Patent Description:
In communication systems, such as Long Term Evolved (LTE) communication systems or the 5th generation wireless systems (<NUM>), dual connectivity (DC) allows user equipments (UEs) to receive data simultaneously from different eNodeBs (eNBs) in order to boost the performance in a heterogeneous network.

Document "<NPL>, shows inter-alia the inter-MN handover flow with SN change.

Document "<NPL>, is a 3GPP contribution discussing the assumption of R15 specifications for <NUM> interruption for EN-DC inter-MN HO, thereby analysing single process steps of said Inter-Mn HO with respect to processing time.

Currently, in a dual connectivity handover procedure, the terminal device always breaks off both connection to a master base station (may be referred as to a source master network device) and the corresponding secondary base station (may be referred as to a source secondary network device), and starts Random Access Chanel (RACH) accessing to a further master base station (may be referred as to a target master network device) and a further secondary base station (may be referred as to a target secondary network device) simultaneously. Connection breaking off with both nodes brings data transmission interruption between the terminal device and the network device.

In general, example embodiments of the present disclosure provide methods, devices and computer readable storage media for dual connectivity handover.

In a first aspect, there is provided method implemented at a target master network device as claimed in claim <NUM>.

In a second aspect, there is provided method implemented at a source master network device as claimed in claim <NUM>.

In a third aspect, there is provided method implemented at a terminal device as claimed in claim <NUM>.

In a fourth aspect, there is provided a network target master device as claimed in claim <NUM>.

In a fifth aspect, there is provided a source master network device as claimed in claim <NUM>.

In a sixth aspect, there is provided a terminal device as claimed in claim <NUM>.

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:.

It is to be understood that these example embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitations as to the scope of the disclosure.

As used herein, the term "network device" or "base station" (BS) 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 next generation NodeB (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, 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, 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.

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.

Now some example embodiments of the present disclosure are described below with reference to the figures. However, those skilled in the art would readily appreciate that the detailed description given herein with respect to these figures is for explanatory purpose as the present disclosure extends beyond theses limited example embodiments.

<FIG> shows an example communication system <NUM> in which example embodiments of the present disclosure can be implemented. In the communication system <NUM>, which is a part of a communication network, includes network devices <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and a terminal device <NUM>. It is to be understood that the communication system <NUM> may include any suitable number of terminal devices. It should be noted that the communication system <NUM> may also include other elements which are omitted for the purpose of clarity. The network devices <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> may communicate with the terminal device <NUM>. The network devices <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> may communicate with each other. It is to be understood that the number of network devices and terminal devices shown in <FIG> is given for the purpose of illustration without suggesting any limitations. The communication system <NUM> may include any suitable number of network devices and terminal devices.

The communication system <NUM> may be regarded as an EN-DC network in <NUM> communication system. Due to the higher frequencies bands used and other reasons, it is deemed better to enable terminal devices to connect to LTE and <NUM> New Radio (NR) simultaneously. This is referred to as Multi-RAT Dual Connectivity (MR-DC). The LTE eNB may be referred to as the MNB to indicate that it is the 'Master' base station (i.e., Master Node, MN) controlling the 'Secondary' <NUM> NR base station (i.e., Secondary Node, SN). A MN <NUM>-<NUM> may select a suitable network device (for example, <NUM>-<NUM>) as a SN in its courage <NUM>. Similarly, a MN <NUM>-<NUM> may select a suitable network device (for example, <NUM>-<NUM>) as SN in its courage <NUM>. Only for the purpose of illustrations, the network devices <NUM>-<NUM> and <NUM>-<NUM> are referred to as MNs hereinafter and the network devices <NUM>-<NUM> and <NUM>-<NUM> are referred to as SNs hereinafter.

In the communication system <NUM>, the terminal device <NUM> may perform a dual connectivity handover. That is, for example, the connection between the terminal device <NUM> and the MN <NUM>-<NUM> and its SN <NUM>-<NUM> may be switched to the connection between the terminal device <NUM> and the MN <NUM>-<NUM> and its SN <NUM>-<NUM>. The handover procedure may be occurred when the location of terminal device <NUM> is changed, for example, the terminal device <NUM> may be moved from the courage <NUM> of the MN <NUM>-<NUM> to the courage <NUM> of the MN <NUM>-<NUM>.

Depending on the communication technologies, the system <NUM> may be a Code Division Multiple Access (CDMA) network, a Time Division Multiple Address (TDMA) network, a Frequency Division Multiple Access (FDMA) network, an Orthogonal Frequency-Division Multiple Access (OFDMA) network, a Single Carrier-Frequency Division Multiple Access (SC-FDMA) network or any others. Communications discussed in the network <NUM> 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 (<NUM>), the second generation (<NUM>), <NUM>, <NUM>, the third generation (<NUM>), the fourth generation (<NUM>), <NUM>, the fifth generation (<NUM>) communication protocols. For clarity, certain aspects of the techniques are described below for LTE, and LTE terminology is used in much of the description below.

Currently, in a MR-DC handover procedure, the terminal device <NUM> always breaks off both connection to a MN <NUM>-<NUM> (may be referred as to a source master network device) and a corresponding SN <NUM>-<NUM> (may be referred as to a source secondary network device), and starts Random Access Chanel (RACH) accessing to a further MN <NUM>-<NUM> (may be referred as to a target master network device) and a further SN <NUM>-<NUM> (may be referred as to a target secondary network device) simultaneously. Connection breaking off with both nodes brings data transmission interruption between the terminal device <NUM> and the network devices <NUM>-<NUM> and <NUM>-<NUM>.

In MR-DC, Inter-Master Node Handover with/without Secondary Node change was defined in TS37. <NUM><NUM>. In RAN#<NUM> (Dec, <NUM>), Motivation for SI on mobility enhancements for New Radio (NR) was discussed in RP-<NUM>. RAN WG2 has concluded that the Rel-<NUM> LTE mobility procedure should be considered as the baseline mechanism also for NR. However, as a mobility procedure in any radio access technology, the NR handover cannot be executed instantaneously and thus some interruption time is also anticipated.

