JP2004289862A - Packet receiving apparatus and packet receiving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a packet receiving apparatus and packet receiving method in which reproduction of the next medium can be started even when a BYE packet can not be received because of a transmission error, and the reproduction can be waited without ending a session when the medium is temporarily interrupted because of a burst error. <P>SOLUTION: An end time judging part 111 takes into account packet loss information from a packet loss monitoring part 110 and the RTP packet receiving situation from an RTP receiving part 106 even when the RTP receiving part 106 does not receive the BYE packet, and when the state of incurring no packet loss and receiving no RTP packet continues for a fixed time, it is judged that medium transmission from a server is ended. The stop of the medium is then instructed to a control command transmitting/receiving part 109. When the RTP receiving part 106 does not receive data but the packet loss occurs in a low-order layer, it is not judged that the medium ends. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a packet receiving device and a packet receiving method.

  Conventionally, there is a technique called SMIL (Synchronized Multimedia Integration Language). This technology has been standardized by the World Wide Web Consortium (W3C) as a method of integrating contents including text, still images, moving images, and audio and describing spatial and temporal arrangement. The SMIL description language is similar to the Hypertext Markup Language (HTML), which is very popular throughout the Internet, but has the advantage of having time information in the content as compared to it.

  Here, a method for a client to reproduce content on a server described by SMIL via a network will be described with reference to the drawings.

  FIG. 5 is a diagram for explaining content distribution using SMIL.

  In this figure, when a user accesses the server 203 from the client 201 via the network 200 and acquires a SMIL file in which content is described, the client 201 interprets the SMIL file. Then, while obtaining media such as text, still images, moving images, and audio described in the file from the servers 202 and 204, the respective media are read at appropriate times based on the time information described in the file. Reproduce. In FIG. 5, the media files such as the SMIL file and the moving image data are stored in the individual servers 202, 203, and 204, respectively, but may be stored in one server.

  Next, a transmission method of the SMIL file and each medium will be described.

  When transmitting media files such as SMIL files, still image data, and text files from a server to a client, TCP (Transmission Control Protocol), which is a reliable protocol similar to HTML widely used on the Internet, is generally used. Used for On the other hand, data that is temporally continuous such as audio data and moving image data is often transmitted using protocols such as RTP (Real-time Transport Protocol) and UDP (User Datagram Protocol) that prioritize real-time properties.

  As a lower protocol for transmitting TCP or RTP / UDP, an IP (Internet Protocol) protocol is generally used.

  The above TCP, RTP, UDP, and IP protocols are all standardized by the Internet Engineering Task Force (IETF), and are widely used mainly on the Internet.

  Next, a content description method of the SMIL file will be briefly described.

  FIG. 6 is a diagram illustrating an example of a sentence described in SMIL.

  In this figure, the numbers 1, 2, ... at the left end are line numbers for explanation, and the right end is an explanation. These are not described in the actual SMIL file.

  The text surrounded by the numerals 1 and 15 indicates that the text is a SMIL document. The contents of the SMIL document include a header portion surrounded by numerals 2 to 8, and a text surrounded by numerals 9 to 14. In the header part, layout information and the like irrelevant to the time information are described. In the text, actual media information and time information related to reproduction are described. Numeral 11 is a control statement for displaying a moving image, and numeral 12 is a control statement for displaying a still image. These are enclosed by <par> like numerals 10 and 13, so that they are reproduced simultaneously. ing. The location of the media is described by "src". Further, the specification regarding the playback time of the media is described using “begin”, “end”, “dur”, and the like. In this case, "begin" designates the media start time, "end" designates the media end time, and "dur" designates the media playback time.

  The description of the numeral 11 indicates that the moving image data designated by "src" is displayed in the area "a" for 3 to 20 seconds. The description of the numeral 12 indicates that the still image data specified by “src” is displayed in the area “b” for 10 seconds.

  In addition to specifying the reproduction start / end by the absolute time as described in the numerals 11 and 12, it is also possible to specify the reproduction in a sequence as shown in Examples 1 and 2 below.

