Mechanism to faster exchange of PDCP UL / DL first missing count after handovers

Abstract

Example embodiments of the present disclosure are directed to a solution for transmission status transfer. A method includes receiving, a configuration from a third apparatus, for triggering the first apparatus to initiate a random access (RA) procedure with a second apparatus; receiving, during the RA procedure, a message from the second apparatus, wherein the message includes packet sequence number information related to a transmission from the first apparatus to the third apparatus; and after completion of the RA procedure with the second apparatus, transmit, to the second apparatus, at least one data packet) based on the packet sequence number information.

Description

TITLE OF THE INVENTION“MECHANISM TO FASTER EXCHANGE OF PDCP UL / DL FIRST MISSING COUNT AFTER HANDOVERS”FIELDS

[0001] Various example embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to methods, devices, apparatuses and computer readable storage medium for transmission status transfer.BACKGROUND

[0002] In the communication networks, when there is a change in location of packet data convergence protocol (PDCP) entity (during such as, handover procedure, or dual connection (DC)-secondary node (SN) addition procedure), the transmitter and the receiver need to exchange PDCP status report, which contain the status of the packet which were not updated by its peer radio link control (RLC) entity. Conventional solutions of the status report transfer may cause a resource wastage and a longer interruption, and thus need to be improved.SUMMARY

[0003] Example embodiments of the present disclosure are directed to methods, devices, apparatuses, computer readable storage medium and computer program for transmission status transfer. A example solution includes: receiving (410-2, 720-2, 810), a configuration (460-1, 720) from a third apparatus (330, 1300), for triggering the first apparatus (310, 1300) to initiate a random access (RA) procedure (495, 780) with a second apparatus (320, 1300); receiving (430-2, 750-2, 820), during the RA procedure (495, 780), a message (480-1, 500B, 500C, 750A) from the second apparatus (320, 1300), wherein the message (480-1, 500B, 500C, 750A) includes packet sequence number information (480-2, 750B) related to a transmission (402, 705B) from the first apparatus (310, 1300) to the third apparatus (330, 1300); and, transmit (440-1, 770-1, 830), to the second apparatus (320, 1300), at least one data packet (490-1, 770A) based on the packet sequence number information (480-2, 750B), after completion of the RA procedure (495, 780) with the second apparatus (320, 1300).

[0004] Another example solution includes: receiving (710-2, 910), from a third apparatus (330, 1300), packet sequence number information (480-2, 750B) related to atransmission (402, 705B) from the first apparatus (310, 1300) to the third apparatus (330, 1300); transmitting (430-1, 750-1, 920), during a random access (RA) procedure (495, 780) with a first apparatus (310, 1300), a message (480-1, 500B, 500C, 750A) to the first apparatus (310, 1300), wherein the message (480-1, 500B, 500C, 750A) includes packet sequence number information (480-2, 750B) related to the transmission (402, 705B) from the first apparatus (310, 1300) to a third apparatus (330, 1300); and receiving (440-2, 770-2, 930), from the first apparatus (310, 1300), at least one data packet (490-1, 770A) based on the packet sequence number information (480-2, 750B), after completion of the RA procedure (495, 780) with the second apparatus (320, 1300).BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Some example embodiments will now be described with reference to the accompanying drawings, where:

[0006] FIG. 1A and FIG. IB illustrate example signaling flows for handover;

[0007] FIG. 2A to FIG. 2C illustrate example signaling flows for RLC status transfer;

[0008] FIG. 3 illustrates an example communication environment in which example embodiments of the present disclosure may be implemented;

[0009] FIG. 4 illustrates a signaling flow of communication according to some example embodiments of the present disclosure;

[0010] FIG. 5 A to FIG. 5C illustrate example diagrams of message structure according to some example embodiments of the present disclosure;

[0011] FIG. 6 A and FIG. 6B illustrate example diagrams of message structure according to some example embodiments of the present disclosure;

[0012] FIG. 7 illustrates a signaling flow of communication according to some example embodiments of the present disclosure;

[0013] FIG. 8 illustrates a flowchart of a method implemented at a first apparatus in accordance with some example embodiments of the present disclosure;

[0014] FIG. 9 illustrates a flowchart of a method implemented at a second apparatus in accordance with some example embodiments of the present disclosure;

[0015] FIG. 10 illustrates a flowchart of a method implemented at a third apparatus in accordance with some example embodiments of the present disclosure;

[0016] FIG. 11 illustrates a flowchart of a method implemented at a first apparatus in accordance with some example embodiments of the present disclosure;

[0017] FIG. 12 illustrates a flowchart of a method implemented at a second apparatus in accordance with some example embodiments of the present disclosure;

[0018] FIG. 13 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

[0019] FIG. 14 illustrates a block diagram of an example computer readable medium in accordance with some example embodiments of the present disclosure.

[0020] Throughout the drawings, the same or similar reference numerals represent the same or similar element.DETAILED DESCRIPTION

[0021] 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 may be further understood that the terms “includes”, “including”, “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.

[0022] In the context of the present disclosure, the term “message” and “further message” and the associated reference designations may be used interchangeably depending on the embodiments described.

[0023] As discussed above, in the communication networks, when there is a change in location of PDCP entity (during such as, handover procedure, or secondary node addition procedure in dual connection mode), the transmitter and the receiver need to exchange (PDCP) status report, which contain the status of the packet which were not updated by its peer RLC entity via RLC status report.

[0024] A PDCP status report may inform the transmitter PDCP entity about which PDCP protocol data units (PDUs) had been successfully received or had not been received by the receiver PDCP entity. This allows the transmitter to avoid retransmitting PDCP SDUs which are already successfully received and to retransmit only the unsuccessful received packets. In some solutions, during an inter-the next generation node B (inter -gNB) handover or secondary node addition (in multi-radio DC, e.g., evolved UMTS terrestrial radio access Network (E-UTRAN) new radio-DC, ENDC), the unacknowledged (unacked) layer 2 (L2) packet by its peer L2 entity on the source gNB(or on master node, MN) via the RLC status report would be acknowledged from the target gNB (or secondary node) PDCP entity, using PDCP status report after successful completion of handover (or secondary node addition) process.

[0025] As illustrated in FIG. 1A and FIG. IB, in case of uplink (UL) direction, the source gNB will assist the target gNB (or secondary node) by sending the “SN Status Transfer” (SN: Sequence Number) report over Xn interface (Step 11-9), which contains the updated status of received / unreceived UL PDCP packets including the PDCP sequence number (represented as RX_Deliv, in the example of FIG. IB, it may be 200), The target gNB may expect to receive in UL direction from UE. The SN status transfer report also contains the PDCP sequence number that the target gNB may use to start assigning for the new packet to be transmitted in downlink (DL) direction. Similarly, UE also send PDCP status report for DL data including indication from which PDCP SN (represented as RX_Deliv) gNB may start sending the DL packets on the target gNB. If the PDCP entity at the receiver receives the packets with sequence number (SN) below RX_Deliv (i.e., lower bound of receiver PDCP window), such packets will be discarded by the PDCP entity. In case that the PDCP status report is not received (or delayed) by the transmitter PDCP entity, the transmitter PDCP may start sending the PDCP packets starting from the SN which are not successfully acknowledged on source gNB (via its RLC, although these packets are successfully received). It means that the transmitter would retransmit the packets which are already successfully received by the receiver PDCP entity at source gNB before the handover or the master node (MN) before secondary node addition. For example, in the example of FIG. IB, although packets till 200 had been successfully received by the source gNB (also may be the MN), as packets 101-200 are unacked, UE needs to re-transmit the packet from packet 101 to the target gNB. However, as the target gNB (also may be the secondary node) had informed that packets till 200 had been successfully received by the source gNB (via such as SN Status Transfer), when the target gNB receives the packets 101-200, the target gNB would discard these packets.

[0026] In some solutions, the UL / DL transmissions are expected to be proceed earlier. For example, if UL grants are allocated by network based on the buffer status report, UE is expected to be free to send the packets present in its UL buffers otherwise UE may waste the granted UL resources. In these cases, the UL / DL transmissions may occur before the status report transfer, and thus may cause a resource waste. For example, in some solutions, after inter-gNB handover or secondary node addition, when DL or ULdata transfer starts before reception of PDCP status report, there may be PDCP out of window packet detections at receiver PDCP entity, which will be discarded (refer to FIG.2A at Steps 21-8 to Steps 21-9 or refer to FIG. 2B at Steps 22-7 to Steps 22-9).

[0027] These discards not only effect communication performance but importantly cause wastage of network resources, increasing the latency of transmission of new packets to the end user which is not expected for time critical applications. Moreover, if there are any layer 1 (LI) hybrid automatic repeat request (HARQ) non- acknowledgments or L2 RLC non-acknowledgments for the old retransmitted PDCP packets on target gNB, it will increase wastage and latency discussed above as the transmitter may keep re-transmitting the old packets until successfully received by receiver after which new PDCP packets may be transmitted.

[0028] In some solutions, if expect to avoid the out of window packets at PDCP by delaying sending of packets (in DL and UL) till the reception of PDCP status report, it will increase in latency of packets towards end user. Refer FIG. 2C for details. In the example of FIG. 2C, the PDCP DL and UL data is delayed till PDCP status report reception, which leads to wastage of UL resources and also increases latency of DL and UL data transmission.

