CN1700669A - Fast handover method for IEEE 802.11 wireless lan networks - Google Patents

Abstract

A fast handover method optimized for IEEE 802.11 networks. In a wireless local area system including a mobile terminal and at least two wireless access points (APs) communicating with the mobile terminal through a unique wireless channel, the fast handover method includes: receiving beacons from neighbor APs and serving APs of the mobile terminal frame signal; generate a first signal based on the beacon frame signal received from each neighbor AP to determine the status of each neighbor AP; compare the first signal and a predetermined threshold; divide the neighbor AP into detected APs, candidate APs and The target AP stores the classification result in a neighbor AP list; and selects an AP for handover based on the classification result of the neighbor AP list.

Description

A fast handover method optimized for IEEE 802.11 networks

technical field

The present invention generally relates to a fast handover method. More particularly, the present invention relates to an Institute of Electrical and Electronics Engineers (IEEE) 802.11 network optimized fast handover method for supporting fast handover of a node through pre-operation for fast handover.

Background technique

Recently, with rapid growth of Internet applications, development of wireless communication technology, and improvement in performance of mobile terminals such as portable computers and personal digital assistants (PDAs), a large number of users use wireless Internet. In a wireless Internet environment, a mobile terminal changes its network point of attachment from time to time due to location movement.

In order for a mobile terminal to perform wireless Internet communication, even when the mobile terminal moves from its home network to a foreign network, high-quality Internet service similar to its home network should be guaranteed. Regarding the mobile terminal changing its network point of attachment, various techniques have been proposed to provide stable wireless Internet service. In particular, the Mobile IP working group of the Internet Engineering Task Force (IETF) has proposed a method in which all mobile terminals can continuously use a specific identifier called an IP address regardless of a network attachment point. The mobile IP working group has defined the mobile IP agreement, and tries to make up for the shortcoming. Also, in order to overcome the problem that the existing IPv4 address system cannot accept the demand for more address growth, Mobile IPv6 technology is being introduced to provide wireless Internet services using IPv6. Since Mobile IPv6 has been introduced, this system has been revised into IETF Internet Draft Version 24, and this system is being planned as an Internet Standard Draft (RFC) system.

According to the mobile IPv6 technology, even when the mobile terminal moves to a foreign network, the mobile terminal still communicates with the corresponding node (CN) through the home agent (HA) using its home address (HA). The HA is a router with registration information of the mobile terminal. When the mobile terminal is connected to a foreign network, the access router of the foreign network assigns a care_of address (CoA) to the mobile terminal as a temporary address, and the mobile terminal registers the assigned CoA with the local address in the home agent In , this is called binding.

Accordingly, the home agent intercepts packets from the corresponding node to the mobile terminal and forwards the intercepted packets to the mobile terminal located in the foreign network using the current CoA of the mobile terminal.

To be assigned a CoA, the mobile terminal establishes a link-layer connection to the foreign network and then receives a Router Advertisement (RA) message from a router of the foreign network. To this end, the mobile terminal can multicast a route request message to the entire network.

Router Advertisement messages provide prefix information for networks. Thus, the mobile terminal generates a new CoA using the network's prefix information and its link layer address (LLA). The mobile terminal sets the generated CoA as its temporary address.

A time delay between 0 and 1 second should be implemented when it is not possible to determine whether the CoA results from the mobile terminal moving to another network or from a reset of the mobile terminal's network interface.

Next, the mobile terminal multicasts a Neighbor Solicitation message including its LLA to the newly linked network, and starts Duplicate Address Detection (hereinafter, referred to as DAD).

If a neighbor advertisement notifying the duplicate address is not received at the mobile terminal within a predetermined time limit (retransmission timer), the corresponding CoA is regarded as a unique CoA, and the mobile terminal uses this unique CoA for network communication. The predetermined time limit defaults to 1000ms.

According to the Mobile IPv6 standard, when a mobile terminal acquires a new link, that is, when the mobile terminal moves to a new IP subnet, fast handover in Mobile IPv6 (FMIPv6) has been proposed as a way to minimize handover delay and packet loss protocol, planning it as an RFC in time.

However, there are considerable problems with FMIPv6, which uses a large amount of handover-related signaling. In particular, FMIPv6 is in the process of being standardized and not optimized for IEEE 802.1x networks. The problems of the conventional fast IPv6 handover method are explained below.

First, it is assumed that conventional fast IPv6 handover is performed in pre-activation mode based on movement prediction. However, it is not clearly specified when the mobile terminal performs Layer 2 handover when the movement prediction is successful in the link before the movement. As such, packet loss may occur when layer 2 handover is not performed correctly after a packet tunneling request message is sent to layer 3.

Movement prediction is broadly divided into movement detection, and new CoA configuration and confirmation. Since the traditional fast IPv6 handover performs two processes respectively, the pre-operation of the handover requires quite a long time, and the chance of successful handover based on prediction is also reduced.

When generating its temporary address for a new link, the mobile terminal needs about 1000ms to check for address duplication. This required time presents the most serious problem for fast switching.

Contents of the invention

An aspect of the present invention that addresses the above and other problems and shortcomings that arise in conventional configurations, provides a method for fast handover optimized for IEEE 802.11 networks in order to enable mobile terminals to adopt Internet Protocol Version 6 (IPv6) is used as the basic stack of the network layer to provide fast IPv6 switching services.

In order to achieve the above aspects and/or features of the present invention, in a wireless local area network including a mobile terminal and at least two wireless access points (APs) communicating with the mobile terminal through a unique wireless channel, the mobile terminal performs fast handover The method includes: receiving a beacon frame signal from a neighbor AP and a serving AP of the mobile terminal; generating a first signal based on the beacon frame signal received from each neighbor AP to determine the status of each neighbor AP; comparing the first signal with a predetermined The threshold of the neighbor AP is divided into detected AP, candidate AP and target AP according to the comparison result, and the classification result is stored in the neighbor AP list; and the AP for handover is selected based on the classification result in the neighbor AP list.

When the strength of the first signal detected from the serving AP is lower than the first threshold THR_1, the handover preparation phase may start.

The handover preparation stage can be divided into the situation when the serving AP currently communicating with the mobile terminal and the neighbor AP establishing new communication with the mobile terminal belong to different subnets, and the situation when the serving AP currently communicating with the mobile terminal and the neighbor AP establishing a new communication with the mobile terminal belong to different subnets. This is the case when the communicating neighbor APs belong to the same subnet.

The handover preparation phase may include: (a) sending Link_Quality_Crosses_Threshold (LQCT) trigger information from layer 2 to layer 3; (b) selecting a candidate AP and a target AP as neighbor APs capable of establishing new communication with the mobile terminal from the neighbor AP list , and retrieve information related to the selected candidate AP and target AP; (c) when the neighbor AP capable of establishing new communication with the mobile terminal and the serving AP currently communicating with the mobile terminal belong to different subnets, according to the Information retrieval sends the medium access control (MAC) address of the mobile terminal, the basic service set identifier (BSSID) of the candidate AP and the target AP, and the fast binding update (FBU) message from the mobile terminal to the management system of the subnet to which the mobile terminal belongs. access router; (d) send the MAC address of the mobile terminal and a handover initiation (HI) message from the access router that manages the subnet of the mobile terminal to the routers connected to the candidate AP and the target AP respectively; (e) send the message in response to the HI HAck message, Router Advertisement (RA) message, and Ω with the guaranteed unique temporary address of the message are sent from the router connected to the candidate AP and the target AP to the access router managing the subnet of the mobile terminal; and (f) combined from the connected The routers to the candidate AP and the target AP receive the RA message and Ω, and send the combined message to the mobile terminal together with a Fast Binding Acknowledgment (FBAck) message.

