JP2007243447A - Packet transmission control apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology of properly estimating a pipe value, detecting a failure of a retransmitting packet, and again retransmitting a discarded retransmitting packet so as to prevent deterioration in the throughput. <P>SOLUTION: A packet transmission control apparatus in a transmission station includes: a means for counting the number of packets during transfer and existing on the network; and a means for transmitting a packet when the number of packets during the transfer is greater than a window size by comparing the number of packets during the transfer with the window size. Further, the packet transmission control apparatus includes: a means for detecting a discarded packet when the transmittal of the retransmitting packet succeeding to a packet is selectively and earlier confirmed; and a means for retransmitting the discarded packet. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for improving the performance of a transfer packet number control device in a communication system in which window flow control and selective retransmission error recovery are performed.

  In a computer network, processing such as retransmission is performed on packets discarded due to congestion or bit errors to provide a reliable communication service for computer users, and to address congestion caused by routers or receiving stations. A function to cope with or prevent the occurrence is required.

  In TCP (Transmission Control Protocol) -SACK (Selective Acknowledgment) (see Non-Patent Document 1), which is a typical protocol of computer networks, the receiving station notifies the transmitting station of the information of the discarded packet, and the transmitting station is designated. It performs error recovery (referred to as selective retransmission error recovery) that retransmits only discarded packets, and provides a reliable communication service to computer users. Furthermore, the number of packets that can be transmitted per round-trip response time is adjusted by window flow control that limits the cumulative number of unconfirmed packets to a predetermined number (called the window size) to deal with congestion. Yes. Here, “a certain packet has been confirmed to be cumulatively delivered” means that all packets that have been transmitted up to that packet are acknowledged.

  In the following description, it is assumed that the transmitting station and the receiving station are executing TCP-SACK defined in Non-Patent Document 1.

  Here, the transfer packet number control apparatus related to the early recovery procedure described in Non-Patent Document 2 is shown below. In actual TCP, a sequence number is assigned to data in byte units. In the following description, it is assumed that data is assigned in packet units.

First, variables managed by the transmitting station will be described.
cwnd: congestion window size. The maximum number of packets that the transmitting station can transmit without cumulative delivery confirmation.
pipe: The number of packets existing in the network on the connection established on the transmitting station and the receiving station. The number of out-of-order packets waiting in the reception buffer of the receiving station is not included.
highACK: Cumulative delivery confirmation sequence number. The highest sequence number in the cumulatively acknowledged packet.
highDATA: transmitted sequence number. The highest sequence number in the transmitted packet.
highRxt: Retransmitted maximum sequence number. The highest sequence number in the retransmitted packet.

Next, a variable managed by the receiving station is defined.
rcvNxt: Expected reception sequence number. The sequence number that the receiving station expects to receive in order next. That is, it is a value obtained by adding 1 to the value of the maximum sequence number in the packet received cumulatively in order.

  FIG. 2 shows the configuration of a computer network system. As shown in FIG. 2, a transmitting station 2 and a receiving station 3 are connected via a network 1. The transmitting station 2 and the receiving station 3 execute TCP having the SACK option defined in Non-Patent Document 1 to deal with packet discard and congestion that occur in the network 1.

  In the network 1, it is assumed that packet discard occurs due to congestion or a bit error.

  FIG. 3 shows functional blocks of the transmitting station 2.

  An example of the scoreboard 204 in the transmitting station 2 is shown in Table 1.

The scoreboard is composed of the following two attributes.
Sequence number: The sequence number of the packet. It takes a value from highACK + 1 to highDATA.
Number of selective acknowledgments: The number of selective acknowledgments based on the SACK information in the received ACK packet. For example, if the corresponding sequence number is included in the SACK block included in the SACK option field, the selective delivery confirmation number of the sequence number is incremented by one. Here, “a certain packet is selectively acknowledged” means “only that packet is acknowledged”.

  The transmitting station 2 includes a packet transmission processing unit 101, an ACK reception processing unit 102, a flow control unit 103, a scoreboard management unit 104, a packet discard confirmation unit 105, a next transmission packet determination unit 106, a transfer packet number estimation unit 107, and an initial transmission packet. It consists of a buffer 201, a retransmission packet buffer 202, a congestion window size register 203, a scoreboard 204, a transfer packet number register 205, a cumulative delivery confirmation sequence number register 206, a transmitted sequence number register 207, and a retransmitted maximum sequence number register 208. ing.

