JP2013176106A - Data communication device and communication program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of malfunction in session disconnection.SOLUTION: A data processing unit for performing transmission/reception with a transmitter through a network receives a series of data for each data to process the received data, in receiving the data. A control processing unit manages a session status of the data communication with the transmitter. An information storage unit stores the session status. A data reception completion determination unit determines whether or not the reception of all of the series of data have been completed, when reception of termination data of the series of data is detected. A data processing unit processes the data from the transmitter depending on the session status stored in the information storage unit. The control processing unit makes the session status transit to an end status, when it is determined that all of the series of data has been completed, and delays the transition of the session status until it is determined that all of the series of data has been completed, when it is determined that all of the series of data has not been completed.

Description

  The present invention relates to a data communication apparatus and a communication program.

  Conventionally, protocol processing such as TCP / IP widely used in the Internet has been realized mainly by software operating on a CPU. However, as the network speed increases in recent years, the CPU's TCP / IP processing load has increased. By using a TOE (TCP / IP Offload Engine) that performs TCP / IP processing using dedicated hardware, high-speed communication is possible. An apparatus for realizing the above has been proposed.

US Publication 2004/0078462 JP 2009-77024

  The TOE is normally controlled by software that runs on the CPU. However, considering the control from the software, there are problems such as poor data transmission performance and incorrect session disconnection.

  An object of one aspect of the present invention is to solve at least one of a problem that data transmission performance is not achieved and a problem that session disconnection does not operate correctly.

  A data communication apparatus according to an aspect of the present invention is a data communication apparatus that performs data communication using a protocol that retransmits the data from the transmission side when data loss is detected.

  The data communication device includes a data processing unit, a control processing unit, an information storage unit, a data end detection unit, and a data reception completion determination unit.

  The data processing unit transmits / receives data to / from a transmitting device via a network, and in reception, receives a series of data for each data, and processes the received data.

  The control processing unit manages a session state of data communication with the transmission device.

  The information storage unit stores the session state.

  The data end detection unit detects that end data at the end of the series of data has been received.

  The data reception completion determination unit determines whether reception of the series of data has been completed when reception of the termination data is detected.

  The data processing unit processes data from the transmission device according to the session state stored in the information storage unit.

  The control processing unit transitions the session state to an end state when it is determined by the data reception completion determination unit that reception of the series of data has been completed, and when it is determined that the data has not been completed And waits for the transition of the session state until it is determined to be completed.

1 is a diagram schematically showing a configuration of a data transmission device according to a first embodiment. FIG. The figure which shows a mode that a memory copy is performed by the delivery of the data between a protocol stack and an application. Explanatory drawing of the method in which NIC writes data directly to the application buffer. The figure for demonstrating a delay confirmation response. FIG. 6 is a diagram for explaining the operation of the first embodiment. The figure which shows the example of application data and the confirmation response with respect to it. The figure which shows another example of application data and the confirmation response with respect to it. FIG. 2 is a diagram showing a configuration in which a copy size specifying unit is added to the apparatus of FIG. FIG. 9 is a diagram showing a configuration in which a transmission rate measurement unit and a delay measurement unit are added to the apparatus of FIG. FIG. 2 is a diagram showing a configuration in which a packet transmission instruction unit is added to the apparatus of FIG. The figure for demonstrating operation | movement of a packet transmission instruction | indication part. FIG. 2 is a diagram showing a configuration in which a buffer management unit is added to the apparatus of FIG. FIG. 5 is a diagram schematically showing a configuration of a data communication apparatus according to a second embodiment. 14 is a flowchart for explaining the operation of the apparatus of FIG. FIG. 14 is a view showing a modification of the apparatus of FIG. FIG. 10 is a diagram schematically showing a configuration of a data communication apparatus according to a third embodiment. FIG. 17 is a flowchart for explaining the operation of the apparatus of FIG. FIG. 17 is a diagram showing a modification of the apparatus in FIG. The figure which shows the header structure of TCP. The figure showing the state name of TCP and its explanation. The figure which shows an example of session information.

(First embodiment)
TCP / IP is the main protocol used in Internet communications. Conventional TCP / IP is mainly realized by software processing, and operates by a CPU such as a personal computer or an embedded device. In such a case, data exchange with the network is mainly performed by a NIC (Network Interface Card) with a MAC / PHY function or an LSI such as a dedicated ASIC or FPGA (hereinafter this is represented by the NIC). explain).

  In the case of reception, a packet received from the network is DMA-transferred from the NIC to the memory, and then protocol processing is performed by the CPU protocol stack software. In the case of transmission, a packet generated on the memory by the protocol stack software of the CPU is read out by the NIC by DMA transfer and transmitted to the network. Normally, the CPU executes application processing in addition to protocol processing, and memory copying is performed by passing data between the protocol stack and the application. The flow of these data is illustrated in FIG.

  As can be seen from FIG. 2, in such a system, data is temporarily buffered between the application buffer and the NIC, and the data travels twice in total on the memory. Therefore, a method has been proposed in which a part of the protocol processing is performed by the NIC so that the NIC directly writes data to the application buffer. Figure 3 shows the data flow in this case. By doing so, the flow of data only makes one round trip on the memory, so it is possible to avoid the overhead in terms of performance and power consumption due to data copying. Although this processing is an example of reception processing, it is desirable that the transmission processing also operates without performing a memory copy.

However, if copying is simply omitted in the transmission process as described above, a problem occurs when the socket API is assumed as the application API. The Socket API has the restriction that only one application data can be specified at a time.
Specifically, as shown in FIG. 4, if the application specifies application data that calls the send () function, the next send () function cannot be called unless the function is returned. Therefore, the next application data transmission instruction cannot be performed until the function returns. On the other hand, if the protocol stack side that has specified application data returns the send () function, the application data may be released. The send () function cannot be returned until the last data acknowledgment is returned, so the send () function cannot be returned. (Note: In the configuration shown in Fig. 2, the data is copied to the stack buffer. (The send () function can be returned when the transmission is not finished.)
The reason why the confirmation response is delayed is, for example, when (A) the receiving device makes a delay confirmation response (described later), (B) when the round-trip delay of the network with the receiving device is large, (C) the receiving device When the processing speed of is slow. In such a case, the return timing of the send () function is delayed, resulting in a no-communication time, resulting in a wasteful reduction in the transmission rate.