[0029] The above issues may occur at least in the inter-gNB handover and secondary node addition scenarios. As each handover (or secondary node additions) contributes to above issues, in case that the number of handovers or secondary node additions increases or if there are too many RLC non- acknowledgment (just after handover completion for previous PDCP packets because of poor signaling and so on), the communication performance may decrease dramatically.

[0030] At least to solve the above issues, the present disclosure proposes a solution for transmission status transfer. With the example embodiments discussed herein, the (PDCP) DL and / or (PDCP) UL packet sequence number information (such as, the count for the first missing packet) may be transferred to the transmitter (i.e., gNB and / or UE), respectively, before DL / UL data transmission starts. As a result, the latency (caused by that the transmitter needs to wait for the PDCP status report to start the DL and UL transmission on the target gNB after HO (or after secondary node addition) may be reduced.

[0031] Principle and implementations of the present disclosure will be described in detail below with reference to the FIG. 3 to FIG. 12.

[0032] FIG. 3 illustrates an example communication environment 300 in which example embodiments of the present disclosure may be implemented. The communication environment 300 includes a first apparatus 310, a second apparatus 320 and a third apparatus 330.

[0033] In some solution, the second apparatus 320 and / or the third apparatus 330 may provide one or more serving area which is called as a cell. In the example of FIG. 3, the second apparatus 320 may provide a cell 340 and the third apparatus 330 may provide a cell 350. The first apparatus 310 may communicate with the second apparatus 320 and / or the third apparatus 330.

[0034] In some example embodiments, the first apparatus 310 may be included in a terminal device / apparatus and the second apparatus 320 and / or the third apparatus 330 may be included in a network device / apparatus serving the terminal device / apparatus.

[0035] In the following, for the purpose of illustration, some example embodiments are described with the first apparatus 310 operating as a terminal apparatus and the second apparatus 320 operating as a network apparatus. However, in some example embodiments, operations described in connection with a terminal apparatus may be implemented at a network apparatus or other apparatus, and operations described in connection with a network apparatus may be implemented at a terminal apparatus or other apparatus.

[0036] In some example embodiments, if the first apparatus 310 is a terminal apparatus and the second apparatus 320 and / or the third apparatus 330 is a network apparatus, a direction from the second apparatus 320 and / or the third apparatus 330 to the first apparatus 310 is referred to as a DL), while a direction from the first apparatus 310 to the second apparatus 320 and / or the third apparatus 330 is referred to as an UL. In DL, the second apparatus 320 and / or the third apparatus 330 is a transmitting (TX) apparatus (or a transmitter) and the first apparatus 310 is a receiving (RX) apparatus (or a receiver). In UL, the first apparatus 310 is a TX apparatus (or a transmitter) and the second apparatus 320 and / or the third apparatus 330 is a RX apparatus (or a receiver).

[0037] In the actual communication scenario, the first apparatus 310, the second apparatus 320 and the third apparatus 330 may move over time. Further, the communication condition may change over time. In summary, the actual communication scenario is complicated. Therefore, the peer PDCP entity may be changed, such as, due to, handover procedure, cell switch procedure, secondary node addition procedure, redirection procedure and so on. In these cases, the first apparatus 310 needs to continuethe previous transmission on a target cell. In the example of FIG. 3, the first apparatus 310 may perform the (UL / DL) transmission on the cell 350 first, then the first apparatus 310 may establish a new connection with the second apparatus 320 and continue to perform the (UL / DL) transmission on the cell 340. In this specific scenario, the third apparatus 330 also may be called as a serving network device and the second apparatus 320 may be called as a target network device.

[0038] It is to be understood that the number of devices and their connections shown in FIG. 3 are only for the purpose of illustration without suggesting any limitation. The communication environment 300 may include any suitable number of devices configured to implementing example embodiments of the present disclosure. Although not shown, it would be appreciated that one or more additional devices may be located in the cell 102, and one or more additional cells may be deployed in the communication environment 100.

[0039] Communications in the communication environment 300 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), 5.5G, 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.

[0040] The present disclosure proposes a solution for transmission status transfer. According to the example embodiments discussed below, a faster exchange of (PDCP) DL / UL first missing count (i.e., the packet sequence number information discussed below) between UE and gNB is enabled, such that the unnecessary retransmission is avoided and data transmission latency is reduced.

[0041] In operation, an RA procedure on the target gNB (or secondary node) in the handover (and secondary node addition) may be a contention-free RACH (CFRA)procedure, to have reduced interruption time comparing to contention-based RACH. In 4-step CFRA, as the preamble is pre-allocated to the UE, gNB is aware of the UE when the Message 1 is received with dedicated preamble. On the target cell, RACH is the first process between UE and gNB. As part of this RACH process, the first message UE receives from network is Message 2 and the first message the gNB received from UE is Message 3 (Message 1 is not considered as Message as only include preamble). In order to reduce the UL / DL data transfer delay or avoid to retransmission of the old PDCP SN which have been already successfully received from / by the source gNB, according to example embodiments of the present disclosure, the first missing count (FMC) information (i.e., the packet sequence number information discussed below) may be exchanged as early as possible between UE and gNB (in UL and DL direction).

[0042] In this way, once the RACH on target cell is successfully performed, the UE / gNB may immediately be ready to receive / transmit the packets with sequence number greater than the FMC.

[0043] Example embodiments will be discussed with reference to FIG. 4, which illustrates a signaling flow 400 for communication in accordance with some example embodiments of the present disclosure. For the purposes of discussion, the signaling flow 400 will be discussed with reference to FIG. 3, for example, by using the first apparatus 310, the second apparatus 320 and the third apparatus 330. In the following discussed, merely for better understanding, in some example embodiments, the first apparatus 310 may include a terminal device, the second apparatus 320 may include a target network device, and the third apparatus 330 may include a source or serving network device.

[0044] Example embodiments about how to exchange the UL packet sequence number information will be discussed first.

[0045] As illustrated in the FIG. 4, a transmission 402 from the first apparatus 310 to the third apparatus 330 (e.g., UL transmission) may be performed between the first apparatus 310 and the third apparatus 330.

[0046] In some cases, a PDCP location change may be triggered, due to such as, handover, secondary node addition, redirection and so on. If so, the third apparatus 330 generates (405) a configuration 460-1 and transmits (420-1) the configuration 460-1 to the first apparatus 310, and the first apparatus receives (410-2) the configuration 460-1 from the third apparatus 330, where the configuration is used for triggering the first apparatus 310 to initiate an RA procedure 495 with the second apparatus 320. In someexample embodiments, the RA procedure 495 may be a contention free random access (CFRA) procedure. It may be noted that the configuration 460-1 may be a mobility configuration (such as handover configuration, redirection configuration, cell switch configuration and so on), a DC-related (such as secondary node addition configuration), or other related configurations. In some embodiments, the configuration 460-1 may be included in a RRCReconfiguration message.

[0047] During the RA procedure 495, the second apparatus 320 transmits (430-1) a message 480-1 to the first apparatus 310, and the first apparatus 310 receives (430-2) the message 480-1 from the second apparatus 320 accordingly. In some example embodiments, the message 480-1 may be a Message 2 in a 4-step RA procedure. Alternatively, in some example embodiments, the message 480-1 may be a Message B in a 2-step RA procedure.

[0048] In particular, the message 480-1 may include (UL) packet sequence number information 480-2 related to the transmission 402. In some example embodiments, the packet sequence number information 480-2 may indicate a sequency number of a first PDCP packet that has not been successfully delivered, for example, RX_Deliv.

[0049] In some example embodiments, the second apparatus 320 may obtain the (UL) packet sequence number information 480-2 from the third apparatus 330 (i.e., the serving / source network device). Specifically, the second apparatus 320 may receive packet sequence number information 480-2 from the third apparatus 330, such as, via Xn interface. As one example, the packet sequence number information 480-2 may be included in the “SN Status Transfer” report, and the packet sequence number information 480-2 may be RX_Deliv.

[0050] In some example embodiments, the packet sequence number information 480-2 may relate to at least one radio bearer and / or at least one logical channel.

[0051] In some example embodiments, the at least one radio bearer and / or the at least one logical channel may be indicated by the configuration 460-1. It may be noted that in other example embodiments, the at least one radio bearer and / or the at least one logical channel also may be indicated by another UE-dedicated message, such as, a radio resource control (RRC) signaling. Alternatively, in some example embodiments, the at least one radio bearer and / or the at least one logical channel may be indicated by the message 480-1 (which will be discussed in detail in the following with reference to FIG. 5B and FIG.5C).

[0052] In some example embodiments, the first apparatus 310 may request the second apparatus 320 to provide the (UL) packet sequence number information 480-2. In one example, the first apparatus 310 may transmit 420-1 a further message 470-1 to the second apparatus 320, where the further message 470-1 may include an indication for requesting the second apparatus 320 to transmit (430-1) the (UL) packet sequence number information 480-2 to the first apparatus 310. As one example, the first apparatus 310 may transmit the Message A (e.g., in case with 2-step RA procedure) to the second apparatus 320, where the Message A may include an indication (for example UC field 610 in Message 600B) for requesting the packet sequence number information 480-2 (such as, UL count information). In response to the indication, the second apparatus 320 may provide the (UL) packet sequence number information 480-2 in the Message B.

