CN110324256A - A kind of Transmitting Data Stream control method - Google Patents

Abstract

The patent of the present invention relates to communication data transmission control, in particular to a streaming data transmission control method, which includes the following operations: dividing data into data segments, dividing each data segment into multiple levels according to the importance of the data, and setting a precision level threshold ; Use the ratio of the congestion window to the round-trip delay as the estimated value of the optimal sending rate of the data, calculate and update the sending probability of each precision level data segment according to this value; send the selected data segments in turn according to the data sending mechanism of TCP; The ACK feedback estimates the congestion status and available bandwidth of the network, thereby updating the congestion window, and actively adjusts the data transmission accuracy to control the amount of data to be transmitted. If the network bandwidth becomes better, increase the accuracy of sending data; otherwise, reduce the accuracy of sending data to ensure the progress of transmission.

Description

A streaming data transmission control method

technical field

The patent of the present invention relates to communication data transmission control, in particular to a streaming data transmission control method.

Background technique

At present, in the construction of end-to-end data transmission services, the network mainly provides two types of service models: one is link-oriented, providing orderly and reliable data delivery services, typically based on TCP (Transmission Control Protocol). Data transmission; the other type is connectionless, providing unordered and unreliable data transmission delivery services, typically based on UDP (User Datagram Protocol) for data transmission.

The TCP transmission protocol can establish an end-to-end bidirectional link through a complex design, provide orderly and reliable streaming data transmission services, and dynamically adjust the data transmission rate according to network load and congestion.

The UDP protocol provides a very primitive and simple data sending and listening interface, and only provides best-effort data transmission capabilities. If orderly and reliable data delivery is required, it needs to be implemented by the application itself. At the same time, the UDP protocol itself does not contain a congestion control mechanism.

With the continuous enrichment of network applications, emerging applications (such as streaming media applications) have put forward new requirements for the service model of network transmission. These new transmission requirements do not require completely reliable data delivery, but do not expect data transmission to be completely unreliable. reliable.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a streaming data transmission control method which can ensure the progress of data transmission by adjusting the transmission precision of data.

In order to achieve the above purpose, the technical solution adopted in this application is a streaming data transmission control method, which includes the following operations:

1) Divide the data into data segments, divide each data segment into multiple levels according to the importance of the data, and set the accuracy level threshold;

2) Use the ratio of the congestion window to the round-trip delay as the estimated value of the best transmission rate of the data, and calculate and update the transmission probability of each precision level data segment according to this value;

3) Send the selected data segments in turn according to the data sending mechanism of TCP;

4) Estimate the congestion status and available bandwidth of the network according to the ACK feedback, so as to update the congestion window, and make the value of the congestion window ≤ the expected sending rate of the data segment * the round-trip delay; wherein,

When the data segment level value is less than the precision level threshold, the data is the basic precision data;

When the data segment level value ≥ the precision level threshold, the data is enhanced precision data;

When the selected basic precision data ACK (Acknowledgement, confirmation character) times out, retransmission is performed, and the congestion window and the transmission probability of each precision level data segment are updated;

When the selected enhanced precision data ACK times out, no retransmission is performed, and only the congestion window and the transmission probability of each precision level data segment are updated;

When the received ACK contains the ECN flag, the congestion window and the transmission probability of each precision level data segment are updated.

The data that the application needs to stream is divided into multiple data levels, some of which require reliable and ordered data delivery, and the other part can tolerate unreliable data delivery; the application expects the network to provide a kind of in-between. "Semi-reliable" Transmission Control Protocol. On the one hand, the protocol can ensure the orderly and reliable delivery of reliable data, and on the other hand, it can dynamically adjust the accuracy of unreliable data transmission according to the load of the link in the transmission path.

This transmission protocol can not only provide more advanced transmission services than UDP, but also simpler than TCP, and can make more full use of network bandwidth and better meet the data transmission requirements of applications.

