Abstract:
A data transmission method with multiple token mechanism in wireless token ring protocol is provided. First, (a) a logical ring with M nodes is provided; (b) a k-th node is selected from the logical ring, and a token in the k-th node is generated; (c) a first message is sent to a (k+1)-th node from the k-th node with the token, and whether the (k+1)-th node responds a second message is judged, if yes, the data to be transmitted is transmitted from the k-th node, otherwise, the token of the k-th node is eliminated; (d) the token is sent to the (k+1)-th node from the k-th node after completing the transmission of the transmitted data of the k-th node, a generation token sequence is generated in a i-th node, and sent to a (i−1)-th node; and (e) the token is generated for the (i−1)-th node with the generation token sequence.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 96130677, filed on Aug. 20, 2007. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a data transmission method for a wireless network. More particularly, the present invention relates to a data transmission method with multiple token mechanism in wireless token ring protocol. 
     2. Description of Related Art 
     With development of wireless communication techniques, wireless networks have been widely used in our daily life. Since transmission lines are not required during wireless communication, the cost for constructing and maintenance of the transmission lines may be avoided. 
     Presently, an 802.11 standard has been defined by the institute of electrical and electronics engineers (IEEE). The 802.11 standard is widely used in different scenes of wireless communication. For example, in a coffee shop for afternoon tea, a user may communicate with others or surf on the Internet via a notebook computer and a wireless access point. However, the wireless access point has to be connected to the transmission lines for the user to connect the Internet. If a plurality of users is about to surf on the Internet simultaneously, the wireless access point may be used as a central controller, by which a medium access control (MAC) protocol of the 802.11 standard is applied in coordination with the wireless access point to avoid a collision during packets transmission. 
     Referring to  FIG. 1  and  FIG. 2 ,  FIG. 1  is a schematic diagram of a MAC protocol of the 802.11 standard.  FIG. 2  is a timing diagram illustrating a relationship of signals according to a MAC protocol of the 802.11 standard. In the 802.11 standard, the MAC protocol of the 802.11 standard is a contention MAC protocol, by which request-to-send (RTS) packets, clear-to-send (CTS) packets and network allocation vector (NAV) information are sent to avoid the collision of the transmission packets. When a node_ 1  is used for transmitting data to a wireless access point W_AP (node_ 1 ˜node_ 4  are wireless communication devices, for example notebook computers, personal digital assistants (PDAs), and cell phones etc.), the node_ 1  transmits the RTS packet and the NAV information (the NAV is packaged within the RTS packet, and is a header of the packet) to the wireless access point W_AP and other nodes, such as a node_ 3  and a node_ 4  within the signal coverage of the node_ 1 , so as to notify the wireless access point W_AP, the node_ 3  and the node_ 4  there will be data to be transmitted, and the time required for transmission (by the NAV information). When the wireless access point W_AP receives the RTS packet, and after a waiting time of short inter frame space (SIFS), the wireless access point W_AP transmits the CTS packet and the NAV information (the NAV is packaged within the CTS packet, and is a header of the packet) to the node_ 1  from which the RTS packet is transmitted and the other nodes within the signal coverage of the wireless access point W_AP, such as the node_ 2 , the node_ 3  and the node_ 4 , so as to notify the node_ 1  that data transmission is permitted, and to notify the node_ 2 , the node_ 3  and the node_ 4  that there will be data to be received, and the time required for receiving (by the NAV information). When the node_ 1  receives the CTS packet, and after the waiting time SIFS, the node_ 1  then transmits a data packet Data_A. When the wireless access point W_AP receives the data packet Data_A successfully, and after the waiting time SIFS, the wireless access point W_AP responds an acknowledgement (ACK) packet to the node_ 1 , so as to notify the node_ 1  that transmission of the data packet Data_A to the wireless access point W_AP is successful. Next, after a waiting time of distributed inter frame space (DIFS), the node_ 1 ˜node_ 4  may contest with each other to determine which node may transmit the packets. 
