JP2008072466A - Communication system and terminal - Google Patents

Abstract

A network that solves the problems of TCP and UDP at the same time and can flexibly cope with the number of communication terminals and the processing capacity is realized.
When a data packet transmitting terminal transmits a data packet to a data packet receiving terminal, and the data packet receiving terminal receives the data packet, the reception confirmation packet is transmitted as data according to a predetermined probability. The packet is transmitted to the terminal on the packet transmission side, and if the terminal on the data packet transmission side does not receive the reception confirmation packet within a predetermined time, the data packet is retransmitted to the terminal on the data packet reception side. Further, if the terminal on the data packet transmission side does not receive the reception confirmation packet, the retransmission is performed a plurality of times within a range not exceeding the predetermined upper limit number of times.
[Selection] Figure 2

Description

  The present invention is used for communication between a plurality of terminals connected via a network. In particular, the present invention relates to a retransmission control technique for data packets.

In order to perform reliable communication on the Internet, TCP (Transmission) defined by Non-Patent Document 1
A communication method called Control Protocol is widely used. In this method, a terminal that receives a data packet always transmits a reception confirmation packet. Non-Patent Document 1 p. 4 “Reliability” describes that “requiring a positive acknowledgment (ACK) from the receiving TCP.” Is requested from the TCP process on the receiving side.

  On the other hand, the UDP (User Datagram Protocol) communication method defined in Non-Patent Document 2 does not perform reception confirmation at all.

  Here, the conventional TCP will be briefly described with reference to FIG. 7 and FIG. FIG. 7 is a diagram illustrating a configuration example of a communication system. FIG. 8 is a sequence diagram showing a TCP communication procedure.

  As shown in FIG. 7, terminals 1 to 3 are connected to the network 4. Consider a situation in which a data packet is transmitted from terminal 1 to terminals 2 and 3. As shown in FIG. 8, the terminal 1 transmits a data packet to the terminals 2 and 3 (S40, S41). When receiving the data packet, the terminals 2 and 3 transmit a reception confirmation packet (S42, S43). The terminal 1 receives the reception confirmation packet from the terminals 2 and 3.

  Next, the terminal 1 transmits a second data packet (S44, S45). Now, assume that the packet to the terminal 2 has not arrived for some reason. Then, the terminal 3 transmits a reception confirmation packet to the terminal 1 (S46), but since the terminal 2 does not transmit a reception confirmation packet to the terminal 1, the terminal 1 transmits a reception confirmation packet from the terminal 2. Cannot receive.

  If the reception confirmation packet does not arrive after waiting for a predetermined time, the terminal 1 retransmits the data packet to the terminal 2 (S47). This time, since the terminal 2 has received the data packet, it transmits a reception confirmation packet to the terminal 1 (S48). As described above, the retransmission is repeated until the reception confirmation packet is received.

  In TCP, it is necessary to receive reception confirmation packets for all transmitted data packets (in fact, a method of sending reception confirmations to a plurality of data packets collectively has been proposed. Receiving is essential).

  Actually, special processing is performed at the start and end of communication, but the description thereof is omitted.

  Next, conventional UDP will be briefly described with reference to FIG. FIG. 9 is a sequence diagram showing a UDP communication procedure. In FIG. 9, terminal 1 transmits a data packet to terminals 2 and 3.

  As shown in FIG. 9, it is assumed that the two data packets transmitted by the terminal 1 (S50 to S53) did not reach the terminal 2 (S52). With UDP, it is not possible to recover packets that have been lost in this way.

IETF Request for Comments 793 IETF Request for Comments 768

  In TCP, a terminal that has transmitted data packets to many terminals receives many reception confirmation packets. This reception load limits the number of terminals that can communicate simultaneously.

  On the other hand, in UDP, the number of terminals that can communicate simultaneously increases, but reliable communication cannot be performed.

  The two communication methods must be implemented as different methods.

  The present invention has been made under such a background, and can solve the problem of TCP and UDP at the same time, and can realize a network that can flexibly cope with the number of communication terminals and the processing capacity. The purpose is to provide a system.

