JP6568571B2 - Data transfer device, data transfer method, and communication device - Google Patents

Description

  Embodiments described herein relate generally to a data transfer device, a data transfer method, and a communication device.

  In a communication apparatus mounted on a server apparatus and a terminal apparatus, Ethernet (registered trademark), IEEE802.11a / b / g / n / ac, or the like is generally used as a MAC layer and physical layer protocol. Generally, TCP / IP, UDP / IP, etc. are used as higher layer protocols. TCP / IP and UDP / IP are widely used on the Internet and the like. Ethernet is currently 1 Gbps, and 10 Gbps is starting to be used in data centers and the like. In addition, the specification of the next generation 40 Gbps / 100 Gbps Ethernet has been completed. Also in IEEE 802.11, the use of several hundred Mbps to several Gbps is expected to be steadily spread in the future.

  With the spread of such high-speed networks, the processing load of the host CPU that controls the high-speed network also increases. In order to reduce the processing load on the host CPU, dedicated hardware such as a TCP / IP offload engine (hereinafter referred to as TOE) has been used. The TOE is a device including a dedicated processor or a dedicated circuit that performs the above-described TCP / IP processing on behalf of the host CPU, and offloads the load of the TCP / IP processing from the host CPU. By using this TOE, it is possible to perform TCP / IP processing at a higher speed than protocol processing by conventional software.

  In transmission processing using a general TOE, a host CPU or the like writes data to be transmitted to a transmission queue, and the TOE reads data from the transmission queue, performs processing such as header generation, and transmits to the network. At this time, the TOE processes data in the order written in the transmission queue.

  In a server apparatus equipped with such a TOE, it is assumed that tens of thousands of TCP sessions are connected simultaneously, and the ability to process each session equally is required. However, according to the prior art, depending on the result of task scheduling on the host side, data of the same session may be continuously written in the transmission queue, and frames may be transmitted in bursts in the same session.

JP 2013-46173 A

  An embodiment of the present invention aims to allocate the network bandwidth to each session as evenly as possible.

  A data transfer apparatus according to an embodiment of the present invention is a data transfer apparatus that communicates with a plurality of opposing devices via a network, and includes a session management unit and a communication processing unit.

  The session management unit sequentially and cyclically selects a plurality of sessions generated for the plurality of opposing devices.

  The communication processing unit performs a data transmission process on the opposite device related to the session selected by the session management unit so as to suppress variation in the amount of data transmitted in each transmission process between the sessions. .

The block diagram which shows the communication apparatus provided with the data transfer apparatus which concerns on 1st Embodiment. The session state transition diagram concerning a 1st embodiment. The flowchart which shows operation | movement of 1st Embodiment. The block diagram which shows the communication apparatus provided with the data transfer apparatus which concerns on 2nd Embodiment. The session state transition diagram concerning a 2nd embodiment. The flowchart which shows operation | movement of 2nd Embodiment. The block diagram which shows the communication apparatus provided with the data transfer apparatus which concerns on 3rd Embodiment. The session state transition diagram concerning a 3rd embodiment. The flowchart which shows operation | movement of 3rd Embodiment.

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

(First embodiment)
FIG. 1 is a block diagram illustrating a communication apparatus including a data transfer apparatus according to the first embodiment. In the figure, a solid line with an arrow indicates a flow of data to be transmitted to the network, and a broken line with an arrow indicates a flow of information other than control or data to be transmitted to the network.

  A communication device 100 illustrated in FIG. 1 is connected to one or more opposing devices 301 via a network 201. The network 201 is a wireless network, a wired network, or a hybrid network thereof, and as an example is the Internet.

  The communication device 100 generates a session according to a communication protocol such as TCP to each of the opposing devices 301 and communicates based on the generated session. As an example, this communication device is a server device that supplies data such as an image, a sound, a moving image, and text in response to a request from the opposing device 301. The form of the communication device is not limited to this, and may be a user terminal such as a smartphone, a PC, a tablet, or a mobile terminal as long as it is a device that generates a session with the opposite device 301 and performs communication. As a specific product form, a form such as a dedicated LSI or an FPGA (Field Programmable Gate Array) can be used in addition to these server devices and PCs, but is not limited thereto.

  Each opposing device 301 may be a user terminal such as a smartphone, a PC, a tablet, or a portable terminal, or may be a household electrical appliance device or the like. Any device that generates a session with the communication device 100 and receives data from the communication device may be used.

  The communication device of FIG. 1 includes a data transfer device 101, a host CPU (processor) 102, a storage device 103, and a transmission buffer 104. The host CPU 102 controls to read data to be transmitted from the storage device 103 and write it to the transmission buffer 104 for each session. Further, the host CPU 102 controls establishment / disconnection of a connection with the opposite device for each session. The data transfer apparatus 101 repeatedly selects each session for each session for which a connection has been established by the host CPU 102 and repeats transmission processing for the selected session. In the transmission process, data is transmitted to the opposite device that generated the session. The data transfer apparatus 101 transmits data so as to suppress variation in the amount of data transmitted in each transmission process between sessions. This gives each session an equal opportunity for transmission and uses the network bandwidth as evenly as possible.

