JP2012134907A - Tcp transfer apparatus and program thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a TCP transfer apparatus which can improve TCP transmission throughput even in cases where a high-speed retransfer algorithm is adopted and the order in which TCP packets arrive is altered by a difference in delay per logic line.SOLUTION: A TCP divided transfer apparatus 3 comprises a TCP packet receive unit 31 which receives TCP packets; a path select unit 33 which selects one logic line L from a plurality of logic lines L and generates transfer information which includes information on a selected logic line; an ACK control unit 35 which destroys an ACK packet when a valid filter is set, or lets an ACK packet pass when a valid filter is not set; a delay amount setting unit 36 which measures a logic line delay amount in advance; and a TCP packet transmit unit 37 which transmits the ACK packet which was permitted to pass by the ACK control unit 35 to a TCP transmit apparatus 1.

Description

  The present invention receives a TCP packet including a sequence number from a transmission-side terminal device, and transfers the received TCP packet to a reception-side terminal device that is the destination of the TCP packet via any of a plurality of logical lines. The present invention relates to a TCP transfer device and a program thereof.

  In recent years, an IP (Internet Protocol) network that is widely used as an information transmission infrastructure is generally a best-effort network in which packet transmission is not guaranteed. For this reason, TCP (Transmission Control Protocol) that confirms transmission is widely used for applications that require packet transmission reliably, such as file transmission (Non-Patent Document 1).

  The basic communication algorithm of TCP will be described below. The transmission side transmits the packet including the sequence number in the header of the packet to be transmitted. Based on the sequence number of the received packet, the receiving side returns a sequence number to be received next as an ACK number in an ACK (Acknowledgement) packet. From the received ACK packet, the transmission side can know to what packet the reception side has successfully received. In addition, for a packet whose reception has not been confirmed for a certain period of time, the transmitting side transmits the same packet again, thereby realizing reliable transmission.

  In TCP, a congestion window and a reception window are used as values for controlling the transmission amount. The congestion window is the amount of data that can be transmitted without waiting for the transmission side to return the ACK packet. The reception window is the amount of data that can be processed at a certain point in time on the receiving side. Here, the congestion window is expanded every time an ACK packet is received, and larger data can be transmitted without waiting for the return of the ACK packet. On the other hand, when a packet loss occurs and an ACK packet for a certain packet cannot be received and the packet is retransmitted, the congestion window is reset to the initial value.

  TCP uses a high-speed retransmission algorithm that detects packet loss and retransmits the packet without waiting for the timeout of the ACK packet. For example, when the transmitting side receives three consecutive ACK packets having the same ACK number, the transmitting side retransmits the packet without waiting for a timeout. In this case, the congestion window is reduced. Furthermore, TCP transmission performance improvement techniques for changing the expansion width or reduction width of the congestion window, such as Reno, New Reno, and Vegas, have been proposed (Non-Patent Documents 2 to 4).

  Here, the maximum throughput of data transmission for confirming transmission is not limited to TCP, and is determined by the maximum size of the reception window and the round trip number delay. In order to avoid the bottleneck due to the maximum size of the reception window, a method of establishing a plurality of TCP connections on a single line can be considered. In this method, the reception window is increased by the number of connections, so that the throughput of TCP transmission is improved.

  On the other hand, when the size of the reception window is sufficient, the transmission rate of the line becomes a bottleneck, and the above-described technique for establishing a plurality of TCP connections on a single line cannot be expected to improve the throughput. In this case, it is possible to increase the total transmission speed of the line and improve the TCP transmission throughput by a technique using a plurality of lines.

RFC793 Transmission Control Protocol RFC2581 TCP Congestion Control RFC3782 The New Reno Modification to TCP ’s Fast Recovery Algorithm TCP Vegas: End to End Congestion Avoidance on a Global Internet.IEEE Journal on Selected Areas in Communication, Vol 13, No. 8, 1465-1480

  However, in the method using a plurality of lines, it is difficult to match the delay amount of each line. For this reason, a packet transmitted on a line with a small delay amount may overtake a packet transmitted on a line with a large delay amount, so that the arrival order of the packets may be switched. When the high-speed retransmission algorithm is adopted, if the arrival order of the packets is changed, the receiving side misunderstands that a packet loss has occurred, and makes a retransmission request for the overtaken packet to the transmitting side. For this reason, the technique using a plurality of lines has a problem that the throughput of TCP transmission does not improve.

This problem will be specifically described with reference to FIG.
In FIG. 9, “PCK” indicates a packet, and numerical values such as “1” and “2” illustrated after PCK indicate the sequence number of the packet. “ACK” indicates an ACK packet, and numerical values such as “1” and “2” illustrated after ACK indicate the ACK number of the ACK packet.

  First, the TCP transmission device 91 on the transmission side transmits PCK1, which is the first packet, to the TCP transmission device 93 on the reception side via a line with a large delay amount (step S91). Next, the TCP transmission device 91 transmits PCK2, which is a packet next to PCK1, to the TCP transmission device 93 via a line with a small delay amount. Here, since the delay amounts of both lines are different, PCK2 arrives at the TCP transmission apparatus 93 earlier than PCK1 (step S92).

  In this case, the TCP transmission apparatus 93 determines that a packet loss of PCK1 has occurred, and transmits ACK1 to the TCP transmission apparatus 91 to request retransmission of PCK1 (step S93). In response to this ACK1, the TCP transmission device 91 resets the congestion window to the initial value, and retransmits PCK1 to the TCP transmission device 93 (step S94).

  As a result, in the method using a plurality of lines, although the packet loss of PCK1 does not occur, the retransmission of PCK1 and the congestion window are reduced by the high-speed retransmission algorithm, so that the throughput of TCP transmission does not improve.

  Therefore, the present invention solves the above-described problems, adopts a high-speed retransmission algorithm, and can improve the TCP transmission throughput even when the arrival order of TCP packets is changed due to a delay difference for each logical line. An object is to provide an apparatus and a program thereof.

  In view of the above-described problems, the TCP transfer device according to the first invention of the present application receives a TCP packet including a sequence number from a transmission-side terminal device, and receives the received TCP packet via any of a plurality of logical lines. A TCP transfer device that transfers a packet to a destination terminal device that is a destination of the TCP packet, and includes a TCP packet reception unit, a route selection unit, an ACK control unit, and an ACK packet transmission unit. And

  According to this configuration, the TCP transfer device receives the TCP packet by the TCP packet receiving unit. In addition, the TCP transfer apparatus selects a logical line to which a TCP packet received by the TCP packet receiving unit is transferred from a plurality of logical lines by a route selection unit according to a predetermined rule, and passes through the selected logical line. Then, the TCP packet is transferred to the receiving terminal device, and transfer information including the sequence number of the transferred TCP packet and the information of the selected logical line that is the selected logical line is generated.

