JP2007281721A - Mobile communication control method, and mobile communication system and router - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To transfer a packet whose hand-over destination router is addressed to a mobile node to the mobile node in the system wherein a layer 3 address of the mobile node is unchanged when the mobile node hands over between routers in a domain. <P>SOLUTION: When an AR_2 of a handover destination receives a tunnel establishment solicitation message including an L2 address and an IP address of the MN (mobile node), the AR_2 generates a proxy neighbor cache to which the L2 address and the IP address of the MN correspond, establishes a tunnel between aggregation ARs AggAR, buffers the packet addressed to the MN and received from the AggAR, and transmits the packet addressed to the MN having been buffered when the MN hands over to itself to the MN on the basis of the proxy neighbor cache. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a mobile communication control method, a mobile communication system, and a router.

  Currently, improvement and development of a “mobile access network” that enables Internet access on mobile terminals is being made. In particular, it is desired to realize a mobile network that can communicate with IP and can move without interruption.

  In Patent Document 1 below, in the environment where a mobile terminal (hereinafter referred to as MN) uses mobile IP as shown in FIG. Whether a message (Router Solicitation: RS) is transmitted to the handover destination access router (new Access Router: nAR) and a router advertisement message (Router Advertisement: RA) is requested and received in (2). Alternatively, attention is paid to a mobile node (MN) that is premised on receiving RA periodically transmitted by a router. The MN generates a care-of-address (hereinafter referred to as CoA) after receiving the RA in (3), and updates the binding to notify the home agent (hereinafter referred to as HA) of the CoA. A message (Binding Update: hereinafter referred to as BU) is transmitted to the nAR. At this time, since there is no Neighbor Cache in the nAR, Neighbor Discovery is performed when a Binding Acknowledgment (BA) is transferred to the MN. Therefore, it is necessary to perform MN L2 address resolution. During this time, in the nAR, the packet addressed to the MN is buffered without being transmitted and is in a state of waiting for transmission. Therefore, when a packet reception time delay of the MN or a packet exceeding the AR buffer area is transferred, a packet loss may occur, and resumption of communication after handover is prevented.

  In order to solve this problem, Patent Document 1 proposes that the MN that transmitted the BU in (3) simultaneously transmits an echo request message (ICMP echo request) to the nAR in (4). . The processing sequence during this period is shown in FIG. The nAR that has received an Internet Control Message Protocol (ICMP) echo request in (4) needs to resolve the L2 address in order to send an echo reply message (ICMP echo reply) to the MN in (7). For this reason, the nAR transmits a neighbor solicitation message (hereinafter referred to as NS) to the MN in (5), and receives a neighbor advertisement message (hereinafter referred to as NA) from the MN in (6). Generates a neighbor cache, and transmits an ICMP echo request to the MN in (7). As a result, since the MN's Neighbor Cache is created in the nAR, when the nAR receives the BA addressed to the MN in (8) and the data packet in (9), (10), and (11), the neighbor discovery (Neighbor Discovery) is performed. Packet transfer can be performed without performing L2 address resolution.

Non-Patent Document 1 below discloses mobility control using an IP tunnel. The technique described in Non-Patent Document 1 is called Proxy Mobile IP (hereinafter, Proxy MIP). As shown in FIG. 4, Proxy MIP uses an IP tunnel between a service node (hereinafter referred to as “SN”) and a base station (hereinafter referred to as “BS”) from a destination (correspondent node: hereinafter referred to as “CN”). The packet transfer route to the MN is determined. In FIG. 4, the address of the IP header added to the packet is as follows. However, IP is version 6 IP.
* MNHA (Mobile Node Home Address): MN's HoA.
* CNA (Correspondent Node Address): IP address of CN.
* CoA (Care of Address): IP address assigned to the interface used when the MN performs communication. The SN of CoA prefix is assigned. Similar to the movement in Mobile IP, CoA notifies the correspondence with HoA by doing BU (Binding Update) to HA.
* HAA (Home Agent Address): IP address of the MN's HA.
* AR @: IP address assigned to the BS to which the MN is linked. In order to make it possible to specify the BS, it is generated from the prefix (64 bits) assigned to the BS one-to-one and the MN interface ID (64 bits). When the BS notifies this address to the SN, the SN can grasp the position of the MN.