     In  FIG. 2 , the node_ 2  is assumed to have successfully obtained a channel utilization privilege. The node_ 2  transmits the RTS packet and the NAV information (the NAV is packaged within the RTS packet, and is a header of the packet) to the wireless access point W_AP and to the node_ 3  and node_ 4  within the signal coverage of the node_ 2 , so as to notify the wireless access point W_AP, the node_ 3  and the node_ 4  there will be data to be transmitted, and the time required for transmission (by the NAV information). When the wireless access point W_AP receives the RTS packet, and after the waiting time of SIFS, the wireless access point W_AP transmits the CTS packet and the NAV information (the NAV is packaged within the CTS packet, and is a header of the packet) to the node_ 2  from which the RTS packet is transmitted and the other nodes within the signal coverage of the wireless access point W_AP, such as the node_ 1 , the node_ 3  and the node_ 4 , so as to notify the node_ 2  that data transmission is permitted, and notify the node_ 1 , node_ 3  and node_ 4  that there will be data to be received, and the time required for receiving (by the NAV information). When the node node_ 2  receives the CTS packet, and after the waiting time SIFS, the node_ 2  then transmits a data packet Data_B. When the wireless access point W_AP receives the data packet Data_B successfully, and after the waiting time SIFS, the wireless access point W_AP responds the ACK packet to the node_ 2 , so as to notify the node_ 2  that transmission of the data packet Data_B to the wireless access point W_AP is successful. Next, after the waiting time DIFS, the node_ 1  node_ 4  may again contest with each other to determine which node may transmit the packet. 
     According to the MAC protocol of the 802.11 standard, a hidden node problem (i.e. the node_ 1  cannot be detected by the node_ 2 ) is solved, such that the packets collision is avoided. However, the MAC protocol of the 802.11 standard requires the wireless access point W_AP to work as the central controller, and the wireless access point W_AP has to be connected to a cable network. If such a network is constructed in a large area or in an outdoor environment, the cost of the construction will be huge. 
     Accordingly, a wireless mesh network using a wireless communication technique of multi-hop is provided. However, the multi-hop wireless mesh network can only be applied to a line topology, and the transmitted packet has to be a fixed length packet. For a network system applying a variable length packet, the variable length packet has to be cut and rearranged to form the fixed length packet. Therefore, signal-processing time during transmission is increased, and equipment cost is increased accordingly. 
     Moreover, a wireless token ring protocol (WTRP) is disclosed recently, and the WTRP allows the multi-hop communication technique to be applied to a ring topology. However, the WTRP may only provide one token to a certain node. In other words, each time only one node is permitted to transmit data, and therefore an output rate of the network system using the WTRP will be decreased due to the above reason. 
     To solve the aforementioned problems, a concept of spatial reuse for generating a plurality tokens is provided by the present invention, and the collision occurred during packets transmission among the plurality of nodes with the tokens, and the problem of the variable length packet cannot be transmitted can be avoided by applying a token elimination mechanism. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a data transmission method with multiple token mechanism in wireless token ring protocol, by which a plurality of tokens is simultaneously applied in a ring topology to enhance an output rate of each node. Moreover, each node may transmit variable length packets, and collision of a plurality of tokens can be avoided. 
     The present invention is directed to another data transmission method with multiple token mechanism in wireless token ring protocol, by which an output rate of each node is increased, variable length packets may be transmitted and the ring topology is adopted. 
     The present invention provides a data transmission method with multiple token mechanism in wireless token ring protocol. First, (a) a logical ring with M nodes is provided, wherein the nodes of the logical ring are logically linked to form a ring. A k-th node in the logical ring is logically linked to a (k+1)-th node and a (k−1)-th node; (b) the k-th node is selected from the logical ring, and a token is generated to the k-th node; (c) a first message is sent to the (k+1)-th node from the k-th node with the token, and whether or not the (k+1)-th node responds a second message to the k-th node with the token is then judged, if yes, data to be transmitted may be sent from the k-th node with the token; (d) after the data is transmitted to the (k+1)-th node from the k-th node with the token, the token is released to the (k+1)-th node from the k-th node, meanwhile, a generation token sequence is generated on the i-th node, and the generation token sequence is sent to the (i−1)-th node; (e) the token is generated to the (i−1)-th node with the generation token sequence. Moreover, the above M is a positive integer, and k and i are positive integers less than M. 
