JP2010074855A - Communication device, communication system, method of detecting missing packet, and program for detecting missing packet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a packet loss speedily by management of a sequence number of only one stage in a receiver when a packet sequence is not reversed in each network in a multipath environment, where the receiver is connected to a transmitter by a plurality of networks. <P>SOLUTION: A communication device includes: a plurality of sequence buffers that store packets until a sequence is checked and are installed for each network; and a missing detection section for determining that missing has occurred when not less than one packet is stored in all of the sequence buffers. Such a configuration is adopted, characteristics, where the packet is stored in the sequence buffer of all of the networks, are watched in the occurrence of the packet loss at the missing detection section, and a packet residence state to a sequence secure buffer installed for each network is monitored. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a communication technique for spreading data by distributing data in a plurality of paths, and in particular, in a multipath environment in which a transmitter and a receiver are connected by a plurality of networks, the order of packets in each network. The present invention relates to a communication apparatus, a communication system, a packet loss detection method, and a packet loss detection program for detecting packet loss (missing) at high speed using a sequence number of only one system when no reverse rotation occurs.

  Conventionally, there is a communication method in which data of one communication flow used in communication between a transmission terminal and a reception terminal is branched into a plurality of flows to restore the original flow. As such a communication method, for example, a TCP (Transmission Control Protocol) transmitted from a transmission terminal is installed by setting a gateway in each of a first LAN (Local Area Network) to which a transmission terminal belongs and a second LAN to which a reception terminal belongs. The connection data is distributed to each communication path in packet units in the first LAN gateway, and the second LAN gateway corrects the order reversal of packets received from a plurality of communication paths according to the TCP sequence number. Has been proposed (see, for example, Patent Document 1).

  In addition, as a method for efficiently using a plurality of communication lines and improving the line utilization rate, a function has been added to the TCP of the terminal so that communication that conventionally uses one TCP connection can be changed to a plurality of TCPs. There is a method of changing to use a connection (for example, see Patent Document 2). In this method, communication performed in one communication flow in communication between the transmission terminal and the reception terminal is divided into a plurality of communication flows and sent in parallel. When data is transmitted from the transmission terminal to the reception terminal, the communication protocol of the transmission terminal divides the data of one communication flow and distributes it to a plurality of communication flows, and the plurality of divided communication flows are one original communication flow. A new header is added to the TCP / IP packet as restoration information for restoration to (i.e., using two system sequence numbers), and data is transmitted in a plurality of communication flows. The communication protocol of the receiving terminal refers to the restoration information of data received from a plurality of communication flows, and restores one communication flow.

JP 2000-261478 A JP 2003-110604 A

  The first problem is that packet loss detection is slow.

  In the communication method of the prior art 1, since it is designed to perform missing determination by sequence (order) abnormality on the assumption that the TCP of the terminal is used in one communication path, a plurality of communication paths are used. When communication is performed, when a sequence inversion occurs due to a difference in delay time of communication paths, it is erroneously detected that a packet loss (packet loss and packet discard is synonymous) has occurred. That is, it cannot be determined whether the packet is discarded or the order is reversed. In order to cope with this problem, if the omission determination due to the sequence (order) abnormality is not performed, only omission determination using a retransmission timeout can be performed, so that there is a problem that detection of packet loss is delayed.

  Since TCP uses packet loss detection as a trigger for retransmission, if the detection of packet loss is delayed, the start of retransmission is also delayed. As a result, throughput is lowered and communication path performance cannot be fully exhibited.

  As a second problem, there was a problem of increasing the cost.

  In the communication method of the prior art 2, it is necessary to provide a two-stage header and use two system sequence numbers. If two system sequence numbers are used, the transfer process and the management mechanism become complicated and the cost increases. was there.

  An object of the present invention is to use a sequence number of only one system in a multipath environment in which a transmitter and a receiver are connected by a plurality of networks, when packet reversal in each network does not occur. , A communication device, a communication system, a packet loss detection method, and a packet loss detection method for detecting packet loss at high speed (that is, using only one system sequence number so that packet discard or order reversal can be determined at high speed), It is to provide a packet loss detection program.

  According to a first aspect of the present invention, when a transmitter and a receiver are connected by a plurality of networks that do not cause packet order reversal in the network, the network stores packets until the order is confirmed. A plurality of order buffers installed for each, and a sequence number added to the packet are confirmed, an extraction control unit for retrieving the packet from the order buffer while restoring the flow order, and an additional for storing the packet sent by retransmission. There is provided a communication apparatus comprising: an over buffer; and a retransmission storage control unit that distributes storage destinations to the order buffer and the overtaking buffer according to a sequence number.

  According to the second aspect of the present invention, when the transmitter and the receiver are connected by a plurality of networks in which packet order inversion does not occur in the network, packets are received until the receiver performs order confirmation. A plurality of sequence buffers installed in each network, a sequence number added to the packet is confirmed, a fetch control unit that retrieves the packet from the sequence buffer while restoring the flow sequence, and sent by retransmission There is provided a communication system comprising: an overtaking buffer for accumulating packets; and a retransmission storage control unit that assigns storage destinations to the order buffer and the overtaking buffer according to a sequence number.

  According to a third aspect of the present invention, when the transmitter and the receiver are connected by a plurality of networks that do not cause a packet order reversal in the network, the receiver checks the order in the order buffer. The packet is accumulated until it is done, the sequence number added to the packet is confirmed, the packet is taken out from the order buffer while restoring the flow order, the packet sent by resending to the overtaking buffer is accumulated, and the sequence number is There is provided a communication method characterized by allocating storage destinations to the order buffer and the overtaking buffer.

  According to the fourth aspect of the present invention, when the transmitter and the receiver are connected by a plurality of networks in which the packet order inversion does not occur in the network, the receiver checks the order in the order buffer. The packet is accumulated until it is done, the sequence number added to the packet is confirmed, the packet is taken out from the order buffer while restoring the flow order, the packet sent by resending to the overtaking buffer is accumulated, and the sequence number is There is provided a program for causing a computer to perform a communication method characterized by allocating storage destinations to the order buffer and the overtaking buffer.

  Next, the effect of the present invention will be described.

  The first effect is that, in a multipath environment in which a transmitter and a receiver are connected by a plurality of networks, when sequence reversal of packets in each network does not occur, only one-stage sequence number is managed. By using this, packet loss can be detected at high speed.

  This is because the loss detection unit in the receiver pays attention to the characteristic that the packet is stored in the order buffer of all networks when packet loss occurs, and the packet retention state in the order guarantee buffer installed for each network. It is because it monitors.

  In addition, in the storage control unit in the receiver, when an abnormality occurs, the packet cannot be taken out from the order buffer, and the overflow of the order buffer installed for each network is monitored by paying attention to the characteristic that the buffer overflows. Because.

  Also, this is because the storage control unit in the receiver cannot monitor the overflow of the sequential buffer installed in each network, paying attention to the characteristic that the packet cannot be taken out from the sequential buffer when an abnormality occurs and the buffer overflows. This is because the capacity determination unit in the receiver sets the size of the order buffer so as to be the minimum necessary based on the delay difference and the bandwidth between the networks.

  The second effect is that in a multipath environment in which a transmitter and a receiver are connected by a plurality of networks, the sequence number of only one stage is managed when the packet order inversion does not occur in each network. By using this, retransmission at the time of packet loss can be started at high speed.

  This is because the loss detection unit in the receiver pays attention to the characteristic that the packet is stored in the order buffer of all networks when packet loss occurs, and the packet retention state in the order guarantee buffer installed for each network. This is because by monitoring, it is possible to detect missing at high speed without using the retransmission timer.

  Also, this is because the storage control unit in the receiver cannot monitor the overflow of the sequential buffer installed in each network, paying attention to the characteristic that the packet cannot be taken out from the sequential buffer when an abnormality occurs and the buffer overflows. This is because a buffer overflow is a trigger for starting retransmission.

  Also, this is because the storage control unit in the receiver cannot monitor the overflow of the sequential buffer installed in each network, paying attention to the characteristic that the packet cannot be taken out from the sequential buffer when an abnormality occurs and the buffer overflows. This is because, when the buffer overflow is triggered by the start of retransmission, the capacity determination unit in the receiver sets the size of the order buffer so as to be the minimum necessary based on the delay difference and the bandwidth between the networks.

