`HSu
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`USOO6345.043B1
`(10) Patent No.:
`US 6,345,043 B1
`(45) Date of Patent:
`Feb. 5, 2002
`
`(54) ACCESS SCHEME FOR AWIRELESS LAN
`STATION TO CONNECT AN ACCESS POINT
`
`(75) Inventor: Yi-Shou Hsu, Hsinchu (TW)
`(73) Assignee: National Datacomm Corporation,
`Hsinchu (TW)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(*) Notice:
`
`6,088,591 A * 7/2000 Trompower et al. ........ 370/331
`6.256,334 B1
`7/2001 Adachi ....................... 370/310
`6,259,898 B1
`7/2001 Lewis ........................ 370/338
`
`* cited b
`cited by examiner
`
`Examiner Wellington Chi
`Pri
`rimary Examiner-wellington nin
`ASSistant Examiner Maikhanh Tran
`(57)
`ABSTRACT
`
`(21) Appl. No.: 09/110,829
`1-1.
`Jul. 6, 1998
`(22) Filed:
`(51) Int. Cl." ............................ H04B 71212; H04J 3/06;
`HO4O 7/20
`(52) U.S. C. - - - - - - - - - - - - - - - - - - - - - - - 370/324; 370/350; 370/509;
`
`An access Scheme for a wireleSS LAN Station to connect an
`access point on the network. This Scheme allows a wireleSS
`Station to finish all the processes from Search to registration
`with an AP at a very high speed. Firstly, the time interval of
`beacon transmission is shortened when a wireleSS Station is
`powered O. Secondly, the authentication phase in tradi
`
`tional registration with an AP is eliminated. Instead, a period
`455/1611; 455/403; 455/435
`of time on each channel is reserved. Accordingly, the wire
`(58) Field of Search ................................. 370/310,324,
`370/328, 347, 350, 498, i. ... leSS LAN Station can use this period to exchange control
`/403,
`s
`frames with the AP without competing with other stations to
`acceSS wireleSS medium. This results in quick access to the
`network.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`5,844,900 A * 12/1998 Hong et al. ................. 370/342
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`2 Claims, 6 Drawing Sheets
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`S12
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`transmit
`data frame
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`data
`received
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`beacon interval is
`due
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`AP
`data
`transfer
`state
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`511
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`transmit beacon
`frame
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`starting reserved period time
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`receive association request
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`AP
`associatio
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`n
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`state
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`transmit
`w
`association
`response frame
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`reserved period time
`is expired
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`switch to
`next channel
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`Sheet 1 of 6
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`Sheet 2 of 6
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`Sheet 3 of 6
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`301
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`"IDLE" state
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`Scannling
`phase
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`302
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`set radio
`channel
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`303
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`BOl.
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`listen to each channel
`and Scan for AP beaCon AP beacon is not
`found, listen to
`next channel
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`EYE AP
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`adopt local hopping
`time and channel
`sequence to
`synchronize with AP
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`305
`authentication
`phase
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`exchange some
`packets with AP for
`authentication
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`306
`association
`phase
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`exchange association
`packets with AP
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`307
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`begin to exchange
`data frames With
`AP
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`FIG. 3 (Prior Art)
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`Sheet 4 of 6
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`l, O1
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`l, O2
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`l,03
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`"IDLE" state
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`Set radio
`Channel
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`start 10 ms
`timer
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`l, 0
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`receive
`AP beacon?
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`adopt local hoppin
`p
`ppling
`time and channel
`sequence to
`synchronize
`With AP
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`timer iS
`timeout?
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`Set hardware to l, O7
`next channel
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`wait for the local
`hopping time to enter
`reserved period
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`l,06
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`108
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`L 09
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`exchange the
`association packets
`With AP
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`l, 10
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`begin to transfer
`data With AP
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`FIG. 4
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`Sheet 5 of 6
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`transmit
`data frame
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`data
`received
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`S10
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`beacon interval is
`due
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`AP
`data
`transfer
`state
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`S11
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`transmit beacon
`frame
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`starting reserved period time
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`520
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`receive association request
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`AP
`association
`reserved
`state
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`transmit
`association
`response frame
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`reserved period time
`is expired
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`switch to
`next channel
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`522
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`FIG. 5
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`EX 1016/ Page 7 Of10
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`1
`ACCESS SCHEME FOR AWIRELESS LAN
`STATION TO CONNECT AN ACCESS POINT
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`US 6,345,043 B1
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`2
`first phase is authentication. This proceSS is used to identify
`whether the Station has the legal right or not to access the
`wireless network via a medium access control (MAC) layer.
