Patent Publication Number: US-2004044720-A1

Title: Method and apparatus for dynamically controlling a real-time multimedia data generation rate

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a method and an apparatus for controlling a real-time multimedia data generation rate according to a present state, i.e., condition, of a wireless channel.  
       [0003] 2. Description of the Related Art  
       [0004] Real-time protocol (RTP) and real-time transport control protocol (RTCP) are protocols used for transmitting real-time multimedia data and for monitoring a state of the real-time multimedia data being transmitted, respectively.  
       [0005] More specifically, RTP is an Internet protocol for transmitting data, such as audio or video data, which is generated in real time. RTP itself does not guarantee successful real-time data transmissions. Rather, RTP assists application programs to transmit and receive streaming data. RTP is generally implemented over user datagram protocol (UDP).  
       [0006] RTCP is a protocol that generally works in conjunction with RTP for maintaining quality-of-service (QoS). While RTP is only involved in data transmission, RTCP monitors data transmission and session information transmission. RTP nodes transmit RTCP packets to one another in order to analyze the network state and periodically notify one another of whether a network is congested.  
       [0007] Since RTP and RTCP are based on UDP, they are not able to provide functions such as guaranteed data quality or reliability of transmitted data, sequence reversal, or prevention of data retransmission. RTP and RTCP, however, can provide an information medium with synchronization necessary for real-time applications, and thus they have been adopted by almost every application program that is executed on the Internet using real-time information, such as a video-on-demand (VOD) service, an audio-on-demand (AOD) Internet Broadcasting, or a video conference service.  
       [0008] In a system capable of generating and transmitting multimedia data in real-time, a multimedia application program senses a network state using RTCP and controls a real-time multimedia data generation rate. Then, a receiving party receives the data with a minimal packet delay depending on the state of the network. More specifically, when the network is in a good state, i.e., operating under favorable conditions, the receiving party is supposed to be provided with high-quality services. However, when the network is in a poor state, i.e., operating under poor conditions, the receiving party is more likely to be provided with poor services. In order to make it possible to adaptively provide services to the receiving party depending on a current state of the network, RTCP is required to precisely identify the network state based on characteristics of the network.  
       [0009] Due to various techniques of transmitting data through wireless communications, however, it is no longer possible to effectively reflect a wireless channel state in adaptive data transmission by simply using the above-described method, which has been widely used in conventional wired networks. Even RTCP is not able to precisely determine the characteristics of a wireless network because information on a wired network and information on the wireless network are combined in the network state information processed by the RTCP layer. Therefore, it is necessary to more precisely determine the characteristics of a network and apply them to the RTCP.  
       [0010] In addition, in a wireless communications environment, packet loss and delays may occur depending on a network load and the wireless channel state. Since such packet losses and delays in multimedia services are generally due to both a poor state of a wired channel and a poor state of a wireless channel, it is almost impossible to determine whether a single monitored undesirable case is attributed to either a poor state of a wired network or a poor state of a wireless network.  
       [0011] In a case of a wireless channel, errors are generated when the wireless channel state abruptly changes. More specifically, a channel state of a wireless network changes in accordance with a passage of time rather than remaining constant. Therefore, even though conventional RTCP is considered appropriate for general monitoring of a network state, a new mechanism capable of dynamically controlling a data generation rate depending on a wireless channel state is necessary.  
       [0012] Furthermore, in a case of real-time multimedia services, a competition method or a polling method is preferred as a media access control (MAC) protocol. Before transmitting real-time multimedia service data, a polling cycle is determined based on a permissible data-transmission-delay time and a permissible data-loss rate. However, the polling method, in which the polling cycle is determined using such static variables associated with real-time multimedia services, is not able to effectively respond to a dynamically varying data generation rate, which may lead to an ineffective use or waste of resources.  
       SUMMARY OF THE INVENTION  
       [0013] The present invention provides a method for dynamically controlling a real-time multimedia data generation rate by sensing wireless channel characteristics and reflecting the wireless channel characteristics in the multimedia data generation rate. Accordingly, as compared to a conventional peer-to-peer data generation rate control method using a real-time transport control protocol (RTCP), the method for dynamically controlling a real-time multimedia data generation rate according to an embodiment of the present invention can more quickly adapt to any wireless channel state, thereby leading to a more efficient use of resources.  