(f) The completion of the operation may mean the completion of the handover preparation phase, and the timer runs for a predetermined time from the completion of the handover preparation phase.

When the strength of the first signal is lower than the first threshold THR_2 detected by the serving AP within the predetermined time, the mobile terminal may enter the handover action phase.

The handover action phase may include: (a) sending a Link_GoingDown (LGD) trigger message from Layer 2 to Layer 3; (b) sending a Mobile Notification (MVN) message from the mobile terminal to an access router managing the subnet of the mobile terminal and including Ω of the unique temporary address; and (c) encapsulation by the access router managing the subnet of the mobile terminal, and sending a MVAck message from the access router to the mobile terminal in response to the MVN message.

When the MVAck message is received at the mobile terminal, (c) operation may send Link_Switch (LS) trigger information from layer 3 to layer 2.

After sending the LS trigger information from layer 3 to layer 2, the handover action phase may further include: attempting to re-associate to the target AP selected from the candidate APs in the neighbor AP list; when re-association is completed, sending from layer 2 to layer 3 Link_Up trigger message; configure the mobile terminal with the new temporary address and RA message contained in Ω obtained from the previous subnet; send a Fast Neighbor Advertisement (FNA) message from the mobile terminal to the access router connected to the target AP; and The packets tunneled by routing in the access router receiving the FNA message are sent to the mobile terminal.

The handover preparation phase may include: (a) sending LQCT trigger information from layer 2 to layer 3; (b) selecting candidate APs and target APs as neighbor APs capable of establishing new communication with the mobile terminal from the neighbor AP list, and retrieving Information related to the selected candidate AP and the target AP; (c) when the neighbor AP capable of establishing new communication with the mobile terminal belongs to the same subnet as the mobile terminal, retrieve the information from the mobile terminal to manage the mobile terminal according to the information The access router of the terminal subnet sends the MAC address of the mobile terminal, the BSSID of the candidate AP and the target AP, and the FBU message; and (d) sends an FBAck in response to the FBU message to the mobile terminal from the access router managing the mobile terminal subnet information.

(d) The completion of the operation may mean the completion of the handover preparation phase, and the timer runs for a predetermined time from the completion of the handover preparation phase.

When the strength of the first signal detected by the serving AP within a predetermined time is lower than the second threshold THR_2, the mobile terminal may enter a handover action phase.

The handover action phase may include: (a) sending LGD trigger information from Layer 2 to Layer 3; (b) sending MVN messages from the mobile terminal to the access router that manages the mobile terminal subnet; The access router of the network caches, and the MVAck message in response to the MVN message is sent from the access router to the mobile terminal.

Operation (c) may send LS trigger information from layer 3 to layer 2 when the MVAck message is received at the mobile terminal.

After sending the MVN message in (b) operation, the handover action phase may further include: when the mobile terminal does not receive the MVAck message from the access router within about 10 ms, retransmit the MVN message; and when the MVN message is retransmitted When no MVAck message is received within 10ms, the LS trigger information is sent from layer 3 to layer 2.

Additional and/or other aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be acquired by practice of the invention.

Description of drawings

These and/or other aspects and advantages of the present invention will become apparent and easier to understand according to the description of the following embodiments in conjunction with the accompanying drawings, wherein:

FIG. 1 is a block diagram of a mobile terminal for fast handover optimized to an IEEE 802.11 network according to an embodiment of the present invention;

FIG. 2A is a graph showing changes in SNR values received from neighboring APs of a mobile terminal;

2B to 2E are graphs showing changes in smoothed SNR calculated by information processing in the first signal processor or the second signal processor;

3 is a schematic diagram illustrating state changes of mobile terminal neighbor APs according to changes in SNR;

FIG. 4 is a graph illustrating SNR variation of neighbor APs over time;

FIG. 5 is a graph illustrating when a handover preparation phase is performed according to an embodiment of the present invention;

6 is a flowchart explaining the handover preparation phase when the serving AP currently communicating with the mobile terminal and the neighbor AP that can establish new communication with the mobile terminal belong to different subnets;

7 is a flowchart explaining the handover preparation phase when the serving AP currently communicating with the mobile terminal and the neighbor AP that can communicate with the mobile terminal belong to the same subnet;

8A and 8B further detail the handover preparation phase;

9A to 9C describe three kinds of moving paths of the mobile terminal during handover;

Fig. 10 is a graph showing when to perform a switching action phase;

11 is a flow chart explaining the handover action stages when the mobile terminal communicates with a target AP belonging to a different subnet; and

FIG. 12 is a flowchart explaining the stages of handover actions when the mobile terminal communicates with a target AP belonging to the same subnet.

Detailed ways

Reference will now be made in detail to embodiments of the invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.

FIG. 1 is a block diagram of a mobile terminal for a fast handover method optimized for an Institute of Electrical and Electronics Engineers (IEEE) 802.11 network according to an embodiment of the present invention. In FIG. 1, the mobile terminal 100 includes: a first transceiver 10, a second receiver 20, a first signal processor 30, a second signal processor 35, a comparator 40, a timer part 50, a neighbor access point ( AP) list manager 60 , memory 70 , and controller 80 . It is to be understood that the mobile terminal 100 may include other components than those mentioned above.

The first transceiver 10 receives data from an AP that is currently communicating with the mobile terminal 100 (hereinafter referred to as a serving AP) through a data channel, provides the received data to the first signal processor 30, and wirelessly transmits a signal intended for serving AP data. The first transceiver 10 communicates with the serving AP according to IEEE 802.11.

The second receiver 20 receives beacon frame signals transmitted from neighbor APs of the mobile terminal 100 at intervals of 100 ms through a control channel, and provides the received beacon frame signals to the second signal processor 35 . The mobile terminal 100 receives beacon frame signals from the AP at certain intervals (for example, 100 ms intervals). Even when the mobile terminal 100 requests a beacon frame signal from a neighbor AP, the mobile terminal 100 may receive the beacon frame signal. An advantage is that the second receiver 20 is implemented using a scouter module. The second receiver 20 has two modes: active mode for scanning neighbor APs and idle mode for suspending scanning.

The first signal processor 30 processes data provided from the first transceiver 10 and forwards the processed data to the controller 80 and the comparator 40 . Specifically, the first signal processor 30 processes a certain parameter contained in the beacon frame signal received from the first transceiver 10, and provides the comparator 40 with a service useful for determining the current communication with the mobile terminal 100. AP wireless channel status data.

Also, the second signal processor 35 processes a certain parameter contained in the beacon frame signal received from the second receiver 20, and provides the comparator with data helpful for determining the wireless channel status of the neighbor APs of the mobile terminal 100 . The certain parameter may be a signal-to-noise ratio (SNR), a received signal strength indicator (RSSI), a bit error rate (BER), and/or a packet error rate (PER), or a combination thereof. In the embodiment of the present invention, the SNR is used to determine the wireless channel status of the neighbor AP of the serving AP currently communicating with the mobile terminal 100 and the wireless channel status of the neighbor AP of the mobile terminal 100 . The first signal processor 30 and the second signal processor 35 process the SNR contained in the beacon frame signal and obtain a smoothed SNR according to Equation 1. The obtained smoothed SNR can be used instead of the SNR.

[equation 1]

Smoothed SNR = K x SNR _c + (1-k) SNR _p .

In Equation 1, K is a variable, SNR _c is the SNR value measured at the current time, and SNR _p is the SNR value measured at the time of the previous cycle.

FIG. 2A is a graph showing changes in SNR values received from neighbor APs of the mobile terminal 100, and FIGS. 2B to 2E show smoothing obtained by signal processing in the first signal processor 30 and the second signal processor 35. changes in the SNR value. Figures 2B to 2E show a more stable change in SNR compared to Figure 2A. Therefore, it is possible to easily determine the wireless channel state of the neighboring APs of the mobile terminal 100 based on the change of the SNR value.