  In the packet transfer using Proxy MIP, a process until a packet transmitted from CN to MN (HoA is MNHA) in FIG. 4 is transferred to MN will be described. A packet sent to the MNHA (1 in FIG. 4) is transferred after being IP-encapsulated with HA as the transmission source and HAA as the transmission destination (2. in FIG. 4). This process is a process in Mobile IP. The packet addressed to the CoA is transferred to the SN, and tunneling for packet transfer in the access network is performed by the SN. This tunneling is performed by changing the packet transmission destination (CoA) to AR @ which is the address of the BS to which the MN is linked (3 in FIG. 4). By recording the correspondence between CoA and AR @ in the BS, the BS can identify the CoA that is the original transmission destination from the transmission destination (AR @). The packet whose transmission destination (AR @) is returned to CoA by the BS is transferred to the MN through the wireless link (4 in FIG. 4).

  When the MN is linked, the BS generates an AR @ using the prefix having a one-to-one relationship with the BS and the MN's CoA interface ID, and notifies the SN of the correspondence between the CoA and the AR @. By generating such an address, the SN can specify the BS to which the MN is linked from the AR @ prefix. Also, the BS can identify the CoA that is the original transfer destination from the interface ID of AR @ that is the transmission destination address of the unspecified packet that has been transferred.

  In this way, for the purpose of the BS reporting the location of the MN to the SN, BU (Binding Update) in Mobile IP is used for a message notifying the correspondence between CoA and AR @. This technique is called Proxy MIP because the BS sends a location registration BU instead of the MN. In this Proxy MIP, since IP tunneling is used between the BS and the SN, CoA does not change as long as handover is performed within the access network. Therefore, it is suitable for the control of micromobility which has been actively studied recently. The purpose of micromobility is not to implement mobility control in the global network like Mobile IP, but to limit mobility and implement mobility control with low control load such as processing load and message transmission / reception.

  Also, in response to the increasing demand for micromobility, there is a trend of studying a mobility control method using tunneling as described in Non-Patent Document 1 and implementing standardization. At present (October 5, 2005), this standardization is being attempted by a group called netlmm of IETF as shown in Non-Patent Document 2 below. Since the study has just begun, requirements for the system architecture have only been presented. In the requirement shown in Non-Patent Document 2, a network configuration as shown in FIG. 5 is considered. A network having this configuration is called an LMM (Localized Mobility Management) network or domain.

  In the network (LMM domain 100) between the aggregation AR (Aggregation AR: hereinafter referred to as AggAR) connected to the CN external network and the AR_1, AR_2, AR_3 connected to the MN, the IP as described in Non-Patent Document 1 A tunneling technique is used to generate a data packet transfer path. The MN generates a CoA using Mobile IP, and notifies the HA of the correspondence between the CoA and the HoA (Home Address) by a BU message. However, the MN does not cause a change in CoA when performing handover between AR_1, AR_2, and AR_3 managed by AggAR. For this reason, the location registration process by performing BU from the MN to the HA is performed only when the handover between the LMM domains 100 is performed.

An area for performing mobility control that does not cause an address change is referred to as an LMM domain. In the following description, “handover” refers to “handover between ARs in an LMM domain” and “handover between LMM domains”. Is described as “handover between ARs across LMM domains”. The LMM network has just begun and there is no clear specification yet. Therefore, there is no specification for a method for generating and controlling an IP tunnel in the LMM domain. Therefore, in the current examination, various methods such as a method using IP-in-IP tunneling have been proposed in addition to Proxy Mobile IP. However, it is common that the AR becomes the first hop router for the MN regardless of which protocol is formulated.
Japanese Patent Laying-Open No. 2005-27047 (Abstract, FIG. 4) Local mobility for 3GPP System Architecture Evolution (Submitted by Nokia) http://www.3gpp.org/ftp/Joint_Meetings/S2R3_0605_Montreal/Docs/SRJ-050061.zip netlmm: draft-kempf-netlmm-nohost-ps-00.txt, draft-kempf-netlmm-nohost-req-00.txt (These are Internet draft texts submitted to the IETF.)

  FIG. 6 is an explanatory diagram showing a system and a communication sequence for explaining the problem to be solved by the present invention. As shown in FIG. 6, normally, the MN that has performed a handover knows AR_1, AR_2, The RSs that request transmission of RA_1, RA_2, and RA_3 are transmitted to AR_3, respectively. On the other hand, the MN that has performed handover in the LMM domain 100 also transmits an RS by processing in the IP stack or MIP stack inside the MN. At this time, information on the link local address of the AR is obtained from the RA, and a default router is set in the MN. At the time of a handover in the LMM domain 100, a system that guarantees that the IP address of the MN does not change is required. Therefore, the MN is studying the realization of a function that does not regenerate the CoA using the RA prefix even when the RA is received. As one method, there is a method in which all prefixes given to RAs advertised by each AR are the same.

