JP5434570B2 - Stream distribution device - Google Patents

Description

  The present invention relates to a stream distribution apparatus and the like, and more particularly to a stream distribution apparatus and the like that uses a network bandwidth as much as possible in a quality non-guaranteed network and realizes streaming without disturbance or interruption.

  The transmission terminal of the stream distribution system described in Patent Literature 1 transmits a redundant packet for reconstructing the lost content packet together with the content packet to the reception terminal. When the content packet is lost, the receiving terminal reconstructs the content packet from the redundant packet and reproduces it. The receiving terminal has a function of feeding back the packet loss rate to the transmitting terminal. If the transmitting terminal determines that the network is congested based on feedback information from the receiving terminal, the transmitting terminal reduces the bit rate. Further, the transmission bit rate is increased by increasing the amount of redundant packets to be transmitted, and it is determined whether or not the network supports a high data rate based on feedback information from the receiving terminal.

  Patent Document 2 describes a receiving node that returns a test stream having the same configuration (packet size and bit rate) as the received test stream to the transmitting node side.

  Patent Document 3 describes a technique for obtaining a test transmission rate from an increasing tendency and a decreasing tendency of a transmission delay time difference.

  Patent Document 4 describes a technique for calculating the slope of an approximate straight line of the buffer amount of image data and controlling the transmission rate.

  Patent Document 5 describes a technique for increasing the bit rate in stages during stream transmission.

JP 2009-027720 A JP 2008-278207 A (paragraphs 0045 to 0047, FIG. 1) JP 2006-074773 (paragraphs 0019 to 0021, FIGS. 1 and 2) Japanese Patent Laying-Open No. 2005-005823 (paragraphs 0054-0060, FIG. 10, FIG. 12) Japanese Patent Laid-Open No. 11-243360 (paragraph 0084, FIG. 1)

Jain and Dovrolis: a measurement tool for end-to-end available bandwidth, In Proceedings of Passive and Active Measurements Workshop, pp. 14-25, 2002.

  However, in order to use the technique of Patent Document 1, it is necessary to feed back the reception state of content such as a packet loss rate from the receiving terminal to the transmitting terminal. Therefore, when the transmitting terminal cannot obtain the feedback of the content reception state, the technique of Patent Document 1 cannot be used. For example, Patent Document 1 describes a packet loss rate feedback method using RTCP RR (Real Time Transport Protocol (RTP) Control Protocol Receiver Report). However, in the environment of STB (Set Top Box) that does not support RTCP and the IPTV (Internet Protocol TeleVision) protocol that clearly indicates the non-use of RTCP, the feedback control of Patent Document 1 cannot be realized.

  Further, in the technique of Patent Document 2, in order to distribute a stream, the receiving node “returns a test stream having the same configuration (packet size and bit rate) as the received test stream to the transmitting node”. A feedback function of the content reception state “return to the transmission node as it is” is required for the reception node. Therefore, the technique of Patent Document 2 cannot be used for a general receiving node that does not have such a function.

  As described above, in the techniques of Patent Documents 1 and 2, if the feedback of the content reception state such as the packet loss rate cannot be obtained from the receiving terminal, the network congestion state cannot be known. Was used as much as possible, and streaming without turbulence and interruptions could not be realized. The technique for solving this problem is neither disclosed nor suggested anywhere in Patent Documents 3-5.

  Therefore, the object of the present invention is to know the network status even when the content reception status feedback such as the packet loss rate is not obtained from the receiving terminal, and as a result, the network bandwidth is used as much as possible and the The aim is to achieve seamless streaming.

The stream distribution apparatus according to the present invention is:
In a stream distribution device that transmits a stream to a receiving terminal via a network,
A transmitter that periodically transmits a probe packet to the receiving terminal;
A receiving unit that receives from the receiving terminal a response packet indicating that the probe packet has been received;
The round-trip delay time required from when the transmitting unit transmits the probe packet to when the receiving unit receives the response packet is calculated. If the round-trip delay time tends to increase, the transmission rate of the stream is A controller that determines that the available bandwidth is exceeded, and determines that the transmission rate is equal to or lower than the available bandwidth if the round-trip delay time does not tend to increase;
It is provided with.

A stream distribution method according to the present invention includes:
In a stream distribution method for transmitting a stream to a receiving terminal via a network,
A transmitting unit that periodically transmits a probe packet to the receiving terminal, and a receiving unit that receives a response packet indicating that the probe packet has been received from the receiving terminal are prepared,
The round-trip delay time required from when the transmitting unit transmits the probe packet to when the receiving unit receives the response packet is calculated. If the round-trip delay time tends to increase, the transmission rate of the stream is It is determined that the available bandwidth is exceeded, and if the round-trip delay time does not tend to increase, it is determined that the transmission rate is equal to or less than the available bandwidth.
It is characterized by that.

The stream distribution program according to the present invention includes:
In a stream distribution program used in a stream distribution device that transmits a stream to a receiving terminal via a network,
When the stream distribution device includes a transmission unit that periodically transmits a probe packet to the reception terminal, a reception unit that receives a response packet indicating that the probe packet has been received from the reception terminal, and a computer ,
Means for calculating a round-trip delay time required from when the transmitting unit transmits the probe packet to when the receiving unit receives the response packet; and if the round-trip delay time tends to increase, As a means for determining that the transmission rate exceeds the available bandwidth, and determining that the transmission rate is equal to or lower than the available bandwidth if the round-trip delay time does not tend to increase,
This is to make the computer function.

