JP2014507817A - Communication apparatus, packet retransmission control method, packet retransmission control program - Google Patents

Abstract

The communication apparatus transfers a TCP / IP processing unit that performs TCP / IP processing, a retransmission control unit that performs packet retransmission control in a layer lower than the TCP layer, and a TCP packet received from the retransmission control unit to the TCP / IP processing unit A rate maintaining unit. The retransmission control unit transmits the TCP packet transmitted from the TCP / IP processing unit to the transmission destination, and transfers the TCP-ACK packet received from the transmission destination to the rate maintaining unit. The rate maintaining unit rewrites the ACK number of the TCP-ACK packet received from the retransmission control unit so that TCP-ACK packets having the same ACK number are not continuously transferred to the TCP / IP processing unit. The TCP-ACK packet is transferred to the TCP / IP processing unit.
[Selection] Figure 2

Description

  The present invention relates to packet retransmission control in packet communication.

  In a packet communication network, a packet being transmitted may be discarded or destroyed. This is due to the occurrence of congestion in the router or switch that forwards the packet, a decrease in signal reception sensitivity, or electromagnetic noise from the outside. In general, packet loss due to discard or destruction is detected by a protocol operating in the application layer or transport layer. Then, under such protocol control, lost packets are retransmitted to ensure the integrity of the data to be transmitted.

  Specifically, the transmission device transmits a packet to the reception device, and the reception device returns an acknowledgment (ACK: ACKnowledgement) packet to the transmission device upon receipt of the packet. Upon reception of this ACK packet, the transmission device recognizes that the transmission packet has successfully reached the reception device. On the other hand, when a packet is lost on the network between the transmission device and the reception device, the transmission device does not receive an ACK packet in response to the packet. If the transmitting device does not receive the ACK packet within a predetermined waiting time after sending the packet, the transmitting device retransmits the packet to the receiving device. The predetermined waiting time is referred to as “Retransmission Time Out (RTO)”. In addition, a transmission apparatus that performs such packet retransmission control includes a storage area for temporarily storing transmission packets until an ACK packet is received. This storage area is hereinafter referred to as a “retransmission buffer”. The

  TCP (Transmission Control Protocol) used in the Internet is a typical transport layer protocol that performs such packet retransmission control.

  A technique related to such packet retransmission control is described in Non-Patent Document 1. According to the related technology, packet retransmission control is performed in a MAC (Media Access Control) layer lower than the TCP layer. The reason is as follows.

  As an example, consider a network having a very short round-trip delay time (RTT) such as a network in a data center. In such a network, by shortening the retransmission timeout to the microsecond level, it is possible to reduce the waiting time until packet retransmission and improve the communication efficiency. However, since TCP is generally implemented in an OS (Operating System), it is difficult to reduce the TCP retransmission timeout to the microsecond level. For example, the accuracy of unit time (Jiffies) in Linux is at most milliseconds, which is insufficient for time measurement in units of microseconds. Therefore, Non-Patent Document 1 solves such a problem by performing packet retransmission control in the MAC layer lower than the OS and shortening the retransmission timeout to the microsecond level.

Toru Takamichi et al., “Ultra-High Speed MAC Technology for Terabit-Class LAN”, IEICE Communication Society Conference, 2008.

  The inventor of the present application has recognized the following problems regarding the case where packet retransmission control is performed in a layer lower than the TCP layer as in the related art. That is, when a packet is lost on the network, packet retransmission by both the lower layer and the TCP layer may occur for the same packet. Such a situation will be described with reference to FIG.

  In FIG. 1, two communication devices are connected to each other via a network. In each communication apparatus, the “TCP / IP processing unit” performs TCP / IP processing, and the “retransmission control unit” performs packet retransmission control in a layer lower than the TCP layer. A solid arrow represents a TCP packet including TCP data sent from the first communication device to the second communication device. Each TCP packet includes 100 bytes of TCP data and belongs to a single flow. A broken arrow represents an ACK packet by TCP (hereinafter referred to as “TCP-ACK packet”) that is returned from the second communication device to the first communication device. The number in the single circle attached to the solid line arrow indicates the sequence number of the TCP packet, and the number in the double circle attached to the broken line arrow indicates the TCP ACK number of the TCP-ACK packet. . For simplicity, transmission / reception of ACK packets by lower layers is not shown. Further, in a general implementation of TCP, a delayed ACK (Delayed ACK) function that aggregates a plurality of ACK packets into one is effective, but in this example, delayed ACK is not considered. These simplifications do not lose generality.

  In the example shown in FIG. 1, the TCP / IP processing unit of the first communication device continuously sends six TCP packets to the second communication device (time T1, T2, T3 in chronological order). , T5, T6, T7). Here, consider a case where the TCP packet with the sequence number “300” sent at time T3 is discarded in the network. The retransmission control unit of the first communication apparatus transmits the TCP packet (sequence number “300”) at time T4, and retransmits the TCP packet (sequence number “300”) at time T8 after the retransmission timeout has elapsed.

  Thereafter, from time T9 to T13, five TCP-ACK packets responding to each of the five TCP packets that have not been discarded arrive at the first communication device in order. The ACK numbers of these five TCP-ACK packets are 200, 300, 300, 300, and 300 in the order of arrival. The reason why the TCP-ACK packets with the ACK number “300” are continuous is that the TCP / IP processing unit of the second communication apparatus does not accept the TCP packet with the sequence number “300”. The second and subsequent TCP-ACK packets having the same ACK number are called “duplicate ACK packets”.

  Here, it is assumed that the TCP / IP processing unit of the first communication device activates fast retransmission when receiving the duplicate ACK packet three times in succession. In this case, the TCP / IP processing unit of the first communication apparatus retransmits the TCP packet with the sequence number “300” when the fourth TCP-ACK packet with the ACK number “300” is received (time T13). .

  The TCP-ACK packet responding to the TCP packet (sequence number “300”) retransmitted by the retransmission control unit at time T8 finally arrives at the first communication device at time T14. However, at this point, the TCP / IP processing unit has already retransmitted the TCP packet (sequence number “300”). That is, the retransmission by the retransmission control unit is not in time as a result.

  As described above, in addition to the retransmission by the retransmission control unit in the lower layer, the TCP packet with the sequence number “300” is also subjected to high-speed retransmission by TCP. Since retransmission is performed in the lower layer, retransmission by TCP is an unnecessary process. Also, the TCP / IP processing unit reduces the congestion window with high-speed retransmission. That is, mischievous high-speed retransmission by TCP not only compresses the network bandwidth, but also reduces TCP throughput and greatly reduces communication efficiency.

  Hereinafter, in the example shown in FIG. 1, conditions for avoiding unnecessary high-speed retransmission due to TCP will be considered.

  First, the retransmission timeout of the retransmission control unit must satisfy the following condition: “Retransmission by the retransmission control unit starts before time T7 when the TCP / IP processing unit transmits the TCP packet with the sequence number“ 600 ”. To be done. " To generalize this condition, it is as follows: “Retransmit before sending the TCP packet (sequence number“ 600 ”) three times after the discarded TCP packet (sequence number“ 300 ”)” The retransmission by the control unit is started. Here, the reason for “after three” is that, in the example of FIG. 1, when the TCP / IP processing unit receives duplicate ACK packets three times in succession, it starts high-speed retransmission. This condition is expressed by the following relational expression (1).

