JP6450175B2 - Packet transmission equipment - Google Patents

Description

  The present invention relates to a packet transmission apparatus that transmits a packet such as an IP (Internet protocol) packet or an Ethernet (registered trademark) packet via a communication path whose transmission speed can be switched. The present invention relates to a packet transmission apparatus that efficiently transmits packets by using a transmission capacity of a communication path using a wireless communication path that switches speeds.

  In data communication using the Internet protocol (IP), data is transmitted by storing data in an IP packet and transmitting the IP packet via a packet transmission device and a communication path. FIG. 7 illustrates a schematic configuration example of a network in a case where the transmitting terminal 50 and the receiving terminal 53 at remote points perform data communication via the packet transmission device 51 and the packet transmission device 52 via the communication path 12 and the communication path 21. Indicates. Here, the transmission terminal 50 and the packet transmission device 51 are interconnected via the communication channel 01 and the communication channel 10, and the communication channel 23 and the communication channel 32 are connected between the reception terminal 53 and the packet transmission device 52. Shall be interconnected via

  In order to effectively transmit the packet by effectively using the transmission capability of the communication path 12, the output speed of the packet output from the transmission terminal 50 to the packet transmission device 51 is as high as possible within the range of the transmission speed of the communication path 12. Need to control to speed.

  In devices that perform data communication using IP, in order to reliably transmit data, the data transmitted in discarded packets is recovered, and the packet output speed is controlled according to the transmission speed of the communication path. Data communication is performed using a data communication protocol provided with a function (congestion control function). TCP (Transmission Control Protocol) is widely used as a data communication protocol for these devices.

  First, in the case where the transmission rate does not change, it will be described that the packet output rate of the transmission terminal 50 is controlled as high as possible within the range of the transmission rate of the communication path 12 by the TCP congestion control function.

  FIG. 8 is a block diagram showing an example of a conventional packet transmission apparatus. The packet transmission devices 51 and 52 in FIG. 7 can have the same configuration, and the packet transmission device 51 will be described as a representative. The packet transmission apparatus 51 includes packet input units 511 and 515, a packet transfer unit 512, packet standby control units 513 and 516, and packet output units 514 and 517.

  The packet input unit 511 receives the packet output from the transmission terminal 50 via the communication path 01 and inputs it to the packet transfer unit 512. The packet input unit 515 receives a packet transmitted from the opposite packet transmission device 52 via the communication path 21 and inputs the packet to the packet transfer unit 512.

  The packet transfer unit 512 analyzes the destination of the input packet to determine the output destination of the packet, and inputs the packet to the packet standby control unit 516 connected to the determined packet output unit 517. Accordingly, the packet transfer unit 512 is configured as a hub or a switch, for example, and is configured to determine the output destination of the packet for the plurality of packet standby control units 516 connected to each of the plurality of packet output units 517. (Not shown).

  Each of the packet standby control unit 513 and the packet standby control unit 516 has a function of temporarily holding the input packet in a buffer, and receives packets to be transmitted from the packet output unit 514 and the packet output unit 517, respectively. The packets are temporarily held in the respective buffers until transmission is possible from the communication paths 12 and 10 to which the respective packet output units 514 and 517 are connected.

  The packet standby control unit 513 and the packet standby control unit 516 determine whether or not the number of packets or the amount of data that can be stored in the buffer has reached a fixed upper limit (predetermined buffer size) when the packet is stored in the buffer. If the buffer size has been reached, it is determined that the packet cannot be stored, and either the input packet or the packet being stored is discarded.

  The packet output unit 514 takes out the packet from the packet standby control unit 513 and transmits the packet to the communication path 12 at the set transmission rate. The packet output unit 517 extracts the packet from the packet standby control unit 516 and transmits the packet to the communication path 10.

  Therefore, the packet transmission apparatus 51 is not able to transmit immediately even if a packet is input because the communication path is in use for transmitting a previously transmitted packet or the communication path cannot be used. In order to prevent the packet from being discarded, the packet is stored in the buffers of the packet standby control units 513 and 516 and held until it can be transmitted to the communication paths 12 and 10. However, the conventional packet transmission device 51 has a fixed upper limit on the number of packets and the amount of data that can be stored in the buffer. When this fixed upper limit (predetermined buffer size) is exceeded, the packet is discarded.

  Next, TCP congestion control will be described. TCP is known as a technique that makes it possible to control the output speed of a packet using a congestion window (cwnd) (see, for example, Patent Document 1).

  When the receiving terminal 53 based on TCP can confirm that the packet output from the transmitting terminal 50 is input to the receiving terminal 53 and correctly transmitted, the position information referring to the data to be received next is acknowledged (ACK). It transmits to the transmission terminal 50 as information. The transmitting terminal 50 performs flow control for outputting data in a range from the position specified by the ACK information to cwnd instead of outputting all data at once. This mechanism limits the maximum packet output rate to the congestion window / round trip delay time. The round trip delay time (RTT) is the time from when a packet is transmitted until the acknowledgment packet for that packet is received.

  In TCP congestion control, the packet sending speed is made to follow the transmission speed of the communication path by adjusting the size of this cwnd. There are several TCP congestion control methods. Loss-based congestion control techniques that gradually increase cwnd until packet loss is detected and rapidly decrease cwnd when packet loss is detected are widely used. (For example, refer to Patent Document 1).

  In TCP New Reno, which is a typical loss-based congestion control technique, the amount of increase in cwnd is 1 packet per RTT, and the amount of decrease is controlled to be ½ of cwnd. FIG. 9 shows an example of the time change of cwnd in TCP New Reno.

