JP6727107B2 - Packet communication system, congestion control method therefor, and congestion control program - Google Patents

Description

The present invention relates to a packet communication system, and more particularly, to a congestion control function of a transport layer.

In current Internet communication, a protocol of TCP/IP (Transmission Control Protocol/Internet Protocol) is used as a standard. TCP, which is a typical communication protocol of the transport layer, is a connection-type reliability protocol and has a retransmission control function and a congestion control function. In TCP, the basic operation is that the receiving side returns an acknowledgment (ACK) indicating that the packet has been received by the transmitting side, and the transmitting side which has received the ACK further transmits the next packet. At this time, network congestion control is performed by adjusting the congestion window (cwnd) that indicates the amount of data that can be transmitted without waiting for ACK. At the start of communication, cwnd performs a slow start in which cwnd is incremented by one packet each time an ACK is received in order to avoid congestion. When a packet loss occurs due to congestion or cwnd exceeds a slow start threshold (ssthresh), a transition is made to a congestion avoidance mode in which control is performed to increase or decrease cwnd so as to avoid congestion.

Various methods of congestion control algorithms have been proposed along with changes in Internet communication. CUBIC (see Non-Patent Document 1), which has become a standard in the Linux kernel 2.6 and later versions, has an RTT (Round Trip Time) fairness because the increase amount of cwnd in the congestion avoidance mode depends on the time from packet loss. It is possible to improve the communication throughput even in a high and high delay environment. In recent years, wireless communication has become common, but wireless communication has a greater variation in communication quality than wired communication, and there is a problem in that throughput decreases due to increased delay due to wireless errors and packet loss.

As a method of improving the throughput in wireless communication, TCP parameters and options such as Westwood that controls unnecessary throughput by estimating the available bandwidth at the time of packet loss, extension of maximum cwnd, use of SACK, etc. There is W-TCP (Wireless-Profiled TCP) tuned for wireless communication.

Also, a cross-layer control method has been studied in which not only the transport layer but also the Internet layer and the data link layer notify the congestion status, wireless handover, and the like to control TCP.

Quick-Start (see Non-Patent Document 2) uses the option area of TCP and IP packets to notify the throughput requested by the transmission side, and if all nodes between the transmission and reception approve, the requested throughput is supported. This is a method of changing to cwnd.

Also, Non-Patent Document 3 introduces a method of using an option area of a TCP packet to explicitly notify a server of available throughput due to a change in a wireless link or the like.

A method has also been proposed in which communication quality is detected and a plurality of congestion control functions are switched based on this communication quality.

Injong Rhee, and Lisong Xu, "CUBIC: A New TCP-Friendly High-Speed TCP Variant", 2008 S. Floyd, 3 others, "Quick-Start for TCP and IP", RFC4782 A. Jain et al., "Mobile Throughput Guidance Inband Signaling Protocol draft-flinck-mobile-throughput-guidance-03", IETF Internet-Draft, 2015

In the wireless network of the 2020s, in order to efficiently accommodate increasing traffic, a Multi-RAT environment in which a plurality of RATs (Radio Access Technology) having different characteristics such as a frequency band used and a cell radius are mixed is used. It is supposed. As shown in FIG. 1, the RAT to be used is, in addition to existing LTE (Long Term Evolution) and Wi-Fi, for example, a wide band with a maximum bandwidth of several G to several tens Gbps by using a high-frequency millimeter wave, but a cell. A small radius and an inexpensive but low-reliability one using an unlicensed band such as a 5 GHz band are considered. In such a Multi-RAT environment, since small cells having a cell radius of several meters to several hundred meters are scattered, switching of cells frequently occurs due to movement of communication terminals, and bandwidth, delay, and PER (Packet Error Rate). Communication quality fluctuates rapidly.

CUBIC, which is the TCP congestion control algorithm described above, is a method that improves throughput in a high-bandwidth, high-delay environment while increasing fairness with RTT and other TCP flows, and is designed to adapt to rapid changes in the communication environment. Not a thing. For this reason, when connecting to a cell using an ultra-wide band millimeter wave having a narrow coverage while communicating by CUBIC in LTE, cwnd is not rapidly increased in order to use the available band. Therefore, when moving, there is a problem that the band is not fully utilized because it leaves the cell before the band is fully used.

Further, since CUBIC determines packet loss as congestion and reduces throughput, when using an unlicensed band, PER increases due to radio wave interference, and there is a problem that throughput is unnecessarily reduced.

Further, the required throughput can be immediately obtained by using the Quick-Start, but in order to use the Quick-Start, all nodes between the transmitting and receiving terminals need to support the Quick-Start.

Further, the switching of the congestion control function based on the above-mentioned communication quality requires the takeover of parameters between the congestion control functions and the synchronization of the control switching timing between the transmitting and receiving terminals.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a packet communication system and a congestion control method therefor, and a congestion control program, which can quickly respond to a sudden change in communication quality such as a band. ..

