JP2004289621A - Data transmission server - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data transmission server capable of suppressing deterioration in the quality of data, even when a packet loss is generated with an increase in transmission rate. <P>SOLUTION: This server is equipped with a data transmitting means for transmitting data to a terminal through a network, a redundant code transmitting means for transmitting a redundant code for suppressing the generation of a transmission error of the data, a receiving means for receiving feedback information from the terminal, a determination means for determining whether the transmission rate increases on the basis of the feedback information, and a rate increasing means for increasing the transmission rate by an increase in the redundant code when the determination means determines that the transmission rate increases. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a data transmission system, and more particularly to a server that transmits encoded media data over a best-effort Internet network or wireless transmission path.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, moving image data has been transmitted by streaming or video telephone in a best-effort transmission path environment such as the Internet network. For the transmission of the moving image data, a protocol called UDP (User Datagram Protocol) which emphasizes real-time property is often used.
[0003]
However, UDP does not include a mechanism for changing a transmission rate using feedback information from a client side, unlike TCP (Transport Control Protocol) used in HTTP or the like. For this reason, when the UDP traffic increases, the phenomenon of occupying the band of the transmission line has often occurred.
[0004]
On the other hand, there is RTP (Real-time Transport Protocol) as a protocol that places importance on real-time properties like UDP. This RTP includes a mechanism for feeding back transmission quality called RTCP (RTP Control Protocol) from the client side at regular intervals. Therefore, the number of systems that control the transmission rate using the RTCP is increasing at present.
[0005]
As such a technique, a data communication device is provided in which a server that packetizes data and transmits the data to a network determines a transmission rate based on a reception state transmitted from a client and transmits the data (see Patent Document 1). .).
[0006]
However, in a system that controls a transmission rate using feedback information such as RTCP, there is a possibility that the quality of a moving image being transmitted may be significantly reduced. In other words, when the server increases the transmission rate in a state where other traffic such as TCP and RTP are mixed on the transmission path, packet loss occurs due to congestion. Therefore, the quality of the moving image being transmitted is significantly reduced.
[0007]
[Patent Document 1]
JP 2001-144802 A (abstract).
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of such problems of the related art. That is, an object of the present invention is to provide a data transmission server that can suppress deterioration of data quality even when a packet loss occurs due to an increase in transmission rate.
[0009]
[Means for Solving the Problems]
The present invention employs the following means in order to solve the above problems.
[0010]
A server according to the present invention includes a data transmitting unit that transmits data to a terminal via a network, a redundant code transmitting unit that transmits a redundant code that suppresses a transmission error of the data, and a reception that receives feedback information from the terminal. Means, determining means for determining an increase or decrease in transmission rate based on the feedback information, and rate increasing means for increasing the transmission rate by increasing the redundant code when the determining means determines to increase the transmission rate. It is characterized by the following.
[0011]
When the transmission rate is increased, for example, congestion may occur. With such a configuration, a change in the transmission path can be detected by configuring the increase in the transmission rate with a redundant code. Therefore, even if data loss occurs when the transmission rate is increased, transmission errors in data to be transmitted can be suppressed.
[0012]
Further, the server of the present invention further comprises: comparing means for comparing the status of the transmission line before and after transmitting the redundant code, and the redundant code increased when the comparing unit determines that there is no change in the status of the transmission line. In place of the above, the data transmitting unit may further include a data increasing unit that increases data transmitted from the data transmitting unit. Further, the server of the present invention may further include a stop unit for stopping transmission of the redundant code when the comparison unit determines that the condition of the transmission path has deteriorated.
[0013]
With such a configuration, when it is determined that there is no change in the state of the transmission path before and after transmitting the redundant code, the rate increase can be replaced with data and transmitted. On the other hand, if it is determined that the state of the transmission path has deteriorated before and after the transmission of the redundant code, the state can be returned to the previous state, that is, the state excluding the redundant code corresponding to the rate increase.
[0014]
Further, the server of the present invention may compare the status of the transmission path before and after transmitting the redundant code based on the feedback information. And, the feedback information may include a packet loss rate, information about intervals at which packets arrive, or a round trip time.
[0015]
Further, the redundant code may be an inter-packet error correction method including parity information between packets, or the redundant code may be generated in order based on data priority.