`After the authentication is passed, the Station needs to
`establish a connection link with the AP by sending an
`asSociation request packet to the AP and waiting to receive
`a response frame from the AP which acknowledges the
`asSociation.
`The general steps taken for a wireless STAby a traditional
`MAC Sub-layer management architecture from Search to
`registration with an AP are shown in FIG. 3. According to
`the design of FIG. 3, a wireless STA shall perform the three
`phases: Scanning phase, authentication phase and associa
`tion phase.
`In the scanning phase, all IEEE 802.11 STAs initially start
`“IDLE” state (step 301). The radio hopping channel shall be
`set by the hardware (step 302). To search for the AP, a
`wireleSS STA shall listen in each channel and Scan for any
`beacon frame transmitted by the AP (step 303). Upon finding
`the channel and receiving the AP beacon, the Scanning phase
`is completed. Otherwise, the wireless STA shall listen in the
`next channel and return to Step 302. A new radio hopping
`channel shall be set.
`After receiving the AP beacon, the receiving wireless STA
`will join a BSS by Setting its local hopping time and channel
`Sequence according to the information contained in the AP
`beacon (step 304) in order to maintain synchronization with
`the AP. The remaining StepS constitute the authentication
`phase and association phase.
`In the authentication phase, IEEE 802.11 in general
`requires bi-directional authentication. At step 305, the wire
`less STA exchanges some packets with the AP for authen
`tication. It may further include three Steps of assertion of
`identity, challenge of assertion and response to challenge.
`In the association phase (step 306), the wireless STA
`eXchanges the association packets with the AP to accomplish
`the AP registration. The communication link between the
`wireless STA and the AP is thus setup. The wireless STA can
`start exchanging data frames with the AP (step 307).
`Because the radio frequency hops between 2.40 GHz and
`2.50 GHz, a wireless LAN station may take a long time to
`find an AP among the 79 channels in Federal Communica
`tions Commissions (FCC) regulation.
`Each frame used in authentication and association should
`be sent in complying with the rule of to 802.11 standard
`(Carrier Sense Multiple Access with Collision Avoidance,
`CSMA/CA). The time consumed for a wireless station to
`complete all the processes of authentication and association
`may vary greatly, and is unpredictable, especially when the
`traffic in the wireless medium is busy. Therefore, the total
`time from Searching for an AP to accomplish the registration
`is unpredictable for the wireless LAN stations that comply
`with 802.11 standard.
`From the foregoing discussions of prior arts, it can be seen
`that the disadvantages as pointed out earlier make the
`conventional access Scheme inappropriate for a wireleSS
`LAN station to connect with an AP. There exists a strong
`need for having a more efficient access Scheme for the
`wireleSS LAN Station to quickly access a wireleSS LAN
`through an AP.
`
`FIELD OF THE INVENTION
`The present invention relates generally to wireleSS local
`area network (LAN) systems, and more particularly to an
`access Scheme for a wireleSS LAN Station to connect an
`access point (AP).
`BACKGROUND OF THE INVENTION
`According to the wireless LAN standard (IEEE 802.11),
`a wireless LAN station needs to connect to an AP for
`accessing a file Server or other WorkStations of a network
`system. The AP connects distributed systems and a set of
`basic Service areas. It provides the communication between
`a local Station in a wireleSS LAN and a remote Station in
`another LAN. It also provides the capability of accessing
`distributed System for a Station.
`FIG. 1 shows the typical hardware architecture of a
`wireless LAN system. As illustrated in FIG. 1, an Ethernet
`LAN 100 may have two basic service sets 101 (BSS) and
`102 (BSS), one workstation 103 and one file server 104.
`Each basic Service Set comprises one access point and two
`wireleSS Stations. Basic Service Set BSS includes the acceSS
`point AP and two stations STA and STA. Basic service set
`BSS includes the access point AP and two stations STA
`and STA. Each wireless station should associate itself with
`one AP before it can communicate with the file server 104
`or the workStation 103 in the Ethernet LAN 100.