The comparator 40 compares the SNR value or the smoothed SNR value provided by the first and second signal processors 30 and 35 with thresholds prestored in the memory 70, and provides the comparison result to the neighbor AP list manager 60 and controller 80 .

The neighbor AP list manager 60 classifies the neighbor APs into detected APs, candidate APs, and target APs based on the comparison result received from the comparator 40 . The neighbor AP list manager 60 updates the neighbor AP list stored in the memory 70 according to the classification. Neighbor AP list manager 60 updates the neighbor AP list stored in memory 80 if the status of the neighbor APs is changed, for example, if a detected AP transitions to a candidate AP, or if a candidate AP transitions to a target AP. A detected AP is the only AP whose signal is detected without guaranteed wireless channel quality. The candidate AP has a wireless channel quality guaranteed to some extent, and the target AP has the maximum value of signals detected from neighbor APs, that is, the maximum SNR value. As will be illustrated, it is possible to resume communication with the mobile terminal 100 between the candidate AP and the target AP.

The timer section 50 is configured with a plurality of timers corresponding to neighbor APs of the mobile terminal 100 . Each timer starts counting from the time when a beacon frame signal is received from a neighbor AP within an interval of 100 ms. When a beacon frame signal is not received from a neighbor AP within an interval of 100 ms, the timer section 50 notifies the neighbor AP list manager 60 that a beacon frame signal is not received. Accordingly, the neighbor AP list manager 60 updates the neighbor AP list stored in the memory 70, as will be explained in further detail later. If no beacon frame signal is received from the neighbor AP at all, the timer section 50 notifies the neighbor AP list manager 60 of this fact, and the neighbor AP list manager 60 deletes the neighbor AP from the neighbor AP list.

The controller 80 analyzes a wireless channel state of a serving AP currently communicating with the mobile terminal 100 by using data received from the first signal processor 30 . If according to the analysis, the wireless channel status of the serving AP is normal, then the controller 80 continues to receive data from the serving AP. Otherwise, if the state of the wireless channel is not normal, the controller 80 starts the switching operation.

Specifically, when the SNR detected from the serving AP currently communicating with the mobile terminal 100 is lower than a predetermined first threshold THR_1, the controller 80 controls the mobile terminal 100 to enter a handover preparation phase. When the SNR detected from the serving AP is lower than a predetermined second threshold THR_2, the controller 80 controls the mobile terminal 100 to be handed over. When the detected SNR is lower than a predetermined third threshold THR_3, the controller 80 interrupts the communication between the mobile terminal 100 and the serving AP. Or the controller tries to reconnect to the serving AP.

FIG. 3 depicts state changes of neighbor APs of the mobile terminal 100 according to SNR changes. In FIG. 3, the first threshold THR_1 is greater than the second threshold THR_2.

Referring to FIG. 3 , the initially detected SNR from the neighbor AP is lower than the predetermined second threshold THR_2. In this case, it is assumed that a neighbor AP is a detected AP (S300). If a beacon frame signal is not received from a neighbor AP within 100 ms in the detected AP state (S310), the neighbor AP list manager 60 controls the neighbor APs to maintain the detected AP state (S300). If a beacon frame signal is not received at all from a neighbor AP even within 300 ms, the neighbor AP list manager 60 deletes the neighbor AP from the neighbor AP list stored in the memory 70 .

In the detected AP state (S300), when the SNR indicating the channel state of the neighbor AP is greater than the predetermined second threshold THR_2, the neighbor AP list manager 60 changes the state of the detected AP to the first candidate AP state (S320). If the SNR indicating the channel state of the detected AP is greater than the predetermined first threshold THR_1, the neighbor AP list manager 60 changes the state of the detected AP to the second candidate AP state (S330).

First, the first candidate AP status is explained. Regarding the first candidate AP state in operation S320, the SNR detected from the neighbor AP is greater than the second threshold THR_2 (S320). In this state, the SNR detected from the neighbor AP is lower than the second threshold THR_2 again, and the state of the neighbor AP returns from the first candidate AP state (S320) to the detected AP state (S300). Thus, in the neighbor AP list stored in the memory 70, the current status of the neighbor AP is changed from the first candidate AP to the detected AP again.

Meanwhile, in the first candidate AP state in operation S320, when the SNR detected from the neighbor AP of the mobile terminal 100 increases and indicates the maximum value among other neighbor APs, the neighbor AP list manager 60 changes the state of the neighbor AP from the first to the second. A candidate AP state (S320) is changed to a target AP state (S340), and the neighbor AP list stored in the memory 70 is updated.

If the SNR indicating the channel state of the target AP (S340) decreases such that the SNR is lower than the SNR detected from other neighboring APs (S350a), or if the second receiver 20 of the mobile terminal 100 does not receive any signal from the other AP (S350a) more than once within the 100 ms interval The target AP receives the beacon frame signal (S350b), then the target AP (S340) changes to the second candidate AP state (S330).

Next, the second candidate AP state (S330) is explained in detail below. When the state is changed from the target AP state (S340) as described above and when the SNR indicating the detected AP channel state also exceeds the first threshold THR_1, the second candidate AP state is determined (S330).

In the second candidate AP state (S330), when the SNR detected from the second candidate AP exceeds the SNR detected from other neighbor APs, the second candidate AP state (S330) returns to the target AP state (S340).

Otherwise, in the second candidate AP state (S330), when the SNR is lower than the first threshold THR_1 (S360a), or when the second receiver 20 of the mobile terminal 100 does not receive a beacon frame signal from the candidate AP more than once ( S360b), the state of the neighbor AP is changed from the second candidate AP state (S330) to the detected AP state (S300).

Figure 4 is a graph showing the SNR variation of neighbor APs over time. In FIG. 4 , AP1 , AP2 , and AP3 represent neighbor APs of the mobile terminal 100 .

As shown in FIG. 4 , the SNR detected from AP1 exceeds a predetermined first threshold THR_1 and is the maximum value among SNRs detected from other neighboring APs at time T1 . In this way, AP1 enters the target AP state. The detected SNRs from AP2 and AP3 are lower than a predetermined second threshold THR_2, thus, AP2 and AP3 maintain the detected AP state.

At time T2, when the SNR detected from AP2 exceeds the second threshold THR_2, the status of AP2 is changed from detected AP to candidate AP. At time T3, the mobile terminal 100 fails to receive a beacon frame signal from AP1 within a specified time, ie, within 100 ms. At time T3, AP1 changes from a target AP to a candidate AP, and thus, the state of AP2 changes from a candidate AP state to a target AP state.

At time T4, the mobile terminal 100 receives a beacon frame signal from AP1, and the SNR detected from AP1 is the maximum value. In this way, the state of AP1 is returned from the candidate AP to the target AP, and the state of AP2 is returned from the target AP to the candidate AP.

At time T5, when the SNR detected from AP2 exceeds the SNR detected from AP1 and becomes the maximum value, AP2 becomes a target AP, and AP1 becomes a candidate AP. At time T6, the SNR detected from AP1 is lower than the second threshold THR_2, thus, AP1 becomes the detected AP.

The above states of neighbor APs from time T1 to T6 can be arranged in Table 1.

[Table 1] time 1 Target AP AP1 Candidate AP none Detected APs AP2, AP3 time 2 Target AP AP1 Candidate AP AP2 Detected APs AP3 time 3 Target AP AP2 Candidate AP AP1 (sync timeout) Detected APs AP3 time 4 Target AP AP1 (resync) Candidate AP AP2 Detected APs AP3 time 5 Target AP AP2 (exchange) Candidate AP AP1 Detected APs AP3 time 6 Target AP AP2 Candidate AP none Detected APs AP1, AP3

The neighbor AP list stored in the memory 70 is managed as described above.

