemented at a first apparatus 110 for wireless communication in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 500 will be described from the perspective of the first apparatus 110 in FIG. 1.

[0099] At block 510, the first apparatus 110 determines to trigger at least one report on at least one discarded data unit (425-1) of a plurality of data units (425) during a termination point change of at least one bearer of the first apparatus from a second apparatus 120 to a third apparatus 130.

[0100] At block 520, the first apparatus 110 sends, in response to the determining to trigger the at least one report, the at least one report to at least one of the second apparatus 120 or the third apparatus 130.

[0101] In some example embodiments, the determining to trigger the at least one report may be based on the at least one discarded data unit (425-1) having satisfied at least one condition.

[0102] In some example embodiments, the at least one condition may include at least one of: a condition that no confirmation of successful delivery of a previous report on the at least one discarded data unit is received by the first apparatus 110; or a condition that a first count value of the at least one discarded data unit is greater than a second count value of a reference discarded data unit but less than a third count value of a non-discarded data unit, where a confirmation of successful delivery of the reference discarded data unit has been received by the first apparatus 110.

[0103] In some example embodiments, the second count value of the reference discarded data unit may be a maximum count value (Vmax) of at least one reference discarded data unit (425-2, 425-x), where confirmation of successful delivery of the at least one reference discarded data unit (425-2, 425-x) to the second apparatus (120, 410) has been received by the first apparatus 110.

[0104] In some example embodiments, the at least one report for the at least one discarded data unit (425-1) may include a PDCP SN gap report (445, 459).

[0105] In some example embodiments, the plurality of data units each may include a PDCP SDU.

[0106] In some example embodiments, the determining to trigger the at least one report on the at least one discarded data unit may be executed during PDCP re-establishment, and the sending of the at least one report for the at least one discarded data unit may be executed as part of the termination point change.

[0107] In some example embodiments, the first apparatus 110 may include a terminal device, the second apparatus 120 may include a source network device, and the third apparatus 130 may include a target network device.

[0108] FIG. 6 shows a flowchart of an example method 600 implemented at a second apparatus 120 for wireless communication in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 600 will be described from the perspective of the second apparatus 120 in FIG. 1.

[0109] At block 610, the second apparatus 120 initiates a termination point change of at least one bearer of a first apparatus 110 from the second apparatus 120 to a third apparatus 130.

[0110] At block 620, the second apparatus 120 receives, from the first apparatus 110, during the termination point change, at least one report on at least one discarded data unit of a plurality of data units.

[0111] In some example embodiments, the at least one report may include: a PDCP SN gapreport.

[0112] In some example embodiments, the plurality of data units each may include a PDCP SDU.

[0113] In some example embodiments, the first apparatus 110 may include a terminal device, the second apparatus 120 may include a source network device, and the third apparatus 130 may include a target network device.

[0114] FIG. 7 shows a flowchart of an example method 700 implemented at a third apparatus 130 for wireless communication in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 700 will be described from the perspective of the third apparatus 130 in FIG. 1.

[0115] At block 710, the third apparatus 130 receives, from a second apparatus 120, a request for a termination point change of at least one bearer of a first apparatus 110 from the second apparatus 110 to the third apparatus 130.

[0116] At block 720, the third apparatus 130 receives, from the first apparatus 110, during the termination point change, at least one report on discarding at least one data unit of a plurality of data units by the first apparatus 110.

[0117] In some example embodiments, the third apparatus 130 may determine, based on the at least one report, that the at least one discarded data unit is unexpected to be received by the third apparatus 130.

[0118] In some example embodiments, the at least one report may include a PDCP SN gap report.

[0119] In some example embodiments, the plurality of data units each may include a PDCP SDU.

[0120] In some example embodiments, the first apparatus 110 may include a terminal device, the second apparatus 120 may include a source network device, and the third apparatus 130may include a target network device.

[0121] FIG. 8 shows a flowchart of an example method 800 implemented at a second apparatus 120 for wireless communication in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 800 will be described from the perspective of the second apparatus 120 in FIG. 1.