  The storage device 103 stores data for transmission. Specific implementation forms of the storage device 103 are, for example, SSD (Solid State Drive), HDD (Hard Disk Drive), SD card, SDRAM, and the like, but are not limited thereto.

  The transmission buffer 104 is a storage area for temporarily holding data. In the transmission buffer 104, an area to be used for each session may be allocated in advance. The transmission buffer 104 may be disposed on the storage device 103 or may be disposed on another device such as a main memory. Further, it may be arranged in the data transfer apparatus 101 described later.

  The host CPU 102 controls the entire communication device 100. The host CPU 102 includes an application unit 21, a connection processing unit 22, and a write control unit 23 as main processing units realized by software. The application unit 21 is a processing unit that executes a data transmission application.

  The connection processing unit 22 generates a session with the counterpart device 301 according to the communication protocol to be used (here, TCP / IP is assumed), and establishes / disconnects a connection for communicating with the counterpart device 301 in the session. Perform the process. The connection processing unit 22 assigns a unique ID to the generated session. This ID is called a session ID. The connection processing unit 22 transmits / receives a control packet for establishing or disconnecting the connection to / from the opposite device 301 via the communication processing unit 14 of the data transfer apparatus 101. Examples of the control packet include a SYN packet, a FIN packet, and a packet transmitted / received accompanying these packets.

  When the connection processing unit 22 establishes or disconnects the connection, the connection processing unit 22 notifies the session management unit 11 of the data transfer apparatus 101 of the connection establishment or disconnection notification. At this time, the session ID that has been established or disconnected is notified. The connection establishment notification may be made when data to be transmitted first occurs in the connection, or when the data is written in the transmission buffer 104 under the control of the data write control unit 23 described later.

  Here, the TCP / IP session refers to a connection managed by four pieces of information of destination IP address / source IP address / destination port number / source port number. Generating a session corresponds to generating a set of these four pieces of information. A certain session has a state in which a connection is established or a state in which a connection is not established (disconnected). TCP / IP performs transmission processing and reception processing for each session with an opposite device related to the session. The data transfer apparatus 101 according to the present embodiment also performs transmission processing and reception processing with the opposite device 301 related to the session for each session.

  The write control unit 23 performs control for writing data stored in the storage device 103 to the transmission buffer 104. An arbitrary method may be used as the writing control method depending on the apparatus configuration. For example, the storage device 103 has a built-in DMAC (direct memory access controller) (not shown), and the write control unit 23 outputs an instruction signal to the DMAC so that the DMAC writes data to the transmission buffer 104. May be. In this case, the write control unit 23 may indicate the write address in the transmission buffer 104 to the DMAC. Alternatively, the host CPU 102 itself may read data from the storage device 103 and write it in the transmission buffer 104. Alternatively, the writing process may be performed using dedicated hardware.

  The host CPU 102 can perform various processes in addition to the processes described above.

  The data transfer apparatus 101 performs data transmission processing and reception processing according to TCP / IP on behalf of the host CPU 102. For each session, the data transfer apparatus 101 reads the data written in the transmission buffer 104 and performs protocol processing such as TCP / IP. As a result, a frame is generated. Then, the generated frame is transmitted to the network 201. Such a data transfer apparatus 101 includes a session management unit 11, a session information storage unit 12, a data reading unit 13, and a communication processing unit 14. The data transfer apparatus 101 may be configured with either hardware or software (program), or may be configured with both.

  When the session management unit 11 receives a connection establishment notification from the connection processing unit 22, the session management unit 11 registers the ID of the session for which the connection has been established. In addition, when the connection disconnection notification is received, the ID of the session disconnected is deleted. Thereby, the session management part 11 grasps | ascertains the session in a connection establishment state inside. Hereinafter, registering or deleting a session ID may be expressed as registering or deleting a session.

  The session management unit 11 cyclically selects each session sequentially based on the registered session ID, and outputs instruction information for instructing the communication processing unit 14 to perform transmission processing for the selected session. As a method for selecting a session cyclically, for example, a method is used in which registered session IDs are held in a queue, session IDs are read sequentially from the top, and the read session IDs are stored again at the end of the queue. May be. The queue is stored in a buffer inside or outside the data transfer apparatus 101.

  Alternatively, a table holding the ID and connection status (established or disconnected) of each session established by the connection processing unit 22 is held in an internal or external buffer of the data transfer apparatus 101. A method may be used in which each entry of the table is sequentially and cyclically checked to select a session in a connection established state. In this case, that a session is registered in the session management unit 11 means that the session ID is registered in the table and the connection state is “established”. In addition to the method described here, a method of selecting a session may be used.

  The session information storage unit 12 stores session information of each session registered in the session management unit 11. The session information includes the value of the above-described session (destination IP address / source IP address / destination port number / source port number) and other information (sequence number, confirmation, etc.) necessary for generating the TCP / IP header. Response number (ACK sequence number), etc.). Further, MSS (Maximum Segment Size) may be included in the session information. If the MSS is common to all sessions, it may be managed separately.

