Patent Description:
In a conventional wireless communications network, there is usually an independent network. Correspondingly, each network has a core network device and an access network device corresponding to the network. <FIG> shows two independent networks. <NUM> network is used as an example. A core network device of <NUM> network may be a serving GPRS support node (SGSN), and an access network device of <NUM> network may be a radio network controller (RNC). For a <NUM> network, an access network device of the <NUM> network may be an eNB, and a core network device of the <NUM> network may be a mobility management entity (MME), or a PDN gateway (P-GW)/gateway GPRS support node (GGSN). When a terminal device is handed over from a network to another, for example, when the terminal device is handed over from a <NUM> network to the <NUM> network, access network devices and core network devices of the two networks need to be scheduled. Specifically, the following procedure or a similar procedure may be included. An RNC determines, based on measurement of UE, a target cell to which a handover needs to be performed, selects a target eNB based on the target cell, and then sends a handover request to an SGSN. The SGSN forwards the handover message to an MME. The MME establishes a connection to an S-GW/P-GW and the eNB in an LTE network. After establishing the connection to the target eNB, the MME notifies the SGSN of a successfully established radio access bearer (RAB), and the SGSN is responsible for notifying the RNC of an unsuccessfully established RAB that needs to be released and a successfully established RAB for which data forwarding is required.

With development of wireless communications technologies, when a network structure changes, an existing solution cannot resolve a problem of switching of a connection between a terminal device and a core network device.

<CIT> discloses a method of user load transfer, comprising the following steps: a communication system comprises a wireless access network node and a core network node, wherein the core network node comprises a core network control node and a core network user surface node; the communication system also comprises at least two core network control nodes and/or two core network user surface nodes, when a first core network node needs to transfer all or partial user load to a second core network node, and the first core network node initiates service switching to the second core network node to transfer all or partial user load.

<CIT> discloses methods and apparatus for a wireless transmit/receive unit (WTRU) to perform a multi-radio access technology (RAT) access (MRA ) operation. The apparatus may include a WTRU non-access stratum (NAS) entity to communicate with a first and second NAS entity of a first and second core network (CN).

Embodiments of the present invention provide a handover method and a terminal device, to provide a more effective handover solution when a network structure changes.

The present invention is defined by a terminal device according to independent claim <NUM> as well as a handover method according to independent claim <NUM> and <NUM>, and a corresponding computer-readable storage medium according to claim <NUM> and <NUM>.

According to the technical solutions provided in the embodiments of the present invention, a new handover solution may be provided. In the system, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

The following <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG> are not according to the invention and are present for illustration purposes only.

An embodiment of the present invention provides a solution based on a communications system shown in <FIG>. As shown in <FIG>, an unclaimed embodiment provides a communications system. The communications system includes an access network device <NUM> (such as an e-eNB), a first core network device <NUM> (such as an EPC), and a second core network device <NUM> (such as a NextGen Core). A corresponding interface may be an S1 interface or an NG1 interface.

The technical solutions in embodiments of the present invention may be applied to various communications systems for data processing, for example, a code division multiple access (CDMA) system, a time division multiple access (TDMA) system, a frequency division multiple access (FDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, and another system. The terms "system" and "network" can be interchanged with each other. Radio technologies such as universal terrestrial radio access (UTRA) and CDMA2000 may be implemented in the CDMA system. The UTRA may include a Wideband CDMA (WCDMA) technology and another technology transformed from CDMA. The CDMA2000 may cover Interim Standard (IS) <NUM> (IS-<NUM>), the IS-<NUM> standard, and the IS-<NUM> standard. A radio technology such as a Global System for Mobile Communications (GSM) may be implemented in the TDMA system. Radio technologies such as evolved universal terrestrial radio access (E-UTRA), ultra mobile broadband (UMB), IEEE <NUM> (Wi-Fi), IEEE <NUM> (WiMAX), IEEE <NUM>, and Flash OFDMA may be implemented in the OFDMA system. The UTRA corresponds to UMTS, and the E-UTRA corresponds to an evolved version of the UMTS. A new version of the UMTS, namely, the E-UTRA, is used in 3GPP long term evolution (LTE) and various versions evolved based on LTE. A 5th Generation (<NUM>) communications system and New Radio (NR) are next generation communications systems under study. In addition, the communications system <NUM> is further applicable to a future-oriented communications technology to which the technical solutions provided in the embodiments of the present invention are applicable. System architectures and service scenarios described in the embodiments of the present invention are intended to more clearly describe the technical solutions in the embodiments of the present invention, but are not intended to limit the technical solutions provided in the embodiments of the present invention. A person of ordinary skill in the art may know that as network architectures evolve and a new service scenario emerges, the technical solutions provided in the embodiments of the present invention are further applicable to a similar technical problem.

A terminal device, also referred to as user equipment (UE), a mobile terminal (MT), mobile user equipment, or the like, may communicate with one or more core networks through a radio access network (RAN). The user equipment may be a mobile terminal such as a mobile phone (or referred to as a "cellular" phone) or a computer with a mobile terminal device. For example, the user equipment may be a portable, pocket-sized, handheld, computer built-in, or in-vehicle mobile apparatus.

An access network device may be an apparatus deployed in a radio access network for providing a wireless communication function for the terminal device. The access network devicemay include macro base stations, micro base stations (also referred to as small cells), relay nodes, access points, and the like in various forms, and may also include control nodes in various forms, such as a network controller. The control node may be connected to a plurality of base stations, and configure resources for a plurality of terminal devices that fall within coverage of the plurality of base stations. In systems using different radio access technologies, devices having a function of the access network device may have different names, for example, may correspond to a base station and a base station controller in <NUM>, or correspond to a base station and an RNC in <NUM>, or an eNB or eNodeB in LTE, or may be a base station (currently, there is no official name, for example, a G-NB or an NX-NB) in <NUM> or NR, or a transmission reception point (TRP). This is not limited in the present invention.