In order to achieve the above object, the present invention includes a radio base station that accommodates a radio terminal, in a packet communication system including a communication device for forming a connection of the transport layer of OSI7 hierarchical model between the mobile station A wireless access quality detecting means for detecting a wireless access quality between a wireless terminal and a wireless base station, and a congestion window for adjusting a congestion window size in a transport layer based on the wireless access quality detected by the wireless access quality detecting means The wireless access quality detecting means calculates a maximum bandwidth that can be used in wireless access between the terminal and the wireless base station, and wirelessly accesses the maximum bandwidth when the maximum bandwidth fluctuates. Notifying the congestion window control means as a quality, the congestion window control means, when the congestion window size exceeds a first threshold value, from the slow start mode to a higher speed than the congestion avoidance mode and more slowly than the slow start mode. When the congestion window size exceeds the second threshold value which is larger than the first threshold value, the control is performed so as to shift from the fast increase mode to the congestion avoidance mode, and the maximum bandwidth notified is increased. Then, the second threshold value is calculated based on the maximum band.
Further, the present invention is a packet communication system including a wireless base station accommodating a wireless terminal and a communication device forming a connection of a transport layer of the OSI 7-layer model between the wireless terminal and the wireless terminal. Radio access quality detecting means for detecting the radio access quality between the station, and a congestion window control means for adjusting the congestion window size in the transport layer based on the radio access quality detected by the radio access quality detecting means, The wireless access quality detection means calculates a maximum bandwidth that can be used in wireless access between the terminal and the wireless base station, and if there is a change in the maximum bandwidth, the maximum bandwidth is used as the wireless access quality to determine the congestion window. Includes a maximum bandwidth detection means for notifying the control means, the congestion window control means, in the congestion avoidance control processing, the increase amount of the congestion window size increase processing with the increase of the notified maximum bandwidth is large and the congestion window size decrease It is characterized in that the amount of decrease in processing is made small, and the amount of increase in processing of increasing the congestion window size is controlled to be small and the amount of decrease in processing of reducing the congestion window size is controlled to be large as the notified maximum bandwidth is decreased.
Further, the present invention is a packet communication system including a wireless base station accommodating a wireless terminal and a communication device forming a connection of a transport layer of the OSI 7-layer model between the wireless terminal and the wireless terminal. Radio access quality detecting means for detecting the radio access quality between the station, and a congestion window control means for adjusting the congestion window size in the transport layer based on the radio access quality detected by the radio access quality detecting means, The wireless access quality detection means calculates a maximum bandwidth that can be used in wireless access between the terminal and the wireless base station, and if there is a change in the maximum bandwidth, the maximum bandwidth is used as the wireless access quality to determine the congestion window. Notifying the control means, the congestion window control means, in the congestion avoidance control process, the greater the difference between the throughput of the communication performed by the terminal and the notified maximum bandwidth, the larger the increase amount in the congestion window size increase process and the congestion window. Decrease the reduction amount during the size reduction process, and reduce the increase amount during the congestion window size increase process as the difference between the throughput of the communication performed by the terminal and the notified maximum bandwidth decreases, and reduce the congestion window size during the packet loss process It is characterized by greatly controlling the amount of time reduction .

According to the present invention, by performing the congestion window control based on the quality change of the wireless access environment, it is possible to detect that the bandwidth has been widened by applying carrier aggregation or dual connectivity during communication by, for example, LTE, and immediately widen the wideband. It is possible to change the control to be used. Further, when the cell moves again to the narrow band cell, fairness with other flows can be maintained by controlling so that cwnd is not rapidly increased.

Further, by considering the wireless transmission quality in the transport layer, it is possible to determine the increase in RTT or PER and the congestion due to a wireless error, so that the throughput is not unnecessarily reduced.

Image diagram explaining Multi-RAT environment Block diagram of packet communication system via proxy Block diagram of packet communication system without proxy Functional configuration diagram of the first embodiment Sequence diagram of the first embodiment Functional configuration diagram of the second embodiment Figure showing an example of maximum bandwidth conversion table Sequence diagram of the second embodiment Functional configuration diagram of the third embodiment Operation flow of wireless transmission quality variation determination unit Other operation flow of wireless transmission quality variation determination unit Sequence diagram of the third embodiment Functional configuration diagram of Embodiment 4 Sequence diagram of the fourth embodiment Functional configuration diagram of Embodiment 5 Congestion window control 1 operation flow Congestion window control 2 operation flow Graph showing the amount of cwnd increase in each mode Congestion window control 3 operation flow Congestion window control 4 operation flow Congestion window controller of existing transport layer Congestion window control 5 operation flow Graph showing increase/decrease amount of cwnd in congestion window control 6 The graph which shows the change of the cwnd increase/decrease amount by the control which combined congestion window control 1 and 6.

FIG. 2 shows a packet communication system for implementing the present invention. The communication system includes a terminal 100, a base station 200, a core node 300 accommodating the base station, a proxy 400 that is a communication device that terminates a transport layer connection of an OSI (Open Systems Interconnection) 7-layer model, and a communication destination of the terminal 100. The server 100 includes a certain server 500, and the terminal 100 communicates with the server 500 via the base station 200, the core node 300, and the proxy 400. The location of the proxy 400 is not limited to the connection point of the Internet, and may be within the core network. Further, as another embodiment, as shown in FIG. 3, the terminal 100 can directly communicate with the server 500 without going through the proxy 400. In this case, the server 500 serves as a communication device that terminates the transport layer connection.

FIG. 21 shows an existing transport layer congestion window control unit. Since the existing congestion window control unit does not acquire information from outside the transport layer, the information available for congestion control is limited to the packet transmission amount, ACK reception amount, packet round trip time (RTT) and the like.

