JP5375416B2 - Stream delivery apparatus, stream delivery system, stream delivery method, and stream delivery program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and automatically set a threshold of reciprocating delay time RTT used when rise of bit rate of a stream to be distributed is determined, in a stream distribution device which distributes the stream to a receiving terminal via network. <P>SOLUTION: A control history storage part stores the reciprocating delay time RTT immediately before the rise in bit rate rise trial in the past as history information. A threshold setting part sets a threshold range of a threshold RTTth by RTT when distribution is possible at the bit rate after the rise and RTT when the distribution is impossible at the bit rate after the rise, based on the history information of the RTT stored in the control history storage part. Then, the threshold RTTth is approached from a lower limit value to an upper limit value of the threshold range with elapse of time. A distribution rate determination part raises the bit rate when the measured reciprocating delay time RTT (RTTm) is less than the threshold RTTth set by the threshold setting part. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a stream distribution device, a stream distribution system, a stream distribution method, and a stream distribution program, and in particular, a stream distribution device, a stream distribution system, and a stream distribution method that divide a stream into packets in a network where communication quality is not guaranteed. And a stream distribution program.

  Currently, there is a service for distributing stream data such as moving image content (also simply referred to as “stream”) via a network. Patent Document 1 describes an example of a technique for controlling a bit rate in accordance with a network state with a receiving terminal in a stream distribution apparatus that distributes this stream. The stream distribution device described in Patent Document 1 operates by receiving a report of packet loss and round trip time (RTT) from a receiving terminal. When a packet loss is reported, the network state is changed. The bit rate to be delivered is lowered by judging that it has deteriorated, and when the round-trip delay time RTT falls below a set threshold value, the bit rate of the stream to be delivered is judged to be judged to have improved.

  Also, a network monitoring device described in Patent Document 2 is disclosed. In this network monitoring apparatus, when the response time measurement unit measures the delay time, stores the history of the delay time, calculates / updates the threshold based on the average value of the delay time, and exceeds the threshold (See paragraphs 0035 to 0042). However, this network monitoring device is intended to monitor the presence or absence of a failure in the IP network, and is not related to an operation for increasing the bit rate of a stream distributed from the stream distribution device.

JP 2008-099261 A JP 2006-165629 A

  The problem with the stream distribution device described in Patent Document 1 described above is that it is necessary to set in advance a threshold for the round-trip delay time RTT for increasing the bit rate of data transfer. The appropriate threshold for increasing the bit rate depends on the bit rate currently being distributed and the bit rate to be increased. That is, when the bit rate is increased from 1 Mbps to 2 Mbps, the threshold of the appropriate round-trip delay time RTT should be different in many cases when it is increased from 2 Mbps to 4 Mbps and from 4 Mbps to 8 Mbps.

  In addition, an appropriate threshold value should be different for each receiving terminal. That is, even if the threshold is for increasing from 1 Mbps to 2 Mbps, it is generally considered that the appropriate threshold is different if the route to the receiving terminal is different. For this reason, setting the threshold values of the round-trip delay times RTT for all bit rates in advance for all receiving terminals requires a huge amount of time and is not practical.

  Further, in the stream distribution device described in Patent Document 1, there is no idea of changing the threshold value such as the round-trip delay time RTT dynamically (self positively) and attempting to increase the bit rate.

  The main object of the present invention is to use a round-trip delay time RTT threshold value for increasing the bit rate in the stream distribution device by using the history information of the round-trip delay time RTT measured at the past bit rate increase trial. It is intended to enable easy and automatic setting, and furthermore, the threshold value of the round-trip delay time RTT is dynamically changed to prevent an inadvertent increase in the bit rate and stagnation at a low bit rate. There is.

The stream distribution device of the present invention stores the round-trip delay time with the receiving terminal when increasing the bit rate of the stream distributed to the receiving terminal as history information for each receiving terminal and bit rate, and this history information A stream distribution apparatus for setting a round-trip delay time threshold when raising the bit rate based on the round-trip delay time with the receiving terminal when attempting to increase the bit rate of the stream delivered to the receiving terminal. Based on the history information of the round trip delay time stored in the control history storage unit and the control history storage unit for storing as history information in association with the combination of the bit rate before and after the increase for each receiving terminal The round-trip delay time between the threshold setting unit for setting the round-trip delay time threshold for increasing the bit rate and the receiving terminal is lower than the threshold. When Tsu, characterized by having a a delivery rate determination unit determines to increase the bit rate of the stream to be distributed to the receiving terminal.

In the stream distribution apparatus of the present invention, the round-trip delay time RTT when attempting to increase the past bit rate is stored as history information for each receiving terminal and bit rate. Then, for example, the threshold value RTTth is set based on the round trip delay time RTT when delivery is possible at the increased bit rate and the round trip delay time RTT when delivery is impossible at the increased bit rate. To do.
As a result, an appropriate threshold value RTTth corresponding to the receiving terminal and the bit rate can be set easily and automatically based on the history information of the round-trip delay time RTT measured at the time of past bit rate increase attempts.

It is a block diagram which shows the structure of the stream delivery system concerning the 1st Embodiment of this invention. 3 is a diagram illustrating a configuration example of a control history storage unit 15. FIG. It is a flowchart which shows operation | movement of 1st Embodiment. It is a graph which shows the 1st setting method of threshold value RTTth of round-trip delay time RTT. It is a graph which shows the 2nd setting method of threshold value RTTth of round-trip delay time RTT. It is a block diagram which shows the structure of the stream delivery system concerning the 2nd Embodiment of this invention. It is a flowchart which shows operation | movement of 2nd Embodiment. It is a 1st sequence diagram which shows the network state estimation method in 2nd Embodiment. It is a 2nd sequence diagram which shows the network state estimation method in 2nd Embodiment. 3 is a diagram illustrating a configuration of a control history storage unit 15 of the stream distribution device 1 in Embodiment 1. FIG. It is a figure which shows the example of threshold value RTTth of the round-trip delay time RTT in Example 1. FIG. It is a figure which shows the example of the report from the receiving terminal 2 in Example 1 to the stream delivery apparatus 1. FIG. It is a figure which shows the example of the raise possible / impossible storage table in the control history memory | storage part 15 of the stream delivery apparatus 1 in Example 1. FIG. It is a figure which shows the example of threshold value RTTth of the round-trip delay time RTT in Example 1. FIG. It is a figure which shows the example of the raise possible / impossible storage table in the control history memory | storage part 15 of the stream delivery apparatus 1 in Example 1. FIG. It is a sequence diagram which shows the network state estimation method in Example 2.