  In the present invention, a first terminal transmits a data packet to a second terminal. When the second terminal receives the data packet, the first terminal transmits a reception confirmation packet to the first terminal according to a predetermined probability. If one terminal does not receive the reception confirmation packet within a predetermined time, the data packet is retransmitted to the second terminal. Further, if the first terminal does not receive the reception confirmation packet, the retransmission can be performed a plurality of times within a range not exceeding the predetermined upper limit number.

  Thereby, it is possible to reduce the load of receiving the reception confirmation packet in the first terminal while maintaining communication reliability. However, since the transmission load of the data packet increases, it is suitable when the reception load is larger than the transmission load.

  Further, by changing the transmission probability of the reception confirmation packet between 0 to 100%, both UDP and TCP can be supported.

  That is, the present invention is a communication system in which a plurality of terminals are connected to a mutually communicable network, and a data packet is transmitted from a first terminal to a second terminal. The feature of the present invention is that The second terminal includes means for transmitting a reception confirmation packet to the first terminal according to a predetermined probability when receiving the data packet, and the first terminal must receive the reception confirmation packet within a predetermined time. For example, a means for retransmitting the data packet to the second terminal is provided.

  Further, the means for retransmitting may comprise means for retransmitting the data packet to the second terminal a plurality of times within a range not exceeding a predetermined upper limit if no reception confirmation packet is received.

  Further, when the present invention is viewed from the viewpoint of the second terminal, the present invention is a communication system in which a plurality of terminals are connected to a network that can communicate with each other, and a data packet is transmitted from the first terminal to the second terminal. The second terminal is characterized by comprising means for transmitting a reception confirmation packet to the first terminal according to a predetermined probability when a data packet is received.

  Further, when the present invention is viewed from the viewpoint of the first terminal, the present invention relates to a communication system in which a plurality of terminals are connected to a network capable of mutual communication, and a data packet is transmitted from the first terminal to the second terminal. The first terminal comprises means for retransmitting a data packet to the second terminal if a reception confirmation packet is not received within a predetermined time, and the means for retransmitting the reception confirmation packet If not received, there is provided means for retransmitting the data packet to the second terminal a plurality of times within a range not exceeding a predetermined upper limit number of times.

  According to the present invention, it is possible to satisfy the requirements for TCP and UDP by adjusting parameters while using a single communication method. Thereby, the network which can respond flexibly according to the number of communication terminals and processing capability is realizable.

  An embodiment of a communication procedure in the communication system of the present invention will be described with reference to the sequence diagram of FIG. In this example, the probability of transmitting the reception confirmation packet is 50%. For example, a terminal that receives a data packet generates a random number of 0.0 to 1.0, and transmits a reception confirmation packet if it is less than 0.5.

  The probability value of 50% may be set in advance or may be indicated by a data packet. In this system, in rare cases, the reception confirmation packet may not be transmitted indefinitely. In preparation for such a case, an upper limit value of the number of retransmissions is determined for a terminal that transmits a data packet. In this example, it is “2”.

  As shown in FIG. 1, the terminal 1 transmits a data packet to the terminals 2 and 3 (S1, S2). When the terminal 2 or 3 receives the data packet, it generates a random number and determines whether or not to transmit a reception confirmation packet. In this example, both the terminals 2 and 3 transmit a reception confirmation packet (S3, S4). Since terminal 1 has received the reception confirmation packet from terminals 2 and 3, terminal 1 does not perform retransmission.

  Next, the terminal 1 transmits a second data packet (S5, S6). It is assumed that the terminal 2 receives the data packet, generates a random number, and decides not to transmit the reception confirmation packet. Then, the terminal 1 resends the data packet after waiting for a while like TCP (S8). It is assumed that the terminal 2 receives the data packet again, generates a random number, and determines again that “the reception confirmation packet is not transmitted”. The terminal 1 retransmits the data packet (S9). Here, since the number of retransmissions reaches the upper limit “2”, the retransmission of the data packet is stopped.

