JP3886811B2 - Communication system, communication method, transmission terminal, reception terminal, and relay device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a communication system, a communication method, and a receiving terminal, a transmitting terminal, and a relay device used for transmitting packet data through a transmission path formed by a plurality of types of communication lines.
[0002]
[Prior art]
In an IP network, transmission data is divided and transmitted in units of packets. The maximum packet size is determined by the type of communication line to be transmitted. This maximum value is called MTU (Maximum Transfer Unit). In many cases, the packet size is set to this MTU value.
[0003]
In an IP network, communication is performed from a transmission terminal to a reception terminal via a plurality of types of communication lines. Therefore, when a packet is transmitted from a communication line with a large MTU to a communication line with a small MTU, the relay device (router) connecting these two communication lines may not be able to transmit unless the packet is further divided. In this case, the packet is divided into smaller unit packets and reconfigured to the original packet at the receiving terminal (IP fragmentation). However, when this phenomenon occurs, if even one packet divided into small units is lost along the way, the original packet cannot be reconstructed on the receiving side. Accordingly, the reception error rate increases when the wireless communication line has a characteristic that the packet is lost due to radio wave interference or noise.
[0004]
Conventionally, in order to solve this problem, there is a method in which a transmission terminal packetizes in advance to a size having the smallest MTU among all communication lines existing on a transmission path from the transmission terminal to the reception terminal. . The size of this MTU is called Path MTU, and this method is called Path MTU Discovery.
[0005]
In this method, the transmitting terminal first creates and transmits a packet with the MTU size of the communication line directly connected. When there is a communication line that cannot transmit a packet of this size, a relay device (router) that transmits the communication line discards the packet and notifies the transmission terminal of an error message. This error message notifies the MTU value of the communication line that could not be transmitted. After receiving the error message, the transmitting terminal transmits the packet with the notified MTU size, and can further prevent the packet from being further divided by the relay route (router) on the transmission route.
[0006]
[Problems to be solved by the invention]
However, in the above-described Path MTU method, when there is a line with a high bit error rate such as a wireless communication line on the transmission path, it is not necessarily optimal to transmit a packet with the Path MTU size depending on the communication situation. Not exclusively. That is, in a wireless communication line, when the bit error rate is high, the possibility that a packet having a large packet size can be normally transmitted is reduced. Therefore, the packet error rate can be reduced by reducing the packet size. However, in the above-described Path MTU method, the packet size is determined without considering the error rate in the wireless communication line, and thus the bit error rate cannot be reduced.
[0007]
In the above-described Path MTU method, in a communication line having a feature that an IP packet is divided into smaller fixed-length frames in a lower layer on the transmission path, the divided frames have a fixed-length frame size. If they do not match, empty data is added to the remaining packet data and adjusted to a fixed-length frame. For example, in a W-CDMA communication line, an IP packet to be transmitted is divided into a fixed size of 42 bytes and transmitted. For example, when an IP packet to be transmitted is 480 bytes, a fixed-length frame of 42 bytes is divided into 11 frames and the remainder of 18 bytes, and 24 bytes of empty data is added to the remainder of 18 bytes. Thus, a 42-byte fixed-length frame is obtained. In this case, useless data is transmitted, which causes a problem that communication efficiency decreases.
[0008]
Therefore, the present invention has been made in view of the above problems, and a communication system and a communication method capable of reducing bit error rate, reducing unnecessary data such as empty data, and improving communication efficiency. An object is to provide a receiving terminal, a transmitting terminal, and a relay device.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention acquires characteristics of multiple types of communication lines when transmitting packet data from a transmission terminal to a reception terminal via a transmission path formed by multiple types of communication lines. Then, according to the acquisition result, the size of the packet related to transmission is determined, and the packet is generated with the determined packet size. In the above invention, it is preferable that the determination is performed by a relay device or a reception terminal on a transmission line, and the determined packet size is notified from the relay device or the reception terminal to the transmission terminal.
[0010]
According to such an invention, in order to determine and generate the size of a packet related to transmission according to the characteristics of all communication lines on the transmission line, the packet division processing performed in the relay device can be omitted. Communication efficiency can be improved.
