Abstract:
A direct handover method and device are provided. The method comprises: receiving a handover message sent by a source side access network node; selecting a destination side core network node, and sending a handover message to the destination side core network node, so that the destination side core network node obtains context information of a UE from a source side core network node; receiving a handover acknowledge message sent by the destination side core network node. The source side access network node sends the handover message to a destination side access network node, the destination side access network node selects the destination side core network node, and sends the handover message to the destination side core network node, and the destination side core network node requests the context information of the UE from the source side core network node, so as to complete the handover.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Patent Application No. PCT/CN2013/086357, filed on Oct. 31, 2013, which claims priority to Chinese Patent Application No. 201210426023.X, filed on Oct. 31, 2012, both of which are hereby incorporated by reference in their entireties. 
     
    
     FIELD 
       [0002]    The invention relates to the filed of communication, and in particular, to a direct handover method and a direct handover device. 
       BACKGROUND 
       [0003]    A source-side node is a communication node used by a terminal in a communication. The source-side node may be, for example, a source-side core network node or a source-side access network node. 
         [0004]    A target-side node is a communication node used by the terminal in the communication after a handover. The target-side node may be, for example, a target-side core network node or a target-side access network node. 
         [0005]    The terminal may usually encounter a problem of handover between communication nodes in the communication. Mainly, an access network node and a core network node are involved in the handover between the communication nodes. If only the access network nodes are involved in the handover between the communication nodes, the handover may be performed between the access network nodes through an X2 interface. The handover between the communication nodes is very complicated if the core network node are involved in the handover. An S1 interface handover may be executed in the handover, once a Mobility Management Entity (MME) alters. A handover procedure starts from a source-side evolved Node B (ENB) and arrives at a target-side MME via a source-side MME. Then, the target-side MME interacts with a target-side ENB and forwards related information to the source-side ENB via the source-side MME, to complete the handover procedure. Multiple times of interactions between MME and ENB are involved in the procedure and the signaling procedure is complicated. Network congestion may be easily caused if many UEs initiate similar handovers. An inter-RAT handover (a handover between GSM EDGE Radio Access Network/Universal Terrestrial Radio Access Network (GERAN/UTRAN) and Evolved Universal Terrestrial Radio Access Network (EUTRAN)) is similar to the above (in the inter-RAT handover, Serving GPRS Support Node (SGSN) provides a service for the GERAN/UTRAN and MME provides a service for the EUTRAN, which is equivalent to the case that CN node alters). Multiple times of interactions between CN and RAN are involved in the handover, which also increases the signalling burden of the network and causes a waste of the network resource. 
       SUMMARY 
       [0006]    Embodiments of the invention intend to provide a direct handover method and a direct handover device, to solve the problems in conventional technologies that the handover procedure is complicated and network congestion is easily caused. 
         [0007]    In one aspect, a direct handover method is provided in the invention. The method includes: 
         [0008]    receiving a handover message transmitted by a source-side access network node; 
         [0009]    selecting a target-side core network node, and transmitting the handover message to the target-side core network node, wherein the target-side core network node acquires context information of User Equipment (UE) from a source-side core network node; and 
         [0010]    receiving a handover acknowledgement message transmitted by the target-side core network node. 
         [0011]    In another aspect, a direct handover method is provided in the invention. The method includes: 
         [0012]    receiving a handover message transmitted by a target-side access network node, wherein the handover message carries identification information of a source-side core network node, and identification allocated for UE by the source-side core network node; 
         [0013]    acquiring an address of the source-side core network node based on the identification information of the source-side core network node, and transmitting a handover request message, wherein the handover request message carries the identification allocated by the source-side core network node for the UE, and the source-side core network node acquires context information of the UE based on the identification information allocated for the UE; and 
         [0014]    receiving a handover request response message transmitted by the source-side core network node. 
         [0015]    In another aspect, a direct handover method is provided in the invention. The method includes: 
         [0016]    transmitting a handover message to a target-side access network node; 
         [0017]    receiving a resource release message transmitted by the target-side access network node; and 
         [0018]    receiving a resource release request transmitted by a source-side core network node, and performing a resource release with the source-side core network node. 
         [0019]    In another aspect, a direct handover method is provided in the invention. The method includes: 
         [0020]    receiving a handover request message transmitted by a target-side core network node, wherein the handover request message includes identification information allocated for UE by a source-side core network node; 
         [0021]    acquiring context information of the UE based on the identification information; and 
         [0022]    transmitting a handover response message to the target-side core network node, wherein the handover response message includes the acquired context information of the UE. 
         [0023]    In another aspect, a direct handover device is provided in the invention. The device includes: 
         [0024]    a handover message reception unit, adapted to receive a handover message transmitted by a source-side access network node; 
         [0025]    a target-side core network node selection unit, adapted to select a target-side core network node after the handover message reception unit receives the handover message; 
         [0026]    a handover message transmitting unit, adapted to transmit the handover message to the target-side core network node selected by the target-side core network node selection unit, wherein the target-side core network node acquires context information of UE from a source-side core network node; and 
         [0027]    a handover acknowledgement message reception unit adapted to receive a handover acknowledgement message transmitted by the target-side core network node, after the handover message transmitting unit transmits the handover message. 