       [0014] In particular, the present invention provides two different embodiments of methods of adjusting a data generation rate depending on a wireless channel state, i.e., an open source control method and a closed source control method. The open source control method is a method for unilaterally controlling a multimedia data generation rate in which a multimedia data generation rate varies using wireless channel information. The closed source control method is a method for controlling a multimedia data generation rate in which wireless resources are allotted to the application program that generates multimedia data in real time according to a real-time multimedia data generation rate.  
       [0015] According to an embodiment of the present invention, there is provided an open-source method for controlling a multimedia data generation rate including generating multimedia data in real time according to a current multimedia data generation rate and transmitting the multimedia data, receiving transmission buffer, through which the multimedia data is transmitted, state information and a multimedia data loss rate during the transmission of the multimedia data, calculating a multimedia data generation rate based on the transmission buffer state information and the multimedia data loss rate, and generating multimedia data in real-time according to the calculated multimedia data generation rate and transmitting the generated multimedia data.  
       [0016] Preferably, calculating a multimedia data generation rate includes receiving the transmission buffer state information and the multimedia data loss rate, calculating a multimedia data generation rate based on the transmission buffer state information, by lowering a current multimedia data generation rate when the transmission buffer state information indicates that a large amount of standby multimedia data exists in the transmission buffer or the multimedia data loss rate is high or increasing the current multimedia data generation rate when the transmission buffer state information indicates that a small amount of standby multimedia data exists in the transmission buffer or the multimedia data loss rate is low, and transmitting the calculated multimedia data generation rate to a data generator.  
       [0017] According to another embodiment of the present invention, an open-source apparatus, which controls a multimedia data generation rate, includes a multimedia data generation and transmission unit for generating multimedia data in real-time according to a current multimedia data generation rate and for transmitting the multimedia data, a buffer state and packet loss rate information reception unit for receiving transmission buffer, through which the multimedia data is transmitted, state information and a multimedia data loss rate during the transmission of the multimedia data, and a multimedia data generation rate calculation unit for calculating a multimedia data generation rate corresponding to the transmission buffer state information and the multimedia data loss rate, wherein the multimedia data generation and transmission unit receives the calculated multimedia data generation rate from the multimedia data generation rate calculation unit, generates multimedia data in real time according to the received multimedia data generation rate, and transmits the multimedia data.  
       [0018] Preferably, the multimedia data generation rate calculation unit calculates the multimedia data generation rate, based on the transmission buffer state information, by lowering a current multimedia data generation rate when the transmission buffer state information indicates that a large amount of standby multimedia data exists in the transmission buffer or the multimedia data loss rate is high, or increasing the current multimedia data generation rate when the transmission buffer state information indicates that a small amount of standby multimedia data exists in the transmission buffer or the multimedia data loss rate is low.  
       [0019] According to still another embodiment of the present invention, a closed-source method for controlling a multimedia data generation rate includes receiving a current multimedia data generation rate, receiving a permissible polling cycle and packet length, calculating a multimedia data generation rate corresponding to the permissible polling cycle and packet length, and generating multimedia data in real time according to the calculated multimedia data generation rate and transmitting the multimedia data.  
       [0020] According to yet another embodiment of the present invention, a closed-source apparatus, which controls a multimedia data generation rate, includes a polling cycle and packet length information reception unit for receiving a permissible polling cycle and packet length information corresponding to a current multimedia data generation rate, a multimedia data generation rate calculation unit for calculating a multimedia data generation rate corresponding to the permissible polling cycle and packet length information, a multimedia data generation and transmission unit for generating multimedia data in real time according to the calculated multimedia data generation rate and for transmitting the multimedia data.  
       [0021] Preferably, the polling cycle and packet length information reception unit includes a WAL of a wireless terminal for issuing a request for a permissible polling cycle and packet length for transmission of multimedia data to a WAL of a wireless AP, and a WAL of the wireless AP for responding to the request issued by the WAL of the wireless terminal by calculating a permissible polling cycle and packet length, depending on a current network state, and for transmitting the permissible polling cycle and packet length to the WAL of the wireless terminal.  