Example 1
<seq>
<video id = "video1" src = "rtsp: //example.com/video1.m4v"/>
<video id = "video2" src = "rtsp: //example.com/video2.m4v"… />
</ seq>
Example 2
<par>
<video id = "video1" src = "rtsp: //example.com/video1.m4v"/>
<video id = "video2" src = "rtsp: //example.com/video2.m4v" begin = "video1.end"… />
</ par>
Examples 1 and 2 are descriptions in which video 2 is reproduced after video 1 has been reproduced. It should be noted that both the examples 1 and 2 are for moving images, but the same applies to moving images and still images.

  Next, an actual operation between the client and the server in the above example will be described.

  FIG. 7 is a sequence diagram in the case of continuously playing back media. In this figure, solid lines represent RTSP (Real Time Streaming Protocol) command and response signals, which are protocols used for controlling real-time data. RTSP is communicated over TCP, a reliable protocol. On the other hand, the actual media data is unreliable as shown by the dotted line, but uses the RTP protocol suitable for real-time communication. A command indicating the end of data is also transmitted using RTP.

  Now, the client interprets the description for reproducing video1 in the SMIL document, and requests the server for reproduction (step 1). The server starts reproduction preparation upon receiving a reproduction request from the client, and returns OK when the preparation is completed (step 2). After returning OK, transmission of video1 data is started (step 3). When the transmission of all the data of video1 is completed, a control signal called RTCP BYE defined by the RTP protocol is transmitted to the client to notify that all the data of video1 have been transmitted (step 4).

  Upon receiving the RTCP (RTP control protocol) BYE, the client transmits a command called RTSP TEARDOWN to end the session (step 5). Upon receiving the TEARDOWN command, the server ends the session and notifies the client of the end (step 6). Since the playback of the video 1 has been completed, the client proceeds to the playback operation of the video 2. From step 7 to step 12, video2 is transmitted according to the same sequence as video1.

  However, this conventional packet receiving method has the following problems.

  In other words, when transmitting real-time data such as audio data or moving image data using a line such as a radio line or the like in which a bit error is likely to occur using RTP, a bit error occurs in an RTCP BYE packet indicating the end of media data. When it occurs, it is discarded by the lower layer of the client as shown in the sequence diagram of FIG. In this case, since the end of the data cannot be recognized by the client, the reproduction of the next medium cannot be started even if all the data transmissions are completed. In addition, when the medium is temporarily suspended due to a burst error, the session may be terminated.

  The present invention has been made in view of the above points, and even when a BYE packet, which is a media end notification packet, cannot be received due to a transmission error, reproduction of the next media can be started and a burst error can be generated. It is an object of the present invention to provide a packet receiving apparatus and a packet receiving method capable of waiting without terminating a session when media is temporarily suspended.

  The packet receiving device of the present invention includes a packet receiving unit that receives a packet transmitted from a server, an error packet detecting unit that detects a transmission error of the packet received by the packet receiving unit, and an error packet detecting unit. Packet discarding means for discarding the error packet detected by the packet receiving means, media receiving means for receiving media data which is audio data or moving image data from a packet received without transmission errors by the packet receiving means, and After the start of the reception of the media data, if the state in which the reception of the media data cannot be continued for a predetermined period of time, and if no error of the packet is detected by the error packet detecting means during that time, the transmission of the media data is completed. And a data end determining means for determining

  According to this configuration, even if a packet for notifying the end of the media data is lost due to a transmission error or the like, if the unreceivable state of the media data continues for a predetermined time and no packet error is detected during that time, Since it is determined that the transmission of the media data has been completed, the reception of the next media data can be promptly resumed.

  Further, in the packet receiving apparatus according to the present invention, in the packet receiving apparatus, even when the media data reception disabled state continues for a predetermined period of time, the error detection of the packet is performed by the error packet detecting unit. Is detected, it is determined that the transmission of the media data from the server has not been completed.

  According to this configuration, when there is a packet loss due to a transmission error or the like, the reception wait state of the media data is maintained. Therefore, when the reception of the media data is temporarily interrupted due to a burst error or the like, an error occurs. Thus, it is possible to reduce a situation in which the session is interrupted.

  The packet receiving apparatus of the present invention is the packet receiving apparatus, wherein the packet receiving means includes an IP packet receiving means for receiving an IP packet, and a UDP packet receiving means for receiving a UDP packet. The means receives a media end signal in an RTP packet obtained from the UDP packet receiving means.

  According to this configuration, by detecting a packet error in the IP layer and the UDP layer positioned lower than the media receiving unit that receives the RTP packet, the BYE packet of the media end signal for notifying the end of the media data is detected. Even if a loss occurs, it is possible to determine the end of media data transmission from the server.