Example embodiments in accordance with the present disclosure provide a method for optimizing the DC handover procedure. During the handover procedure, the terminal device may keep one connection with a network device (either a MN or a SN) for data transmission. Therefore, there is no data interruption in the handover procedure. More details of the example embodiments of the present disclosure will be discussed with reference to <FIG>.

Principle and implementations of the present disclosure will be described in detail below with reference to <FIG>, which shows processes <NUM>-<NUM> according to example embodiments of the present disclosure. For the purpose of discussion, the processes <NUM>-<NUM> will be described with reference to <FIG>. The processes <NUM>-<NUM> may involve a dual connectivity handover.

In DC implementation, the user traffic is split in Packet Data Convergence Protocol (PDCP). In DC, the data bearer which is split in PDCP is called split bearer. Specifically, there are multiple carriers in the master cell group (MCG) and multiple carriers in the secondary cell group (SCG). In the LTE DC, the data plane radio bearer may be independently served by the MN or the SN, or may be simultaneously served by the MN and the MN. When it is served by the MN only, it is called MCG bearer (MCG: MeNB controlled serving cell group). When it is served by the SN only, it is called SCG bearer (SCG: SeNB controlled serving cell group), and when it is served by MN and MN simultaneously, it is called split bearer.

In the MCG bearer, control plane signaling is usually always carried by the MN for transmission. In the SCG bearer mode, the same data bearer (uplink and downlink) is allocated to the MN or SN by the Serving Gateway (S-GW) control. The data stream is separately transmitted by the MN and the SN after the S-GW is divided. In the split bearer mode, the S1-U connection only exists between the MN and the S-GW, and all downlink data streams are first transmitted to the MN, and then the MN transmits some data by the X2 interface after being split according to a certain algorithm and ratio. Finally, data is transmitted to the terminal device simultaneously via the MN and the SN.

In the example embodiments in accordance with <FIG>, the network device <NUM>-<NUM> may be regarded as a network device connecting with the terminal device <NUM>. The network device <NUM>-<NUM> involves a secondary network device <NUM>-<NUM>, which is also connecting with the terminal device <NUM>. Both network devices <NUM>-<NUM> and <NUM>-<NUM> are referred to as source network devices. The network devices <NUM>-<NUM> represents a master network device (MN) and the network device <NUM>-<NUM> represents a secondary network device (SN) associated with the master network device <NUM>-<NUM>. The network devices <NUM>-<NUM> and <NUM>-<NUM> are network devices to which the terminal device <NUM> is to be connected and both of them are referred to as target network devices.

The example embodiments illustrated in <FIG> refer to the case of the split bearer with NR PDCP terminated in MN (i.e. MCG split bearer), while the example embodiments illustrated in <FIG> refer to the case of split bearer with NR PDCP terminated in SN (i.e. SCG split bearer). In <FIG>, the data transmissions are represented in dotted lines and the control signaling are represented in solid lines.

<FIG> shows a diagram of an example process <NUM> for a dual connectivity handover in accordance with some example embodiments of the present disclosure.

As shown in <FIG>, S-GW <NUM> transmits <NUM> the data stream to the network device <NUM>-<NUM>. The data is split into two data branches. From the network device <NUM>-<NUM>, one data branch is transmitted <NUM> to the network device <NUM>-<NUM> and the other data branch is transmitted <NUM> to the terminal device <NUM> simultaneously. The terminal device <NUM>-<NUM> also transmits <NUM> the data stream to the terminal device <NUM>.

Once a handover procedure is triggered, the network device <NUM>-<NUM> transmits <NUM> a handover request for a dual connectivity handover procedure to the network device <NUM>-<NUM>. The handover request indicates that a dual connectivity handover procedure of a terminal device to a target network device will be performed.

If the network device <NUM>-<NUM>, referred as to a master network device, involves no corresponding secondary network device, the network device <NUM>-<NUM> transmits <NUM> a SgNB addition request to the network device <NUM>-<NUM> to add the network device <NUM>-<NUM> as a corresponding secondary network device. The network device <NUM>-<NUM> transmits <NUM>, to the network device <NUM>-<NUM>, an acknowledge for the SgNB addition request to confirm the addition procedure.

For the handover request transmitted from the network device <NUM>-<NUM>, the network device <NUM>-<NUM> determines <NUM> a first type of a target network device for a first handover of the dual connectivity handover procedure and transmits <NUM>, to the network device <NUM>-<NUM> a first message indicating the first type of the target network device for the terminal device <NUM> to be connected with in the first handover. As an example, the first type may indicate whether a network device is a master network device or a secondary network device. As another example, the first type may indicate whether a network device is a master network device or one of a plurality of secondary network devices.

In this case, the first type of the target network device may be a target secondary network device. Thus, the network device <NUM>-<NUM> transmits <NUM> a SgNB release request to the network device <NUM>-<NUM> to indicate that the network device <NUM>-<NUM> is to be disconnected with the terminal device <NUM>. The network device <NUM>-<NUM> transmits <NUM>, to the network device <NUM>-<NUM>, an acknowledge for the SgNB release request to confirm the release procedure. As shown in <FIG>, the data stream transmitted <NUM> from the S-GW <NUM> then may be transmitted <NUM> to the terminal device <NUM> via the connection between the network device <NUM>-<NUM> and the terminal device <NUM> only.

The network device <NUM>-<NUM> transmits <NUM>, to the terminal device <NUM>, a second message indicating the first type of the target network device. In this case that the first type of the target network device is a target secondary network device, the terminal device <NUM> may be informed that the connection of the terminal device <NUM> and the network device <NUM>-<NUM> is broken off. Correspondingly, the terminal device <NUM> may be informed that the connection between the terminal device <NUM> and a target secondary network device, i.e. the network device <NUM>-<NUM> as shown in <FIG>, will be established.