  With this congestion control function, the packet output speed of the transmitting terminal 50 gradually increases as cwnd increases. When this output speed exceeds the transmission speed of the communication path 12, the packet speed input to the packet transmission apparatus 51 exceeds the packet speed transmitted by the packet transmission apparatus 51, and the amount of packets stored in the buffer in the packet standby control unit 513 is increased. Over time, the accumulated amount of packets reaches the fixed upper limit (predetermined buffer size), and packet discard occurs. When detecting a packet loss from the ACK information, the transmitting terminal 50 decreases cwnd and decreases the packet output rate. By repeating this, the packet output speed of the transmitting terminal 50 is controlled to be close to the transmission speed of the communication path by the TCP congestion control function.

  As described above, the output speed of the packet of the transmission terminal 50 is controlled to be close to the transmission speed of the communication path 12 by the TCP congestion control function.

  Here, even when the transmission rate of the communication path 12 is switched by the conventional packet transmission device 51, the data transmission rate is automatically adjusted by the congestion control function.

  That is, when the transmission rate is increased, initially, the packet transmission rate of the packet transmission device 51 exceeds the packet output rate of the transmission terminal 50, and the packet storage amount of the buffer in the packet standby control unit 513 decreases. If the switching occurs when the cwnd value at the time of switching the transmission rate is small and the packet accumulation amount is small, the buffer is depleted and there is no packet to transmit, and the next packet is input to the packet transmission device 51. Until the communication path 12 becomes empty. The phenomenon in which the communication path 12 is vacant and packet transmission is intermittent is that cwnd gradually expands, the packet rate to be transmitted increases, reaches a new transmission rate, and packets are continuously buffered. Continue until it accumulates. While this phenomenon continues, no packet loss occurs.

Japanese Patent Laying-Open No. 2005-151202

  As described above, even when the transmission rate of the communication path 12 is switched by the conventional packet transmission device 51, the data transmission rate is automatically adjusted by the congestion control function. However, since the expansion of cwnd is performed slowly, even if the transmission rate is increased, the output rate of the packet of the transmission terminal 50 does not immediately increase to the new transmission rate, and a period in which the communication path 12 is vacant. There is a problem that becomes longer. Therefore, the conventional packet transmission device 51 has a problem that this problem is likely to occur because the maximum value of cwnd is small when the transmission speed is low.

  Conversely, when the transmission rate decreases, the packet input interval to the receiving terminal 53 increases, the output interval of ACK information transmitted to the transmitting terminal 50 also increases, and the packet output rate at the transmitting terminal 50 is automatically suppressed. .

  However, the interval of the ACK information to the transmitting terminal 50 changes after the RTT has elapsed since the transmission rate has decreased. During this time, the packet output speed at the transmission terminal 50 remains unchanged before the transmission speed is changed. For this reason, the number of packets waiting for transmission in the packet transmission apparatus 51 increases rapidly. As a result, in the conventional packet transmission apparatus 51, there is a case where a state exceeding the upper limit that can be stored in the buffer in the packet standby control unit 513 continues and a large amount of packet loss occurs.

  Further, the excess of the packet from when the transmission rate is reduced to when the output rate of the packet of the transmission terminal 50 is suppressed is temporary. For such a temporary increase in communication volume, a sufficient amount is required before the part that becomes a bottleneck where the communication speed is low in the middle part of the network (for example, a part corresponding to the packet waiting control unit 513). A technique for smoothing the communication amount by providing a smoothing device that combines a buffer and a circuit that precisely controls a band is known (see, for example, Patent Document 1). However, until the transmission rate on the communication path 12 decreases and the RTT time elapses, or the output speed of the packet of the transmission terminal 50 after the RTT time elapses until the output speed of the packet of the transmission terminal 50 is suppressed. Since it does not become lower than the transmission speed of the communication path 12 after reducing the transmission speed, even if smoothing cannot be made lower than the transmission speed of the communication path 12, even if the smoothing device is added, a large amount The problem of packet loss cannot be solved.

  Thus, in the conventional packet transmission device 51, even if the transmission rate of the communication path 12 is increased, the cwnd of the transmission terminal 50 using the loss-based congestion control technique does not increase immediately. When the value of cwnd is small, there is a problem that packets are transmitted intermittently and a state in which the communication path 12 is vacant continues for a long time and the communication path 12 cannot be used effectively.

  Further, when the transmission speed of the communication path 12 is lowered, a large amount of packet loss may occur. A large amount of packet loss has an effect on other communications, and there are problems such as data loss in real-time communications, a decrease in response due to retransmission of missing data, and a decrease in communication speed.

  Therefore, the present invention has been made in view of the above-described problems, and an object of the present invention is to enable continuous packet transmission even when the transmission speed of the communication path 12 is increased. A packet transmission apparatus having a function of changing the transmission rate of the communication path 12 and performing packet standby control according to the change of the transmission rate in order to suppress the occurrence of a large amount of packet loss even when the transmission rate decreases. is there.

