Patent Publication Number: US-2023156551-A1

Title: Methods, devices, and computer readable medium for communication

Description:
TECHNICAL FIELD 
     Embodiments of the present disclosure generally relate to the field of telecommunication, and in particular, to methods, devices, and computer readable medium for communication. 
     BACKGROUND 
     In communication systems, a handover is a process in telecommunications and mobile communications in which a connected cellular call or a data session is transferred from one cell site (base station) to another without disconnecting the session. Handovers are a core element in planning and deploying cellular networks. It allows users to create data sessions or connect phone calls on the move. This process keeps the calls and data sessions connected even if a user moves from one cell site to another. During handover, there may be expected interruptions. 
     SUMMARY 
     In general, example embodiments of the present disclosure provide a solution for handling data inactivity for handover. 
     In a first aspect, there is provided a method for communication. The method comprises receiving, at a terminal device and from a source network device, a configuration of a data inactivity timer associated with the source network device. The method further comprises receiving from the source network device a command to handover from the source network device to the target network device, the terminal device being able to connect with the target network device while maintaining a connection with the source network device. The method also comprises in accordance with a determination that the data inactivity timer is expired, maintaining the terminal device to be in a radio resource control, RRC, connected state. 
     In a second aspect, there is provided a method for communication. The method comprises transmitting, at a source network device and to a terminal device, a configuration of a data inactivity timer associated with the source network device. The method also comprises transmitting to the terminal device network device a command to handover from the source network device to the target network device, the terminal device being able to connect with the target network device while maintaining a connection with the source network device. The method further comprises in accordance with a determination that the data inactivity timer is expired, releasing a link between the terminal device and the source network device. 
     In a third aspect, there is provided a terminal device. The terminal device comprises a processing unit; and a memory coupled to the processing unit and storing instructions thereon, the instructions, when executed by the processing unit, causing the terminal device to perform acts comprising: receiving, at the terminal device and from a source network device, a configuration of a data inactivity timer associated with the source network device; receiving from the source network device a command to handover from the source network device to the target network device, the terminal device being able to connect with the target network device while maintaining a connection with the source network device; and in accordance with a determination that the data inactivity timer is expired, maintaining the terminal device to be in a radio resource control, RRC, connected state. 
     In a fourth aspect, there is provided a source network device. The source network device comprises a processing unit; and a memory coupled to the processing unit and storing instructions thereon, the instructions, when executed by the processing unit, causing the source network device to perform acts comprising: transmitting, at the source network device and to a terminal device, a configuration of a data inactivity timer associated with the source network device; transmitting to the terminal device network device a command to handover from the source network device to the target network device, the terminal device being able to connect with the target network device while maintaining a connection with the source network device; and in accordance with a determination that the data inactivity timer is expired, releasing a link between the terminal device and the source network device. 
     In a fifth aspect, there is provided a computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor, causing the at least one processor to carry out the method according to any one of the first aspect, second aspect or third aspect. 
     Other features of the present disclosure will become easily comprehensible through the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Through the more detailed description of some example embodiments of the present disclosure in the accompanying drawings, the above and other objects, features and advantages of the present disclosure will become more apparent, wherein: 
         FIG.  1    is a schematic diagram of a communication environment in which embodiments of the present disclosure can be implemented; 
         FIG.  2    illustrates a signaling flow for handling data inactivity according to some embodiments of the present disclosure; 
         FIG.  3    illustrates a signaling flow for handling data inactivity according to some embodiments of the present disclosure; 
         FIG.  4    is a flowchart of an example method in accordance with an embodiment of the present disclosure; 
         FIG.  5    is a flowchart of an example method in accordance with an embodiment of the present disclosure; and 
         FIG.  6    is a simplified block diagram of a device that is suitable for implementing embodiments of the present disclosure. 
     
    
    
     Throughout the drawings, the same or similar reference numerals represent the same or similar element. 
     DETAILED DESCRIPTION 
     Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitations as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below. 
     In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of  ordinary skills in the art to which this disclosure belongs. 