It is a block diagram which shows the structure of the 1st Embodiment of this invention. 6 is a flowchart showing an order confirmation operation 221 in the take-out control unit 22; 5 is a flowchart showing a missing detection operation 222 in the take-out control unit 22. 6 is a block diagram illustrating an example of an operation when the missing detection operation 222 is normal. FIG. FIG. 11 is a block diagram illustrating an example of an operation when a missing detection operation 222 is abnormal. It is a block diagram which shows the structure of the 2nd Embodiment of this invention. It is a flowchart which shows the order confirmation operation | movement 221A in 22 A of extraction control parts. It is a flowchart which shows the missing | missing detection operation | movement 222A in the extraction control part 22A. It is a flowchart which shows the packet extraction operation | movement 223 in the extraction control part 22A. It is a block diagram which shows the operation example at the time of normal of the missing detection operation | movement 222A. It is a block diagram which shows the operation example at the time of abnormality of the missing detection operation | movement 222A. It is a block diagram which shows the structure of the 3rd Embodiment of this invention. 5 is a flowchart showing the operation of a storage control unit 271. It is a block diagram which shows the structure of the 4th Embodiment of this invention. It is a block diagram which shows the structure of the 5th Embodiment of this invention. It is a flowchart which shows operation | movement of the storage control part 271A.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

  In the following description, communication between a pair of transmitter and receiver is defined as one flow. Also, a route through which a certain flow flows is defined as a path. For example, when communicating by distributing one flow to four networks (networks), it is said that communication is performed using four paths. When communicating by distributing two flows to four networks (networks), there are eight Communicate using a path. However, in the following description, since description will be made focusing on one flow, as a result, the network and the path are synonymous.

(First embodiment)
(Description of configuration)
With reference to FIG. 1, the structure in this Embodiment is demonstrated.

  The transmitter 1 includes a data transmission unit 11, a SEQ addition unit 12, a retransmission buffer 13, a distribution unit 14, and a retransmission timer 15.

  The data transmitter 11 generates data to be transmitted to the receiver 2 and passes it to the SEQ adder 12. In general, a server application or the like corresponds to the data transmission unit.

  The SEQ grant unit 12 receives data to be transmitted from the data transmission unit 12 to the receiver 2, divides the data into sizes that can be transferred by the networks 31 to 34, and divides the individual data (hereinafter referred to as packets). A header and an ordinal number (also referred to as a sequence number, hereinafter referred to as “SEQ”) necessary for transfer are set and transferred to the retransmission buffer 13.

  The retransmission buffer 13 is a FIFO buffer, and performs the following operations.

  (1) Receive and store a packet with a SEQ from the SEQ grant unit 12.

  (2) Send a copy of the packet to the distribution unit 14 in accordance with a predetermined speed and number. At this time, the retransmission timer 15 is set.

  (3) A delivery confirmation (ACK) is received from the ACK transmission unit 23, and a stored packet having a value equal to or smaller than the received sequence number described in the ACK is deleted. At this time, the retransmission timer 15 is reset.

  (4) In (3), if the sequence number described in the ACK is the same as the sequence number described in the previously received ACK, it is regarded as a retransmission request (duplicate ACK) and is described in the ACK. The packets after the sequence number are retransmitted to the distribution unit 14 in accordance with a predetermined speed and number as in (2).

  (5) When the retransmission timer 15 expires, the packet after the sequence number described in the previously received ACK is retransmitted to the distribution unit 14 according to a predetermined speed and number as in (2). Send.

  The distribution unit 14 sequentially distributes the packets arriving from the retransmission buffer 13 to the networks 31 to 34 by round robin.

  When receiving a set request from the retransmission buffer 13, the retransmission timer 15 notifies the retransmission buffer 13 of expiration of the timer when a preset time has elapsed.

  The receiver 2 includes an order buffer 211 to 214, a loss detection unit 20, an extraction control unit 22, an ACK transmission unit 23, an output buffer 24, a SEQ deletion unit 25, and a data reception unit 26.

  The order buffer 211 is a FIFO buffer, receives a packet from the network 31, temporarily stores it, and notifies the extraction control unit 22 of storage completion. Further, the packet stored in the output buffer 24 is transferred in accordance with an instruction from the take-out control unit 22.

  The order buffer 211 compares the sequence number of the packet arriving from the network 31 with the sequence number of the packet arriving from the network 31 last time. Alternatively, if they are the same, it is assumed that retransmission has occurred, and all stored packets are discarded.

  The order buffer 212 is a FIFO buffer, receives a packet from the network 32, temporarily stores it, and notifies the extraction control unit 22 of storage completion. Further, the packet stored in the output buffer 24 is transferred in accordance with an instruction from the take-out control unit 22.

  The order buffer 212 compares the sequence number of the packet arriving from the network 32 with the sequence number of the packet arriving from the network 32 last time, and whether the SEQ of the packet arriving at this time is smaller than the SEQ of the packet arriving at the previous time. Alternatively, if they are the same, it is assumed that retransmission has occurred, and all stored packets are discarded.

  The order buffer 213 is a FIFO buffer, receives a packet from the network 33, temporarily stores it, and notifies the extraction control unit 22 of the storage completion. Further, the packet stored in the output buffer 24 is transferred in accordance with an instruction from the take-out control unit 22.

  The order buffer 213 compares the sequence number of the packet arriving from the network 33 with the sequence number of the packet arriving from the network 33 last time, and whether the SEQ of the packet arriving at this time is smaller than the SEQ of the packet arriving at the previous time. Alternatively, if they are the same, it is assumed that retransmission has occurred, and all stored packets are discarded.

  The order buffer 214 is a FIFO buffer, receives a packet from the network 34, temporarily stores it, and notifies the extraction control unit 22 of storage completion. Further, the packet stored in the output buffer 24 is transferred in accordance with an instruction from the take-out control unit 22.

  The order buffer 214 compares the sequence number of the packet arriving from the network 34 with the sequence number of the packet arriving from the network 34 last time. Alternatively, if they are the same, it is assumed that retransmission has occurred, and all stored packets are discarded.

  Upon receiving notification of completion of packet extraction from the extraction control unit 22, the loss detection unit 20 confirms the presence or absence of packet loss. If a packet loss is found, a retransmission request is made to the ACK transmission unit 23.

  Upon receiving the storage completion notification from the order buffers 211 to 214, the take-out control unit 22 performs the order confirmation operation 221, and transfers the packet to the output buffer 24 according to the sequence of SEQ. At this time, the ACK transmission unit 23 is notified of the SEQ of the packet transferred to the output buffer 24.

  The ACK transmission unit 23 performs the following operation. In the present application, a description will be given of the 1ACK method in which an ACK of one packet is transmitted every time one packet transfer to the output buffer 24 is completed, but N (N is 1 or more) packet arrival reports are collectively performed by one ACK. The N_ACK method may be used.

  (1) Upon receipt of a SEQ notification of the packet transferred from the take-out control unit 22 to the output buffer 24, a delivery confirmation packet (hereinafter referred to as ACK) including the SEQ is generated and notified to the retransmission buffer 13. At this time, ACK is notified using one of the networks 31 to 34. Further, the received SEQ is stored.

  (2) Upon receiving a retransmission request from the loss detection unit 20, an ACK including the SEQ stored in (1) is generated again and notified to the retransmission buffer 13. At this time, ACK is notified using one of the networks 31 to 34. The ACK in (2) is handled as a duplicate ACK (retransmission request) in the retransmission buffer 13. The ACK of (2) may be copied and transferred using all of the networks 31 to 34. In this case, it is necessary to provide a lock mechanism in the retransmission buffer 13 so that retransmission does not occur frequently in the retransmission buffer 13. There is.

  The output buffer 24 is a FIFO buffer, and receives and stores packets from the order buffers 211 to 214. When there is a request from the SEQ deleting unit 25, the data is output to the SEQ deleting unit 25 in the order in which they are stored.

  The SEQ deletion unit 25 receives the packet from the output buffer 24, deletes the SEQ and the header, and transfers the data after the SEQ deletion to the data reception unit 26.

