KR100738533B1 - Handoff method in WLAN network and WLAN network - Google Patents

Abstract

The present invention relates to a WLAN network and a handoff method in a WLAN network, wherein a mobile terminal detects a current location through communication with a GPS (Global Positioning Service) satellite, Comparing the configuration of all the cells constituting the LAN network and the location information of each cell, to identify the cell on the wireless LAN network corresponding to the current location of the mobile terminal, and at least one AP located at a short distance from the identified cell ( By calculating the handoff expected cell information consisting of an Access Point, it is possible to perform a handoff without a separate AP scanning process, thereby significantly reducing the AP scanning delay time generated during the handoff process.

Description

Wireless LAN and Method for Performing Predicting Handoffs Thereof}

1 is a view showing the configuration of a typical wireless LAN network.

2 is a diagram illustrating a handoff process of an existing WLAN network.

3 is a diagram illustrating handoff delay time by cause in a handoff process of a conventional WLAN network.

4 illustrates the structure of a composite network in accordance with the present invention.

5 is a block diagram of a terminal according to the present invention;

6 is a diagram illustrating a subcell structure of a wireless LAN network according to the present invention.

7 is a diagram showing the structure of a cell information storage unit according to the present invention;

8 is a diagram illustrating a handoff operation flow of an entire network when a terminal moves according to the present invention.

9 is a diagram illustrating a handoff operation flow of a terminal according to the present invention.

* Description of the symbols for the main parts of the drawings *

400: station 401: control unit

402: cell information storage unit 403: GPS receiving module

404: WLAN module 405: expected cell storage

410-1, 410-2: Access Point (Access Point: AP)

420: GPS satellite

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless local area network (WLAN) network, and more particularly, to a wireless LAN network and a predicted handoff method in a WLAN network in which a handoff predicted AP is performed in advance.

In recent years, the transmission speed of wireless local area communication (hereinafter referred to as WLAN) has developed at an alarming rate. Cellular networks still have low throughput to provide multimedia services, while wireless LANs offer Internet access services of 54 Mbps. Wireless LAN, which has a wide bandwidth and low cost, is becoming a competitive technology that can be applied to a mobile communication environment.

1 shows a configuration of a general wireless LAN network.

In general, a WLAN network includes a terminal (Station or Node) 120 that wants to access a network, and access points 110-1 and 110-2 relaying the same, and the access points are connected to the backbone network. It is connected.

The terminal 120 is often a laptop or PDA operated by a battery, but is not necessarily limited to a portable device.

Frames in an 802.11 network must be converted to other types of frames in the process of being transferred to another network. An access point performs bridging between these networks. In addition, the backbone network serves to deliver a frame to the destination of the access point, the Ethernet network is a typical example.

The terminal 120 equipped with a wireless LAN module for wireless LAN access is provided with a data service through the wireless LAN access point 110-1, and one access point covers only a limited area. When the terminal moves to another access point 110-2 area, a handoff occurs. The connection of a terminal from one access point to another access point is called inter AP handoff, and this process is called re-association in the IEEE 802.11 standard. The UE needs to search for a new access point for handoff, and this search takes a considerable amount of time, which is a major factor causing service delay.

The search latency of such an access point is a problem that must be solved for a real-time multimedia service such as Voice over Internet Protocol (VoIP).

Wireless LAN handoff, defined by IEEE 802.11 for wireless LAN, has three major steps: scanning, authentication, and re-association.

2 shows a handoff process of a conventional WLAN network.

When the terminal moves from the access point area to which the terminal is connected to another access point area, the mobile terminal scans all channels provided by several adjacent access points (S200). IEEE802.11 introduces two scanning methods.

The first method is passive scanning, which waits until the mobile terminal has successfully received signals from all channels and received a beacon message of the identified access point to determine the presence of the access point. do. This method has the advantage of low overhead, while the delay is too long. A method for compensating for the disadvantages of passive scanning is an active scanning method, and the handoff procedure of FIG. 2 represents a case of taking active scanning.

When the active scanning is selected, the mobile station broadcasts a probe request for each channel (S201), and waits for a minimum channel time (MinChannelTime) for a response from each channel (S202). . The mobile terminal scans all channels and receives all beacon messages or probe responses to connect to the most appropriate access point.