[0016]
With such a configuration, even if a packet loss occurs in the transmission path, it is possible to recover the lost packet using the redundancy code.
[0017]
Further, for example, it is assumed that a redundant code of an intra frame (I frame) in MPEG data is preferentially generated. When priority is given to the intra frame, even if a packet loss occurs when the transmission rate is increased, it is possible to minimize image quality deterioration.
[0018]
Further, the present invention may be such that the above-mentioned program is stored in a readable storage medium.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0020]
FIG. 1 is a diagram illustrating the principle of the present invention, and FIG. 2 is a block diagram illustrating a transmission system according to the present embodiment. FIG. 3 is a configuration diagram of an FEC packet, FIG. 4 is a configuration diagram of an RTP header, and FIG. 5 is a configuration diagram of an FEC header. FIG. 6 is a diagram illustrating a method of generating FEC parity information. 7 to 9 are diagrams showing the processing flow of the rate control unit.
<Principle of transmission system>
With reference to FIG. 1, the principle of the transmission system of the present invention and the function of each component will be described together with the flow of media data.
[0021]
This transmission system includes a server 10 and a client 30 connected via a network 20. Here, the network 20 includes, for example, a LAN operated in an organization or the Internet to which an unspecified number of networks are connected, and the form thereof is not specified.
[0022]
First, processing on the server 10 side after media data is input will be described.
[0023]
The server 10 includes an encoding unit 11, a packetizer 12, a data transmission unit 13, a rate control unit 14, a feedback reception unit 15, a switch 16, a redundant code generation unit 17, and a redundant code transmission unit 18.
[0024]
The encoding unit 11 encodes the input media data. Then, the packetizer 12 packetizes the encoded data and adds a header. The data transmission unit 13 transmits the media data as a packet to the client 30 via the network 20.
[0025]
The feedback receiving unit 15 receives the feedback information from the client 30 as a packet. This feedback information includes the packet loss rate, the jitter, the reception time of the parity information, and the like. The feedback information is used to detect congestion on the transmission path.
[0026]
Then, the rate control unit 14 determines a transmission rate based on the received feedback information. After that, the rate control unit 14 controls the encoding unit 11, the switch 16, and the redundant code generation unit 17 so that the transmission rate becomes the determined transmission rate. Here, when determining that the transmission rate is to be increased, the rate control unit 14 instructs the switch 16 to increase the transmission rate.
[0027]
The switch 16 duplicates the encoded data packet generated by the packetizer 12. Then, the switch 16 sends the duplicate encoded data packet to the redundant code generation unit 17. This encoded data packet is stored in a buffer (not shown) in the redundant code generator 17.
[0028]
Then, when a fixed amount of encoded data packets in the buffer is accumulated, the redundant code generation unit 17 generates parity information as a redundant code. The redundant code transmitting unit 18 adds a header to the parity information to generate a packet. Then, the redundant code transmission unit 18 transmits the redundant code including the parity information to the client 30 via the network 20.
[0029]
Next, processing on the client 30 side will be described.
[0030]
The client 30 includes a data receiving unit 31, a data restoring unit 32, a decoding unit 33, a display unit 34, a feedback information generating unit 35, a feedback information transmitting unit 36, and a redundant code receiving unit 37.
[0031]
The data receiving unit 31 receives the media data as a packet via the network 20. Then, the data receiving unit 31 sends the received media data to the data restoring unit 32. Further, the data receiving unit 31 measures a packet loss and a packet receiving interval (hereinafter, referred to as jitter), and sends the measured information to the feedback information generating unit 35.
[0032]
The data restoration unit 32 restores media data. That is, when there is a packet loss, the data restoration unit 32 restores the lost packet from the parity information received by the redundant code reception unit 37. Then, the decoding unit 33 decodes the encoded packet data. Thereafter, the display unit 34 displays the decrypted media data as a moving image.
[0033]
On the other hand, the redundant code receiving unit 37 receives the parity information from the redundant code transmitting unit 18 as a redundant code. Then, the redundancy code receiving unit 37 sends the parity information to the data restoring unit 32. The redundant code receiving unit 37 measures a packet loss and a packet receiving interval (hereinafter, referred to as jitter), and sends the measured information to the feedback information generating unit 35.
