DESCRIPTION WIRELESS COMMUNICATION SYSTEM, WIRELESS COMMUNICATION DEVICE AND WIRELESS COMMUNICATION METHOD, AND COMPUTER PROGRAM Technical Field The present invention relates to a wireless communication system wherein a plurality of wireless stations communicate with one another as in wireless LAN (Local Area Network) or PAN (Personal Area Network) , a wireless communication device and a wireless communication method, and a computer program. More particularly, it relates to a wireless communication system, a wireless communication device and a wireless communication method, and a computer program wherein random access is made based on carrier detection by CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). Further more particularly, the present invention relates to a wireless communication system, a wireless communication device and a wireless communication method, and a computer program wherein access control is carried out based on CSMAusing the RTS/CTS method to maintain communication quality. Further more particularly, it relates to a wire less communication system, a wireless communication device and a wireless communication method/ and a computer program wherein a plurality of classes of frames, such as RTS, CTS, DATA, and ACK, are multiplexed and thereby flexible transmitting and receiving procedures are provided and overheads are reduced. Background Art The wireless network has received widespread attention as a communication system which relieves users of cable wiring between wire communication devices . With the wireless network, the majority of cables can be omitted in working spaces, such as off ices; therefore, communication terminals, such as personal computers (PCs), can be relatively easily relocated. As wireless LAN systems become faster and inexpensive, recently the demand for the wireless network has been significantly increased. In particular, these days, the introduction of personal area network (PAN) has been considered to build a small-scale wireless network among a plurality of pieces of electronic equipment existing in people' s surroundings to carry out information communication. For example, different wireless communication systems and wireless communication devices are defined using frequency bands, such as 2.4-GHz band and 5-GHz band, for which licenses from competent authorities are unnecessary. Typical standards related to wireless network include IEEE (The Institute of Electrical and Electronics Engineers) 802.11 (Refer to Non-Patent Document 1, for example .), HiperLAN/2 (Refer to Non-Patent Document 2 or Non-Patent Document 3, for example . ) , IEEE802 .15. 3, and Bluetooth communication. With respect to the IEEE802.il standard, various wireless transmission methods, such as the IEEE802.11a standard and the IEEE802.11b standard, are present depending on differences in wireless communication method and frequency band used. To build j local area network using radio engineering, e following method is generally used: one device, designated as "access point" or "coordinator," that functions as control station is provided in the area. Then the network is formed under the centralized control of the control station. In wireless networks provided with an access point, an access control method based on bandwidth reservation is in wide use. In this method, when information is transmitted from some communication device, a band required for the information transmission is reserved at the access point. Thus, transmission channels are utilized so that collision with information transmission by other communication devices will beprevented. That is, byproviding an access point, synchronous wireless communication, wherein the communication devices within the wireless network synchronize them with one another, is carried out. However, a problem arises if asynchronous communication is carried out between a transmitting communication device and a receiving communication devices in a wireless communication system provided with an access point: wireless communication must be carried out through the access point without exception, and thus the efficiency of transmission channel utilization is reduced by half. To cope with this, vad-hoc communication" in which terminals asynchronously communicate directly with each other has been devised a;> another method for building a wireless network. In particular, in small-scale wireless networks consisting of a relatively small number of clients located nearby, the ad-hoc ifccommunication js believed to be appropriate. In the ad-hoc communication, any terminals can carry out wireless communication directly, or randomly, with each other without use of any specific access point. In ad-hoc wireless communication systems, a central control station does not exist; therefore, it is suitable for constituting, for example, a home network comprising household electric appliances. The ad-hoc network has the following features, for example: even if one unit becomes faulty or is turned off, routing is automatically changed, and thus the network is less prone to fail; packets are caused to hop aplurality of times between mobile stations, and thereby data can be transmitted a re I at ively long way with a high data rate maintained. Various cases of ad-hoc system development have been known. (Refer to Non-Patent Document 5, for example.) For example, the IEEE802.il wireless LAN systems are provided with ad-hoc mode in which the system autonomously and decentralizedly operates in a peer to peer manner without providing a control station. With respect to wireless LAN networks in the ad-hoc environment, it is generally known that a problem of hidden terminal occurs. Hidden terminal is a communication station which can be heard by one communication station as the counterpart of communication but cannot be heard by the other when communicat Ion is carried out between the specific communication stations. Hidden terminals cannot carry out negotiation between them, and thus transmit operation can collide. As one of methodologies for solving such a problem of hidden terminal/ CSMA/CA according to the RTS/CTS procedure is known. The CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) is a connecting method wherein multiple access is made based on carrier detection. In wireless communication, it is difficult for a communication device to receive signals by which the device itself transmits information. Therefore, the communication device confirms that there is no information transmission from other communication devices by the CSMA/CA (Collision Avoidance) system, not by the CSMA/CD (Collision Detection) system. Then, the communication device starts its own information transmission, and thereby collision is avoided. The CSMA system is an access method suitable for asynchronous data communication, such as file transfer and electronic mail. In the RTS/CTS method, the communication station as the origin of data transmission transmits a request to send packet RTS (Request To Send) . In response to the reception of a response packet CTS (Clear To Send) from the communication station as the destination of data transmission, the transmitting communication station starts data transmission. When hidden terminals receive either or both of RTS and CTS, they set their own transmission stop period. The transmission stop period is equivalent to a pcsriod during which data transmission is expected to be performed based on the RTS/CTS procedure . Thus, collision can be avoided. Hidden terminals for the transmitter station receive CTS and set a transmission stop period to avoid collision with data packets. Hidden terminals for the receiver station ^receive RTS and stop a transmission period to avoid collision with ACK. Here, the wireless network will be described with IEEE802.11a, an expansion standard to IEEE802.il, taken as an example. FIG. 15 illustrates the frame format specified by IEEE802.11a. In the figure, a preamble which indicates the presence of packet is added to the head of each packet. For the preamble, known symbol patterns are defined in the standard. Based on these known patterns, receivers can judge whether a receive signal corresponds to a preamble or not. Following the preamble, SIGNAL field is defined. In the SIGNAL field, information required for decoding the information portion of the packet concerned is placed. The information required for decoding packets is designated as PLCP header (Physical Layer Convergence Protocol header) . The PLCP header includes: RATE field which indicates the transmission rate of an information portion (This includes Service field as part of PLCP header; however, it is hereafter simply and generically referred to as "information portion" for the purpose of simplifying the explanation.) ; LENGTH field which indicates the length of information portion; parity bit; Tail bit of encoder; and the like. Receivers decode the subsequent information portions based on the result of decoding the RATE and LENGTH fields in the PLCP header. The SIGNAL portion where the PLCP header is placed is subjected to encoding resistant to noise, and is transmitted 6Mbps, In case of normal packets, the information portion is transmitted in a transmission rate mode in which the highest bit rate is provided to the extend that the occurrence of errors is minimized according to the SNR or the like of the receiver. IEEE802.1Ia defines eight classes of transmission rate modes: 6, 9, 12, .18, 24, 36, and54Mbps, and any of themis selected. If a transmitter/receiver is positioned nearby, a high-bit rate transmission rate mode is selected. A communication station positioned far away cannot decode this information sometimes. The information portion is transferred as PSDU (Physical Layer Service Data Unit) to the data link layer as the higher level layer. FIG. 16 illustrates the constitution of the PSDU frame field. IEEE802.il defines several frame types. Here, description will be given only to four types of frames, RTS, CTS, ACK, and DATA, required for describing the present invention. For each frame, Frame Control field and Duration field are defined in common. The Frame Control field holds information indicating the rype and use of the frame concerned, and more specifically, it describes the information listed in Table 1. The Duration field holds information on the use of NAV (Network Allocation Vector) (to be described later), and describes the time that elapses before the transaction of the packet concerned is completed.