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

[First Embodiment]
FIG. 1 is a diagram showing a configuration of a stream distribution system according to the first embodiment of the present invention. As shown in FIG. 1, the stream distribution system of the present invention includes a stream distribution device 1 that distributes a stream (content such as a moving image) through a network and a receiving terminal 2 that receives and reproduces the stream.

  The stream distribution device 1 and the receiving terminal 2 are connected by a network such as the Internet where a usable bandwidth is not guaranteed. In addition, the stream distribution device 1 may be connected to a plurality of receiving terminals 2.

  The stream distribution device 1 includes a stream transmission unit 11 that transmits a stream to the reception terminal 2, a content storage unit 12 that stores content to be distributed as a stream to the reception terminal 2, and a report reception unit that receives a report from the reception terminal 2. 13. A distribution rate determination unit 14 for determining (determining) a bit rate of content to be distributed to the receiving terminal 2, a control history storage unit 15 for storing past control history information, and a bit rate increase based on the control history information A threshold value setting unit 16 for setting a threshold value RTTth of a round-trip delay time RTT for performing the above and a distribution management unit 17 for managing the start and end of stream distribution.

  First, when receiving a distribution request message from the receiving terminal 2, the distribution management unit 17 acquires a list of bit rates that can be distributed from the content storage unit 12, and distributes the distribution content to the distribution rate determination unit 14. And a list of bit rates and instructing the start of distribution.

  In the present embodiment, hereinafter, description will be made assuming that the receiving terminal 2 is one. When there are a plurality of receiving terminals 2, identifiers of the receiving terminals are added to the communication contents between the processing units indicated by reference numerals 11 to 17, but they are omitted here.

  The stream transmission unit 11 extracts the content of the bit rate instructed from the distribution rate determination unit 14 from the content storage unit 12 and transmits the content to the reception terminal 2. The content transmission from the stream distribution device 1 to the receiving terminal 2 uses a connectionless protocol as a transport protocol, and congestion control, arrival confirmation and retransmission are not performed by the transport protocol. Also, when the stream transmission unit 11 is instructed to change the bit rate from the distribution rate determination unit 14 during content distribution, the stream transmission unit 11 switches the bit rate instantaneously so that there is no interruption in reproduction at the receiving terminal 2.

  In the case of video content, it may be compressed using inter-frame prediction such as MPEG-2 or MPEG-4. The content compressed using inter-frame prediction is composed of an I frame that can be decoded independently, and a P frame and a B frame that are decoded using information of preceding and succeeding frames. At this time, if the bit rate is switched immediately before the P frame or the B frame, the receiving terminal 2 cannot correctly decode because there is no previous frame. Therefore, in the case of content compressed using inter-frame prediction, switching is performed immediately before the I frame.

  The content storage unit 12 is a processing unit that stores content data (stream data) to be transmitted from the stream transmission unit 11 to the reception terminal 2, and each content is encoded and held in advance at a plurality of bit rates. Alternatively, it may be a storage unit that temporarily stores the content data transcoded to the requested bit rate from the stream transmission unit 11.

  The report receiving unit 13 receives the report information on the reception state transmitted by the receiving terminal 2 and notifies the distribution rate determining unit 14 of the presence / absence of packet loss and the round trip delay time RTT. At this time, when the packet loss rate is reported from the receiving terminal 2, the packet loss rate may be notified to the distribution rate determination unit 14.

  When the distribution management unit 17 gives an instruction to start content distribution, the distribution rate determination unit 14 determines an initial distribution rate and instructs the stream transmission unit 11 to start transmission. The initial delivery rate is a method of selecting the lowest bit rate among the contents to be delivered, and when the stream delivery device 1 knows the type and line type of the receiving terminal 2, use those information. Any method may be used, such as a method for determining the available bandwidth before the start of distribution, or a method for determining based on the estimated value.

  Further, the distribution rate determination unit 14 receives notification of the presence / absence of packet loss and the round trip delay time RTT from the report reception unit 13 during content distribution, and sets the bit rate of the content to be distributed to 1 when packet loss occurs. Decide that the level will be lowered, and instruct the stream transmitter. When the packet loss rate is notified from the report receiving unit 13, the bit rate may be decreased by one step if the packet loss rate exceeds a specified value. If no packet loss has occurred, the threshold value setting unit 16 receives the round-trip delay time RTTth for increasing the bit rate, and the round-trip delay time RTT notified from the report receiving unit 13 (the latest measured And the round-trip delay time RTTm).

  As a result, if “RTTm ≧ RTTth”, it is decided not to change the bit rate, and the stream transmission unit 11 is not instructed to change the bit rate. On the other hand, if “RTTm <RTTth”, it is determined that the bit rate to be distributed is increased by one step, and the stream transmission unit 11 is instructed.

  When the increase in the bit rate is determined, the distribution rate determination unit 14 stores the round-trip delay time RTTm, determines whether or not the increased bit rate can be distributed without packet loss, and the control history storage unit 15 (update method will be described later), and updates the history information in the control history storage unit 15 to the threshold setting unit 16.

  Whether or not delivery can be performed without packet loss at the increased bit rate is determined by whether or not the occurrence of packet loss is notified by a report from the receiving terminal 2 immediately after the bit rate is increased. Further, it may be determined not only immediately after the bit rate is increased but also whether or not the occurrence of packet loss is notified by a report of the specified number of times and the specified time after the bit rate is increased. When not only the presence / absence of packet loss but also the packet loss rate is notified from the report receiving unit 13, it may be determined based on whether or not the packet loss rate exceeds a specified value.

  The control history storage unit 15 is a processing unit that stores information on the control history in the distribution rate determination unit 14. FIG. 2 is a diagram illustrating a configuration example of the control history storage unit 15.

  As shown in FIG. 2, the control history storage unit 15 includes an ascending / descending storage table 151 (151-1, 151-2,...) For each receiving terminal (terminal 1, terminal 2, terminal 3,...). Each ascending / decreasing storage table 151 is composed of a set of a bit rate before ascending 1511, a bit rate after ascending 1512, an ascending RTT 1513, and an ascending RTT 1514.

  The ascendable RTT 1513 and the ascendable RTT 1514 are areas for storing the round-trip delay time RTT immediately before the bit rate 1511 before ascending to the bit rate 1512 after ascending. Stored in the ascending RTT 1513 is a round-trip delay time RTT when the bit rate 1511 before ascending can be increased from the bit rate 1511 before ascending to the bit rate 1512 after ascending. The round-trip delay time RTT when it is impossible to increase from the rate 1511 to the bit rate 1512 after increasing.

