TWI492581B - Retransmission system for real-time video streams multicasting and method thereof - Google Patents

Description

Instant broadcast stream retransmission system and method thereof

The invention relates to a real-time video stream system, in particular to a group broadcast retransmission system with a live video stream with a multicast retransmission function and a method thereof.

In recent years, with the popularity and flourishing of the Internet, people are increasingly demanding the transmission and reception of instant information. Among them, the way to convey instant information through video and audio is more vivid than the text, so more and more people tend to watch instant video to get information.

Generally speaking, the instant video on the network is transmitted through a network protocol such as TCP or UDP. Since TCP does not support the multicast function and has a large load on the video server, the UDP multicast mechanism is usually selected. Transmitting instant video and audio, this method can greatly reduce the load of the video server compared to TCP single-cast (Unicast), and reduce the video and audio playback time difference of individual users. However, since UDP itself does not support the Acknowledgement (ACK) and retransmission mechanism, when the audio and video data is lost or the transmission process is wrong, the lost or incorrect audio and video data cannot be retransmitted, resulting in poor quality of the audio and video. problem.

In view of this, a Hybrid Automatic Retransmission Request (HARQ) method is proposed to improve the reliability of the multicast system by using Negative Acknowledgement (NACK) and retransmission. . However, the above method does not fully consider the effective retransmission time of the instant video and audio, that is to say, the retransmitted video and audio data may be a wasteful bandwidth before the play point, so that the quality of the instant video and audio cannot be significantly improved. Therefore, the above method is still However, it is impossible to effectively solve the problem of poor quality of instant audio and video in a group broadcast environment.

In summary, it can be seen that in the prior art, there has been a problem of poor quality of instant video and audio in a group broadcast environment for a long time, so it is necessary to propose an improved technical means to solve this problem.

The invention discloses a group broadcast retransmission system for instant video stream and a method thereof.

First, the present invention discloses a group broadcast retransmission system for instant video stream, and the system includes: a source end, an action end, and a base end. The source is used to transmit the packet; the mobile terminal is configured to receive the forwarded packet and transmit a Negative Acknowledgement (NACK). The base end includes: a transmission module, a buffer module, a threshold module, a timing module, a delay module, a setting module, and a retransmission module. The transmission module is configured to receive the packet from the source end and forward the packet to the mobile terminal, and receive the negative acknowledgement packet from the mobile terminal; the buffer module is configured to retransmit the request block (ARQ block) when forwarding the packet to the mobile terminal. Preserving to the retransmission buffer (retransmission buffer); the threshold module is used to calculate the retransmission threshold (Threshold) according to the number of negative acknowledgment packets retransmitted by the same retransmission request block and the number of mobile terminals. The timing module is configured to calculate the retransmission timeout value (RTO) of each mobile terminal using the Jacobson algorithm, and select the maximum retransmission timeout value as the waiting negative acknowledgement packet time (WNT _MAX ); the delay mode The group is configured to select the shortest time as the allowable delay time (T _D ) in the retransmission delay time (T _R ) of the retransmission request block of each mobile terminal; the setting module is configured to set the waiting for negative acknowledgement packet time as retransmission Time (RT), and during this retransmission time, the shortest time is selected to wait for the negative acknowledgement packet time and the allowable delay time to be reset to the retransmission time; and the retransmission module is used to receive the negative acknowledgement When the accumulated number of packets reaches the retransmission threshold and the retransmission time is met, the retransmission request block is retransmitted to the mobile terminal, and when the retransmission time is satisfied but the accumulated number of negative acknowledgement packets received does not reach the retransmission threshold At the time, the base end does not retransmit the retransmission request block and removes the retransmission request block from the retransmission buffer.