     As used herein, the term “network device” refers to a device which is capable of providing or hosting a cell or coverage where terminal devices can communicate. Examples of a network device include, but not limited to, a Node B (NodeB or NB), an Evolved NodeB (eNodeB or eNB), a NodeB in new radio access (gNB) a Remote Radio Unit (RRU), a radio head (RH), a remote radio head (RRH), a low power node such as a femto node, a pico node, a satellite network device, an aircraft network device, and the like. For the purpose of discussion, in the following, some example embodiments will be described with reference to eNB as examples of the network device. 
     As used herein, the term “terminal device” refers to any device having wireless or wired communication capabilities. Examples of the terminal device include, but not limited to, user equipment (UE), personal computers, desktops, mobile phones, cellular phones, smart phones, personal digital assistants (PDAs), portable computers, tablets, wearable devices, internet of things (IoT) devices, Internet of Everything (IoE) devices, machine type communication (MTC) devices, device on vehicle for V2X communication where X means pedestrian, vehicle, or infrastructure/network, or image capture devices such as digital cameras, gaming devices, music storage and playback appliances, or Internet appliances enabling wireless or wired Internet access and browsing and the like. In the following description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably. 
     Communications discussed herein may use conform to any suitable standards including, but not limited to, New Radio Access (NR), Long Term Evolution (LTE), LTE-Evolution, LTE-Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), Code Division Multiple Access (CDMA), cdma2000, and Global System for Mobile Communications (GSM) and the like. Furthermore, the communications may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include, but not limited to, the first generation (1G), the second generation (2G), 2.5G, 2.85G, the third generation (3G), the fourth generation (4G), 4.5G, the fifth generation (5G) communication protocols. The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies. 
     As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term “includes” and its variants are to be read as open terms that mean “includes, but is not limited to.” The term “based on” is to be read as “based at least in part on.” The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment.” The term “another embodiment” is to be read as “at least one other embodiment.” The terms “first,” “second,” and the like may refer to different or same objects. Other definitions, explicit and implicit, may be included below. 
     In some examples, values, procedures, or apparatus are referred to as “best,” “lowest,” “highest,” “minimum,” “maximum,” or the like. It will be appreciated that such descriptions are intended to indicate that a selection among many used functional alternatives can be made, and such selections need not be better, smaller, higher, or otherwise preferable to other selections. 
     To reduce handover interruption, dual active protocol stack (DAPS) handover has been introduced. DAPS Handover is a handover procedure that maintains the source gNB connection after reception of RRC message for handover and until releasing the source cell after successful random access to the target gNB. 
     After receiving the DAPS handover command, the terminal device may create a medium access control (MAC) entity for the target network device and may establish a radio link control (RLC) entity and an associated logical channel for each data radio bearer configured with DAPS. For a data radio bearer (DRB) configured with DAPS, the terminal device may reconfigure a packet data convergence protocol (PDCP) entity with separate security and a robust header compression (ROHC) function for the source network device and the target network devices. The terminal device may also associate the PDCP entities with the RLC entities configured by the source network device and the target network devices, respectively. The terminal device may retain the rest configuration of the source network device until releasing the connection with the source network device. 
     Further, a data inactivity timer has been introduced in long term evolution (LTE) and new radio (NR) communication systems to fix radio resource control (RCC) state mismatching problem. In legacy handover, the MAC entity is reset and the data inactivity timer is stopped. And the data inactivity timer may not restart until the first uplink packet is transmitted to the target network device. Therefore, the expiry of data inactivity timer does not happen during the legacy handover. 
     For DAPS handover, since the MAC entity associated with the source network device is not reset, and a new MAC entity associated with the target network device is established. The data inactivity timer of the MAC entity of the source network device may continue running. Therefore, it is possible that data inactivity timer of the source network device may be expired during the DAPS handover. 
     As the data inactivity timer configuration is still valid for the source network device, how to handle this data inactivity timer for the source network device is not clear. Meanwhile, a further data inactivity timer may also be configured for the target network device, which will result in two data inactivity timers running for two MAC entities during the DAPS handover. 
     Moreover, as listen-before-talk (LBT) monitoring may still be performed at the MAC entity associated with the source network device, consistent LBT failure can happen for the MAC entity associated with the source network device and the MAC entity associated with the source network device, consistent LBT failure for the source network device shall not lead to radio link failure. 