         [0028]    In another aspect, a direct handover device is provided in the invention. The device includes: 
         [0029]    a handover message reception unit, adapted to receive a handover message transmitted by a target-side access network node, wherein the handover message carries identification information of a source-side core network node and identification information allocated for UE by the source-side core network node; 
         [0030]    a source-side core network node address acquisition unit, adapted to acquire an address of the source-side core network node, based on the identification information of the source-side core network node received by the handover message reception unit; 
         [0031]    a handover request message transmitting unit, adapted to transmit a handover request message to the source-side core network node, an address of the source-side core network node being acquired by the source-side core network node address acquisition unit, wherein the source-side core network node acquires context information of the UE based on the identification information allocated for the UE and carried in the handover request message; and 
         [0032]    a handover response message reception unit, adapted to receive a handover response message transmitted by the source-side core network node, after the handover request message transmitting unit transmits the handover request message. 
         [0033]    In another aspect, a direct handover device is provided in the invention. The device includes: 
         [0034]    a handover message transmitting unit, adapted to transmit a handover message to a target-side access network node; 
         [0035]    a resource release message reception unit adapted to receive a resource release message transmitted by the target-side access network node, after the handover message transmitting unit transmits the handover message; 
         [0036]    a resource release request reception unit adapted to receive a resource release request initiated by a source-side core network node, after the resource release message reception unit receives the resource release message; and 
         [0037]    a resource release unit adapted to performing a resource release with the source-side core network node, based on the resource release request received by the resource release request reception unit. 
         [0038]    In another aspect, a direct handover device is provided in the invention. The device includes: 
         [0039]    a handover request message reception unit adapted to receive a handover request message transmitted by a target-side core network node, wherein the handover request message includes identification information allocated for UE by a source-side core network node; 
         [0040]    a context information acquisition unit, adapted to acquire context information of the UE based on the identification information allocated for the UE in the handover request message received by the handover request message reception unit; and 
         [0041]    a handover response message transmitting unit adapted to transmit a handover response message to the target-side core network node after the context information acquisition unit acquires the context information, wherein the handover response message includes the context information of the UE acquired by the context information acquisition unit. 
         [0042]    In the embodiments of the invention, the source-side access network node transmits the handover message to the target-side access network node, the target-side access network node selects the target-side core network node and transmits the handover message to the target-side core network node, and the target-side core network node requests for context information of the UE from the source-side core network node, thereby completing a handover. Thus, the handover may be implemented through less times of signalling interactions between nodes, which avoids network congestion caused by multiple times of signalling interactions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0043]    For illustrating technical solutions in embodiments of the invention more clearly, drawings to be used in describing the embodiments or conventional technologies are briefly described hereinafter. Apparently, the following described drawings are merely a part of the embodiments of the invention, and other drawings may be obtained by those skilled in the art based on those drawings without creative efforts. 
           [0044]      FIG. 1  is a flowchart of a direct handover method according to an embodiment of the invention; 
           [0045]      FIG. 2  is a flowchart of a direct handover method according to another embodiment of the invention; 
           [0046]      FIG. 3  is a flowchart of a direct handover method according to further another embodiment of the invention; 
           [0047]      FIG. 4  is a flowchart of a direct handover method according to further another embodiment of the invention; 
           [0048]      FIG. 5  is a flowchart of a direct handover method according to further another embodiment of the invention; 
           [0049]      FIG. 6  is a structural diagram of a direct handover device according to an embodiment of the invention; 
           [0050]      FIG. 7  is a structural diagram of a direct handover device according to another embodiment of the invention; 
           [0051]      FIG. 8  is a structural diagram of a direct handover device according to further another embodiment of the invention; 
           [0052]      FIG. 9  is a structural diagram of a direct handover device according to further another embodiment of the invention; 
           [0053]      FIG. 10  is a structural diagram of a direct handover apparatus according to an embodiment of the invention; 
           [0054]      FIG. 11  is a structural diagram of a direct handover apparatus according to another embodiment of the invention; 
           [0055]      FIG. 12  is a structural diagram of a direct handover apparatus according to further another embodiment of the invention; and 
           [0056]      FIG. 13  is a structural diagram of a direct handover apparatus according to further another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0057]    To make objectives, technical solutions and advantages of the invention clearer and more understandable, the invention is further clarified hereinafter in conjunction with drawings and embodiments. It should be understood that the embodiments described herein are merely to explain rather than to limit the invention. 
         [0058]    Explanations are made with the embodiments, to explain the technical solutions of the invention. 
         [0059]      FIG. 1  is a flowchart of a direct handover method according to an embodiment of the invention. The method includes the followings steps. 
         [0060]    In step S 101 , a source-side access network node transmits a handover message to a target-side access network node. The handover message carries identification information of a source-side core network node and identification information allocated for UE by the source-side core network node. 
         [0061]    In an embodiment of the invention, the source-side access network node transmits the handover message to the target-side access network node, and the handover message carries the identification information of the source-side core network node and the identification information allocated for UE by the source-side core network node. In different communication networks, identification information of the source-side core network node is different, and identification information allocated for UE by the source-side core network node is also different. Details will be described as follows. 
         [0062]    (1). In the case that the source-side access network node is an evolved node base station (eNB), the target-side access network node is an eNB, and the source-side core network node is an mobility management entity (MME), the identification information of the source-side core network node includes but is not limited to a globally unique MME identifier (GUMMEI), and the identification information allocated for the UE by the source-side core network node includes but is not limited to a Source MME UE SIAP ID. 
         [0063]    (2). In the case that the source-side access network node is a radio network controller (RNC), the target-side access network node is an RNC, and the source-side core network node is a serving GPRS support node (SGSN), the identification information of the source-side core network node includes but is not limited to a global core network identifier (Global CN-ID), or a combination of a routing area identifier (RAI) and an network resource identifier (NRI), and the identification information allocated for the UE by the source-side core network node includes but is not limited to an Old Iu Signalling Connection Identifier. 