  According to the present invention, the round-trip delay time required from when the probe packet is transmitted to when the response packet is received is calculated, and whether or not the transmission rate exceeds the available bandwidth depending on whether or not the round-trip delay time increases. Therefore, the network status can be known even when the feedback of the content reception status such as the packet loss rate cannot be obtained from the receiving terminal.

3 is a block diagram illustrating a transmission terminal according to Embodiment 1. FIG. It is a block diagram which shows an example of the control part of FIG. FIG. 3 [1] is a timing chart showing the behavior of the packet when the transmission rate exceeds the available bandwidth, and FIG. 3 [2] is a timing chart showing the behavior of the packet when the transmission rate is equal to or lower than the available bandwidth. It is. It is a graph which shows the relationship between a content rate and a transmission rate. 4 is a flowchart illustrating an overall operation in the transmission terminal according to the first exemplary embodiment. 4 is a flowchart illustrating a method for determining a content rate and a transmission rate in the first embodiment. 10 is a flowchart illustrating a method for determining a content rate and a transmission rate in the second embodiment. 10 is a flowchart illustrating a method for determining a content rate and a transmission rate in the third embodiment. FIG. 9 is a chart showing the relationship between the transmission time and the number of transmission packets in the first embodiment, FIG. 9 [1] is when distribution starts, and FIG. 9 [2] increases the number of packets transmitted at one time when the transmission rate increases. FIG. 9 [3] shows a case where the packet transmission interval is shortened. 10 is a chart showing a change in transmission rate in the second embodiment. FIG. 11 [1] is a chart showing the relationship between the round-trip delay time and the transmission rate increase rate in the third embodiment, and FIG. 11 [2] shows the slope of the approximate line and the transmission rate decrease rate in the third embodiment. It is a chart which shows a relationship.

  Next, embodiments for carrying out the invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a transmitting terminal according to the first embodiment of the present invention. FIG. 2 is a block diagram illustrating an example of the control unit in FIG. Hereinafter, description will be given based on these drawings.

  The transmission terminal 10, the packet transmission unit 15, and the probe packet reception unit 16 in the first exemplary embodiment correspond to “stream distribution device”, “transmission unit”, and “reception unit” in the claims, respectively. The transmission terminal 10 is a stream distribution device that transmits a stream to the reception terminal 20 via the network 21, and indicates that the packet transmission unit 15 that periodically transmits the probe packet to the reception terminal 20 and that the probe packet has been received. A probe packet receiving unit 16 that receives a response packet from the receiving terminal 20 and a control unit 17 are provided. The control unit 17 calculates the round-trip delay time required from when the packet transmission unit 15 transmits the probe packet to when the probe packet reception unit 16 receives the response packet. It is determined that the transmission rate of the stream exceeds the available bandwidth. If the round-trip delay time does not tend to increase, it is determined that the transmission rate is equal to or lower than the available bandwidth. The probe packet is, for example, an echo request packet.

  According to the transmission terminal 10, the round-trip delay time required from the transmission of the probe packet to the reception of the response packet is periodically measured, and the transmission rate is set according to whether the round-trip delay time increases or not. Since it is determined whether or not it exceeds the value, the state of the network 21 can be known even when feedback of the content reception state such as the packet loss rate cannot be obtained from the receiving terminal 20.

  Moreover, you may comprise the transmission terminal 10 as follows.

  The control unit 17 decreases the transmission rate when it is determined that the transmission rate exceeds the available bandwidth, and increases the transmission rate when it is determined that the transmission rate is equal to or lower than the available bandwidth. In this case, the network bandwidth can be used as much as possible, and streaming without disturbance or interruption can be realized.

  Here, the definition of the transmission rate in this specification will be described with reference to FIG. FIG. 4 is a graph showing the relationship between the content rate and the transmission rate. In FIG. 4, the horizontal axis represents the time from the start of transmission, and the vertical axis represents the accumulated transmission data amount.

  In a normal transmission method, the accumulated transmission data amount is proportional to the elapsed time, as indicated by a broken line in the figure. At this time, the accumulated transmission data amount when t seconds have elapsed from the start of distribution of the content of A [bps] is A × t [bits]. On the other hand, when the transmission rate is B [bps] (B ≧ A), the transmission of the content of A × t [bits] is completed in (A / B) × t seconds from the start of transmission, and then (1 -(A / B)) It is also possible to send in such a manner that transmission is not performed for t seconds (solid line in the figure). In this specification, B at this time is defined as a transmission rate.

  The control unit 17 may be configured as follows. When it is determined that the transmission rate exceeds the usable bandwidth, (1) if the transmission rate is higher than the content rate that is the content of the stream, the transmission rate is reduced to the content rate, and (2 If the content rate and the transmission rate are the same, the content rate is lowered and the transmission rate is lowered to the lowered content rate. When it is determined that the transmission rate is equal to or lower than the available bandwidth, (3) if the transmission rate is higher than the content rate, the content rate is increased and the transmission rate is adjusted to the increased content rate. If the transmission rate is the same, the transmission rate is increased.

  The stream distribution method according to the first embodiment captures the operation of the transmission terminal 10 as a method invention. That is, the stream delivery method of the first embodiment is a stream delivery method for sending a stream to the receiving terminal 20 via the network 21. The packet sending unit 15 that periodically sends a probe packet to the receiving terminal 20, and the probe packet And a probe packet receiving unit 16 that receives a response packet indicating that the packet has been received from the receiving terminal 20, and after the packet transmitting unit 15 transmits the probe packet until the probe packet receiving unit 16 receives the response packet. Calculate the required round-trip delay time. If this round-trip delay time is increasing, it is determined that the stream transmission rate exceeds the usable bandwidth. If the round-trip delay time is not increasing, the transmission rate is less than the usable bandwidth. It is judged that it is.