  An embodiment of the present invention that solves the above problems is shown in FIG. FIG. 1 shows a basic configuration, and a typical example is realized by a PC, a server, an ASIC, an FPGA (Field Programmable Gate Array), and the like. The apparatus in FIG. 1 is a data transmission apparatus that performs continuous data transmission while receiving an acknowledgment based on a data sequence number from an opposite reception apparatus based on a communication protocol such as the TCP / IP protocol. .

  The data transmission apparatus includes a data transmission instruction unit 101, a packet transmission instruction unit 102, a data storage unit 103, a data reading unit 104, a header generation unit 105, a packet generation unit 106, a network I / F unit 107, and an acknowledgment response reception unit 108. The packet retransmission instruction unit 109, the data copy unit 110, and the transmission completion determination unit 111.

  The data transmission instruction unit 101 generates a data transmission instruction that instructs transmission of application data.

  The packet transmission instruction unit 102 generates a packet transmission instruction for continuously transmitting each packet based on the data transmission instruction.

  The data storage unit 103 has a data storage area for storing application data to be transmitted and a temporary buffer area (hereinafter referred to as a temporary buffer).

  In response to the packet transmission instruction, the data reading unit 104 reads one packet of application data from the data storage area of the data storage unit 103.

  The header generation unit 105 receives a packet transmission instruction and generates a header including sequence number information of data included in the packet to be transmitted.

  The packet generation unit 106 generates a packet from the generated header and the read data.

  The network I / F unit 107 transmits the generated packet to the network and receives the packet from the network.

  The confirmation response receiving unit 108 receives the confirmation response packet including the confirmation response sequence number information indicating how much of the transmitted packet data has been received.

  The packet retransmission instruction unit 109 identifies data to be retransmitted from the received acknowledgment response sequence number information, and instructs the data reading unit 104 and the header generation unit 105 to transmit a packet of the identified data.

  When the data reading unit 104 reads data, the data copying unit 110 stores the read data as a copy in the data storage unit 103 when the data is data within a predetermined number of bytes from the end of the application data. .

  The transmission completion determination unit 111 reads the data until the end of the application data by the data reading unit 104, and includes a confirmation response sequence number information corresponding to bytes within a predetermined number of bytes counted from the end of the application data Is received, the transmission completion of the application data is determined, and the transmission completion is notified to the data transmission instruction unit 101. When transmission completion is determined, application data to be transmitted next is overwritten in the data storage area of the data storage unit 103.

  As an example, the data transmission instruction unit 101 is application software on the host CPU of the data transmission device, the data storage unit 103 is an external memory such as SDRAM, and the other parts are hardware other than the host CPU such as NIC, ASIC, and FPGA. Although the form implement | achieved by hardware is considered, it is not the limitation. For example, the other part may be realized by software.

  The specific processing flow is as follows. First, the data transmission instructing unit 101 instructs the packet transmission instructing unit 102 to specify application data to be transmitted, for example, by specifying the start address and length (address 0x42000000, length 1 MB, etc.) on the memory. This is realized by, for example, the send () function of the Socket API.

  The packet transmission instruction unit 102 cuts out designated application data for each packet data length (for example, the maximum segment size of TCP, 1460 bytes, etc.) from the top. The packet transmission instruction unit 102 designates the start address, length, sequence number of the start data, and the like of the extracted data, and continuously generates a header generation instruction to the header generation unit 105 and a data read instruction to the data reading unit 104. put out.

  For example, if the sequence number starts from 1, the instruction for the first packet is expressed as address 0x42000000, length 1460 bytes, sequence number 1 of the first data (byte). This means a byte string having a length of 1460 bytes starting from sequence number 1, and actually indicates data of sequence numbers 1 to 1460. The second packet instruction is address 0x420005b4, length 1460 bytes, sequence number 1461, and the third packet instruction is address 0x42000b68, length 1460 bytes, sequence number 2921. Here, an example is shown in which one sequence number is assigned to each byte, but the present invention is not limited to this.

  If the application data is 1MB (= 1024 x 1024 bytes), 1024 x 1024/1460 = 718 remainder 296, so the length is 1460 bytes up to the 718th packet, and the last 719th packet has a length of 296. It becomes a byte. That is, the instruction of the last 719th packet is address 0x420ffed8, length 296 bytes, sequence number 1048281.

  The header generation unit 105 generates a TCP / IP header including a sequence number designated based on such an instruction based on the protocol specification. The data reading unit 104 reads data from the data storage unit 103 for a specified length from a specified address. The header generation unit 105 passes the generated header to the packet generation unit 106, and the data reading unit 104 passes the read data to the subsequent packet generation unit 106.

  The packet generation unit 106 combines them to generate a packet, adds a checksum and the like to the header, and passes them to the network I / F unit 107. The network I / F unit 107 transmits the packet toward a receiving device on the network.

  When the transmitted packet is received by the receiving device, the receiving device returns an acknowledgment of reception based on the protocol specification. That is, the sequence number of the expected data next to the received data is included in the acknowledgment packet as the acknowledgment sequence number, and responds to the transmitting apparatus.

  The transmitting device receives the acknowledgment packet and looks at the acknowledgment sequence number, thereby confirming that the data before the sequence number has reached the receiving device.

  If a packet is lost on the network, the receiving device receives a packet with a discrete sequence number. In this case, for example, in the TCP / IP protocol specification, the receiving apparatus responds with the sequence number of the expected data next to the sequence number of the last data received continuously.

  For example, first, a packet with a sequence number of 1 and a length of 1460 bytes was received and an acknowledgment sequence number 1461 was responded. Then, a packet of sequence number 1461 and a length of 1460 bytes was received and an acknowledgment sequence number of 2921 was returned. And Next, reception of the packet with the sequence number 2921 is expected. However, it is assumed that this packet is lost on the network, and the next packet with a sequence number of 4381 and a length of 1460 bytes is received. In this case, since the data received up to the sequence number 2920 is continuously received, the confirmation response packet having the confirmation response sequence number 2921 is returned.