When the scanning step S200 is completed, the authentication process S210 is continued. When the mobile terminal 120 transmits an authentication request (Authentication Request) to a new AP (110-1) that is determined to be connected to a new (S211), the new AP (110-1) receiving this is a mobile terminal requesting access Check whether the 120 has the right authority to access the network and transmits an authentication response to the mobile terminal 120 (S212).

 Authentication is a process of recognizing the existence of the mobile terminal and authorizing the mobile terminal to access basic services of the access point. Since wireless networks cannot provide physical security that is inherently wired, additional authentication routines are needed to confirm that the user has access to the network.

As a final step of the handoff, a re-association process S220 is required. The reassociation is a process of releasing the connection with the existing AP which was originally connected, and associating with the new AP which is about to newly connect, and the re-association request is initialized by the mobile terminal (S205). The new AP 110-1 transmits a handoff request to the existing AP 100-2, and the existing AP 110-2 receiving the handoff response includes a handoff response including information necessary for recombination ( Handoff Response) is provided to the new AP 110-1 (S223). The operation between the existing AP and the new AP is defined in the Inter Access Point Protocol (IAPP). Upon receiving the handoff response, the new AP 110-1 transmits a re-association response to the mobile terminal 120 (S224).

FIG. 3 illustrates handoff delay time for each cause in a handoff process of a conventional WLAN network.

The four graphs of FIG. 3 show handoff latency experiments as a result of performing handoff for each WLAN equipment manufacturer. As shown in FIG. 3, when the graph 1 is a system having a Cisco terminal and an Lucent AP, the graph 2 is a Lucent terminal and a Cisco AP, and a graph 3 is a terminal of a ZoomAir company. Lucent AP, graph 4 shows that the handoff delay time in a system having a Cisco terminal and a Cisco AP.

In each case, the color of the graph is different according to the cause of the handoff delay. The cause of the delay is divided into three causes: probe delay, authentication delay, and reassociation delay. In all four graphs, we can see the overwhelming majority of probe delays among the three delay sources. In other words, regardless of manufacturer differences, the most significant cause of delay in WLAN handoff is that the probe process is the most important factor of delay.

As such, a selective scanning method is also used to reduce the search time during handoff.However, this method also basically uses a minimum channel time (MinChannelTime) for short waiting time to find an optimal channel and a maximum channel time for a long time. It is difficult to expect effective search time reduction in that it takes up to (MaxChannelTime).

Here, a need arises for a channel search method that can significantly reduce the delay time that occurs during handoff of a WLAN mobile terminal.

The present invention to solve the above problems, by detecting the current position of the terminal through the communication with the GPS satellites used in the handoff procedure of the wireless LAN network to reduce the channel search time when performing the handoff It is an object of the present invention to provide a handoff method in a network and a WLAN network.