A packet transmission apparatus according to a first aspect of the present invention is a packet transmission apparatus having a function of changing a transmission rate of a communication path, a packet output unit that transmits a packet at a set transmission rate, and a transmission from the packet output unit A variable upper limit on the number of packets or the amount of data that can be stored in the buffer by monitoring a change in transmission rate from the packet output unit when temporarily holding the packet to be stored in the buffer and storing the packet in the buffer A packet standby control unit having a buffer threshold value control unit that controls a buffer threshold value that regulates the buffer threshold value, and the buffer threshold value control unit changes the transmission rate at a time interval shorter than a predetermined specified time. the have a means for controlling to change the buffer threshold according to the speed change, and the buffer threshold control unit is configured A value obtained by multiplying a product of an initial transmission rate having an initial value of a transmission rate at a measurement start time of a predetermined specified time and the predetermined specified time by a predetermined fixed correction coefficient, the initial transmission rate and A value obtained by continuously integrating the time difference with the current transmission rate at which the change in the transmission rate is detected is added as a buffer correction value , and the predetermined specified time is connected to the packet transmission apparatus for communication. Or a round-trip delay time between the transmitting terminal and the receiving terminal that receives a packet from the transmitting terminal, or a certain margin is added to the round-trip delay time between the packet transmitting apparatus and the opposite packet transmitting apparatus characterized by a time.

The packet transmission apparatus according to the second aspect of the present invention is a packet transmission apparatus having a function of changing a transmission rate of a communication path, and a packet output unit that transmits a packet at a set transmission rate, and the packet output unit The number of packets or the amount of data that can be stored in the buffer by monitoring the change in the transmission rate from the packet output unit when temporarily storing the packet to be transmitted from the buffer and storing the packet in the buffer A packet standby control unit having a buffer threshold value control unit that controls a buffer threshold value that defines an upper limit of the buffer threshold value, and the buffer threshold value control unit changes the transmission rate at a time interval shorter than a predetermined specified time. and means for controlling to change the buffer threshold in accordance with the speed change of the transmission rate, the and the buffer threshold controller The initial transmission rate is obtained by multiplying a product of an initial transmission rate having an initial value of a transmission rate at the measurement start time of the predetermined specified time and the predetermined specified time by a predetermined fixed correction coefficient. And a value obtained by integrating the time difference at a predetermined sampling time interval with respect to the difference between the current transmission rate at which the change of the transmission rate is detected, and adding the buffer correction value as the predetermined specified time, The round-trip delay time between the transmission terminal that is connected to the packet transmission device and the reception terminal that receives the packet from the transmission terminal, or the round-trip delay time between the packet transmission device and the opposite packet transmission device It is characterized by the time when a certain margin is added .

A packet transmission device according to a third aspect of the present invention is a packet transmission device having a function of changing a transmission rate of a communication path, the packet output unit transmitting a packet at a set transmission rate, and the packet output unit The number of packets or the amount of data that can be stored in the buffer by monitoring the change in the transmission rate from the packet output unit when temporarily storing the packet to be transmitted from the buffer and storing the packet in the buffer A packet standby control unit having a buffer threshold value control unit that controls a buffer threshold value that defines an upper limit of the buffer threshold value, and the buffer threshold value control unit changes the transmission rate at a time interval shorter than a predetermined specified time. and means for controlling to change the buffer threshold in accordance with the speed change of the transmission rate, the and the buffer threshold controller Changing the transmission rate with respect to a value obtained by multiplying the product of the initial transmission rate with the transmission rate value at the start of measurement of the predetermined specified time as an initial value and the predetermined specified time by a predetermined fixed correction coefficient Based on the buffer threshold that is currently set at the time of detection, the reference speed that is the transmission speed when the buffer threshold is set, the time at which a change in the transmission speed is detected and the speed increase is determined, and the predetermined specified time. 4 is held, and the buffer threshold change scheduled time is determined by distinguishing when the transmission rate is increased or decreased. set, when changing of the transmission rate, and then summed to determine the buffer correction value at changing the scheduled time of the buffer threshold is configured to control the buffer threshold, the predetermined specified time Is a round-trip delay time between a transmitting terminal that is communicatively connected to the packet transmission apparatus and a receiving terminal that receives a packet from the transmission terminal, or a round-trip between the packet transmission apparatus and the opposite packet transmission apparatus The delay time is a time obtained by adding a certain margin .

  In the packet transmission device according to the third aspect of the present invention, the buffer threshold control unit monitors the change in the transmission rate until the buffer threshold change scheduled time as the buffer threshold control based on the buffer correction value, If the transmission speed decreases before the scheduled time for changing the buffer threshold, and if it is below the currently set reference speed, the buffer threshold is set to the reference speed and the transmission after the speed change. The difference is increased by a value obtained by multiplying the difference with the predetermined prescribed time, and the reference speed is updated with the transmission speed after the speed change, and the buffer threshold is not scheduled to be changed. If there is a decrease in the transmission speed before the scheduled time for changing the buffer threshold, if the speed is not below the currently set reference speed, the buffer The transmission rate change is continuously monitored until the threshold change scheduled time, and when there is an increase in the transmission rate before the buffer threshold change scheduled time elapses, the predetermined rate from the point of the speed increase is determined. The buffer threshold change schedule time is set and reserved so that the buffer threshold is changed after the lapse of a specified time, and the buffer threshold change schedule is determined to be valid without changing the currently set reference speed and buffer threshold. When the buffer threshold change scheduled time is reached, the buffer threshold is a value obtained by multiplying the difference between the current transmission rate and the reference rate immediately before the buffer threshold change scheduled time by the predetermined specified time. Control is performed by subtracting from the currently set buffer threshold.

  Further, in the packet transmission apparatus according to the present invention, the buffer threshold value control unit has means for further adding a fixed correction value corresponding to the jitter amount of the communication path to the buffer correction value when the buffer threshold value is changed. Features.

