JP2009015392A - Communication device and communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication device preventing reduction of throughput of TCP (Transmission Control Protocol). <P>SOLUTION: This communication device having an ALG (Application Level Gateway) processing function has: a TCP sequence number change processing part 24 deciding whether or not a received packet is a subsequent packet transmitted in succession to a missing packet based on a TCP sequence number of the received packet; and a subsequent packet reception processing part 18 generating a proxy ACK (ACKnowledgement) packet destined to a destination of the missing packet having TCP data length of 0, and having no TCP data portion when it is decided that the received packet is the subsequent packet. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a communication apparatus and a communication method having an ALG (Application Level Gateway) function.

  A conventional ALG (Application Level Gateway) performs TCP (Transmission Control) when a communication device executes NAT (Network Address Translation) for translating a packet address or NAPT (Network Address Port Translation) for translating both an address and a port. Protocol) The data part is read, and an auxiliary process for updating a necessary part of information written in the TCP data part (for example, an address and port number specified by NAPT) is executed.

  Thus, even in an environment where the relaying communication device communicates using NAT / NAPT, the communication terminal and the partner terminal can establish a communication session without being aware of the presence of the NAT / NAPT of the relaying communication device ( For example, refer nonpatent literature 1).

  In addition, since the ALG updates the information such as the port number written in the TCP data portion, the message length may change together with the message content. Therefore, the TCP transmission sequence number, ACK sequence number, IP (Internet Protocol) It is also necessary to change the checksum and TCP checksum.

  In order to efficiently change the information during the execution of ALG, a method has been proposed in which the checksum is updated only for a specific changed portion instead of recalculating the entire TCP / IP checksum. (For example, Non-Patent Document 2 below). Also, a method has been proposed in which the ALG processing unit of the relaying communication apparatus has a TCP sequence number difference list before and after NAT / NAPT and automatically increases or decreases the TCP sequence number (for example, Non-Patent Document 3 below). .

  On the other hand, RTSP (Real Time Streaming Protocol) has recently been used as a protocol for controlling streaming distribution of audio and video signals (see Non-Patent Document 4 below). RTSP control messages are generally distributed over TCP, and the following two types of distribution methods are defined for streaming data.

  The first delivery method is a normal delivery method using a UDP (User Datagram Protocol) session for RTP (Real-time Transport Protocol) / RTCP (RTP Control Protocol) data separately from a TCP session for RTSP control messages. (Hereinafter referred to as UDP distribution). As for the port number used in UDP distribution, RTP / RTCP port numbers are described in client_port and server_port included in RTSP “SETUP” / “200 OK” messages distributed over TCP. Therefore, in order to use RTSP in a NAT / NAPT environment, RTSP-ALG, which is a kind of the above ALG, is required. The RTSP-ALG reads the client_port and server_port information included in the “SETUP” / “200 OK” message from the control TCP session, and opens / closes the static UDP-NAPT.

  Another distribution method is an optional distribution method (hereinafter referred to as IL (Interleave) distribution) in which RTP / RTCP data is further superimposed on a TCP session for RTSP control messages. The RTP / RTCP data superimposed on the RTSP control message can be separated by determining whether or not the head of the RTSP message is “$”. The data length is described immediately after the RTP / RTCP data. The RTSP-ALG performs control to skip RTP / RTCP data in order to interpret only the control message from the multiplexed data.

  Which of the above two distribution methods is used is determined by a “SETUP” message transmitted by the RTSP client. Therefore, RTSP-ALG needs to be compatible with both distribution methods.

Internet Engineering Task Force (IETF) RFC2663, “IP Network Address Translator (NAT) Terminology and Considerations”, 1999 IETF RFC1631, “The IP Network Address Translator (NAT)”, 1994 IETF RFC2766, “Network Address Translation-Protocol Translation (NAT-PT)”, 2000 IETF RFC2326, “Real Time Streaming Protocol (RTSP)”, 1998

  However, according to the conventional technique, when even one missing packet occurs in the TCP layer, the subsequent TCP after the missing TCP packet is received until the ALG processing unit of the relaying communication apparatus receives a retransmission packet of the missing TCP packet. Do not send any packets to the other side. For this reason, there was a problem that the throughput at the TCP level may be extremely reduced.

  The reason for not transmitting subsequent TCP packets after the missing TCP packet is that if the TCP data part of the missing TCP packet contains a part that should be updated by ALG, the total TCP data length changes before and after ALG processing. This is because there is a possibility. When the TCP data part is updated by ALG and the TCP data length changes as a result, the change in the TCP data length will affect the sequence number of the subsequent TCP packet. That is, when a retransmission packet of a missing TCP packet is received later, a TCP data editing process involving a change in TCP data length may be necessary in the TCP data portion of the retransmission packet. The TCP sequence number cannot be consistent with the retransmitted packet received in step 1, and the TCP session may fail.

  On the other hand, even if the TCP packet is lost, the communication terminal that has transmitted the missing TCP packet does not wait for an “ACK (ACKnowledgement)” from the other terminal and waits for a certain amount of subsequent TCP packets based on TCP layer window transmission control. Send. For this reason, the ALG processing unit of the relay communication apparatus receives subsequent TCP packets after the missing TCP packet even after the missing TCP packet occurs.

  Therefore, generally, as described above, in the ALG process of the relay communication apparatus, when a missing TCP packet is detected, subsequent TCP packets are discarded until the missing TCP packet is retransmitted. The process of discarding the subsequent TCP packet is executed until the ALG processing unit of the relaying communication apparatus receives a retransmission packet of the missing TCP packet transmitted from the communication terminal. Subsequent subsequent TCP packets cannot be transmitted to the partner terminal.

  In other words, in the discarding process of the subsequent TCP packet executed by the ALG of the relay communication apparatus, the other terminal detects the discarding of the subsequent TCP packet after the missing TCP packet, and the missing packet is detected by selective “ACK” or duplicate “ACK”. It continues until the transmission terminal is notified and the missing TCP packet is retransmitted from the communication terminal, that is, one packet round-trip time (RTT).

  If 1 RTT becomes longer, the ALG processing unit of the communication device that relays becomes unable to continuously transmit a plurality of subsequent TCP packets. As described above, the TCP of the communication terminal that is the source of transmission is the ALG process of the relay communication device. Cannot detect that the subsequent TCP packet is discarded. Therefore, when the source communication terminal receives selective “ACK” or duplicate “ACK” from the other terminal, it detects that the dropped packet and a plurality of subsequent TCP packets are discarded in the network, and the discard occurs. The reason is that heavy congestion has occurred in the network. As a result, the TCP level congestion control between the communication terminals operates, and there arises a problem that the throughput at the TCP level is extremely lowered as described above.