     Currently, if the data inactivity timer is expired, the terminal device may enter into RRC idle state. However, this is not suitable for the DAPS handover. When the data inactivity timer of the source network device is expired, the terminal device may enter into the RRC idle state. But since the target network device is still expecting to establish connection with the UE, it is not disable for the UE to go to IDLE mode. 
     In order to solve at least part of the aforementioned problems, new technologies in handling data inactivity for handover are needed. According to embodiments of the present disclosure, if an expiration of a data inactivity timer occurs during a handover, a terminal device maintains in a RRC connected state. The terminal device releases a link with the source network device. Further, the terminal device is able to ignore the expiration of the data inactivity timer during the handover. In this way, the impact of data inactivity of the source network device is properly handled. Further, it avoids the terminal device being in RRC idle state for the target network device. 
       FIG.  1    illustrates a schematic diagram of a communication system in which embodiments of the present disclosure can be implemented. The communication system  100 , which is a part of a communication network, comprises a terminal device  310 - 1 , a  terminal device  110 - 2 , . . . , a terminal device  110 -N, which can be collectively referred to as “terminal device(s)  110 .” The number N can be any suitable integer number. 
     The communication system  100  further comprises network terminal device  120 - 1 , a network device  120 - 2 , . . . , a network device  120 -M, which can be collectively referred to as “network device(s)  120 .” The number M can be any suitable integer number. In the communication system  100 , the network devices  120  and the terminal devices  110  can communicate data and control information to each other. Only for the purpose of illustrations, the network device  120 - 1  can be regarded as a source network device and the network device  120 - 2  can be regarded as a target network device. The numbers of terminal devices and network devices shown in  FIG.  1    are given for the purpose of illustration without suggesting any limitations. 
     Communications in the communication system  100  may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols of the first generation (1G), the second generation (2G), the third generation (3G), the fourth generation (4G) and the fifth generation (5G) and on 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, comprising but not limited to: Code Divided Multiple Address (CDMA), Frequency Divided Multiple Address (FDMA), Time Divided Multiple Address (TDMA), Frequency Divided Duplexer (FDD), Time Divided Duplexer (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Divided Multiple Access (OFDMA) and/or any other technologies currently known or to be developed in the future. 
     Embodiments of the present disclosure will be described in detail below. Reference is first made to  FIG.  2   , which shows a signaling chart illustrating process  200  among network devices according to some example embodiments of the present disclosure. Only for the purpose of discussion, the process  200  will be described with reference to  FIG.  1   . The process  200  may involve the terminal device  110 - 1  and the network device  120 - 1  in  FIG.  1   . 
     The source network device  120 - 1  transmits  2005  to the terminal device  110 - 1  a configuration of a data inactivity timer associated with the source network device  120 - 1  to the terminal device  110 - 1 . For example, the terminal device  110 - 1  may be configured by RRC with a data inactivity monitoring functionality when the terminal device  110 - 1  is in RRC_CONNECTED state. The data inactivity operation can be controlled by configuring the data inactivity timer. The data inactivity timer may be restarted after the terminal device  110 - 1  performs the data reception and/or transmission with the source network device  120 - 1 . 
     The source network device  120 - 1  transmits  2010  a command to handover from the source network device  120 - 1  to the target network device  120 - 2 . The terminal device  110 - 1  may be able to connect with the target network device  120 - 2  while maintaining a connection with the source network device  120 - 1 . In other words, the handover may be a DAPS handover. 
     If the data inactivity timer is expired, the terminal device  110 - 1  maintains  2015  the RRC connected state. In some embodiments, if the data inactivity timer is expired, the lower layer (for example, the MAC layer) may inform the RRC layer the expiration of the data inactivity timer, for example, by transmitting an indication of the expiration. The terminal device  110 - 1  may determine whether the terminal device  110 - 1  has accessed to the target network device  120 - 2 . For example, if the terminal device  110 - 1  has not accessed to the target network device  120 - 2 , the terminal device  110 - 1  may ignore  2020  the expiration of the data inactivity timer and maintain itself in the RRC connected state. 