  However, even if such a method is adopted, since the AR becomes the first hop router for the MN, the MN default router needs to be the handover destination AR. For this reason, the MN after the handover cannot transmit the data packet until the default router change process is completed. Moreover, even if seamless handover is realized by setting the prefix advertised by the AR as a single prefix in the LMM domain and avoiding the MN's IP address change, the AR has the MN's NC (Neighbor Cache). Without it, the transfer of the packet addressed to the MN to the MN cannot be started.

  Therefore, it is effective to generate the NC before the data packet addressed to the MN arrives at the AR by adopting the method as in Patent Document 1. However, in Patent Document 1, it is necessary for the MN to send an ICMP echo request to the AR at every handover, and the MN needs to perform a special process for standard IP. Therefore, this method is a method that hinders general-purpose operation, and is contrary to the requirement of NETLMM to avoid special changes to the terminal. Further, in the method of Patent Document 1, since each MN performs handover, an ICMP echo request and an ICMP echo reply are transmitted and received between the MN and the AR, so the control message compresses the bandwidth on the radio link between the MN and the AR. It is also a problem to cause it. The above problem is not mentioned in Non-Patent Document 1 and Non-Patent Document 2, and no solution is presented.

  In view of the above-described problems of the prior art, the present invention provides a system in which the layer 3 address of the mobile node does not change when the mobile node performs handover between routers in the domain. An object of the present invention is to provide a mobile communication control method, a mobile communication system, and a router that can immediately transfer to a mobile node without performing ND (Neighbor Discovery) processing.

In order to achieve the above object, the present invention provides a mobile communication control method in which a layer 3 address of a mobile node does not change when a mobile node performs handover between routers in a domain.
Establishing a tunnel and forwarding packets between a first router to which the mobile node is currently connected and an aggregation router in the domain;
Transmitting a tunnel establishment request message including the layer 2 address and the layer 3 address of the mobile node from the first router to a neighboring second router;
Generating a proxy neighbor cache corresponding to the layer 2 address and the layer 3 address of the mobile node in the second router that has received the tunnel establishment request message;
Establishing a tunnel between the second router and the aggregation router;
Enabling the proxy neighbor cache on the second router after the tunnel is established, and buffering packets destined to the mobile node received from the aggregation router at the second router;
When the mobile node is handed over to the second router, the second router sends the buffered packet addressed to the mobile node to the mobile node based on the proxy neighbor cache; ,
To have.
According to the above method, the packet destined for the mobile node can be immediately transferred to the mobile node without performing ND (Neighbor Discovery) processing.

Further, the present invention further includes a step in which the first router determines the second router to be a transmission destination of the tunnel establishment request message with reference to the neighboring router installation information held in advance. To have.
Further, according to the present invention, the aggregation router holds the installation information of each router in advance, and the first router becomes the transmission destination of the tunnel establishment request message by making an inquiry to the aggregation router. A step of grasping the second router is provided.
In the present invention, the mobile node searches for neighboring routers and notifies the first router so that the first router becomes the second router to which the tunnel establishment request message is transmitted. It has a step to grasp.

In order to achieve the above object, the present invention is a mobile communication system in which a layer 3 address of a mobile node does not change when a mobile node performs handover between routers in a domain.
Means for establishing a tunnel and forwarding packets between a first router to which the mobile node is currently connected and an aggregation router in the domain;
Means for transmitting a tunnel establishment request message including the layer 2 address and the layer 3 address of the mobile node from the first router to a neighboring second router;
Means for generating a proxy neighbor cache corresponding to the layer 2 address and the layer 3 address of the mobile node in the second router that has received the tunnel establishment request message;
Means for establishing a tunnel between the second router and the aggregation router;
Means for enabling the proxy neighbor cache on the second router after the tunnel is established and buffering packets destined to the mobile node received from the aggregation router at the second router;
Means for transmitting, to the mobile node, packets destined for the mobile node that the second router has buffered based on the proxy neighbor cache when the mobile node hands over to the second router; ,
It was set as the structure which has.
With the above-described configuration, a packet destined for the mobile node can be immediately transferred to the mobile node without performing ND (Neighbor Discovery) processing.