According to an aspect of the present invention, there is provided a mobile terminal comprising: a GPS module configured to determine current location information of the mobile terminal through communication with a Global Positioning Service (GPS) satellite; A cell information storage unit configured to store configuration of all cells constituting the WLAN network and location information of each cell; And receiving current location information from the GPS module, comparing the current location of the received mobile terminal with location information of each cell stored in the cell information storage unit, and identifying a cell on the WLAN network corresponding to the current location. The controller may include a control unit for calculating handoff expected cell information including at least one access point (AP) located at a short distance from the identified cell.
Here, the mobile terminal further includes a prediction cell storage unit for storing the calculated handoff prediction cell information, and a WLAN module for performing a handoff by skipping an AP scanning process using the handoff prediction cell information. .
The GPS module may represent the location information in the form of GPS coordinate values.
The configuration of all cells constituting the WLAN network and location information of each cell may include all cell information included in the WLAN network, sub cell information included in each cell, and GPS coordinate value information of each cell and sub cell. At least one of the.
The controller compares the GPS coordinate values of the mobile terminal with the configuration of all cells constituting the wireless LAN network and location information of each cell, and includes at least one AP located at a short distance except for an AP to which the mobile terminal is connected. Is calculated, and priority is given according to the number of sub-cell hops from each of the calculated APs to the mobile terminals to calculate handoff expected cell information.
In addition, according to an aspect of the wireless LAN network according to the present invention, GPS satellites providing location information, and the current location information through the communication with the GPS satellites to determine the location of each cell constituting the network, Identify a cell on a network corresponding to a current location, calculate handoff prediction cell information composed of at least one access point (AP) located at a short distance from the identified cell, and use the handoff prediction cell information to determine an AP. A mobile terminal may perform a handoff without a scanning process.
The mobile terminal compares its PS coordinate value with the configuration of all cells constituting the network and location information of each cell, and calculates at least one AP located at a short distance except for the AP to which the mobile terminal is connected. According to the number of sub-cell hops from each of the calculated APs to the mobile terminal, priority is given to each of the calculated APs to calculate handoff expected cell information.
On the other hand, according to one aspect of the mobile terminal handoff method in a wireless LAN network according to the present invention, the mobile terminal comprises the steps of storing the configuration of the entire cell constituting the wireless LAN network and the location information of each cell; Determining, by the mobile terminal, its current location through communication with a Global Positioning Service (GPS) satellite; Comparing the current location of the identified mobile terminal with the location information of each stored cell, to identify a cell on the wireless LAN network corresponding to the current location of the mobile terminal, at least one AP located at a short distance from the identified cell And calculating handoff expected cell information configured as an access point.
The handoff method may further include storing the calculated handoff expected cell information by the mobile terminal, and performing a handoff by skipping an AP scanning process using the handoff expected cell information by the mobile terminal. Include.
The calculating of the handoff prediction cell information may include comparing the GPS coordinate values of the mobile terminal with the configuration of all cells constituting the wireless LAN network and location information of each cell, and excluding the AP to which the mobile terminal is connected. At least one AP located at is calculated, and priority is given according to the number of subcell hops from each of the calculated APs to the mobile terminal to calculate handoff expected cell information.

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Hereinafter, a preferred embodiment according to the present invention will be described in detail with reference to the drawings.

4 shows a structure of a WLAN network to which the present invention is applied.

As shown in FIG. 4, the present invention is based on a WLAN network based on IEEE802.11, but additionally applies a GPS satellite in addition to the WLAN network.

In the WLAN network, access points 410-1 and 410-2 relaying a terminal and a backbone network are located, and a GPS satellite 420 is connected to the terminal 410 for a Global Positioning Service (GPS) service. Communicate

The terminal 400 according to the present invention not only communicates with the WLAN network through the access points 410-1 and 420-2, but also with the GPS satellite 420 to receive location information including coordinate values of the terminal. Communicate

5 shows a block configuration of a terminal according to the present invention.

The terminal 400 of FIG. 5 includes a GPS receiving module 403, a wireless LAN module 404, a handoff expected AP storage unit 405, a cell information storage unit 402, and a control unit 401.

The GPS receiving module 403 provides the controller 401 with the coordinate values of the terminal 400 received from the GPS satellite 420.

The cell information storage unit 402 includes information on the WLAN cell. The information on the WLAN cell includes information on all cells included in the entire WLAN network, and also includes information on subcells included in each cell and GPS coordinate values of each cell. It also includes information about the relationships between adjacent cells so that the cell structure can be understood more clearly.

Here, there may be various methods for acquiring cell information at the initial setting of the cell information storage unit 420. For example, at the manufacturing stage of the terminal, the structure of the WLAN cell is made into a database, a method of software upgrade of cell information changed thereafter, a specific web site is provided to provide current cell information, and the terminal user accesses the corresponding site. There are several ways, such as downloading to the terminal.

A detailed form of cell information will be described in detail with reference to FIG. 7.

The controller 401 calculates handoff expected cell information using the coordinate values of the terminal and the cell information provided from the GPS receiving module 403. The control unit 401 that grasps the location information of the terminal through the communication with the GPS satellite 420 is a wireless LAN when the terminal 400 moves through the location information and the WLAN cell information stored in the cell information storage unit 402. Information on whether to move to a cell, that is, handoff expected cell information, is detected.

The detected handoff prediction cell information is stored in the prediction cell storage unit 405. The handoff prediction cell information stored in the prediction cell storage unit 405 is three AP lists arranged according to the priority. Of course, the number of APs may vary according to the expected cell detection algorithm. The handoff anticipated cell information is updated whenever the UE moves by changing the position of the AP.

The WLAN module 404 performs the actual WLAN handoff using the handoff expected cell information stored in the expected cell storage unit 405.

