JP4788221B2 - Radio access network system and handoff control method for controlling handoff - Google Patents

Description

  The present invention relates to a radio access network (RAN) system and a handoff control method for controlling handoff.

  FIG. 1 is a cell configuration diagram in the prior art.

  The mobile station 1 is located in the communication area of the base station 2A and connects the radio link with the base station 2A. The base stations 2B to 2G are adjacent to each other around the base station 2A, and the mobile station 1 may perform handoff with any of the base stations 2B to 2G due to subsequent movement. However, it is unclear in which direction the mobile station 1 will move in the future. Therefore, the communication operator of the radio access network needs to prepare for the mobile station 1 to handoff from the base station 2A to the base stations 2B to 2G.

  FIG. 2 is a configuration diagram of a RAN system in the prior art.

  The RAN system of FIG. 2 is configured in a hierarchy from the uppermost layer access gateway 4 connected to the IP network toward the lowermost layer base station 2. The access gateway 4 is connected to one or more routers 5 which are lower layers. Further, the router 5 is connected to a plurality of switches 3 which are lower layers. A base station 2 is connected to each port of the switch 3. Base station 2 is connected to mobile station 1 via a wireless link. The mobile station 1 connects a radio link with a base station covering the position according to the moved position.

  According to FIG. 2, the mobile station 1 is moving from the communication area of the base station 2A to the communication area of the base station 2B. At this time, in order to continue communication of the mobile station 1, control of handoff from the base station 2A to the base station 2B is necessary.

  In order to prevent the data reception of the mobile station 1 from being interrupted during the handoff, the access gateway 4 transmits in advance the data to be received by the mobile station 1 to the base stations 2B to 2G that may be the movement destination. . Thereby, the mobile station 1 can receive the same packet as the packet transmitted from the source base station 2A also from the destination base station (any one of 2B to 2G). Such a transmission method is called “divert transmission” (see, for example, Non-Patent Document 2). According to the divert transmission of FIG. 2, the same data packet is transmitted from the base stations 2A and 2B to the mobile station 1 during the handoff.

  FIG. 3 is a sequence diagram of the RAN system in the prior art. The packet flow in the system of FIG. 2 will be described with reference to FIG.

(S301) The data packet transmitted from the access gateway 4 is transferred to the source base station 2A via the router 5 and the switch 3A, and is received by the mobile station 1.

(S302) It is assumed that the mobile station 1 is moving from the communication area of the source base station 2A to the communication area of the destination base station 2B. Also, assume that the mobile station 1 determines that the radio link of the base station 2B is better than the radio link of the base station 2A, for example, depending on the communication state such as the reception level. At this time, the mobile station 1 transmits a handoff request to the base stations 2A and 2B, and starts handoff. The source base station 2A that has received the handoff request transmits a data copy request to the access gateway 4 via the switch 3A and the router 5.

(S303) Upon receiving the data copy request, the access gateway 4 copies the data packet addressed to the base station 2A to the data packet addressed to the base station 2B, and transmits these two data packets to the router 5. Here, the amount of data between the access gateway 4 and the router 5 is doubled by handoff. For the two copied data packets, the router 5 transmits a data packet addressed to the base station 2A to the switch 3A, and transmits a data packet addressed to the base station 2B to the switch 3B. The switch 3A transmits a data packet addressed to the base station 2A to the base station 2A. The switch 3B transmits a data packet addressed to the base station 2B to the base station 2B. The mobile station 1 can receive the data packet transmitted from the base station 2A and the data packet transmitted from the base station 2B during the handoff.

(S304) The source base station 2A transmits a handoff permission to the mobile station 1. On the other hand, the mobile station 1 enters the handoff state by transmitting the handoff start to the base stations 2A and 2B. Thereafter, the mobile station 1 transmits a handoff completion to the base stations 2A and 2B. In response to this, the source base station 2A transmits a handoff completion confirmation to the mobile station 1. Also, the destination base station 2B also transmits a handoff completion confirmation to the mobile station 1. Thereby, the handoff ends.

(S305) The mobile station 1 transmits handoff completion to the base stations 2A and 2B. At this time, the movement-destination base station 2B transmits data copy completion to the access gateway 4 via the switch 3B and the router 5. The access gateway 4 ends the data copy process.