  Here, for example, in RTSP-ALG in the case of UDP distribution, RTP / RTCP packets for streaming distribution are transmitted / received on UDP, so even if the throughput of the RTSP control message TCP decreases, the control response slightly deteriorates. However, no major problems occur.

  However, in RTSP-ALG in the case of IL distribution, RTP / RTCP data is distributed on the RTSP control message TCP, so that if the TCP transmission rate decreases, the transmission rate of streaming data distribution will decrease. There was a big problem that streaming at a high bit rate could not be performed.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a communication device and a communication method that prevent a decrease in TCP throughput.

  In order to solve the above-described problems and achieve the object, the present invention is a communication apparatus having an ALG processing function for updating TCP data, and based on the TCP sequence number of a received packet, TCP sequence number determination processing means for determining whether the packet is a subsequent packet that is subsequently transmitted, and when the TCP sequence number determination processing means determines that the packet is a subsequent packet, there is no TCP data portion and the TCP data length And subsequent packet generation processing means for generating a proxy ACK packet with the destination of the missing packet set to 0 as a destination.

  According to the present invention, when the ALG processing of the communication device that relays a packet receives a subsequent packet transmitted subsequent to the missing packet, the proxy ACK packet with the TCP data length set to 0 without discarding the subsequent packet Is transmitted to the transmission destination terminal of the lost packet, and it is possible to prevent a decrease in TCP throughput.

  Embodiments of a communication apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a functional configuration example of a communication device according to a first embodiment of the present invention. As shown in FIG. 1, the communication apparatus according to the present embodiment includes an individual ALG processing unit 1 that performs individual ALG processing for each protocol, an ALG common processing unit 2 that performs common ALG processing independent of protocols, and NAT. A NAT / NAPT common processing unit 3 for performing / NAPT processing.

  The individual ALG processing unit 1 includes a message analysis processing unit 11 that analyzes a TCP message, an ALG state transition processing unit 12 that performs state transition processing based on the analysis result of the message, and TCP data for editing TCP data. And a TCP data editing information generation processing unit 14 for generating editing information. The ALG state transition processing unit includes a state management unit 13 that is a storage unit for storing information for managing state transitions.

  The ALG common processing unit 2 includes a TCP sequence number determination processing unit 15 that classifies packets based on a TCP sequence number, a new packet reception processing unit 17 that performs reception processing of a new packet, and a packet that is transmitted following the missing packet. A subsequent packet reception processing unit 18 that performs subsequent packet reception processing, a retransmission packet reception processing unit 20 that performs retransmission packet reception processing, a proxy ACK generation processing unit 21 that generates a later-described proxy ACK packet, and TCP data A TCP data editing processing unit 22 that edits TCP data based on editing information, and a TCP sequence number change processing unit 24 that performs a TCP sequence number changing process.

  The TCP sequence number determination processing unit 15 includes a TCP reception sequence number management unit 16 for storing a TCP reception sequence number. The subsequent packet reception processing unit 18 includes a subsequent packet management unit 19 for storing subsequent packets. The TCP data editing processing unit 22 includes a TCP data editing information management unit 23 for storing TCP data editing information. The TCP sequence number change processing unit 24 also includes an ACK sequence number change processing unit 25 that changes the ACK sequence number, a TCP sequence number difference management unit 26 for storing TCP sequence number difference information, and a sequence of transmission data. And a transmission sequence number change processing unit 27 for changing the number.

  The NAT / NAPT common processing unit 3 includes a reception-side NAPT conversion processing unit 28 that performs NAT / NAPT conversion processing of received packets, a NAT / NAPT conversion information management unit 29 that stores NAT / NAPT conversion information, and a transmission. A transmission side NAPT conversion processing unit 30 that performs NAT / NAPT conversion processing of the packet.

  The communication apparatus according to the present embodiment performs NAT / NAPT conversion processing and ALG processing on the communication terminal, and relays to the communication partner terminal of the communication terminal. In the following description, a communication terminal in which the communication device of the present embodiment changes an address or a port number by NAT / NAPT conversion processing is simply referred to as a communication terminal, and a communication terminal that is a communication destination of the communication terminal is referred to as a partner terminal. And In addition, a communication direction from the communication terminal to the partner terminal is referred to as a forward direction, and a communication direction from the partner terminal to the communication terminal is referred to as a reverse direction.

  In the present embodiment, NAT / NAPT conversion information is stored in the NAT / NAPT conversion information management unit 29. FIG. 2 is a diagram illustrating an example of NAT / NAPT conversion information according to the present embodiment. As shown in FIG. 2, the NAT / NAPT conversion information of this embodiment includes the source address, source port number, destination address, destination port number, protocol (protocol type), ALG (ALG type, not ALG target) Contains "translation address" and translation port number. Since this NAT / NAPT conversion information has respective entries 101 to 105 generated in the forward communication, the calling address and the calling port number are the same as the value of the transmission source communication terminal in the forward direction. Become. The translated address and translated port number are the address and port number after NAT / NAPT conversion, respectively, and the outgoing address and outgoing port number are converted into the translated address and translated port number, respectively, during forward communication. It will be. In this case, the port number is also converted by assuming NAPT. However, in the case of NAT, it is sufficient to use only the translation address without using the translation port number.

  Since the counterpart terminal transmits the packet to the source address and source port number of the forward packet, that is, the translation address and the translation port number, in the case of communication in the reverse direction, the communication apparatus of the present embodiment In order to transmit to the communication terminal, the converted address and the converted port number are converted into the address and port number of the communication terminal, that is, the source address and the source port number of the NAT / NAPT conversion information, and then transmitted. Thus, in reverse communication, reverse conversion is performed using forward NAPT conversion information.

  Next, the operation of the present embodiment will be described. First, normal packet reception processing will be described. The reception-side NAPT conversion processing unit 28 receives reception I / F (Interface) information (information on which type of I / F is received) via a packet reception I / F processing unit (not shown) of the communication apparatus according to the present embodiment. ) And a received TCP packet. The packet reception I / F processing unit performs processing for each type of I / F, and the I / F type includes a NAPT execution I / F (I / F processing using NAPT). The reception-side NAPT conversion processing unit 28 does not perform conversion processing when the received I / F information is not a NAPT execution I / F.