The fast handover optimization method for IEEE 802.11 network according to the embodiment of the present invention mainly includes a handover preparation phase and a handover action phase. When the value indicating the channel state of the serving AP currently communicating with the mobile terminal 100, ie SNR, is lower than a predetermined first threshold THR_1, the handover preparation phase is performed. When the value indicating the channel state of the serving AP currently communicating with the mobile terminal 100—that is, the SNR—is lower than a predetermined second threshold THR_2, a handover action is performed. Note that, as explained above, the first threshold THR_1 is greater than the second threshold THR_2.

Next, the handover preparation phase and the handover action phase are explained in this order. Once the handover preparation phase starts, the mobile terminal 100 determines candidate APs, then retrieves information related to the determined candidate APs and target APs in a neighbor AP list managed therein, and obtains information on the candidate APs and target APs. Next, the mobile terminal 100 sends the fast binding update (FBU) message, the basic service set identifier (BSSID) of the target AP and the candidate AP, and its medium access control (MAC) address to its designated access router (AR). ).

FIG. 5 is a graph showing when the handover preparation phase is performed according to an embodiment of the present invention. In FIG. 5, when the SNR indicating the channel state of the serving AP currently communicating with the mobile terminal 100 is lower than the predetermined first threshold THR_1, a Link_Quality_Crosses_Threshold (LQCT) trigger message is sent from layer 2 to layer 3, and then handover preparation is performed. operate.

The handover preparation phase is carried out differently in different situations. For example, a case occurs when a serving AP currently communicates with the mobile terminal 100 and a neighbor AP (candidate AP or target AP) with which the mobile terminal 100 can perform new communication belongs to a different subnet. As another example, the second case occurs when the serving AP currently communicating with the mobile terminal 100 belongs to the same subnet as the neighbor AP (candidate AP or target AP) with which the mobile terminal 100 can perform new communication.

6 is a flowchart explaining when a serving AP currently communicating with the mobile terminal 100 and a neighbor AP (candidate AP or target AP) with which the mobile terminal 100 may establish new communication belong to different subnets.

Referring to FIG. 6, when the SNR indicating the channel state of the serving AP communicating with the mobile terminal 100 is lower than a predetermined first threshold THR_1, LQCT trigger information is transmitted from layer 2 to layer 3 (S610). The mobile terminal 100 transmits the FBU message, its MAC address, and the BSSIDs of the target AP and the candidate AP to an access router (hereinafter referred to as PAR for brevity) that manages the subnet to which the mobile terminal 100 belongs (S620). The BSSID of the AP contains the MAC address information of the AP.

Meanwhile, the locking operation is performed from when the mobile terminal 100 transmits the FBU message, its MAC address, and the BSSIDs of the candidate AP and the target AP. Once the locking operation is performed, even when a new candidate AP is found from among the neighbor APs of the mobile terminal 100, the neighbor AP list manager 60 cannot add the new candidate AP to the neighbor AP list stored in the memory 70, while Instead, the new candidate AP is inserted into the waiting queue. The mobile terminal 100 can only delete APs from APs arranged in the neighbor AP list, and determine a new target AP among candidate APs. When the target AP is determined and a Mobile Notification (MVN) message is sent to the target AP, or when a preset time has elapsed after the mobile terminal 100 receives a Fast Binding Acknowledgment (FBAck) message, the locking operation stops, which will A detailed description.

The PAR that receives information from the mobile terminal 100 checks the addresses of access routers (hereinafter referred to as NARs for brevity) respectively connected to target APs and candidate APs that can communicate with the mobile terminal 100 using the CAR table. Note that NAR and PAR belong to different subnets.

Table 2 shows a typical CAR table.

[Table 2] BSSID of the neighbor AP router address network prefix Survival time (s) 00:02:2D:46:47:23 3ffe:100::1 3ffe:100::/64 300 01:02:DD:26:10:09 3ffe:101::1 3ffe:101::/64 400 22:14:A1:AA:B2:1A 3ffe:101::1 3ffe:101::/64 400

In Table 2, the PAR can obtain the address of the router NAR connected to the neighbor AP, that is, the candidate AP and the target AP among the neighbor APs, which can communicate with the mobile terminal 100, based on the BSSID of the neighbor AP of the CAR table.

Next, the PAR transmits the MAC address of the mobile terminal 100 and a Handover Initiate (HI) message to the addresses of the routers NAR respectively connected to the candidate AP and the target AP (S630).

Upon receiving the MAC address of the mobile terminal 100 and the HI message from the PAR, the NAR sends to the PAR a Handover Acknowledgment (HAck) message in response to the HI message, a Router Advertisement (RA) message, and a temporary Ω of the message of the address (S640). At this time, if other mobile terminals join the subnet of the NAR, then the other mobile terminals can use Ω. To prevent this, each NAR protects Ω by using a Proxy NeighborCache Entry as described in RFC 2642.

Typically, each router generates a number of new temporary addresses suitable for the network prefixes managed by the router as described in RFC 3041, or obtains addresses from a DHCPv6 server. Generated or obtained addresses are checked for duplicates according to the standard Duplicate Address Detection (DAD) of RFC 2641. Unique addresses based on a duplicate check are stored in an address pool managed by the router. Ω is defined as a message containing one of a certain number of ephemeral addresses stored in an address pool with guaranteed uniqueness. According to the above explanation, acceptance of RA message and Ω at PAR means completion of motion detection and DAD.

The PAR managing the subnet of the mobile terminal 100 combines the RA message and Ω received from the NAR connected to the target AP and the candidate AP, and transmits the combined RA message and Ω to the mobile terminal 100 together with the FBAck message (S650). Upon receiving the combined RA message and Ω together with the FBAck message, the mobile terminal 100 terminates the handover preparation phase and operates the timer section 50 to count a predetermined time, for example approximately 3 seconds. When the predetermined time has elapsed, the aforementioned locking operation is stopped.

7 is a flowchart explaining a handover preparation phase when a serving AP currently communicating with the mobile terminal 100 and a neighbor AP that can communicate with the mobile terminal 100 belong to the same subnet.

Referring to FIG. 7, the SNR indicating the channel status of the serving AP communicating with the mobile terminal 100 is lower than the first threshold THR_1, generating an LQCT trigger (S710). Next, the mobile terminal 100 transmits the FBU message, its MAC address, and BSSIDs of candidate APs and target APs belonging to the same subnet as the serving AP communicating with the mobile terminal 100 to the AR connected thereto (S720).

Since the neighbor AP that can communicate with the mobile terminal 100 again and the mobile terminal 100 belong to the same subnet, IP handover is not necessary. But switching according to the specification of IEEE 802.11 is still required. In this way, the AR transmits an FBAck message to the mobile terminal 100 (S730), thereby completing the handover preparation operation. The mobile terminal 100 operates the timer section 50 to count a predetermined time, for example, approximately 3 seconds. When the predetermined time has elapsed, the aforementioned locking operation is terminated.

Figures 8A and 8B further detail the handover preparation phase. Among them, it is assumed that AP1 and AP4 each represent a candidate AP, AP3 represents a detected AP, and AP2 represents a target AP. The serving AP currently communicating with the mobile terminal 100 and AP1 as a candidate AP belong to the same subnet, and both are connected to the same second router R2. Likewise, AP3 as a detected AP and AP4 as a candidate AP belong to the same subnet and are connected to the same router, ie, the third router R3. AP2 is connected to a fourth router R4.

