JP6688122B2 - Communication device and control method thereof - Google Patents

Description

  The present invention relates to a communication control technique in packet communication that uses an acknowledgment.

  In order to guarantee the reliability of communication in data communication, conventionally, there is a method of transmitting an acknowledgment called ACK (ACKnowledgement) from a receiving side to a transmitting side when receiving packetized data. This allows the transmitting side to know that the receiving side has received the data normally. For example, as shown in Patent Document 1, in TCP (Transmission Control Protocol) widely used in Internet communication, packets are managed in octet units by sequence numbers. Then, the sequence number of the received packet is returned as an ACK packet.

  Further, in the TCP ACK packet, the free space of the reception buffer is notified as the window size, and the transmitting side can continuously transmit the data up to the notified window size without receiving the ACK packet. After transmitting the data up to the window size, the transmitting side does not transmit the data until receiving the ACK packet from the receiving side and notifying the new window size.

JP-A-2000-22744

  However, in a communication method using a confirmation response such as TCP, the next data may not be transmitted depending on the communication situation. For example, if the transmitting side transmits data without receiving an ACK until the receiving buffer on the receiving side is filled, the next data cannot be transmitted. That is, the transmission of the next data by the transmission side is also delayed due to the delay in the generation and transmission of the ACK on the reception side. As a result, the data transfer rate between the transmitting side and the receiving side becomes slow.

  The present invention has been made in view of the above problems, and an object of the present invention is to improve the data transfer rate in communication using confirmation responses.

In order to solve the above problems, the communication device according to the present invention has the following configuration. That is, in a communication device, a generation unit that generates an acknowledgment packet for a data packet transmitted from another communication device, a reception unit that performs a reception process for a data packet received from the other communication device, and the data packet And a transmitting means for transmitting an acknowledgment packet corresponding to the data packet generated by the generating means when the receiving means receives the data packet, and the generating means has a lower priority than the receiving process by the receiving means. As a task, the process of generating an acknowledgment packet for at least a part of the data packets is started prior to the reception of the data packets.

  According to the present invention, it is possible to provide a technique capable of improving the data transfer rate in the communication using the confirmation response.

It is a figure explaining the structure of the TCP / IP stack which concerns on 1st Embodiment. It is a block diagram which shows the structure of a communication apparatus. 6 is an operation flowchart of ACK packet generation in the first embodiment. It is a figure which shows the example of the priority of a task. It is a figure which shows the structure of a TCP connection management mechanism. It is a figure which shows the transmission position and structure of an ACK packet with respect to a received packet. 6 is an operation flowchart of ACK packet transmission in the first embodiment. It is a figure explaining the effect in TCP communication which concerns on 1st Embodiment. It is a figure which shows the structure of various packets. 7 is an operation flowchart of ACK packet generation in the second embodiment. 9 is an operation flowchart of ACK packet generation in the third embodiment. It is an operation | movement flowchart of ACK packet transmission in 3rd Embodiment. It is a figure which shows the transmission position of the ACK packet with respect to the received packet in 4th Embodiment. 20 is an operation flowchart of ACK packet transmission in Modification 1 of the fourth embodiment. 20 is an operation flowchart of ACK packet transmission in Modification 2 of the fourth embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Note that the following embodiments are merely examples, and are not intended to limit the scope of the present invention.

(First embodiment)
As a first embodiment of the communication device according to the present invention, a communication device that performs TCP / IP communication will be described as an example and described below. In particular, prior to the reception of the data packet coming from the opposite device, the process of generating the confirmation response packet (ACK packet) for the data reception is started, and the ACK packet can be transmitted in a shorter period when the data packet is received. The form will be described.

<Device configuration>
FIG. 1 is a diagram illustrating the configuration of the TCP / IP stack according to the first embodiment. FIG. 2 is a block diagram showing the configuration of the communication device 212 equipped with the TCP / IP stack shown in FIG.

  The communication device 212 has a CPU 202, a DRAM 203 that is a work memory, and a ROM 209 that stores programs executed by the CPU 202. Further, the communication device 212 has a LAN module 204 for performing communication via the network 210 such as the Ethernet (registered trademark) standard.