       [0022] According to a further embodiment of the present invention, a closed-source method for controlling a multimedia data generation rate includes issuing a request for a permissible polling cycle and packet length information, which is necessary for wireless channel allocation, from a wireless adaptation layer (WAL) of a wireless terminal to a WAL of a wireless access point (AP), and responding to the request issued by the WAL of the wireless terminal by calculating a permissible polling cycle and packet length, depending on a current network state, and transmitting the permissible polling cycle and packet length from the WAL of the wireless AP to the WAL of the wireless terminal.  
       [0023] According to still a further embodiment of the present invention, a method for controlling a multimedia data generation rate through negotiations between a wireless terminal and a wireless AP includes receiving a current multimedia data generation rate, calculating a polling cycle for each session and a packet length for each polling cycle, corresponding to the current multimedia data generation rate, and issuing a request for a permissible polling cycle for each session and a permissible packet length for each permissible polling cycle to a WAL of the wireless AP, and receiving the permissible polling cycle for each session and the permissible packet length for each permissible polling cycle from the WAL of the wireless AP and adjusting the current multimedia data generation rate depending on the permissible polling cycle for each session and the permissible packet length for each permissible polling cycle.  
       [0024] According to still another embodiment of the present invention, a method for controlling a multimedia data generation rate through negotiations between a wireless terminal and a wireless access point (AP) includes receiving a request for a permissible polling cycle and packet length issued by a wireless adaptation layer (WAL) of the wireless terminal, and calculating a predetermined polling cycle for each session and a predetermined packet length for each predetermined polling cycle, which can be accommodated at a given moment in consideration of a current network state and transmitting calculation results to the WAL of the wireless terminal.  
       [0025] According to yet another embodiment of the present invention, there is provided a computer-readable recording medium on which a program enabling any of the above-described methods described above is recorded. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0026] The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail preferred embodiments thereof with reference to the attached drawings in which:  
     [0027]FIG. 1 is a diagram illustrating a structure of a network protocol stack in which a plurality of wireless terminals are connected to and communicate with a single wireless access point (AP);  
     [0028]FIG. 2 is a diagram illustrating an open source method for controlling a multimedia data generation rate according to a preferred embodiment of the present invention;  
     [0029]FIG. 3 is a flowchart for the open source method for controlling a multimedia data generation rate;  
     [0030]FIG. 4 is a block diagram of an open source apparatus for controlling a multimedia data generation rate according to a preferred embodiment of the present invention;  
     [0031]FIG. 5 is a block diagram illustrating a closed source method for controlling a multimedia data generation rate according to a preferred embodiment of the present invention;  
     [0032]FIG. 6 is a flowchart for the closed source method for controlling a multimedia data generation rate;  
     [0033]FIG. 7 is a diagram illustrating operations of and signal transmissions between a wireless adaptation layer (WAL) of a wireless access point (AP) and a WAL of a wireless terminal for negotiations on a polling cycle and the length of a multimedia data packet to be transmitted; and  
     [0034]FIG. 8 is a block diagram of a closed-source type apparatus for controlling a multimedia data generation rate according to a preferred embodiment of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0035] Korean Patent Application No. 2002-52289, filed on Aug. 31, 2002, and entitled: “Method and Apparatus for Dynamically Controlling a Real-time Multimedia Data Generation Rate,” is incorporated by reference herein in its entirety.  
     [0036] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout.  
     [0037]FIG. 1 is a diagram illustrating a structure of a network protocol stack in which a plurality of wireless terminals are connected to and communicate with a single wireless access point (AP).  
     [0038] As shown in FIG. 1, in a wireless communications network including a first and a second wireless terminal  110   a  and  110   b  and a wireless AP  120 , real-time multimedia data from the first wireless terminal  110   a  is transmitted to an external network via a bridging module  121  in the wireless AP  120 . When transmitting real-time multimedia data, the first and second wireless terminals  110   a  and  110   b  monitor the current transmission state of data packets and vary the data generation rate of an application program that generates multimedia data in real time accordingly. This monitoring method has been widely adopted in conventional wired communications systems. This monitoring method, however, may cause serious problems of data packet loss and delays over a network. Therefore, the present invention provides a method for adjusting a data generation rate based on a network state based on an assumption that packet loss and delays may be caused by an overloaded network.  
     [0039] The present invention provides two different embodiments of methods of adjusting a data generation rate, i.e., an open source method for controlling a multimedia data generation rate and a closed source method for controlling a multimedia data generation rate.  