  The data receiving unit 26 receives data from the SEQ deleting unit 26. Generally called a client application.

  The network 31 is a network that connects between the transmitter 1 and the receiver 2. It is assumed that the network 31 is a network such as Ethernet (registered trademark) that does not reverse the order of packets in the network. In FIG. 1, the network 31 is represented by a single line. However, in practice, a switch or the like may exist in addition to the link as long as packet order inversion does not occur in the network. The networks 31, 32, 33, and 34 are physically or logically cut off by a VLAN or the like, and do not cross each other.

  The networks 32 to 34 are the same networks as the network 31.

(Description of operation)
With reference to the flowchart of FIG. 2, the order confirmation operation 221 in the take-out control unit 22 will be described.

  When one packet is stored in any of the order buffers 211 to 214, a storage completion notification is sent to the extraction control unit 22, and the order confirmation operation 221 is activated (step 22101).

  The SEQ of the packet stored at the head (on the output buffer 24 side) of the order buffer 211 is confirmed (step 22102).

  Compare the SEQ (head SEQ) of the first packet of the order buffer 211 confirmed in step 22102 with the SEQ (sequence expected reception SEQ, hereinafter referred to as expected SEQ) that the sequence control unit 22 intends to transmit to the output buffer 24 (hereinafter referred to as the expected SEQ). Step 22103).

  If the leading SEQ and the expected SEQ match in step 22103, the packet is extracted from the order buffer 211 and sent to the output buffer 24 (step 22104).

  The ACK transmission unit 23 is requested to transmit an acknowledgment packet (ACK). This ACK stores the SEQ of the expected SEQ, and notifies the transmitter 1 that reception and ordering up to the expected SEQ have been completed (step 22105).

  Increment expected SEQ. That is, expected SEQ = expected SEQ + 1 (step 22106).

  Steps 22107 to 22111 perform the same operations as steps 22102 to 22106 with respect to the order buffer 212.

  Steps 22112 to 22116 perform the same operation as steps 22102 to 22106 with respect to the order buffer 213.

  Steps 22117 to 22121 perform the same operations as steps 22102 to 22106 with respect to the order buffer 214.

  During the execution of steps 22102 to 22121, the number of packets taken out from the order buffer and sent to the output buffer is counted. If the number is 1 or more (YES in step 22122), steps 22102 and after are executed again. If the number of packets taken out from the order buffer and sent to the output buffer is 0, that is, there is no packet that can be transferred to the output buffer 23 (that is, can be ordered) in any of the order buffers 211 to 214. (NO in step 22122), step 22123 is executed.

  The drop detection unit 20 is notified of the completion of packet extraction, and the drop detection operation is started (step 22123).

  With reference to the flowchart of FIG. 3, the operation of the missing detection unit 20 will be described.

  When the order confirmation operation 221 is completed, a missing detection operation is started (step 2001).

  The number of packets stored in the order buffer 211 is confirmed (step 2002).

  If the number of packets stored in the order buffer 211 is 0, the operation is terminated. When the number of stored packets is 1 or more, the process proceeds to step 2004 (step 2003).

  Steps 2004 and 2005 perform the same operations as steps 2002 and 2003 with respect to the order buffer 212.

  Steps 2006 and 2007 perform the same operation as the steps 2002 and 2003 with respect to the order buffer 213.

  Step 2008 and step 2009 perform the same operation as step 2002 and step 2003 with respect to the order buffer 214.

  As a result of executing Steps 2002 to 2009, if the storage of one or more packets is confirmed in all the order buffers 211 to 214 (YES in Step 2009), a retransmission request is made to the ACK transmission unit. The ACK transmission unit generates an ACK (duplicate ACK) including the same SEQ as the previously transmitted ACK, and makes a retransmission request to the transmitter 1 (step 2010).

(Operation example)
(Overview of operation)
Hereinafter, with reference to FIG. 1, the operation | movement outline | summary of the transmitter 1 in this Embodiment and the transmitter 2 is demonstrated.

  In the transmitter 1, the data transmission unit 11 generates data for the data reception unit 26 and sends the data to the SEQ grant unit 12.

  The SEQ assigning unit 12 divides the data from the data transmitting unit 12 into a size that can be transferred by the networks 31 to 34 and attaches a header to generate a packet. Further, a sequence number (SEQ) is assigned to the packet for ordering so that the receiver 2 can restore the data, and the packet is transferred to the retransmission buffer 13.

  The retransmission buffer 13 receives the packet from the SEQ adding unit 12 and temporarily stores it. Then, a copy of the stored packet is sent to the distribution unit 14 according to a preset transmission rate, window size, and the like.

  The distribution unit 14 distributes and transmits the packet received from the retransmission buffer 13 to each of the networks 31 to 34 by round robin or the like. For example, a packet with a sequence of SEQ is distributed to the networks 31 to 34 such that the packet of SEQ15 is the network 31, the packet of SEQ16 is the network 32, the packet of SEQ17 is the network 33, and the packet of SEQ18 is the network 34.

  The networks 31 to 34 send the packets sent from the transmitter 1 to the receiver 2.

  The order buffer 211 stores packets arriving from the network 31 and notifies the extraction control unit 22 of the completion of storage. Upon receipt of the storage completion notification from the order buffer 211, the take-out control unit 22 activates the order confirmation operation 221.

  Similarly, the order buffers 212 to 214 store packets arriving from the networks 32 to 34 and notify the extraction control unit 22 of the completion of storage. The take-out control unit 22 receives the storage completion notification from the order buffers 212 to 214 and activates the order confirmation operation 221.

  The order confirmation operation 221 examines the SEQ of the packet stored at the head of the order buffers 211 to 214, and if it matches the SEQ to be sent to the output buffer 24 next, extracts this packet and sends it to the output buffer 24. Request the ACK transmission unit to transmit ACK. For example, when transfer to the output buffer 24 has been completed up to SEQ = 5 before, if a packet of SEQ = 6 is stored at the head of any of the order buffers 211 to 214, this is taken out and output to the output buffer 24. And request ACK transmission of SEQ = 6.

  The order confirmation operation 221 notifies the missing detection unit 20 of the completion of extraction if no packet to be transferred to the output buffer can be found in any of the order buffers 211 to 214.

  The missing detection unit 20 checks the number of packets stored in the order buffers 211 to 214, and makes a retransmission request to the ACK transmission unit if storage of packets is confirmed in all the order buffers.

  The output buffer 24 receives the packets from the order buffers 211 to 214, and extracts and transfers the packets by the FIFO method in response to a request from the SEQ deletion unit 25.

  The SEQ deletion unit 25 takes out the packet from the output buffer 24, deletes the header (including SEQ), and transfers the data to the data reception unit 26.

  The data receiving unit 26 receives data from the SEQ deleting unit 25 and performs various processes.

  When the retransmission buffer 13 receives an ACK from the ACK transmission unit 23 via any of the networks 31 to 34, the retransmission buffer 13 confirms the SEQ included in the ACK.

  The retransmission buffer 13 deletes packets up to the SEQ from the retransmission buffer 13 if a SEQ larger than the SEQ of the previously received ACK is included. If the same SEQ as the SEQ of the ACK received last time is included, it is regarded as a duplicate ACK (retransmission request), and the packets stored in the retransmission buffer are immediately retransmitted in order from the lowest SEQ.

(Normal missing detection operation example)
Hereinafter, with reference to FIG. 4, an operation example of the loss detection unit 20 without packet loss (normal time) will be described.

  FIG. 4 shows an example in which a larger delay occurs in the network 33 than in the networks 31 to 34, and the arrival of the packet with SEQ = 6 is delayed.

  Since the networks 31, 32, and 34 have less delay than the network 33, the packets arrive at the order buffers 211, 212, and 214 faster than when the packets pass through the network 33.

  In FIG. 4, the packets from SEQ1 to SEQ5 are transferred to the output buffer 24 by the order confirmation operation 221, and ACK1 to ACK5 are transmitted from the ACK transmission unit 23 to these packets.

  In the state of FIG. 4, since the packet 6 is on the network 33 and is not stored in the order buffer 213, the order confirmation operation 221 is completed when the packet with SEQ = 5 is transferred to the output buffer 24. The missing detection unit 20 is notified of the completion of extraction.