(S306) The data packet transmitted from the access gateway 4 is transferred to the source base station 2B via the router 5 and the switch 3B, and is received by the mobile station 1.

“Cdma2000 Wireless IP Network Standard”, P.S0001-B v2.0, 3GPP2, [online], September 2004, [searched on June 28, 2005], Internet <URL: http: //www.3gpp2 .org / Public_html / specs / P.S0001-B_v2.0_041004.pdf> A. O'Neill, S. Corson and G. Tsirtsis, "Generalized IP handoff", Internet Draft, draft-oneill-craps-handoff-00, August 2000, Work in Progress. IT Glossary, [online], [Search June 28, 2005], Internet <URL: http://e-words.jp/w/VLAN.html> J. Case, M. Fedor, M. Schoffstall and J. Davin, "A Simple Network Management Protocol (SNMP)", RFC 1157, May 1990, IETF

  According to the prior art, when a handoff request is transmitted from the mobile station 1, the access gateway 4 as an upper layer needs to copy and transmit the same data packet to the destinations of the plurality of base stations 2. Therefore, an excessive load is applied to the access gateway 4 that copies the packet. In addition, during the handoff, the same data packet is transferred between the access gateway 4 and the router 5 and the communication band is wasted.

  Furthermore, in the existing RAN system, communication between the access gateway and the base station is often performed by IP. Therefore, in order to transfer the data packet to the correct destination base station, all the installed base stations A database is required. The larger the RAN system, the larger the database, and the search cost for finding a target destination base station increases.

  Therefore, an object of the present invention is to provide a radio access network system and a handoff control method capable of reducing the load on the RAN system necessary for handoff.

According to the radio access network system of the present invention,
A mobile station, a plurality of base stations that communicate wirelessly with the mobile station, a VLAN switch that has a VLAN table based on the VLAN function and communicates with the base station,
The mobile station has a handoff message transmission means for transmitting a handoff request including its VLAN identifier to the base station,
The base station has a registration message transmitting means for transmitting a port registration request including the VLAN identifier to the VLAN switch when receiving the handoff request as the movement destination,
The VLAN switch has a VLAN table that registers the VLAN identifier included in the port registration request in association with the port number that received the port registration request.

According to another embodiment of the radio access network system of the present invention,
A gateway that communicates with the VLAN switch;
The VLAN switch further includes registration message transfer means for transferring the received port registration request to the gateway,
The gateway adds a VLAN table that registers the VLAN identifier included in the port registration request in association with the source address included in the port registration request, and a VLAN tag that includes the VLAN identifier corresponding to the address of the data packet. It is also preferable to have a packet transfer means for deleting and transferring.

Further, according to another embodiment of the radio access network system of the present invention,
The mobile station handoff message transmission means transmits a handoff completion including its own VLAN identifier to the base station,
The registration message transmitting means of the base station transmits a port deletion request including the VLAN identifier to the VLAN switch when receiving the handoff completion as the movement source,
In the VLAN table of the VLAN switch, it is also preferable to delete the registration item corresponding to the VLAN identifier included in the port deletion request from the VLAN table.

Furthermore, according to another embodiment of the radio access network system of the present invention,
The registration message transfer means of the VLAN switch transfers the received port deletion request to the gateway,
The gateway preferably deletes the registration item corresponding to the VLAN identifier included in the port deletion request from the VLAN table.

  Further, according to another embodiment of the radio access network system of the present invention, the registration message transmission means of the base station and the registration message transfer means of the VLAN switch are a port registration request based on SNMP (Simple Network Management Protocol) and It is also preferable to transmit / receive a port deletion request.

According to the handoff control method in the radio access network system of the present invention,
The radio access network system includes a mobile station, a plurality of base stations that communicate with the mobile station wirelessly, a VLAN switch that has a VLAN table based on the VLAN function and communicates with the base station,
A first step in which a mobile station transmits a handoff request including its VLAN identifier to a base station;
A second step of transmitting a port registration request including a VLAN identifier to a VLAN switch when the base station receives a handoff request as a destination;
The VLAN switch includes a third step of registering the VLAN identifier included in the port registration request in the VLAN table in association with the port number that has received the port registration request.

According to another embodiment of the handoff control method of the present invention,
A gateway that communicates with the VLAN switch;
In the third step, the VLAN switch forwards the received port registration request to the gateway.
The gateway registers the VLAN identifier included in the port registration request in association with the source address included in the port registration request in the VLAN table, and adds a VLAN tag including the VLAN identifier corresponding to the address of the data packet. Or it is also preferable to delete and transfer.