  The packet transmission processing unit 101 stores a packet stored in an initial transmission packet buffer 201 storing an initial transmission packet (referred to as an initial transmission packet) or a retransmission packet buffer 202 storing an original packet in preparation for retransmission. And the packet is transmitted to the network 1.

  Further, the following processing is performed according to the type of the transmitted packet.

  When the initial transmission packet is transmitted, the sequence number of the initial transmission packet is acquired, and the value is set to highDATA and written in the transmitted sequence number register 207.

  When a retransmission packet is transmitted, the sequence number of the retransmission packet is acquired. If the sequence number is larger than the value highRxt in the retransmitted maximum sequence number register 208, the value is updated as highRxt, and the retransmitted maximum sequence number register 208 is written.

  The ACK reception processing unit 102 receives the ACK received from the receiving station 3 via the network 1 and performs processing according to the information in the ACK. The detailed procedure of the ACK reception processing unit 102 will be described later.

  The flow control unit 103 uses the information of the congestion window size cwnd in the congestion window size register 203 and the information pipe of the transfer packet number register 205 in which the estimated number of transfer packets is stored, and “true” when cwnd ≧ pipe. return it. Otherwise, return “false”. As a result, the number of packets existing between the transmitting station 2 and the receiving station 3 is limited to cwnd.

  The scoreboard management unit 104 manages the scoreboard 204 based on the SACK information in the ACK received by the ACK receiving unit 102. Specifically, the sequence number of the packet selectively confirmed in the SACK block is acquired, and the number of selective acknowledgments of the corresponding sequence number in the score board 204 is increased by one.

The packet discard confirmation unit 105 checks whether the designated packet (with a sequence number of N) is discarded. If both of the following two conditions A1 and A2 are satisfied, it is assumed that the packet with the sequence number N is confirmed to be discarded.
A1: The packet with the sequence number N has not been confirmed to be delivered cumulatively or selectively.
A2: DupThresh (usually 3) times or more, a packet having a sequence number greater than N has been selectively confirmed. Here, “DupThresh” is a parameter that can be set by the administrator.

  The next transmission packet determination unit 106 determines the next packet to be (re) transmitted.

In the prior art, a packet that satisfies the following conditions is obtained.
B1: The sequence number is larger than highRxt and has the smallest sequence number among the packets confirmed to be discarded by the packet discard confirmation function.
B2: When there is no packet satisfying the condition B1, the sequence number is highRxt.

  The transfer packet number estimation unit 107 calculates a pipe value by the following calculation algorithm and writes the value in the transfer packet number register 205.

Pipe Calculation Algorithm The following processing is performed for packets whose sequence number is higher than ACK + 1 and lower than highDATA.
C1: For a packet whose discard has not been confirmed by the processing in the packet discard confirming unit 105: Pipe is incremented by one.
C2: For packets whose sequence number is highRxt or less: Pipe is incremented by one.

ACK Reception Processing at Transmitting Station 2 The processing procedure of the ACK reception processing unit 102 described above will be described.

Case 1: When a duplicate ACK (ACK having the same transmission confirmation sequence number of an ACK that has already been received by the transmitting station) is received DupThresh times, packet discarding occurs between the transmitting station 2 and the receiving station 3 It is assumed that it has occurred and the early recovery process is started. However, if it is already in the early recovery process (that is, in the early recovery state), the following process is skipped.
1. Early recovery.
2. The congestion window size register 203 is updated by setting cwnd ← cwnd / 2.
3. Of the packets that have not been confirmed to be delivered, the packet having the smallest sequence number is retransmitted. In particular,
(A) The sequence number of a packet having a sequence number obtained by adding 1 to the value in the cumulative delivery confirmation sequence number register 206 is acquired.
(B) The packet transmission processing unit 101 is used to find a retransmission packet with the sequence number from the retransmission packet buffer 202 and retransmit the packet.
4). The pipe value is calculated using the transfer packet number estimation unit 107.
5). The flow control unit 103 is inquired, and the following processing A is performed as long as “true”, that is, cwnd ≧ pipe.
(A) The next transmission packet determination unit 106 is used to determine the next packet to be (re) transmitted.
(B) The packet transmission processing unit 101 is used to retrieve the corresponding packet from the initial transmission packet buffer 201 or the retransmission packet buffer 202, transmit the packet, and a related register (the transmitted sequence number register 207 or the retransmitted maximum) Update the sequence number register 208).
(C) The pipe value is incremented by 1, and the value is stored in the transfer packet number register 205.