  The missing detection unit 20 checks the number of packets stored in the order buffers 211 to 214. Here, since the number of packets stored in the order buffer 213 is 0, it is assumed that no loss has occurred, and the operation is completed.

  As described above, when there is no order reversal in each of the networks 31 to 34 and no packet loss occurs, any one or more of the order buffers 211 to 214 is It will always be empty.

  In the situation where no packet loss occurs, the order buffers 211 to 214 store packets corresponding to the difference in delay time of the networks 31 to 34, so that the network of the most delayed network (network 33 in FIG. 4) is stored. The stored packet in the order buffer (order buffer 213 in FIG. 4) for storing the packet is zero.

(Example of missing detection operation in case of abnormality)
Hereinafter, with reference to FIG. 5, an operation example of the loss detection unit 20 when a packet loss occurs (at the time of abnormality) will be described.

  FIG. 5 shows an example in which a packet with SEQ = 6 is lost (lost) in the network 33.

  Further, since the network 33 has a larger delay than the other networks, and the networks 31, 32, and 34 have a smaller delay than the network 33, the order buffers 211, 212, and 214 are compared with the case of passing through the network 33. Assume that packets arrive fast.

  In FIG. 5, it is assumed that the packet sequence confirmation from SEQ1 to SEQ5 is completed and transferred to the output buffer 24, and ACK1 to ACK5 are transmitted from the ACK transmission unit 23 to these packets.

  Here, when the SEQ = 12 packet sent to the network 33 next to the missing SEQ = 6 packet is stored in the order buffer 213, the order confirmation operation 221 is activated. However, since there is no packet that can be sent to the output buffer 24, the dropout detection unit 20 is immediately notified of the removal completion.

  The missing detection unit 20 checks the number of packets stored in the order buffers 211 to 214. Here, the storage of the packet is confirmed in all the order buffers including the order buffer 213, and it is considered that the packet is missing, and a retransmission request is made to the ACK transmission unit 23.

  The ACK transmission unit 23 receives a retransmission request from the loss detection unit 20 and transmits an ACK including SEQ = 5 that is the same as the previously transmitted ACK (ACK = 5). Since the ACK of the same number arrives continuously, the transmitter 1 determines that there is a retransmission request and retransmits the packet in the retransmission buffer.

  As described above, when no order inversion occurs in each of the networks 31 to 34, if a packet loss occurs, the packets are stored in all the order buffers 211 to 214. . By determining packet loss based on this characteristic, a high-speed retransmission request can be made.

  In a multipath environment, if there is no packet loss determination described in the present embodiment, the receiver 2 cannot make a retransmission request to the transmitter 1, so the transmitter 1 uses the retransmission timer 15 to perform retransmission. There is no choice but to do. However, in general, the retransmission timer 15 needs to set a large value of at least 1 RTT in order to prevent malfunction, and therefore it takes time to start retransmission. For this reason, when the packet loss determination mechanism described in the present embodiment is used, it is possible to perform missing detection and retransmission faster than the retransmission timer.

(Effect of this embodiment)
Next, the effect of this embodiment will be described.

  When the invention described in this embodiment is used, in a multipath environment in which a transmitter and a receiver are connected by a plurality of networks, when the order of packets in each network does not reverse, only one stage is used. The packet loss can be detected at high speed using the management of the sequence number.

  This is because the loss detection unit in the receiver pays attention to the characteristic that packets are stored in the order buffers of all networks when packet loss occurs, and the packet retention state in the order guarantee buffer installed for each network It is because it monitors.

  Further, when the invention described in this embodiment is used, in a multipath environment in which a transmitter and a receiver are connected by a plurality of networks, when packet order reversal in each network does not occur, 1 Retransmission at the time of packet loss can be started at high speed using the management of the sequence number of only the stage.

  This is because the loss detection unit in the receiver pays attention to the characteristic that packets are stored in the order buffers of all networks when packet loss occurs, and the packet retention state in the order guarantee buffer installed for each network This is because by monitoring, it is possible to detect missing at high speed without using the retransmission timer.

(Second Embodiment)
In the second embodiment of the present invention, when the output buffer 24 in the first embodiment does not exist and the order buffers 211 to 214 also serve as the output buffer 24, or the extraction speed from the order buffers 211 to 214 is high. It is a form when it is late.

(Description of configuration)
With reference to FIG. 6, the configuration of the present embodiment will be described.

  The transmitter 1 has the same configuration as that of the first embodiment and performs the same operation.

  The receiver 2 does not include the output buffer 24 in the first embodiment, the missing detector 20 becomes the missing detector 20A, and the takeout controller 22 becomes the takeout controller 22A. Different from 2.

  Upon receiving the extraction completion notification from the extraction control unit 22A, the loss detection unit 20A confirms whether there is a packet loss. If a packet loss is found, a retransmission request is made to the ACK transmission unit 23.

  The take-out control unit 22A performs the following operation.

  (1) Upon receiving a storage completion notification from the order buffers 211 to 214, the order confirmation operation 221A is performed. If the sequence of SEQ is correct, the number of waiting for extraction is incremented. At this time, the ACK transmission unit 23 is notified of the SEQ of the packet waiting to be taken out.

  (2) A packet extraction operation 223 is performed, and a packet is extracted and transferred to the SEQ deletion unit 25 in response to a request from the SEQ deletion unit 25.

(Description of operation)
With reference to the flowchart of FIG. 7, the order confirmation operation 221A in the take-out control unit 22A will be described.

  When one packet is stored in any of the order buffers 211 to 214, a storage completion notification is sent to the extraction control unit 22, and the order confirmation operation 221 is activated (step 22101).

  The SEQ of the packet stored at the head (on the output buffer 24 side) of the order buffer 211 is confirmed (step 22102).

  The sequence of the first packet in the sequence buffer 211 confirmed in step 22102 (first sequence) is compared with the next sequence sequence that the sequence control unit 22 intends to confirm the sequence (reception expected SEQ, hereinafter referred to as expected SEQ) (step 22103). .

  If the top SEQ and the expected SEQ match at step 22103, the number of waiting for extraction in the order buffer 211 is incremented (step 22104A).

  The ACK transmission unit 23 is requested to transmit an acknowledgment packet (ACK). This ACK stores the SEQ of the expected SEQ, and notifies the transmitter 1 that reception and ordering up to the expected SEQ have been completed (step 22105).

  Increment expected SEQ. That is, expected SEQ = expected SEQ + 1 (step 22106).

  Steps 22107 to 22111 perform the same operations as steps 22102 to 22106 with respect to the order buffer 212.

  Steps 22112 to 22116 perform the same operation as steps 22102 to 22106 with respect to the order buffer 213.

  Steps 22117 to 22121 perform the same operations as steps 22102 to 22106 with respect to the order buffer 214.

  During the execution of step 22102 to step 22121, the number of times the take-out waiting number is incremented is counted. If it is 1 or more (YES in step 22122A), step 22102 and subsequent steps are executed again. If the number of packets taken out from the order buffer and sent to the output buffer is zero (NO in step 22122A), that is, packets that can be transferred to the output buffer 23 (that is, packets that can be ordered) are stored in the order buffers 211 to 214. If none exists, step 22123A is executed.

  Notification of completion of removal is sent to the missing detection unit 20A (step 22123A).

  The packet extraction operation 222 in the extraction control unit 22A will be described with reference to the flowchart of FIG.

  In response to a packet extraction request from the SEQ deletion unit 25, a packet extraction operation 222 is activated (step 22201).

  The sequence of the packet stored in the head of the order buffer 211 (SEQ deletion unit 25 side) is confirmed (step 22202).

  The SEQ (head SEQ) of the first packet in the order buffer 211 confirmed in step 22202 is compared with the SEQ (ordering waiting SEQ) that the order control unit 22 next extracts and tries to transmit to the SEQ deletion unit 25 (step 22203). .

  If the leading SEQ and the extraction waiting SEQ match in step 22203, the packet is extracted from the order buffer 211 and sent to the SEQ deletion unit 25 (step 22204).

  The removal waiting number in the order buffer 211 is decremented (step 22205).