`When a wireless LAN station is powered on, it first looks
`for an AP. After it finds an AP, the wireless LAN station
`register itself with the AP. The station can then synchronize
`with the AP and, thereafter, transmit and receive information
`packet to and from the AP
`According to the wireless LAN standard (IEEE 802.11),
`the bandwidth used in the RF (radio frequency) is between
`2.40 GHz and 2.50 GHz among 79 channels in the US and
`Canada areas. The frequency hopping radio signal shall hop
`in the frequency band between 2.40 GHz and 2.50 GHz as
`shown in FIG. 2. The AP shall be the timing master and shall
`perform the TSF (timing Synchronization function) to keep
`the timers for all wireless stations in the same BSS synchro
`nized. For each channel, the AP shall periodically transmit
`Special frames called beacons each containing a copy of its
`TSF timer and hopping Sequence to Synchronize other
`wireless stations in a BSS. The AP shall broadcast a gener
`ated beacon frame at a fixed time interval referred to as a
`beacon interval.
`A receiving wireleSS STA shall always accept the timing
`information in beacons sent from the AP servicing its BSS.
`If a wireless STA’s TSF timer is different from the times
`tamp in the received beacon frame, the receiving wireleSS
`STA shall set the value of its local timer to the received
`timestamp value.
`Traditionally, when an AP is powered on in a basic service
`Set, it periodically broadcasts a beacon frame to all wireleSS
`STAS in the service set. The beacon frame contains the
`information for synchronizing with the AP and the informa
`tion is referred to by the wireless STA looking for the AP.
`Because the beacon interval used in the traditional approach
`is long (100 mini Seconds), it could increase the Search time
`for an AP to the wireless STA looking for the AP
`A wireleSS LAN Station needs to do a registration before
`it can communicate with an AP. According to 802.11
`Standard, the registration should include two phases. The
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`SUMMARY OF THE INVENTION
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`65
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`This invention has been made to overcome the above
`mentioned drawbacks and inefficiencies in a wireleSS LAN.
`The primary object of the present invention is to provide a
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`new scheme that allows a wireless LAN station to finish all
`the processes from Search to registration with an AP at a very
`high Speed.
`In accomplishing that object, the present invention
`changes the method of Searching for an AP when a wireleSS
`LAN station is powered on. The time interval of beacon
`transmission is reduced from 100 mini seconds to 10 mini
`Seconds. Thus, the time used in Searching for an AP is
`shortened because the wireless LAN station only needs to
`Stay in a channel for 10 mini Seconds to Search for the
`beacon frame on each hopping channel. For FCC regulation,
`this change reduces the search time from 7900 (79* 100)
`mini seconds to 790 (79*10) mini seconds.
`Another object of the invention is to solve the problem
`that the time consumed for a wireleSS Station to complete all
`the processes of authentication and asSociation may vary a
`lot and the required time is unpredictable. Because upper
`layer applications do the authentication as well as check a
`Station which logins in to the Server, the present invention
`omits the authentication process first. It is expected that the
`network security shall not be affected much due to the
`elimination of the authentication process in wireleSS LAN
`MAC layer.
`In addition, the present invention reserves a period of time
`dedicated to Sending the association control packets on each
`channel. The data packet cannot be sent in this period for an
`AP and other associated Stations. Therefore, when the station
`is just turned on and trying to associate with an AP, it can use
`this reserved period to exchange the control frames with the
`AP without having to compete with other Stations to acceSS
`the wireleSS medium.
`Briefly, this invention discloses a scheme to shorten the
`time in searching for an AP for a wireless LAN station by
`reducing the time interval of the beacon transmission.
`Accordingly, it reduces the Search time by a ratio 1/10.
`In addition, when a wireless LAN station needs to do a
`registration before it can communicate with an AP, the
`invention eliminates the authentication process, and reserves
`a period of time on each channel for Sending the association
`40
`control packets. Accordingly, it allows a wireleSS LAN
`Station to finish all the processes from Search to registration
`with an AP at a very high Speed.