  Here, the route selection unit only needs to select at least a logical line (upward direction of the logical line) for transferring the TCP packet, and is necessarily required to select a logical line (downward direction of the logical line) to which the ACK packet is returned. There is no. If the route selection unit does not select the downlink direction of the logical line, the downlink direction of the logical line is notified as return line information.

  Further, as long as the plurality of logical lines are constructed at least in a partial section from the TCP transfer apparatus to the receiving terminal apparatus, it is not necessary to construct the entire logical line in the entire section from the TCP transfer apparatus to the receiving terminal apparatus. For example, when another TCP transfer device is arranged between the TCP transfer device and the receiving terminal device, a plurality of logical lines are constructed in a section from the TCP transfer device to another TCP transfer device. In this case, one logical line is constructed in the remaining section from the other TCP transfer device to the receiving terminal device.

  Also, the TCP transfer device receives an ACK packet, which is a response to the TCP packet transferred by the route selection unit, from the receiving terminal device by the ACK control unit, and discards or passes the received ACK packet by the filter. And a TCP transfer apparatus transmits the ACK packet which the ACK control part passed by the ACK packet transmission part to a transmission side terminal device.

  Further, the TCP transfer device calculates the delay amount of the selected logical line included in the transfer information generated by the route selection unit based on the logical line delay amount preset for each logical line by the ACK control unit, A filter is set in which the calculated delay amount of the selected logical line is a valid period after the TCP packet is transferred and the sequence number included in the transfer information is the ACK number to be discarded.

  Here, when the arrival order of the TCP packets is changed, the receiving side terminal device misunderstands that a packet loss has occurred, and returns an ACK packet to request retransmission of the overtaken TCP packet. In this case, the ACK control unit discards the ACK packet transmitted by misunderstanding as the packet loss by the filter. Therefore, the TCP transfer apparatus can prevent the TCP terminal from retransmitting the TCP packet and reducing the congestion window even though the transmitting terminal apparatus does not receive the ACK packet and no packet loss has occurred. .

  Further, the TCP transfer apparatus according to the second invention of the present application is a delay amount setting means in which the ACK control unit measures the round trip delay time for each logical line in advance and sets the measured round trip delay time as the logical line delay amount. It is preferable to further provide.

  In the TCP transfer device according to the third invention of the present application, the ACK control unit receives an ACK packet within the effective period of the filter, and the ACK number of the received ACK packet matches the ACK number to be discarded by the filter. It is preferable to discard the ACK packet.

  In the TCP transfer device according to the fourth invention of the present application, the route selection unit encapsulates the TCP packet received by the TCP packet reception unit with a protocol header other than TCP, and the encapsulated TCP packet is received on the receiving side terminal device. It is preferable to forward to

  The TCP transfer apparatus according to the first invention of the present application can also be realized by a TCP transfer program that causes a general computer to function as a TCP packet receiver, a path selector, an ACK controller, and an ACK packet transmitter.

According to the present invention, the following excellent effects can be obtained.
According to the first invention of this application, since the ACK packet returned by the receiving terminal device due to a packet loss is discarded by the filter, the transmitting terminal device does not receive this ACK packet. As a result, according to the first invention of the present application, it is possible to prevent the TCP packet retransmission and the congestion window from being reduced even though no packet loss occurs, and to improve the TCP transmission throughput. .

  According to the second aspect of the present invention, the effective period of the filter can be set to an appropriate length using the round-trip delay time. For this reason, according to the second invention of this application, since the ACK packet is transmitted to the transmission side terminal device after the effective period of the filter has elapsed, when the TCP packet needs to be retransmitted due to packet loss, the transmission side terminal The device can retransmit the TCP packet quickly.

  According to the third invention of the present application, an ACK packet that requests transmission of a new TCP packet is passed, and only an ACK packet that requests retransmission of a TCP packet that has already been transmitted is discarded, so that the ACK packet is discarded more than necessary. There is no.

  According to the fourth aspect of the present invention, by encapsulating the TCP packet with another protocol header, the TCP packet can be transmitted to the receiving terminal device using a protocol other than TCP.

1 is a schematic diagram of a TCP division transfer system including a TCP division transfer device according to a first embodiment of the present invention. It is a block diagram which shows the structure of the TCP division | segmentation transfer apparatus of FIG. FIG. 3 is a sequence diagram showing an operation of the TCP division transfer apparatus of FIG. 1 in a case where the arrival order of TCP packets is switched. FIG. 3 is a sequence diagram illustrating an operation of the TCP division transfer apparatus of FIG. It is the schematic of the TCP division | segmentation transfer system containing the TCP division | segmentation transfer apparatus which concerns on 2nd, 3rd embodiment of this invention. It is a block diagram which shows the structure of the TCP division | segmentation transfer apparatus of FIG. It is a figure explaining the data structure of the TCP packet encapsulated with the IP header in 2nd Embodiment of this invention. It is a figure explaining the data structure of the TCP packet encapsulated by the UDP header in 3rd Embodiment of this invention. It is a sequence diagram explaining the problem of a prior art.

(First embodiment)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In each embodiment, means having the same function are denoted by the same reference numerals and description thereof is omitted.

[Outline of TCP split transfer system]
With reference to FIG. 1, the outline of the TCP division transfer system 100 including the TCP division transfer apparatus 3 according to the first embodiment of the present invention will be described.
As shown in FIG. 1, a TCP division transfer system 100 divides a TCP stream into a plurality of logical lines and transmits them, and includes a TCP transmission apparatus (transmission side terminal apparatus) 1 and a TCP division transfer apparatus (TCP transfer). Device) 3, TCP division transfer device (other TCP transfer device) 5, and TCP transmission device (reception side terminal device) 7.

  In the first embodiment, the TCP transmission device 1 will be described as transferring a TCP packet toward the TCP transmission device 7. In the following description, the direction from the TCP transmission device 1 to the TCP transmission device 7 may be referred to as “uplink direction”, and the direction from the TCP transmission device 7 to the TCP transmission device 1 may be referred to as “downlink direction”.

The TCP transmission device 1 is a device having a TCP transmission function, for example, a general computer having a network interface (not shown).
Here, TCP transmission apparatus 1 via the logical channel _{L A,} are connected to the TCP division transfer unit 3. Then, the TCP transmission device 1 transmits a TCP packet created by a general client server application (for example, HTTP, SMTP, FTP, TELNET) to the TCP division transfer device 3.

The TCP division transfer device 3 receives a TCP packet from the TCP transmission device 1 and passes through any one of a plurality of logical lines L ₁ , L ₂ ,..., L _m (m is an arbitrary integer equal to or greater than 2). The received TCP packet is transferred to the TCP transmission device 7 that is the destination of the TCP packet.