     Alternatively or in addition, the terminal device  110 - 1  may release  2025  a link between the source network device  120 - 1  and the terminal device  110 - 1 . For example, the terminal device  110 - 1  may suspend the transmission of all DRBs with the source network device  120 - 1 . In addition, the terminal device  110 - 1  may reset the MAC entity associated with the source network device  120 - 1 . In some embodiments, if the terminal device  110 - 1  does not access to the target network device  120 - 2 , the terminal device  110 - 1  may keep the RRC configuration of the source network device  120 - 1 . Alternatively or in addition, the terminal device  110 - 1  may stop  2030  the communication on a link between the source network device  120 - 1  and the terminal device  110 - 1 . 
     In some embodiments, the data inactivity timer may be expired after the terminal device  110 - 1  succeeds in accessing to the target network device  120 - 2 . In this situation, the terminal device  110 - 1  may also stop  2025  the communication on the link between the source network device  120 - 1  and the terminal device  110 - 1 . The terminal device  110 - 1  may release  2030  a link between the source network device  120 - 1  and the terminal device  110 - 1 . Further, the terminal device  110 - 1  may release the RRC configuration of the source network device  120 - 1 . For example, the terminal device  110 - 1  may reset the MAC entity associated with the source network device  120 - 1  and the MAC configuration associated with the source network device  120 - 1 . For each DAPS bearer, the terminal device  110 - 1  may release the RLC entity associated with the source network device  120 - 1  and reconfigure the PDCP entity to release DAPS. 
     In some embodiments, if the data inactivity timer is expired after the terminal device  110 - 1  succeeds in accessing to the target network device  120 - 2 , the terminal device  110 - 1  may ignore the expiration of the data inactivity timer and maintain itself in the RRC connected state. 
     In other embodiments, the data inactivity timer associated with the source network device  120 - 1  may be released. For example, the source network device  120 - 1  may transmit an indication to the terminal device  110 - 1 . The indication may be transmitted via the RRC message before the configuration of the DAPS handover. The indication may be used to release the data inactivity timer. The terminal device  110 - 1  may release  2040  the data inactivity timer based on the indication. Alternatively, the data inactivity timer may be released upon an implicit indication. For example, if the RRC message of the handover is received, the terminal device  110 - 1  may release  2040  the data inactivity timer. 
     Alternatively, the source network device  120 - 1  may transmit a further configuration of the data inactivity timer to the terminal device  110 - 1 . The further configuration may indicate an updated duration of the data inactivity timer. The terminal device  110 - 1  may extend  2050  a duration of the data inactivity timer based on the further configuration. For example, the extended duration may be longer than T 304 . 
     Alternatively, after the terminal device  110 - 1  succeeds in random accessing to the target network device  120 - 1 , a further data inactivity timer of the target network device  120 - 2  may be expired as well. Reference is made to  FIG.  3   , which shows a signaling chart illustrating process  300  among network devices according to some example embodiments of the present disclosure. Only for the purpose of discussion, the process  300  will be described with reference to  FIG.  1   . The process  300  may involve the terminal device  110 - 1  and the network device  120 - 1  in  FIG.  1   . 
     The source network device  120 - 1  may transmit  3005  a command to handover from the source network device  120 - 1  to the target network device  120 - 2 . The terminal device  110 - 1  may be able to connect with the target network device  120 - 2  while maintaining a connection with the source network device  120 - 1 . In other words, the handover may be a DAPS handover. 
     The terminal device  110 - 1  may activate  3010  the further data inactivity timer associated with the target network device  120 - 2 . In some embodiments, if the further data inactivity timer is expired, the lower layer (for example, the MAC layer) may inform the RRC layer the expiration of the further data inactivity timer, for example, by transmitting an indication of the expiration. The terminal device  110 - 1  may enter  3035  into the RRC idle state after the further data inactivity timer is expired. 
