A method and apparatus informs nodes included in a wireless local area network (LAN) of how to avoid access collision in a wireless LAN. A wireless LAN access point or an independent basic service set (IBSS) control station receives a Contention-Free-End (cf-End) frame, compares a basic service set id (bssid) of the received cf-End frame of the access point or the IBSS, and rebroadcasts the received cf-End frame if the comparison result indicates that the two bssids coincide with each other. Thus, all stations included in one BSS can receive the same time information for controlling medium access.
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7. An apparatus for delivering transmitting a control Contention Free-End (cf-End) frame received through a wireless LAN, the apparatus comprising:
a recipient address information checking unit which checks recipient address information receiver configured to check a basic service Set id (bssid) included in the control a cf-End frame when the control frame including time information for medium access is received, the cf-End frame including a duration field of a mac header set to zero; and
a resending unit which broadcasts the received control transmitter configured to broadcast the cf-End frame in a selective manner based on the checking result, directly in response to determining the basic service Set id in the cf-End frame matches a bssid of a basic service Set (BSS) where the apparatus is included, wherein said transmitter is configured to broadcast the cf-End frame when a short inter frame space (SIFS) elapses after the cf-End frame was received, and
wherein, in the control frame, a duration field of a mac header has a value of 0, wherein the control frame is a cf-End frame,
wherein, the resending unit broadcasts the cf-End frame if the checking result indicates that a recipient address recorded in the cf-End frame is a broadcast address, and a bssid recorded in the cf-End frame coincides with a bssid of a BSS (basic service set), and
wherein, the resending unit broadcasts the received cf-End frame when a SIFS elapses after the cf-End frame wherein a network allocation vector (NAV) of a recipient of the cf-End frame is reset upon a receipt of the cf-End frame.
1. A method of delivering transmitting a control Contention Free-End (cf-End) frame for a device which communicates through a wireless local area network (LAN), the method comprising steps performed by a first station of:
receiving a control frame including time information for controlling medium access and recipient address information;
checking recipient address information a basic service Set id (bssid) included in a cf-End frame, the cf-End frame including a duration field of a mac header set to zero; and
broadcasting the received control frame in a selective manner based on a checking result, to a second station, the cf-End frame directly in response to determining the basic service Set id (bssid) in the cf-End frame matches a bssid of a basic service Set (BSS) where said first station is included, wherein the step of broadcasting the cf-End frame to said second station comprises the step of broadcasting the cf-End frame when a short inter frame space (SIFS) elapses after the cf-End frame was received, and
wherein, in the control frame, a duration field of a mac (medium access control) header has a value of 0,
wherein the control frame is a Contention-Free-End (cf-End) frame,
wherein the broadcasting the received control frame comprises broadcasting the received cf-END frame if the checking result indicates that a basic service set id (bssid) recorded in the cf-End frame coincides with a bssid of a BSS (basic service set), and
wherein the broadcasting the received control frame further comprises broadcasting the received cf-END frame when a short inter-frame space (SIFS) elapses after the cf-End frame is received wherein a network allocation vector (NAV) of said second station is reset upon a receipt of the cf-End frame.
2. The method of
0. 3. A non-transitory computer-readable medium having embodied thereon a computer program for executing the method of
4. The method of
0. 5. A non-transitory computer-readable medium having embodied thereon a computer program for executing the method of
0. 6. A non-transitory computer-readable medium having embodied thereon a computer program for executing the method of
8. An access point comprising the apparatus of
9. A wireless LAN station which comprises the apparatus of
0. 10. The method of claim 1, wherein the cf-End frame is transmitted by said first station to indicate a completion of a transmission opportunity of said first station.
0. 11. The method of claim 10, wherein another station that receives the cf-End frame resets a network allocation vector (NAV) so said another station is operable to contend for medium access.
0. 12. The apparatus of claim 7, wherein said apparatus is configured to transmit the cf-End frame to indicate a completion of a transmission opportunity.
