JP7680392B2 - COMMUNICATION CONTROL DEVICE, CONTROL METHOD, COMMUNICATION SYSTEM, AND PROGRAM - Google Patents

Description

The present invention relates to a communication control device, a control method, a communication system, and a program in a communication system that relays TCP sessions.

Transmission Control Protocol (TCP) is used to send and receive data over a network. Flow control is performed when sending and receiving data using TCP (References 1 and 2). A communication device that receives data (hereafter referred to as a receiving device) notifies the communication device that transmits data (hereafter referred to as a transmitting device) of the reception status of packets from the transmitting device by sending an acknowledgement (ACK) or a negative acknowledgement (NACK). Note that an ACK indicates that a packet has been received normally, and a NACK indicates that a packet has been lost.

In flow control, the transmitting device manages the transmission window size. The transmission window size specifies the number of packets that the transmitting device can transmit without receiving an ACK from the receiving device. The transmitting device increases or decreases the transmission window size based on the reception status reported by the receiving device, i.e., ACK or NACK. Generally, the transmitting device decreases the transmission window size when it receives a NACK, and increases the transmission window size according to a predetermined algorithm while only an ACK is being received. The number of packets that the transmitting device transmits is adjusted according to the transmission window size according to the network conditions, thereby achieving flow control.

In conventional TCP communication, in order to achieve high-speed TCP communication in an environment with a long round-trip time, it is necessary to increase the transmission window size. However, because the transmission window size increases when communication is successful, if data loss occurs during communication, this prevents the transmission window size from increasing. On the Internet, data loss cannot be completely eliminated, so communication speeds are limited to a certain level.

As shown in Figure 1 (A), when TCP communication is performed between two nodes, a transmitter and a receiver, if the transmission window size is _wt and the delay time it takes for a packet to travel round trip (round trip delay time) is _rt , the throughput is _wt / _rt , and the throughput decreases in inverse proportion to the round trip delay time.

Non-Patent Document 2 discloses a method of relaying TCP communication as a means for realizing high-speed communication in an environment with a large round-trip delay time. When relaying TCP communication, a relay node has a receiving function and a transmitting function. As shown in Fig. 1 (B), by selecting a relay node whose round-trip delay times r t1 and r _t2 of each section (the section between the transmitting node and the relay node, and the section between the relay node and the receiving _node ) are smaller than the round-trip delay time between the transmitting and receiving nodes, it is possible to improve throughput.

"BBR: Congestion-Based Congestion Control," ACM Queue, Vol. 14, No. 5, pp. 50, Oct 2016. "Towards Multi-Domain Congestion Control in Next-Generation Networks," Proceedings of 2019 IEEE Wireless Communications and Networking Conference (WCNC), 2019.

Here, if a relay node is used to relay communication between a sender and a receiver at the time communication between the sender and the receiver starts, the communication may end before the communication speed between the sender and the receiver reaches a sufficiently high speed, which creates an issue of imposing a load on the relay node without providing the benefit of improved throughput due to the relay node.

The present invention has been made in consideration of the above problems, and provides a technology for appropriately switching a TCP session in progress to a TCP session relayed by a relay node.

According to one aspect of the present invention, a communication control device provided in a source node or a destination node includes :
A determination means for determining whether a transmission control protocol (TCP) session of a switching source which is performing communication satisfies a predetermined condition;
a determining means for determining, from among a plurality of candidate relay nodes, a relay device that will relay the communication corresponding to the switching source TCP session;
an instruction means for establishing a switching destination TCP session between the relay device determined by the determination means and each of the source node and destination node of the switching source TCP session when the determination means determines that the switching source TCP session satisfies the predetermined condition, and for instructing execution of a pre-communication, which is different from the communication associated with the switching source TCP session, in the switching destination TCP session;
a switching means for switching the communication from the source TCP session to the destination TCP session after the preliminary communication is performed;
The present invention is characterized by comprising:

The present invention provides a technology that appropriately switches a TCP session in progress to a TCP session relayed by a relay node.

1A is a diagram showing the throughput of a TCP session that does not include a relay node, and FIG. 1B is a diagram showing the throughput of a TCP session that includes a relay node. FIG. 1 is an explanatory diagram of a communication system according to an embodiment of the present invention. FIG. 2 is a diagram showing the configuration of a transmitting node and a receiving node. FIG. 2 is a diagram showing the configuration of a relay node. FIG. 4 is a sequence diagram showing a process executed by the communication system.