  The ACK generation processing task 110 is a task that generates an ACK packet that is an acknowledgment of the received data. The applications that make up the application task 101 are communication applications that send and receive data. In the first embodiment, the TCP / IP transmission process is performed by the application task 101.

  The reception buffer 102 is a reception buffer for the above-mentioned communication application, and the data received by the reception processing task 103 via the reception queue 104 is copied. The reading of the received data by the above-described communication application is performed via the reception buffer 102. The reception queue 104 is a queue into which the packet received by the LAN driver 106 is inserted. The reception queue 104 is configured in the DRAM 203, for example.

  The transmission queue 105 is a queue into which the TCP / IP packet generated by the TCP / IP transmission process of the application task 101 is inserted. The transmission queue 105 is configured in the DRAM 203, for example.

  The LAN driver 106 is a functional unit that controls the LAN module 204 and transmits / receives a packet via the LAN 210 conforming to the Ethernet (registered trademark) standard or the like. The ACK packet buffer 107 is a buffer for filling the generated ACK packet, and is configured in the DRAM 203. The TCP connection management mechanism 108 is a functional unit that manages TCP connections and is configured in the DRAM 203.

<Device operation>
FIG. 5 is a diagram showing the structure of the TCP connection management mechanism 108. The TCP connection management mechanism 108 includes a TCP connection management structure 401, an ACK packet management structure 402 for managing the generated ACK packet, and a TCP connection structure head 403 holding the head of the TCP management connection structure. The TCP connection management structure 401 is linked from the TCP connection management structure head 403. The next (successive) TCP connection management structure 401 is linked by the "next TCP connection" pointer.

  FIG. 3 is an operation flowchart of ACK packet generation in the first embodiment.

  In S302, the CPU 202 waits for an event of task execution, and when an event is derived, the process proceeds to S303. In S303, the CPU 202 extracts the "next TCP connection" from the TCP connection management structure head 403. In S304, the CPU 202 determines whether or not the next TCP connection exists. If there is no TCP connection (that is, if the value of "next TCP connection" of the TCP connection management structure 401 is NULL), the process returns to the event wait (S302). If there is a TCP connection (that is, "next TCP connection" of the TCP connection management structure 401 is not NULL), the process proceeds to S305.

  In S305, the CPU 202 extracts the generated confirmation response number (generated ACK number) from the TCP connection management structure 401. In S306, the CPU 202 obtains the maximum value of the ACK number to be generated from the reception buffer size and the generated ACK number. By setting the maximum value of the ACK number to be generated, it is possible to prevent the ACK packet from being generated indefinitely. The maximum value of the ACK number to be generated can be calculated as follows based on the window size on the receiving side, for example.

Maximum value of ACK number to be generated = Received sequence number + Reception side window size−Generated ACK number In S307, the CPU 202 compares the generated ACK number with the maximum value of the ACK number to be generated. If the generated ACK number is smaller than the maximum value of the planned ACK number, the process proceeds to S308, and if the generated ACK number is equal to or larger than the maximum value of the planned ACK number, the process proceeds to S310.

  In S308, the CPU 202 generates an ACK packet and updates the generated ACK number. However, when the corresponding data packet has not been received, the sequence number and window size are unknown parameters in the generation of the ACK packet. When the data is sent as the sequence number, the window size depends on the read timing of the application using TCP. Therefore, when the ACK packet is generated, "0" is put in the sequence number and the window size, the checksum is calculated, and the checksum is substituted for the checksum of the ACK packet. Then, when transmitting the ACK packet, the confirmed sequence number and window size are substituted so that the sequence number and window size are added to the checksum. Generation of the ACK packet and updating of the ACK number will be further described with reference to FIG.

  FIG. 6 is a diagram showing a transmission position (timing) and a structure of an ACK packet with respect to a received packet. In TCP, it is recommended that one ACK packet be transmitted when data of a size larger than the maximum segment size (MSS) is received, that is, when two packets are received. . Therefore, in FIG. 6, the generated ACK number is obtained by adding (MSS × 2) to the generated ACK number.