Here, the TCP division transfer device 3 is connected to the TCP division transfer device 5 via a plurality of logical lines L ₁ , L ₂ ,..., L _m . Then, the TCP division transfer device 3 selects one logical line L from the plurality of logical lines L ₁ , L ₂ ,..., L _m . Further, the TCP division transfer device 3 transfers the TCP packet received from the TCP transmission device 1 to the TCP division transfer device 5 via the selected logical line L.
The configuration of the TCP division transfer device 3 will be described later.

Logical lines _{L (L A, L B,} L 1, L 2, ···, L m) is the physical line pairs that are used in the respective TCP transmission uplink and downlink, or uplink and downlink It is composed of one physical line that is commonly used for TCP transmission.
The relationship between the logical line L and the physical line will be described in the second and subsequent embodiments.

The TCP division transfer device 5 is a device having the same configuration as the TCP division transfer device 3.
Here, TCP division transfer device 5, through a logical line _{L B,} are connected to the TCP transmission device 7. Then, the TCP division transfer device 5 transmits the TCP packet transferred from the TCP division transfer device 3 to the TCP transmission device 7.
Furthermore, TCP division transfer device 5, the logic circuit delay of the logic circuit L _B (e.g., round trip time (RTT: Round Trip Time)) and that measured in advance will be described later why.

The TCP transmission device 7 is a device having the same configuration as the TCP transmission device 1.
Here, the TCP transmission device 7 receives a TCP packet from the TCP division transfer device 5 and processes the TCP packet by a client server application corresponding to the transmission destination port number of the TCP packet. At this time, the TCP transmission device 7 calculates the sequence number of the TCP packet to be received next as the ACK number based on the sequence number of the received TCP packet. Then, the TCP transmission device 7 generates an ACK packet storing the calculated ACK number, and returns it to the TCP transmission device 1.

  The TCP transmission device 7 determines whether a packet loss has occurred by a general method. For example, the TCP transmission device 7 determines that a packet loss has occurred when a TCP packet cannot be received for a certain period of time or when a TCP packet cannot be received in the order of sequence numbers. Here, when a packet loss occurs, the TCP transmission device 7 requests the TCP transmission device 1 to retransmit the TCP packet. Specifically, the TCP transmission device 7 calculates an ACK number that represents the sequence number of the TCP packet that could not be received, generates an ACK packet that stores this ACK number, and returns it to the TCP transmission device 1. .

As described above, in the TCP division transfer system 100, the TCP packet is transmitted from the TCP transmission apparatus 1 to the TCP transmission apparatus 7 via the TCP division transfer apparatuses 3 and 5. In the TCP division transfer system 100, an ACK packet for this TCP packet is returned to the TCP transmission apparatus 1 from the TCP transmission apparatus 7 via the TCP division transfer apparatuses 5 and 3.
Further, the TCP split transfer system 100, a plurality of logical lines _{L 1,} L 2, · · ·, to the delay difference _{L m} occurs even if the order of arrival TCP packets are switched, TCP division transfer apparatus described below 3 prevents that harmful effect.

[Configuration of TCP split transfer device]
With reference to FIG. 2, the configuration of the TCP division transfer apparatus 3 will be described (see FIG. 1 as appropriate).
As shown in FIG. 2, the TCP division transfer device 3 includes a TCP packet receiving unit 31, a route selection unit 33, an ACK control unit 35, and a TCP packet transmission unit (ACK packet transmission unit) 37.
In FIG. 2, each logical line L is illustrated separately in the upstream direction and the downstream direction for easy understanding.

TCP packet receiving unit 31, via a logical channel _{L A,} it is to receive the TCP packet sent by TCP transmission device 1. Then, the TCP packet receiving unit 31 outputs the received TCP packet to the route selecting unit 33.

Route selection unit 33 selects a plurality of logical lines _{L 1,} L 2, · · ·, from the _{L m,} a logical line L that TCP packets received by the TCP packet receiver 31 is transferred by a predetermined rule The TCP packet is transferred to the TCP transmission device 7 via the selected logical line L, and transfer information including the sequence number of the transferred TCP packet and information indicating the selected logical line L is generated. It is.

Here, the route selection unit 33 selects the logical line L by encapsulating the TCP packet with IP. In other words, the route selection unit 33 uses a logical line L that transfers a TCP packet from among a plurality of logical lines L ₁ , L ₂ ,..., L _m according to a rule implemented in the IP layer (network layer). Select. As a method of selecting the logical line L, for example, a method of selecting the logical line L at random from a plurality of logical lines L ₁ , L ₂ ,..., L _m , or based on a predetermined ratio A selection method (weighted round robin) is given. Then, the path selection unit 33 transfers the TCP packet output from the TCP packet reception unit 31 to the TCP division transfer device 5 via the selected logical line L.

  At this time, the path selection unit 33 generates transfer information including the sequence number of the TCP packet transferred to the TCP division transfer device 5 and information on the selected logical line that is the selected logical line L. Then, the route selection unit 33 outputs the generated transfer information to the ACK control unit 35.

Hereinafter, the delay amount setting unit 36 will be described prior to the ACK control unit 35.
The delay amount setting unit 36 measures in advance a logical line delay amount indicating a delay amount for each of the logical lines L ₁ , L ₂ ,..., L _m . The delay amount setting unit 36 stores the measured logical line delay amount in a memory or the like (not shown).

Here, the delay amount setting unit 36 measures the round-trip delay time as the logical line delay amount. Specifically, the delay amount setting unit 36 transmits the measurement packet to the TCP division transfer device 5 through the logical lines L ₁ , L ₂ ,..., L _m . When receiving the measurement packet, TCP division transfer device 5, measured in advance from delaying only the logical line delay of the logic circuit L _B, TCP division transfer device response packet (ACK packet) for the measurement packet Return to 3. Then, the delay amount setting unit 36, a logic circuit L _1, L _2, · · ·, each L _m, and the sending time of the measurement packet, the difference between the reception time of the response packet to the measurement packet, logic line _{L 1, L 2, ···,} measured as a logical line delay amount for each _{L m.}

As described above, the logic circuit _{L 1,} L 2, · · ·, the logical line delay amount for each _{L m,} a plurality of logical lines _{L 1,} L 2, · · ·, is _{L m} was constructed sections ( in addition to the round trip time of the TCP between the divided transfer device 3 and 5), is possible to reflect the round trip delay time of the logic circuit L _B is constructed sections (between TCP division transfer device 5 and the TCP transmission device 7) preferable. Thereby, the delay amount setting unit 36 can measure a more accurate logical line delay amount.

  The ACK control unit 35 includes the delay amount setting unit 36 described above, receives an ACK packet as a response to the TCP packet transferred by the route selection unit 33 from the TCP transmission device 7, and filters the received ACK packet ( Discarded or passed through (not shown).