In addition, the present invention discloses a method for replaying a real-time video stream, which is applied to the base end. The steps include: when the base end receives the packet from the source end and forwards the packet to the mobile terminal, the retransmission request block is temporarily stored. To the retransmission buffer; the base end receives the negative acknowledgment packet from the mobile terminal; calculates the retransmission threshold according to the number of negative acknowledgment packets retransmitted by the same retransmission request block and the number of the mobile terminal; The algorithm calculates the retransmission timeout value of each mobile terminal, and selects the largest retransmission timeout value as the waiting for negative acknowledgement packet time; selects the shortest time in the retransmission delay time of the retransmission request block of each mobile terminal. As the allowable delay time; set the waiting for negative acknowledgement packet time as the retransmission time, and during this retransmission time, continuously select the shortest time in the waiting for negative acknowledgement packet time and allowable delay time to reset to the retransmission time; when received If the cumulative number of negative acknowledgement packets reaches the retransmission threshold and the retransmission time is met, the retransmission request block is retransmitted to the mobile terminal, and when When a sufficient number of retransmission times, but the cumulative negative acknowledgments received retransmission packet does not reach the threshold, the base end of the retransmission request is not to retransmit the block and the retransmission request transmission buffer block weight is removed.

The system and method disclosed by the present invention are as above, and the difference from the prior art is that the present invention calculates the retransmission threshold, the allowable delay time, and the retransmission time through the base end, so that when the retransmission time is satisfied, the negative acknowledgement packet is used. When the accumulated number reaches the retransmission threshold, the retransmission request block is retransmitted to the mobile terminal, and when the cumulative number of negative acknowledgement packets does not reach the retransmission threshold, the retransmission request block is moved from the retransmission buffer. In addition, the retransmission request block that retransmits the base end can be played back by the mobile terminal.

Through the above technical means, the present invention can achieve the technical effect of improving the quality of real-time audio and video in a multicast environment.

110‧‧‧Source

120‧‧‧Action side

130‧‧‧Base

131‧‧‧Transmission module

132‧‧‧buffer module

133‧‧‧ Threshold Module

134‧‧‧Timekeeping Module

135‧‧‧Delay module

136‧‧‧Setting module

137‧‧‧Retransmission module

310‧‧‧Retransmission buffer

320‧‧‧Transmission buffer

330‧‧‧ Receive buffer

Step 210‧‧‧ When the base end receives the packet from at least one source and forwards it to at least one mobile terminal, temporarily stores the retransmission request block (ARQ block) into a retransmission buffer (Retransmission buffer)

Step 220‧‧‧ The base end receives a negative acknowledgement packet (NACK) from the mobile terminal

Step 221. The ratio of a block sequence number of the retransmission request block requesting retransmission to the negative acknowledgement packet matches the retransmission request block in the retransmission buffer, and when it does not match, indicates a retransmission request. The block exceeds the allowable delay time has been removed, and the number of negative acknowledgement packets is accumulated when the comparison matches

Step 230‧‧‧ Calculate a retransmission threshold (Threshold) by retransmitting the number of negative acknowledgement packets of the same retransmission request block and the number of mobile terminals

Step 231‧‧‧ Detect the network bandwidth and the current data volume, and adjust the retransmission threshold according to the ratio of the detected network bandwidth to the current data volume

Step 240‧‧‧ Calculate a retransmission timeout value (RTO) for each action end using the Jacobson algorithm, and select the maximum retransmission timeout value as a wait for negative acknowledgement packet time (WNT _MAX )

Step 250‧‧‧ Select the shortest time as the allowable delay time (T _D ) in the retransmission delay time (T _R ) of the retransmission request block of each mobile terminal

Step 260‧‧‧ set the waiting negative acknowledgement packet time to a retransmission time (RT), and during the retransmission time, continuously select the shortest time in the waiting negative acknowledgement packet time and the allowable delay time to reset For this retransmission time

Step 270‧‧‧ When the accumulated number of negative acknowledgement packets received reaches the retransmission threshold and the retransmission time is satisfied, the retransmission request block is retransmitted to the mobile terminal, and when the retransmission time is satisfied but received When the cumulative number of negative acknowledgement packets does not reach the retransmission threshold, the base station does not retransmit the retransmission request block and removes the retransmission request block from the retransmission buffer.