According to another embodiment of the handoff control method of the present invention,
A fourth step in which the mobile station transmits a handoff completion including its VLAN identifier to the base station;
A fifth step of transmitting a port deletion request including the VLAN identifier to the VLAN switch when the base station receives the handoff completion as the movement source;
It is also preferable that the VLAN switch has a sixth step of deleting the registration item corresponding to the VLAN identifier included in the port deletion request from the VLAN table.

Furthermore, according to another embodiment of the handoff control method of the present invention,
The registration message transfer means of the VLAN switch transfers the received port deletion request to the gateway,
The gateway preferably deletes the registration item corresponding to the VLAN identifier included in the port deletion request from the VLAN table.

  Furthermore, according to another embodiment of the handoff control method of the present invention, the port registration request and / or the port deletion request is preferably a message based on SNMP.

  According to the present invention, since the RAN is configured by a VLAN switch having a VLAN function, a logical virtual LAN can be easily constructed by setting the VLAN switch. In particular, according to the present invention, the port registration request and the port deletion request transferred at the start of handoff are set so that the VLAN switch related to the handoff belongs to the VLAN or is excluded from the VLAN.

  Also, according to the present invention, it is not necessary for the access gateway to copy the data packet at the time of handoff, and the load on the entire RAN can be reduced. When performing divert transmission according to the prior art, the access gateway must copy the packet after judging the necessity of packet copy by looking at the destination header for each data packet. Such a method not only places a load on the access gateway for each handoff, but also requires the transfer of the copied packets between the access gateway and the base station, increasing the load on the entire RAN. I must. In particular, the access gateway is often installed as a center side facility of a mobile phone carrier network, and it is important to reduce the load. On the other hand, according to the present invention, it is possible to control the route of a packet by simply adding / deleting a port to / from the VLAN table of the VLAN switch, so that a node for copying the packet becomes unnecessary. In addition, according to the present invention, it is not necessary for the access gateway to discover the destination base station, and it is not necessary to check the IP address.

  In addition, hardware copy by the VLAN switch is performed only in a portion close to the base station in the hierarchical RAN. Therefore, the load is not concentrated on the access gateway, and the network near the center, that is, the network near the access gateway is not loaded.

  Furthermore, according to the present invention, the management content for handoff can be reduced. In the prior art, in order to perform divert transmission, it is necessary to manage the IP address information of the destination base station. It is necessary to look at the list of IP addresses and perform processing so that the IP packet is transmitted to an appropriate base station. In contrast, in the present invention, when a VLAN switch that has passed a port registration request or port deletion request for handoff adds the port to the VLAN table, the IP packet is automatically transferred to the destination base station. The Therefore, it is not necessary to manage a list of IP addresses of base stations as in the prior art.

  Furthermore, according to the present invention, since the entire RAN can be configured by an inexpensive VLAN switch, the cost of the entire network can be reduced.

  Therefore, according to the present invention, the load on the RAN system required for handoff can be reduced.

  Hereinafter, the best embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 4 is a cell configuration diagram of a base station for the mobile station 1 in the present invention.

  In the present invention, during the handoff, the communication area of the source base station 2A and the communication area of the destination base station 2B are logically connected to the mobile station 1 on the same LAN. Constitute. For this purpose, the present invention comprises a VLAN switch having a VLAN (Virtual LAN) function instead of a router or a switch. By registering the VLAN identifier (VLAN-ID) of the mobile station 1 in the VLAN switch as a node, the same packet can be transferred to a plurality of routes. As a result, according to FIG. 4, the mobile station 1 can receive the same data packet from the source base station 2A and the destination base station 2B. Of course, if there is a possibility that the mobile station 1 moves to another base station (for example, the base station 2D) in addition to the base station 2B, the base station 2A, The base station 2B and the base station 2D can receive the same data packet. In the following description, it is assumed that the mobile station moves between the base station 2A and the base station 2B.

  FIG. 5 is a configuration diagram of the RAN system according to the present invention.

  The system shown in FIG. 5 is different from the system shown in FIG. 2 in that the system includes a VLAN switch having a VLAN function instead of a router or a switch constituting the RAN.