[0034]
The feedback information generator 35 receives information sent from the data receiver 31 and the redundant code receiver 37. This information includes the packet loss rate, jitter, or the reception time of the parity information. This information is called feedback information. This feedback information is information necessary for detecting congestion on the transmission path. The feedback information generator 35 generates a packet from the feedback information.
[0035]
Then, the feedback transmission unit 36 transmits the generated packet to the server 10 at regular intervals. Thereafter, the server 10 receives the feedback information as a packet in the feedback receiving unit 15.
[0036]
Next, control for increasing the transmission rate in the rate control unit 14 will be described. First, the redundant code transmission unit 18 transmits an increase in the transmission rate as a redundant code. Here, the transmission rate of the server 10 increases in proportion to the amount of data in which the redundant code transmission unit 18 has transmitted the redundant code. On the other hand, the feedback information receiving unit 15 receives feedback information from the client 30.
[0037]
Then, the rate control unit 14 determines the state of the network from the feedback information. That is, the rate control unit 14 determines a change in the network transmission situation due to the increase in the transmission rate by transmitting the redundant code. This transmission status means the presence or absence of congestion on the transmission path, the rate of congestion, and the like.
[0038]
If the rate control unit 14 determines that there is no change in the state of the network, the redundant code transmitted so far is replaced with the encoded media data, and the data transmission unit 13 further transmits the encoded media data. That is, in such a case, the server 10 can transmit more encoded media data by increasing the transmission rate.
[0039]
On the other hand, when determining that there has been a change in the state of the network, the rate control unit 14 stops transmitting the redundant code. In such a case, the data amount of the media data transmitted by the server 10 does not change.
[0040]
However, there is a case where congestion occurs due to an increase in the transmission rate and a packet loss of media data occurs. Therefore, the quality of the media data may be degraded. Even in such a case, the client 30 can recover the lost packet using the transmitted redundant code. Therefore, even if a packet loss occurs due to an increase in the transmission rate, it is possible to suppress deterioration of the quality of the media data.
[0041]
In the present embodiment, the redundant code is an inter-packet FEC (Forward Error Correction) system in which parity information can be added between a plurality of packets. The FEC packet will be described with reference to FIG.
[0042]
In addition, the transmission system can assign priorities according to the encoding method of the encoded media data. Then, the transmission system may control the generation frequency of the parity information of the encoded media data according to the order.
[0043]
When parity information is generated in this way, even if congestion occurs when the transmission rate is increased, FEC packets can be preferentially allocated and restored. Therefore, it is possible to suppress the deterioration in order from the priority information in the media data.
<Structure of FEC packet>
The FEC packet 21 includes an RTP header 22, an FEC header 23, and an FEC recovery 24. The RTP header 22 is data for controlling RTP. The FEC header 23 is FEC control data. The FEC recovery 24 includes the parity information of the RTP packet shown in FIG.
[0044]
The format of the FEC packet complies with the definition of the FEC between packets in the Internet (IP / UDP) network (RFC2733: “An RTP Payload Format for Generic Forward Error Correction”). In RFC 2733, an FEC packet in which the parity of the entire packet is calculated is provided for a plurality of RTP packets. By doing so, when a packet loss occurs, the lost packet is restored using the FEC packet.
[0045]
When increasing the transmission rate, the server 10 transmits the FEC packet 21 as a redundant code before transmitting the media data. Then, the FEC packet 21 is used to detect the congestion state of the transmission path when the transmission rate is increased.
[0046]
Next, the configuration of the RTP header 22 will be described with reference to FIG. The RTP header 22 includes a VER field 40, a P field 41, an X field 42, a CC field 43, an M field 44, a PT field 45, a Sequence Number field 46, a Time Stamp field 47, an SSRC field 48, and a CSRC field 49. You. The RTP header 22 is added to an FEC packet or an encoded packet of media data for RTP control.
[0047]
The 2-bit VER field 40 indicates the RTP version number. Currently it is version 2. Each packet starts with this VER field. The P field 41 includes one padding bit. This padding bit indicates whether the end of the packet is padded.
[0048]
The X field 42 includes one extension bit. This extension bit becomes “1” when an extension header is provided immediately after the RTP header. The CC (CSRC count) field 43 indicates the number of CSRCs (contributing source identifiers).