  A packet 501 indicated by a dotted-line rectangle represents a predicted packet that arrives (that is, a packet that has not been received at this time). The packet 501 also describes the “sequence number start position” and the “TCP data size” of the packet. For example, in the packet 501, “2” is the sequence number and “1460” is the TCP MSS size (data size in the packet).

  A timing 502 indicated by a triangle mark indicates a temporal position at which the ACK packet is transmitted. Here, as described above, an example is shown in which the second packet is received and then transmitted. The ACK packet 503 shows an example of the structure of the generated ACK packet. In FIG. 6, since the initial value of the sequence number of the packet including the data to be received is “2” and the MSS size × 2 = 2920, the ACK numbers of the generated ACK packets are “2922” and “5842”, respectively. , "8762".

  In S309, the CPU 202 queues the generated ACK packet at the end of the generated ACK packet management queue of the ACK packet management structure.

  In S310, the CPU 202 does not need to generate any more ACK packet for the TCP connection currently being focused on, so the CPU 202 extracts the next TCP connection management structure 401.

  The event waiting (S302) is released when the application reads data, receives a TCP-SYN packet, or transmits a TCP-SYN packet. It is also performed when a TCP data packet is received, when a TCP data packet is transmitted, and when a TCP connection is disconnected.

  FIG. 4 is a diagram showing an example of the priority order of ACK packet generation (FIG. 3). FIG. 4A shows the priority order of the tasks when the ACK packet is generated by the idle task. The higher the task is, the higher the priority is, and the lower the task is, the lower the priority is. The idle task is a task that is executed in the device built-in OS in the idle state where there is no other process to be executed and does not perform any process. In (a), by incorporating an ACK generation process here, it can be executed when there is no process to be performed, that is, when there is no other task to be processed in the CPU.

  Further, FIG. 4B shows the priority order of tasks when a dedicated task for generating an ACK packet is provided. (B) shows a case where a task dedicated to ACK generation is provided as a task having a slightly higher priority than the idle task. Further, (c) shows a case where an independent ACK generation processing task is provided for each application task. Even with this configuration, the idle task can be executed in a state immediately before execution, that is, when the CPU has no other task to process.

  When the network processing is prioritized over the processing other than the network, the priority of the ACK generation task may be set higher than the priority of the processing other than the network. Further, it may be configured to be performed before the TCP communication is started, such as immediately after receiving the TCP connection request or after completing the TCP connection.

  FIG. 7 is an operation flowchart of ACK packet transmission in the first embodiment. This operation waits for the reception of the TCP packet, and is triggered by the reception of the TCP packet in S601.

  In S601, the CPU 202 receives a TCP packet. In S602, the CPU 202 searches the TCP connection management structure corresponding to the received TCP packet from the destination address, the destination port number, the source address, the source port number, etc. of the TCP packet. Here, as a result of the search, the TCP connection management structure 401 is specified.

  In S603, the CPU 202 determines whether or not the TCP connection management structure corresponding to the received TCP packet exists. If it exists, the process proceeds to S604, and if it does not exist, the process proceeds to S613. In S613, the CPU 202 transmits a TCP_Reset (TCP-RST) packet, and then proceeds to S618 and ends the processing.

  In S604, the CPU 202 performs TCP reception processing such as queuing the data of the received packet in the TCP connection management structure corresponding to the received packet and controlling the order of the received data.

  In S605, the CPU 202 determines whether to send an ACK for the received data. If no ACK is sent, the process advances to step S618 to end the process. When transmitting an ACK, in S606, the CPU 202 checks the ACK packet of the TCP connection management structure, and in S607, the CPU 202 determines whether or not there is a generated ACK packet. If there is no generated ACK packet, in S614, an ACK packet corresponding to the received data is generated and transmitted, and then the process proceeds to S618 and ends the processing. If there is a generated ACK packet, the process proceeds to S608.