  According to the present invention, the maximum value of cwnd of a transmission terminal using loss-based congestion control can be maintained high even when the transmission speed of the communication path is reduced, and the transmission speed of the communication path is switched from low speed to high speed. Sometimes, packet transmission can be prevented from being intermittent, and efficient packet transmission that effectively utilizes the transmission capability of the communication path can be realized.

  Further, when the transmission speed of the communication path is lowered, the buffer overflows, and the occurrence of a large amount of packet loss can be suppressed or prevented. As a result, data loss in real-time communication due to a large amount of packet loss, response deterioration due to retransmission of missing data, and other communication effects such as communication speed are prevented, and the transmission capacity of the communication path is effectively utilized. Thus, efficient packet transmission can be realized. In particular, according to the present invention, packet loss due to buffer overflow can be prevented even when the transmission rate is changed at a time interval shorter than the specified time.

It is a block diagram of the packet transmission apparatus of one Embodiment by this invention. (A), (b) is a figure which shows the operation example of the transmission rate at the time of buffer threshold value control of Example 1 in the packet transmission apparatus of one Embodiment by this invention, and a buffer threshold value, respectively. It is a flowchart of the buffer threshold value control of Example 2 in the packet transmission apparatus of one Embodiment by this invention. (A), (b) is a figure which shows the operation example of the transmission rate at the time of buffer threshold value control of Example 2 in the packet transmission apparatus of one Embodiment by this invention, and a buffer threshold value, respectively. It is a flowchart of the buffer threshold value control of Example 3 in the packet transmission apparatus of one Embodiment by this invention. (A), (b) is a figure which shows the operation example of the transmission rate at the time of buffer threshold value control of Example 3 in the packet transmission apparatus of one Embodiment by this invention, and a buffer threshold value, respectively. It is a figure which shows the example of schematic structure of a network in case a transmission terminal and a receiving terminal perform data communication via a packet transmission apparatus and a packet transmission apparatus. It is a block diagram which shows an example of the conventional packet transmission apparatus. It is a figure which shows the example of the time change of the congestion window (cwnd) in TCP New Reno.

  Hereinafter, a packet transmission apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a packet transmission device 51a according to an embodiment of the present invention.

  As shown in FIG. 7, a network is assumed in which a transmission terminal 50 and a reception terminal 53 at remote points perform data communication via the packet transmission device 51 and the packet transmission device 52 via the communication path 12 and the communication path 21. The packet transmission device 51a according to the present invention will be described as being provided in place of the conventional packet transmission device 51. It is assumed that the communication path 12 has the slowest transmission speed among the communication paths 01, 12, and 23 that transmit packets in the direction from the transmission terminal 50 to the reception terminal 53. Each device performs data communication using TCP.

  In the packet transmission device 51a according to the embodiment of the present invention shown in FIG. 1, the same components as those of the conventional packet transmission device 51 shown in FIG. That is, the packet transmission device 51a according to an embodiment of the present invention includes packet input units 511 and 515, a packet transfer unit 512, packet standby control units 513a and 516, and packet output units 514 and 517, and includes a packet standby control unit. 513a is different from the conventional packet transmission apparatus 51 in that it includes a buffer threshold value control unit 518.

  The packet input unit 511 receives the packet output from the transmission terminal 50 via the communication path 01 and inputs it to the packet transfer unit 512. The packet input unit 515 receives a packet transmitted from the opposite packet transmission device 52 via the communication path 21 and inputs the packet to the packet transfer unit 512.

  The packet transfer unit 512 analyzes the destination of the input packet to determine the output destination of the packet, and inputs the packet to the packet standby control unit 516 connected to the determined packet output unit 517. Accordingly, the packet transfer unit 512 is configured as a hub or a switch, for example, and is configured to determine the output destination of the packet for the plurality of packet standby control units 516 connected to each of the plurality of packet output units 517. (Not shown).

  The packet standby control unit 513a and the packet standby control unit 516 have a function of temporarily storing the input packets in the buffers, and receive packets to be transmitted from the packet output unit 514 and the packet output unit 517, respectively. The packets are temporarily held in the respective buffers until transmission is possible from the communication paths 12 and 10 to which the respective packet output units 514 and 517 are connected.

  However, the packet standby control unit 513a determines whether or not the number of packets or the amount of data that can be stored in the buffer has reached a variable upper limit (hereinafter referred to as “buffer threshold”) when the packet is stored in the buffer. If this buffer threshold is reached, it is determined that the packet cannot be stored, and either the input packet or the packet being stored is discarded.

  On the other hand, when storing the packet in the buffer, the packet standby control unit 516 determines whether or not the number of packets or the amount of data that can be stored in the buffer has reached a fixed upper limit (predetermined buffer size). If it has reached, it is determined that the packet cannot be stored, and either the input packet or the packet being stored is discarded.

  The packet output unit 514 takes out the packet from the packet standby control unit 513a, and transmits the packet to the communication path 12 at a set transmission rate that can be changed. The packet output unit 517 extracts the packet from the packet standby control unit 516 and transmits the packet to the communication path 10.

  Therefore, the packet transmission device 51a cannot transmit immediately even when a packet is input due to reasons such as when the communication path is being used for transmission of a previously transmitted packet or because the communication path cannot be used. In order to prevent the packet from being discarded, the packet is stored in the buffers of the packet standby control units 513a and 516 and held until it can be transmitted to the communication paths 12 and 10. The packet transmission device 51a according to the present invention has a variable upper limit (buffer threshold) in the number of packets and the amount of data that can be stored in the buffer by the function of the buffer threshold control unit 518 included in the packet standby control unit 513a. When the buffer threshold is exceeded, the packet is discarded.