When the SNR detected from the serving AP communicating with the mobile terminal 100 is lower than the first threshold THR_1 and the LQCT trigger message is sent from layer 2 to layer 3, the mobile terminal 100 sends to the second router R2 managing the subnet of the mobile terminal 100 The FBU message, its MAC address, the BSSID of AP2 as the target AP, and the BSSIDs of AP1 and AP4 as candidate APs. When sharing the second router R2 with AP1 belonging to the same subnet as the serving AP communicating with the mobile terminal 100, AP2 and AP4 belonging to different subnets with the serving AP communicating with the mobile terminal 100 are respectively connected to the fourth router R4 and the third router R4. Router R3.

Since AP2 and AP4 belong to different subnets from the mobile terminal 100, the second router R2 sends the MAC address of the mobile terminal 100 to the fourth router R4 connected to AP2 as the target AP and the third router R3 connected to AP4 as the candidate AP and HI news. As for AP1 connected to the second router R2 located in the same subnet as the mobile terminal 100 , the second router R2 does not need to send the MAC address of the mobile terminal 100 and the HI message. Instead, the second router R2 sends an FBAck message to the mobile terminal 100 .

Upon receiving the MAC address of the mobile terminal 100 and the HI message from the second router R2, the fourth router R4 connected to AP2 as the target AP sends an HAck message in response to the HI message, an RA' message, and an Ω including the unique temporary address ' to the second router R2. Likewise, the third router R3 connected to AP4 as a candidate AP sends an HAck message in response to the HI message, an RA" message, and Ω" including a unique temporary address to the second router R2.

The second router R2 combines the HAck message, RA' message and Ω' received from the fourth router R4 connected to AP2 as the target AP with the HAck message, RA'' received from the third router R3 connected to AP4 as the candidate AP The message is combined with Ω″, and the combined message is sent to the mobile terminal 100 together with the FBAck message.

9A to 9C depict three moving paths of the mobile terminal 100 during handover. FIG. 9A depicts a switching action phase performed within a predetermined time, which is basically within 3 seconds counted by the timer section 50 after the switching preparation phase according to an embodiment of the present invention. Specifically, after the handover preparation phase is completed, the SNR detected from the serving AP is lower than the second threshold THR_2 within a predetermined time counted by the timer section 50 . The mobile terminal 100 normally enters the handover preparation phase. The mobile terminal 100 stops the locking operation on the candidate APs, and selects a target AP among the candidate APs.

FIG. 93 shows the case when the mobile terminal 100 does not enter the handover action phase within the predetermined time for 3 seconds counted by the timer section 50 after the handover preparation phase. After completing the handover preparation phase, when the SNR detected from the serving AP is not lower than the second threshold THR_2 and is between the first threshold THR_1 and the second THR_2 within the predetermined time counted by the timer part 50, the handover preparation phase is Restart after a predetermined time. The mobile terminal 100 updates candidate APs in the neighbor AP list based on the waiting queued AP list, and selects a target AP from the updated candidate APs. Next, the mobile terminal 100 resends the updated BSSIDs of the candidate AP and the target AP, the MAC address of the mobile terminal 100, and the FBU message to its AR.

FIG. 9C depicts handover initialization of the mobile terminal 100 . After the handover preparation phase is completed, when the SNR detected from the serving AP exceeds the first threshold THR_1 within a predetermined time for 3 seconds counted by the timer section 50, initialization is performed. During initialization, neighbor AP list manager 60 deletes all candidate APs and target APs from the neighbor AP list stored in memory 70 . Subsequently, the neighbor AP list is reorganized by comparing the SNR detected from the neighbor APs using the passive scan to a predetermined threshold.

Fig. 10 is a graph showing when switching action phases are performed. In FIG. 10 , when the SNR detected by the serving AP currently communicating with the mobile terminal 100 is lower than the second threshold THR_2, a LinkGoingDown (LGD) trigger message is sent from layer 2 to layer 3, and a switching action is performed at layer 3.

The handover action phase is similar to the handover preparation phase. Likewise, the handover action phase is performed depending on whether the target AP to communicate with the mobile terminal 100 and the mobile terminal 100 belong to the same subnet.

FIG. 11 is a flowchart explaining the handover action stages when the mobile terminal 100 communicates with a target AP belonging to a different subnet. Operations S610 to S650 in FIG. 11 are performed in the handover preparation phase, and thus are not shown here for brevity.

Referring to FIG. 11 , when the SNR detected from the serving AP currently communicating with the mobile terminal 100 is lower than the second threshold THR_2, LGD trigger information is transmitted from layer 2 to layer 3 (S1110). The mobile terminal 100 transmits a moving notification (MVN) message and Ω including a unique temporary address to the PAR managing the subnet of the mobile terminal 100 (S1120). The MVN message notifies the PAR of the movement of the mobile terminal 100 .

Upon receiving the MVN message and Ω (S1120), the PAR intercepts packets intended to be transmitted to the previous temporary address of the mobile terminal 100, and starts tunneling to the new temporary address contained in Ω (S1130). After encapsulation, the PAR transmits a MVAck message in response to the MVN message to the mobile terminal 100 (S1140).

Upon receiving the MVAck message, the mobile terminal 100 transmits link switching (LS) trigger information from layer 3 to layer 2 (S1150).

Meanwhile, in operation S1120, if the mobile terminal 100 does not receive the MVAck message within 10 ms after sending the MVN message to the PAR managing the subnet of the mobile terminal 100, the mobile terminal 100 resends the MVN message to the PAR. Even when the MVAck message is not received within 10 ms after retransmission, the mobile terminal 100 transmits LS trigger information from layer 3 to layer 2 (S1150). Also, when the SNR detected from the serving AP currently communicating with the mobile terminal 100 is lower than the third threshold THR_3, LS trigger information is transmitted from layer 3 to layer 2 (S1150). The third threshold THR_3 is lower than the first threshold THR_1 and the second threshold THR_2.

When the LS trigger information is transmitted from layer 3 to layer 2 (S1150), the mobile terminal 100 attempts to re-associate to the selected target AP (S1160).

After the reassociation is completed, Link_Up trigger information is sent from layer 2 to layer 3 (S1170). Next, the mobile terminal 100 is configured using the RA message received from the previous subnet and the new temporary address contained in Ω (S1180). In more detail, the mobile terminal 100 processes the RA received from the previous subnet as if the RA was normally received from the new NAR connected to the target AP. The mobile terminal 100 assigns to its interface the new temporary address contained in Ω received in the previous network.

Next, the mobile terminal 100 sends a Fast Neighbor Advertisement (FNA) message to the NAR connected to the target AP to inform the new network of the joining of the mobile terminal 100 (S1190).

The NAR receiving the FNA message transmits the packet encapsulated by the normal routing procedure to the mobile terminal 100 (S1195). If the FNA message is received from the mobile terminal 100, and at the same time, the NAR receives the packet encapsulated by the PAR and caches the packet intended to be transmitted to the new temporary address contained in Ω, then the cached packet is delivered to the mobile terminal 100 (S1195) . NAR changes the proxy neighbor cache to the normal neighbor cache and stops the Ω guard.

FIG. 12 is a flowchart explaining a handover action stage when the mobile terminal 100 communicates with a target AP belonging to the same subnetwork. Operations S710 to S730 in FIG. 12 are performed in the handover preparation stage, and thus are not illustrated for the sake of brevity.