Relational expression (1):
{Retransmission timeout of retransmission controller} <{Time required for transmission of three TCP packets}

  Also, the retransmission timeout cannot be set shorter than the network RTT. Therefore, the following relational expression (2) also needs to be satisfied.

Relational expression (2):
{Retransmission timeout of retransmission controller} ≧ {RTT of network}

  From the relational expression (1) and the relational expression (2), the following relational expression (3) is obtained.

Relational expression (3):
{Network RTT} <{Time required to send three TCP packets}

  In order to avoid occurrence of unnecessary high-speed retransmission due to TCP, the relational expression (3) needs to be satisfied. However, it is extremely difficult to establish the relational expression (3) in an actual network. For example, when the network is Ethernet, the minimum frame length is 64 bytes, and the minimum inter-frame gap is 20 bytes. In this case, the right side of the relational expression (3) is 3 × (64 + 20) × 8 / {network line speed [bit / second]}. For example, when the line speed of the network is 10 gigabits / second, the relational expression (3) becomes the following relational expression (4).

Relational expression (4):
{Network RTT} <0.2016 microseconds

  The RTT of a general data center network is said to be several tens to several hundreds of microseconds, which is significantly different from the above-mentioned 0.2016 microseconds. Therefore, it is not easy to establish relational expressions (3) and (4) in an actual network. In the future, conditions will become more severe as the main line speed shifts to 40 gigabits / second or 100 gigabits / second.

  As described above, according to the related art, when packet retransmission control is performed in a lower layer, there is a possibility that communication efficiency may be reduced.

  An object of the present invention is to provide a technique capable of preventing a reduction in communication efficiency when performing packet retransmission control in a lower layer.

  In one aspect of the present invention, a communication device is provided. The communication device includes a TCP / IP processing unit that performs TCP / IP processing, a retransmission control unit that performs packet retransmission control in a layer lower than the TCP layer, and a TCP packet received from the retransmission control unit to the TCP / IP processing unit. A rate maintaining unit for transfer. The retransmission control unit transmits the TCP packet transmitted from the TCP / IP processing unit to the transmission destination as a transmission packet, receives a TCP-ACK packet responding to the transmission packet from the transmission destination, and maintains the rate of the received TCP-ACK packet. Forward to department. The rate maintaining unit rewrites the ACK number of the TCP-ACK packet received from the retransmission control unit so that TCP-ACK packets having the same ACK number are not continuously transferred to the TCP / IP processing unit. The TCP-ACK packet is transferred to the TCP / IP processing unit.

  In another aspect of the present invention, a packet retransmission control method in a communication apparatus is provided. The packet retransmission control method includes (A) a step of performing packet retransmission control in a lower layer lower than the TCP layer with respect to the TCP packet transmitted from the TCP layer, and (B) from the transmission destination of the TCP packet to the TCP packet. Receiving a responding TCP-ACK packet; and (C) transferring the received TCP-ACK packet from the lower layer to the TCP layer. The (C) forwarding step includes (C1) rewriting the ACK number of the received TCP-ACK packet so that TCP-ACK packets having the same ACK number are not continuously transferred to the TCP layer; (C2) transferring the rewritten TCP-ACK packet to the TCP layer.

  In still another aspect of the present invention, a packet retransmission control program for causing a computer to realize a packet retransmission control function is provided. The packet retransmission control function includes a TCP / IP processing function for performing TCP / IP processing, a retransmission control function for performing packet retransmission control in a layer lower than the TCP layer, and a TCP packet received from the retransmission control function by TCP / IP processing. A rate maintaining function for transferring to the function. The retransmission control function transmits a TCP packet transmitted from the TCP / IP processing function to a transmission destination as a transmission packet, receives a TCP-ACK packet responding to the transmission packet from the transmission destination, and maintains the rate of the received TCP-ACK packet. Transfer to function. The rate maintenance function rewrites the ACK number of the TCP-ACK packet received from the retransmission control function so that TCP-ACK packets having the same ACK number are not continuously transferred to the TCP / IP processing function. The TCP-ACK packet is transferred to the TCP / IP processing function.

  According to the present invention, it is possible to prevent a decrease in communication efficiency when performing packet retransmission control in a lower layer.

FIG. 1 is a sequence diagram for explaining the problem. FIG. 2 is a block diagram showing a configuration of the communication apparatus according to the embodiment of the present invention. FIG. 3 is a block diagram showing a configuration of the retransmission control unit in the embodiment of the present invention. FIG. 4 is a conceptual diagram showing the configuration of the retransmission buffer. FIG. 5 is a block diagram showing a configuration of the rate maintaining unit in the embodiment of the present invention. FIG. 6 is a conceptual diagram showing the configuration of the flow table in the embodiment of the present invention. FIG. 7 is a flowchart showing the processing of the registration unit in the embodiment of the present invention. FIG. 8A is a flowchart showing processing of the rewriting unit in the embodiment of the present invention. FIG. 8B is a flowchart showing processing of the rewriting unit according to the embodiment of the present invention. FIG. 9 is a sequence diagram showing an example of operation of the communication apparatus according to the embodiment of the present invention. FIG. 10 is a table showing an example of the contents of the flow table in the embodiment of the present invention. FIG. 11 is a diagram showing a configuration when the communication device according to the embodiment of the present invention is applied to an information processing device.

  Embodiments of the present invention will be described with reference to the accompanying drawings.

1. Configuration 1-1. Overall Configuration FIG. 2 is a block diagram showing a configuration of the communication apparatus 1 according to the embodiment of the present invention. The communication device 1 according to the present embodiment includes an application processing unit 10, a TCP / IP processing unit 11, a rate maintaining unit 12, a retransmission control unit 13, and a lower layer processing unit 14.

  The application processing unit 10 operates a communication application such as a web server or a mail server.

  The TCP / IP processing unit 11 performs processing of a TCP layer and an IP (Internet Protocol) layer. The TCP / IP processing unit 11 has a general packet retransmission control function based on TCP. The TCP / IP processing unit 11 and the application processing unit 10 are generally connected via a socket.

  The lower layer processing unit 14 performs physical layer and link layer processing. The protocol of the physical layer and the link layer is Ethernet (registered trademark) or the like. The lower layer processing unit 14 transmits the transmission packet 22 input from the retransmission control unit 13 to the network 2 according to a predetermined procedure. Further, the lower layer processing unit 14 outputs the received packet 23 received from the network 2 to the retransmission control unit 13.