[0049]
The M field 44 includes one marker bit. This marker bit indicates the boundary of the application data. The 7-bit PT field 45 indicates the encoding system of the payload type application data. The 16-bit Sequence Number field 46 contains the sequence number of the packet. The sequence numbers are assigned in the order of packet transmission.
[0050]
The Time Stamp field 47 is a 32-bit value, and indicates the time at which the first byte of this packet was transmitted. The SSRC (synchronous transmission source identifier) field 48 is a 32-bit value and indicates the transmission source of the packet. The CSRC (Contributing Source Identifier) field 49 indicates the synchronization of the mixed stream. This CSRC field 49 has a variable length.
[0051]
Next, the configuration of the FEC header will be described with reference to FIG. The FEC header 22 includes an SN Base field 50, a Length recovery field 51, a PT recovery field 53, a Mask field 54, and a TS recovery field 55. The FEC header is added to control FEC recovery parity information.
[0052]
The SN Base field 50 indicates the offset of the sequence number of the RTP packet to be subjected to the FEC processing. The Length recovery field 51 indicates parity information of the length of the RTP packet. The E field 52 indicates the extension of the header. The PT recovery field 53 indicates parity information of the payload type. The Mask field 54 indicates the number of the RTP packet to be subjected to the FEC processing. The TS recovery field 55 indicates parity information of the time stamp.
<Block diagram of transmission system>
As the present embodiment, a case where MPEG-4 moving image code data is transmitted using RTP / RTCP will be described with reference to FIG. FIG. 2 is a block diagram of the transmission system according to the present embodiment.
[0053]
This transmission system transmits data between a server 100 and a client 300 connected via the Internet 200 using RTP / RTCP. Note that the RTCP includes a Sender Report (SR) transmitted from the server 100 to the client 300 and a Receiver Report (RR) transmitted from the client 300 to the server 100.
[0054]
First, the processing on the server 100 side after the moving image data is input will be described.
[0055]
The server 100 includes an MPEG-4 encoding unit 101, a packetizer 102, an RTP transmission unit 103, a rate control unit 104, an SR transmission unit 105, an RR reception unit 109, a switch 106, an FEC generation unit 107, an FEC transmission unit 108, and an RR And a transmission unit 109.
[0056]
The MPEG-4 encoding unit 101 encodes the input moving image data.
[0057]
Then, the packetizer 102 packetizes the encoded data and adds an RTP header shown in FIG.
[0058]
The RTP transmission unit 103 transmits moving image data as encoded data packets to the client 300 via the Internet network 200.
[0059]
Next, processing on the client 300 side will be described. The client 300 includes an RTP receiving unit 301, a data restoring unit 302, an MPEG-4 decoding unit 303, a display unit 304, a feedback information generating unit 305, an SR receiving unit 306, an FEC receiving unit 307, and an RR transmitting unit 308.
[0060]
The RTP receiving unit 301 receives an encoded data packet via the Internet network 200. Then, RTP receiving section 301 sends the received encoded data packet to data restoring section 302. In addition, the RTP receiving unit 301 measures the packet loss and the jitter with reference to the sequence number 46 of the RTP header shown in FIG. 4, and sends the measured information to the feedback information generating unit 305.
[0061]
The data restoration unit 302 restores the encoded data packet. That is, when there is a packet loss, the data restoration unit 302 restores the lost packet. Then, the MPEG-4 decoding unit 303 decodes the encoded packet data. After that, the display unit 304 displays the decoded data as a moving image.
[0062]
Next, generation, transmission, and reception of feedback information and control of a transmission rate will be described. In the present embodiment, server 100 controls the transmission rate when RR receiving section 109 receives an RR packet.
[0063]
First, in the client 300, the feedback information generation unit 305 generates an RR packet based on the packet loss rate, the jitter information, and the SR packet information. The packet loss rate and the jitter information are sent from the FEC receiving unit 307 that receives the FEC packet 21 and the RTP receiving unit 301 that receives the RTP packet 21. Note that the SR packet information is the time at which an SR packet transmitted from the server 100 at regular intervals is received. The reception time is used when the server 100 calculates the land trip time. The format of the SR packet and the RR packet conforms to the format described in RFC (Request For Comments) 1889. This RFC1889 is described in IETF (The Internet Engineering Task Force).
