Method and apparatus for transmitting router advertisement and router solicitation messages through access point

A method and apparatus for transmitting a message in a wireless network environment are provided. The method of computing an interval of message transmission in an access point located in a specific subnet, includes determining whether the access point is an edge access point located at a boundary between the specific subnet and a neighboring subnet, and computing an interval of transmission of a router advertisement (RA) message containing information regarding the specific subnet based on the determination result.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the priority of Korean Patent Application No. 10-2006-0006286, filed on Jan. 20, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for transmitting messages in a radio network environment, and more particularly, to a method and apparatus for effectively transmitting messages in a radio network environment according to a mobile internet protocol (MIP).

2. Description of the Related Art

As the performances of mobile nodes, such as notebook computers and personal digital assistants (PDAs) have been improved and mobile communication technologies have been developed, the number of mobile node users has significantly increased. Accordingly, a mobile internet protocol (MIP) that uses an internet protocol (IP) address as a mobile node identifier has been introduced. In particular, MIP is a technology whereby even if the location of a mobile node is changed, a node can continuously communicate with a mobile node by using the IP address of the mobile node.

FIG. 1is a diagram of a related art wireless network environment. Referring toFIG. 1, the related art wireless network environment includes a home agent (HA)11, an access point (AP) A12, a mobile node (MN)13, a correspondent node (CN)14, a foreign agent (FA) A15, an AP B16, a FA B17, and an AP C18.

Each of the HA11, the FA A15, and the FA B17, which are a type of access router (AR), manages a subnet in which it is located. That is, the HA11manages a subnet A, the FA A15manages a subnet C, and the FA B17manages a subnet D. The AP A12, the AP B16, and the AP C18communicate with ARs, such as the HA11, the FA A15, and the FA B17, by wire, and communicate with the MN13wirelessly to connect the MN13to a wired network.

When the CN14transmits a packet using the IP address of the MN13as a destination address, the packet is processed according to the MIP, as follows. If the MN13is located in the subnet A managed by the HA11, the packet arrives at the MN13via the HA11and the AP A12. However, if the MN13leaves the subnet A and is then located in the subnet C managed by the FA A15, the HA11intercepts the packet and delivers it to the FA A15by tunneling. In this case, the current IP address of the MN13, which is referred to as a COA (Care Of Address), becomes different from the original IP address thereof. In order to perform tunneling, the HA11must recognize the COA of the MN13. Thus, the MN13transmits a binding update message containing information, such as the COA of the MN13, to the HA11. Similarly, the packet is processed as described above when the MN13leaves the subnet C and is moved to the subnet D managed by the FA A17.

FIG. 2is a diagram illustrating a handover process in a related art wireless network environment. Referring toFIG. 2, an MN25sequentially passes through a cell managed by an AP A22, a cell managed by an AP B23, and a cell managed by an AP C24. The MN25must generate a COA for use in a subnet in which it is now located in order that the MN25can communicate with other nodes while moving in a subnet managed by an AR21, the COA containing a subnet prefix. Thus, the MN25must have information regarding the subnet to generate the COA.

Thus, the AR21periodically broadcasts a router advertisement (RA) message containing the information regarding the subnet. Also, the MN25may transmit a router solicitation (RS) message requesting transmission of the RA message. However, the RA message that is periodically broadcast is rebroadcast to the MN13by the AP A22, the AP B23, or the AP C24that wirelessly receive the RA message from the AR21. In this case, unlike wired resources, wireless resource bandwidth for a wireless channel is significantly limited, and thus, broadcasting of the RA message causes serious waste of wireless channel bandwidth.

In particular, if a large amount of time is needed to perform a handover process in which the MN25moves from a subnet managed by the AR21to a new subnet, communications established with the MN25is discontinued, thereby degrading the communication performance of the MN25. Thus, the handover process must be expedited. However, when a transmission interval during which the RA message is transmitted is shortened to expedite the handover process, waste of wireless channel bandwidth becomes worse. Also, when the MN25transmits the RS message and the RA message is broadcast in response to the RS message, waste of wireless channel bandwidth is substantial.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for guaranteeing smooth handover to a mobile node while reducing waste of wireless channel bandwidth caused by broadcasting a router advertisement (RA) message.

