JP5550438B2 - Window control device, window control method, and window control program - Google Patents

Description

  The present invention relates to a window control device, a window control method, and a window control program for controlling a maximum window size according to a communication protocol based on a radio congestion level.

  Conventionally, cognitive radio technology has been proposed. This is a technique for improving the frequency utilization efficiency by recognizing the usage status of a plurality of wireless systems having different characteristics and adaptively using the plurality of wireless systems. In order to improve the frequency utilization efficiency, it is necessary to increase the transmission rate of a best effort packet such as TCP while giving priority to a packet with high quality (QoS) required by an application.

  However, in TCP, the maximum window size is determined regardless of the network state, and in some cases, packet transmission exceeding the upper limit of the allowable throughput of the network is performed. For this reason, packet loss due to buffer overflow and its retransmission occur, which not only lowers its own throughput but also adversely affects other communications.

  For example, in TCP-Reno, the congestion window is increased at a constant speed while no congestion is detected, and when congestion is detected, the congestion window is decreased by half, thereby achieving high throughput within a range in which the network is not congested. Control the congestion window so that In other words, since the congestion is generated and the throughput is adjusted in such a way as to recognize the congestion, not only the throughput of the communication is lowered but also packet loss occurs due to the congestion in other communications.

  Further, in TCP, the window size is changed in a sawtooth manner by repeating the process of increasing the window size until it is congested, halving it, and increasing it. The average throughput is the average of the saw-shaped part, indicating that not only the frequency utilization efficiency is low, but also packet loss occurs in the part where the window size is halved. At this time, even when an application that does not allow packet loss is operating as another communication, it may cause a packet loss of the application.

  FIG. 8 is a diagram showing a schematic configuration of the wireless LAN system. Also, FIG. 9 shows the throughput characteristics when two sets of wireless LANs (Link1 and Link2) transmit and receive data with the configuration shown in FIG. 8, that is, experimental results of the amount of data per unit time reaching the counterpart terminal. FIG. In FIG. 9, in the state where Link 1 is transmitting UDP data from STA 1 to AP 1 at 30 Mbps (originally the reception throughput is about 29 Mbps), the UDP transmission rate is changed from STA 2 of Link 2 to AP 2 on the same channel. In this case, the reception throughput is shown.

  As can be seen from FIG. 9, when the radio is congested, the total throughput is increased or decreased so as to be substantially constant. However, this is a case where there are two transmission / reception terminals. Here, the difference between the transmission rate and the reception throughput represents a packet loss due to buffer overflow. In the case of TCP or the like, this packet loss causes re-transmission, and the same packet flies twice and three times on the radio, leading to a reduction in overall throughput.

  In order to solve these problems, in Patent Document 1, the congestion window is controlled according to a preset target bandwidth without causing the network to enter a serious congestion state. Specifically, the communication system includes a relay node that transmits and receives data between a plurality of communication terminals via a network and relays communication between the communication terminals, and either of the communication terminal and the relay node is Either the accumulated difference between the preset target band and the actually output band or the history of the difference is held. Based on the value held, the congestion control parameter representing the increase and decrease of the congestion window is changed. Here, independently of the network status, the throughput is adjusted so as to obtain the bandwidth specified by the user, and the bandwidth specified by the user is set as the target bandwidth.

  On the other hand, Non-Patent Document 1 describes a plurality of methods for estimating a bandwidth using a probe packet and controlling a socket buffer. For example, by transmitting two packets at a certain time interval, measuring the time when the two packets were received on the receiving side, and comparing the time interval transmitted on the transmitting side, the link that becomes the bottleneck in the route This is a method of estimating the bandwidth and controlling the TCP reception window size accordingly.

JP 2007-097144 A

C. Dovrolis, "Bandwidth estimation in computer networks: measurement techniques & applications" CCN '05 Keynote, Oct. 2005.

  However, the technique described in Patent Document 1 is premised on band designation that ignores the state of the network. In a wireless environment in which the band is narrower than the wired network and the transmission speed fluctuates, the network is serious. May lead to excessive congestion. Further, in the technique described in Non-Patent Document 1, since the load on the network is increased by the probe packet, the measurement cannot be performed very frequently, and therefore, there is a possibility that the network bandwidth cannot be tracked.