[0064]
Then, the client 300 transmits an RR packet to the server 100 as feedback information.
[0065]
On the other hand, when the RR packet is received by the RR receiving unit 109, the server 100 calculates a round trip time based on the feedback information. The round trip time can be calculated from the transmission time of the SR packet and the reception time of the RR packet on the server 100 side, and the time from the reception of the SR packet to the transmission of the RR packet on the client 300 side.
[0066]
In the present embodiment, rate control section 104 controls the transmission rate based on the round trip time and the packet loss rate.
[0067]
Next, control of the transmission rate by the rate control unit 104 according to the packet loss rate and the round trip time will be described. When the packet loss rate exceeds a predetermined threshold (for example, 5%) or when the round trip time exceeds a predetermined threshold (for example, 200 ms), the rate control unit 104 reduces the transmission rate.
[0068]
On the other hand, when both the packet loss rate and the round trip time are equal to or smaller than the threshold, the rate control unit 104 increases the transmission rate.
[0069]
When the packet loss rate is equal to or less than the threshold and the round trip time exceeds the threshold, the rate control unit 104 fixes the transmission rate. That is, the rate control unit 104 keeps the transmission rate as it is.
[0070]
Next, a process when the rate control unit 104 determines to increase the transmission rate will be described. The rate control unit 104 makes a determination based on the rate of congestion on the transmission path.
[0071]
First, the server 100 transmits a redundant code as an increase in the transmission rate. Here, the format of the redundant code to be transmitted uses an inter-packet FEC (RFC 2733: “An RTP Payload Format for Generic Forward Error Correction”) in the Internet (IP / UDP) network. In RFC 2733, an FEC packet in which the parity of the entire packet is calculated is provided for a plurality of RTP packets. By doing so, when a packet loss occurs, the lost packet can be recovered using the FEC packet. In addition, RFC 2733 recommends that an FEC packet be added at a rate of one packet to at least 24 RTP packets.
[0072]
Then, after determining that the transmission rate is to be increased, the rate control unit 104 instructs the switch 106 to generate an FEC packet. The switch 106 duplicates the encoded data packet generated by the packetizer 102. Then, the switch 106 sends the duplicated packet to an FEC generation buffer (not shown) in the FEC generation unit 107.
[0073]
When a predetermined amount (for example, 24 packets) of the copied FEC packets is accumulated in the FEC generation buffer, the FEC generation unit 107 generates parity information. Further, the rate control unit 104 gives a priority to the encoded data packet and instructs the FEC generation unit 107.
[0074]
The FEC generation unit 107 generates parity information according to the priority. This priority can be, for example, the ratio of the I frame to the P frame of the encoded data packet is 7: 3. Here, it is possible to recognize which of the I and P frames each packet contains by referring to vop_coding_type in the header extension code of the MPEG-4 video packet header. Also, as shown in FIG. 6, this parity information can be generated by calculating exclusive OR in bit units for each RTP packet selected according to the priority.
[0075]
Then, the FEC transmission unit 108 adds an FEC header 23 as shown in FIG. 5 to the generated parity information. Further, the FEC transmitting unit 108 adds the RTP header 22 to generate the FEC packet 21 as shown in FIG.
[0076]
Note that the number of encoded data buckets is the same as the number of data packets at the maximum. In that case, the same FEC packet 21 as the data packet is generated, and the same packet is transmitted twice.
[0077]
On the other hand, on the client 300 side, the FEC packet 21 is received by the FEC receiving unit 307 shown in FIG.
[0078]
The data restoration unit 302 determines the loss of a packet selected from the FEC packets 21 according to the priority. Here, when the data restoration unit 302 determines that the number of lost packets is “0” or “2 packets” or more, the data restoration unit 302 sends the packet to the decoding unit 303 without performing data restoration processing.
[0079]
On the other hand, if the data restoration unit 302 determines that the lost packet is “one packet”, the data restoration unit 302 restores the lost packet using the FEC packet 21. After that, the data restoration unit 302 sends the encoded data to the MPEG-4 decoding unit 303.