  The VLAN is defined in IEEE 802.1Q, and broadcast or multicast between work groups is realized by a VLAN tag attached to a data link header of a data packet (see, for example, Non-Patent Document 3). This is a technique for making terminals that are physically connected to different switches appear logically in the same network.

Table 1 is a frame configuration diagram defined by IEEE 802.1Q.

  According to Table 1, the data link header includes a MAC (Media Access Control) header and a 4-byte VLAN tag. The VLAN tag has a protocol type (2 bytes), a priority (3 bits), a CFI (Cononical Format Indicator) (1 bit), and a VLAN-ID (12 bits).

  A VLAN switch having a VLAN function has a VLAN table in which VLAN-IDs are associated with port numbers. In the VLAN table, a plurality of VLAN-IDs can be specified for the same port number. The VLAN switch updates its VLAN table according to the received port registration request or port deletion request.

Table 2 is a VLAN table included in the VLAN switch. Using this table, the VLAN switch provides a virtual LAN for data packets.

Table 3 is a VLAN table included in the gateway 4. The gateway 4 stores the VLAN-ID in association with the IP address.

  Note that a VLAN switch having a VLAN function outputs the same packet to a plurality of ports, but this operation is performed in hardware. Accordingly, since software processing such as analysis of the header of the data packet is not necessary, the load on the entire system can be significantly reduced.

  According to the system of FIG. 5, the access gateway 4 transmits a data packet addressed to the base station 2A to the VLAN switch 3E in the lower layer in order to realize divert transmission. According to the present invention, the access gateway 4 does not copy data packets. The VLAN switch 3E transmits the data packet to the VLAN switches 3A and 3B according to the VLAN table. Furthermore, the VLAN switch 3A transmits the data packet to the base station 2A according to the VLAN table. Further, the VLAN switch 3B transmits the data packet to the base station 2B according to the VLAN table. The mobile station 1 can receive the data packet transmitted from the base station 2A and the data packet transmitted from the base station 2B.

  FIG. 6 is a sequence diagram of the RAN system according to the present invention.

  The sequence in FIG. 6 differs from the sequence in FIG. 3 at the time of handoff request from the mobile station 1 (S602) and the time of completion of handoff from the mobile station 1 (S605). Also, the procedure for transferring data packets from the access gateway 4 to the mobile station 1 is different.

The mobile station 1 stores in advance a VLAN-ID that is an identifier of the VLAN to which the mobile station 1 belongs in the storage unit.
(S601) The data packet transmitted from the access gateway 4 is transferred to the source base station 2A via the VLAN switches 3E and 3A and received by the mobile station 1.

(S602) It is assumed that the mobile station 1 is moving from the communication area of the source base station 2A to the communication area of the destination base station 2B. Further, it is assumed that the mobile station 1 determines that the radio link of the base station 2B is better than the radio link of the base station 2A. At this time, the mobile station 1 transmits a handoff request to the base stations 2A and 2B.

  The handoff request message includes the VLAN-ID to which the mobile station 1 belongs.

  The destination base station 2B that has received the handoff request from the mobile station 1 transmits a port registration request to the VLAN switch 3B. The port registration request includes the VLAN-ID included in the handoff request.

  The VLAN switch 3B that has received the port registration request associates the VLAN-ID included in the port registration request with the port number that has received the port registration request and registers it in the VLAN table. Then, the VLAN switch 3B transfers the received port registration request to the VLAN switch 3E of the upper layer.

  The VLAN switch 3E that has received the port registration request associates the VLAN-ID included in the port registration request with the port number that has received the port registration request and registers it in the VLAN table. Then, the VLAN switch 3E transfers the received port registration request to the access gateway 4 of the upper layer.

  The access gateway 4 that has received the port registration request associates the IP address included in the port registration request with the VLAN-ID included in the port registration request, and registers them in the VLAN table.

(S603) The access gateway 4 transmits a data packet to be transmitted to the base station 2A to the switch 3E. According to this embodiment, the amount of data between the access gateway 4 and the switch 3E is not increased by handoff, as in S303 in FIG. 3 of the prior art. The switch 3E refers to the VLAN table, and outputs the data packet simultaneously to the port connected to the VLAN switch 3A and the port connected to the VLAN switch 3B.