  The stream distribution program according to the first embodiment is for causing the computer 30 (FIG. 2) to function as the control unit 17. The stream distribution program according to the first embodiment is used for the transmission terminal 10 that transmits a stream to the reception terminal 20 via the network 21. The transmission terminal 10 includes a packet transmission unit 15 that periodically transmits a probe packet to the reception terminal 20, a probe packet reception unit 16 that receives a response packet indicating that the probe packet has been received from the reception terminal 20, and a computer 30. Is provided. At this time, the stream distribution program according to the first embodiment includes means for calculating a round trip delay time required from when the packet transmission unit 15 transmits the probe packet to when the probe packet reception unit 16 receives the response packet, and As a means for determining that the transmission rate of the stream exceeds the usable bandwidth if the round-trip delay time is increasing, and determining that the transmission rate is equal to or less than the usable bandwidth if the round-trip delay time is not increasing ( That is, as the control unit 17), the computer 30 functions.

  As shown in FIG. 2, the computer 30 includes a CPU 31, a ROM 32, a RAM 33, a bus 34, an input / output interface 35, and the like, and is connected to the packet transmission unit 15, the probe packet reception unit 16, and the like. The CPU 31 reads, interprets, and executes the stream distribution program of the first embodiment stored in the ROM 32 or the RAM 33. It should be noted that the functions such as the content packet generator 13 described later may also be a stream distribution program that is realized by the computer 30.

  The stream distribution method and program according to the first embodiment exhibit the same operations and effects as the transmission terminal 10 and can adopt various configurations according to the configuration of the transmission terminal 10.

  Hereinafter, the transmission terminal 10 will be described in more detail.

  Referring to FIG. 1, the stream distribution system according to the first exemplary embodiment includes a transmission terminal 10 that distributes content and a reception terminal 20 that receives and reproduces the content. The transmission terminal 10 and the reception terminal 20 are connected via a network 21. There may be a plurality of receiving terminals 20. The transmission terminal 10 according to the first embodiment includes a content storage unit 12, a content packet generation unit 13, and the like in addition to the packet transmission unit 15, the probe packet reception unit 16, and the control unit 17 described above. The control unit 17 includes a distribution control unit 11 and a probe packet generation unit 14.

  The transmission terminal 10 includes a distribution control unit 11, a content storage unit 12, a content packet generation unit 13, a probe packet generation unit 14, a packet transmission unit 15, a probe packet reception unit 16, and the like. The distribution control unit 11 receives the reception time of the response packet for each probe packet from the probe packet receiving unit 16, determines the content rate and the transmission rate to be distributed, and sends the content packet and the content packet generation unit 13 and the probe packet generation unit 14 Instructs generation of a probe packet. The content storage unit 12 stores content in a form that can be distributed at a plurality of bit rates. The content packet generation unit 13 extracts content data from the content storage unit 12 to generate a content packet, and transfers the generated content packet to the packet transmission unit 15. The probe packet generation unit 14 generates an echo request packet that is a probe packet, and transfers this to the packet transmission unit 15. The packet transmission unit 15 transmits each packet generated by the content packet generation unit 13 and the probe packet generation unit 14 to the network 21. The probe packet reception unit 16 receives a response packet to the transmitted probe packet and sets the reception time. Notify the delivery control unit 11

  Here, the operation principle of the stream distribution system of the first embodiment will be described.

  An IP network has the following properties. If the transmission rate from the transmission terminal 10 exceeds the usable bandwidth between the transmission terminal 10 and the reception terminal 20, the delay time increases as the packet is transmitted later. Conversely, if the transmission rate is less than or equal to the available bandwidth, the delay time does not increase even for packets transmitted later.

  FIG. 3 [1] is a timing chart showing the behavior of the packet when the transmission rate exceeds the available bandwidth, and FIG. 3 [2] is a timing chart showing the behavior of the packet when the transmission rate is equal to or lower than the available bandwidth. It is. In other words, FIG. 3 [1] shows a packet delay when a packet is transmitted at a bit rate higher than the available bandwidth, and FIG. 3 [2] shows a packet delay when the packet is transmitted at a bit rate lower than the available bandwidth. Indicates delay. Hereinafter, description will be given based on these drawings.

  In FIG. 3, the vertical direction represents the passage of time, the arrows represent packets, and the higher the density of the arrows, the higher the rate. Packets transmitted at a rate exceeding the available bandwidth are stored in the router queue until they can be transmitted after arrival at the router immediately before the link with the smallest available bandwidth, and are output when transmission is possible.

  As shown in FIG. 3 [1], if the transmission rate exceeds the available bandwidth, the time stored in the queue increases as the packet becomes backward, so the delay time (received after being transmitted by the transmitting terminal 10) Time until it arrives at the terminal 20) increases.

  On the other hand, as shown in FIG. 3 [2], when the transmission rate is equal to or lower than the usable bandwidth, the packet transmitted from the transmitting terminal 10 is transmitted immediately without being stored in the queue of the router immediately before the minimum usable bandwidth link. Is done. Therefore, the delay time of each packet is constant regardless of the transmission order.