  The take-out waiting SEQ is incremented. It should be noted that the number of waiting for withdrawal and the waiting for waiting SEQ are different parameters (step 22206).

  Steps 22207 to 22211 perform the same operation as steps 22202 to 22206 with respect to the order buffer 212.

  Steps 22212 to 22216 perform the same operations as steps 22202 to 22206 with respect to the order buffer 213.

  Steps 22217 to 22221 perform the same operations as steps 22202 to 22206 with respect to the order buffer 214.

  With reference to the flowchart of FIG. 9, the operation of the missing detection unit 20A will be described.

  Upon completion of the order confirmation operation 221A, a missing detection operation is started (step 2001A).

  The number of packets stored in the order buffer 211 is confirmed (step 2002).

  If the number of packets stored in the order buffer 211-the number of waiting for extraction in the order buffer 211 is 0, the operation is terminated. When the number of stored packets−the number of waiting for extraction is 1 or more, the process proceeds to step 2004 (step 2003A).

  Step 2004 and Step 2005A perform the same operation as Step 2002 and Step 2003A with respect to the order buffer 212.

  Step 2006 and Step 2007A perform the same operation as Step 2002 and Step 2003A with respect to the order buffer 213.

  Step 2008 and Step 2009A perform the same operation as Step 2002 and Step 2003A with respect to the order buffer 214.

  As a result of executing Steps 2002 to 2009A, if the total of the number of storages and the number of waiting for extraction is 1 or more in all the order buffers 211 to 214, a retransmission request is made to the ACK transmission unit. The ACK transmission unit generates an ACK (duplicate ACK) including the same SEQ as the previously transmitted ACK, and makes a retransmission request to the transmitter 1 (step 2010).

(Operation example)
(Normal missing detection operation example)
Hereinafter, with reference to FIG. 10, an operation example of the loss detection unit 20 </ b> A when there is no packet loss (normal time) will be described.

  FIG. 10 shows an example in which a larger delay occurs in the network 33 than in the networks 31 to 34, and the arrival of the packet with SEQ = 12 is delayed.

  Since the networks 31, 32, and 34 have less delay than the network 33, the packets arrive at the order buffers 211, 212, and 214 faster than when the packets pass through the network 33.

  In FIG. 10, the order confirmation of the packets from SEQ1 to SEQ11 is completed by the order confirmation operation 221A, and ACK1 to ACK11 are transmitted from the ACK transmission unit 23 to these packets. Further, the packets from SEQ1 to SEQ3 are transferred to the SEQ deleting unit 25 by the packet extracting operation 222. The packets of SEQ4 to SEQ11 have already been confirmed in order, but the order buffers 211 to 214 are waiting for an extraction request from the SEQ deletion unit 25.

  In the state of FIG. 10, since the packet 12 is on the network 33 and is not stored in the order buffer 213, when the order confirmation of the packet with SEQ = 11 is completed, the order confirmation operation 221A is completed and missing. The detection completion is notified to the detection unit 20A.

  The missing detection unit 20A checks the number of packets stored in the order buffers 211 to 214 and the number of packets waiting for extraction. In the order buffers 211, 212, and 214, the number of stored packets is 3 and the number of waiting for extraction is 2. However, in the order buffer 213, the number of stored packets is 2 and the number of waiting for extraction is 2, so the number of stored packets− Since the number of waiting for extraction is 0, it is considered that no omission has occurred, and the operation is completed.

  As described above, when there is no order reversal in each of the networks 31 to 34 and no packet loss occurs, any one or more of the order buffers 211 to 214 may be used. The number of stored packets−the number of waiting for extraction is always 0.

  In the situation where no packet loss occurs, the order buffers 211 to 214 store packets corresponding to the difference in delay time between the networks 31 to 34, so that the most delayed network (the network 33 in FIG. 10) The stored packet in the order buffer (order buffer 213 in FIG. 10) for storing the packet is zero.

(Example of missing detection operation in case of abnormality)
Hereinafter, with reference to FIG. 11, an operation example of the loss detection operation 222A at the time of packet loss occurrence (abnormality) will be described.

  FIG. 5 shows an example in which a packet with SEQ = 12 is lost (lost) in the network 33.

  Further, since the network 33 has a larger delay than the other networks, and the networks 31, 32, and 34 have a smaller delay than the network 33, the order buffers 211, 212, and 214 are compared with the case of passing through the network 33. Assume that packets arrive fast.

  In FIG. 11, the order confirmation of the packets SEQ1 to SEQ11 is completed by the order confirmation operation 221A, and ACK1 to ACK11 are sent from the ACK transmission unit 23 to these packets. Further, the packets from SEQ1 to SEQ3 are transferred to the SEQ deleting unit 25 by the packet extracting operation 223. The packets of SEQ4 to SEQ11 have already been confirmed in order, but the order buffers 211 to 214 are waiting for an extraction request from the SEQ deletion unit 25.

  Here, when the SEQ = 20 packet sent to the network 33 next to the missing SEQ = 12 packet is stored in the order buffer 213, the order confirmation operation 221A is activated. However, since there is no packet whose order can be confirmed, the missing detection operation 222A is activated immediately.

  The missing detection operation 222A checks the number of packets stored in the order buffers 211 to 214. Here, in all the order buffers including the order buffer 213, since the number of stored packets is 3 and the number of waiting for extraction is 2, the number of stored packets minus the number of waiting for extraction is 1, so that it is considered that a loss has occurred. Then, a retransmission request is made to the ACK transmission unit 23.

  The ACK transmission unit 23 receives a retransmission request from the missing detection operation 222A in the extraction control unit 22, and transmits an ACK including SEQ = 11 that is the same as the previously transmitted ACK (ACK = 11). Since the ACK of the same number arrives continuously, the transmitter 1 determines that there is a retransmission request and retransmits the packet in the retransmission buffer.

  As described above, when there is no order reversal in each of the networks 31 to 34, if a packet loss occurs, the number of stored packets in all the order buffers 211 to 214 is − The number of waiting for extraction> 0. By determining packet loss based on this characteristic, a high-speed retransmission request can be made.

(Effect of this embodiment)
Next, the effect of this embodiment will be described.

  When the invention described in this embodiment is used, in a multipath environment in which a transmitter and a receiver are connected by a plurality of networks, when the order of packets in each network does not reverse, only one stage is used. The packet loss can be detected at high speed using the management of the sequence number.

  This is because the loss detection unit in the receiver pays attention to the characteristic that the packet is stored in the order buffer of all networks when packet loss occurs, and the packet retention state in the order guarantee buffer installed for each network. It is because it monitors.

  Further, when the invention described in this embodiment is used, in a multipath environment in which a transmitter and a receiver are connected by a plurality of networks, when packet order reversal in each network does not occur, 1 Retransmission at the time of packet loss can be started at high speed using the management of the sequence number of only the stage.

  This is because the loss detection unit in the receiver pays attention to the characteristic that the packet is stored in the order buffer of all networks when packet loss occurs, and the packet retention state in the order guarantee buffer installed for each network. This is because by monitoring, it is possible to detect missing at high speed without using the retransmission timer.

(Third embodiment)
In the third embodiment of the present invention, storage controllers 271 to 274 are provided between the networks 31 to 34 and the order buffers 211 to 214 in the first embodiment to detect packet loss due to overflow of the order buffer. It is a form to perform.

  It should be noted that only one of the missing detection in the present embodiment and the missing detection (missing detection operation 222) in the first embodiment can be used, or both can be used in combination. In the following description, it is assumed that even if the order confirmation operation 221 is completed, the missing detection operation 222 is not performed (the combined use of the missing detection in the first embodiment).

(Description of configuration)
With reference to FIG. 12, the structure in this Embodiment is demonstrated.

  The transmitter 1 has the same configuration as that of the first embodiment and performs the same operation.

  The receiver 2 is different in that storage control units 271 to 274 exist between the networks 31 to 34 and the order buffers 211 to 214 in the first embodiment.

  The storage control unit 271 performs the following operation.

  (1) The sequence number of the packet arriving from the network 31 is compared with the sequence number of the packet arriving from the network 31 last time, and the SEQ of the packet arriving this time is smaller than or equal to the SEQ of the packet arriving last time. If it is, it is assumed that retransmission has occurred, and all stored packets are discarded.