The following embodiments are described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be combined in any desired manner. In addition, the same reference numbers are used for the same or similar configurations, and duplicate descriptions will be omitted.

In the communication system according to this embodiment, after starting communication in a TCP session between a sending node and a receiving node, communication is switched to a TCP session between the sending node and a relay node, and between the relay node and a receiving node at an appropriate timing. This makes it possible to avoid a situation where communication is terminated due to data being exhausted before the communication speed increases, resulting in an unnecessary increase in the processing load of the relay node without obtaining the benefit of the increased speed achieved by inserting a relay node.

Figure 2 is a diagram showing a communication system according to this embodiment. The communication system 1 shown in Figure 2 includes a transmitting node 10, a receiving node 20, and a number of relay nodes 30. The transmitting node 10, the receiving node 20, and the number of relay nodes 30 are communication devices connected to each other so as to be able to communicate with each other via a network 2.

The sending node 10 is an example of a communication control device that establishes a TCP session with the receiving node 20, executes flow control to perform data communication, and determines whether to have the relay node 30 relay the data. The sending node 10 is, for example, a server on the Internet. The receiving node 20 is, for example, a user device including a smartphone or a personal computer.

Network 2 is a network capable of sending and receiving packets using the TCP protocol, and may include the Internet at least in part.

The relay node 30 is a communication device that relays communication by establishing a TCP session with each of the transmitting node 10 and the receiving node 20, and performing flow control in each communication section to forward a data packet received from the transmitting node 10 to the receiving node 20. In this embodiment, as shown in FIG. 1, the transmitting node 10 is described as selecting one of the three relay nodes 30 to relay communication. However, the number of relay nodes is not limited to three, and may be one or more.

The configuration of the transmitting node 10 and the receiving node 20 according to this embodiment will be described with reference to FIG. 3. In one example, the transmitting node 10 and the receiving node 20 have a processor 301, a ROM 302, a RAM 303, a storage device 304, and a communication circuit 305. The processor 301 of the transmitting node 10 and the receiving node 20 executes a program recorded in, for example, the ROM (Read Only Memory) 302, the RAM (Random Access Memory) 303, or the storage device 304.

By executing the processor, the processor 301 executes the functions of the flow control unit 311, the trigger detection unit 312, the relay node selection unit 313, the advance adjustment unit 314, and the session switching unit 315. The processor 301 includes one or more processors such as a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), a DSP (Digital Signal Processor), etc. The processor 301 also executes a program stored in the ROM 302, the RAM 303, or the storage device 304 to control the entire transmitting node 10 and the receiving node 20.

The sending node 10 and the receiving node 20 may be provided with dedicated hardware for executing each function, or some functions may be executed by hardware and other functions may be executed by a computer running a program. Also, all functions may be executed by a computer and a program.

Also, either the transmitting node 10 or the receiving node 20 may have the functions of the trigger detection unit 312, the relay node selection unit 313, the pre-adjustment unit 314, and the session switching unit 315. In other words, at least one of the transmitting node 10 and the receiving node 20 may have the functions of a communication control device, and the functions of the communication control device may be realized by the transmitting node 10 and the receiving node 20. In this embodiment, the description will be given assuming that the transmitting node 10 has the functions of the trigger detection unit 312, the relay node selection unit 313, the pre-adjustment unit 314, and the session switching unit 315.

The flow control unit 311 transmits data packets in a TCP session according to the transmission window size, and controls the transmission window size based on the ACK/NACK signal received in response to the data packet.

The trigger detection unit 312 monitors the TCP session between the sender and receiver, and detects the occurrence of a trigger event. When it detects the occurrence of a trigger event, it causes the relay node 30 to relay communication between the sender node 10 and the receiver node 20.

The trigger event is, for example, that the transmission window size has not changed for a predetermined period, for example, 30 seconds. For example, the trigger event is that the transmission window size _wt in the predetermined period is within a predetermined range from the maximum value of the maximum transmission window size _wmax in the predetermined period, i.e., a× _wmax ≦ _wt ≦ _wmax , where a is a variable that defines the range of the window size and is 0<a<1. In one example, a=0.9.

