JP2011182032A - Handoff method between femtocell and system thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a handoff method, capable of continuously managing a user terminal in the same call control network, even after a handoff in a network environment where a femtocell selects any of among a plurality of call control networks. <P>SOLUTION: A call-control network selecting unit 11 selects any of among an access network NWa and a core network NWc, in response to a connection request from the user terminal. A selection result notifying unit 12 adds a result of selection as call-control network information to the received connection request. A call control executing section 13 transfers the connection request added with the call-control network information to a user terminal of a communication party via the selected network. A call-control network identifying unit 14 identifies a call-control network before a handoff, on the basis of the call-control network information added to a received reconnection request. The call-control executing section 13 transfers the reconnection request to the user terminal of the communication party via the identified call connection network. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a handoff method and system between femtocells in which a femtocell selects one of a plurality of call control networks including an access network that accommodates the femtocell.

  In a mobile network using a small base station such as a femtocell, there are a plurality of call control networks including an IMS (IP Multimedia Subsystem) existing in the core network and an access network accommodating the femtocell. In the standard connection form of the femtocell, SIP (Session Initiation Protocol) based IMS is used for searching for a partner terminal in data communication (for example, VoIP) between user terminals. Since IMS is arranged in the core network, all call control messages must pass through the core network, and there is a concern that the load on the core network will increase.

  To solve this, an overlay is constructed between femtocells using P2P-based SIP (P2P-SIP), and when it is estimated that the search for the partner terminal will be completed within a certain time, the overlay is used. Non-Patent Document 1 discloses a technology that uses IMS when the number exceeds the limit. A handoff procedure in such a mobile network is disclosed in Non-Patent Document 2.

Sugano et al., "Core-overlay-linked session control method to realize minimum core", IEICE General Conference 2009, B-6-101, 2009. Tsunehiko Chiba and Hidetoshi Yokota, "Proposal and Evaluation of Handoff Method Using Proxy Type MOBIKE", Information Processing Society of Japan Research Report, Vol.2008 No.107, October 2008.

  In a mobile network using small base stations such as femtocells, in a network environment where there are multiple call control networks such as an overlay network for call control constructed by IMS and multiple femtocells that exist in the core network, femtocells If a handoff occurs between the two, the IP address needs to be updated by SIP re-INVITE after the handoff according to the change of the connection destination femtocell, and it is necessary to continue management in the same call control network after the handoff.

  However, in an environment where the femtocell selects a plurality of call control networks, the call control network may change before and after handoff.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems of the prior art, and in a network environment in which a femtocell selects one of a plurality of call control networks, a handoff method capable of continuing management with the same call control network after handoff and To provide a system.

  In order to achieve the above object, the present invention relates to each femtocell and user terminal in a handoff system between femtocells in which the femtocell selects any of a plurality of call control networks including an access network accommodating the femtocell. Is characterized by the following measures.

  (1) Each femtocell adds means for selecting either the access network or another call control network in response to a connection request received from a user terminal, and identification information of the selected network in the connection request Then, the call control network before handoff is identified based on the means for transferring to the user terminal of the communication partner via the selected call control network and the network identification information described in the reconnection request received from the user terminal. And means for transferring a connection request to the user terminal of the communication partner via the identified call control network.

  (2) Each user terminal stores means for storing the network identification information described in the received connection request, and means for transmitting a reconnection request in which the network identification information is described to the destination femtocell during handoff It was equipped with.

  According to the present invention, in a handoff system between femtocells in which a femtocell selects one of a plurality of call control networks including an access network that accommodates the femtocell, call control is performed by the same call control network before and after the handoff. It will be possible to continue management.

It is the block diagram which showed the structure of the mobile network to which this invention is applied. It is a functional block diagram of the femtocell to which the present invention is applied. It is the sequence flow which showed the procedure which registers a core network (IMS) as a call control network. It is the sequence flow which showed the procedure which registers an overlay network (access network) as a call control network. It is the sequence flow which showed the procedure of handoff.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a mobile network to which the present invention is applied.

  The access network NWa is composed of a plurality of femtocells, and the femtocells and overlay emulators construct an overlay network based on Chord-based P2P-SIP. Hereinafter, the access network NWa may be expressed as an overlay network NWa.