  Hereinafter, the buffer threshold value control of the first to third embodiments in the buffer threshold value control unit 518 will be described in order. The buffer threshold value control unit 518 uses a value obtained by adding the buffer correction value to the initial buffer threshold value as a buffer threshold value, and the buffer threshold value control of each embodiment is configured by generating and controlling the buffer correction value in different ways. The The predetermined initial buffer threshold value is an initial transmission speed and a predetermined time that have a predetermined transmission time value at the start of measurement of a predetermined specified time (that is, a predetermined round-trip delay time Ttt described later, for example, RTT). And a product of a fixed correction coefficient α. The value of the fixed correction coefficient α may be “1”, “a value less than 1” or “a value greater than 1”, and is a predetermined value. Here, “the value to add the buffer correction value to the initial buffer threshold” means that when the buffer correction value becomes a negative value, the absolute value of the buffer correction value is subtracted from the initial buffer threshold. pay attention to. On the other hand, in order to enhance the understanding of the present invention, when expressed as “add” specifically, the absolute value of the target value is added, and when expressed as “subtract” specifically, It is assumed that the absolute value is reduced.

(Buffer threshold control of the first embodiment)
First, buffer threshold control according to the first embodiment by the buffer threshold controller 518 will be described. In the buffer threshold value control of the first embodiment by the buffer threshold value control unit 518, a value obtained by continuously integrating the difference between the initial transmission rate and the current transmission rate at which the speed change is detected is set as the buffer correction value.

  FIGS. 2A and 2B show operation examples of the transmission rate and the buffer threshold in the buffer threshold control of the first embodiment by the buffer threshold controller 518 in the packet transmission device 51a, respectively. As shown in FIG. 2A, when the transmission rate decreases from S0 to S1 at time t0 and increases to S2 at time t2, for example, as shown in FIG. The buffer threshold value th at time t until (Trtt) elapses is a value obtained by adding (S0−S1) × (t−t0) as a buffer correction value to the initial buffer threshold value th0.

  The buffer threshold value may be obtained by “adding” a further fixed correction value in addition to adding the buffer correction value. For example, a large jitter may occur in the communication path 01, the communication path 12, the communication path 23, the communication path 32, the communication path 21, and the communication path 10. In such a case, it is preferable to “add” the fixed correction value to the buffer correction value in accordance with the magnitude of jitter.

  Thus, by configuring the buffer threshold value control unit 518 with the buffer threshold value control of the first embodiment, packet loss due to buffer overflow can be prevented even when the transmission rate is changed at a time interval shorter than the specified time (Tttt). it can.

(Buffer threshold control of the second embodiment)
Next, buffer threshold value control according to the second embodiment by the buffer threshold value control unit 518 will be described. In the buffer threshold value control of the second embodiment by the buffer threshold value control unit 518, a value obtained by time-integrating a difference between the initial transmission rate and the current transmission rate at which the rate change is detected at a predetermined sampling time interval is a buffer correction value. And

  FIG. 3 is a flowchart of buffer threshold control according to the second embodiment by the buffer threshold control unit 518. Also in this example, the buffer threshold value control unit 518 uses the value obtained by adding the buffer correction value to the initial buffer threshold value as the buffer threshold value, and this buffer correction value is constituted by a value obtained by time integration based on a predetermined sampling time. The In this example as well, a further fixed correction value may be added to the buffer correction value.

  First, as an initialization process, the buffer threshold control unit 518 initializes the recording of the transmission rate up to the past specified time with a value equal to the current transmission rate (step S1), and monitors the value of (transmission rate difference) as 0. (Step S2). At this time, the buffer threshold control unit 518 sets the predetermined initial buffer threshold described above as the buffer threshold.

  Subsequently, the buffer threshold control unit 518 waits for the elapse of a predetermined sampling time (step S3), and adds (transmission speed difference) × (sampling time) as a buffer correction value to the buffer threshold (step S4). . Note that the monitored value (transmission speed difference) is updated in a subsequent step.

  Subsequently, the buffer threshold value control unit 518 acquires a new transmission rate when the sampling time has elapsed and records it as the current transmission rate (step S5), and the (transmission rate before the specified time)-(new The value of (transmission speed difference) is calculated and held (transmission speed difference) is updated (step S6).

  Then, until initialization, step S3 and subsequent steps are repeated, and the buffer threshold control unit 518 waits for the elapse of a predetermined sampling time, and sets (buffer speed difference) × (sampling time) as the buffer correction value for the buffer threshold. Add as

  FIGS. 4A and 4B show operation examples of the transmission rate and the buffer threshold in the buffer threshold control of the second embodiment by the buffer threshold control unit 518 in the packet transmission device 51a, respectively. As shown in FIG. 4A, when the transmission rate decreases from S0 to S1 at time t0 and increases to S2 at time t2, for example, as shown in FIG. The buffer threshold th at time t until (Trtt) elapses is a value obtained by adding (S0−S1) × (t−t0) as a buffer correction value to the initial buffer threshold th0 at a constant sampling time st interval. When the buffer correction value is negative, subtraction is performed.

  Thus, by configuring the buffer threshold control unit 518 with the buffer threshold control of the second embodiment, packet loss due to buffer overflow can be prevented even when the transmission rate is changed at a time interval shorter than the specified time (Tttt). it can.