In order to achieve the above object, the present invention provides the second communication system in a mobile communication system in which a layer 3 address of the mobile node does not change when the mobile node is handed over from the first router to the second router in the domain. Router,
When receiving the tunnel establishment request message including the layer 2 address of the mobile node and the layer 3 address transmitted by the mobile node currently connected to the first router, the layer 2 address of the mobile node Proxy neighbor cache generation means for generating a proxy neighbor cache corresponding to the layer 3 address;
Tunnel establishment means for establishing a tunnel between aggregation routers in the domain;
Buffering means for enabling the proxy neighbor cache after the tunnel is established and buffering packets destined to the mobile node received from the aggregation router;
Means for transmitting, to the mobile node, the packet addressed to the mobile node, which has been buffered, based on the proxy neighbor cache when the mobile node hands over to the second router;
It was set as the structure which has.
With the above-described configuration, a packet destined for the mobile node can be immediately transferred to the mobile node without performing ND (Neighbor Discovery) processing.

  According to the present invention, after completion of a mobile node handover in an LMM domain or the like, a data packet transferred to the handover destination router can be immediately transferred to the MN without performing NDP (Neighbor Discovery Protocol) processing. . Further, the packet transmission from the mobile node can be performed immediately without performing the NDP process after the handover is completed. As a result, it is possible to seamlessly resume packet transmission / reception between the mobile node and the handover destination router after handover of the mobile node.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of a mobile communication system according to the present invention, and FIG. 2 is an explanatory diagram showing a communication sequence of the mobile communication system of FIG.

  The present invention focuses on the MN that performs mobile communication and the AR that is the link destination of the MN within the LMM domain 100 having the network configuration of FIG. FIG. 1 shows a solution technique, and FIG. 2 shows a sequence diagram of processing at that time. 1 and 2 show a state in which the MN connected to AR_1 is handed over to AR_2. It is assumed that a P2MP (point-to-multipoint) is constructed for AggAR and AR_2 located in the vicinity of AR_1 to which the MN is linked as a route for packet transfer in the LMM domain 100 of FIG. In AggAR, when a packet destined for the MN is transferred from outside the LMM domain 100, the packet is copied and transferred on the P2MP path. In each of AR_1, AR_2, and AR_3, a packet copied and transferred by AggAR is buffered, and when the MN is linked, the buffered packet is transferred to the MN. This makes it possible to provide soft handover by avoiding packet loss during handover processing for the MN that performs handover between AR_1, AR_2, and AR_3.

  Hereinafter, an embodiment of the present invention will be described. First, a description will be given of a method for immediately restarting packet transmission when the MN that has performed handover does not perform ND (Neighbor Discovery) for the handover destination AR. The AR_1, AR_2, and AR_3 in the LMM domain 100 have the same node information that is advertised by RA (Router Advertisement). This is to prevent the MN from changing the default router (= AggAR) even when the LMM domain 100 is handed over. The own node information advertised in common in each RA is the L2 address of AR_1, AR_2, AR_3, and the L3 link local address (hereinafter referred to as LL address) of AR_1, AR_2, AR_3. The router lifetime indicating the valid time of the default router may be arbitrarily set for each of AR_1, AR_2, and AR_3, or may be common to each of AR_1, AR_2, and AR_3.

  When the MN performs automatic address generation, the RA advertises a prefix to generate an L3 address. This prefix may be unique within the LMM domain 100, or may be different for each MN. Good. If the MN has a function that guarantees that the L3 address will not change when performing handover between AR_1, AR_2, and AR_3 in the LMM domain 100, the advertising method and management of the prefix to the MN Is not limited. In this description, it is assumed that the only prefix is advertised to the MN within the LMM domain 100.

  As described above, since the MN holds a common address as the default router, the MN that the MN linked to AR_1 before the handover has in the NC (Neighbor Cache) has an MN even if it receives RA from AR_2. NCs are the same. Therefore, since the MN that has completed the handover from AR_1 to AR_2 does not need to change the default router and the NC, it can immediately resume packet transmission.