         [0064]    (3) In the case that the source-side access network node is an RNC, the target-side access network node is an eNB, and the source-side core network node is an SGSN, the identification information of the source-side core network node includes but is not limited to a Global CN-ID, a combination of an RAI and an NRI, or a GUMMEI into which a combination of an RAI and an NRI is mapped; and the identification information allocated for the UE by the source-side core network node includes but is not limited to an Old Iu Signalling Connection Identifier. 
         [0065]    (4) In the case that the source-side access network node is an eNB, the target-side access network node is an RNC, and the source-side core network node is an MME, the identification information of the source-side core network node includes but is not limited to a GUMMEI, or a combination of an RAI and an NRI, where a GUMMEI is mapped into the combination; and the identification information allocated for the UE by the source-side core network node includes but is not limited to a Source MME UE SIAP ID. 
         [0066]    In step S 102 , the target-side access network node selects a target-side core network node and transmits the handover message to the target-side core network node. The handover message also includes the identification information of the source-side core network node and the identification information allocated for the UE by the source-side core network node as described above. The handover message includes but is not limited to a Path Switch Request (path switch request) message or an Enhanced Relocation Complete Request message. 
         [0067]    In an embodiment of the invention, the target-side access network node may select the target-side core network node based on a condition of load balance. That is, a target-side core network node with a lowest load is selected and accessed to implement the load balance. 
         [0068]    In step S 103 , the target-side core network node acquires an address of the source-side core network node based on the identification information of the source-side core network node, and transmits a handover request message to the source-side core network node. The handover request message includes the identification information allocated for the UE by the source-side core network node. 
         [0069]    In step S 104 , the source-side core network node transmits a handover response message to the target-side core network node. The handover response message includes an international mobile subscriber identifier (IMSI) of the UE, context information for mobility management, and context information for session management. 
         [0070]    In step S 105 , the target-side core network node sends a bearer update request or a bearer creating request to a user plane node. The user plane node may be a serving gateway (S-GW). 
         [0071]    In an embodiment of the invention, a connected user plane node S-GW may alters in a handover process of communication nodes. Hence, the bearer update request is transmitted if the user plane node S-GW does not alter; and the bearer creating request is transmitted if the user plane node S-GW alters. 
         [0072]    In step S 106 , the user plane node S-GW transmits to the target-side core network node a bearer update acknowledgement message or a bearer creating acknowledgement message. 
         [0073]    In step S 107 , the target-side core network node transmits a handover acknowledgement message to the source-side core network node. 
         [0074]    In step S 108 , the target-side core network node transmits the handover acknowledgement message to the target-side access network node. 
         [0075]    In step S 109 , the target-side access network node transmits a resource release message to the source-side access network node. 
         [0076]    In step S 110 , the source-side core network node initiates a resource release with the source-side access network node after receiving the handover acknowledgement message. 
         [0077]    It should be noted that, an inter-SGSN handover which occurs when the UE locates in a GERAN is similar to the above descriptions, where the RNC/eNB is replaced by a Base Station System (BSS), the identification information for the UE is a TLLI temporary logical link identity. Other steps are similar to the above descriptions, which will be omitted herein. 
         [0078]    In an embodiment of the invention, the source-side access network node transmits the handover message to the target-side access network node, the target-side access network node selects the target-side core network node and transmits the handover message to the target-side core network node, and the target-side core network node requests for context information of the UE from the source-side core network node, thereby completing a handover. Thus, the handover may be implemented through less times of signalling interactions between nodes, which avoids network congestion caused by multiple times of signalling interactions. 
         [0079]    It should be noted that in the embodiment of the invention, the access network node may be RNC, BSS and eNB, the core network node may be MME and SGSN, and the user plane node may be S-GW, P-GW and GGSN. 
         [0080]      FIG. 2  is a flowchart of a direct handover method according to another embodiment of the invention. The method includes the followings steps. 
         [0081]    In step S 201 , a handover message transmitted by a source-side access network node is received. 
         [0082]    In an embodiment of the invention, the source-side access network node transmits the handover message to a target-side access network node. The handover message carries identification information of a source-side core network node and identification information allocated for UE by the source-side core network node. In different communication networks, identification information of the source-side core network node is different, and identification information allocated for the UE by the source-side core network node is also different. Details will be described as follows. 
         [0083]    (1). In the case that the source-side access network node is an evolved node base station (eNB), the target-side access network node is an eNB, and the source-side core network node is a mobility management entity (MME), the identification information of the source-side core network node includes but is not limited to a globally unique MME identifier (GUMMEI), and the identification information allocated for the UE by the source-side core network node includes but is not limited to a Source MME UE SIAP ID. 
         [0084]    (2). In the case that the source-side access network node is a radio network controller (RNC), the target-side access network node is an RNC, and the source-side core network node is a serving GPRS support node (SGSN), the identification information of the source-side core network node includes but is not limited to a global core network identifier (Global CN-ID) or a combination of a routing area identifier (RAI) and a network resource identifier (NRI), and the identification information allocated for the UE by the source-side core network node includes but is not limited to an Old Iu Signalling Connection Identifier. 
         [0085]    (3) In the case that the source-side access network node is an RNC, the target-side access network node is an eNB, and the source-side core network node is an SGSN, the identification information of the source-side core network node includes but is not limited to a Global CN-ID, a combination of an RAI and an NRI, or a GUMMEI into which a combination of an RAI and an NRI is mapped; and the identification information allocated for the UE by the source-side core network node includes but is not limited to an Old Iu Signalling Connection Identifier. 