  The core network NWc accommodates a security gateway (SeGW) 22 and an IMS 23, and each femtocell # 1, # 2... Of the overlay network NWa is secured to the SeGW 22 of the core network NWc with a secure IPSec tunnel 21 based on IKEv2. And securely communicate with the IMS 23.

  Each user terminal UA is an IMS client, transmits and receives application data such as voice data and video data of VoIP (Voice over IP) based on SIP, performs authentication processing in the PPP procedure, Get DNS address. Further, in order to directly transmit and receive application data between femtocells, the SIP INVITE and the 200 OK SDP field are converted into a format communicable within the access network NWa.

  FIG. 2 is a functional block diagram showing the configuration of the main part of each of the femtocells # 1, # 2,..., Where the configuration unnecessary for the description of the present invention is omitted.

  The call control network selection unit 11 selects either the access network NWa or another call control network (in FIG. 1, the core network NWc) in response to the SIP INVITE received from the user terminal UA # 1. As will be described later in detail, the selection result notifying unit 12 adds the selection result as call control network information to the SIP extension header of the received SIP INVITE. The call control execution unit 13 transfers the SIP INVITE in which the call control network information is added to the user terminal UA # 2 as a communication partner via the selected network.

  At this time, the communication partner user terminal UA # 2 extracts and stores the call control network information from the SIP INVITE, and adds the call control network information to 200 OK and returns it to the user terminal UA # 1. The user terminal UA # 1 extracts the call control network information from the 200 OK and stores it similarly. Thereby, both user terminals UA # 1 and UA # 2 communicating with each other can recognize the call control network.

  After the communication path via the selected call control network is established between the user terminals UA # 1 and UA # 2 as described above, one user terminal UA moves to another femtocell area. When a reconnection request (SIP re-INVITE) is transmitted, the stored call control network information is added to the SIP extension header.

  The call control network identification unit 14 of each femtocell # 1, # 2... Identifies the call control network before handoff based on the call control network information added to the received SIP re-INVITE. The call control execution unit 13 transfers the SIP re-INVITE to the user terminal of the communication partner via the identified call control network.

  Next, the operation of the present embodiment will be described in detail along the sequence flow of FIGS. Here, the description starts from a state in which user terminal UA # 1 is located in the area of femtocell # 1 and user terminal UA # 2 is located in the area of femtocell # 3.

  When user terminal UA # 1 is activated at time t1 in FIG. 3 and a lower link is established between user terminal UA # 1 and femtocell # 1 at time t2, at time t3, SeGW 22 and femto in core network NWc are established. An IPSec tunnel 21 is established with the cell # 1. The femtocell # 1 acquires the global IP address (IP # A) assigned to the user terminal UA # 1 from the SeGW 22 via the IPSec tunnel and notifies the user terminal UA # 1.

  At time t4, a SIP REGISTER (location registration request) is transmitted from the user terminal UA # 1 to the femtocell # 1. The SIP REGISTER describes the SIP URI and contact address (IP # A) of the user terminal UA # 1. The femtocell # 1 transfers the received SIP REGISTER to the IMS 23 via the IPSec tunnel 21 and the SeGW 22 at time t5, and also transfers it to the overlay network NWa configured by P2PSIP at time t6 to RELOAD (REsource LOcation And Discovery) registration.

  When user terminal UA # 2 is activated at time t7, at time t8, a lower ring is established between user terminal UA # 2 and femtocell # 3 in the same manner as described above, and femtocell ## 2 and SeGW22 Is established, the global IP address (IP # B) of the user terminal UA # 2 is acquired, and the location registration of the user terminal UA # 2 is performed by both the IMS 23 of the core network NWc and the overlay network NWa. To be done.

  Thereafter, when a call origination operation is performed from the user terminal UA # 1 to the user terminal UA # 2 at time t9, a SIP INVITE (connection request) is transmitted from the user terminal UA # 1 to the femtocell # 1 at time t10. . In this SIP INVITE, the user terminal UA # 2 is described as a destination, and in the SDP field, the global IP address (IP # A) of the user terminal UA # 1 is described as an IP address to be used for media transmission.