The above-mentioned ECN (Explicit Congestion Notification) is an explicit congestion notification, which is a mechanism used by some versions of TCP to let the intermediate device notify the sender of network congestion in advance. The above-mentioned one data segment corresponds to a data segment (segment) in the TCP message.

Further, during the data segment sending process, the reserved fields in the TCP options of the SYN message and the ACK message are used to negotiate and confirm the maximum number of precision classifications, the precision level threshold and the expected sending rate according to the preset process. SYN stands for Synchronize Sequence Numbers, which is a synchronization flag. The flag is only valid when the TCP connection is established by the three-way handshake. It prompts the server of the TCP connection to check the sequence number, which is the initial sequence number of the initial end of the TCP connection (usually the client). ACK is the Acknowledgement Number. The confirmation number contained in the confirmation number column in the TCP header is the next expected sequence number, and at the same time indicates that the remote system has successfully received all data before the number.

Further, the preset process includes the following operations:

The negotiation of the maximum number of precision levels, the threshold of precision levels, and the expected sending rate occurs during the TCP link establishment phase. At this time, the sender carries the P value and the RD_MAX value in the TCP options field of SYN to indicate the maximum number of precision levels that the sender can support, respectively. And the maximum expected sending rate; and PD_DEFAULT and RD_DEFAULT indicate the maximum number of precision levels and the expected sending rate recommended by the sender;

Among them, the receiving end saves the received values of P, RD_MAX, PD_DEFAULT, and RD_DEFAULT locally; in the process of ACKing the SYN message, the receiving end sends the required precision level threshold and required expected sending rate through the ACK message. TCP options, confirm to the sender;

Among them, the accuracy level threshold value fed back by the receiver is less than the maximum number of accuracy levels advertised by the sender, and the expected sending rate is less than or equal to the RD_MAX value advertised by the sender;

If the receiving end does not provide feedback, the transmitting end uses PD_DEFAULT and RD_DEFAULT by default as the accuracy level threshold and expected sending rate of the transmission task corresponding to the receiving end. (For P, RD_MAX, PD_DEFAULT, RD_DEFAULT, the sender will send it to the receiver during the connection stage. At this time, the receiver can feed back its own PD and RD. At other times, the receiver can feed back the new PD and RD again to achieve The purpose of updating this value.)

Further, the receiving end composes a plurality of consecutive data segments into data blocks, and decodes in units of data blocks, which can tolerate the absence of enhanced precision data segments. When data is sent, the data segments are numbered according to the sending sequence, and the number of the data segment to be sent takes the value j, starts from 0, and is sent together with the data segment; when the receiving end receives the data segment, it can calculate the data segment. The data block number value corresponding to the segment is k=j div P, where div represents an integer division operation; the corresponding precision level information is i=j mod P, where mod is a remainder operation.

If all data segments in the data block k have been received, decode the data block;

If there is a data block whose number value is less than k and the data segments of the basic precision data have been collected but have not been decoded at the receiving end, the data block is decoded.

Further, all data segments to be transmitted are numbered and configured; each data segment carries the number of the data segment and the precision level number indicating the importance of the data segment; the level number and the data segment number are stored in the TCP data segment. In the reserved field of TCP options, the data segment number is independent of the seq sequence number in the TCP header.

Further, when the ratio of the congestion window to the network round-trip delay is used as the estimated value of the optimal sending rate of the data, the first preset strategy is used to randomly select and transmit the data segment to be transmitted; the first preset The strategy is:

P is the maximum precision classification number;

PD is the precision level threshold;

i is the grade number;

RD is the expected sending rate;

For each data segment with precision level i, the data segment transmission probability Pr(i) is selected;

Assuming that the round-trip delay of the current network is rtt and the size of the congestion control window is cwnd, then the value of Pr(i) is:

For the accuracy class i<PD, Pr(i)=1;

For a precision class of PD≤i≤P-1, Pr(i)=1-max(0,min(1,i-cwnd/rtt*P/RD)).