Case 2: When an ACK packet including SACK information is received in the early recovery state. The scoreboard 204 is updated using the scoreboard management unit 104.
2. A pipe value is calculated using the transfer packet number estimation unit 205, and the value is stored in the transfer packet number register 205.
3. The flow control unit 103 is inquired, and the above-described processing A is performed as long as “true”, that is, cwnd ≧ pipe.

  Case 3: In the early recovery state, when the early recovery process is started, when the last transmitted packet receives an ACK confirming delivery, the early recovery process is terminated (leaving the early recovery state).

  FIG. 3 shows functional blocks in the receiving station 3. The receiving station 3 includes a packet reception processing unit 301, an ACK transmission processing unit 302, a SACK information creation unit 303, a reception buffer 401, and an expected reception sequence number register 402.

When receiving a packet from the transmitting station 2, the packet reception processing unit 301 performs the following processing.
1. The sequence number of the received packet is compared with the expected reception sequence number rcvNxt stored in the expected reception sequence number register 402, and the following processing is performed according to the result.
(A) When the sequence number of the received packet is equal to rcvNxt, the received packet is stored in the receive buffer 401, arranged in order, and one rcvNxt is added each time all the in-order packets are transferred to the upper layer. .
(B) If the sequence number of the received packet is different from rcvNxt, the received packet is stored in the receive buffer 401.
2. Requests ACK transmission processing unit 302 to transmit ACK.

When there is an ACK transmission request from the packet reception processing unit 301, the ACK transmission processing unit 302 performs the following processing.
1. The SACK information creation unit 303 is requested to create packet information stored in the reception buffer 401, and a SACK field is created based on the result.
2. The expected reception sequence number rcvNxt stored in the expected reception sequence number register 402 is acquired, and the value is set in the delivery confirmation sequence number field.
3. The created ACK is transmitted to the transmitting station 2.

When there is a SACK information creation request from the ACK transmission processing unit 302, the SACK information creation unit 303 accesses the reception buffer 401, checks the sequence number of the stored packet, and returns information necessary for creating the SACK field. .
M.M. Mathis, J. et al. Mahdavi, S .; Floyd, A.D. Romanow, “TCP selective acknowledgment option”, RFC 2018, October, 1996. E. Blanton, M.M. Allman, K.M. Fall, L.L. Wang, “A conservative selective acknowledgment (SACK) -based loss recovery Algorithm for TCP”, RFC 3517, April, 2003.

In order to clarify the problems of the prior art described above, the following scenario is given as an example (see FIG. 5).
1. Packets with sequence numbers 5-12 have been transmitted.
2. Among the above packets, the packet with the sequence number 6-9 was discarded.
3. Among the retransmitted packets, the packet with the sequence number 7-9 is discarded again.

Here, the information given to the ACK used in this example is
Delivery confirmation sequence number. The value of rcvNxt is entered, and corresponds to X of ACK = X in the example of FIG.
SACK sequence number block. The reception buffer 401 shows information on a set (block) of sequence numbers of packets that exist continuously. In FIG. 5, Y in (Y, Z) is the sequence number of the leftmost packet of the block, and Z is the sequence number of the rightmost block + 1.
It is.

  Hereinafter, a case where DupThresh is set to 1 will be considered.

When an ACK is received for an initial transmission packet with a sequence number of 10 First, consider a case where an ACK (501 in FIG. 5) for a packet with an order number of 10 is received.

  By receiving this ACK, the transmitting station 2 has continuously received DupThresh (= 1) duplicate ACKs, and performs the processing of case 1 described above. In other words, an early recovery state is entered, the packet with sequence number highACK + 1, that is, 6 packets are retransmitted, and highRxt is set to 6.

  Table 2 shows the scoreboard after the transmitting station 2 receives the ACK 501 and retransmits the packet with the sequence number of 6.