(TABLE REMOVE) In addition to the foregoing, the Data frame contains: four address fields Addrl to Addr4 for identifying the communication stations as the origin of transmission and the destination and others; sequence field (SEQ); Frame Body which is the primary information to be provided to the upper level layer; and FCS (Frame Check Sequence) which is a checksum. In addition to the foregoing, the RTS frame contains: Receiver Address (RA) which indicates the destination; Transmitter Address (TA) which indicates the origin of transmission; and FCS which is a checksum. In addition to the foregoing, the CTS frame and ACK frame contain RA which indicates the destination and FCS which is a checksum. Here description will be given to the method for coping with access contention defined in IEEE802.il. IEEE802 .11 defines four types of inter frame spaces (IFS ) : SIFS (Short IFS), PIFS (PCF IFS), DIFS (DCF IFS), and EIFS (extended IFS) in ascending order. IEEE802 .1 1 adopts CSMA as a basic media access procedure (described above). Before a transmitter transmits something, the state of the medium is monitored and further a backoff timer is actuated for a random time. The transmitter is provided with transmission right only when there is no a transmit signal during this period, and the transmitter can transmit packets on the medium. When a normal packet is transmitted according to the CSMA procedure, the DCF (Distributed Coordination Function) operate as follows: after the transmission of a packet of some kind is completed, the state of the medium is monitored only for a DIFS. If there is no transmit signal during this period, randombackof f is carried out. If there is no transmit signal during this period, either, then transmission right is provided. When a packet, such as ACK, whose degree of urgency is exceptionally high is transmitted, it is permitted to transmit the packet after a short inter frame space SIFS. Thus, packets whose degree of urgency is high can be transmitted before packets transmitted according to the normal CSMA procedure. To sum up, the reason why different types of inter frame spaces IFS are defined is as follows: packets competing for transmission right are given priorities according to whether their IFS is SIFS, PIFS, or DIFS, that is, according to the length of inter frame space. Next, description will be given to the RTS/CTS procedure in IEEE802.il, referring to FIG. 17 to FIG. 19. With respect to wireless LAN networks in the ad-hoc environment, it is generally known that a problem of hidden terminal occurs. CSMA/CA according to the RTS/CTS procedure is known as one of methodologies for alleviating most of this problem (described above). IEEE802.il also adopts this methodology. FIG. 17 schematically illustrates an example of the operation of the RTS/CTS procedure . This figure shows an example in which information (Data) of some kind is transmitted from STAO to STA1. Prior to the actual transmission of information, STAO transmits an RTS (Request To Send) packet to STA1 as the destination of information according to the CSMA procedure . In response to the reception of the RTS packet, STA1 transmits a CTS (Clear To Send) packet to STAO, feeding back that STA1 has successfully received the RTS. If the transmitting STAO successfully receives the CTS packet, themedium is considered to be clear, and the transmission of information (Data) packets is immediately started. WhenSTAl has successfully received the information (Data) packets, STA1 returns an ACK packet. Thus, the transmission and reception transaction equivalent to one packet is completed. FIG. 18 illustrates action which can take place in surrounding stations when the RTS/CTS procedure is carried out between a transmitter station and a receiver station. In this figure, the following communication environment is assumed: four communication stations, STA2, STAO, STA1, and STAB, exist, and communication stations adjoining to each other in the figure are located with in the range of radio waves . Here, it is assumed that STAO desires to transmit information to STA1. The transmitting STAO confirms that the medium is clear for a certain period (from time TO to time Tl) according to the CSMA procedure. Then, STAG starts the transmission of an RTS jacket to STA1 at time Tl „ In the Type/Subtype field of the Frame Control field of the RTS packet, information which indicates the packet concerned is RTS is described; in the Duration field, the time that lapses before the transmission and reception transaction for the packet concerned is completed (i.e. the time until time T8) is described ; in the RA field, the address of the destination communication station (STA1) is described; and in the TA field, the address of the transmitter station (STAO) itself is described. Here, attention should be paid to the following point: for STAO to describe in the Duration field the time that lapses before the transaction according to the RTS/CTS procedure is completed, the time when the transaction is completed must be determined when RTS is transmitted. More specific description will be given. The transmitting STAO must determine all the transmission rate mode, including CTS packet, Data packet, and ACK packet to be subsequently transmitted and received in the transaction in question, when it transmits RTS. The transmission rate mode determined here relates to the entire transaction, and it is not permitted to set an individual transmission rate mode with respect to each packet transmission within a transaction. FIG. 19 illustrates the procedure according to which the transmitting STAO determines a transmission rate mode with time at which the transaction is completed is (T8 in FIG. 4} . Therefore, the transmission rate mode is determined only due to inf ormat ion held by the transmitter station when it transmits RTS (based on the amount of data communicated in the entire transaction, the transmission rate, and the like). The transmission rate of each of the CTS, DATA, and ACK frames thereafter transmitted and received is basically in accordance with the rate applied in the RTS. That is, it is not permitted to set an individual transmission rate mode with respect to each packet transmission within a transaction. Here, description will be given, referring to FIG . 18 again. The RTS packet is received also by STA2 which is positioned in the vicinity of STAG. When 3TA2 receives the RTS signal, STA2 discovers the preamble and thus starts receive operation. Further, STA2 decodes PSDU based on the information obtained by decoding the PLCP header. Then, STA2 recognizes from the Frame Control field in the PSDU that the packet in question is RTS packet, and knows that STAG desires to transmit information of some kind. Further, STA2 recognizes from the RA field that STA2 itself is not the destination communication station. Then, STA2 does not monitor the medium and recognizes that the medium is occupied until the transaction in question is completed, and stops its own transmission so as not to hinder STAO's desire to send. To refer to this operation, it is said that a surrounding station "sets NAV (Network Allocation Vector)." The NAV is effective during the period indicated in the Duration field, and STA2 is kept in transmission prohibited state until time The RTS packet is received also by STA1 which is the intended destination. STA1 decodes the PSDU according to the same procedure as described above, and thereby recognizes that STAG desires to transmit packets to STA1 itself. Then, STA1 waits for a SIFS (described above) and returns a CTS packet at time T3. At this time, the transmission rate mode of the CTS packet must be identical with that of RTS . Further, in the Frame Control field of the PSDU, it is described that the packet concerned isCTSpacket; in the Duration field, the time that elapses between the transaction concerned is completed (i.e. time until time T8) is described; and in the RA field, the address of the destination communication station (STA1) is described. The CTS packet is received also by STA3 which is positioned in the vicinity of STA1 as the destination of transmission. STA1 decodes the PSDU according to the same procedure as described above, and recognizes that "some nearby communication station is expected to receive packets until time T8." STA3 sets an NAV and refrains from its own transmission until the transaction concerned is completed so as not to hinder STA1' sdesiretoreceive. The NAV is effective during the period indicated in the Duration field, and STA3 is also kept in transmission prohibited state until time T8. The CTS packet is received also by STAG as the destination. STAO decodes the PSDU according to the same procedure as described above, and recocmize.s that STA1 has ant roaHv 1-0 STAG waits for a SIFS, and starts the transmission of Data packet time T5. If the transmission of the Data packet is completed at time T6 and STA1 decodes them without any error, STA1 waits for a SIFS and returns ACK at time TV. When STAO receives it, the transmission and reception transaction equivalent to one packet is completed at time T8. At time T8, STA2 and STA3 which are nearby communication stations put down the NAV, and return to ordinary transmitting and receiving state. In summary, in the above-mentioned RTS/CTS procedure, the following surrounding stations are prohibited from carrying out transmission: a ''surrounding station for STAO as the transmitter station," or STA2, which could receive RTS, and a "surrounding station for STA1 as the receiver station," or STA3, which could receive CTS. Thus, information transmission from STAO to STA1 and a return of ACK are carried out without being hindered by a sudden transmit, signal from surrounding stations . Therefore, the communication quality is maintained. FIG. 20 illustrates an example of an operation sequence followed when the above-mentioned packet transmission and reception transaction based on the RTS/CTS procedure in IEEE802.il is implemented with traffic through TCP/IP (Transmission Control Protocol/Internet Protocol) . The TCP/IP is a typical communication protocol for transmission control and path cont.ro L. Even i f communication is of one way in terms of application, ACK is returned by the TCP layer typically every two segments, and it is brought into the form of asymmetrical two-way communication jn the MAC layer. The ACK of the TCP layer is small in amount of data, and thus RTS/CTS is not used together. However, RTS/CTS is used together with respect to data traffic. The figure illustrates such an example. In the example illustrated in FIG. 20, packets equivalent to 24 times in total are transmitted and received in the MAC layer to transmit five segments, DataO to Data4 . That is, while the operation in the TCP layer is relatively simple, complicated operation is performed in the MAC layer. As described up to this point, problems of access contention and bandwidth assurance can be solved by implementing the transmitting and receiving procedures based on CSMA in combination with the RTS/CTS method in accordance with IEEE802 . 