  That is, if the delay time when transmitting at a certain rate has an increasing tendency, the transmission rate exceeds the available bandwidth, and if there is no increasing tendency, it can be determined that the transmission rate is equal to or lower than the available bandwidth. Since this principle can be used not only in IP networks but also in packet switched networks in general, the subject of the present invention is not limited to IP networks. The transmission terminal 10 according to the first embodiment determines the magnitude relationship between the transmission rate and the available bandwidth depending on whether or not the round-trip delay time of the probe packet transmitted to the reception terminal 20 tends to increase, and based on the determination result To control the content rate and transmission rate.

  By setting the transmission rate to a value different from the content rate, it is possible to compare the rate between the rate higher than the currently distributed content rate and the available bandwidth, so it is possible to determine whether the content rate can be increased. .

  Next, the overall operation of the transmission terminal 10 according to the first embodiment will be described in detail with reference to the flowchart of FIG. Hereinafter, a description will be given based on FIGS. 1 and 5.

  At the start of distribution, the distribution control unit 11 determines an initial content rate, a transmission rate, and a probe packet transmission interval (step S11), generates a content packet to the content packet generation unit 13, and generates a probe packet. Each is instructed to the generation unit 14. The initial content rate and transmission rate can be determined by any method, such as a method that uses preset values, a method that determines based on past information, or a method that distributes content with the lowest bit rate that can be distributed. May be.

  Subsequently, the content packet generation unit 13 extracts content data at a rate instructed from the distribution control unit 11 from the content storage unit 12, generates a content packet, and transmits the content packet at the designated transmission rate to the packet transmission unit 15 (Step S12). At the same time, the probe packet generator 14 generates probe packets at intervals instructed by the distribution controller 11 and transfers them to the packet transmitter 15 (step S12).

  Subsequently, the packet transmitting unit 15 sends the content packet generated by the content packet generating unit 13 and the probe packet generated by the probe packet generating unit 14 to the network 21 (step S13).

  Finally, the distribution control unit 11 determines a content rate and a transmission rate (step S14). Thereafter, the operation of the transmission terminal 10 returns to step S12.

  Here, the content rate and transmission rate determination method in step 14 will be described in detail with reference to the flowchart of FIG. Hereinafter, a description will be given based on FIGS. 1 and 6.

  The distribution control unit 11 receives the reception time of each probe packet from the probe packet reception unit 16 (step S1401), and calculates a round trip delay time based on the transmission time stored in the distribution control unit 11 (step S1402). This transmission time is, for example, the time when the packet transmission unit 15 sends the probe packet to the network 21, that is, the transmission time when the distribution control unit 11 instructs the probe packet generation unit 14 to generate the probe packet. Therefore, the round-trip delay time is obtained by the equation (round-trip delay time) = (reception time) − (transmission time).

  Subsequently, when receiving the prescribed number of probe packets, the distribution control unit 11 determines whether or not there is an increasing tendency of the round-trip delay time (step S1403). As an example of a method for determining the presence or absence of an increase tendency of the round-trip delay time, plotting the round-trip delay time at each transmission time in a graph in which the horizontal axis is the probe packet transmission time and the vertical axis is the round-trip delay time, There is a method in which an approximate straight line of points is obtained by the least square method, and it is determined that there is an increasing tendency if the slope is not less than a specified value, and there is no increasing tendency if it is less than the specified value. Alternatively, a determination method of Pathload (see Non-Patent Document 1) that is an available bandwidth estimation method may be used. In Pathload, values of PCT (Pairwise Comparison Test) and PDT (Pairwise Difference Test) are calculated from the delay time of a predetermined number of probe packets, and the presence or absence of an increasing tendency is determined based on these values. Further, if an echo response is not returned even after a specified time has elapsed since the echo request was transmitted to the receiving terminal 20, it is determined that the packet is lost, and if the packet loss rate of the probe packet is equal to or greater than the specified value, the transmission rate is available. It may be determined that the bandwidth is exceeded.

  The subsequent processing is based on the following four combinations of whether or not the transmission rate and the content rate are the same (step S1404) and whether or not the round-trip delay time tends to increase (steps S1405 and S1406). Different.

  (1). When the transmission rate and the content rate are the same and the round-trip delay time does not tend to increase (Yes in step S1404, No in step S1405). In this case, in order to determine whether or not the content rate can be increased, the content rate is not changed and the transmission rate is made the same as the content rate one level higher than the current content rate (step S1407).

  (2). When the transmission rate and the content rate are the same and the round-trip delay time tends to increase (Yes in step S1404, Yes in step S1405). In this case, it is determined that the current content rate exceeds the available bandwidth, the content rate is lowered by one level, and the transmission rate is made the same as the content rate after the reduction (step S1408).

  (3). When the transmission rate is different from the content rate (that is, the transmission rate is a content rate one level higher) and the round-trip delay time tends to increase (No in step S1404, Yes in step S1406). In this case, it is determined that distribution is impossible at the content rate one level above, and the transmission rate is the same as the content rate currently being distributed (step S1409).

  (4). When the transmission rate is different from the content rate (that is, the transmission rate is a content rate one level higher), and the round-trip delay time does not tend to increase (No in step S1404, No in step S1406). In this case, it is determined that distribution is possible at a content rate one level higher, and the content rate is increased by one level (step S1410). In FIG. 6, the determination of whether or not the transmission rate and the content rate are the same (step S1404) is made first, and the determination of whether or not the round-trip delay time tends to increase (steps S1405 and S1406) is made later. As long as the above-mentioned four combinations are obtained, the compliance may be reversed.