この時、順序番号がｈｉｇｈＡＣＫ＋１（＝６）以上で、ｈｉｇｈＤＡＴＡ（＝１２）以下のパケットで、累積的もしくは選択的に送達確認されていないパケットの順序番号の集合は｛１１，１２｝である。よって、ｐｉｐｅ算出アルゴリズムＣ１でのｐｉｐｅ値は２となる。一方、ｈｉｇｈＲｘｔ=６であるため、ｐｉｐｅ算出アルゴリズムＣ２の条件でのｐｉｐｅ値は１となる。ゆえに、最終的なｐｉｐｅ値は３（＝２＋１）となる。

At this time, the set of sequence numbers of packets whose sequence numbers are higher than ACK + 1 (= 6) and lower than highDATA (= 12) and whose delivery has not been confirmed cumulatively or selectively is {11, 12}. Therefore, the pipe value in the pipe calculation algorithm C1 is 2. On the other hand, since highRxt = 6, the pipe value is 1 under the condition of the pipe calculation algorithm C2. Therefore, the final pipe value is 3 (= 2 + 1).

  As can be seen from FIG. 5, since the packet with the sequence number 5 was received in order by the receiving station 3, it was not on the network 1, the packet with the sequence number 6 was discarded but retransmitted, and the sequence number 7-9. The packet with the sequence number of 10 has arrived at the receiving station 3 but is in the reception buffer 401 due to an error in the sequence. The packets with the sequence numbers of 11 and 12 have been transmitted, but the delivery has not been confirmed.

  Therefore, at this time, a packet with the sequence number {6, 11, 12} exists on the network 1 between the transmitting station 2 and the receiving station 3.

  At this time, the value obtained by the processing of the transfer packet number estimation unit 107 matches the actual number of transfer packets.

  If the congestion window size cwnd before reception of ACK for the packet with the sequence number 10 is 12, cwnd is halved to 6 by the procedure of case 1 after reception of this ACK.

  Therefore, the transmitting station can transmit cwnd-pipe = 6-3 = 3 retransmission packets or initial transmission packets.

  Therefore, in this example, 7-9 packets are retransmitted.

When an ACK is received for an initial transmission packet with an order number of 11 Next, consider a time when an ACK (502 in FIG. 4) for a packet with an order number of 11 is received.

  Table 3 shows the scoreboard after receiving ACK 502.

転送パケット数推定部１０７の処理でのｐｉｐｅ算出アルゴリズムＣ１の条件でのｐｉｐｅ値は１となり、Ｃ２の条件でのｐｉｐｅ値は４となるため、最終的なｐｉｐｅ値は５となり、実際の転送パケット数と一致する。

The pipe value under the condition of the pipe calculation algorithm C1 in the process of the transfer packet number estimation unit 107 is 1, and the pipe value under the condition of C2 is 4, so the final pipe value is 5, and the actual transfer packet Matches the number.

  Note that cwnd-pipe = 6-5 = 1 packets can be transmitted. However, in the processing result in the next transmission packet determination unit 106, there is no packet to be transmitted, so the transmitting station 2 does not transmit anything.

When an ACK is received for an initial transmission packet with a sequence number of 12, this case operates correctly as in the previous section.

When ACK is received for retransmission packet with order number 9 Next, processing when an ACK (503 in FIG. 5) for a retransmission packet with order number 9 is received will be described.

  Table 4 shows the scoreboard after receiving ACK 503.

スコアボードの表４より、累積的もしくは選択的に送達確認されていないパケットの順序番号の集合は、｛６，７，８｝である。また、上記のパケットの廃棄は、パケット廃棄確認処理により、確認されている。よって、ｐｉｐｅ値算出アルゴリズムＣ１の条件でのｐｉｐｅ値は０となる。

From Table 4 of the scoreboard, the set of sequence numbers of packets that have not been confirmed to be delivered cumulatively or selectively is {6, 7, 8}. Further, the packet discard has been confirmed by the packet discard confirmation processing. Therefore, the pipe value under the condition of the pipe value calculation algorithm C1 is zero.

  Since highRxt = 8, the pipe value under the condition of the pipe calculation algorithm C2 is 3, and the final pipe value is 3.

  However, since all the retransmitted packets 6-8 are discarded, the actual pipe value is zero.

  That is, since the discarded retransmission packets are added, the pipe value has been overestimated.