The sender transmits data at the desired transmission rate when the bandwidth is sufficient, and dynamically reduces the transmission accuracy when the bandwidth is insufficient to maintain the same or similar transmission progress while avoiding congestion.

The above-mentioned data precision or data precision level is characterized by the transmission probability of the data segment. Pr(i) is a number between 0 and 1, indicating the probability that the data segment with precision level i is selected for transmission. If it is 1, it means that 100% of the data segments of this level are transmitted; if it is 0, it means that all data segments of this level are not transmitted.

Further, the sender judges whether there is packet loss during the transmission process according to whether it receives the feedback ACK and the TCP data segment acknowledgment number confirmed by the ACK;

If the ACK of the basic precision data times out, the data segment will be retransmitted, and the size of the sliding window will be adjusted according to the original TCP policy, and the transmission probability of each precision level data segment will be updated at the same time;

If the ACK of the enhanced precision data times out, no retransmission is performed, the size of the sliding window is adjusted according to the second preset strategy, and the transmission probability of each precision level data segment is updated at the same time;

If the ACK received by the sender carries the ECN flag, the size of the sliding window is adjusted according to the original TCP policy, and the transmission probability of each precision level data segment is updated according to the new sliding window value.

When some versions of TCP protocol receive multiple ACKs with the same acknowledgment number, they also think that the network has lost packets and will actively retransmit them; at the same time, some versions of TCP also introduce mechanisms such as SACK. In these cases, the sender adjusts the size of the sliding window according to the original policy of the corresponding version of TCP, and updates the sending probability of each precision level data segment.

Further, the second preset strategy is: the size of the congestion control window after adjustment=the size of the congestion control window before adjustment−1.

Further, for a data block whose basic precision data segment has been collected but not yet decoded, when the time when the basic precision data is collected exceeds the preset time T, the receiving end immediately performs decoding.

Further, if the network intermediate device supports strict multi-priority queue scheduling, the number of supported priorities is set as PS, and the data segment of the basic precision data carries the highest priority 0; the precision level values are PD, PD+1, ... ,min(P-1, PD+PS-1) data segments of enhanced precision data carry priorities 1, 2, 3, ..., PS-1 respectively, and data segments of other precision levels carry priority value PS-1.

The present invention includes at least one of the following beneficial effects:

It can actively adjust the transmission accuracy of data and control the amount of data to be transmitted according to the feedback information of the available bandwidth of the link. If the network bandwidth becomes better, increase the accuracy of sending data; otherwise, reduce the accuracy of sending data, thereby reducing the amount to be sent and ensuring the progress of transmission.

According to the accuracy level, the data is divided into two categories that require reliable transmission and those that do not require reliable transmission. When packet loss occurs during transmission, only the lost reliable data is retransmitted to avoid the drop in the effective throughput of the network and prevent the transmission protocol from being blocked by the loss of unreliable data.

The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Additional aspects and advantages of the present invention will, in part, be set forth in, and will become apparent from, the following description. or learned through the practice of the present invention.

Description of drawings

The accompanying drawings that constitute a part of the present invention are used to assist the understanding of the present invention, and the content provided in the drawings and their related descriptions in the present invention can be used to explain the present invention, but do not constitute an improper limitation of the present invention. In the attached image:

1 is a schematic diagram for explaining a streaming data transmission control method in an embodiment of the embodiment;

Fig. 2 is a schematic diagram for explaining data segment, data block transmission and numbering sequence in the embodiment;

Detailed ways

The present invention will be clearly and completely described below with reference to the accompanying drawings. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. Before the present invention is described in conjunction with accompanying drawings 1 and 2, it should be noted that:

The technical solutions and technical features provided in the various parts including the following description in the present invention can be combined with each other under the condition of no conflict.