  Next, a method for immediately transferring a packet transferred from the AggAR to the MN from the AR_2 which is the handover destination of the MN to the MN will be described. The MN's L2 address, LL address, and L3 global address (hereinafter, these three addresses are referred to as MN address information) are held for ARs around the AR to which the MN is linked. The MN address information is notified to the neighboring AR by the AR to which the MN is linked. Each AR holds this MN address information as an NC (hereinafter, proxy neighbor cache). The state of “proxy” is defined and held as “the state where the MN is not linked but there is a possibility of handover”. When the MN is linked, the AR immediately causes a state transition from the “proxy” state to the “reachable” state, and starts to transfer the packet buffered in the AR. It should be noted that for selection of “peripheral ARs” of ARs to which the MN is linked, ARs that are geographically located in the vicinity of the ARs may be selected. Also, there is a method in which the MN's wireless transmission function is used to notify the MN's link destination AR of the AR around the MN, and the MN's link destination AR selects the AR around the MN using that information.

  A method of using the proxy neighbor cache (proxy NC) will be described using the processing sequence at the time of handover in FIG. A to E in FIG. 2 correspond to A to E in FIG. FIG. 2 illustrates a case where the MN turns on the power under AR_1. At this time, the following two points are not performed in order to explain the generation process of the proxy NC. First, the MN is linked to AR_1, but the path between AggAR and AR_2 is not included in the P2MP path for MN. Second, there is no proxy NC in AR_2. The process that satisfies these two points is performed on AR_2 around the link destination AR_1 every time the MN executes handover between ARs.

  (1) The MN linked to AR_1 implements NDP performed at the start of IP communication with AR_1. As a result, AR_1 notifies the MN of the prefix of the LMM domain 100, and the MN generates an address. Further, the MN notifies the MN address information to AR_1 according to NDP prior to communication. Alternatively, AR_1 collects MN address information according to NDP in order to transfer a packet addressed to MN from AR_1. This process is a standard IP process and is not shown in FIG.

(2) Immediately after the MN links to AR_1 in (1), AR_1 sets the IP address of the MN (MN-IPaddr) and the IP address of AR_1 (AR_1-IPaddr) in order to establish a path between AR_1 and AggAR. A tunnel establishment request message is transmitted to AggAR. By notifying this message including the MN address information, it is used as an ID for identifying the MN path in the AggAR.
(3) AggAR transmits a tunnel establishment response message including the IP address of the MN (MN-IPaddr) and the IP address of AR_1 (AR_1-IPaddr) to AR_1, and establishes a path between AggAR and AR_1. At this time, the tunnel establishment response message may be notified including a list of ARs around AR_1. When the path is established, AR_1 starts to transfer the packet addressed to the MN and the packet transmitted by the MN.

A. In addition, the AR_1 requests the peripheral AR (AR_2 in FIG. 2) where the MN may be handed over to participate in the P2MP path and generate the proxy NC, so that the MN's L2 address (MN-L2addr ) And an IP address (MN-IPaddr) are transmitted. This message includes MN address information.
(4) Upon receiving the tunnel establishment request message, AR_2 holds the MN address information as a proxy NC. The state of this NC is “proxy”, and no packet should be transferred to this address. Further, packet buffering for this NC is assumed to be “invalid”.
(5) The AR_2 that generated the proxy NC requests the MN's IP address (MN-IPaddr) and the AR_2 IP address (AR_2-) in order to request the participation of the MN in the P2MP path and the start of packet transfer duplicated by the AggAR A tunnel establishment request message including IPaddr) is transmitted to AggAR. This message includes MN address information.
(6) AggAR sends a tunnel establishment response message including the IP address of MN (MN-IPaddr) and the IP address of AR_2 (AR_2-IPaddr) to AR_2, and establishes a path between AggAR and AR_2. AR_2 is accommodated in the P2MP path. The AggAR that has received the notification of the MN address information from AR_2 identifies from the MN address information whether a path for MN already exists or whether a tunnel establishment request has been made for the first time.

B. In AR_2 that has received the tunnel establishment response message, packet buffering for the entry of proxy NC is set to “valid”.
(7) Thereafter, when a packet addressed to MN is transferred from AggAR, it is buffered.
(8) Thereafter, when the MN leaves the link with AR_1 and links with AR_2, the MN sends an L2 link establishment message including the MN's L2 address (MN-L2addr) in order to establish a link with AR_2. Transmit to AR_2.
(9) AR_2 transmits an L2 link establishment response message including the MN's L2 address (MN-L2addr) to the MN, and notifies the MN of the completion of the link establishment process with the MN.

C. As a result, since AR_2 establishes a link with the MN, the state of the MN entry held as the proxy NC is set to “reachable”.
D. Start buffered packet transfer.
E. After that, AR_2 transmits a tunnel establishment request message similar to (2) to the peripheral AR, and requests the AR in the vicinity of AR_2 to generate a proxy NC and participate in the P2MP path for the MN. To do.