11. Meanwhile, several problems described below are left unsolved. (1) Imperfection of Transmission Rate When data is transmitted and received according to the RTS/CTS procedure, the transmission rate of data packets must be determined before an RTS packet is transmitted. This is because, for a transmitter station to describe in the Duration field the time that lapses before a transaction based on the RTS/CTS procedure is completed, the time at which the transaction is completed must be determined when it transmits an RTS . This means that all the transmission rate mode, including CTS packet, Data packet, and ACK packet subsequently transmitted and received in that transaction must be determined when RTS is transmitted. The transmission rate mode determined when RTS transmitted relates to the entire transaction; it is not permitted to set an individual transmission rate mode with respect to each packet transmission within a transaction. Therefore, the transmission rate is imperfect. Further, transmitter stations cannot grasp the state of reception in receiver stations in real time. Therefore, determining the transmission rate of the entire transaction when RTS is transmitted results in a lower probability that data packets are transmitted at the optimal transmission rate corresponding to the state of reception in the receiver station. An example will be taken. Patent Document 1 discloses a method for packet transfer communication. The method is such that, when the receiving end receives an RTS packet, it measures the environment and state of communication at that point of time; then, the receiving end adds the result of the measurement to the CTS packet and returns it to the transmitting end; thereby the transmitting end optimizes the communication rate and the like. However, this case is also nothing but another case where the transmitting end determines the transmission rate of the entire transaction before it transmits an RTS packet. Therefore, the imperfection of transmission rate is not eliminated. value obtained by dividing the amount of transmitted data by %the transmission rate; and describe the determined value in RTS . Patent Document 1 describes that the CTS transmitter station determines a transmission rate through the reception of RTS; however it does not refer to how to obtain the value in the Duration field described in RTS by the RTS transmitter station prior thereto. If the CTS transmitting station sets a high transmission rate, the transaction is completed ahead of the Duration determined when RTS is transmitted. As a result, the surrounding stations which heard the RTS still keep a NAV set and refrain from their own transmission after the transaction is completed, and this is a wast e of bandwidth. If the CTS transmitting station sets a low transmission rate, the transaction is not completed even after the Duration determined when RTS is transmitted has passed. Nevertheless, surrounding stations which heard RTS put down the NAV and start transmit operation, and this induces collision. (2) Difficulty of Data Unit Multiplexing with RTS/CTS Used Together In the conventionally known RTS/CTS procedure, the data transmitting end determines a data rate before it transmits an RTS. It; does not give consideration to the following: the data receiving end determines a data rate and further transmits a plurality of data units as one data packet. To enhance the efficiency of the MAC layer (Refer to FIG. 20.), it is preferably that the receiving end should be capable of determining a data rate and transmitting aplurality of data units as one data packet. lowever, the conventional RTS/CTS format cannot implement this. (3) Concomitant Use of Delay Acknowledgement and RTS/CTS Procedure The IEEE802.il standard is premised on the immediate ACK wherein an acknowledgement (ACK) is returned as soon as data is received. To reduce the overhead of ACK packets, delay ACK can be used. However, some problems arise. For example, if delay ACK is used together with the RTS/CTS procedure, there is a possibility that an RTS is transmitted for the purpose of retransmission before an ACK cannot be returned to the transmitting end. Thus, with the existing format, the concomitant use of delay acknowledgement and the RTS/CTS procedure has its limit in the enhancement of efficiency. (4) Methodology For Selective Acknowledgement It is known that carrying out selective acknowledgement enhances the efficiency of the MAC layer. The IEEE802.il standard does not give consideration to selective acknowledgement itself. The selective acknowledgement referred to here is a retransmission control method. In this method, ACK or NACK information is fed back to the transmitting end with respect to an arbitrary packet which was or was not successfully received. Thereby, retransmission is carried out only with respect to packets which the receiving end could not receive. Implementation of selective acknowledgement requires massive memory and its processing places a significant burden; therefore, it has not be actually applied so much. However, necessity for selective acknowledgement will be more and more increased in the future. With this being the situation, the following case is expected: communication stations in the initial stage do not have selective acknowledgement implemented but communication stations developed later have selective acknowledgement implemented. In this case, it is unfavorable that both cannot communicate with each other, and a format wherein downward compatibility is maintained is desired. Further, up to now consideration has not given to concomitant use of selective acknowledgement, a technique for the receiving end to determine a data rate, and the RTS/CTS procedure. Therefore, this cannot be implemented by the existing format. (5) Influence of Overhead Produced in MAC Layer The IEEE802 .11 standards independently defines RTS frame, CTS frame, ACK frame, and the like. (Refer to FIG. 16.) For this reason, if individual information is to be transmitted, they must be respectively transmitted by separate frames. However, each time a frame is transmitted, overheads, such as preamble, are produced. Inparticular, if the transmission rate is high, the amount of overheads becomes too large to neglect. Needless to add, increase in overheads in the MAC layer is undesirable oecause it contributes in such a direction as to limit the bandwidth which can be provided for the upper level layers, such as TCP/IP. [Patent Document 1] Japanese Unexamined Patent Publication No. 2000-151639 [Non-Patent Document 1] International Standard ISO/IEC 8802-11: 1999(E) ANSI/IEEE Std 802.11, 1999 Edition, Partll: Wireless LANMediumAccess Control (MAC) and Physical Layer (PHY) Specifications [Non-Patent Document 2] ETSI Standard ETSI TS 101 761-1 VI.3.1 Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer; Parti: Basic Data Transport Functions [Non-Patent Document 3] ETSI TS 101 761-2 VI.3. 1 Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer; Part2: Radio Link Control (RLC) sublayer [Non-Patent Document 4] C.K.Tho, "AdHocMobile Wireless Network" (Prentice Hall PTR) Disclosure of Invention An object of the present invention is to provide an excellent wireless communication system, wireless communication device and wireless communication method, and computer program wherein the RTS/CTS method is used together and yet access control based on CSMA can be favorably carried out. Another object of the present invention to provide an excellent wireless communication system, wireless communication device and wireless communication method, and tpcomputer program wherein a plurality of types of frames, such as RTS, CTS, DATA, and ACK, are multiplexed and thereby flexile transmitting and receiving procedures can be provided and overheads can be reduced. The present invention has been made with the above problems taken into account. A first aspect of the present invention is a wireless communication system wherein random access is carried out using together the RTS/CTS method in which a communication station as the origin of data transmission transmits a request to send packet RTS, and starts data transmission in response to the reception of a response packet CTS from a communication station as the destination of data transmission. The RTS receiving communication station measures the quality of a receive signal, determines a data rate based on the result of the measurement, describes the data rate in CTS, and transmits the CTS. The CTS receiving communication station carries out data transmission as the outcome of the reception of the CTS information based on the data rate described in the CTS. The "system" described here refers to what is obtained by logically aggregating a plurality of devices (or functional modules which implement specific functions) . It does not matter whether the devices or functional modules are placed in a single enclosure or not. The RTS transmitting communication station describes in RTS the time that lapses before the reception of a packet, ^including CTS information, transmitted as the outcome of the reception of RTS information is completed, as medium reservation time information Duration. The CTS transmitting communication station describes in CTS the time that lapses before the reception of a data packet; transmitted as the outcome of the reception of CTS information is completed, as medium reservation time information Duration. Other communication stations that receive RTS or CTS set a NAV (Network Allocation Vector) , and keep it in effect for the medium reservation time information Duration and bring themselves in transmission prohibited state . In a wireless communication system according to the first aspect of the present invention, a transmission rate can be selected based on the quality of receive signal. Therefore, the imperfection of transmission rate can be wiped off. Here, the following constitution may be adopted: the RTS sending communication station describes in RTS factor information referred to by the RTS receiving communication station when it determines a data rate. The RTS receiving communication station determines a data rate with consideration given to the factor information described in the RTS, in addition to the result of measurement of the quality of receive signal. As the factor information described here, information related to whether a high data rate should be aggressively determined or a low data rate should be passively determined the transmission error rate for the RTS receiving communication "Ifstation. Then, based on the result of the measurement, factor information (Pate Strategy) is determined. Or, factor information may be determined based on the difference in transmission power between RTS packet and data packet, the causal relationship between data rate and transmission power, or the like. In these cases, a data rate is determined according to the quality of RTS receive signal at the receiving end. A transmission rate is determined with consideration additionally given to information, such as error rate monitored by the transmitting end. Therefore, the correspondence between reception quality and error rate arising from fluctuation in channel state or fluctuation in the amount of interference can be corrected in two steps. Further, the following constitution may be adopted: the RTS transmitting communication station describes in RTS information related to one or more data units the station tries to transmit. The RTS receiving communication station determines medium reservation time information Duration in which the reception of all the data packets is completed. The medium reservation time information Duration is determined based on the information related to the data units, described in the RTS transmission is carried out based on the data rate described %Ln the CTS so that the data transmission will be completed in a time specified by the medium reservation time information. Examples of the information related to data units, referred to here, include: the data length of each data unit for which transmission is tried; the sum of data lengths of one or more data units for which transmission is tried; the length of time required for transmitting one or more data units for which transmission is tried; information on the number of data units for which transmission is tried (in this case, however, data units are of fixed length); and the like. In these cases, the RTS/CTS procedure can