In addition, the embodiments of the present invention referred to in the following description are generally only a part of the embodiments of the present invention, not all of the embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

Regarding the terms and units in the present invention. The term "comprising" and any variations thereof in the description and claims of the present invention and related parts are intended to cover the non-exclusive inclusion.

1 and 2, this embodiment adopts a bandwidth-aware hierarchical multi-precision data semi-reliable streaming data transmission control method. The control method can be implemented by extending the existing TCP transmission protocol (supporting the extension on different versions of TCP). The method includes three types of participants in implementation: a data sending end, a receiving end, and one or more network intermediate forwarding devices. The transmission control scheme is completed through the cooperation of the sender and the receiver.

The network service model adopted:

In this control method, the requirement of each data transmission task is described by the triplet <P, PD, RD>. P is the maximum number of precision levels, PD is the precision level threshold, and RD is the optimal data transmission rate. Indicates that each piece of data to be transmitted by the application can be divided into 0, 1, ..., P-1, a total of P precision levels (the lower the level value, the more important); among them, the data segment with the precision level value less than PD needs to be reliable and orderly The data delivery is called basic precision data; and the data segment whose precision level value is greater than or equal to PD only needs best-effort data transmission service, called enhanced precision data; the data transmission rate expected by the application is RD, called it is the expected sending rate. The values of <P, PD, RD> are negotiated by the data sender and receiver during link establishment or data transmission.

As shown in Figure 2, one row is a data block, and k, k+1, ... are the data block numbers. Each row contains multiple data segments, and j is the data segment number. A data segment is just put into a TCP data segment for transmission.

That is, k is the data block number, and j is the data segment number. Each data block contains at most P data segments. When decoding, the more complete the data segment received in a data block, the more accurate the data obtained by decoding. i and j will be carried in the data segment for transmission. For the receiving end, the k value corresponding to the data segment can be inversely calculated through j and the P that the sending end informs the receiving end when the link is established.

In this scheme, the data to be transmitted is evenly divided into multiple data blocks, and each data block is encoded into P precision levels; the data of the same precision level in each data block is packed into the same data segment , the numbering and transmission are performed layer by layer. A data segment corresponds to a data packet in TCP transmission, and the size of the data segment is determined according to the maximum segment size (MSS) of TCP in the network. The numbering in the data segment adopts a cyclic numbering method, which is independent from the TCP data segment sequence number value seq. After receiving the data segment, the receiving end decodes and recovers the content of each data block. If part of the precision classification data in a data block is missing (that is, the data is incomplete), the receiving end can still perform decoding and recovery, but the result obtained by decoding will be inaccurate. For each data block, the more complete the data segment received by the receiver, the more accurate the data obtained by decoding; and the lower the level value of the data segment, the greater the contribution to the decoding accuracy.

In the face of the above transmission requirements, a TCP-like network transmission link is established between the sender and the receiver, and data transmission is performed in a streaming manner; the link is disconnected after the transmission is completed.

During the link establishment process, the sender and receiver negotiate and confirm the <P, PD, RD> parameters of the transmission task. During transmission, the receiving end can update this parameter.

Let the current sender's congestion window size be cwnd, and the network round-trip delay value is rtt.

Referring to Figure 1, the steps of the method can be carried out as follows:

1. The sender uses the ratio of cwnd to rtt as the estimated value of the best sending rate of data, and determines which precision data segments are selected for transmission. The specific method is to adjust the transmission probability Pr(i) of each precision level data segment. Value, where i=0,1,...,P-1; for the data segment with precision level i, the sender randomly selects whether to send with probability Pr(i);

2. The sender sends the selected data segments in turn according to the TCP data sending mechanism, and the receiver confirms the received data segments;

3. The sender estimates the congestion status and available bandwidth of the network according to the ACK feedback, so as to update the congestion window cwnd, so that the value of cwnd does not exceed the product of the expected sending rate RD and the round-trip delay rtt;

If the selected basic precision data ACK times out, the sender retransmits and updates cwnd and Pr(i); if the selected enhanced precision data ACK times out, the sender does not retransmit, only updates cwnd and Pr(i) ); if the received ACK contains the ECN flag, update cwnd and Pr(i).