  2, when the round-trip delay time RTT is “Rok1_1, Rok1_2,...” During distribution at the bit rate BR1 [bps], the bit rate BR2 [bps] When the round-trip delay time RTT is “Rng1_1, Rng1_2,...”, It indicates that the distribution was not possible at the bit rate BR2 [bps].

  If the terminal that has been delivered for the first time has not been tried to increase the bit rate so far, a sufficiently small value is stored in the RTT 1513 that can be increased as an initial value and sufficient for the RTT 1514 that cannot be increased. Assume that a large value is stored.

  The delivery rate determination unit 14 searches for and records a record in which the bit rate before the increase and the bit rate after the increase match from the increase / decrease storage table 151 of the control history storage unit 15 after determining whether the increased bit rate can be distributed. The round-trip delay time RTTm is stored in the ascending RTT or the ascending RTT.

  The threshold setting unit 16 calculates the threshold RTTth of the round-trip delay time RTT for increasing the bit rate based on the history information stored in the control history storage unit 15 (the increase / decrease storage table 151), and notifies the distribution rate determination unit 14 To do. When the threshold setting unit 16 is notified of the update of the control history storage unit 15 from the distribution rate determination unit 14, the threshold setting unit 16 extracts the contents of the increase / decrease storage table 151 from the control history storage unit 15 and increases the bit rate by one level. Find the upper and lower threshold values.

The lower limit RTTlb of the threshold is the maximum value of the round trip delay time RTT stored in the ascending RTT 1513,
max {Rok1_1, Rok1_2, ..., Rok1_n},
The average value (Rok1_1 + Rok1_2 +... + Rok1_n) / n is determined.

Further, the upper limit RTTub of the threshold is the minimum value of the round-trip delay time RTT stored in the RTT 1514 that cannot be increased,
min {Rng1_1, Rng1_2,..., Rng1_m},
The average value (Rng1_1 + Rng1_2 +... + Rng1_m) / m is determined.

  Next, the threshold value RTTth is determined in the range of [lower limit RTTlb, upper limit RTTub]. As the threshold value RTTth, a method of approaching the lower limit RTTlb from the lower limit RTTlb to the upper limit RTTub as time passes. This is to reduce the number of trials for increasing the bit rate and to prevent the bit rate from becoming stagnant.

  If the bit rate is raised even though it cannot be raised, the reproduction at the receiving terminal 2 is interrupted or disturbed. Therefore, it is desirable to reduce the bit rate increase as much as possible. On the other hand, if the number of trials is reduced, the bit rate may be increased, but it may remain stagnant at a low bit rate without being increased. By bringing the threshold value RTTth closer to the upper limit RTTub from the lower limit RTTlb, initially, the round-trip delay time RTT is small, the network state is very good, and the bit rate is increased only when there is a high possibility of delivery even if it is increased. As the time elapses, an increase in the bit rate is likely to occur, and a stagnation at a low bit rate can be prevented.

Specifically, as shown in FIG. 4, the initial value is “RTTth = RTTlb”, and the threshold value RTTth is set between the lower limit RTTlb and the upper limit RTTub.
RTTth = RTTth + α (α: increase in one treatment),
There is a way to change.

Or, as shown in FIG. 5, RTTth = RTTth + (β ^ i (RTTub−RTTlb)) (β: constant satisfying 0 <β <1, i: number of changes),
There are ways to change.

  The intervals for changing the threshold, α and β, are determined in advance. Further, the threshold value may be changed by a method other than that described here.

  The reception terminal 2 includes a stream reception unit 21 that receives a stream from the stream distribution device 1 through a network, and a report transmission unit 22 that notifies the stream distribution device 1 of a reception state.

  The stream reception unit 21 is connected to the report transmission unit 22, receives a stream from the stream distribution device 1, measures a reception state such as packet loss, and notifies the report transmission unit 22.

  The report transmission unit 22 periodically feeds back a report including the reception state information notified from the stream reception unit 21 to the stream distribution device 1. In the above-described example, the round-trip delay time RTT obtained from the latest report is compared with the threshold value RTTth. However, fluctuations may occur in the round trip delay time RTT due to the occurrence of cross traffic. In order to absorb the influence of this fluctuation, a moving average of the round-trip delay time RTT may be used.

That is, when the latest i round-trip delay times RTT among the reports received from the receiving terminal 2 are R1, R2, R3,.
RTTm = (a1 · R1 + a2 · R2 +... + Ai · Ri) / i (a1,..., Ai: weighting coefficient).

Next, the overall operation of the present embodiment will be described in detail with reference to the flowchart of FIG.
First, at the start of stream distribution, the distribution management unit 17 instructs the distribution rate determination unit 14 to start distribution, and the distribution rate determination unit 14 determines an initial distribution rate (initial bit rate) (step S01).

  Next, a threshold value for changing from the bit rate currently being distributed to a bit rate one step higher is determined. The distribution rate determining unit 14 notifies the threshold setting unit 16 of the initial distribution rate and the bit rate one level higher, and the threshold setting unit 16 retrieves the corresponding record from the ascending / decreasing storage table 151 of the control history storage unit 15.

  The threshold setting unit 16 determines the upper limit RTTub and the lower limit RTTlb of the threshold based on the extracted record (step S02), determines the threshold RTTth from the range of [RTTlb, RTTub] (step S03), and the distribution rate. The threshold value RTTth is notified at the time of a request from the determination unit 14.

  As described above, the threshold value RTTth approaches the upper limit RTTub from the lower limit RTTlb with time (see FIGS. 4 and 5). Therefore, the threshold setting unit 16 changes the threshold RTTth as necessary based on the elapsed time since the previous threshold RTTth was changed and the number of comparisons with the measured round-trip delay time RTTm (step S03).

  Hereinafter, the bit rate of the currently distributed content (stream) is BR1, the bit rate one step higher than BR1, the bit rate one step higher than BR2, the bit rate one step higher than BR2, and the bit rate one step lower than BR3 and BR1 Is represented as BR0.

  When receiving the reception status report from the receiving terminal 2, the report receiving unit 13 notifies the distribution rate determining unit 14 of the presence or absence of packet loss and the round trip delay time RTT (step S04). The distribution rate determination unit 14 first determines whether or not there is a packet loss (step S05). If packet loss has occurred (step S05: Yes), the delivery rate is lowered by one step from BR1 to BR0 (step S06), and the process returns to step S02.