     Alternatively, if the further data inactivity timer is expired, the terminal device  110 - 1  may determine  3020  whether the link between the source network device  120 - 1  and the terminal device  110 - 1  is maintained or not. In some embodiments, if the link between the source network device  120 - 1  and the terminal device  110 - 1  is maintained, the terminal device  110 - 1  may ignore  3025  the expiration of the further data inactivity timer. The further data inactivity timer may be reset  3030  at the MAC layer of the terminal device  110 - 1 . Alternatively, if the link between the source network device  120 - 1  and the terminal device  110 - 1  has been released, the terminal device  110 - 1  may enter  3035  into the RRC idle state. 
     In other embodiments, the further data inactivity timer associated with the target network device  120 - 2  may not be configured before the data inactivity timer associated with the source network device  120 - 1  is released. For example, the command transmitted  3005  from the source network device  120 - 1  may exclude the configuration of the further data inactivity timer. 
     According to embodiment of the present disclosure, if an expiration of the data inactivity timer associated with the source network device occurs during a handover, the terminal device maintains in a RRC connected state. In this way, the impact of data inactivity of the source network device is properly handled. Further, it avoids the terminal device being in RRC idle state for the target network device. Moreover, the impact of data inactivity of the target network device is also properly handled. 
       FIG.  4    shows a flowchart of an example method  400  in accordance with an embodiment of the present disclosure. Only for the purpose of illustrations, the method  400  can be implemented at a terminal device  110 - 1  as shown in  FIG.  1   . 
     At block  410 , the terminal device  110 - 1  receives from the source network device  120 - 1  a configuration of a data inactivity timer associated with the source network device  120 - 1  to the terminal device  110 - 1 . For example, the terminal device  110 - 1  may be configured by RRC with a data inactivity monitoring functionality when the terminal device  110 - 1  is in RRC CONNECTED state. The data inactivity operation can be controlled by configuring the data inactivity timer. The data inactivity timer may be restarted after the terminal device  110 - 1  performs the data reception and/or transmission with the source network device  120 - 1 . 
     At block  420 , the terminal device  110 - 1  receives a command to handover from the source network device  120 - 1  to the target network device  120 - 2 . The terminal device  110 - 1  may be able to connect with the target network device  120 - 2  while maintaining a connection with the source network device  120 - 1 . In other words, the handover may be a DAPS handover. 
     At block  430 , if the data inactivity timer is expired, the terminal device  110 - 1  maintains the RRC connected state. In some embodiments, if the data inactivity timer is expired, the lower layer (for example, the MAC layer) may inform the RRC layer the expiration of the data inactivity timer, for example, by transmitting an indication of the expiration. The terminal device  110 - 1  may determine whether the terminal device  110 - 1  is able to access the target network device  120 - 2 . For example, if the terminal device  110 - 1  does not access to the target network device  120 - 2 , the terminal device  110 - 1  may ignore the expiration of the data inactivity timer and maintain itself in the RRC connected state. Alternatively or in addition, the terminal device  110 - 1  may stop the communication on a link between the source network device  120 - 1  and the terminal device  110 - 1 . 
     In some embodiments, if the data inactivity timer is expired, the terminal device  110 - 1  releases a link between the source network device  120 - 1  and the terminal device  110 - 1 . For example, the terminal device  110 - 1  may suspend the transmission of all DRBs with the source network device  120 - 1 . In addition, the terminal device  110 - 1  may reset the MAC entity associated with the source network device  120 - 1 . In some embodiments, if the terminal device  110 - 1  does not access to the target network device  120 - 2 , the terminal device  110 - 1  may keep the RRC configuration of the source network device  120 - 1 . 
     In some embodiments, the data inactivity timer may be expired after the terminal device  110 - 1  succeeds in accessing to the target network device  120 - 2 . In this situation, the terminal device  110 - 1  may also stop  2025  the communication on the link between the source network device  120 - 1  and the terminal device  110 - 1 . The terminal device  110 - 1  may release a link between the source network device  120 - 1  and the terminal device  110 - 1 . Further, the terminal device  110 - 1  may release the RRC configuration of the source network device  120 - 1 . For example, the terminal device  110 - 1  may reset the MAC entity associated with the source network device  120 - 1  and the MAC configuration associated with the source network device  120 - 1 . For each DAPS bearer, the terminal device  110 - 1  may release the RLC entity associated with the source network device  120 - 1  and reconfigure the PDCP entity to release DAPS. 