The present invention also provides a computer readable medium having recorded thereon a computer program for executing the above method.

According to an aspect of the present invention, there is provided a method of computing an interval of message transmission in an access point located in a specific subnet, the method comprising determining whether the access point is an edge access point located at a boundary between the specific subnet and a neighboring subnet, and computing an interval of transmission of a first message containing information regarding the specific subnet based on the determination result.

According to another aspect of the present invention, there is provided an apparatus for computing an interval of message transmission in an access point located in a specific subnet, the apparatus comprising a determination unit which determines whether the access point is an edge access point located at a boundary between the specific subnet and a neighboring subnet, and a computing unit which computes an interval of transmission of a first message containing information regarding the specific subnet based on the determination result from the determination unit.

According to another aspect of the present invention, there is provided a computer readable medium having recorded thereon a computer program for the above method.

According to another aspect of the present invention, there is provided a method of transmitting a message in an access point located in a specific subnet, the method comprising determining whether the access point is an edge access point located at a boundary between the specific subnet and a neighboring subnet, computing an interval of transmission of a first message containing information regarding the specific subnet, based on the determination result, and transmitting the first message at the computed interval.

According to another aspect of the present invention, there is provided an apparatus for transmitting a message in an access point located in a specific subnet, the apparatus comprising a determination unit which determines whether the access point is an edge access point located at a boundary between the specific subnet and a neighboring subnet; a computing unit which computes an interval of transmission of a first message containing information regarding the specific subnet, based on the determination result; and a transmitter which transmits the first message at the computed interval.

According to another aspect of the present invention, there is provided a computer readable medium having recorded thereon a computer program for the above method.

According to another aspect of the present invention, there is provided a method of transmitting a message in an access point located in a specific subnet, the method comprising receiving a second message from a mobile node, the second message requesting a first message containing information regarding the specific subnet, when the second message is received, measuring an amount of time elapsed from a point of time when the first message stored in the access point has been received, and selectively transmitting the first message based on the elapsed amount of time.

According to another aspect of the present invention, there is provided an apparatus for transmitting a message in an access point being located in a specific subnet, the apparatus comprising a receiver which receives a second message from a mobile node, the second message requesting a first message containing information regarding the specific subnet, a measurement unit which measures an amount of time elapsed from a point of time when the first message stored in the access point has been received, when the second message is received, and a transmitter which selectively transmits the first message based on the elapsed amount of time.

According to another aspect of the present invention, there is provided a computer readable medium having recorded thereon a computer program for the above method.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3is a diagram illustrating a handover process performed in a wireless network environment according to an exemplary embodiment of the present invention. Referring toFIG. 3, a mobile node (MN)35sequentially passes through a cell managed by an access point (AP) A32, a cell managed by an AP B33, and a cell managed by an AP C34. To prevent wireless channel bandwidth from being wasted due to periodically broadcasting a router advertisement (RA) message, the AP A32, the AP B33, and the AP C34hold the RA message without broadcasting it, when they receive the RA message from an access router (AR)31. Next, each of the AP A32, the AP B33, and the AP C34sets a transmission interval at which the RA message is transmitted to reduce the amount of wireless channel traffic, and transmits the RA message in the transmission interval. That is, each of the AP A32, the AP B33, and the AP C34sets the transmission interval as long as possible so as to efficiently use wireless channel bandwidth. However, if handover occurs due to movement of the MN35to a new subnet from a subnet managed by the AR31, the transmission interval is reduced to guarantee the communication quality of the MN35.

FIG. 4is a diagram illustrating a related art wireless network environment established between ARs A41and B42. Referring toFIG. 4, in the related art wireless network environment, a subnet A managed by the AR A41is designed to partially overlap a neighboring subnet B managed by the AR B42. The overlap is designed to prevent a discontinuity in communications between mobile nodes.

Conventionally, upon receiving an RA message from the ARs A41and B42, APs broadcast it immediately, and therefore, all of the APs in the subnet A transmit the RA message at the same time. However, even if a mobile node located in a cell managed by an AP A411in the center of the subnet A moves in the cell, handover does not occur, and thus, a reduction in a transmission interval at which the RA message is transmitted causes waste of wireless channel bandwidth. In contrast, if a mobile node located in a cell managed by APs B412and C413on the edge of the subnet A moves in the cell, handover is very likely to occur, and thus, smooth handover is not guaranteed if the transmission interval of the RA message is increased.