be used together and further data units can be effectively multiplexed. Further, the RTS/CTS procedure and delay ACK can be implemented. As a result, the amount of overheads produced in the MAC layer can be reduced. In this case, when the RTS receiving communication station determines medium reservation time information after the reception of RTS, the station takes into account the time at which the station itself completes data reception. Or, when the RTS receiving communication station determines medium reservation time information aftert he reception of RTS, itgives consideration so that the period information described in the RTS is not exceeded. For example, the following constitution may be adopted: the RTS transmicting communication station assigns sequence numbers to transmit data units, and describes in RTS the first sequence number of data the station tries to transmit. Thereby, sthe station notifies of information related to the data units it tries to transmit. Meanwhile, the RTS receiving communication station refers to the first sequence number of data unit, described in the RTS, and extracts and excludes data units the station has already received from data units for which transmission is tried. Then, the station determines medium reservation time information. Further, if selective acknowledgement is applied, the following constitution may be adopted: the RTS transmitting communication station describes reception acknowledgement information in RTS. The reception acknowledgement information includes the first sequence number of data units for which data transmission is tried andbit map information obtainedby mapping the reception confirmation information on the subsequent data units into bits corresponding to the relative positions to the first sequence number. Further, the station generates information related to the data units with only data units for which reception confirmation has not been obtained taken as objects to be transmitted. Meanwhile, the RTS receiving received are included in data units as obj ects to be transmitted, Ijpdescribed in RTS, the station describes ACK information in CTS. In this case, the CTS receiving communication station excludes data units the RTS receiving communication station has already received from objects to be transmitted based on the ACK information added to the CTS. Then, the station carries out data transmission based on the data rate described in the CTS. Further, 1 he following constitution may be adopted: the RTS receiving communication station stores one or more pieces of data length .information of data units taken as objects to be transmitted, of data for which transmission is tried as the outcome of the H.TS, Then, the station describes in CTS the sequence number of the last data unit stored. In this case, the CTS receiving communication station stores the sequence number of the la.st data unit described in the CTS. When an RTS is transmitted next time, the station generates information related to data .inits for which transmission is tried in such form that the data unit indicated by the sequence number of the last data unit. Ls not included in objects to be transmitted. sequence numbers of data units completely received in the order %fcf sequence number and the bit map information represented by mapping the state of reception of data of the subsequent sequence numbers into relative bit positions from the sequence numbers. The station transmits the reception acknowledgement information ACK. The transmitting and receiving communication stations add information indicating a causal data flow to transmit data and acknowledgement, In a wireless communication system according to the second aspect of the present invention, information required for selective acknowledgement is managed on a data flow-by-data flow basis. Such information includes the sequence numbers of completely received data units, bit map information wherein the state of reception of the subsequent data units are described, andthelike. Thus, a plurality of service classes canbe handled by different sequence numbers. Therefore, communication can be maintained regardless of whether selective acknowledgement is implemented or not. disregards the bit map information transmitted from the receiving %end, and transmits the bit map information to be transmitted with zero set for all the bits of the bit map field. Thus, the transmitter stations can ensure communication with receiver stations which support the selective acknowledgement function. Further, with respect to at least one data flow, the ARQ system wherein sequence numbers are not assigned is adopted. When Link session is established, data is transmitted and received through the data flow, and thereby the sequence numbers of the transmitter station and the receiver station are synchronized with each other. A third aspect of the present invention is a wireless communicat ion system wherein random access is carried out using the RTS/CTS method together. The RTS/CTS method is such that: the communication station as the origin of data transmission transmits a request to send packet RTS. In response to the reception of a response packet CTS from the communication station as the destination of data transmission, the communication station as the origin of data transmission starts data transmission. The transmission and reception of packets wherein any two or more of request to send RTS, confirmative advice CTS, data, and acknowledgement ACK are multiplexed are permitted. The amount of overheads produced in the MAC layer can be significantly reduced by including pieces of information, such as RTS, CTS, DATA, and ACK, having different purposes in one packet. In this case, the communication station which receives containing RTS information transmits apacket containing CTS information according to the contents of the RTS. The communication station which receives a packet containing CTS information transmits a packet containing data according to the contents of the CTS. Here, the following constitution may be adopted: the RTS transmitting communication station can specify whether the receiving communication station may add RTS information to CTS or not. In this case, in RTS, first information which indicates whether RTS information may be added to CTS transmitted as the outcome of the RTS or not is described. Then, the RTS receiving communication station judges whether it may add RTS information to CTS based on the first information in the RTS. If there is data the station desires to transmit to the RTS transmitting communication station, it adds RTS information for the purpose of transmitting the data to CTS, and transmits the CTS. In this case, the RTS transmitting communication station determines the first information, for example, based on information elements contained in the packets received in the past from the station to which the RTS is directed. The information element described here refers to More bit which indicates the presence of subsequent transmit data in the packet, and the like. Alternatively, it may be judged from other means than information elements that subsequent transmit data is present in the station to which the RTS is directed to determine the first information. Examples include the following case: a station receives an RTS from a station to which RTS is directed, wever, the receiving station itself received a packet from another surrounding station and thus has set a NAV. Therefore, the station cannot return a CTS, and the data transmission sequence is stopped. There are also cases where it can be judged based on any other communicationhistory that subsequent transmit data is present in the station to which RTS is directed. Further, the following constitution may be adopted: the RTS receiving communication station recognizes from the information in the RTS that the RTS transmitting communication station is trying to transmit data the receiving communication station itself has already received. In this case, the RTS receiving communication station adds ACK information to CTS to notify of the state of data reception. Further, the following constitution may be adopted: in the data transmitting and receiving procedure, the data transmitting communication station specifies whether the data receiving communication station should return an ACK. The ACK includes immediate ACK and delay ACK. In this case, the following constitution may be adopted: the data receiving communication station receives data requesting ACK, from the data transmitting communication station. If the data receiving communication station judges that it has not transmitted an ACK of the data, it: adds ACK information when it transmits a packet of some kind to the data transmitting communication station. In some cases, ACK information maybe added at the transmitter station' s request. At this time, if the transmitter station judges that it has not received ACK information related to previously transmitted data, %:t sends a request to add ACK information. However, with respect to packets in which RTS information is solely transmitted, ACK information need not be added by way of exception. Further, data requesting an ACK may be transmitted as a packet directed to two or more communication stations. Further, the following constitution may be adopted: the RTS transmitting communication station requests the RTS receiving communication station to return an ACK of data which has been transmitted so far. In this case, the RTS transmitting communication station multiplexes an ACK request for requesting a return of ACK into an RTS for starting the next data transmission transaction, and transmits it. Even if the RTS transmitting communication station requests an ACK, the ACK is not returned sometimes. Possible causes include that transmit data was not properly received, that data was property received but the reception of ACK failed, and the like. In t hese cases, the RTS transmitting communication station must veri f y whether to retransmit data . In these cases, the RTS transmitting communication station may multiplex an ACK request requesting a return of ACK into an RTS for starting data retransmission transaction, and transmit it. The communication station which received an RTS with an ACK request multiplexed returns an ACK which indicates whether it has properly completed the reception of data transmitted from the RTS transmittj ng communication station. If the station has failed to receive data transmitted from the RTS transmitting communication station, it may multiplex an ACK indicating that it failed to properly receive the data. Then, it may return a CTS requesting to retransmit the data. A fourth aspect of the present invention is a wireless communication system wherein the data transmitting communication station acquires transmission right on the medium and carries out data communication between it and the data receiving communication station. After data transmission from the data transmitting communication station is stopped, the presence or absence of subsequent data at the data transmitting communication station is detected. If the subsequent data is present, it is made easier for the data transmitting communication station to acquire transmission right for transmitting the subsequent data. The state in which, though the subsequent data is present