Various methods may be used by the controller 401 to detect handoff prediction cell information. However, the present invention proposes a method for extracting three handoff prediction APs. The controller 401 compares the position of the current terminal with the position of each AP stored in the database of the WLAN cell, and selects the AP located closest to the terminal by a preset number. At this time, the AP currently connected to the terminal is excluded. This is because the mobile station does not handoff even if the subcells are different in the service area of the AP currently being accessed. For each selected AP, the number of hops to be moved from the terminal to the service area of the corresponding AP is calculated. Here, the unit of the hop is a sub-cell unit, but the sub-cells will be described in detail with reference to FIGS. 6 and 7. Priority is given to each AP according to the number of mobile hops from the terminal, and the AP with the smallest number of mobile hops has the highest priority.

The control unit 401 performs the scanning process from the higher priority AP to the lower priority AP using the calculated handoff cell information. If the scanning process with the AP having the highest priority is successfully performed, scanning is not necessary for other APs.

The WLAN module 404 is responsible for performing WLAN handoff according to the handoff expected cell information grasped by the controller 401.

6 shows a subcell structure of a WLAN network according to the present invention.

In the present invention, the cell of the WLAN centered on the access point is further divided into six logical sub-cells. In FIG. 6, seven access points constitute seven cells, and each cell is divided into six sub-cells.

The WLAN cell 3 is divided into sub-cells 3-1, 3-2, 3-3, 3-4, 3-5, and 3-6. The reason for re-partitioning the WLAN cell is to allocate the correct mobile access point to the terminal during handoff. Which sub-cell the terminal is located can be determined by comparing the coordinate value of the terminal provided from the GPS satellite 420 and the coordinate value of the AP sub-cells.

In the WLAN network, handoff occurs when the access point to which the terminal is connected is changed. For example, when the UE moves from the 3-5 sub-cell of FIG. 6 to the 7-2 sub-cell, and moves from the 3-3 sub-cell to the 2-6 sub-cell. However, if the sub-cells are different but the cells are the same, as in the case of moving from the 3-3 sub-cell to the 3-4 sub-cell, the handoff does not occur because the access points to which they are connected are the same.

6 shows that the WLAN cell and the sub-cell have a hexagonal shape, but the scope of the present invention is not limited to the hexagonal sub-cell shape. If other adjacent cells can be determined in a limited number will all be included in the scope of the present invention.

7 shows a structure of a cell information storage unit according to the present invention.

In FIG. 5, it has been described that the cell information storage unit 402 includes information on the WLAN cell. 7 shows that the cell information storage unit 402 can take the form of a list.

As shown in FIG. 7, the cell information storage unit 402 includes a list of all WLAN network cells and a list of sub-cells of each WLAN cell. Also shown are GPS coordinate values for each WLAN cell. In this case, the GPS coordinate value indicates the center of the cell, that is, the position of each AP. Although not shown in FIG. 7, the cell information storage unit 402 also holds GPS coordinate values for each subcell. The GPS coordinate value for the subcell is compared with the GPS coordinate value of the terminal and used to determine in which subcell the terminal is currently located.

The GPS coordinates of AP 1 can be confirmed to be 206028.95 and 175787.66 based on Vessel TM. Here, the method of displaying the GPS coordinate values may be used in various ways, such as latitude and longitude, in addition to Vessel ™, and which method should be determined by the system designer or administrator.

FIG. 7 also includes a handoff mapping list, and it is easy to determine how the respective cells included in the AP cell list and the subcell list are adjacent to each other. That is, it shows what neighboring cells are adjacent to each AP and subcells. Looking at the handoff mapping list, it can be easily seen that the cell adjacent to the subcell 3-1 is 8-4 and the cell adjacent to the 3-2 is 5-5. The handoff mapping list is used to calculate the number of hops from the subcell in which the terminal is currently located to the handoff anticipated AP during handoff to determine the handoff anticipated priority among candidate APs.

It is possible to determine the WLAN cell where the terminal is located by using the various lists presented above. For example, the following method may be used.

8 shows a handoff operation flow of the entire network when the terminal moves according to the present invention.