  If the received I / F information is a NAPT execution I / F, the receiving side NAT / NAPT conversion processing unit 28 performs a NAPT conversion process based on the NAT / NAPT conversion information. However, when the received TCP packet is a backward packet, the reverse conversion is performed as described above, so the source address, source port number, destination address, destination port number, protocol of the received received TCP packet, respectively, Searches for an entry of NAPT conversion information having the same destination address, destination port, translation address, translation port number, and protocol.

  If there is a corresponding NAPT conversion information entry as a result of the search, the receiving side NAT / NAPT conversion processing unit 28 determines the incoming address and the incoming port number of the received TCP packet based on the information, and the originating address of the entry. ., And the checksum of the IP header / TCP header is corrected to reflect the change of the address and port number. If the corresponding NAPT conversion information does not exist as a result of the search, the receiving side NAT / NAPT conversion processing unit 28 discards the received TCP packet.

  Next, when there is a corresponding NAPT conversion information entry, the receiving side NAT / NAPT conversion processing unit 28 refers to the ALG item of the entry and determines whether the packet is an ALG target packet. If the packet is not an ALG target packet, it is not necessary to edit the sequence number and TCP data of the received TCP packet. Therefore, the reception side NAT / NAPT conversion processing unit 28 converts the packet as a non-ALG target TCP packet as it is and performs the transmission side NAPT conversion. The data is transmitted to the processing unit 30. Then, the transmission side NAPT conversion process sends a non-ALG target TCP packet to a transmission I / F processing unit (not shown) and requests transmission of the packet.

  When transmitting a packet, the transmission-side NAPT conversion processing unit 30 determines the type of transmission I / F of the packet (for example, whether it is a NAPT execution I / F) based on the destination address of the packet. If the I / F determined for the non-ALG target TCP packet is the NAPT execution I / F, the transmission side NAPT conversion processing unit 30 sets the source address and source port number of the non-ALG target TCP packet as the conversion address and conversion port number. Change each one. In addition, the checksum of the IP header / TCP header of the non-ALG target packet is updated to reflect the change of the address and port number. Then, the transmission side NAPT conversion process sends a non-ALG target TCP packet to the transmission I / F processing unit and requests transmission of the packet.

  The processing of non-ALG packets has been described above. Next, processing of ALG target packets will be described. When determining that the packet is an ALG target packet when determining whether the packet is an ALG target packet, the reception-side NAPT conversion processing unit 28 sets the received TCP packet as an ALG target packet to change the ACK sequence number. To the unit 25.

  Based on the TCP sequence number difference information, the ACK sequence number change processing unit 25 performs conversion of the ACK sequence number of the ALG target TCP packet according to the following procedure. FIG. 3 is a diagram illustrating an example of a TCP sequence number difference list and a packet before and after conversion stored in the TCP sequence number difference management unit. The pre-conversion packets 201 to 207 indicate packets transmitted from the communication terminal and received by the communication device. The post-conversion packets 211 to 217 are the sequence numbers (ACK sequence) of the pre-conversion packets 201 to 207 by the TCP sequence number change processing unit 24. Number and transmission sequence number) are changed. In addition, post-conversion packets 231 to 237 indicate packets transmitted from the counterpart terminal, and pre-conversion packets 221 to 227 are transmitted by the TCP sequence number change processing unit 24 in order to transmit the packets 231 to 237 to the communication device. The packet after performing the inverse transformation of is shown.

  In the figure showing the pre-conversion packets 201 to 207 and 221 to 227 and the post-conversion packets 211 to 217 and 231 to 237 in FIG. 3, the transmission sequence number (Seq), TCP data length (len), and ACK sequence of each packet are shown. A number (Ack) is shown.

  As shown in FIG. 3, the TCP sequence number difference information includes a pre-conversion sequence number and a post-conversion sequence number for the forward direction and the reverse direction, respectively. These pieces of information are stored in the TCP sequence number difference management unit 29 for each TCP session.

  The TCP sequence number difference information is held for managing the change of the sequence number, and is stored by the TCP data editing processing unit 22 as will be described later. In the example of FIG. 2, it is assumed that the pre-conversion packet 205 is changed to a post-conversion packet 215 by changing the TCP data length from 1000 bytes to 1002 bytes by the TCP data editing processing unit 22. Then, also for the post-conversion packet 214 corresponding to the next pre-conversion packet 204, it is necessary to shift the transmission sequence number by an amount corresponding to the change in the TCP length of the post-conversion packet 215 and change the transmission sequence number from 13000 to 13002. There is.

  Here, the description returns to the operation of the ACK sequence number change processing unit 25. The ACK sequence number change processing unit 25 searches the TCP sequence number difference management unit to acquire TCP sequence number difference information corresponding to a session that is uniquely determined from the incoming / outgoing address, outgoing / incoming port, and protocol of the received ALG target packet. To do.

  The ACK sequence number change processing unit 25 searches for a sequence number that matches the ACK sequence number of the received TCP packet from the converted sequence numbers in the forward and reverse directions of the acquired TCP sequence difference information. Then, the ACK sequence number change processing unit 25 changes the ACK sequence number of the received TCP packet to the pre-conversion sequence number corresponding to the search result (the post-conversion sequence number that matches the ACK sequence number). For example, the transmission sequence numbers of the pre-conversion packets 201 to 207 are converted into post-conversion packets 211 to 217, for example. Also, the checksum of the TCP packet is updated simultaneously with the sequence number conversion.

  For example, in the pre-conversion packet 205 in the forward direction, “Ack = 42005”, and there is a number “42005” that matches the post-conversion sequence number in the reverse direction of the TCP sequence number difference information. Since the pre-conversion sequence number corresponding to the post-conversion sequence number “42005” in the TCP sequence number difference information of FIG. 3 is “42000”, the pre-conversion packet 205 is converted to “Ack = 42000”. Further, “Ack = 13002” in the post-conversion packet 234 in the reverse direction, there is a number “13002” that matches the post-conversion sequence number in the forward direction of the TCP sequence number difference list. Since the pre-conversion sequence number corresponding to “13002” in the TCP sequence number difference information of FIG. 3 is “13000”, the post-conversion packet 234 is converted to “Ack = 13000”.