Step 410‧‧‧Transfer ARQ Block

Step 420‧‧‧ Calculate WNT _MAX

Step 430‧‧‧Set WNT _MAX to RT

Step 440‧‧‧Retransmission timeout

Step 450‧‧‧ Received NACK

Step 460‧‧‧NACK reaches the retransmission threshold

Step 470‧‧‧ Calculate T _D

Step 480‧‧‧Reset the value of the smallest of WNT _MAX and T _D to RT

Step 490‧‧‧NACK reaches the retransmission threshold

Step 500‧‧‧Retransmit ARQ Block

Step 510‧‧‧Remove the ARQ Block from the retransmission buffer

FIG. 1 is a system block diagram of a multicast playback system for instant video streaming of the present invention.

2A and 2B are flowcharts of a method for multicasting a live video stream retransmission method according to the present invention.

Figure 3 is a schematic diagram of the buffer and time of the base end and the mobile end of the present invention.

4A and 4B are flowcharts showing the steps of the base end retransmission retransmission request block (ARQ Block) of the present invention.

The embodiments of the present invention will be described in detail below with reference to the drawings and embodiments, so that the application of the technical means to solve the technical problems and achieve the technical effects can be fully understood and implemented.

Before describing the multicast retransmission system and method of the instant video stream disclosed in the present invention, the environment to which the present invention is applied is described. The present invention is applied to an environment having a source end, an action end, and a base end. At the base end, and the three can communicate with each other through wired or wireless networks. In addition, the source can provide streaming data for network cameras, computers, etc.; the mobile terminal can be a notebook computer, a tablet computer, or a smart phone. Or personal digital assistants... and other mobile devices; the base can be implemented using a computer, such as a personal computer.

The following describes the group broadcast retransmission system and method for the instant video stream of the present invention in conjunction with the drawings. Please refer to "FIG. 1", which is the group broadcast retransmission system of the instant video stream of the present invention. A system block diagram, the system comprising: a source end 110, an action end 120, and a base end 130. The source end 110 is configured to transmit a packet. For example, when the source terminal 110 is an IP camera, it can transmit a packet containing audio and video data. Since the source end 110 is a conventional technology, it will not be repeated here.

The mobile terminal 120 is configured to receive the packet forwarded by the base end 130 and transmit a negative acknowledgement packet. In actual implementation, the mobile terminal 120 combines according to the received packets to play the instant video.

As for the base end 130, the transmission module 131 and the buffer module are included. The group 132, the threshold module 133, the timing module 134, the delay module 135, the setting module 136, and the retransmission module 137. The transmission module 131 is configured to receive the packet from the source end 110 and forward it to the mobile terminal 120, and receive the negative acknowledgement packet from the mobile terminal 120, and the receiving and forwarding are implemented by means of a wired or wireless network.

The buffer module 132 is configured to temporarily store the retransmission request block to the retransmission buffer when forwarding the packet to the mobile terminal 120. In actual implementation, the buffer module 132 further includes a block sequence number (Block Sequence Number) of the retransmission request block that is required to be retransmitted when the transmission module 131 receives the negative acknowledgement packet. The BSN) is consistent with the retransmission request block in the retransmission buffer. When it does not match, it indicates that the retransmission request block has exceeded the allowable delay time, and the number of negative acknowledgement packets is accumulated when the comparison matches.

The threshold module 133 is configured to calculate the retransmission threshold by retransmitting the number of negative acknowledgement packets of the same retransmission request block and the number of the mobile terminal 120 of the multicast. In actual implementation, the number of negative acknowledgement packets requiring retransmission of the same retransmission request block may be expressed as “N _NACK ”, and the number of mobile terminals 120 of the multicast broadcast may be represented as “N _MS ”, and the retransmission threshold may be represented. as follows:

In particular, the threshold module 133 can detect the network bandwidth and the current data amount, and adjust the retransmission threshold according to the ratio of the detected network bandwidth to the current data amount, in other words, The retransmission threshold can be adjusted according to the network condition, and the network condition can be determined by the ratio of the current data volume to the bandwidth allocated by the base station 130. When the ratio is small, the retransmission threshold is reduced; Conversely, when the ratio is large, the retransmission threshold is increased.

