JP6417097B2 - 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. 3 shows a schematic configuration example of a network in the 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 a device that performs data communication using IP, in order to reliably transmit data, a function (congestion) that recovers data transmitted in a discarded packet or controls the output speed of a packet according to the transmission speed of a communication path. Data communication is performed using a data communication protocol having a 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. 4 is a block diagram illustrating an example of a conventional packet transmission apparatus. The packet transmission devices 51 and 52 in FIG. 3 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. 5 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.

  Specifically, the expansion speed of cwnd is 1 packet per RTT in TCP New Reno, and it takes (time increase amount / packet size) × RTT time to reach a new speed. is there. For example, in communication with an RTT of 10 ms and a packet size of 1500 bytes, it takes 83 seconds to increase by 100 Mbps.

  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 device according to the present invention is a packet transmission device 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 packet that is transmitted from the packet output unit. Temporarily hold in the buffer until it can be transmitted from the communication path connected to the packet output unit, when storing the packet in the buffer, monitoring the change in the transmission rate from the packet output unit, A packet standby control unit having a buffer threshold control unit that controls to change a buffer threshold that defines a variable upper limit for the number of packets or the amount of data that can be stored in the buffer when the transmission rate is changed, and the buffer threshold The control unit sets the buffer threshold when the transmission rate from the packet output unit is changed to a lower speed than before the change. Large, and when changing faster than before the change, at the time elapsed after the speed change predetermined specified time or more, and that you reduce the buffer threshold.

  In the packet transmission device according to the present invention, the buffer threshold value control unit may change the buffer threshold value when the transmission rate from the packet output unit is lower than before the change (speed before change−speed after change). ) X Enlarged by the specified time and when changing to a higher speed than before the change, the buffer threshold is set to (the speed after the change-the speed before the change) at the time when a predetermined specified time has elapsed since the speed change. It is characterized by being reduced by a specified time.

  In the packet transmission apparatus according to the present invention, the specified time is a round-trip delay time between a transmission terminal that is communicatively connected to the packet transmission apparatus and a reception terminal that receives a packet from the transmission terminal. To do.

  In the packet transmission apparatus according to the present invention, the specified time is a value obtained by adding a certain margin to a round-trip delay time between the packet transmission apparatus and the opposite packet transmission apparatus.

  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.

It is a block diagram of the packet transmission apparatus of one Embodiment by this invention. It is a flowchart of buffer threshold value control in the packet transmission apparatus of one Embodiment by this invention. 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. 3, a network is assumed in which a transmitting terminal 50 and a 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. 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 control unit 518 will be described in detail. FIG. 2 is a flowchart of buffer threshold control by the buffer threshold controller 518 in the packet transmission device 51a.

  In the packet transmission device 51a of the present invention, the buffer threshold control unit 518 monitors the change in the transmission rate of the communication path 12 by the packet standby control unit 513a (step S1). When the transmission speed is changed to a lower speed than before the change (step S2: Yes), the buffer threshold of the buffer included in the packet waiting control unit 513a is set to (the speed before the change−the speed after the change) × It increases by a specified time (that is, a predetermined round-trip delay time described later) (step S3).

  Conversely, when changing the transmission speed of the communication path 12 at the packet standby control unit 513a, when changing to a higher speed than before the change (step S2: No), a specified time (ie, described later) after the speed change. When the predetermined round-trip delay time has elapsed, the buffer threshold of the buffer of the packet standby control unit 513a is reduced by (the speed after change−the speed before the change) × the specified time (step S4).

  The “specified time” is desirable to generalize the round-trip delay time between the transmission terminal 50 and the reception terminal 53 that actually perform data communication. However, the transmission delay of the communication path 12 and the communication path 21 is When the transmission delay is extremely larger than the transmission delay of the other communication path, a more precise buffer threshold value control is performed by setting a value obtained by adding a certain margin to the round-trip delay time between the packet transmission device 51a and the packet transmission device 52. Is possible.

  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 (4)

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;
A packet transmitted from the packet output unit is temporarily held in a buffer until it can be transmitted from a communication path connected to the packet output unit, and when the packet is stored in the buffer, the packet output unit A packet waiting unit having a buffer threshold control unit that monitors a change in the transmission rate and controls to change a buffer threshold that defines a variable upper limit for the number of packets or the amount of data that can be stored in the buffer when the transmission rate is changed A control unit ,
The buffer threshold value controller is
When the transmission rate from the packet output unit is changed to a lower speed than before the change, the buffer threshold value is enlarged, and when changing to a higher speed than before the change, when a predetermined specified time or more has elapsed after the change of the speed in a packet transmission apparatus which is characterized that you reduce the buffer threshold. The buffer threshold value controller is
When the transmission rate from the packet output unit is changed to a lower speed than before the change, the buffer threshold value is increased by (pre-change-speed after change) × specified time and changed to a higher speed than before the change. is the time elapsed after the speed change predetermined specified time or more, the buffer threshold - characterized by reduced by (the changed speed of the pre-change speed) × specified time, according to claim 1 Packet transmission equipment. The predetermined time is characterized by a round trip time between the receiving terminal that receives a packet from the transmission terminal and the transmission terminal communication connection to the packet transmission device, according to claim 1 or 2 Packet transmission equipment. The predetermined time is characterized by a value obtained by adding a certain margin to the round trip time of the packet transmission device to face the packet transmission device, a packet transmission apparatus according to claim 1 or 2.