  Therefore, if the pipe value is correctly estimated, 6 (= cwnd) packets can be transmitted. However, according to the specification of RFC3517, only 3 (= 6-3) packets can be transmitted.

  If new packets arrive in the early recovery state, those packets cannot be transmitted by the conventional technique. That is, a throughput drop phenomenon occurs.

Occurrence of timeout In the conventional technique, since there is no function for detecting the failure of a retransmitted packet, when a retransmitted packet is discarded, it cannot be retransmitted again during the early recovery phase. The discarding of the retransmission packet causes a retransmission timer timeout (see FIG. 5). In general, the timeout value is set to be larger than the round-trip response time, so that the throughput greatly decreases due to the timeout. In the case of the conventional technique in which only one packet is retransmitted every time-out, the throughput further decreases.

  From the above, it can be seen that the pipe value estimated in the conventional system becomes an overestimated value and the throughput is suppressed.

  Furthermore, since the discard of the retransmitted packet can be recovered only by a timeout, there is a problem that the throughput further decreases in a network environment where the packet discard frequently occurs.

  An object of the present invention is to appropriately estimate a pipe value, detect a failure of a retransmission packet, retransmit a discarded retransmission packet again, and prevent a decrease in throughput.

Correction of Pipe Value Estimation Algorithm In the conventional method, since the retransmitted packet confirmed to be discarded is counted as the pipe value, the present invention corrects the conventional pipe value count as follows.

  In cumulatively or selectively unconfirmed delivery packets, packets that are not confirmed to be discarded are counted, and the pipe value is used as the count result value.

  In other words, a means for counting packets that have not been confirmed to be discarded among packets that have not been confirmed to be delivered cumulatively or selectively, and a means for setting the count result as the number of transfer packets are added.

Addition of resending failure confirmation function In the conventional system, the transmitting station cannot detect the failure of the resent packet during the early recovery procedure. Therefore, a retransmission failure confirmation function is added.

  In the present invention, when a subsequent retransmission packet of a certain retransmission packet is selectively confirmed in advance, it is assumed that the retransmission of the packet has failed, and discard of the retransmission packet is detected. That is, a means for detecting whether or not a subsequent retransmission packet is selectively confirmed first in a certain retransmission packet is added.

In order to specifically realize the above means, the following variables are added.
recipientSACK: last selective delivery confirmation sequence number. Order number of recent newly confirmed selective delivery confirmation currentRxtNum: the number of retransmissions of the latest selective delivery confirmation. The number of retransmissions of a packet having the order number of the recipientSACK Further, if the following means is added, the failure of the retransmission packet can be confirmed.

Means for setting the total number of packets that have not been confirmed to be discarded as the number of transfer packets Means for recognizing that the retransmitted packet has been discarded when delivery is confirmed selectively. The order number is higher than highACK and lower than highDATA, and discarded. Means for setting the total number of packets that have not been confirmed as the number of transfer packets means for determining the number of retransmissions for each packet;
Means for obtaining a recentSACK that is the sequence number of a packet that has recently been confirmed for selective delivery;
means for obtaining a receiveRxtNum that is the number of retransmissions of a packet having a sequence number of the receiveSACK;
Means for detecting packet drops;
Means for detecting a packet whose number of retransmissions is 1 or more and less than receiveRxtNum, the discard is not confirmed, and the order number is smaller than the presentSACK. Means for recognizing that the retransmission of the packet has failed. In this technique, packets discarded during the early recovery procedure cannot be retransmitted. Therefore, a discard retransmission function was added.

  When an ACK packet including SACK information is received, a packet for which retransmission has failed may be transmitted with priority. That is, a means for sequentially retransmitting from the packet with the smallest sequence number among the packets for which retransmission failed is added.

  According to the present invention, since the number of transfer packets can be estimated with high accuracy, a higher throughput than that of the conventional method can be expected. In addition, the probability that a meaningless timeout occurs is smaller than that of the conventional method. Furthermore, it is not necessary to change the implementation on the receiving station side or the packet configuration.

  Next, embodiments of the present invention will be described with reference to the drawings.

  In this embodiment, the receiving station 3 has the same function as the conventional one. FIG. 1 is a functional block diagram of the transmitting station 2 in this embodiment.