With respect to the congestion window control of the existing transport layer, in the present invention, (1) the terminal 100 or the base station 200 calculates the wireless access quality, and the transmission side communication device (the terminal 100 or the proxy 400 or the server 500) receives the transport information. (2) Control for adjusting the congestion window size cwnd of TCP based on wireless access quality in the transport layer control unit of the transmission side communication device (terminal 100 or proxy 400 or server 500) It is characterized by performing.

The wireless access quality is, for example, the maximum bandwidth that can be used by the terminal 100 (hereinafter simply referred to as the maximum bandwidth), the wireless transmission quality between the terminal 100 and the base station 200 (eg, RSSI (Received Signal Strength Indicator), SINR). (Signal to Interference Noise Ratio), CQI (Channel Quality Indicator) in LTE, and the like, which are indicators indicating the quality of the wireless access environment.

There are the following five embodiments (1) of notifying the quality of the radio access environment of the present invention.

[Embodiment 1] Form in which base station 200 notifies proxy 400 of maximum bandwidth [Embodiment 2] Form in which terminal 100 notifies proxy 400 of maximum bandwidth [Embodiment 3] Radio transmission quality from base station 200 to proxy 400 [Embodiment 4] Embodiment 4 that notifies the wireless transmission quality from the terminal 100 to the proxy 400 [Embodiment 5] Embodiment that performs TCP congestion window control in the terminal 100 Hereinafter, each embodiment will be described in detail.

[Embodiment 1]
The first embodiment is a form in which the base station 200 notifies the proxy 400 of the maximum bandwidth available to the terminal 100. The functions of the base station 200 and the proxy 400 according to the first embodiment are shown in FIG. The base station 200 calculates the maximum bandwidth that can be used by the terminal 100 from the frequency band that can be assigned to the terminal 100, the modulation method, the presence or absence of MIMO (Multiple-Input Multiple-Output) usage, the number of communication flows that share a wireless link, and the like. The maximum bandwidth calculating unit 201 is provided. In the transport layer, the proxy 400 includes an RTT measuring unit 401 that measures RTT for each packet transmission/reception, an access quality monitoring unit 402 that detects fluctuations in wireless access quality, an RTT acquired from the RTT measuring unit 401, and an access quality monitoring unit. It has a congestion window control unit 403 which reflects the congestion window control of TCP based on the maximum bandwidth acquired from 402. FIG. 5 shows a sequence diagram of the first embodiment.

As shown in FIG. 5, when the maximum bandwidth calculation unit 201 detects a variation in the maximum bandwidth, it notifies the access quality monitoring unit 402 of the maximum bandwidth. The congestion window control unit 403 acquires the RTT from the RTT measurement unit 401, acquires the maximum bandwidth from the access quality monitoring unit 402, and controls the congestion window based on the RTT and the maximum bandwidth.

When the terminal 100 communicates with the server 500 without going through the proxy 400 (see FIG. 3), the server 500 has the function of the proxy 400.

[Embodiment 2]
The second embodiment is a form in which the terminal 100 notifies the proxy 400 of the maximum bandwidth. The functions of the terminal 100 and the proxy 400 according to the second embodiment are shown in FIG. The terminal 100 has a wireless communication management unit 101 for managing the type of wireless access being used, frequency band, MIMO usage, etc., a maximum band conversion table 102 for converting the maximum band from the communication environment in use, and the maximum band has been changed. At this time, the wireless quality notifying unit 103 is provided to notify the access quality monitoring unit 402 of the proxy 400 of the maximum bandwidth. The wireless quality notifying unit 103 notifies the proxy 400 side by adding maximum bandwidth information to the option area or the payload section of the header part of the TCP ACK packet. The proxy 400 has the same function as that of the first embodiment, and when the maximum bandwidth changes, the congestion window control unit 403 performs the same TCP congestion window control as that of the first embodiment.

The maximum bandwidth conversion table 102 is shown in FIG. Although the terminal 100 cannot know the exact maximum bandwidth in the table of FIG. 7, the advantage of the second embodiment is that the present invention can be implemented without modifying the base station.

The procedure after notifying the access quality monitoring unit 402 of the maximum bandwidth is the same as in the first embodiment. FIG. 8 shows a sequence diagram of the first embodiment.

When the terminal 100 communicates with the server 500 without going through the proxy 400 (see FIG. 3), the server 500 has the function of the proxy 400.

[Third Embodiment]
The third embodiment is a form in which the base station 200 notifies the proxy 400 of the wireless transmission quality. The functions of the base station 200 and the proxy 400 of the third embodiment are shown in FIG. The terminal 100 includes a wireless communication management unit 101 that detects radio wave reception quality from the base station 200 as wireless transmission quality, and a wireless quality notification unit 103 that periodically notifies the base station 200 of the detected wireless transmission quality. As the wireless transmission quality, CQI or the like is used for LTE in addition to RSSI and SINR. The base station 200 has a wireless transmission quality acquisition unit 202 that acquires the wireless transmission quality from the wireless quality notification unit 103, and a wireless transmission quality variation determination unit 203 that determines a variation in the wireless transmission quality of the terminal 100 from the wireless transmission qualities acquired a plurality of times. It is equipped with. When RSSI and SINR are used, class values obtained by classifying the RSSI and SINR values into several classes (eg, classes 1 to 15) representing good quality are used. Since the wireless transmission quality changes every moment depending on the usage status of the terminal 100, the wireless transmission quality variation determination is performed such as an average value of the wireless transmission quality of a plurality of times or a process of considering that the wireless transmission quality has changed when a certain number of times exceeds the reference value. This is performed in the section 203.