  (2) Upon arrival of packets from the network 31, the number of stored packets in the order buffer 211 is confirmed. If the number of stored packets exceeds the maximum storable number, all stored packets are discarded and a retransmission request is made. Do.

(Description of operation)
The operation of the storage control unit 271 will be described with reference to the flowchart of FIG.

  When a packet arrives from the network 31, the storage control operation is activated (step 27101).

  The sequence number of the packet that arrived this time is compared with the sequence number of the packet that arrived last time (step 27101).

  When the SEQ of the packet that has arrived this time is smaller than or the same as the SEQ of the packet that has arrived last time, it is determined that retransmission has occurred, and all the packets stored in the order buffer 211 are discarded. At this time, if there is an extraction waiting packet described in the second embodiment, the extraction waiting packet is not discarded, and all the rest other than the extraction waiting packet are discarded (step 27103).

  When the packet arrives next time, the SEQ of the packet that has arrived this time is recorded in order to make the determination in step 27102 (step 27104).

  The number of packets stored in the order buffer 211 is confirmed (step 27105).

  The number of packets stored in the order buffer 211 (number of stored packets) is compared with the maximum storable number in the order buffer 211 (step 27106).

  If the number of stored packets is equal to the maximum storable number, storing a packet that has arrived this time will overflow the sequence buffer, so all packets stored in the sequence buffer 211 are discarded. At this time, if there is an extraction waiting packet described in the second embodiment, the extraction waiting packet is not discarded, and the rest other than the extraction waiting packet are discarded (step 27107).

  Since the packet is lost due to the discard in step 27107, a retransmission request is made to the ACK transmission unit 23. At this time, the operation of the storage control unit may be ended (END), or the packet that has just arrived at step 27109 may be stored. When the packet that has arrived this time is stored, if retransmission is performed in response to the retransmission request transmitted in this step, the packet is discarded by the retransmission detection operation in step 27103 (step 27108).

  The current arrival packet is stored in the order buffer 211 (step 27109).

  The order confirmation operation 221 is activated (step 27110).

(Operation example)
(Operation example when the sequence buffer overflows)
The operation when the order buffer 211 overflows will be described with reference to FIG.

  In FIG. 12, it is assumed that the number of packets equal to the maximum storable number are already accumulated in the order buffer 211. Further, it is assumed that the SEQ of the packet that has arrived at the storage control unit 271 last time (finally) is 26. Further, it is assumed that the maximum storable number of the order buffer 211 is 40. Assume that the sequence confirmation up to SEQ = 55 is completed and ACK = 55 is transmitted.

  In the above state, when a packet (SEQ = 133) arrives at the receiver 2 from the network 31, the packet is delivered to the storage control unit 271.

  The storage control unit 271 first compares the SEQ (133) of the packet that has arrived with the SEQ (126) of the packet that has arrived last time, and determines that no retransmission has occurred because the SEQ is larger than the previous time.

  Next, the storage control unit 271 confirms the number of stored packets in the order buffer 211. Then, 40 packets are currently stored. Since this is equal to the maximum storable number, all 40 already stored packets are discarded and a retransmission request is made to the ACK transmission unit 23.

  The ACK transmission unit 23 receives a retransmission request from the storage control unit 271 and transmits an ACK (ACK = 55) including the same SEQ as the SEQ (55) of the previously transmitted ACK stored in the ACK transmission unit 23. .

  The retransmission buffer 13 in the transmitter 1 receives ACK = 55 from the receiver 2. Then, since the SEQ of this ACK is the same as the SEQ of the ACK that arrived last time, all the packets in the retransmission buffer are retransmitted to the distribution unit 14 in order from the packet of SEQ = 56.

  The distribution unit 14 distributes the packets retransmitted from the retransmission buffer to the networks 31 to 34. Here, it is assumed that the packet with SEQ = 56 is distributed to the network 31.

  In the above state, when a packet (SEQ = 56) arrives at the receiver 2 from the network 31, it is delivered to the storage control unit 271.

  The storage controller 271 first compares the SEQ (56) of the packet that has arrived with the SEQ (126) of the packet that has arrived last time, and determines that retransmission has occurred since the SEQ is smaller than the previous time, and has already decided the order. All the packets stored in the buffer 211 are discarded, and the packet that has arrived this time is stored in the order buffer 211.

  As described above, when the order buffer 211 overflows, it is determined that a packet loss has occurred due to buffer flush (total discard), and a retransmission request is made.

  The case where the order guarantee buffer overflows is a case where the takeout control unit 22 cannot take out the packet from the order buffer due to a failure such as packet loss. In such a state, it is difficult to return to a normal state unless retransmission is performed in many cases. Also, if the buffer overflows, the packets that have already stayed in the sequential buffer become unnecessary if retransmission is performed.

  In a multipath environment, if there is no packet loss determination described in the present embodiment, the receiver 2 cannot make a retransmission request to the transmitter 1, so the transmitter 1 uses the retransmission timer 15 to perform retransmission. There is no choice but to do. However, in general, the retransmission timer 15 needs to set a large value of at least 1 RTT in order to prevent malfunction, and therefore it takes time to start retransmission.

  For this reason, when the packet loss determination mechanism described in the present embodiment is used, a loss determination (retransmission request) is performed faster than the loss determination by the retransmission timer by determining the packet loss when the order buffer 211 overflows. I can do things.

  When a packet arrives due to retransmission, retransmission is determined based on the sequence number, and when it is determined that retransmission has occurred, buffer flush (all discards) is performed. Thereby, the on-the-fly packet which becomes unnecessary by retransmission can be appropriately discarded.

(Effect of this embodiment)
Next, the effect of this embodiment will be described.

  When the invention described in this embodiment is used, in a multipath environment in which a transmitter and a receiver are connected by a plurality of networks, when the order of packets in each network does not reverse, only one stage is used. By using this sequence number management, it is possible to detect abnormalities such as packet loss at high speed.

  This is because the storage controller in the receiver cannot take out packets from the sequence buffer when an abnormality occurs, and monitors the overflow of the sequence buffer installed in each network, focusing on the characteristics of buffer overflow. is there.

  Further, when the invention described in this embodiment is used, in a multipath environment in which a transmitter and a receiver are connected by a plurality of networks, when packet order reversal in each network does not occur, 1 Retransmission can be started at high speed using the management of sequence numbers of only stages.

  This is because the storage control unit in the receiver cannot monitor packets from the order buffer when an abnormality occurs and monitors the overflow of the order buffer installed in each network, focusing on the characteristic that the buffer overflows. This is because overflow is a trigger for starting retransmission.

(Fourth embodiment)
The fourth embodiment of the present invention determines the maximum storable number (capacity) of the order buffers 211 to 214 from the bandwidths of the networks 31 to 34 and the delay difference with respect to the third embodiment. This speeds up the abnormality detection (retransmission start) due to buffer overflow.

  The order buffers 211 to 214 are for absorbing the delay difference between the networks 31 to 34. Therefore, the order buffer only needs to have a product size of “the difference between the maximum round trip delay and the minimum round trip delay among the round trip delays of the networks 31 to 34” and the “band of the networks 31 to 34”. If a packet is accumulated in the order buffers 211 to 214 beyond this size, it can be considered that an abnormality such as a packet loss has occurred. This embodiment uses this characteristic to speed up the abnormality detection and the retransmission start described in the third embodiment.

(Description of configuration)
With reference to FIG. 14, the structure in this Embodiment is demonstrated.

  The transmitter 1 differs from the configuration of the third embodiment shown in FIG. 12 in that the distribution unit 14 is a distribution unit 14A and an internal clock 19 is added.

  In addition to the operation of the distribution unit 14 described in the first embodiment, the distribution unit 14A is provided from the internal clock 19 in the packet header when receiving the packet from the retransmission buffer 13 and transferring the packet to the networks 31 to 34. It has a function to describe the received time information.

  The built-in clock 19 is a clock built in the transmitter 1 and provides time information to the sorting unit 14.

  The receiver 2 is different from the configuration of the third embodiment shown in FIG. 12 in that a capacity determination unit 28 and a built-in clock 29 are added.