A core network device may be a device used in a network after the access network device, and is usually connected to the access network device, and there may be a plurality of core network devices based on functions. In systems using different radio access technologies, devices having a function of the core network device may have different names, for example, may correspond to an MME or an S-GW in LTE, or correspond to an SGSN/GGSN in <NUM>, and has no official name in <NUM>, such as an NG-Core.

An embodiment of the present invention provides a handover method. The method is applied to a communications system shown in <FIG>. The communications system includes a terminal device, an access network device, a first core network device, and a second core network device. The first core network device and the second core network device communicate with the terminal device by using the same access network device. Further, the first core network device and the second core network device may use different core network technologies. For example, the first core network device may use an LTE core network technology, and the second core network device may use a <NUM> core network technology. For another example, the first core network device may use the <NUM> core network technology, and the second core network device may use the LTE core network technology.

The terminal device establishes a connection to the second core network device. The terminal device may establish the connection to the second core network device in a known manner. Usually, the terminal device establishes the connection to the second core network device by using the access network device. However, a person skilled in the art may understand that the connection may be established in another manner. For example, the terminal device directly sends a message to the second core network device.

The access network device sends a first message to the second core network device, where the first message includes information about a route distinguisher of the first core network device or information about an identifier of the access network device in a first core network. The information about the route distinguisher of the first core network device is used to indicate a route of a message that is to be sent by the second core network device to the first core network device. For example, the information about the route distinguisher of the first core network device may be information that includes a tracking area code TAC. The information about the identifier of the access network device in the first core network may be information about the identifier of the access network device when the access network device communicates with the first core network device. It may be understood that the information about the identifier may be the identifier, or may be an index or other information. It should be noted that the information about the route distinguisher of the first core network device and the information about the identifier of the access network device in the first core network are information that can be used by the second core network device, and do not necessarily need to be sent by using the first message. It may be understood that, when the second core network device may obtain one of the two pieces of information in another manner, for example, through an agreement, the first message may not include the piece of information that can be learned of by the second core network device. Certainly, the first message may alternatively include the information about the route distinguisher of the first core network device and the information about the identifier of the access network device in the first core network. It may be understood that because the first core network device and the second core network device communicate with the terminal device by using the same access network device, the access network device learns of related information of the first core network device, namely, information that may be included in the first message.

The second core network device receives a capability message, where the capability message is used to indicate that the terminal device supports the terminal device in establishing a connection to the first core network device. It may be understood that the capability message may be sent by the terminal device to the second core network device, or may be sent by the access network device to the second core network device. For example, the capability message may be a non-access stratum NAS message.

The second core network device determines that a connection between the terminal device and the second core network device needs to be switched to a connection between the terminal device and the first core network device. Further, the second core network device may determine, based on a condition of the second core network device, that the switching is required. For example, no more services can be accepted based on a load status of the second core network device. For example, a threshold is exceeded for a condition. Alternatively, the switching may be triggered based on an event, for example, an event that a message sent by another network element is received.

The second core network device sends a change message to the first core network device, where the change message is used to notify the first core network device that the connection between the terminal device and the second core network device needs to be switched to the connection between the terminal device and the first core network device. Optionally, the change message includes at least one or a combination of the following content: a first key of the terminal device, the information about the identifier of the access network device in the first core network, and information about an identifier of the terminal device on a second core network interface. Because the second core network device has established the connection to the terminal device, the second core network device has stored the first key of the terminal device. The second core network device may obtain, based on the information about the route distinguisher of the first core network device, a route for sending the change message to the first core network device. Further, the second core network device sends the change message after generating the message. The information about the identifier of the terminal device on the second core network interface may be used to indicate which terminal device needs to be processed. The identifier of the terminal device on the second core network interface includes an identifier used to identify the terminal device on an interface through which the access network device communicates with the second core network device, for example, may be an S1 AP UE ID.

The second core network device may notify, by using the change message, another network element that the switching is required, and trigger a subsequent procedure.

The first core network device generates a change instruction message, where the change instruction message is used to instruct the access network device to instruct the terminal device to perform an update. Optionally, the change instruction message includes a second key of the terminal device and/or the information about the identifier of the terminal device on the second core network interface, and the second key is obtained based on the first key.

After receiving the change message, the first core network device may learn that the first core network device is to accept a task of establishing a connection to the terminal device, and correspondingly, the first core network device prepares a resource to prepare to establish communication with the terminal device. If the first core network device determines that the first core network device cannot accept the task, the first core network device may feed back a reject message to the second core network device (not shown), and the second core network device then searches for another core network device or another processing manner based on the reject message (not shown).

The first key is a key that is used for communication between the terminal device and the second core network device and that is adapted to a second core network technology. The first core network device deduces the adapted second key of the terminal device in the first core network based on the first key of the terminal device by using a core network technology of the first core network device.

The first core network device sends the change instruction message to the access network device. Further, the first core network device may send the change instruction message to the access network device based on the information about the identifier of the access network device in the first core network.

The access network device generates an update message, where the update message is used to instruct the terminal device to perform an update, and optionally, the update message is used to instruct the terminal device to update a NAS type and/or update a key of the terminal device. The updated key of the terminal device is obtained based on a local key stored on the terminal device. Optionally, a new key is deduced from the local key by using a deduction method that is the same as that of the first core network device.

The access network device may learn of, based on the information about the identifier of the terminal device on the second core network interface, a terminal device that needs to update a key. The access network device receives and locally stores the second key, so as to use the second key when communicating with the terminal device.

The access network device notifies the terminal device of the update message.