  The present invention has been made in view of such circumstances, and by determining the maximum window size of TCP according to the wireless environment, it suppresses packet loss, reduces retransmission, and improves frequency utilization efficiency. An object is to provide a window control device, a window control method, and a window control program.

  (1) In order to achieve the above object, the present invention takes the following measures. That is, the window control device of the present invention is a window control device that controls the maximum window size according to the communication protocol based on the wireless congestion level, and receives packets transmitted and received between a plurality of wireless communication devices. A congestion degree estimation unit that estimates a radio congestion level, and a window control unit that calculates a maximum window size corresponding to a packet size based on the estimated radio congestion level, and at least one of transmission time and reception time The total window size is controlled to be equal to or smaller than the calculated maximum window size.

  Thus, since the maximum window size corresponding to the communication protocol is determined based on the wireless environment, it is possible to suppress packet loss, reduce retransmission, and improve frequency utilization efficiency. For example, when the communication protocol is TCP (Transmission Control Protocol), it is possible to limit the TCP window size from the wireless congestion level and the wireless modulation scheme so that the wireless congestion level does not become 100%.

  (2) Further, the window control device of the present invention is characterized in that when a plurality of sessions are activated, the total window size of each session is controlled to be equal to or less than the maximum window size.

  As described above, when a plurality of sessions are activated, the total window size of each session is controlled to be equal to or less than the maximum window size, so that packet loss is suppressed, retransmission is reduced, and frequency use efficiency is improved. Can do. For example, when the communication protocol is TCP (Transmission Control Protocol), the total window size of each TCP is constant from the wireless congestion level and the wireless modulation method so that the wireless congestion level is not 100%. It becomes possible to restrict.

  (3) Further, in the window control device of the present invention, the window control unit uses the estimated wireless congestion to determine the UDP indicated by the number of packets per second used in at least one UDP (User Datagram Protocol) communication. The maximum window size is calculated by subtracting the usage time rate.

  In this way, the maximum window size is calculated by subtracting the UDP usage rate indicated by the number of packets per second used in at least one UDP communication from the estimated radio congestion level, thereby suppressing packet loss. Retransmission can be reduced and frequency utilization efficiency can be improved. For example, when the communication protocol is TCP (Transmission Control Protocol), TCP is determined from the wireless congestion level and the wireless modulation method so that the UDP transmission rate is not affected and the wireless congestion level is not 100%. It is possible to limit the window size.

  (4) Further, in the window control device of the present invention, the window control unit calculates the maximum window size following a change in radio quality.

  As described above, the maximum window size is calculated following the change in the radio quality, so that the throughput can be controlled in accordance with the change in the radio environment.

  (5) Moreover, the window control apparatus of this invention controls the maximum window size of TCP (Transmission Control Protocol) based on a radio | wireless congestion degree.

  In this way, the maximum window size of TCP (Transmission Control Protocol) is controlled based on the degree of radio congestion, thus reducing TCP demerits, suppressing packet loss, reducing retransmission, and improving frequency utilization efficiency. be able to. That is, it is possible to limit the TCP window size from the wireless congestion level and the wireless modulation scheme so that the wireless congestion level does not become 100%.

  (6) Further, the window control method of the present invention is a window control method for controlling the maximum window size according to the communication protocol based on the radio congestion degree, and in the congestion degree estimation unit, a plurality of radio communication apparatuses Receiving a packet being transmitted / received in step (a), estimating a radio congestion level, and calculating a maximum window size corresponding to the packet size based on the estimated radio congestion level in a window control unit, at least And at least one window size at the time of transmission or reception is controlled to be equal to or smaller than the calculated maximum window size.

  Thus, since the maximum window size corresponding to the communication protocol is determined based on the wireless environment, it is possible to suppress packet loss, reduce retransmission, and improve frequency utilization efficiency. For example, when the communication protocol is TCP (Transmission Control Protocol), it is possible to limit the TCP window size from the wireless congestion level and the wireless modulation scheme so that the wireless congestion level does not become 100%.