  The capacity determination unit 28 receives the bandwidth information of the networks 31 to 34 and the transmission time information of the packet described in the header of the arrival packet from the storage control units 271 to 274, and further receives the time information from the built-in clock 29, Calculate the round trip delay time for each network. Then, the maximum storable number (capacity) of the order buffers 211 to 214 is determined and set from the calculated round-trip delay time and bandwidth.

  The built-in clock 29 is a clock built in the receiver 2 and provides time information to the capacity determination unit 28. The built-in clock 29 and the built-in clock 19 may or may not be synchronized.

(Operation example)
(When the built-in clock 19 and the built-in clock 29 are synchronized)
The operation of the capacity determination unit 28 when the internal clock 19 and the internal clock 29 are synchronized and a packet is transmitted to the network 31 will be described with reference to FIG.

  A packet is transmitted from the retransmission buffer 13 in the transmitter 1 and arrives at the distribution unit 14A.

  The distributing unit 14A acquires time information from the built-in clock 19 and embeds transmission time information in the header of the packet that has arrived from the retransmission buffer 13. Then, the data is transmitted to the network 31.

  When the storage control unit 271 in the receiver 2 receives a packet from the network 31, the number of received bytes per unit time from the network 31 (reception rate, hereinafter referred to as bandwidth) and transmission time information described in the packet Is notified to the capacity determination unit 28.

  Upon receiving notification of the bandwidth and transmission time from the storage control unit 271, the capacity determination unit 28 obtains the reception time from the built-in clock 29, and calculates and records the round-trip delay time (RTT) of the network 31 from the following equation. .

RTT = (reception time−transmission time) × 2
The capacity determination unit 28 compares the recorded RTTs of the networks 31 to 34 to check the maximum (maximum RTT) and minimum (minimum RTT). Then, the capacity of the order guarantee buffer 211 is determined by the following equation.

Capacity of order buffer 211 = (maximum RTT−minimum RTT) × bandwidth of network 31 The order guarantee buffer 211 receives the capacity notification from the capacity determination unit 28 and sets the maximum storable amount (the maximum storable amount is , Bits, bytes, number, etc., are converted and set as appropriate).

  In the above, the capacity determining operation of the order buffer 211 when a packet is transmitted to the network 31 has been described as an example. Similarly, when the packet is transmitted to the networks 32 to 34, the capacity of the order buffer 212 to 214 is also described. Can be determined.

  The capacity of the order buffer determined by the above operation is a capacity that can absorb the delay difference between the networks 31 to 34. If the packet is to be accumulated beyond this (order buffer overflow occurs), it is considered that an abnormality such as a packet loss has occurred. Therefore, according to the present embodiment, the capacity of the order buffers 211 to 214 is set as small as possible, and the overflow of the order buffers 211 to 214 is monitored according to the third embodiment, so that anomaly detection can be performed at high speed. Can be used as a trigger for the start of high-speed retransmission.

(When built-in clock 19 and built-in clock 29 are not synchronized)
When the built-in clock 19 and the built-in clock 29 are not synchronized and the time of the built-in clock 29 is advanced by α from the time of the built-in clock 19, the RTT can be expressed as follows.

Maximum RTT = (Reception time a + α−Transmission time a) × 2
Minimum RTT = (reception time b + α−transmission time b) × 2
At this time, the capacity of the order buffer is as follows.

Order buffer capacity = (maximum RTT−minimum RTT) × bandwidth = {(reception time a + α−transmission time a) − (reception time b + α−transmission time b)} × 2 × bandwidth = (reception time a−transmission time a−reception) Time b + Transmission time b) × 2 × Band From the above formula, α is canceled out, so that the built-in clock 19 and the built-in clock 29 are not synchronized, and the time of the built-in clock 29 is greater than the time of the built-in clock 19 Even if it is only advanced, the capacity of the order buffer can be determined.

(Effect of this embodiment)
Next, the effect of this embodiment will be described.

  When the invention described in this embodiment is used, in a multipath environment in which a transmitter and a receiver are connected by a plurality of networks, when the order of packets in each network does not reverse, only one stage is used. By using this sequence number management, it is possible to detect abnormalities such as packet loss at high speed.

  This is because the storage control unit in the receiver cannot monitor packets from the order buffer when an error occurs and monitors the overflow of the order buffer installed in each network. This is because the capacity determination unit in the receiver sets the size of the order buffer so as to be the minimum necessary from the delay difference and the bandwidth between the networks.

  Further, when the invention described in this embodiment is used, in a multipath environment in which a transmitter and a receiver are connected by a plurality of networks, when packet order reversal in each network does not occur, 1 Retransmission can be started at high speed using the management of sequence numbers of only stages.

  This is because the storage controller in the receiver cannot take out packets from the sequence buffer when an abnormality occurs, and pays attention to the characteristic that the buffer overflows. This is because when the overflow is triggered by the start of retransmission, the capacity determination unit in the receiver sets the size of the order buffer so as to be the minimum necessary from the delay difference and the bandwidth between networks.

(Fifth embodiment)
The fifth embodiment of the present invention performs selective retransmission of only missing packets by Selective ACK instead of retransmission by GO-BACK-N, compared to the first embodiment.

(Description of configuration)
With reference to FIG. 15, the configuration of the present embodiment will be described.

  The transmitter 1 is different from the configuration of the first embodiment shown in FIG. 1 in that the retransmission buffer 13 is the retransmission buffer 13A, the sequence buffers 211 to 214 are the sequence buffers 211A to 214A, and the ACK transmission unit 23 is The difference is that each is changed to an ACK transmission unit 23A, and an overtaking buffer 215 and storage control units 271A to 274A are added.

  In addition to the operations (1) to (5) of the retransmission buffer 13 in the first embodiment, the retransmission buffer 13A performs the following operations.

  (6) A negative acknowledgment (NACK) is received from the ACK transmission unit 23 and a copy of the packet having the sequence number value described in the NACK is retransmitted to the distribution unit 14.

  The order buffer 211 </ b> A is a FIFO buffer similar to the order buffer 211, receives a packet from the network 31, temporarily stores it, and notifies the takeout control unit 22 of storage completion. Further, the packet stored in the output buffer 24 is transferred in accordance with an instruction from the take-out control unit 22. However, unlike the order buffer 211, the sequence number of the packet arriving from the network 31 is compared with the sequence number of the packet arriving from the network 31 last time. If it is smaller or the same, it is considered that retransmission has occurred, and all stored packets are not discarded.

  The order buffers 212A to 214A perform the same operation as the order buffer 211A.

  The overtaking buffer 215 receives the packet retransmitted by NACK from the storage control units 271A to 274A, and notifies the extraction control unit 22 of the storage. Then, the packet being stored is transferred to the output buffer 24 according to an instruction from the take-out control unit 22. Note that the storage control unit 22 handles the overtaking buffer 215 as a buffer similar to the order buffers 211A to 214A.

  The ACK transmission unit 23A performs the following operation. In the present application, a description will be given of the 1ACK method in which an ACK of one packet is transmitted every time one packet transfer to the output buffer 24 is completed, but N (N is 1 or more) packet arrival reports are collectively performed by one ACK. The N_ACK method may be used.

  (1) Upon receiving the SEQ notification of the packet transferred from the take-out control unit 23 to the output buffer 24, a delivery confirmation packet (hereinafter referred to as ACK) including the SEQ is generated and notified to the retransmission buffer 13. At this time, ACK is notified using one of the networks 31 to 34. Further, the received SEQ is stored.

  (2) Upon receiving a retransmission request from the loss detection unit 20 and the storage control units 271A to 274A, a NACK packet (negative acknowledgment packet) having the value of SEQ + 1 stored in (1) is generated and notified to the retransmission buffer 13A. At this time, NACK is notified using one of the networks 31 to 34. The NACK in (2) may be copied and transferred using all of the networks 31 to 34. In this case, it is necessary to provide a lock mechanism or the like in the retransmission buffer 13A so that retransmission does not occur frequently in the retransmission buffer 13A. There is.

  The storage controllers 271A to 274A perform the following operations.