[0011]
In the above invention, a redundant packet holding information for restoring lost packet data when the packet data is lost is generated, and the lost packet data is restored based on the information held in the redundant packet Is preferred. In this case, the probability that transmission data can be normally received by the receiving terminal can be improved, and the possibility that the retransmission of the IP packet becomes necessary due to the loss of the IP packet can be reduced.
[0012]
In the above invention, when a wireless communication line exists on the transmission path, the error rate of the wireless communication line is measured, and the size of the packet related to transmission is changed and set according to the measurement result. preferable. In this case, the rate of IP packets discarded due to bit errors in the wireless communication line can be reduced. In other words, basically, the larger the IP packet size, the better the transmission efficiency, but the larger the packet size, the higher the probability of being discarded in a wireless communication line with a high bit error rate, resulting in poor transmission efficiency. Become. Therefore, in a wireless communication line with a high bit error rate, the transmission efficiency can be improved by setting the IP packet size small.
[0013]
In the above invention, when there is a communication line having a feature that a packet related to transmission is further divided into a fixed size in a lower layer and transmitted on the transmission path, the size of the packet transmitted by the transmitting terminal is fixed. It is preferable to set an integer multiple of the size. In this case, when the IP packet is further divided into fixed lengths in the lower layer, the entire IP packet can be divided into fixed length frames, so it is necessary to add empty data to adjust to the fixed length frame. The transmission efficiency is improved.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
(Constitution)
Hereinafter, an embodiment of a communication system according to an embodiment of the present invention will be described. FIG. 1 is a schematic diagram illustrating a network configuration of a communication system according to the present embodiment, and FIG. 2 is a block diagram illustrating an internal configuration of each device installed on the network.
[0015]
Note that the communication system according to the present embodiment is a communication method for realizing a new transport communication method MSP different from the existing transport layer communication methods TCP and UDP, and a moving image is transmitted from the transmission terminal 1 to the reception terminal 4. A case where transmission is performed in real time will be described as an example. Specifically, in the communication system according to the present embodiment, the transmission terminal 1, the relay device 2, the relay device 3, and the reception terminal 4 are connected via a communication line.
[0016]
The transmission terminal 1 includes a transmission application 11, and by executing the transmission application 11, moving image information is transmitted via the relay device 2 and the relay device 3 for each frame (information of one still image). The MTU is connected to the relay device 2 via a 1500-byte wired communication line. In the present embodiment, it is assumed that the frame F1 of the moving image information transmitted from the transmission terminal 1 has a data size larger than the MTU of each communication line on the transmission path.
[0017]
In particular, the transmission terminal 1 according to the present embodiment includes a feature acquisition unit 14 that acquires the characteristics of all communication lines on the transmission path by an error message to be described later, and according to the acquisition result of the feature acquisition unit 14. A packet generating means 13 for determining a size of a packet for transmission and generating a packet with the determined packet size; and a redundant packet for holding information for restoring lost packet data when the packet data is lost It has redundant packet generating means 12 for generating, and transmitting / receiving means 15 for transmitting various packets and receiving error messages.
[0018]
The transmission terminal 1 has a function of transferring data from the application layer to the network layer via the transport layer. When transferring data between these layers, the frame is divided into a plurality of packet data. In addition, it has a function to add necessary headers.
[0019]
The relay device 2 relays the frame F1 received from the transmission terminal 1 to the relay device 3, and the MTU is connected to the relay device 3 via a 500-byte wireless communication line to transmit a packet. At this time, the IP packet to be transmitted is divided into fixed-length frames of 40 bytes and transmitted to the relay device 3. The relay device 3 relays the frame received from the relay device 2 to the receiving terminal 4. The MTU is connected to the receiving terminal 4 via a 1500-byte wired communication line and is divided by the relay device 2. The original fixed-length frame is reconstructed and the original IP packet is assembled, and then transferred to the receiving terminal 4.