The mobile terminal 400 communicating with the WLAN network communicates with the GPS satellite 420 for a new AP scanning. The terminal grasps its position represented by a coordinate value through communication with the GPS satellite 420 (S801). The terminal 400 detects information on the AP for which handoff is expected from the current location of the terminal 400 by using its own location information (coordinate value information of the terminal) and cell information of the entire WLAN network. (S802).

Looking at the process of detecting the handoff expected cell information in detail, by comparing the position of each AP stored in the database of the current terminal and the position of the AP is located closest to the terminal except the AP to which the current terminal is connected. Select an AP set. For each of the selected APs, the UE calculates the number of subcell hops to be moved from the current subcell to the service area of the corresponding AP. Priority is given to each AP according to the number of mobile hops from the terminal, and the AP with the smallest number of mobile hops has the highest priority. The reason for selecting three APs is to increase handoff completion by providing at least two APs to be accessed in lanes when the connection with the AP having the highest priority fails.

The terminal 400 performs the scanning process from the higher priority AP to the lower priority AP using the handoff slaughter cell information calculated as described above (S903). If the scanning process with the AP having the highest priority is successfully performed, scanning is not necessary for other APs. That is, the AP scanning may be one time or may be two or three times.

Once the scanning step is completed, the authentication process will continue. When the terminal 400 transmits an authentication request (Authentication Request) to a new AP 340-2 determined to be newly connected (S905), the received new AP 340-2 receives the terminal 400 requesting access. Check whether the right authority to access the network and transmits an authentication response (Authentication Response) to the terminal 400 (S806).

When the authentication is completed, the terminal 400 transmits a re-association request to the new AP 340-2 (S807). The new AP 340-2 transmits a handoff request to the existing AP 340-1 (S808), and the existing AP 340-1 receiving the received information includes information necessary for recombination. A handoff response is provided to the new AP 340-2 (S809). Upon receiving the handoff response, the new AP 340-2 transmits a re-association response to the terminal 400 (S810).

Comparing the procedure of FIG. 8 with the procedure of FIG. 2, it can be seen that the two procedures are significantly different in the scanning process.

9 shows a handoff operation flow of a terminal according to the present invention.

As the terminal moves, it grasps its position represented by a coordinate value through communication with the GPS satellite 420 (S901). The location of the terminal may be set by the system administrator to be performed regularly or whenever a specific event occurs. The terminal checks the ID of the subcell to which it belongs by comparing its GPS coordinate value and GPS coordinate value of each subcell on the cell information (S902). After identifying the subcell to which it belongs, the UE calculates three candidate APs located closest to the current location of the UE for the remaining APs except the AP to which the corresponding subcell belongs (S903). At this time, the distance between the terminal and each AP is calculated using the coordinate value of the terminal and the coordinate value of each AP. When three candidate AP lists are determined, the number of subcell hops from the subcell in which the UE is currently located is calculated for each AP (S904). That is, the number of hops indicates how many subcells can be met to the corresponding AP from the subcell in which the current UE is located. When the hop count for each AP is calculated, priority is given to the three candidate APs with the AP having the smallest hop number as the highest priority (S905). When the candidate AP list is created, the candidate AP list is stored (S906).

The terminal uses the stored candidate AP list when handing off. When the terminal needs to move and perform handoff (Yes in S907), the terminal uses the candidate AP list calculated in the above procedure without performing a separate AP scanning process. The probe request message is transmitted using the signal (S908). That is, the probe request message is transmitted to the AP having the highest priority among the candidate AP list. If a probe response is received from the AP having the highest priority (YES in S909), no further probe request is required. However, if there is no response from the highest priority AP, the probe request message is transmitted to the second priority AP (S908). If the probe response is not received continuously, it is checked whether a probe request is performed for all APs in the candidate AP list (S910), and if a probe request for all APs in the list is performed (S912).

When a probe response is received through the candidate AP list or when a response is exchanged with a specific AP through a general scanning procedure, an AP to be handed off is determined, and an authentication and recombination procedure is performed with the corresponding AP (S911).

In the embodiment shown in FIG. 9, three candidate APs are assumed, but the scope of the present invention does not limit the number of candidate APs to 3, and may be adjusted to an appropriate number in consideration of load of the terminal and effective handoff. something to do.

