US20050083832A1 - Wireless local area network system, fault recovery method, and recording medium stored therein a computer program executing the fault recovery process - Google Patents
Wireless local area network system, fault recovery method, and recording medium stored therein a computer program executing the fault recovery process Download PDFInfo
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- US20050083832A1 US20050083832A1 US10/980,158 US98015804A US2005083832A1 US 20050083832 A1 US20050083832 A1 US 20050083832A1 US 98015804 A US98015804 A US 98015804A US 2005083832 A1 US2005083832 A1 US 2005083832A1
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- 238000011084 recovery Methods 0.000 title claims abstract description 17
- 238000004590 computer program Methods 0.000 title claims abstract description 7
- 238000004891 communication Methods 0.000 claims description 42
- 230000003247 decreasing effect Effects 0.000 abstract description 5
- 238000010586 diagram Methods 0.000 description 24
- 238000005516 engineering process Methods 0.000 description 6
- 230000007423 decrease Effects 0.000 description 4
- 238000001514 detection method Methods 0.000 description 3
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W24/00—Supervisory, monitoring or testing arrangements
- H04W24/04—Arrangements for maintaining operational condition
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L41/00—Arrangements for maintenance, administration or management of data switching networks, e.g. of packet switching networks
- H04L41/06—Management of faults, events, alarms or notifications
- H04L41/0654—Management of faults, events, alarms or notifications using network fault recovery
- H04L41/0659—Management of faults, events, alarms or notifications using network fault recovery by isolating or reconfiguring faulty entities
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W76/00—Connection management
- H04W76/10—Connection setup
- H04W76/19—Connection re-establishment
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W84/00—Network topologies
- H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
- H04W84/10—Small scale networks; Flat hierarchical networks
- H04W84/12—WLAN [Wireless Local Area Networks]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
- H04W88/02—Terminal devices
- H04W88/04—Terminal devices adapted for relaying to or from another terminal or user
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
- H04W88/08—Access point devices
Definitions
- the present invention relates to a wireless local area network (LAN) system, a fault recovery method, and a recording medium stored therein a computer program or executing the fault recovering process. More particularly, the present invention relates to a technology for preventing the throughput of the whole LAN system from being decreased even when a fault occurs in an access point.
- LAN wireless local area network
- LAN local area network
- Japanese Patent Laid-Open Publication No. Hei 7-312597 discloses a wireless LAN system that prevents packets from being lost. This technology will be described below as a first conventional example.
- FIG. 10 is a block diagram showing the wireless LAN system according to the first conventional example.
- a wireless LAN system 110 shown in FIG. 10 , consists of a client terminal 18 connected to a wired LAN 112 , a LAN cable 120 forming the wired LAN 112 , access points 122 and 124 performing as bridges to the wired LAN 112 , and wireless terminals 130 and 134 which, in conjunction with the access points 122 and 124 , form wireless LANs 114 and 116 , respectively.
- the access point 122 or 124 transmits the packet to the wireless LAN 114 or 116 or transmits the packet to the wired LAN 112 .
- the system prevents a packet loss caused by a conflict in accessing the medium or an interference with other communication networks using the same frequency band.
- Japanese Patent Laid-Open Publication No. Hei 8-242232 discloses a wireless terminal LAN having a repeater. This technology will be described as a second conventional example.
- FIG. 11 is a block diagram of the wireless LAN system of the second conventional example.
- the wireless terminal LAN shown in FIG. 11 , consists of wireless terminals 202 - 210 and a wireless repeater 201 containing a transceiver 220 .
- the system according to this conventional example has the special wireless repeater 201 and, through this wireless repeater 201 , re-transmits packets to reduce conflicts in radio waves.
- the system can prevent the throughput of the whole LAN from being decreased.
- Japanese Patent Laid-Open Publication No. Hei 9-215044 discloses a priority switching technology for a cellular wireless LAN. This technology will be described as a third conventional example.
- FIG. 12 is a block diagram of the wireless LAN system according to the third conventional example.
- the wireless LAN system shown in FIG. 12 , consists of a plurality of portable units 302 that are wireless terminals, a house computer 304 connected to a wired LAN, and a plurality of access points 305 that perform as bridges to the wired LAN.
- the portable unit 302 searches and identifies the access point 305 best suited for communication, based on the intensity of radio waves from, and the loading factor of, the plurality of the access points 305 .
- FIG. 13 is a block diagram of a wireless LAN system according to the fourth conventional example.
- FIG. 14 is a flowchart showing a fault recovery processing of the wireless LAN system according to the fourth conventional example.
- the wireless LAN system shown in FIG. 13 , consists of access points Pa and Pb that perform as bridges to a wired LAN system Lw, client terminals Ca-Cd that are wireless terminals communicating with the access points Pa and Pb, and a LAN cable 405 consisting the wired LAN system Lw.
- the access points Pa and Pb transmit beacon information Iba and Ibb, respectively, at regular intervals (step S 101 in FIG. 14 ).
- the client terminal Ca When the client terminal Ca receives the beacon information Iba from the access point Pa at power-on time or roaming time, the client terminal Ca transmits a management frame back to the access point Pa to start negotiation with the access point Pa and then starts communication with the access point Pa.
- the client terminal Cb also starts negotiation with the access point Pb and then starts communication with the access point Pb according to the same procedure (step S 102 in FIG. 14 ).
- step S 103 in FIG. 14 when the access point Pa fails for some reason or other (step S 103 in FIG. 14 ), the client terminal Ca cannot continue communication with the access point Pa. So, the client terminal Ca starts searching for another access point Pb (step S 104 in FIG. 14 ).
- step S 105 in FIG. 14 If another access point Pb is near the client terminal Ca (step S 105 in FIG. 14 ), there is no problem because the client terminal Ca can immediately establish a link with the access point Pb to continue communication (step S 106 in FIG. 14 ).