Based on the second message, the first handover is to be performed by the terminal device <NUM>. The terminal device <NUM> transmits <NUM> a first random request to the network device <NUM>-<NUM> to request an access to the network device <NUM>-<NUM>. The first random request may be responded by the network device <NUM>-<NUM>. After the RACH access is successful, the terminal device <NUM> transmits <NUM>, to the network device <NUM>-<NUM>, a first confirmation message indicating that the terminal device <NUM> confirms a success of a configuration of the network device <NUM>-<NUM> for the first handover. For example, the first confirmation message may be an uplink Signaling Radio Bearer (SRB) with packaged Radio Resource Control (RRC) message. The RRC message may be referred as to "RRCConnectionReconfigurationComplete2. " The network device <NUM>-<NUM> may forward <NUM> the RRC message to the network device <NUM>-<NUM> and the network device <NUM>-<NUM> may generate a second message based on the first confirmation message to indicate that first handover is completed.

The network device <NUM>-<NUM> transmits <NUM> the second message to the network device <NUM>-<NUM>, to indicate that the connection between the terminal device <NUM> and the network device <NUM>-<NUM> is established successfully and to enable a second handover of the dual connectivity handover procedure to be performed. The network device <NUM>-<NUM> may also transmit <NUM>, to the network device <NUM>-<NUM>, a third message to indicate that the SgNB reconfiguration is completed.

After the first handover, the data stream transmitted <NUM> from the S-GW may be forwarded <NUM> from the network device <NUM>-<NUM> to the network device <NUM>-<NUM>. Then the data stream may be forwarded <NUM> to the network device <NUM>-<NUM> and transmitted <NUM> to the terminal device <NUM> from the network device <NUM>-<NUM>.

After connected with the network device <NUM>-<NUM>, i.e. a target secondary network device, the terminal device <NUM> performs a second handover of the dual connectivity handover procedure. The terminal device <NUM> transmits a second random request to a second type of the target device.

In this case, the terminal device <NUM> may transmit <NUM> the second random request to the network device <NUM>-<NUM>, i.e. a target master the network device, to request an access to the network device <NUM>-<NUM>. The second random request may be responded by the network device <NUM>-<NUM>. After the RACH access is successful, the terminal device <NUM> transmits <NUM>, to the network device <NUM>-<NUM>, a second confirmation message indicating that the terminal device <NUM> confirms a success of a configuration of the network device <NUM>-<NUM> for the second handover. For example, the second confirmation message may be a RRC message. The RRC message may be referred as to "RRCConnectionReconfigurationComplete1.

As shown in <FIG>, after the second handover, in the user plane, S-GW <NUM> transmits <NUM> the data stream to the network device <NUM>-<NUM>. The data is split into two data branches. From the network device <NUM>-<NUM>, one data branch is transmitted to the terminal device <NUM> and the other data branch is transmitted to the network device <NUM>-<NUM> simultaneously. The terminal device <NUM>-<NUM> then transmits the data stream to terminal device <NUM>.

<FIG> shows a diagram of an example process <NUM> for a dual connectivity handover according to some example embodiments of the present disclosure. In the process <NUM> of <FIG>, the actions <NUM>-<NUM> are substantially similar with the action <NUM>-<NUM> of the process <NUM> illustrated in <FIG>. Therefore, the description for the actions <NUM>-<NUM> is omitted here.

In this case, the first type of the target network device may be a target master network device, the terminal device <NUM> then may be disconnected with the network device <NUM>-<NUM>. As shown in <FIG>, the data stream transmitted <NUM> from the S-GW <NUM> may be forwarded <NUM> to the network device <NUM>-<NUM> and transmitted <NUM> to the terminal device <NUM> via the connection between the network device <NUM>-<NUM> and the terminal device <NUM> only.

The network device <NUM>-<NUM> transmits <NUM>, to the terminal device <NUM>, a second message indicating the first type of the target network device. In this case that the first type of the target network device is a target master network device, the terminal device <NUM> may be informed that the connection of the terminal device <NUM> and the network device <NUM>-<NUM> is broken off. Correspondingly, the terminal device <NUM> may be informed that the connection between the terminal device <NUM> and a target master network device, i.e. the network device <NUM>-<NUM> as shown in <FIG>, will be established.

Based on the second message, the first handover is to be performed by the terminal device <NUM>. The terminal device <NUM> transmits <NUM> a first random request to the network device <NUM>-<NUM> to request an access to the network device <NUM>-<NUM>. The first random request may be responded by the network device <NUM>-<NUM>. After the RACH access is successful, the terminal device <NUM> transmits <NUM>, to the network device <NUM>-<NUM>, a first confirmation message indicating that the terminal device <NUM> confirms a success of a configuration of the network device <NUM>-<NUM> for the first handover. For example, the first confirmation message may be an RRC message. The RRC message may be referred as to "RRCConnectionReconfigurationComplete1. " The the network device <NUM>-<NUM> may generate a second message based on the first confirmation message to indicate that first handover is completed.

The network device <NUM>-<NUM> transmits <NUM> the third message to the network device <NUM>-<NUM>, to indicate that the connection between the terminal device <NUM> and the network device <NUM>-<NUM> is established successfully and to enable a second handover of the dual connectivity handover procedure to be performed.

After the first handover, the data stream transmitted <NUM> from the S-GW may be forwarded <NUM> from the network device <NUM>-<NUM> to the network device <NUM>-<NUM>. Then the data stream may be transmitted <NUM> to the terminal device <NUM> from the network device <NUM>-<NUM>.

When the second handover is to be performed, the network device <NUM>-<NUM> transmits <NUM> a SgNB release request to the network device <NUM>-<NUM> to indicate that the network device <NUM>-<NUM> is to be disconnected with the terminal device <NUM>. The network device <NUM>-<NUM> transmits <NUM>, to the network device <NUM>-<NUM>, an acknowledge for the SgNB release request to confirm the release procedure.

After connected with the network device <NUM>-<NUM>, i.e. a target master network device, the terminal device <NUM> performs a second handover of the dual connectivity handover procedure. The terminal device <NUM> transmits a second random request to a second type of the target device. In this case, the terminal device <NUM> may transmit <NUM> the second random request to the network device <NUM>-<NUM>, i.e. a target secondary the network device, to request an access to the network device <NUM>-<NUM>. The second random request may be responded by the network device <NUM>-<NUM>.