at the data transmitting communication station, data transmission is stopped corresponds to the following cases, for example: cases where an RTS from the data transmitting communication station reaches the data receiving communication station and the data receiving communication station returns a CTS, but the data transmitting communication station does not start data transmission; and cases where transmit data does not reach the data receiving communication station. The data receiving communication station can detect the presence/absence of the subsequent data at the data transmitting communication station can include in a packet a specific information element indicating the presence/absence of the subsequent data and transmit the packet. In this case, the data receiving communication station checks the information element, and can thereby detect the presence/absence of the subsequent data at the data transmitting communication station. According to CSMA, it is confirmed only for a predetermined period that the medium is clear, and then the operation waits only for an arbitrary backoff time before transmission right is acquired. In the communication environment wherein medium access control is carried out based on CSMA, the data receiving communication station tries to acquire transmission right on the medium, and transmits a signal onto the medium for eliminating other communication stations' transmission right. Thereby, it can be made easier for the data transmitting communication station to acquire transmission right for transmitting the subsequent data. In medium access control with the RTS/CTS method used together, the communication station as the origin of data transmission transmits a request to sendpacket RTS . In response to the reception of a response packet CTS from the communication station as the destination of data transmission, it starts data transmission. In case this medium access control is carried out, the data receiving communication station transmits a dummy RTS onto the medium for eliminating other communication stations' transmission right. Thereby, it can be made easier for the data transmitting communication station to transmit an RTS for transmitting the subsequent data. For example, when the data :ransmitting communication station receives a dummy RTS, it can transmit an RTS with a shorter frame space for transmitting the subsequent, data . A fifth aspect of the present invention is a computer program written in a computer-readable format for performing on a computer system processing for controlling communicating operation in the communication environment wherein random access is carried out: with the RTS/CTS method used together. In the RTS/CTS method, the communication station as the origin of data transmission transmits a request to send packet RTS; in response to the reception of a response packet CTS from the communication station as the destination of data transmission, it starts data transmission. The program comprises: a communication quality measuring step in which, when an RTS is received, the quality of receive signal is measured; a data rate determining step in which a data rate is determined based on the measured quality of receive signal; a CTS transmitting step in which the data rate is described in CTS as the outcome of the received RTS, and the CTS is transmitted; and a data transmitting step in which, when CTS information is received, data transmission as the outcome of the CTS information is carried out based on the data rate described in the CTS. A sixth aspect of the present invention is a computer program written in a computer-readable format for carrying out on a computer system control of communicating operation for transmitting and receiving a plurality of data units . Sequence numbers are assigned to transmit data units to identify the data units. If selective acknowledgement is applied, the following steps are provided: a step in which, in response to data reception, the sequence numbers of completely received data units in the order of sequence number, and bit map information represented by mapping the state of reception of data of the subsequent sequence numbers into relative bit positions from the sequence numbers, are described in reception acknowledgement information ACK and are transmitted; and a step in which information indicating a causal data flow is added, and transmit data and an acknowledgement are transmitted. A seventh aspect of the present invention is a computer program written in a computer-readable format for performing and acknowledgement ACK, is generated; and a packet transfer communication step in which a packet wherein any two or more pieces of information of request to send RTS, confirmative advice CTS, data, and acknowledgement ACK are multiplexed is transmitted and received. An eighth aspect of the present invention is a computer program written in a computer-readable format for performing on a computer systemprocessing for controlling the communicating operation in the following communication environment: in the communication environment, the communication station acquires transmission right on the medium before it carries out data communication. The program comprises: a step in which the presence/absence of transmit data from other communication stations is detected; and a medium access control step in which, in response to the detection of the presence of transmit data from other communication stations, a signal for eliminating the other communication stations' transmission right is transmitted onto the medium so as to make easier for the relevant communication station to acquire transmission right for transmitting data. The computer programs according to the fifth to eighth aspects of the present invention are computer programs written in a computer-readable format for performing predetermined processing on a computer system by definition. In other words, when installed on a computer system, the computer programs according to the fifth to eighth aspects of the present invention deliver synergistic action on the computer system and operate as wireless communication devices. When a plurality of such tfireless communication devices are started to build a wireless network, the same action and effect as with the wireless communication systems according to the first to fourth aspects of the present invention can be obtained. According to the present invention, an excellent wireless communication system, wireless communication device and wireless communication method, and computer program wherein the RTS/CTS method is used together and further access control can be favorably carried out based on CSMA can be provided. Further, according to the present invention, an excellent wireless communication system, wireless communication device and wireless communication method, and computer program wherein a plurality of types of frames, such as RTS, CTS, DATA, and ACK, are multiplexed, and thereby flexible transmitting and receiving procedures can be provided and overheads can be reduced can be provided. According to the present invention, a transmission rate can be selected based on the quality of receive signals. Therefore, the imperfection of transmission rate can be eliminated. In addition, when a transmission rate is determined, information, such as the error rate monitoredby the transmitting end, is also taken into account. Therefore, the correspondence between reception quality and error rate arising from fluctuation in channel state or fluctuation in the amount of interference can be corrected in two steps. Further, according to the present invention, data units can be effectively multiplexed while the RTS/CTS procedure is i*used together. Further, the RTS/CTS procedure and delay ACK canbe implemented. As a result, the amount of overheads produced in the MAC layer can be reduced. Further, according to the present invention, communication can be maintained regardless of whether selective acknowledgement is implemented or not. Further, according to the present invention, the amount of overheads produced in the MAC layer can be significantly reduced by including pieces of information, such as RTS, CTS, DATA, and ACK, having different purposes in one packet. Other objects, features, and advantages of the present invention will be apparent from the embodiments of the present invent ion described later and the more detailed description taken in connection with the accompanying drawings. Brief Description of Drawings FIG. 1 is a drawing illustrating an example of the disposition of communication devices constituting a wireless communication system in an embodiment of the present invention. FIG. 2 is a drawing schematically illustrating the functional consti tution of a wireless communication device which operates as a communication station in a wireless network in an embodiment of the present, invention. FIG. 3 is a drawing illustrating an example of a frame format used in a wireless communication system according to the present invention. FIG, 4 is a drawing illustrating an example of the Constitution of E;SDU. FIG. 5 is a drawing illustrating several examples of PSDUs which can be defined. FIG, & is a drawing explaining the process for determining a transmission rate in a wireless communication system according to the present invention. FIG. 7 is a drawing illustrating an example of the operation sequence of the RTS/CTS procedure according to the present invention. FIG. 8 is a drawing illustrating an example of the application of transmitting and receiving procedures according to the present invention. FIG. 9 is a drawing illustrating another example of the application of transmitting and receiving procedures according to the present invention. FIG. 10 is a drawing illustrating a further example of the application of transmitting and receiving procedures according to the present invention. FIG. 11 is a drawing illustrating the acknowledgement procedure related to data other than data flow 0 assumed in the present invention. FIG. 12 is a drawing illustrating a concrete example of the interaction o f individual fields which occurs when selective acknowledgement LS carried out with RTS/CTS used together. FIG. 13 is a drawing illustrating an example of data transmittinq and receivincr Drocedures takpn whpn Hplav APK the RTS/CTS procedure are applied. FIG. 14 is a drawing illustrating an example of the sequence in which traffic is transmitted and received through TCP/IP in accordance with the MAC procedure according to the present invention. FIG. 15 is a drawing illustrating the frame format according to IEEE802.11a. FIG. 1 6 is a drawing illustrating the constitution of frame fields in PSDU. FIG. 17 is a drawing schematically illustrating an example of the operation of the RTS/CTS procedure. FIG. 18 is a drawing explaining the action which can occur at surrounding stations when the RTS/CTS procedure is carried out between the transmitter station and the receiver station. FIG. 19 is a drawing explaining the procedure for determining the transmission rate mode of the entire transaction when STAO as the origin of transmission transmits an RTS. FIG. 20 is a drawing illustrating an example of the operation sequence in which packet transmission and reception transaction based on the RTS/CTS procedure according to IEEE802.il is implemented with