In terms of implementation, the method can be modified and extended based on the existing TCP protocols of various versions to realize the corresponding control design, and can also be completely redesigned. The extension based on the existing TCP can be compatible with the existing network equipment, and can be realized by multiplexing the existing TCP code, so it is a preferred embodiment of the present invention.

In this method, during the link establishment (or data transmission) process, the sender and the receiver use the SYN message (or normal data message, that is, the data message when sending data after the TCP link is established, except in the initial stage of link establishment. In addition to the negotiation and configuration of related parameters, it can also be renegotiated during the data transmission process. At this time, the TCP link has been established, and the parameter transmission is completed with the help of data packets instead of SYN packets.) and ACK packets The reserved fields in TCP options negotiate and confirm the <P, PD, RD> parameters of the task according to the preset process.

The default flow here is:

The negotiation of <P, PD, RD> occurs in the TCP link establishment/handshake phase. At this time, the sender carries the P value and the RD_MAX value in the TCPoptions field of SYN, which respectively indicate the maximum number of precision levels that the sender can support, and the maximum Sending speed; and PD_DEFAULT and RD_DEFAULT indicate the PD value and RD value recommended by the sender. The receiver saves the received P, RD_MAX, PD_DEFAULT, and RD_DEFAULT values locally.

In the process of ACKing the SYN message, the receiver confirms the required PD value and RD value to the sender through the TCPoptions of the ACK message. The PD receiving the disconnection feedback must be smaller than the P value advertised by the sender, and the RD value should not be higher than the RD_MAX value advertised by the sender.

If the receiving end does not feedback, the transmitting end adopts PD_DEFAULT and RD_DEFAULT as the PD and RD values of the corresponding transmission task of the receiving end by default.

During the data segment sending process, the receiving segment can also update PD and RD, but it is not guaranteed to be successful. At this time, the receiver sends a new PD value and RD value to the TCP options of M consecutive ACK messages to the sender. The value of M is set according to the network conditions, and the typical value is 5. After the sender receives it, it updates the PD value and RD value corresponding to the receiving node.

The design of using the reserved fields in TCP options to transmit related information is shown in Table 1:

Table 1

The sender numbers and configures all data segments to be transmitted. Each data segment carries a data segment number j (this number is independent of the seq sequence number in the TCP header). j is stored in the TCP options reserved field of the TCP data segment.

According to the cwnd value of the current link, the sender will randomly select and transmit the data segments to be transmitted through the first strategy in turn; the goal of the first strategy is that the protocol transmits data at the rate RD when the bandwidth is sufficient, and the bandwidth is insufficient. The transmission accuracy is dynamically reduced from time to time to maintain the same or similar transmission progress while avoiding congestion. The method used is random packet loss, and for each data segment with precision level i, it is selected with the probability of Pr(i). Assuming that the round-trip delay of the current network is rtt and the size of the congestion control window is cwnd, then the values of Pr(i) are as follows:

For the accuracy class i<PD, Pr(i)=1;

For a precision class of PD≤i≤P-1, Pr(i)=1-max(0,min(1,i-cwnd/rtt*P/RD)).

The sender determines whether packet loss occurs during the transmission process according to whether it receives the ACK feedback from the receiver and the TCP data segment acknowledgment number confirmed by the ACK. If the ACK of the basic precision data segment times out, the data segment will be retransmitted, and the size of the sliding window will be adjusted according to the original TCP policy; if the ACK of the enhanced precision data segment has timed out, no retransmission will be performed. The second strategy adjusts the size of the sliding window; if the received ACK carries the ECN mark, or in other cases, the size of the sliding window is adjusted according to the original TCP strategy. The aforementioned second strategy is cwnd=cwnd−1.