         [0086]    (4) In the case that the source-side access network node is an eNB, the target-side access network node is an RNC, and the source-side core network node is an MME, the identification information of the source-side core network node includes but is not limited to a GUMMEI, or a combination of an RAI and an NRI, where a GUMMEI is mapped into the combination; and the identification information allocated for the UE by the source-side core network node includes but is not limited to a Source MME UE SIAP ID. 
         [0087]    In step S 202 , a target-side core network node is selected and the handover message is transmitted to the target-side core network node. The handover message also includes the identification information of the source-side core network node and the identification information allocated for the UE by the source-side core network node as described above. Hence, the target-side core network node acquires context information of the UE from the source-side core network node. The context information includes an international mobile subscriber identifier (IMSI) of the UE, context information of mobility management, and context information of session management. 
         [0088]    In an embodiment of the invention, the target-side access network node may select the target-side core network node based on a condition of load balance. That is, a target-side core network node with a lowest load is selected and accessed to implement the load balance. 
         [0089]    In step S 203 , a handover acknowledgement message transmitted by the target-side core network node is received. 
         [0090]    In an embodiment of the invention, the target-side access network node confirms that a communication link is established between the target-side core network node and the target-side access network node, after receiving the handover acknowledgement message transmitted by the target-side core network node. The target-side access network node transmits a resource release message to the source-side access network node, to make the source-side access network node release resource which is no longer used. 
         [0091]    According to an optional embodiment of the invention, after the step S 203 , the method further includes the following step: 
         [0092]    transmitting a resource release message to the source-side access network node based on the handover acknowledgement message, where the source-side access network node releases a resource between the source-side access network node and the source-side core network node. 
         [0093]    In an embodiment of the invention, the source-side access network node transmits the handover message to the target-side access network node; and the target-side access network node selects the target-side core network node and transmits the handover message to the target-side core network node. The target-side core network node requests for the context information of the UE from the source-side core network node, thereby completing a handover. The handover may be implemented through less times of signalling interactions between nodes, which avoids network congestion caused by multiple times of signalling interactions. 
         [0094]      FIG. 3  is a flowchart of a direct handover method according to further another embodiment of the invention. The method includes the followings steps. 
         [0095]    In step S 301 , a handover message transmitted by a target-side access network node is received. The handover message carries identification information of a source-side core network node and identification information allocated for UE by the source-side core network node. 
         [0096]    In an embodiment of the invention, a target-side core network node receives the handover message transmitted by the target-side access network node. The target-side core network node may be selected by the target-side access network node based on a condition of load balance. A target-side core network node with a lowest load is selected and accessed to achieve the load balance. 
         [0097]    In step S 302 , an address of the source-side core network node is acquired based on the identification information of the source-side core network node, and a handover request message is transmitted to the source-side core network node. The handover request message includes the identification information allocated for the UE by the source-side core network node. 
         [0098]    In step S 303 , a handover response message transmitted by the source-side core network node is received. The handover response message includes an international mobile subscriber identifier (IMSI) of the UE, context information of mobility management, and context information of session management. 
         [0099]    In step S 304 , a bearer update request or a bearer creating request is transmitted to a user plane node, where the user plane node may be a serving gateway (S-GW). 
         [0100]    In an embodiment of the invention, a connected user plane node S-GW may alters in a handover process of communication nodes. Hence, the bearer update request is transmitted if the user plane node S-GW does not alter; and the bearer creating request is transmitted if the user plane node S-GW alters. 
         [0101]    In step S 305 , a bearer update acknowledgement message or bearer creating acknowledgement message transmitted by the user plane node S-GW is received, a handover acknowledgement message is transmitted to the source-side core network node, and the handover acknowledgement message is transmitted to the target-side access network node. 
         [0102]    In an embodiment of the invention, the target-side core network node informs source-side nodes that the handover is completed, after receiving the bearer update acknowledgement message or bearer creating acknowledgement message from the S-GW. Specifically, the target-side core network node transmits the handover acknowledgement message to the target-side access network node and the source-side core network node respectively, and the source-side core network node initiates a resource release to a source-side access network node. 
         [0103]    In an embodiment of the invention, the source-side access network node transmits the handover message to the target-side access network node, the target-side access network node selects the target-side core network node and transmits the handover message to the target-side core network node, and the target-side core network node requests for context information of the UE from the source-side core network node, thereby completing a handover. The handover may be implemented through less times of signalling interactions between nodes, which avoids network congestion caused by multiple times of signalling interactions. 
         [0104]      FIG. 4  is a flowchart of a direct handover method according to further another embodiment of the invention. The method includes the followings steps. 
         [0105]    In step S 401 , a handover message is transmitted to a target-side access network node. 
         [0106]    In an embodiment of the invention, a source-side access network node transmits to the target-side access network node a handover starting message, i.e., the handover message. The handover message carries identification information of a source-side core network node and identification information allocated for UE by the source-side core network node. In a subsequent step, a target-side core network node may acquire an address of the source-side core network node based on the identification information of the source-side core network node. The target-side core network node may acquire context information of the UE from the source-side core network node based on the identification information allocated for the UE by the source-side core network node. 
         [0107]    In step S 402 , a resource release message transmitted by the target-side access network node is received. 