[0020]
Specifically, as shown in FIG. 2B, the relay devices 2 and 3 include a packet relay unit 21 (31) that relays a packet and a packet size setting unit that sets the size of a packet transmitted by the transmission terminal 1. 23 (33), and notification means 22 (32) for notifying the transmission terminal 1 of the packet size set by the packet size setting means 23 (33).
[0021]
Furthermore, the relay devices 2 and 3 are related to the error rate measuring means 24 (34) for measuring the error rate of the wireless communication line as the characteristic acquiring means for acquiring the characteristics of the plurality of types of communication lines, and the transmission on the transmission line. When there is a communication line having a characteristic that a packet is further divided into a fixed size and transmitted in a lower layer, it has division size acquisition means 25 (35) for acquiring the fixed details.
[0022]
The packet size setting means 23 sets the size of the packet to be transmitted by the transmitting terminal 1 to an integral multiple of the fixed size based on the fixed size acquired by the divided size acquisition means 25 (35). The size of the packet related to transmission is changed and set according to the measurement result of the error rate measuring means 24 (34).
[0023]
The divided size acquisition unit 25 (35) according to the present embodiment includes a flow cache therein, and an IP packet passing through the relay device is first passed through the relay device by referring to the flow. And has a function of notifying the packet size setting means 23 (33) of the division size only for the first-passed packet. This flow cache also has a function of registering the flow of packets that are routed for the first time. The error rate measuring means 24 includes a memory for storing a threshold value of the packet damage rate, measures the damage rate of the packet relayed by the packet relay means 21 (31), and determines the damage rate and the threshold value. Only when the threshold is exceeded, the error rate is output to the packet size setting means 23 (33).
[0024]
Specifically, as shown in FIG. 2 (c), the receiving terminal 4 is based on transmission / reception means 41 for transmitting / receiving packets, redundant packet receiving means 42 for receiving redundant packets, and information held in the redundant packets. The packet restoration means 43 for restoring lost packet data, the packet size setting means 46 for setting the size of a packet to be transmitted from the transmission terminal 1, and the packet size set by the packet size setting means 46 are transmitted. Notification means 45 for notifying the terminal 1.
[0025]
The receiving terminal 4 processes and reproduces the frame received from the relay device 3 as information of one moving image frame by the transmission application 44. The receiving terminal 4 has a function of transferring data from the network layer to the application layer through the transport layer. When transferring data between these layers, the receiving terminal 4 deletes unnecessary headers, It also has a function to assemble packet data.
[0026]
Further, the receiving terminal 4 includes, as characteristic acquisition means for acquiring characteristics of a plurality of types of communication lines, an error rate measurement means 47 for measuring an error rate of the wireless communication line, and a lower layer in which packets relating to transmission are transmitted on the transmission path When there is a communication line having a characteristic of being further divided and transmitted in a fixed size, a divided size acquiring means 48 for acquiring the fixed details is provided.
[0027]
The packet size setting means 46 sets the size of the packet to be transmitted by the transmitting terminal 1 to an integral multiple of the fixed size based on the fixed size acquired by the division size acquisition means 48, or measures this error rate. Depending on the measurement result of the means 47, the size of the packet related to transmission is changed and set.
[0028]
(Operation)
The operation of the communication system having the above configuration will be described. FIG. 3 is an explanatory diagram showing a transmission data division / transmission process from the transmission terminal 1 to the relay device 2, and FIG. 3 is an explanatory diagram showing a process of receiving data reconstruction from the relay device 3 to the reception terminal 4.
[0029]
First, the transmission application 11 of the transmission terminal 1 transmits moving image information for each frame (information for one still image). More specifically, as shown in FIG. 3, the moving image transmission application 11 passes one frame of data F1 of the moving image as one transmission data to the transport layer via the packet generation unit 13. In this transport layer, the transmission data delivered from the transmission application 11 is divided into packet data of the same size. In the present embodiment, the data is divided into four parts d1 to d4. At this time, in the present embodiment, when equal division is not possible, empty data is added to data having insufficient size to adjust to equal size. When no forward error correction code is used, it is not necessary to add empty data. In this embodiment, as shown in FIG. 2, empty data is added to the data d4, and the data d1, d2, d3, and d4 are all adjusted to have the same size.