  The retransmission control unit 13 is provided between the TCP / IP processing unit 11 and the lower layer processing unit 14. The retransmission control unit 13 has a function of performing packet retransmission control in a layer lower than the TCP layer (TCP / IP processing unit 11). Specifically, the retransmission control unit 13 receives the TCP packet 20 transmitted from the TCP / IP processing unit 11. The retransmission control unit 13 performs retransmission control processing on the received TCP packet 20 and transmits it to the lower layer processing unit 14 as a transmission packet 22. In addition, the retransmission control unit 13 receives the received packet 23 from the lower layer processing unit 14. When the received packet 23 is a lower layer ACK packet, the retransmission control unit 13 terminates the lower layer ACK packet. When the received packet 23 includes the TCP packet 20, the retransmission control unit 13 transfers the TCP packet 20 to the rate maintaining unit 12, generates a lower layer ACK packet, and uses it as a transmission source. Send back. The TCP packet 20 received from the lower layer processing unit 14 may be a TCP-ACK packet (an ACK packet by TCP and a TCP packet having an ACK number) in response to the transmission packet 22 transmitted to the transmission destination. . Furthermore, when the retransmission control unit 13 receives the retransmission instruction 21 from the rate maintaining unit 12, the retransmission control unit 13 retransmits the corresponding TCP packet 20 in accordance with the retransmission instruction 21. The retransmission control unit 13 will be described in detail later.

  The rate maintaining unit 12 is provided between the TCP / IP processing unit 11 and the retransmission control unit 13. The rate maintaining unit 12 receives the TCP packet 20 transmitted from the TCP / IP processing unit 11 and appropriately stores information regarding the received TCP packet 20. Further, the rate maintaining unit 12 receives the TCP packet 20 from the retransmission control unit 13. The TCP packet 20 received from the retransmission control unit 13 includes a TCP-ACK packet responding to the transmission packet 22 transmitted to the transmission destination. The rate maintaining unit 12 transfers the TCP packet 20 received from the retransmission control unit 13 to the TCP / IP processing unit 11. However, at this time, the rate maintaining unit 12 rewrites the ACK number of the TCP-ACK packet as necessary so that the high-speed retransmission is not activated in the TCP / IP processing unit 11. Specifically, the rate maintaining unit 12 prevents the TCP-ACK packets having the same ACK number from being continuously transferred to the TCP / IP processing unit 11, that is, the TCP / IP processing unit 11 receives duplicate ACK packets. The ACK number of the TCP-ACK packet is rewritten so as not to occur. Then, the rate maintaining unit 12 transfers the rewritten TCP-ACK packet to the TCP / IP processing unit 11. Furthermore, the rate maintaining unit 12 issues a retransmission instruction 21 to the retransmission control unit 13 as necessary. The rate maintaining unit 12 will be described in detail later.

  The network 2 transfers the TCP packet 20 to an appropriate destination along a predetermined transfer path or according to destination information included in the TCP packet 20. In the network 2, a plurality of transmission devices exemplified by routers and switches are connected to each other by transmission lines. In the network 2, the TCP packet 20 being transferred may be lost due to factors such as electromagnetic noise and traffic congestion.

1-2. Retransmission control unit 13
FIG. 3 shows a configuration example of the retransmission control unit 13 of the communication apparatus 1. The retransmission control unit 13 includes a transmission unit 30, a retransmission buffer 31, a reception unit 32, and a multiplexing unit 33.

  The retransmission buffer 31 is used to temporarily hold the transmitted TCP packet 20. The holding period is from when the TCP packet 20 is transmitted until a lower-layer ACK packet responding to the TCP packet 20 is received. FIG. 4 shows a configuration example of the retransmission buffer 31. The retransmission buffer 31 is a FIFO (First-In First-Out) type queue having zero or more queue entries 61. Each queue entry 61 corresponds to each TCP packet 20 input from the TCP / IP processing unit 11 to the retransmission control unit 13 and includes information on the corresponding TCP packet 20. Specifically, each queue entry 61 includes a TCP packet 62 and a time stamp 63. The TCP packet 62 is the TCP packet 20 written in the retransmission buffer 31. The time stamp 63 is the time when the TCP packet 20 is written in the retransmission buffer 31, and is used for determination of retransmission timeout.

  Referring to FIG. 3 again, the transmission unit 30 receives the TCP packet 20 transmitted from the TCP / IP processing unit 11. The transmission unit 30 writes the TCP packet 20 in the retransmission buffer 31 and outputs it to the multiplexing unit 33. Further, the transmission unit 30 reads the TCP packet 62 of the queue entry 61 for which the retransmission timeout has elapsed from the retransmission buffer 31 and outputs it to the multiplexing unit 33. Further, the transmitting unit 30 may receive a retransmission instruction 21 including a packet identifier from the rate maintaining unit 12. The “packet identifier” includes, for example, a MAC layer destination / source address / VLAN tag, an IP layer source / destination address, a TCP layer source / destination port number / ACK number, and the like included in the packet header. Part or all of The transmission unit 30 extracts a packet identifier from the received retransmission instruction 21, searches the retransmission buffer 31 for a TCP packet 62 corresponding to the packet identifier, reads the found TCP packet 62 from the retransmission buffer 31, The data is output to the multiplexing unit 33.

  The receiving unit 32 receives the received packet 23 from the lower layer processing unit 14. When the received packet 23 is the TCP packet 20, the receiving unit 32 transfers the TCP packet 20 to the rate maintaining unit 12. Further, the receiving unit 32 generates a lower layer ACK packet 39 whose destination is the transmission source of the TCP packet 20, and outputs the lower layer ACK packet 39 to the multiplexing unit 33. At this time, the receiving unit 32 extracts a packet identifier from the TCP packet 20 and gives the extracted packet identifier to the lower layer ACK packet 39. On the other hand, when the received packet 23 is the lower layer ACK packet 39, the receiving unit 32 terminates the lower layer ACK packet 39. Further, the receiving unit 32 extracts a packet identifier from the lower layer ACK packet 39, searches the retransmission buffer 31 for a queue entry 61 having a TCP packet 62 corresponding to the packet identifier, and finds the found queue entry 61. delete.

  The multiplexing unit 33 multiplexes the TCP packet 20 received from the transmission unit 30 and the lower layer ACK packet 39 received from the reception unit 32 in units of packets, and outputs them to the lower layer processing unit 14 as the transmission packet 22.

1-3. Rate maintenance unit 12
FIG. 5 illustrates a configuration example of the rate maintaining unit 12 of the communication device 1. The rate maintaining unit 12 includes a registration unit 40, a flow table 41, and a rewriting unit 42.

  The flow table 41 holds information used by the rate maintaining unit 12 to appropriately rewrite the ACK number of the TCP-ACK packet. FIG. 6 shows a configuration example of the flow table 41. The flow table 41 has a flow entry 50 for each flow with which the communication apparatus 1 is communicating. Each flow entry 50 includes a flow identifier 51, an expected ACK number 52, a reception flag 53, a reception ACK number 54, a transmission ACK number 55, and a duplicate ACK count 56.

  The flow identifier 51 is a flow identifier associated with the flow entry 50. The “flow identifier” is, for example, a part of the MAC layer destination / source address / VLAN tag, IP layer source / destination address, TCP layer source / destination port number, etc. included in the packet header Or everything.

  The expected ACK number 52 is the last ACK number of the TCP-ACK packet that the TCP / IP processing unit 11 expects to receive.

  The reception flag 53 is a flag indicating whether or not the rate maintaining unit 12 has received a TCP-ACK packet from the retransmission control unit 13. Regarding this flow, if the TCP-ACK packet has been received even once, the reception flag 53 becomes “true”, and if it has never been received, the reception flag 53 becomes “false”.