  In steps S1407 and S1410, instead of increasing immediately when the round-trip delay time does not tend to increase, it may be increased when there is no continuous increase several times. In step S1407, the transmission rate may be set higher than the one-stage content rate, and the rate higher than the one-stage content rate may be compared with the available bandwidth.

  By performing these processes, it is possible to increase the content rate only when there is a surplus in the available bandwidth, and it is possible to prevent the playback terminal from being stopped or disturbed due to insufficient available bandwidth after the content rate is increased.

  Next, the effect of the first embodiment will be described. According to the first embodiment, if the receiving terminal has a function of responding to an echo request in addition to the content receiving function, the network band can be provided even if the receiving terminal does not have a feedback function of the content receiving state. It can be used as much as possible to achieve streaming without disruption or interruption. Since almost all receiving terminals that support the Internet Protocol (IP) used in the Internet are equipped with an ICMP (Internet Control Message Protocol) Echo function, the present invention is applied to almost all cases in stream distribution over the Internet. Can be used.

  FIG. 7 is a flowchart illustrating a method for determining a content rate and a transmission rate according to the second embodiment. The second embodiment is different from the first embodiment in the content rate and transmission rate determination method (step S14 in FIG. 5) in the distribution control unit 11. Hereinafter, the detailed operation of step S14 in FIG. 5 according to the second embodiment will be described in detail with reference to FIGS.

  The operations from step S1401 to step S1403 in FIG. 5 are the same as those in the first embodiment. The subsequent processing differs depending on whether or not the round-trip delay time tends to increase (step S1411).

  If the round-trip delay time tends to increase (step S1411 is Yes), it is determined whether the transmission rate and the content rate are the same (step S1412). When the transmission rate is different from the content rate (No in step S1412) (that is, when the transmission rate is larger than the content rate), it is determined that the current transmission rate exceeds the available bandwidth and the transmission rate is set as the content rate. The same change is made (step S1414). If the transmission rate is equal to the content rate (Yes in step S1412), it is determined that the current content rate exceeds the usable bandwidth, the content rate is decreased by one step, and the content rate after the transmission rate is decreased (Step S1415).

  On the other hand, if the round-trip delay time does not tend to increase (No in step S1411), the transmission rate is increased (step S1413). The amount of increase in the transmission rate in step S1413 is determined in advance, for example, by 10%. The amount of increase in the transmission rate may be an absolute amount such as 500 kbps, in addition to the constant rate from the current transmission rate. Further, if the transmission rate is 1 Mbps or more, it may be changed according to the transmission rate, such as 500 kbps if it is less than 1 Mbps, or 100 kbps.

  Subsequently, the increased transmission rate is compared with the one-stage content rate (step S1416), and if the transmission rate exceeds the one-stage content rate, it is determined that distribution is possible with the one-stage content rate. Thus, the content rate is increased by one level (step S1417). At this time, the content rate is not increased as soon as the transmission rate exceeds the one-stage content rate, but the content rate is increased when the transmission rate exceeds the one-stage content rate by a certain percentage (for example, 10%). It is good.

  By performing these processes, it is possible to increase the content rate only when there is a margin in the available bandwidth as in the first embodiment. After the content rate is increased, the playback terminal is stopped or disturbed due to insufficient available bandwidth. Can be prevented.

  Next, the effect of the second embodiment will be described. In the second embodiment, since the transmission rate is gradually increased, packet loss hardly occurs. If the transmission rate greatly exceeds the available bandwidth, the queue of the network device overflows and a content packet is lost, and there is a possibility that playback at the receiving terminal 20 is interrupted or disrupted. Therefore, by gradually increasing the transmission rate, the possibility that the transmission rate will greatly exceed the available bandwidth is reduced, so that packet loss is less likely to occur.

  Other configurations, operations, and effects of the second embodiment are the same as those of the first embodiment.

  FIG. 8 is a flowchart illustrating a method for determining a content rate and a transmission rate according to the third embodiment. The third embodiment is also different from the first and second embodiments in the content rate and transmission rate determination method (step S14 in FIG. 5) in the distribution control unit 11. Hereinafter, the detailed operation of step S14 in FIG. 5 according to the third embodiment will be described in detail with reference to FIGS.

  The operations from step S1401 to step S1411 are the same as those in the second embodiment. In the third embodiment, when it is determined that the round-trip delay time does not tend to increase (No in step S1411), the amount of increase in the transmission rate is determined from the behavior of the round-trip delay time (step S1423).

  Even when the transmission rate is equal to or lower than the available bandwidth, the round-trip delay time varies differently when the transmission rate is significantly smaller than the available bandwidth and when the transmission rate is close to the available bandwidth. For example, when the transmission rate is significantly smaller than the usable bandwidth, the variance of the round trip delay time is small, and when the transmission rate is close to the usable bandwidth, the variance of the round trip delay time is large. In the third embodiment, the increase in the transmission rate is increased when the variance of the round trip delay time of the probe packet is small, and the increase in the transmission rate is decreased when the variance is large.

  If the round-trip delay time has an increasing tendency (Yes in step S1411), the amount of decrease in the transmission rate is determined from the increasing tendency (step S1422).

  When the transmission rate is significantly higher than the usable bandwidth, the slope of the approximate line described in the first embodiment is increased, and probe packet loss is likely to occur. On the other hand, if the amount that the transmission rate exceeds the available bandwidth is small, the slope of the approximate line becomes small and probe packet loss is less likely to occur. In the third embodiment, the amount of decrease in the transmission rate is determined in accordance with the magnitude of the gradient when the round trip delay time of the probe packet is approximated to a straight line and the loss rate of the probe packet.