An operation example of the wireless transmission quality variation determination unit 203 is shown in FIGS. In the example of FIG. 10, an average value of wireless transmission quality (Q ₁ (overlined to represent “average” in FIG. 10; the same applies in the following)) is calculated at regular intervals ( Steps S101 and S102), if the difference between the previously calculated average value (Q ₁ ) and the newly calculated average value (Q ₂ ) of wireless transmission quality exceeds a reference value that is considered to have changed wireless transmission quality, the quality changes. It is determined that it has done (steps S103 to S107). In the example of FIG. 11, two reference values 1 and 2 are defined, and if the acquired wireless transmission quality is larger than the reference value 1, it is determined that the quality is better than the current wireless transmission quality of the terminal 100 (steps S111 to S113). If it is smaller than the reference value 2, it is determined that the quality is lower than the current transmission quality of the terminal 100 (steps S114 to S115). If it is determined that the quality is good or bad a certain number of times within a certain period, it is determined that the wireless transmission quality has changed (steps S116 to S117).

The proxy 400 has the same functions as those of the first and second embodiments, and when the wireless transmission quality variation determination unit 203 determines that the wireless transmission quality has changed, the access quality monitoring unit 402 detects the changed wireless transmission quality. Notice. The access quality management unit 402 notifies the congestion window control unit 403 of the wireless transmission quality, and changes the congestion window control of TCP. FIG. 12 shows a sequence diagram of the third embodiment.

When the terminal 100 communicates with the server 500 without going through the proxy 400 (see FIG. 3), the server 500 has the function of the proxy 400.

[Embodiment 4]
The fourth embodiment is a form in which the terminal 100 notifies the proxy 400 of the wireless transmission quality. The functions of the terminal 100 and the proxy 400 according to the fourth embodiment are shown in FIG. The terminal 100 has a wireless communication management unit 101 that detects wireless transmission quality from communication with the base station 200, a wireless transmission quality variation determination unit 104 that determines quality variation from multiple times of wireless transmission quality, and wireless transmission quality has changed. The wireless quality notification unit 103 is provided for notifying the proxy 400 at the time. The proxy 400 has the same functional units as those in the third embodiment. The wireless transmission quality variation determination unit 104 performs the same processing (FIGS. 10 and 11) as the wireless transmission quality variation determination unit 203 according to the third embodiment. That is, the fourth embodiment is characterized in that the terminal 100 side determines the variation of the wireless transmission quality, which is performed by the base station 200 in the third embodiment. The wireless transmission quality notification from the wireless quality notifying unit 103 to the proxy 400 is performed by adding wireless transmission quality information to the option area or the payload portion of the header portion of the TCP ACK packet, as in the second embodiment. Notify to. A sequence diagram of the fourth embodiment is shown in FIG.

When the terminal 100 communicates with the server 500 without going through the proxy 400 (see FIG. 3), the server 500 has the function of the proxy 400.

[Fifth Embodiment]
The fifth embodiment is a mode of performing TCP congestion window control in the terminal 100. The function of the fifth embodiment is shown in FIG. In the first to fourth embodiments, the proxy 400 is the transmission side, but in the fifth embodiment, the terminal 100 side is the transmission side, and the terminal 100 includes the RTT measurement unit 105 and the congestion window control unit 106. The function of the access quality monitoring unit 401 of the proxy 400 is performed by the wireless communication management unit 101 that manages the frequency band of the wireless access to be used, the modulation method, and the like, and detects the wireless transmission quality such as RSSI and SINR.

Since the wireless transmission quality can be grasped by the terminal 100, the terminal is equipped with a wireless transmission quality variation determination unit 104 that determines quality variation from the wireless transmission quality for a certain period.

When converting the maximum bandwidth on the terminal 100 side, the maximum bandwidth conversion table 102 is provided, and the maximum bandwidth is converted from the used bandwidth, the modulation method, etc. managed by the wireless communication management unit 101, and the congestion window control unit Notify 106.

When an accurate maximum band is calculated on the base station 200 side from radio resources that can be assigned to the terminal 100, the base station 200 includes a maximum band calculation unit 201 to calculate the maximum band, and wireless communication of the terminal 100 is performed. Notify the management unit 101.

Although the maximum bandwidth is acquired as the wireless access quality in the first and second embodiments and the wireless transmission quality is acquired as the wireless access quality in the third and fourth embodiments, the maximum bandwidth and the wireless transmission quality are acquired as the wireless access quality. Both may be acquired. That is, as other embodiments, a combination of the first and third embodiments, a combination of the first and fourth embodiments, a combination of the second and third embodiments, a combination of the second and fourth embodiments, and the like can be considered.

Next, (2) control for adjusting the congestion window size cwnd of TCP based on the wireless access quality of the present invention described above will be described. Here, the unit of band is bps (bit per second), the unit of cwnd and ssthresh is MSS (maximum segment size), and the unit of RTT is second.