- step S 105 in FIG. 14 the client terminal Ca continues search processing until it successfully searches for the access point Pb (step S 104 in FIG. 14 ).
- This search processing is executed by the client terminal Ca for transmitting a management frame (probe) that is communication control management information.
- a management frame probe
- the client terminal Ca continues transmitting the management frame, during this search processing, at an interval shorter than that for a normal communication frame.
- the client terminal Ca frequently transmits the management frame at an interval shorter than that for the normal communication frame. This increases the radio wave interference around the client terminal Ca and therefore decreases the throughput of the whole LAN system L.
- the client terminal Ca frequently transmits the management frame at an interval shorter than that for the normal communication frame.
- This processing has some problems with the client terminal Ca being battery-powered. For example, this processing consumes more battery power for communication and therefore shortens battery life. And, the increase in power consumption causes a quickly decrease in the power voltage, sometimes suddenly disconnecting the power of the portable information terminal and thus destroying data due to a communication interruption.
- the duplicated system configuration is built usually for the access points Pa and Pb as a fail-safe against the shutdown of the whole LAN system L.
- This shutdown may be caused by such conditions as a fault in access point Pa or Pb or the disconnection of a LAN cable 405 .
- duplicating the access points Pa and Pb allows the access points Pa and Pb to transmit radio waves frequently during the above search processing. This increases the radio wave interference and therefore decreases the throughput of the whole LAN system.
- An object of the present invention is to provide a wireless LAN system that prevents throughput from being decreased even when an access point fails, a fault recovery method, and a recording medium storing therein a computer program executing the fault recovery process.
- the wireless LAN (Local Area Network) system consisting of a plurality of access points and a plurality of client terminals; wherein each of the plurality of access points consists of: a main unit for communicating with the client terminals, a first fault detecting unit for detecting a fault on the main unit, and a disconnection controlling unit for disconnecting the client terminal connected to the access point where the fault was detected by the first fault detecting unit; and wherein each of the plurality of client terminals consists of: a transceiver unit for communicating with the access point, a search controlling unit for searching for another client terminal to which the client terminal disconnected from the access point is to be connected, and a connection controlling unit for connecting the disconnected client terminal to the searched client terminal by the search controlling unit.
- the fault recovery method consisting of a plurality of access points and a plurality of client terminals, the method consisting of the steps of: detecting, by each of the access points, whether a fault occurs on each of the access points itself; disconnecting, by the access point which has detected the fault, the client terminal connected thereto; searching for, by the disconnected client terminal, another of the client terminals to which the disconnected client terminal is to be connected; and connecting the disconnected client terminal to the searched client terminal.
- the recording medium stores therein a computer program for executing a fault recovery process according to the present invention consisting of a plurality of access points and a plurality of client terminals, the process consisting of the steps of: detecting, by each of the access points, whether a fault occurs on each of the access points itself; disconnecting, by the access point which has detected the fault, the client terminal connected thereto; searching for, by the disconnected client terminal, another of the client terminals to which the disconnected client terminal is to be connected; and connecting the disconnected client terminal to the searched client terminal.
- a client terminal connected to this access point is disconnected.
- the system according to the present invention connects the client terminal to another client terminal. And, through this another client terminal, the disconnected client terminal connects to another access point. This prevents the load from being concentrated at another access point.
- FIG. 1 is a block diagram showing a wireless LAN system in an embodiment of the present invention.
- FIG. 2 is a block diagram of an access point of the wireless LAN system according to the FIG. 1 embodiment.
- FIG. 3 is a block diagram of a client terminal of the wireless LAN system according to the FIG. 1 embodiment.
- FIG. 4 is a flowchart showing a fault recovery processing of the wireless LAN system according to the FIG. 1 embodiment.
- FIG. 5 is a diagram showing communication processing in the normal state of the wireless LAN system according to the FIG. 1 embodiment.
- FIG. 6 is a diagram showing disconnection processing in the fault occurring state of the wireless LAN system according to the FIG. 1 embodiment.
- FIG. 7 is a diagram showing search processing in the fault occurring state the wireless LAN system according to the FIG. 1 embodiment.
- FIG. 8 is a diagram showing connection processing in the fault occurring state of the wireless LAN system according to the FIG. 1 embodiment.
- FIG. 9 is a diagram showing another connection processing in the fault occurring state of the wireless LAN system according to the FIG. 1 embodiment.
- FIG. 10 is a block diagram of the wireless LAN system according to the first conventional example.
- FIG. 11 is a block diagram of the wireless LAN system according to the second conventional example.
- FIG. 12 is a block diagram of the wireless LAN system according to the third conventional example.
- FIG. 13 is a block diagram of the wireless LAN system according to the fourth conventional example.
- FIG. 14 is a flowchart showing a fault recovery processing of the wireless LAN system according to the fourth conventional example.
- FIG. 1 is a block diagram showing a wireless LAN system in an embodiment of the present invention.
- a wireless LAN system Ll shown in FIG. 1 , consists of access points Pa and Pb that are bridges to a wired LAN system Lw and client terminals Ca-Cd that are wireless communication terminals communicating with these access points Pa and Pb.
- This wireless LAN system Ll uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) as the communication protocol. Note that any number of the access points Pa and Pb and the client terminals Ca-Cd may be used.
- CSMA/CA Carrier Sense Multiple Access with Collision Avoidance
- the wired LAN system Lw consists of the access points Pa and Pb, which are bridges to the wireless LAN system Ll, and a LAN cable 5 which is, for example, an Ethernet cable connecting the access points Pa and Pb.
- This wired LAN system Lw uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD) as the communication protocol.
- CSMA/CD Carrier Sense Multiple Access with Collision Detection
- FIG. 2 is a block diagram of an access point of the wireless LAN system according to the FIG. 1 embodiment.