FIG. 5is a diagram of a wireless network environment established between ARs according to an exemplary embodiment of the present invention. Referring toFIG. 5, the wireless network environment is designed based on the wireless network environment ofFIG. 3, in which all APs store a RA message from an AR A51or an AR B52without broadcasting it.

In particular, even if a mobile node located in a cell managed by an AP A511in the center of a subnet A moves in the cell, handover does not occur, and thus, the AP A511increases a transmission interval in which the RA message is transmitted. In contrast, if a mobile node located in a cell managed by an edge AP B512and an edge AP C513in the subnet A moves in the cell, handover is very likely to occur, and thus, the edge AP B412and edge AP C413reduces the transmission interval of the RA message.

FIG. 6is a block diagram of an apparatus that receives and transmits an RA message and a router solicitation (RS) message according to an exemplary embodiment of the present invention. Referring toFIG. 6, the apparatus is included in an AP62that manages one of a plurality of cells constituting a subnet. The apparatus includes a message determination unit621, an RA update unit622, an RA storage unit623, an edge AP determination unit624, an edge count value controller625, an RA transmission interval computing unit626, an RA elapsed time measurement unit627, an RA/RS transmission determination unit628, a wired network interface629, and a wireless network interface6210.

The message determination unit621determines the type of message received via the wired network interface629or the wireless network interface6210. The message determination unit621also determines whether the message received via the wired network interface629is an RA message that contains information regarding a subnet or whether the message received via the wireless network interface6210is an RS message requesting the RA message. The RA message is provided by an AR61and contains information regarding a subnet A. The RS message is transmitted to request the RA message.

Also, when the message determination unit621determines that the message received via the wired network interface629is an RA message, the message determination unit621compares the received RA message with an RA message stored in the AP62, i.e., an RA message stored in the RA storage unit623, and determines whether the original RA message has been changed according to the comparison result. That is, the message determination unit621compares the RA message received via the wired network interface629with an RA message stored in the RA storage unit623, and determines that the original RA message has been changed when the received RA message is different from the stored RA message.

When the message determination unit621determines that the message received via the wired network interface629is an RA message, the RA update unit622updates the RA message stored in the RA storage unit623with the received RA message.

When the message determination unit621determines that the message received via the wired network interface629is an RS message, the edge AP determination unit624determines whether the AP62is an edge AP located at the boundary between the subnet A and a neighboring subnet, based on the information contained in the received RS message. In particular, according to an exemplary embodiment of the present invention, the edge AP determination unit624determines whether the AP62is an edge AP located at the boundary between the subnet A and the neighboring subnet, based on the source address of the received RS message, i.e., the address of a site where the received RS message is transmitted.

If the AP62is an edge AP located at the boundary between the subnet A and the neighboring subnet, the AP62may receive a RS message from a mobile node in the subnet A or a mobile node in the neighboring subnet. However, if the AP62receives the RS message from the mobile node in the neighboring subnet, the subnet of the source address of the RS message is different from the subnet A in which the AP62is located. Specifically, the edge AP determination unit624compares the subnet of the source address of the RS message with the subnet A in which the AP62is located, and determines that the AP62is an edge AP located at the boundary between the subnet A and the neighboring subnet when the subnets are not the same.

Whenever the edge AP determination unit624determines that the AP62is an edge AP, the edge count value controller625increases an edge count value indicating the number of boundaries, between neighboring subnets and the subnet A, at which the AP62is located. A large edge count value indicates that the AP62receives RS messages from mobile nodes being respectively located in a large number of neighboring subnets of the subnet A, and a small edge count value indicates that the AP62receives RS messages from mobile nodes being respectively located in a small number of neighboring subnets of the subnet A.

The edge count value controller625also determines whether the amount of time, during which the edge AP determination unit624consecutively determines that the AP62is not an edge AP, reaches an edge threshold time, and reduces the edge count value when the amount of the time reaches the edge threshold time. The amount of time, during which the edge AP determination unit624consecutively determines that the AP62is not an edge AP, reaches an edge threshold time when there is no mobile node entering the subnet A from any one of the neighboring subnets for the edge threshold time, or when any mobile node entering the subnet A from the neighboring subnet(s) does not transmit the RS message for the edge threshold time. In particular, in the former case, the AP62is not an edge AP, and in the latter case, the AP62is an edge AP but a current transmission interval at which the RS message is transmitted is so short that the AP62need not transmit the RS message.

