Method for transmitting frames in a wireless local area network

On the case of receiving data frame from a station, the method of the present invention instructs the repeater to replace the content of the receiver address field by the address of the bridge when receiving the frame transmitted from the station, and then forwards the frames to the bridge. On the case of receiving a data frame transmitted from the bridge, the repeater can replace the content of transmitter address field by the address of the repeater itself, and then forwards the data frame to the station.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for transmitting frames in a wireless local area network and data structure for the same, and more particularly, to a method and data structure for a repeater in a wireless local area network to transmit frames according to the IEEE 802.11 protocol.

2. Description of the Related Art

The IEEE 802.11 defines the format of data frame for wireless local area network.FIG. 1illustrates some important fields of a data frame defined in IEEE 802.11. The data frame includes four address fields for recording basic service set identifier (BSSID), source address (SA), destination address (DA), transmitter address (TA) and receiver address (RA).

The destination address can be a unique address or a broadcast address, which is the destination of the frame. The source address is the address of the station, which generates the frame. The transmitter address is the address of the station, which transmits the frame in wireless medium, and the transmitter is connected to an access point (AP) in a wireless distribution system. The receiver address is the address of the next station, which will receive the frame, and the receiver also connects to the access point in the wireless distribution system.

The access point can be a bridge or a repeater. The bridge is used to connect the wireless local area network and the local area network such as ether network for sharing the Internet source. The repeater transmits signal in a circuitous manner to overcome the obstacle of the building so as to elongate the communication distance. Each station decides whether to receive a frame according to the content of the address1field. A station will receive the frame if the content of the address1is the same as the address of the station itself, otherwise it will discard the frame. The receiver can transmit an acknowledgement frame to the address recorded in the address2field if necessary.

FIG. 2Aillustrates some important fields of a data frame10transmitted from a source station to a repeater, andFIG. 2Billustrates some important fields of a data frame12forwarded to a bridge by the repeater. As shown inFIG. 2AandFIG. 2B, the repeater must transform the data frame10into data frame12before forwarding to the bridge. The logic value of the “To DS” field is set to 1 for indicating that the data frame12is transmitted to an access point (the bridge) of a distribution system, and the logic value of the “From DS” field is set to 1 for indicating that the data frame12is transmitted from an access point (the repeater). The address1field records the receiver address (the address of the bridge), the address2field records the transmitter address (the address of the repeater), the address3field records the destination address and the address4field records the source address.

After receiving the data frame12, the bridge will transmit an acknowledgement frame to the repeater according the address recorded in the address2field of the data frame12, and the repeater will transmit an acknowledgement frame to the source station according the address recorded in the address2field of the data frame10. To transform the data frame10into data frame12, the repeater must change the content of the “From DS” field, the address1field, the address2field, the address3field and the address4field. Additionally, the above-mentioned method is inconvenient to design and increases the cost, since the data frame12, transmitted from the repeater to the bridge, completely uses 4 address fields to store the bridge address, the repeater address, the destination address and the source address, respectively.

The bridge must identify the type of the repeater before receiving data frame from or transmitting to the repeater. However, the repeater and the bridge made by different companies might use proprietary protocol to transmit or receive frames that increase the complexity for setting a bridge which does not conform to requirement of the market.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for transmitting frames in a wireless local area network and data structure for the same, which allows a station and a bridge to transmit frames without concerning the forwarding process performed by a repeater.

In order to achieve the above-mentioned object, the present invention provides a method for transmitting frames in a wireless local area network and data structure for the same. The wireless local area network comprises repeater coupled to a station and a bridge. On the case of receiving data frame from a station, the repeater replaces the content of the receiver address field by the address of the bridge when receiving the frame transmitted from the station, and then forwards the frames to the bridge. On the case of receiving a data frame transmitted from the bridge, the repeater replaces the content of transmitter address field by the address of the repeater itself, and then forwards the data frame to the station.

Compared with the prior art, the present invention possesses the following advantages:1. During the forwarding process, the basic service set identifier (the address of the access point) of the data frame is the only one field to be changed by the repeater according to the present invention. However, there are five fields of the data frame to be changed according to the prior art, respectively.2. When the bridge is receiving a data frame, the data frame can be regarded as one transmitted directed from the source station, without concerning the forwarding process performed by the repeater.3. When the bridge is transmitting a data frame, the data frame can be regarded as one transmitted directly to the destination station, without concerning the forwarding process performed by the repeater.4. The repeater using the present invention is adaptable for the access point which conforms to the IEEE 802.11.