  Then, even if subsequent subsequent packets arrive at the receiving device, all of the confirmation response sequence numbers included in the confirmation response packet from the receiving device are 2921. Therefore, the confirmation response packets with the confirmation response sequence number 2921 are duplicated.

  The transmitting apparatus can detect that a packet starting with the sequence number is lost on the network by detecting the duplicate acknowledgment sequence number. That is, the packet retransmission instruction unit 109 described above identifies the packet with the duplicate acknowledgment sequence number as a packet to be retransmitted, and issues a retransmission instruction for the sequence number 2921.

  Specifically, the address 0x42000b68 (calculated by adding the difference between the sequence number 2921 and the start sequence number 1 to the start address 0x42000000 of the application data), the length 1460 bytes, and the sequence number 2921 is output. Based on this instruction, the header generation unit 105, the data reading unit 104, the packet generation unit 106, and the network I / F unit 107 transmit a retransmission packet to the network in the same manner as described above.

  The method for specifying the retransmission packet is not limited to the above. For example, if no acknowledgment is returned for a certain period of time, the maximum acknowledgment sequence number received at that time is specified as the sequence number of the retransmission packet. The method of doing is also mentioned. These retransmitted packet specifying methods are merely examples, and other specific methods specified based on protocol specifications such as TCP / IP are also applicable to the embodiment of the present invention. These specific methods are not related to the embodiment of the present invention, and do not limit the embodiment of the present invention.

  Further, since the acknowledgment receiving unit 108 operates when receiving a packet, it is typically performed asynchronously with packet transmission processing by other functional units. Therefore, the confirmation response sequence number information received by the confirmation response receiving unit 108 may be temporarily stored in a memory or the like (not shown) by the confirmation response receiving unit 108 when the confirmation response packet is received. In this case, the transmission completion determination unit 111, the packet retransmission instruction unit 109, and all other functional units that refer to the information on the acknowledgment sequence number at the time of packet transmission acquire the information on the acknowledgment sequence number by reading this memory or the like. To do.

  As described above, packet transmission is performed while directly reading application data, and packet retransmission based on an acknowledgment is performed. Finally, when an acknowledgment packet including an acknowledgment sequence number corresponding to the byte next to the last byte of application data is received, it can be confirmed that all data has been delivered to the other party.

  However, reception of an acknowledgment packet including an acknowledgment sequence number corresponding to the byte following the last byte may be delayed as described above (see FIG. 4). This is due to the delay confirmation response (A) described above. The delay confirmation response (A) corresponds to, for example, Delayed ACK in TCP / IP. Since it is not always necessary to receive an acknowledgment every time a receiving device receives a data packet, every two packets of data are acknowledged together in order to reduce the communication load and the processing load of the transmitting / receiving device. Is to issue. In the delayed acknowledgment, when the last transmission data is 2 packets and the segment length of these 2 packets is the maximum segment length, an acknowledgment is returned without delay, but when the last transmission data is 1 packet, Alternatively, when the segment length of the last packet in the case of two packets is less than the maximum segment length, there is a feature that the confirmation response is delayed depending on the specification.

  Therefore, in the embodiment of the present invention, the transmission completion is determined without waiting for it completely, and the next application data can be transmitted. This will be described in detail with reference to FIG. FIG. 5 shows a data string to be transmitted, which is described so that the sequence number increases in the right direction.

  First, the data transmission instruction unit 101 designates application data (1) (thick line portion). Then, the packet transmission instruction unit 102 divides the data into seven packets as shown in the figure, and sequentially issues packet transmission instructions. Based on this transmission instruction, the data reading unit 104 reads data from the data storage unit (memory) 103 for each packet, the header generation unit 105 generates a header, and the packet generation unit 106 generates these data and header. Based on the above, a packet is generated and transmitted via the network IF unit 107.

  Here, when the data to be read is within a predetermined length from the end of the application data (in this case, the length of data for two packets), the data reading unit 104 temporarily stores the data for retransmission. The data is stored in an area (temporary buffer) different from the area (data storage area) where the application data of the unit 103 is stored. In other words, as shown in FIG. 5, the data copying unit 110 converts the data read by the data reading unit 104 into a temporary buffer (2) in an area (for example, 0x60000000) different from the area where the application data is stored. Copy to (3).

  In parallel with the above operations, the acknowledgment packets from the receiving device are sequentially received. If the acknowledgment sequence number included in the received packet is greater than or equal to the sequence number corresponding to the first data copied to the temporary buffer, the data with the sequence number smaller than the copied data (here, the current It was confirmed that all of the application data (corresponding to data not copied) could be delivered to the receiving side. Therefore, at that time, the transmission completion determination unit 111 determines the completion of transmission of application data and notifies the data transmission instruction unit 101 of the completion. For example, when a send instruction is issued by the send () function of the Socket API, this is notified when the send () function returns.

  Then, the data transmission instruction unit 101 designates the next application data (5) (three lines in FIG. 5) by calling the send () function again, and the packet transmission instruction unit 102 similarly converts the data into a packet. Divide and send instructions. The next application is written in the data storage area of the data storage unit 103. This may be written in the same area as the previous application data, or may be written in another area.

  Here, when retransmitting the data in response to the confirmation response from the receiving device, when retransmitting the data of the sequence numbers after (6) in the figure, the data reading unit 104 directly reads the data from the next application data (6). When retransmitting the data with the sequence number before (6), the data reading unit 104 reads the data from the temporary buffer (2) in which the previously copied data is stored.

  By operating in this way, even when the confirmation response from the receiving apparatus is delayed without copying all the data, the next application data can be transmitted without waiting. As a result, continuous data transmission with little no-communication time becomes possible, and high-speed data transmission can be realized with low power consumption.

  In the above example, an example in which data of a length of two packets from the end of the application data is copied to the temporary buffer is shown, but this length is not limited to this.