Specifically, the ACK control unit 35 calculates the delay amount of the logical line L indicated by the transfer information output from the route selection unit 33 based on the logical line delay amount measured by the delay amount setting unit 36. In other words, the ACK control unit 35 includes logical lines L ₁ , L ₂ ,..., L configured by an uplink physical line to which the TCP packet is transferred and a downlink physical line to which the ACK packet is returned. _{The m} round-trip delay time is calculated as the delay amount of the logical line L. Then, the ACK control unit 35 sets a filter in which the calculated delay amount of the logical lines L ₁ , L ₂ ,..., L _m is set as the valid period and the sequence number of the transfer information is set as the discard target ACK number. .

  Here, when the ACK packet is received from the TCP transmission device 7, the ACK control unit 35 has a time when the ACK packet is received within the valid period, and the ACK number of the ACK packet matches the ACK number to be discarded. It is determined whether a valid filter is set. Here, when a valid filter is set for the received ACK packet, the ACK control unit 35 discards the ACK packet. On the other hand, when a valid filter is not set for the received ACK packet, the ACK control unit 35 passes the ACK packet.

TCP packet transmission unit 37, an ACK packet ACK control unit 35 is passed, via a logical channel _{L A,} it is to transfer the TCP transmission device 1.

[Operation of TCP division transfer device: Case where TCP packet arrival order is switched]
With reference to FIG. 3, the operation of the TCP division transfer apparatus 3 will be described by taking as an example a case where the arrival order of TCP packets is switched (see FIG. 2 as appropriate).

In FIG. 3, “PCK” indicates a packet, and numerical values such as “1” and “2” illustrated after PCK indicate the sequence number of the TCP packet. “ACK” indicates an ACK packet, and numerical values such as “1” and “2” illustrated after ACK indicate the ACK number of the ACK packet.
In FIG. 3, the vertical axis indicates time, and the effective periods of the filters α and β are indicated by hatching.
Further, in FIG. 3, PCK1 via the logic circuit _{L 1} delay amount is large is transmitted, via the logic circuit _{L 2} delay than the logic circuit _{L 1} is small, PCK2 is transmitted.

  The TCP division transfer device 3 receives PCK1 from the TCP transmission device 1 by the TCP packet reception unit 31 (step S1). The PCK1 is assigned a sequence number “1” indicating that it is the leading TCP packet.

TCP division transfer device 3, the path selection unit 33, a plurality of logical lines _{L 1,} L 2, · · ·, select the logical line _{L 1} from the _{L m,} through a logical line _{L 1,} TCP PCK1 is transferred to the transmission apparatus 7. Further, the TCP division transfer device 3 generates transfer information with the sequence number “1” and the selected logical line L ₁ by the route selection unit 33 and outputs the transfer information to the ACK control unit 35 (step S2).

In the TCP division transfer device 3, the ACK control unit 35 sets the filter α with the discard target ACK number “1” based on the transfer information from the route selection unit 33 (step S3). The filter α, since the delay amount of the logical line L ₁ is large, the validity period is prolonged.

  The TCP division transfer device 3 receives the PCK 2 from the TCP transmission device 1 by the TCP packet receiving unit 31 (step S4). The PCK2 is assigned a sequence number “2” indicating that it is the next TCP packet after the PCK1.

The TCP division transfer device 3 selects the logical line L ₂ from among the plurality of logical lines L ₁ , L ₂ ,..., L _m by the path selection unit 33 and transmits the TCP via the logical line L _2. PCK2 is transferred to the transmission device 7. Furthermore, TCP division transfer device 3, the route selection unit 33 generates forwarding information that the sequence number "2" and selected logical lines _{L 2,} and outputs the ACK control unit 35 (step S5).

In the TCP division transfer device 3, the ACK control unit 35 sets the filter β with the discard target ACK number “2” based on the transfer information from the route selection unit 33 (step S6). The filter β, since the delay amount of the logical circuit L ₂ is smaller than the logical line L _1, the lifetime of the filter α becomes shorter.

In this case, the TCP division transfer device 3 transfers PCK1 toward the TCP transmission device 7 before PCK2. However, since the delay amount is larger than the logical line _{L 2} of the logical line _{L 1,} the TCP transmission device 7, PCK2 arrives before the PCK1. In this case, the TCP transmission device 7 misunderstands that the packet loss of the PCK 1 has occurred, and returns an ACK packet with the ACK number “1” to the TCP transmission device 1. Therefore, the TCP division transfer device 3 receives this ACK1 by the ACK control unit 35 (step S7).

  Here, ACK1 is received within the effective period of the filter α, and the ACK number “1” of ACK1 matches the ACK number “1” to be discarded of the filter α. That is, since a valid filter for ACK1 is set, the TCP division transfer apparatus 3 discards this ACK1 by the ACK control unit 35 (step S8).

  After the PCK1 arrives, the TCP transmission device 7 returns an ACK packet with the ACK number “3” to the TCP transmission device 1 to request a TCP packet with the sequence number “3”. Therefore, the TCP division transfer device 3 receives this ACK3 by the ACK control unit 35 (step S9).

  Here, since the TCP packet with the sequence number “3” is not transferred, the TCP division transfer apparatus 3 is not set with an effective filter for ACK3. Therefore, the TCP division transfer device 3 causes the ACK control unit 35 to pass this ACK 3 to the TCP transmission device 1 (step S10).

  Thereafter, the TCP transmission device 1 transmits the PCK 3 toward the TCP transmission device 7 in response to the ACK 3. As described above, in the TCP division transfer system 100, after the PCK1 overtaken by the PCK2 arrives at the TCP transmission apparatus 7, the normal TCP transmission processing is restored.

  As described above, in the TCP division transfer device 3, since the ACK1 returned by the TCP transmission device 7 due to a packet loss is discarded by the filter, the TCP transmission device 1 does not receive this ACK1. That is, the TCP division transfer device 3 passes an ACK packet requesting transmission of a new TCP packet and discards the ACK packet more than necessary, such as discarding the ACK packet requesting retransmission of the already transmitted TCP packet. There is no destruction. As a result, the TCP division transfer device 3 can prevent a situation in which the retransmission of the TCP packet and the reduction of the congestion window are performed in spite of no packet loss, and can improve the throughput of TCP transmission.

  Here, in FIG. 3, a case is considered in which a packet loss of PCK1 occurs after the TCP division transfer device 3 transfers PCK1. Then, the TCP transmission device 7 transmits ACK1 to the TCP transmission device 1 in order to request retransmission of PCK1. In this case, since this ACK1 is discarded by the filter α, it seems that PCK1 cannot be retransmitted. However, since the effective period of the filter α is set to an appropriate length in the TCP division transfer apparatus 3, the ACK1 is passed to the TCP transmission apparatus 1 after the effective period has elapsed. Therefore, the TCP transmission device 1 can quickly retransmit the PCK1 when it is necessary to retransmit the PCK1 due to packet loss.