In the first and second embodiments in which the maximum bandwidth is acquired as the wireless access quality, the congestion window control unit 403 performs any one of the following congestion window controls 1, 2, 5, 6 or a combination of these controls.
[Congestion window control 1] Change control of ssthresh based on maximum bandwidth [Congestion window control 2] High speed cwnd increase control considering maximum bandwidth [Congestion window control 5] Cwnd decrease control based on maximum bandwidth [Congestion window control 6] Cwnd increase control based on maximum bandwidth

In the third and fourth embodiments in which the wireless transmission quality is acquired as the wireless access quality, the congestion window control unit 403 performs the following congestion window control 3.
[Congestion window control 3] cwnd control when RTT increases in consideration of wireless transmission quality

Further, in the embodiment in which the bandwidth control and the wireless transmission quality are acquired as the wireless access quality, the congestion window control unit 403 sets the maximum bandwidth acquired in the first and second embodiments, the wireless transmission quality acquired in the third embodiment, and the RTT. Then, the following congestion window control 4 is performed.
[Congestion window control 4] Maximum bandwidth, wireless transmission quality, change control of cwnd increase/decrease parameter by RTT

The congestion window control unit 106 of the terminal 100 according to the fifth embodiment also performs any one of the congestion window controls 1 to 6 or any combination thereof based on the acquired maximum bandwidth, wireless transmission quality, and RTT.

[Congestion window control 1]
The congestion window control 1 is ssthresh change control based on the maximum bandwidth. FIG. 16 shows an operation flow of the congestion window control 1. Here, the maximum band previously detected by the wireless communication management unit 101 or the access quality monitoring unit 402 is B ₁ , and the newly detected maximum band is B ₂ .

(1) Step S1
When the maximum bandwidth B ₂ newly detected by the wireless communication management unit 101 or the access quality monitoring unit 402 is different from the previously detected maximum bandwidth B ₁ , the maximum bandwidth is set to the congestion window control unit (106 or 403). Notice. If the maximum bandwidth does not change, normal congestion control is performed.

(2) Step S2
If B ₁ <B ₂ , the process proceeds to step S3.

(3) Step S3
The ssthresh is calculated based on the maximum bandwidth B ₂ and the RTT acquired from the RTT measurement unit (105 or 401). The following equation can be considered as a method of determining ssthresh. The following expression shows a value obtained by multiplying cwnd corresponding to the maximum band in the current RTT by γ. γ may be a constant or may be varied depending on the wireless transmission quality and RTT.

By increasing ssthresh based on the maximum band, it is possible to shift to the slow start mode and immediately use the band.

(4) Step 4
If cwnd≧ssthresh, congestion avoidance mode that controls to increase/decrease cwnd so as to avoid congestion (step S5), and if cwnd<ssthresh, slow start mode that doubles cwnd every RTT (step S6) Move to. As the algorithm for the congestion avoidance mode, it is conceivable to use an existing congestion avoidance algorithm such as TCP Reno or CUBIC or a control algorithm for the congestion window control 4, 5, 6 of the present invention.

[Congestion window control 2]
The congestion window control 2 is a high speed cwnd increase control in consideration of the maximum bandwidth. FIG. 17 shows an operation flow of the congestion window control 2. Congestion window control 2 performs control to increase cwnd at a high speed up to a threshold based on the maximum bandwidth when the maximum bandwidth increases, as in congestion window control 1. However, if cwnd starts slow from a large state, it may increase cwnd abruptly and cause serious congestion, so congestion window control 2 is faster than normal congestion avoidance mode and slower than slow start mode. Introduces a new fast cwnd increase mode that slowly increases cwnd. Here, the normal congestion avoidance mode is any one of those used in existing congestion avoidance algorithms such as TCP Reno and CUBIC. The high-speed cwnd increase mode is an improvement of the cwnd increase/decrease process with respect to the normal congestion avoidance mode.

In the congestion window control 2, the value of ssthresh calculated in the congestion window control 1 is set as ssthresh' (step S23). If it is determined in step S26 that cwnd<ssthresh', the process proceeds to the high speed cwnd increase mode in step S28. ssthresh' is set to 0 at the time of high-speed retransmission transfer or timeout, and the high-speed cwnd increase mode is ended.

The control in the high speed cwnd increasing mode may be the following control, for example.

(A) The following control is performed to double the window size (cwnd′) when the maximum bandwidth is updated, with the increase amount set to an initial value of 1 for each RTT. cwnd ₀ indicates the window size at the time of receiving the first ACK after the maximum bandwidth change.

(B) When the increase amount of cwnd in the normal congestion avoidance mode is larger than that in the above control, the following control that uses the larger increase amount is performed.

FIG. 18 shows the amount of increase in cwnd in each control mode. In FIG. 18, the amount of increase in cwnd when the maximum bandwidth increases at time T is shown.

[Congestion window control 3]
The congestion window control 3 is cwnd control when RTT is increased in consideration of wireless transmission quality. The operation flow of the congestion window control 3 is shown in FIG. The congestion window control 3 may be used alone as the congestion control algorithm itself, or may be used in combination with the slow start mode as the congestion avoidance mode. Also, the congestion window control 3 may be implemented as an improvement of an existing congestion avoidance algorithm such as TCP Reno or CUBIC.