     According to an embodiment of the present invention, in the step (c) of the data transmission method with multiple token mechanism in wireless token ring protocol, if the k-th node with the token judges that the (k+1)-th node does not respond the second message, the k-th node with the token then eliminates its own token. Moreover, the data transmitting method with multiple token mechanism in wireless token ring protocol may be applied to an 802.11 standard. 
     The present invention provides another data transmission method with multiple token mechanism in wireless token ring protocol. First, (a) a plurality of nodes are provided, wherein the nodes are logically linked to form a logical ring. Each node in the logical ring is logically linked to a first adjacent node and a second adjacent node, and the second adjacent node is logically linked to a third adjacent node; (b) a node is selected from the nodes within the logical ring, and a token is generated on the selected node; (c) a first message is sent to the first adjacent node from the node with the token, and the first adjacent node determines whether or not to transmit a second message to the node with the token according to a judgment of whether the first adjacent node is in a non-busy state; (d) if the node with the token receives the second message output from the first adjacent node, whether the node with the token is about to transmit data to the first adjacent node is then determined; (e) if the node with the token is about to transmit the data to the first adjacent node, the node with the token transmits the data to the first adjacent node, and after the first adjacent node receives the data, the first adjacent node responds a third message to the node with the token, and the node with the token then releases the token to the first adjacent node; (f) if the node with the token has no data to be transmitted to the first adjacent node, the node with the token then releases the token to the first adjacent node; (g) after the node with the token releases the token to the first adjacent node, the second adjacent node generates a generation token sequence and transmits the generation token sequence to the third adjacent node; (h) the token is generated to the node with the generation token sequence. 
     According to an embodiment of the present invention, in the step(e), if the first adjacent node does not respond the second message to the node with the token, the node with the token then eliminates its own token. Moreover, the aforementioned data transmission method with multiple token mechanism in wireless token ring protocol may be applied to the 802.11 standard. 
     According to an embodiment of the present invention, the first adjacent node is logically clockwise (anti-clockwise) linked with the node, the second adjacent node is logically anti-clockwise (clockwise) linked with the node, and the third adjacent node is logically anti-clockwise (clockwise) linked with the second adjacent node. 
     Since a concept of spatial reuse and a token elimination mechanism are applied in the present invention, the data transmitting method of the present invention with multiple token mechanism in wireless token ring protocol may be applied to the network system applying the variable length packet. The network system applying the data transmitting method of the present invention with multiple token mechanism in wireless token ring protocol allows the plurality of tokens to be used simultaneously on the nodes in the network system, so as to improve the output rate of each node. Moreover, in the data transmission method of the present invention, the token elimination mechanism is applied to avoid the collision of the plurality of tokens, such that each node within the network may transmit the variable length packets freely. 
     In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a MAC protocol of the 802.11 standard. 
         FIG. 2  is a timing diagram of illustrating a relationship of signals according to a MAC protocol of the 802.11 standard. 
         FIG. 3A  is a state flowchart illustrating a data transmitting method with multiple token mechanism in wireless token ring protocol according to an embodiment of the present invention. 
         FIG. 3B  is a state flowchart illustrating a situation that a response of a third message is required from the node_ 4  to the node_ 3 . 
         FIG. 3C  is a timing diagram illustrating a relationship of the signals according to the embodiment of  FIG. 3A  and  FIG. 3B . 
         FIG. 3D  is a timing diagram illustrating a relationship of the signals when  FIG. 3C  is applied to a system complied with the 802.11 standard. 
         FIG. 4A  is another state flowchart illustrating a data transmitting method with multiple token mechanism in wireless token ring protocol according to an embodiment of the present invention. 
         FIG. 4B  is a timing diagram illustrating a relationship of the signals according to the embodiment of  FIG. 4A . 
         FIG. 5A  is another state flowchart illustrating a data transmitting method with multiple token mechanism in wireless token ring protocol according to an embodiment of the present invention. 