[0080]
The RTP receiving unit 301 calculates a loss rate of the received RTP packet, and sends it to the feedback information generating unit 305. Further, the FEC receiving unit 307 calculates the loss rate of the received FEC packet 21 and sends it to the feedback information generating unit 305.
[0081]
The feedback information generation unit 305 generates an RR packet, and transmits the RR packet from the RR transmission unit 308 to the server 100.
[0082]
Next, the server 100 acquires the packet loss rate from the RR packet received by the RR receiving unit 109, and calculates the round trip time.
[0083]
Then, the rate control unit 104 determines whether the rate increases or decreases using the packet loss rate and the round trip time.
[0084]
When determining that the transmission rate is to be increased, the rate control unit 104 instructs the switch 106 to stop generating the FEC packet. Here, the server 100 stops transmitting the FEC packet 21.
[0085]
Further, the rate control unit 104 instructs the MPEG-4 encoding unit 101 to transmit encoded data corresponding to the increment of the FEC packet 21. Here, since the MPEG-4 encoding unit 101 increases the encoding rate, the server 100 can transmit the MPEG-4 data at the increased transmission rate.
[0086]
On the other hand, when determining that the transmission rate is to be reduced, the rate control unit 104 instructs the switch 106 to stop sending the encoded packet data to the FEC generation unit 107. In this case, the rate control unit 104 does not instruct the MPEG-4 encoding unit 101 to decrease the encoding rate.
<Parity information generation method>
With reference to FIG. 6, a method for generating parity information of an RTP packet will be described.
[0087]
The server generates parity information on the packetized MPEG-4 data in order to recover the lost packet. This parity information is generated by the FEC generation unit 107 of the server 100.
[0088]
The parity information generated here is transmitted to the client as the FEC packet 21. The format of the FEC packet 21 complies with an inter-packet FEC (RFC2733: “An RTP Payload Format for Generic Forward Error Correction”) in the Internet (IP / UDP) network. In RFC 2733, an FEC packet 21 in which the parity of the entire packet is calculated is provided for a plurality of RTP packets. In this way, when a packet loss occurs, the lost packet is restored using the FEC packet 21.
[0089]
Then, the client receiving the FEC packet 21 restores the MPEG-4 data based on the parity information.
[0090]
In the present embodiment, the FEC packet 21 has parity information on the RTP packets 1 to 4.
[0091]
The first bit (F1) of the FEC packet 21 can be generated by calculating the exclusive OR of the first bit (a1, b1, c1, d1) of each RTP packet. Similarly, the FEC packet 21 can be generated by taking the exclusive OR of the RTP packet for each bit.
[0092]
Here, an example in which the RTP packet 3 is lost will be described.
The client can restore the RTP packet 3 (c1) by using the received RTP packet (a1, b1, d1) and the FEC packet (F1) to make the exclusive OR match. Similarly, the client can restore the RTP packet 3 (c2 to c5).
<Process Flow of Rate Control Unit>
With reference to FIG. 7, the processing of the rate control unit will be described. FIG. 7 is a diagram illustrating a processing flow of the rate control unit 104.
[0093]
The server 100 receives the feedback information (RR) from the client 300 (S701). Then, the rate control unit 104 determines whether the packet loss rate is smaller than the threshold 1 or the land trip time is smaller than the threshold 2 (S702).
[0094]
If the rate control unit 104 determines in S702 that both the packet loss rate and the land trip time are smaller than the threshold, the rate control unit 104 turns on the switch 106 (S703). Here, turning on the switch 106 means control for generating the FEC packet 21.
[0095]
Then, the rate control unit 104 notifies the FEC generation unit 107 of the increase in the transmission rate and the priority ratio (S704). Then, the FEC generation unit 107 generates the FEC packet 21 (S705). Then, the FEC transmission unit 108 transmits the FEC packet 21 to the client 300 (S706).
[0096]
On the other hand, when it is determined in S702 that one or both of the packet loss rate and the land trip time are equal to or larger than the threshold, the rate control unit 104 fixes or decreases the coding rate (S707).
[0097]
Next, with reference to FIG. 8, the processing of the rate control unit when the state of the transmission path has not changed after the transmission of the FEC packet 21 will be described. FIG. 8 is a diagram illustrating a processing flow of the rate control unit 104.