  The content reception / playback apparatus of the present invention is characterized in that the packet reception apparatus and the data reception determination means of the packet reception apparatus terminate real-time data in a state where the media reception signal is not received by the media reception means of the packet reception apparatus. And a control command transmitting means for transmitting a session end command to the server when the server is notified.

  According to this configuration, even if a packet for transmitting the media end signal is lost due to a transmission error or the like, it is determined that the transmission of the media data has been completed and the session end command is transmitted to the server. Of the media data can be resumed.

  Further, the content receiving / playing device of the present invention employs a configuration in which the content receiving / playing device includes a playback / display unit that plays and displays the media data received by the media receiving unit in accordance with the content description language.

  According to this configuration, the media data of the content can be reproduced and displayed according to the content description language such as SMIL or HTML.

  The communication terminal of the present invention employs a configuration including the above device.

  According to this configuration, the media data of the content can be reproduced and displayed in the SMIL or HTML description language. Furthermore, even if a packet for transmitting the media end signal is lost due to a transmission error or the like, it is determined that the transmission of the media data has been completed, and a session end command is transmitted to the server. Can be.

  The packet receiving method according to the present invention is configured such that, after starting reception of media data that is audio data or moving image data sent from a server, when the unreceivable state of the media data continues for a predetermined time, and during that time, the media data is transmitted. If the packet loss cannot be detected in the UDP layer or the IP layer located lower than the receiving RTP receiving means, it is determined that all the media data transmission from the server has been completed, and the session is terminated. If the data reproduction process is executed and the packet loss can be detected in the UDP layer and the IP layer during the predetermined period of time in which the media data cannot be received, the transmission of the media data from the server is not completed. judge.

  According to this method, by detecting a packet error in the IP layer and the UDP layer located lower than the media receiving unit that receives the RTP packet, the BYE packet of the media end signal for notifying the end of the media data is detected. Even if a loss occurs, it is possible to determine the end of media data transmission from the server.

  If there is a packet loss due to a transmission error or the like, the reception wait state of the media data is maintained. Therefore, when the reception of the media data is temporarily interrupted due to a burst error or the like, the session is erroneously interrupted. It is possible to reduce the situation that occurs.

  A recording medium according to the present invention is a computer-readable recording medium storing a content reception / reproduction program, wherein the content reception / reproduction program includes a packet reception procedure for receiving a packet transmitted from a server; An error packet detection procedure for detecting a transmission error of the packet received in the procedure, a packet discard procedure for discarding the error packet detected in the error packet detection procedure, A media receiving procedure for receiving media data that is audio data or moving picture data from the received packet, and the media receiving procedure starts receiving the media data after the media data receiving disabled state continues for a predetermined time, and In the error packet detection procedure, If not issued, it is determined that the transmission of the media data has been completed, and even if the unreceivable state of the media data has continued for a predetermined period of time, if a packet error is detected in the packet detection procedure during that time, the A data end determination procedure for determining that the transmission of media data from the server has not ended.

  By applying this recording medium to a packet receiving device having a configuration in which a computer is installed and which is controlled by software, even if a packet for notifying the end of the media data due to a transmission error or the like is lost, the media data cannot be received. If the packet continues for a predetermined period of time and if no packet error is detected during that time, it is determined that the transmission of the media data has been completed, so that the reception of the next media data can be resumed promptly.

  If there is a packet loss due to a transmission error or the like, the reception wait state of the media data is maintained. Therefore, when the reception of the media data is temporarily interrupted due to a burst error or the like, the session is erroneously interrupted. Can be reduced.

  As described above, according to the present invention, it is possible to appropriately determine the end time even when a content whose playback time is not specified is reproduced and a BYE packet is not correctly received. Can be. Furthermore, even if playback is interrupted due to packet loss, the packet loss is monitored and used to determine the end time. A situation in which reproduction cannot be performed can be avoided.

  The gist of the present invention is that the loss of a BYE packet indicating the end of media data due to a transmission loss or the like is monitored by monitoring a packet loss in an IP layer or a UDP layer located lower than the RTP receiving means that is an RTP packet receiving means. Even if it occurs, the end of the media data is determined, and the end of the media is prevented from being erroneously determined.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a content reception / playback apparatus according to an embodiment of the present invention.