         FIG. 5B  is a timing diagram illustrating a relationship of the signals according to the embodiment of  FIG. 5A . 
         FIG. 6  is a schematic diagram illustrating an embodiment when the node_ 2 , the node_ 3  and the node_ 4  are located in a dense area. 
         FIG. 7  is a performance comparison diagram between a data transmitting method with multiple token mechanism in wireless token ring protocol provided by the present invention and a conventional data transmitting method of wireless token ring protocol. 
         FIG. 8  is a performance comparison diagram between a data transmitting method with multiple token mechanism in wireless token ring protocol provided by the present invention and a conventional data transmitting method of wireless token ring protocol when there exists a dense area. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     To improve an output rate of a node, transmit a variable length packet and adopt a ring topology, a concept of spatial reuse is provided by the present invention to enhance an existing wireless token ring protocol, and a token elimination mechanism is provided, such that a network system applying a data transmission method of the present invention with multiple token mechanism in wireless token ring protocol may transmit the variable length packets. 
       FIG. 3A  is a state flowchart illustrating a data transmitting method with multiple token mechanism in wireless token ring protocol according to an embodiment of the present invention. Referring to  FIG. 3A , a plurality of nodes node_ 1 ˜node_ 8  are logically formed a logical ring. For example, a node_ 3  within the logical ring is logically linked to a node_ 2  and a node_ 4 ; the node_ 2  is logically linked to a node_ 1  and the node_ 3 ; a node_ 8  is logically linked to the node_ 1  and a node_ 7 . The node_ 1 ˜node_ 8  may be computers having wireless network interface cards, cell phones, PDAs or other wireless communication devices. 
     The embodiment illustrated in  FIG. 3A  includes the following steps. First, step S 300 , a node is selected from the logical ring according to the method of the present invention. In the present embodiment, the selected node is assumed to be the node_ 3 , and a token is generated to the node_ 3 . For convenience, in  FIG. 3A  to  FIG. 6 , the nodes surrounded by dash lines represent the node with the token. 
     Next, step S 301 , the node_ 3  with the token transmits a first message to the node_ 4 , and the node_ 4  receives the first message and determines whether or not to respond a second message to the node_ 3 . In the present embodiment of  FIG. 3A , the second message is assumed to be responded to the node_ 3  by the node_ 4 , and in an embodiment of  FIG. 4A , a situation of no response of the second message will be described. 
     Referring to  FIG. 3A  again, next, step S 302 , the node_ 4  responds the second message to the node_ 3  to notify the node_ 3  data transmission is allowed. Step S 303 , after the node_ 3  receives the second message, the node_ 3  transmits a Data_ 3  to the node_ 4 . In the present embodiment, the node_ 3  in  FIG. 3A  is assumed to have the Data_ 3  to be transmitted to the node_ 4 , and in the embodiment of  FIG. 5A , a situation of no data to be transmitted from the node_ 3  will be described. 
     Next, when the transmission of the Data_ 3  to the node_ 4  from the node_ 3  is confirmed to be successful, a step S 304  may be undertaken. Step S 304 , the node_ 3  releases the token to the node_ 4 , and meanwhile the node_ 2  within the signal coverage of the node_ 3  may overhear the token release of the node_ 3 . The present embodiment provides a token generation mechanism, by which when the node_ 2  overhears the token release of the node_ 3 , the node_ 2  generates a generation token sequence GTS, and transmits the generation token sequence GTS to the node_ 1 . 
     Next, at step S 305 , the node_ 1  receives the generation token sequence GTS and generates a new token. Finally, the node_ 1  with the token may start to transmit data to the other nodes in the network. Namely, the logical ring now has two tokens, and two nodes may transmit data simultaneously. Therefore, the output rate of each node is improved. 
     According to the steps S 304  and S 305 , a concept of spatial reuse is applied to the present invention, and if there is no interference occurred among the transmitted signals, an idle node may output the generation token sequence GTS to generate a new token, so as to improve the output rate of each node. Moreover, in the above embodiment, the generation token sequence GTS is generated by the node_ 2 . However, the generation token sequence GTS may be generated by other nodes as long as no interference occurred among the transmitted signals. For example, the generation token sequence GTS may be generated by the node_ 3  which releases the token or the node_ 1  located far away from the node_ 3 . 