  The ACK sequence number change processing unit 25 changes the ACK sequence number of the received TCP packet in this way, and transmits the changed received TCP packet to the TCP sequence number determination processing unit 15 as an ACK sequence number corrected packet.

  Next, the TCP sequence number determination processing unit 15 determines that the ACK sequence number corrected packet is a retransmission packet (a packet having a transmission sequence number smaller than the maximum value of the transmission sequence number already received), a new packet (next reception is received). Packet with expected transmission sequence number), subsequent packet (packet sent after missing new packet, packet with transmission sequence number higher than expected transmission sequence number), or above packet It is determined whether it is. FIG. 4 is a flowchart illustrating an example of the determination processing procedure of the TCP sequence number determination processing unit 15.

  This determination is performed by comparing the transmission sequence number of the packet whose ACK sequence number has been corrected with the transmission sequence number of the packet expected to be received next. For this purpose, the TCP reception sequence number management unit 16 stores TCP reception sequence number information in the TCP reception sequence number management unit 16. FIG. 5 shows an example of TCP reception sequence number information. In the TCP reception sequence number information, for each TCP session identification (source address, source port number, destination address, destination port number), the maximum received sequence number and the next reception are expected in the forward direction and the reverse direction, respectively. The sequence number (next reception expected sequence number) is included. If the TCP reception sequence number information is a new packet after the determination of the four types of packets, it is updated as described later.

  When receiving the ACK sequence number corrected packet (step S11), the TCP sequence number determination processing unit 15 acquires TCP reception sequence information corresponding to the TCP session identifier of the ACK sequence number corrected packet, and the ACK sequence number has been corrected. It is determined whether the transmission sequence number of the packet is equal to or smaller than the received maximum transmission sequence number in the forward direction or the reverse direction of the acquired TCP reception sequence information (step S12). Here, when the ACK sequence number corrected packet is in the forward direction, it is compared with the received maximum transmission sequence number in the forward direction of the TCP reception sequence information, and when it is in the reverse direction, the reception of the TCP reception sequence information in the reverse direction is performed. Compared with the maximum transmitted sequence number. If the ACK sequence number corrected packet is smaller (YES in step S12), it is determined that the packet is a retransmission packet (step S18).

  On the other hand, when the transmission sequence number of the packet with the corrected ACK sequence number is larger than the transmission sequence number in the forward direction or the reverse direction of the acquired TCP reception sequence information (NO in step S12), the TCP sequence number determination processing unit 15 further Then, it is determined whether or not the transmission sequence number of the packet whose ACK sequence number has been corrected is larger than the next reception expected sequence number in the forward direction or the reverse direction of the acquired TCP reception sequence information (step S13).

  If it is determined that the transmission sequence number of the ACK sequence number corrected packet is greater than the next reception expected sequence number in the forward or reverse direction of the acquired TCP reception sequence information (YES in step S13), the packet is determined as a subsequent packet. (Step S19).

  When it is determined that the transmission sequence number of the ACK sequence number modified packet is equal to or less than the next reception expected sequence number in the forward or reverse direction of the acquired TCP reception sequence information (NO in step S13), the TCP sequence number determination processing unit 15 further determines whether or not the transmission sequence number of the packet with the corrected ACK sequence number is smaller than the next expected reception sequence number (step S14). If it is determined that the transmission sequence number of the packet with the ACK sequence number corrected is smaller than the expected next reception sequence number (Yes in step S14), the packet is determined to be an abnormal packet.

  When it is determined that the transmission sequence number of the ACK sequence number modified packet is not smaller than the next reception expected sequence number (the transmission sequence number of the ACK sequence number modified packet is equal to the next reception expected sequence number) (NO in step S14), The TCP sequence number determination processing unit 15 updates the TCP sequence number information. Specifically, the received maximum transmission sequence number in the forward or reverse direction of the TCP sequence number information is updated to the transmission sequence number of the packet whose ACK sequence number has been corrected (step S15), and the next reception expected sequence number is Update to “transmission sequence number of ACK sequence number corrected packet + TCP data length of ACK sequence number corrected packet”. Then, the TCP sequence number determination processing unit 16 determines that the packet is a new packet (step S17).

  When the TCP sequence number determination processing unit 16 determines that the packet is a new packet after the above packet type determination processing, the TCP sequence number determination processing unit 16 transmits the ACK sequence number corrected packet to the new packet reception processing unit 17. Further, the TCP sequence number determination processing unit 16 sends the ACK sequence number corrected packet to the subsequent packet reception processing unit 18 when it is determined as a subsequent packet, and to the retransmission packet reception processing unit 20 when it is determined as a retransmission packet. Send. If it is determined that the packet is abnormal, abnormal processing such as discarding the packet or disconnecting the TCP session because ALG cannot process the packet is performed.

  Next, processing of an ACK sequence number corrected packet determined as a new packet (hereinafter referred to as a new packet) will be described. The new packet reception processing unit 18 transmits the transmission sequence number, TCP data part, and TCP data length of the new packet as new TCP data to the protocol-specific individual ALG processing unit 1. Also, the new packet is transmitted to the TCP data editing processing unit 22.

  The configuration of the individual ALG processing unit 1 depends on the implementation, but generally has the configuration described with reference to FIG. First, the message analysis processing unit 11 of the individual ALG processing unit 1 delimits the TCP data transmitted as a continuous stream of byte strings into unique message units of the ALG target protocol corresponding to the data, and Analyze the contents. The individual ALG processing unit 1 outputs the analysis result to the ALG state transition processing unit 12 and the TCP data editing information generation processing unit 14.

  The ALG target protocol may have multiple states managed between the arrival and departure terminals. The ALG state transition processing unit 12 stores ALG state information indicating the current state in the ALG information management unit 13, and when it is necessary to perform state transition based on the analysis result of the message analysis processing unit 11, The ALG state information is rewritten and the ALG state information is notified to the TCP data editing information generation processing unit 14.

  The TCP data editing information generation processing unit 14 determines how to change the TCP data of the new packet based on the analysis result of the message analysis processing unit 11 and the ALG state information, and sends the TCP data editing processing unit 22 the TCP data. Notify as editing information. FIG. 6 is a diagram illustrating an example of TCP data editing information. As shown in FIG. 6, the TCP data editing information includes a TCP session identifier, a direction (forward direction or reverse direction), a transmission sequence number, a TCP data length, a change position offset, a change data length (data length of a change target part), It includes update data and update data length, and is expressed in a format independent of the type of ALG. The change position offset indicates an offset amount from the start position of the data of the corresponding transmission sequence number to the start position of the data to be changed.