After the RACH access is successful, the terminal device <NUM> transmits <NUM>, to the network device <NUM>-<NUM>, a second confirmation message indicating that the terminal device <NUM> confirms a success of a configuration of the network device <NUM>-<NUM> for the second handover. For example, the second confirmation message may be a RRC message. The RRC message may be referred as to "RRCConnectionReconfigurationComplete2. " The network device <NUM>-<NUM> may also transmit <NUM>, to the network device <NUM>-<NUM>, a third message to indicate that the SgNB reconfiguration is completed.

As shown in <FIG>, after the second handover, in the user plane, S-GW <NUM> transmits <NUM> the data stream to the network device <NUM>-<NUM>. The data stream is split into two data branches. From the network device <NUM>-<NUM>, one data branch is transmitted to the terminal device <NUM> and the other data branch is transmitted to the network device <NUM>-<NUM> simultaneously. The terminal device <NUM>-<NUM> then transmits the data stream to terminal device <NUM>.

As described above, <FIG> show example embodiments in accordance with present disclosure in a case of MCG split bearer. In this way, during the DC handover, the terminal device can keep one connection with a source network device for data transmission to avoid the data interrupt in the handover procedure. As another example, the optimization of handover may be also performed in a case of SCG split bearer. With reference to <FIG>, the example embodiments in accordance with present disclosure in a case of SCG split bearer will be described as below.

<FIG> shows a diagram of an example process <NUM> for a dual connectivity handover according to some example embodiments of the present disclosure.

As shown in <FIG>, S-GW <NUM> transmits <NUM> the data stream to the network device <NUM>-<NUM> via the network device <NUM>-<NUM>. The data is split into two data branches. From the network device <NUM>-<NUM>, one data branch is transmitted <NUM> to the network device <NUM>-<NUM> and forwarded <NUM> to the terminal device <NUM>, and the other data branch is transmitted <NUM> to the terminal device <NUM>.

In this case, the first type of the target network device may be a target secondary network device. Thus, the network device <NUM>-<NUM> transmits <NUM> a X2 message to the network device <NUM>-<NUM> to indicate that the network device <NUM>-<NUM> is to be connected with the terminal device and the network device <NUM>-<NUM> is to be disconnected with the terminal device <NUM>.

As shown in <FIG>, in the user plane, the data stream transmitted <NUM> from the S-GW <NUM> then may be transmitted <NUM> to the network device <NUM>-<NUM> from the network device <NUM>-<NUM> and forwarded <NUM> to the terminal device <NUM> via the connection between the network device <NUM>-<NUM> and the terminal device <NUM> only.

The network device <NUM>-<NUM> transmits <NUM>, to the terminal device <NUM>, a second message indicating the first type of the target network device. In the case that the first type of the target network device is a target secondary network device, the terminal device <NUM> may be informed that the connection of the terminal device <NUM> and the network device <NUM>-<NUM> is broken off. Correspondingly, the terminal device <NUM> may be informed that the connection between the terminal device <NUM> and a target secondary network device, i.e. the network device <NUM>-<NUM> as shown in <FIG>, will be established.

Based on the second message, the first handover is to be performed by the terminal device <NUM>. The terminal device <NUM> transmits <NUM> a first random request to the network device <NUM>-<NUM> to request an access to the network device <NUM>-<NUM>. The first random request may be responded by the network device <NUM>-<NUM>. After the RACH access is successful, the terminal device <NUM> transmits <NUM> to the network device <NUM>-<NUM>, a first confirmation message indicating that the terminal device <NUM> confirms a success of a configuration of the network device <NUM>-<NUM> for the first handover. For example, the first confirmation message may be an uplink Signaling Radio Bearer (SRB) with packaged Radio Resource Control (RRC) message. The RRC message may be referred as to "RRCConnectionReconfigurationComplete2. " The network device <NUM>-<NUM> may forward <NUM> the RRC message to the network device <NUM>-<NUM> and the network device <NUM>-<NUM> may generate a second message based on the first confirmation message to indicate that first handover is completed. The network device <NUM>-<NUM> may transmit <NUM>, to the network device <NUM>-<NUM>, a third message to indicate that the SgNB reconfiguration is completed.

The network device <NUM>-<NUM> transmits <NUM> the second message to the network device <NUM>-<NUM>, to indicate that the connection between the terminal device <NUM> and the network device <NUM>-<NUM> is established successfully and NR PDCP has been new established in network device <NUM>-<NUM>, to enable a second handover of the dual connectivity handover procedure to be performed. Thus, the network device <NUM>-<NUM> transmits <NUM> a SgNB release request to the network device <NUM>-<NUM> to indicate that the network device <NUM>-<NUM> is to be disconnected with the terminal device <NUM>. The network device <NUM>-<NUM> transmits <NUM>, to the network device <NUM>-<NUM>, an acknowledge for the SgNB release request to confirm the release procedure.

After the first handover, the data stream transmitted <NUM> from the S-GW may be forwarded <NUM> from the network device <NUM>-<NUM> to the network device <NUM>-<NUM>. Then the data stream may be forwarded <NUM> to the network device <NUM>-<NUM> and then forwarded <NUM> to the network device <NUM>-<NUM>. The network device <NUM>-<NUM> may transmit <NUM> the data stream to the terminal device <NUM>.

After connected with the network device <NUM>-<NUM>, i.e. a target secondary network device, the terminal device <NUM> performs a second handover of the dual connectivity handover procedure. The terminal device <NUM> transmits a second random request to a second type of the target device. In this case, the terminal device <NUM> may transmit <NUM> the second random request to the network device <NUM>-<NUM>, i.e. a target master the network device, to request an access to the network device <NUM>-<NUM>. The second random request may be responded by the network device <NUM>-<NUM>. After the RACH access is successful, the terminal device <NUM> transmits <NUM>, to the network device <NUM>-<NUM>, a second confirmation message indicating that the terminal device <NUM> confirms a success of a configuration of the network device <NUM>-<NUM> for the second handover. For example, the second confirmation message may be a RRC message. The RRC message may be referred as to "RRCConnectionReconfigurationComplete1.

In the process <NUM> of <FIG>, the actions <NUM>-<NUM> are substantially similar with the action <NUM>-<NUM> of the process <NUM> illustrated in <FIG>. Therefore, the description for the actions <NUM>-<NUM> is omitted here.