  The terminal 3 receives the data packet, generates a random number, determines that “send reception confirmation packet” is transmitted, and transmits the reception confirmation packet to the terminal 1 (S7). Thereby, retransmission of the data packet from the terminal 1 to the terminal 3 is not performed.

  Compared to the TCP example, the number of reception confirmation packets is reduced, and the number of retransmitted data packets is increased. This shows that the communication procedure of this embodiment is effective when the reception load of the terminal 1 is larger than the transmission load.

  The reception process accompanied by the interruption process to the user space may be heavier than the transmission process. In addition, the timing cannot be selected for reception (it is not known when a packet is sent), whereas the transmission timing can be selected for transmission. Therefore, transmission processing can be performed when there is a margin. Further, the communication procedure of this embodiment is also effective when the line capacity toward the terminal 1 is small.

  Furthermore, when the communication procedure of the present embodiment is applied to a video / audio conference system, a great effect can be expected. That is, in the video / audio conference system, a message of one speaker is transmitted to many conference participants. The transmission load at this time is not so large if a multicast address or the like is used.

  On the other hand, since a single speaker's terminal receives and processes reception confirmation packets transmitted from the terminals of many conference participants who have received messages from the speaker, the reception load on the speaker's terminal is extremely high. It will increase.

  When the communication procedure of the present embodiment is applied to a video / audio conference system, it is possible to realize communication with higher reliability than UDP while suppressing such an increase in reception load.

  Note that unlike TCP, a situation in which a data packet does not reach the communication procedure of this embodiment may occur. This is because TCP requests a 100% reception confirmation packet, but does not request it in the communication procedure of the present embodiment. Therefore, the reason why the reception confirmation packet is not returned is “random number result” or “data packet does not reach” That's because I don't know. The communication procedure of the present embodiment is effective for situations where it is desired to deliver data as reliably as possible, but at the same time to reduce the communication load.

  In the following description, a terminal on the data packet transmission side is simply referred to as a “transmission side terminal”, and a data packet reception side terminal is simply referred to as a “reception side terminal”.

  2 shows a block diagram of the terminal 1 on the transmission side, FIG. 3 shows a flowchart of the processing procedure of the data packet storage unit 14 in the terminal 1 on the transmission side, and FIG. 14 is a flowchart of a processing procedure of the unit 15.

  When a packet is generated by the data packet generation unit 11, the generated packet is temporarily stored in the data packet storage unit 14. The data packet storage unit 14 transmits the data packet from the transmission unit 16 to the receiving terminal that has not received the reception confirmation from the reception confirmation checklist holding unit 15 (S10).

  When receiving the reception confirmation packet from the reception unit 17 (S20), the reception confirmation checklist holding unit 15 checks the receiving terminal that has transmitted the reception confirmation packet (S21). The result of this check is notified to the data packet storage unit 14 (S22). The reception confirmation check list 18 held by the reception confirmation check list holding unit 15 records a state corresponding to terminal identification information (terminal ID). In the example of FIG. 2, the state is “completed” when the reception confirmation packet is received, and the state is “not yet” when the reception confirmation packet is not received.

  The data packet storage unit 14 transmits the data packet from the transmission unit 16 to the receiving side terminal that has not received the reception confirmation from the reception confirmation check list holding unit 15 (S10), and then transmits the data packet to the retransmission counter 13. Notify the transmission result.

  Upon receiving this notification, the retransmission number counter 13 adds “1” to the count value corresponding to the receiving terminal, and the timer 12 receives the count value of the retransmission number counter 13 added by “1”. The timing is started from that point to the terminal on the side, and after the set time has elapsed, the data packet storage unit 14 is notified that the retransmission timing for the terminal on the receiving side has arrived.

  When the data packet storage unit 14 receives the notification from the timer 12 (S12), the data packet storage unit 14 confirms the notification from the reception check list holding unit 15 and receives no reception confirmation from the receiving terminal. Retransmits the data packet from the transmitter 16 toward the receiving terminal (S10).