  Further, one set of TCP data editing information is generated for each changed portion. For example, it is assumed that “address = 192.168.0.1, port = 8000” of TCP data of a new packet is changed to “address = 133.9.3.1, port = 10000”. Assuming that the address position offset is 8 and the port position offset is 25, the TCP data editing information is “change position offset = 8, change data length = 11, update data =“ 133.9.3.1 ”, update data length = 9. And “change position offset = 25, change data length = 4, update data =“ 10000 ”, update data length = 5”.

  The TCP data editing processing unit 22 stores the notified TCP data editing information in the TCP data editing information management unit 23 in a format as shown in FIG. The TCP data editing processing unit 22 searches the TCP data editing information for information corresponding to the new packet received from the new packet reception processing unit 17 using the session identifier as a key. When the information with the matching session identifier is obtained, the TCP data editing processing unit 22 edits the new packet based on the information.

  The editing method at this time will be described with reference to FIG. FIG. 7 is a diagram for explaining the editing method. The change offset, change data length, and change location corresponding to the first set of TCP data editing information corresponding to the new packet are assumed to be change offset # 1, change data length # 1, and change location # 1, respectively. Similarly, the numbers # 2 and # 3 are assigned to the change offset, the change data length, and the change location corresponding to the second and third sets of TCP data editing information, respectively. Here, these TCP data editing information is set to # 1, # 2,... In ascending order of change position offset. At the time of storing the TCP data editing information, the TCP data editing information may be arranged in ascending order of the change position offset in this way, or the TCP data editing information read after the search may be arranged in ascending order of the changing position offset. . Further, the new packet before editing is shown in the upper part of the arrow in FIG. 7, and the edited packet is shown in the lower part of the arrow.

  First, it is not necessary to change the data up to the first set change position offset in the new packet before editing. The TCP data editing processing unit 22 holds the data of the part that is not changed from the head position to the change offset # 1. The part without the next change is from the position of “change offset # 1 + change data length # 1” to the beginning of the next change (“change offset # 2”), and this part is held. In this way, the TCP data editing processing unit 22 holds the cut portion #N from the top or “change offset + change data length #N (N is a natural number)” to “change offset # (N + 1)”. Then, the TCP data editing processing unit 22 copies the first set of update data as the update location # 1 next to the stored cut location # 1. Similarly, the post-edit packet as shown in the lower part of the arrow in FIG. 7 is generated by alternately copying the cutout portion and the update data. The TCP data editing processing unit 22 transmits the generated edited packet to the transmission sequence number change processing unit 27.

  If the TCP data length is different between the new packet before editing and the edited packet as a result of editing, it is necessary to change the transmission sequence number and ACK sequence number of TCP packets after the edited packet. Therefore, the TCP data editing processing unit 22 registers the sequence number difference information in the TCP sequence number difference management unit 26 of the TCP sequence number change processing unit 24. The sequence number difference information to be registered is calculated as “sequence number of received TCP packet + TCP data length” for the sequence number before conversion, and “sequence number of received TCP packet + TCP data length + TCP before and after change” for the sequence number after conversion. Calculated as “data length difference”. At this time, if the sequence number difference information is already registered for the same sequence number before conversion, the conversion is performed as “the sequence number after conversion corresponding to those sequence numbers before conversion + the difference between the TCP data lengths before and after the change”. Update the sequence number later.

  Next, the transmission sequence number change processing unit 27 changes the transmission sequence number of the edited packet based on the TCP sequence number difference information. Specifically, the pre-conversion sequence number of the TCP sequence number difference information that matches the transmission sequence number of the new packet is searched, and if there is a match, it is changed to the corresponding post-conversion sequence number. If the TCP data has not been edited before that, it is necessary to change the sequence number for packets that arrive after the edited packet, but it is necessary to change the transmission sequence number for the edited packet itself. Absent. However, if the TCP data length has changed before that, it is changed based on the TCP sequence number difference information.

  For example, the pre-conversion packet 205 in FIG. 3 becomes the conversion packet 215 after the processing by the transmission sequence number change processing unit 27, but the transmission sequence number remains 12000 and has not been changed. In the post-conversion packet 214 corresponding to the next pre-conversion packet 204, the transmission sequence number is changed from 13000 to 13002. When new packet editing processing is performed in this way, it is necessary to change the transmission sequence number for the packets thereafter.

  After changing the transmission sequence number, the transmission sequence number change processing unit 27 also updates the checksum to reflect the change. Then, the transmission sequence number change processing unit 27 transmits the new packet with the changed transmission sequence number to the transmission side NAPT conversion processing unit 30. The transmission side NAPT conversion processing unit 30 obtains an entry in which the packet's source address, source port number, destination address, destination port number and protocol match from the NAT / NAPT conversion information, and the source address and source port number. Is changed to the translation address and translation port number of the corresponding entry. Also, the checksum of the packet is updated in response to the change of the source address and the source port number.

  In this way, by executing the change of the arrival / departure address / port number, transmission / ACK sequence number, and TCP data editing, for example, the pre-conversion packets 201 to 207 in the forward direction in FIG. 3 are converted into the converted packets 211 to 217, for example. In the reverse direction, the converted packets 231 to 237 are reversely converted to the pre-conversion packets 221 to 227.

  Next, processing of subsequent packets will be described. The TCP sequence number determination processing unit 15 transmits a packet determined to be a subsequent packet (hereinafter referred to as a subsequent packet) to the subsequent packet reception processing unit 18. The subsequent packet reception processing unit 18 stores the subsequent packets received by the subsequent packet management unit 19 in the order of sequence numbers. The transmitted subsequent packets are also stored in the subsequent packet management unit in the order of sequence numbers. Further, the subsequent packet reception processing unit 18 transmits the subsequent packet to the proxy ACK generation processing unit 21 that is a feature of the present invention.

  The proxy ACK generation processing unit 21 copies the IP header and the TCP header from the subsequent packet, and generates a proxy ACK packet having the IP header and the TCP header and having a TCP data length of “0”. However, the transmission sequence number of the proxy ACK packet is the next reception expected sequence number of the TCP reception sequence number information stored in the TCP reception sequence number management unit 16. Then, the proxy ACK generation processing unit 21 calculates the checksum of the proxy ACK packet, sets the checksum, and transmits the proxy ACK packet to the transmission sequence number change processing unit 27. Here, the transmission sequence number of the proxy ACK packet is set to the next reception expected sequence number, but is not limited thereto, and may be set to another numerical value such as a value equal to or higher than the next reception expected sequence number.