[0053] In the following, more details about the message 480-1 (such as, Message 2 / Message B) will be discussed with reference to FIG. 5A to FIG. 5C.

[0054] In the example of FIG. 5 A, which illustrates an example subheader 500A. In the example of FIG. 5A, existing MAC subheader used in RAR (Message 2) have 2 reserved bits, which are proposed to indicate about uplink and downlink counts (UC and DC) fields, used for the newly-introduced features as discussed in the present disclosure. In some example embodiments, when UC is set as 1, it may indicate that uplink FMC count (i.e., (UL) packet sequence number information 480-2) details are followed for each configured bearer / logical channel via the present MAC subheader. In some example embodiments, when DC is set as 1, it may indicate that downlink FMC count (i.e., (DL) packet sequence number information 470-2) is requested from the UE. So, UE may include PDCP DL FMC (Rx_deliv) information in RACH Message 3 using MAC subheader(such as, message 600B illustrated in FIG. 6B) towards gNB. In case of MAC subheader of Message 3 / Message A, UE may use configured LCID as part of a MAC subheader.

[0055] In some example embodiments, the message 480-1 further includes a first field, such as, the field ‘UC’ in the message 500B illustrated in FIG. 5B or the message 500C illustrated in FIG. 5C. In some example embodiments, if the first field 510 is set to a first value (such as, ‘1’), the (UL) packet sequence number information 480-2 (such as, UL count information in message 500B or message 500C) may be included in the message 480-1. Accordingly, in some example embodiments, if the first field 510 is set to a second value (such as, ‘0’), the packet sequence number information 480-2 is absent in the message 480-1.

[0056] In the example of FIG. 500B and 500C, the fled UC (Uplink Count) may be introduced. In case UC is set as 1 indicated the uplink count details are followed in subsequent octets for respective DRB identity. If UC is set as 0, then uplink count may be not included. Further, in case E is set as 1 in the second octet, uplink count of other DRB are followed after this DRB.

[0057] In the example of FIG. 500B and 500C, the fled DC (Downlink Count) may be introduced. In case DC is set as 1, gNB is requesting UE to include DL count in Message 3 (RRC Reconfiguration complete or MAC sub-header using any reserved LCID fields) for all the DRB’s for which uplink count is received. If DC is set as 0, UE may need not to send DL count along with MSG3 or MAC Subheader.

[0058] As discussed above, the packet sequence number information 480-2 may be related to the at least one radio bearer and / or the at least one logical channel, and the at least one radio bearer and / or the at least one logical channel may be indicated by the message 480-1. Refer to FIG. 5C, where the message 500C may include the field 530 which may indicate the at least one radio bearer and / or the at least one logical channel.

[0059] It may be noted although the examples above are given based on extending the existing MAC subheader, it is possible to introduce a new MAC subheader or MAC Control Element (MAC CE) to carry UL count and / or DL count as well.

[0060] According to the above processes, the first apparatus 310 may obtain the (UL) packet sequence number information 480-2. As a result, after completion of the RA procedure 495, based on the (UL) packet sequence number information 480-2, the first apparatus 310 transmit (440-1) at least one data packet 490-1 to the second apparatus 320, and the second apparatus 320 receives (440-2) at least one data packet 490-1 accordingly.

[0061] That is, the UL packet sequence number information 480-2 may be exchanged during the RA procedure. In this way, the correct UL transmission may be proceeded once the first apparatus 310 has switched to the target cell.

[0062] The above example processes are mainly about how to exchange the UL packet sequence number information. In the following, example embodiments about how to exchange the DL packet sequence number information will be discussed.

[0063] As illustrated in the FIG. 4, (DL) transmission 401 from the third apparatus 330 to the first apparatus 310 may be performed between the first apparatus 310 and the third apparatus 330.

[0064] In some cases, a PDCP location change may be triggered, due to such as,handover, secondary node addition, redirection and so on. If so, the third apparatus 330 generates (405) a configuration 460-1 and transmits (420-1) the configuration 460-1 to the first apparatus 310, and the first apparatus receives (410-2) the configuration 460-1 from the third apparatus 330, where the configuration is used for triggering the first apparatus 310 to initiate an RA procedure 495 with the second apparatus 320. In some example embodiments, the RA procedure 495 may be a CFRA procedure. It may be noted that the configuration 460-1 may be a mobility configuration (such as handover configuration, redirection configuration, cell switch configuration and so on), a DC-related (such as secondary node addition configuration), or other related configurations.

[0065] During the RA procedure 495, the first apparatus 310 transmits (420-1) a message 470-1 to the second apparatus 320, and the second apparatus 320 receive (420-2) the message 470-1 accordingly. In some example embodiments, wherein the message 470-1 may be a message 3 in a 4-step RA procedure or a message A in a 2-step RA procedure.

[0066] In particular, the message 470-1 may include (DL) packet sequence number information 470-2 related to the (DL) transmission 401. In some example embodiments, the (DL) packet sequence number information 470-2 may indicate a sequency number of a first PDCP packet that has not been successfully delivered.

[0067] In some example embodiments, the packet sequence number information 470-2 may relate to at least one radio bearer and / or at least one logical channel.

[0068] In some example embodiments, the at least one radio bearer and / or the at least one logical channel may be indicated by the configuration 460-1. It may be noted that in other example embodiments, the at least one radio bearer and / or the at least one logical channel also may be indicated by another UE-dedicated message, such as, an RRC signaling. Alternatively, in some example embodiments, the at least one radio bearer and / or the at least one logical channel may be indicated by the message 470-1 (which will be discussed in detail in the following with reference to FIG. 6B).

[0069] In some example embodiments, the second apparatus 320 may request the first apparatus 310 to report the packet sequence number information 470-2 to the second apparatus 320. In one example, the second apparatus 320 may transmit (430-1) a message 480-1 to the first apparatus 310, where the message 480-1 includes an indication (such the field 520 in FIG. B and FIG. 5C) indicating the first apparatus 310 to report the (DL) packet sequence number information 470-2. The first apparatus 310 may receive (430-2)the message 480-1 from the second apparatus 320 accordingly. In response to the indication 520 included in the message 480-1 , the first apparatus 310 may include the (DL) packet sequence number information 470-2 in the message 470-1. As one example, the second apparatus 320 may transmit the Message 2 to the first apparatus 310, where the Message 2 may include an indication indicating the first apparatus 310 to report the (DL) packet sequence number information 470-2 (such as, DL count information). In response to this request, the first apparatus 310 may provide the (DL) packet sequence number information 470-2 in the Message 3.

[0070] In the following, more details about the message 470-1 (such as, Message 3 / Message A) will be discussed with reference to FIG. 6 A and FIG. 6B.

[0071] In the example of FIG. 6 A, which illustrates an example subheader. As may be seen, two reserved bits may be used for the newly-introduced features as discussed herein.

[0072] In some example embodiments, the message 470-1 may include a first field, such as, the field ‘DC’ in the message 600B illustrated in FIG. 6B. In some example embodiments, if the first field 620 is set to a first value (such as, ‘1’), the packet (DL) sequence number information 470-2 may be included in the message 470-1. Accordingly, in some example embodiments, if the first field 620 is set to a second value (such as, ‘0’), the (DL) packet sequence number information 470-2 may be absent in the message 470-1.

[0073] As discussed above, the packet sequence number information 470-2 may be related to the at least one radio bearer and / or the at least one logical channel, and the at least one radio bearer and / or the at least one logical channel may be indicated by the message 480-1. As illustrated in the FIG. 6B, the message 600B may include the field 630 which may indicate the at least one radio bearer and / or the at least one logical channel.

[0074] In the example of FIG. 600B, the fled DC (Downlink Count) may be introduced. In case DC is set as 1 indicated, the downlink count details are followed in subsequent octets for respective DRB / LCID identity. If DC is set as 0, then downlink count may be not included.

[0075] In the example of 600B, the fled UC (Uplink Count) may be introduced. In case UC is set as 1, UE is requesting gNB to include UL count in Message 2 / B for all the DRB’s for which uplink count is received. If UC is set as 0, gNB may need not to send UL count.

[0076] It may be noted that any reserved UL LCID value may be used by UE MACentity to inform the DL Count to network in Message 3. It may be noted although the examples above are given based on extending the existing MAC subheader, it is possible to introduce a new MAC subheader to carry Uplink count and / or DL count as well.

[0077] According to the above processes, the second apparatus 320 may obtain the DL packet sequence number information 470-2. As a result, after completion of the RA procedure 495, the second apparatus 320 may transmits (450-1) at least one data packet 490-1 based on the packet sequence number information 470-2, and the first apparatus 310 receives (450-2), from the second apparatus 320, at least one data packet (490-2, 775A) based on the packet sequence number information 470-2, with the second apparatus 320.

[0078] That is, the DL packet sequence number information 470-2 may be exchanged during the RA procedure. In this way, the correct DL transmission may be proceeded once the first apparatus 310 has switched to the target cell.

[0079] It may be noted that, although the UL packet sequence number information exchanging and the DL packet sequence number information exchanging are discussed separably, the UL and DL sequence number information exchanging may be performed in one RA procedure, i.e., the above example embodiments may be combined in any suitable manner. Merely for a better understanding, some example embodiments about UL and DL combination are discussed in the following.