The RA transmission interval computing unit626computes the transmission interval of the RA message by the equation given below. In particular, the edge count value is initially set to 1, and when the transmission interval of the RA message is computed by the following equation, the edge count value controller625increases or reduces the edge count value of 1.
RA transmission interval=basic transmission interval/(predetermined weight×edge count value)  (1)

That is, the RA transmission interval computing unit626computes the transmission interval of the RA message by dividing the basic transmission interval of the RA message by a product of the predetermined weight and the edge count value that is increased or reduced by the edge count value controller625. Here, the basic transmission interval indicates a transmission interval of the RA message applied to a general AP according to the mobile internet protocol (MIP). The predetermined weight indicates a value that can be suitably adjusted for a wireless network environment according to an exemplary embodiment of the present invention. For example, if the load on communications established in the wireless network environment according to an exemplary embodiment of the present invention is great, the predetermined weight is set to a value larger than 1 so as to reduce the transmission interval of the RA message. If the load on the communications is not great, the predetermined weight is set to a value smaller than 1 so as to increase the transmission interval of the RA message.

When the wireless network interface6210receives an RS message, the RA elapsed time measurement unit627measures an amount of time elapsed from a point of time when the RA message stored in the AP62(the RA message stored in the RA storage unit623) was received.

If the elapsed amount of time measured by the RA elapsed time measurement unit627is less than an elapsed threshold time, the RA/RS transmission determination unit628determines that the RA message stored in the RA storage unit623is to be transmitted to the mobile node transmitting the RS message. Also, if the elapsed amount of time is greater than the threshold time, the RA/RS transmission determination unit628determines that the RS message is to be transmitted to the AR61which is the original destination router. Here, the threshold time may be the transmission interval of the RA message computed by the RA transmission interval computing unit626, or may be another value.

The wired network interface629periodically receives the RA message from the AR61. Also, the wired network interface629selectively transmits the RS message to the AR61which is the original destination, based on the elapsed amount of time measured by the RA elapsed time measurement unit627. In detail, when the RA/RS transmission determination unit628determines that the RS message is to be transmitted to the AR61, the wired network interface629transmits the RS message from the mobile node to the AR61. A wired broadcast method is performed to receive and transmit messages via the wired network interface629, but it would be apparent to those of ordinary skill in the art that another method may be performed in this case.

The wireless network interface6210receives the RS message from a mobile node. Also, the wireless network interface6210transmits the RA message stored in the AP62(the RA message stored in the RA storage unit623) to the mobile node during the transmission interval computed by the RA transmission interval computing unit626.

However, when the message determination unit621determines that the RA message has been changed, the wireless network interface6210transmits the RA message during the basic transmission interval so that the mobile node can receive the RA message during the basic transmission interval according to the MIP, thereby allowing the apparatus ofFIG. 6to operate completely according to the MIP.

Also, the wireless network interface6210selectively transmits the RA message to the mobile node transmitting the RS message, based on the elapsed amount of time measured by the RA elapsed time measurement unit627. More specifically, when the RA/RS transmission determination unit628determines that the RA message is to be transmitted, the wireless network interface6210transmits the RA message stored in the AP62(the RA message stored in the RA storage unit623) to the mobile node. In general, a wireless broadcast method is used to transmit and receive messages via the wireless network interface6210, but it would be apparent to those of ordinary skill in the art that another method may be performed in this case.

FIG. 7is a flowchart illustrating a method of processing an RA message according to an exemplary embodiment of the present invention. Referring toFIG. 7, the method includes operations performed by the AP62illustrated inFIG. 6according to time series. Thus, although not described here, the above operation of the AP62with reference toFIG. 6is also applicable to the method ofFIG. 7.

Referring toFIGS. 6 and 7, in operation71, the AP62receives an RA message from the AR61.

In operation72, the AP62compares the RA message received in operation71with a RA message stored in the AP62(the RA message stored in the RA storage unit623).