The timing module 134 is configured to calculate a Retransmission Timeout (RTO) of each of the mobile terminals 120 using a Jacobson algorithm, and select a maximum retransmission timeout value as a wait for a negative acknowledgement packet. Time (WNT _MAX ), which can be expressed as follows: WNT _MAX = MAX[RTO _MS1 , RTO _MS2 , ..., RTO _MSn ]

Where "RTO _MS1 " represents the retransmission timeout value of the first mobile terminal 120, "RTO _MS2 " represents the retransmission timeout value of the second mobile terminal 120, and so on, "RTO _MSn " represents the nth The retransmission timeout value of the mobile terminal 120, and "WNT _MAX " is the largest among the retransmission timeout values of these mobile terminals 120. Since the Jacobson algorithm calculates the retransmission timeout value as a conventional technique, it will not be repeated.

The delay module 135 is configured to transmit a negative acknowledgement packet at each mobile terminal 120 until the mobile terminal 120 processes the base station 130 to transmit a retransmission delay time (T _R ) corresponding to the retransmission request block corresponding to the negative acknowledgement packet. As the allowable delay time (T _D ), the allowable delay time can be expressed as follows: T _D =min[T _{R_MS1} , T _{R_MS2} , . . . , T _{R_MSn} ]

_Wherein, "T R_MS1" represents the first mobile terminal 120 requests retransmission block retransmission delay _time, "T R_MS2" action represents the second end 120 of the retransmission request retransmission delay block, and to Such a push, "T _{R_MSn} " represents the retransmission delay time of the retransmission request block of the nth mobile terminal 120. In actual implementation, the retransmission delay time (T _R ) of the retransmission request block means that the mobile terminal 120 transmits a negative acknowledgement packet to the base end 130, and the base end 130 receives the retransmission request block and places it on the base end 130. The retransmission buffer is transmitted until the transmitted retransmission request block is received by the mobile terminal 120 and placed in the buffer of the mobile terminal 120 until the entire time of processing, which can be expressed as follows: T _R =T _NACK +T _wait +T _ARQ +T _HOL

Where "T _NACK " represents the transmission time of the negative acknowledgement packet, "T _wait " represents the retransmission request block is placed in the retransmission buffer of the base end 130 until the time of transmission, and "T _ARQ " represents the retransmission request area The transmission time of the block, "T _HOL " refers to the time during which the retransmission request block is received by the mobile terminal 120 and placed in the buffer of the mobile terminal 120 until it is processed. In practical implementation, the small value of “T _HOL ” means that the application layer does not buffer too much data. When the retransmission request block is received, it must be combined into video and audio data and played in a short time. Otherwise, when “T _HOL "A large value means that the application layer has buffered a lot of audio and video data waiting to be played.

The setting module 136 is configured to set the waiting for negative acknowledgement packet time as the retransmission time (RT), and in the retransmission time, continuously select the shortest time in the waiting for the negative acknowledgement packet time and the allowable delay time to reset to the retransmission time. The retransmission time can be expressed as follows: RT=min[WNT _MAX , T _D ]

Among them, "WNT _MAX " and "T _D " have been described in detail above, so no further details are given here. In actual implementation, after the base end 130 broadcasts the packet, the setting module 136 sets the waiting negative acknowledgement packet time "WNT _MAX " to the retransmission time "RT", and during the retransmission time, the base end 130 The received negative acknowledgement packet will be counted. When the cumulative number of negative acknowledgement packets exceeds the retransmission threshold, the setup module 136 will wait for the negative acknowledgement packet time "WNT _MAX " and the allowable delay time "T _D ". The shortest selection time is reset to the retransmission time "RT".

The retransmission module 137 is configured to retransmit the retransmission request block to the mobile terminal 120 when the accumulated number of received negative acknowledgement packets reaches the retransmission threshold and meet the retransmission time, and when the retransmission time is met but When the accumulated number of negative acknowledgement packets received does not reach the retransmission threshold, the base end 130 does not retransmit the retransmission request block and removes the retransmission request block from the retransmission buffer. In this way, the retransmitted retransmission request block can not only meet the retransmission requirement of the mobile terminal 120, but also enable the retransmitted retransmission request block to arrive at the mobile terminal 120 and still have to be played in combination.