[0080] In case of a 4-step RA, the first apparatus 310 receives (410-2), a configuration 461 from a third apparatus 330, for triggering the first apparatus 310 to initiate a 4-step RA procedure 495. In some example embodiments, the configuration 460-1 may include an indication 460-2 indicating the first apparatus 310 to report the DL packet sequence number information 470-2 by using Message 3.

[0081] In some example embodiments, during the RA procedure 495, the first apparatus 310 receives (430-2) a Message 2 from the second apparatus 320, where the Message 2 includes (UL) packet sequence number information related to an (UL) transmission 402 from the first apparatus 310 to the third apparatus 330. Optionally, in some example embodiments, the Message 2 may include an indication indicating the first apparatus 310 to report the DL packet sequence number information 470-2.

[0082] In some example embodiments, during the RA procedure 495, the first apparatus 310 transmit (440-1) a further message (470-1) (e.g., Message 3) to the second apparatus 320, wherein the Message 3 includes further packet or DL packet sequence numberinformation (470-2) related to the DL transmission 401 from the third apparatus 330 to the first apparatus 310.

[0083] After completion of the RA procedure 495, the first apparatus 310 transmits (440-1) to the second apparatus 320, at least one data packet 490-1 based on the UL packet sequence number information, and the second apparatus 320 receives (440-2) at least one data packet 490-1 based on the UL packet sequence number information accordingly.

[0084] After completion of the RA procedure 495 with the second apparatus 320, the first apparatus 310 receive (450-2), from the second apparatus 320, at least one further data packet (490-2) based on the DL packet sequence number information. Accordingly, after completion of the RA procedure 495, the second apparatus 320 transmits (450-1, 775-1), to the first apparatus 310, at least one further data packet 492 based on the DL packet sequence number information accordingly.

[0085] In case of a 2-step RA, the first apparatus 310 receives (410-2), a configuration 460-1 from a third apparatus 330, for triggering the first apparatus 310 to initiate an RA procedure 49) with a second apparatus 320. In some example embodiments, the configuration 460-1 may include an indication 460-2 indicating the first apparatus 310 to report the further packet sequence number information 470-2.

[0086] In some example embodiments, during the RA procedure 495, the first apparatus 310 transmit (440-1) a Message A to the second apparatus 320, where the Message A includes DL packet sequence number information related to the transmission 401. Optionally, the Message A may include an indication requesting the second apparatus 320 to provide the UL packet sequence number information.

[0087] During the RA procedure 495, the first apparatus 310 receives (430-2) a Message B from the second apparatus 320, wherein the message B includes (UL) packet sequence number information related to the transmission 402 from the first apparatus 310 to the third apparatus 330.

[0088] After completion of the RA procedure 495, the first apparatus 310 transmits (440-1) to the second apparatus 320, at least one data packet 490-1 based on the UL packet sequence number information, and the second apparatus 320 receives (440-2) at least one data packet 490-1 based on the UL packet sequence number information accordingly.

[0089] After completion of the RA procedure 495 with the second apparatus 320, the first apparatus 310 receive (450-2), from the second apparatus 320, at least one further data packet (490-2) based on the DL packet sequence number information. Accordingly,after completion of the RA procedure 495, the second apparatus 320 transmits (450-1, 775-1), to the first apparatus 310, at least one further data packet 492 based on the DL packet sequence number information accordingly.

[0090] For better understanding about the above process, example embodiments will be further discussed with reference to FIG. 7, which illustrates a signaling flow 700 for communication in accordance with some example embodiments of the present disclosure. For the purposes of discussion, the signaling flow 700 will be discussed with reference to FIG. 3, for example, by using the first apparatus 310 and the second apparatus 320.

[0091] In operation, the first apparatus 310 and the third apparatus 330 may communicate (705-1, 705-2) with each other, such as, perform DL transmission 705A and UL transmission 705B.

[0092] When there is change in PDCP entity location, e.g., during inter-gNB handovers or DC-SN (secondary node) addition, PDCP feedback may be used in form of PDCP status report to share the updated status of L2 packets and recover the missed packet and not to retransmit the successfully received packet on the third apparatus 330 (i.e., the source gNB or the MN) between UE and network.

[0093] In some example embodiments, Handover Re quest 710A may be sent (710-1, 710-2) from the third apparatus 330 (i.e., the source gNB or MN) to the second apparatus 320 (i.e., the target gNB or the secondary node). In some example embodiments, the second apparatus 320 may send (715-1, 715-2) HandoverRequestAck 715A to the third apparatus 330.

[0094] The second apparatus 320 may send (720-1, 720-2) the RRCReconfiguration 720 A which may include HO configuration (or may request for UL / DL FMC Count exchange) to the first apparatus 310. In some example embodiments, the request for PDCP UL / DL FMC could also be configured by the gNB as part of handover / secondary node configuration in RRC Reconfiguration message to support 2-step RACH procedure.

[0095] In some example embodiments, SN Status Transfer message 730A may be sent (730-1, 730-2) from the third apparatus 330 (i.e., the source gNB or MN) to the second apparatus 320 (i.e., the target gNB or the secondary node) to share the latest PDCP uplink packet status. In some example embodiments, the third apparatus 330 may send (735-1, 735-2) DL data 735A to the third apparatus 330.

[0096] In the example of FIG. 7, the first apparatus 310 may have (725) some unacked L2 packets. In the following, the first apparatus 310 may start (740) the RA procedurewith the second apparatus 320. During the 4-step RA procedure 780, the first apparatus 310 may transmit (745-1, 745-2) Message 1 745A to the second apparatus 320. The second apparatus 320 may transmit (750-1,750-2) Message 2 750A to the first apparatus 310, where the Message 2750A includes UL FMC information 750B. The first apparatus 310 may transmit (755-1, 755-2) Message 1 755A to the second apparatus 320, where the Message 3 755 A includes DL FMC information 755B. The second apparatus 320 may transmit (760-1,760-2) Message 4760A to the first apparatus 310.

[0097] In some example embodiments, during the CFRA handover or secondary node addition configuration via RRC message, the bearers which require UL / DL FMC transfer during RACH procedure may be explicitly configured.

[0098] In some example embodiments, during CFRA RACH procedure execution, the third apparatus 330 may include the PDCP UL FMC(RX_DELIV) data in MSG2 towards UE for all the bearers (which may be 1) configured in RRC message by increasing order of bearer identity; alternatively, the bearer identity could also be provided in the MSG2 MAC subHeader itself, such as, in FIG. 5B and FIG. 5C). PDCP UL FMC was informed to the second apparatus 320 by the third apparatus 330 via ‘SN (Sequence number) status Transfer message.

[0099] Based on a successful RA, the second apparatus 320 may transmit (765-1,765-2) UL grants 765A based on the BSR reported in Message 3. In this way, once the RACH is successfully completed, both UE and gNB are aware of the PDCP Sequence Number the transmission may start (i.e. after FMC).

[0100] In some cases, if any of UL and DL count are not exchanges during RACH, the transmitter will fall back to legacy way of working. In the example of FIG. 7, PDCP STATUS REPORT (for UL data) along with DL data having PDCP SN (>=DL count) 770A may be transmitted (770-1, 770-2) from the first apparatus 310 to the second apparatus 320. PDCP STATUS REPORT (for DL data) along with UL data having PDCP SN (>= UL count) 775A may be transmitted (775-1, 775-2) from the first apparatus 310 to the second apparatus 320.

[0101] FIG. 8 shows a flowchart of an example method 800 implemented at a first apparatus for wireless communication in accordance with some example embodiments of the present disclosure. The first apparatus may be the first apparatus 310 in FIG. 3 and below examples will be discussed with reference to FIG. 4 to FIG. 7.

[0102] At block 810, the first apparatus receives (410-2, 720-2, 810), a configuration(460-1, 720) from a third apparatus (330, 1300), for triggering the first apparatus (310, 1300) to initiate a random access (RA) procedure (495, 780) with a second apparatus (320, 1300). At block 820, the first apparatus receives (430-2, 750-2, 820), during the RA procedure (495, 780), a message (480-1, 500B, 500C, 750A) from the second apparatus (320, 1300), wherein the message (480-1, 500B, 500C, 750A) includes packet sequence number information (480-2, 750B) related to a transmission (402, 705B) from the first apparatus (310, 1300) to the third apparatus (330, 1300). At block 830, after completion of the RA procedure (495, 780) with the second apparatus (320, 1300), the first apparatus receives transmits (440-1, 770-1, 830), to the second apparatus (320, 1300), at least one data packet (490-1, 770A) based on the packet sequence number information (480-2, 750B).

[0103] In some example embodiments, all the example embodiments discussed with reference to FIG. 4 to FIG. 7 may be applicable to the first apparatus. Merely for brevity, the same contents are omitted.

[0104] FIG. 9 shows a flowchart of an example method 900 implemented at a second apparatus for wireless communication in accordance with some example embodiments of the present disclosure. The second apparatus may be the second apparatus 320 in FIG. 3 and below examples will be discussed with reference to FIG. 4 to FIG. 7.