[Operation of TCP division transfer device: Case in which the arrival order of TCP packets does not change]
With reference to FIG. 4, the operation of the TCP division transfer apparatus 3 will be described by taking as an example a case where the arrival order of TCP packets does not change (see FIG. 2 as appropriate).
In FIG. 4, description will be made assuming that the delay amounts of the logical lines L ₁ and L ₂ are approximately the same.

The processing in steps S11 and S12 is the same as the processing in steps S1 and S2 in FIG.
In the TCP division transfer device 3, the ACK control unit 35 sets the filter α with the discard target ACK number “1” based on the transfer information from the route selection unit 33 (step S13).

  In this case, since the arrival order of PCK 1 and 2 does not change, the TCP transmission device 7 sends an ACK packet of ACK number “2” to the TCP transmission device 1 in order to request transmission of the next TCP packet of PCK 1. Return to Therefore, the TCP division transfer device 3 receives ACK2 from the TCP transmission device 7 by the ACK control unit 35 (step S14).

  Here, since the TCP packet having the sequence number “2” is not transferred to the TCP division transfer device 3, an effective filter for ACK2 is not set. Therefore, the TCP division transfer device 3 causes the ACK control unit 35 to pass this ACK2 to the TCP transmission device 1 (step S15).

  Thereafter, the TCP transmission device 1 transmits PCK2 to the TCP transmission device 7 in response to the ACK2. Thus, in the TCP division transfer system 100, when the arrival order of the PCKs 1 and 2 is not changed, normal TCP transmission processing can be continued.

  The TCP division transfer apparatus 3 according to the first embodiment of the present invention has been described above, but the present invention is not limited to this. Hereinafter, various modifications of the TCP division transfer apparatus 3 will be described (see FIGS. 1 and 2 as appropriate).

(Modification 1)
In the first embodiment describes the round trip time as a logical line delay, in the present invention, as a logical line delay, various indicating the communication quality of the logical lines _{L 1, L 2, ···,} L m Indicators can be used. For example, the delay amount setting unit 36 can use a bit rate or a coding error rate as the logical line delay amount.

Specifically, the delay amount setting unit 36 defines in advance a delay amount calculation function in which the bit rate and the logical line delay amount are in an inversely proportional relationship. Then, the delay amount setting unit 36 measures the bit rate of the logical lines L ₁ , L ₂ ,..., L _m , and gives the measured bit rate as an argument to the delay amount calculation function. Calculate the amount.

In addition, the delay amount setting unit 36 defines in advance a delay amount calculation function in which the encoding error rate and the logical line delay amount are in a proportional relationship. Then, the coding error rate of the logical lines L ₁ , L ₂ ,..., L _m is measured, and the measured coding error rate is given as an argument to the delay amount calculation function, thereby calculating the logical line delay amount. To do.

(Modification 2)
In the first embodiment, it has been described that the TCP packet is transmitted from the TCP transmission device 1 to the TCP transmission device 7, but actually, the TCP transmission devices 1 and 7 may transmit the TCP packet to each other. . Therefore, each unit of the TCP transmission device 1 in FIG. 2 may have a function described below.

  When the TCP transmission device 7 transmits a TCP packet to the TCP transmission device 1, the TCP transmission device 1 returns an ACK packet that does not include transmission data to the TCP transmission device 7. Therefore, when the TCP packet input from the TCP packet receiving unit 31 is this ACK packet, the route selection unit 33 does not generate transfer information and does not need to output this transfer information to the ACK control unit 35.

  The ACK control unit 35 may receive a TCP packet other than the ACK packet from the TCP transmission device 7. Therefore, when transmission data is included in the received TCP packet, the ACK control unit 35 may allow the TCP packet to pass through without being discarded by the filter.

Delay amount setting section 36, the logic circuit delay of the logic circuit L _A (e.g., round trip time) may be measured in advance. Then, when receiving the measurement packet from the TCP split transfer apparatus 5, ACK control unit 35, after delayed by the logical lines delay amount of the logical channel L _A delay amount setting section 36 is measured, for the measurement packet The response packet is returned to the TCP division transfer device 5.
In this way, TCP division transfer unit 3, the logical line delay amount TCP division transfer device 5 is measured, it is possible to reflect the logical line delay of the logic circuit L _A.

In the first embodiment, the TCP division transfer device 3 sets a filter when transmitting a TCP packet (for example, step S3 in FIG. 3), but when receiving an ACK packet (for example, FIG. 3). A filter can also be set in step S8).
Hereinafter, a case where a filter is set when an ACK packet is received will be described as a second embodiment, and a case where a filter is set when a TCP packet is transmitted will be described in detail as a third embodiment.

(Second Embodiment)
[Outline of TCP split transfer system]
With reference to FIG. 5, the difference between the TCP division transfer system 100B and the first embodiment will be described. Specifically, the TCP division transfer system 100B uses a plurality of IP lines P (P _A , P _B , P ₁ , P ₂ ,..., P _n ) and encapsulates a TCP packet with an IP header. This is different from the first embodiment.

  As shown in FIG. 5, the TCP division transfer system 100B transmits a TCP stream via an external IP network (for example, Ethernet (registered trademark) LAN) NW, and a TCP transmission apparatus (transmission side terminal apparatus). 1, a TCP division transfer device (TCP transfer device) 3 </ b> B, a TCP division transfer device 5 </ b> B, and a TCP transmission device (reception-side terminal device) 7.

  In the second embodiment, the TCP division transfer device 3B selects the uplink direction of the logical line L (see FIG. 1), and transfers the TCP packet using the uplink direction of the logical line L. Also, the TCP division transfer device 5B selects in advance the downlink direction of the logical line L, and returns an ACK packet using the downlink direction of the logical line L. Then, after receiving the ACK packet, the TCP division transfer device 3B determines the downlink direction of the logical line L from the header of the ACK packet. That is, the TCP division transfer device 3B cannot determine the entire logical line L including the uplink direction and the downlink direction until the ACK packet is received, and therefore sets a filter when the ACK packet is received.

The IP line P (P _A , P _B , P ₁ , P ₂ ,..., P _n ) is connected to an IP interface (see FIG. 6) having unique IP addresses at both ends in the upstream and downstream directions. Physical line.

The TCP transmission devices 1 and 7 are the same devices as those in FIG.
TCP transmission apparatus 1 via the IP line _{P A,} and is connected to the TCP division transfer device 3B. Furthermore, TCP transmission device 7, via the IP line _{P B,} and is connected to the TCP division transfer unit 5B.