Alternatively, the trigger event may be, for example, the transmission window size acquired a predetermined number of times most recently, for example, five times, being within a predetermined range. In this case, the trigger detection unit 312 stores the acquired transmission window size in the RAM 303 or the storage device 304. Then, the trigger detection unit 312 can determine that the transmission window size acquired a predetermined number of times most recently is within the predetermined range _when the value of the other transmission window size is within the predetermined range with respect to the maximum value _wmax of the transmission window size values wt of the most recent five times, for example, _wmax ≧ _wt ≧0.9× _wmax .

As a result, when the variation in the transmission window size relative to the maximum transmission window size within a specified period is small, i.e., when the transmission window size is not expected to increase beyond the maximum transmission window size, improved throughput can be expected by communicating via a relay node 30 selected by the method described below.

In another example, the trigger event is, for example, that the transmission window size has not changed within a predetermined period and is equal to or greater than a predetermined value. For example, the trigger event is that the transmission window size _wt within a predetermined period is within a predetermined range from the maximum value of the maximum transmission window size _wmax within the predetermined period, i.e., a× _wmax ≦ _wt ≦ _wmax , and a predetermined value b≦ _wt , where b is a threshold value that enables the introduction of a relay node, and is, for example, a value such as b=10 Mbps.

Alternatively, the trigger event may be, for example, the transmission window size acquired a predetermined number of times most recently, for example, five times, being within a predetermined range and being equal to or greater than a predetermined value. In this case, the trigger detection unit 312 stores the acquired transmission window size in the RAM 303 or the storage device 304. Then, when the value of the other transmission window size is within a predetermined range with respect to the maximum value _wmax of the transmission window size values _wt of the most recent five times, for example _wmax ≧ _wt ≧0.9× _wmax , and the predetermined value b≦ _wt , the trigger detection unit 312 can determine that the transmission window size acquired a predetermined number of times most recently is within a predetermined range and is equal to or greater than a predetermined value.

As a result, if communication has been performed for a specified period of time with a throughput equal to or greater than a specified value and the transmission window size has not fluctuated during the specified period, i.e., if high-throughput communication is being performed, applications such as large-volume streaming may be in use, and it can be determined that there is a high possibility that high-throughput communication will continue in the future. In such cases, by performing communication via a relay node 30 selected by the method described below, the benefits of relaying communication by the relay node 30 can be obtained.

Moreover, the trigger event is, for example, a transmission window size being equal to or larger than a predetermined value. In this case, when the acquired transmission window size value _wt is a predetermined value b≦ _wt , the trigger detection unit 312 determines that the relay node 30 is to relay the communication session. As a result, when it is determined that high throughput is required, the relay node 30 can improve the throughput by performing communication via the relay node 30, and the relay node 30 provides an advantage in relaying communication.

The relay node selection unit 313 selects a relay node 30 from among the multiple relay nodes 30 to relay communication between the transmitting node 10 and the receiving node 20, and instructs the selected relay node 30 to establish a session between the transmitting node 10 and the receiving node 20. The relay node selection unit 313 selects a relay node 30 that is likely to improve throughput by relaying communication. As shown in FIG. 1, the throughput can be improved by shortening the round-trip delay time required for a packet to travel round trip. For this reason, the relay node selection unit 313 according to this embodiment selects a relay node 30 based on the round-trip delay time between the transmitting node 10 and the receiving node 20 and the relay node 30. In one example, one of the transmitting node 10 and the receiving node 20 may select a candidate relay node 30, and the other may determine a relay node 30 to relay communication from among the candidate relay nodes 30.

Before relaying a communication session to the relay node 30 selected by the relay node selection unit 313, the pre-adjustment unit 314 transmits and receives dummy data to increase the transmission window size of the session (post-switching session) including the session between the transmitting node 10 and the relay node 30 and the session between the relay node 30 and the receiving node 20 while maintaining the session (pre-switching session) between the transmitting node 10 and the receiving node 20. This makes it possible to improve the throughput of the post-switching session before switching communication to the post-switching session.

After the pre-adjustment unit 314 performs pre-adjustment of the post-switching session, the session switching unit 315 sends an instruction to switch communication from the pre-switching session between the transmitting node 10 and the receiving node 20 to the post-switching session.