  The VLAN switch 3A refers to the VLAN table and transmits the data packet to the base station 2A. The VLAN switch 3B refers to the VLAN table and transmits the data packet to the base station 2B. The mobile station 1 can receive the data packet transmitted from the base station 2A and the data packet transmitted from the base station 2B during the handoff.

(S604) Similar to S304 described above, the mobile station 1 performs handoff between the source base station 2A and the destination base station 2B.

(S605) The mobile station 1 transmits handoff completion to the base stations 2A and 2B. The handoff completion message includes the VLAN-ID to which the mobile station 1 belongs.

  The source base station 2A that has received the handoff completion from the mobile station 1 transmits a port deletion request including the VLAN-ID of the mobile station 1 to the VLAN switch 3A. The VLAN switch 3A deletes the registration item corresponding to the VLAN-ID from the VLAN table. Furthermore, the VLAN switch 3A transmits the handoff completion to the VLAN switch 3E of the upper layer. The VLAN switch 3E deletes the registration item corresponding to the VLAN-ID from the VLAN table. Further, the VLAN switch 3E transmits the handoff completion to the access gateway 4 of the upper layer.

(S606) The data packet transmitted from the access gateway 4 is transferred to the destination base station 2B via the VLAN switches 3E and 3B and received by the mobile station 1.

  FIG. 7 is a functional configuration diagram of apparatuses in the RAN system of the present invention.

  The mobile station 1 includes a packet transmission / reception unit 10, a handoff control unit 11, a handoff message transmission unit 12, and a VLAN-ID holding unit 13. The handoff message transmission unit 12 transmits a handoff request or a handoff completion message based on a handoff start or end instruction from the handoff control unit 11. These messages include information about the VLAN of the mobile station 1 stored in the VLAN-ID holding unit 13. The packet transmitting / receiving unit 10 transmits / receives a data packet in which a VLAN tag including a VLAN-ID is added to the data link header.

  The base station 2 includes a packet transfer unit 20, a handoff message reception unit 21, and a registration message transmission unit 22. The handoff message receiving unit 21 receives a handoff request or handoff completion message from the mobile station 1. The registration message transmission unit 22 is notified that these messages have been received. The registration message transmission unit 22 transmits a port registration request in response to a handoff request, and transmits a port deletion request in response to the completion of handoff.

  The VLAN switch 3 includes a packet transfer unit 30, a port switch unit 31, a VLAN table unit 32, and a registration message transfer unit 33. The port switch unit 31 includes a plurality of ports, and is connected to the base station 2 for each port. The port switch unit 31 outputs the data packet received from the packet transfer unit 30 from the port corresponding to the VLAN-ID according to the registered contents of the VLAN table unit 32. The VLAN table unit 32 holds a table in which VLAN-IDs are associated with each port number, as in Table 2 described above. The registration message transfer unit 33 instructs the VLAN table unit 32 to be updated according to the port registration request or the port deletion request received from the base station 2. Further, the registration message transfer unit 33 transfers the received request messages to the VLAN switch or access gateway in the upper layer.

  The access gateway 4 includes a packet transfer unit 40, a VLAN table unit 41, and a registration message reception unit 42. The packet transfer unit 40 deletes the VLAN tag from the data packet received from the VLAN switch and transfers it to the IP network. On the other hand, a VLAN tag is added to the data packet received from the IP network and transferred to the VLAN switch. The VLAN table unit 41 holds a table in which a VLAN-ID is associated with each IP address, as in Table 3 described above. The registration message receiving unit 42 instructs the VLAN table unit 41 to be updated according to the port registration request or the port deletion request received from the VLAN switch 3. In the case where the RAN is related to a mobile phone business facility, the access gateway 4 is preferably a packet control node.

  The port registration request or the port deletion request can be easily realized by SNMP which is a network management protocol. Accordingly, the registration message transmission unit 22 of the base station 2 operates as a manager, and the registration message transfer unit 33 of the VLAN switch operates as an agent. The registration message transfer unit 33 of the VLAN switch further operates as a manager, and the registration message reception unit 42 of the access gateway 4 operates as an agent.

  According to the above-described various embodiments of the present invention, those skilled in the art can easily make various changes, modifications, and omissions in the technical idea and scope of the present invention. The above description is merely an example, and is not intended to be restrictive. The invention is limited only as defined in the following claims and the equivalents thereto.