     [0040] In the open source method for controlling a multimedia data generation rate, the real-time multimedia data generation rate is controlled using a transmission buffer state of a wireless medium access control (MAC) module of a wireless terminal and other information, such as a packet loss rate.  
     [0041] In the closed source method for controlling a multimedia data generation rate, the appropriate real-time multimedia data generation rate of an application program, which generates multimedia data in real time in a wireless terminal, is directly applied from an access point (AP) or determined through negotiation with a wireless AP. The closed source method will be described in greater detail with reference to FIGS. 5 and 6.  
     [0042]FIG. 2 is a diagram illustrating an open source method for controlling a multimedia data generation rate according to a preferred embodiment of the present invention.  
     [0043] Conventionally, multimedia data is transmitted using real-time protocol (RTP) and the multimedia data generation rate is controlled by RTCP, which monitors a state of a network between a receiving party, i.e., a wireless AP, and a sending party, i.e., a wireless terminal. However, in the open source method for controlling a multimedia data generation rate of the present invention, information  210  is transmitted to the RTCP layer from the MAC layer of a wireless terminal. The information  210  includes a multimedia data loss rate (packet loss rate) and a state of a transmission buffer used for transmitting multimedia data (transmission buffer standby rate).  
     [0044] If a large amount of standby multimedia data builds up in the transmission buffer or the multimedia data loss rate is high, the RTCP layer lowers the multimedia data generation rate. Alternately, if a small amount of standby multimedia data exists in the transmission buffer and the multimedia data loss rate is low, the RTCP layer increases the multimedia data generation rate. By considering this information, the multimedia data generation rate is controlled in real time.  
     [0045] Thereafter, real-time multimedia data generation rate information  220  is transmitted to a data generator  240  that generates multimedia data  230  in real time. The data generator  240  generates real-time multimedia data  230  and transmits the generated real-time multimedia data  230  via RTP.  
     [0046]FIG. 3 is a flowchart for the open source method for controlling a multimedia data generation rate as shown in FIG. 2. Referring to FIG. 3, in step  310 , a data generator generates multimedia data according to a current multimedia data generation rate and transmits the multimedia data to a wireless terminal or a wireless AP via RTP.  
     [0047] Thereafter, in step  320 , an RTCP layer receives multimedia data loss rate information and the state of a transmission buffer that receives multimedia data transmitted from the MAC layer. As described above, the multimedia data generated in step  310  is transmitted to the wireless terminal via the transmission buffer. When the network is in a poor state, the amount of standby multimedia data waiting to be transmitted increases.  
     [0048] Alternately, when the network is in a good state, multimedia data is transmitted as soon as it is generated, thereby decreasing the amount of standby multimedia data. Thus, the transmission buffer state indicates an amount of such standby multimedia data waiting to be transmitted in the transmission buffer. In addition, when the network is in a poor state, a significant amount of data loss may occur during the transmission of the multimedia data. The RTCP layer receives this multimedia data loss rate information.  
     [0049] In step  330 , the RTCP layer calculates a multimedia data generation rate based on the transmission buffer state and the multimedia data loss rate information and transmits the calculated multimedia data generation rate to the data generator. More specifically, when a large amount of standby multimedia data exists in the transmission buffer or a multimedia data loss rate is high, the RTCP layer lowers the current multimedia data generation rate. Alternately, when a small amount of standby multimedia data exists in the transmission buffer or the multimedia data loss rate is low, the RTCP layer increases the current multimedia data generation rate. By considering this information, the multimedia data generation rate can be controlled in real time.  
     [0050] Subsequently, in step  340 , the data generator generates multimedia data according to the received multimedia data generation rate and transmits the multimedia data to the RTP layer.  
     [0051]FIG. 4 is a block diagram of an open source apparatus for controlling a multimedia data generation rate according to a preferred embodiment of the present invention. Referring to FIG. 4, the open source apparatus includes a multimedia data generation and transmission unit  410 , a buffer state and packet loss rate information reception unit  420 , and a multimedia data generation rate calculation unit  430 .  
     [0052] In operation, the multimedia data generation and transmission unit  410  generates multimedia data in real time according to current multimedia data generation rate information and transmits the multimedia data to a wireless terminal or a wireless AP via RTP.  