  The reception ACK number 54 is the ACK number of the TCP-ACK packet that the rate maintaining unit 12 received from the retransmission control unit 13 last time. If no TCP-ACK packet has been received for the flow, the reception ACK number 54 is indefinite.

  The transmission ACK number 55 is the ACK number of the latest TCP-ACK packet that has been transferred from the rate maintaining unit 12 to the TCP / IP processing unit 11. If no TCP-ACK packet has been transferred for the flow, the transmission ACK number 55 is indefinite.

  The duplicate ACK count 56 indicates the number of duplicate ACK packets that the rate maintaining unit 12 continuously receives from the retransmission control unit 13. That is, the duplicate ACK count 56 indicates the consecutive count when the ACK numbers of the TCP-ACK packets received from the retransmission control unit 13 continuously take the same value. When reception of the duplicate ACK packet is interrupted, the duplicate ACK count 56 is reset. For example, when the ACK numbers of the past three TCP-ACK packets 20 received from the retransmission control unit 13 by the rate maintaining unit 12 are 100, 200, and 200 in time series order, the duplicate ACK count 56 is 1. For example, when the ACK numbers of the past three TCP-ACK packets 20 are 300, 300, and 400 in time series order, the duplicate ACK count 56 becomes zero.

  Referring to FIG. 5 again, the registration unit 40 receives the TCP packet 20 transmitted from the TCP / IP processing unit 11. The registration unit 40 extracts the flow identifier 71 from the received TCP packet 20. In addition, the registration unit 40 calculates the expected ACK number 70 by adding the TCP sequence number of the received TCP packet 20 and the TCP data length. Further, the registration unit 40 searches the flow table 41 to check whether there is a flow entry 50 (hit entry) having the same flow identifier 51 as the extracted flow identifier 71.

  When the hit entry 50 does not exist in the flow table 41, the registration unit 40 creates a new flow entry 50 corresponding to the flow identifier 71 in the flow table 41. In the new flow entry 50, the flow identifier 51 and the expected ACK number 52 are set to the flow identifier 71 and the expected ACK number 70, respectively. The reception flag 53 is set to “false”. The reception ACK number 54, the transmission ACK number 55, and the duplicate ACK count 56 remain undefined.

  On the other hand, when the hit entry 50 exists in the flow table 41, the registration unit 40 compares the expected ACK number 52 and the expected ACK number 70 included in the hit entry 50. When the expected ACK number 70 is larger than the expected ACK number 52, the registration unit 40 updates the expected ACK number 52 of the hit entry 50 with the expected ACK number 70. The operation of the registration unit 40 will be described in detail later.

  The rewriting unit 42 receives the TCP packet 20 from the retransmission control unit 13. If the received TCP packet 20 is not a TCP-ACK packet, the rewrite unit 42 transfers the TCP packet 20 to the TCP / IP processing unit 11.

  On the other hand, when the received TCP packet 20 is a TCP-ACK packet, the rewriting unit 42 extracts the flow identifier 71 from the TCP-ACK packet 20. The rewriting unit 42 searches the flow table 41 and extracts a flow entry 50 (hit entry) having the same flow identifier 51 as the extracted flow identifier 71.

  Based on the contents of the hit entry 50, the rewrite unit 42 determines whether to execute “rewrite” of the ACK number of the received TCP-ACK packet 20. When “rewriting” is performed, the rewriting unit 42 rewrites the ACK number according to a predetermined calculation formula, and transfers the rewritten TCP-ACK packet 20 to the TCP / IP processing unit 11. On the other hand, when “rewriting” is not performed, the rewriting unit 42 transfers the received TCP-ACK packet 20 to the TCP / IP processing unit 11 as it is.

  The “rewriting” of the ACK number will be further described. According to the present embodiment, the rewriting unit 42 rewrites the ACK number so that the high-speed retransmission is not activated in the TCP / IP processing unit 11. Therefore, the rewriting unit 42 prevents the TCP-ACK packet 20 having the same ACK number from being continuously transferred to the TCP / IP processing unit 11, that is, no duplicate ACK packet is generated in the TCP / IP processing unit 11. Thus, the ACK number of the TCP-ACK packet 20 is rewritten. For example, the rewriting unit 42 performs rewriting so that the ACK number of the TCP-ACK packet 20 transferred to the TCP / IP processing unit 11 increases monotonously. More specifically, the rewriting unit 42 refers to the transmission ACK number of the hit entry 50 and performs rewriting so that the ACK number of the latest TCP-ACK packet 20 is larger than the transmission ACK number. However, the rewriting unit 42 performs rewriting so that the ACK number after rewriting does not exceed the ACK number before rewriting.

  The rewriting unit 42 refers to the received ACK number of the hit entry 50 and compares the ACK number of the received TCP-ACK packet 20 with the received ACK number 54. If the ACK number matches the received ACK number 54 (previous ACK number), the TCP-ACK packet 20 is a duplicate ACK packet. In this case, the rewriting unit 42 increments the duplicate ACK count 56 of the hit entry 50 by one. On the other hand, when the ACK number is larger than the received ACK number 54, the rewriting unit 42 resets (initializes) the duplicate ACK count 56 of the hit entry 50 to zero.

  Further, the rewriting unit 42 refers to the duplicate ACK count 56 and determines whether or not the duplicate ACK count 56 satisfies a predetermined high-speed retransmission condition. When the duplicate ACK count 56 satisfies a predetermined high-speed retransmission condition, the rewriting unit 42 extracts a packet identifier from the received TCP-ACK packet 20. Then, the rewrite unit 42 issues a retransmission instruction 21 including the extracted packet identifier to the retransmission control unit 13. That is, the rewriting unit 42 causes the retransmission control unit 13 to execute high-speed retransmission processing instead of the TCP / IP processing unit 11.

  When transferring the TCP-ACK packet 20 to the TCP / IP processing unit 11, the rewriting unit 42 appropriately updates the reception ACK number 54 and transmission ACK number 55 of the hit entry 50. The operation of the rewriting unit 42 will be described in detail later.

2. Processing flow 2-1. Processing of Registration Unit 40 FIG. 7 is a flowchart showing processing of the registration unit 40 of the rate maintaining unit 12.

  In step S <b> 100, the registration unit 40 waits for input of the TCP packet 20 from the TCP / IP processing unit 11.

  In step S <b> 101, the registration unit 40 calculates an expected ACK number 70 based on the input header information of the TCP packet 20. The expected ACK number 70 is the sum of the TCP sequence number of the TCP packet 20 and the TCP data length.

  In step S <b> 102, the registration unit 40 extracts the flow identifier 71 from the input TCP packet 20.

  In step S <b> 103, the registration unit 40 searches the flow table 41 and checks whether or not a flow entry 50 (hit entry) having the same flow identifier 51 as the extracted flow identifier 71 exists in the flow table 41.

  If the search for the hit entry 50 is successful (step S104; Yes), the process proceeds to step S106. On the other hand, when the search fails (step S104; No), the process proceeds to step S105.

  In step S105, the registration unit 40 creates a new flow entry 50 corresponding to the flow identifier 71 extracted in step S102 in the flow table 41. Here, the registration unit 40 initializes each field of the new flow entry 50 as follows. That is, the registration unit 40 initializes the flow identifier 51 to the flow identifier 71 extracted in step S102, the expected ACK number 52 to the expected ACK number 70 calculated in step S101, and the reception flag 53 to “false”. . It is not necessary to initialize the reception ACK number 54, the transmission ACK number 55, and the duplicate ACK count 56. Step S105 is one of the final steps.