Next, please refer to "2A" and "2B", "2A" and "2B" are the multicast retransmission methods of the instant video stream, which are applied at the base end 130, and the steps include When the base end 130 receives the packet from the source end 110 and forwards the packet to the mobile terminal 120, the retransmission request block is temporarily stored in the retransmission buffer (step 210); the base end 130 receives a negative acknowledgement from the mobile terminal 120. Packet (step 220); retransmission threshold is calculated according to the number of negative acknowledgement packets retransmitted by the same retransmission request block and the number of mobile terminals of the multicast (step 230); each is calculated by the Jacobson algorithm The mobile terminal 120 retransmits the timeout value and selects the largest retransmission timeout value as a wait for negative acknowledgement Packet time (step 240); selecting the shortest time as the allowable delay time in the retransmission delay time of the retransmission request block of each mobile terminal 120 (step 250); setting the waiting for negative acknowledgement packet time as the retransmission time (RT) And, during this retransmission time, continuously select the shortest time in the waiting for the negative acknowledgement packet time and the allowable delay time to reset to the retransmission time (step 260); when the cumulative number of negative acknowledgement packets received reaches the retransmission When the threshold value and the retransmission time are met, the retransmission request block is retransmitted to the mobile terminal 120, and when the retransmission time is satisfied but the accumulated number of negative acknowledgement packets received does not reach the retransmission threshold, the base end 130 will The retransmission request block is not retransmitted and the retransmission request block is removed from the retransmission buffer (step 270). Through the above steps, the retransmission threshold, the allowable delay time, and the retransmission time can be calculated through the base end 130, so that when the retransmission time is satisfied, when the cumulative number of negative confirmation packets reaches the retransmission threshold, the weight will be heavy. The request request block is retransmitted to the mobile terminal 120, and when the cumulative number of negative acknowledgement packets does not reach the retransmission threshold, the retransmission request block is removed from the retransmission buffer, and the base station 130 retransmits the retransmission. The request block can be played in combination by the mobile terminal 120.

In particular, after step 220, the block sequence number of the retransmission request block that is required to be retransmitted to the negative acknowledgement packet is matched with the retransmission request block in the retransmission buffer, and when it does not match, the weight is indicated. The request request block exceeds the allowable delay time has been removed, and the number of negative acknowledgement packets is accumulated when the comparison matches (step 221); and after step 230, the network bandwidth and the current data amount are detected, and according to the detection The ratio of the obtained network bandwidth to the current data amount adjusts the retransmission threshold (step 231).

The following is a description of the following examples in conjunction with "3D" to "4B". Please refer to "3" and "3" for a buffer and time diagram of the base and mobile terminals of the present invention. As mentioned above, the base end 130 will receive a "NACK" and temporarily retransmit the retransmission request block (ARQ Block) in the retransmission buffer 310 for retransmission; the mobile terminal 120 will transmit "NACK" and receive "ARQ Block". . In actual implementation, in the buffer portion, the base end 130 receives the "NACK" transmitted by the mobile terminal 120 through the transmission buffer 320, and the mobile terminal 120 stores the received from the base end 130 through the receive buffer 330. "ARQ Block". In addition, in the time portion, the period during which the mobile terminal 120 transmits "NACK" to the base station 130 is indicated as "T _NACK "; and the time when the base station 130 transmits the "ARQ Block" to the mobile terminal 120 is indicated as " T _ARQ ”. Since the receiving buffer 330 can sequentially store a plurality of "ARQ Blocks" received from the base end 130, the waiting time of these "ARQ Blocks" until being processed is expressed as "T _HOL ", as for the part of the base end 130, The time at which the retransmitted "ARQ Block" is waiting to be transmitted in the retransmission buffer 310 is expressed as "T _wait ", and the "T _wait " can be expressed as follows:

The "N _wait " is the number of all the "ARQ Blocks" before the "ARQ Block" retransmitted in the retransmission buffer 310, and the "w" is the scheduling weight assigned to the multicast connection by the base station 130. (scheduling weight).

