reference now should be made to the drawings , in which the same reference numerals are used throughout the different drawings to designate the same or similar components . fig1 is a configuration diagram of a wlan system that performs a qos function on a voice frame in an rf link section in accordance with an embodiment of the present invention . fig1 schematically illustrates an example of the wlan system according to the present invention . those skilled in the art can understand that other elements are included in the wlan system . referring to fig1 , a bss 100 includes a plurality of mobile terminals ( mts ) 120 and 130 and a single ap 110 , and constitutes a wlan . the mts 120 and 130 are connected to the ap 100 via an rf link . the wlan is connected to an internet backbone ( ib ) 150 via an internet protocol ( ip ) router 140 . in this case , data is transmitted via an upstream path extending from the mts 120 and 130 through the ap 110 to the ib 150 and via a downstream path extending from the ib 150 through the ap 110 to the mts 120 and 130 . the mts 120 and 130 and the ap 110 employ dcf modules 111 , 121 and 131 conforming to the ieee 802 . 11 - 1999 standard and ptdm modules 112 , 122 and 131 conforming to the present invention . the mts 120 and 130 existing in the bss 100 are equipped with voice codecs having the same creation period of a frame . the mts 120 and 130 possess qslot managers 123 and 133 , respectively , and manage information on the creation period of a voice frame and qslot information . the ap 110 possesses a qslot manager 114 and a qslot list 113 , and manages the qslots of the mts 120 and 130 that are connected to the ap 110 . in fig1 , the mts 120 and 130 exchange frames , including qos information , with the ap 110 before the transmission of a voice frame , are assigned qslots through which voice frames can be transmitted , and then transmits the voice frames . the frame exchange process and the transmission of a voice frame using a qslot are described with reference to fig2 and fig4 , 5 and 6 , respectively . fig2 a to 2 c are diagrams showing processes of exchanging qos frames to manage a qslot in accordance with the present invention . as shown in fig2 a to 2 c , a qslot management mode according to the present invention includes qslot setting 210 shown in fig2 a , qslot change 220 shown in fig2 b , and qslot removal shown in fig2 c . with reference to fig2 a , a qos frame exchange process for the qslot setting 210 according to the present invention is described . referring to fig2 a , when there is a voice frame to be transmitted , the mt 211 transmits a qslot request to send ( qrts ) frame to the ap 212 at step 213 . the ap 212 , having received the qrts frame , transmits a qslot grant to send ( qgts ) frame , including a qslot number ( qn ) 332 ( shown in fig3 ), to the mt 211 according to a set qslot list 113 at step 214 . in this case , the qn is the unique number of a qslot that is assigned to the mt 211 . the mt 211 , having been assigned the qn 316 by the ap 212 , waits for the reception of a qos beacon ( q - beacon ) from the ap 212 , and extracts qslot information from the q - beacon and transmits the voice frame to the ap 212 in a corresponding qslot when the q - beacon 215 is received from the ap 212 at step 215 , at step 216 . the ap 212 , having received the voice frame from the mt 211 , terminates the frame exchange by transmitting an ack frame at step 217 . the transmission of the voice frame in the qslot is described in detail with reference to fig4 . with reference to fig2 b , a qos frame exchange process for the qslot change 220 according to the present invention is described . referring to fig2 b , when the ap 222 intends to change the qn of the mt 221 to keep the qslot list 113 minimized , the ap 222 transmits a qslot change request to send ( qcrts ) frame to the mt 221 at step 223 . the mt 221 , having received the qcrts frame , updates the qn and transmits an ack to the ap 222 at step 224 . with reference to fig2 c , a qos frame exchange process for the qslot removal 230 according to the present invention is described . referring to fig2 c , after completing the transmission of the voice frame , the mt 231 transmits a qslot remove request to send ( qrrts ) frame , which is used to remove the qn from the qslot list 113 that is located in the ap 232 , to the ap 232 at step 233 . the ap 233 , having received the qrrts frame , removes the qslot list of the mt from the qslot list 113 and then transmits an ack to the mt 231 at step 234 . fig3 is a diagram showing the formats of frames that are used to perform the qos frame exchange processes according to an embodiment of the present invention . referring to fig3 , a qos beacon ( q - beacon ) 310 includes a beacon frame , which is used for ieee 802 . 11 , and an additional information field 311 . the information field 311 includes an identifier ( id ), a data length ( length ) 313 , a qslot network allocation vector ( qnav ) 314 , a qos frame transmission interval ( qtx - int ) 315 , a qslot number ( qslot number : qn ) 316 and a qslot time ( qslot time : qt ) 317 . in this case , the id 312 is allocated to tdm parameter setting ( tdm parameter set ). the length 313 indicates the length of the information field 311 on a bit basis . the qnav 314 indicates the length of a contention free period ( cfp ). the qtx - int 315 indicates the creation period of a voice frame . the qn 316 is an identification number that is allocated to an mt . the qt 317 starts from one and increases in proportion to the number of mts that have requested qslots . the qt 317 is the length of qslots that corresponds to the qn 316 . when a plurality of mts have requested qslots from the ap , the qn 316 and the qt 317 exist , the number of each of which corresponds to the number of mts . a qslot request to send ( qrts ) frame 320 is used when the mt requests a qslot . in this case , a receiver address 321 is the ap , and a transmitter address 322 is the mt that requests the qslot . a qvoice rate 323 is transmission rate information that is used when the mt transmits a voice frame . the ap calculates the qt 317 using the qvoice rate . the qtx - int 324 indicates the creation period of the voice frame of the mt . a qslot grant to send ( qgts ) frame 330 is used when the ap allocates the qn to the mt . the receiver address 