  If no packet loss has occurred (step S05: No), the round-trip delay time RTTm notified from the report receiving unit 13 is compared with the threshold value RTTth notified from the threshold setting unit 16 (step S07). When the round-trip delay time RTTm is not less than the threshold value RTTth (step S07: No), the bit rate is not changed, and the process returns to step S03.

  When the round-trip delay time RTTm falls below the threshold value RTTth (step S07: Yes), the distribution rate determination unit 14 determines to increase the distribution rate by one step from the bit rate BR1 to BR2, and the stream transmission unit 11 The distribution rate is increased by one level (step S08).

  After increasing the distribution rate, the distribution rate determining unit 14 determines whether or not distribution is possible at the increased rate (BR2) (step S09). As described above, this determination is made based on whether or not packet loss has occurred in the report after changing the distribution rate.

  When delivery is possible (step S09: Yes), the round-trip delay time RTTm measured immediately before the rise is the bit rate before rise in the rise enable / disable storage table 151 of the control history storage unit 15 is BR1 and the bit rate after rise is BR2. The entry is added to the ascending RTT 1513 (step S12), and the process returns to step S02.

  On the other hand, when distribution cannot be performed at the bit rate BR2 (step S09: No), the round-trip delay time RTTm is added to the RTT 1514 that cannot be increased (step S10), the distribution rate is returned to BR1 (step S11), and the process returns to step S02. .

  As described above, in the stream distribution device of the present invention, the round-trip delay time RTT at the time of past bit rate increase trials is stored as history information for each receiving terminal and can be distributed at the increased bit rate. If the round-trip delay time RTT is used to set the lower limit value of the threshold, and if the bit rate after the increase cannot be delivered, the round-trip delay time RTT is used to set the upper limit value of the threshold value, and the time elapses At the same time, the threshold value is made closer to the upper limit value from the lower limit value.

  Thereby, the threshold value according to the receiving terminal and the bit rate can be set easily and automatically from the history information of the round trip delay time RTT measured at the time of the trial of increasing the past bit rate. In addition, it is possible to prevent an inadvertent increase in the bit rate and a stagnation of trials for increasing the bit rate. That is, if the threshold value is set large, the bit rate is increased even when the network condition is not so good, so that the video cannot be distributed at the increased bit rate, and the video is often disturbed or interrupted. On the other hand, if the threshold value is set to be small, even if the bit rate can be increased, it does not increase, and low-quality content continues to be delivered to the receiving terminal. In the present invention, since the threshold value is gradually approached from the lower limit value to the upper limit value within the threshold setting range as time elapses, the bit rate is increased only when there is a high possibility that the bit rate can be distributed after the increase. The stream (image etc.) to be transmitted can be prevented from being disturbed or interrupted, and the bit rate can be easily increased over time, thereby preventing stagnation.

  Note that the stream distribution device 1 and the receiving terminal 2 shown in FIG. 1 have a computer system including a CPU therein. A series of processing steps relating to the above-described processing is stored in a computer-readable recording medium in the form of a program, and the above-described processing is performed by the computer reading and executing this program. In addition, the stream distribution device 1 is configured by a server device or the like, and an input device, a display device, or the like (none of them are displayed) is connected to the stream distribution device 1 as peripheral devices. Here, the input device refers to an input device such as a keyboard and a mouse. The display device refers to a CRT (Cathode Ray Tube), a liquid crystal display device, or the like.

Although the first embodiment of the present invention has been described above, the stream distribution apparatus of the present invention shown in FIG. 1 is connected to the reception terminal 2 when attempting to increase the bit rate of the stream distributed to the reception terminal 2. And the round trip delay time RTT stored in the control history storage unit 15 for each receiving terminal 2 and stored as history information in association with the combination of the bit rate before and after the rise. When the round-trip delay time RTT between the threshold value setting unit 16 for setting the round-trip delay time RTT threshold RTTth for increasing the bit rate based on the history information of the time RTT and the receiving terminal 2 falls below the threshold RTTth And a distribution rate determining unit 14 for determining that the bit rate of the stream to be distributed to the receiving terminal 2 is increased.
As a result, the threshold value RTTth of the round-trip delay time RTT for increasing the bit rate is determined based on the history information of the round-trip delay time RTT measured in the past trials for increasing the bit rate for each receiving terminal 2 and bit rate. Easy and automatic setting.

In addition, the control history storage unit 15 cannot distribute the round-trip delay time RTT with the receiving terminal 2 immediately before the bit rate is increased, and the round-trip delay time that can be distributed after the bit rate is increased, and cannot be distributed after the bit rate is increased. Are stored in the ascending / decreasing storage table 151 (FIG. 2).
As a result, when the bit rate is increased, it is possible to classify and store the round-trip delay time RTT information when the delivery is possible and the round-trip delay time RTT when the delivery is impossible, Based on this history information, the threshold value RTTth can be easily set.

Further, the threshold setting unit 16 is based on the round-trip delay time RTT that can be distributed after the bit rate increase and the round-trip delay time RTT that cannot be distributed after the bit rate increase stored in the control history storage unit 15. A threshold setting range is determined, and a threshold value RTTth is set from within the threshold setting range.
Thus, the threshold setting range is determined based on the history information of the round-trip delay time RTT when delivery is possible and the history information of the round-trip delay time RTT when delivery is impossible. The threshold value RTTth can be set from within.

Further, the threshold setting unit 16 changes the threshold RTTth within the threshold setting range. In this case, the threshold setting unit 16 changes the setting so that the threshold RTTth approaches the upper limit value from the lower limit value as time passes.
As a result, the threshold of the round-trip delay time RTT can be dynamically changed to actively try to increase the bit rate, preventing an inadvertent increase in the bit rate and stagnation of the bit rate increase attempt. it can.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to the drawings.

  FIG. 6 is a diagram showing a configuration of a stream distribution system according to the second embodiment of the present invention. As shown in FIG. 6, the stream distribution device 1A according to the second embodiment of the present invention is deleted by the report receiving unit 13 as compared with the stream distribution device 1 of the first embodiment shown in FIG. However, the difference is that a network state estimation unit 18 that estimates a network state from information of a management session with the receiving terminal 2A is added. Other configurations are the same as those of the stream distribution device 1 and the reception terminal 1 shown in FIG. For this reason, the same code | symbol is attached | subjected to the same component.

  In addition, the receiving terminal 2A, compared with the receiving terminal 1 of the first embodiment shown in FIG. 1, has the report transmission unit 22 deleted, and exchanges session information with the stream distribution device 1A. The difference is that the part 23 is added.