     In the above embodiment, the node_ 1 ˜node_ 8  within the logical ring are arranged anticlockwise. However, if the node_ 1 ˜node_ 8  are arranged clockwise, it is still construed to be within the scope of the present invention. 
     To avoid a situation that none of the nodes node_ 1 ˜-node_ 8  within the logical ring has the token, all the nodes node 1 ˜node_ 8  are in an idle state, and the node_ 3  selected at the beginning may be a super node. The super node may automatically generate the token when none of the nodes node_ 1 ˜node_ 8  within the logical ring has the token. 
     Whether the aforementioned node_ 4  responds the second message to the node_ 3  with the token is determined by whether the node_ 4  is receiving a transmitted data from a node other than the node_ 3 , or whether the node_ 4  is transmitting the Data_ 4  to a node_ 5 . In other words, the node_ 4  may respond the second message to the node_ 3  with the token, when the node_ 4  is in a non-busy state and is allowed to receive the Data_ 3  transmitted from the node_ 3 . 
     Next, referring to  FIG. 3B ,  FIG. 3B  is a state flowchart illustrating a situation that a response is required from the node_ 4  when data transmission is completed. At step S 303 , after the data is successfully transmitted to the node_ 4  from the node_ 3 , a step S 303 - a  may further be undertaken. At step S 303 - a , after the node_ 4  receives the Data_ 3  successfully, the node_ 4  responds a third message to the node_ 3 , such that the node_ 3  may confirm the data transmission of the Data_ 3  from the node_ 3  to the node_ 4  is successful. The step  303 - a  is generally applied in a communication network where an ACK information is required, for example, a transmission control protocol (TCP) network. However, in an application of real-time video transmission, the ACK information is not required after the data is transmitted, for example, a user data protocol (UDP) network. 
       FIG. 3C  is a timing diagram illustrating a relationship of the signals according to the embodiment of  FIG. 3A  and  FIG. 3B . Referring to  FIG. 3C , to avoid a packet collision, when the signals are transmitted between the nodes, there will be a waiting time for a first time or a second time. As shown in  FIG. 3C , when the node_ 4  receives the first message, the node_ 4  first waits for the first time, and then determines whether or not to transmit the second message to the node_ 3 . When the node_ 3  receives the second message, and after the waiting time of the first time, the node_ 3  transmits the Data_ 3  to the node_ 4 . When the node_ 4  successfully receives the Data_ 3 , again after the waiting time of the first time, the node_ 4  responds the third message to the node_ 3 . Then, the node_ 3  receives the third message, and after the waiting time of the first time, the node_ 3  releases the token to the node_ 4 . Next, the node_ 4  receives the token, and after the waiting time of the second time, the node_ 4  transmits the first message to the node_ 5 . Moreover, when the node_ 4  obtains the token from the node_ 3 , and after the waiting time of the first time, the generation token sequence GTS is generated and is transmitted to the node_ 1 . After the node_ 1  receives the generation token sequence GTS, the node_ 1  generates the token, and after the waiting time of the first time, the node_ 1  transmits the first message to the node_ 2 . 
     However, the first time and the second time used in the above embodiment are not intended to limit scope of the present invention, the waiting time for signal transmission between the nodes may be determined by an actual requirement of different network. Moreover,  FIG. 3D  is a timing diagram illustrating a relationship of the signals when  FIG. 3C  is applied to a system complied with the 802.11 standard. Referring to  FIG. 3D , the first message is a RTS packet including a first NAV information; the second message is a CTS packet including a second NAV information; the third message is an ACK packet. The first time is the time for SIFS, and the second time is the time for DIFS. 