  In the figure, the content receiving and reproducing apparatus according to the present embodiment includes an antenna 101, a transmitting / receiving unit 102, an IP packet transmitting / receiving unit 103, a TCP transmitting / receiving unit 104, a UDP receiving unit 105, an RTP receiving unit 106, It comprises a control unit 107, a packet loss monitoring unit 110, and an end time determination unit 111. The content control unit 107 includes a reproduction display unit 108 and a control command transmission / reception unit 109.

  The transmission / reception unit 102 performs wireless processing (processing such as down-conversion and A / D conversion) and demodulation processing on the IP packet received via the antenna 101, and inputs the demodulated packet signal to the IP packet transmission / reception unit 103. Further, it performs modulation processing and wireless processing on the packet signal input from IP packet transmitting / receiving section 103, and emits the IP packet after the wireless processing from antenna 101 to the air. The IP packet transmitting / receiving unit 103 transmits / receives the IP packet, checks an error of the received IP packet, and inputs an IP header of the IP packet to the packet loss monitoring unit 110 if there is an error, and then discards the packet itself. I do. On the other hand, if there is no error in the received IP packet, the IP header of the IP packet is deleted, and then input to the TCP transmission / reception unit 104 in the case of the TCP segment and to the UDP reception unit 105 in the case of the UDP segment.

  The TCP transmission / reception unit 104 inputs the TCP segment input from the IP packet transmission / reception unit 103 to the control command transmission / reception unit 109 of the content control unit 107. Further, the control command input from control command transmitting / receiving section 109 of content control section 107 is input to IP packet transmitting / receiving section 103 as a TCP segment. The UDP receiving unit 105 checks an error included in the UDP segment input from the IP packet transmitting / receiving unit 103, and if there is an error, inputs the header of the UDP segment to the packet loss monitoring unit 110, and then outputs the segment itself. Discard. On the other hand, if there is no error, the UDP segment is converted to an RTP packet and input to the RTP receiving unit 106. The RTP receiving unit 106 inputs the input RTP packet to the reproduction display unit 108 of the content control unit 107, and reports the reception status of the RTP packet to the end time determination unit 111.

  In the content control unit 107, the control command transmitting / receiving unit 109 receives a control command from a server (not shown) using a TCP / IP packet. Further, a control command is transmitted to a server (not shown) using a TCP / IP packet. Further, it instructs the playback display unit 108 to start or stop playback of the media according to the description of the content. The reproduction display unit 108 reproduces and displays the media data included in the RTP packet input from the RTP reception unit 106 according to an instruction from the control command transmission / reception unit 109.

  When the RTP receiving unit 106 receives a BYE packet indicating the end of the medium, the end time determining unit 111 determines that the medium has ended and inputs the BYE packet to the control command transmitting / receiving unit 109.

  Further, even when the BYE packet is not received by the RTP receiving unit 106, the end time determining unit 111 considers the packet loss information from the packet loss monitoring unit 110 and the RTP packet reception status information from the RTP receiving unit 106. If no packet loss has occurred and no RTP packet has been received for a certain period of time, it is determined that the transmission of media data from the server has been completed, and the control command transmitting / receiving unit 109 is instructed to stop the media. In this case, even if the RTP receiving unit 106 has not received an RTP packet, it is not determined that the transmission of the media data has been completed if a lower layer packet loss has occurred from the packet loss information.

  That is, if a packet loss has occurred in the IP layer or the UDP layer, it is not determined that the transmission of the media data has ended even if the RTP packet has not been received for a certain period of time. Note that, even if the RTP receiving unit 106 does not receive the RTP packet, the case where the packet loss of the lower layer has occurred is the case where the reproduction is interrupted on the reproduction display unit 108.

  Here, the operation when the BYE packet is discarded due to an error and the end time of the media is not notified to the client will be described.

  FIG. 2 is a sequence diagram showing an operation when a transmission error occurs in a BYE packet during continuous reproduction of media. In this figure, steps 1 to 3 are the same as the sequence diagram of FIG.

  In FIG. 2, when an error occurs in a BYE packet due to a transmission error, the BYE packet is discarded on the client side (step 4). At this point, since the transmission of the media data has already been completed from the server, the media data is not transmitted, but the client does not know whether the transmission of the media data has been completed. For this reason, the client side maintains the state in which the media data can be received for a certain period of time, and if the media data cannot be received during that time, determines that the transmission of the media data has ended and requests the server to disconnect the session (step 5).