Referring to FIG. 12, when the SNR detected from the serving AP currently communicating with the mobile terminal 100 is lower than the second threshold THR 2, LGD trigger information is sent from layer 2 to layer 3 (S1210). The mobile terminal 100 sends the MVN message to its AR (S1220). The AR receiving the MVN message starts caching (S1230) and sends a MVAck message to the mobile terminal 100 in response to the MVN message (S1240). Upon receiving the MVAck message, the mobile terminal 100 immediately transmits LS trigger information from layer 3 to layer 2 (S1250). In operation S1220, if the mobile terminal 100 does not receive the MVAck message within 10 ms after sending the MVN message to the AR managing the subnet of the mobile terminal 100, the mobile terminal 100 resends the MVN message to the AR. Even when the MVAck message has not been received within 10 ms after the retransmission, the mobile terminal 100 transmits LS trigger information from layer 3 to layer 2 (S1250). Also, when the SNR detected from the serving AP currently communicating with the mobile terminal 100 is lower than the third threshold THR_3, LS trigger information is transmitted from layer 3 to layer 2 (S1250). The third threshold THR_3 is lower than the first threshold THR_1 and the second threshold THR_2.

After transmitting the LS trigger information from layer 3 to layer 2 (S1250), the mobile terminal 100 attempts to re-associate to the selected target AP (S1260).

Once the re-association is completed, Link_Up trigger information is transmitted from layer 2 to layer 3 (S1270). Next, the mobile terminal 100 sends an FNA message to the AR (S1280). The AR receiving the FNA message forwards the buffered packet to the mobile terminal 100 (S1290). Therefore, a fast handover method optimized for IEEE 802.11 networks can be performed. The fast handover method has been illustrated for IEEE 802.11 networks in this embodiment, but is not limited to these networks. It should be understood that the fast handover method can be applied to other IEEE 802.1x networks.

As described above, since movement prediction and duplicate address detection are performed in a single process, fast switching can be achieved.

Compared with the prior art, packet loss can be prevented since switching in layer 2 is synchronized with packet encapsulation.

Furthermore, the locking operation is performed at a predetermined time from when the FBU message is sent to the candidate AP and the target AP, regardless of a new candidate AP discovered when the mobile terminal makes a sudden change to its moving path. Switching errors can thus be avoided.

Although several embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention. The scope is defined by the claims and their equivalents.

Claims (79)