  As described above, the reason why the acknowledgment response is delayed is as follows. (A) When the receiving device is making a delay acknowledgment, (B) When the round-trip delay of the network with the receiving device is large, (C) If the processing speed is slow, etc.

  As described above, the delay confirmation response in (A) corresponds to Delayed ACK in TCP / IP, etc., and reduces the communication load and the processing load of the transmission / reception device in order to reduce the communication load by 2 packets each time data is received. It is to send a confirmation response collectively. In this case, if the packet is not lost on the network, the acknowledgment of the packet that is earlier than the last two packets from the end of the data is always returned without delay regardless of the size of any application data. . Therefore, if the transmitting device always copies two packets of data and does not wait for the confirmation response, and sends the next application data, the data is always unaffected by the delayed confirmation response. You can send.

  This is explained in more detail as follows. FIG. 6 shows the application data and the confirmation response (solid arrow). Normally, the last packet is shorter than the maximum segment size in this way, but in this case, the maximum segment size × 1 + the last short packet (the length of the dotted arrow) is copied.

  The above is for the case where the number of packets is an even number. However, if the number of packets is an odd number as shown in FIG. 7, the confirmation response for only the last short packet will be delayed. You only need to copy the packet.

  In this way, the size that should be copied due to the odd / even number of packets is the last 2 packets or the last 1 packet, but as a worst case it is always possible to copy the last 2 packets It is not affected by delay. More optimally, it is desirable to predict which one of the above will occur, and to operate so as to copy only one packet when one packet is sufficient. FIG. 8 shows a configuration including a copy size specifying unit 112 for specifying the data size to be copied based on such a determination. Elements having the same names as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted except for extended processing. The copy size specifying unit 112 determines whether the number of packets is even or odd, determines that only the last two packets are copied when the number is even, and copies only the last one packet when the number is odd, and notifies the data copy unit 110 of the copy. Alternatively, if the number is even, the data length of the last two packets is specified. If the number is odd, the data length of the last one packet is specified, and the specified data length is notified to the data copy unit 110. The data copy unit 110 performs copying according to the notified information.

  Also, the above is a form corresponding to the reason (A) that the confirmation response is delayed as described above, but (B) when the round-trip delay of the network with the receiving device is large, (C) when the processing speed of the receiving device is slow In response to the above, the following modes are possible. In the transmission apparatus, the elapsed time from the time when the corresponding response of the even-numbered packet immediately returned is transmitted, that is, the delay time of the acknowledgment, and the current data transmission bit rate are measured. Then, the data size corresponding to the product of the delay time and the data transmission bit rate is further copied to the size of one packet or two packets described above. The data size corresponding to the product may be the value of the product itself, or may be the maximum segment length × 2 when the maximum segment length × 2 is equal to or greater than the value of the product. When the maximum segment length x 2 is less than the product value, it is less than the product value and is the maximum multiple of the maximum segment length x 2, or the product value greater than or equal to the maximum segment length x 2 It may be the minimum value. In the transmission completion determination, the transmission completion can be determined without waiting for the confirmation response of the additionally copied data.

  FIG. 9 shows a configuration including a delay measuring unit 113 that measures the delay time of the confirmation response and a transmission rate measuring unit 114 that measures the transmission bit rate. Elements having the same names as those in FIG. 8 are denoted by the same reference numerals, and redundant description is omitted except for extended processing. The delay measurement unit 113 measures the delay time from when the packet generation unit passes the packet to the network I / F unit until the confirmation response is received for the even-numbered packet that returns immediately. The transmission rate measuring unit 114 obtains a transmission bit rate by measuring the transmission data length per unit time in the data transmission by observing the transmission of the packet generated by the packet generation unit 106. Based on the delay time and the transmission bit rate, the copy size specifying unit 112 specifies the size to be additionally copied, and copies only the value obtained by adding the specified size to the data size (for example, 2 packets) described above. I do. The transmission completion determination unit 111 determines transmission completion when it transmits all the data packets and receives an acknowledgment indicating the sequence number of the first byte or more of the data to be copied. With such a configuration, even if the delays (B) and (C) are added, continuous data transmission can be realized without being affected by the delay.

  Next, processing when data transmission further proceeds will be described. In the above example, the process in which the transmission of the next application data is executed following the transmission of certain application data has been described.

  When the transmission of the “next application data” proceeds and approaches its end, data is eventually copied to the temporary buffer in the same manner as the transmission of the first application data. However, at this point, the confirmation response to the last data of the first application data (= the last data on the temporary buffer to which the first application data was copied) (that is, the confirmation response of the sequence number (6) in FIG. 5) is returned. If not, the data in the temporary buffer may still be retransmitted, so it is necessary to leave the data in the temporary buffer.

  Therefore, if the next application data is copied to the temporary buffer in that state, the data on the temporary buffer will be overwritten by the next application data. In this case, there arises a problem that data different from the original is retransmitted. A form that avoids this problem is shown in FIG.

  FIG. 10 includes, in addition to FIG. 1, a packet transmission suppression unit 115 that temporarily stops the packet transmission instruction of the packet transmission instruction unit 102. Elements having the same names as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted except for extended processing.

  FIG. 11 is the same as (1) to (6) in FIG. 5, with the addition of (7) indicating the start point of copying application data (5) to the temporary buffer.

  As described above, it is assumed that transmission of the next application data has reached this (7). At this time, the packet transmission suppressing unit 115 causes the packet transmission instructing unit 102 to temporarily stop packet transmission while the confirmation response of the last data (6) of the previous application data is not returned. When the confirmation response is returned, the packet transmission is resumed. By operating in this way, the previous application data remaining in the temporary buffer is not overwritten with the current application data, so that the above-mentioned problem can be avoided.