  When retransmission is performed, the result is notified to the retransmission counter 13, and the retransmission counter 13 further adds “1” to the count value for the receiving terminal, and the timer 12 starts timing.

  Although the procedures of steps S10 to S12 are repeatedly executed, an upper limit is set for the retransmission count value, and when the count value reaches the upper limit (S11), even if reception confirmation is not performed, the receiving side The retransmission to the terminal is terminated (S13).

  FIG. 5 shows a block diagram of the terminals 2 and 3 on the receiving side, and FIG. 6 shows a flowchart of the processing procedure of the terminals 2 and 3 on the receiving side. When the receiving unit 23 of the receiving side terminals 2 and 3 receives the data packet (S30), the random number generating unit 24 generates a random number (S31), and if the random number is less than 0.5 (S32), the reception confirmation packet The generation unit 21 generates a reception confirmation packet and transmits the reception confirmation packet from the transmission unit 22 (S33). If the random number is 0.5 or more (S32), the reception confirmation packet is not generated.

  In the present embodiment, in order to make the explanation easy to understand, the transmission side terminal 1 and the reception side terminals 2 and 3 have been described as different configurations. However, actually, one terminal is connected to the transmission side terminal 1 and the reception side. The terminals 2 and 3 are also combined, and one terminal is a transmitting terminal when there is a terminal, and a receiving terminal when there is another terminal.

  According to the present invention, since it is possible to configure a network that can flexibly cope with the number of communication terminals and processing capability, it is possible to improve convenience for both network users and administrators. For example, it is suitable for use in communication in which the reception load is larger than the transmission load of the terminal, such as the video / audio conference system described above.

The sequence diagram which shows the Example of the communication procedure in the communication system of this invention. The block diagram of the terminal of the transmission side in the communication system of this invention. The flowchart which shows the process sequence of the data packet memory | storage part of the terminal of the transmission side in the communication system of this invention. The flowchart which shows the process sequence of the reception confirmation checklist holding | maintenance part of the terminal of the transmission side in the communication system of this invention. The block diagram of the terminal of the receiving side in the communication system of this invention. The flowchart which shows the process sequence of the terminal of the receiving side in the communication system of this invention. The figure which shows a network structure. The sequence diagram which shows the communication procedure of TCP. The sequence diagram which shows the communication procedure of UDP.

Explanation of symbols

1-3 Terminal 4 Network 11 Data packet generation unit 12 Timer 13 Retransmission counter 14 Data packet storage unit 15 Reception confirmation checklist holding unit 16, 22 Transmission unit 17, 23 Reception unit 18 Reception confirmation checklist 21 Reception confirmation packet generation Part 24 Random number generator

Claims (4)

In a communication system in which a plurality of terminals are connected to a mutually communicable network and transmit data packets from a first terminal to a second terminal,
The second terminal comprises means for transmitting a reception confirmation packet to the first terminal according to a predetermined probability when receiving the data packet;
If the first terminal does not receive a reception confirmation packet within a predetermined time, the first terminal includes means for retransmitting a data packet to the second terminal.   2. The communication system according to claim 1, wherein the means for retransmitting includes means for retransmitting a data packet to the second terminal a plurality of times within a range not exceeding a predetermined upper limit number unless receiving a reception confirmation packet. . In the second terminal of the communication system in which a plurality of terminals are connected to a mutually communicable network and transmit data packets from the first terminal to the second terminal.
A terminal comprising: means for transmitting a reception confirmation packet to the transmitting terminal according to a predetermined probability when a data packet is received. In the first terminal of the communication system, in which a plurality of terminals are connected to a mutually communicable network and transmit data packets from the first terminal to the second terminal,
Means for retransmitting a data packet to the second terminal if no acknowledgment packet is received within a predetermined time;
The retransmitting means comprises means for retransmitting the data packet to the second terminal a plurality of times within a range not exceeding a predetermined upper limit if no reception confirmation packet is received.

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