     [0053] The buffer state and packet loss rate information reception unit  420  receives state information of a transmission buffer that receives the multimedia data being transmitted and multimedia data loss rate information during the transmission of the multimedia data from a MAC layer via RTCP.  
     [0054] Specifically, when a network is in a poor state, i.e., operating under poor network conditions, the amount of standby multimedia data waiting to be transmitted increases. Alternately, when the network is in a good state, i.e., operating under good network conditions, multimedia data is transmitted as soon as it is generated, thereby decreasing an amount of standby multimedia data. Accordingly, the transmission buffer state indicates the amount of such standby multimedia data waiting to be transmitted in the transmission buffer. In addition, under poor network conditions, a significant amount of data loss may occur during the transmission of the multimedia data. The RTCP layer receives this multimedia data loss rate information.  
     [0055] The multimedia data generation rate calculation unit  430  calculates a multimedia data generation rate corresponding to the transmission buffer state information and the multimedia data loss rate information of the multimedia data being transmitted. Specifically, when a large amount of standby multimedia data exists in the transmission buffer or a multimedia data loss rate is high, the multimedia data generation rate calculation unit  430  lowers the current multimedia data generation rate. Alternately, when a small amount of standby multimedia data exists in the transmission buffer or the multimedia data loss rate is low, the multimedia data generation rate calculation unit  430  increases the current multimedia data generation rate. By considering this information, the multimedia data generation rate can be controlled in real time.  
     [0056] In addition, the multimedia data generation and transmission unit  410  receives the multimedia data generation rate from the multimedia data generation rate calculation unit  430 , and generates and transmits multimedia data in real time.  
     [0057]FIG. 5 is a diagram illustrating a closed source method for controlling a multimedia data generation rate. More specifically, FIG. 5 shows data transmission among a wireless terminal  530 , a wireless AP  510 , and a protocol stack.  
     [0058] As opposed to the open source method for controlling a multimedia data generation rate, the closed source method for controlling a multimedia data generation rate dynamically creates reservations of wireless resources when a multimedia data generation rate varies. A multimedia application program that is able to generate multimedia data in real time determines, with the help of a wireless adaptation layer (WAL)  520  of a wireless terminal, whether a wireless AP  510  can allot resources thereto, according to a polling cycle corresponding to a current multimedia data generation rate and a multimedia data packet length.  
     [0059] Polling is a process that provides a wireless terminal an opportunity to transmit multimedia data to an AP. More specifically, whenever a polling signal is received, the wireless terminal is allowed to transmit multimedia data to the AP. When the multimedia data generation rate varies, the WAL  520  of the wireless terminal negotiates with the wireless AP  510  on the polling cycle and the multimedia data packet length.  
     [0060]FIG. 6 is a flowchart for the closed source method for controlling a multimedia data generation rate as shown in FIG. 5. Referring to FIG. 6, in step  610 , a WAL of a wireless terminal receives a current multimedia data generation rate from the RTCP layer of the wireless terminal.  
     [0061] In step  620 , the WAL of the wireless terminal negotiates with the WAL of the wireless AP on a polling cycle and a multimedia data packet length for allotting a wireless channel. More specifically, the WAL of the wireless terminal calculates the polling cycle and the multimedia data packet length corresponding to the current multimedia data generation rate and issues a request for a permissible polling cycle corresponding to a current channel state and packet length information of multimedia data currently being transmitted to the WAL of the wireless AP. Then the WAL of the wireless AP transmits the permissible polling cycle and the multimedia data packet length information to the WAL of the wireless terminal.  
     [0062] Thereafter, in step  630 , the current multimedia data generation rate is adjusted based on the polling cycle and the multimedia data packet length information transmitted from the WAL of the wireless terminal. Then, the adjusted multimedia data generation rate is transmitted to a data generator.  
     [0063] Subsequently, in step  640 , the data generator generates multimedia data according to the received multimedia data generation rate and transmits the generated multimedia data to the RTP layer.  
     [0064]FIG. 7 is a diagram illustrating processes performed and signals transmitted between the WAL of a wireless terminal and the WAL of a wireless AP during negotiations over a polling cycle and the packet length of multimedia data to be transmitted.  