[0105] At block 910, the second apparatus receives, from a third apparatus (330, 1300), packet sequence number information (480-2, 750B) related to a transmission (402, 705B) from the first apparatus (310, 1300) to the third apparatus (330, 1300). At block 920, the second apparatus transmits (430-1, 750-1, 920), during a random access (RA) procedure (495, 780) with a first apparatus (310, 1300), a message (480-1, 500B, 500C, 750A) to the first apparatus (310, 1300), wherein the message (480-1, 500B, 500C, 750A) includes packet sequence number information (480-2, 750B) related to the transmission (402, 705B) from the first apparatus (310, 1300) to a third apparatus (330, 1300). At block 930, the second apparatus receives (440-2, 770-2, 930), from the first apparatus (310, 1300), at least one data packet (490-1, 770A) based on the packet sequence number information (480-2, 750B), after completion of the RA procedure (495, 780) with the second apparatus (320, 1300).

[0106] In some example embodiments, all the example embodiments discussed with reference to FIG. 4 to FIG. 7 may be applicable to the second apparatus. Merely for brevity, the same contents are omitted.

[0107] FIG. 10 shows a flowchart of an example method 1000 implemented at a first apparatus for wireless communication in accordance with some example embodiments of the present disclosure. The first apparatus may be the first apparatus 310 in FIG. 3 and below examples will be discussed with reference to FIG. 4 to FIG. 7.

[0108] At block 1010, the first apparatus receives (410-2, 720-2, 1010) a configuration (460-1, 720) from a third apparatus (330, 1300), for triggering the first apparatus (310, 1300) to initiate a random access (RA) procedure (495, 780) with a second apparatus (320, 1300). At block 1020, the first apparatus transmits (420-1, 755-1, 1020), during the RA procedure (495, 780) with the second apparatus (320, 1300), a message (470-1, 600B, 755 A) to the second apparatus (320, 1300), wherein the message (470-1, 600B, 755 A) includes packet sequence number information (470-2, 755B) related to a transmission (401, 705 A) from the third apparatus (330, 1300) to the first apparatus (310, 1300). At block 1030, the first apparatus receives (450-2, 775-2, 1020), from the second apparatus (320, 1300), at least one data packet (490-2, 775A) based on the packet sequence number information (470-2, 755B), after completion of the RA procedure (495, 780) with the second apparatus (320, 1300).

[0109] In some example embodiments, all the example embodiments discussed with reference to FIG. 4 to FIG. 7 may be applicable to the first apparatus. Merely for brevity, the same contents are omitted.

[0110] FIG. 11 shows a flowchart of an example method 1100 implemented at a second apparatus for wireless communication in accordance with some example embodiments of the present disclosure. The second apparatus may be the second apparatus 320 in FIG. 3 and below examples will be discussed with reference to FIG. 4 to FIG. 7.

[0111] At block 1110, the second apparatus receives (420-2, 755-2, 1110), during a random access (RA) procedure (495, 780) with a first apparatus (310, 1300), a message (470-1, 600B, 755A) from the first apparatus (310, 1300), wherein the message (470-1, 600B, 755A) includes packet sequence number information (470-2, 755B) related to a transmission (401, 705 A) from the third apparatus (330, 1300) to the first apparatus (310, 1300). At block 1120, second apparatus transmits (450-1, 775-1, 1120), to the first apparatus (310, 1300), at least one data packet (490-2, 775A) based on the packet sequence number information (470-2, 755B), after completion of the RA procedure (495, 780) with the second apparatus (320, 1300).

[0112] In some example embodiments, all the example embodiments discussed withreference to FIG. 4 to FIG. 7 may be applicable to the second apparatus. Merely for brevity, the same contents are omitted.

[0113] FIG. 12 shows a flowchart of an example method 1200 implemented at a third apparatus for wireless communication in accordance with some example embodiments of the present disclosure. The third apparatus may be the second apparatus 330 in FIG. 3 and below examples will be discussed with reference to FIG. 4 to FIG. 7.

[0114] At block 1210, the third apparatus generates (405, 1210) a configuration (460-1, 720) for triggering the first apparatus (310, 1300) to initiate a random access (RA) procedure (495, 780) with a second apparatus (320, 1300), wherein the configuration (460-1, 720) includes at least one of the following: an indication (460-2) indicating the first apparatus (310, 1300) to report packet sequence number information (470-2, 755B) related to a transmission (401, 705A) from the third apparatus (330, 1300) to the first apparatus (310, 1300) to the second apparatus (320, 1300), or at least one radio bearer and / or at least one logical channel related to the packet sequence number information (470-2, 755B). At block 1220, the third apparatus transmits(410-l, 1220), the configuration (460-1, 720) to the first apparatus (310, 1300).

[0115] In some example embodiments, all the example embodiments discussed with reference to FIG. 4 to FIG. 7 may be applicable to the third apparatus. Merely for brevity, the same contents are omitted.

[0116] In some example embodiments, a first apparatus for wireless communication capable of performing any of the method 800 or 1000 may include means for performing the respective operations of the method 800 or 1000. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The first apparatus for wireless communication may be implemented as or included in the first apparatus 310 in FIG. 3.

[0117] In some example embodiments, the first apparatus (310 1300) for wireless communication includes means for receiving (410-2, 720-2, 810), a configuration (460-1, 720) from a third apparatus (330, 1300), for triggering the first apparatus (310, 1300) to initiate a random access (RA) procedure (495, 780) with a second apparatus (320, 1300); means for receiving (430-2, 750-2, 820), during the RA procedure (495, 780), a message (480-1, 500B, 500C, 750A) from the second apparatus (320, 1300), wherein the message (480-1, 500B, 500C, 750A) includes packet sequence number information (480-2, 750B) related to a transmission (402, 705B) from the first apparatus (310, 1300) to the thirdapparatus (330, 1300); and means for after completion of the RA procedure (495, 780) with the second apparatus (320, 1300), transmitting (440-1, 770-1, 830), to the second apparatus (320, 1300), at least one data packet (490-1, 770A) based on the packet sequence number information (480-2, 750B).

[0118] In some example embodiments, the first apparatus (310 1300) for wireless communication includes receive(410-2, 720-2, 1010) a configuration (460-1, 720) from a third apparatus (330, 1300), for triggering the first apparatus (310, 1300) to initiate a random access (RA) procedure (495, 780) with a second apparatus (320, 1300); means for transmitting (420-1, 755-1, 1020), during the RA procedure (495, 780) with the second apparatus (320, 1300), a message (470-1, 600B, 755A) to the second apparatus (320, 1300), wherein the message (470-1, 600B, 755A) includes packet sequence number information (470-2, 755B) related to a transmission (401, 705A) from the third apparatus (330, 1300) to the first apparatus (310, 1300); and means for receiving (450-2, 775-2, 1020), from the second apparatus (320, 1300), at least one data packet (490-2, 775A) based on the packet sequence number information (470-2, 755B), after completion of the RA procedure (495, 780) with the second apparatus (320, 1300).

[0119] In some example embodiments, a second apparatus for wireless communication capable of performing any of the method 900 or 1100 may include means for performing the respective operations of the method 900 or 1100. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus for wireless communication may be implemented as or included in the second apparatus 320 in FIG. 3.

[0120] In some example embodiments, the second apparatus (320 1300) for wireless communication includes at least one memory (1320) storing instructions that, when executed by the at least one processor (1310), cause the second apparatus (320, 1300) to: means for receiving (710-2, 910), from a third apparatus (330, 1300), packet sequence number information (480-2, 750B) related to a transmission (402, 705B) from the first apparatus (310, 1300) to the third apparatus (330, 1300); means for transmitting (430-1, 750-1, 920), during a random access (RA) procedure (495, 780) with a first apparatus (310, 1300), a message (480-1, 500B, 500C, 750A) to the first apparatus (310, 1300), wherein the message (480-1, 500B, 500C, 750A) includes packet sequence number information (480-2, 750B) related to the transmission (402, 705B) from the first apparatus (310, 1300) to a third apparatus (330, 1300); and means for receiving (440-2, 770-2, 930), from thefirst apparatus (310, 1300), at least one data packet (490-1, 770A) based on the packet sequence number information (480-2, 750B), after completion of the RA procedure (495, 780) with the second apparatus (320, 1300).

[0121] In some example embodiments, the second apparatus (320 1300) for wireless communication includes means for receiving (420-2, 755-2, 1110), during a random access (RA) procedure (495, 780) with a first apparatus (310, 1300), a message (470-1, 600B, 755A) from the first apparatus (310, 1300), wherein the message (470-1, 600B, 755A) includes packet sequence number information (470-2, 755B) related to a transmission (401, 705 A) from the third apparatus (330, 1300) to the first apparatus (310, 1300); and means for transmitting (450-1, 775-1, 1120), to the first apparatus (310, 1300), at least one data packet (490-2, 775A) based on the packet sequence number information (470-2, 755B), after completion of the RA procedure (495, 780) with the second apparatus (320, 1300).

[0122] In some example embodiments, a third apparatus for wireless communication capable of performing any of the method 1200 may include means for performing the respective operations of the method 1200. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The third apparatus for wireless communication may be implemented as or included in the third apparatus 330 in FIG. 3.

[0123] In some example embodiments, the third apparatus (330 1300) for wireless communication includes means for generating (405, 1210) a configuration (460-1, 720) for triggering the first apparatus (310, 1300) to initiate a random access (RA) procedure (495, 780) with a second apparatus (320, 1300), wherein the configuration (460-1, 720) includes at least one of the following: an indication (460-2) indicating the first apparatus (310, 1300) to report packet sequence number information (470-2, 755B) related to a transmission (401, 705 A) from the third apparatus (330, 1300) to the first apparatus (310, 1300) to the second apparatus (320, 1300), or at least one radio bearer and / or at least one logical channel related to the packet sequence number information (470-2, 755B); and means for transmitting (410-1, 1220), the configuration (460-1, 720) to the first apparatus (310, 1300).