  (7) The program of the present invention is a window control program for controlling the maximum window size according to the communication protocol based on the radio congestion level, and receives packets transmitted and received between a plurality of radio communication devices. A process for estimating a radio congestion level, a process for calculating a maximum window size corresponding to a packet size based on the estimated radio congestion level, and a calculation of at least one total window size at the time of transmission or reception A process for performing control to make the maximum window size or less and a series of processes are commanded so as to be readable and executable by a computer.

  Thus, since the maximum window size corresponding to the communication protocol is determined based on the wireless environment, it is possible to suppress packet loss, reduce retransmission, and improve frequency utilization efficiency. For example, when the communication protocol is TCP (Transmission Control Protocol), it is possible to limit the TCP window size from the wireless congestion level and the wireless modulation scheme so that the wireless congestion level does not become 100%.

  According to the present invention, since the maximum window size corresponding to the communication protocol is determined based on the wireless environment, it is possible to suppress packet loss, reduce retransmission, and improve frequency utilization efficiency. For example, when the communication protocol is TCP (Transmission Control Protocol), packet loss and retransmission in the radio section are reduced by controlling the window size of TCP so that the radio congestion level does not become 100%. be able to.

It is a figure which shows the calculation method of packet time. It is a figure which shows the time change of the wireless congestion degree, and the change of the usable time rate which tracks it. It is a figure which shows schematic structure of a window control apparatus. It is a figure which shows the comparative example of the change of a window size, and the change of the window size by TCP-Reno. It is a block diagram which shows schematic structure of the window control apparatus which concerns on 2nd Embodiment. It is a block diagram which shows schematic structure of the window control apparatus which concerns on 3rd Embodiment. It is a block diagram which shows schematic structure of the window control apparatus which concerns on 4th Embodiment. It is a figure which shows schematic structure of a wireless LAN system. FIG. 9 is a diagram illustrating an experiment result of throughput characteristics, that is, a data amount per unit time reaching a counterpart terminal when two sets of wireless LANs (Link1 and Link2) transmit and receive data in the configuration illustrated in FIG.

  In the present invention, a wireless occupancy estimation technique of a wireless LAN is applied to obtain a bandwidth that can be used from the available time rate and the current modulation method, and the transmission congestion window size and the reception window are matched to the bandwidth. Change the size adaptively. This suppresses the occurrence of serious congestion at least in the wireless region.

  The wireless LAN radio occupancy rate estimation technique is, for example, DIFS (Distributed Inter Frame Space), SIFS (Short Inter Frame Space), or backoff based on the packet information of the wireless LAN obtained by the packet information storage means. It is possible to use a technique for calculating the total time required for packet transmission, including time that is indispensable for operation of a simple wireless LAN. In this technique, the sequence number of a packet is checked, a packet drop rate is obtained, and the number of missed packets is complemented to measure the degree of congestion with high accuracy. In addition to this technique, a technique has been proposed in which a retransmission flag (initial transmission = 0, retransmission = 1) is used to check and complement the sequence number for only the initial transmission packet. In the former technique, when an initial transmission packet is missed and a retransmission packet is received, the sequence number is not supplemented, so that an accurate packet error rate cannot be obtained. For this reason, accurate estimation of the packet error rate is realized by the latter technique. Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment / when only TCP is used)
FIG. 1 is a diagram illustrating a packet time calculation method. Method 1 indicates the time rate at which radio waves are actually emitted, and Method 2 indicates the time rate including DIFS, SIFS, and Backoff. PLCP (Physical Layer Convergence Procedure) preamble, PLCP header (fixed time), MAC header, data and FCS (transmission time varies depending on the modulation method) specified in the wireless LAN format for each packet Ask for.

Here, PLCPpreamble and PLCPHead (sig) are PLCP preamble and PLCP signal time [μs], PLCPHead (serv) and MACHead are PLCP service and MAC header, Data byte count [bytes], and Rate is physical layer transmission. Indicates the rate [Mbps]. In the wireless LAN, CSMA / CA provided with IFS and Backoff is used. Therefore, T_Method 2 shown in FIG. 1 is a method for obtaining the radio occupancy rate as the total time including IFS and Backoff, which are essential waiting times in CSMA / CA.