  Femtocell # 1 that has received the SIP INVITE determines whether or not the SIP INVITE is an initial INVITE at time t11. In this embodiment, only the INVITE (re-INVITE) retransmitted after handoff describes information (hereinafter referred to as call control network information) that specifies the call control network before handoff, and other initial INVITEs. Does not describe call control network information. Therefore, here, based on whether or not the call control network information is described in the SIP INVITE, it is determined whether or not the SIP INVITE is the initial INVITE. Since it is initially determined as the initial INVITE, at time t12, either the overlay network NWa or the core network NWc (IMS23) is selected as the call control network.

  In the present embodiment, the delay time and / or the number of connection sessions when searching for the partner terminal (UA # 2) in the overlay network NWa, and the delay time and / or the number of connection sessions when searching in the IMS 23 of the core network NWc Are compared, and a network having a shorter delay time (a network having a smaller number of connection sessions) is selected as the call control network.

  For an application transmitted / received after call establishment, if an encryption key is described in the SIP INVITE, the overlay network Nwa or the core network NWc (IMS23) is selected based on the search time, and the encryption key is described. If not, the core network NWc (IMS23) is selected. Here, the description will be continued assuming that the IMS 23 of the core network NWc is selected as the call control network and the overlay network NWa is selected as the application data transfer network.

  When IMS 23 is selected as the call control network, at time t13, the SIP INVITE is transmitted from femtocell # 1 through the IPSec tunnel 21 and SeGW 22 to IMS 23, and further relayed through femtocell # 3 to user terminal UA. Received by # 2. In this SIP INVITE, “IMS” is added to the SIP extension header as the call control network information, and application data transmitted / received after the establishment of a call is transmitted / received directly between femtocells without being transferred to the SeGW 22. Therefore, the IP address in the SDP field is rewritten from the global IP address (IP # A) of the user terminal UA # 1 to the IP address (IP # 1) of the femtocell # 1.

  The user UA # 2 that has received the SIP INVITE saves the call control network information (here, IMS) described in the SIP INVITE at time t14, and at time t15, the call control network information is set to 200 OK. (IMS) is described, and further, the global IP address (IP # B) of user UA # 2 is described in the SDP field and transmitted to femtocell # 3.

  The femtocell # 3 rewrites the IP address described in the received 200 OK SDP field from the IP # B to the IP address (IP # 3) of the femtocell # 3 and transfers it to the IMS 23. The 200OK is transferred from the IMS 23 to the user terminal UA # 1 through the femtocell # 1. When the user terminal UA # 1 receives the 200 OK, the user terminal UA # 1 stores the call control network information (here, IMS) at the time t16 similarly to the user terminal UA # 2.

  Through the above procedure, transmission / reception of application data relayed through the femtocell # 1, the overlay network NWa, and the femtocell # 3 is started between the user terminals UA # 1 and UA # 2. At this time, the IP # A and IP # 3 are used as destination IP addresses between the user terminal UA # 1 and the femtocell # 1, and IP # 1 and IP # 3 are used between the femtocells # 1 and # 3. IP # 1 and IP # B are used between the femtocell # 3 and the user terminal UA # 2.

  In contrast, when overlay network NWa is selected as the call control network at time t12, SIP INVITE is transferred from femtocell # 1 to overlay network NWa at time t17 in FIG. Relay and forward to user terminal UA # 2. In this SIP INVITE, the user terminal UA # 2 is described as the destination, the IP address (IP # 1) of the femtocell # 1 is described as the session start terminal in the SDP field, and the call control network is described in the SIP extension header “Overlay” is described as information. Receiving this SIP INVITE, user terminal UA # 2 stores the call control network information (here, “overlay”) at time t18.

  At time t19, 200 OK is transmitted from the user terminal UA # 2 to the femtocell # 3. In this 200 OK, the global IP address (IP # B) of the user terminal UA # 2 is described as the session start terminal in the SDP field, and “overlay” is described as the call control network information in the SIP extension header. At time t20, the femtocell # 3 that has received the 200 OK rewrites the SDP field to the IP address (IP # 3) of the femtocell # 3 and forwards it to the overlay network NWa, and relays the femtocell # 1. Received by the user terminal UA # 1. Receiving the 200 OK, the user terminal UA # 1 stores the call control network information (here, “overlay”) at time t21.