1. A fast switching method for a mobile terminal in a wireless local area system, said wireless local area system comprising a mobile terminal and a plurality of wireless access points (APs), the plurality of wireless access points (APs) One of them is the serving AP currently communicating with the mobile terminal, and the other wireless access points in the plurality of wireless access points (AP) represent neighbor APs of the mobile terminal communicating with the mobile terminal through a unique wireless channel, so The methods described include: Receive beacon frame signals from neighbor APs and serving APs of the mobile terminal; generating a first signal based on beacon frame signals received from each neighboring AP to determine the status of each neighboring AP; Comparing the first signal with a predetermined threshold, classifying neighbor APs into detected APs, candidate APs, and target APs according to the comparison results, and storing the classification results in a neighbor AP list; and APs for handover are selected based on the classification results in the neighbor AP list. 2. The fast handover method according to claim 1, wherein the beacon frame signal is received from the AP to the mobile terminal at intervals. 3. The fast handover method according to claim 1, wherein the beacon frame signal is received from the AP to the mobile terminal when the mobile terminal requests the beacon frame signal. 4. The fast handover method according to claim 1 , wherein said first signal is one of Signal-to-Noise Ratio (SNR), Received Signal Strength Indication (RSSI), Bit Error Rate (BER), and Packet Error Rate (PER) . 5. The fast handover method according to claim 4, wherein, when the first signal is an SNR, the SNR is processed to generate a smooth SNR, the generated smooth SNR is compared with a predetermined threshold, and the neighbor APs are divided into Detected APs, candidate APs, and target APs. 6. The fast handover method according to claim 5, wherein said smooth SNR is obtained from the following equation: Smoothed SNR=K×SNR _c +(1-K)SNR _p , where K is the variable, SNR _c is the SNR measured at the current time, and SNR _p is the SNR measured at the previous time period. 7. according to the fast switching method of claim 1, wherein The predetermined thresholds include: a first threshold THR_1, a second threshold THR_2, and a third threshold THR_3, and The first threshold THR_1 is greater than the second threshold THR_2, and the second threshold THR_2 is greater than the third threshold THR_3. 8. The fast handover method according to claim 1, wherein the candidate AP and the target AP establish a new communication with the mobile terminal. 9. The fast handover method according to claim 1, wherein when the first signal is initially detected from the neighbor AP and the strength of the first signal detected from the neighbor AP is lower than the second threshold THR_2, it is determined that the neighbor AP is in the detected AP state. 10. The fast handover method according to claim 9, wherein, when the mobile terminal does not receive a beacon frame signal from the neighbor AP within a 100 ms interval more than once while the neighbor AP is in the detected AP state, the neighbor AP maintains the detected AP state. AP status. 11. The fast handover method according to claim 9, wherein when the mobile terminal does not receive a beacon frame signal from the neighbor AP more than once within 300 ms while the neighbor AP is in the detected AP state, the mobile terminal is deleted from the neighbor AP list The neighbor AP. 12. The fast handover method according to claim 9, wherein when the strength of the first signal detected from the neighbor AP exceeds the second threshold THR_2 while the neighbor AP is in the detected AP state, the neighbor AP is switched from the detected AP state to Change to the first candidate AP state. 13. The fast handover method according to claim 12, wherein, when the neighbor AP is in the first candidate AP state, the strength of the first signal detected from the neighbor AP exceeds the first signal detected from other neighbor APs of the mobile terminal. When the strength of the signal is high, the neighbor AP changes from the first candidate AP to the target AP state. 14. The fast handover method according to claim 12, wherein, when the strength of the first signal detected from the neighbor AP is lower than the second threshold THR_2 while the neighbor AP is in the first candidate AP state, the neighbor AP switches from the first candidate AP to A candidate AP state changes to the detected AP state. 15. The fast handover method according to claim 13, wherein, when the neighbor AP is in the target AP state, the intensity of the first signal detected from the neighbor AP is lower than that of the first signal detected from other neighbor APs of the mobile terminal Intensity, the neighbor AP changes from the target AP state to the second candidate AP state. 16. The fast handover method according to claim 13, wherein when the mobile terminal does not receive a beacon frame signal from the neighbor AP more than once within a 100 ms interval while the neighbor AP is in the state of the target AP, the neighbor AP is switched from the target AP The AP state changes to the second candidate AP state. 17. The fast handover method according to claim 15, wherein, when the strength of the first signal detected from the neighbor AP is lower than the first threshold THR_1 while the neighbor AP is in the second candidate AP state, the neighbor AP is switched from the second candidate AP The state of the two candidate APs is changed to the detected AP state. 18. The fast handover method according to claim 15, wherein, when the neighbor AP is in the second candidate AP state, the mobile terminal does not receive a beacon frame signal from the neighbor AP more than once within a 100 ms interval, the neighbor AP Change from the second candidate AP state to the detected AP state. 19. The fast handover method according to claim 18, wherein, when the intensity of the first signal detected from the neighbor AP exceeds the first threshold THR_1 while the neighbor AP is in the detected AP state, the neighbor AP is switched from the detected AP The state changes to the second candidate AP state. 20. The fast handover method according to claim 1, wherein the handover preparation phase starts when the strength of the first signal detected from the serving AP is lower than a first threshold THR_1. 21. The fast handover method according to claim 20, wherein when the serving AP currently communicating with the mobile terminal and the neighbor AP establishing a new communication with the mobile terminal belong to different subnets, or when the serving AP currently communicating with the mobile terminal and The handover preparation phase occurs when the neighbor AP with which the mobile terminal establishes new communication belongs to the same subnet. 22. The fast handover method according to claim 20, wherein the handover preparation phase comprises: (a) Send Link_Quality_Crosses_Threshold (LQCT) trigger information from layer 2 to layer 3; (b) selecting a candidate AP and a target AP as each neighbor AP capable of establishing new communication with the mobile terminal from the list of neighbor APs, and retrieving information related to the selected candidate APs and target APs; (c) When the neighbor AP that can establish a new communication with the mobile terminal and the serving AP that is currently communicating with the mobile terminal belong to different subnets, according to information retrieval, the mobile terminal sends a message to the access router that manages the subnet to which the mobile terminal belongs. The medium access control (MAC) address of the mobile terminal, the basic service set identifier (BSSID) of the candidate AP and the target AP, and a fast binding update (FBU) message; (d) sending the MAC address of the mobile terminal and a handover initiation (HI) message to routers connected to the candidate AP and the target AP from the access router managing the mobile terminal subnet; (e) Send a Handover Acknowledgment (Hack) message in response to the HI message, a Router Advertisement (RA) message, and a unique temporary address with a guarantee from the routers connected to the candidate AP and the target AP to the access router managing the mobile terminal subnet Ω; and (f) Combine the RA message and Ω received from the routers connected to the candidate AP and the target AP, and send the combined message to the mobile terminal together with a Fast Binding Acknowledgment (FBAck) message. 23. The fast handover method according to claim 22, wherein, after the (c) operation, even when a new candidate AP is found in the neighbor APs of the mobile terminal, a locking operation is performed to prevent adding the new candidate AP to the neighbors list of APs. 24. The fast handover method according to claim 23, further comprising inserting the newly discovered candidate AP into a waiting queue. 25. The fast handover method according to claim 22, wherein the (d) operation checks a new access router (NAR) connected to the candidate AP and the target AP based on the BSSIDs of the candidate AP and the target AP obtained from the CAR table. 26. The fast handover method according to claim 22, wherein the BSSIDs of the candidate AP and the target AP include MAC address information related to the candidate AP and the target AP. 27. The fast switching method according to claim 22, wherein the completion of (f) operation comprises: Signals the completion of the handover preparation phase, and The timer runs for a predetermined time from the completion of the handover preparation phase. 28. The fast switching method according to claim 27, wherein said predetermined time is about 3 seconds. 29. The fast handover method according to claim 27, when the strength of the first signal is lower than the first threshold THR_2 detected from the serving AP within a predetermined time, the mobile terminal enters the handover action stage. 30. The fast handover method according to claim 29, wherein when the mobile terminal enters the handover action phase, the locking operation for the candidate APs is terminated, and the target AP is reselected from the candidate APs. 31. The fast handover method according to claim 27, wherein when the strength of the first signal detected from the serving AP is between the first threshold THR_1 and the second threshold THR_2 within the predetermined time, after the predetermined time, restart Execute the handover preparation phase. 32. The fast handover method according to claim 31, wherein when the handover preparation phase is re-executed, the candidate AP inserted into the waiting queue is updated to the neighbor AP list, and the target AP is selected from the candidate APs of the updated neighbor AP list . 33. The fast handover method according to claim 27, wherein when the strength of the first signal detected from the serving AP exceeds the first threshold THR_1 within a predetermined time, initialization is performed to delete all candidate APs and target APs from the neighbor AP list . 34. The fast handover method according to claim 29, wherein said handover action phase comprises: (a) Send Link_GoingDown (LGD) trigger information from layer 2 to layer 3; (b) sending a Mobile Notification (MVN) message and Ω including a unique temporary address from the mobile terminal to the access router managing the mobile terminal's subnet; and (c) Encapsulation by an access router managing the subnet of the mobile terminal, and sending a MVAck message in response to the MVN message from the access router to the mobile terminal. 35. The fast handover method according to claim 34, wherein the MVN message notifies the access router of information indicating movement of the mobile terminal. 36. The fast handover method according to claim 34, wherein the (c) operation intercepts packets of the previous temporary address intended to be transmitted to the mobile terminal in the access router, and encapsulates the intercepted packet into a new temporary address contained in Ω . 37. The fast switching method according to claim 34, wherein the (c) operation transmits Link_Switch (LS) trigger information from layer 3 to layer 2 when the MVAck message is received at the mobile terminal. 38. The fast handover method according to claim 34, wherein the LS trigger information is sent from layer 3 to layer 2 when the strength of the first signal detected from the serving AP is lower than a third threshold THR_3. 39. The fast switching method according to claim 34, after sending the MVN message in (b) operation, further comprising: When the mobile terminal does not receive the MVAck message from the access router within about 10 ms, resend the MVN message; and When the MVAck message is not received within 10 ms after resending the MVN message, the LS trigger information is sent from layer 3 to layer 2. 40. The fast handover method according to claim 37, after sending LS trigger information from layer 3 to layer 2, further comprising: Attempt to re-associate to the target AP selected from the candidate APs in the neighbor AP list; When the reassociation is completed, a Link_Up trigger message is sent from layer 2 to layer 3; Configure the mobile terminal with the new temporary address and RA message contained in Ω obtained from the previous subnet; sending a Fast Neighbor Advertisement (FNA) message from the mobile terminal to an access router connected to the target AP; and The encapsulated packet is routed through the access router that received the FNA message to the mobile terminal. 