In this case, the first type of the target network device may be a target master network device, the terminal device <NUM> then may be disconnected with the network device <NUM>-<NUM>. As shown in <FIG>, in the user plane, the data stream transmitted <NUM> from the S-GW <NUM> then maybe transmitted <NUM> to the terminal device <NUM> from the network device <NUM>-<NUM> via the connection between the network device <NUM>-<NUM> and the terminal device <NUM> only.

The network device <NUM>-<NUM> transmits <NUM> the third message to the network device <NUM>-<NUM>, to indicate that the connection between the terminal device <NUM> and the network device <NUM>-<NUM> is established successfully and NR PDCP has been new established in the network device <NUM>-<NUM>, to enable a second handover of the dual connectivity handover procedure to be performed. The network device <NUM>-<NUM> may transmit <NUM>, to the network device <NUM>-<NUM>, a fourth message to indicate that the SgNB reconfiguration is completed.

After the first handover, the data stream transmitted <NUM> from the S-GW may be forwarded <NUM> from the network device <NUM>-<NUM> to the network device <NUM>-<NUM>. The network device <NUM>-<NUM> may forward <NUM> the data stream to the network device <NUM>-<NUM> and then the data stream may be transmitted <NUM> to the terminal device <NUM> from the network device <NUM>-<NUM>.

After the RACH access is successful, the terminal device <NUM> transmits <NUM>, to the network device <NUM>-<NUM>, a second confirmation message indicating that the terminal device <NUM> confirms a success of a configuration of the network device <NUM>-<NUM> for the second handover. For example, the second confirmation message may be a RRC message. The RRC message may be referred as to "RRCConnectionReconfigurationComplete2.

According the example embodiments illustrated in <FIG>, the optimization for a DC handover could be implemented in both MCG split bearer and SCG split bearer. For both MCG split bearer and SCG split bearer, the DC handover may be performed without data interruption.

More details of the example embodiments in accordance with the present disclosure will be described with reference to <FIG>.

<FIG> shows a flowchart of an example method <NUM> for a dual connectivity handover according to some example embodiments of the present disclosure. The method <NUM> can be implemented at the network device <NUM>-<NUM> as shown in <FIG>. For the purpose of discussion, the method <NUM> will be described with reference to <FIG>.

At block <NUM>, after receiving a request for a dual connectivity handover procedure of a terminal device, the network device <NUM>-<NUM> determines a first type of a target network device for a first handover of the dual connectivity handover procedure. The first type indicates whether a network device is a master network device or a secondary network device.

At block <NUM>, the network device <NUM>-<NUM> transmits, to the source master network device (the network device <NUM>-<NUM> in <FIG>), a first message indicating the first type of the target network device for the terminal device to be connected with in the first handover, so that the terminal device <NUM> is disconnected with the first type of a source network device.

At block <NUM>, if the terminal device <NUM> is connected with the first type of the target network device, the network device <NUM>-<NUM> transmits, to the source master network device, a second message indicating that the first handover is completed, to enable a second handover of the dual connectivity handover procedure to be performed. In the second handover, the terminal device <NUM> is connected with a second type of a target network device and disconnected with the second type of a source network device. The second type is different from the first type and indicates whether a network device is a master network device or a secondary network device.

In some example embodiments, the first type of the target network device is a target secondary network device. The network device <NUM>-<NUM> may receive, from the target secondary network device (the network device <NUM>-<NUM> in <FIG>), a first confirmation message indicating that the terminal device <NUM> confirms a success of a configuration of the target secondary network device for the first handover and generate the second message based on the first confirmation message to indicate that first handover is completed.

In some example embodiments, the method <NUM> may further comprise: if the network device <NUM>-<NUM> receives a random access request from the terminal device <NUM>, the network device <NUM>-<NUM> may transmit an acknowledge for the random access request to the terminal device <NUM> and receive, from the terminal device <NUM>, a second confirmation message indicating that the terminal device <NUM> confirms a success of a configuration of the target master network device (the network device <NUM>-<NUM> in <FIG>) for the second handover.

In some example embodiments, the first type of the target network device is a target secondary network device. If the network device <NUM>-<NUM> receives data transmitted from the source master network device, the network device <NUM>-<NUM> may forward the data to the target secondary network device, so that the data is transmitted to the terminal device from the target secondary network device.

In some example embodiments, the first type of the target network device is a target master network device. If the network device <NUM>-<NUM> receives a random access request from the terminal device <NUM>, the network device <NUM>-<NUM> may transmit an acknowledge for the random access request to the terminal device <NUM> and receive, from the terminal device <NUM>, a first confirmation message indicating that the terminal device <NUM> confirms a success of a configuration of the target master network device (the network device <NUM>-<NUM> in <FIG>) for the first handover and generate the second message based on the first confirmation message to indicate that first handover is completed.

In some example embodiments, the method <NUM> may further comprise: the network device <NUM>-<NUM> may receive, from the terminal device <NUM>, a second confirmation message indicating that the terminal device <NUM> confirms a success of a configuration of a target source network device (the network device <NUM>-<NUM> in <FIG>) for the second handover.

In some example embodiments, the first type of the target network device is a target master network device. If the network device <NUM>-<NUM> receives data transmitted from the source master network device, the network device <NUM>-<NUM> may transmit the data to the terminal device and receive the data from the terminal device.

At block <NUM>, the network device <NUM>-<NUM> transmits a request for a dual connectivity handover procedure of a terminal device <NUM> to a target master network device (the network device <NUM>-<NUM> in <FIG>).

At block <NUM>, if the network device <NUM>-<NUM> receives, from the target master network device, a first message indicating a first type of a target network device for the terminal device <NUM> to be connected with in a first handover of the dual connectivity handover procedure, the network device <NUM>-<NUM> transmits, to the terminal device <NUM>, an indication of the first type of the target network device, so that the terminal device <NUM> is disconnected with the first type of a source network device for the terminal device to be connected with. The first type indicates whether a network device is a master network device or a secondary network device.