  In step S106, the registration unit 40 compares the expected ACK number 52 of the hit entry 50 searched in step S103 with the expected ACK number 70 calculated in step S101. If the expected ACK number 70 is larger than the expected ACK number 52, the registration unit 40 updates the expected ACK number 52 of the hit entry 50 with the expected ACK number 70. Step S106 is one of the final steps.

2-2. Processing of Rewriting Unit 42 FIGS. 8A and 8B are flowcharts showing processing of the rewriting unit 42 of the rate maintaining unit 12.

  In step S <b> 200, the rewriting unit 42 waits for input of the TCP packet 20 from the retransmission control unit 13.

  In step S201, the rewriting unit 42 checks the ACK flag in the TCP header of the input TCP packet 20. If the ACK flag is set, the rewriting unit 42 determines that a valid ACK number is included in the TCP packet 20, and the process proceeds to step S202. On the other hand, if the ACK flag is not set, the process proceeds to step S221.

  In step S <b> 202, the rewriting unit 42 substitutes the ACK number in the TCP header of the input TCP packet 20 (TCP-ACK packet) into the original ACK number 72. Here, the original ACK number 72 is a temporary variable that is referred to and updated only in this flowchart.

  In step S <b> 203, the rewrite unit 42 extracts the flow identifier 71 from the input TCP packet 20.

  In step S204, the rewriting unit 42 searches the flow table 41, and whether or not a flow entry 50 (hit entry) having the same flow identifier 51 as the flow identifier 71 extracted in step S203 exists in the flow table 41. Check out.

  If the search for the hit entry 50 is successful (step S205; Yes), the process proceeds to step S206. On the other hand, if the search fails (step S205; No), the process proceeds to step S221.

  In step S <b> 206, the rewrite unit 42 acquires the expected ACK number 52, the reception flag 53, the reception ACK number 54, the transmission ACK number 55, and the duplicate ACK count 56 from the hit entry 50.

  In step S207, the rewriting unit 42 checks the acquired reception flag 53. If the reception flag 53 is “true”, the process proceeds to step S210. If the reception flag 53 is “false”, the process proceeds to step S208.

  In step S210, the rewriting unit 42 compares the original ACK number 72 with the expected ACK number 52 acquired in step S206. If the original ACK number 72 is greater than or equal to the expected ACK number 52 (step 210; Yes), the process proceeds to step S209. On the other hand, when the original ACK number 72 is smaller than the expected ACK number 52 (step 210; No), the process proceeds to step S211.

  In step S208, the rewriting unit 42 rewrites the reception flag 53 of the hit entry 50 to “true”.

  In step S209, the rewriting unit 42 substitutes the original ACK number 72 for both the reception ACK number 54 and the transmission ACK number 55 of the hit entry 50. The rewrite unit 42 resets the duplicate ACK count 56 of the hit entry 50 to zero. Thereafter, the process proceeds to step S221.

  In step S211, the rewriting unit 42 compares the original ACK number 72 with the reception ACK number 54 acquired in step S206. If the original ACK number 72 is greater than the received ACK number 54, the process proceeds to step S213. If the original ACK number 72 is equal to the received ACK number 54, the process proceeds to step S215. If the original ACK number 72 is smaller than the received ACK number 54, the process proceeds to step S221.

  In step S <b> 213, the rewriting unit 42 substitutes a new ACK number 73 for a value obtained by adding a predetermined positive number Δ (for example, 1) to the received ACK number 54 and the original ACK number 72. Here, the new ACK number 73 is a temporary variable that is referred to and updated only in this flowchart.

  In step S <b> 214, the rewriting unit 42 substitutes the original ACK number 72 for the reception ACK number 54 of the hit entry 50. Furthermore, the rewriting unit 42 resets the duplicate ACK count 56 of the hit entry 50 to zero. Thereafter, the process proceeds to step S219.

  In step S <b> 215, the rewriting unit 42 substitutes a new ACK number 73 for a value obtained by adding a predetermined positive number Δ (for example, 1) to the transmission ACK number 55 and the original ACK number 72.

  In step S216, the rewriting unit 42 increments the duplicate ACK count 56 of the hit entry 50 by one.

  In step S217, the rewriting unit 42 determines whether or not the number of duplicate ACKs 56 after step S216 satisfies a predetermined high-speed retransmission condition. Here, the fast retransmission condition is “the number of duplicate ACKs 56 is 5 or more”. If the duplicate ACK count 56 satisfies the fast retransmission condition (step S217; Yes), the process proceeds to step S218. On the other hand, if the duplicate ACK count 56 does not satisfy the fast retransmission condition (step S217; No), the process proceeds to step S219.

  In step S218, the rewriting unit 42 extracts a packet identifier from the TCP packet 20 input in step S200. Then, the rewriting unit 42 issues a retransmission instruction 21 including the packet identifier to the retransmission control unit 13. Thereafter, the process proceeds to step S219.

  In step S 219, the rewriting unit 42 substitutes the new ACK number 73 for the transmission ACK number 55 of the hit entry 50. That is, the rewriting unit 42 updates the transmission ACK number 55 of the hit entry 50.

  In step S220, the rewriting unit 42 substitutes the new ACK number 73 for the ACK number in the TCP header of the TCP packet 20 input in step S200. That is, the rewriting unit 42 performs “rewriting” of the ACK number. Thereafter, the process proceeds to step S221.

  In step S <b> 221, the rewriting unit 42 outputs the TCP packet 20 input in step S <b> 200 or the TCP-ACK packet 20 that has been “rewritten” in step S <b> 220 to the TCP / IP processing unit 11. Step S221 is the final step.

2-3. Processing Example Next, an example of processing according to the present embodiment will be described with reference to FIGS. 9 and 10.

  In FIG. 9, two communication apparatuses 1-1 and 1-2 are connected to each other via the network 2. The communication device 1-1 transmits TCP data, and the communication device 1-2 receives it. A solid arrow represents a TCP packet 20 including TCP data sent from the communication device 1-1 to the communication device 1-2. Each TCP packet 20 includes 100 bytes of TCP data and belongs to a single flow. A broken arrow represents the TCP-ACK packet 20 returned from the communication device 1-2 to the communication device 1-1. The number in the single circle attached to the solid line arrow indicates the sequence number of the TCP packet 20, and the number in the double circle attached to the broken line arrow indicates the TCP ACK number of the TCP-ACK packet 20. Indicates. For simplicity, transmission / reception of the lower layer ACK packet 39 is not shown. In this example, delayed ACK is not considered. These simplifications do not lose generality.

  FIG. 10 shows the contents of the flow entry 50 of the flow table 41 of the communication apparatus 1-1 at times T1 to T14 in the sequence diagram of FIG.

  The TCP / IP processing unit 11 of the communication device 1-1 continuously sends six TCP packets 20 to the communication device 1-2 (in time series order, times T1, T2, T3, T5, T6, T7). ). Here, it is assumed that the TCP packet 20 with the sequence number “300” sent at time T 3 is discarded in the network 2. The retransmission control unit 13 of the communication apparatus 1-1 transmits the TCP packet 20 (sequence number “300”) at time T4, and the TCP packet 20 (sequence number “300”) at time T8 after the retransmission timeout has elapsed. resend.