  Similarly to the case of a new packet, the transmission sequence number change processing unit 27 needs to change the transmission sequence number for a proxy ACK packet when the TCP data length is changed in a TCP packet received before the proxy ACK packet. is there. Therefore, the transmission sequence number change processing unit 27 acquires sequence number difference information having a matching pre-conversion sequence difference number with the transmission sequence number of the proxy ACK packet as a key, and transmits the transmission sequence of the proxy ACK packet based on the acquired information. Change the number to the corresponding converted sequence difference number. The checksum is also updated when the transmission sequence number is changed.

  Then, the transmission sequence number change processing unit 27 transmits the proxy ACK packet to the transmission side NAPT conversion processing unit 30. The transmission side NAPT conversion processing unit 30 performs address and port number conversion processing in the same manner as the processing for a new packet, and also updates the checksum of the proxy ACK packet.

  When such a proxy ACK packet is transmitted, the partner terminal receives the proxy ACK packet. By receiving a proxy ACK packet with no contradiction in sequence numbers, the counterpart terminal can avoid congestion control and prevent a decrease in TCP throughput.

  Next, when the lost packet is retransmitted after the subsequent packet, the retransmitted lost packet is processed as a retransmitted packet, and thereafter, the processing of a new packet is started again. At this time, in this embodiment, a packet having the contents of the subsequent packet is transmitted as a resume packet before the new packet transmitted after the retransmitted missing packet. Next, processing of the restart packet will be described.

  When the new packet reception processing unit 17 receives the retransmitted missing packet as a new packet, the new packet reception processing unit 17 acquires the subsequent packet stored in the subsequent packet management unit 19 as a resume packet. The processing procedure of the resume packet is the same as that of a normal new packet, but only the ACK sequence number is set as the ACK sequence number of the lost packet retransmitted unlike the normal case. Subsequent processing is performed by the processing of the individual ALG processing unit 1, the processing of the TCP data editing processing unit 22, the processing of the transmission sequence number change processing unit 27, and the processing of the transmission side NAPT conversion processing unit 30, as with the new packet. Is called.

  FIG. 8 is a diagram for explaining packet conversion when a subsequent packet is included. The pre-conversion packets 301 to 307 are packets transmitted from the communication terminal and received by the communication device, and the post-conversion packets 311 to 319 are packets obtained by converting the pre-conversion packets 301 to 307 by the communication device of this embodiment. Show. The post-conversion packets 331 to 337 indicate the packets transmitted from the counterpart terminal. The pre-conversion packets 321 to 327 are transmitted by the TCP sequence number change processing unit 24 in order to transmit the post-conversion packets 331 to 337 to the communication device. A packet after reverse conversion of the sequence number is shown. FIG. 8 shows an example in which the pre-conversion packet 305 is lost, the pre-conversion packets 304 and 303 are transmitted as subsequent packets, and the pre-conversion packet 302 is transmitted as a retransmission packet of the missing packet 305.

  As shown in FIG. 8, the pre-conversion packets 303 and 304, which are subsequent packets, are converted into proxy ACK packets and transmitted as post-conversion packets 315 and 316. Then, the pre-conversion packet 302 that is a retransmission packet is processed as a new packet and transmitted as a post-conversion packet 314. After the converted packet 314, the restart packets 312 and 313 after conversion corresponding to the subsequent packets 304 and 305 before conversion are transmitted in FIG.

  Next, the retransmission packet process will be described. The TCP sequence number determination processing unit 15 transmits a packet determined as a retransmission packet (hereinafter referred to as a retransmission packet) to the retransmission packet reception processing unit 20. The retransmission packet reception processing unit 20 transmits the retransmission packet to the TCP data editing processing unit 22.

  The TCP data editing processing unit 22 searches the TCP data editing information stored in the TCP data editing information management unit 23 using the transmission sequence number of the retransmission packet as a key, and is similar to a new TCP packet according to the matched search TCP editing information. Edit the TCP data part. For retransmission packets, sequence number difference information is not registered even if the TCP data length changes as a result of editing. Then, the TCP data editing processing unit 22 transmits the edited retransmission packet to the transmission sequence number change processing unit 27.

  If the TCP data length has changed in the TCP packet before receiving the retransmission packet, it is necessary to change the transmission sequence number of the retransmission packet. For this reason, the transmission sequence number change processing unit 27 searches the TCP sequence number difference information for a matching pre-conversion sequence number using the retransmission packet transmission sequence number as a key, and searches for the retransmission packet transmission sequence number. Change to the post-conversion sequence number corresponding to the pre-conversion sequence number. At the same time, the checksum is updated.

  Then, the transmission sequence number change processing unit 27 transmits the retransmission packet to the transmission side NAPT conversion processing unit, and the transmission side NAPT conversion processing unit performs the address and port number conversion processing in the same manner as other packets. In addition, the checksum of the IP header and TCP header of the retransmission packet is updated in accordance with the change.

  FIG. 9 is a diagram illustrating a state before and after conversion of a retransmission packet. Packets 401 to 407 indicate packets transmitted from the communication terminal and received by the communication apparatus, and post-conversion packets 411 to 417 indicate packets obtained by converting the pre-conversion packets 401 to 407 by the communication apparatus according to the present embodiment. Yes. In addition, the post-conversion packets 431 to 437 indicate packets transmitted from the counterpart terminal, and the pre-conversion packets 421 to 427 are transmitted by the TCP sequence number change processing unit 24 in order to transmit the packets 431 to 437 to the communication device. The packet after performing the inverse transformation of is shown. In addition, since it is a figure for demonstrating a retransmission packet here, it abbreviate | omits about the restart packet. When the retransmission packet of the pre-conversion packet 405 is the pre-conversion packet 402, the pre-conversion packet 402 is converted into a post-conversion packet 412 and transmitted.

  In this embodiment, the ALG process and the NAPT process are combined. However, the ALG process and the NAPT process may be combined, or may be combined with the NAT process, and may be combined with the Ipv4-Ipv6 translator process.

  In this embodiment, the checksum is not recalculated in order to reduce the checksum recalculation load. Every time the TCP packet is edited by ALG, the IP header and the TCP header are checked according to the edit difference. The sum is adjusted, but the checksum may not be adjusted, and the checksum may be recalculated and added at the end.