  The session information also includes buffer information for specifying in which position in the transmission buffer 104 the data for the session is written. The buffer information includes information for specifying an address storing data that has not yet been transmitted in the transmission buffer 104. For example, the buffer information includes a read pointer that indicates the end address of data that has been read in the transmission buffer 104 (or the start address of data that has not been read yet), a write pointer that indicates the end address of data that has been written, and It may be a pair. The buffer information may be configured by other representation methods.

  The session information storage unit 12 may be arranged in the data transfer apparatus 101 or may be arranged outside the data transfer apparatus 101 (for example, a main memory). The session information may be registered in the session information storage unit 12 when a session is registered in the session management unit 11 (that is, a session ID is registered), and may be deleted when the session is deleted from the session management unit 11. The session information in the session information storage unit 12 may be updated when a transmission process corresponding to the session is performed, when data corresponding to the session is written in the transmission buffer 104, or the like. The registration, deletion, and update of the session information described here are performed by the host CPU 102 or the data transfer apparatus 101, and either may be configured to be performed.

  For example, the session management unit 11 of the data transfer apparatus 101 may generate session information when registering a session ID, and store the session information in the session information storage unit 12. Information necessary for generating session information may be acquired from the host CPU 102. Alternatively, when registering a session in the session management unit 11, the connection processing unit 22 of the host CPU 102 or another processing unit may generate session information and store it in the session information storage unit 12.

  Further, the session management unit 11 of the data transfer apparatus 101 may delete the corresponding session information from the session information storage unit 12 when deleting the session ID. Alternatively, when the session ID is deleted from the session management unit 11, the connection processing unit 22 of the host CPU 102 or another processing unit may delete the session information from the session information storage unit 12.

  Further, when data is written in the transmission buffer 104 under the control of the write control unit 23 of the host CPU 102, the host CPU 102 or the data transfer device 101 updates the corresponding session information (for example, buffer information in the session information). May be. Further, when the communication processing unit 14 of the data transfer apparatus 101 executes transmission processing, the corresponding session information (buffer information, sequence number, etc.) may be updated.

  The data reading unit 13 reads data from the transmission buffer 104 in response to a data reading instruction from the communication processing unit 14. The data reading unit 13 sends the read data to the communication processing unit 14. The read address in the transmission buffer 104 may be configured such that the communication processing unit 14 calculates from the buffer information in the session information and notifies the communication processing unit 14, or the data reading unit 13 calculates from the buffer information. Also good. Alternatively, the buffer information may be separated from the session information and managed by the data reading unit 13.

  The communication processing unit 14 performs data transmission processing for each session that is cyclically instructed from the session management unit 11. The communication processing unit 14 can know information such as the position and size of untransmitted data in the transmission buffer 104 by confirming buffer information corresponding to the session. Therefore, based on the buffer information, data can be read from the transmission buffer 104 and transmitted.

  Specifically, when a session to be transmitted next is designated by the session management unit 11, the communication processing unit 14 acquires the corresponding session information, and acquires a sequence number or an acknowledgment number included in the session information, A TCP / IP header is generated from the port number and the like. In addition, the data reading unit 13 is instructed to read data corresponding to the session. At this time, a read address may be calculated from the buffer information in the session information and notified to the data reading unit 13. The communication processing unit 14 acquires the data read by the data reading unit 13, and generates a frame by combining the acquired data with the above-described header and a separately calculated checksum. The communication processing unit 14 sends the generated frame to the network 201.

  In addition to the data transmission described here, the communication processing unit 14 performs a data reception process from the opposite device 301 and a transmission / reception process such as an ACK packet, a FIN packet, and an RST packet. When the communication processing unit 14 receives the above-described control packet from the network 201, the communication processing unit 14 passes the control packet information to the host CPU 102 via a memory such as a main memory. Further, the communication processing unit 14 may generate a control packet based on information passed from the host CPU 102 and transmit it to the network 201. The host CPU 101 may generate the control packet.

  FIG. 2 shows a state transition diagram of one session in the data transfer apparatus 101. There are a non-offload processing state A101 and an offload processing state A102 as session states.

  A certain session is in the non-offload processing state A101 as an initial state when the session is generated by the connection processing unit 22. When a connection is established for the session and the session is registered in the session management unit 11, the session state transitions to the offload processing state A102 (T101). When the session is deleted from the session management unit 11, the session transits to the non-offload processing state A101 (T102).

  In the offload processing state A102, the session is selected cyclically (equally) by the session management unit 11 together with other session groups in the offload processing state A102, and the communication processing unit 14 relates to the session. Transmission processing is performed. That is, each session in the offload processing state A102 is equally assigned a transmission opportunity and can transmit data. On the other hand, the session in the non-offload processing state A101 is not registered in the session management unit 11, and no transmission opportunity is given.

  That is, the host CPU 102 requests the data transfer apparatus 101 to perform an arbitrary session transmission process by registering a session ID in the session management unit 11. The data transfer apparatus 101 performs the transmission process equally for the sessions registered in the session management unit 11 in order. Further, the host CPU 102 can notify the disconnection of the connection, thereby excluding the session ID registered in the session management unit 11, thereby stopping the transmission processing by the data transfer apparatus 101 for the session.