- the access point Pa shown in FIG. 2 , consists of a main unit 1 a, a fault detecting unit 10 a, a disconnection controlling unit 20 a, a fault detecting unit 30 a, and a permission information generating unit 40 a.
- the main unit 1 a is a relaying unit connecting the wired LAN system Lw ( FIG. 1 ) and the wireless LAN system Ll ( FIG. 1 ).
- the main unit 1 a communicates with the client terminals Ca and Cb ( FIG. 1 ) included in an area Aa ( FIG. 1 ) served by the access point Pa by radio waves. Not only the radio waves but also other wireless communication media such as an infrared ray may be used as the communication medium.
- the main unit 1 a transmits management information, called beacon information Iba ( FIG. 1 ), at regular intervals.
- the beacon information is composed of synchronization information, packet transmission control information, and so on.
- the main unit 1 a maintains the synchronization of the whole LAN system and, at the same time, controls communication so that a packet collision is avoided.
- the fault detecting unit 10 a is means for monitoring the status of communication between the wired LAN system Lw and the main unit 1 a.
- the fault detecting unit 10 a detects that the main unit 1 a has been disconnected from the LAN cable 5 and outputs a fault detecting signal Sha.
- the disconnection controlling unit 20 a In response to the fault detecting signal Sha, the disconnection controlling unit 20 a outputs a disconnect signal Sda to the main unit 1 a to instruct the main unit 1 a to disconnect the client terminal Ca ( FIG. 1 ) being connected.
- the fault detecting unit 30 a receives the beacon information Ibb ( FIG. 1 ) from the other access point Pb ( FIG. 1 ). If the fault detecting unit 30 a detects that the other access point Pb ( FIG. 1 ) has failed, the fault detecting unit 30 a outputs a fault detecting signal Spa.
- the permission information generating unit 40 a transmits permission information Ip which permits all the client terminals under control of the access point Pa, that is, Ca and Cb ( FIG. 1 ), to accept the urgent identification (ID) code.
- a main unit 1 b , a fault detecting unit 10 b, a disconnection controlling unit 20 b, a fault detecting unit 30 b, and a permission information generating unit 40 b of the access point Pb each have the configuration similar to that of the corresponding unit of the access point Pa.
- FIG. 3 is a block diagram of a client terminal of the wireless LAN system according to the FIG. 1 embodiment.
- the client terminal Ca shown in FIG. 3 consists of a transceiver unit 50 a, a search controlling unit 60 a, a connection controlling unit 70 a, and a repeat controlling unit 80 a.
- the transceiver unit 50 a communicates with the access points Pa and Pb ( FIG. 1 ) by radio waves.
- the search controlling unit 60 a transmits a management frame through the transceiver unit 50 a to search for another client terminal Cb-Cd to which the client terminal Ca will be connected.
- connection controlling unit 70 a connects the client terminal Ca, through the transceiver unit 50 a, to one of the client terminals Cb-Cd that was searched for by the search controlling unit 60 a.
- the repeat controlling unit 80 a instructs the transceiver unit 50 a to perform communication processing for the MAC (Media Access Control) sub-layer and lower-level layers for data to be communicated between one of the client terminals Cb-Cd and the access point Pa or Pb ( FIG. 1 ).
- MAC Media Access Control
- Transceiver units 50 b - 50 d , search controlling units 60 b - 60 d , connection controlling units 70 b - 70 d , and repeat controlling units 80 b - 80 d of the client terminals Cb-Cd each have the configuration similar to that of client terminal Ca.
- the client terminals Ca-Cd may be, for example, standalone computers, POS (Point-Of-Sales) terminals, or portable information terminals with the radio communication function, or computers, POS terminals, or portable information terminals with no radio communication function but with a radio communication adapter connected.
- POS Point-Of-Sales
- portable information terminals with the radio communication function or computers, POS terminals, or portable information terminals with no radio communication function but with a radio communication adapter connected.
- FIG. 4 is a flowchart showing a fault recovery processing of the wireless LAN system according to the FIG. 1 embodiment.
- the access points Pa and Pb transmit the beacon information Iba and Ibb at regular intervals, respectively (step S 1 in FIG. 4 ).
- FIG. 5 is a diagram showing communication processing in the normal state of the wireless LAN system according to the FIG. 1 embodiment.
- the client terminal Ca Upon receiving the beacon information Iba from the access point Pa at power-on time or roaming time, the client terminal Ca transmits the management frame back to the access point Pa to perform negotiation therewith. The client terminal Ca then starts communication with the access point Pa as shown in FIG. 5 (step S 2 in FIG. 4 ).
- Each of the client terminals Cb-Cd performs negotiation with the access point Pb in the same way as described above and, as shown in FIG. 5 , starts communication with the access point Pb.
- FIG. 6 is a diagram showing disconnection processing in the fault occurring state the wireless LAN system according to the FIG. 1 embodiment.
- a fault occurs on the access point Pa as shown in FIG. 6 (step S 3 in FIG. 4 ).
- the cause of this fault is, for example, a fault in the main unit 1 a ( FIG. 2 ) of the access point Pa or the disconnection of the LAN cable 5 connected to the main unit 1 a ( FIG. 2 ).
- the fault detecting unit 10 a ( FIG. 2 ) of the access point Pa monitors the status of communication between the wired LAN system Lw and the main unit 1 a ( FIG. 2 ).
- the fault detecting unit 10 a detects a fault on the main unit 1 a of the access point Pa or on the LAN cable 5 connected therewith, the fault detecting unit 10 a ( FIG. 2 ) outputs the fault detection signal Sha ( FIG. 2 ) to the disconnection controlling unit 20 a ( FIG. 2 ).
- the disconnection controlling unit 20 a ( FIG. 2 ) disconnects the client terminal Ca, which is connected to the access point Pa at that time, from the access point Pa and forces communication between them to terminate (step S 4 in FIG. 4 ).