traffic through TCP/IP. FIG. 21 is a drawing explaining an example of the application of transmitting and receiving procedures according to the present invention. FIG. 22 is ct drawing explaining another example of the application of transmitting and receiving procedures according to the present invention. FIG. 23 is a drawing explaining a further example of transmitting ana receiving procedures according to the present invention. FIG. 24 is a drawing explaining the mechanism for controlling the judgment of whether "information indicating that an RTS may be multiplexed into a CTS" should be set or not. FIG. 25 is another drawing explaining the mechanism for control ling the judgment of whether "information indicating that an RTS may be multiplexed into a CTS" should be set or not. FIG. 26 is a further drawing explaining the mechanism for controlling the judgment of whether "information indicating that an RTS may be multiplexed into a CTS" should be set or not. Best Mode for Carrying Out the Invention Referring to the drawings, the embodiments of the present invention will be described in detail below. A. System Configuration The propagation path for communication the present invention assumes is wireless, and a network is built among a plurality of communication stations. The communication the present invention assumes is store and forward traffic, in which information is transferred on a packet-by-packet basis. With respect to each communication station, the following description assumes single-channel station; however, the present invention can be expanded to cases where a transmission medium comprising a plurality of frequency channels, that is, multiple channels is used. In a wireless network according to the present invention, Ifeach communication station can directly (randomly) transmit information in accordance with an access procedure based on CSMA (Carrier Sense Multiple Access). Thus, the communication stations can build an autonomous and decentralized wireless network. The autonomous and decentralized wireless communication system does not have the relation of control station and controlled station. In such a wireless communication system, for example, each communication station sends beacon information. The station thereby informs other communication station located nearby (i.e. within the range of communication) of the presence of itself, and informs them of the constitution of the network. A communication station whichnewly emerges in some communication station's range of communication receives a beacon signal, and thereby detects that it has entered the range of communication. Further, the station decodes the information described in the beacon, and can thereby recognize the network and participate in the network. In the wireless network according to thepresent invention, communication stations exchange beacon signals, and modestly and temporally synchronize with each other . Thus, transmission control is carried out wherein channel resources are effectively utilized by transmission (MAC) frames having the time division multiple access structure. Therefore, each communication station can implement an access method based on temporal synchronization, such as reserving a bandwidth and setting a preferential period of use. The processing at each communication station, described below, is basically carried out at every communication station that participates in the network. In some cases, however, the processing described below is not necessarily performed by all the communication stations constituting the network. FIG. 1 illustrates an example of the disposition of communication devices which constitute the wireless communication system in an embodiment of the present invention. This wireless communication system does not have the relation of control station and controlled station. In this communication system, each communication device autonomously and decentralizedly operates, and an ad-hoc network is formed. The figure shows how the communication device #0 to the communication device #6 are distributed in the same space. In the figure, each communication device's range of communication is indicated by broken line. Each communication device can communicate with other communication devices located within its range, and the range of communication is defined as a range in which a signal transmitted by each station interferes with other communication devices. More specific description will be given. The communication device #0 is located in a range in which it; can communicate with the communication devices #1 and #4 located nearby; the communication device #1 is located in a range in which it can communicate with the communication devices #0, #2, and #4 located nearby; the communication device #2 is located in a range in which it can communicate with the communication devices #1, #3, and #6 located nearby; the Communication dejvice #3 is located in a range in which it can communicate with the communication device #2 located nearby; the communication device #4 is located in a range in which it can communicate with the communication devices #0, #1, and #5 located nearby; the communication device #5 is located in a range in which it can communicate with the communication device #4 located nearby; and the communication device #6 is located in a range in which i t can communicate with the communication device #2 located nearby. When communication is carried out between certain communication devices, a "hidden terminal" exists. Hidden terminal is defined as a communication device which can be heard by either of the communication devices communicating with each other but cannot by the other. The scope of the present invention is not limited to the above ad-hoc environment. It can be widely applied to other modes of communication wherein each communication station can directly and asynchronously transmit information in accordance with the acces s procedure based on CSMAwith the RTS/CTS procedure used together. FIG. 2 schematically illustrates the functional constitution of a wireless communication device which operates as a communication station in a wireless network in an embodiment autonomous and decentralized communication environment in which rogram described in a computer-readable format for carrying out on a computer system the processing for controlling communicating operation in a communication environment: in which random access is made concomitantly using the RTS/CTS method wherein a communication station as the origin of data transmission transmits a request to send packet RTS and starts data transmission in response to the reception of a response packet CTS from a communication station as the destination of data transmission, the computer program comprising: a communication qualitymeasuring step in which the quality of receive signal is measured when an RTS is received; a data rate determining step in which a data rate is determined based on the measured quality of receive signal; a CTS transmitting step in which the data rate is described in a CTS as the outcome of the received RTS and transmitted; and a data transmitting step in which, when CTS information is received, data transmission as the outcome of the CTS information is carried out based on the data rate described in the CTS. 76. A computer program described in a computer-readable format for carrying out on a computer system the control of communicating operation for transmitting and receiving a plurality of data units, the computer program comprising the steps of: assigning sequence numbers to transmit data units to identify the data units, and, if selective acknowledgement is applied, describing in reception acknowledgement information ACK the sequence numbers of completely received data units in the order of sequence number and bit map information represented by mapping the state of reception of data of the subsequent sequence numbers into relative bit positions from the sequence numbers in response to data reception, and transmitting the information; and adding information indicating a causal data flow when transmitting transmit data and an acknowledgement in response to data transmission/reception. 77. A computer program described in a computer-readable format for carrying oat on a computer system the processing for controlling communicating operation in a communication environment in which random access is made concomitantly using the RTS/CTS method wherein a communication station as the origin ,, t data transmission transmits a request to send packet RTS and starts data transmission in response to the reception of a response packet CTS from a communication station as the destination of data transmission, the computer program comprising: an information generating step in which information of request to send RTS, confirmative advice CTS, data, and acknowledgement ACK is generated; and a packet transfer communication step in which a packet in which any two or more pieces of information of request to send RTS, confirmative advice CTS, data, and acknowledgement ACK are multiplexed is transmitted and received. 78. A wireless communication system in which random access is made concomitantly using the RTS/CTS method wherein a communication station as the origin of data transmission transmits a request to send packet RTS and starts data transmission in response to the reception of a response packet CTS from a communication station as the destination of data transmission, wherein the RTS transmitting communication station transmits an RTS in which information related to one or more data units for which transmission is tried is described. 79. The wireless communication system according to Claim 78, wherein the information related to data units is the data length of each data unit for which transmission is tried. %f 80. The wireless communication system according to Claim 78, wherein the information related to data units is the sum of the data lengths of one or mo re data units for which transmission is tried. 81. The wireless communication system according to Claim 78, wherein the information related to data units is the time length required for transmitting one or more data units for which transmission is tried. 82. The wireless communication system according to Claim 78, wherein the information related to data units is information on the number of data units for which transmission is tried. 83. The wireless communication system according to Claim 78, wherein, when the RTS receiving communication station determines medium reservation time information after the reception of RTS, the station takes into account the time at which the station itself completes data reception. 84. The wireless communication system according to Claim 78, wherein the RTS transmitting communication station describes in RTS information on the period until the time until which the communication station itself can transmit, and wherein the RTS receiving communication station gives consideration so that said information on the period described \ , in the RTS i s not: exceeded when it determines medium reservation time information after the reception of RTS. 85. The wireless communication system according to Claim 78, wherein the RTS transmitting communication station describes in RTS the time that lapses before the reception of a packet containing CTS information, transmitted as the outcome of the reception of RTS information, as medium reservation time information , and wherein other communication stations which receive RTS set a NAV, and keep it effective and communication stations themselves in transmission prohibited state over the duration of medium reservation time information. 