  More optimally, it may be as follows. Even if the confirmation response for data (6) is not returned, if the confirmation response is one packet before data (6), the first packet data of the two packets in the temporary buffer Means that since the delivery has been confirmed, retransmission is unnecessary and the data can be released. Therefore, in this case, the packet transmission of (7) is performed, the packet data is copied to the first packet area of the temporary buffer, and the packet transmission instruction is stopped when the transmission of the next packet from (7) is reached. It may operate to

  However, transmission suppression as described above may degrade the performance. For example, this is remarkable when the application data is smaller than the copy size to the temporary buffer. This is because all application data is copied to the temporary buffer in this case, that is, if no confirmation response of the last data of the previous application data is returned at this time, no data can be transmitted. In order to prevent the performance from being degraded even in such a case, it is desirable to manage more complicated temporary buffers. Figure 12 shows the configuration in that case. FIG. 12 includes a buffer management unit for managing temporary buffers in addition to FIG. Elements having the same names as those in FIG. 10 are denoted by the same reference numerals, and redundant description is omitted except for extended processing.

  As an example of the operation of the buffer management unit 116, a form in which a plurality of temporary buffers and their address information are managed can be considered. For example, if you have 8 temporary buffers 1 to 8, temporary application 1 uses temporary buffer 1 and next application data uses temporary buffer 2 and the next application data copy. By using the temporary buffer 3, it is possible to transmit eight application data even when no confirmation response is returned. Also, if an acknowledgment of the last data of the first application data is returned, the first temporary buffer can be released and used for copying the ninth application data, and so on.

  Since the number of temporary buffers is limited, it is necessary to suppress packet transmission when it is depleted, but by managing multiple temporary buffers like this, multiple application data can be sent without waiting for confirmation responses. Can be transmitted, and as a result, the aforementioned performance degradation can be reduced.

  As another example, a form in which data to be copied is linked is conceivable. The case where the performance degradation is noticeable when the application data is smaller than the copy size to the temporary buffer has been described. For example, in this case, the first application data is copied from the beginning, and then the same temporary buffer is next copied. Copy the application data.

  For example, when the first copy of application data is 1000 bytes and the next application data is 3 bytes, the 3 bytes are copied to the 1001st to 1003rd bytes of the same temporary buffer. If the next application data is 15 bytes, the data is copied to the 1004th to 1018th bytes of the same temporary buffer. In this state, when retransmitting a packet starting with the sequence number of the first data of the first copy of the application data, all these 1018 bytes are read out and a concatenated packet is transmitted.

  Only the first 1000 bytes were actually lost on the network, and the subsequent 18 bytes may have already reached the receiving device, in which case the receiving device simply discards the 18 bytes. It may not be a problem.

  As described above, even in such an operation, a plurality of application data can be transmitted without waiting for a confirmation response, and the above-described performance degradation can be reduced. In addition, information on where one packet is from (for example, information of 1000 bytes, 3 bytes, and 15 bytes in this case) is kept separately, and based on this information, only 1000 bytes in the retransmission explained earlier May be retransmitted.

(Second embodiment) (FIN reception configuration)
Conventionally, protocol processing such as TCP / IP widely used in the Internet has been realized mainly by software operating on a CPU. However, as the network speed increases in recent years, the CPU's TCP / IP processing load has increased. By using a TOE (TCP / IP Offload Engine) that performs TCP / IP processing using dedicated hardware, high-speed communication is possible. An apparatus for realizing the above has been proposed.

  A conventional data communication device is equipped with a communication adapter for low-speed processing and a communication adapter for high-speed processing. Only TCP session connection and disconnection packet processing with complicated algorithms is executed by the communication adapter for low-speed processing. Some high-speed adapters execute only packet processing for payload transmission including data. However, this device receives a segment (hereinafter referred to as the FIN segment) in which FIN is set in the control flag for disconnecting the session when data is retransmitted due to loss on the network. Sometimes there was a problem. When the low-speed adapter receives the FIN segment, the session state transitions to CLOSE-WAIT. However, if this state transition occurs while data retransmission is occurring as described above, the communication adapter for high-speed processing There was a problem that data could not be received.

  Hereinafter, a second embodiment for solving such a problem will be described in detail.

FIG. 13 is a block diagram showing a data communication apparatus according to the second embodiment of the present invention.
The data communication apparatus according to the second embodiment receives content from the client via the network via TCP and stores it in the storage, or conversely transmits the content accumulated in the storage to the client via the network. It is a content storage server.

  This server includes a CPU 201, a system memory 202, a storage 203, and a TOE 204, which are connected by a local bus or a bus such as PCI Express.

  The CPU 201 includes a control processing unit 215. The TOE 204 includes a data processing unit 211, a data end detection unit 212, a data reception completion determination unit 213, a data end reception completion notification unit 214, and an information sharing unit 216.

  The data processing unit 211 performs processing for transmitting and receiving data via the network 220. Specifically, the data processing unit 211 receives a series of data for each data from the counterpart device via the network.

  The data end detection unit 212 detects data end information (FIN flag) included in the received data. The data end information corresponds to a data communication end instruction. The end data at the end of the series of data includes this data end information.

  When data end information is detected, the data reception completion determination unit 213 determines whether reception of all data in a series of data is completed.

  When it is determined that reception of all data up to the end of data has been completed, the data end reception completion notifying unit 214 notifies the data processing unit 211 to notify the communication partner device that reception of all data has been completed. Instruct.

  The control processing unit 215 controls the state of the terminal itself (session state) in data communication.

  The information sharing unit 216 holds session information shared by the control processing unit 215 and the data processing unit 211. The session information includes a session state controlled by the control processing unit 215. The data processing unit 211 performs data communication based on the session information held by the information sharing unit 216. For example, the data processing unit 211 receives data from the counterpart device while the session state is ESTABLISHED, but does not receive data when it is CLOSE-WAIT 1.

  This device communicates using TCP defined in RFC793. Figure 19 shows the TCP header structure.

  An example in which content is stored in a storage from a client via a network using this apparatus will be described.

  First, in this apparatus, after initialization processing of each unit, the control processing unit 215 of the CPU 201 prepares for establishing a TCP session. A list of TCP session states is shown in the table of FIG. Since this apparatus operates as a server, TCP session information is created with a predetermined port number such as 50000, and the state is set to LISTEN. “Local user” in the figure means an application or the like that runs on the CPU of this apparatus. An example of session information is shown in the table of FIG. This session information is held in the information sharing unit 216 for each session. Note that the session information may use a IP address and a port number to create a hash list to speed up the matching session search.