  Focus on the flow table 41 of the communication device 1-1. At time T1, no TCP packet 20 has yet arrived at the rate maintaining unit 12 of the communication device 1-1. Therefore, the content of the flow table 41 is empty and there is no valid flow entry 50.

  From time T1 to time T2, a TCP packet 20 having a length of 100 bytes and having a TCP sequence number “100” is input to the registration unit 40 of the rate maintaining unit 12 of the communication apparatus 1-1. In step S101, the expected ACK number 70 is calculated as “200 (= 100 + 100)”. In step S102, the flow identifier 71 is “flow A”. At this time, the flow table 41 is empty, and the flow entry 50 corresponding to “flow A” does not exist (step S104; No). Accordingly, a new flow entry 50 is added to the flow table 41 in step S105. As a result, the content of the flow table 41 changes to the content of the row at time T2 in FIG.

  From time T2 to time T3, a TCP packet 20 having a length of 100 bytes and having a TCP sequence number “200” is input to the registration unit 40 of the rate maintaining unit 12 of the communication device 1-1. In step S101, the expected ACK number 70 is calculated as “300 (= 200 + 100)”. In step S102, the flow identifier 71 is “flow A”. At this time, the flow entry 50 (hit entry) corresponding to “flow A” already exists in the flow table 41 (step S104; Yes). Accordingly, in step S106, the expected ACK number 52 of the hit entry 50 is updated from 200 to 300.

  The registration unit 40 of the rate maintaining unit 12 of the communication device 1-1 is the same as the above also during the time T3 to T4, the time T5 to T6, the time T6 to T7, and the time T7 to T8. To work.

  Thereafter, from time T9 to T13, five TCP-ACK packets 20 responding to the five TCP packets 20 that have not been discarded arrive at the communication device 1-1 in order. The ACK numbers of these five TCP-ACK packets 20 are 200, 300, 300, 300, and 300 in the order of arrival. The reason why the TCP-ACK packet 20 with the ACK number “300” continues is that the TCP / IP processing unit 11 of the communication device 1-2 does not accept the TCP packet 20 with the sequence number “300”.

  Again, pay attention to the flow table 41 of the communication device 1-1. From time T8 to T9, the TCP-ACK packet 20 with the ACK number “200” is input to the rewriting unit 42 of the rate maintaining unit 12 of the communication device 1-1. In step S202, the original ACK number 72 becomes “200”. In step S203, the flow identifier 71 is “flow A”. At this time, the flow entry 50 (hit entry) corresponding to “flow A” already exists in the flow table 41 (step S205; Yes). At this time, the reception flag 53 of the hit entry 50 is “false”. Therefore, step S208 and step S209 are performed, and as a result, the content of the flow table 41 changes to the content of the row at time T9 in FIG. The ACK number is not rewritten this time, and the TCP-ACK packet 20 with the ACK number “200” is transferred to the TCP / IP processing unit 11 as it is in step S221.

  From time T9 to T10, the TCP-ACK packet 20 whose ACK number is “300” is input to the rewriting unit 42 of the rate maintaining unit 12 of the communication device 1-1. In step S202, the original ACK number 72 is “300”. In step S203, the flow identifier 71 is “flow A”. At this time, the flow entry 50 (hit entry) corresponding to “flow A” already exists in the flow table 41 (step S205; Yes). Further, since the reception flag 53 of the hit entry 50 is “true”, the process proceeds to step S210. Since the original ACK number 72 = “300” is smaller than the expected ACK number 52 = “700” (step S210; No), the process proceeds to step S211. In step S211, the original ACK number 72 = "300" is larger than the received ACK number 54 = "200". Therefore, step S213 is performed, and the new ACK number 73 becomes “201 = (received ACK number 54+“ 1 ”)”. Thereafter, steps S214 and S219 are executed. As a result, the reception ACK number 54 is “300” and the transmission ACK number 55 is updated to “201”. That is, the transmission ACK number 55 is updated to a value that is larger than the transmission ACK number 55 = “200” before update and does not exceed the original ACK number 72 = “300”. In step S220, the ACK number of the TCP-ACK packet 20 is rewritten from “300” to “201”. In step S 221, the TCP-ACK packet 20 whose ACK number is “201” is transferred to the TCP / IP processing unit 11.

  From time T10 to T11, the TCP-ACK packet 20 whose ACK number is “300” is input to the rewriting unit 42 of the rate maintaining unit 12 of the communication device 1-1. Since the processing up to immediately before step S211 is the same as the previous processing, the description thereof is omitted. In step S211, the original ACK number 72 = "300" is the same as the received ACK number 54 = "300". Therefore, step S215 is performed, and the new ACK number 73 becomes “202 = (transmission ACK number 55+“ 1 ”)”. In step S216, the duplicate ACK count 56 of the hit entry 50 is incremented and changes from “0” to “1”. In this example, it is assumed that the fast retransmission condition is “the number of duplicate ACKs 56 is 5 or more”. In this case, since the duplicate ACK count 56 does not satisfy the high-speed retransmission condition (step S217; No), the process proceeds to step S219. As a result, the transmission ACK number 55 is updated to “202”. That is, the transmission ACK number 55 is updated to a value that is larger than the transmission ACK number 55 = “201” before update and does not exceed the original ACK number 72 = “300”. In step S220, the ACK number of the TCP-ACK packet 20 is rewritten from “300” to “202”. In step S 221, the TCP-ACK packet 20 with the ACK number “202” is transferred to the TCP / IP processing unit 11.

  The TCP-ACK packet 20 whose ACK number is “300” is input to the rewrite unit 42 of the rate maintaining unit 12 of the communication device 1-1 also between the time T11 and T12 and between the time T12 and T13. . Since the operation at this time is the same as the previous operation, the description is omitted.

  From time T13 to T14, the TCP-ACK packet 20 whose ACK number is “700” is input to the rewriting unit 42 of the rate maintaining unit 12 of the communication device 1-1. This TCP-ACK packet 20 responds to the TCP packet 20 retransmitted by the retransmission control unit 13 at time T8. In step S202, the original ACK number 72 becomes “700”. Steps S203 to S207 are the same as the previous time. In step S210, the original ACK number 72 = "700" is greater than or equal to the expected ACK number 52 = "700" (step S210; Yes). Accordingly, step S209 is performed, and the content of the flow table 41 changes to the content of the row at time T14 in FIG. The ACK number is not rewritten this time, and the TCP-ACK packet 20 with the ACK number “700” is transferred to the TCP / IP processing unit 11 as it is in step S221.

  In summary, the ACK numbers of the TCP-ACK packet 20 received by the TCP / IP processing unit 11 of the communication device 1-1 via the rate maintaining unit 12 are 200, 201, 202, 203, 204 in chronological order. , 700. Since the same ACK number is not consecutive, it is possible to prevent the TCP / IP processing unit 11 from starting high-speed retransmission.