- FIG. 7 is a diagram showing search processing in the fault occurring state of the wireless LAN system according to the FIG. 1 embodiment.
- the search controlling unit 60 a ( FIG. 3 ) of the disconnected client terminal Ca transmits a management frame, which is management information, through the transceiver unit 50 a ( FIG. 3 ) to search for another client terminal Cb-Cd to which the client terminal Ca is to be connected (step S 5 in FIG. 4 ).
- the fault detecting unit 30 b ( FIG. 2 ) of the other access point Pb detects the occurrence of the fault in the access point Pa based on the beacon information Iba, starts the operation of the permission information generating unit 40 b ( FIG. 2 ).
- the fault detecting unit 30 b ( FIG. 2 ) transmits the permission information Ip to the client terminals Cb-Cd through the main unit 1 b ( FIG. 2 ) (step S 6 in FIG. 4 ).
- the transceiver units 50 b - 50 d ( FIG. 3 ) of the client terminals Cb-Cd in the area Ab under control of the access point Pb are set to the emergency ID reception permitting state (step S 7 in FIG. 4 ).
- FIG. 8 is a diagram showing connection processing in the fault occurring state of the wireless LAN system according to the FIG. 1 embodiment.
- the connection controlling unit 70 a ( FIG. 3 ) of the disconnected client terminal Ca transmits the emergency ID code to the client terminal Cd through the transceiver unit 50 a ( FIG. 3 ).
- the connection controlling unit 70 a ( FIG. 3 ) then performs connection processing such as log-in processing for the client terminal Cd that was searched for during the search processing (step S 8 in FIG. 4 ).
- the client terminal Cd controls communication between the client terminal Cd itself and the access point Pb and, at the same time, relays data to be communicated between the client terminal Ca and the access point Pb (step S 9 in FIG. 4 ).
- the client terminal Cd performs as a repeater that relays communication data of the client terminal Ca that is a disconnected client terminal.
- the equal distribution system is used and all client terminals Ca-Cd operate under the same logic. Therefore, all client terminals Ca-Cd are eligible for a repeater.
- the emergency ID code is used for all the client terminals Ca-Cd commonly. This allows the client terminal Ca to connect to one of the client terminals Cb-Cd.
- the fault recovery processing for the whole LAN system L is completed by executing the above steps.
- FIG. 9 is a diagram showing another connection processing in the fault occurring state of the wireless LAN system according to the FIG. 1 embodiment.
- the client terminal Ca obtains communication information from the client terminal Cd. This communication information includes information on the access point Pb to which the client terminal Ca can access.
- the search controlling unit 60 a and the connection controlling unit 70 a of the client terminal Ca negotiate directly with the access point Pb to connect the client terminal Ca thereto (steps S 18 and S 19 in FIG. 4 ).
- This method prevents the communication load from being concentrated at the client terminal Cd, thus minimizing a decrease in the throughput of the wireless LAN system Ll.
- each of the access points Pa and Pb consists of the main unit 1 a or 1 b , fault detecting unit 10 a or 10 b, disconnection controlling unit 20 a or 20 b, fault detecting unit 30 a or 30 b, and permission information generating unit 40 a or 40 b, respectively.
- the units except the main unit 1 a and 1 b may be implemented by a software program built in the access points Pa and Pb. As shown in FIG. 2 , this software program is stored on a recording medium 96 a or 96 b , such as a memory contained in the access point Pa or access point Pb. Processing means 97 a or 97 b , such as the CPU (Central Processing Unit), is provided to read this program for execution.
- CPU Central Processing Unit
- each of the client terminals Ca-Cd consists of each of the transceiver units 50 a - 50 d , each of the search controlling units 60 a - 60 d , each of the connection controlling unit s 70 a - 70 d , and each of the repeat controlling units 80 a - 80 d , respectively.
- These units except the transceiver units 50 a - 50 d may be implemented by a software program built in each of the client terminals Ca-Cd. As shown in FIG. 3 , this software program may be stored on each recording medium 98 a - 98 d such as a memory contained in each client terminal Ca-Cd.
- Each processing means 99 a - 99 d such as the CPU, is provided to read this program for execution.
- the system according to the present invention eliminates the need for a client terminal connected to that access point to wait until another access point transmits beacon information. Instead, the client terminal automatically searches for another nearby client terminal and causes the nearby client terminal to perform as a repeater. This allows management information required for communication control to be obtained easily and quickly. As a result, communication among client terminals may be reestablished more quickly than in the conventional examples described above.
- the system according to the present invention prevents a plurality of client terminals with no connection destination from attempting to connect to the same access point at the same time.
- This access-point load balancing ability prevents the throughput of the whole LAN system from being decreased.
Abstract
The present invention provides a wireless local area network (LAN) system preventing throughput from being decreased even when a fault occurs in an access point, a fault recovery method, and a recording medium stored therein a computer program for executing the fault recovering process. The method for use in a wireless local area network system comprising a plurality of access points and a plurality of client terminals, the method comprising the steps of: detecting, by each of the access points, whether a fault occurs on each of the access points itself; disconnecting, by the access point which has detected the fault, the client terminal connected thereto; searching for, by the disconnected client terminal, another of the client terminals to which the disconnected client terminal is to be connected; and connecting the disconnected client terminal to the searched client terminal.
Description
- 1. Field of the Invention
- The present invention relates to a wireless local area network (LAN) system, a fault recovery method, and a recording medium stored therein a computer program or executing the fault recovering process. More particularly, the present invention relates to a technology for preventing the throughput of the whole LAN system from being decreased even when a fault occurs in an access point.
- 2. Description of the Prior Art
- Conventionally, there has been a wireless local area network (LAN) system connected to a wired LAN and many wireless terminals.