         [0108]    In an embodiment of the invention, a target-side node (including the target-side core network node and the target-side access network node) may transmit the resource release message to a source-side node after a completion of the handover. Specifically, the source-side access network node receives the resource release message transmitted by the target-side access network node, and the source-side core network node receives the resource release message transmitted by the target-side core network node. 
         [0109]    In step S 403 , a resource release request transmitted by the source-side core network node is received, and a resource release is performed with the source-side core network node. 
         [0110]    In an embodiment of the invention, the source-side node starts releasing the resource after receiving the resource release message. Specifically, the source-side core network node initiates the resource release request to the source-side access network node, and the source-side access network node performs the resource release based on the request. 
         [0111]      FIG. 5  is a flowchart of a direct handover method according to further another embodiment of the invention. The method includes the followings steps. 
         [0112]    In step S 501 , a handover request message transmitted by a target-side core network node is received. The handover request message includes identification information allocated for UE by a source-side core network node. 
         [0113]    In an embodiment of the invention, the source-side core network node receives the handover request message transmitted by the target-side core network node, where the handover request message includes the identification information allocated for the UE by the source-side core network node. 
         [0114]    In step S 502 , context information of the UE is acquired based on the identification information. 
         [0115]    In an embodiment of the invention, the source-side core network node searches for the stored context information of the UE based on the identification information. The context information includes an international mobile subscriber identifier IMSI of the UE, context information of mobility management, and context information of session management. 
         [0116]    In step S 503 , a handover response message is transmitted to the target-side core network node. The handover response message includes the acquired context information of the UE. 
         [0117]    In an embodiment of the invention, the source-side core network node transmits the handover response message to the target-side core network node, in response to the handover request message in the step S 501 . The handover response message includes the acquired context information of the UE. The target-side core network node may build context information with the UE based on the context information of the UE. 
         [0118]    According to an optional embodiment of the invention, after the step S 503 , the method further includes the following steps: 
         [0119]    S 504 , receiving a handover acknowledgement message transmitted by the target-side core network node; and 
         [0120]    S 505 , initiating a resource release to a source-side access network node, based on the handover acknowledgement message. 
         [0121]      FIG. 6  is a structural diagram of a direct handover device according to an embodiment target-side core network node selection unit of the invention, and only parts related to the embodiment of the invention are shown for convenience of explanation. The device includes following units. 
         [0122]    A handover message reception unit  61  is adapted to receive a handover message transmitted by a source-side access network node. 
         [0123]    In an embodiment of the invention, the source-side access network node transmits the handover message to a target-side access network node, and the handover message carries identification information of a source-side core network node and identification information allocated for UE by the source-side core network node. In different communication networks, identification information of the source-side core network node is different, and identification information allocated for the UE by the source-side core network node is also different. Details will be described as follows. 
         [0124]    (1). In the case that the source-side access network node is an evolved node based station (eNB), the target-side access network node is an eNB, and the source-side core network node is a mobility management entity (MME), the identification information of the source-side core network node includes but is not limited to a globally unique MME identifier (GUMMEI), and the identification information allocated for the UE by the source-side core network node includes but is not limited to a Source MME UE SIAP ID. 
         [0125]    (2). In the case that the source-side access network node is a radio network controller (RNC), the target-side access network node is an RNC, and the source-side core network node is a serving GPRS support node (SGSN), the identification information of the source-side core network node includes but is not limited to a global core network identifier (Global CN-ID) or a combination of a routing area identifier (RAI) and a network resource identifier (NRI), and the identification information allocated for the UE by the source-side core network node includes but is not limited to an Old Iu Signalling Connection Identifier. 
         [0126]    (3) In the case that the source-side access network node is an RNC, the target-side access network node is an eNB, and the source-side core network node is an SGSN, the identification information of the source-side core network node includes but is not limited to a Global CN-ID, a combination of an RAI and an NRI, or a GUMMEI into which a combination of an RAI and an NRI is mapped, and the identification information allocated for the UE by the source-side core network node includes but is not limited to an Old Iu Signalling Connection Identifier. 
         [0127]    (4) In the case that the source-side access network node is an eNB, the target-side access network node is an RNC, and the source-side core network node is an MME, the identification information of the source-side core network node includes but is not limited to a GUMMEI, or a combination of an RAI and an NRI, where a GUMMEI is mapped into the combination; and the identification information allocated for the UE by the source-side core network node includes but is not limited to a Source MME UE SIAP ID. 
         [0128]    A target-side core network node selection unit  62  is adapted to select a target-side core network node after the handover message reception unit  61  receives the handover message. 
         [0129]    A handover message transmitting unit  63  is adapted to transmit a handover message to the target-side core network node selected by the target-side core network node selection unit  62 . The handover message also includes the identification information of the source-side core network node and the identification information allocated for the UE by the source-side core network node as described above. 
         [0130]    In an embodiment of the invention, the target-side access network node may select the target-side core network node based on a condition of load balance. That is, a target-side core network node with a lowest load is selected and accessed to achieve the load balance. 
         [0131]    A handover acknowledgement message reception unit  64  is adapted to receive a handover acknowledgement message transmitted by the target-side core network node, after the handover message transmitting unit  63  transmits the handover message. 
         [0132]    A resource release message transmitting unit  65  is adapted to transmit a resource release message to the source-side access network node based on the handover acknowledgement message received by the handover acknowledgement message reception unit  64 , after the handover acknowledgement message reception unit  64  receives the handover acknowledgement message. 