  With this preparation, a TCP connection request is made from another communication device (hereinafter referred to as a partner device). In TCP, connection is established by a procedure called three-way handshake. From the partner device, for example, set the unused port number assigned by the OS as the start port number, set the standby port number 50000 of this device as the end port number, sequence number, data offset, window size, checksum Then, a TCP segment (hereinafter referred to as SYN segment) in which only the SYN is set in the control flag is transmitted with the emergency pointer set appropriately.

  In this apparatus that has received this via the network, the data processing unit 211 first performs reception processing of the TCP lower layer protocol. Here, the lower layer protocol is, for example, Ethernet (R) for the physical layer and the data link layer, and IPv4 (Internet Protocol version 4) for the network layer. After the lower layer protocol processing is performed, TCP reception processing is performed.

  In the TCP reception process, first, it is determined whether the TCP checksum is correct, and it is confirmed that the segment is not broken. After confirming that the segment is not broken, search for session information.

  In this apparatus, since the CPU 201 and the TOE 204 perform TCP / IP processing in cooperation, the information sharing unit 216 shares session information. The information sharing unit 216 may be realized by an SRAM (Static Random Access Memory) in the TOE 204 or may be realized on a system memory.

  The data processing unit 211 confirms the control flag field of the received segment. In addition, the data processing unit 211 confirms whether or not there is a session in the information sharing unit 216 that matches the start point IP address, end point IP address, start point port, and end point port of the received TCP segment, and the session state thereof. .

  If there is a session that matches the received segment and the data contained in the segment is within the reception window range, the data processing unit 211 writes the data to the system memory 202, saves the data to the storage 203, RCV_NXT, RCV_WND, etc. Session information update processing is performed, and a segment (ACK segment) in which ACK is set in the control flag is transmitted to the partner apparatus.

However, when the session information RCV_SHUT is set, the data processing unit 211 does not process the data even if the segment includes data. Further, the data processing unit 211 passes the frame to the control processing unit 215 and performs processing in the control processing unit 215 when any of the following conditions is satisfied.
-Session status is SYN-RECEIVED (hereinafter SYN-RECV)-Session information RCV_SHUT is set-The received segment is an ACK for the sent FIN segment-In the control flag of the received segment, Either RST, SYN, or FIN is set
RCV_SHUT prohibits subsequent segment reception. The control processing unit 215 can specify whether to prohibit only transmission, only reception, or both transmission and reception as options when disconnecting the session. At this time, RCV_SHUT is set when reception is prohibited.

  The control processing unit 215 has a function for processing TCP that does not match the session information. When a SYN segment is received from the client, the session state is set to the LISTEN state from the session information of the information sharing unit 216. And search for a session that matches the start point IP address, end point IP address, and end point port.

  If there is no match, the data processing unit 211 is instructed to transmit a TCP segment with the control flag set to RST.

  On the other hand, if there is a matching session, the session state is changed to SYN-RECV, and the information such as the initialized sequence number, the acknowledgment number increased by 1 and the window size is stored as session information.

  Thereafter, the data processing unit 211 is instructed to transmit a TCP segment (hereinafter referred to as SYN-ACK) in which SYN and ACK are set in the control flag.

  When the client receives this SYN-ACK segment, it transmits an ACK segment corresponding to the SYN-ACK segment.

  Upon receiving this, the data processing unit 211 performs a lower layer protocol process, calculates a TCP checksum, and searches for a session if the segment is not broken. As a result of the search, matching session information is found, and since the session state is SYN-RECV, the frame is passed to the control processing unit 215 of the CPU. The control processing unit 215 recognizes that it is an ACK segment for SYN, and changes the session state to the ESTABLISHED state.

  Only in the SYN-RECIEVED state or SYN-SENT state, when the ACK segment for the SYN segment is received and changed to the ESTABLISHED state, the confirmation response number is incremented by 1 on the TOE 204 side and the session state is changed to the ESTABLISHED state. A specific state control processing unit (not shown) may be provided. By providing the specific state control processing unit, it is possible to perform communication without missing a data segment even when the operation speed of the CPU is not sufficient.

  When the state becomes the ESTABLISHED state, data is transmitted from the client. In this data transfer, a TCP segment including data is transmitted, and in this apparatus that has received it, the data processing unit 211 performs a checksum calculation of the lower layer protocol and TCP, and searches for a session from the information sharing unit 216. . In this case, if a matching session is found and the data included in the segment is within the range of the reception window, the session information such as RCV_NXT and RCV_WND of the information sharing unit 216 is updated, the data is written on the system memory 202, and the storage 203 Save to. Further, an ACK segment for the received data is generated and transmitted to the client via the network.

  FIG. 14 is a flowchart showing the operation of the data communication apparatus according to the second embodiment of the present invention.

  When all of the data to be transmitted is transmitted, the client generates a segment with FIN set in the control flag and transmits it to disconnect the session.

  The data processing unit 211 receives a segment from the client, performs lower layer protocol processing, performs TCP checksum calculation, and searches for a matching session from the information sharing unit 216 (S101). In this case, a session whose status is ESTABLISHED is found. Next, it is confirmed whether the sequence number is within the reception window and the confirmation response number, and if the data is within the range of the reception window, among the session information of the information sharing unit 216, RCV_NXT, RCV_WND, etc. The value is updated, the data is written to the system memory 202, and the data is stored in the storage 203. Also, an ACK segment is transmitted to the partner apparatus.

  The data end detection unit 212 determines whether or not reception of a segment whose FIN is set in the control flag has been detected (S102). If not detected (NO in S102), the process returns to step S201.

  When reception of a segment in which FIN is set is detected (YES in S102), the fact that FIN has been received is set in the FIN_RECV entry of the session information of the information sharing unit 216 (S103). Further, the sequence number of the last data included in the FIN segment is stored in FIN_SEQ (S103).