The TCP division transfer device 3B receives a TCP packet from the TCP transmission device 1 and passes through any of a plurality of IP lines P ₁ , P ₂ ,..., P _n (n is an arbitrary integer greater than or equal to 2) The received TCP packet is transferred to the TCP transmission device 7 that is the destination of the TCP packet.

Here, the TCP division transfer device 3B is connected to the TCP division transfer device 5B via a plurality of IP lines P ₁ , P ₂ ,..., P _n . Then, TCP division transfer apparatus 3B, a plurality of IP line _{P 1,} P 2, · · ·, among _{P n,} selects the IP line P to be used in the uplink logical channel L. Further, the TCP division transfer device 3B transfers the TCP packet received from the TCP transmission device 1 to the TCP division transfer device 5B via the selected IP line P.
The configuration of the TCP division transfer device 3B will be described later.

The TCP division transfer device 5B has the same configuration as the TCP division transfer device 3B.
Here, the TCP division transfer device 5B preselects the IP line P (the logical line downlink direction) for returning the ACK packet. For example, the TCP division transfer device 5B selects the IP line P to be used in the downlink direction of the logical line by the same method as the route selection unit 33 in FIG. Then, the TCP division transfer device 5B transmits the TCP packet transferred from the TCP division transfer device 3B to the TCP transmission device 7. At this time, the TCP division transfer device 5B returns an ACK packet for the TCP packet via the selected IP line P.

Hereinafter, the relationship between the logical line L (see FIG. 1) and the physical line (IP line P) will be described.
The logical line L is composed of a pair of an upstream IP line P used for TCP packet transfer and a downstream IP line P used for ACK return. If a logical line _{L 1} in FIG. 1 as an example, and so using the IP line _{P 1} in the uplink logical channel _{L 1,} use the IP line _{P 2} in the downlink logical channel _{L 1,} IP line P _1, composed of a pair of _{P 2.}
Further, the logical line L may be configured by a single IP line P so that the upstream direction and the downstream direction are common. If a logical line L ₁ in FIG. 1 as an example, so that use IP line P ₁ in the uplink and downlink logical channel L _1, consists of a single IP line P _1.

[Configuration of TCP split transfer device]
With reference to FIG. 6, the configuration of the TCP division transfer apparatus 3B will be described (see FIG. 5 as appropriate).
As shown in FIG. 6, the TCP division transfer device 3B includes an IP interface 30 (30 _A , 30 ₁ , 30 ₂ ,..., 30 _n ), a TCP packet reception unit 31B, a route selection unit 33B, and an ACK. A control unit 35B and a TCP packet transmission unit (ACK packet transmission unit) 37B are provided.

The IP interface 30 (30 _A , 30 ₁ , 30 ₂ ,..., 30 _n ) is, for example, a network interface in which a unique IP address is set in advance. Also, IP interface _{30 (30 A, 30 1,} 30 2, ···, 30 n) is, IP line _{P (P A, P 1,} P 2, ···, P n) are connected to the .

Here, IP interface 30 _A receives a TCP packet transmitted from TCP transmission device 1 to the TCP transmission device 7, and outputs the TCP packet reception section 31B. In this case, as a method for identifying the TCP packet transmitted toward the TCP transmission device 7, for example, a method for determining whether the destination of the TCP packet matches the IP address of the TCP transmission device 7 can be used.
In the second embodiment, an IP header is added to the TCP packet received from the TCP transmission device 1. Hereinafter, a TCP packet to which an IP header is added may be referred to as an “original IP packet”.

TCP packet receiving section 31B via the IP interface 30 _A, it is to receive the original IP packet transmitted by the TCP transmission device 1. Then, the TCP packet reception unit 31B outputs the received original IP packet to the route selection unit 33B.

Path selection section 33B, a plurality of IP line _{P 1,} P 2, · · ·, among _{P n,} the IP line P a predetermined rule original IP packet received by the TCP packet receiver 31B is transferred Select and transfer the encapsulated IP packet to the TCP transmission device 7 via the selected IP line P, and generate transfer information including the sequence number of the transferred IP packet and the information of the selected logical line To do.

  Here, the route selection unit 33B selects the IP line P to be used in the upstream direction of the logical line L by the same method as the route selection unit 33 in FIG. Then, the route selection unit 33B encapsulates the original IP packet with the IP header, and outputs it to the IP interface 30 corresponding to the selected IP line P. For example, when “IP in IP Tunneling” defined in RFC1853 is used, the route selection unit 33B encapsulates the original IP packet as shown in FIG.

  In the example of FIG. 7, the route selection unit 33B sets the version to “4”, the header length to “5”, and the Type of Service to “0”. Further, the route selection unit 33B sets a value obtained by adding “20” to the length of the original IP packet as the IP packet length. In addition, the route selection unit 33B sets, for example, “4” meaning IPv4 as the protocol number. Further, the route selection unit 33B calculates and sets the header checksum by a method defined in RFC791.

Further, the route selection unit 33B sets the IP address of the IP interface 30 corresponding to the selected IP line P as the source IP address. Further, the route selection unit 33B sets the IP address of the IP interface connected to the downstream end in the selected IP line P as the destination IP address. In other words, the IP address of the IP interface (not shown) provided in the TCP division transfer apparatus 5B is set as the destination IP address.
That is, in the second embodiment, for example, a combination of a source IP address and a destination IP address can be used as information on the selected logical line (information on the IP line P used in the upstream direction of the logical line L).

Further, the route selection unit 33B sets the identifier, the flag, the fragment offset, and the lifetime to the same values as those stored in the IP header in the original IP packet.
Hereinafter, returning to FIG. 6, the description of the route selection unit 33B will be continued.

  In addition, the route selection unit 33B generates transfer information including the sequence number of the original IP packet transferred to the TCP division transfer device 5B and information on the selected logical line. Then, the route selection unit 33B outputs the generated transfer information to the ACK control unit 35B.

The IP interfaces 30 ₁ , 30 ₂ ,..., 30 _n are IP lines P ₁ , IP ₁ connected to the IP packets (original IP packets encapsulated by the IP header) input from the route selection unit 33B, respectively. Output to the TCP division transfer apparatus 5B via P ₂ ,..., P _n .

Also, IP interface _{30 1, 30 2, ···,} 30 n is, IP line _P 1 which are respectively connected _to, P _{2, ···,} via the _{P n,} same IP as ACK packet (Fig. 7 ACK packet encapsulated in the header) is received from the TCP transmission apparatus 7, and this ACK packet is output to the ACK control unit 35B. In this case, as an identification method of the returned ACK packet to TCP transmission device 1, for example IP interface _{30 1,} 30 2, ..., destination IP address to the IP address of the 30 _n coincide, the original IP packet A method of determining whether the destination IP address matches the IP address of the TCP transmission device 1 in the IP header can be used.