331 is the mt that transmits the qrts frame . the qn 332 is a q slot id number that the mt , having requested the qslot , can use . a qslot change request to send ( qgrts ) frame 340 is used when the ap changes the qn of the mt that is connected thereto . the ap updates the qslot list to keep the length of the qnav minimized . in order to update the qslot list , the change of the qn of the mt may be requested . in this case , the qn 342 to be changed is inserted into the qcrts frame 340 and transmitted to a corresponding mt . the mt , having received the qcrts frame 340 , updates the qn . a qslot remove request to send ( qrrts ) frame 350 is used when the mt requests that the qn of the mt should be removed from the qslot list of the ap after completing the transmission of a voice frame . the qn 351 is the qslot id number that the mt is currently using . fig4 is a diagram showing the division of an rf link 160 according to the creation period of a voice frame in accordance with an embodiment of the present invention . referring to fig4 , the qtx - int 410 is the time that divides two q - beacons 420 and 430 according to the creation period of a qos voice ( qvoice ) frame ( e . g ., 160 bytes per 20 ms ). each qtx - int 410 includes a cfp 411 and a contention period ( cp ) 413 , and the cfp 411 includes one or more qslots 411 a , 411 b and 411 c . after the cfp 411 , a dcf inter frame space ( difs ) 412 , that is , the time interval between frames that is used in the dcf , is waited for , and the cp 413 is then entered . every mt suppresses the transmission of a frame by setting a qnav 414 for a cfp . however , the mt , having been allocated a qslot , can transmit a voice frame in the qslot . fig5 is a diagram showing a process of transmitting a voice frame using a qslot in a qtx - int based on the ptdm in accordance with an embodiment of the present invention . referring to fig5 , mt 1 and mt 2 intending to transmit voice frames request qns by transmitting qrts frames to the ap . the ap , having received the qrts frames 1 and 2 , allocates qslot 1 511 and qslot 2 512 to the mt 1 and the mt 2 , respectively . the mt 1 and the mt 2 , having been allocated the qns , wait for the reception of q - beacons 540 . the information field of each q - beacon 540 includes a qn and qt that correspond to the mt 1 or mt 2 . qslots are created in the order of qslot 1 , qslot 2 , qslot 3 , . . . , with the qn increasing from one by one on the basis of the q - beacon . when the q - beacon 540 is received , every mt extracts a qnav 550 and sets the length of a cfp 510 , the mt 1 and the mt 2 prepare for the transmission of voice frames in corresponding qslots 511 and 512 , and the remaining mts defer the transmission of frames . since the mt 1 has a qn of one , the mt 1 waits for a pifs 511 a , which is the time interval between frames that is used in the pcf , after completing the reception of the q - beacon . if the rf link 160 is idle after the pifs , the mt 1 transmits a voice frame qvoice 1 511 b . the ap , having normally received the qvoice 1 , transmits an ack 1 511 d and terminates the qslot 1 after the sifs 512 c . after the qslots are all terminated ( that is , the cfps are terminated ) and the difs 520 is waited for , an ap and mts within the same bbs can transmit frames through contention in the cp 530 under the dcf . in the cp , all the mts and the ap check the remaining time of the qtx - int before the transmission of frames , and defer the transmission of frames to the next cp if the time required for the exchange of frames is longer than the remaining time of the qtx - int . fig6 is a diagram showing a process in which an ap transmits a voice frame from mt 1 to mt 3 ( the mt 1 and the mt 3 pertain to the same bss ). referring to fig6 , when the qvoice frame is transmitted from the mt 1 to the mt 2 ( the mt 1 and mt 2 pertain to the same bss ), the ap stores the qvoice 1 received from the qslot 1 611 , waits for the pifs 613 a after the cfp 610 has been terminated , and then transmits the qvoice 3 613 b ( qvoice 1 frame transferred from the mt 1 to the mt 2 ) to the mt 3 . the mt 3 normally receives the qvoice 3 and then transmits ack 3 613 d after the sifs 613 c , thus completing the frame exchange process . if the ap does not transfer a qvoice frame any further , a difs is waited for and a delayed cp then begins . for the mt 1 and the mt 2 , frames can be transmitted after a cfp and a difs , so that the ap that waits only for a pifs acquires the right to use the rf link . in the meantime , the above - described embodiments may be written in the form of a computer program that can be executed on a computer , and can be implemented in a general - purpose digital computer using a computer - readable storage medium . the methods according to the present invention may be implemented on computer - readable storage media in the form of computer - readable code . the computer - readable storage media include all types of storage media in which computer system - readable data are stored . although examples of the computer readable storage media are read - only memory ( rom ), random access memory ( ram ), compact disk ( cd )- rom , a magnetic tape , a floppy disk , and an optical data storage , the methods according to the present invention can be implemented in the form of transmission via the internet . furthermore , the computer - readable storage media are distributed throughout a computer system connected via a network , and code , which can be read by a computer in a distributed manner , can be stored and executed . in accordance with the present invention , an rf link is divided according to the creation period of a voice frame using ptdm , a qslot is provided to each mt in each period and a voice frame is transmitted via the qslot , so that the voice frame can be transmitted without contention in the qslot , and the qos of an rf link section can be improved due to the decrease in frame transmission time and jitter because the voice frame is transmitted in a scheduled time . although the preferred embodiments of the present invention have been disclosed for illustrative purposes , those skilled in the art will appreciate that various modifications , additions and substitutions are possible , without departing from the scope and spirit of the invention as disclosed in the accompanying claims .