       FIG. 4A  is a state flowchart illustrating a data transmission method with multiple token mechanism in wireless token ring protocol according to an embodiment of the present invention. Referring to  FIG. 4A , at step S 400 , the node_ 7  and the node_ 8  all have tokens, and the node_ 8  is transmitting a Data_ 8  to the node_ 1 . At step S 401 , the node_ 7  transmits the first message to the node_ 8 , however the node_ 8  is in a busy state, and therefore the node_ 8  will not respond the second message to the node_ 7 . At step S 402 , since the node_ 7  does not receive the second message, the node_ 7  may eliminate the token, and after the node_ 8  confirms the Data_ 8  is successfully transmitted to the node_ 1 , a step S 403  may be undertaken. According to the above step S 402 , the present embodiment provides a token elimination mechanism, by which when the node does not receive the second message from the next node, it will automatically eliminate its own token, such that packets collision during transmission in the network can be avoided. 
     Referring to  FIG. 4A  again, at step S 403 , after the node_ 8  successfully sends the Data_ 8 , the node_ 8  releases the token to the node_ 1 , while the node_ 7  generates the generation token sequence GTS and transmits the generation token sequence GTS to the node_ 6 . At step S 404 , the node_ 6  receives the generation token sequence GTS and generates the token. 
     The embodiment of  FIG. 4A  may be applied to a situation that the node_ 8  transmits the packets with a larger length, and the other nodes node_ 2 ˜node_ 7  transmit the packets with a smaller length, and therefore based on the token elimination mechanism, the method of the present invention may be applied to the network system with variable length packets. 
       FIG. 4B  is a timing diagram illustrating a relationship of the signals according to the embodiment of  FIG. 4A . Referring to  FIG. 4B , to avoid the packet collision, when the signals are transmitted between the nodes, there will be the waiting time for the first time or the second time. As shown in  FIG. 4B , the node_ 8  is transmitting Data_ 1  to the node_ 1 . Though the node_ 7  transmits the first message to the node_ 8 , the node_ 8  is in the busy state, and therefore the node_ 8  will not transmit the second message to the node_ 7 . Accordingly, the node_ 7  may eliminate its own token. 
     However, the first time and the second time used in the above embodiment are not intended to limit the scope of the present invention, the waiting time for signal transmission between the nodes may be determined by an actual requirement of different network. Moreover, the embodiment shown in  FIG. 4B  may be applied to the network complied with the 802.11 standard. In this case, the first message is the RTS packet including the first NAV information; the second message is the CTS packet including the second NAV information; and the third message is the ACK packet. The first time is the time for SIFS, and the second time is the time for DIFS. 
       FIG. 5A  is a state flowchart illustrating a data transmission method with multiple token mechanism in wireless token ring protocol according to an embodiment of the present invention. The embodiment of  FIG. 5A  includes the following steps: at step S 500 , a node is selected from the logical ring (the node_ 3  is assumed to be selected), and the token is generated in the node_ 3 . Next, at step S 501 , the node_ 3  with the token transmits the first message to the node_ 4 . The node_ 4  receives the first message and determines whether or not to respond the second message to the node_ 3  (the node_ 4  is assumed to respond the second message to the node_ 3  in the embodiment of  FIG. 5A ). At step S 502 , the node_ 4  responds the second message to the node_ 3  to notify the node_ 3  that the data is allowed to be transmitted. Next, step S 503 , since the node_ 3  has no data to be transmitted, the node_ 3  releases the token to the node_ 4 , and the node_ 2  may generate the generation token sequence GTS and transmit the generation token sequence GTS to the node_ 1 . At step S 504 , the node_ 1  receives the generation token sequence GTS and generates the token. 
       FIG. 5B  is a timing diagram illustrating a relationship of the signals according to the embodiment of  FIG. 5A . Referring to  FIG. 5B , to avoid the packet collision, when the signals are transmitted between the nodes, there will be the waiting time for the first time or the second time. As shown in  FIG. 5B , when the node_ 4  receives the first message, the node_ 4  waits for the first time, and then determines whether or not to respond the second message to the node_ 3 . Since the node_ 3  has no data to be transmitted, and therefore when the node_ 3  receives the second message, and after the waiting time of the first time, the node_ 3  releases the token to the node_ 4 . Next, after the node_ 4  obtains the token, and after the waiting time of the second time, the node_ 4  transmits the first message to the node_ 5 . Moreover, when the node_ 4  obtains the token from the node_ 3 , and after the waiting time of the first time, the generation token sequence GTS is generated and is transmitted to the node_ 1 . After the node_ 1  receives the generation token sequence GTS, the node_ 1  generates the token, and after the waiting time of the first time, the node_ 1  transmits the first message to the node_ 2 . 