(1) Step S31
The RTT measurement unit (105 or 401) measures the RTT for each packet transmission and reception, and notifies the congestion window control unit (106 or 403) of the average value of the RTTs of a plurality of times as RTT ₁ .

(2) Step S32
The terminal 100 or the proxy 400 detects a change in wireless transmission quality and notifies the congestion window control unit (106 or 403).

(3) Step S33
The congestion window control unit (106 or 403) is notified of the average value of a plurality of RTTs measured by the RTT measurement unit (105 or 401) as RTT ₂ .

(4) Step S34
If the RTT has increased (RTT ₂ >RTT ₁ ) before and after the change in the wireless transmission quality, the process proceeds to step S35.

(5) Step S35
It is assumed that the wireless transmission quality is Q, and the higher the value of Q, the better the quality. The congestion window control unit (106 or 403) manages the reference value RV _{1 for} judging that the wireless transmission quality is low and the reference value RV ₂ for judging that the wireless transmission quality is high. If Q<RV ₁ , then the RTT It is determined that the increase is due to the deterioration of the wireless transmission quality, and control is performed to increase cwnd in order to maintain the throughput (step S36). If Q>RV ₂ , it is determined that the increase in RTT is due to congestion, and cwnd is decreased to avoid congestion (Sstep 38).

As an example of the increase amount of cwnd in step S36, the following equation that maintains the throughput at RTT ₁ is considered.

ｃｗｎｄ’：ＲＴＴ増加前のｃｗｎｄ

cwnd': cwnd before RTT increase

As an example of reducing cwnd in step S37, control for reducing cwnd as in the following equation can be considered.

Further, by using ECN (Explicit Congestion Notification) together, more accurate congestion determination becomes possible.

[Congestion window control 4]
The congestion window control 4 is control of changing the maximum bandwidth, wireless transmission quality, and cwnd increase/decrease parameter by RTT. FIG. 20 shows an operation flow of the congestion window control 4. The congestion window control 4 changes the cwnd increase/decrease parameter according to the maximum bandwidth, the wireless transmission quality, and the RTT in the congestion avoidance control processing used in arbitrary TCP congestion control such as TCP Reno and CUBIC. A general AIMD (Additive-Increase/Multiplicative-Decrease) control of the existing TCP congestion control is expressed by the following equation.

Here, for example, in TCP Reno, α=1/cwnd and β=1/2, and in HighSpeed TCP, control is performed to determine α and β from the current cwnd.

In steps S41 and S42 of FIG. 20, when the value of the maximum bandwidth B ₁ acquired last time in the terminal 100 or the proxy 400 is different from the value of the maximum bandwidth B ₂ newly acquired, in the congestion window control unit (106 or 403), the maximum When the bandwidth increases (B ₁ <B ₂ ), the cwnd increase amount during the congestion window size increase process in TCP congestion control is increased, and the cwnd decrease amount during the congestion window size decrease process is decreased, and the maximum bandwidth decreases. In the case (B ₁ >B ₂ ), control is performed such that the cwnd increase amount during the congestion window size increasing process is small and the cwnd decrease amount during the congestion window size decreasing process is large. The congestion window size increasing process may be, for example, when an ACK is received. Further, the congestion window size reduction processing may be, for example, packet loss (during duplicate ACK reception or ACK reception timeout).

In step S43 of FIG. 20, similarly to steps S31 to S35 of the congestion window control 3, the newly acquired RTT ₂ is larger than the previously acquired RTT ₁ by the RTT measurement unit (105 or 401), and the terminal 100 Alternatively, if the wireless transmission quality Q acquired by the proxy 400 exceeds the reference value RV ₂ for determining that the wireless transmission quality managed by the congestion window control unit (106 or 403) is high, it is determined that the increase in RTT is due to congestion. , Cwnd increase amount is reduced and cwnd decrease amount is increased.

The control of the cwnd increase/decrease amount is not limited to the AIMD control, and it is conceivable to perform the same control with respect to the parameters C and β in the control formula of the following TCP CUBIC, for example.

[Congestion window control 5]
The congestion window control 5 is, for example, in the congestion avoidance control process used in any TCP congestion control such as TCP Reno or CUBIC, the current communication throughput (cwnd/RTT) of the terminal 100 is newly added to the terminal 100 or the proxy 400. When it is larger than the acquired maximum band B, the control for immediately lowering cwnd is performed. The operation flow of the congestion window control 5 is shown in FIG. The amount of decrease in cwnd performed in step S53 of FIG. 22 is controlled to reduce the communication throughput of the terminal 100 to B, which is the maximum band, as in the following equation.

The above-mentioned reduction of cwnd is performed in order to prevent congestion due to the packet being transmitted by the terminal 100 exceeding the maximum available bandwidth.