At block <NUM>, the network device <NUM>-<NUM> receives, from the target master network device, a second message indicating that the first handover is completed, to enable a second handover of the dual connectivity handover procedure to be performed. In the second handover, the terminal device being connected with a second type of a target network device and disconnected with the second type of a source network device. The second type is different from the first type and indicating whether a network device is a master network device or a secondary network device.

In some example embodiments, the method <NUM> may further comprise if the network device <NUM>-<NUM> receives the first message, the network device <NUM>-<NUM> may transmit to, a secondary source network device (the network device <NUM>-<NUM> in <FIG>), a third message indicating the first type of the target network device for the terminal device <NUM> to be connected with in the first handover of the dual connectivity handover procedure.

In some example embodiments, the first type of the target network device is a target secondary network device. The method may further comprise if the network device <NUM>-<NUM> receives the first message, the network device <NUM>-<NUM> may receive transmitting data received from a gateway to terminal device and receive the data from the terminal device.

In some example embodiments, the first type of the target network device is a target master network device. The method may further comprise if the network device <NUM>-<NUM> receives the first message, the network device <NUM>-<NUM> may transmit data received from a gateway to a source secondary network device, so that the date is transmitted from the source secondary network device to the terminal device.

In some example embodiments, the first type of the target network device is a target secondary network device. The method may further comprise if the network device <NUM>-<NUM> receives the second message, the network device <NUM>-<NUM> may forward data received from a gateway to the target master network device, so that the data is transmitted to the target secondary network device, the data being transmitted from the target secondary network device to the terminal device.

In some example embodiments, the first type of the target network device is a target master network device. The method may further comprise if the network device <NUM>-<NUM> receives the second message, the network device <NUM>-<NUM> may forward data received from a gateway to the target master network device, so that the data is transmitted to the terminal device from the target master network device.

<FIG> shows a flowchart of an example method <NUM> for a dual connectivity handover according to some example embodiments of the present disclosure. The method <NUM> can be implemented at the terminal device <NUM> as shown in <FIG>. For the purpose of discussion, the method <NUM> will be described with reference to <FIG>.

At block <NUM>, the terminal device <NUM> receives, from a source master network device (the network device <NUM>-<NUM> in <FIG>), an indication of a first type of a target network device for the terminal device <NUM> to be connected with in a first handover of the dual connectivity handover procedure. The first type indicating whether a network device is a master network device or a secondary network device.

At block <NUM>, the terminal device <NUM> performs the first handover based on the indication.

At block <NUM>, if the terminal device <NUM> is connected with the first type of the target network device, the terminal device <NUM> performs a second handover of the dual connectivity handover procedure. In the second handover, the terminal device is connected with a second type of a target network device and disconnected with the second type of a source network device. The second type is different from the first type and indicating whether a network device is a master network device or a secondary network device.

In some example embodiments, the first type of the target network device is a target secondary network device. The terminal device <NUM> may transmit a first random access request to the target secondary network device (the network device <NUM>-<NUM> in <FIG>). If receiving an acknowledge for the first random access request from the target secondary network device, the terminal device <NUM> may transmit, to the target secondary network device, a first confirmation message indicating that the terminal device <NUM> confirms a success of a configuration of the target secondary network device for the first handover.

In some example embodiments, the first type of the target network device is a target secondary network device. The terminal device <NUM> may transmit a second random access request to a target master network device (the network device <NUM>-<NUM> in <FIG>). If receiving an acknowledge for the second random access request from the target master network device, the terminal device <NUM> may transmit, to the target master network device, a second confirmation message indicating that the terminal device confirms a success of a configuration of the target master network device for the second handover.

In some example embodiments, the first type of the target network device is a target master network device. The terminal device <NUM> may transmit a first random access request to the target master network device (the network device <NUM>-<NUM> in <FIG>). If receiving an acknowledge for the first random access request from the target master network device, the terminal device <NUM> may transmit, to target master network device, a first confirmation message indicating that the terminal device <NUM> confirms a success of a configuration of target master network device for the first handover.

In some example embodiments, the first type of the target network device is a target master network device. The terminal device <NUM> may transmit a second random access request to a target secondary network device (the network device <NUM>-<NUM> in <FIG>). If receiving an acknowledge for the second random access request from the target secondary network device, the terminal device <NUM> may transmit, to the target master network device (the network device <NUM>-<NUM> in <FIG>), a second confirmation message indicating that the terminal device <NUM> confirms a success of a configuration of target secondary network device for the second handover.

In some example embodiments, the method <NUM> may further comprise if the terminal device <NUM> receives the indication of the first type of the target network device being a target secondary network device, the terminal device <NUM> receives data transmitted from the source master network device and transmits the data to the source master network device.

In some example embodiments, the method <NUM> may further comprise if the terminal device <NUM> receives the indication of the first type of the target network device being a target master network device, the terminal device <NUM> receives data from a source secondary network device and transmits the data to the source secondary network device.

In some example embodiments, the method <NUM> may further comprise if the terminal device <NUM> is connected with the first type of the target network device, the terminal device <NUM> receives data from the first type of the target network device and transmits data to the first type of the target network device.

<FIG> a flowchart of an example method <NUM> for a dual connectivity handover according to some example embodiments of the present disclosure. The method <NUM> can be implemented at the network device <NUM>-<NUM> as shown in <FIG>. For the purpose of discussion, the method <NUM> will be described with reference to <FIG>.

At block <NUM>, if the terminal device <NUM> receives an indication of a first type of a target network device for a terminal device to be connected with in a first handover of the dual connectivity handover procedure by the terminal device and the indication of the first type of the target network device is a target secondary network device, the network device <NUM>-<NUM> receives a random access request from a terminal device <NUM>. At block <NUM>, the network device <NUM>-<NUM> transmits an acknowledge for the random access request to the terminal device <NUM>.

In some example embodiments, the method <NUM> may further comprise the network device <NUM>-<NUM> may receive, from the terminal device, a first confirmation message indicating that the terminal device confirms a success of a configuration of a target secondary network device for a first handover and transmit the first confirmation to a target master network device via forwarding by the target secondary network.

In some example embodiments, the method <NUM> may further comprise if the first handover is completed, the network device <NUM>-<NUM> may receive data forwarded from a source master network device; and transmit the data to the terminal device.