In operation73, if the comparison result in operation72reveals that the RA messages are not the same, the AP62performs operation74, and if the RA messages are the same, the AP62performs operation75.

In operation74, the AP62transmits the RA message during a basic transmission interval.

In operation75, the AP62updates the RA message stored in the AP62(the RA message stored in the RA storage unit623) with the RA message received in operation71.

FIG. 8is a flowchart illustrating a method of processing an RS message according to an exemplary embodiment of the present invention. Referring toFIG. 8, the method includes operations performed by the AP62illustrated inFIG. 6according to time series. Thus, although not described here, the above operation of the AP62with reference toFIG. 6is also applicable to the method ofFIG. 8.

Referring toFIGS. 6 and 8, in operation81, the AP62receives an RS message from the mobile node63.

In operation82, the AP62compares the address of a subnet via which the RS message received in operation81was transmitted with the address of a subnet A in which the AP62is located.

In operation83, if the comparison result in operation82reveals that the addresses are not the same, the AP62determines the AP62as an edge AP being located at the boundary between the subnet A and a neighboring subnet, and performs operation84. If the addresses are the same, the AP62performs operation85.

In operation84, the AP62increases an edge count value indicating the number of boundaries, between neighboring subnets and the subnet A, the AP62is located.

In operation85, the AP62determines whether the amount of time during which the AP62is consecutively determined not to be an edge AP, reaches an edge threshold time. If the amount of time reaches the edge threshold time, the AP62performs operation86. If the amount of time does not reach the edge threshold time, the method is completed.

In operation86, the AP62reduces the edge count value.

In operation87, the AP62computes a transmission interval of the RA message by dividing a basic transmission interval of the RA message by a product of a predetermined weight and the edge count value that is increased in operation84or reduced in operation86.

Referring toFIG. 8, the following operations are performed together with operations82through87.

In operation88, the AP62measures an amount of time elapsed from a point of time when the RS message stored in the AP62(the RA message stored in the RA storage unit623) was received.

In operation89, the AP62determines whether the elapsed amount of time measured in operation88is less than an elapsed threshold time. The AP62performs operation810when the elapsed amount of time is less than the threshold time, and performs operation812when the elapsed amount of time is otherwise.

In operation810, the AP62determines the RA message stored in the AP62(the RA message stored in the RA storage unit623) is to be transmitted.

In operation811, the AP62transmits the RA message stored in the AP62(the RA message stored in the RA storage unit623) to the mobile node63.

In operation812, the AP62determines that the RS message from the mobile node63is to be transmitted to the AR61which is the original destination.

In operation813, the AP62transmits the RS message to the AR61.

FIG. 9is a flowchart illustrating a method of transmitting an RA message according to an exemplary embodiment of the present invention. Referring toFIG. 9, the method includes operations performed by the AP62ofFIG. 6according to timing series. Therefore, although not described here, the above operation of the AP62with reference toFIG. 6is also applicable to the method ofFIG. 9.

Referring toFIGS. 6 and 9, in operation91, the AP62determines whether a current transmission interval of an RA message reaches the same amount of time as a transmission interval of a RA message computed by Equation (1). If the current transmission interval reaches the same amount of time as the computed transmission interval, operation92is performed. If the current transmission interval does not reach the same amount of time as the computed transmission interval, the method is completed.

In operation92, the AP62transmits an RA message stored therein (the RA message stored in the RA storage unit623) to a mobile node.

The above exemplary embodiments of the present invention may be embodied as a computer readable program, and realized in a general digital computer that can execute the program via a computer readable medium.

Examples of the computer readable medium include a magnetic storage medium (a ROM, a floppy disk, a hard disc, etc.), an optical recoding medium (a CD-ROM, a DVD, etc.), and even carrier waves (such as in transmission over the Internet).

According to an exemplary embodiment of the present invention, a transmission interval at which an RA message is transmitted is determined according to whether an AP is an edge AP. Therefore, the transmission interval is increased in a region in which handover is not likely to occur, and reduced in a region in which handover is likely to occur, thereby minimizing waste of wireless channel bandwidth and guaranteeing smooth handover in a mobile node. Accordingly, it is possible to efficiently use wireless resources and reduce a length of time needed for handover, thereby maximizing the throughput of the overall communications network.