  Finally, based on the transmission rate determined in step S1422 and step S1423, the content rate is determined in step S1424. The content rate can be determined by selecting a content rate that is equal to or lower than the transmission rate from among the distributable content rates.

  In other words, when increasing the transmission rate, the control unit 17 in Embodiment 3 changes the increase rate of the transmission rate according to the degree of variation in the round-trip delay time, and transmits the transmission rate when decreasing the transmission rate. The rate of decrease in transmission rate is changed according to the amount by which the rate exceeds the available bandwidth.

  Next, the effect of the third embodiment will be described. In the third embodiment, not only the magnitude relationship between the transmission rate and the available bandwidth, but also the amount of change in the transmission rate is determined based on information on how much the transmission rate is different from the available bandwidth. The ability to follow fluctuations is improved.

  Other configurations, operations, and effects of the third embodiment are the same as those of the first and second embodiments.

  Next, Examples 1 to 3 that further embody the first to third embodiments will be described. FIG. 9 is a chart showing the relationship between the transmission time and the number of transmitted packets in the first embodiment, FIG. 9 [1] is a distribution start time, and FIG. 9 [2] is an increase in the number of packets transmitted at one time. FIG. 9 [3] shows a case where the packet transmission interval is shortened. Hereinafter, a description will be given based on FIGS. 1 and 9.

  Example 1 is an example in which Embodiment 1 is further embodied. In the first embodiment, the transmission terminal 10 and the reception terminal 20 are connected via the Internet as the network 21. Content distribution from the transmission terminal 10 to the reception terminal 20 is performed by RTP (Realtime Transport Protocol), and UDP (User Datagram Protocol) is used as a transport protocol. ICMP Echo is used for the probe packet. An ICMP Echo Request is transmitted from the transmitting terminal 10 to the receiving terminal 20, and when the receiving terminal 20 receives the ICMP Echo, it returns an ICMP Echo Reply to the transmitting terminal 10. Since the ICMP Echo function is implemented in almost all terminals that support IP, the present invention can be used in almost all receiving terminals. In addition to ICMP Echo, UDP Echo may be used.

  The transmission terminal 10 is a server device. The distribution control unit 11, the content packet generation unit 13, and the probe packet generation unit 14 are realized by a program executed by the CPU 31 (FIG. 2) of the server device. The content storage unit 12 is a magnetic disk device built in the server device, and stores each video content encoded at a plurality of bit rates. The content may be audio other than video. In the first embodiment, it is assumed that video contents encoded at 2 Mbps, 4 Mbps, and 6 Mbps are stored. The packet transmission unit 15 and the probe packet reception unit 16 are network interface cards of the server device. The receiving terminal 20 is a terminal that receives and reproduces media such as video and audio, such as a set top box for IPTV, a mobile phone terminal, a PDA (Personal Digital Assistant), and a PC (Personal Computer). Echo function is implemented.

  At the start of distribution, the transmission terminal 10 determines an initial content rate and distribution rate. Here, it is assumed that the lowest quality of the contents stored in the content storage unit 12 is selected, and both the content rate and the transmission rate are 2 Mbps. When the data size per RTP packet is 1000 bytes, the number of RTP packets transmitted per second is 250 (= 2000000 [bps] / 8 [b / B] / 1000 [B / packet]). When the packet transmission interval is 10 milliseconds, the number of RTP packets transmitted at one time is 2.5 (2 and 3 are alternately transmitted) (FIG. 9 [1]).

At this time, an ICMP Echo Request is transmitted immediately before, immediately after, and in the middle of the content packet.
It is desirable that the ICMP Echo Request be as small as possible so as not to be a load on the network 21 as much as possible. Further, by changing the ID field and sequence number field of the ICMP Echo header for each transmission packet, it is possible to identify which echo request is a response packet when receiving an echo response from the receiving terminal 20.

  Here, when both the content rate and the transmission rate are set to 2 Mbps, it is assumed that the round-trip delay time does not increase. When the transmission rate is equal to the content rate and the round-trip delay time does not tend to increase, the transmission rate is increased by one level without changing the content rate in order to determine whether or not the content rate can be distributed by one level. To the content rate (step S1407 in FIG. 6). In the first embodiment, the transmission rate is increased to 4 Mbps.

  As a method of increasing the transmission rate, there are a method of increasing the number of transmission packets at one time without changing the packet transmission interval and a method of changing the packet transmission interval without changing the number of transmission packets at one time. There are two possible ways.

  The former method for increasing the number of transmission packets will be considered in an example in which the transmission rate of packets for 0.1 seconds (25 in the case of 2 Mbps content) is changed. In the method of increasing the number of transmission packets at one time, as shown in FIG. 9 [2], five (= 2.5 × (4 Mbps / 2 Mbps)) content packets are transmitted at 10 millisecond intervals. Then, it is determined whether or not the available bandwidth is 4 Mbps or more based on whether or not the probe packet transmitted together with the content packet has an increasing tendency. Based on the result, it is determined whether to increase the content rate to 4 Mbps.

  On the other hand, in the latter method of changing the packet transmission interval, as shown in FIG. 9 [3], 2.5 content packets (alternately between 2 and 3) are sent at intervals of 5 milliseconds. Send. Then, it is determined whether or not the available bandwidth is 4 Mbps or more based on whether or not the round-trip delay time of the probe packet tends to increase. As a result of the determination, if there is no increasing tendency, the content rate is increased to 4 Mbps, and if there is an increasing tendency, the transmission rate is decreased to 2 Mbps.