[0030]
Next, the redundant packet generation means 12 generates some redundant data d5 and d6 from the divided data d1, d2, d3, d4 by a Reed Solomon code (one of forward error correction codes). In this embodiment, as shown in FIG. 2, two redundant data d5, d6 are generated from data d1, d2, d3, d4. Then, an MSP header H1 including information that can be reconfigured on the receiving side is added to each data and passed to the network layer. In the network layer, an IP header H2 used for route control on the IP network is added to the data passed from the transport layer, and is sent to the communication line as IP packets P1 to P6 via the transmission / reception means 15.
[0031]
On the other hand, a process of data transmission in the receiving terminal 4 is shown. First, as shown in FIG. 4, the IP packets P1 to P6 are received from the communication line via the transmission / reception means 41, the IP header is removed at the network layer, and it is passed to the transport layer. In the transport layer, the data d1 to d4 transferred from the IP layer are reconstructed, and one frame of moving image data is generated and transferred to the transmission application 44 located in the application layer.
[0032]
In the example shown in FIG. 4, the IP packet 3 of the transmitted IP packets is lost in the middle. In this case, the IP header H2 of the IP packets P1, P2, P4, P5 and P6 is removed at the network layer and transferred to the packet restoration means 43 located in the transport layer. In the transport layer, data 3 is restored by forward error correction decoding using data d1, d2, d4 and redundant data d5 and d6 using information of the transport header. Using the data d1, d2, d4 and the restored data d3, the original moving image frame data is reconstructed and passed to the transmission application 44.
[0033]
(Data structure in the transport layer)
Next, the communication method of the transport layer will be described in detail with reference to FIG. FIG. 5 is an explanatory diagram showing a data structure of data d1 to d6 transmitted in the transport layer in the present embodiment. As shown in the figure, the data d1 to d6 are composed of an MSP header and a data part.
[0034]
The MSP header is added when individual data obtained by dividing the data passed from the application and redundant data generated from the data are passed to the network layer. The source port number, destination port number, It consists of various fields for storing data length, checksum, block ID, block length, number of data, number of redundant data, sequence number, and the like.
[0035]
The port number field is used to identify a port number in the transport layer, and identifies which application among a plurality of applications running on the same host (computer) should be passed data. Is. The port number includes a transmission source port number and a destination port number. Since the port number is stored in a 16-bit field in the MSP header, 65535 types of port numbers can be used in one host.
[0036]
The data length field stores the size of individual data after dividing one frame of the moving image by the transport layer. As described above, when empty data is added because it cannot be divided equally, the data size including empty data is stored.
[0037]
The checksum field stores an identifier for checking whether a piece of data after being divided in the transport layer is correctly received. With this identifier, it is possible to check whether data is damaged due to a bit error in the wireless communication line.
[0038]
The block ID field stores an ID added to the data of one frame of the moving image passed from the application layer. The IDs are assigned in order from 1 in the moving image playback order. As a result, the same block ID is assigned to each piece of data generated by dividing one moving image frame in the transport layer. The same block ID is also assigned to redundant data generated from each divided data. Thereby, it is possible to determine which block (moving image frame) each piece of data received by the receiving terminal 4 belongs to. Since this field is 16 bits, when an ID is allocated up to 65535, the next ID is allocated again from 1. The next block length field can store the size of data passed from the application layer. As a result, it is possible to remove the empty data added when the transmission terminal cannot be divided equally from the data reconstructed by the reception terminal.
[0039]
The data number field indicates how many pieces of data passed from the application at the transmitting terminal are divided. This makes it possible to determine the number of data for reconstructing data to be passed to the application. On the receiving side, when data (including redundant data) reaches the number of values in this field, it is possible to reconstruct data of one moving image frame to be passed to the application. Receiving terminal 4 starts reconstruction at the time when data is collected by the number of values in this field.
[0040]
The field of the number of redundant data indicates how many redundant data are generated for one block (one frame of moving image) at the transmission terminal. If more packets than the number of values in this field of data belonging to a block are lost, the block cannot be reconstructed. In the receiving terminal, if more packets than the value of this field are lost, or if the data belonging to the next block arrives before the number of reconfigurable data is collected, the data is not reconstructed until then. Discard the collected data.