  In S608 and S609, the CPU 202 compares “the sum of the sequence number and the data size in the received packet (that is, the ACK number to respond)” with the “ACK number of the generated ACK packet”. If the ACK number of the generated ACK packet is larger than the ACK number to be responded to, the process proceeds to S614 and a new ACK packet is generated and transmitted. On the other hand, if the ACK number of the generated ACK packet and the ACK number to be responded are the same, the process proceeds to S615, and if the ACK number of the generated ACK packet is smaller than the ACK number to be responded, the process proceeds to S610.

  In S615, the CPU 202 adjusts the generated ACK packet. Specifically, the sequence number and the reception buffer remaining amount are substituted into the ACK packet from the TCP connection management structure. Then, those values are added to the checksum. After that, in S616, the CPU 202 transmits the adjusted generated ACK packet. In S617, after the transmitted ACK packet is made free, that is, the ACK packet currently focused on is discarded, and the process proceeds to S618 and ends the process.

  In S610, the CPU 202 checks whether there is a next generated ACK packet. If there is the next generated ACK packet, the process proceeds to S611. On the other hand, if there is no next generated ACK packet, the process advances to step S615 to adjust and transmit the currently generated generated ACK packet.

  In step S <b> 611, the CPU 202 compares “the sum of the sequence number and the data size in the received packet (that is, the ACK number to respond)” with the “ACK number of the next generated ACK packet”. If the next ACK number is smaller, the process proceeds to S612, the current generated ACK packet is freed, the next generated ACK is set as the current generated ACK, and the process returns to S609. On the other hand, if the next ACK number is larger, the next generated ACK packet is for data that has not been received, and thus the processing proceeds to step S615 to adjust the currently generated generated ACK packet. Send.

<IP header generation in ACK packet>
Various processes included in the ACK packet generation process (S308) will be described with reference to FIGS. 5 and 9. 9A shows the structure of the TCP ACK packet, and FIG. 9B shows the structure of the TCP header and the virtual header.

  The TCP ACK packet is composed of an IP header (20 bytes) and a TCP header (20 bytes). By transmitting this packet, the sender is notified that TCP data has been received. The virtual header and the TCP header are used to calculate the TCP checksum.

  First, the TCP connection management structure 401 is referenced, the source IP address and the destination IP address are checked, and the source IP address and the destination IP address of the virtual header are substituted. Substitute “0x00” for Zero of the virtual header, “0x06” indicating TCP for the protocol number, and “20” that is the TCP header length for the TCP length.

  Further, the TCP connection management structure 401 is referred to, the source port number and the destination port number are checked, and the source port number and the destination port number of the TCP header are copied. Further, referring to the TCP connection management structure 401, the transmitted sequence number and the received sequence number are checked, and each is substituted for the transmitted number of the TCP header and the ACK number of the TCP header.

  "5" is substituted for the header length by 20/4 (because it is expressed in units of 32 bits). Since Flag + Reserved is an ACK packet, an "ACK flag" is set. Furthermore, the remaining receive buffer size at this time is substituted into the window size. Substitute "0" for the checksum and "0" for the urgent pointer. The checksum of the virtual header + TCP header is calculated, and is substituted for the checksum. Next, the virtual header is removed while leaving the TCP header, and the IP header is generated.

  Next, a value is substituted for each part of the generated IP header. The information of the TCP connection management structure 401 is substituted for the source IP address and the destination IP address. “40” which is the IP header length + TCP header length is substituted for the total length. “0x06” indicating TCP is assigned to the protocol number, and “0” is assigned to the header checksum. Then, the result of calculating the checksum of 20 bytes of the IP header is substituted for the header checksum.

  As described above, generation of an ACK packet includes generation of a virtual header, generation of a TCP header, calculation of a virtual header checksum, calculation of a TCP header checksum, generation of an IP header, and calculation of an IP header checksum. . Since such various data processings are required, it takes a certain amount of time to generate the ACK packet.