  In the second embodiment, the distribution management unit 17 of the stream distribution device 1A and the management information communication unit 23 of the receiving terminal 2A are connected to a management session using a connection type protocol. The connection-type protocol has an acknowledgment function, and when the receiving side receives data transmitted from the transmitting side, an acknowledgment is transmitted from the receiving side to the transmitting side.

  In addition, when there is a negative response meaning non-delivery of data from the receiving side, or when a confirmation response cannot be received even after a predetermined time has elapsed after transmission, the data is retransmitted. If the confirmation response cannot be received even after a predetermined number of retransmissions, the upper layer is notified that the transmission has not been completed.

  In this management session, a distribution request is made from the reception terminal 2A to the stream distribution apparatus 1A before the distribution is started, and is used for alive monitoring from the stream distribution apparatus 1A to the reception terminal 2A during distribution. Life / death monitoring is performed by transmitting life / death monitoring data (for example, life / death monitoring packet) from the stream distribution device 1A to the receiving terminal 2A at a predetermined interval. When the alive monitoring data reaches the receiving terminal 2A, a confirmation response is transmitted from the receiving terminal 2A to the stream distribution device 1A, and the stream distribution device 1A that has received the confirmation response maintains the connection with the receiving terminal 2A. Make sure.

  If the connection with the terminal cannot be confirmed for a predetermined number of times, the stream distribution device 1A determines that the receiving terminal 2A has been disconnected and stops the distribution.

  The network state estimation unit 18 of the stream distribution device 1A monitors this life / death monitoring communication and estimates the network state. The network state estimation unit 18 stores the time when the life / death monitoring data is transmitted from the distribution management unit 17 to the receiving terminal 2A, and calculates the difference from the time when the confirmation response is received as the round-trip delay time RTT. Further, when retransmission occurs in the connection type protocol, it is determined that a packet loss has occurred. The network state estimation unit 18 notifies the distribution rate determination unit 14 of this result, and the distribution rate determination unit 14 operates in the same manner as in the first embodiment (for example, when packet loss occurs, Decrease the bit rate of the stream to be delivered by one step).

  Next, the operation of the second embodiment will be described with reference to the flowchart of FIG. In the second embodiment, step S04 in which the report receiving unit 13 receives the report from the receiving terminal 2 in the flowchart shown in FIG. 3 is replaced with step S13 in which the network state estimating unit 18 estimates the network state. Different from the first embodiment. Other steps are the same as those in the flowchart shown in FIG. For this reason, the same processing contents are denoted by the same reference numerals, and redundant description is omitted.

  The round-trip delay time RTT and the packet loss estimation method in the network state estimation unit 18 will be described with reference to the sequence diagrams of FIGS.

  FIG. 8 is a sequence diagram when packet loss does not occur. With reference to the sequence diagram shown in FIG. 8, first, the distribution management unit 17 of the stream distribution device 1A transmits the data for alive monitoring to the receiving terminal 2A (step S101). Then, the network state estimation unit 18 stores the transmission time Tsend (Step S102).

  When the management information communication unit 23 of the receiving terminal 2A receives the alive monitoring data from the stream distribution device 1A (step S103), it transmits a confirmation response to the stream distribution device 1A (step S104).

  Assuming that the time when the confirmation response arrives at the stream distribution device 1A is Trcv, the network state estimation unit 18 calculates “round trip delay time RTTm = Trcv−Tsend”, and the distribution rate together with the fact that no packet loss has occurred. Notify the determination unit 14.

  FIG. 9 is a sequence diagram when packet loss occurs. With reference to the sequence diagram shown in FIG. 9, first, the life management data of the stream distribution device 1A is transmitted to the receiving terminal 2A (step S201). Then, the network state estimation unit 18 stores the transmission time Tsend (step S202).

  The delivery management unit 17 of the stream delivery device 1A retransmits the life / death monitoring data by the connection-type protocol when the confirmation response cannot be received from the receiving terminal 2A even after a lapse of a predetermined time after sending the life / death monitoring data. (Step S203). The network state estimation unit 18 stores that packet loss has occurred when retransmission is performed, and changes the transmission time Tsend to the transmission time of retransmission data (step S204).

  When the management information communication unit 23 of the receiving terminal 2A receives the alive monitoring data from the stream distribution device 1A (step S205), it transmits a response confirmation (step S206). The network state estimation unit 18 of the stream distribution device 1A that has received this response confirmation calculates “round trip delay time RTTm = Trcv−Tsend”, and notifies the distribution rate determination unit 14 of the occurrence of a packet loss.

  As described above, in the second embodiment, the network state estimation unit 18 of the stream distribution device 1A performs the round trip delay time RTT and the packet from the alive monitoring communication between the stream distribution device 1A and the reception terminal 2A. By estimating the presence / absence of a loss, even in the receiving terminal 2A that does not report the reception state, the threshold corresponding to the receiving terminal and the bit rate can be easily determined from the control history information of the round-trip delay time RTT at the past bit rate trial. Can be set automatically. Further, as in the first embodiment, it is possible to prevent an inadvertent increase in the bit rate and a stagnation in trials for increasing the bit rate.

  Note that the stream distribution device 1A and the reception terminal 1A shown in FIG. 6 have a computer system including a CPU therein. A series of processing steps relating to the above-described processing is stored in a computer-readable recording medium in the form of a program, and the above-described processing is performed by the computer reading and executing this program. Further, it is assumed that the stream distribution device 1A is configured by a server device or the like, and an input device, a display device, and the like (none of them are displayed) are connected to the stream distribution device 1A as peripheral devices. Here, the input device refers to an input device such as a keyboard and a mouse. The display device refers to a CRT (Cathode Ray Tube), a liquid crystal display device, or the like.

  Next, the operation of the stream distribution system of the present invention will be described using a specific embodiment. Example 1 shows a specific example of the stream distribution system according to the first embodiment shown in FIG. In the first embodiment, it is assumed that the stream distribution device 1 and the receiving terminal 2 are connected via the Internet.

  Content distribution from the stream distribution device 1 to the receiving terminal 2 is performed by RTP (Real-time Transport Protocol), and transmission of a report from the receiving terminal 2 to the stream distribution device 1 is performed by RTCP (RTP Control Protocol). For both RTP and RTCP, UDP (User Datagram Protocol) is used as the transport protocol.

  The stream distribution device 1 is configured by a server device. The stream transmission unit 11 is realized by a combination of a program executed by the CPU of the server device (a program in which a series of processes in the stream transmission unit is described) and a network interface card (hereinafter abbreviated as NIC). The stream transmission unit 11 divides the content data extracted from the content storage unit 12 into an appropriate size, and generates a packet in which an RTP header, a UDP header, an IP header, and an Ethernet (registered trademark) header are added to each divided data. And transmitted to the receiving terminal 2. In addition, a message “RTCP SR (Sender Report)” is periodically transmitted to the receiving terminal 2. In the first embodiment, the transmission interval of the message “RTCP SR” is 5 seconds.