The terminal device updates the local key and/or changes the non-access stratum NAS type based on the update message. The updating a NAS type includes: updating a NAS type used for communication with the second core network device to a NAS type used for communication with the first core network device; and the updating a key of the terminal device includes: updating the first key used for communication with the second core network device to the second key used for communication with the first core network device. Further, the local key of the terminal device is used for communication with the second core network device, and the key needs to be updated now. To be specific, there is a mapping relationship between the local key of the terminal device and the first key of the terminal device on the second core network device. The mapping relationship may be that the first key is the same as the second key or the first key may be obtained through an operation. Because the first core network device has updated the first key on a network side to the second key that meets a requirement of the first core network device, the terminal device needs to obtain the new key in a corresponding deduction manner, so as to meet a requirement for communication with the first core network device. Correspondingly, an original NAS type also needs to be updated to meet a requirement for communication with the first core network device instead of meeting a requirement for communication with the second core network device. For example, a NAS type of <NUM> is updated to a NAS type of <NUM>.

The access network device sends an acknowledgement message to the first core network device, where the acknowledgement message is used to indicate that the access network device and the terminal device complete the switching.

The first core network device sends a release message to the second core network device, where the release message is used to instruct the second core network device to release the connection between the terminal device and the second core network device.

The method may further include step <NUM>' as an alternative to steps <NUM> and <NUM>: The access network device sends a release message to the second core network device, where the release message is used to instruct the second core network device to release the connection between the terminal device and the second core network device.

Further, the second core network device releases the connection between the terminal device and the second core network device (not shown).

Based on a handover procedure initiated by the second core network device, the connection between the terminal device and the second core network device may be switched to the connection between the terminal device and the first core network device without switching of the access network device, so that a network communication requirement is efficiently met.

Further, in a network communication process, the terminal device updates the key of the terminal device and a used communication protocol in a timely manner, to successfully complete the switching.

In the flowchart of <FIG>, a dashed line indicates that the step is optional. To be specific, one or a combination of steps <NUM>, <NUM>, <NUM>, and <NUM>' may be omitted, and one or a combination of steps <NUM>, <NUM>, and <NUM>' may be omitted. Specifically, when the second core network device has learned of the information about the route distinguisher of the first core network device or the information about the identifier of the access network device in the first core network, step <NUM> may be omitted, in other words, the first message does not need to be transmitted. When the second core network device has learned that the terminal device supports the terminal device in establishing the connection to the first core network device, steps <NUM> and <NUM>' may be omitted, in other words, the capability information does not need to be transmitted. When the second core network device has a proper mechanism, for example, a timeout mechanism, to release the connection between the terminal device and the second core network device, steps <NUM>, <NUM>, and <NUM>' may be omitted, in other words, the release message does not need to be transmitted to release a resource. It may be understood that omitting the foregoing steps does not affect a technical effect of the solution in <FIG>, and does not affect functions of various network elements.

For various network elements in <FIG>, the following different methods may be obtained. The following methods are consistent with the method in <FIG>, and details are not described again for a same part. The steps and the related descriptions of the method in <FIG> may provide reference and have similar advantages to the following methods. For brevity of description, details are not described again. It may be understood that in the following methods, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

A handover method is used by the second core network device and includes the following steps.

The second core network device determines that a connection between the terminal device and the second core network device needs to be switched to a connection between the terminal device and the first core network device.

The second core network device sends a change message to the first core network device, where the change message is used to notify the first core network device that the connection between the terminal device and the second core network device needs to be switched to the connection between the terminal device and the first core network device. Optionally, the change message includes at least one or a combination of the following content: a first key of the terminal device, information about an identifier of the access network device in a first core network, and information about an identifier of the terminal device on a second core network interface.

The second core network device determines that the switching is required, and sends the change message, to trigger a handover procedure and enable another network element to prepare for the switching. Therefore, a requirement of a network is met. In the network, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

Further, the handover method further includes the following step: <NUM>. The terminal device establishes a connection to the second core network device.

Further, the handover method further includes:.

The second core network device may learn of required information in a handover procedure by using the first message or the capability message, to prepare well for the handover procedure.

Further, the handover method further includes:
receiving, by the second core network device, a release message, where the release message is used to instruct the second core network device to release the connection between the terminal device and the second core network device.

Further, the handover method further includes:
releasing, by the second core network device, the connection between the terminal device and the second core network device.

The second core network device may complete resource release by using the foregoing release procedure, to save resources.

A handover method is used by the first core network device and includes:
receiving, by the first core network device, a change message, where the change message is used to notify the first core network device that a connection between the terminal device and the second core network device needs to be switched to a connection between the terminal device and the first core network device. Optionally, the change message includes at least one or a combination of the following content: a first key of the terminal device, information about an identifier of the access network device in a first core network, and information about an identifier of the terminal device on a second core network interface.

The first core network device generates a change instruction message, where the change instruction message is used to instruct the access network device to instruct the terminal device to perform an update. The change instruction message may include a second key of the terminal device and/or the information about the identifier of the terminal device on the second core network interface, and the second key is obtained based on the first key.

The first core network device sends the change instruction message to the access network device.

The first core network device may learn, by receiving the change message, that the first core network device needs to connect to the terminal device, and the first core network device may notify, by using the change instruction message, another network element that the first core network device and the second core network device prepare well for the switching, to meet a requirement of a network. In the network, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

Further, the handover method further includes:
receiving, by the first core network device, an acknowledgement message, where the acknowledgement message is used to indicate that the access network device and the terminal device complete the switching.

Based on the foregoing release procedure, the first core network device may help the second core network device complete resource release, to save resources.

A handover method is used by the access network device and includes:
receiving, by the access network device, a change instruction message, where the change instruction message is used to instruct the access network device to instruct the terminal device to perform an update. Optionally, the change instruction message includes a second key of the terminal device and/or information about an identifier of the terminal device on a second core network interface.

The access network device generates an update message, where the update message is used to instruct the terminal device to perform an update. Optionally, the update message is used to instruct the terminal device to update a NAS type and/or update a key of the terminal device.

The access network device may learn, by receiving the change instruction message, that the second core network device and the first core network device prepare well for switching. The access network device may start an update procedure on a terminal side by generating and sending the update message, to meet a requirement of a network. In the network, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

Further, the handover method further includes:
sending, by the access network device, a first message, where the first message includes information about a route distinguisher of the first core network device or information about an identifier of the access network device in a first core network.