86. The wireless communication system according to Claim 78, wherein the RTS receiving communication station measures the quality of receive signal and determines a data rate based on the result of measurement. wherein the GTS receiving communication station carries /Ait data transmission as the outcome of the reception of GTS information based on the data rate described in the GTS. 89. The wireless communication system according to Claim 78, wherein the GTS transmitting communication station describes in GTS the time that lapses before the reception of a data packet, transmitted as the outcome of the reception of GTS information, as medium reservation time information , and wherein other communication stations which receive GTS set a NAV, and keep it effective and themselves in transmission prohibited state over the duration of medium reservation time information. 90. The wireless communication system according to Claim 89, wherein the GTS transmitting communication station determines medium reservation time information which corresponds to the time period during which the reception of a data unit, transmitted from the RTS transmitting end, is corresponds to the time period during which the reception of ajl the data units is completed. Ir 92. The wireless communication system according to Claim 89, wherein the CTS receiving communication station carries out data transmission as the outcome of the reception of CTS information based on the data rate described in the CTS so that the transmission is completed within the time specified by the medium reservation time information. 93. The wireless communication system according to Claim 78, wherein the RTS transmitting communication station assigns sequence numbers to transmit data units, describes in RTS the first sequence number of data it tries to transmit, and notifies of information related to the data units it tries to transmit. 94. The wireless communication system according to Claim 93, wherein the RTS receiving communication station refers to the first sequence number of data units described in RTS, extracts data units already received from data units for which transmission is tried, excludes them from objects to be received, and then determines medium reservation time information. 95. The wireless communication system according to Claim 93, wherein, if selective acknowledgement is applied, the RTS transmitting communication station describes in RTS reception acknowledgement information containing the first sequence ^umber of data units for which data transmission is tried and ^f-^ bit map information obtained by mapping the reception confirmation information on the subsequent data units into bits corresponding to the relative positions to the first sequence number, and further generates information related to said data units with only data units for which reception confirmation has not been obtained taken as objects to be transmitted, and wherein, if selective acknowledgement is applied, the RTS receiving communication station refers to said bit map information described in the RTS, extracts data units it has already received from data units for which transmission is tried, and then determines medium reservation time information. 96. The wireless communication system according to Claim 93, wherein the RTS receiving communication station stores one or more pieces of data length information of data units to be received, of data for which transmission is tried as the out come of the RTS, and describes in CTS the sequence number of the last data unit stored. 97. The wireless communication system according to Claim 96, wherein the CTS receiving communication station stores the sequence number of said last data unit described in the CTS, and generates information related to data units for which transmission is tried in such form that the data unit indicated hv fhp .spcmenr.e number of said last data unit is not included in objects to be transmitted when an RTS is transmitted next * ime. ir- 98. The wireless communication system according to Claim 78, wherein, if a data unit already received is included in the data units to be transmitted described in the RTS, the RTS receiving communication station describes ACK information in CTS. 99. The wireless communication system according to Claim 78, wherein the CTS receiving communication station excludes the data unit;? already received by the RTS receiving communication station from the objects to be transmitted based on the ACK information added to the CTS, and carries out data transmission based on the data rate described in the CTS. 100. A wireless communication device which makes random access concomitantly using the RTS/CTS method wherein a communication station as the origin of data transmission transmits a request to send packet PTS and starts data transmission in response to the reception of a response packet CTS from a communication station as the destination of data transmission, the wireless communication device comprising: an RTS transmitting means which transmits an RTS when data transmission is requested; a data transmitting means which, when CTS information is received, carries out data transmission as the outcome of the CTS information; and a CTS transmitting means which, when an RTS is received, transmits a CTS as the outcome of the RTS, wherein said RTS transmitting means transmits an RTS in which information related to one or more data units for which transmission is tried is described. 101. The wireless communication device according to Claim 100, wherein the information related to data units is the data length of each data unit for which transmission is tried. 102. The wireless communication device according to Claim 100, wherein the information related to data units is the sum of the data lengths of one ormore data units for which transmission is tried. 103. The wireless communication device according to Claim 100, wherein the information related to data units is the time length required for transmitting one or more data units for which transmission is tried. 104. The wireless communication device according to Claim 100, wherein the information related to data units is information on the number of data units for which transmission is tried. 105. The wireless communication device according to Claim 100, wherein saidCTS transmittingmeans describes inCTSmedium reservation time information which is determined after the reception of RTS with consideration given to the time at which the communication device itself completes data reception. 106. The wireless communication device according to Claim 100, wherein said RTS transmitting means describes in RTS information on the period until the time until which the communication device itself can transmit, and wherein s a id CTS transmittingmeans describes inCTSmedium reservation time information determined with consideration given so that said information on the period described in the received RTS is not exceeded. 107. The wireless communication device according to Claim 100, wherein said RTS transmitting means describes in RTS the time that lapses before the reception of a packet containing CTS information, transmitted as the outcome of the reception of RTS information, as medium reservation time information. 108. The wireless communication device according to Claim 100, further comprising: a communication quality measuring means which measures the quality of receive signal when an RTS is received; and a data rate determining means which determines a data rate based on the measured quality of receive signal. 109. The wireless communication device according to Claim 100, wherein said CTS transmitting means describes in CTS a data rate at which it desires to receive, and transmits the CTS. 110. The wireless communication device according to Claim 109, wherein said data transmitting means carries out data transmission as the outcome of the reception of CTS information based on the data rate described in the CTS. 111. The wireless communication device according to Claim 100, wherein said CTS transmitting means describes in CTS the time that lapses before the reception of a data packet, transmitted as the outcome of the reception of CTS information, as medium reservation time information . 112. The wireless communication device according to Claim 111, wherein said CTS transmitting means determines medium reservation time information which corresponds to the time period during which the reception of a data unit, transmitted from the RTS transmitting end, is completed based on the information reletted to each data unit described in the received RTS. 113. The wireless communication device according to Claim 106, wherein, if an RTS in which it is described that a plurality of data units are transmitted is received, said CTS transmitting means determines medium reservation time information which corresponds to the time period during which the reception of XL1 the data units is completed. 114. The wireless communication device according to Claim 111, wherein said data transmitting means carries out data transmission as the outcome of the reception of CTS information based on the data rate described in the received CTS so that the transmission is completed within the time specified by the medium reservation time information. 115. The wireless communication device according to Claim 100, wherein said RTS transmitting means assigns sequence numbers to transmit data units, describes in RTS the first sequence number of data it tries to transmit, and notifies of information related to the data units it tries to transmit. 116. The wireless communication device according to Claim 115, wherein said CTS transmit ting means describes in CTS medium reservation time information determined after referring to the first sequence number of data units described in RTS, extracting data units already received from data units for which transmission is tried, and excluding them from objects to be received. 117. The wireless communication device according to Claim 115, wherein, if selective acknowledgement is applied, said RTS transmitting means describes in RTS reception acknowledgement information containing the first sequence number of data units for which data transmission is tried and ir bit map information obtained by mapping the reception confirmation information on the subsequent data units into bits corresponding to the relative positions to the first sequence number, and further generates information related to said data units with only data units for which reception confirmation has not been obtained taken as objects to be transmitted, and wherein, if selective acknowledgement is applied, said CTS transmitting means describes in CTS medium reservation time information determined after referring to said bit map information described in the received RTS, and extracting data units it has already received from data units for which transmission is tried. 