At block <NUM>, the network device <NUM>-<NUM> receives, from a source master network device, an indication of a first type of a target network device for the terminal device to be connected with in a first handover of the dual connectivity handover procedure, the first type indicating whether a network device is a master network device or a secondary network device.

In some example embodiments, the first type of the target network device is a target secondary network device. The method <NUM> may further comprise if the network device <NUM>-<NUM> receives the indication of the first type of the target network device, the network device <NUM>-<NUM> may transmit data received from a gateway to a source master network device, so that the date is transmitted from the source master network device to the terminal device.

In some example embodiments, the first type of the target network device is a target master network device. The method <NUM> may further comprise if the network device <NUM>-<NUM> receives the indication of the first type of the target network device, the network device <NUM>-<NUM> may transmit data received from a gateway to terminal device and receive data from the terminal device.

In some example embodiments, the method <NUM> may further comprises if the first handover is completed, the network device <NUM>-<NUM> may transmit data received from a gateway to the source master network device, so that the data is transmitted to the first type of a target network device from the source master network device.

As described above, during the handover procedure, the terminal device may keep one connection with a network device (either a MN or a SN) for data transmission. Therefore, there is no data interruption in the handover procedure.

In some example embodiments, an apparatus capable of performing the method <NUM> (for example, the network device <NUM>-<NUM>) may comprise means for performing the respective steps of the method <NUM>. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus comprises: means for in response to receiving a request for a dual connectivity handover procedure of a terminal device, determining a first type of a target network device for a first handover of the dual connectivity handover procedure, the first type indicating whether a network device is a master network device or a secondary network device; means for transmitting, to a source master network device, a first message indicating the first type of the target network device for the terminal device to be connected with in the first handover, so that the terminal device is disconnected with the first type of a source network device; and means for in response to the terminal device being connected with the first type of the target network device, transmitting, to the source master network device, a second message indicating that the first handover is completed, to enable a second handover of the dual connectivity handover procedure to be performed, the terminal device being connected with a second type of a target network device and disconnected with the second type of a source network device in the second handover, the second type being different from the first type and indicating whether a network device is a master network device or a secondary network device.

In some example embodiments, the first type of the target network device is a target secondary network device. The means for transmitting comprises: means for receiving, from the target secondary network device, a first confirmation message indicating that the terminal device confirms a success of a configuration of the target secondary network device for the first handover; and means for generating the second message based on the first confirmation message to indicate that first handover is completed.

In some example embodiments, the apparatus further comprises: means for in response to receiving a random access request from the terminal device, transmitting an acknowledge for the random access request to the terminal device; and means for receiving, from the terminal device, a second confirmation message indicating that the terminal device confirms a success of a configuration of the target master network device for the second handover.

In some example embodiments, the first type of the target network device is a target secondary network device. The means for transmitting comprises: means for in response to receiving data transmitted from the source master network device, forwarding the data to the target secondary network device, so that the data is transmitted to the terminal device from the target secondary network device.

In some example embodiments, the first type of the target network device is a target master network device. The means for transmitting comprises: means for in response to receiving a random access request from the terminal device, transmitting an acknowledge for the random access request to the terminal device; means for receiving, from the terminal device, a first confirmation message indicating that the terminal device confirms a success of a configuration of the target master network device for the first handover; and means for generating the second message based on the first confirmation message to indicate that first handover is completed.

In some example embodiments, the apparatus further comprises: means for receiving, from the terminal device, a second confirmation message indicating that the terminal device confirms a success of a configuration of a target source network device for the second handover.

In some example embodiments, the first type of the target network device is a target master network device. The means for transmitting comprises: means for in response to receiving data transmitted from the source master network device, transmitting the data to the terminal device.

In some example embodiments, the apparatus comprises: means for transmitting a request for a dual connectivity handover procedure of a terminal device to a target master network device; means for in response to receiving, from the target master network device, a first message indicating a first type of a target network device for the terminal device to be connected with in a first handover of the dual connectivity handover procedure, transmitting, to the terminal device, an indication of the first type of the target network device, so that the terminal device is disconnected with the first type of a source network device for the terminal device to be connected with, the first type indicating whether a network device is a master network device or a secondary network device; and means for receiving, from the target master network device, a second message indicating that the first handover is completed, to enable a second handover of the dual connectivity handover procedure to be performed, the terminal device being connected with a second type of a target network device and disconnected with the second type of a source network device in the second handover, the second type being different from the first type and indicating whether a network device is a master network device or a secondary network device.

In some example embodiments, the apparatus further comprises: means for in response to receiving the first message, transmitting, to a secondary source network device, a third message indicating the first type of the target network device for the terminal device to be connected with in the first handover of the dual connectivity handover procedure.

In some example embodiments, the first type of the target network device is a target secondary network device. The apparatus further comprises: means for in response to receiving the first message, transmitting data received from a gateway to terminal device and receiving data from terminal device.

In some example embodiments, the first type of the target network device is a target master network device. The apparatus further comprises: means for in response to receiving the first message, transmitting data received from a gateway to a source secondary network device, so that the date is transmitted from the source secondary network device to the terminal device.

In some example embodiments, the first type of the target network device is a target secondary network device. The apparatus further comprises: means for in response to receiving the second message, forwarding data received from a gateway to the target master network device, so that the data is transmitted to the target secondary network device, the data being transmitted from the target secondary network device to the terminal device.

In some example embodiments, the first type of the target network device is a target master network device. The apparatus further comprises: means for in response to receiving the second message, forwarding data received from a gateway to the target master network device, so that the data is transmitted to the terminal device from the target master network device.

In some example embodiments, an apparatus capable of performing the method <NUM> (for example, the terminal device <NUM>) may comprise means for performing the respective steps of the method <NUM>. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus comprises: means for receiving, from a source master network device, an indication of a first type of a target network device to be connected with in a first handover of the dual connectivity handover procedure, the first type indicating whether a network device is a master network device or a secondary network device; means for performing the first handover based on the indication of a first type of a target network device; and means for in response to the terminal device being connected with the first type of the target network device, performing a second handover of the dual connectivity handover procedure, the terminal device being connected with a second type of a target network device and disconnected with the second type of a source network device in the second handover, the second type being different from the first type and indicating whether a network device is a master network device or a secondary network device.