The access network device may notify another network element of required information in a handover procedure by using the first message, to prepare well for the handover procedure.

Further, the handover method further includes the following step:
<NUM>. The access network device sends an acknowledgement message to the first core network device, where the acknowledgement message is used to indicate that the access network device and the terminal device complete switching.

Further, the handover method further includes the following step:
<NUM>'. The access network device sends a release message to the second core network device, where the release message is used to instruct the second core network device to release a connection between the terminal device and the second core network device.

Based on the foregoing release procedure, the access network device may help the second core network device complete resource release, to save resources.

A handover method is used by the terminal device and includes:.

The updating a NAS type includes: updating a NAS type used for communication with the second core network device to a NAS type used for communication with the first core network device; and the updating a key of the terminal device includes: updating a first key used for communication with the second core network device to a second key used for communication with the first core network device.

The terminal device may complete, by using the update message and completing a corresponding update action, a handover from the second core network device to the first core network device, to meet a requirement of a network. In the network, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

Further, the handover method further includes:
sending, by the terminal device, a capability message, where the capability message is used to indicate that the terminal device supports the terminal device in establishing a connection to the first core network device.

The terminal device notifies, by using the capability information, another network element that the terminal device may support communication with the first core network device, to prepare well for switching.

An embodiment of the present invention provides a communications system. The communications system includes a terminal device, an access network device, a first core network device, and a second core network device. The first core network device and the second core network device communicate with the terminal device by using the same access network device. The system may use the handover method shown in <FIG>. Further, the first core network device and the second core network device may use different core network technologies. For example, the first core network device may be a core network device that uses an LTE core network technical specification, and the second core network device may be a core network device that uses a <NUM> core network technical specification.

The following devices may be related to the steps of the method described in <FIG>. Therefore, the steps and the related descriptions of the method in <FIG> may provide reference and have similar advantages to the following devices. For brevity of description, details are not described again. It may be understood that in the following embodiments, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

As shown in <FIG>, a second core network device <NUM> includes:.

Optionally, the change message includes at least one or a combination of the following content: a first key of the terminal device, information about an identifier of the access network device in a first core network, and information about an identifier of the terminal device on a second core network interface.

Further, in the second core network device, the terminal device establishes a connection to the second core network device.

Further, in the second core network device,.

Further, in the second core network device,
the transceiver unit is configured to receive a release message, where the release message is used to instruct the second core network device to release the connection between the terminal device and the second core network device.

Further, in the second core network device,
the processing unit is configured to release the connection between the terminal device and the second core network device.

As shown in <FIG>, a first core network device <NUM> includes:.

The transceiver unit <NUM> is further configured to send the change instruction message to the access network device.

The first core network device may learn, by receiving the change message, that the first core network device needs to connect to the terminal device, and the first core network device may notify, by using the change instruction message, another network element that the first core network device and the second core network device prepare well for the switching, to meet a requirement of anetwork. In the network, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

Further, in the first core network device,.

As shown in <FIG>, an access network device <NUM> includes:.

The transceiver unit <NUM> is further configured to send the update message to the terminal device.

As shown in <FIG>, a terminal device includes:.

The terminal device notifies, by using the capability message, another network element that the terminal device may support communication with the first core network device, to prepare well for switching.

An embodiment of the present invention provides a handover method. The method is applied to a communications system shown in <FIG>. The communications system includes a terminal device, an access network device, a first core network device, and a second core network device. The first core network device and the second core network device communicate with the terminal device by using the same access network device. It can be learned that the second embodiment is basically similar to the first embodiment. A difference lies in that, in the first embodiment, the second core network device determines that a connection between the terminal device and the second core network device needs to be switched to a connection between the terminal device and the first core network device, but in the second embodiment, the access network device determines that the switching is required.

Based on a handover procedure initiated by the access network device, the connection between the terminal device and the second core network device may be switched to the connection between the terminal device and the first core network device without switching of the access network device, so that a network communication requirement is efficiently met.

For brevity of description, a same reference numeral is used for a same part in <FIG> and <FIG>. Therefore, details are not described again. Different parts such as steps <NUM>, <NUM>, <NUM>, and <NUM> are described in detail. It may be understood that the related descriptions in <FIG> may be used to explain the technical solution in <FIG>.

The terminal device establishes a connection to the second core network device by using the access network device.

The access network device sends a first message to the second core network device, where the first message includes information about a route distinguisher of the first core network device or information about an identifier of the access network device in a first core network.

The access network device determines that a connection between the terminal device and the second core network device needs to be switched to a connection between the terminal device and the first core network device. Further, the access network device may initiate the switching based on a condition of the access network or a status of the second core network device. For example, the access network device speculates that no more services can be accepted based on a load status of the second core network device. Alternatively, the access network device receives a message of the second core network device and is notified that the switching is required, and in this case, the access network device actively determines that the switching is required. It may be understood that the access network device may alternatively receive a message sent by another network element, to trigger the switching.

The access network device sends a change message to the second core network device, where the change message is used to notify the second core network device that the connection between the terminal device and the second core network device needs to be switched to the connection between the terminal device and the first core network device. Optionally, the change message includes information about an identifier of the terminal device on a second core network interface. The identifier of the terminal device on the second core network interface is an identifier used to identify the terminal device on an interface through which the access network device communicates with the second core network device.

Optionally, the change message may include the information about the route distinguisher of the first core network device and/or the information about the identifier of the access network device in the first core network. It may be understood that the two types of information are used by the second core network device. If the second core network device has learned of the information or a part of the information in another manner, it is unnecessary to send the known information by using step <NUM> or step <NUM>. It may be understood that one or both of the information about the route distinguisher of the first core network device and the information about the identifier of the access network device in the first core network may be sent by using the first message in step <NUM>. In this case, the change message in step <NUM> may not include information that has been sent by using the first message. Alternatively, one or both of the information about the route distinguisher of the first core network device and the information about the identifier of the access network device in the first core network may be sent by using the change message in step <NUM>. In this case, the first message in step <NUM> may not include information that needs to be sent by using the change message, or even step <NUM> is omitted.