[Congestion window control 6],
The congestion window control 6 controls the increase/decrease amount of cwnd based on the current throughput of communication performed by the terminal 100, the maximum bandwidth, and the RTT in the congestion avoidance control processing used in arbitrary TCP congestion control such as TCP Reno and CUBIC. It is a control for adjusting. As the throughput of communication performed by the terminal 100 is smaller than the maximum bandwidth acquired by the terminal 100 or the proxy 400, the increase amount of cwnd in the congestion window size increasing process in the TCP congestion control is large, and the congestion window size decreasing process is The decrease amount of cwnd is reduced, and the increase amount of cwnd during the congestion window size increasing process is decreased as the current throughput of communication performed by the terminal 100 approaches the notified maximum bandwidth, and the decrease of cwnd during the congestion window size decreasing process is performed. Control to increase the amount. The congestion window size increasing process may be, for example, when an ACK is received. Further, the congestion window size reduction processing may be, for example, packet loss (during duplicate ACK reception or ACK reception timeout). FIG. 23 shows changes in the cwnd increase/decrease amount of the congestion window control 6. The above control can be realized, for example, by calculating α and β in Equation 6 by Equation 9 in the following equation. It is conceivable that α ₁ , α ₂ , β ₁ , and β ₂ in the equation 9 are constants, or may be varied depending on the wireless transmission quality and RTT.

Further, control is performed such that the increase amount of cwnd increases as the RTT of communication performed by the terminal 100 increases. In AIMD control such as TCP Reno, a certain amount of cwnd is increased each time an ACK is received. Therefore, the communication with a smaller RTT has a faster increase in cnwd, and the communication with a larger RTT has a slower increase in cwnd. For this reason, although fairness between communications having different RTTs is not high, by increasing the increase amount of cwnd for communications having a higher RTT, it is possible to reduce the difference in communication throughput due to the magnitude of RTT. This control can be realized, for example, by expressing α _{1 of the} above equation 9 as a function of RTT as in the following equation. It is conceivable that α ₃ is a constant or may be varied depending on the wireless transmission quality.

The congestion window controls 1 to 6 may be individually controlled, but may be controlled in combination. For example, FIG. 24 shows a control example in which the congestion window control 1 and the congestion window control 6 are combined. In the example of FIG. 24, when the maximum available bandwidth of the terminal 100 is changed from B to B′, according to the congestion window control 1, a slow start is performed until cwnd reaches γ(B′·RTT)/MSS. .. Then, according to the congestion window control 6, the increase amount is suppressed as cwnd approaches cwnd _B′ .

Although the embodiment of the present invention has been described in detail above, the present invention is not limited to this. For example, the communication format such as LTE described in the above embodiment is an example thereof, and the present invention can be implemented in other communication formats. The present invention can also be implemented in determining the packet transfer rate of a protocol other than TCP (such as SCTP or a UDP-based protocol such as QUIC proposed by Google).

100...Terminal 101...Wireless communication management unit 102...Maximum bandwidth conversion table 103...Radio quality notification unit 104...Radio transmission quality variation determination unit 105...RTT measurement unit 106...Congestion window control unit 200...Radio base station 201...Maximum bandwidth calculation Unit 202... Wireless transmission quality acquisition unit 203... Wireless transmission quality variation determination unit 300... Core node 400... Proxy 401... RTT measurement unit 402... Access quality monitoring unit 403... Congestion window control unit 500... Server

Claims (9)