  Next, an operation when a burst error, which is known to occur frequently on a wireless line, occurs. Note that a burst error is an error pattern in which transmission errors occur intensively for a certain period of time.

  FIG. 3 is a sequence diagram showing an operation when a burst error occurs in a media packet in continuous reproduction of media. In this sequence diagram, as in FIG. 2, in step 3, media data is transmitted from the server to the client in a plurality of packets.

  In FIG. 3, if a burst error occurs during transmission of media data from the server to the client, an error occurs in consecutive packets. Therefore, a process of detecting the error in the IP layer and the UDP layer and discarding all the errors is performed. As a result, the RTP receiving unit 106 cannot receive any media data while a burst error occurs. Since the packet loss information is output from the IP layer and the UDP layer, the end time determination unit 111 does not determine that the reception of the media data has ended. Therefore, the client maintains the state in which the media data can be received, and then resumes receiving the media data when the burst error ends.

  As described above, according to the content reception / playback apparatus of the present embodiment, when a content whose playback time is not specified is played back, even if a BYE packet for notifying the end of media data is lost due to a transmission error or the like, a loss occurs. If the unreceivable state of the media data continues for a predetermined time and if no packet error is detected during that time, it is determined that the transmission of the media data has been completed, so that the reception of the next media data is immediately resumed. It becomes possible.

  When a packet error due to a transmission error or the like is detected, the media data reception wait state is maintained. Therefore, when the reception of the media data is temporarily interrupted due to a burst error or the like, the session is erroneously interrupted. This makes it possible to avoid a situation in which the reproduction is stopped and the subsequent data cannot be reproduced.

  In the above-described embodiment, the content receiving / reproducing apparatus that receives and reproduces content has been described. However, a packet receiving apparatus that removes the content control unit 107 and performs only reception of content may be used. FIG. 4 shows the configuration of the packet receiving apparatus.

  Further, in the above-described embodiment, a case has been described in which the content is received and played back with a hardware configuration. However, the present invention is not limited to this, and the content reception / playback can be performed as software. For example, a program for performing content reception and reproduction may be stored in a computer-readable recording medium, and the program may be recorded in a RAM (Random Access Memory) of the computer, and the computer may be operated according to the program.

  The packet receiving program detects, for example, a packet receiving procedure for receiving a packet transmitted from a server, an error packet detecting procedure for detecting a transmission error of a packet received in the packet receiving procedure, and an error packet detecting procedure. A packet discarding procedure for discarding the erroneous packet received, a media receiving procedure for receiving media data that is audio data or video data from a packet received without a transmission error in the packet receiving procedure, and a media receiving procedure for receiving media data. After the start, if the unreceivable state of the media data continues for a predetermined time, and if no error of the packet is detected in the error packet detection procedure during that time, it is determined that the transmission of the media data is completed, and the transmission of the media data is determined. Even if the unreceivable state continues for a predetermined time, an error packet If DOO detection procedure error packet in is detected, it is to anda data end determining step determines that the transmission of the media data is not completed from the server.

  Even in the case of controlling by software, the same operation and effect as in the above embodiment are exhibited. That is, even if a loss of a packet notifying the end of the media data occurs due to a transmission error or the like, if the unreceivable state of the media data continues for a predetermined time, and if no packet error is detected during that time, the media data is lost. Since it is determined that the transmission has been completed, the reception of the next media data can be promptly resumed. If there is a packet loss due to a transmission error or the like, the reception wait state of the media data is maintained. Therefore, if the reception of the media data is temporarily interrupted due to a burst error or the like, the session is erroneously interrupted. Can be reduced.

  A recording medium for recording a program for performing content reception and reproduction may be a magnetic storage unit, an optical storage unit, or a magneto-optical storage unit, in addition to the semiconductor storage unit such as the RAM.

  Further, in the above embodiment, SMIL is used as the content description language, but HTML may be used as another description language. Alternatively, the media may be simply reproduced repeatedly without describing the content.

  Further, in the above-described embodiment, a case has been described where a plurality of media included in the content are continuously played back. However, the content may be such that one media is live-broadcasted. In the case of live broadcasting, the end time is often not specified, and therefore, by using the present invention, it is possible to correctly end reproduction even for live broadcasting content.