`The foregoing and other objects, features, aspects and
`advantages of the present invention will become more
`apparent from a careful reading of a detailed description
`provided herein below, with appropriate reference to the
`accompanying drawings.
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`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 illustrates the typical hardware architecture for a
`wireless LAN system.
`FIG. 2 illustrates that the radio signal shall hop among 79
`channels within the frequency band between 2.40 GHZ-2.50
`GHz in the U.S. and Canada areas according to IEEE 802.11
`Standards.
`FIG. 3 illustrates the general steps taken by a traditional
`MAC sub-layer management architecture for a wireless STA
`from Search to registration with an AP.
`60
`FIG. 4 shows a flow diagram illustrating the general Steps
`taken by a wireleSS STA from Search to registration with an
`AP according to the invention when a wireless LAN station
`is powered on.
`FIG. 5 shows a finite state machine for an AP in a channel,
`illustrating the current AP states existing for the flow in FIG.
`4.
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`4
`FIGS. 6a-6b illustrate the beacon interval for AP trans
`mitting beacon and the reserved period on each channel
`according to the present invention respectively.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`In the present invention, the primary point of novelty is
`the Scheme that allows a wireless LAN station to finish all
`the processes from Search to registration with an AP at a very
`high speed. FIG. 4 shows the flow chart for a wireless STA
`from Search to registration with an AP according to the
`invention when a wireless LAN station is powered on. When
`a wireleSS LAN Station performs all the Steps from Search to
`registration with the AP, the finite state machine for the AP
`employed therein is shown in FIG. 5.
`With reference first to FIG. 4, a wireless STA initially
`starts at an “IDLE” state (step 401). The radio channel is set
`by the hardware (step 402). Because, the present invention
`shortens the time interval of beacon transmission to 10 mini
`seconds, it starts a 10 minisecond timer (step 403). Then, the
`wireleSS STA listens in each channel and Scans for any
`beacon frame transmitted by the AP.
`At step 404, the wireless STA checks whether an AP
`beacon is received. Upon finding the channel and receiving
`the AP beacon, the Scanning phase is completed.
`Otherwise, the wireless STA checks whether the timer is
`timeout (step 405). If the timer is timeout, the wireless STA
`sets hardware to the next channel (step 407) and returns to
`step 402. If the timer is not timeout, at step 405, the wireless
`STA continues to check whether an AP beacon is received.
`The wireless STA only needs to stay in a channel for 10
`mini seconds to listen for the beacon frame on each hopping
`channel. For FCC regulation, this invention reduces the
`search time from 7900 (79* 100) mini seconds to 790
`(79* 10) mini seconds.
`After receiving the AP beacon, in order to maintain
`synchronization with the AP, at step 406, the receiving
`wireleSS STA Sets local hopping time and channel Sequence
`to be same as the information contained in the AP beacon.
`In the steps as shown in FIG. 4, the invention does not
`perform authentication process. In Stead, it reserves a period
`of time on each channel for Sending the association control
`packets. Accordingly, at step 408, the wireless STA waits for
`the local hopping time to enter the reserved period.
`In the association phase (step 409), the wireless STA
`eXchanges the association packets with the AP to accomplish
`the AP registration. The communication connection between
`the wireless STA and the AP is thus setup. At step 410, the
`wireless STA starts the data transfer with the AP.
`The state machine given by FIG. 5 comprises two states
`for an AP. One is a data transferring state 510 of the AP in
`the scanning phase of the wireless STA. The other is a
`reserved state 520 of the AP in the association phase of the
`wireless STA.
`In state 510, the allowed transferring frames are either a
`data frame or a beacon frame as shown in steps 511 and 512.
`AS mentioned before, the AP broadcasts a beacon frame at
`a fixed time interval on each channel. The AP Schedules a
`beacon frame transmission including Setting the beacon
`interval of beacon frame transmission as well as Setting the
`exact time of transmitting a beacon frame as the next frame
`for transmission. After the AP completes the beacon frame
`transmission, it goes back to the data transferring State.
`As shown in FIG. 5, in state 510, the AP can transfer data
`too. After the AP completes the data frame transmission, it
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`goes back to the data transferring State. When data receiving
`is completed, the AP also goes back to the data transferring
`State.