(Buffer threshold control of the third embodiment)
Next, buffer threshold value control according to the third embodiment by the buffer threshold value control unit 518 will be described. In the buffer threshold value control of the third embodiment by the buffer threshold value control unit 518, “current buffer threshold value (active buffer threshold value)” and “current buffer threshold value” setting that are set when a change in transmission rate is detected. "Reference speed" that is the transmission speed at the time, "buffer threshold scheduled change time" that is determined based on the time when the transmission speed change is detected and the speed increase is determined (speed increase time) and a specified time (for example, RTT), In addition, the four parameter values of whether or not the buffer threshold is scheduled to be changed are retained, and control is not performed by time integration as in the first and second embodiments, and the transmission speed is increased and decreased. Determine the buffer threshold change scheduled time, and control the buffer threshold by determining the buffer correction value to be added to the initial buffer threshold at the transmission rate change or buffer threshold change scheduled time That. As a result, the control for changing the buffer threshold according to the change in the transmission rate is simplified to prevent packet loss due to buffer overflow.

  FIG. 5 is a flowchart of buffer threshold control according to the third embodiment by the buffer threshold controller 518. Also in this example, the buffer threshold value control unit 518 uses the value obtained by adding the buffer correction value to the initial buffer threshold value described above as the buffer threshold value. This buffer correction value is a value automatically controlled based on the above four parameter values. Composed.

  First, as an initialization process, the buffer threshold control unit 518 initializes the “reference speed” with a value (initial transmission speed) equal to the current transmission speed, and sets the above-described predetermined initial buffer threshold as the “buffer threshold”. At the same time, it is set and held as “no buffer threshold is scheduled to be changed” (step S11). In this initialization process, “the buffer threshold is not scheduled to be changed” is set, and therefore “the buffer threshold is scheduled to be changed” is set to a time when a predetermined time (for example, RTT) has elapsed.

  As a basic operation, the buffer threshold control unit 518 monitors the change of the transmission rate until the “buffer threshold change scheduled time” (step S12), and the transmission rate decreases before the “buffer threshold change scheduled time” elapses. If there is (Step S13: No, Step S14: Yes), if the transmission speed after the speed change is lower than the currently set reference speed (Step S15: Yes), the buffer speed is set to the reference speed and the speed. The difference between the changed transmission speed and a specified time (for example, RTT) is added and controlled by adding and increasing, and the "current buffer threshold" to be held is updated, and the "reference speed" to be held is the speed concerned. Updating is performed at the changed transmission rate, and “there is no plan to change the buffer threshold” (step S16). Thereafter, the transmission rate change is continuously monitored until the “buffer threshold change scheduled time” (step S12).

  On the other hand, when the transmission speed has increased before the “buffer threshold change scheduled time” has elapsed (step S13: No, step S14: No), after a specified time (for example, RTT) has elapsed since the speed increase. Set and reserve “scheduled buffer threshold change time” to change the buffer threshold, and set “the buffer threshold is scheduled to be changed” without changing the reference speed and the buffer threshold during operation (step S17). Thereby, the change of the buffer threshold is postponed until the decrease in the number of packets stored in the buffer is reduced. In particular, when the speed increases step by step, the “buffer threshold change scheduled time” is automatically updated, and is set to a time that is a specified time after the last time the speed increased (that is, the speed increase time). Is done. Thereafter, the transmission rate change is continuously monitored until the “buffer threshold change scheduled time” (step S12).

  In step S14, it operates when a change in the transmission speed is detected. Even if the transmission speed increases and then decreases again, the reference speed is changed if the speed is not lower than the reference speed. No (step S15: No), and thereafter, the transmission rate change is monitored until the “buffer threshold change scheduled time” (step S12).

  Then, when the “buffer threshold change scheduled time” is reached (step S13: Yes), the buffer threshold is set to the difference between the current transmission rate and the reference rate in consideration of the possibility that the transmission rate is slightly slow. A value obtained by multiplying a value obtained by multiplying a specified time (for example, RTT) by “subtracting” from the “current buffer threshold value” that is held is controlled as a new “buffer threshold value”, and the current transmission rate value is The “current buffer threshold” is updated as “speed”, and “there is no plan to change the buffer threshold” (step S18).

  As shown in FIG. 6, the “current buffer threshold” is “subtracted” by updating “after the lapse of a specified time (for example, RTT) since the last speed increase” as in this example. Buffer threshold control can be realized.

  FIGS. 6A and 6B show an operation example of the transmission rate and the buffer threshold in the buffer threshold control of the third embodiment by the buffer threshold controller 518 in the packet transmission device 51a, respectively. As shown in FIG. 6A, it is assumed that the transmission speed at the time of transmission increases and decreases step by step, and that there is a delay of a specified time (for example, RTT) with respect to the speed of the data confirmed to be received. Then, from the relationship between the stepwise increase / decrease in the transmission speed at the time of transmission shown in FIG. 6A and the speed of the data that has been confirmed to be received, as shown in FIG. 6B, when the amount of packets stored in the buffer changes. To do.

  In order to prevent packet loss due to buffer overflow, the buffer threshold th may be controlled in accordance with the change in the buffer amount. Therefore, in “C1” and “C2” shown in FIG. 6B, the buffer threshold value is increased by a value obtained by multiplying the difference between the reference speed and the transmission speed after the speed change by a specified time (for example, RTT). Then, the “current buffer threshold value” to be held and updated is updated, and the “reference speed” to be held is updated with the transmission rate after the speed change, and “there is no plan to change the buffer threshold” (FIG. 5). Step S16 shown in FIG.

  In “C3” illustrated in FIG. 6B, “buffer threshold scheduled change time” so that the buffer threshold is changed after a specified time (for example, RTT) has elapsed from the point of speed increase due to the increase in transmission speed. Is set and reserved, and “the buffer threshold is scheduled to be changed” without changing the reference speed (processing in step S17 shown in FIG. 5).