When the receiving end receives the data segment j, the data block number value k=j div P corresponding to the data segment represents an integer division operation; the corresponding precision level information is i=j mod P, where mod is a remainder operation.

If all the data segments in the data block k have been received, the data block is decoded; if there is a number value less than k at the receiving end, and the data segments of the basic precision data have been collected as the data blocks that have not been decoded, the data block will be decoded. block to decode.

For the data blocks whose basic precision data segments have been collected but not yet decoded, if the time for collecting the basic precision data exceeds T (T can be rtt), the receiving end will immediately perform decoding.

If the network intermediary supports strict multi-priority queue scheduling. Assuming that the number of supported priorities is PS, then the data segment for the basic precision data carries the highest priority 0; the precision level values are PD, PD+1, ..., min(P-1, PD+PS-1) enhancements The data segments of the precision data carry priorities 1, 2, 3, ..., PS-1 respectively, and the data segments of other precision levels carry the priority value PS-1.

With the streaming data transmission control method of this embodiment, the sender can actively adjust the data sending accuracy and control the amount of data to be transmitted according to the available bandwidth information of the link fed back by the receiver. If the network bandwidth becomes better, increase the accuracy of sending data; otherwise, reduce the accuracy of sending data, thereby reducing the amount to be sent and ensuring the progress of transmission. According to the accuracy level, the data is divided into two categories that require reliable transmission and those that do not require reliable transmission. When packet loss occurs during transmission, only the lost reliable data is retransmitted to avoid the drop in effective throughput and prevent the transmission protocol from being blocked by the loss of unreliable data.

The content of the present invention has been described above. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. Based on the above content of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

Claims (10)

1. A streaming data transmission control method, comprising the operations of:

1) dividing data into data segments, dividing each data segment into a plurality of levels according to the importance degree of the data, and setting a precision level threshold;

2) using the ratio of the congestion window to the round trip delay as the optimal sending rate estimation value of the data, and calculating and updating the sending probability of the data segment of each precision grade according to the value;

3) sequentially sending the selected data segments according to a data sending mechanism of the TCP;

4) estimating the congestion state and available bandwidth of the network according to the ACK feedback, updating a congestion window according to the congestion state and the available bandwidth, and enabling the value of the congestion window to be less than or equal to the expected sending rate of the data segment and the round trip delay; wherein,

when the grade value of the data segment is less than the precision grade threshold value, the data is basic precision data;

when the grade value of the data segment is larger than or equal to the precision grade threshold value, the data is enhanced precision data;

when the selected basic precision data ACK is overtime, retransmission is carried out, and the sending probability of the congestion window and the data segments of each precision grade is updated;

when the selected enhanced precision data ACK is overtime, retransmission is not carried out, and only the sending probability of the congestion window and the data segments of each precision grade is updated;

and when the received ACK comprises the ECN mark, updating the congestion window and the sending probability of the data segment with each precision level.

2. The streaming data transmission control method according to claim 1, wherein during the data segment transmission process, the reserved fields in the TCP options of the SYN packet and the ACK packet are used to negotiate and confirm the maximum precision classification number, the precision classification threshold value, and the expected transmission rate of the task according to a preset flow.

3. The streaming data transmission control method according to claim 2, wherein the predetermined procedure comprises the following operations:

the negotiation of the maximum precision grading number, the precision grade threshold value and the expected sending rate occurs in a TCP link establishing stage; at this time, the sending end carries a P value and an RD _ MAX value in a TCP options field of the SYN, which respectively represent the maximum precision grading number and the maximum expected sending rate that the sending end can support; and PD _ DEFAULT and RD _ DEFAULT represent the maximum number of precision steps recommended by the transmitting end and the desired transmission rate;

the receiving end stores the received P, RD _ MAX, PD _ DEFAULT and RD _ DEFAULT values in the local; in the process of carrying out ACK on the SYN message, the receiving end confirms the required precision level threshold value and the required expected sending rate to the sending end through TCPoptions of the ACK message;

wherein, the precision grade threshold value fed back by the receiving end is less than the maximum precision grading number announced by the transmitting end, and the expected transmitting speed is less than or equal to the RD _ MAX value announced by the transmitting end;

if the receiving end does not feed back, the transmitting end adopts PD _ DEFAULT and RD _ DEFAULT as the accuracy level threshold value and the expected transmission rate of the transmission task corresponding to the receiving end by DEFAULT.