  The content storage unit 12 is a storage device such as a magnetic disk device built in the server device, and stores each video content encoded at a plurality of bit rates. It is assumed that the content storage unit 12 in the first embodiment stores three types of content A, B, and C. Content A and B store bit rates of 1 Mbps, 2 Mbps, 4 Mbps, and 8 Mbps, and content C stores bit rates of 1 Mbps, 2 Mbps, 4 Mbps, 6 Mbps, and 8 Mbps. Content A, B and content C differ in that content C stores 6 Mbps. The content stored in the content storage unit 12 may be an image or a sound.

  The report receiving unit 13 is realized by a combination of a program executed by the CPU (a program in which a series of processing steps in the report receiving unit are described) and the NIC in the same manner as the stream transmitting unit 11 and a message “RTCP RR” from the terminal. (Receiver Report) "is calculated, the packet loss rate and the round-trip delay time RTT are calculated and notified to the distribution rate determining unit 14.

  The packet loss rate can be obtained from the “fraction lost” field or “cumulative number of packets lost” field of the message “RTCP RR”. The round trip delay time RTT can be obtained from the “LSR” field and the “DLSR” field of the message “RTCP RR”.

  The function of the distribution rate determination unit 14 is realized by the CPU reading and executing a program describing a series of processing steps. The control history storage unit 15 is a part of the main memory of the server device. The functions of the threshold setting unit 16 and the distribution management unit 17 are realized when the CPU reads and executes a program describing a series of processing steps.

  When the content storage unit 12 stores the contents A, B, and C, the ascending / descending storage table 151 of the control history storage unit 15 is as shown in FIG. “Entry with bit rate before increase of 1 Mbps and bit rate after increase of 2 Mbps” and “entry of bit rate before increase of 2 Mbps and bit rate after increase of 4 Mbps” are used for all of contents A, B, and C .

  The “entry with the bit rate before increase of 4 Mbps and the bit rate after increase of 6 Mbps” and the “entry of bit rate before increase of 6 Mbps and the bit rate after increase of 8 Mbps” are used only for the content C, and the “bit rate before increase” "Entries with an increase of 4 Mbps and a bit rate of 8 Mbps" are used for the contents A and B. In the case of a terminal that has never been delivered, an initial value is stored in the ascending RTT 1513 and the ascending RTT 1514.

  In the first embodiment, the initial value of the ascending RTT 1513 is set to 0 [s], and the initial value of the ascending RTT 1514 is set to 1 [s]. The receiving terminal 2 is a set top box (STB) for IPTV (Internet Protocol TeleVision). The stream reception unit 21 and the report transmission unit 22 are realized by a combination of a program executed by the CPU (a program describing a series of processing steps in the stream transmission unit and the report transmission unit) and the NIC.

  The stream reception unit 21 in the reception terminal 2 receives the packet distributed from the stream distribution device 1, decodes the RTP, UDP, IP, and Ethernet (registered trademark) headers, and decodes the content (not shown). Forward to.

  At the time of RTP decoding in the stream reception unit 21, various data necessary for transmission of the message “RTCP RR” are collected and notified to the report transmission unit 22. The message “RTCP SR” transmitted from the stream distribution device 1 is received and transferred to the report transmission unit 22.

  The report transmission unit 22 transmits the message “RTCP RR” to the stream distribution device 1 based on the information obtained from the stream reception unit 21. In the first embodiment, the transmission interval of the message “RTCP RR” is 1 second. The receiving terminal 2 may be not only a set top box (STB) but also a PC (Personal Computer), a PDA (Personal Digital Assistant), a mobile phone terminal, or the like.

  Next, in the first embodiment, an operation when the stream distribution device 1 receives a content A distribution request from the receiving terminal 2 will be described with reference to the flowchart of FIG.

  The distribution management unit 17 refers to the content storage unit 12, notifies the distribution rate determination unit 14 that the content A can be distributed at 1 Mbps, 2 Mbps, 4 Mbps, and 8 Mbps, and instructs the start of distribution. The distribution rate determination unit 14 determines a bit rate (distribution rate) at the start of distribution from among the distributable bit rates (step S01). Here, a method of starting distribution at the lowest possible bit rate is adopted, and distribution is started at 1 Mbps.

  Next, the delivery rate determination unit 14 determines a threshold value for increasing the bit rate. Since the bit rate on one stage of 1 Mbps is 2 Mbps, an entry is extracted from the increase / decrease storage table 151 of the control history storage unit 15 so that the bit rate before increase 1511 is 1 Mbps and the bit rate after increase 1512 is 2 Mbps.

  Next, a threshold lower limit RTTlb is determined from the ascending RTT 1513 of the extracted entry, and a threshold upper limit RTTub is determined from the ascending RTT 1514 (step S02). In the first embodiment, assuming that the maximum value of the ascending RTT 1513 is the lower limit RTTlb and the minimum value of the ascending RTT 1514 is the upper limit RTTub, “RTTlb = 0 [s], RTTub = 1 [s]”.

Next, a threshold for increasing the bit rate is determined from the lower limit RTTlb and the upper limit RTTub (step S03). In the first embodiment, the initial value is “RTTth = RTTlb”, and the threshold value RTTth is between the lower limit RTTlb and the upper limit RTTub.
RTTth = RTTth + α (α: increase in one treatment),
And the threshold value RTTth is updated every time a report is received twice, so that “α = (RTTub−RTTlb) / 10”. At this time, the threshold value RTTth changes as shown in FIG.

  On the other hand, when the report shown in FIG. 12 is transmitted from the terminal, the threshold value RTTth is 0.2 and the round trip delay time RTTm is 0.18 at the fifth time (RTTm <RTTth), and the bit rate is increased from 1 Mbps to 2 Mbps. (Step S08). Next, it is determined whether or not distribution is possible at an increased bit rate of 2 Mbps (step S09). In the first embodiment, it is determined that delivery is not possible when a packet loss is reported in a report immediately after the bit rate increases. Here, it is assumed that a packet loss is reported in the report immediately after the increase (step S09: No). At this time, 0.18 is added to the ascendable RTT 1514 in the ascendability table 151 (FIG. 13) (step S10), the bit rate is reduced to 1 Mbps (step S11), and the process returns to step S02.