[0122] At block 810, the second apparatus 120 determines that at least one data unit of a plurality of uplink data units has been discarded by a first apparatus 110.

[0123] At block 820, the second apparatus 120 sends, to a third apparatus 130, an indication of the at least one discarded uplink data unit, during a termination point change of at least one bearer of the first apparatus 110 from the second apparatus 120 to the third apparatus 130.

[0124] In some example embodiments, the second apparatus 120 may receive, from the first apparatus 110, at least one report on the at least one discarded uplink data unit.

[0125] In some example embodiments, the at least one report on the at least one discarded uplink data unit may include a PDCP SN gap report.

[0126] In some example embodiments, the second apparatus 120 may determine that the at least one discarded uplink data unit has satisfied at least one condition; and may send the indication based on the determining that the at least one discarded uplink data unit has satisfied the at least one condition.

[0127] In some example embodiments, the at least one condition may include a condition that a first count value of the at least one discarded uplink data unit is greater than a fourth count value of an unreceived uplink data unit, and the fourth count value of the unreceived uplink data unit is to be indicated to the third apparatus 130.

[0128] In some example embodiments, the fourth count value of the unreceived uplink data unit may be a lowest count value of at least one unreceived uplink data unit, where the at least one unreceived data units (425-3, 425-4) are expected to be received from the first apparatus (110, 405).

[0129] In some example embodiments, the lowest count value may be to be indicated to the third apparatus 130 in a SN status transfer message.

[0130] In some example embodiments, the indication of the at least one discarded uplink data unit may be sent in at least one of: the SN status transfer message, or a message separate from the SN status transfer message.

[0131] In some example embodiments, the plurality of uplink data units each may include a PDCP SDU.

[0132] In some example embodiments, the first apparatus 110 may include a terminal device, the second apparatus 120 may include a source network device, and the third apparatus 130 may include a target network device.

[0133] FIG. 9 shows a flowchart of an example method 900 implemented at a third apparatus 130 in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 900 will be described from the perspective of the third apparatus 130 in FIG. 1.

[0134] At block 910, the third apparatus 130 receives, from a second apparatus 120, a request for termination point change of at least one bearer of a first apparatus 110 from the second apparatus 120 to the third apparatus 130.

[0135] At block 920, the third apparatus 130 receives, from the second apparatus 120, during the termination point change, an indication of at least one discarded data unit of a plurality of uplink data units.

[0136] In some example embodiments, the third apparatus 130 may determine, based on the indication of the at least one discarded uplink data unit, that the at least one discarded uplink data unit is unexpected to be received by the third apparatus 130.

[0137] In some example embodiments, the indication of the at least one discarded uplink data unit may be received in at least one of: a SN status transfer message, or a message separate from the SN status transfer message.

[0138] In some example embodiments, the plurality of uplink data units each may include aPDCP SDU.

[0139] In some example embodiments, the first apparatus 110 may include a terminal device, the second apparatus 120 may include a source network device, and the third apparatus 130 may include a target network device.

[0140] FIG. 10 shows a flowchart of an example method 1000 implemented at a second apparatus 120 in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1000 will be described from the perspective of the second apparatus 120 in FIG. 1.

[0141] At block 1010, the second apparatus 120 determines that at least one data unit of a plurality of downlink data units has been discarded by the second apparatus 120.

[0142] At block 1020, the second apparatus 120 sends, to a third apparatus 130, an indication of the at least one discarded downlink data unit, during a termination point change of at least one bearer of a first apparatus 110 from the second apparatus 120 to the third apparatus 130.

[0143] In some example embodiments, the indication of the at least one discarded downlink data unit may be sent in at least one of: a SN status transfer message, or a message separate from the SN status transfer message.

[0144] In some example embodiments, the plurality of data units each may include a PDCP SDU.

[0145] In some example embodiments, the first apparatus 110 may include a terminal device, the second apparatus 120 may include a source network device, and the third apparatus 130 may include a target network device.