[0041]
In the sequence number field, numbers are assigned to individual data divided in the transport layer in order from 1 from the top data. Thereby, even if certain data is lost, it is possible to detect which data has been lost. Each redundant data is also numbered from 1 in order from the top of the redundant data. The sequence number of redundant data is used for forward error correction decoding processing.
[0042]
Various flag bits are set in the flag field. The meaning indicated by the flag when 1 is stored in each bit is effective. First, the DATA flag indicates that this data is not redundant data but data obtained by dividing the data passed from the application layer. The FEC flag indicates that this data is redundant data. The ACK flag is used in a message for confirming that data has been successfully reconstructed from the receiving terminal. When this message is sent from the receiving terminal 4, no data part is attached after the transport header. The block ID field of the transport header stores the ID of the block that has been confirmed to be reconfigured and reports it to the transmitting terminal. The NACK flag is used for a message reporting that data could not be reconstructed at the receiving terminal 4. The message structure is the same as that of the ACK message. When the transmitting terminal receives the NACK message, it increases the number of redundant data to be generated. The ECN flag is used in combination with the NACK flag, and indicates that a packet lost in the middle is not caused by noise or interference of the wireless communication line but is caused by network congestion. When packets are lost due to network congestion, increasing the number of redundant data at the transmitting terminal only promotes congestion, so the number of redundant data is not increased.
[0043]
(Split adjustment process)
Next, adjustment of the division size when the transmission terminal 1 divides data of one frame of moving image will be described. The division size is notified from the relay devices 2 and 3 on the network and the receiving terminal 4 using an ICMP error message as shown in FIG.
[0044]
In this embodiment, the ICMP error message is configured according to a standardized format.
[0045]
Specifically, in the ICMP error message format according to the present embodiment, an area of 32 bits is secured, and an error type, error code, checksum, field 1 and field 2 are allocated.
[0046]
The error type is stored in the first 8 bits. Here, 3 indicating all meanings that the host cannot be reached is stored. The next 8 bits store an error code. In the system described here, 4 indicating all the meanings necessary for division is stored. The next 16 bits store a checksum, which is used to check whether this ICMP message has been received correctly. The next 16-bit field 1 and 16-bit field 2 store different data depending on the communication method.
[0047]
(1) Operation of relay device 3
The relay device 3 notifies the recommended value of the packet size based on the bit error rate in the wireless communication line.
[0048]
That is, when the BER (bit error rate) is high in the wireless communication line between the relay device 2 and the relay device 3, a packet with a large packet size has a higher packet loss rate than a packet with a small packet size. When the rate at which packets cannot be received correctly due to bit errors increases, the relay device 3 notifies the transmitting terminal 1 using an ICMP error message so as to reduce the packet size. In this case, in the field 2 of the ICMP error message, a value half the size (average value) of the received IP packet is stored and transmitted to the transmission terminal 1. Upon receiving this notification, the feature acquisition unit 14 of the transmission terminal 1 sets the size of dividing one moving image frame in the packet generation unit 13 to be equal to or smaller than the value of the field 2 of the ICMP error message.
[0049]
Specifically, when the error rate measuring unit 34 of the relay device 3 receives data corrupted by a bit error at a certain ratio or more, it calculates an error rate based on the data and sends the calculation result to the packet size setting unit 33. In the packet size setting means 33, the packet size to be transmitted by the transmission terminal 1 is set. Here, the packet size is set to be small in order to reduce the error rate. Then, the notification means 32 transmits an ICMP error message to the transmission terminal 1 to notify the packet to be transmitted with a reduced packet size (however, if there is a bit error in the IP header portion of the IP packet, transmission is performed). (The ICMP error message cannot be sent to the sending terminal 1 because the terminal address is unknown.)