The second core network device generates a change acknowledgement message, where the change acknowledgement message is used to notify the first core network device that the connection between the terminal device and the second core network device needs to be switched to the connection between the terminal device and the first core network device. Optionally, the change acknowledgement message includes one or a combination of the following three items: a first key of the terminal device, the information about the identifier of the access network device in the first core network, and the information about the identifier of the terminal device on the second core network interface. The second core network device receives the change message, learns that the connection between the terminal device and the second core network device needs to be switched to the connection between the terminal device and the first core network device, and correspondingly prepares a communication resource. To enable the first core network device to successfully connect to the terminal device, the second core network device sends corresponding information. The first key of the terminal device, the information about the identifier of the access network device in the first core network, and the information about the identifier of the terminal device on the second core network interface are similar to or consistent with those in the solution in <FIG>. Details are not described again.

The second core network device sends the change acknowledgement message to the first core network device.

Optionally, the second core network device may find the first core network device based on the information about the route distinguisher of the first core network device.

The access network device generates an update message, where the update message is used to instruct the terminal device to update a NAS type and/or update a key of the terminal device. The updated key of the terminal device is obtained based on a local key stored on the terminal device.

The access network device notifies the terminal device of the update message, where the update message is used to instruct the terminal device to perform an update, and optionally, the update message is used to instruct the terminal device to update the NAS type and/or update the key of the terminal device.

The terminal device updates the local key and/or changes the non-access stratum NAS type based on the update message.

In the flowchart of <FIG>, a dashed line indicates that the step is optional. To be specific, one or a combination of steps <NUM>, <NUM>, <NUM>, and <NUM>' may be omitted, and one or a combination of steps <NUM>, <NUM>, and <NUM>' may be omitted.

For various network elements in <FIG>, the following different methods may be obtained. The following methods are consistent with the method in <FIG>, and details are not described again for a same part. The steps and the related descriptions of the methods in <FIG> and <FIG> may provide reference and have similar advantages to the following methods. For brevity of description, details are not described again. It may be understood that in the following methods, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

A handover method is used by the second core network device and includes:
receiving, by the second core network device, a change message, where the change message is used to notify the second core network device that a connection between the terminal device and the second core network device needs to be switched to a connection between the terminal device and the first core network device. Optionally, the change message includes information about an identifier of the terminal device on a second core network interface, and the identifier of the terminal device on the second core network interface is an identifier used to identify the terminal device on an interface through which the access network device communicates with the second core network device.

The second core network device generates a change acknowledgement message, where the change acknowledgement message is used to notify the first core network device that the connection between the terminal device and the second core network device needs to be switched to the connection between the terminal device and the first core network device. Optionally, the change acknowledgement message includes one or a combination of the following three items: a first key of the terminal device, information about an identifier of the access network device in a first core network, and the information about the identifier of the terminal device on the second core network interface.

The second core network device sends the change message, to trigger a handover procedure and enable another network element to prepare for the switching. Therefore, a requirement of a network is met. In the network, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

Further, the handover method further includes:
receiving, by the second core network device, a first message, where the first message includes information about a route distinguisher of the first core network device or the information about the identifier of the access network device in the first core network.

The second core network device may learn of required information in a handover procedure by using the first message, to prepare well for the handover procedure.

A handover method is used by the first core network device and includes:
receiving, by the first core network device, a change acknowledgement message, where the change acknowledgement message is used to notify the first core network device that a connection between the terminal device and the second core network device needs to be switched to a connection between the terminal device and the first core network device. Optionally, the change acknowledgement message includes one or a combination of the following three items: a first key of the terminal device, information about an identifier of the access network device in a first core network, and information about an identifier of the terminal device on a second core network interface.

The first core network device may learn, by receiving the change acknowledgement message, that the first core network device needs to connect to the terminal device, and the first core network device may notify, by using the change instruction message, another network element that the first core network device and the second core network device prepare well for the switching, to meet a requirement of a network. In the network, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

A handover method is used by the access network device and includes the following steps.

The access network device determines that a connection between the terminal device and the second core network device needs to be switched to a connection between the terminal device and the first core network device.

The access network device sends a change message to the second core network device, where the change message is used to notify the second core network device that the connection between the terminal device and the second core network device needs to be switched to the connection between the terminal device and the first core network device. The change message includes information about an identifier of the terminal device on a second core network interface, and the identifier of the terminal device on the second core network interface is an identifier used to identify the terminal device on an interface through which the access network device communicates with the second core network device.

The access network device determines that the switching is required, and sends the change message, to trigger a handover procedure and enable another network element to prepare for the switching. Therefore, a requirement of a network is met. In the network, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

Further, the handover method further includes:
receiving, by the access network device, a change instruction message, where the change instruction message is used to instruct the access network device to instruct the terminal device to perform an update. Optionally, the change instruction message includes a second key of the terminal device and/or the information about the identifier of the terminal device on the second core network interface.

The access network device generates an update message, where the update message is used to instruct the terminal device to perform an update, and optionally, the update message is used to instruct the terminal device to update a NAS type and/or update a key of the terminal device. The updated key of the terminal device is obtained based on a local key stored on the terminal device.

The access network device may learn, by receiving the change instruction message, that the second core network device and the first core network device prepare well for the switching. The access network device may start an update procedure on a terminal side by generating and sending the update message, to meet a requirement of a network.

Further, the handover method further includes the following step:.

The access network device sends a release message to the second core network device, where the release message is used to instruct the second core network device to release the connection between the terminal device and the second core network device.

An embodiment of the present invention provides a communications system. The communications system includes a terminal device, an access network device, a first core network device, and a second core network device. The first core network device and the second core network device communicate with the terminal device by using the same access network device. The system may use the handover method shown in <FIG>. Further, the first core network device and the second core network device may use different core network technologies. Refer to the explanation in <FIG>.