[0146] FIG. 11 shows a flowchart of an example method 1100 implemented at a third apparatus 130 in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1100 will be described from the perspective of the third apparatus 130 in FIG. 1.

[0147] At block 1110, the third apparatus 130 receives, from a second apparatus 120, a request for termination point change of at least one bearer of a first apparatus 110 from the second apparatus 120 to the third apparatus 130.

[0148] At block 1120, the third apparatus 130 receives, from the second apparatus 120, during the termination point change, a first indication of at least one discarded data unit of a plurality of downlink data units.

[0149] In some example embodiments, the third apparatus 130 may send, to the first apparatus 110, a second indication of the at least one discarded downlink data unit.

[0150] In some example embodiments, the second indication of the at least one discarded downlink data unit may be sent to the first apparatus 110 in a PDCP SN gap report.

[0151] In some example embodiments, the third apparatus 130 may determine, based on the indication of the at least one discarded downlink data unit, that the at least one discarded downlink data unit is unexpected to be received by the third apparatus 130.

[0152] In some example embodiments, the first indication of the at least one discarded downlink data unit may be received in at least one of: a SN status transfer message, or a message separate from the SN status transfer message.

[0153] In some example embodiments, the plurality of downlink data units each may include a PDCP SDU.

[0154] In some example embodiments, the first apparatus 110 may include a terminal device, the second apparatus 120 may include a source network device, and the third apparatus 130 may include a target network device.

[0155] In some example embodiments, the first apparatus 110, the second apparatus 120 and the third apparatus 130 may include means for performing the respective operations of the methods 500 to 1100. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

[0156] FIG. 12 is a simplified block diagram of a device 1200 that is suitable for implementing example embodiments of the present disclosure. The device 1200 may be provided to implement a communication device, for example, the first apparatus 110 or the second apparatus 120 as shown in FIG. 1. As shown, the device 1200 includes one or more processors 1210, one or more memories 1220 coupled to the processor 1210, and one or more communication modules 1240 coupled to the processor 1210.

[0157] The communication module 1240 is for bidirectional communications. The communication module 1240 has one or more communication interfaces to facilitate communication with one or more other modules or devices. The communication interfaces may represent any interface that is necessary for communication with other network elements. In some example embodiments, the communication module 1240 may include at least one antenna.

[0158] The processor 1210 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1200 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.

[0159] The memory 1220 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 1224, an electrically programmable read only memory (EPROM), a flash memory, a hard disk, a compact disc (CD), a digital video disk (DVD), an optical disk, a laser disk, and other magnetic storage and / or optical storage. Examples of the volatile memories include, but are not limited to, a random-access memory (RAM) 1222 and other volatile memories that will not last in the power-down duration.

[0160] A computer program 1230 includes computer executable instructions that are executed by the associated processor 1210. The instructions of the program 1230 may includeinstructions for performing operations / acts of some example embodiments of the present disclosure. The program 1230 may be stored in the memory, e.g., the ROM 1224. The processor 1210 may perform any suitable actions and processing by loading the program 1230 into the RAM 1222.

[0161] The example embodiments of the present disclosure may be implemented by means of the program 1230 so that the device 1200 may perform any process of the disclosure as discussed with reference to FIG. 1 to FIG. 7. The example embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

[0162] In some example embodiments, the program 1230 may be tangibly contained in a computer readable medium which may be included in the device 1200 (such as in the memory 1220) or other storage devices that are accessible by the device 1200. The device 1200 may load the program 1230 from the computer readable medium to the RAM 1222 for execution. In some example embodiments, the computer readable medium may include any types of non- transitory storage medium, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. 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).

[0163] FIG. 13 shows an example of the computer readable medium 1300 which may be in form of CD, DVD or other optical storage disk. The computer readable medium 1300 has the program 1230 stored thereon.

[0164] Generally, various 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, and other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. Although various aspects of 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 beimplemented 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.

[0165] Some example embodiments of the present disclosure also provide at least one computer program product tangibly stored on a computer readable medium, such as a non- transitory computer readable medium. The computer program product includes computerexecutable instructions, such as those included in program modules, being executed in a device on a target physical or virtual processor, to carry out any of the methods as described above. 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 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.