The data reception completion determination unit 213 reads the session information RCV_NXT and FIN_SEQ from the information sharing unit 216, and determines whether RCV_NXT has reached FIN_SEQ (S104). At this time, if RCV_NXT has not yet reached FIN_SEQ (NO in S104), every time a new segment is received, the data processing unit 211 notifies the data reception completion determination unit 213 to determine whether the data reception has been completed. Do.
When the data end is detected and the data reception is completed (YES in S104), the control processing unit 215 is notified, and the data end reception completion notifying unit 214 notifies the data processing unit 211 to transmit the ACK segment for the FIN segment. Instruct (S105). Also, the control processing unit 215 changes the state from ESTABLISHED to CLOSE-WAIT (S106). Note that the confirmation response number at this time treats FIN as 1-byte data and transmits the value of FIN_SEQ + 1 as the confirmation response number.

  When the above ACK segment is received by the client, the session disconnection on the client side is completed and a half-closed state is entered. The server detects the completion and transmits the FIN segment. When the client returns an ACK segment for the FIN, the server disconnects the session.

  In the above description, the case where the TOE 204 includes the data reception completion determination unit 213 has been described. However, a configuration in which the data reception completion determination unit 216 is included in the CPU 205 as illustrated in FIG. In this case, the data processing unit 211 notifies the data reception completion determination unit 216 that a new segment has arrived by interruption. In each case, the data reception completion determination unit 216 reads the RCV_NXT and FIN_SEQ of the session information from the information sharing unit 216, notifies the control processing unit 215 if RCV_NXT has reached FIN_SEQ, and the control processing unit 215 performs state transition. .

  Further, it is possible to adopt a configuration in which the data processing unit 211 does not notify the data reception completion determination unit 213 by interruption. In this case, the data reception completion determination unit 213 compares the RCV_NXT and FIN_SEQ values of the session information of the information sharing unit 216 at regular intervals such as 10 ms, and notifies the control processing unit 215 when RCV_NXT reaches FIN_SEQ. can do.

  In the above, the means for passing a frame from the data processing unit 211 to the control processing unit 215 may be realized using an interrupt, a register, and a shared memory. For example, a ring buffer configured with an entry indicating a pointer to the storage location of the frame is created, and the control processing unit 215 and the data processing unit 211 notify the index number of the processing completed via the register of the TOE 204, Notify event occurrence by interrupt.

  In addition, if the partner device transmits the FIN segment after confirming the reception of the ACK segment for all segments other than the FIN segment, whether or not all segments have been received after receiving the FIN segment with this device. It is not necessary to make a determination, and the development cost can be reduced.

  As described above, according to the data communication apparatus according to the second embodiment, even when a FIN segment is received when loss or the like occurs on the network and data is retransmitted, all data is received. Since the session state transition (ESTABLISHED → CLOSE-WAIT 1) is performed after completing the process, it is possible to receive all the retransmission data.

(Third embodiment) (FIN transmission configuration)
Conventionally, protocol processing such as TCP / IP widely used in the Internet or the like has been realized mainly by software operating on a CPU. However, as the network speed increases in recent years, the CPU's TCP / IP processing load has increased. By using a TOE (TCP / IP Offload Engine) that performs TCP / IP processing using dedicated hardware, high-speed communication is possible. An apparatus for realizing the above has been proposed.

  A conventional data communication device is equipped with a communication adapter for low-speed processing and a communication adapter for high-speed processing. Only TCP session connection and disconnection packet processing with complicated algorithms is executed by the communication adapter for low-speed processing. Some high-speed adapters execute only packet processing for payload transmission including data.

  However, in the transmission of the FIN segment, since the communication adapter for low speed processing and the communication adapter for high speed processing operate asynchronously, a problem may occur when the FIN segment is transmitted.

  The FIN segment is handled as 1-byte data, but if the receiving side's window size is determined to be 1 byte or more and the communication adapter for low-speed processing sends the FIN segment, the window size is actually zero. The segment that violated the flow control will be transmitted.

  In addition, when transmitting an ACK segment for the FIN segment, if data is continuously transmitted from the communication adapter for high-speed processing on the receiving side, the communication adapter for low-speed processing cannot calculate a correct confirmation response number.

  In addition, let's send the FIN segment in a situation where the communication adapter for high-speed processing on the sending side continues to send data generated by hardware separate from the low-speed adapter to the receiving side independently of the low-speed adapter. Then, the sequence number assigned to the FIN segment cannot be calculated correctly.

  Hereinafter, a third embodiment for solving these problems will be described in detail.

  FIG. 16 is a block diagram showing a data communication apparatus according to the third embodiment of the present invention.

  The data communication apparatus according to the third embodiment is a videophone server, displays video from the client (audio is also output from the speaker), and captures video (including input audio from the microphone) captured by the video camera. Send to.

  This device consists of a CPU 301, a system memory 302, a video camera 303 with a microphone, a display 304 with speakers, and a TOE 305, each of which includes a local bus, a bus such as PCI Express, IEEE1394, HDMI (High-Definition Multimedia Interface) ) Etc. Note that the display controller, decoder, and encoder are omitted. In the CPU 301, an application related to video display operates.

  The CPU 301 includes a control processing unit 312. The TOE 305 includes a data processing unit 311, a control processing unit 312, an information sharing unit 313, a data end setting unit 314, and a data end transmission determination unit 315.

  The data processing unit 311 performs processing for transmitting and receiving data via the network 320.

  The control processing unit 312 controls the state of the terminal (session state) in data communication.

  The information sharing unit 313 holds session information shared between the control processing unit 312 and the data processing unit 313. The session information includes information such as the session state and flow control information (for example, window size) used in flow control.

  The data termination setting unit 314 generates termination notification data (FIN segment) for notifying completion of data transmission (end of session), and instructs the data processing unit 311 to transmit termination notification data.

  The data end transmission determination unit 315 determines whether or not the end notification data can be transmitted to the partner apparatus based on the flow control information of the information sharing unit 313.

  In the following example, video data is transmitted from a client via a network using TCP, the video represented by the video data is displayed on the server side of the apparatus, and video data is transmitted from the server to the client in the same TCP session. explain.