  In step S02, an upper limit RTTub and a lower limit RTTlb are determined for increasing the bit rate to 2 Mbps again. “RTTlb = 0, RTTub = 0.18”, and the threshold value RTTth is as shown in FIG. After the bit rate is changed to 1 Mbps, if the round trip delay time RTTm becomes 0.030 [s] in the fifth iteration and falls below the threshold value RTTth (0.036 [s]), the bit rate is increased again to 2 Mbps and 2 Mbps. To determine whether it can be distributed. If it is reported in the first report that no packet loss has occurred after starting distribution at 2 Mbps, it is determined that distribution is possible at 2 Mbps, and 0.030 [s] is added to the ascending RTT 1513 in the ascending / decreasing storage table 151. (FIG. 15).

  Thereafter, the process returns to step S02, and a threshold for increasing the bit rate from 2 Mbps to 4 Mbps is set. The threshold value RTTth is the same as that in FIG. If occurrence of packet loss is reported in the report during distribution at the bit rate of 2 Mbps (step S05: Yes), the bit rate is changed to 1 Mbps (step S06), and the process returns to step S02.

  As described above, in the first embodiment, the report receiving unit 13 of the stream distribution device 1 receives the report of the reception state transmitted by the receiving terminal 2 via the Internet, and based on this report, the packet By detecting the presence / absence of loss and the round-trip delay time RTT, the history information of the round-trip delay time RTT at the time of increasing the bit rate is stored in the control history storage unit 15. Then, based on the control history information of the round-trip delay time RTT at the time of the trial of increasing the bit rate in the past, a threshold corresponding to the receiving terminal and the bit rate is automatically set. In addition, the threshold value RTTth is dynamically changed from the lower limit RTTlb to the upper limit RTTub of the threshold setting range, so that the bit rate may be inadvertently increased and the bit rate may be increased. To prevent stagnation.

The second example shows a specific example of the stream distribution system according to the second embodiment shown in FIG.
As described above, in the stream distribution device 1A in the second embodiment shown in FIG. 6, the report receiving unit 13 is deleted as compared with the stream distribution device 1 in the first embodiment shown in FIG. The difference is that a network state estimation unit 18 that estimates a network state from information of a management session with 2A is added. The receiving terminal 2A is different from the first embodiment in that the report transmitting unit 22 is deleted and a management information communication unit 23 for exchanging session information with the stream delivery device 1A is added.

  The distribution management unit 17 and the network state estimation unit 18 according to the second embodiment have functions according to a program executed by the CPU of the server apparatus (a program in which a series of processes in the distribution management unit and the network state estimation unit is described). Realized. The function of the management information communication unit 23 is realized by a program executed by the CPU of the set top box STB. The distribution management unit 17 of the stream distribution device 1A and the management information communication unit 23 of the receiving terminal 2A communicate by RTSP (Real Time Streaming Protocol), and the protocol RTSP uses TCP (Transmission Control Protocol) as a transport protocol. .

  The receiving terminal 2A makes a distribution request to the stream distribution apparatus 1A using the protocol RTSP. When receiving the distribution request from the receiving terminal 2A, the distribution management unit 17 in the stream distribution device 1A instructs the distribution rate determination unit 14 to start distribution. After the start of distribution, the life management packet is transmitted from the distribution management unit 17 to the receiving terminal 2A using the RTSP session. When the management information communication unit 23 of the receiving terminal 2A receives the alive monitoring packet, it transmits a response confirmation to the stream distribution device 1A.

  Next, the operation of the network state estimation unit 18 in the second embodiment will be described using a specific example. FIG. 16 is a sequence diagram illustrating a network state estimation method according to the second embodiment, and illustrates a flow of alive monitoring processing between the stream distribution device 1A and the reception terminal 2A.

  Referring to FIG. 16, when the alive monitoring packet is transmitted to receiving terminal 2A at time 0: 00: 00.100 (100 milliseconds after 0:00), network state estimating unit 18 stores this time. deep. Assume that this alive monitoring packet is received by the receiving terminal 2A at time 0: 00: 10.110 and a response confirmation packet is transmitted at time 0: 00: 10.111.

  When the stream distribution device 1A receives the response confirmation packet at time 0: 00: 10.121, the network state estimation unit 18 does not generate any packet loss, and the round-trip delay time RTT is 21 milliseconds (= 0: 00: 00). : 00.121-0: 00: 00.100) to the distribution rate determination unit 14.

  Thereafter, it is assumed that the next alive monitoring packet is transmitted at time 0: 00: 01.100. When the packet is lost before the alive monitoring packet reaches the terminal, the confirmation response from the receiving terminal 2A is not sent, so that the retransmission is performed by TCP after a fixed time has elapsed (in the example of FIG. 16, it is set to 500 milliseconds). Is done. When this retransmission is performed, the network state estimation unit 18 determines that a packet loss has occurred. When receiving the confirmation response to the resent alive monitoring packet, the network state estimation unit 18 has a packet loss and the round trip delay time RTT is 61 milliseconds (= 0: 00: 00.661-0: 00: 01. 600), the distribution rate determination unit 14 is notified.

  As described above, in the second embodiment, the network status estimation unit of the stream distribution device 1A is transmitted from the stream distribution device 1A to the receiving terminal 2A by using the RTSP session in the Internet to transmit the alive monitoring packet. 18, the round-trip delay time RTT between the stream distribution device 1 </ b> A and the receiving terminal 2 </ b> A and the presence / absence of packet loss are estimated. Thereby, even in the receiving terminal 2A that does not report the reception state, the threshold RTTth corresponding to the receiving terminal 2A and the bit rate can be easily and automatically set from the control history information of the round-trip delay time RTT at the past bit rate trial. . Further, as in the first embodiment, it is possible to prevent an inadvertent increase in the bit rate and a stagnation in trials for increasing the bit rate.

  Although the embodiment of the present invention has been described above, the stream distribution device 1 shown in FIG. 1 and the stream distribution device 1A shown in FIG. 6 are configured by a server device or the like as described above, and have a computer system inside. doing. A series of processes related to the above-described process is stored in a computer-readable recording medium in the form of a program, and the above-described process is performed by the computer reading and executing this program.

  That is, each process in the stream distribution devices 1 and 1A is realized by a central processing unit such as a CPU reading the above program into a main storage device such as a ROM or a RAM, and executing information processing and arithmetic processing. Is.

  Here, the computer-readable recording medium means a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like. Alternatively, the computer program may be distributed to the computer via a communication line, and the computer that has received the distribution may execute the program.