[0166] Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. The program code 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 code, 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.

[0167] In the context of the present disclosure, the computer program code 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 medium, and the like.

[0168] The computer readable medium may be a computer readable signal medium or acomputer 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 readonly memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0169] Further, although 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. Eikewise, although 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 embodiments. Unless explicitly stated, certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, unless explicitly stated, various features that are described in the context of a single embodiment may also be implemented in a plurality of embodiments separately or in any suitable sub-combination.

[0170] 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.

[0171] 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 examplesdescribed herein.

[0172] Example 1. A second apparatus (120, 410, 305) for wireless communication, including: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus (120, 410, 305) at least to: determine (250, 446, 1010) that at least one data unit (one or more of: 258, 433-1) of a plurality of downlink data units (433) has been discarded by the second apparatus (120, 410, 305); and send (255, 448, 1020), to a third apparatus (130, 415, 310), an indication (256, 449) of the at least one discarded downlink data unit (one or more of: 258, 433-1), during termination point change of at least one bearer of a first apparatus (110, 405) from the second apparatus (120, 410, 305) to the third apparatus (130, 415, 310).

[0173] Example 2. The second apparatus (120, 410, 305) of example 1, wherein the indication (256, 449) of the at least one discarded downlink data unit (258, 433-1) is sent in at least one of: a sequence number (SN) status transfer message (315, 447), or a message separate from the SN status transfer message (315).

[0174] Example 3. The second apparatus (120, 410, 305) of example 1 or 2, wherein the plurality of downlink data units (433) each includes a packet data convergence protocol service data unit (PDCP SDU).

[0175] Example 4. The second apparatus (120, 410, 305) of any of examples 1 to 3, wherein the first apparatus (110, 405) includes a terminal device, the second apparatus (120, 410, 305) includes a source network device, and the third apparatus (130, 415, 310) includes a target network device.

[0176] Example 5. A third apparatus (130, 415, 310) for wireless communication, including: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the third apparatus (130, 415, 310) at least to: receive (210, 426, 1110), from a second apparatus (120, 410, 305), a request (206) for termination point change of at least one bearer of a first apparatus (110, 405) from the second apparatus (120, 410, 305) to the third apparatus (130, 415, 310); and receive (260, 448, 1120), from the second apparatus(120, 410, 305), during the termination point change, a first indication (256, 449) of at least one discarded data unit (258, 433-1) of a plurality of downlink data units (433).

[0177] Example 6. The third apparatus (130, 415, 310) of example 5, wherein the instructions that, when executed by the at least one processor, further cause the third apparatus (130, 415, 310) to: send (454), to the first apparatus (110, 405), a second indication (455) of the at least one discarded downlink data unit (433-1).

[0178] Example 7. The third apparatus (120, 410, 305) of example 6, wherein the second indication (455) of the at least one discarded downlink data unit (433-1) is sent to the first apparatus (110, 405) in a packet data convergence protocol sequence number (PDCP SN) gap report (453).

[0179] Example 8. The third apparatus (130, 415, 310) of any of examples 5 to 7, wherein the instructions that, when executed by the at least one processor, further cause the third apparatus (130, 415, 310) to: determine (452), based on the first indication (256, 449) of the at least one discarded downlink data unit (258, 433-1), that the at least one discarded downlink data unit (258, 433-1) is unexpected to be received by the third apparatus.

[0180] Example 9. The third apparatus (130, 415, 310) of any of examples 5 to 8, wherein the first indication (256, 449) of the at least one discarded downlink data unit (258, 433-1) is received in at least one of: a sequence number (SN) status transfer message (315, 447), or a message separate from the SN status transfer message (315).

[0181] Example 10. The third apparatus (130, 415, 310) of any of examples 5 to 9, wherein the plurality of downlink data units (433) each includes a packet data convergence protocol service data unit (PDCP SDU).