[0124] FIG. 13 is a simplified block diagram of a device 1300 that is suitable for implementing example embodiments of the present disclosure. The device 1300 may be provided to implement a communication device, for example, the first apparatus 310, thesecond apparatus 320 and the third apparatus 330 as shown in FIG. 3. As shown, the device 1300 includes one or more processors 1310, one or more memories 1320 coupled to the processor 1310, and one or more communication modules 1340 coupled to the processor 1310.

[0125] The communication module 1340 is for bidirectional communications. The communication module 1340 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 1340 may include at least one antenna.

[0126] The processor 1310 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 1300 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.

[0127] The memory 1320 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) 1324, 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) 1322 and other volatile memories that will not last in the power-down duration.

[0128] A computer program 1330 includes computer executable instructions that are executed by the associated processor 1310. The instructions of the program 1330 may include instructions for performing operations / acts of some example embodiments of the present disclosure. The program 1330 may be stored in the memory, e.g., the ROM 1324. The processor 1310 may perform any suitable actions and processing by loading the program 1330 into the RAM 1322.

[0129] The example embodiments of the present disclosure may be implemented by means of the program 1330 so that the device 1300 may perform any process of the disclosure as discussed with reference to FIG. 3 to FIG. 12. The example embodimentsof the present disclosure may also be implemented by hardware or by a combination of software and hardware.

[0130] In some example embodiments, the program 1330 may be tangibly contained in a computer readable medium which may be included in the device 1300 (such as in the memory 1320) or other storage devices that are accessible by the device 1300. The device 1300 may load the program 1330 from the computer readable medium to the RAM 1322 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).

[0131] FIG. 14 shows an example of the computer readable medium 1400 which may be in form of CD, DVD or other optical storage disk. The computer readable medium 1400 has the program 1330 stored thereon.

[0132] In one aspect, there is provided a first apparatus (310, 1300) for wireless communication, may include: at least one processor (1310); and at least one memory (1320) storing instructions that, when executed by the at least one processor (1310), cause the first apparatus (310, 1300) to: receive (410-2, 720-2, 810), a configuration (460-1, 720) from a third apparatus (330, 1300), for triggering the first apparatus (310, 1300) to initiate a random access (RA) procedure (495, 780) with a second apparatus (320, 1300); receive (430-2, 750-2, 820), during the RA procedure (495, 780), a message (480-1, 500B, 500C, 750A) from the second apparatus (320, 1300), wherein the message (480-1, 500B, 500C, 750A) may include packet sequence number information (480-2, 750B) related to a transmission (402, 705B) from the first apparatus (310, 1300) to the third apparatus (330, 1300); and after completion of the RA procedure (495, 780) with the second apparatus (320, 1300), transmit (440-1, 770-1, 830), to the second apparatus (320, 1300), at least one data packet (490-1, 770A) based on the packet sequence number information (480-2, 750B).

[0133] In some example embodiments, the packet sequence number information (480-2, 750B) relates to at least one radio bearer and / or at least one logical channel.

[0134] In some example embodiments, the at least one radio bearer is indicated by the message (480-1, 500B, 500C, 750A) or the configuration (460-1, 720), and / or the at least one logical channel is indicated by the message (480-1, 500B, 500C, 750A) or theconfiguration (460-1, 720).

[0135] In some example embodiments, the first apparatus (310, 1300) is further caused to: during the RA procedure (495, 780), transmit (420-1, 755-1) a further message (470-1, 600B, 755A) to the second apparatus (320, 1300), the further message (470-1, 600B, 755A) may include an indication (610) requesting the second apparatus (320, 1300) to transmit (430-1) the packet sequence number information (480-2, 750B) to the first apparatus (310, 1300).

[0136] In some example embodiments, the message (480-1, 500B, 500C, 750A) further may include a first field (510), and in accordance with a determination that the first field (510) is set to a first value, the packet sequence number information (480-2, 750B) is included in the message (480-1, 500B, 500C, 750A); and in accordance with a determination that the first field (510) is set to a second value, the packet sequence number information (480-2, 750B) is absent in the message (480-1, 500B, 500C, 750A).

[0137] In some example embodiments, the first apparatus (310, 1300) is further caused to: during the RA procedure (495, 780) with the second apparatus (320, 1300), transmit (440-1, 755-1) a further message (470-1, 600B, 755A) to the second apparatus (320, 1300), wherein the further message (470-1, 600B, 755A) may include further packet sequence number information (470-2, 755B) related to a transmission (401, 705A) from the third apparatus (330, 1300) to the first apparatus (310, 1300); and after completion of the RA procedure (495, 780) with the second apparatus (320, 1300), receive (450-2, 775-2), from the second apparatus (320, 1300), at least one further data packet (490-2, 775 A) based on the further packet sequence number information (470-2, 755B).

[0138] In some example embodiments, the message (480-1, 500B, 500C, 750A) further may include an indication (520) indicating the first apparatus (310, 1300) to report the further packet sequence number information (470-2, 755B); and the first apparatus is further caused to in response to the indication (520), transmit the further message (470-1, 600B, 755 A) may include the further packet sequence number information (470-2, 755B) to the second apparatus (320, 1300).

[0139] In some example embodiments, the configuration (460-1, 720) may include an indication (460-2) indicating the first apparatus (310, 1300) to report the further packet sequence number information (470-2, 755B).

[0140] In some example embodiments, the further message (470-1, 600B, 755A) further may include a first field (620), and in accordance with a determination that the first field(620) is set to a first value, the further packet sequence number information (470-2, 755B) is included in the further message (470-1, 600B, 755A); and in accordance with a determination that the first field (620) is set to a second value, the further packet sequence number information (470-2, 755B) is absent in the further message (470-1, 600B, 755 A).

[0141] In some example embodiments, the further message (470-1, 600B, 755 A) is a message 3 in a 4-step RA procedure or a message A in a 2-step RA procedure.

[0142] In some example embodiments, the packet sequence number information (480-2, 750B) indicates a sequency number of a first packet data convergence protocol (PDCP) packet that has not been successfully delivered.

[0143] In some example embodiments, the message (480-1, 500B, 500C, 750A) is a message 2 in a 4-step RA procedure or a message B in a 2-step RA procedure.

[0144] In some example embodiments, the RA procedure (495, 780) is a contention free random access (CFRA) procedure.

[0145] In some example embodiments, the first apparatus (310, 1300) may include a terminal device, the second apparatus (320, 1300) may include a target network device, and the third apparatus (330, 1300) may include a source network device.

[0146] In one aspect, there is provided a second apparatus (320, 1300) for wireless communication, may include: at least one processor; and at least one processor (1310); and at least one memory (1320) storing instructions that, when executed by the at least one processor (1310), cause the second apparatus (320, 1300) to: receive (710-2, 910), from a third apparatus (330, 1300), packet sequence number information (480-2, 750B) related to a transmission (402, 705B) from the first apparatus (310, 1300) to the third apparatus (330, 1300); transmit (430-1, 750-1, 920), during a random access (RA) procedure (495, 780) with a first apparatus (310, 1300), a message (480-1, 500B, 500C, 750A) to the first apparatus (310, 1300), wherein the message (480-1, 500B, 500C, 750A) may include packet sequence number information (480-2, 750B) related to the transmission (402, 705B) from the first apparatus (310, 1300) to a third apparatus (330, 1300); and receive (440-2, 770-2, 930), from the first apparatus (310, 1300), at least one data packet (490-1, 770A) based on the packet sequence number information (480-2, 750B), after completion of the RA procedure (495, 780) with the second apparatus (320, 1300).

[0147] In some example embodiments, the packet sequence number information (480-2, 750B) relates to at least one radio bearer and / or at least one logical channel.

[0148] In some example embodiments, the at least one radio bearer and / or the at least one logical channel is indicated by the message (480-1, 500B, 500C, 750A).

[0149] In some example embodiments, the second apparatus is further caused to: during the RA procedure (495, 780), receive (420-2, 755-2) a further message (470-1, 600B, 755A) from the first second apparatus (320, 1300), the further message (470-1, 600B, 755A) may include an indication (610) requesting the second apparatus (320, 1300) to transmit the packet sequence number information (480-2, 750B).

[0150] In some example embodiments, the message (480-1, 500B, 500C, 750A) further may include a first field (510), and in accordance with a determination that the first field (510) is set to a first value, the first packet sequence number information (480-2, 750B) is included in the message (480-1, 500B, 500C, 750A); and in accordance with a determination that the first field (510) is set to a second value, the first packet sequence number information (480-2, 750B) is absent in the message (480-1, 500B, 500C, 750A).

[0151] In some example embodiments, the second apparatus (320, 1300) is further caused to: during the RA procedure (495, 780) with the second apparatus (320, 1300), receive (440-2, 755-2) a further message (470-1, 600B, 755A) from the first apparatus (310, 1300), wherein the further message (470-1, 600B, 755 A) may include further packet sequence number information (470-2, 755B) related to a transmission (401, 705 A) from the third apparatus (330, 1300) to the first apparatus (310, 1300); and after completion of the RA procedure (495, 780) with the second apparatus (320, 1300), transmit (450-1, 775-1), to the first apparatus (310, 1300), at least one further data packet (490-2, 775A) based on the further packet sequence number information (470-2, 755B).