     In some embodiments, if the data inactivity timer is expired after the terminal device  110 - 1  succeeds in accessing to the target network device  120 - 2 , the terminal device  110 - 1  may ignore the expiration of the data inactivity timer and maintain itself in the RRC connected state. 
     In other embodiments, the data inactivity timer associated with the source network device  120 - 1  may be released. For example, the source network device  120 - 1  may transmit an indication to the terminal device  110 - 1 . The indication may be transmitted via the RRC message before the configuration of the DAPS handover. The indication may be used to release the data inactivity timer. The terminal device  110 - 1  may release the data inactivity timer based on the indication. Alternatively, the data inactivity timer may be released upon an implicit indication. For example, if the RRC message of the handover is received, the terminal device  110 - 1  may release the data inactivity timer. 
     Alternatively, the source network device  120 - 1  may transmit a further configuration of the data inactivity timer to the terminal device  110 - 1 . The further configuration may indicate an updated duration of the data inactivity timer. The terminal device  110 - 1  may extend a duration of the data inactivity timer based on the further configuration. For example, the extended duration may be longer than T 304 . 
     Alternatively, after the terminal device  110 - 1  succeeds in random accessing to the target network device  120 - 2 , a further data inactivity timer of the target network device  120 - 2  may be expired as well. In some embodiments, the terminal device  110 - 1  may activate the further data inactivity timer associated with the target network device  120 - 2 . In some embodiments, if the further data inactivity timer is expired, the lower layer (for example, the MAC layer) may inform the RRC layer the expiration of the further data inactivity timer, for example, by transmitting an indication of the expiration. The terminal device  110 - 1  may enter  3035  into the RRC idle state after the further data inactivity timer is expired. 
     Alternatively, if the further data inactivity timer is expired, the terminal device  110 - 1  may determine whether the link between the source network device  120 - 1  and the terminal device  110 - 1  is maintained or not. In some embodiments, if the link between the source network device  120 - 1  and the terminal device  110 - 1  is maintained, the terminal device  110 - 1  may ignore the expiration of the further data inactivity timer. The further data inactivity timer may be reset at the MAC layer of the terminal device  110 - 1 . Alternatively, if the link between the source network device  120 - 1  and the terminal device  110 - 1  has been released, the terminal device  110 - 1  may enter into the RRC idle state. 
     In other embodiments, the further data inactivity timer associated with the target network device  120 - 2  may not be configured before the data inactivity timer associated with the source network device  120 - 1  is released. For example, the command transmitted  3005  from the source network device  120 - 1  may exclude the configuration of the further data inactivity timer. 
     In some embodiments, the terminal device  110 - 1  may perform listen-before-talk (LBT) on the link between the terminal device  110 - 1  and the source network device  120 - 1 . If the number of LBT failures exceeds a threshold number, if the terminal device  110 - 1  has not accessed to the target network device  120 - 2 , the terminal device  110 - 1  may determine that the radio link failure occurs on the link. In other words, if the indication of consistent LBT failures comes from the MAC entity of the source network device  120 - 1 , the terminal device  110 - 1  may consider the radio link failure to be detected. The terminal device  110 - 1  may stay in the RRC connected state. Alternatively or in addition, the terminal device  110 - 1  may stop the communication on a link between the source network device  120 - 1  and the terminal device  110 - 1 . The terminal device  110 - 1  may release a link between the source network device  120 - 1  and the terminal device  110 - 1 . For example, the terminal device  110 - 1  may suspend the transmission of all DRBs with the source network device  120 - 1 . In addition, the terminal device  110 - 1  may reset the MAC entity associated with the source network device  120 - 1 . 
     Alternatively, the terminal device  110 - 1  may perform the LBT on a further link between the terminal device  110 - 1  and the source network device  120 - 2 . If the number of LBT failures exceeds a further threshold number, the terminal device  110 - 1  may determine that the radio link failure occurs on the further link. In other words, if the indication of consistent LBT failures comes from the MAC entity of the target network device  120 - 2 , the terminal device  110 - 1  may consider the radio link failure to be detected. In some embodiments, the terminal device  110 - 1  may initiate a link recovery for recover the link. 