  In the transmission station in the present embodiment, the packet transmission processing unit 101, the transfer packet number estimation unit 107, and the scoreboard 204 in the transmission station in the prior art of FIG. In this case, the scoreboard 1204 replaces the retransmission failure confirmation detection unit 1108 for confirming the retransmission failure of the retransmission packet, the latest selective delivery confirmation sequence number register 1201 in which the value of the reentSACK is held, and the value of the currentRxtNum. A last selective delivery confirmation sequence number register 1202 has been added.

  In the scoreboard 1204, an element indicating the number of retransmissions is added.

  The pipe calculation algorithm in the transfer packet number estimation unit 1106 is removed from the condition (b) in the conventional pipe calculation algorithm.

  Next, the function of the retransmission failure confirmation unit 1108, which is an added functional block, will be described.

It is checked whether the retransmission of the designated packet (sequence number is M) has failed.
1. A high ACK is obtained from the cumulative delivery confirmation sequence number register 206.
2. ReceiveSACK is obtained from the latest selective delivery confirmation sequence number register 1201.
3. ReceiveRxtNum is acquired from the latest selective delivery confirmation retransmission number register 1202.
4). Returns true when the following conditions are met:

  The packet discard confirmation unit 105 has not confirmed the discard.

The sequence number M is higher than ACK + 1 and less than the presentSACK. In the scoreboard 1204, the number of retransmissions of the sequence number M is 1 or more and less than or equal to reentRxtNum.

  Next, the function of the corrected functional block will be described.

Next transmission packet determination unit 1106
The following condition B0 is added before the condition B1 in the prior art.
B0: It has the smallest sequence number among the packets whose retransmission failure has been confirmed by the processing in the retransmission failure confirmation unit 1108.
By adding the above condition B0, even if the retransmission packet is discarded again, it can be retransmitted during the early recovery state.

Packet transmission processor 1101
In the prior art processing, the following processing is added.
When a retransmission packet is transmitted: One retransmission number is added on the scoreboard 1204.

  Transfer packet number estimation unit 1106: The pipe value is obtained by the above-described pipe calculation algorithm, and the value is written in the transfer packet number register 205.

In this embodiment, a process when an ACK 503 is received when applied to the scenario shown in FIG. 5 will be described.
When the ACK for the first transmission packet with the sequence number 10 is received, the same operation as the conventional function is performed, but the scoreboard update process is different. However, the scoreboard is as shown in Table 5.

・次に、順序番号が９の再送パケットに対するＡＣＫを受信した時
この時、新たに選択的送達確認したパケットの順序番号は９である。よって、ｒｅｃｅｎｔＳＡＣＫは９となる。表５より、順序番号が９の再送回数値は１であるため、ｒｅｃｅｎｔＲｘｔＮｕｍは１となる。

Next, when an ACK is received for a retransmitted packet whose sequence number is 9, the sequence number of the packet that is newly confirmed for selective delivery is 9 at this time. Therefore, the presentSACK is 9. As shown in Table 5, since the number of retransmissions having the sequence number 9 is 1, the currentRxtNum is 1.

  By the processing in the retransmission failure confirmation unit 1108, the failure of retransmission of the packets having the sequence numbers 6 to 8 is confirmed.

  Also, the pipe value obtained by the transfer packet estimation unit 1107 by the pipe calculation algorithm of the present invention is 0, which matches the actual value. Thus, the modified next transmission packet determination unit 1106 can retransmit the packets from 6 to 8 sequentially without time-out.

  Next, let us consider a case where a packet with only the sequence number 7 is discarded among the retransmitted packets with the sequence numbers 6 to 8. Table 6 shows the scoreboard after receiving an ACK that accumulatively confirms packets with sequence number 6 and selectively acknowledges packets with sequence number 8.

この時、ｒｅｃｅｎｔＳＡＣＫは８となり、表６よりｒｅｃｅｎｔＲｘｔＮｕｍは２となる。再送失敗確認部１１０８での処理により、順序番号が７のパケットの廃棄が確認される。次送信パケット決定部１１０６により、このパケットは再送される。

At this time, the receiveSACK is 8 and the receiveRxtNum is 2 from Table 6. By the processing in the retransmission failure confirmation unit 1108, it is confirmed that the packet with the sequence number 7 is discarded. The next transmission packet determination unit 1106 retransmits this packet.