  In “C4” shown in FIG. 6B, even if the transmission speed increases again after the transmission speed increases, the reference speed is not changed unless it is lower than the reference speed (shown in FIG. 5). Step S15).

  In “C5” shown in FIG. 6B, “buffer threshold scheduled change time” so that the buffer threshold is changed after a lapse of a specified time (for example, RTT) from the point of speed increase due to the increase in transmission speed. Is set and reserved, and “the buffer threshold is scheduled to be changed” without changing the reference speed and the buffer threshold during the operation (processing in step S17 shown in FIG. 5).

  In “C6” shown in FIG. 6B, the “buffer threshold change scheduled time” is set, and the buffer threshold is set to the difference between the current transmission rate and the reference rate immediately before the buffer threshold change scheduled time. (For example, RTT) is controlled by “subtracting” from the “current buffer threshold value” held by the multiplied value, and the current transmission speed value is updated as the “reference speed” and “current buffer threshold value” "Is updated, and" there is no plan to change the buffer threshold "(processing in step S18 shown in FIG. 5).

  As described above, in the buffer threshold value control according to the third embodiment, the “current buffer threshold value”, “reference speed”, and the change in the transmission rate that are set when the change in the transmission rate is detected, and the rate increase is determined. Holds four parameter values, “buffer threshold change scheduled time” determined based on time (speed increase time) and specified time (for example, RTT), and “buffer buffer change planned presence / absence”, and transmits. A buffer threshold change scheduled time is determined by distinguishing between speed increase and decrease, and a buffer correction value is determined at the transmission speed change or buffer threshold change scheduled time to control the buffer threshold. As a result, the control for changing the buffer threshold according to the change in the transmission rate is simplified to prevent packet loss due to buffer overflow.

  Also in this example, a further fixed correction value may be added to the buffer correction value. For example, a large jitter may occur in the communication path 01, the communication path 12, the communication path 23, the communication path 32, the communication path 21, and the communication path 10. In such a case, it is preferable to “add” the fixed correction value to the buffer correction value in accordance with the magnitude of jitter.

  Thus, by configuring the buffer threshold control unit 518 with the buffer threshold control of the third embodiment, packet loss due to buffer overflow can be prevented even when the transmission rate is changed at a time interval shorter than the specified time (Tttt). it can.

  It should be noted that the “specified time (Ttt)” in each embodiment is desirable for generalization to be a round trip delay time (RTT) between the transmission terminal 50 and the reception terminal 53 that actually perform data communication. When the transmission delay of the communication path 12 and the communication path 21 is extremely larger than the transmission delay of other communication paths, a fixed margin is provided for the round-trip delay time (RTT) between the packet transmission apparatus 51a and the packet transmission apparatus 52. It becomes more accurate by taking the value added.

  The function of the buffer threshold control unit 518 prevents the occurrence of a large amount of packet loss by storing in the buffer all packets from when the transmission rate is reduced until the output rate of the packet of the transmitting terminal 50 is reduced. can do.

  Also, if the buffer threshold is the same value, the maximum value of cwnd decreases as the transmission speed is low. However, the maximum value of cwnd when the transmission speed is decreased by increasing the buffer threshold at low speed. Can be prevented, and cwnd during high-speed transmission can be maintained. With this effect, even if packet transmission becomes intermittent due to a shortage of cwnd that occurs when the transmission speed of the communication path 12 is switched from low speed to high speed, this can be prevented from continuing for a long time.

  The present invention has been described with reference to specific embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the technical idea thereof. For example, if it is necessary to update a part of a packet such as a packet header at the time of packet transfer according to the regulation of the packet communication protocol, the packet transfer unit 512 can be configured to perform this process.

  In addition, the packet transfer unit 512 is not included in the application in which the packet received by the packet input unit 511 is always output as it is from the packet output unit 514, and the packet received by the packet input unit 515 is always output from the packet output unit 517 as it is. It can be. In this case, the packet input unit 511 directly inputs the received packet to the packet standby control unit 513a, and the packet input unit 515 directly inputs the received packet to the packet standby control unit 516.

  Further, a transmission side packet transmission device configured by a packet input unit 511, a packet standby control unit 513a and a packet output unit 514, and a reception side packet transmission device configured by a packet input unit 515, a packet standby control unit 516 and a packet output unit 517 A network may be configured by the two packet transmission apparatuses. In this configuration, a transmission side packet transmission apparatus that transmits a packet to the communication path 12 capable of changing the transmission speed is an object of the present invention, and a conventional packet transmission apparatus may be used as the reception side packet transmission apparatus.

  According to the present invention, it is possible to realize efficient packet transmission that effectively uses the transmission capability of the communication path, which is useful for a packet transmission apparatus having a function of changing the transmission speed of the communication path.