[0050]
FIG. 7 shows a processing procedure until the relay device 3 transmits an ICMP error message. First, when the data (IP packet) transmitted from the relay device 2 is received by the packet relay unit 31 (S101), the error rate measuring unit 34 checks whether or not there is a bit error in the data (S102). If there is no bit error in the transmission data, the IP packet damage rate is reduced (S107), and the IP packet is processed normally (S108). On the other hand, if it is determined in step S102 that there is a bit error in the transmission data, the IP packet corruption rate is increased (S103), and it is checked whether the IP packet corruption rate exceeds the threshold (S104). If the IP packet damage rate does not exceed the threshold value, the IP packet is discarded (S106). If it is determined in step S104 that the IP packet damage rate exceeds the threshold, the packet size setting unit 33 sets the packet size according to the damage rate, and the setting result is sent to the transmitting terminal 1 by the ICMP error message. Send. Thereafter, the packet relay unit 31 discards the IP packet (S105).
[0051]
(2) Operation of relay device 2
On the other hand, in the wireless communication line between the relay device 2 and the relay device 3 in FIG. 1, the IP packet to be transmitted is divided into 40-byte fixed-length frames. In this case, when a 500-byte packet is transmitted, it is divided into 12 40-byte divided frames, and 20 bytes of empty data are added to the remaining 20 bytes for transmission. Since this 20-byte empty data is useless, the relay device 2 notifies the transmission terminal 1 using an ICMP error message so that the transmission terminal generates a packet that is an integer multiple of 40 bytes in advance. That is, 40 is stored in the field 1 of the ICMP error message and transmitted to the transmission terminal 1. Upon receiving this notification, the transmission terminal 1 adjusts the transmission data division size to an integer multiple of 40 bytes.
[0052]
FIG. 8 shows the processing procedure of the relay device 2. Upon receiving the transmission data (IP packet) (S201), the division size acquisition unit 25 of the relay device 2 checks whether the size of the IP packet is an integer multiple of 40 bytes (S202).
[0053]
If the size of the IP packet is not an integer multiple of 40 bytes, it is checked whether or not the flow information (source address and source port number) of the IP packet exists (S203). Check whether the flow passes through 2. This is performed by checking whether or not the flow is registered in the flow cache of the relay device 2. If the flow is registered in the flow cache, the IP packet is processed normally (206).
[0054]
On the other hand, if it is determined in step S203 that the flow is not registered in the flow cache, the division size acquisition unit 25 determines that the flow passes through the relay device 2 for the first time, and registers the flow in the flow cache. (S205), the fact that the fixed-length frame is 40 bytes is sent to the packet size setting means 23. The packet size setting means 23 sets the packet size based on this, and the setting result is sent from the notification means 22 to the packet size setting means 23. The sending terminal 1 is notified by sending an ICMP error message (S204). Thereafter, the packet relay means 21 normally processes the IP packet (S206). At this time, the flow registered in the flow cache is lost when a certain time elapses.
[0055]
(Example of change)
In addition, this invention is not limited to embodiment mentioned above, A various change can be added.
[0056]
For example, in the above-described embodiment, the packet size setting means is provided in the relay devices 2 and 3 and the receiving terminal 4, and the packet size set in the relay devices 2 and 3 and the receiving terminal 4 is transmitted to the ICMP error message. The feature acquisition unit 14 of the terminal 1 is notified, but the packet size setting unit is provided in the transmission terminal, and only the error rate in the communication line and the fixed length of the divided packet are notified to the ICMP error message. The packet size may be set.
[0057]
In this embodiment, the feature acquisition unit 14 provided in the transmission terminal 1 receives the ICMP error message and acquires the feature of each communication line by the ICMP error message. For example, the feature acquisition unit 14 14 may be provided with an error rate measurement unit and a division size acquisition unit, and the transmission terminal 1 side may acquire the error rate and the division fixed size.
[0058]
【The invention's effect】
According to the present invention, when packet data is transmitted from a transmission terminal to a reception terminal via a transmission path formed by a plurality of types of communication lines, the bit error rate is reduced and useless data such as empty data is reduced. Can be reduced and communication efficiency can be improved.
[Brief description of the drawings]
FIG. 1 is a network configuration diagram of a communication system according to an embodiment of the present invention.