- Japanese Patent Laid-Open Publication No. Hei 7-312597 (disclosed in Japan on Nov. 28, 1995) discloses a wireless LAN system that prevents packets from being lost. This technology will be described below as a first conventional example.
-
FIG. 10 is a block diagram showing the wireless LAN system according to the first conventional example. Awireless LAN system 110, shown inFIG. 10 , consists of a client terminal 18 connected to awired LAN 112, aLAN cable 120 forming thewired LAN 112,access points wired LAN 112, andwireless terminals access points wireless LANs - In the system of this conventional example, when the source
wireless terminal 130 transmits a packet to the destinationwireless terminal 134 but thewireless terminal 134 does not respond to it, theaccess point wireless LAN wired LAN 112. In this way, the system prevents a packet loss caused by a conflict in accessing the medium or an interference with other communication networks using the same frequency band. - Japanese Patent Laid-Open Publication No. Hei 8-242232 (disclosed in Japan on Sep. 17, 1996) discloses a wireless terminal LAN having a repeater. This technology will be described as a second conventional example.
-
FIG. 11 is a block diagram of the wireless LAN system of the second conventional example. The wireless terminal LAN, shown inFIG. 11 , consists of wireless terminals 202-210 and awireless repeater 201 containing atransceiver 220. - The system according to this conventional example has the special
wireless repeater 201 and, through thiswireless repeater 201, re-transmits packets to reduce conflicts in radio waves. Thus, the system can prevent the throughput of the whole LAN from being decreased. - Japanese Patent Laid-Open Publication No. Hei 9-215044 (disclosed in Japan on Aug. 15, 1997) discloses a priority switching technology for a cellular wireless LAN. This technology will be described as a third conventional example.
-
FIG. 12 is a block diagram of the wireless LAN system according to the third conventional example. The wireless LAN system, shown inFIG. 12 , consists of a plurality ofportable units 302 that are wireless terminals, ahouse computer 304 connected to a wired LAN, and a plurality ofaccess points 305 that perform as bridges to the wired LAN. - In the system according to this conventional example, the
portable unit 302 searches and identifies theaccess point 305 best suited for communication, based on the intensity of radio waves from, and the loading factor of, the plurality of theaccess points 305. - In addition, to make the advantages of the present invention clearer, a virtual technology with a configuration equivalent to that of the system according to the present invention will be described as a fourth conventional example.
-
FIG. 13 is a block diagram of a wireless LAN system according to the fourth conventional example.FIG. 14 is a flowchart showing a fault recovery processing of the wireless LAN system according to the fourth conventional example. - The wireless LAN system, shown in
FIG. 13 , consists of access points Pa and Pb that perform as bridges to a wired LAN system Lw, client terminals Ca-Cd that are wireless terminals communicating with the access points Pa and Pb, and aLAN cable 405 consisting the wired LAN system Lw. - As shown in
FIG. 13 , the access points Pa and Pb transmit beacon information Iba and Ibb, respectively, at regular intervals (step S101 inFIG. 14 ). - When the client terminal Ca receives the beacon information Iba from the access point Pa at power-on time or roaming time, the client terminal Ca transmits a management frame back to the access point Pa to start negotiation with the access point Pa and then starts communication with the access point Pa.
- The client terminal Cb also starts negotiation with the access point Pb and then starts communication with the access point Pb according to the same procedure (step S102 in
FIG. 14 ). - At this point, when the access point Pa fails for some reason or other (step S103 in
FIG. 14 ), the client terminal Ca cannot continue communication with the access point Pa. So, the client terminal Ca starts searching for another access point Pb (step S104 inFIG. 14 ). - If another access point Pb is near the client terminal Ca (step S105 in
FIG. 14 ), there is no problem because the client terminal Ca can immediately establish a link with the access point Pb to continue communication (step S106 inFIG. 14 ). - However, if another access point Pb is not near the client terminal Ca (step S105 in
FIG. 14 ), the client terminal Ca continues search processing until it successfully searches for the access point Pb (step S104 inFIG. 14 ). - This search processing is executed by the client terminal Ca for transmitting a management frame (probe) that is communication control management information. To establish the link to the access point Pb as soon as possible and to continue communication reliably, the client terminal Ca continues transmitting the management frame, during this search processing, at an interval shorter than that for a normal communication frame.
- However, the above processing has the problems described below.
- First, in the above search processing, the client terminal Ca frequently transmits the management frame at an interval shorter than that for the normal communication frame. This increases the radio wave interference around the client terminal Ca and therefore decreases the throughput of the whole LAN system L.
- Second, in the above search processing, the client terminal Ca frequently transmits the management frame at an interval shorter than that for the normal communication frame. This processing has some problems with the client terminal Ca being battery-powered. For example, this processing consumes more battery power for communication and therefore shortens battery life. And, the increase in power consumption causes a quickly decrease in the power voltage, sometimes suddenly disconnecting the power of the portable information terminal and thus destroying data due to a communication interruption.
- Third, in a wireless LAN system Ll, the duplicated system configuration is built usually for the access points Pa and Pb as a fail-safe against the shutdown of the whole LAN system L. This shutdown may be caused by such conditions as a fault in access point Pa or Pb or the disconnection of a
LAN cable 405. However, in a wireless LAN system used generally in Japan, whose frequency bandwidth is only one third of a wireless LAN system generally used in the United States, duplicating the access points Pa and Pb allows the access points Pa and Pb to transmit radio waves frequently during the above search processing. This increases the radio wave interference and therefore decreases the throughput of the whole LAN system. - An object of the present invention is to provide a wireless LAN system that prevents throughput from being decreased even when an access point fails, a fault recovery method, and a recording medium storing therein a computer program executing the fault recovery process.