`AS mentioned earlier, the present invention reserves a
`period of time on each channel for Sending the association
`control packets. Once Starting the reserved period time, the
`AP enters the reserved state 520 in the association phase of
`the wireless STA.
`During the reserved period, only association request or
`response is allowed. Therefore, when the receiving wireleSS
`STA is just turned on and trying to associate with the AP, it
`can exchange the control frames with AP only using this
`reserved period.
`AS Shown in State 520, when receiving association request
`is completed, the AP Starts transmitting association response
`frame as shown in Step 521. Upon completing the
`transmission, the AP goes back to the state 520. In addition,
`during the reserved period, the AP doesn’t transfer data
`frame or data packet.
`Once the reserved period expires, as shown in Step 522,
`the APSwitches to the next channel and continues to proceSS
`operations of states 510 and 520.
`Because the reserved period is dedicated to Sending the
`asSociation control packet, the receiving wireleSS STA can
`use this reserved period to exchange the control frames with
`AP. And, the receiving wireless STA doesn't need to com
`pete with the other stations that are transferring data with AP
`Therefore, it won’t delay and the processing time from
`Search to registration with an AP can also be guaranteed.
`FIG. 6a illustrates the beacon interval for the AP to
`transmit beacon according to the present invention. Beacons
`are generated for transmission by the AP once every beacon
`interval. In the embodiment of the present invention, the
`beacon interval is 10 mini Seconds.
`FIG. 6b illustrates the reserved period on each channel
`according to the present invention. The reserved period is
`dedicated to Sending only the association control packets. AS
`shown in the FIG. 6b, neither the data frame nor the beacon
`frame can be sent in this period for AP and other associated
`Stations.
`There are Several factors in Selecting the range for the
`reserved period. One is the number of booting up Stations to
`be Supported for achieving the quick association. AS is
`known, a wireless LAN station takes about 2 ms to finish the
`registration process with an AP after it finds the AP. In the
`case of five wireless stations in a wireless LAN, if they are
`booted up at the same time, according to the present
`invention, the time of reserved period should be set to the
`value that is longer than 25 mS in order to accomplish the
`registration for all Stations.
`
`6
`Because the data packet transfer is inhibited during the
`reserved period, the throughput bandwidth of the wireless
`LAN System is Scarified. For longer reserved period, the
`wireless LAN system scarifies more throughput bandwidth.
`The present invention generally takes 5% Scarified
`throughput bandwidth. In the sense that, if five wireless
`LAN Stations are allowed to Start up in the same time, the
`present invention Specifies the reserved period to be 10 ms
`for each hopping channel having 200 ms of dwell time.
`Although this invention has been described with a certain
`degree of particularity, it is to be understood that the present
`disclosure has been made by way of preferred embodiments
`only and that numerous changes in the detailed construction
`and combination as well as arrangement of parts may be
`restored to without departing from the Spirit and Scope of the
`invention as hereinafter Set forth.
`What is claimed is:
`1. An access point State machine for establishing a con
`nection link with wireleSS Stations for a wireless local area
`network System having at least one basic Service Sets, each
`basic Service Set containing an access point and at least one
`wireleSS Station, comprising:
`data transfer State for transmitting beacon frames and
`accessing data frames by Said access point, Said access
`point Scheduling a beacon frame as the next frame for
`transmission, transmitting a beacon frame at a fixed
`time interval on each hopping channel, and Selecting a
`reserved period of time on each hopping channel for
`eXchanging association control packets with Said wire
`leSS Stations, and
`asSociation reserved State for exchanging Said association
`control packets with Said wireleSS Stations and Switch
`ing to next hopping channel for continuing Said data
`transfer state and association reserved State, said asso
`ciation control packets including association requests
`received from Said wireleSS Stations and association
`response frames transmitted by Said access point, Said
`access point transmitting an association response frame
`after an association request is received;
`wherein Said access point enterS Said reserved association
`State from Said data transfer State once Said reserved
`period of time Starts, and Said access point Switches to
`next hopping channel for continuing Said data transfer
`State and association reserved State once Said reserved
`period expires.
`2. The access point State machine according to claim 1,
`wherein Said access point refers to a plurality of parameters
`including the number of booting up wireleSS Stations and the
`throughput bandwidth of the wireless LAN system for
`Selecting the length of Said reserved period of time.
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