  In general stream distribution, when the bit rate of content increases, the number of packets transmitted at one time is changed without changing the content transmission interval. Therefore, when the former method is used, it is possible to compare the transmission rate and the available bandwidth with the same transmission pattern as after the content rate has increased. On the other hand, in the case of the latter method, when one probe packet is transmitted per transmission, more probe packets are transmitted. Therefore, it is possible to compare the transmission rate and the available bandwidth from many samples. Is possible.

  FIG. 10 is a chart illustrating changes in transmission rate in the second embodiment. Hereinafter, a description will be given with reference to FIG.

  Example 2 is an example in which Embodiment 2 is further embodied. When the content rate and the transmission rate are both 2 Mbps and there is no tendency to increase the round trip delay time, the transmission rate is increased to 4 Mbps in the first embodiment, whereas the transmission rate is gradually increased in the second embodiment. . An example when the transmission rate is increased by 10% is shown in FIG. If the round-trip delay time does not tend to increase, the transmission rate is increased to 2.2 Mbps, 2.42 Mbps, and so on. If this process is executed nine times, the transmission rate exceeds 4 Mbps. Change to 4 Mbps.

  Other configurations, operations, and effects in the second embodiment are the same as those in the first embodiment.

  FIG. 11 [1] is a chart showing the relationship between the round-trip delay time and the transmission rate increase rate in the third embodiment, and FIG. 11 [2] shows the slope of the approximate line and the transmission rate decrease rate in the third embodiment. It is a chart which shows a relationship. Hereinafter, a description will be given based on FIGS. 8 and 11.

  Example 3 is an example in which Embodiment 3 is further embodied. In the third embodiment, the rate of increase of the transmission rate when the round-trip delay time does not tend to increase is determined according to the variance of the round-trip delay time, and the rate of decrease of the transmission rate when the round-trip delay time tends to increase is approximated by a straight line It is determined according to the inclination of.

The increase rate of the transmission rate is determined as shown in FIG. 11 [1]. FIG. 11 [1] shows that the transmission rate is increased by 20% if the round-trip delay time variance is below a certain threshold a, increased by 10% if greater than a and less than b, and increased by 5% if greater than b. Represents. In FIG. 11 [2], the rate of decrease of the transmission rate is changed according to the slope of the approximate straight line obtained when determining whether or not the round-trip delay time tends to increase.

  It is assumed that both the content rate and the transmission rate are 2 Mbps at the start of distribution. At this time, if it is determined in step S1411 in FIG. 8 that the round-trip delay time does not tend to increase, the process proceeds to a determination step for increasing the transmission rate (step S1423 in FIG. 8). In step S1423, the amount of increase in the transmission rate is determined based on the variance of the round trip delay time. When the variance v of the round-trip delay time is less than a, the transmission rate is increased by 20% to 2.4 Mbps. Next, when the obtained variance v of the round trip delay time is b ≧ v> a, the transmission rate is further increased by 10% to 2.64 Mbps.

  Subsequently, it is assumed that when the transmission rate is 2.64 Mbps, an increasing tendency appears in the round-trip delay time of the probe packet. If an increase tendency appears in the round trip delay time, the amount of change in the transmission rate is determined based on the slope w of the approximate line (step S1422 in FIG. 8). At this time, if w ≦ d, the transmission rate is reduced by 10% to 2.38 Mbps.

  Other configurations, operations, and effects in the third embodiment are the same as those in the first and second embodiments.

  As mentioned above, although this invention was demonstrated with reference to said each embodiment and each Example, this invention is not limited to each said embodiment and each Example. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention. In addition, the present invention includes a combination of a part or all of the configurations of the above embodiments and examples as appropriate.

  The present invention can be applied to, for example, a distribution server used for a video distribution service on the Internet, a video conference system, and the like.

  Finally, examples that can be described in the scope of the claims as a configuration of the present invention are described as additional notes below.

(Supplementary Note 1) A stream distribution device that transmits a stream to a receiving terminal via a network,
The distribution control unit of the stream distribution device includes:
Determine if there is a tendency to increase the round-trip delay time of probe packets sent periodically,
When there is a tendency to increase, it is determined that the transmission rate of the stream exceeds the available bandwidth, and when there is no tendency to increase, it is determined that the transmission rate is equal to or lower than the available bandwidth.
The stream delivery apparatus characterized by the above-mentioned.

(Supplementary note 2) The stream distribution device according to supplementary note 1, wherein
Set the transmission rate higher than the content rate,
By comparing the probe packet with a rate higher than the content rate by determining whether or not there is a tendency to increase the round-trip delay time of the probe packet,
The stream delivery apparatus characterized by the above-mentioned.

(Supplementary note 3) The stream distribution device according to supplementary note 2, wherein
Increasing the transmission rate by increasing the number of transmission packets at each transmission time of content packets,
The stream delivery apparatus characterized by the above-mentioned.

(Supplementary note 4) The stream distribution device according to supplementary note 2,
Increasing the transmission rate by shortening the transmission interval of content packets;
The stream delivery apparatus characterized by the above-mentioned.

(Additional remark 5) It is a stream delivery apparatus of Additional remark 3 or 4, Comprising:
Transmitting a probe packet when transmitting the content packet;
The stream delivery apparatus characterized by the above-mentioned.