  FIG. 3 is a flowchart of transmission processing in the data transfer apparatus 101.

(Step S101) First, the session management unit 11 selects one session from the sessions managed by itself, and notifies the communication processing unit 14 to start transmission processing for the session.

(Step S <b> 102) The communication processing unit 14 reads the session information corresponding to the session notified from the session management unit 11 from the session information storage unit 12. The communication processing unit 14 specifies information necessary for reading data from the read session information, and sends the specified information to the data reading unit 13 together with a read instruction. Information necessary for reading data may include, for example, a read address (buffer information) in the transmission buffer 104, an MSS (Maximum Segment Size), and the like. When the data reading unit 13 manages these pieces of information internally, the communication processing unit 14 may be configured to send only a reading instruction.

(Step S <b> 103) The data reading unit 13 reads data from the transmission buffer 104 in accordance with a reading instruction from the communication processing unit 14. For example, the data stored in one frame is read.

  For example, when the MSS is set to 1460 bytes and 4 KB data exists in the transmission buffer 104, the data is read by 1460 bytes out of 4 KB. Alternatively, when MSS is set to 1460 bytes and 512 bytes of data exist in the transmission buffer 104, 512 bytes of data are read. In the present embodiment, it is assumed that one frame is transmitted in one transmission process for each session, but a predetermined plurality of frames may be transmitted. In this case, the data stored in each frame is read out by the number of frames. Naturally, when there is no data to be stored in the frame, the number of frames to be transmitted is smaller than the predetermined number. That is, the upper limit value of the number of frames transmitted in each session and each transmission process is common.

(Step S104) Upon receiving data from the data reading unit 13, the communication processing unit 14 generates a header based on the session information and combines the header with the data. Also, a checksum is calculated from the header and data, and the calculation result is further added to the data to generate a frame. The communication processing unit 14 outputs the generated frame to the network 201.

(Step S105) The communication processing unit 14 updates session information corresponding to the session that transmitted the frame. For example, the sequence number (sent sequence number) in the session information is updated based on the size of the data transmitted this time. Further, the buffer information in the session information is updated from the address read from the transmission buffer 104 this time, the size of the data transmitted this time, or the like. In addition, the values of other items in the session information are updated as necessary. However, the buffer information may be updated at a timing when an ACK packet corresponding to the transmitted data is received in consideration of retransmission processing.

(Modification)
In the first embodiment, TCP is assumed as a communication protocol, and a session in which a connection is established is selected by the session management unit. However, when a connectionless protocol such as UDP is used, it is simple. In addition, each established session can be selected. This applies similarly to second and third embodiments described later.

  As described above, according to the communication device according to the first embodiment, the transmission process is executed in order (cyclically) for each session, and the variation in the amount of data transmitted in each transmission process between the sessions is varied. Suppress. For example, the number of frames equal to or less than the upper limit value is transmitted in each session and each transmission process. As a result, the network bandwidth can be equally allocated to each session, and frames can be prevented from being transmitted in bursts in a specific session.

(Second Embodiment)
In the present embodiment, only sessions in which data exists in the transmission buffer 104 among sessions managed by the session management unit 11 are selected as targets for transmission processing. In the first embodiment, as long as it is registered in the session management unit 11, a session for which there is no data to be transmitted is also selected. For this reason, when the transmission processing operation is performed for the session, there is no data to be transmitted. Therefore, the data transmission is not performed, and the session information read operation performed so far, analysis thereof, etc. Is wasted (skipping motion). This becomes an extra load for the data transfer apparatus, and the use efficiency of the network band is lowered for the time of the operation. Therefore, in the present embodiment, this problem is solved by excluding sessions having no data to be transmitted from session selection targets for transmission processing.

  FIG. 4 is a block diagram illustrating a communication device including a data transfer device according to the second embodiment. Elements having the same names as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted except for processing that has been changed or expanded.

  The data transfer apparatus 101 in the communication apparatus 200 according to the present embodiment includes a buffer state management unit 17 in addition to the processing units according to the first embodiment. The buffer status management unit 17 manages the setting of the status of each session registered in the session management unit 11 according to the data storage status in the transmission buffer 104.

  FIG. 5 shows a state transition diagram of one session in the data transfer apparatus 101.

  In addition to the non-offload processing state A101 and the offload processing state A102 in the first embodiment, an offload processing state (data waiting) A103 is provided. Here, the offload processing state A102 described in the first embodiment is expressed as an offload processing state (transmittable) A102 and is distinguished from the offload processing state (data waiting) A103. The offload processing state (transmittable) A102 corresponds to the first state of the session, and the offload processing state (data waiting) A103 corresponds to the second state of the session.

  The offload processing state (data waiting) A103 is a state in which a connection is established for a certain session and is registered in the session management unit 11, but no transmission data exists in the transmission buffer 104. In this state, the session management unit 11 excludes the session from selection targets for transmission processing.

  The buffer state management unit 17 manages the settings of the offload processing state (transmittable) A102 and the offload processing state (data waiting) A103 for each session managed by the session management unit 11.