         [0133]    In an embodiment of the invention, the source-side access network node transmits the handover message to the target-side access network node, the target-side access network node selects the target-side core network node and transmits the handover message to the target-side core network node, and the target-side core network node requests for context information of the UE from the source-side core network node, thereby completing a handover. Thus, the handover may be implemented through less times of signalling interactions between nodes, which avoids network congestion caused by multiple times of signalling interactions. 
         [0134]      FIG. 7  is a structural diagram of a direct handover device according to another embodiment of the invention, and only parts related to the embodiment of the invention are shown for convenience of explanation. The device includes following units. 
         [0135]    A handover message reception unit  71  is adapted to receive a handover message transmitted by a target-side access network node. The handover message carries identification information of a source-side core network node and identification information allocated for UE by the source-side core network node. 
         [0136]    In an embodiment of the invention, a target-side core network node receives the handover message transmitted by the target-side access network node. The target-side core network node is selected by the target-side access network node based on a condition of load balance. A target-side core network node with a lowest load is selected and accessed to achieve the load balance. 
         [0137]    A source-side core network node address acquisition unit  72  is adapted to acquire an address of the source-side core network node, based on the identification information of the source-side core network node received by the handover message reception unit  71 . 
         [0138]    A handover request message transmitting unit  73  is adapted to transmit a handover request message to the source-side core network node, an address of the source-side core network node being acquired by the source-side core network node address acquisition unit  72 . The handover request message includes the identification information allocated for the UE by the source-side core network node and acquired by the handover message reception unit  71 . 
         [0139]    A handover response reception unit  74  is adapted to receive a handover response message transmitted by the source-side core network node, after the handover request message transmitting unit  73  transmits the handover request message. The handover response message includes an international mobile subscriber identifier (IMSI) of the UE, context information of mobility management, and context information of session management. 
         [0140]    A bearer request transmitting unit  75  is adapted to transmit a bearer update request or a bearer creating request to a user plane node after the handover response reception unit  74  receives the handover response message, where the user plane node may be a serving gateway (S-GW). 
         [0141]    In an embodiment of the invention, a connected user plane node S-GW may alters in a handover process of communication nodes. Hence, the bearer update request is transmitted if the user plane node S-GW does not alter; and the bearer creating request is transmitted if the user plane node S-GW alters. 
         [0142]    The bearer acknowledgement reception unit  76  is adapted to receive a bearer update acknowledgement message or a bearer creating acknowledgement message transmitted by the user plane node S-GW, after the bearer request transmitting unit  75  transmits a bearer update request or a bearer creating request. 
         [0143]    A handover acknowledgement message transmitting unit  77  is adapted to transmit a handover acknowledgement message to the source-side core network node after the handover response reception unit  74  receives the handover response message, where the source-side core network node initiates a resource release to a source-side access network node. 
         [0144]    In an embodiment of the invention, the source-side access network node transmits the handover message to the target-side access network node, the target-side access network node selects the target-side core network node and transmits the handover message to the target-side core network node, and the target-side core network node requests for context information of the UE from the source-side core network node, thereby completing a handover. Thus, the handover may be implemented through less times of signalling interactions between nodes, which avoids network congestion caused by multiple times of signalling interactions. 
         [0145]      FIG. 8  is a structural diagram of a direct handover device according to further another embodiment of the invention. The device includes following units. 
         [0146]    A handover message transmitting unit  81  is adapted to transmit a handover message to a target-side access network node. 
         [0147]    In an embodiment of the invention, the handover message transmitting unit  81  transmits to the target-side access network node a handover starting message, i.e., the handover message. The handover message carries identification information of a source-side core network node and identification information allocated for UE by the source-side core network node. In a subsequent step, a target-side core network node may acquire an address of the source-side core network node based on the identification information of the source-side core network node. The target-side core network node may acquire context information of the UE from the source-side core network node based on the identification information allocated for the UE by the source-side core network node. 
         [0148]    A resource release message reception unit  82  is adapted to receive a resource release message transmitted by the target-side access network node, after the handover message transmitting unit  81  transmits the handover message. 
         [0149]    In an embodiment of the invention, a target-side node (including the target-side core network node and the target-side access network node) may transmit the resource release message to a source-side node after a completion of a handover. Specifically, a source-side access network node receives the resource release message transmitted by the target-side access network node, and the source-side core network node receives the resource release message transmitted by the target-side core network node. 
         [0150]    A resource release request reception unit  83  is adapted to receive a resource release request initiated by the source-side core network node, after the resource release message reception unit  82  receives the resource release message. 
         [0151]    A resource release unit  84  is adapted to perform a resource release with the source-side core network node, based on the resource release request received by the resource release request reception unit  83 . 
         [0152]    In an embodiment of the invention, the source-side node starts releasing the resource after receiving the resource release message. Specifically, the source-side core network node transmits the resource release request to the source-side access network node, and the source-side access network node release the resource based on the request. 
         [0153]      FIG. 9  is a structural diagram of a direct handover device according to further another embodiment of the invention. The device includes following units. 
         [0154]    A handover request message reception unit  91  is adapted to receive a handover request message transmitted by a target-side core network node. The handover request message includes identification information allocated for UE by a source-side core network node. 
         [0155]    In an embodiment of the invention, the handover request message reception unit  91  receives the handover request message transmitted by the target-side core network node, where the handover request message includes the identification information allocated for the UE by the source-side core network node. 
         [0156]    A context information acquisition unit  92  is adapted to acquire context information of the UE, based on the identification information allocated for the UE and carried in the handover request message received by the handover request message reception unit  91   
         [0157]    In an embodiment of the invention, the source-side core network node searches for the stored context information of the UE based on the identification information. The context information includes an international mobile subscriber identifier IMSI of the UE, context information of mobility management, and context information of session management. 