The configuration of the relay node 30 will be described with reference to FIG. 4. In one example, the relay node has a processor 401, a ROM 402, a RAM 403, a storage device 404, and a communication circuit 405. The processor 401 of the relay node 30 executes a program recorded in, for example, the ROM 402, the RAM 403, or the storage device 404.

The processor 401 executes the functions of a flow control unit 411, an instruction receiving unit 412, and a pre-adjustment unit 413 by executing the processor. The processor 401 includes one or more processors such as a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), a DSP (Digital Signal Processor), etc. The processor 401 also executes a program stored in the ROM 402, the RAM 403, or the storage device 404 to control the entire relay node 30.

The communication circuit 405 simultaneously establishes a communication session with the transmitting node 10 and a communication session with the receiving node 20, and the flow control unit 411 controls each session independently. In one example, the communication circuit 405 has multiple communication interfaces that communicate with each of the transmitting node 10 and the receiving node 20.

The instruction receiving unit 412 receives a session establishment instruction sent from the relay node selection unit 313, and establishes a session with each of the transmitting node 10 and the receiving node 20 in accordance with the instruction.

The pre-adjustment unit 413 sends and receives dummy data in the session established by the instruction receiving unit 412, and expands the window size of the post-switching session before switching communication to the post-switching session.

With reference to Figure 5, an example of a processing sequence executed by the communication system 1 according to this embodiment will be described.

First, in S501, the transmitting node 10 and the receiving node 20 establish a TCP session, and in S502, communication begins. At this point, the trigger detection unit 312 begins monitoring the communication status. In S501, a TCP session can be established using existing technology. After communication begins in S502, the transmitting node 10 and the receiving node 20 communicate using the communication session from which the switch was made, although this is not shown.

Then, in S502, the trigger detection unit 312 determines whether the session established in S501 (the session before switching) satisfies the conditions for determining to use the relay node 30.

If the conditions for determining whether to use the relay node 30 are not met, the communication status continues to be monitored. If it is determined that the conditions for determining whether to use the relay node 30 are met, the process proceeds to S504, where the relay node selection unit 313 selects a relay node 30. In this embodiment, the relay node selection unit 313 of the sending node 10 selects candidate relay nodes 30. In S504, the relay node selection unit 313 of the sending node 10 executes a program that measures delay times of ping commands, etc., for multiple relay nodes 30, and selects a predetermined number of relay nodes 30, for example five relay nodes 30, from among the multiple relay nodes 30 in order of shortest round-trip delay times.

In one example, the sending node 10 may measure the round-trip delay times for multiple relay nodes 30 at a predetermined time interval, for example, every minute, and store the measured round-trip delay times in the memory device 304 in association with the relay nodes 30. In step S504, a candidate relay node 30 may be selected based on the round-trip delay times stored in the memory device 304.

After selecting the relay node 30 in S504, the relay node selection unit 313 advances the process to S505 and transmits a relay request signal to the receiving node 20. The relay request signal transmitted to the receiving node 20 in S505 notifies the destination port number of the TCP communication of the receiving node 20 used in the session before switching and the session number of the transmitting side to be used in the switching process described later in S510. The session number may be generated using, for example, a pseudorandom function. In addition, the relay request signal transmitted to the relay node 30 in S505 includes a list that associates candidate relay nodes 30 with their respective round trip delay times.

When the relay node selection unit 313 of the sending node 10 selects one relay node 30 to relay the communication in S504, the relay request signal only needs to include the port number of the TCP communication used in the session before switching, the session number used in the switching process described later in S510, and information specifying the relay node 30. In such a case, the relay request signal does not need to include a list that associates candidate relay nodes 30 with their respective round-trip delay times.

In S506, the receiving node 20 determines whether the destination port number of the TCP communication included in the relay request signal is used for communication, and if so, specifies that the TCP communication corresponding to the destination port number is to be relayed. In addition, in S506, the relay node selection unit 313 of the receiving node 20 obtains the round-trip delay time for the candidate relay node included in the relay request signal, and selects a relay node 30 to relay the communication. In S506, the relay node selection unit 313 of the receiving node 20 executes a program that measures delay times such as ping commands for multiple relay nodes 30, and selects a predetermined number of relay nodes 30, for example, five relay nodes 30, from among the multiple relay nodes 30 in order of the shortest round-trip delay times. Alternatively, the receiving node 20 may measure the round-trip delay times for multiple relay nodes 30 at predetermined time intervals, for example, every minute, associate the measured round-trip delay times with the relay nodes 30, and store the measured round-trip delay times in the storage device 304, and in S506 select candidate relay nodes 30 based on the round-trip delay times stored in the storage device 304.