41. The fast handover method according to claim 40, wherein when the access router connected to the target AP initially receives the packet encapsulated in PAR and caches the packet intended for the new temporary address contained in Ω, the slave mobile terminal When the FNA message is received, the buffered packet is transmitted to the mobile terminal. 42. The fast handover method according to claim 20, wherein said handover preparation phase comprises: (a) sending LQCT trigger information from layer 2 to layer 3; (b) selecting candidate APs and target APs as neighbor APs capable of establishing new communication with the mobile terminal from the list of neighbor APs, and retrieving information related to the selected candidate APs and target APs; (c) When the neighbor AP that can establish a new communication with the mobile terminal belongs to the same subnet as the mobile terminal, according to the information retrieval, send the MAC address of the mobile terminal to the access router that manages the subnet of the mobile terminal, the candidate BSSID of AP and target AP, and FBU message; and (d) Sending an FBAck message in response to the FBU message from the access router managing the subnet of the mobile terminal to the mobile terminal. 43. The fast handover method according to claim 42, wherein, after the (c) operation, even when a new candidate AP is found in the neighbor APs of the mobile terminal, a locking operation is performed, and it is not allowed to add the new candidate AP to in the neighbor AP list. 44. The fast handover method according to claim 43, wherein the newly discovered candidate AP is inserted into a waiting queue. 45. The fast handover method according to claim 42, wherein the BSSIDs of the candidate AP and the target AP include MAC address information of the candidate AP and the target AP. 46. The fast switching method according to claim 42, wherein the completion of (d) operation comprises: Signals the completion of the handover preparation phase, and The timer runs for a predetermined time from the completion of the handover preparation phase. 47. The fast switching method according to claim 46, wherein said predetermined time is approximately 3 seconds. 48. The fast handover method according to claim 46, wherein when the strength of the first signal detected from the serving AP is lower than the second threshold THR_2 within a predetermined time, the mobile terminal enters the handover action phase. 49. The fast handover method according to claim 48, wherein when the mobile terminal enters the handover action phase, the locking operation for the candidate APs is terminated, and the target AP is reselected from the candidate APs. 50. The fast handover method according to claim 46, wherein when the strength of the first signal detected from the serving AP is between the first threshold THR_1 and the second threshold THR_2 within the predetermined time, after the predetermined time, Execute the switchover preparation phase again. 51. The fast handover method according to claim 50, wherein when the handover preparation phase is re-executed, the candidate APs inserted into the waiting queue are updated to the neighbor AP list, and the target AP is selected from the candidate APs of the updated neighbor AP list. 52. The fast handover method according to claim 46, further comprising performing initialization to delete all candidate APs and Target AP. 53. The fast handover method according to claim 48, wherein said handover action phase comprises: (a) sending LGD trigger information from layer 2 to layer 3; (b) sending an MVN message from the mobile terminal to an access router managing the mobile terminal's subnet; and (c) By managing the access router cache of the subnet of the mobile terminal, and sending the MVAck message in response to the MVN message from the access router to the mobile terminal. 54. The fast handover method according to claim 53, wherein the MVN message notifies the access router of information indicating movement of the mobile terminal. 55. The fast handover method according to claim 53, wherein (c) operates to send LS trigger information from layer 3 to layer 2 when the MVAck message is received at the mobile terminal. 56. The fast handover method according to claim 53, wherein the LS trigger information is sent from layer 3 to layer 2 when the strength of the first signal detected from the serving AP is lower than a third threshold THR_3. 57. The fast switching method according to claim 53, after sending the MVN message in (b) operation, further comprising: When the mobile terminal does not receive the MVAck message from the access router within about 10 ms, resend the MVN message; and When the MVAck message is not received within 10 ms after resending the MVN message, the LS trigger information is sent from layer 3 to layer 2. 58. The fast handover method according to claim 55, further comprising: When sending LS trigger information from layer 3 to layer 2, try to re-associate to the target AP selected from the candidate AP; After completing the re-association, send Link_Up trigger information from layer 2 to layer 3; sending an FNA message from the mobile terminal to an access router connected to the target AP; and The buffered packets are sent from the access router connected to the target AP to the mobile terminal. 59. A mobile device comprising memory, the mobile device employing an Institute of Electrical and Electronics Engineers (IEEE) 802.11 network optimized method for fast handover from one access point (AP) to another AP, the mobile device comprising: a transceiver for receiving signals from and sending signals to the serving AP currently communicating with the mobile terminal, and for receiving beacon frame signals sent from neighbor APs of the mobile device; a signal processor, providing it with the received signal and the beacon frame signal, so as to process the signal of the serving AP, and process the parameters contained in each beacon frame signal; A comparator for comparing the parameters of each beacon frame signal with a threshold pre-stored in the memory; Neighbor AP list manager for prioritizing neighbor APs in the list based on comparison; a timer for judging the timing of each beacon frame signal to signal the neighbor list manager to remove a neighbor AP from the list based on said judgment; and The controller is used to determine whether the signal of the serving AP is normal, and if it is not normal, it starts to switch the communication to the high-priority neighbor AP that has not been deleted. 60. The mobile device of claim 59, wherein the transceiver comprises a first transceiver for communicating with the serving AP in accordance with the IEEE 802.11 standard. 61. The mobile device of claim 59, wherein the beacon frame signal is transmitted at 100 ms intervals. 62. The mobile device according to claim 59, wherein the transceiver comprises a second receiver which itself comprises a search module such that the second receiver can operate in an active mode to scan for neighbor APs and can operate in an idle mode to pause scanning. 63. The mobile device of claim 59, wherein the signal processor comprises first and second signal processors for processing parameters contained in the beacon frame signal. 64. The mobile device according to claim 59, wherein said parameter may be a signal-to-noise ratio (SNR), a received signal strength indicator (RSSI), a bit error rate (BER), and/or a packet error rate (PER) or their derivatives combination. 65. The mobile device according to claim 64, wherein the first and second signal processors process SNR contained in the beacon frame signal and obtain a smoothed SNR. 66. The mobile device of claim 59, wherein the neighbor AP list manager prioritizes the neighbor APs by classifying the neighbor APs into detected APs, candidate APs, and target APs according to comparison results received from the comparator. 67. The mobile device of claim 66, wherein the neighbor AP list manager updates the neighbor AP list if the detected AP is handed over to the candidate AP or if the candidate AP is handed over to the target AP. 68. The mobile device according to claim 67, wherein the detected AP is an AP whose signal is detected alone without guaranteed wireless channel quality, the candidate AP has a guaranteed quality to a certain degree, and the target AP has a quality detected from among neighboring APs. the maximum value of the signal. 69. The mobile device according to claim 59, wherein the timers include a plurality of timers corresponding to neighboring APs such that each timer counts the timing of the beacon frame signal from a time when the beacon frame signal is received at 100 ms intervals. 70. The mobile device of claim 69, wherein the timer notifies the neighbor AP list manager that the beacon frame signal is not received from the neighbor AP when the beacon frame signal is not received at 100 ms intervals. 71. The mobile device according to claim 70, wherein if no beacon frame signal is received from a neighbor AP, the timer notifies the neighbor AP list manager that no beacon frame signal is received from the neighbor AP, and the neighbor AP list manager receives Delete neighbor APs from the AP list. 72. The mobile device of claim 59, wherein the controller continues to receive data from the serving AP if the serving AP signal is normal. 73. The mobile device of claim 72, wherein the controller controls the mobile device to enter a handover preparation phase when a signal-to-noise ratio (SNR) of the serving AP signal is lower than a predetermined first threshold THR_1. 74. The mobile device of claim 73, wherein the controller controls the mobile device to handover when the SNR of the serving AP signal is lower than a predetermined second threshold THR_2. 75. The mobile device of claim 74, wherein the controller interrupts communication between the mobile device and the serving AP when the SNR of the serving AP signal is lower than a predetermined third threshold THR_3. 76. The mobile device of claim 75, wherein the controller reconnects the serving AP to the mobile device. 77. A mobile device comprising memory, the mobile device employing an Institute of Electrical and Electronics Engineers (IEEE) 802.11 network optimized method for fast handover from one access point (AP) to another AP, the mobile device comprising: a transceiver for receiving signals from and sending signals to the serving AP currently communicating with the mobile terminal, and for receiving beacon frame signals sent from neighboring APs of the mobile device; a signal processor, providing the received signal and the beacon frame signal to it, so as to process the signal of the serving AP, and process the parameters contained in each beacon frame signal; A comparator for comparing the parameters of each beacon frame signal with a threshold pre-stored in the memory; a neighbor AP manager for prioritizing neighbor APs based on the comparison; and The controller is used to determine whether the signal of the serving AP is normal, and if not, start switching communication to a high-priority neighbor AP. 78. A mobile device comprising memory, the mobile device employing a fast handover method from one access point (AP) to another AP, the mobile device comprising: a transceiver for receiving signals from and sending signals to the serving AP currently communicating with the mobile terminal, and for receiving beacon frame signals sent from neighbor APs of the mobile device; a signal processor, providing the received signal and the beacon frame signal to it, so as to process the signal of the serving AP, and process the parameters contained in each beacon frame signal; A comparator for comparing the parameters of each beacon frame signal with a threshold pre-stored in the memory; Neighbor AP list manager for prioritizing neighbor APs in the list based on comparison; a timer for judging the timing of each beacon frame signal to signal the neighbor list manager to remove a neighbor AP from the list based on said judgment; and The controller is used to determine whether the signal of the serving AP is normal, and if it is not normal, it starts to switch the communication to the high-priority neighbor AP that has not been deleted. 79. A mobile device comprising memory, the mobile device employing a fast handoff method from one access point (AP) to another AP, the mobile device comprising: a transceiver for receiving signals from and sending signals to the serving AP currently communicating with the mobile terminal, and for receiving beacon frame signals sent from neighboring APs of the mobile device; a signal processor, providing it with the received signal and the beacon frame signal, so as to process the signal of the serving AP, and process the parameters contained in each beacon frame signal; A comparator for comparing the parameters of each beacon frame signal with a threshold pre-stored in the memory; a neighbor AP manager for prioritizing neighbor APs based on a ratio; and The controller is used to determine whether the signal of the serving AP is normal, and if not, start switching communication to a high-priority neighbor AP.

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