  (1) The sequence number of the packet arriving from the network 31 is compared with the sequence number of the packet arriving from the network 31 last time, and the SEQ of the packet arriving this time is smaller than or equal to the SEQ of the packet arriving last time. If it is, it is assumed that retransmission has occurred, and the packet is transferred to the overtaking buffer 215.

  (2) When retransmission does not occur in (1), the packet arriving from the network 31 is transferred to the order buffer 211A. At this time, the number of stored packets in the order buffer 211A is confirmed. If the maximum number of packets that can be stored is exceeded if the arrival packets are stored, all the stored packets in the order buffer 211A are discarded and the ACK transmission unit 23A is notified. Request retransmission.

(Description of operation)
The operation in the storage control unit 271A will be described with reference to the flowchart in FIG.

  The operation of the storage control unit 271A is different from the operation of the storage control unit 271 shown in FIG. 13 in that step 27103 is changed to step 27103A.

  If the SEQ of the packet that has arrived this time is smaller than or equal to the SEQ of the packet that has arrived last time, it is determined that retransmission has occurred, and the packet that arrived is transferred to the overtaking buffer 215 and the process ends (step 27103A). .

(Operation example)
(Example of missing detection operation in case of abnormality)
Hereinafter, with reference to FIG. 5, an operation example of the loss detection unit 20 and the ACK transmission unit 23 </ b> A when a packet loss occurs (abnormal state) will be described. In FIG. 5, the ACK transmission unit 23 is described, but here it is read as the ACK transmission unit 23A.

  FIG. 5 shows an example in which a packet with SEQ = 6 is lost (lost) in the network 33.

  Further, since the network 33 has a larger delay than the other networks, and the networks 31, 32, and 34 have a smaller delay than the network 33, the order buffers 211, 212, and 214 are compared with the case of passing through the network 33. Assume that packets arrive fast.

  In FIG. 5, it is assumed that the packet sequence confirmation from SEQ1 to SEQ5 is completed and transferred to the output buffer 24, and ACK1 to ACK5 are transmitted from the ACK transmission unit 23 to these packets.

  Here, when the SEQ = 12 packet sent to the network 33 next to the missing SEQ = 6 packet is stored in the order buffer 213, the order confirmation operation 221 is activated. However, since there is no packet that can be sent to the output buffer 24, the dropout detection unit 20 is immediately notified of the removal completion.

  The missing detection unit 20 checks the number of packets stored in the order buffers 211 to 214. Here, the storage of the packet is confirmed in all the order buffers including the order buffer 213, and it is assumed that a loss has occurred, and a retransmission request is made to the ACK transmission unit 23A.

  The ACK transmission unit 23A receives a retransmission request from the loss detection unit 20, and transmits a NACK (negative acknowledgment) including SEQ = 6 obtained by adding 1 to the ACK (ACK = 5) transmitted last time. Since the NACK has arrived, the transmitter 1 determines that there is a retransmission request and retransmits the packet with SEQ = 6.

  The packet of SEQ = 6 transmitted by the retransmission is transferred to the overtaking buffer 215 by the storage control units 271A to 274A in the receiver 2, and is transferred from the overtaking buffer 215 to the output buffer 214.

  As described above, by combining the loss detection by the loss detection unit 20 and the selective retransmission of only the lost packet by the selective ACK, it is possible to detect a failure at a high speed and minimize the bandwidth compression during the retransmission. Can be suppressed. By using such a method, the fault detection performance equivalent to that of the conventional technology 2 and the bandwidth compression rate equivalent to that of the conventional technology 2 at the time of retransmission can be achieved with a simpler mechanism (using only one stage of SEQ) than that of the conventional technology 2. realizable.

(Effect of this embodiment)
Next, the effect of this embodiment will be described.

  When the invention described in this embodiment is used, in a multipath environment in which a transmitter and a receiver are connected by a plurality of networks, when the order of packets in each network does not reverse, only one stage is used. The packet loss can be detected at high speed using the management of the sequence number.

  This is because the loss detection unit in the receiver pays attention to the characteristic that the packet is stored in the order buffer of all networks when packet loss occurs, and the packet retention state in the order guarantee buffer installed for each network. It is because it monitors.

  Further, when the invention described in this embodiment is used, in a multipath environment in which a transmitter and a receiver are connected by a plurality of networks, when packet order reversal in each network does not occur, 1 Retransmission at the time of packet loss can be started at high speed using the management of the sequence number of only the stage.

  This is because the loss detection unit in the receiver pays attention to the characteristic that the packet is stored in the order buffer of all networks when packet loss occurs, and the packet retention state in the order guarantee buffer installed for each network. This is because by monitoring, it is possible to detect missing at high speed without using the retransmission timer.

  In the above embodiment and embodiment, the description has been made using the term “packet”. However, the present invention can be similarly applied to a frame (such as an Ethernet (registered trademark) frame).

  Although the present invention has been described with reference to the preferred embodiments and embodiments, the present invention is not necessarily limited to the above embodiments and embodiments, and various modifications can be made within the scope of the technical idea. Can be implemented. Of course, the embodiment and the embodiment described above can also be implemented in combination with each other.

  The present invention can be applied to an Ethernet (registered trademark) switch, a router, and the like that transfer a large amount of data at high speed using a plurality of networks. It can also be applied to a network interface card (NIC) that connects servers at high speed.

DESCRIPTION OF SYMBOLS 1 Transmitter 2 Receiver 11 Data part 12 SEQ provision part 13 Retransmission buffer 14 Distribution part 14A Distribution part 15 Retransmission timer 19 Built-in clock 22 Extraction control part 22A Extraction control part 23 ACK transmission part 24 Output buffer 25 SEQ deletion part 26 Data reception Unit 28 capacity determination unit 29 internal clock 211 order buffer 212 order buffer 213 order buffer 214 order buffer 221 order confirmation operation 221A order confirmation operation 222 missing detection operation 222A missing detection operation 223 packet extraction operation 271 storage control unit 272 storage control unit 273 storage Control unit 274 Storage control unit

Claims (8)

In the case where the transmitter and the receiver are connected by a plurality of networks that do not cause packet order reversal in the network,
Multiple sequence buffers installed in each network that accumulate packets until the sequence is confirmed,
An extraction control unit for confirming the sequence number added to the packet and extracting the packet from the order buffer while restoring the flow order;
An overtaking buffer that accumulates packets sent by resending;
A communication apparatus comprising: a retransmission storage control unit that allocates storage destinations to the order buffer and the overtaking buffer according to a sequence number. The communication device
The communication apparatus according to claim 1, further comprising: an ACK transmission unit that makes a retransmission request when a loss is detected. In the case where the transmitter and the receiver are connected by a plurality of networks that do not cause packet order reversal in the network,
The receiver is
Multiple sequence buffers installed in each network that accumulate packets until the sequence is confirmed,
An extraction control unit for confirming the sequence number added to the packet and extracting the packet from the order buffer while restoring the flow order;
An overtaking buffer that accumulates packets sent by resending;
A communication system, comprising: a retransmission storage control unit that allocates storage destinations to the order buffer and the overtaking buffer according to a sequence number. The receiver
The communication system according to claim 3, further comprising: an ACK transmission unit that makes a retransmission request when a loss is detected. In the case where the transmitter and the receiver are connected by a plurality of networks that do not cause packet order reversal in the network,
The receiver is
Packets are accumulated until the order is confirmed in the order buffer.
Check the sequence number added to the packet, retrieve the packet from the order buffer while restoring the flow order,
Accumulate packets sent by resending in the overtaking buffer,
A communication method, wherein a storage destination is allocated to the order buffer and the overtaking buffer according to a sequence number. The receiver
The communication method according to claim 5, wherein a retransmission request is made when a loss is detected. When the transmitter and the receiver are connected by multiple networks that do not cause packet order reversal in the network,
The receiver is
Packets are accumulated until the order is confirmed in the order buffer.
Check the sequence number added to the packet, retrieve the packet from the order buffer while restoring the flow order,
Accumulate packets sent by resending in the overtaking buffer,
A program for causing a computer to perform a communication method, wherein a storage destination is assigned to the order buffer and the overtaking buffer according to a sequence number. The receiver
The program according to claim 7, wherein a retransmission request is made when a loss is detected.

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