  Although the embodiments of the present invention have been described above, the stream distribution system and the stream distribution apparatus of the present invention are not limited to the above-described illustrated examples, and various types can be made without departing from the gist of the present invention. Of course, changes can be made.

  The present invention can be applied to a stream distribution system used for a video distribution service on the Internet, a video monitoring system for transferring video captured by a monitoring camera to a monitoring center, and the like.

  DESCRIPTION OF SYMBOLS 1,1A ... Stream delivery apparatus, 2,2A ... Receiving terminal, 11 ... Stream transmission part, 12 ... Content storage part, 13 ... Report reception part, 14 ... Delivery rate determination 15 ... Control history storage unit 16 ... Threshold setting unit 17 ... Distribution management unit 18 ... Network state estimation unit 21 ... Stream reception unit 22 ... Report transmission , 23... Management information communication unit, 151... Ascendability storage table, 1511... Bit rate before ascent, 1512... Bitrate after ascent, 1513. Unable to rise RTT

Claims (20)

The round-trip delay time with the receiving terminal when increasing the bit rate of the stream distributed to the receiving terminal is stored as history information for each receiving terminal and bit rate, and the bit rate is increased based on this history information. A stream delivery device for setting a round-trip delay time threshold at the time ,
The round-trip delay time with the receiving terminal when attempting to increase the bit rate of the stream delivered to the receiving terminal is stored as history information in association with the combination of the bit rate before and after the increase for each receiving terminal. A control history storage unit;
A threshold value setting unit for setting a threshold value for the round trip delay time when increasing the bit rate based on the history information of the round trip delay time stored in the control history storage unit;
A delivery rate determination unit that determines to increase the bit rate of a stream to be delivered to the receiving terminal when a round-trip delay time with the receiving terminal is below the threshold;
A stream distribution apparatus comprising: The control history storage unit was unable to deliver the round trip delay time with the receiving terminal immediately before raising the bit rate after the bit rate was raised and the round trip delay time that could be delivered after the bit rate was raised. Classify and store as round trip delay time,
The stream delivery apparatus according to claim 1 , wherein The threshold setting unit sets a threshold based on a round trip delay time that can be distributed after the bit rate increase stored in the control history storage unit and a round trip delay time that cannot be distributed after the bit rate increase. Determining a range, and setting the threshold value from within the threshold setting range;
The stream delivery apparatus according to claim 2 , wherein The threshold setting unit sets a lower limit of a threshold setting range from the round-trip delay time that could be distributed, and sets an upper limit of the threshold setting range from the round-trip delay time that could not be distributed. Item 4. The stream delivery device according to Item 3 . The threshold setting unit changes the threshold within the threshold setting range.
The stream delivery apparatus according to claim 4 , wherein The threshold setting unit changes the setting within the threshold setting range so as to approach the upper limit value from the lower limit value as time elapses.
The stream delivery apparatus according to claim 5 , wherein A report receiving unit for receiving report information of a reception state from the receiving terminal;
Based on the report information, the presence / absence of the round trip delay time and packet loss is determined.
Streaming apparatus according to any one of claims 1 6, characterized in that. The stream distribution device transmits a life / death monitoring data to the receiving terminal, and has a network state estimation unit that estimates a round trip delay time and a packet loss based on a confirmation response to the life / death monitoring data.
Streaming apparatus according to any one of claims 1 6, characterized in that. After the stream delivery device transmits the alive monitoring data to the receiving terminal, the time until receiving the confirmation response from the receiving terminal is the round-trip delay time,
The occurrence of retransmission of the data for alive monitoring by a transport protocol is the occurrence of packet loss.
The stream distribution apparatus according to claim 8 , wherein: A stream delivery device according to any one of claims 1 to 9 ;
Multiple receiving terminals,
A stream distribution system comprising: A stream distribution method in a stream distribution device for distributing a stream to a receiving terminal via a network,
By the computer in the stream distribution device,
The round-trip delay time with the receiving terminal when increasing the bit rate of the stream distributed to the receiving terminal is stored as history information for each receiving terminal and bit rate, and the bit rate is increased based on this history information. The procedure for setting the threshold for the round trip delay time is
Characterized as being done ,
The round-trip delay time with the receiving terminal when attempting to increase the bit rate of the stream delivered to the receiving terminal is stored as history information in association with the combination of the bit rate before and after the increase for each receiving terminal. Control history storage procedure;
A threshold setting procedure for setting a round-trip delay time threshold when the bit rate is increased based on the round-trip delay history information stored by the control history storage procedure;
A delivery rate determination procedure for determining to increase the bit rate of a stream to be delivered to the receiving terminal when the round-trip delay time with the receiving terminal is below the threshold;
A stream delivery method characterized in that is performed. According to the control history storing procedure, the round trip delay time with the receiving terminal immediately before raising the bit rate was not able to be delivered after the round trip delay time that could be delivered after the bit rate was raised and the bit rate was raised. Classify and store as round trip delay time,
The stream delivery method according to claim 11 . The threshold setting procedure sets the threshold based on the round-trip delay time that can be distributed after the bit rate increase stored by the control history storage procedure and the round-trip delay time that cannot be distributed after the bit rate increase. Determining a range, and setting the threshold value from within the threshold setting range;
The stream distribution method according to claim 12 . The threshold setting procedure sets a lower limit of a threshold setting range from the round-trip delay time that could be distributed, and sets an upper limit of the threshold setting range from the round-trip delay time that could not be distributed. Item 14. The stream delivery method according to Item 13 . The threshold value is changed within the threshold setting range by the threshold setting procedure.
The stream delivery method according to claim 14 . By the threshold setting procedure, within the threshold setting range, the threshold is changed so as to approach the upper limit value from the lower limit value as time elapses.
The stream delivery method according to claim 15 , wherein: A report reception procedure is performed for receiving report information of a reception state from the receiving terminal,
Based on the report information, the presence / absence of the round trip delay time and packet loss is determined.
Streaming method according to claim 11, wherein 16 of the. The stream distribution device transmits life and death monitoring data to the receiving terminal, and based on a confirmation response to the life and death monitoring data, a network state estimation procedure for estimating a round trip delay time and a packet loss is performed.
Streaming method according to claim 11, wherein 16 of the. After the stream delivery device transmits the alive monitoring data to the receiving terminal, the time until receiving the confirmation response from the receiving terminal is the round-trip delay time,
The occurrence of retransmission of the data for alive monitoring by a transport protocol is the occurrence of packet loss.
The stream delivery method according to claim 18 . A stream distribution program for causing a computer in a stream distribution apparatus to execute each processing procedure in the stream distribution method according to any one of claims 11 to 19 .

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