  Since the process until the session is established is the same as that of the second embodiment, description thereof is omitted. After the session is established, when the state changes to the ESTABLISHED state, video is transmitted from the client to the server.

  The received data is processed by the data processing unit 211 as in the second embodiment, and an image is displayed on the display 304 via the system memory 302. On the other hand, this server transmits video data captured by the video camera 303 to the client via the network 320 using the same TCP session.

  In the client, when data is received, the client transmits a segment in which ACK is set in the control flag and the sequence number that has been normally received is set as the confirmation response number in order to notify that data reception has been completed normally.

  FIG. 17 is a flowchart showing a session disconnection operation of the data communication apparatus according to the third embodiment of the present invention.

  When terminating a call, it is necessary to send a FIN segment with FIN set in the control flag to disconnect the TCP session. Hereinafter, the case where the call is disconnected from the server is described as an example.

  First, the application operating on the CPU 301 instructs the video camera to stop outputting the captured video. Next, the control processing unit 312 changes the session state of the information sharing unit 313 from ESTABLISHED to FIN-WAIT-1 (S201).

  Next, the data end transmission determination unit 315 reads the session information from the information sharing unit 313, and determines whether or not the transmission window size SND_WND (flow control information) is 0 (S202). In TCP, since the FIN flag is regarded as data of 1 byte, if the SND_WND is 0, the FIN segment cannot be transmitted. Therefore, the data end transmission determination unit 315 determines whether the FIN segment can be transmitted based on whether the window size is 1 byte or more.

  If possible, the data end setting unit 314 instructs the data processing unit 311 to transmit a segment (FIN segment) in which FIN is set in the control flag. Upon receiving the instruction, the data processing unit 311 reads the session information RCV_NXT and SND_NXT of the information sharing unit 313, sets the confirmation response number and the sequence number, respectively, and transmits the FIN segment (S205).

  On the other hand, if transmission is not possible, a process of waiting until the transmission window opens is performed (NO in S203 and S204). That is, the received data is processed by the data processing unit 311 until there is a window update notification from the counterpart device. When the transmission window size of the own device is updated (YES in S204), the determination is performed again (S202).

  As described above, by using this embodiment, the window size is inspected inside the TOE and the FIN segment is generated, so that the FIN segment appropriately reflecting the window size of the partner apparatus can be transmitted. Therefore, the problem that the FIN segment is not received due to insufficient window size is prevented.

  Even when data is received from the counterpart device and the RCV_NXT of the session information of the information sharing unit 313 is constantly changing, the confirmation response number of the FIN segment can be set correctly.

  In the above embodiment, the case where the FIN segment is transmitted after the data transmission from the server is stopped has been described. However, the FIN segment may be transmitted while the data transmission is continued. Even in this case, since the sequence number is set inside the TOE, the sequence number of the FIN segment can be set correctly.

  In the above description, the case where the FIN is transmitted has been described. However, a segment in which the control flag is set to RST may be transmitted using the data end setting unit 314. In the case of RST, since it is not necessary to check the transmission window size, the determination at the data end transmission determination unit 315 is always true.

  In addition, as shown in FIG. 18, the data end setting unit 314 and the data end transmission determination unit 315 may be provided in the CPU 301 instead of the TOE 305. In this case, when the transmission window size changes, the data end transmission determination unit 315 may be notified by an interrupt from the data processing unit 311 to determine whether the FIN segment can be transmitted. . Further, the data end transmission determination unit 315 may use a timer or the like to read the transmission window size from the information sharing unit 313 at regular intervals and determine whether transmission is possible.

  The embodiment of the present invention has been described above. The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  In addition, at least a part of the device described in the above-described embodiment may be configured by hardware or software. Further, a program that realizes at least a part of the functions of the apparatus may be stored in a recording medium such as a flexible disk or a CD-ROM, and read and executed by a computer. The recording medium is not limited to a removable medium such as a magnetic disk or an optical disk, but may be a fixed recording medium such as a hard disk device or a memory.

  Further, a program that realizes at least a part of the functions of the apparatus may be distributed via a communication line (including wireless communication) such as the Internet. Further, the program may be distributed in a state where the program is encrypted, modulated or compressed, and stored in a recording medium via a wired line such as the Internet or a wireless line.

Claims (3)

A data communication device that performs data communication using a protocol that retransmits the data from the transmission side when data loss is detected, and transmits / receives data to / from the transmission device via a network, A data processing unit that receives each data and processes the received data;
A control processing unit for managing a session state of data communication with the transmission device;
An information storage unit for storing the session state;
A data end detection unit for detecting that end data at the end of the series of data has been received;
A data reception completion determination unit that determines whether or not reception of the series of data has been completed when reception of the termination data is detected;
With
The data processing unit processes data from the transmission device according to the session state stored in the information storage unit,
The control processing unit transitions the session state to an end state when it is determined by the data reception completion determination unit that reception of the series of data has been completed, and when it is determined that the data has not been completed A data communication device that waits for the transition of the session state until it is determined that the session has been completed. When the data reception completion determination unit determines that the reception of the series of data has been completed, the data reception completion notification unit further transmits notification data indicating that the reception has been completed to the transmission device. 2. The data communication apparatus according to claim 1, wherein: A communication program to be executed by a data communication apparatus for performing data communication using a protocol for retransmitting the data from the transmission side when loss of data is detected,
A data processing step of transmitting and receiving data via a network with a transmission device, receiving a series of data for each of the data, and processing the received data;
A control processing step of managing a session state of data communication with the transmission device and writing the session state in an information storage unit;
A data end detection step for detecting that end data at the end of the series of data has been received;
A data reception completion determination step for determining whether or not reception of the series of data has been completed when reception of the termination data is detected;
With
The data processing step processes data from the transmission device according to the session state stored in the information storage unit,
When it is determined that the reception of the series of data is all completed by the data reception completion determination step, the control processing step transitions the session state to the end state, and when it is determined that the reception is not completed. A communication program that waits for the transition of the session state until it is determined to be completed.

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