  The ACK control unit 35B includes a delay amount setting unit 36, receives an ACK packet as a response to the IP packet transferred by the route selection unit 33B from the TCP transmission device 7, and filters the received ACK packet (not shown). ) To be discarded or passed.

  Here, the ACK control unit 35B determines the uplink direction of the logical line L based on the transfer information from the route selection unit 33B, and determines the downlink direction of the logical line L based on the IP header of the received ACK packet. In other words, the ACK control unit 35B determines the IP line P to which the ACK packet is returned as the downlink direction of the logical line L. Then, the ACK control unit 35B sets a filter in the same manner as the ACK control unit 35 in FIG. 2, and discards or passes the ACK packet received by this filter.

TCP packet transmission unit 37B is an ACK packet ACK control unit 35B has passed through the IP interface 30 _A, is to send the TCP transmission device 1. In this case, the IP interface 30 _A transmits the ACK packet passed by the ACK control unit 35 B to the TCP transmission device 1.

  As described above, the TCP division transfer device 3B prevents the TCP packet retransmission and the congestion window from being reduced even though no packet loss has occurred, as with the TCP division transfer device 3 in FIG. And the throughput of TCP transmission can be improved. Further, since the TCP division transfer device 3B encapsulates the TCP packet with the IP header, the TCP packet can be transferred to the TCP transmission device 7 via the external network NW that is transmitted by IP.

In the second embodiment, the IP interface 30 (30 _A , 30 ₁ , 30 ₂ ,..., 30 _n ) and the IP line P (P _A , P ₁ , P ₂ ,..., P _n ) However, the present invention is not limited to this. Eg, TCP division transfer apparatus 3B, the IP interface 30 _A, IP interface _{P 1,} P 2, · · ·, may be shared with one of _{P n.} Further, for example, in the TCP division transfer apparatus 3B, the IP interfaces P ₁ , P ₂ ,..., P _n may be configured by at least two IP interfaces 30.

(Third embodiment)
[Outline of TCP split transfer system]
Returning to FIG. 5, as an outline of the TCP division transfer system 100 </ b> C, differences from the second embodiment will be described. Specifically, the TCP division transfer system 100C is different from the second embodiment in that a TCP packet is encapsulated with a UDP (User Datagram Protocol) header.

  As shown in FIG. 5, the TCP split transfer system 100C transmits a TCP stream via an external IP network (for example, Ethernet LAN) NW, and includes a TCP transmission apparatus (transmission side terminal apparatus) 1 and a TCP A division transfer device (TCP transfer device) 3C, a TCP division transfer device 5C, and a TCP transmission device (reception side terminal device) 7 are provided.

  In the third embodiment, the TCP division transfer device 3C selects the uplink direction and the downlink direction of the logical line L (see FIG. 1), and transfers the TCP packet using the uplink direction of the logical line L. That is, since the TCP division transfer device 3C can determine the entire logical line L including the uplink direction and the downlink direction when transmitting the TCP packet, it sets a filter. At this time, the TCP division transfer device 3C notifies the return line information to the TCP division transfer device 5C. Then, the TCP division transfer device 5C returns an ACK packet using the downlink direction of the logical line L notified by the return line information.

TCP division transfer unit 3C receives the TCP packet from the TCP transmission device 1, a plurality of IP line _{P 1,} P 2, · · ·, through one of _{P n,} a TCP packet received, the TCP packet Is transferred to the TCP transmission device 7 that is the destination of the message.
Here, TCP division transfer apparatus 3C, a plurality of IP line _{P 1,} P 2, · · ·, among _{P n,} selects the IP line P to be used in the uplink and downlink logical channel L. Then, the TCP division transfer device 3C encapsulates the TCP packet with the UDP header storing the return line information, and transfers it to the TCP division transfer device 5C.

The TCP division transfer device 5C has the same configuration as the TCP division transfer device 3C.
Here, the TCP division transfer device 5C determines the IP line P to be used in the downstream direction of the logical line L from the return line information stored in the UDP header of the TCP packet. Then, the TCP division transfer device 5C returns an ACK packet for this TCP packet via the determined IP line P.

[Configuration of TCP split transfer device]
Returning to FIG. 6, the difference of the configuration of the TCP division transfer apparatus 3 </ b> C from the second embodiment will be mainly described (see FIG. 5 as appropriate).
As shown in FIG. 6, the TCP division transfer device 3C includes an IP interface 30 (30 _A , 30 ₁ , 30 ₂ ,..., 30 _n ), a TCP packet reception unit 31B, a route selection unit 33C, and an ACK. A control unit 35C and a TCP packet transmission unit (ACK packet transmission unit) 37B are provided.

  The route selection unit 33C selects the IP line P to be used in the uplink direction and the downlink direction of the logical line L in the same manner as the route selection unit 33 in FIG. Then, the route selection unit 33C encapsulates the original IP packet with a UDP header and outputs it to the IP interface 30 corresponding to the selected IP line P. For example, when “IP in IP Tunneling” defined in RFC1853 is used, the route selection unit 33C encapsulates the original IP packet as shown in FIG.

  In the example of FIG. 8, the route selection unit 33C sets the version to “4”, the header length to “5”, and the Type of Service to “0”. Further, the route selection unit 33C sets a value obtained by adding “36” to the length of the original IP packet as the IP packet length. In addition, the path selection unit 33C sets “17” meaning UDP, for example, as the protocol number. In addition, the path selection unit 33C calculates and sets the header checksum by a method specified in RFC791.

  Further, the route selection unit 33C sets the IP address of the IP interface 30 corresponding to the selected IP line P (upward direction of the logical line L) as the source IP address. Further, the route selection unit 33C sets, as the destination IP address, the IP address of the IP interface connected to the end in the down direction in the selected IP line P (upward direction of the logical line L). In other words, the IP address of the IP interface (not shown) provided in the TCP division transfer apparatus 5C is set as the destination IP address.

  Further, the route selection unit 33C sets values determined by the user as the transmission source port number and the destination port number. Further, the path selection unit 33C sets a value obtained by adding “16” to the length of the original IP packet as the UDP packet length. In addition, the route selection unit 33C calculates and sets the checksum by a method defined in RFC768.

  Further, the route selection unit 33C sets the IP address of the IP interface connected to the end in the down direction in the selected IP line P (downward direction of the logical line L) as the return line transmission source IP address. In other words, the IP address of the IP interface provided in the TCP division transfer apparatus 5C is set as the return line source IP address. Further, the route selection unit 33C sets the IP address of the IP interface 30 corresponding to the selected IP line P (downward direction of the logical line L) as the return line destination IP address.