- The wireless LAN (Local Area Network) system according to the present invention consisting of a plurality of access points and a plurality of client terminals; wherein each of the plurality of access points consists of: a main unit for communicating with the client terminals, a first fault detecting unit for detecting a fault on the main unit, and a disconnection controlling unit for disconnecting the client terminal connected to the access point where the fault was detected by the first fault detecting unit; and wherein each of the plurality of client terminals consists of: a transceiver unit for communicating with the access point, a search controlling unit for searching for another client terminal to which the client terminal disconnected from the access point is to be connected, and a connection controlling unit for connecting the disconnected client terminal to the searched client terminal by the search controlling unit.
- The fault recovery method according to the present invention consisting of a plurality of access points and a plurality of client terminals, the method consisting of the steps of: detecting, by each of the access points, whether a fault occurs on each of the access points itself; disconnecting, by the access point which has detected the fault, the client terminal connected thereto; searching for, by the disconnected client terminal, another of the client terminals to which the disconnected client terminal is to be connected; and connecting the disconnected client terminal to the searched client terminal.
- The recording medium stores therein a computer program for executing a fault recovery process according to the present invention consisting of a plurality of access points and a plurality of client terminals, the process consisting of the steps of: detecting, by each of the access points, whether a fault occurs on each of the access points itself; disconnecting, by the access point which has detected the fault, the client terminal connected thereto; searching for, by the disconnected client terminal, another of the client terminals to which the disconnected client terminal is to be connected; and connecting the disconnected client terminal to the searched client terminal.
- When a fault occurs in an access point, a client terminal connected to this access point is disconnected. Instead of connecting the disconnected client terminal to another access point as in the conventional example, the system according to the present invention connects the client terminal to another client terminal. And, through this another client terminal, the disconnected client terminal connects to another access point. This prevents the load from being concentrated at another access point.
-
FIG. 1 is a block diagram showing a wireless LAN system in an embodiment of the present invention. -
FIG. 2 is a block diagram of an access point of the wireless LAN system according to theFIG. 1 embodiment. -
FIG. 3 is a block diagram of a client terminal of the wireless LAN system according to theFIG. 1 embodiment. -
FIG. 4 is a flowchart showing a fault recovery processing of the wireless LAN system according to theFIG. 1 embodiment. -
FIG. 5 is a diagram showing communication processing in the normal state of the wireless LAN system according to theFIG. 1 embodiment. -
FIG. 6 is a diagram showing disconnection processing in the fault occurring state of the wireless LAN system according to theFIG. 1 embodiment. -
FIG. 7 is a diagram showing search processing in the fault occurring state the wireless LAN system according to theFIG. 1 embodiment. -
FIG. 8 is a diagram showing connection processing in the fault occurring state of the wireless LAN system according to theFIG. 1 embodiment. -
FIG. 9 is a diagram showing another connection processing in the fault occurring state of the wireless LAN system according to theFIG. 1 embodiment. -
FIG. 10 is a block diagram of the wireless LAN system according to the first conventional example. -
FIG. 11 is a block diagram of the wireless LAN system according to the second conventional example. -
FIG. 12 is a block diagram of the wireless LAN system according to the third conventional example. -
FIG. 13 is a block diagram of the wireless LAN system according to the fourth conventional example. -
FIG. 14 is a flowchart showing a fault recovery processing of the wireless LAN system according to the fourth conventional example. -
FIG. 1 is a block diagram showing a wireless LAN system in an embodiment of the present invention. - A wireless LAN system Ll, shown in
FIG. 1 , consists of access points Pa and Pb that are bridges to a wired LAN system Lw and client terminals Ca-Cd that are wireless communication terminals communicating with these access points Pa and Pb. - This wireless LAN system Ll uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) as the communication protocol. Note that any number of the access points Pa and Pb and the client terminals Ca-Cd may be used.
- On the other hand, the wired LAN system Lw consists of the access points Pa and Pb, which are bridges to the wireless LAN system Ll, and a
LAN cable 5 which is, for example, an Ethernet cable connecting the access points Pa and Pb. This wired LAN system Lw uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD) as the communication protocol. -
FIG. 2 is a block diagram of an access point of the wireless LAN system according to theFIG. 1 embodiment. The access point Pa, shown inFIG. 2 , consists of amain unit 1 a, afault detecting unit 10 a, adisconnection controlling unit 20 a, afault detecting unit 30 a, and a permissioninformation generating unit 40 a. - The
main unit 1 a is a relaying unit connecting the wired LAN system Lw (FIG. 1 ) and the wireless LAN system Ll (FIG. 1 ). Themain unit 1 a communicates with the client terminals Ca and Cb (FIG. 1 ) included in an area Aa (FIG. 1 ) served by the access point Pa by radio waves. Not only the radio waves but also other wireless communication media such as an infrared ray may be used as the communication medium. - In addition, the
main unit 1 a transmits management information, called beacon information Iba (FIG. 1 ), at regular intervals. The beacon information is composed of synchronization information, packet transmission control information, and so on. By exchanging the beacon information Iba and Ibb (FIG. 1 ) with the other access point Pb, themain unit 1 a maintains the synchronization of the whole LAN system and, at the same time, controls communication so that a packet collision is avoided. - The
fault detecting unit 10 a is means for monitoring the status of communication between the wired LAN system Lw and themain unit 1 a. When themain unit 1 a of the access point Pa fails or theLAN cable 5 is disconnected, thefault detecting unit 10 a detects that themain unit 1 a has been disconnected from theLAN cable 5 and outputs a fault detecting signal Sha. - In response to the fault detecting signal Sha, the
disconnection controlling unit 20 a outputs a disconnect signal Sda to themain unit 1 a to instruct themain unit 1 a to disconnect the client terminal Ca (FIG. 1 ) being connected. - The