  The IFS used a time length determined by the packet type. In addition, the average Backoff time was used for Backoff. The values set as IFS and Backoff can be grasped only on the transmitter side. Therefore, from the standpoint of measuring IFS and Backoff, calculation is performed using an average value here.

  In this way, the wireless usage time including the waiting time, which is indispensable as in Method 2 of FIG. 1, is obtained for each packet, and the time rate at which the wireless is used per second is calculated as the wireless congestion degree (the wireless is It is the percentage of time used and indicates that 100% is used at 1). However, the wireless congestion degree obtained here uses a wireless congestion degree obtained from a packet other than a packet transmitted and received by itself and a broadcast packet such as beacon.

  Next, the usable time rate is obtained from the difference between the reference value and the wireless usage congestion degree. FIG. 2 is a diagram illustrating a change in the wireless congestion level with time and a change in the usable time rate following the change. The usable time rate is obtained as 1 or a value obtained by subtracting the wireless congestion degree from the reference value. However, the degree of wireless congestion does not increase in proportion to the number of packets, but if the transmission rate is increased when the congestion has been raised to some extent, the degree of congestion may suddenly approach 1 due to packet collisions, etc. It is necessary to obtain the usable time rate based on the value considering the above.

  For example, when the wireless congestion level suddenly increases from around 0.95, the usable time rate is obtained by subtracting the wireless congestion level from 0.95 as a reference value as shown in FIG. .

  Next, the number of packets that can be transmitted per second using the packet size as a parameter is obtained from the available time rate by performing the reverse calculation of FIG. Specifically, the time required to transmit the Data packet by adding the preamble, header time, and indispensable waiting time in FIG. 1 to the time of the data portion obtained by dividing the packet size by the modulation rate. Ask for. Also, the time required for transmitting one data packet is obtained by obtaining and adding the Ack time for the Data packet. Then, the number of Data packets that can be transmitted per second is obtained by dividing the usable time rate by the time obtained above, and the maximum number of packets is obtained.

A value obtained by multiplying the maximum number of packets by the packet size is the maximum possible throughput for the packet size that can be used in the wireless system (changes with respect to the packet size as described above). The maximum window size MAXWIN is determined from the maximum possible throughput and RTT (Round Trip Time). The relationship between RTT, maximum window size, and maximum possible throughput is as follows.
(Maximum possible throughput) = (MAXWIN) / (RTT)
Here, MAXWIN is the maximum window size, and RTT is the round trip delay time. If you transform the expression,
(MAXWIN) = (maximum possible throughput) * (RTT)
That is, by setting the above MAXWIN as the upper limit of the window size, congestion on the radio can be avoided, and even when the radio environment changes, an optimal TCP communication can be performed by adjusting the window size.

  FIG. 3 is a diagram illustrating a schematic configuration of the window control device according to the first embodiment. In the window control device 10-1, the radio circuit 11 transmits all destination packet information received from the access point 1 to the congestion level measurement circuit 12. The congestion level measurement circuit 12 calculates the usable time rate and transmits it to the window control circuit 13. The window control circuit 13 determines MAXWIN (maximum window size) in consideration of the packet size to be transmitted and received, the ACK size, and the like. At this time, the window control circuit 13 receives the packet size information from the TCP circuit 14 and performs calculation. Next, the determined MAXWIN is transmitted to the TCP circuit 14.

  The TCP circuit 14 performs control so that CWIN does not exceed MAXWIN in the case of transmission. In the case of reception, control is performed so that RWIN does not exceed MAXWIN. When transmitting and receiving, control is performed so that the sum of CWIN and RWIN does not exceed MAXWIN.

  The congestion degree measuring circuit 12 constitutes a congestion degree estimation unit, and the window control circuit 13 constitutes a window control unit.

  FIG. 4 is a diagram illustrating a comparative example of a change in window size according to the present embodiment and a change in window size due to TCP-Reno. In the present embodiment, the window size changes along the usable time rate, and TCP-Reno takes a saw-like shape with the usable time rate as a maximum value. Also at this time, TCP-Reno exceeds the usable time rate and causes congestion, thereby reducing the radio quality. On the other hand, according to the present embodiment, the wireless quality is not deteriorated.