[0152] In some example embodiments, the further message (470-1, 600B, 755 A) is a message 3 in a 4-step RA procedure or a message A in a 2-step RA procedure.

[0153] In some example embodiments, the packet sequence number information (480-2, 750B) indicates a sequency number of the first packet data convergence protocol (PDCP) packet that has not been successfully delivered.

[0154] In some example embodiments, the message (480-1, 500B, 500C, 750A) is a message 2 in a 4-step RA procedure or a message B in a 2-step RA procedure.

[0155] In one aspect, there is provided a first apparatus (310, 1300) for wireless communication, may include: at least one processor (1310); and at least one memory (1320) storing instructions that, when executed by the at least one processor (1310), cause the first apparatus (310, 1300) to: receive (410-2, 720-2, 1010) a configuration (460-1,720) from a third apparatus (330, 1300), for triggering the first apparatus (310, 1300) to initiate a random access (RA) procedure (495, 780) with a second apparatus (320, 1300); transmit (420-1, 755-1, 1020), during the RA procedure (495, 780) with the second apparatus (320, 1300), a message (470-1, 600B, 755A) to the second apparatus (320, 1300), wherein the message (470-1, 600B, 755 A) may include packet sequence number information (470-2, 755B) related to a transmission (401, 705A) from the third apparatus (330, 1300) to the first apparatus (310, 1300); and receive (450-2, 775-2, 1020), from the second apparatus (320, 1300), at least one data packet (490-2, 775A) based on the packet sequence number information (470-2, 755B), after completion of the RA procedure (495, 780) with the second apparatus (320, 1300).

[0156] In some example embodiments, the packet sequence number information (470-2, 755B) relates to at least one radio bearer and / or at least one logical channel.

[0157] In some example embodiments, the at least one radio bearer is indicated by the message (470-1, 600B, 755A) or the configuration (460-1, 720), and / or the at least one logical channel is indicated by the message (470-1, 600B, 755A) or the configuration (460-1, 720).

[0158] In some example embodiments, the first apparatus (310, 1300) is further caused to: during the RA procedure (495, 780), receive, from the second apparatus (320, 1300), a further message (480-1, 500B, 500C, 750A) may include an indication (520) indicating the first apparatus (310, 1300) to report the packet sequence number information (470-2, 755B); and in response to the indication (520), transmit the message (470-1, 600B, 755A) may include the packet sequence number information (470-2, 755B) to the second apparatus (320, 1300).

[0159] In some example embodiments, the configuration (460-1, 720) may include an indication (460-2) indicating the first apparatus (310, 1300) to report the packet sequence number information (470-2, 755B).

[0160] In some example embodiments, the message (470-1, 600B, 755A) further may include a first field (620), and in accordance with a determination that the first field (620) is set to a first value, the packet sequence number information (470-2, 755B) is included in the message (470-1, 600B, 755 A); and in accordance with a determination that the first field (620) is set to a second value, the packet sequence number information (470-2, 755B) is absent in the message (470-1, 600B, 755A).

[0161] In some example embodiments, the packet sequence number information (470-2, 755B) is a sequency number of the first packet data convergence protocol (PDCP) packet that has not been successfully delivered.

[0162] In some example embodiments, the message (470-1, 600B, 755A) is a message 3 in a 4-step RA procedure or a message A in a 2-step RA procedure.

[0163] In some example embodiments, the RA procedure (495, 780) is a contention free random access (CFRA) procedure.

[0164] In some example embodiments, the first apparatus (310, 1300) may include a terminal device, the second apparatus (320, 1300) may include a target network device, and the third apparatus (330, 1300) may include a serving network device.

[0165] In one aspect, there is provided a second apparatus (320, 1300) for wireless communication, may include: at least one processor (1310); and at least one memory (1320) storing instructions that, when executed by the at least one processor (1310), cause the second apparatus (320, 1300) to: receive (420-2, 755-2, 1110), during a random access (RA) procedure (495, 780) with a first apparatus (310, 1300), a message (470-1, 600B, 755 A) from the first apparatus (310, 1300), wherein the message (470-1, 600B, 755 A) may include packet sequence number information (470-2, 755B) related to a transmission (401, 705A) from the third apparatus (330, 1300) to the first apparatus (310, 1300); and transmit (450-1, 775-1, 1120), to the first apparatus (310, 1300), at least one data packet (490-2, 775A) based on the packet sequence number information (470-2, 755B), after completion of the RA procedure (495, 780) with the second apparatus (320, 1300).

[0166] In some example embodiments, the packet sequence number information (470-2, 755B) relates to at least one radio bearer and / or at least one logical channel.

[0167] In some example embodiments, the at least one radio bearer and / or the at least one logical channel is indicated by the message (470-1, 600B, 755A).

[0168] In some example embodiments, 14. The second apparatus (320, 1300) of any of claimsl 1 to 13, wherein the second apparatus (320, 1300) is further caused to: during the RA procedure (495, 780), transmit(430-l, 750-1), to the first apparatus (310, 1300), a further message (480-1, 500B, 500C, 750A) may include an indication (520) indicating the first apparatus (310, 1300) to report the packet sequence number information (470-2, 755B).

[0169] In some example embodiments, the message (470-1, 600B, 755A) further may include a first field (620), and in accordance with a determination that the first field (620) is set to a first value, the packet sequence number information (470-2, 755B) is includedin the message (470-1, 600B, 755 A); and in accordance with a determination that the first field (620) is set to a second value, the packet sequence number information (470-2, 755B) is absent in the message (470-1, 600B, 755A).

[0170] In some example embodiments, the packet sequence number information (470-2, 755B) is a sequency number of the first packet data convergence protocol (PDCP) packet that has not been successfully delivered.

[0171] In some example embodiments, the message (470-1, 600B, 755 A) is a message 3 in a 4-step RA procedure or a message A in a 2-step RA procedure.

[0172] In some example embodiments, the RA procedure (495, 780) is a contention free random access (CFRA) procedure.

[0173] In some example embodiments, the first apparatus (310, 1300) may include a terminal device, the second apparatus (320, 1300) may include a target network device, and the third apparatus (330, 1300) may include a source network device.

[0174] In one aspect, there is provided a third apparatus (330, 1300) for wireless communication, may include: at least one processor (1310); and at least one memory (1320) storing instructions that, when executed by the at least one processor (1310), cause the third apparatus (330, 1300) to: generate (405, 1210) a configuration (460-1, 720) for triggering the first apparatus (310, 1300) to initiate a random access (RA) procedure (495, 780) with a second apparatus (320, 1300), wherein the configuration (460-1, 720) may include at least one of the following: an indication (460-2) indicating the first apparatus (310, 1300) to report packet sequence number information (470-2, 755B) related to a transmission (401, 705 A) from the third apparatus (330, 1300) to the first apparatus (310, 1300) to the second apparatus (320, 1300), or at least one radio bearer and / or at least one logical channel related to the packet sequence number information (470-2, 755B); and transmit (410-1, 1220), the configuration (460-1, 720) to the first apparatus (310, 1300).

[0175] In some example embodiments, the third apparatus (330, 1300) is further caused to: transmit (710-1), to the second apparatus (320, 1300), further packet sequence number information (480-2, 750B) related to a transmission (402, 705B) from the first apparatus (310, 1300) to the third apparatus (330, 1300), such that the second apparatus (320, 1300) transmit the further packet sequence number information (480-2, 750B) to the first apparatus (310, 1300) during the RA procedure (495, 780).

[0176] In some example embodiments, the packet sequence number information (470- 2, 755B) is a sequency number of the first packet data convergence protocol (PDCP)packet that has not been successfully delivered.

[0177] 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 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.

[0178] 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.

[0179] 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.

[0180] 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 toperform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like.

[0181] 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), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0182] Further, although operations are depicted in a particular order, this may 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, although several specific implementation details are contained in the above discussions, these may 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.

[0183] 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.

Claims

We Claim:

1. A first apparatus (310, 1300) for wireless communication, comprising: at least one processor (1310); andat least one memory (1320) storing instructions that, when executed by the at least one processor (1310), cause the first apparatus (310, 1300) to:receive (410-2, 720-2, 810), a configuration (460-1, 720) from a third apparatus (330, 1300), for triggering the first apparatus (310, 1300) to initiate a random access (RA) procedure (495, 780) with a second apparatus (320, 1300);receive (430-2, 750-2, 820), during the RA procedure (495, 780), a message (480-1, 500B, 500C, 750A) from the second apparatus (320, 1300), wherein the message (480-1, 500B, 500C, 750A) comprises packet sequence number information (480-2, 750B) related to a transmission (402, 705B) from the first apparatus (310, 1300) to the third apparatus (330, 1300); andafter completion of the RA procedure (495, 780) with the second apparatus (320, 1300), transmit (440-1, 770-1, 830), to the second apparatus (320, 1300), at least one data packet (490-1, 770A) based on the packet sequence number information (480-2, 750B).

2. The first apparatus (310, 1300) of claim 1, wherein the packet sequence number information (480-2, 750B) relates to at least one radio bearer and / or at least one logical channel.