fault detecting unit 30 a receives the beacon information Ibb (FIG. 1 ) from the other access point Pb (FIG. 1 ). If thefault detecting unit 30 a detects that the other access point Pb (FIG. 1 ) has failed, thefault detecting unit 30 a outputs a fault detecting signal Spa. - In response to the fault detecting signal Spa, the permission
information generating unit 40 a transmits permission information Ip which permits all the client terminals under control of the access point Pa, that is, Ca and Cb (FIG. 1 ), to accept the urgent identification (ID) code. - A
main unit 1 b, afault detecting unit 10 b, adisconnection controlling unit 20 b, afault detecting unit 30 b, and a permissioninformation generating unit 40 b of the access point Pb each have the configuration similar to that of the corresponding unit of the access point Pa. -
FIG. 3 is a block diagram of a client terminal of the wireless LAN system according to theFIG. 1 embodiment. The client terminal Ca shown inFIG. 3 consists of atransceiver unit 50 a, asearch controlling unit 60 a, aconnection controlling unit 70 a, and arepeat controlling unit 80 a. - The
transceiver unit 50 a communicates with the access points Pa and Pb (FIG. 1 ) by radio waves. - When communication is forced to terminate by the access point Pa or Pb, the
search controlling unit 60 a transmits a management frame through thetransceiver unit 50 a to search for another client terminal Cb-Cd to which the client terminal Ca will be connected. - The
connection controlling unit 70 a connects the client terminal Ca, through thetransceiver unit 50 a, to one of the client terminals Cb-Cd that was searched for by thesearch controlling unit 60 a. - When a connection request is received from the connection controlling unit 70 b-70 d of one of the other client terminals Cb-Cd, the
repeat controlling unit 80 a instructs thetransceiver unit 50 a to perform communication processing for the MAC (Media Access Control) sub-layer and lower-level layers for data to be communicated between one of the client terminals Cb-Cd and the access point Pa or Pb (FIG. 1 ). - Transceiver units 50 b-50 d, search controlling units 60 b-60 d, connection controlling units 70 b-70 d, and repeat controlling units 80 b-80 d of the client terminals Cb-Cd each have the configuration similar to that of client terminal Ca.
- The client terminals Ca-Cd may be, for example, standalone computers, POS (Point-Of-Sales) terminals, or portable information terminals with the radio communication function, or computers, POS terminals, or portable information terminals with no radio communication function but with a radio communication adapter connected.
-
FIG. 4 is a flowchart showing a fault recovery processing of the wireless LAN system according to theFIG. 1 embodiment. - As shown in
FIG. 1 , the access points Pa and Pb transmit the beacon information Iba and Ibb at regular intervals, respectively (step S1 inFIG. 4 ). -
FIG. 5 is a diagram showing communication processing in the normal state of the wireless LAN system according to theFIG. 1 embodiment. Upon receiving the beacon information Iba from the access point Pa at power-on time or roaming time, the client terminal Ca transmits the management frame back to the access point Pa to perform negotiation therewith. The client terminal Ca then starts communication with the access point Pa as shown inFIG. 5 (step S2 inFIG. 4 ). - Each of the client terminals Cb-Cd performs negotiation with the access point Pb in the same way as described above and, as shown in
FIG. 5 , starts communication with the access point Pb. - Because this negotiation processing is a basic wireless LAN system technology that is well known, its description is omitted here.
-
FIG. 6 is a diagram showing disconnection processing in the fault occurring state the wireless LAN system according to theFIG. 1 embodiment. Assume that, during normal communication processing shown inFIG. 5 , a fault occurs on the access point Pa as shown inFIG. 6 (step S3 inFIG. 4 ). The cause of this fault is, for example, a fault in themain unit 1 a (FIG. 2 ) of the access point Pa or the disconnection of theLAN cable 5 connected to themain unit 1 a (FIG. 2 ). - The
fault detecting unit 10 a (FIG. 2 ) of the access point Pa monitors the status of communication between the wired LAN system Lw and themain unit 1 a (FIG. 2 ). When thefault detecting unit 10 a detects a fault on themain unit 1 a of the access point Pa or on theLAN cable 5 connected therewith, thefault detecting unit 10 a (FIG. 2 ) outputs the fault detection signal Sha (FIG. 2 ) to thedisconnection controlling unit 20 a (FIG. 2 ). In response to the fault detection signal Sha (FIG. 2 ), thedisconnection controlling unit 20 a (FIG. 2 ) disconnects the client terminal Ca, which is connected to the access point Pa at that time, from the access point Pa and forces communication between them to terminate (step S4 inFIG. 4 ). -
FIG. 7 is a diagram showing search processing in the fault occurring state of the wireless LAN system according to theFIG. 1 embodiment. As shown inFIG. 7 , thesearch controlling unit 60 a (FIG. 3 ) of the disconnected client terminal Ca transmits a management frame, which is management information, through thetransceiver unit 50 a (FIG. 3 ) to search for another client terminal Cb-Cd to which the client terminal Ca is to be connected (step S5 inFIG. 4 ). - On the other hand, the
fault detecting unit 30 b (FIG. 2 ) of the other access point Pb detects the occurrence of the fault in the access point Pa based on the beacon information Iba, starts the operation of the permissioninformation generating unit 40 b (FIG. 2 ). Thefault detecting unit 30 b (FIG. 2 ) transmits the permission information Ip to the client terminals Cb-Cd through themain unit 1 b (FIG. 2 ) (step S6 inFIG. 4 ). - Upon receiving the permission information Ip, the transceiver units 50 b-50 d (
FIG. 3 ) of the client terminals Cb-Cd in the area Ab under control of the access point Pb are set to the emergency ID reception permitting state (step S7 inFIG. 4 ). -
FIG. 8 is a diagram showing connection processing in the fault occurring state of the wireless LAN system according to theFIG. 1 embodiment. Theconnection controlling unit 70 a (FIG. 3 ) of the disconnected client terminal Ca transmits the emergency ID code to the client terminal Cd through thetransceiver unit 50 a (FIG. 3 ). Theconnection controlling unit 70 a (FIG. 3 ) then performs connection processing such as log-in processing for the client terminal Cd that was searched for during the search processing (step S8 inFIG. 4 ). - The client terminal Cd controls communication between the client terminal Cd itself and the access point Pb and, at the same time, relays data to be communicated between the client terminal Ca and the access point Pb (step S9 in
FIG. 4 ). - In this way, the client terminal Cd performs as a repeater that relays communication data of the client terminal Ca that is a disconnected client terminal. In this embodiment, the equal distribution system is used and all client terminals Ca-Cd operate under the same logic. Therefore, all client terminals Ca-Cd are eligible for a repeater.