  For example, in the offload processing state (transmittable) A102, when it is detected that no data exists in the transmission buffer 104, the communication processing unit 14 notifies the buffer state management unit 17 to that effect. Receiving the notification, the buffer state management unit 17 sets the state of the session in the session management unit 11 to the offload processing state (data waiting) A103 (T103).

  Here, not the non-offload processing state A101 but the offload processing state (data waiting) A103 is set because the data transfer apparatus 101 does not transfer data from the transmission buffer 104, This is because control-related transmission / reception processing such as an ACK packet, FIN packet, and RST packet needs to be performed with the opposite device 301. That is, as long as a session is registered in the session management unit 11, the data transfer apparatus operates so that the control-related transmission / reception process is performed without performing the data transmission process.

  Further, when the write control unit 23 writes data to the transmission buffer 104 by the control, the write control unit 23 notifies the buffer state management unit 17 to that effect. Upon receiving the notification, the buffer state management unit 17 changes the state of the session in the session management unit 11 from the offload processing state (data waiting) A103 to the offload processing state (transmittable) A102 (T104). If the session is originally in the offload processing state (transmittable) A102, the state is maintained.

  In the offload processing state (waiting for data) A103, when receiving a disconnection notification from the connection processing unit 22, the session management unit 11 deletes the registration of the session. That is, the session ID of the session is deleted. As a result, the session transitions to the non-offload processing state A101 (T105).

  The session management unit 11 cyclically selects only the sessions in the offload processing state (transmittable) A102 and causes the communication processing unit 14 to execute transmission processing. As a result, a connection is established, but it is not necessary to start the transmission processing operation for a session in which no data exists in the transmission buffer 104.

  FIG. 6 is a flowchart of transmission processing in the data transfer apparatus 101 according to the present embodiment. More specifically, this flowchart shows a flow of processing performed for a session registered in the session management unit 11 and in the offload processing state (transmittable) A102.

(Step S201) The session management unit 11 selects one session in the offload processing state (transmittable) A102 from the sessions managed by the session management unit 11 and starts transmission processing for the session. The communication processing unit 14 is notified.

(Step S202) The communication processing unit 14 reads out the session information corresponding to the notified session from the session information storage unit 12. The communication processing unit 14 specifies information (for example, buffer information, MSS, etc.) necessary for reading data from the transmission buffer 104 from the session information.

(Step S203) The communication processing unit 14 determines whether there is transmission data in the transmission buffer 104 from the specified information. For example, when the buffer information indicates that there is no address to be read (for example, when the read pointer and the write pointer match), it is determined that there is no data in the transmission buffer 104. In other cases, it can be determined that data exists.

(Step S207) When the communication processing unit 14 determines that there is no data in the transmission buffer 104, the communication processing unit 14 notifies the buffer state management unit 17 to that effect. The buffer state management unit 17 sets the state of the session to the offload processing state (data waiting) A103. Thereafter, the process returns to step S201.

(Step S204) On the other hand, when the communication processing unit 14 determines that data is present in the transmission buffer 104, the communication processing unit 14 sends a read instruction and, if necessary, buffer information or the like to the data reading unit 13. send. The data reading unit 13 reads from the transmission buffer 104 as much data as is stored in one frame, for example, according to the read instruction. As in the first embodiment, for each session, transmission for one frame is assumed for each transmission process. However, a plurality of frames may be transmitted in one transmission process.

(Step S205) Upon receiving data from the data reading unit 13, the communication processing unit 14 generates a header based on the session information, and combines the generated header with the data. In addition, a checksum is calculated from the header and data, and the calculation result is further added to the data to generate a frame. The communication processing unit 14 outputs the generated frame to the network 201.

(Step S206) After transmitting the frame, the communication processing unit 14 updates the session information of the session in the session information storage unit 12. For example, the sequence number (sent sequence number) in the session information is updated according to the size of the data transmitted this time. Also, the buffer information in the session information is updated according to the address from which the data transmitted this time is read. The buffer information may be updated at a timing when an ACK packet corresponding to the transmitted frame is received in consideration of retransmission processing.

  In the processing described above, the communication processing unit 14 determines whether data exists in the transmission buffer 104 at the start of the transmission processing, but determines whether data exists in the transmission buffer 104 after the transmission processing is completed. May be performed. That is, the processing in steps S203 and S206 in FIG. 6 may be performed after step S205 or S206.

  In the above-described embodiment, the communication processing unit 14 determines whether data exists in the transmission buffer 104. However, the buffer state management unit 17 may perform this determination. In this case, the buffer state management unit 17 receives a notification of the address of data newly written in the transmission buffer 104 for each session from the write control unit 23, and reads out from the transmission buffer 104 from the communication processing unit 14. Notification of the address of the received data (or the address of the data that has been transmitted and received the ACK packet) is received. The buffer status management unit 17 uses, for example, the end address of the written data as a write pointer and the end address of the read data as a read pointer, and manages it in a buffer (memory) inside or outside the data transfer apparatus 101. The buffer state management unit 17 can determine whether there is data that has not yet been read by comparing these pointers. When it is detected that there is data that has not yet been read, the session state is changed to the offload state (data waiting) A103.