(Supplementary note 6) The stream distribution device according to any one of supplementary notes 1 to 5,
The probe packet is an echo request packet;
The stream delivery apparatus characterized by the above-mentioned.

(Supplementary note 7) The stream distribution device according to any one of supplementary notes 1 to 6,
Reducing the transmission rate when it is determined that the transmission rate exceeds the available bandwidth,
The stream delivery apparatus characterized by the above-mentioned.

(Supplementary note 8) The stream distribution device according to supplementary notes 1 to 7,
Increasing the transmission rate when it is determined that the transmission rate is less than or equal to the available bandwidth,
The stream delivery apparatus characterized by the above-mentioned.

(Supplementary note 9) The stream distribution device according to supplementary note 7,
When it is determined that the transmission rate exceeds the available bandwidth,
If the transmission rate is higher than the content rate, the transmission rate is reduced to the same rate as the content rate,
If the transmission rate and the content rate are the same, the content rate is reduced by one step from what is currently distributed, and the transmission rate is made the same as the content rate after the reduction.
The stream delivery apparatus characterized by the above-mentioned.

(Supplementary note 10) The stream distribution device according to supplementary note 7,
When it is determined that the transmission rate exceeds the available bandwidth, the rate of decrease of the transmission rate is changed according to the amount by which the transmission rate exceeds the available bandwidth.
The stream delivery apparatus characterized by the above-mentioned.

(Supplementary note 11) The stream distribution device according to supplementary note 8,
When it is determined that the transmission rate is equal to or lower than the available bandwidth,
If the transmission rate and the content rate are the same, the transmission rate is set to be the same as the content rate that is one level higher than what is currently distributed,
If the transmission rate is the same as the content rate one level above what is currently distributed, the content rate is increased by one level;
The stream delivery apparatus characterized by the above-mentioned.

(Supplementary note 12) The stream distribution device according to supplementary note 8,
If it is determined that the transmission rate is less than or equal to the available bandwidth, the transmission rate is increased by a predetermined amount;
The stream delivery apparatus characterized by the above-mentioned.

(Supplementary note 13) The stream distribution device according to supplementary note 8,
When it is determined that the transmission rate is equal to or less than the available bandwidth, the rate of increase of the transmission rate is changed according to the degree of variation in the round-trip delay time of the probe packet.
The stream delivery apparatus characterized by the above-mentioned.

(Additional remark 14) It has the stream delivery apparatus as described in any one of additional remarks 1 thru | or 13.
A stream distribution system characterized by that.

10 Sending terminal (stream distribution device)
DESCRIPTION OF SYMBOLS 11 Distribution control part 12 Content memory | storage part 13 Content packet generation part 14 Probe packet generation part 15 Packet transmission part (transmission part)
16 Probe packet receiver (receiver)
17 Control unit 20 Receiving terminal 21 Network (Internet)
30 Computer 31 CPU
32 ROM
33 RAM
34 bus 35 I / O interface

Claims (5)

In a stream distribution device that transmits a stream to a receiving terminal via a network,
A transmitter that periodically transmits a probe packet to the receiving terminal;
A receiving unit that receives from the receiving terminal a response packet indicating that the probe packet has been received;
The round-trip delay time required from when the transmitting unit transmits the probe packet to when the receiving unit receives the response packet is calculated. If the round-trip delay time tends to increase, the transmission rate of the stream is A controller that determines that the available bandwidth is exceeded, and determines that the transmission rate is equal to or lower than the available bandwidth if the round-trip delay time does not tend to increase;
Equipped with a,
The controller is
When it is determined that the transmission rate exceeds the available bandwidth,
If the transmission rate is higher than the content rate that is the content rate of the stream, the transmission rate is reduced to the content rate,
If the content rate and the transmission rate are the same, the content rate is reduced and the transmission rate is reduced to the content rate after the reduction.
The stream delivery apparatus characterized by the above-mentioned. The stream distribution apparatus according to claim 1 ,
The control unit, when decreasing the transmission rate, changes the rate of decrease of the transmission rate according to the amount that the transmission rate exceeds the available bandwidth,
The stream delivery apparatus characterized by the above-mentioned.   In a stream distribution device that transmits a stream to a receiving terminal via a network,
  A transmitter that periodically transmits a probe packet to the receiving terminal;
  A receiving unit that receives from the receiving terminal a response packet indicating that the probe packet has been received;
  The round-trip delay time required from when the transmitting unit transmits the probe packet to when the receiving unit receives the response packet is calculated. If the round-trip delay time tends to increase, the transmission rate of the stream is A controller that determines that the available bandwidth is exceeded, and determines that the transmission rate is equal to or lower than the available bandwidth if the round-trip delay time does not tend to increase;
  With
  The controller is
  When it is determined that the transmission rate is equal to or lower than the available bandwidth,
  If the transmission rate is higher than the content rate that is the content rate of the stream, the content rate is increased and the transmission rate is adjusted to the increased content rate,
  If the content rate and the transmission rate are the same, the transmission rate is increased.
  The stream delivery apparatus characterized by the above-mentioned. The stream distribution apparatus according to claim 3 , wherein
The control unit, when increasing the transmission rate, changes the rate of increase of the transmission rate according to the degree of variation in the round-trip delay time,
The stream delivery apparatus characterized by the above-mentioned. The stream distribution device according to any one of claims 1 to 4 ,
The probe packet is an echo request packet;
The stream delivery apparatus characterized by the above-mentioned.

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