[0098]
The server 100 receives the feedback information (RR) from the client 300 (S801). This feedback information includes information on the rate of congestion when the transmission rate is increased by the FEC packet 21.
[0099]
Then, the rate control unit 104 determines whether the packet loss rate is smaller than the threshold 1 or the land trip time is smaller than the threshold 2 (S802).
[0100]
If the rate control unit 104 determines in S802 that both the packet loss rate and the land trip time are smaller than the threshold, the rate control unit 104 turns off the switch 106 (S803). The switch 106 stops generating the FEC packet 21. That is, the server 100 stops transmitting the FEC packet 21.
[0101]
Then, the rate control unit 104 instructs the MPEG-4 generation unit 101 to increase the coding rate (S804). Here, the MPEG-4 encoding unit 101 increases the encoding rate. Then, the server 100 can transmit the MPEG-4 data at the increased transmission rate.
[0102]
On the other hand, when it is determined in S802 that one or both of the packet loss rate and the land trip time are equal to or greater than the threshold, the rate control unit 104 fixes or decreases the coding rate (S805).
[0103]
Next, with reference to FIG. 9, the processing of the rate control unit when the status of the transmission path changes after the transmission of the FEC packet 21 is described.
[0104]
FIG. 9 is a diagram illustrating a processing flow of the rate control unit 104.
[0105]
The server 100 receives the feedback information (RR) from the client 300 (S901). Then, the rate control unit 104 determines whether the packet loss rate is greater than the threshold 1 or the land trip time is greater than the threshold 2 (S902).
[0106]
In S902, when the rate control unit 104 determines that one of the packet loss rate and the land trip time is larger than the threshold, the rate control unit 104 turns off the switch 106 (S903). Here, the switch 106 stops generating the FEC packet. That is, the server 100 stops transmitting the FEC packet 21.
[0107]
On the other hand, if it is determined in S902 that both the packet loss rate and the land trip time are larger than the threshold, the rate control unit 104 fixes or increases the coding rate (S904).
<Effects of Embodiment>
According to the present embodiment, even if data loss occurs when the transmission rate is increased, transmission errors of data to be transmitted can be suppressed.
[0108]
Further, when it is determined that there is no change in the state of the transmission path before and after transmitting the redundant code, the rate increase can be replaced with data and transmitted. On the other hand, if it is determined that the state of the transmission path has deteriorated before and after the transmission of the redundant code, the state can be returned to the previous state, that is, the state excluding the redundant code corresponding to the rate increase.
[0109]
Further, even if a packet loss occurs in the transmission path, the lost packet can be restored using the redundancy code.
[0110]
Further, for example, it is assumed that a redundant code of an intra frame (I frame) in MPEG data is preferentially generated. When priority is given to the intra frame, even if a packet loss occurs when the transmission rate is increased, it is possible to minimize image quality deterioration.
<Computer readable storage medium>
A program that causes a computer to execute any of the processes of the above-described embodiments can be recorded on a computer-readable storage medium. Then, by causing a computer to read and execute the program in the storage medium, the system described in the above embodiment can be provided.
[0111]
Here, a computer-readable storage medium refers to a storage medium that stores information such as data and programs by electrical, magnetic, optical, mechanical, or chemical action and can be read by a computer. . Among such storage media, those removable from a computer include, for example, a flexible disk, a magneto-optical disk, a CD-ROM, a CD-R / W, a DVD, a DAT, an 8 mm tape, and a memory card.
[0112]
Further, a recording medium fixed to the computer includes a hard disk, a ROM (Read Only Memory), and the like.
[0113]
The above embodiment does not limit the scope of the present invention in any way, and various modifications may be appropriately made within a range that can be understood by those skilled in the art.
<Others>
Further, this embodiment discloses the following invention.
(Supplementary Note 1) Data transmission means for transmitting data to a terminal via a network;
Redundant code transmitting means for transmitting a redundant code for suppressing the data transmission error,
Receiving means for receiving feedback information from the terminal,
Judgment means for judging increase or decrease of the transmission rate based on the feedback information
A server that includes a rate increasing unit that increases the transmission rate by increasing the redundant code when the determination unit determines that the transmission rate is to be increased.