0. 13. The apparatus of claim 12, wherein another station that is configured to receive the cf-End frame is configured to reset a network allocation vector (NAV) so said another station is operable to contend for medium access.
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This application claims priority from Korean Patent Application No. 10-2006-0032408, filed on Apr. 10, 2006 in the Korean Intellectual Property Office, and U.S. Provisional Patent Application No. 60/756,216, filed on Jan. 5, 2006, in the U.S. Patent and Trademarks Office, the disclosures of which are incorporated herein in their entirety by reference.
1. Field of the Invention
The present invention relates to a wireless local area network (LAN), and more particularly, to a method of informing nodes included in the wireless LAN of how to avoid access collisions in a wireless LAN.
2. Description of the Related Art
Medium access control (MAC) using a carrier sensing multiple access with collision avoidance (CSMA/CA) method is used in a wireless LAN.
In the CSMA/CA method, physical carrier sensing and virtual carrier sensing are used for carrier sensing. In physical carrier sensing, a physical layer (PHY) determines whether a received power equal to or greater than a specific value is detected, and informs a medium access control (MAC) layer of whether a medium is in a busy or idle state, thereby sensing a carrier. In virtual carrier sensing, if a MAC protocol data unit (MPDU) can be correctly extracted from a received PHY protocol data unit (PPDU), a header field of the MPDU, that is, a duration/ID field, is analyzed, and the medium is deemed to be in the busy state during a scheduled time for using the medium. Stations determine whether the medium is in the busy state by using the two carrier sensing methods, and do not access the medium if in the busy state.
Referring to
In
As described above, in virtual carrier sensing, the CSMA/CA can be effectively used only when the MAC protocol data unit/PHY service data unit (MPDU/PSDU) are analyzed without errors. That is, virtual carrier sensing can be carried out only when a MAC header value can be correctly read. However, if data is sent using a high data transfer rate and an error occurs due to an unstable channel condition, or a receiving station cannot cope with the high data transfer speed, virtual carrier sensing cannot be carried out because the received MPDU/PSDU cannot be analyzed. Therefore, the CSMA/CA method becomes ineffective. Accordingly, when a legacy station which operates in accordance with the IEEE 802.11 a/b/g standard and a high throughput (HT) station having a higher capability than the legacy station coexist in the wireless LAN, and when a HT format is sent, the legacy station cannot analyze the HT format frame, causing ineffective operation of a CSMA/CA mechanism. The HT station may be a multi-input-multi-output (MIMO) station which has data transferring capability superior to a station operating in accordance with the 802.11 a/b/g standard.
In order to solve the above problems, an IEEE 802.11n standard has been in development. Referring to
When the EPP is used, medium access collision can be avoided, but stations have to contend unfairly to attain permission for medium access.
Referring to
Accordingly, correct CSMA/CA can be carried out in the wireless LAN by using the CF-End frame, thereby ensuring a fair contention among stations. However, if the CF-End frame is not sent to all stations included in the wireless LAN, such advantages cannot be attained. As shown in
Exemplary embodiments of the present invention overcome the above disadvantages and other disadvantages not described above. Also, the present invention is not required to overcome the disadvantages described above, and an exemplary embodiment of the present invention may not overcome any of the problems described above.
The present invention provides a method and apparatus which allow stations connected in a wireless LAN to receive a control frame having information regarding media access.
According to an aspect of the present invention, there is provided a method of delivering a control frame for a device which communicates through a wireless LAN, the method comprising receiving a control frame including time information for controlling medium access, checking recipient address information included in the control frame, and broadcasting the received control frame in a selective manner based on the checking result.
In the aforementioned aspect of the present invention, the control frame may be a CF-End frame, and in the broadcasting the received control frame, if the checking result indicates that a basic service set ID (BSSID) recorded in the CF-End frame coincides with a BSSID of a BSS (basic service set), the CF-End frame may be broadcast.