  INDUSTRIAL APPLICABILITY The present invention is suitable for use in a packet receiving apparatus and a packet receiving method of a system for transmitting real-time data such as audio data or moving image data using a line where a bit error easily occurs, such as a wireless line, using RTP. is there.

FIG. 1 is a block diagram showing a configuration of a content reception / playback apparatus according to an embodiment of the present invention. Sequence diagram for explaining the operation of the content reception / playback apparatus according to the embodiment of the present invention during continuous media playback. Sequence diagram for explaining the operation of the content reception / playback apparatus according to the embodiment of the present invention during continuous media playback. FIG. 1 is a block diagram showing a configuration of a packet receiving device according to an embodiment of the present invention. Diagram for explaining content distribution using SMIL Diagram for explaining contents described in SMIL Sequence diagram for continuous playback of media Sequence diagram for explaining a problem at the time of conventional continuous reproduction of media

Explanation of reference numerals

Reference Signs List 101 antenna 102 transmission / reception unit 103 IP packet transmission / reception unit 104 TCP transmission / reception unit 105 UDP reception unit 106 RTP reception unit 107 content control unit 108 playback display unit 109 control command transmission / reception unit 110 packet loss monitoring unit 111 end time determination unit

Claims (8)

A packet receiving means for receiving a packet transmitted from the server;
Error packet detecting means for detecting a transmission error of a packet received by the packet receiving means,
Packet discarding means for discarding the error packet detected by the error packet detecting means,
Media receiving means for receiving media data that is audio data or moving image data from a packet received without transmission errors in the packet receiving means,
After the media receiving means starts receiving the media data, if the unreceivable state of the media data continues for a predetermined time, and if no error of the packet is detected by the error packet detecting means during that time, the media data A packet receiving apparatus comprising: a data end determining unit that determines that transmission has ended.   The data end determination unit terminates the transmission of the media data from the server even if the unreceivable state of the media data continues for a predetermined time if a packet error is detected by the error packet detection unit during that time. The packet receiving device according to claim 1, wherein it is determined that the packet has not been received.   The packet receiving means includes an IP packet receiving means for receiving an IP packet, and a UDP packet receiving means for receiving a UDP packet, and the media receiving means uses a RTP packet obtained from the UDP packet receiving means to transmit a media. 3. The packet receiving apparatus according to claim 1, wherein the packet receiving apparatus receives an end signal. A packet receiving apparatus according to any one of claims 1 to 3,
In a state where the media end signal is not received by the media receiving unit of the packet receiving device, when the end of the real-time data is notified from the data end determining unit of the packet receiving device, a session end command is sent to the server. And a control command transmitting means for transmitting.   5. The content receiving / reproducing apparatus according to claim 4, further comprising a reproducing / displaying means for reproducing and displaying the media data received by said media receiving means in accordance with a content description language.   A communication terminal comprising the device according to claim 1.   When reception of the media data, which is audio data or moving image data sent from the server, is started for a predetermined period of time after the start of reception of the media data, which is lower than the RTP receiving means for receiving the media data during that time. If the packet loss cannot be detected in the UDP layer and the IP layer located in the server, it is determined that all the transmission of the media data from the server has been completed, the session is terminated, and the next media data reproducing process is executed. A packet, characterized in that it is determined that transmission of media data from the server has not been completed if a packet loss can be detected in the UDP layer and the IP layer during a predetermined period of time in which the media data cannot be received. Receiving method.   A computer-readable recording medium storing a content reception / playback program, wherein the content reception / playback program includes a packet reception procedure for receiving a packet transmitted from a server, and a packet received in the packet reception procedure. An error packet detection procedure for detecting a transmission error of the packet, a packet discard procedure for discarding the error packet detected in the error packet detection procedure, and voice data and / or video from the packet received without transmission error in the packet reception procedure. A media receiving procedure for receiving media data that is data; and a step in which the media receiving procedure starts receiving the media data, and when the unreceivable state of the media data continues for a predetermined time, and in the meantime, the error packet detecting procedure is performed. If no packet error is detected It is determined that the transmission of the media data has ended, and even if the unreceivable state of the media data continues for a predetermined time, if an error of the packet is detected in the packet detection procedure during that time, the media data from the server is A data end determination procedure for determining that transmission has not been completed.

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