118. The wireless communication device according to Claim 115, wherein said CTS transmitting means stores one or more pieces of data length information of data units to be received, of data for which transmission is tried as the outcome of the received RTS, and describes in CTS the sequence number of the last data unit stored. 119. The wireless communication device according to Claim 118, wherein said data transmitting means stores the sequence number of said last data unit described in CTS, and generates information related to data units for which transmission is tried in such form that the data unit indicated by the sequence number ofsaid last data unit is not included in objects tobe transmitted when an RTS is transmitted next time. 120. The wireless communication device according to Claim 100, wherein, if a data unit already received is included in the data units to be transmitted described in the RTS, said CTS transmitting means describes ACK information in CTS. 121. The wireless communication device according to Claim 100, wherein said data transmitting means excludes the data units already receivedby the RTS receiving communication station from the objects to be transmitted based on the ACK information added to the CTS, and carries out data transmission based on the data rate described in the CTS. 122. A wireless communication method for making random access concomitantly using the RTS/CTS method wherein a communication station as the origin of data transmission transmits a request to send packet RTS and starts data transmission in response to the reception of a response packet CTS from a communication station as the destination of data transmission, the method comprising: an RTS transmitting step in which, when data transmission is requested, an RTS in which information related to one or more data units for which transmission is tried is described is transmitted; a CTS transmitting step in which, when an RTS is received, a CTS in which medium reservation time information determined based on the information related to each data unit described in the RTS and the data rate is transmitted; and a data transmitting step in which, when CTS information is received, data transmission as the outcome of the reception of the CTS information is carried out so that the transmission is completed within the time specified by the medium reservation time information. 123 . A computer program described in a computer-readable format for carrying out on a computer system the processing for controlling communicating operation in a communication environment in which random access is made concomitantly using the RTS/CTS method wherein a communication station as the origin of data transmission transmits a request to send packet RTS and starts data transmission in response to the reception of a response packet CTS from a communication station as the destination of data transmission, the computer program comprising: an RTS transmitting step in which, when data transmission is requested, an RTS in which information related to one or more data units for which transmission is tried is described is transmitted; a CTS transmitting step in which, when an RTS is received, a CTS in which medium reservation time information determined based on the information related to each data unit described in the RTS and the data rate is described is transmitted; and a data transmitting step in which, when CTS information i.s received, data transmission as the outcome of the reception of CTS information is carried out so that the transmission is completed within the time specified by the medium reservation time information. 124 . A wireless communication system in which a data transmitting communication station acquires transmission right on a medium and then carries out data communication with a data receiving communication station, wherein, after data transmission from the data transmitting communication station is stopped, it is detected whether the subsequent data is present in the data transmitting communication station or not, and, if the subsequent data is present, it is made easier for the data transmitting communication station to acquire transmission right for transmitting the subsequent data. 125. The wireless communication system according to Claim 124, in which medium access control wherein each communication station confirms that; saa d medium is clear only for a predetermined time, waits for an arbitrary backoff time, and then acquires transmission right is carried out by each communication station, wherein, when the data receiving communication station detects the presence of the subsequent data in the data transmitting communication station, the data receiving communication station tries to acquire transmission right on said medium, and transmits a signal onto said medium for °,lirainating other communication stations' transmission right and thereby makes it easier for the data transmitting communication station to acquire transmission right for transmitting the subsequent data. 126. The wireless communication system according to Claim 124, in which medium access control is carried out by each communication station concomitantly using the RTS/CTS method wherein a communication station as the origin of data transmission transmits a request to send packet RTS and starts data transmission in response to the reception of a response packet CTS from a communication station as the destination of data transmission, wherein, when the data receiving communication station detects the presence of the subsequent data in the data transmitting communication station, the data receiving communication station transmits a dummy RTS or an RTS onto said medium for eliminating other communication stations' transmission right, and thereby makes it easier for the data transmitting communication station to transmit an RTS for transmitting the subsequent data. 127. The wireless communication system according to Claim 124, wherein the presence or absence of the subsequent data in the data transmitting communication station is detected based communication station and the data receiving communication station in the past. 128. The wireless communication system according to Claim 124, wherein the presence or absence of the subsequent data in the data transmitting communication station is detectedbased on that an RTS from the data transmitting communication station reaches the data receiving communication station and the data receiving communication station can not return a CTS, or that after the data receiving communication station returns a CTS, transmit data does not reach the data receiving communication station. 129. The wireless communication system according to Claim 124, wherein the presence or absence of the subsequent data in the data transmitting communication station is detectedbased on specific information elements indicating the presence or absence of the subsequent data, contained in the data transmitted from the data transmitting communication station. 130. A wireless communication device which operates in a communication environment in which each communication station acquires transmission right on the medium before carrying out data communication, comprising: a communicating means which transmits and receives data on said medium; a data processing means which processes transmit/receive data; and a medium access controlling means which controls access operation on said medium, wherein, after data transmission from the data transmitting communication station is stopped, said data processing means detects the presence or absence of the subsequent data in the data transmitting communication station, and wherein, if the subsequent data is present, said medium access controlling means makes it easier for the data transmitting communication station to acquire transmission right for transmitting the subsequent data. 131. The wireless communication device according to Claim 130, wherein said medium access controlling means carries out medium access control wherein it confirms that said medium only for a predetermined time, waits for an arbitrary backoff time, and then acquires transmission right, and, if it detects the presence of the subsequent data in the data transmitting communication station, tries to acquire transmission right on said medium, transmits a signal to said medium for eliminating other communication stations' transmission right, and thereby makes it easier for the data transmitting communication station to acquire transmission right for transmitting the subsequent data. 132. The wireless communication device according to Claim 130, wherein said medium access controlling means carries out medium access control concomitantly using the RTS/CTS method wherein a communication station as the origin of data transmission transmits a request to send packet RTS and starts data transmission in response to the reception of a response packet CTS from a communication station as the destination of data transmission, and, if it detects the presence of the subsequent data in the data transmitting communication station, transmits a dummy RTS or an RTS onto said medium for eliminating other communication stations' transmission right, and thereby makes it easier for the data transmitting communication station to acquire transmission right for transmitting the subsequent data. 133. The wireless communication device according to Claim 130, wherein said data processing means detects the presence or absence of the subsequent data in the data transmitting communication station based on the history of communication with the data transmitting communication station in the past. 134. The wireless communication device according to Claim 130, wherein said data processing means detects the presence or absence of the subsequent data in the data transmitting communication station based on that it can not return a CTS in response to an P.TS from the data transmitting communication station, or that it returns a CTS in response to an RTS from the data transmitting communication station thereafter the transmission of transmit data from the data transmitting communication station is stopped. 135. The wireless communication device according to Claim 130, wherein said data processing means detects the presence or absence of the subsequent data in the data transmitting communication station based on specific information elements indicating the presence or absence of the subsequent data, contained in the data transmitted from the data transmitting communication station. 136. A wireless communication method in a communication environment in which each communication station acquires transmission right on the medium before carrying out data communication, comprising: a step in which the presence or absence of transmit data from other communication stations is detected; and environment in which each communication station acquires transmission right on the medium before carrying out data communication, the computer program comprising: a step in which the presence or absence of transmit data from other communication stations is detected; and a medium access control step in which, in response to detection of the presence of transmit data from another communication station, a signal is transmitted onto said medium for eliminating other communication stations' transmission right so as to make it easier for the communication station to acquire transmission right for transmitting data.