  As described above, in this embodiment, after a lost packet occurs, when a subsequent packet is received, the packet is not transmitted to the partner terminal until the lost packet is retransmitted. The proxy ACK packet with TCP data length = “0” is transmitted to the partner terminal. For this reason, it is possible to prevent the counterpart terminal from detecting a retransmission timeout and lowering the TCP transmittable rate.

  Also, the transmission sequence number of the proxy ACK packet is calculated by adding the transmission sequence number of the missing packet from the transmission sequence number of the new packet having the largest transmission sequence number received before that and the TCP data length and assigning it to the proxy ACK packet. I did it. Therefore, the transmission sequence number of the missing packet can be notified to the partner terminal without waiting for the missing packet itself to be retransmitted.

  Further, when a subsequent packet is further received before receiving the retransmitted missing packet, a proxy ACK packet is further transmitted in response to the reception of the subsequent packet. For this reason, even when a lost packet to be retransmitted cannot be received for a long time, the counterpart terminal does not detect a retransmission timeout. Therefore, it is possible to prevent a decrease in the TCP transmittable rate caused by detecting a retransmission timeout.

  In addition, when a subsequent packet is further received before receiving the retransmitted missing packet, the ACK sequence number of the proxy ACK packet to be transmitted is increased according to the ACK sequence number of the subsequent packet to be received, and the same ACK sequence The proxy ACK packet with the number was not sent. For this reason, it is possible to prevent the counterpart terminal from decreasing the TCP transmittable rate by detecting the duplicate ACK without receiving the duplicate ACK (packet of the same ACK sequence number) at the counterpart terminal.

  Also, when the subsequent packet is received, the subsequent packet is held inside, and after receiving the lost packet retransmitted from the terminal, the subsequent packet held inside is transmitted as a resume packet. For this reason, ALG processing can be resumed without waiting for the communication terminal to retransmit the subsequent packet.

Embodiment 2. FIG.
FIG. 10 is a diagram illustrating an example of a functional configuration of the communication apparatus according to the second embodiment of the present invention. As shown in FIG. 10, the communication apparatus according to the present embodiment replaces the individual ALG processing unit 1 of the communication apparatus according to the first embodiment with an RTSP-ALG processing unit 34, and causes the subsequent packet reception processing unit 18 to perform subsequent packet reception processing. The communication device of the first embodiment is the same as that of the first embodiment except that the ALG common processing unit 2 is replaced with the ALG common processing unit 2a instead of the unit 18a. Components having the same functions as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The RTSP-ALG processing unit 34 according to the present embodiment can be considered as a kind of the individual ALG processing unit 1. The RTSP-ALG processing unit of the present embodiment includes an RTSP message analysis processing unit 35, an RTSP state transition processing unit 36, and a TCP data editing information generation processing unit 38. The RTSP state transition processing unit 23 includes a state management unit 37. The RTSP message analysis processing unit 35, the RTSP-ALG processing unit, and the TCP data editing information generation processing unit 38 are respectively the message analysis processing unit 11, the ALG state transition processing unit 12, and the TCP data editing information generation processing unit 14 of the first embodiment. Has the same function.

  In the first embodiment, a general ALG process capable of editing a missing packet is assumed. However, in this embodiment, there is no possibility of editing a missing packet in the ALG process (changed by the ALG process). Since the item to be processed is determined, for example, if it is known that the packet does not include the item to be changed, there is no possibility of editing), and the subsequent packet is transmitted as it is.

  Depending on the ALG target protocol or ALG status, whether or not there is a possibility that the data of the TCP packet will not be edited from the sequence number of the TCP packet that is missing under certain conditions (there is no possibility of editing the data). Judgment may be possible. For example, in the protocol used in ALG, there are many protocols that indicate the boundary of each ALG message by describing the variable length ALG message in the TLV (Type Length Value) format that indicates the ALG type, ALG message length, and ALG value. Exists. In such a protocol that uses the TLV format, it is possible to determine whether editing is required in the ALG processing based on the ALG message type, and thus the editability can be determined.

  Furthermore, it may be possible to skip to the ALG message boundary without interpreting the contents. In RTSP-ALG, the message boundary is indicated by “\ r \ n \ r \ n”, which is not generally applicable. For example, the Content-Length length is indicated in the RTSP header part, and from the sequence number of the missing TCP packet, When it is possible to reliably determine that the data of the missing TCP packet includes only the Content-Data portion that does not need to be edited by RTSP-ALG, it can be determined that there is no editability.

  Similarly, in RTSP-ALG, when IL distribution data (LL data) is included, the IL distribution data can be skipped without interpreting the contents by normal ALG processing. That is, since the portion that can be skipped by the ALG process is not edited, it can be determined that there is no possibility of TCP data editing when the missing packet is IL distribution data.

  FIG. 11 is a diagram illustrating an example of a TCP packet including IL data. In FIG. 11, TCP packets 501 to 506 indicate TCP packets including IL distribution data, and data 511 to 516 indicate data portions of the TCP packets. For example, if the TCP packet 502 is missing, it can be determined that there is no possibility of TCP data editing because the TCP packet 502 is an IL data packet.

  As described above, when the message length to the next ALG message boundary is generally indicated at the head part, the ALG processing unit may be able to determine the editability of the missing TCP packet relatively easily.

  Next, the operation of the present embodiment will be described. Processing until the received TCP packet is transmitted to the TCP sequence number determination processing unit 15 is the same as in the first embodiment. The TCP sequence number determination processing unit 15 transmits the packet determined as the subsequent packet to the subsequent packet reception processing unit 18a. The subsequent packet reception processing unit 18a inquires the RTSP state transition processing unit 36 about the editability of the TCP data of the missing packet together with the next reception expected transmission sequence number and the transmission sequence number of the subsequent packet.

  In RTSP-ALG, only the address or port number description part in the SETUP message and the address or port number description part in the “200 OK” response message to the SETUP message are necessary to be edited in the ALG process. Therefore, the RTSP state transition processing unit 36 tracks the state of the ALG process, and if the SETUP message is transmitted from the client to the server and is not waiting for a response from the server, the TCP data editing for the server to the client is performed. It can be determined that there is no possibility.

  Next, when the subsequent packet reception processing unit 18 a receives a response from the RTSP state transition processing unit 36 that there is no possibility of editing the TCP data, it registers the sequence number difference information in the TCP sequence number difference management unit 26. The difference information to be registered at this time is the received TCP sequence number for the pre-conversion sequence, and the received “TCP sequence number + the difference value from the previous sequence number” for the post-conversion sequence number.