Here, in S506, the relay node selection unit 313 of the receiving node 20 selects a relay node 30 based on the round-trip delay time (sender delay time) between a specific relay node 30 and the transmitting node 10 and the round-trip delay time (receiver delay time) between the specific relay node 30 and the receiving node 20.

In one example, it is determined that the communication is to be relayed by the relay node 30 among multiple candidate relay nodes that has the smallest sum of the sending side delay time and the receiving side delay time. Note that it is determined not to relay the communication for a candidate relay node for which either the sending side delay time or the receiving side delay time is greater than the round-trip delay time between the sending node 10 and the receiving node 20.

It may also be determined that the communication is to be relayed by the relay node 30 among multiple candidate relay nodes that has the smallest difference between the sending side delay time and the receiving side delay time.

The receiving node 20 that selected the relay node 30 transmits a relay response signal including the identification information of the relay node 30 selected in S507 to the transmitting node 10. Also, in S507, the receiving node 20 notifies the transmitting node 10 of the session number of the receiving side to be used in the switching process described later in S510. The session number may be generated, for example, using a pseudo-random function.

In S508, the transmitting node 10 that has received the relay response signal transmits a relay instruction signal to the relay node 30 contained in the relay response signal. The relay instruction signal contains the IP addresses and port numbers of the transmitting node 10 and the receiving node 20, as well as the session numbers of the transmitting side and the receiving side, as the source TCP session information.

The relay node 30 that receives the relay instruction signal transmits a relay notification signal to the receiving node 20 in S509. The relay notification signal includes, as TCP session information of the switching source, the IP addresses and port numbers of the sending node 10 and the receiving node 20, and the session numbers of the sending side and the receiving side.

The receiving node 20 determines whether the TCP session information received from the relay node 30 matches the TCP session information that the receiving node 20 stores in the storage device 304. If the information matches, it determines that relaying by the relay node 30 is permitted, and transmits a relay notification response to the relay node 30 in S510. The relay notification response includes information indicating the relay receiving port number that the receiving node 20 uses in the switching destination TCP session, and information indicating the session numbers of the sending and receiving sides.

The relay node 30 that has received the relay notification response transmits a relay instruction response to the sending node 10 in S511. The relay instruction response includes information indicating the session numbers of the sending and receiving sides, and information indicating the relay port number that the relay node 30 uses to establish a TCP session with the sending node 10.

In addition, in parallel with the relay instruction response of S511, the relay node 30 establishes a TCP session with the receiving node 20 in S512. Here, the relay node 30 establishes the TCP session by specifying the relay receiving port number included in the relay notification response.

The sending node 10 that receives the relay instruction response transmits a response confirmation signal to the relay node 30 in S513. The response confirmation signal includes the session numbers of the sending side and the receiving side.

Furthermore, the sending node 10, which received the response confirmation signal in S513, establishes a TCP session with the relay node 30 in S514. In S514, the sending node 10 specifies the relay port number included in the relay instruction response received in S511 to establish a TCP session.

At S515, the sending node 10 sends an adjustment setting signal to the receiving node 20. The adjustment setting signal includes, for example, information indicating a threshold that the window size of the switching destination TCP session must exceed. For example, the threshold may be a fixed value such as 1 MB, or may be determined based on the window size of the switching source TCP session.

In another example, the adjustment setting signal includes information indicating the amount of dummy data to be transmitted. In one example, this may be determined based on the window size of the source TCP session. For example, if dummy data twice the maximum window size of the source TCP session is transmitted, the window size will be the same as that of the source TCP session if there is no packet loss. Therefore, in one example, the amount of dummy data to be transmitted may be indicated so that dummy data twice the maximum window size of the source TCP session is transmitted. This allows the transmitting node 10 to perform pre-communication until the window size of the destination TCP session becomes larger than a predetermined value.