As shown in "4A" and "4B", "4A" and "4B" are flowcharts of the steps of the base station retransmitting the retransmission request block (ARQ Block). First, after the base station 130 transmits the "ARQ Block" (step 410), it calculates an operation waiting for the negative confirmation packet time "WNT _MAX " (step 420), and sets "WNT _MAX " as the retransmission time "RT" (step 430). Next, it is judged whether "RT" is out of time (step 440), and if it is not timed, it is judged whether or not a negative acknowledgement packet "NACK" is received (step 450), and if the result of the judgment is that a negative acknowledgement packet is accepted, then "NACK" is continued. Whether the number reaches the retransmission threshold (step 460), the allowable delay time "T _D " is calculated when the retransmission threshold is reached (step 470), and the minimum is taken between "WNT _MAX " and "T _D " The value of the person is reset to "RT" (step 480). Additionally, if step 450 does not receive a negative acknowledgement packet, step 460 does not reach the retransmission threshold, or step 480 is performed, then step 440 is returned.

As stated above, if it is determined in step 440 that the timeout has elapsed, then it is determined whether the number of "NACKs" has reached the retransmission threshold (step 490), and if the retransmission threshold is not reached, the base end 130 does not retransmit the retransmission request. The block will also remove the "ARQ Block" from the retransmission buffer (step 510), otherwise the "ARQ Block" will be retransmitted if the retransmission threshold is reached (step 500). In other words, when the base station 130 multicasts, the retransmission time is set, and the received "NACK" is continuously counted during the retransmission time, when the cumulative number of "NACKs" of a retransmission request block exceeds When the threshold is retransmitted, the smallest value of "WNT _MAX " and "T _D " is reset to "RT", and retransmission is performed when the "RT" time is over. By controlling the time, the retransmitted "ARQ Block" arrives at the mobile terminal 120 and is still ready to be played.

In summary, it can be seen that the difference between the present invention and the prior art is that the retransmission threshold, the allowable delay time, and the retransmission time are calculated through the base end, so that when the retransmission time is satisfied, the cumulative number of negative acknowledgement packets is determined. When the retransmission threshold is reached, the retransmission request block is retransmitted to the mobile terminal, and when the cumulative number of negative acknowledgement packets does not reach the retransmission threshold, the retransmission request block is removed from the retransmission buffer, so that The retransmission request block retransmitted by the base end can be played by the mobile terminal in combination, and the technical problem can be solved by the prior art, thereby achieving the technical effect of improving the real-time audio and video quality in the multicast environment.

While the present invention has been described above in the foregoing embodiments, it is not intended to limit the invention, and the invention may be modified and modified without departing from the spirit and scope of the invention. The scope of patent protection shall be subject to the definition of the scope of the patent application attached to this specification.

110‧‧‧Source

120‧‧‧Action side

130‧‧‧Base

131‧‧‧Transmission module

132‧‧‧buffer module

133‧‧‧ Threshold Module

134‧‧‧Timekeeping Module

135‧‧‧Delay module

136‧‧‧Setting module

137‧‧‧Retransmission module

Claims (10)