  Proceeding to FIG. 5, after “IMS” is stored as call control network information in the user terminal UA # 2 at the time t16, the user terminal UA # 1 moves at time t23 and receives radio field intensity from the femtocell # 1. If the received radio wave intensity from femtocell # 2 becomes stronger than that, handoff is executed, and at time t24, lower link establishment and IPSec tunnel 21 are established between user terminal UA # 1 and femtocell # 2 in the same manner as described above. Establishment and acquisition of a global IP address, and location registration to both the IMS 23 and the overlay network NWa are performed.

  At time t25, the SIP re-INVITE is transmitted from the user terminal UA # 1 to the femtocell # 2. In this SIP re-INVITE, the user terminal UA # 2 is described as the destination, “IMS” is described as the call control network information, and the global IP address (IP # A) of the user terminal UA # 1 is described in the SDP field. is described.

  At time t26, the SIP re-INVITE is referred to in the femtocell # 2, and here, “IMS” is described as the call control network information. Therefore, it is determined as a handoff of the session in which the call control network is IMS23. . At time t27, the SIP re-INVITE is forwarded from the femtocell # 2 to the IMS 23 via the IPSec tunnel 21 and SeGW 22, and further forwarded to the user terminal UA # 2 via the femtocell # 3. At time t28, the IP address of the connection destination in the user terminal UA # 2 is changed from the IP address (IP # 1) of the femtocell # 1 to the IP address (IP # 2) of the femtocell # 2.

  At time t29, 200 OK is transmitted from the user terminal UA # 2 to the femtocell # 3. In this 200 OK, “IMS” is described as call control network information, and the global IP address (IP # B) of the user terminal UA # 2 is described in the SDP field. Femtocell # 3 rewrites and relays the IP address described in the received 200 OK SDP field to IP address # 3 of femtocell # 3. This 200 OK is received by the user terminal UA # 1 through the IMS 23 and the femtocell # 2.

  Through the above procedure, application data relayed through the femtocell # 2, the overlay network NWa, and the femtocell # 3 is performed between the user terminals UA # 1 and UA # 2. At this time, the IP # A and IP # 3 are used as destination IP addresses between the user terminal UA # 1 and the femtocell # 2, and IP # 2 and IP # 3 are used between the femtocells # 1 and # 3. IP # 2 and IP # B are used between the femtocell # 3 and the user terminal UA # 2.

  DESCRIPTION OF SYMBOLS 11 ... Call control network selection part, 12 ... Selection result notification part, 13 ... Call control execution part, 14 ... Call control network identification part, 21 ... IPSec tunnel, 22 ... Security gateway (SeGW), 23 ... IMS

Claims (4)

In a handoff system between femtocells in which a femtocell selects one of a plurality of call control networks including an access network that accommodates the femtocell,
The femtocell is
Means for selecting either the access network or another call control network in response to a connection request received from a user terminal;
Means for adding identification information of the selected network to the connection request and transferring it to the user terminal of the communication partner via the selected call control network;
Each of the user terminals is
Means for storing the network identification information described in the received connection request;
Means for transmitting a reconnection request in which the network identification information is described to the destination femtocell at the time of handoff,
The femtocell further
Means for identifying a call control network before handoff based on network identification information described in a reconnection request received from a user terminal;
Means for transferring the connection request to the user terminal of the communication partner via the identified call control network.   The inter-femtocell handoff system according to claim 1, wherein the access network is an overlay network constructed by a plurality of femtocells. One of the other call control networks is a core network including IMS,
Each femtocell and the core network are connected by a secure communication tunnel,
The inter-femtocell handoff system according to claim 1 or 2, wherein call control of the core network is executed by the IMS. In a handoff method between femtocells in which a femtocell selects one of a plurality of call control networks including an access network that accommodates the femtocell,
The femtocell is
Selecting either the access network or another call control network in response to a connection request received from a user terminal;
Adding the identification information of the selected network to the connection request and transferring to the user terminal of the communication partner via the selected call control network,
Each of the user terminals is
A procedure for storing the network identification information described in the received connection request;
Performing a procedure of transmitting a reconnection request in which the network identification information is described to a destination femtocell at the time of handoff;
The femtocell further
A procedure for identifying a call control network before handoff based on network identification information described in a reconnection request received from a user terminal;
And a procedure for transferring the connection request to the user terminal of the communication partner via the identified call control network.

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