The following devices may be related to the steps of the method described in <FIG>. Therefore, the steps and the related descriptions of the methods in <FIG> and <FIG> may provide reference and have similar advantages to the following devices. For brevity of description, details are not described again. It may be understood that in the following embodiments, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

The transceiver unit <NUM> is further configured to send the change acknowledgement message to the first core network device.

Further, in the second core network device,
the transceiver unit is configured to receive a first message, where the first message includes information about a route distinguisher of the first core network device or the information about the identifier of the access network device in the first core network.

Further, in the access network device,
the transceiver unit <NUM> is configured to send a first message, where the first message includes information about a route distinguisher of the first core network device or information about an identifier of the access network device in a first core network.

Further, in the access network device,
the transceiver unit <NUM> is configured to receive a change instruction message, where the change instruction message is used to instruct the access network device to instruct the terminal device to perform an update. Optionally, the change instruction message includes a second key of the terminal device and/or the information about the identifier of the terminal device on the second core network interface.

The processing unit <NUM> is configured to generate an update message, where the update message is used to instruct the terminal device to perform an update, and optionally, the update message is used to instruct the terminal device to update a NAS type and/or update a key of the terminal device.

The transceiver unit <NUM> is configured to notify the terminal device of the update message.

The updating a NAS type includes: updating a NAS type used for communication with a second core network device to a NAS type used for communication with a first core network device; and the updating a key of the terminal device includes: updating a first key used for communication with the second core network device to a second key used for communication with the first core network device.

The terminal device may complete, by using the update message and completing a corresponding update action, a handover from the second core network device to the first core network device, to meet a requirement of a network. In the network, the first core network device and the second core network device communicate with the terminal device by using a same access network device.

An embodiment of the present invention provides a handover method. The method is applied to a communications system shown in <FIG>. The communications system includes a terminal device, a first access network device, a second access network device, a first core network device, and a second core network device. The first core network device and the second core network device communicate with the terminal device by using the same first access network device. Further, the first core network device and the second core network device may use different core network technologies. Refer to the explanation in <FIG>. The first access network device may be compatible with two different core network technologies.

It can be learned that the third embodiment is partially similar to the first embodiment. A same thing lies in that a connection between the terminal device and the second core network device needs to be switched to a connection between the terminal device and the first core network device, and a difference lies in that the terminal device initially establishes a connection to the second core network device by using the second access network device, instead of using the first access network device. The second access network device does not necessarily need to be directly connected to the first core network device. For brevity of description, a same reference numeral is used for a same part or similar parts in <FIG> and <FIG>. Therefore, details are not described again. It may be understood that the related descriptions in <FIG> may be used to explain the technical solution in <FIG>.

The terminal device establishes a connection to the second core network device by using the second access network device. The terminal device may establish the connection to the second core network device in a known manner. Usually, the terminal device establishes the connection to the second core network device by using an access network device. However, a person skilled in the art may understand that the connection may be established in another manner. For example, the terminal device directly sends a message to the second core network device.

The first access network device sends a first message to the second core network device, where the first message includes information about a route distinguisher of the first core network device or information about an identifier of the access network device in a first core network. The information about the route distinguisher of the first core network device is used to indicate a route of a message that is to be sent by the second core network device to the first core network device. Refer to the related descriptions in <FIG>.

The second core network device receives a capability message, where the capability message is used to indicate that the terminal device supports the terminal device in establishing a connection to the first core network device. It may be understood that the capability message may be sent by the terminal device to the second core network device, or may be sent by the first access network device to the second core network device. For example, the capability message may be a non-access stratum NAS message.

The second access network device generates a handover message, where the handover message is used to indicate that a connection between the terminal device and the second access network device needs to be switched to a connection between the terminal device and the first access network device. Further, the handover message includes information about an identifier of the terminal device on a second core network interface. The identifier of the terminal device on the second core network interface includes an identifier used to identify the terminal device on an interface through which the access network device communicates with the second core network device, for example, may be an S1 AP UE ID. The second access network device initiates a handover procedure between access network devices based on the handover message. Specifically, for determining, by the second access network device, a condition on which the handover procedure between the access network devices needs to be initiated, refer to a related technology of an inter-cell handover in the prior art.

The second access network device sends the handover message to the first access network device.

The second access network device sends the handover message to instruct another network element to prepare to establish a connection to the terminal device.

The first access network device generates a report message, where the report message is used to notify the second core network device that the connection between the terminal device and the second access network device needs to be switched to the connection between the terminal device and the first access network device. Further, the report message includes the information about the identifier of the terminal device on the second core network interface. Similar to the change message in the second embodiment, the report message may further include the information about the route distinguisher of the first core network device or the information about the identifier of the access network device in the first core network.

The first access network device sends the report message to the second core network device. It may be understood that steps <NUM> to <NUM> are similar to a conventional inter-cell handover procedure, to be specific, a terminal device needs to be handed over from a second access network device in a second network to a first access network device, but the first access network device is further connected to a first core network device, and is a relatively special access network device.

The second core network device determines that a connection between the terminal device and the second core network device needs to be switched to a connection between the terminal device and the first core network device. Refer to step <NUM> in <FIG>. Details are not described again. For example, the second core network device considers that a <NUM> service capability of the first access network device is insufficient, and a <NUM> service capability of the first access network device needs to be used, and therefore a handover procedure between core network devices is initiated. Correspondingly, a handover from the second access network device to the first access network device is performed, but a network type is also changed.

The second core network device sends a change message to the first core network device, where the change message is used to notify the first core network device that the connection between the terminal device and the second core network device needs to be switched to the connection between the terminal device and the first core network device. Optionally, the change message includes at least one or a combination of the following content: a first key of the terminal device, the information about the identifier of the access network device in the first core network, and the information about the identifier of the terminal device on the second core network interface. Refer to step <NUM>. Details are not described again.