- Thus, at emergency time, even if the ID code of the client terminal Ca is different from the ID code of the Client terminal Cd, the emergency ID code is used for all the client terminals Ca-Cd commonly. This allows the client terminal Ca to connect to one of the client terminals Cb-Cd.
- The fault recovery processing for the whole LAN system L is completed by executing the above steps.
-
FIG. 9 is a diagram showing another connection processing in the fault occurring state of the wireless LAN system according to theFIG. 1 embodiment. Instead of the processing shown inFIG. 8 in which the client terminal Ca connects to the access point Pb through therepeat controlling unit 80 a of the client terminal Cd (steps S8 and S9 inFIG. 4 ), the client terminal Ca obtains communication information from the client terminal Cd. This communication information includes information on the access point Pb to which the client terminal Ca can access. Then, thesearch controlling unit 60 a and theconnection controlling unit 70 a of the client terminal Ca negotiate directly with the access point Pb to connect the client terminal Ca thereto (steps S18 and S19 inFIG. 4 ). - This method prevents the communication load from being concentrated at the client terminal Cd, thus minimizing a decrease in the throughput of the wireless LAN system Ll.
- In the above embodiments, each of the access points Pa and Pb consists of the
main unit fault detecting unit disconnection controlling unit fault detecting unit information generating unit main unit FIG. 2 , this software program is stored on arecording medium - On the other hand, each of the client terminals Ca-Cd consists of each of the transceiver units 50 a-50 d, each of the search controlling units 60 a-60 d, each of the connection controlling unit s70 a-70 d, and each of the repeat controlling units 80 a-80 d, respectively. These units except the transceiver units 50 a-50 d may be implemented by a software program built in each of the client terminals Ca-Cd. As shown in
FIG. 3 , this software program may be stored on each recording medium 98 a-98 d such as a memory contained in each client terminal Ca-Cd. Each processing means 99 a-99 d, such as the CPU, is provided to read this program for execution. - Even when a fault occurs in an access point, the system according to the present invention eliminates the need for a client terminal connected to that access point to wait until another access point transmits beacon information. Instead, the client terminal automatically searches for another nearby client terminal and causes the nearby client terminal to perform as a repeater. This allows management information required for communication control to be obtained easily and quickly. As a result, communication among client terminals may be reestablished more quickly than in the conventional examples described above.
- In addition, the system according to the present invention prevents a plurality of client terminals with no connection destination from attempting to connect to the same access point at the same time. This access-point load balancing ability prevents the throughput of the whole LAN system from being decreased.
Claims (6)
1. A wireless local area network system comprising a plurality of access points and a plurality of client terminals;
wherein each of said plurality of access points comprises:
a main unit for communicating with said client terminals,
a first fault detecting unit for detecting a fault on said main unit, and
a disconnection controlling unit for disconnecting said client terminal connected to said access point where said fault was detected by said first fault detecting unit; and
wherein each of said plurality of client terminals comprises:
a transceiver unit for communicating with said access point,
a search controlling unit for searching for another client terminal to which said client terminal disconnected from said access point is to be connected, and
a connection controlling unit for connecting said disconnected client terminal to said searched client terminal by said search controlling unit independent of the plurality of access points.
2. The wireless local area network system as defined in claim 1 , wherein each of said client terminals further comprises a repeat controlling unit for controlling communication between said disconnected client terminal and one of said access points connected to said searched client terminal.
3. A fault recovery method for use in a wireless local area network system comprising a plurality of access points and a plurality of client terminals, the method comprising the steps of:
detecting, by each of said access points, whether a fault occurs on each of said access points itself;
disconnecting, by said access point which has detected said fault, said client terminal connected thereto;
searching for, by said disconnected client terminal, another of said client terminals to which said disconnected client terminal is to be connected; and
connecting said disconnected client terminal to said searched client terminal independent of the plurality of access points.
4. The fault recovery method for use in a wireless local area network system as defined in claim 3 , further comprising the step of controlling, by said searched client terminal, communication between said disconnected client terminal and another of said access points connected to said searched client terminal.
5. A recording medium storing therein a computer program for executing a fault recovery process for use in a wireless local area network system comprising a plurality of access points and a plurality of client terminals, the process comprising the steps of:
detecting, by each of said access points, whether a fault occurs on each of said access points itself;
disconnecting, by said access point which has detected said fault, said client terminal connected thereto;
searching for, by said disconnected client terminal, another of said client terminals to which said disconnected client terminal is to be connected; and
connecting said disconnected client terminal to said searched client terminal independent of the plurality of access points.
6. The recording medium storing therein a computer program for executing the fault recovery process for use in a wireless local area network system as defined in claim 5 , further comprising the step of controlling, by said searched client terminal, communication between said disconnected client terminal and another of said access points connected to said searched client terminal.
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Also Published As
Publication number | Publication date |
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JP3251272B2 (en) | 2002-01-28 |
JP2000349787A (en) | 2000-12-15 |
US6877104B1 (en) | 2005-04-05 |
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