         [0158]    A handover response message transmitting unit  93  is adapted to transmit a handover response message to the target-side core network node after the context information acquisition unit  92  acquires the context information. The handover response message includes the context information of the UE, which is acquired by the context information acquisition unit  92 . 
         [0159]    In an embodiment of the invention, the handover response message transmitting unit transmits the handover response message to the target-side core network node. The handover response message includes the acquired context information of the UE. The target-side core network node may build context information with the UE based on the context information of the UE. 
         [0160]    According to an optional embodiment of the invention, the device further includes: 
         [0161]    a handover acknowledgement message reception unit  94  is adapted receive a handover acknowledgement message transmitted by the target-side core network node, after the handover response message transmitting unit  93  transmits the handover response message; and 
         [0162]    a resource release initiation unit  95  is adapted to initiate a resource release to a source-side access network node, based on the handover acknowledgement message received by the handover acknowledgement message reception unit  94 . 
         [0163]      FIG. 10  is a structural diagram of a direct handover apparatus according to an embodiment of the invention. The apparatus includes an input unit  101 , a processor  102  and an output unit  103 . The processor  102  executes the following steps. 
         [0164]    A handover message transmitted by a source-side access network node is received. 
         [0165]    In an embodiment of the invention, the source-side access network node transmits the handover message to a target-side access network node, and the handover message carries identification information of a source-side core network node and identification information allocated for UE by the source-side core network node. In different communication networks, identification information of the source-side core network node is different, and identification information for the UE allocated by the source-side core network node is also different. Details will be described as follows. 
         [0166]    (1). In the case that the source-side access network node is an evolved node base station (eNB), the target-side access network node is an eNB, and the source-side core network node is a mobility management entity (MME), the identification information of the source-side core network node includes but is not limited to a globally unique MME identifier (GUMMEI), and the identification information allocated for the UE by the source-side core network node includes but is not limited to a Source MME UE S1AP ID. 
         [0167]    (2). In the case that the source-side access network node is a radio network controller (RNC), the target-side access network node is an RNC, and the source-side core network node is a serving GPRS support node (SGSN), the identification information of the source-side core network node includes but is not limited to a global core network identifier (Global CN-ID), or a combination of a routing area identifier (RAI) and a network resource identifier (NRI), and the identification information allocated for the UE by the source-side core network node includes but is not limited to an Old Iu Signalling Connection Identifier. 
         [0168]    (3) In the case that the source-side access network node is an RNC, the target-side access network node is an eNB, and the source-side core network node is an SGSN, the identification information of the source-side core network node includes but is not limited to a Global CN-ID, a combination of an RAI and an NRI, or a GUMMEI into which a combination of an RAI and an NRI is mapped; and the identification information allocated for the UE by the source-side core network node includes but is not limited to an Old Iu Signalling Connection Identifier. 
         [0169]    (4) In the case that the source-side access network node is an eNB, the target-side access network node is an RNC, and the source-side core network node is an MME, the identification information of the source-side core network node includes but is not limited to a GUMMEI, or a combination of an RAI and an NRI, where a GUMMEI is mapped into the combination; and the identification information allocated for the UE by the source-side core network node includes but is not limited to a Source MME UE S1AP ID. 
         [0170]    A target-side core network node is selected, and a handover message is transmitted to the target-side core network node. The handover message also includes the identification information of the source-side core network node and the identification information allocated for the UE by the source-side core network node as described above, to make the target-side core network node acquire context information of the UE from the source-side core network node. The context information includes an international mobile subscriber identifier (IMSI) of the UE, context information of mobility management, and context information of session management. 
         [0171]    In an embodiment of the invention, the target-side access network node may select the target-side core network node based on a condition of load balance. That is, a target-side core network node with a lowest load is selected and accessed to implement the load balance. 
         [0172]    A handover acknowledgement message transmitted by the target-side core network node is received. 
         [0173]    In an embodiment of the invention, the target-side access network node confirms that a communication link is established between the target-side core network node and the target-side access network node, after receiving the handover acknowledgement message transmitted by the target-side core network node. Then, the target-side access network node transmits a resource release message to the source-side access network node, to make the source-side access network node release resource which is no longer used. 
         [0174]    According to an optional embodiment of the invention, the processor  112  further executes the following step: 
         [0175]    transmitting a resource release message to the source-side access network node based on the handover acknowledgement message, where a resource between the source-side access network node and the source-side core network node is released. 
         [0176]    In an embodiment of the invention, the source-side access network node transmits the handover message to the target-side access network node, the target-side access network node selects the target-side core network node and transmits the handover message to the target-side core network node, and the target-side core network node requests for the context information of the UE from the source-side core network node, thereby completing a handover. Thus, the handover may be implemented through less times of signalling interactions between nodes, which avoids network congestion caused by multiple times of signalling interactions. 
         [0177]      FIG. 11  is a structural diagram of a direct handover apparatus according to an embodiment of the invention. The apparatus includes an input unit  111 , a processor  112  and an output unit  113 . The processor  112  executes the following steps. 
         [0178]    A handover message transmitted by a target-side access network node is received. The handover message carries identification information of a source-side core network node, and identification information allocated for UE by the source-side core network node. 
         [0179]    In an embodiment of the invention, a target-side core network node receives the handover message transmitted by the target-side access network node. The target-side core network node may be selected by the target-side access network node based on a condition of load balance. A target-side core network node with a lowest load is selected and accessed to achieve the load balance. 