At S516, the receiving node 20 transmits a setting response signal to the transmitting node 10 in response to the adjustment setting signal. At S517, the transmitting node 10 performs pre-communication to transmit dummy data to the relay node 30. The relay node 30 transfers the received dummy data to the receiving node 20. The dummy data may be, for example, a pseudo-random bit string. By successfully transmitting the dummy data, the window sizes of the TCP session between the transmitting node 10 and the relay node 30 and the TCP session between the relay node 30 and the receiving node 20 can be increased.

At S518, the transmitting node 10 and the receiving node 20 determine to switch the communication session. In one example, the transmitting node 10 and the receiving node 20 determine to switch the communication session when the transmission and reception of the amount of dummy data specified in the adjustment setting signal has ended. In another example, the transmitting node 10 and the receiving node 20 determine to switch the communication session when the window size of the TCP session at the switching destination becomes equal to or larger than a predetermined value. Note that, in one example, the transmitting node 10 and the receiving node 20, or the transmitting node 10 and the relay node 30, may transmit and receive information regarding the window size of the TCP session between the transmitting node 10 and the relay node 30 and the window size of the TCP session between the receiving node 20 and the relay node 30.

If it is determined in S518 that the communication session should be switched, the sending node 10 transmits the data communication that was being sent in the original TCP session in the new TCP session. This allows the TCP session to be switched with the window size increased.

As described above, the communication control device according to this embodiment determines to relay a TCP session to a relay node 30 whose round trip time between the transmitting node 10 and the relay node 30 and between the relay node 30 and the receiving node 20 are shorter than the round trip time between the transmitting node 10 and the receiving node 20. This is expected to improve throughput by relaying communications through the relay node.

The communication control device according to this embodiment also determines a relay node 30 that will relay the TCP session between the sending node 10 and the receiving node 20, and establishes a switching destination TCP session via the relay node 30. Then, in the switching destination TCP session, pre-communication that is not related to the communication of the switching source TCP session is performed. Then, when the window size of the switching destination TCP session becomes equal to or greater than a predetermined value, communication associated with the switching source TCP session is performed in the switching destination TCP session. This allows TCP session switching to be performed in a situation where throughput can be improved, and relaying of communication by the relay node 30 can be started at an appropriate time.

The communication control device according to this embodiment also determines a relay node 30 when a TCP session between a sending node 10 and a receiving node 20 satisfies a predetermined condition that determines that a benefit will be gained by relaying the communication, and initiates the establishment of a switching destination TCP session via the relay node 30 and session switching. This makes it possible to avoid switching to a switching destination TCP session in a situation where no benefit will be gained by relaying the communication, thereby avoiding a load on the relay node 30.

<Other embodiments>
In the present embodiment, the relay node selection unit 313 has been described as selecting the relay node 30 based on the round trip delay time (transmission side delay time) between the transmitting node 10 and the relay node 30 and the round trip delay time (reception side delay time) between the receiving node 20 and the relay node 30. In one example, the relay node selection unit 313 may store the maximum window size in past communications in the storage device 304, and select the relay node 30 based on the maximum window size (transmission side window size) between the transmitting node 10 and the relay node 30 and the maximum window size (reception side window size) between the receiving node 20 and the relay node 30. For example, by selecting the relay node 30 with the maximum evaluation value S below, it is possible to have the communication relayed by the relay node 30 that is expected to have a high throughput.

S = min {(sender window size)/(sender delay time), (receiver window size)/(receiver delay time)}
Here, min{ } is a function that selects the minimum of two values.

In addition, in this embodiment, the sender and receiver session numbers included in the signals transmitted in S508 to S511, and S513, S515, and S516 are used to verify the authenticity of the signal sender. However, other authentication techniques may be applied to verify the authenticity of the signal sender, and in such cases, the signals transmitted in S508 to S511, and S513, S515, and S516 may not include the sender and receiver session numbers.

In this embodiment, the process of S503 has been described as determining whether or not to establish a TCP session via the relay node 30 based only on the window size of the TCP session at the switching source. In one example, the process of S503 may be executed based on the round trip time to the candidate relay node. For example, the sending node 10 may measure the round trip time (w _t ) between the receiving node 20 and the round trip time (w _t1 ) between the receiving node 20 and the candidate relay node, and may determine that a trigger event has occurred when a candidate relay node with a round trip time smaller than the round trip time between the receiving node 20 by a predetermined percentage or more may be detected. For example, a trigger event may be determined to have occurred when a candidate relay node that satisfies w _t1 < 0.8 × w _t is detected. In such a case, the round trip time (w _t2 ) between the candidate relay node and the receiving node 20 may be measured in S506, w _t2 may be received in S507, and if w _t2 < 0.8 × w _t , it may be determined that a TCP session after switching is to be established with the candidate relay node.