FIG. 2 is a block diagram showing an internal configuration of each device according to the embodiment.
FIG. 3 is an explanatory diagram showing a transmission data division / transmission process in the transmission terminal according to the embodiment;
FIG. 4 is an explanatory diagram showing a reconfiguration process of received data in the receiving terminal according to the embodiment.
FIG. 5 is a schematic diagram showing a format of an MSP header according to the present embodiment.
FIG. 6 is a schematic diagram showing a format of an ICMP error message according to the present embodiment.
FIG. 7 is a flowchart showing the operation of the relay device that notifies the recommended value of the packet size by the bit error rate in the present embodiment.
FIG. 8 is a flowchart showing a processing procedure of a relay device that divides into fixed-length frames in the present embodiment.
[Explanation of symbols]
1 ... Sending terminal
2, 3 ... Relay equipment
4 ... Receiving terminal
11, 44 ... Transmission application
12 ... Redundant packet generation means
13: Packet generation means
14 ... Feature acquisition means
15 ... Transmission means
21, 31, 42 ... packet relay means
22, 32, 45 ... notification means
23, 33, 46 ... Packet size setting means
24, 34, 47 ... error rate measuring means
25, 35, 48 ... division size setting means

Claims (6)

A communication system for transmitting packet data from a transmission terminal to a reception terminal via a transmission path formed by a plurality of types of communication lines,
A division size acquisition means for acquiring the fixed size when there is a communication line having a feature that the packet for transmission is further divided into a fixed size and transmitted in a lower layer; and
A packet size setting means for setting the size of a packet transmitted by the transmitting terminal to an integral multiple of the fixed size;
A communication system comprising: packet generation means for determining a size of a packet related to the transmission according to the setting of the packet size setting means, and generating a packet with the determined size. A communication method for transmitting packet data from a transmission terminal to a reception terminal via a transmission path formed by a plurality of types of communication lines,
Acquiring a fixed size when there is a communication line having a feature that the packet for transmission is further divided into a fixed size and transmitted in a lower layer; and
Setting the size of a packet to be transmitted by the transmitting terminal to an integral multiple of the fixed size;
And determining a size of the packet related to the transmission according to the set size of the packet, and generating a packet with the determined size. A transmission terminal that transmits packet data via a transmission path formed by a plurality of types of communication lines to a reception terminal,
Feature acquisition means for acquiring the size of a packet set to an integral multiple of the fixed size when there is a communication line having a feature in which the packet for transmission is further divided into a fixed size and transmitted in a lower layer When,
Packet generation means for determining the size of the packet related to the transmission according to the setting of the acquired packet size, and generating a packet with the determined size;
Transmitting means comprising: transmitting means for transmitting the generated packet to the receiving terminal. A receiving terminal that receives packet data from a transmitting terminal via a transmission path formed by a plurality of types of communication lines,
A division size acquisition means for acquiring the fixed size when there is a communication line having a feature that the packet for transmission is further divided into a fixed size and transmitted in a lower layer; and
A packet size setting means for setting the size of a packet transmitted by the transmitting terminal to an integral multiple of the fixed size;
Notification means for notifying the transmitting terminal of the size of the packet set by the packet size setting means;
And a packet receiving means for receiving a packet generated with the size of the packet notified by the notifying means. A relay device that relays packet data transmitted from a transmission terminal to a reception terminal via a transmission path formed by a plurality of types of communication lines,
A division size acquisition means for acquiring the fixed size when there is a communication line having a feature that the packet for transmission is further divided into a fixed size and transmitted in a lower layer; and
A packet size setting means for setting the size of a packet transmitted by the transmitting terminal to an integral multiple of the fixed size;
Notification means for notifying the transmitting terminal of the size of the packet set by the packet size setting means;
A relay device comprising: a packet relay unit that relays a packet generated with the packet size notified by the notification unit. The notifying means notifies the transmitting terminal of the size of the packet set by the packet size setting means when a packet that is not generated with a packet size that is an integral multiple of the fixed size is relayed for the first time. The relay device according to claim 5.

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