<Effect>
FIG. 8 is a diagram illustrating an effect in TCP communication according to the first embodiment. FIG. 8A shows a transmission / reception operation in the conventional technique, and FIG. 8B shows a transmission / reception operation in the first embodiment. Each of them exemplarily shows data transmission from the transmission side device to the reception side device and ACK transmission from the reception side device to the transmission side device after the TCP connection is established. In FIG. 8, the vertical direction indicates the passage of time. Particularly, the respective times of “ACK generation”, “reception processing”, and “idle” in the receiving side device are shown as an example.

  Note that “ACK generation” is the time required for processing from ACK generation to ACK transmission, “Reception processing” is the time required for processing from TCP packet reception to data reading by an application, and “idle” is CPU idle. It's time.

  In order to simplify the explanation, in FIG. 8, it is assumed that the amount of data transmitted in each packet transmitted by the transmitting device is in MSS units. Further, it is assumed that the receiving buffer of the receiving side device becomes full when receiving an MSS × 4 packet. Furthermore, in the following description, the transmission of the first six packets (A to F) will be described in detail, but the same operation is performed for the subsequent packets.

-Transmission / reception operation in the related art The transmission-side device transmits packets (here, four packets A, B, C, and D) corresponding to the window size (remaining reception buffer size) of the reception-side device. The receiving device performs a reception process each time a packet is received. In TCP, when receiving a large number of packets in succession, the receiving device transmits an ACK once when receiving 2 × MSS data. Therefore, here, the receiving side device performs the reception process of two packets (A, B), and after completion of these reception processes, an ACK (“A + B” in the figure) indicating that the packets up to B have been received. ) Is generated and transmitted. Similarly, the following two packets (C, D) are received, and after completion of these reception processes, an ACK (“C + D” in the figure) indicating that packets up to D have been received is generated, Send.

  Since the window size of the other party is full when the sending device sends the above four packets (A, B, C, D), the sending device receives the ACK sent by the receiving device. The next packet (E and later) cannot be transmitted until after.

  When the transmitting device receives the ACK packet (“A + B” described above), it knows that the window size is vacant by 2 MSS, and thus transmits the two packets (E, F). At this point, the receiving-side device has completed the reception process of two packets (C, D) and the transmission of ACK (“C + D” in the figure) for these packets. However, since the receiving device has not received the next packet (after E), it is executing the idle task. After that, when the receiving side device receives two packets (E, F), each of them performs a receiving process, generates an ACK (“E + F” in the figure) indicating that the packets up to F have been received, and transmits the ACK. .

-Transmission / reception operation in the first embodiment The transmission-side device transmits packets for the window size of the reception-side device (here, four packets A, B, C, and D). The reception side device performs the reception process of two packets (A, B), and after completion of these reception processes, generates and transmits ACK indicating that the packets up to B have been received. Similarly, reception processing of two packets (C, D) is performed, and after completion of these reception processings, an ACK indicating that packets up to D have been received is generated and transmitted. The operation up to this point is the same as in the prior art.

  After transmitting the ACK (“C + D”), the receiving device receives the ACK corresponding to the subsequent packet until the arrival of the subsequent packet (after E) (that is, the period of “idle” in the conventional operation). Is generated. When receiving the packet (E), the receiving side device performs the receiving process of the packet, and when receiving the packet (F), the receiving device performs the receiving process of the packet.

  The receiving device selects and transmits ACK (“E + F” in the figure) indicating that the packets up to F have been received according to the operation of FIG. 7. That is, since the previously generated ACK is selected and used, the corresponding ACK (“E + F”) can be transmitted in a shorter time than before after receiving the packets up to F. By performing the same operation thereafter, the time until the receiving side device receives the R packet can be shortened by δ. That is, the same amount of data can be transmitted in a shorter time, and the data can be transmitted from the transmission side device to the reception side device at high speed.

  As described above, according to the first embodiment, the ACK packet generation process in TCP communication is started prior to the reception of the corresponding data packet. As a result, at least a part of the generation process of the ACK packet is completed when the corresponding data packet is received, so that the ACK packet can be transmitted promptly and the communication time can be shortened. Becomes In particular, by executing the generation of the ACK packet in the task with the low priority or the idle task, it becomes possible to use the CPU more effectively without adversely affecting other processing.