  Next, the subsequent packet reception processing unit 18 a transmits the subsequent packet to the transmission sequence number change processing unit 27. The processing of the transmission sequence number change processing unit 27 and the transmission side NAPT conversion processing unit 30 is the same as the processing related to the new packet in the first embodiment.

  FIG. 12 is a diagram illustrating a state before and after conversion of a packet when a packet having no editability is lost. In FIG. 12, pre-conversion packets 601 to 607 indicate packets transmitted from the communication terminal and received by the communication device, and post-conversion packets 611 to 617 are converted from the pre-conversion packets 601 to 607 by the communication device of the present embodiment. Shows the received packet. In addition, post-conversion packets 631 to 637 indicate packets transmitted from the counterpart terminal, and before-conversion packets 621 to 627 are transmitted by the TCP sequence number change processing unit 24 in order to transmit the post-conversion packets 631 to 637 to the communication device. A packet after reverse conversion of the sequence number is shown.

  The example of FIG. 12 shows a case where the post-conversion packet 634 is lost, and a post-conversion packet 635 that is a subsequent packet after the missing packet is transmitted as a pre-conversion packet 624 after reverse conversion of the sequence number. .

  In this embodiment, the case where the ATSP-ALG processing unit is provided as the individual ALG processing unit has been described. However, the present invention is not limited to this, and any other ALG processing can be used as long as the individual ALG processing unit can determine the editability of the packet. May be used.

  As described above, in this embodiment, when the subsequent packet reception processing unit 18a receives a subsequent packet after the missing packet, the RTSP state transition processing unit is inquired about the possibility of changing the TCP data length of the missing packet, and the RTSP state. When there is a response from the transition processing unit that there is no possibility of changing the TCP data length, the subsequent packet reception processing unit 18a transmits the subsequent packet without waiting. For this reason, it is possible to transmit subsequent packets more quickly than in the first embodiment.

  As described above, the communication device and the communication method according to the present invention are useful for a communication system that performs ALG (Application Level Gateway) processing, and in particular, a communication system that needs to maintain high TCP throughput while applying ALG. Suitable for

It is a figure which shows the function structural example of Embodiment 1 of the communication apparatus concerning this invention. It is a figure which shows an example of NAT / NAPT conversion information. It is a figure which shows an example of the packet before and behind a TCP sequence number difference list stored in a TCP sequence number difference management part. It is a flowchart which shows an example of the determination process procedure of a TCP sequence number determination process part. It is a figure which shows an example of TCP reception sequence number information. It is a figure which shows an example of TCP data edit information. It is a figure for demonstrating the editing method. It is a figure for demonstrating conversion of the packet in case a subsequent packet is included. It is a figure which shows the mode before and behind conversion of a resending packet. It is a figure which shows the function structural example of Embodiment 2 of the communication apparatus concerning this invention. It is a figure which shows an example of the TCP packet containing IL data. It is a figure which shows the mode before and after conversion of the packet when the packet without editability is missing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Individual ALG process part 2, 2a ALG common process part 3 NAT / NAPT common process part 11 Message analysis process part 12 ALG state transition process part 13 State management part 14 TCP data edit information generation process part 15 TCP sequence number determination process part 16 TCP reception sequence number management unit 17 New packet reception processing unit 18, 18a Subsequent packet reception processing unit 19 Subsequent packet management unit 20 Retransmission packet reception processing unit 21 Proxy ACK generation processing unit 22 TCP data editing processing unit 23 TCP data editing information management unit 24 TCP sequence number change processing unit 25 ACK sequence number change processing unit 26 TCP sequence number difference management unit 27 Transmission sequence number change processing unit 28 Reception side NAPT conversion processing unit 29 NAT / NAPT conversion information management unit 30 Transmission side NAPT Conversion processing unit 34 RTSP-ALG processing unit 35 RTSP message analysis processing unit 36 RTSP state transition processing unit 37 State management unit 38 TCP data editing information generation processing unit 101-105 entries 201-207, 221-227, 301-307, 321 -327, 401-407, 421-427, 601-607, 621-627 Pre-conversion packet 211-217, 231-237, 311-319, 331-337, 411-417, 431-437, 611-617, 631 ~ 637 packet after conversion 501 ~ 506 TCP packet 511 ~ 516 data

Claims (7)

A communication device having an ALG processing function for updating TCP data,
TCP sequence number determination processing means for determining whether or not the packet is a subsequent packet that is subsequently transmitted after the missing packet, based on the TCP sequence number of the received packet;
When the TCP sequence number determination processing unit determines that the packet is a subsequent packet, the subsequent packet generation processing unit generates a proxy ACK packet destined for the destination of the missing packet with no TCP data portion and a TCP data length of 0,
A communication apparatus comprising:   The transmission sequence number of the proxy ACK packet is a value obtained by adding the TCP data length of a packet having the maximum sequence number to the maximum transmission sequence number received before that time. Communication equipment.   The communication apparatus according to claim 1, wherein the subsequent packet generation processing unit assigns an ACK sequence number of the proxy ACK packet based on an ACK sequence of the received subsequent packet.   4. The subsequent packet generation processing means further generates another proxy ACK packet when a subsequent packet is further received before receiving a retransmission packet of a missing packet. Communication equipment. The subsequent packet generation processing means includes:
Keep subsequent packets,
The communication apparatus according to claim 1, wherein when the retransmission packet of the missing packet is received, the subsequent packet held is transmitted as a resume packet. ALG state transition processing means for managing the ALG state based on the content of the ALG message of the received packet and determining whether or not there is a possibility of changing TCP data for each received packet based on the ALG state;
Further comprising
The subsequent packet generation processing unit acquires the determination result from the ALG state transition processing unit when the subsequent packet is received, and passes the subsequent packet as it is when the determination result indicates that there is no possibility of change. The communication device according to claim 1, wherein A communication method of a communication apparatus having an ALG processing function for updating TCP data,
A TCP sequence number determination step for determining whether or not the packet is a subsequent packet that is transmitted after the missing packet based on the TCP sequence number of the received packet;
A subsequent packet generation step of generating a proxy ACK packet destined for the destination of a missing packet with no TCP data portion and having a TCP data length of 0 when it is determined as a subsequent packet in the TCP sequence number determination step;
A communication method comprising:

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