A packet communication system comprising: a wireless base station accommodating a wireless terminal; and a communication device for forming a connection of a transport layer of the OSI 7-layer model with the wireless terminal,
Radio access quality detection means for detecting the radio access quality between the radio terminal and the radio base station,
A congestion window control means for adjusting the congestion window size in the transport layer based on the wireless access quality detected by the wireless access quality detection means,
The wireless access quality detection means calculates a maximum bandwidth that can be used in wireless access between the terminal and the wireless base station, and if there is a change in the maximum bandwidth, the maximum bandwidth is used as the wireless access quality to determine the congestion window. Notify the control means,
The congestion window control means, when the congestion window size exceeds a first threshold value, shifts from the slow start mode to a high speed increase mode in which the congestion window size is increased faster than the congestion avoidance mode and more slowly than the slow start mode. When the size exceeds a second threshold value that is larger than the first threshold value, control is performed to shift from the fast increase mode to the congestion avoidance mode, and when the notified maximum bandwidth increases, the first bandwidth is increased based on the maximum bandwidth. A packet communication system, wherein a threshold value of 2 is calculated. A packet communication system comprising: a wireless base station accommodating a wireless terminal; and a communication device for forming a connection of a transport layer of the OSI 7-layer model with the wireless terminal,
Radio access quality detection means for detecting the radio access quality between the radio terminal and the radio base station,
And a congestion window control means for adjusting the congestion window size in the transport layer based on the wireless access quality detected by the wireless access quality detection means,
The wireless access quality detection means calculates a maximum bandwidth that can be used in wireless access between the terminal and the wireless base station, and if there is a change in the maximum bandwidth, the maximum bandwidth is used as the wireless access quality to determine the congestion window. Including maximum bandwidth detection means to notify the control means,
The congestion window control means, in the congestion avoidance control process, the increase amount during the congestion window size increase process is increased and the decrease amount during the congestion window size decrease process is reduced with the increase of the notified maximum bandwidth, and the notification is made. A packet communication system characterized in that the increase amount during the congestion window size increasing process is controlled to be small and the decrease amount during the congestion window size decreasing process is controlled to be large with a decrease in the maximum bandwidth. RTT measuring means for measuring RTT between the wireless terminal and the communication device,
The wireless access quality detection means monitors the wireless transmission quality in wireless access between the terminal and the wireless base station, and if there is a variation in the wireless transmission quality, the wireless transmission quality is regarded as the wireless access quality and the congestion window Including wireless transmission quality detection means for notifying the control means,
In the congestion avoidance control processing, the congestion window control means is based on a change in the notified wireless transmission quality and an increase or decrease in the RTT measured by the RTT measurement means, whether the increase in the RTT is due to a decrease in the wireless transmission quality or due to congestion. If it is determined that the increase in RTT is due to congestion, decrease the increase amount of the congestion window size during the congestion window size increase process and decrease the decrease amount of the congestion window size during the congestion window size decrease process. The packet communication system according to claim 2 . A packet communication system comprising: a wireless base station accommodating a wireless terminal; and a communication device for forming a connection of a transport layer of the OSI 7-layer model with the wireless terminal,
Radio access quality detection means for detecting the radio access quality between the radio terminal and the radio base station,
And a congestion window control means for adjusting the congestion window size in the transport layer based on the wireless access quality detected by the wireless access quality detection means,
The wireless access quality detection means calculates a maximum bandwidth that can be used in wireless access between the terminal and the wireless base station, and if there is a change in the maximum bandwidth, the maximum bandwidth is used as the wireless access quality to determine the congestion window. Notify the control means,
The congestion window control means, in the congestion avoidance control process, the greater the difference between the throughput of the communication performed by the terminal and the notified maximum bandwidth, the greater the increase amount during the congestion window size increase process and the decrease during the congestion window size decrease process. A small amount, a small increase in the congestion window size increase process and a large decrease amount in the packet window loss congestion window decrease process as the difference between the throughput of communication performed by the terminal and the notified maximum bandwidth decreases. A packet communication system characterized by controlling. RTT measuring means for measuring RTT between the wireless terminal and the communication device,
The congestion window control means, when performing control to increase the congestion window size in the congestion avoidance control processing, increases the increase amount of the congestion window size for a communication with a larger RTT measured by the RTT measurement means. The packet communication system according to claim 4 . A congestion control method in a packet communication system comprising: a wireless base station accommodating a wireless terminal; and a communication device that forms a transport layer connection of the OSI 7-layer model with the wireless terminal,
A first step in which wireless access quality detecting means detects a wireless access quality between the wireless terminal and the wireless base station;
A second step in which the congestion window control means adjusts the congestion window size in the transport layer based on the radio access quality detected by the radio access quality detection means,
In the first step, the wireless access quality detecting means calculates a maximum bandwidth that can be used in wireless access between the terminal and the wireless base station, and wirelessly determines the maximum bandwidth when there is a change in the maximum bandwidth. Notify the congestion window control means as access quality,
In the second step, the congestion window control means increases the congestion window size from the slow start mode to a speed faster than the congestion avoidance mode and more slowly than the slow start mode when the congestion window size exceeds a first threshold value. When the congestion window size exceeds a second threshold value that is larger than the first threshold value, control is performed to shift from the fast increase mode to the congestion avoidance mode, and when the notified maximum bandwidth increases, the maximum bandwidth increases. A congestion control method in a packet communication system, wherein the second threshold value is calculated based on A congestion control method in a packet communication system comprising: a wireless base station accommodating a wireless terminal; and a communication device that forms a transport layer connection of the OSI 7-layer model with the wireless terminal,
A first step in which wireless access quality detecting means detects a wireless access quality between the wireless terminal and the wireless base station;
A second step in which the congestion window control means adjusts the congestion window size in the transport layer based on the radio access quality detected by the radio access quality detection means,
In the first step, the wireless access quality detecting means calculates a maximum bandwidth that can be used in wireless access between the terminal and the wireless base station, and wirelessly determines the maximum bandwidth when there is a change in the maximum bandwidth. Notify the congestion window control means as access quality,
In the second step, the congestion window control means, in the congestion avoidance control process, increase the increase amount during the congestion window size increase process and increase the decrease amount during the congestion window size decrease process as the notified maximum bandwidth increases. A congestion control method in a packet communication system, which is characterized in that the amount of increase in the congestion window size increasing process is decreased and the amount of decrease in the congestion window size decreasing process is controlled to be large with the decrease in the notified maximum bandwidth. .. A congestion control method in a packet communication system comprising: a wireless base station accommodating a wireless terminal; and a communication device that forms a transport layer connection of the OSI 7-layer model with the wireless terminal,
A first step in which wireless access quality detecting means detects a wireless access quality between the wireless terminal and the wireless base station;
A second step in which the congestion window control means adjusts the congestion window size in the transport layer based on the radio access quality detected by the radio access quality detection means,
In the first step, the wireless access quality detecting means calculates a maximum bandwidth that can be used in wireless access between the terminal and the wireless base station, and wirelessly determines the maximum bandwidth when there is a change in the maximum bandwidth. Notify the congestion window control means as access quality,
In the second step, the congestion window control means, in the congestion avoidance control process, the larger the difference between the throughput of communication performed by the terminal and the notified maximum bandwidth, the larger the increase amount in the congestion window size increasing process and the congestion window. Decrease the reduction amount during the size reduction process, and reduce the increase amount during the congestion window size increase process as the difference between the throughput of the communication performed by the terminal and the notified maximum bandwidth decreases, and reduce the congestion window size during the packet loss process A congestion control method in a packet communication system, which is characterized in that the amount of decrease in time is greatly controlled. Congestion control program for causing to function as each unit of the packet communication system according to the computer in any one of claims 1 to 5.

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