4. The streaming data transmission control method according to claim 1, wherein the receiving end composes a plurality of consecutive data segments into a data block, and decodes in units of data blocks; numbering the data segments according to a sending sequence when data are sent, and taking a value j of the sent data segment number; when the receiving end receives the data segment, the receiving end can calculate that the number value of the data block corresponding to the data segment is k ═ j div P, wherein div represents integer division operation; the corresponding precision grade information is i ═ j mod P, where mod is the remainder operation.

If all data segments in the data block k have been received, decoding the data block;

and if the number value of the receiving end is smaller than k, decoding the data block which is completely received but not decoded in the data segment of the basic precision data.

5. The streaming data transmission control method according to claim 4, wherein the receiving end performs decoding immediately when a time for which the base-precision data is received exceeds a predetermined time T for a data block for which the base-precision data is received and not yet decoded.

6. The streaming data transmission control method according to claim 1, wherein when a ratio of a congestion window to a network round trip delay is used as an optimal sending rate estimation value of data, a first preset strategy is adopted to randomly select and transmit a data segment to be transmitted; the first preset strategy is as follows:

p is the maximum precision grading number;

PD is a precision grade threshold;

i is a grade number;

RD is the desired transmission rate;

for each data segment with the accuracy grade i, selecting the data segment with the data segment sending probability Pr (i);

assuming that the round trip delay of the current network is rtt and the size of the congestion control window is cwnd, the values of pr (i) are:

for a precision level of i < PD, pr (i) ═ 1;

for a precision rating of PD ≦ i ≦ P-1, Pr (i) 1-max (0, min (1, i-cwnd/rtt P/RD)).

7. The streaming data transmission control method according to claim 1, wherein the sending end determines whether packet loss occurs in the transmission process according to whether the feedback ACK and the TCP data segment acknowledgment number acknowledged by the ACK are received;

if the ACK of the basic precision data is overtime, retransmitting the data segment, adjusting the size of a sliding window according to the original strategy of the TCP and updating the sending probability of the data segment of each precision grade;

if the ACK of the enhanced precision data is overtime, retransmission is not carried out, the size of the sliding window is adjusted according to a second preset strategy, and the sending probability of each precision grade data segment is updated at the same time;

and if the ACK received by the sending end carries the ECN mark, adjusting the size of the sliding window according to the original strategy of the TCP, and updating the sending probability of the data segments of each precision grade according to the new value of the sliding window.

8. The streaming data transmission control method of claim 7, wherein the second preset policy is: the adjusted congestion control window size is equal to the congestion control window size before adjustment-1.

9. The streaming data transmission control method according to claim 1, wherein all data segments to be transmitted are numbered and configured; each data segment carries the number of the data segment and the precision grade number indicating the importance degree of the data segment; and the grade number and the data segment number are stored in a TCP options reserved field of the TCP data segment, wherein the data segment number is independent from the seq sequence number in the TCP message header.

10. The streaming data transmission control method according to claim 1, wherein if the network intermediate device supports strict multi-priority queue scheduling, the supported number of priorities is set to PS, and the data segment of the basic precision data carries the highest priority 0; the data segments of the enhanced precision data with precision grade values of PD, PD +1, …, min (P-1, PD + PS-1) carry priority values of 1, 2, 3, …, PS-1 respectively, and the data segments of the other precision grades carry priority values of PS-1.