A real-time video streaming multicast broadcast retransmission system, the system comprising: at least one source end, each source end is configured to transmit a packet; and at least one mobile terminal is configured to receive the forwarded packet and transmit a negative acknowledgement packet (NACK) And a base end, the base end includes: a transmission module, configured to receive a packet from the source end and forward the packet to the mobile terminal, and receive a negative acknowledgement packet from the mobile terminal; a buffer module, To forward the retransmission request block (ARQ block) to a retransmission buffer (Retransmission buffer) when the packet is forwarded to the mobile terminal; a threshold module for retransmitting the same retransmission request as required The number of negative acknowledgment packets of the block and the number of mobile terminals of the grouping are calculated by a four-step operation to calculate a retransmission threshold (Threshold); a timing module is used to calculate a retransmission of each mobile terminal using the Jacobson algorithm. Time value (RTO), and select the maximum retransmission timeout value as a wait for negative acknowledgement packet time (WNT _MAX ); a delay module for retransmission delay time of the retransmission request block at each mobile terminal ( T _R) selected Shortest allowable time as a delay time (T _D); a setting module for the waiting time is set to a negative acknowledgment packet retransmission time (RT), and within the retransmission time for the negative acknowledgment wait And selecting, in the packetization time and the allowable delay time, the shortest time to reset to the retransmission time; and a retransmission module, when the accumulated number of negative acknowledgement packets received reaches the retransmission threshold and satisfies the retransmission At time, the retransmission request block is retransmitted to the mobile terminal, and when the retransmission time is satisfied but the accumulated number of negative acknowledgement packets received does not reach the retransmission threshold, the base station does not retransmit the retransmission request block and The retransmission request block is removed from the retransmission buffer. The multicast retransmission system of the instant video stream according to the first aspect of the patent application, wherein the buffer module further comprises: when the transmission module receives the negative acknowledgement packet, requesting retransmission of the negative acknowledgement packet Whether the sequence number of a block of the retransmission request block matches the retransmission request block in the retransmission buffer, and if the sequence does not match, the retransmission request block is removed from the retransmission buffer, when the comparison matches Accumulate the number of negative confirmation packets. A multicast retransmission system for instant video streaming according to claim 1 of the patent application, wherein the retransmission threshold is a ratio of the number of negative acknowledgement packets (N _NACK ) to the number of mobile terminals (N _MS ) . According to the instant broadcast stream retransmission system of claim 1, wherein the threshold module further comprises detecting the network bandwidth and the current data amount, and according to the detected network bandwidth and current The ratio of the amount of data adjusts the retransmission threshold. A multicast retransmission system for instant video streaming according to claim 1 of the patent application, wherein the retransmission request block of the mobile terminal requests a processing delay retransmission delay time (T _R ) for the mobile terminal to transmit a negative acknowledgement packet to the base end The base station places the retransmission request block requesting the retransmission request in the retransmission buffer until it is transmitted, and the retransmission request block is received by the mobile terminal and placed in the buffer of the action end until the processed time . A method for multicast playback of instant video stream is applied to a base end, and the steps include: when the base end receives a packet from at least one source end and forwards the packet to at least one mobile terminal, the request block is retransmitted ( The ARQ block is temporarily stored in a retransmission buffer; the base receives a negative acknowledgement packet (NACK) from the mobile terminal; retransmits the number of negative acknowledgement packets of the same retransmission request block and multicast according to requirements The number of mobile terminals is calculated by a four-operation operation to calculate a retransmission threshold (Threshold); a Jacobson algorithm is used to calculate a retransmission timeout value (RTO) for each mobile terminal, and the maximum retransmission timeout value is selected as a wait. Negative acknowledgement packet time (WNT _MAX ); select the shortest time as the allowable delay time (T _D ) in the retransmission delay time (T _R ) of the retransmission request block of each mobile terminal; Set to a retransmission time (RT), and during the retransmission time, continuously select the shortest time in the waiting negative acknowledgement packet time and the allowable delay time to reset to the retransmission time; and when receiving When the cumulative number of negative acknowledgement packets reaches the retransmission threshold and the retransmission time is met, the retransmission request block is retransmitted to the mobile terminal, and the cumulative number of negative acknowledgement packets received but the retransmission time is satisfied When the retransmission threshold is not reached, the base station does not retransmit the retransmission request block and removes the retransmission request block from the retransmission buffer. According to the multicast retransmission method of the instant video stream of claim 6, wherein the step of receiving the negative acknowledgement packet further comprises a block of a retransmission request block that requires retransmission to the negative acknowledgement packet. Whether the sequence number matches the retransmission request block in the retransmission buffer, and when it does not match, indicating that the retransmission request block exceeds the allowable delay time has been removed, and the number of the negative acknowledgement packets is accumulated when the comparison matches A step of. A multicast retransmission method for instant video streaming according to claim 6 of the patent application scope, wherein the retransmission threshold is a ratio of the number of the negative acknowledgement packets (N _NACK ) to the number of mobile terminals (N _MS ) . The method for replaying a live video stream according to the sixth application of the patent scope, wherein the method further comprises detecting a network bandwidth and a current data amount, and according to the detected network bandwidth and the current data volume. The ratio adjusts the retransmission threshold. According to the multicast retransmission method of the instant video stream of claim 6, wherein the retransmission delay time (T _R ) of the retransmission request block of the mobile terminal is a mobile terminal transmitting a negative acknowledgement packet to the base end, the base The retransmission request block that requests the retransmission of the negative acknowledgement packet is placed in the retransmission buffer until it is transmitted, and the retransmission request block is received by the mobile terminal and placed in the buffer of the mobile terminal until the time of processing.