  In the above description, it is assumed that the CPU performs all the processing related to the generation of the ACK packet, but a part of the processing may be offloaded to hardware.

(Second embodiment)
The second embodiment will describe a mode in which the ACK packet generation process described in the first embodiment is performed only for a predetermined type of communication connection, for example, a TCP connection that receives a large amount of data.

  FIG. 10 is an operation flowchart of ACK packet generation in the second embodiment. Note that FIG. 10 corresponds to FIG. 3 with S1111 added between S304 and S305. Specifically, in S1111, the CPU 202 determines, with respect to the TCP connection determined to exist in S304, whether the TCP connection is a TCP connection that receives a large amount of data.

  Then, only in the case of a TCP connection that receives a large amount of data, an ACK packet is generated in advance. That is, if the TCP connection does not receive a large amount of data, the ACK packet is not generated in advance, but the ACK packet is generated after the data packet is received.

  It should be noted that whether or not to receive a large amount of data is determined, for example, based on whether or not the flag of the TCP connection management structure 401 includes a flag indicating that a large amount of data will be received. That is, an application that receives a large amount of data sets a flag indicating that a large amount of data will be received before or during communication in the TCP connection management structure 401.

  Also, instead of the application setting the flag, the protocol stack may be configured to set the flag. For example, the head of the received packet may be read, and a flag indicating that a large amount of data is received when the data is image data or moving image data may be set.

  As described above, according to the second embodiment, the ACK packet is generated in advance only when a large amount of data such as image data and audio data is received. As a result, the amount of memory used for the ACK packet generated in advance can be reduced, and the CPU can be used for other processing.

(Third Embodiment)
In the third embodiment, a form will be described in which an ACK packet generated in advance based on the number of simultaneous connections is limited. In the following description, an example will be described in which the upper limit value (ACK_MAX) of the number of ACK packets that can be generated is determined based on the number of simultaneous connections.

  FIG. 11 is an operation flowchart of ACK packet generation in the third embodiment. FIG. 11 corresponds to FIG. 3 with S1211 and S1212 added between S307 and S308. In addition, FIG. 12 is an operation flowchart of ACK packet transmission in the third embodiment. Note that FIG. 12 corresponds to FIG. 7 in which S1319 and S1320 are added after ACK is free (S612 and S617).

  In the following description, ACK_MAX is an upper limit value for the number of ACK packets to be generated, and ack_now is a parameter indicating the number of ACK packets currently generated. The value of ACK_MAX may be statically determined based on the size of the memory installed in the communication device 212, or may be set by the user of the communication device 212. Further, the value of ack_now is cleared to zero when the communication device 212 is started up or when the TCP stack is started up (at the time of start-up, the number of generated ACK packets is 0).

  Specifically, in S307 of the ACK packet generation flow (FIG. 11), the generated ACK number is compared with the planned ACK number, and if the generated ACK number is smaller than the planned ACK number, the process proceeds to S1211.

  In S1211, the CPU 202 compares ack_now with ACK_MAX. If ack_now is smaller than ACK_MAX, ack_now is incremented (incremented) by 1 in S1212, and an ACK packet is generated in S308.

  On the other hand, in the case of making ACK free in the ACK packet transmission flow (FIG. 12), ack_now is decremented by 1 (decrement). This makes it possible to correctly manage the number of currently generated ACK packets.

  As described above, according to the third embodiment, it is possible to set an upper limit on the number of generated ACK packets. As a result, when the number of simultaneous TCP connections is large, it is possible to prevent excessive memory consumption due to the generation of a large number of ACK packets. The ACK_MAX may be determined for each TCP connection. Also, a different maximum number (ACK_MAX) may be set for each TCP connection. When setting a different maximum number (ACK_MAX) for each TCP connection, the upper limit value may be determined using a value obtained by dividing the connection reception buffer size by the MSS.

(Fourth Embodiment)
In the fourth embodiment, the operation when the data size of the received data packet does not match the predicted size will be described.

  FIG. 13 is a diagram showing the transmission position of the ACK packet with respect to the received packet in the fourth embodiment. The dotted-line rectangle indicates that the receiving-side device has not received, and the solid-line rectangle indicates that the receiving-side terminal has already received.