It is a block diagram of the transmitting station of the computer network system by one Embodiment of this invention. It is a block diagram of the conventional computer network system. It is a block diagram of the transmitting station in the computer network system of FIG. It is a block diagram of the receiving station in the computer network system of FIG. FIG. 3 is a sequence diagram (part 1) illustrating a flow of packets and ACKs in the computer network system of FIG. It is a sequence diagram which shows the flow of the packet and ACK in the computer network system of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Computer network 2 Transmission station 3 Receiving station 101,1101 Packet transmission process part 102 ACK reception process part 103 Flow control part 104 Score board management part 105 Packet discard confirmation part 106,1106 Next transmission packet transmission part 107,1107 Estimate number of transfer packets Section 1108 Retransmission failure confirmation section 201 Initial transmission packet buffer 202 Retransmission packet buffer 203 Congestion window size register 204, 1204 Scoreboard 205 Transfer packet number register 206 Cumulative confirmation sequence number register 207 Transmitted sequence number register 208 Retransmitted maximum sequence number register 301 packet reception processing unit 302 ACK transmission processing unit 303 SACK information generation unit 401 reception buffer 402 reception expected sequence number register 1201 latest selective delivery probability Acknowledgment sequence number register 1202 Last selective delivery confirmation retransmission number register

Claims (9)

The transmitting station assigns a sequence number to the packet and transmits the packet. The receiving station notifies the transmitting station of the sequence number of the packet received in a cumulative order, and the receiving station stores the packet that is out of order. In the communication system for limiting the window size, which is the cumulative number of unacknowledged packets existing on the network between the transmitting station and the receiving station, in the transmitting station,
In the transmitter station
A packet having means for counting the number of packets being transferred existing on the network, and means for comparing the number of packets being transferred with a window size, and transmitting a packet when the number of packets being transferred is larger than the window size. Transmission control device. In cumulative or selectively unacknowledged packets,
A means of counting packets that have not been confirmed to be discarded;
The packet transmission control device according to claim 1, further comprising: means for setting the count result as the number of transfer packets. Means for obtaining highACK, which is the maximum sequence number of packets that are cumulatively acknowledged;
Means for obtaining highDATA which is the maximum sequence number in the transmitted packet;
Means for detecting the total number of packets whose sequence number is higher than highACK and lower than highDATA and whose discard is not confirmed;
The packet transmission control device according to claim 2, further comprising means for setting the total number as the number of transfer packets. The transmitting station assigns a sequence number to the packet and transmits the packet. The receiving station notifies the transmitting station of the sequence number of the packet received in a cumulative order, and the receiving station stores the packet that is out of order. In the communication system for limiting the window size, which is the cumulative number of unacknowledged packets existing on the network between the transmitting station and the receiving station, in the transmitting station,
A packet transmission control apparatus having a means for detecting discard of a retransmission packet in a transmitting station. The transmitting station is
Means for detecting whether a subsequent retransmission packet has been selectively acknowledged first in a certain retransmission packet;
The packet transmission control device according to claim 4, further comprising: means for recognizing that the retransmission packet is discarded when delivery is selectively confirmed. Means for determining the number of retransmissions for each packet;
Means for obtaining a recentSACK that is a sequence number of a packet that has recently been selectively confirmed for delivery;
Means for obtaining the currentRxtNum, which is the number of retransmissions of the packet having the order number of the presentSACK;
A means of confirming packet discard;
Means for detecting a packet whose number of retransmissions is not less than 1 and not more than the presentRxtNum, the discard is not confirmed, and the sequence number is smaller than the presentSACK;
The packet transmission control device according to claim 5, further comprising: a unit that recognizes that retransmission of the packet has failed.   The packet transmission control device according to claim 6, comprising means for transmitting the packet that the transmission station has recognized as having failed in retransmission.   The packet transmission control device according to claim 7, further comprising means for retransmitting sequentially from a packet with a smaller sequence number among packets recognized as having failed in retransmission. The transmitting station is
In packets that have not been acknowledged cumulatively or selectively,
9. The method according to any one of claims 2 to 8, further comprising means for recognizing that the discard of the packet is confirmed when the packet having the sequence number larger than the sequence number of the packet is selectively confirmed for a predetermined number of times or more. The packet transmission control device according to claim 1.

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