  As described above, according to the communication apparatus according to the second embodiment, the frame transmission process is sequentially executed only for a session in which a connection is established and data exists in the transmission buffer 104. This makes it possible to transfer efficiently while using the bandwidth equally between sessions.

(Third embodiment)
In TCP, the receiving communication device currently notifies the transmitting communication device of the data size that can be received by the receiving device as the window size (reception window size). This window size is included in the header of the data packet or ACK packet. Generally, the reception window size is set to the size of an empty area of its own reception buffer.
The communication device on the transmission side uses the reception window size of the communication device on the reception side as its transmission window size, and controls transmission (flow control) so that data transmission larger than the transmission window size is not performed. This is to prevent buffer overflow in the receiving communication apparatus. If an overflow occurs in the reception buffer of the communication device on the receiving side, a TCP / IP retransmission process occurs, and more packets than usual are transmitted to the network.

  In addition, there is a possibility that a buffer exists in a communication device (for example, a relay device such as a router) on the communication path of the network and the buffer may overflow. Therefore, in TCP, the transmission side performs transmission processing so as not to cause congestion while limiting the data size to be transmitted by congestion control. At this time, the data size to be transmitted is determined by the congestion window on the transmission side. In TCP congestion control, the congestion window size is initially started from a small value, and the congestion window size is increased every time an ACK packet is received from the receiving side (data arrives at the receiving side). If the congestion window size is increased and a duplicate ACK or retransmission timeout occurs, it is judged that a packet loss (congestion) has occurred due to a buffer overflow on the communication path, and the congestion window size is reduced. Let In this way, in TCP, transmission processing is performed while limiting the data size to be transmitted, thereby preventing network congestion as much as possible. There are various congestion control algorithms, but since this embodiment does not depend on the type of the congestion control algorithm, further explanation is omitted.

The communication device on the transmission side interrupts the transmission process when either the transmission window size (reception window size of the opposite device) or the congestion window size falls below a certain threshold.
That is, if at least one of the window sizes is equal to or smaller than the threshold value, transmission is interrupted for the session. For this threshold value, for example, a value such as MSS is used. The session for which transmission is interrupted receives an ACK packet from the opposite device, the transmission window size (opposite reception window size) and the congestion window size are updated, and if any window size exceeds the threshold, transmission is performed. Resumed.

  As described above, in TCP, flow control and congestion control are performed using a transmission window and a congestion window. Therefore, even when there is a connection established state and data exists in the transmission buffer, transmission is not performed. There is. If the transmission process is performed while ignoring the flow control and the congestion control, there is a possibility that the transfer efficiency is lowered. For example, if the receiving buffer on the receiving side (opposite device side) is extremely small, sending data with a size smaller than the above threshold of the transmission window may reduce transfer efficiency and prevent transfer at the maximum speed There is. In addition, when the session communication path is congested, even if data with a size smaller than the above threshold value of the congestion window is transmitted, the transfer efficiency similarly decreases and it becomes impossible to transfer at the maximum speed. Sex exists. In addition, if the transmission process shown in the flowchart of the first or second embodiment is performed in the state where the flow control and the congestion control are performed, the session whose transmission is restricted by the flow control and the congestion control is performed. If the operation of the transmission process is taken, data is not transmitted after all, and the operations such as the session information reading operation and the analysis performed so far are wasted (idling operation). This becomes an extra load for the data transfer apparatus, and the use efficiency of the network band is lowered for the time of the operation. Therefore, in the third embodiment, a session for performing transmission processing is determined in consideration of the state of flow control and congestion control.

  FIG. 7 is a block diagram illustrating a communication apparatus including a data transfer apparatus according to the third embodiment. Elements having the same names as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted except for processing that has been changed or expanded.

  The communication processing unit 14 of the communication device 300 includes a transmission processing unit 16 that performs transmission processing and a reception processing unit 15 that performs reception processing. The communication processing unit 14 has a function of executing a TCP congestion control algorithm. In the first and second embodiments as well, the communication processing unit 14 includes a processing unit that performs transmission processing and a unit that performs reception processing. In the present embodiment, these are explicitly described. .

  The data transfer apparatus 101 of the present embodiment includes a window state management unit 18 in addition to the processing units of the first embodiment. The window state management unit 18 controls the setting of the session state managed by the session management unit 11 in accordance with the state of the transmission window and the congestion window (that is, the state of flow control and congestion control).

  FIG. 8 shows a state transition diagram of one session in the data transfer apparatus 101.

  In addition to the non-offload processing state A101 and the offload processing state A102 in the first embodiment, an offload processing state (waiting for window update) 104 is provided. In order to distinguish the offload processing state described in the first embodiment from the offload processing state (waiting for window update) 104, it is expressed as an offload state (transmittable) A102. The offload processing state (transmittable) A102 corresponds to the first state of the session, and the offload processing state (waiting for window update) A104 corresponds to the second state of the session.