(Second embodiment / when there are multiple TCP (sessions))
FIG. 5 is a block diagram showing a schematic configuration of the window control apparatus according to the second embodiment. In this window control apparatus 10-2, the radio circuit 11 transmits all destination packet information received from the access point 1 to the congestion level measurement circuit 12. The congestion level measurement circuit 12 calculates the usable time rate and transmits it to the window control circuit 13. The window control circuit 13 determines MAXWIN in consideration of the packet size to be transmitted / received, the ACK size, and the like. At this time, the window control circuit 13 receives the packet size information from the TCP circuits 14-1 and 14-2 and performs calculation.

  Each MAXWIN is obtained according to the packet size desired by each TCP. In this case, the total is controlled to be equal to or less than the usable time rate. Further, it is necessary to determine the MAXWIN and the time rate distribution rate in accordance with the importance (QoS) of the data. In the case of the same level of QoS, it may be possible to simply halve each. Then, the determined MAXWIN is transmitted to the TCP circuits 14-1 and 14-2. The TCP circuits 14-1 and 14-2 perform control so that CWIN does not exceed MAXWIN in the case of transmission. In the case of reception, control is performed so that RWIN does not exceed MAXWIN. When transmitting and receiving, control is performed so that the sum of CWIN and RWIN does not exceed MAXWIN.

(Third embodiment / when UDP exists)
FIG. 6 is a block diagram illustrating a schematic configuration of the window control device according to the third embodiment. In this window control device 10-3, the radio circuit 11 transmits all destination packet information received from the access point 1 to the congestion level measurement circuit 12. The congestion level measurement circuit 12 calculates the usable time rate and transmits it to the window control circuit 13. The window control circuit 13 determines MAXWIN in consideration of the packet size to be transmitted / received, the ACK size, and the like. At this time, the window control circuit 13 receives the packet size information from the TCP circuit 14 and performs calculation. In addition, the number of packets per second used by the UDP circuit 15 is obtained, and the time rate (UDP usage time rate) required based on this is obtained, and {1- (radio congestion) − (UDP usage time rate) } To obtain the TCP MAXWIN. In this case, the total is controlled to be equal to or less than the usable time rate. Then, the determined MAXWIN is transmitted to the TCP circuit 14.

  The TCP circuit 14 performs control so that CWIN does not exceed MAXWIN in the case of transmission. In the case of reception, control is performed so that RWIN does not exceed MAXWIN. When transmitting and receiving, control is performed so that the sum of CWIN and RWIN does not exceed MAXWIN.

(Fourth embodiment / when there are multiple UDPs and multiple TCPs)
FIG. 7 is a block diagram showing a schematic configuration of the window control apparatus according to the fourth embodiment. In this window control device 10-4, the wireless circuit 11 transmits all destination packet information received from the access point 1 to the congestion degree measuring circuit 12. The congestion level measurement circuit 12 calculates the usable time rate and transmits it to the window control circuit 13. The window control circuit 13 determines MAXWIN in consideration of the packet size to be transmitted / received, the ACK size, and the like. At this time, the window control circuit 13 receives the packet size information from the TCP circuits 14-1 to 14-n and performs calculation.

  The number of packets per second used by the UDP circuits 15-1 to 15-n is obtained, and the time rate (UDP usage time rate) required based on the obtained number is obtained, and {1- (wireless congestion) − (Maximum UDP usage time)} MAXWIN of TCP is obtained. In this case, the total is controlled to be equal to or less than the usable time rate. Each MAXWIN is obtained according to the packet size desired by each TCP. In this case, the total is controlled to be equal to or less than the usable time rate. Further, it is necessary to determine the MAXWIN and the time rate distribution rate in accordance with the importance (QoS) of the data. In the case of the same level of QoS, it may be possible to simply halve each. Then, the determined MAXWIN is transmitted to the TCP circuits 14-1 to 14-n. The TCP circuits 14-1 to 14-n perform control so that CWIN does not exceed MAXWIN in the case of transmission. In the case of reception, control is performed so that RWIN does not exceed MAXWIN. When transmitting and receiving, control is performed so that the sum of CWIN and RWIN does not exceed MAXWIN.