  Assuming that the packet group shown in FIG. 13A is received, it is assumed that the ACK is generated at the timing 502 in FIG. However, actually, as shown in FIG. 13B, a packet like the received packet 501-03 may be received. In this case, the transmission timing and the ACK number of the ACK packet deviate from the reception timing of the data packet and the delimiter unit of the data size, such as timing 502-02 and timing 502-03.

  Incidentally, in TCP, data delivery confirmation is managed in byte units (sequence numbers) instead of packet units. Therefore, even if the ACK packet generated in advance is transmitted, the data communication can be normally continued. Therefore, for example, in FIG. 13B, when the packet 501-05 is received, an ACK packet is transmitted at timing 502-02.

  As described above, even when the “ACK number” of the generated ACK packet and the “sequence number of the received packet + data size” do not match, it is possible to continue data communication normally. That is, by transmitting an ACK packet having an ACK number smaller than “the received packet sequence number + data size”, communication can be continued without recreating the ACK packet.

-Modification 1
As described above, in TCP, communication can be normally continued without returning an ACK packet in units of received data packets. However, an ACK packet may be returned in units of received packets.

  FIG. 13C is a diagram showing the transmission position of the ACK packet with respect to the received packet in the first modification of the fourth embodiment. The ACK packets transmitted at timings 512-01 and 512-02 are the same as the ACK packets transmitted at timings 502-01 and 502-02 in FIG. 13B described above. On the other hand, the ACK packet transmitted at timing 512-03 is generated and transmitted so as to be an acknowledgment for the unit of the received packet. In FIG. 13C, the ACK number of the generated ACK packet is shown in parentheses below each timing.

  FIG. 14 is an operation flowchart of ACK packet transmission in the first modification of the fourth embodiment. Note that FIG. 14 corresponds to FIG. 7 with S1619 added. In FIG. 14, the process proceeds to S610 when the “sum of the sequence number (of the received packet) and the data size” of the generated ACK packet of interest is smaller than the “ACK number”. Specifically, this is a case where the ACK numbers of the generated ACK packets that are currently focused are deviated.

  If there is no next ACK packet in that state, in S1619, the CPU 202 rewrites the generated ACK number of the TCP connection management structure to a value based on the sequence number and data size of the received packet. As a result, for example, the ACK number of the ACK packet to be transmitted at the timing 512-03 was changed from “8762 (= 2 + 1460 × 6)” to “8032 (= 5112 + 1460 × 2)”. Become. That is, the deviation of the ACK number is corrected, and it becomes possible to send back an ACK packet in units of received data.

-Modification 2
By the way, a problem may occur when the data size of the received data packet is different from the predicted size and the response shown in FIG. 13B is made. Specifically, when the ACK packet is transmitted at the timing 502-02 in FIG. 13B and the packets after the packet 501-06 are not received, the received data (a part of the packet 501-05) is received. Will not be sent. Therefore, in the second modification, a timer for forced transmission is provided for the generated ACK packet, and the ACK packet is transmitted when the timer fires.

  FIG. 15 is an operation flowchart of ACK packet transmission in the second modification of the fourth embodiment. Note that FIG. 15 corresponds to FIG. 7 with addition of S1719, S1720, and S1721. In FIG. 15, the process proceeds to S610 when the “sum of the sequence number (of the received packet) and the data size” of the generated ACK packet of interest is smaller than the “ACK number”. Specifically, this is a case where the ACK numbers of the generated ACK packets that are currently focused are deviated.

  If there is no next ACK packet in that state, the CPU 202 sets the ACK forced transmission timer in S1719. When another ACK packet is transmitted (S614, S616), it is not necessary to transmit the ACK packet due to timeout. Therefore, in S1720 and S1721, the ACK forced transmission timer is controlled to be turned off. On the other hand, when the ACK forced transmission timer times out, the generated ACK packet is transmitted as an ACK packet for the data received so far.

  With this configuration, even when the data size of the received data packet is different from the predicted size, it is possible to prevent omission of the ACK packet reply to the received data.