The first core network device generates a change instruction message, where the change instruction message is used to instruct the access network device to instruct the terminal device to perform an update. Optionally, the change instruction message includes a second key of the terminal device and/or the information about the identifier of the terminal device on the second core network interface, and the second key is obtained based on the first key. Refer to the solution in <FIG>.

The first core network device sends the change instruction message to the first access network device. Further, the first core network device may send the change instruction message to the access network device based on the information about the identifier of the access network device in the first core network.

The first access network device generates an update message, where the update message is used to instruct the terminal device to perform an update, and optionally, the update message is used to instruct the terminal device to update a NAS type and/or update a key of the terminal device. The updated key of the terminal device is obtained based on a local key stored on the terminal device. Optionally, a new key is deduced from the local key by using a deduction method that is the same as that of the first core network device.

The first access network device notifies the terminal device of the update message.

It may be understood that, if the first access network device has completed an inter-cell handover from the second access network device, in other words, the first access network device has established a direct connection to the terminal device, the second access network device no longer needs to be used, and the first access network device may directly notify the terminal device of the update message. It may be understood that, as an alternative solution, the first access network device may use the second access network device to forward the update message (not shown), in other words, the second access network device does not process the update message and only forwards the update message.

Optionally, the method may further include: sending, by the first access network device, a message to the second access network device (not shown), where the message is used to indicate to the second access network device that the switching has been completed and the connection to the terminal device may be released. The message may be sent before the update message, or may be sent after the update message, and a similar function may be alternatively completed by using information carried in the update message.

The terminal device updates the local key and/or changes the non-access stratum NAS type based on the update message. Refer to the solution in <FIG>.

For the terminal device, only a conventional inter-cell handover is initially initiated. To be specific, the handover from the second access network device to the first access network device is performed. However, because the first access network device accesses the first core network device in addition to accessing the second core network device, the second core network device further triggers a handover from the second core network device to the first core network device based on the conventional inter-cell handover, so that different service quality is provided. For example, UE originally performs only an inter-cell handover in a <NUM> network. Because a target base station is an e-eNB, and the base station may also access a <NUM> network, a core network device of <NUM> further hands over the UE to the <NUM> network, and a corresponding core network device also becomes an EPC of <NUM> It can be learned that, in an early stage of establishing the <NUM> network, because a service capability of <NUM> is insufficient, the UE can be handed over to the <NUM> network more quickly by using the foregoing solution, so that a handover requirement is met.

In the flowchart of <FIG>, a dashed line indicates that the step is optional. To be specific, one or a combination of steps <NUM>, <NUM>, <NUM>, and <NUM>' may be omitted, and one or a combination of steps <NUM>, <NUM>, and <NUM>' may be omitted. Refer to the explanation in <FIG>.

For various network elements in <FIG>, the following different methods may be obtained. The following methods are consistent with the method in <FIG>, and details are not described again for a same part. The steps and the related descriptions of the method in <FIG> may provide reference and have similar advantages to the following methods. For brevity of description, details are not described again. It may be understood that in the following methods, the first core network device and the second core network device communicate with the terminal device by using the same first access network device.

A handover method is used by the second core network device and includes:
receiving, by the second core network device, a report message, where the report message is used to notify the second core network device that a connection between the terminal device and the second access network device needs to be switched to a connection between the terminal device and the first access network device. Further, the report message includes information about an identifier of the terminal device on a second core network interface.

The second core network device sends a change message to the first core network device, where the change message is used to notify the first core network device that the connection between the terminal device and the second core network device needs to be switched to the connection between the terminal device and the first core network device. Optionally, the change message includes at least one or a combination of the following content: a first key of the terminal device, information about an identifier of the access network device in a first core network, and the information about the identifier of the terminal device on the second core network interface.

A handover method is used by the first access network device and includes:
receiving, by the first access network device, a handover message, where the handover message is used to indicate that a connection between the terminal device and the second access network device needs to be switched to a connection between the terminal device and the first access network device. Further, the handover message includes information about an identifier of the terminal device on a second core network interface, and the identifier of the terminal device on the second core network interface includes an identifier used to identify the terminal device on an interface through which the access network device communicates with the second core network device.

The first access network device generates a report message, where the report message is used to notify the second core network device that the connection between the terminal device and the second access network device needs to be switched to the connection between the terminal device and the first access network device. Further, the report message includes the information about the identifier of the terminal device on the second core network interface.

The first access network device sends the report message to the second core network device.

Optionally, the report message may further include information about a route distinguisher of the first core network device or information about an identifier of the access network device in a first core network.

By using the handover message and generating the report message, the first access network device may prepare for the switching and transmit related information to the core network device, to meet a requirement of a network.

A handover method is used by the first access network device and includes:
receiving, by the access network device, a change instruction message, where the change instruction message is used to instruct the first access network device to instruct the terminal device to perform an update. Optionally, the change instruction message includes a second key of the terminal device and/or information about an identifier of the terminal device on a second core network interface.

The access network device generates an update message, where the update message is used to instruct the terminal device to perform an update, and optionally, the update message is used to instruct the terminal device to update a NAS type and/or update a key of the terminal device.

The access network device may learn, by receiving the change instruction message, that the second core network device and the first core network device prepare well for the switching. The access network device may start an update procedure on a terminal side by generating and sending the update message, to meet a requirement of a network. In the network, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

Further, the handover method further includes the following step:
<NUM>. The access network device sends an acknowledgement message to the first core network device, where the acknowledgement message is used to indicate that the access network device and the terminal device complete the switching.

Further, the handover method further includes the following step:
<NUM>'. The access network device sends a release message to the second core network device, where the release message is used to instruct the second core network device to release the connection between the terminal device and the second core network device.

The terminal device notifies, by using the capability information, another network element that the terminal device may support communication with the first core network device, to prepare well for the switching.

A handover method is used by an access network device. The access network device is the second access network device, and the method includes the following steps.