In addition, in the broadcasting the received control frame, when a time of SIFS short inter-frame space (SIFS) elapses after the CF-End frame is received in the receiving a control frame, the received CF-End frame may be broadcast.
In addition, if the wireless LAN is an infrastructure BSS, the device is an access point of the infrastructure BSS, and the wireless LAN is an IBSS (independent BSS), then the device may be an IBSS control station that sends a beacon frame.
According to another aspect of the present invention, there is provided a computer-readable medium having embodied thereon a computer program for executing the method above.
According to another aspect of the present invention, there is provided an apparatus for delivering a control frame received through a wireless LAN, the apparatus comprising a recipient address information checking unit which checks recipient address information included in the control frame when the control frame including time information for medium access is received, and a resending unit which broadcasts the received control frame in a selective manner based on the checking result.
According to another aspect of the present invention, there is provided an access point having the apparatus above.
According to another aspect of the present invention, there is provided a wireless LAN station which has the apparatus above, and operates the apparatus only when the wireless LAN station operates as an IBSS control station that sends a beacon frame in the independent BSS.
The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
Although the case where a control CF-End frame is used so that the transmitting station returns the TxOP has been described, the present exemplary embodiment is not limited thereto, and other types of frames may be used if the frames have a function for resetting the NAV of each station, and if a duration field of each MAC header thereof is set to 0. The same will be also applied hereinafter.
Referring to
Station C is not allowed to resend all received CF-End frames. Medium access control (MAC) of each station is performed for a medium used in one BSS. Thus, if station C is located in a position in which frames sent from two or more different BSSs can be received, an error may occur during the MAC of the stations.
Therefore, when station C receives the CF-End frame, station C reads its address field to compare a basic service set ID (BSSID) of the CF-End frame with a BSSID of a BSS in which station C is included. Then, only when the two BSSIDs coincide with each other, station C resends the CF-End frame. Otherwise, station C drops the CF-End frame.
An access point or an IBSS control station receives a CF-End frame (operation 710), and then compares an BSSID recorded in an address field of the received CF-End frame with a BSSID of a BSS where the access point or the IBSS is included (operation 720). If the BSSID recorded in the address field of the CF-End frame coincides with the BSSID of the BSS where the access point or the IBSS is included, the access point or the IBSS rebroadcasts the received CF-End frame so that the CF-End frame can be delivered to a hidden node of the BSS where the access point or the IBSS is included (operation 740). Otherwise, the access point or the IBSS drops the CF-End frame (operation 730).
Referring to
The recipient address information checking unit 800 receives the CF-End frame sent from a first station 850, and then compares a BSSID recorded in an address field of the received CF-End frame with a BSSID of a BSS which is controlled by the access point 870. If the two BSSIDs do not coincide with each other, the recipient address information checking unit 800 drops the CF-End frame.
If the BSSID recorded in the address field of the received CF-End frame coincides with the BSSID of the BSS which is controlled by the access point 870, the resending unit 820 broadcasts the received CF-End frame so that the CF-End frame can be delivered to a second station 860 that is a hidden node.
Accordingly, in the present invention, all stations included in one BSS can receive the same time information for controlling medium access, thereby solving a hidden node problem. Ultimately, a correct CSMA/CA mechanism can be implemented in a wireless LAN, and a fair contention for medium access among the stations can be ensured.
The exemplary embodiments of the present invention can be written as computer programs which are embodied on computer readable recording media and can be implemented in general-use digital computers that execute the programs using computer readable recording media. Examples of the computer readable recording media include magnetic storage media (e.g., ROM, floppy disks, hard disks, etc.), optical recording media (e.g., CD-ROMs, or DVDs), and storage media such as carrier waves (e.g., transmission through the Internet).
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The exemplary embodiments should be considered in descriptive sense only and not for purposes of limitation. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.
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