DESCRIPTION OF SYMBOLS 50 Transmission terminal 51 Conventional packet transmission apparatus 51a Packet transmission apparatus based on this invention 52 Conventional packet transmission apparatus 53 Reception terminal 511,515 Packet input part 512 Packet transfer part 513,513a, 516 Packet standby control part 514,517 Packet output 518 Buffer threshold value control unit

Claims (5)

A packet transmission device having a function of changing the transmission speed of a communication path,
A packet output unit for transmitting packets at a set transmission rate;
The number of packets or data that can be stored in the buffer by monitoring the change in the transmission rate from the packet output unit when temporarily storing the packet transmitted from the packet output unit in the buffer and storing the packet in the buffer A packet waiting control unit having a buffer threshold value control unit that controls a buffer threshold value that defines a variable upper limit on the amount,
Said buffer threshold controller, when changing the transmission rate in a shorter time interval than the predetermined specified time, have a means for controlling to change the buffer threshold in accordance with the speed change of the transmission rate, and the The buffer threshold value controller is configured to multiply a product of an initial transmission rate and a predetermined specified time with a transmission rate value at the start of measurement of the predetermined specified time by a predetermined fixed correction coefficient. The difference between the initial transmission rate and the current transmission rate at which the change in the transmission rate is detected is continuously added as a buffer correction value .
The predetermined specified time is a round-trip delay time between a transmitting terminal that is communicatively connected to the packet transmission apparatus and a receiving terminal that receives a packet from the transmitting terminal, or a packet facing the packet transmission apparatus A packet transmission apparatus characterized in that a time obtained by adding a certain margin to a round-trip delay time with the transmission apparatus. A packet transmission device having a function of changing the transmission speed of a communication path,
A packet output unit for transmitting packets at a set transmission rate;
The number of packets or data that can be stored in the buffer by monitoring the change in the transmission rate from the packet output unit when temporarily storing the packet transmitted from the packet output unit in the buffer and storing the packet in the buffer A packet waiting control unit having a buffer threshold value control unit that controls a buffer threshold value that defines a variable upper limit on the amount,
The buffer threshold control unit has means for controlling to change the buffer threshold according to a change in the transmission rate when changing the transmission rate at a time interval shorter than a predetermined specified time, and The buffer threshold value controller is configured to multiply a product of an initial transmission rate and a predetermined specified time with a transmission rate value at the start of measurement of the predetermined specified time by a predetermined fixed correction coefficient. The difference between the initial transmission rate and the current transmission rate at which the change in the transmission rate is detected is configured to add a value obtained by time integration at a predetermined sampling time interval as a buffer correction value ,
The predetermined specified time is a round-trip delay time between a transmitting terminal that is communicatively connected to the packet transmission apparatus and a receiving terminal that receives a packet from the transmitting terminal, or a packet facing the packet transmission apparatus packet transmission device characterized in that a time obtained by adding a predetermined margin to the round trip time between the transmission device. A packet transmission device having a function of changing the transmission speed of a communication path,
A packet output unit for transmitting packets at a set transmission rate;
The number of packets or data that can be stored in the buffer by monitoring the change in the transmission rate from the packet output unit when temporarily storing the packet transmitted from the packet output unit in the buffer and storing the packet in the buffer A packet waiting control unit having a buffer threshold value control unit that controls a buffer threshold value that defines a variable upper limit on the amount,
The buffer threshold control unit has means for controlling to change the buffer threshold according to a change in the transmission rate when changing the transmission rate at a time interval shorter than a predetermined specified time, and The buffer threshold value controller is configured to multiply a product of an initial transmission rate and a predetermined specified time with a transmission rate value at the start of measurement of the predetermined specified time by a predetermined fixed correction coefficient. A buffer threshold that is currently set when a change in transmission speed is detected, a reference speed that is the transmission speed when the buffer threshold is set, a time at which a change in transmission speed is detected and a speed increase is determined, and Holds the four parameter values of the buffer threshold scheduled change time determined based on a predetermined specified time and whether or not the buffer threshold is scheduled to be changed, and indicates when the transmission rate increases and decreases. Betsushite determine the changes expected time of said buffer threshold is configured to control the time of changing the transmission rate, and then summed to determine the buffer correction value at changing the scheduled time of the buffer threshold the buffer threshold,
The predetermined specified time is a round-trip delay time between a transmitting terminal that is communicatively connected to the packet transmission apparatus and a receiving terminal that receives a packet from the transmitting terminal, or a packet facing the packet transmission apparatus packet transmission device characterized in that a time obtained by adding a predetermined margin to the round trip time between the transmission device. The buffer threshold control unit, as buffer threshold control based on the buffer correction value,
Monitor the change in the transmission rate until the buffer threshold change scheduled time,
If the transmission rate decreases before the scheduled time for the buffer threshold change, and if it falls below the currently set reference rate, the buffer threshold is set to the reference rate and the rate change after the rate change. The difference between the transmission speed and the value multiplied by the predetermined specified time is added and controlled, and the reference speed is updated with the transmission speed after the speed change, and the buffer threshold is not scheduled to be changed.
If there is a decrease in the transmission speed before the buffer threshold change scheduled time elapses, and if it is not lower than the currently set reference speed, the transmission speed change until the buffer threshold change scheduled time. Continuously monitoring
When there is an increase in the transmission speed before the scheduled time for changing the buffer threshold, the buffer threshold is scheduled to be changed so that the buffer threshold is changed after the predetermined specified time has elapsed since the speed increase. Set the time and make a reservation, and change the buffer threshold without changing the currently set reference speed and buffer threshold,
When the buffer threshold change scheduled time is reached, the buffer threshold is calculated by multiplying the difference between the current transmission rate and the reference rate immediately before the buffer threshold change scheduled time by the predetermined specified time. 4. The packet transmission apparatus according to claim 3 , wherein the packet transmission apparatus is controlled by subtracting from a set buffer threshold value. Said buffer threshold control unit in the buffer correction value at the time of change of the buffer threshold, characterized in that it comprises means for additional fixed correction value corresponding to the jitter amount of the channel, of claims 1 to 4 The packet transmission apparatus according to any one of claims.