It is a cell block diagram in a prior art. It is a block diagram of the RAN system in a prior art. It is a sequence diagram of the RAN system in a prior art. It is a cell block diagram of the base station with respect to the mobile station 1 in this invention. It is a block diagram of the RAN system in this invention. It is a sequence diagram of the RAN system in this invention. It is a function block diagram of the apparatus in the RAN system of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mobile station 10 Packet transmission / reception part 11 Handoff control part 12 Handoff message transmission part 13 VLAN-ID holding | maintenance part 2 Base station 21 Packet transfer part 22 Handoff message reception part 23 Registration message transmission part 3 VLAN switch, switch 30 Packet transfer part 31 Port Switch unit 32 VLAN table unit 33 Registration message transfer unit 4 Access gateway 41 Packet transfer unit 42 VLAN table unit 43 Registration message reception unit 5 Router 6 IP network

Claims (10)

A mobile station, a plurality of base stations that communicate wirelessly with the mobile station, a VLAN switch that has a VLAN table based on a VLAN function and communicates with the base station,
The mobile station has handoff message transmission means for transmitting a handoff request including its own VLAN identifier to the base station,
The base station has a registration message transmitting means for transmitting a port registration request including the VLAN identifier to the VLAN switch when receiving the handoff request as a destination.
The wireless access network system, wherein the VLAN switch includes the VLAN table for registering the VLAN identifier included in the port registration request in association with the port number that received the port registration request. A gateway that communicates with the VLAN switch;
The VLAN switch further includes registration message transfer means for transferring the received port registration request to the gateway,
The gateway registers the VLAN identifier in association with the VLAN identifier included in the port registration request and the VLAN table for registering the source address included in the port registration request in association with the address of the data packet. The wireless access network system according to claim 1, further comprising: a packet transfer unit configured to add or delete a VLAN tag including the packet. The handoff message transmission means of the mobile station transmits a handoff completion including its own VLAN identifier to the base station,
The registration message transmission means of the base station transmits a port deletion request including the VLAN identifier to the VLAN switch when receiving the handoff completion as a movement source,
The wireless access network system according to claim 1 or 2, wherein the VLAN table of the VLAN switch deletes a registration item corresponding to the VLAN identifier included in the port deletion request from the VLAN table. The registration message transfer means of the VLAN switch transfers the received port deletion request to the gateway,
The radio access network system according to claim 3, wherein the gateway deletes a registration item corresponding to the VLAN identifier included in the port deletion request from the VLAN table.   5. The registration message transmission unit of the base station and the registration message transfer unit of the VLAN switch transmit and receive the port registration request and / or the port deletion request based on SNMP. The radio access network system according to any one of the above. In a handoff control method in a radio access network system,
The radio access network system includes a mobile station, a plurality of base stations that communicate with the mobile station wirelessly, a VLAN switch that has a VLAN table based on a VLAN function and communicates with the base station,
A first step in which the mobile station sends a handoff request including its VLAN identifier to the base station;
A second step of transmitting a port registration request including the VLAN identifier to the VLAN switch when the base station receives the handoff request as a destination;
The VLAN switch includes a third step of registering the VLAN identifier included in the port registration request in association with the port number that has received the port registration request in the VLAN table. Method. A gateway that communicates with the VLAN switch;
In the third step, the VLAN switch forwards the received port registration request to the gateway, and
The gateway registers the VLAN identifier included in the port registration request in association with the source address included in the port registration request in the VLAN table, and corresponds the VLAN identifier to the address of the data packet. The wireless access network system according to claim 6, wherein the VLAN tag is added or deleted for transfer. A fourth step in which the mobile station transmits a handoff completion including its VLAN identifier to the base station;
A fifth step of transmitting a port deletion request including the VLAN identifier to the VLAN switch when the base station receives the handoff completion as a movement source;
The handoff control method according to claim 6 or 7, wherein the VLAN switch has a sixth step of deleting a registration item corresponding to the VLAN identifier included in the port deletion request from the VLAN table. . The registration message transfer means of the VLAN switch transfers the received port deletion request to the gateway,
The handoff control method according to claim 8, wherein the gateway deletes a registration item corresponding to the VLAN identifier included in the port deletion request from the VLAN table. The handoff control method according to any one of claims 6 to 9, wherein the port registration request and / or the port deletion request is a message based on SNMP.

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