       FIG.  5    shows a flowchart of an example method  500  in accordance with an embodiment of the present disclosure. Only for the purpose of illustrations, the method  500  can be implemented at a source network device  120 - 1  as shown in  FIG.  1   . 
     At block  510 , the source network device  120 - 1  transmits to the terminal device  110 - 1  a configuration of a data inactivity timer associated with the source network device  120 - 1  to the terminal device  110 - 1 . For example, the terminal device  110 - 1  may be configured by RRC with a data inactivity monitoring functionality when the terminal device  110 - 1  is in RRC_CONNECTED state. The data inactivity operation can be controlled by configuring the data inactivity timer. The data inactivity timer may be restarted after the terminal device  110 - 1  performs the data reception and/or transmission with the source network device  120 - 1 . 
     At block  520 , the source network device  120 - 1  transmits a command to handover from the source network device  120 - 1  to the target network device  120 - 2 . The terminal device  110 - 1  may be able to connect with the target network device  120 - 2  while maintaining a connection with the source network device  120 - 1 . In other words, the handover may be a DAPS handover. 
     In other embodiments, the further data inactivity timer associated with the target network device  120 - 2  may not be configured before the data inactivity timer associated with the source network device  120 - 1  is released. For example, the command transmitted from the source network device  120 - 1  may exclude the configuration of the further data inactivity timer. 
     In other embodiments, the data inactivity timer associated with the source network device  120 - 1  may be released. For example, the source network device  120 - 1  may transmit  2035  an indication to the terminal device  110 - 1 . The indication may be transmitted via the RRC message before the configuration of the DAPS handover. The indication may be used to release the data inactivity timer. Alternatively, the data inactivity timer may be released upon an implicit indication. 
     Alternatively, the source network device  120 - 1  may transmit a further configuration of the data inactivity timer to the terminal device  110 - 1 . The further configuration may indicate an updated duration of the data inactivity timer. 
       FIG.  6    is a simplified block diagram of a device  600  that is suitable for implementing embodiments of the present disclosure. The device  600  can be considered as a further example implementation of the terminal device  110  and the network device  120  as shown in  FIG.  1   . Accordingly, the device  600  can be implemented at or as at least a part of the terminal device  110  or the network device  120 . 
     As shown, the device  600  includes a processor  610 , a memory  620  coupled to the processor  610 , a suitable transmitter (TX) and receiver (RX)  640  coupled to the processor  610 , and a communication interface coupled to the TX/RX  640 . The memory  620  stores at least a part of a program  630 . The TX/RX  640  is for bidirectional communications. The TX/RX  640  has at least one antenna to facilitate communication, though in practice an Access Node mentioned in this application may have several ones. The communication interface may represent any interface that is necessary for communication with other network elements, such as X2 interface for bidirectional communications between eNBs, S1 interface for communication between a Mobility Management Entity (MME)/Serving Gateway (S-GW) and the eNB, Un interface for communication between the eNB and a relay node (RN), or Uu interface for communication between the eNB and a terminal device. 
     The program  630  is assumed to include program instructions that, when executed by the associated processor  610 , enable the device  600  to operate in accordance with the embodiments of the present disclosure, as discussed herein with reference to  FIGS.  2  to  4   . The embodiments herein may be implemented by computer software executable by the processor  610  of the device  600 , or by hardware, or by a combination of software and hardware. The processor  610  may be configured to implement various embodiments of the present disclosure. Furthermore, a combination of the processor  610  and memory  620  may form processing means  650  adapted to implement various embodiments of the present disclosure. 
     The memory  620  may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology, such as a non-transitory computer readable storage medium, semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. While only one memory  620  is shown in the device  600 , there may be several physically distinct memory modules in the device  600 . The processor  610  may be of any type suitable to the local technical network, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device  600  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. 
     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, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representation, it will be appreciated that the blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof 
     The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the process or method as described above with reference to any of  FIGS.  4 - 10   . 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. 
     Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server. 
     The above program code may be embodied on a machine readable medium, which may be any tangible medium that may contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine 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 machine 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. 
     Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination. 
     Although the present disclosure has been described in language 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.