The above procedures (S901 to S912) are repeated whenever the terminal performs a handoff. The location of the terminal using the GPS satellite and the update procedure of the candidate AP list may be set by the system administrator to be repeated periodically or under a specific condition. In fact, it is preferable that the handoff is more frequently performed in terms of more accurate handoff prediction cell identification than location information update and candidate AP list update.

The present invention can significantly reduce the handoff time of the entire wireless LAN terminal by shortening the channel scanning process, which takes up a large portion of the time during the handoff process, thereby improving the quality of the wireless LAN network.

Claims (15)

In a mobile terminal on a wireless LAN network, A GPS module configured to determine current location information of the mobile terminal through communication with a Global Positioning Service (GPS) satellite; A cell information storage unit configured to store configuration of all cells constituting the WLAN network and location information of each cell; And Receive current location information from the GPS module, compare the current location of the received mobile terminal with the location information of each cell stored in the cell information storage unit, to identify the cell on the WLAN network corresponding to the current location, And a control unit for calculating handoff expected cell information including at least one AP located at a short distance from the identified cell. The method of claim 1, And a prediction cell storage unit for storing the calculated handoff prediction cell information. The method of claim 1, The mobile terminal further comprises a wireless LAN module performing a handoff by skipping an AP scanning process using the handoff expected cell information. The method of claim 1, The GPS module, And the location information is expressed in the form of GPS coordinate values. The method of claim 1, Configuration of all the cells constituting the WLAN network and location information of each cell, And at least one of total cell information included in the WLAN network, sub cell information included in each cell, and GPS coordinate value information of each cell and sub cell. The method of claim 4, wherein The control unit, Comparing the GPS coordinate value of the mobile terminal and the configuration of the entire cell constituting the wireless LAN network and the location information of each cell, calculates at least one AP located at a short distance except the AP to which the mobile terminal is connected, Mobile terminal, characterized in that the priority is given according to the number of sub-cell hops from each of the calculated AP to the mobile terminal to calculate the handoff expected cell information. GPS satellites providing location information; and Identifying the current location information through the communication with the GPS satellite and comparing the location of each cell constituting the network, to identify the cell on the network corresponding to the current location, and at least one located near A mobile LAN network comprising a mobile terminal for calculating handoff prediction cell information configured as an access point (AP), and performing handoff without an AP scanning process using the handoff prediction cell information. The method of claim 7, wherein The configuration of all the cells constituting the network and the location information of each cell, And at least one of total cell information included in the network, sub cell information included in each cell, and GPS coordinate value information of each cell and sub cell. The method of claim 7, wherein The mobile terminal, Comparing its PS coordinate value with the configuration of all cells constituting the network and location information of each cell, calculating at least one AP located at a short distance except the AP to which the mobile terminal is connected, and calculating the calculated AP The WLAN network, characterized in that the handoff expected cell information is calculated by giving priority to each of the calculated APs according to the number of sub-cell hops from each to the mobile terminal. Storing, by the mobile terminal, the configuration of all cells constituting the WLAN network and location information of each cell; Determining, by the mobile terminal, its current location through communication with a Global Positioning Service (GPS) satellite; Comparing the current location of the identified mobile terminal with the location information of each stored cell, to identify a cell on the wireless LAN network corresponding to the current location of the mobile terminal, at least one AP located at a short distance from the identified cell Computing handoff expected cell information consisting of (Access Point). The method of claim 10, The mobile terminal further comprises the step of storing the calculated handoff expected cell information. The method of claim 10, The mobile terminal further comprises the step of skipping the AP scanning process using the handoff expected cell information and performing a handoff. The method of claim 10, The location information of each cell is represented in the form of a GPS coordinate value handoff method in a wireless LAN network. The method of claim 10, Configuration of all the cells constituting the WLAN network and location information of each cell, And at least one of total cell information included in the WLAN network, sub cell information included in each cell, and GPS coordinate value information of each cell and sub cell. The method of claim 13, The calculating of the handoff expected cell information may include: Comparing the GPS coordinate value of the mobile terminal and the configuration of the entire cell constituting the wireless LAN network and the location information of each cell, calculates at least one AP located at a short distance except the AP to which the mobile terminal is connected, A handoff method in a WLAN network, wherein the handoff expected cell information is calculated by assigning priority according to the number of subcell hops from each of the calculated APs to the mobile terminal.

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