(Other embodiments)
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program. It can also be realized by the processing. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  101 application task; 102 reception buffer; 103 reception processing task; 104 reception queue; 105 transmission queue; 106 LAN driver; 107 ACK packet buffer; 108 TCP connection management mechanism; 110 ACK generation processing task

Claims (12)

A communication device,
Generating means for generating an acknowledgment packet for a data packet transmitted from another communication device;
Receiving means for receiving data packets received from the other communication device;
Transmitting means for transmitting an acknowledgment packet corresponding to the data packet generated by the generating means when the data packet is received,
Have
The generation means starts the generation processing of the acknowledgment packet for at least a part of the data packets as a task having a lower priority than the reception processing by the reception means prior to the reception of the data packets. Communication device. When the data packet is received, when the confirmation response packet corresponding to the data packet has already been generated by the generation unit, the transmission unit transmits the generated confirmation response packet to the data packet. If the corresponding acknowledgment packet is not generated by the generating means, that the acknowledgment packet corresponding to the data packet after being generated Ri by said generating means, for transmitting an acknowledgment packet the generated The communication device according to claim 1, wherein the communication device is a communication device. The generation means is realized by the CPU executing a program,
The generation means performs the generation processing of the acknowledgment packet for the data packet prior to the reception of the data packet when there is no task having a higher priority than the generation processing in the CPU or when the CPU is in the idle state. The communication device according to claim 1, wherein the communication device executes. The communication according to any one of claims 1 to 3, further comprising setting means for setting an upper limit value of the number of confirmation response packets that can be generated by the generation means for unreceived data packets. apparatus. The communication device and the other communication device perform communication conforming to TCP (Transmission Control Protocol),
It further comprises a determining means for determining the acknowledgment number of the acknowledgment packet for the unreceived data packet based on the sequence number and the maximum segment size described in the TCP header of the already received data packet. The communication device according to any one of items 1 to 4. When the communication connection with the other communication device is a communication connection of a predetermined type, the generation means starts the generation processing of the confirmation response packet for the data packet before receiving the data packet. The communication device according to claim 1, wherein the communication device is a communication device. Whether or not the communication connection with the other communication device is the predetermined type of communication connection is used by the flag set in the connection management structure by the application using the communication connection and the communication connection. 7. The communication device according to claim 6, further comprising a determination unit that determines based on at least one of the flags set in the connection management structure by the protocol stack. When a data packet is received, it has a comparison means for comparing the sum of the sequence number and the data size in the data packet with the confirmation response number of the confirmation response packet already generated by the generation means,
When it is determined by the comparison means that there is no acknowledgment packet having the acknowledgment number that matches the sum, the transmitting means transmits an acknowledgment packet having the acknowledgment number smaller than the sum. The communication device according to any one of claims 1 to 7, which is characterized. When a data packet is received, it has a comparison means for comparing the sum of the sequence number and the data size in the data packet with the confirmation response number of the confirmation response packet already generated by the generation means,
When it is determined by the comparison unit that there is no acknowledgment packet having the acknowledgment number that matches the sum, the generation unit determines the acknowledgment number of the acknowledgment packet having the acknowledgment number smaller than the sum. To the sum value above,
8. The communication device according to claim 1, wherein the transmission unit transmits the rewritten confirmation response packet.   The reception process includes at least queuing of data related to a data packet transmitted from the other communication device, or an order control process.
The communication device according to claim 1, wherein the communication device is a communication device. A method of controlling a communication device, comprising:
A generation step of generating an acknowledgment packet for a data packet transmitted from another communication device,
A receiving step of performing a receiving process for a data packet received from the other communication device,
A transmitting step of transmitting an acknowledgment packet corresponding to the data packet generated by the generating step when the data packet is received,
Including,
The generation processing of the acknowledgment packet for at least a part of the data packets in the generation step is started prior to the reception of the data packets as a task having a lower priority than the reception processing in the reception step. that control how to be. Program for causing a computer to function as each unit of the communication apparatus according to any one of claims 1 to 10.

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