The access network device generates a handover message, where the handover message is used to indicate that a connection between the terminal device and the second access network device needs to be switched to a connection between the terminal device and the first access network device. Further, the handover message includes information about an identifier of the terminal device on a second core network interface. The identifier of the terminal device on the second core network interface includes an identifier used to identify the terminal device on an interface through which the access network device communicates with the second core network device, for example, may be an S1 AP UE ID.

The access network device sends the handover message to the first access network device.

An embodiment of the present invention provides a communications system. The communications system includes a terminal device, a first access network device, a second access network device, a first core network device, and a second core network device. The first core network device and the second core network device communicate with the terminal device by using the same first access network device. The system may use the handover method shown in <FIG>. Further, the first core network device and the second core network device may use different core network technologies. For example, the first core network device may be a core network device that uses an LTE core network technical specification, and the second core network device may be a core network device that uses a <NUM> core network technical specification. For another example, the first core network device may be a core network device that uses the <NUM> core network technical specification, and the second core network device may be a core network device that uses the LTE core network technical specification. The first access network device may be compatible with two different core network technologies.

The following devices may be related to the steps of the method described in <FIG>. Therefore, the steps and the related descriptions of the method in <FIG> may provide reference and have similar advantages to the following devices. For brevity of description, details are not described again. It may be understood that in the following embodiments, the first core network device and the second core network device communicate with the terminal device by using the same first access network device.

The transceiver unit <NUM> is further configured to send a change message to the first core network device, where the change message is used to notify the first core network device that the connection between the terminal device and the second core network device needs to be switched to the connection between the terminal device and the first core network device. Optionally, the change message includes a first key of the terminal device and/or information about an identifier of the access network device in a first core network.

As shown in <FIG>, an access network device <NUM> is provided. The access network device is a first access network device and includes:.

The transceiver unit <NUM> is further configured to send the report message to the second core network device.

Optionally, the report message may further include information about a route distinguisher of a first core network device or information about an identifier of the access network device in a first core network.

A first access network device <NUM> includes:.

The transceiver unit <NUM> is further configured to notify the terminal device of the update message.

The terminal device may complete, by using the update message and completing a corresponding update action, a handover from a second core network device to a first core network device, to meet a requirement of a network. In the network, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

As shown in <FIG>, a second access network device <NUM> includes:.

The terminal device may complete, by using an update message and completing a corresponding update action, a handover from the second core network device to a first core network device, to meet a requirement of a network. In the network, the first core network device and the second core network device communicate with the terminal device by using the same access network device.

In the foregoing embodiments, the core network device, the access network device, and the terminal device shown in <FIG> are collectively referred to as communications devices. The processing unit used in these communications devices may be implemented by a processor, and the transceiver unit may be implemented by a transceiver. The transceiver may also include necessary components such as a transmitter, a receiver, and an antenna. A structure shown in <FIG> or <FIG> may be used for these communications devices. For ease of description, details are not described.

It may be understood that, although not shown, the communications devices may further include another apparatus such as an input apparatus, an output apparatus, and a battery. The processor may include a function of operating one or more software programs. The software program may be stored in a memory. The processor and a software instruction stored in the memory may be usually configured as an action performed by the communications devices. For example, the processor can operate a connection program. The memory may be a read-only memory, a flash memory, or a magnetic storage device, such as a hard disk, a floppy disk drive, or a magnetic tape. The memory may store one or more software programs, instructions, information blocks, pieces of data, and the like.

Optionally, in some embodiments, the memory may separately store instructions used to perform the methods performed by the communications devices in the methods shown in <FIG>. The processor may execute the instructions stored in the memory, to complete, in combination with other hardware (such as the transmitter, the receiver, and the antenna), the steps performed by the communications devices in the methods shown in <FIG>. For a specific working process and advantageous effects, refer to the descriptions of the communications devices in the embodiments shown in <FIG>.

Steps in the foregoing methods can be implemented by using a hardware integrated logical circuit in the processor, or by using instructions in a form of software. The processor may be a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA) or another programmable logical device, a discrete gate or transistor logic device, or a discrete hardware component. The processor may implement or perform the methods, the steps, and logical block diagrams that are disclosed in the embodiments of the present invention. The general-purpose processor may be a microprocessor, or the processor may be any conventional processor or the like. Steps of the methods disclosed with reference to the embodiments of the present invention may be directly performed and accomplished by using a hardware decoding processor, or may be performed and accomplished by using a combination of hardware and software modules in the decoding processor. The software module may be located in a mature storage medium in the art, such as a random access memory (RAM), a flash memory, a read-only memory (ROM), a programmable read-only memory, an electrically erasable programmable memory, or a register. The storage medium is located in the memory, and the processor reads instructions in the memory and completes the steps in the foregoing methods in combination with hardware of the processor.

A person skilled in the art can implement the described functions by using different methods with regard to each specific application.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, and may be located in one position, or may be distributed on a plurality of network units.

In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units may be integrated into one unit.

When the functions are implemented in the form of a software functional unit and sold or used as an independent product, the functions may be stored in a computer-readable storage medium. Based on such an understanding, the technical solutions of the present invention essentially, or the part contributing to the prior art, or some of the technical solutions may be implemented in a form of a software product. The computer software product is stored in a storage medium and includes several instructions for instructing a computer device (which may be a personal computer, a server, a network device, or the like) or a processor to perform all or some of the steps of the methods described in the embodiments of the present invention. The foregoing storage medium includes any medium that can store program code, such as a USB flash drive, a removable hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disc.

Claim 1:
A terminal device (<NUM>), comprising:
a transceiver unit (<NUM>), configured to receive an update message, wherein the update message is used to instruct the terminal device to update a non-access stratum, NAS, type and/or update a key of the terminal device; and
a processing unit (<NUM>), configured to update the NAS type and/or update the key of the terminal device, wherein
the updating a NAS type comprises: updating a NAS type used for communication with a second core network device to a NAS type used for communication with a first core network device; and
the updating a key of the terminal device comprises: updating a first key used for communication with the second core network device to a second key used for communication with the first core network device; and
the first core network device and the second core network device communicate with the terminal device by using a same access network device.