PREFERRED EMBODIMENT OF THE PRESENT INVENTION

FIG. 3is a schematic diagram of a network20. The network20comprises a bridge22(an access point), a repeater24(also an access point) wireless coupling with the bridge22, a station26wireless coupling with the repeater24and a station28electrically connected the bridge22. The station26belongs to the basic service set of the repeater24, and the station28is a remote station connecting the bridge by the local area network/wide area network. When the station26needs to transmit a data to the station28, the data will be added with a header to form a data frame that is then transmitted to the station28through repeater24and bridge22.

FIG. 4Aillustrates some important fields of data frame40transmitted to the repeater24by the station26according to the present invention. The logic value of the first field (the “To DS” field) is set to 1, indicating that the data frame40is transmitted to an access point (the repeater24) of a distribution system. The logic value of the second field (the “From DS” field) is set to 0, indicating that the data frame40is not transmitted from an access point of a distribution system. The address1field records the BSSID of the repeater24, the address2field records the address of the station26, the address3field records the address of the station28and the address4field is not used. After receiving the data frame40, the repeater24will transmit an acknowledgement frame to the station26according to the address recorded in the address2field of the data frame40.

FIG. 4Billustrates some important fields of a data frame42transmitted to the bridge22by the repeater24according to the present invention. When receiving the data frame40from the station26, the repeater24transforms the data frame40into data frame42by replacing the BSSID recorded in the address1field with the identifier of the bridge22. As shown inFIG. 4B, the logic value of the first field and the second field is kept the same, the address1field for recording the receiver address is changed into the identifier of the bridge22, the contents of the address2field and the address3field are kept the same and the address4field is still not used. When receiving the data frame42, the bridge22will transmit an acknowledgement frame to the station26according to the address recorded in the address2field. Since the station26belongs to the basic service set of the repeater24, the repeater24receives the acknowledgement frame instead of the station26. However, the repeater24will not forward this acknowledgement frame to the station26since the repeater24had transmitted an acknowledgement frame to the station26when receiving the data frame40from the station26before.

Although the data frame42is transmitted from an access point (the repeater24) to another access point (the bridge22), the present invention method only changes the content of the address1field, and keeps all the other fields of the data frame the same. Besides, only three address fields are used to record the BSSID of the bridge22, the address of the station26and the address of the station28. Therefore, when the bridge22received the data frame42, the data frame42can be regarded as one transmitted directly from the source station26, not from the repeater24. Besides, the bridge22also regards the acknowledgement frame as one transmitted directly to the station26, not to the repeater22.

FIG. 5Aillustrates some important fields of a data frame50transmitted to the station26by the bridge22according to the present invention. The logic value of the first field is set to 0, indicating that the data frame50is not transmitted to an access point of a distribution system, and the logic value of the second field is set to 1, indicating that the data frame50is transmitted from an access point of a distribution system. The address1field records the destination address (the address of the station26), the address2field records the BSSID of the bridge22, the address3field records the source address (the address of the station28) and the address4is not used. Since the address recorded in the address1field of the data frame50belongs to the basic service set of the repeater24, the repeater24has to receive the data frame50instead of the station26, and transmit an acknowledgement frame to the bridge22.

FIG. 5Billustrates some important fields of a data frame52transmitted to the station26by the repeater24according to the present invention. After receiving the data frame50instead of the station26, the repeater24will transform the data frame50into the data frame52by changing the content of the BSSID field into the identifier of the repeater24, and then forward the data frame52to the station26. The logic value of the first field and the second field is kept the same, the content of the address2field for recording the transmitter address has changed into the identifier of the repeater24, address1field and the address3field are also kept the same and the address4field is still not used. After receiving the data frame52, the station26will transmit an acknowledgement frame to the repeater24according the address recorded in the address2field.

Although the data frame50is transmitted from an access point (the bridge22) to another access point (the repeater24) of a distribution system, the bridge22transmits the data frame50with a format for transmitting to a station, not with a format for transmitting to an access point of a distribution system.

In other words, when the station26transmits a data frame to the bridge22through the repeater24, the bridge22can regard the data frame as one transmitted directly from the station26, not from the repeater24. When the bridge22transmits a data frame to the station26through repeater24, the bridge22can regard that the data frame is transmitted directly to the station26, not forwarded by the repeater.

Compared with the prior art, a repeater using the present invention method for transmitting frames will possess the following advantages:1. During the forwarding process, the basic service set identifier (the address of the access point) of the data frame is the only one field to be changed by the repeater according to the present invention. However, there are five fields of the data frame to be changed according to the prior art.2. When the bridge is receiving a data frame, the data frame can be regarded as one transmitted directly from the source station, without concerning the forwarding process performed by the repeater.3. When the bridge is transmitting a data frame, the data frame can be regarded as one transmitted directly to the destination station, without concerning the forwarding process performed by the repeater.4. The repeater using the present invention is adaptable for the access point, which conforms to IEEE 802.11.