  The offload processing state (waiting for window update) 104 is a state where a connection has been established and registered in the session management unit 11, but at least one of the window sizes of the transmission window and the congestion window is equal to or smaller than a threshold value. A state in which the window size of the transmission window is equal to or smaller than a threshold value may be expressed as “the transmission window is closed”, and a state larger than the threshold value may be expressed as “the transmission window is open”. A state where the window size of the congestion window is equal to or smaller than a threshold value may be expressed as “the congestion window is closed”, and a state larger than the threshold value may be expressed as “the congestion window is open”. The transmission window threshold and the congestion window threshold may be the same or different. For example, MSS may be used for both threshold values. Sessions in which the window is closed are excluded from selection targets of the session management unit 11 and transmission processing is not performed.

  The window state management unit 18 manages the settings of the offload processing state (transmittable) A102 and the offload processing state (waiting for window update) A104 for each session registered in the session management unit 11.

  For example, if the transmission processing unit 16 detects that the window is closed at the start of transmission processing for the session in the offload processing state (transmittable) A102, the window state management unit 18 is notified of this fact. . Upon receiving the notification, the window state management unit 18 transitions the state of the session to an offload processing state (waiting for window update) A104 (T106). The non-offload processing state A101, not the offload processing state (waiting for window update) A104, is that data transmission from the transmission buffer 104 is not performed, but data reception processing from the opposite device 301, ACK packet, or FIN packet This is because the transmission / reception process of the RST packet needs to be performed. That is, as long as a session is registered in the session management unit 11, the data transfer apparatus operates so that the control-related transmission / reception process is performed without performing the data transmission process.

  On the other hand, in the offload processing state (waiting for window update) A104, the reception processing unit 15 receives the ACK packet from the opposite device 301, and each window size for transmission and congestion is determined according to the window size in the TCP packet and the TCP congestion algorithm. Is updated (which may be maintained at the same value), each window size is compared to a threshold value. When both are larger than the threshold value, the reception processing unit 15 notifies the window state management unit 18 of this fact. Upon receiving the notification, the window state management unit 18 transitions the state of the session to the offload processing state (transmittable) A102 (T107). Alternatively, it may be configured such that when an ACK packet is received without confirming whether each window size is larger than the threshold, the state immediately transitions to the offload processing state (transmittable) A102. This is because when receiving an ACK packet, it can be considered that there is a high possibility that each window size will be updated. If any one of the window sizes remains below the threshold value, the offload processing state (transmittable) is possible. This is because even if the transition is made to A102, it is possible to transit again to the offload processing state (waiting for window update) A104 during the next transmission process.

  In addition, in the offload processing state (waiting for window update) A104, when receiving a disconnection notification from the connection processing unit 22, the session management unit 11 deletes the registration of the session. That is, the session ID of the session is deleted. As a result, the session transitions to the non-offload processing state A101 (T108).

The values of the transmission window size and the congestion window size may be managed by being included in the session information of each session. For example, when new values of the transmission window size and the congestion window size are acquired by receiving the ACK packet in the reception processing unit 15, the updated value is written (overwritten) in the session information of the corresponding session. Also good.
In addition, the window state management unit 18 compares each window size in the session information with each threshold value periodically or when any event occurs, and controls the setting of the session state according to the determination method described above. Also good. As an arbitrary event, for example, when at least one of the window sizes in the session information is updated, the communication processing unit may notify the window state management unit 18 of this, and this may be used as a trigger. It is not limited to this.

  FIG. 9 is a flowchart of transmission processing in the data transfer apparatus 101 according to the present embodiment. More specifically, this flowchart shows a flow of processing performed for a session registered in the session management unit 11 and in the offload processing state (transmittable) A102.

(Step S301) The session management unit 11 selects one session in the offload processing state (transmittable) A102 from the sessions managed by the session management unit 11, and starts transmission processing for the session. The communication processing unit 14 is notified.

(Step S302) The transmission processing unit 16 of the communication processing unit 14 reads out the session information corresponding to the notified session from the session information storage unit 12.

(Step S303) The transmission processing unit 16 determines whether the transmission window and the congestion window are open from the values of the window sizes of the transmission window and the congestion window included in the session information. That is, it is determined whether each window size value is larger than the threshold value.

(Step S307) If at least one of the windows is closed, that is, if the value of at least one of the windows is equal to or smaller than the threshold value, the transmission processing unit 16 notifies the window state management unit 18 to that effect. The window state management unit 18 sets the state of the session to the offload processing state (waiting for window update) A104. Thereafter, the process returns to step S301.

(Step S304) On the other hand, if both windows are open, the transmission processing unit 16 sends a read instruction and, if necessary, buffer information or the like to the data reading unit 13. The data reading unit 13 reads from the transmission buffer 104, for example, the data stored in one frame in accordance with the read instruction. Similar to the first embodiment, a plurality of frames may be transmitted in one transmission process. However, the upper limit value of the data size to be read is the minimum value of the transmission window size or the congestion window size.

(Step S305) Upon receiving data from the data reading unit 13, the transmission processing unit 16 generates a header based on the session information, and combines the generated header with the data. In addition, a checksum is calculated from the header and data, and the calculation result is further combined with the data to generate a frame. The transmission processing unit 16 outputs the generated frame to the network 201.