(Fifth embodiment / time variation)
The wireless environment changes from moment to moment, and the way radio is used, that is, the degree of radio congestion also changes from moment to moment. Therefore, in the first to fourth embodiments, the congestion degree measurement circuit 12, the window control circuit 13, the TCP circuit 14 (including a plurality of cases), and the UDP circuit 15 (including a plurality of cases) are included. ) Is preferably measured with as short a period as possible to change the window size. For example, by measuring the degree of congestion at 100 ms intervals and determining the window size based on the result, its own CWIN can be changed instantaneously, and by changing the RWIN, the Ack reaches the sender side Although a delay occurs, it is possible to control the throughput according to the wireless environment at a relatively high speed.

  In addition to the degree of wireless congestion required for communication performed by other terminals, the quality (modulation method and transmission speed) on its own radio link changes or other communication is started. By recalculating the maximum window size and controlling to the optimum maximum window size, it is possible to control so as not to cause serious congestion in the radio region.

(Sixth embodiment / in the case of a protocol other than TCP)
As in the first to fifth embodiments, the wireless congestion degree is obtained and transmitted to the window control circuit 13 to obtain MAXWIN. The MAXWIN obtained here is transmitted to a protocol for each session such as TCP or DCCP, and control is performed so that the sum of RWIN and CWIN does not exceed MAXWIN.

  As described above, according to the embodiment, it is possible to determine the maximum TCP window size according to the wireless environment. In addition, packet loss can be suppressed, retransmission can be reduced, and frequency use efficiency can be improved.

DESCRIPTION OF SYMBOLS 1 Access point 10-1 to 10-4 Window control apparatus 11 Wireless circuit 12 Congestion degree measurement circuit 13 Window control circuit 14, 14-1, 14-2, 14-n TCP circuit 15, 15-1, 15-2, 15-n UDP circuit

Claims (6)

A window control device that controls a maximum window size according to a communication protocol based on a radio congestion level,
A congestion degree estimation unit that receives packets transmitted and received between a plurality of wireless communication devices and estimates a wireless congestion degree;
A window control unit that calculates a maximum window size corresponding to the packet size based on the estimated wireless congestion degree, and
It controls row stomach to at least one of the total window size at the time of the send or receive less than the maximum window size described above is calculated,
If you start multiple sessions, the total window size of each session, window control device comprising a row of Ukoto control for less than the maximum window size. The window control unit calculates the maximum window size by subtracting the UDP usage time rate indicated by the number of packets per second used in at least one UDP (User Datagram Protocol) communication from the estimated wireless congestion level. window control apparatus according to claim 1, characterized in that. The window control device according to claim 1 , wherein the window control unit calculates the maximum window size following a change in wireless quality . 2. The window control apparatus according to claim 1, wherein a maximum window size of TCP (Transmission Control Protocol) is controlled based on a radio congestion degree . A window control method for controlling a maximum window size according to a communication protocol based on a radio congestion level,
In the congestion level estimation unit, receiving packets transmitted and received between a plurality of wireless communication devices, estimating the wireless congestion level,
In the window control unit, based on the estimated wireless congestion degree, calculating a maximum window size corresponding to the packet size, at least,
Performing control so that at least one of all window sizes at the time of transmission or reception is equal to or less than the calculated maximum window size,
A window control method comprising: controlling a total window size of each session to be equal to or less than a maximum window size when a plurality of sessions are activated. A window control program for controlling the maximum window size according to the communication protocol based on the radio congestion level,
A process of receiving packets transmitted and received between a plurality of wireless communication devices and estimating a wireless congestion degree;
A process of calculating a maximum window size corresponding to the packet size based on the estimated radio congestion degree;
A process of performing control so that at least one full window size at the time of transmission or reception is equal to or less than the calculated maximum window size;
When multiple sessions are started, the process of controlling the total window size of each session to be equal to or less than the maximum window size, and a series of processes are commanded to be readable and executable by a computer. Window control program.