In some example embodiments, the first type of the target network device is a target secondary network device. The means for performing comprises: means for transmitting a first random access request to the target secondary network device; and means for in response to receiving an acknowledge for the first random access request from the target secondary network device, transmitting, to the target secondary network device, a first confirmation message indicating that the terminal device confirms a success of a configuration of the target secondary network device for the first handover.

In some example embodiments, the first type of the target network device is a target secondary network device. The means for performing comprises: means for transmitting a second random access request to a target master network device; and means for in response to receiving an acknowledge for the second random access request from the target master network device, transmitting, to the target master network device, a second confirmation message indicating that the terminal device confirms a success of a configuration of the target master network device for the second handover.

In some example embodiments, the first type of the target network device is a target master network device. The means for performing comprises: means for transmitting a first random access request to the target master network device; and means for in response to receiving an acknowledge for the first random access request from the target master network device, transmitting, to target master network device, a first confirmation message indicating that the terminal device confirms a success of a configuration of target master network device for the first handover.

In some example embodiments, the first type of the target network device is a target master network device. The means for performing comprises: means for transmitting a second random access request to a target secondary network device; and means for in response to receiving an acknowledge for the second random access request from the target secondary network device, transmitting, to the target master network device, a second confirmation message indicating that the terminal device confirms a success of a configuration of target secondary network device for the second handover.

In some example embodiments, the apparatus further comprises: means for in response to receiving the indication of a first type of a target network device being a target secondary network device, receiving data transmitted from the source master network device and sending data to the source master network device.

In some example embodiments, the apparatus further comprises: means for in response to receiving the indication of a first type of a target network device being a target master network device, receiving data from a source secondary network device and sending data to the source secondary network device.

In some example embodiments, the apparatus further comprises: means for in response to being connected with the first type of the target network device, receiving data from the first type of the target network device and sending data to the first type of the target network device.

In some example embodiments, an apparatus capable of performing the method <NUM> (for example, the terminal device <NUM>-<NUM>) may comprise means for performing the respective steps of the method <NUM>. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus comprises: means for in response to receiving an indication of a first type of a target network device for a terminal device to be connected with in a first handover of the dual connectivity handover procedure by the terminal device and the indication of the first type of the target network device being a target secondary network device, receiving a random access request from a terminal device; and means for transmitting an acknowledge for the random access request to the terminal device.

In some example embodiments, the apparatus further comprises: means for receiving, from the terminal device, a first confirmation message indicating that the terminal device confirms a success of a configuration of a target secondary network device for a first handover; and means for transmitting the first confirmation to a target master network device.

In some example embodiments, the apparatus further comprises: means for in response to the first handover is completed, receiving data forwarded from a source master network device; and means for transmitting the data to the terminal device.

In some example embodiments, the apparatus comprises means for receiving, from a source master network device, an indication of a first type of a target network device for the terminal device to be connected with in a first handover of the dual connectivity handover procedure, the first type indicating whether a network device is a master network device or a secondary network device.

In some example embodiments, the first type of the target network device is a target secondary network device. The apparatus further comprises: means for in response to receiving the indication of the first type of the target network device, transmitting data received from a gateway to a source master network device, so that the date is transmitted from the source master network device to the terminal device.

In some example embodiments, the first type of the target network device is a target secondary network device. The apparatus further comprises: means for in response to receiving the indication of the first type of the target network device, transmitting data received from a gateway to terminal device.

In some example embodiments, the apparatus further comprises means for in response to the first handover is completed, transmitting data received from a gateway to the source master network device, so that the data is transmitted to the first type of a target network device from the source master network device.

<FIG> is a simplified block diagram of a device <NUM> that is suitable for implementing example embodiments of the present disclosure. The device <NUM> can be considered as a further example implementation of a terminal device <NUM> as shown in <FIG>. Accordingly, the device <NUM> can be implemented at or as at least a part of the terminal device <NUM>.

As shown, the device <NUM> includes a processor <NUM>, a memory <NUM> coupled to the processor <NUM>, a suitable transmitter (TX) and receiver (RX) <NUM> coupled to the processor <NUM>, and a communication interface coupled to the TX/RX <NUM>. The memory <NUM> stores at least a part of a program <NUM>. The TX/RX <NUM> is for bidirectional communications. The TX/RX <NUM> 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 <NUM> is assumed to include program instructions that, when executed by the associated processor <NUM>, enable the device <NUM> to operate in accordance with the example embodiments of the present disclosure, as discussed herein with reference to <FIG>. The example embodiments herein may be implemented by computer software executable by the processor <NUM> of the device <NUM>, or by hardware, or by a combination of software and hardware. The processor <NUM> may be configured to implement various example embodiments of the present disclosure. Furthermore, a combination of the processor <NUM> and memory <NUM> may form processing means <NUM> adapted to implement various example embodiments of the present disclosure.

The memory <NUM> 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 <NUM> is shown in the device <NUM>, there may be several physically distinct memory modules in the device <NUM>. The processor <NUM> 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.

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 <FIG> o <NUM> 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.

Examples of the carrier include a signal, computer readable media.

Claim 1:
A terminal device (<NUM>) for a dual connectivity handover, comprising:
at least one processor (<NUM>); and
at least one memory (<NUM>) including computer program code (<NUM>), the at least one memory and computer program code configured to, with the at least one processor, carry out the following steps at the terminal device:
receiving, from a source master network device (<NUM>-<NUM>), an indication (<NUM>, <NUM>, <NUM>, <NUM>) of a first type of a target network device for the terminal device to be connected with in a first handover of the dual connectivity handover procedure, the first type indicating whether a network device is a master network device or secondary network device, the first type being determined by a target master network device (<NUM>-<NUM>);
performing the first handover based on the indication of the first type of the target network device; and
in response to being connected with the first type of the target network device, performing a second handover of the dual connectivity handover procedure, the terminal device being connected with a second type of a target network device and disconnected with the second type of a source network device in the second handover, the second type being different from the first type and indicating whether a network device is a master network device or secondary network device.