         [0180]    An address of the source-side core network node is acquired based on the identification information of the source-side core network node, and a handover request message is transmitted to the source-side core network node. The handover request message includes the identification information allocated for the UE by the source-side core network node. 
         [0181]    A handover response message transmitted by the source-side core network node is received. The handover response message includes an international mobile subscriber identifier (IMSI) of the UE, context information of mobility management, and context information of session management. 
         [0182]    A bearer update request or a bearer creating request is transmitted to a user plane node, where the user plane node may be a serving gateway (S-GW). 
         [0183]    In an embodiment of the invention, a connected user plane node S-GW may alters in a handover process of communication nodes. Hence, the bearer update request is transmitted if the user plane node S-GW does not alter; and the bearer creating request is transmitted if the user plane node S-GW alters. 
         [0184]    A bearer update acknowledgement message or bearer creating acknowledgement message transmitted by the user plane node S-GW is received, a handover acknowledgement message is transmitted to the source-side core network node, and a handover acknowledgement message is transmitted to the target-side access network node. 
         [0185]    In an embodiment of the invention, the target-side core network node informs source-side nodes that the handover is completed, after receiving the bearer update acknowledgement message or bearer creating acknowledgement message from the S-GW. Specifically, the target-side core network node transmits the handover acknowledgement message to the target-side access network node and the source-side core network node respectively, and the source-side core network node initiates a resource release to a source-side access network node. 
         [0186]    In an embodiment of the invention, the source-side access network node transmits the handover message to the target-side access network node, the target-side access network node selects the target-side core network node and transmits the handover message to the target-side core network node, and the target-side core network node requests for context information of the UE from the source-side core network node, thereby completing a handover. Thus, the handover may be implemented through less times of signalling interactions between nodes, which avoids network congestion caused by multiple times of signalling interactions. 
         [0187]      FIG. 12  is a structural diagram of a direct handover apparatus according to another embodiment of the invention. The apparatus includes an input unit  121 , a processor and an output unit  123 . The processor  122  executes the following steps. 
         [0188]    A handover message is transmitted to a target-side access network node. 
         [0189]    In an embodiment of the invention, a source-side access network node transmits to the target-side access network node a handover starting message, i.e., the handover message. The handover message carries identification information of a source-side core network node and identification information allocated for UE by the source-side core network node. In a subsequent step, a target-side core network node may acquire an address of the source-side core network node based on the identification information of the source-side core network node. The target-side core network node may acquire context information of the UE from the source-side core network node based on the identification information allocated for the UE by the source-side core network node. 
         [0190]    A resource release message transmitted by the target-side access network node is received. 
         [0191]    In an embodiment of the invention, a target-side node (including the target-side core network node and the target-side access network node) may transmit the resource release message to a source-side node after a completion of the handover. Specifically, the source-side access network node receives the resource release message transmitted by the target-side access network node, and the source-side core network node receives the resource release message transmitted by the target-side core network node. 
         [0192]    A resource release request transmitted by the source-side core network node is received, and a resource release is performed with the source-side core network node. 
         [0193]    In an embodiment of the invention, the source-side node starts releasing the resource after receiving the resource release message. Specifically, the source-side core network node initiates the resource release request to the source-side access network node, and the source-side access network node performs the resource release based on the request. 
         [0194]      FIG. 13  is a structural diagram of a direct handover apparatus according to further another embodiment of the invention. The apparatus includes an input unit  131 , a processor and an output unit  133 . The processor  132  executes the following steps. 
         [0195]    A handover request message transmitted by a target-side core network node is received. The handover request message includes identification information allocated for UE by a source-side core network node. 
         [0196]    In an embodiment of the invention, the source-side core network node receives the handover request message transmitted by the target-side core network node, where the handover request message includes the identification information allocated for the UE by the source-side core network node. 
         [0197]    Context information of the UE is acquired based on the identification information. 
         [0198]    In an embodiment of the invention, the source-side core network node searches for the stored context information of the UE based on the identification information. The context information includes an international mobile subscriber identifier IMSI of the UE, context information of mobility management, and context information of session management. 
         [0199]    A handover response message is transmitted to the target-side core network node. The handover response message includes the acquired context information of the UE. 
         [0200]    In an embodiment of the invention, the source-side core network node transmits the handover response message to the target-side core network node in response to the handover request message in the foregoing step. The handover response message includes the acquired context information of the UE. The target-side core network node may build context information with the UE based on the context information of the UE. 
         [0201]    According to an optional embodiment of the invention, the processor  132  further executes the following step: 
         [0202]    receiving a handover acknowledgement message transmitted by the target-side core network node; and 
         [0203]    initiating a resource release to a source-side access network node based on the handover acknowledgement message. 
         [0204]    Those skilled in the art may understand that the respective units in the embodiments are merely divided according to functional logic, but it is not limited to the above division as long as corresponding functions can be achieved. In addition, specific names of the respective functional units are merely intended to conveniently distinguish the functional units from each other, rather than to limit the protection scope of the invention. 
         [0205]    It is also understandable for those skilled in the art that all of or a part of the steps of the methods according to the embodiments may be performed by related hardware instructed by a program. The program may be stored in a computer readable storage medium. The storage medium includes an ROM/RAM, a magnetic disk, an optical disk, etc. 
         [0206]    Those disclosed are merely preferred embodiments of the invention, which are not intended to limit the invention. Any modification, equivalent replacements and improvements made within the spirit and principle of the invention should all fall within the protection scope of the invention.