  The determination of the handover destination AR to which the AR in the link transmits the tunnel establishment request message may be based on the AR installation information that each AR has in a fixed manner. Alternatively, the AR may be determined by inquiring of the AggAR. In addition, the MN may grasp the information by collecting information on the AR existing in the vicinity of the own node and notifying the AR in the link.

  In the present invention, when a mobile node performs handover between routers in a domain, the layer 3 address of the mobile node does not change, the handover destination router performs ND (Neighbor Discovery) processing on the packet addressed to the mobile node. Therefore, it can be immediately transferred to a mobile node without being used, and can be used for an LMM (Localized Mobility Management) network or the like.

The block diagram which shows one Embodiment of the mobile communication system which concerns on this invention Explanatory drawing which shows the communication sequence of the mobile communication system of FIG. Explanatory drawing which shows the communication sequence of the conventional mobile communication system Explanatory drawing showing another conventional mobile communication system and its communication sequence Still another conventional mobile communication system and an explanatory diagram showing its communication sequence Explanatory drawing which shows the system for demonstrating the problem which this invention tends to solve, and its communication sequence

Explanation of symbols

100 LMM domain MN mobile node AR_1, AR_2, AR_3 Access router
AggAR aggregation router

Claims (6)

A mobile communication control method in which a layer 3 address of the mobile node does not change when a mobile node performs handover between routers in a domain,
Establishing a tunnel and forwarding packets between a first router to which the mobile node is currently connected and an aggregation router in the domain;
Transmitting a tunnel establishment request message including the layer 2 address and the layer 3 address of the mobile node from the first router to a neighboring second router;
Generating a proxy neighbor cache corresponding to the layer 2 address and the layer 3 address of the mobile node in the second router that has received the tunnel establishment request message;
Establishing a tunnel between the second router and the aggregation router;
Enabling the proxy neighbor cache on the second router after the tunnel is established, and buffering packets destined to the mobile node received from the aggregation router at the second router;
When the mobile node is handed over to the second router, the second router sends the buffered packet addressed to the mobile node to the mobile node based on the proxy neighbor cache; ,
A mobile communication control method.   2. The step according to claim 1, wherein the first router has a step of determining the second router as a transmission destination of the tunnel establishment request message with reference to installation information of neighboring routers held in advance. Mobile communication control method.   The aggregation router holds the installation information of each router in advance, and the first router knows the second router that is the transmission destination of the tunnel establishment request message by making an inquiry to the aggregation router. The mobile communication control method according to claim 1, further comprising the step of:   The mobile node searches for neighboring routers and notifies the first router, whereby the first router grasps the second router that is the transmission destination of the tunnel establishment request message. Item 4. The mobile communication control method according to Item 1. A mobile communication system in which a layer 3 address of a mobile node does not change when a mobile node performs handover between routers in a domain,
Means for establishing a tunnel and forwarding packets between a first router to which the mobile node is currently connected and an aggregation router in the domain;
Means for transmitting a tunnel establishment request message including the layer 2 address and the layer 3 address of the mobile node from the first router to a neighboring second router;
Means for generating a proxy neighbor cache corresponding to the layer 2 address and the layer 3 address of the mobile node in the second router that has received the tunnel establishment request message;
Means for establishing a tunnel between the second router and the aggregation router;
Means for enabling the proxy neighbor cache on the second router after the tunnel is established and buffering packets destined to the mobile node received from the aggregation router at the second router;
Means for transmitting, to the mobile node, packets destined for the mobile node that the second router has buffered based on the proxy neighbor cache when the mobile node hands over to the second router; ,
A mobile communication system. The second router in a mobile communication system in which a layer 3 address of the mobile node does not change when a mobile node hands over from a first router in a domain to a second router;
When receiving the tunnel establishment request message including the layer 2 address of the mobile node and the layer 3 address transmitted by the mobile node currently connected to the first router, the layer 2 address of the mobile node Proxy neighbor cache generation means for generating a proxy neighbor cache corresponding to the layer 3 address;
Tunnel establishment means for establishing a tunnel between aggregation routers in the domain;
Buffering means for enabling the proxy neighbor cache after the tunnel is established and buffering packets destined to the mobile node received from the aggregation router;
Means for transmitting, to the mobile node, the packet addressed to the mobile node, which has been buffered, based on the proxy neighbor cache when the mobile node hands over to the second router;
Router with.