(Step S306) After the transmission of the frame, the transmission processing unit 16 updates the session information of the session in the session information storage unit 12. For example, the sequence number (sent sequence number) in the session information is updated according to the size of the data transmitted this time. Also, the buffer information in the session information is updated from the read address of the data transmitted this time.

  In addition, the reception process part 15 updates the transmission window size and congestion window size in session information, when an ACK packet etc. are received from an opposing apparatus. When the value of both window sizes exceeds the threshold value from the state below the threshold value due to the update, the window state management unit 18 is notified accordingly. Upon receiving the notification, the window state management unit 18 updates the state of the corresponding session to an offload processing state (transmittable).

  In the above-described embodiment, the transmission process is controlled using both the transmission window and the congestion window. However, the control may be performed using only one of the windows. For example, when the transmission window is used, if the transmission window size is larger than the threshold value, the state of the session is set as an offload processing state (transmission is possible), and the session is set as a transmission processing target. If the value is equal to or less than the threshold value, the session is not subjected to transmission processing in the offload processing state (waiting for window update). Similarly, when the congestion window is used, if the congestion window size is larger than the threshold value, the state of the session is set as an offload processing state (transmittable), and the session is subjected to transmission processing. If the value is equal to or less than the threshold value, the session is not subjected to transmission processing in the offload processing state (waiting for window update).

  As described above, according to the communication apparatus according to the third embodiment, the transmission process is sequentially and cyclically executed only for the session in which the window is open among the sessions in which the connection is established. Thus, it is possible to efficiently transfer while using the bandwidth equally.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements 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.

11: Session management unit 12: Session information storage unit 13: Data reading unit 14: Communication processing unit 15: Reception processing unit 16: Transmission processing unit 17: Buffer state management unit 18: Window state management unit 21: Application unit 22: Connection Processing unit 23: Write control unit 101: Data transfer device 102: Host CPU
103: Storage device 104: Transmission buffer 201: Network 301: Counter device

Claims (8)

A data transfer device that communicates with a plurality of opposing devices via a network,
A window for setting the first state for the session when the value of the transmission window size of the plurality of sessions generated for the plurality of opposite devices is larger than the threshold, and the second state when the value is equal to or smaller than the threshold A state management unit;
A session management unit that sequentially and cyclically selects sessions in which the first state is set;
A communication processing unit that performs a data transmission process on the opposite device related to the session selected by the session management unit,
When the communication processing unit receives an acknowledgment packet related to the session from the opposite device, the session management unit sets the session state to the first state regardless of the value of the transmission window size. Set to the data transfer device. A data transfer device that communicates with a plurality of opposing devices via a network,
A window for setting the first state for the session when the value of the congestion window size of the plurality of sessions generated for the plurality of opposite devices is larger than the threshold, and the second state when the value is less than the threshold A state management unit;
A session management unit that sequentially and cyclically selects sessions in which the first state is set;
A communication processing unit that performs a data transmission process on the opposite device related to the session selected by the session management unit,
When the communication processing unit receives an acknowledgment packet related to the session from the opposite device, the session management unit sets the session state to the first state regardless of the value of the congestion window size. Set to the data transfer device. The data transfer apparatus according to claim 1, wherein the plurality of sessions are sessions in which connections are established with the plurality of opposite devices. The data transfer device according to any one of claims 1 to 3, wherein the communication processing unit communicates with the opposite device according to TCP / IP. A host CPU that generates the session for the plurality of opposing devices;
A data transfer device according to any one of claims 1 to 4,
A communication device comprising: The host CPU includes a connection processing unit that controls establishment and disconnection of the connection with the opposite device for the session,
When the connection processing unit establishes the connection, it notifies the data transfer device of the identifier of the session that established the connection,
The communication apparatus according to claim 5, wherein the session management unit of the data transfer apparatus selects the session based on an identifier notified from the host CPU. A data transfer method for communicating with a plurality of opposing devices via a network,
A window for setting the first state for the session when the value of the transmission window size of the plurality of sessions generated for the plurality of opposite devices is larger than the threshold, and the second state when the value is equal to or smaller than the threshold A state management step;
A session management step for sequentially and cyclically selecting the sessions in which the first state is set;
A communication processing step of performing a data transmission process on the opposite device related to the session selected in the session management step,
When an acknowledgment packet related to the session is received from the opposite device in the communication processing step, the session management step sets the session state to the first state regardless of the value of the transmission window size. Set the data transfer method to. A data transfer method for communicating with a plurality of opposing devices via a network,
A window for setting the first state for the session when the value of the congestion window size of the plurality of sessions generated for the plurality of opposite devices is larger than the threshold, and the second state when the value is less than the threshold A state management step;
A session management step for sequentially and cyclically selecting the sessions in which the first state is set;
A communication processing step of performing a data transmission process on the opposite device related to the session selected in the session management step,
In the session management step, when an acknowledgment packet related to the session is received from the opposite device in the communication processing step, the session state is set to the first state regardless of the value of the congestion window size. Set the data transfer method to.

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