[0182] Example 11. The third apparatus (130, 415, 310) of any of examples 5 to 10, wherein the first apparatus (110, 405) includes a terminal device, the second apparatus (120, 410, 305) includes a source network device, and the third apparatus (130, 415, 310) includes a target network device.

[0183] Example 12. A second apparatus for wireless communication, including: means for determining (250, 452, 1010) that at least one data unit of a plurality of downlink data units has been discarded by the second apparatus (120, 410, 305); and means for sending (255, 454, 1020), to a third apparatus (130, 415, 310), an indication of the at least one discarded downlink data unit, during termination point change of at least one bearer of a first apparatus (110, 405) from the second apparatus (120, 410, 305) to the third apparatus (130, 415, 310).

[0184] Example 13. A third apparatus for wireless communication, including: means for receiving (210, 425, 1110), from a second apparatus (120, 410, 305), a request (206) for termination point change of at least one bearer of a first apparatus (110, 405) from the second apparatus (120, 410, 305) to the third apparatus (130, 415, 310); and means for receiving (260, 454, 1120), from the second apparatus (120, 410, 305), during the termination point change, a first indication of at least one discarded data unit of a plurality of downlink data units.

Claims

WHAT IS CLAIMED IS:

1. A second apparatus for wireless communication, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus at least to: determine that at least one data unit of a plurality of downlink data units has been discarded by the second apparatus; and send, to a third apparatus, an indication of the at least one discarded downlink data unit, during termination point change of at least one bearer of a first apparatus from the second apparatus to the third apparatus.

2. The second apparatus of claim 1, wherein the indication of the at least one discarded downlink data unit is sent in at least one of: a sequence number (SN) status transfer message, or a message separate from the SN status transfer message.

3. The second apparatus of claim 1 or 2, wherein the plurality of downlink data units each comprises a packet data convergence protocol service data unit (PDCP SDU).

4. The second apparatus of any of claims 1 to 3, wherein the first apparatus comprises a terminal device, the second apparatus comprises a source network device, and the third apparatus comprises a target network device.

5. A third apparatus for wireless communication, comprising:at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the third apparatus at least to: receive, from a second apparatus, a request for termination point change of at least one bearer of a first apparatus from the second apparatus to the third apparatus; and receive, from the second apparatus, during the termination point change, a first indication of at least one discarded data unit of a plurality of downlink data units.

6. The third apparatus of claim 5, wherein the instructions that, when executed by the at least one processor, further cause the third apparatus to: send, to the first apparatus, a second indication of the at least one discarded downlink data unit.

7. The third apparatus of claim 6, wherein the second indication of the at least one discarded downlink data unit is sent to the first apparatus in a packet data convergence protocol sequence number (PDCP SN) gap report.

8. The third apparatus of any of claims 5 to 7, wherein the instructions that, when executed by the at least one processor, further cause the third apparatus to: determine, based on the first indication of the at least one discarded downlink data unit, that the at least one discarded downlink data unit is unexpected to be received by the third apparatus.

9. The third apparatus of any of claims 5 to 8, wherein the first indication of the at least one discarded downlink data unit is received in at least one of: a sequence number (SN) status transfer message, ora message separate from the SN status transfer message.

10. The third apparatus of any of claims 5 to 9, wherein the plurality of downlink data units each comprises a packet data convergence protocol service data unit (PDCP SDU).

11. The third apparatus of any of claims 5 to 10, wherein the first apparatus comprises a terminal device, the second apparatus comprises a source network device, and the third apparatus comprises a target network device.

12. A second apparatus for wireless communication, comprising: means for determining that at least one data unit of a plurality of downlink data units has been discarded by the second apparatus; and means for sending, to a third apparatus, an indication of the at least one discarded downlink data unit, during termination point change of at least one bearer of a first apparatus from the second apparatus to the third apparatus.

13. A third apparatus for wireless communication, comprising: means for receiving, from a second apparatus, a request for termination point change of at least one bearer of a first apparatus from the second apparatus to the third apparatus; and means for receiving, from the second apparatus, during the termination point change, a first indication of at least one discarded data unit of a plurality of downlink data units.

Images