     [0065] A wireless terminal  530  generates multimedia data based on a predetermined multimedia data generation rate. In  710 , the predetermined multimedia data generation rate is transmitted from the RTCP layer of the wireless terminal to the WAL of the wireless terminal. Then, in  720 , in order to maintain a desired multimedia data generation rate, the WAL calculates a polling cycle for each session and a packet length for each calculated polling cycle. The packet length and the polling cycle are then transmitted to the wireless AP using the predetermined multimedia data generation rate.  
     [0066] Finally, the wireless terminal  530  transmits the multimedia data to the wireless AP  510  on a packet-by-packet basis according to the polling cycle, where each packet length is the same as the packet length calculated by the WAL.  
     [0067] Next, in  730 , the WAL of the wireless terminal  530  issues to the WAL of the wireless AP  510  a request for a predetermined polling cycle for each session and a packet length for each predetermined polling cycle, which can be permitted by the WAL of the wireless AP in consideration of the current network state.  
     [0068] In response to the request issued by the WAL of the wireless terminal  530 , in  740 , the WAL of the wireless AP  510  calculates the permissible polling cycle for each session and the packet length for each permissible polling cycle by referring to the current network state and its own resources. More specifically, if the current network state is poor, the WAL of the wireless AP  510  lengthens the polling cycle and shortens the packet length to reduce the multimedia data transmission rate. Alternately, if the current network state is good, the WAL of the wireless AP  510  shortens the polling cycle and lengthens the packet length to increase the multimedia data generation rate.  
     [0069] Thereafter, in  750 , the calculated polling cycle and packet length are transmitted to the WAL of the wireless terminal  530  and then to the MAC layer, so that, in  760 , they can be reflected in scheduling. In  770 , the wireless terminal  530  calculates a multimedia data generation rate based on the polling cycle and packet length calculated by the wireless AP  510 , and, in  780 , transmits the calculated multimedia data generation rate to the RTCP layer. By considering this information, the wireless terminal  530  can dynamically control a multimedia data generation rate in real-time depending on a wireless channel state, a network state, and a resource allocation of a wireless AP  510 .  
     [0070]FIG. 8 is a block diagram of a closed source apparatus for controlling a multimedia data generation rate according to a preferred embodiment of the present invention. The closed source apparatus includes a polling cycle and packet length information reception unit  810 , a multimedia data generation rate calculation unit  820 , and a multimedia data generation and transmission unit  830 .  
     [0071] The polling cycle and packet length information reception unit  810  receives permissible polling cycle and packet length information corresponding to a current multimedia data generation rate. A WAL of a wireless terminal issues a request for a polling cycle and a packet length appropriate for transmission of multimedia (at a given moment) to a WAL of a wireless AP. In response to the request issued by the WAL of the wireless terminal, the WAL of the wireless AP transmits a permissible polling cycle and packet length to the WAL of the wireless terminal, which are obtained in consideration of the current network state.  
     [0072] The multimedia data generation rate calculation unit  820  calculates a multimedia data generation rate corresponding to the permissible polling cycle and packet length.  
     [0073] The multimedia data generation and transmission unit  830  generates multimedia data according to the calculated multimedia data generation rate and transmits the generated multimedia data.  
     [0074] The embodiments of the present invention set forth herein may be written into programs that can be executed in a common digital computer using a computer-readable recording medium. The types of computer-readable recording medium include a magnetic storage medium, such as ROM, a floppy disk, or a hard disk; an optical recording medium, such as CD-ROM or a DVD; and a carrier wave, such as data transmission through the Internet.  
     [0075] As described above, according to the present invention, a multimedia data generation rate is controlled depending on a current wireless channel state. More specifically, the open source method for controlling a multimedia data generation rate according to the present invention controls a multimedia data generation rate depending on a variable channel state; the closed source method for controlling a multimedia data generation rate controls a multimedia data generation rate using an application program of a wireless terminal that controls the multimedia data generation rate depending on a channel state and generates multimedia data in real-time based on results of controlling the multimedia data generation rate. Therefore, the present invention is able to provide real-time multimedia services more quickly and more responsively to the variable wireless channel state, and is able to more efficiently exploit resources, as compared to conventional peer-to-peer-type multimedia data generation rate control methods using RTCP.  
     [0076] Preferred embodiments of the present invention have been disclosed herein and, although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.