     However, the first time and the second time used in the above embodiment are not intended to limit the scope of the present invention, the waiting time for signal transmission between the nodes may be determined by an actual requirement of different network. Moreover, the embodiment shown in  FIG. 5B  may be applied to the network complied with the 802.11 standard. In this case, the first message is the RTS packet including the first NAV information; the second message is the CTS packet including the second NAV information; and the third message is the ACK packet. The first time is the time for SIFS, and the second time is the time for DIFS. 
       FIG. 6  is a schematic diagram illustrating an embodiment when the node_ 2 , the node_ 3  and the node_ 4  are located in a dense area. The distances respectively between the node_ 2 , the node_ 3  and the node_ 4  are relatively close, resulting in the fact that the output rates of the node_ 2 , the node_ 3  and the node_ 4  located in the dense area are decreased. Therefore, the method of the present invention may be modified moderately, by which a conventional data transmission method of wireless token ring protocol may be applied to the node_ 2 , the node_ 3  and the node_ 4  located in the dense area, and the data transmission method with multiple token mechanism in wireless token ring protocol provided by the present invention may be applied to the nodes located outside the dense area. 
     Referring to  FIG. 7  and  FIG. 8 ,  FIG. 7  is a performance comparison diagram between a data transmission method with multiple token mechanism in wireless token ring protocol provided by the present invention and a conventional data transmission method of wireless token ring protocol.  FIG. 8  is a performance comparison diagram between a data transmitting method with multiple token mechanism in wireless token ring protocol provided by the present invention and a conventional data transmitting method of wireless token ring protocol when there exists a dense area. As shown in  FIG. 7 , a simulation environment of this performance comparison diagram includes the following features: 18 nodes, packet length of 1024 bytes and 1500 bytes, and no dense area exists. As shown in  FIG. 7 , the curve  700  is a performance curve of the data transmission method of the present invention, and the curve  701  is the performance curve of the conventional data transmitting method of wireless token ring protocol. When an offered load is increased, a throughput per node of the curve  700  is increased accordingly, while the throughput has an upper limit. The throughput per node of the curve  701  is fixed. Therefore, the data transmission method of the present invention has a better performance than that of the conventional data transmission method of wireless token ring protocol. Referring to  FIG. 8 , the simulation environment of this performance comparison diagram includes the following features: 18 nodes, fixed packet length, and there exists the dense area. As shown in  FIG. 8 , the curve  800  is the performance curve of the data transmitting method of the present invention, wherein the dense area includes three nodes; the curve  801  is the performance curve of the data transmission method of the present invention, wherein the dense area includes six nodes; and the curve  802  is the performance curve of the conventional data transmitting method of wireless token ring protocol, wherein the dense area includes six nodes. When the offered load is less than 100 Kbps, the performance of the curve  802  is better than that of the curve  801 ; when the offered load is greater than 100 Kbps, the performances of the curve  800  and the curve  801  are better than that of the curve  802 . Moreover, the more the nodes are included within the dense area, the poorer the performance is. 
     Therefore, to improve the performance under a low offered load, the method of the present invention may be modified moderately, by which a conventional data transmission method of wireless token ring protocol may be applied to the nodes located in the dense area, and the data transmission method with multiple token mechanism in wireless token ring protocol provided by the present invention may be applied to the nodes located outside the dense area. 
     In summary, the concept of spatial reuse is applied in the present invention, such that the nodes within the network may simultaneously generate the plurality of tokens, so as to improve the output rate of each node. Moreover, the present invention further provides a token elimination mechanism to avoid the collision of the transmission packets when the plurality of tokens is applied, and meanwhile the nodes within the network may transmit the variable length packets. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.