  That is, in the third embodiment, for example, a combination of a transmission source IP address and a destination IP address and a return line transmission source IP address and a return line destination IP address can be used as the information on the selected logical line. Here, the combination of the transmission source IP address and the destination IP address indicates the uplink direction of the logical line L, and the combination of the return line transmission source IP address and the return line destination IP address is the downlink direction of the logical line L (that is, return line information). ).

Further, the route selection unit 33C sets the identifier, the flag, the fragment offset, and the lifetime to the same value as the value stored in the IP header in the original IP packet.
Hereinafter, returning to FIG. 6, the description of the route selection unit 33C will be continued.

  Further, the route selection unit 33C generates transfer information including the sequence number of the original IP packet transferred to the TCP division transfer device 5C and the information of the selected IP line P. Then, the route selection unit 33C outputs the generated transfer information to the ACK control unit 35C.

  The ACK control unit 35C determines the uplink direction and the downlink direction of the logical line L based on the transfer information from the route selection unit 33C. Then, the ACK control unit 35C sets a filter in the same manner as the ACK control unit 35 in FIG. 2, and discards or passes the ACK packet received by this filter. That is, the ACK control unit 35C can set the filter without waiting for the return of the ACK packet.

  As described above, the TCP division transfer device 3C can prevent the TCP packet retransmission and the congestion window from being reduced in spite of no packet loss, as with the TCP division transfer device 3B. Transmission throughput can be improved. Further, since the TCP division transfer device 3C encapsulates the TCP packet with the UDP header, it can transfer the TCP packet to the TCP transmission device 7 via the external network NW that transmits by UDP.

(Modification 3)
In the third embodiment, the route selection unit 33C has been described as selecting the downlink direction of the logical line L. However, the present invention is not limited to this. For example, the TCP division transfer device 5C may select in advance the downlink direction of the logical line L in the same manner as the TCP division transfer device 3C, and notify the TCP division transfer device 3C in advance as return line information. .

In this case, the ACK control unit 35C receives the IP packet in which the return line information is stored from the TCP division transfer apparatus 5C via the IP interfaces 30 ₁ , 30 ₂ ,..., 30 _n . Then, the ACK control unit 35C extracts the return line information included in the received IP packet and outputs it to the route selection unit 33C.

The route selection unit 33C selects the IP line P to be used in the upstream direction of the logical line L by the method described above. Further, the route selection unit 33C uses the IP line P designated by the return line information from the ACK control unit 35C as the downlink direction of the logical line L.
As described above, the TCP division transfer device 3C can perform TCP transmission using the return line information notified from the TCP division transfer device 5C.

  In each embodiment, two TCP division transfer apparatuses are arranged so as to face each other. However, only one TCP division transfer apparatus according to the present invention may be arranged on the network.

In each embodiment, the TCP division transfer apparatus according to the present invention has been described as an independent apparatus. However, in the present invention, hardware resources such as a CPU and a memory included in a general computer are coordinated as the above-described units. It can also be realized by a TCP division transfer program to be operated. This program may be distributed via a communication line, or may be distributed by writing in a recording medium such as a CD-ROM or a flash memory.
The TCP division transfer device according to the present invention may be built in a network transfer device such as a router.

1 TCP transmission device (transmission side terminal device)
3,3B, 3C TCP split transfer device (TCP transfer device)
30, 30 _A , 30 ₁ , 30 ₂ ,..., 30 _n IP interface 31, 31 B TCP packet receiver 33, 33 B Path selector 35, 35 B ACK controller 36 Delay amount setting unit 37, 37 B TCP packet transmitter (ACK packet transmitter)
5, 5B, 5C TCP division transfer device 7 TCP transmission device (receiving side terminal device)
100, 100B, 100C TCP split transfer system L, L _A , L _B , L ₁ , L ₂ , L _m logical line P, P _A , P _B , P ₁ , P ₂ , P _n IP line

Claims (5)

A TCP packet including a sequence number is received from a transmission-side terminal device, and the received TCP packet is transferred to a reception-side terminal device that is the destination of the TCP packet via one of a plurality of logical lines. A TCP transfer device,
A TCP packet receiver for receiving the TCP packet;
A logical line to which a TCP packet received by the TCP packet receiving unit is transferred is selected from the plurality of logical lines according to a predetermined rule, and the TCP packet is sent to the receiving side via the selected logical line. A path selection unit that transfers the information to the terminal device and generates transfer information including the sequence number of the transferred TCP packet and information of the selected logical line that is the selected logical line;
An ACK control unit that receives an ACK packet that is a response to the TCP packet transferred by the route selection unit from the receiving terminal device, and discards or passes the received ACK packet by a filter;
An ACK packet transmitter that transmits the ACK packet passed by the ACK controller to the transmitting terminal device,
The ACK control unit
Based on the logical line delay amount set in advance for each logical line, the delay amount of the selected logical line included in the transfer information generated by the route selection unit is calculated, and the calculated delay amount of the selected logical line is calculated. A TCP transfer apparatus, wherein the filter is set to a valid period after the TCP packet is transferred, and the sequence number included in the transfer information is set as a discard target ACK number. The ACK control unit
A delay amount setting means for measuring round-trip delay time for each logical line in advance and setting the measured round-trip delay time as the logical line delay amount;
The TCP transfer device according to claim 1, further comprising:   The ACK control unit receives the ACK packet within the effective period of the filter, and discards the ACK packet when the received ACK number of the ACK packet matches the discard target ACK number of the filter. The TCP transfer device according to claim 1, wherein:   The route selection unit encapsulates a TCP packet received by the TCP packet reception unit with a protocol header other than TCP, and transfers the encapsulated TCP packet toward the receiving terminal device. The TCP transfer device according to any one of claims 1 to 3. A TCP packet including a sequence number is received from a transmission-side terminal device, and the received TCP packet is transferred to a reception-side terminal device that is the destination of the TCP packet via one of a plurality of logical lines. For the computer,
A TCP packet receiver for receiving the TCP packet;
A logical line to which a TCP packet received by the TCP packet receiving unit is transferred is selected from the plurality of logical lines according to a predetermined rule, and the TCP packet is sent to the receiving side via the selected logical line. A path selection unit that forwards information to the terminal device and generates transfer information including information on the selected logical line that is the sequence number of the transferred TCP packet and the selected logical line;
An ACK control unit that receives an ACK packet that is a response to the TCP packet transferred by the route selection unit from the receiving terminal device, and discards or passes the received ACK packet by a filter;
Function as an ACK packet transmitting unit that transmits the ACK packet passed by the ACK control unit to the transmitting terminal device,
The ACK control unit
Based on the logical line delay amount set in advance for each logical line, the delay amount of the selected logical line included in the transfer information generated by the route selection unit is calculated, and the calculated delay amount of the selected logical line is calculated. A TCP transfer program, wherein the filter is set to a valid period after the TCP packet is transferred, and the sequence number included in the transfer information is set as a discard target ACK number.

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