3. Effect As described above, according to the present embodiment, even if a duplicate ACK packet is input to the communication device 1, the rate maintaining unit 12 of the communication device 1 does not have the same ACK number consecutively. As described above, “rewriting” is performed, and the rewritten TCP-ACK packet is transferred to the TCP / IP processing unit 11. Therefore, the TCP / IP processing unit 11 does not detect the arrival of duplicate ACK packets. In other words, the packet loss is concealed from the upper layer TCP / IP processing unit 11. As a result, unnecessary high-speed retransmission by the TCP / IP processing unit 11 is prevented and the congestion window is not reduced. Therefore, it is possible to prevent situations such as network bandwidth pressure, TCP throughput decrease, and communication efficiency decrease.

  Further, the “rewriting” of the ACK number by the rate maintaining unit 12 is performed so that the TCP does not malfunction. Specifically, the ACK number after rewriting (new ACK number 73) does not exceed the ACK number before rewriting (original ACK number 72). Further, the ACK number (new ACK number 73) increases monotonously in a narrow sense. When these conditions are not satisfied, the rate maintaining unit 12 does not “rewrite” the ACK number for safety.

  Furthermore, when the original ACK number 72 (ACK number of the received TCP-ACK packet 20) is equal to or higher than the expected ACK number 52 (step S210; Yes), the rate maintaining unit 12 does not perform “rewriting” of the ACK number. The reason is as follows. If “rewriting” is performed even when the original ACK number 72 is the same as the expected ACK number 52, the ACK number after rewriting (new ACK number 73) may be smaller than the expected ACK number 52. Then, the TCP / IP processing unit 11 cannot receive the TCP-ACK packet 20 with the expected ACK number and cannot complete the TCP communication. Therefore, the expected ACK number 70 is calculated in advance by the registration unit 40 of the rate maintaining unit 12, and the expected ACK number 70 is recorded in the flow table 41.

4). Hardware Configuration The communication device 1 according to the present embodiment is applicable to an information processing device such as a PC (Personal Computer). FIG. 11 shows a configuration when the communication device 1 is applied to an information processing device. As illustrated in FIG. 11, the communication device 1 (information processing device) includes a data processing device 200 and a storage device 201.

  Examples of the storage device 201 include a RAM (Random Access Memory) and an HDD (Hard Disk Drive). The storage device 201 stores a retransmission buffer 31, a flow table 41, work memories 202, 203, 204, and the like.

  The data processing device 200 includes a CPU (Central Processing Unit). The data processing device 200 includes an application processing unit 210, a TCP / IP processing unit 211, a rate maintaining unit 212, a retransmission control unit 213, and a lower layer processing unit 214. The application processing unit 210, the TCP / IP processing unit 211, and the lower layer processing unit 214 are the same as the application processing unit 10, the TCP / IP processing unit 11, and the lower layer processing unit 14, respectively. However, the application processing unit 210, the TCP / IP processing unit 211, and the lower layer processing unit 214 use the work memories 202, 203, and 204 in the storage device 201 as storage areas necessary for operation. The rate maintaining unit 212 is the same as the rate maintaining unit 12 described above except that the flow table 41 in the storage device 201 is used. The retransmission control unit 213 is the same as the retransmission control unit 13 described above except that the retransmission buffer 31 in the storage device 201 is used.

  Note that these functional blocks included in the data processing device 200 are realized by the data processing device 200 executing a packet retransmission control program. The packet retransmission control program is a computer program executed by the data processing device 200 and is stored in the storage device 201. The packet retransmission control program may be recorded on a computer-readable recording medium.

  The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the above-described embodiments, and can be appropriately changed by those skilled in the art without departing from the scope of the invention.

  A part or all of the above-described embodiment can be described as in the following supplementary notes, but is not limited thereto.

(Appendix 1)
A TCP / IP processing unit for performing TCP / IP processing;
A retransmission control unit that performs packet retransmission control in a layer lower than the TCP layer;
A rate maintaining unit that transfers a TCP packet received from the retransmission control unit to the TCP / IP processing unit, and
The retransmission control unit transmits a TCP packet transmitted from the TCP / IP processing unit as a transmission packet to a transmission destination, receives a TCP-ACK packet responding to the transmission packet from the transmission destination, and receives the received TCP- Transfer ACK packet to the rate maintaining unit,
The rate maintaining unit rewrites the ACK number of the TCP-ACK packet received from the retransmission control unit so that TCP-ACK packets having the same ACK number are not continuously transferred to the TCP / IP processing unit. A communication device that transfers the rewritten TCP-ACK packet to the TCP / IP processing unit.

(Appendix 2)
The communication device according to attachment 1, wherein
The rate maintaining unit performs the rewriting so that the ACK number of a TCP-ACK packet transferred to the TCP / IP processing unit monotonously increases.

(Appendix 3)
The communication device according to attachment 2, wherein
The rate maintaining unit includes a flow table having a flow entry for each flow,
The flow entry includes a transmission ACK number that is the ACK number of the latest TCP-ACK packet that has been transferred to the TCP / IP processing unit,
When a new TCP-ACK packet is received from the retransmission control unit, the rate maintaining unit refers to the transmission ACK number of the flow entry in the flow table, and the ACK number of the new TCP-ACK packet. A communication device that performs the rewriting so that becomes larger than the transmission ACK number, and further updates the transmission ACK number.

(Appendix 4)
The communication device according to attachment 3, wherein
The communication apparatus according to claim 1, wherein the rate maintaining unit rewrites the new TCP-ACK packet so that the ACK number after the rewriting does not exceed the ACK number before the rewriting.

(Appendix 5)
The communication device according to appendix 4, wherein
The flow entry further includes an expected ACK number that is the ACK number of a TCP-ACK packet expected to be received later,
The rate maintaining unit updates the expected ACK number of the corresponding flow entry in the flow table based on the TCP packet transmitted from the TCP / IP processing unit,
When the new TCP-ACK packet is received from the retransmission control unit, the rate maintaining unit refers to the expected ACK number of the corresponding flow entry in the flow table,
The communication apparatus according to claim 1, wherein when the ACK number of the new TCP-ACK packet is greater than or equal to the expected ACK number, the rate maintaining unit does not perform the rewriting.

(Appendix 6)
The communication device according to any one of appendices 1 to 5,
The rate maintaining unit includes a flow table having a flow entry for each flow,
The flow entry is
A reception ACK number that is the ACK number of the TCP-ACK packet received last time from the retransmission control unit;
Including the number of duplicate ACKs and
When a new TCP-ACK packet is received from the retransmission control unit, the rate maintaining unit refers to the reception ACK number of the corresponding flow entry in the flow table,
If the ACK number of the new TCP-ACK packet is greater than the received ACK number, the rate maintaining unit initializes the number of duplicate ACKs of the corresponding flow entry in the flow table,
When the ACK number of the new TCP-ACK packet is the same as the received ACK number, the rate maintaining unit increments the number of duplicate ACKs of the corresponding flow entry in the flow table,
When the number of duplicate ACKs satisfies a predetermined condition, the rate maintaining unit instructs the retransmission control unit to retransmit the transmission packet corresponding to the ACK number.