(Supplementary Note 2) Comparison means for comparing the status of the transmission path before and after transmitting the redundant code,
The server according to claim 1, further comprising: a data increasing unit configured to increase data transmitted from the data transmitting unit in place of the increased redundant code when the comparing unit determines that there is no change in the status of the transmission path. .
(Supplementary note 3) The server according to supplementary note 2, further comprising a stop unit that stops transmission of the redundant code when the comparison unit determines that the condition of the transmission path has deteriorated.
(Supplementary note 4) The server according to supplementary note 2 or 3, wherein the comparing unit compares the status of the transmission path before and after transmitting the redundant code based on the feedback information.
(Supplementary note 5) The server according to supplementary note 4, wherein the feedback information includes a packet loss rate.
(Supplementary note 6) The server according to Supplementary note 4, wherein the feedback information includes information on an interval at which packets arrive.
(Supplementary note 7) The server according to any one of claims 4 to 6, wherein the feedback information includes a round trip time.
(Supplementary note 8) The server according to supplementary note 4, wherein the redundant code is an inter-packet error correction method including parity information between packets.
(Supplementary note 9) The server according to supplementary note 4, wherein the redundant codes are generated in order based on data priority.
[0114]
【The invention's effect】
As described above, the present invention can provide a data transmission server that can suppress deterioration of data quality even when packet loss occurs due to an increase in transmission rate.
[Brief description of the drawings]
FIG. 1 is a diagram showing the principle of the present invention.
FIG. 2 is a block diagram illustrating a transmission system according to the present embodiment.
FIG. 3 is a configuration diagram of an FEC packet.
FIG. 4 is a configuration diagram of an RTP header.
FIG. 5 is a configuration diagram of an FEC header.
FIG. 6 is a diagram illustrating a method of generating FEC parity information.
FIG. 7 is a diagram illustrating a processing flow of a rate control unit.
FIG. 8 is a diagram illustrating a processing flow of a rate control unit.
FIG. 9 is a diagram showing a processing flow of a rate control unit.
[Explanation of symbols]
10, 100 ... server
11: Encoding unit
12 ... Packetizer
102 ... Packetizer
13 Data transmission unit
14, 104 ... rate control unit
15. Feedback information receiving unit
16, 106 ... Switch
17 Redundant code generator
18 Redundant code transmission unit
20 ... Network
21 ... RTP packet
22 ... RTP header
23: FEC header
24: FEC recovery
30, 300… Client
31 Data receiving unit
32, 302: Data restoration unit
33 ... Decoding unit
34, 304 ... display unit
35, 305: feedback information generation unit
36 ... Feedback transmitter
37 ... Redundant code receiving unit
41 ... V
42 ... P
43 ... X
44 ... C
45 ... M
45 ... PT
46… Sequence Number
47 ... Time Stamp
48 ... SSRC
49… CSRC
51 ... SN base
52 ... Length recovery
53 ... E
54… PT recovery
55… TS recovery
101: MPEG-4 encoding unit
103 ... RTP transmission unit
105 ... SR transmission unit
107: FEC generation unit
108 ... FEC transmission unit
109 ... RR receiving section
200 ... Internet network
301 ... RTP receiving unit
303: MPEG-4 decoding unit
306 ... SR receiving unit
307 ... FEC receiving unit
308 ... RR transmission section

Claims (5)

Data transmission means for transmitting data to the terminal via the network;
Redundant code transmitting means for transmitting a redundant code for suppressing the data transmission error,
Receiving means for receiving feedback information from the terminal,
Judgment means for judging increase or decrease of the transmission rate based on the feedback information
A server that includes a rate increasing unit that increases the transmission rate by increasing the redundant code when the determination unit determines that the transmission rate is to be increased. Comparing means for comparing the status of the transmission path before and after transmitting the redundant code,
2. The data increasing unit according to claim 1, further comprising: a data increasing unit configured to increase data transmitted from the data transmitting unit in place of the increased redundant code when the comparing unit determines that there is no change in the status of the transmission path. server. 3. The server according to claim 2, further comprising a stop unit that stops transmission of the redundant code when the comparison unit determines that the condition of the transmission path has deteriorated. The server according to any one of claims 1 to 3, wherein the comparing unit compares the status of the transmission path before and after transmitting the redundant code based on the feedback information. The server according to claim 4, wherein the feedback information includes a packet loss rate.

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