3. The first apparatus (310, 1300) of claim 2, wherein the at least one radio bearer is indicated by the message (480-1, 500B, 500C, 750A) or the configuration (460-1, 720), and / or the at least one logical channel is indicated by the message (480-1, 500B, 500C, 750A) or the configuration (460-1, 720).

4. The first apparatus (310, 1300) of any of claims 1 to 3, wherein the first apparatus (310, 1300) is further caused to:during the RA procedure (495, 780), transmit (420-1, 755-1) a further message (470-1, 600B, 755A) to the second apparatus (320, 1300), the further message (470-1, 600B, 755A) comprising an indication (610) requesting the second apparatus (320, 1300) to transmit (430-1) the packet sequence number information (480-2, 750B) to the firstapparatus (310, 1300).

5. The first apparatus (310, 1300) of any of claims 1 to 4, wherein the message (480-1, 500B, 500C, 750A) further comprises a first field (510), and wherein,in accordance with a determination that the first field (510) is set to a first value, the packet sequence number information (480-2, 750B) is comprised in the message (480- 1, 500B, 500C, 750A); andin accordance with a determination that the first field (510) is set to a second value, the packet sequence number information (480-2, 750B) is absent in the message (480-1, 500B, 500C, 750A).

6. The first apparatus (310, 1300) of any of claims 1 to 5, wherein the first apparatus (310, 1300) is further caused to:during the RA procedure (495, 780) with the second apparatus (320, 1300), transmit (440-1, 755-1) a further message (470-1, 600B, 755A) to the second apparatus (320, 1300), wherein the further message (470-1, 600B, 755 A) comprises further packet sequence number information (470-2, 755B) related to a transmission (401, 705 A) from the third apparatus (330, 1300) to the first apparatus (310, 1300); andafter completion of the RA procedure (495, 780) with the second apparatus (320, 1300), receive (450-2, 775-2), from the second apparatus (320, 1300), at least one further data packet (490-2, 775A) based on the further packet sequence number information (470- 2, 755B).

7. The first apparatus (310, 1300) of claim 6, wherein the message (480-1, 500B, 500C, 750A) further comprises an indication (520) indicating the first apparatus (310, 1300) to report the further packet sequence number information (470-2, 755B), and wherein the first apparatus is further caused to:in response to the indication (520), transmit the further message (470-1, 600B, 755A) comprising the further packet sequence number information (470-2, 755B) to the second apparatus (320, 1300).

8. The first apparatus (310, 1300) of claim 6, wherein the configuration (460-1, 720) comprises an indication (460-2) indicating the first apparatus (310, 1300) to reportthe further packet sequence number information (470-2, 755B).

9. The first apparatus (310, 1300) of any of claims 6 to 8, wherein the further message (470-1, 600B, 755 A) further comprises a first field (620), and wherein,in accordance with a determination that the first field (620) is set to a first value, the further packet sequence number information (470-2, 755B) is comprised in the further message (470-1, 600B, 755A); andin accordance with a determination that the first field (620) is set to a second value, the further packet sequence number information (470-2, 755B) is absent in the further message (470-1, 600B, 755A).

10. The first apparatus (310, 1300) of any of claims 6 to 9, wherein the further message (470-1, 600B, 755A) is a message 3 in a 4-step RA procedure or a message A in a 2-step RA procedure.

11. The first apparatus (310, 1300) of any of claims 1 to 10, wherein the packet sequence number information (480-2, 750B) indicates a sequency number of a first packet data convergence protocol (PDCP) packet that has not been successfully delivered.

12. The first apparatus (310, 1300) of any of claims 1 to 11, wherein the message (480-1, 500B, 500C, 750A) is a message 2 in a 4-step RA procedure or a message B in a 2-step RA procedure.

13. The first apparatus (310, 1300) of any of claims 1 to 12, wherein the RA procedure (495, 780) is a contention free random access (CFRA) procedure.

14. The first apparatus (310, 1300) of any of claims 1 to 13, wherein the first apparatus (310, 1300) comprises a terminal device, the second apparatus (320, 1300) comprises a target network device, and the third apparatus (330, 1300) comprises a source network device.

15. A second apparatus (320, 1300) for wireless communication, comprising:at least one processor; andat least one processor (1310); andat least one memory (1320) storing instructions that, when executed by the at least one processor (1310), cause the second apparatus (320, 1300) to:receive (710-2, 910), from a third apparatus (330, 1300), packet sequence number information (480-2, 750B) related to a transmission (402, 705B) from the first apparatus (310, 1300) to the third apparatus (330, 1300);transmit (430-1, 750-1, 920), during a random access (RA) procedure (495, 780) with a first apparatus (310, 1300), a message (480-1, 500B, 500C, 750A) to the first apparatus (310, 1300), wherein the message (480-1, 500B, 500C, 750A) comprises packet sequence number information (480-2, 750B) related to the transmission (402, 705B) from the first apparatus (310, 1300) to a third apparatus (330, 1300); andreceive (440-2, 770-2, 930), from the first apparatus (310, 1300), at least one data packet (490-1, 770A) based on the packet sequence number information (480-2, 750B), after completion of the RA procedure (495, 780) with the second apparatus (320, 1300).

16. The second apparatus (320, 1300) of claim 15, wherein the packet sequence number information (480-2, 750B) relates to at least one radio bearer and / or at least one logical channel.

17. The second apparatus (320, 1300) of claim 16, wherein the at least one radio bearer and / or the at least one logical channel is indicated by the message (480-1, 500B, 500C, 750A).

18. The second apparatus (320, 1300) of any of claims 15 to 16, wherein the second apparatus is further caused to:during the RA procedure (495, 780), receive (420-2, 755-2) a further message (470-1, 600B, 755 A) from the first second apparatus (320, 1300), the further message (470-1, 600B, 755A) comprising an indication (610) requesting the second apparatus (320, 1300) to transmit the packet sequence number information (480-2, 750B).

19. The second apparatus (320, 1300) of any of claims 15 to 18, wherein the message (480-1, 500B, 500C, 750A) further comprises a first field (510), and wherein,in accordance with a determination that the first field (510) is set to a first value, the first packet sequence number information (480-2, 750B) is comprised in the message (480-1, 500B, 500C, 750A); andin accordance with a determination that the first field (510) is set to a second value, the first packet sequence number information (480-2, 750B) is absent in the message (480-l, 500B, 500C, 750A).

20. The second apparatus (320, 1300) of any of claims 15 to 19, wherein the second apparatus (320, 1300) is further caused to:during the RA procedure (495, 780) with the second apparatus (320, 1300), receive (440-2, 755-2) a further message (470-1, 600B, 755A) from the first apparatus (310, 1300), wherein the further message (470-1, 600B, 755A) comprises further packet sequence number information (470-2, 755B) related to a transmission (401, 705A) from the third apparatus (330, 1300) to the first apparatus (310, 1300); andafter completion of the RA procedure (495, 780) with the second apparatus (320, 1300), transmit (450-1, 775-1), to the first apparatus (310, 1300), at least one further data packet (490-2, 775A) based on the further packet sequence number information (470-2, 755B).

21. The second apparatus (320, 1300) of claim 20, wherein the further message (470-1, 600B, 755A) is a message 3 in a 4-step RA procedure or a message A in a 2-step RA procedure.

22. The second apparatus (320, 1300) of any of claims 15 to 21, wherein the packet sequence number information (480-2, 750B) indicates a sequency number of the first packet data convergence protocol (PDCP) packet that has not been successfully delivered.

23. The second apparatus (320, 1300) of any of claims 15 to 22, wherein the message (480-1, 500B, 500C, 750A) is a message 2 in a 4-step RA procedure or a message B in a 2-step RA procedure.

24. A method for a terminal device, comprising:receiving (410-2, 720-2, 810), a configuration (460-1, 720) from a source networkdevice (330, 1300), for triggering the terminal device (310, 1300) to initiate a random access (RA) procedure (495, 780) with a target network device (320, 1300);receiving (430-2, 750-2, 820), during the RA procedure (495, 780), a message (480-1, 500B, 500C, 750A) from the target network device (320, 1300), wherein the message (480-1, 500B, 500C, 750A) comprises packet sequence number information (480-2, 750B) related to a transmission (402, 705B) from the terminal device (310, 1300) to the third apparatus (330, 1300); andafter completion of the RA procedure (495, 780) with the target network device (320, 1300), transmitting (440-1, 770-1, 830), to the target network device (320, 1300), at least one data packet (490-1, 770A) based on the packet sequence number information (480-2, 750B).

25. A method for a target network device (320, 1300), comprising: receiving (710-2, 910), from a source network device (330, 1300), packet sequence number information (480-2, 750B) related to a transmission (402, 705B) from the terminal device (310, 1300) to the source network device (330, 1300);during a random access (RA) procedure (495, 780) with a terminal device (310, 1300), transmitting (430-1, 750-1, 920) a message (480-1, 500B, 500C, 750A) to the terminal device (310, 1300), wherein the message (480-1, 500B, 500C, 750A) comprises packet sequence number information (480-2, 750B) related to the transmission (402, 705B) from the terminal device (310, 1300) to a source network device (330, 1300); and after completion of the RA procedure (495, 780) with the target network device (320, 1300), receiving (440-2, 770-2, 930), from the terminal device (310, 1300), at least one data packet (490-1, 770A) based on the packet sequence number information (480-2, 750B).

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