(Appendix 7)
A packet retransmission control method in a communication device,
With respect to a TCP packet transmitted from the TCP layer, performing packet retransmission control in a lower layer lower than the TCP layer;
Receiving a TCP-ACK packet in response to the TCP packet from a destination of the TCP packet;
Transferring the received TCP-ACK packet from the lower layer to the TCP layer,
The transferring step includes:
Rewriting the ACK number of the received TCP-ACK packet so that TCP-ACK packets having the same ACK number are not continuously transferred to the TCP layer;
Transferring the rewritten TCP-ACK packet to the TCP layer; and a packet retransmission control method.

(Appendix 8)
A packet retransmission control program for causing a computer to implement a packet retransmission control function,
The packet retransmission control function is:
TCP / IP processing function for performing TCP / IP processing;
A retransmission control function for performing packet retransmission control in a layer lower than the TCP layer;
A rate maintaining function for transferring a TCP packet received from the retransmission control function to the TCP / IP processing function;
The retransmission control function transmits a TCP packet transmitted from the TCP / IP processing function to a transmission destination as a transmission packet, receives a TCP-ACK packet responding to the transmission packet from the transmission destination, and receives the received TCP- Transfer ACK packet to the rate maintenance function,
The rate maintaining function rewrites the ACK number of the TCP-ACK packet received from the retransmission control function so that TCP-ACK packets having the same ACK number are not continuously transferred to the TCP / IP processing function. A packet retransmission control program for transferring the rewritten TCP-ACK packet to the TCP / IP processing function.

  This application claims the priority on the basis of the Japan patent application 2011-003894 for which it applied on January 12, 2011, and takes in those the indications of all here.

DESCRIPTION OF SYMBOLS 1 Communication apparatus 2 Network 10 Application processing part 11 TCP / IP processing part 12 Rate maintenance part 13 Retransmission control part 14 Lower layer processing part 20 TCP packet 21 Retransmission instruction 22 Transmission packet 23 Reception packet 30 Transmission part 31 Retransmission buffer 32 Reception part 33 Multiplexing part 39 Lower layer ACK packet 40 Registration part 41 Flow table 42 Rewriting part 50 Flow entry 51 Flow identifier 52 Expected ACK number 53 Reception flag 54 Reception ACK number 55 Transmission ACK number 56 Number of duplicate ACKs 61 Queue entry 62 TCP packet 63 Time stamp 70 Expected ACK number 71 Flow identifier 72 Original ACK number 73 New ACK number 200 Data processing device 201 Storage device 202 Work memory 203 Work memory 204 Word Memory 210 application processing unit 211 TCP / IP processing section 212 rate holding section 213 retransmission control unit 214 lower layer processing unit

Claims (8)

A TCP / IP processing unit for performing TCP / IP processing;
A retransmission control unit that performs packet retransmission control in a layer lower than the TCP layer;
A rate maintaining unit that transfers a TCP packet received from the retransmission control unit to the TCP / IP processing unit, and
The retransmission control unit transmits a TCP packet transmitted from the TCP / IP processing unit as a transmission packet to a transmission destination, receives a TCP-ACK packet responding to the transmission packet from the transmission destination, and receives the received TCP- Transfer ACK packet to the rate maintaining unit,
The rate maintaining unit rewrites the ACK number of the TCP-ACK packet received from the retransmission control unit so that TCP-ACK packets having the same ACK number are not continuously transferred to the TCP / IP processing unit. A communication device that transfers the rewritten TCP-ACK packet to the TCP / IP processing unit. The communication device according to claim 1,
The rate maintaining unit performs the rewriting so that the ACK number of a TCP-ACK packet transferred to the TCP / IP processing unit monotonously increases. The communication device according to claim 2,
The rate maintaining unit includes a flow table having a flow entry for each flow,
The flow entry includes a transmission ACK number that is the ACK number of the latest TCP-ACK packet that has been transferred to the TCP / IP processing unit,
When a new TCP-ACK packet is received from the retransmission control unit, the rate maintaining unit refers to the transmission ACK number of the flow entry in the flow table, and the ACK number of the new TCP-ACK packet. A communication device that performs the rewriting so that becomes larger than the transmission ACK number, and further updates the transmission ACK number. The communication device according to claim 3,
The communication apparatus according to claim 1, wherein the rate maintaining unit rewrites the new TCP-ACK packet so that the ACK number after the rewriting does not exceed the ACK number before the rewriting. The communication device according to claim 4,
The flow entry further includes an expected ACK number that is the ACK number of a TCP-ACK packet expected to be received later,
The rate maintaining unit updates the expected ACK number of the corresponding flow entry in the flow table based on the TCP packet transmitted from the TCP / IP processing unit,
When the new TCP-ACK packet is received from the retransmission control unit, the rate maintaining unit refers to the expected ACK number of the corresponding flow entry in the flow table,
The communication apparatus according to claim 1, wherein when the ACK number of the new TCP-ACK packet is greater than or equal to the expected ACK number, the rate maintaining unit does not perform the rewriting. The communication device according to any one of claims 1 to 5,
The rate maintaining unit includes a flow table having a flow entry for each flow,
The flow entry is
A reception ACK number that is the ACK number of the TCP-ACK packet received last time from the retransmission control unit;
Including the number of duplicate ACKs and
When a new TCP-ACK packet is received from the retransmission control unit, the rate maintaining unit refers to the reception ACK number of the corresponding flow entry in the flow table,
If the ACK number of the new TCP-ACK packet is greater than the received ACK number, the rate maintaining unit initializes the number of duplicate ACKs of the corresponding flow entry in the flow table,
When the ACK number of the new TCP-ACK packet is the same as the received ACK number, the rate maintaining unit increments the number of duplicate ACKs of the corresponding flow entry in the flow table,
When the number of duplicate ACKs satisfies a predetermined condition, the rate maintaining unit instructs the retransmission control unit to retransmit the transmission packet corresponding to the ACK number. A packet retransmission control method in a communication device,
With respect to a TCP packet transmitted from the TCP layer, performing packet retransmission control in a lower layer lower than the TCP layer;
Receiving a TCP-ACK packet in response to the TCP packet from a destination of the TCP packet;
Transferring the received TCP-ACK packet from the lower layer to the TCP layer,
The transferring step includes:
Rewriting the ACK number of the received TCP-ACK packet so that TCP-ACK packets having the same ACK number are not continuously transferred to the TCP layer;
Transferring the rewritten TCP-ACK packet to the TCP layer; and a packet retransmission control method. A packet retransmission control program for causing a computer to implement a packet retransmission control function,
The packet retransmission control function is:
TCP / IP processing function for performing TCP / IP processing;
A retransmission control function for performing packet retransmission control in a layer lower than the TCP layer;
A rate maintaining function for transferring a TCP packet received from the retransmission control function to the TCP / IP processing function;
The retransmission control function transmits a TCP packet transmitted from the TCP / IP processing function to a transmission destination as a transmission packet, receives a TCP-ACK packet responding to the transmission packet from the transmission destination, and receives the received TCP- Transfer ACK packet to the rate maintenance function,
The rate maintaining function rewrites the ACK number of the TCP-ACK packet received from the retransmission control function so that TCP-ACK packets having the same ACK number are not continuously transferred to the TCP / IP processing function. A packet retransmission control program for transferring the rewritten TCP-ACK packet to the TCP / IP processing function.

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