The communication device according to the present invention, i.e., the above-mentioned transmitting node 10, receiving node 20, and relay node, can be realized by a program that, when executed by one or more processors of a device, causes the device to operate as the transmitting node 10 and/or the receiving node 20 and/or the relay node 30. These programs can be stored in a device-readable storage medium or distributed via a network.

The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the invention.

10: Sending node, 20: Receiving node, 30: Relay node

Claims (11)

A communication control device provided in a source node or a destination node ,
A determination means for determining whether a transmission control protocol (TCP) session of a switching source which is performing communication satisfies a predetermined condition;
a determining means for determining, from among a plurality of candidate relay nodes, a relay device that will relay the communication corresponding to the switching source TCP session;
an instruction means for establishing a switching destination TCP session between the relay device determined by the determination means and each of the source node and destination node of the switching source TCP session when the determination means determines that the switching source TCP session satisfies the predetermined condition, and for instructing execution of a pre-communication, which is different from the communication associated with the switching source TCP session, in the switching destination TCP session;
a switching means for switching the communication from the source TCP session to the destination TCP session after the preliminary communication is performed;
A communication control device comprising: The communication control device according to claim 1, characterized in that the specified condition is that the window size of the switching source TCP session acquired multiple times in the most recent specified period is within a specified range. The communication control device according to claim 1 or 2, characterized in that the specified condition is that the window size of the switching source TCP session acquired during the most recent specified period is equal to or larger than a specified threshold. The determining means is
For each of the plurality of candidate relay nodes, a first delay time required for a packet to travel to and from the source node and a second delay time required for a packet to travel to and from the destination node are obtained;
4. The communication control device according to claim 1, further comprising: determining, as the relay device, a candidate relay node whose first delay time and whose second delay time are smaller than the delay time required for a packet to travel round trip between the source node and the destination node. 5. The communication control device according to claim 4, wherein the determining means determines, as the relay device, a candidate relay node having a smallest sum of the first delay time and the second delay time of each of the plurality of candidate relay nodes. 5. The communication control device according to claim 4, wherein the determining means determines, as the relay device, a candidate relay node having a smallest difference between the first delay time and the second delay time of each of the plurality of candidate relay nodes. the instruction means instructs to communicate a predetermined amount of dummy data in the preliminary communication,
7. The communication control device according to claim 1 , wherein the predetermined amount is determined based on a window size of the TCP session of the switching source. The communication control device according to any one of claims 1 to 3, characterized in that the switching means switches communication to the destination TCP session when the window size of the destination TCP session becomes equal to or larger than the window size of the source TCP session. A communication control method executed by a communication control device provided in a source node or a destination node , comprising:
Determining whether a Transmission Control Protocol (TCP) session of the switching source that is performing communication satisfies a predetermined condition;
determining a relay device that relays the communication corresponding to the switching source TCP session from among a plurality of candidate relay nodes;
when it is determined that the source TCP session satisfies the predetermined condition, establishing a destination TCP session between the determined relay device and each of the source node and the destination node of the source TCP session, and instructing execution of a pre -communication in the destination TCP session that is different from the communication associated with the source TCP session;
switching the communication from the source TCP session to the destination TCP session after performing the pre-communication;
A communication control method comprising: A communication system including a transmitting node, a receiving node, and a relay node,
a determination means for determining whether a transmission control protocol (TCP) session of a switching source, which is communicating between the transmitting node and the receiving node, satisfies a predetermined condition;
a determining means for determining, from among a plurality of candidate relay nodes, a relay device that will relay the communication corresponding to the switching source TCP session;
an instruction means for establishing a switching destination TCP session between the relay device determined by the determination means and each of the transmitting node and the receiving node when it is determined that the switching source TCP session satisfies the predetermined condition, and for instructing execution of a pre-communication, which is different from the communication associated with the switching source TCP session, in the switching destination TCP session;
a switching means for switching the communication from the source TCP session to the destination TCP session after the preliminary communication is performed;
A communication system comprising: A program, when executed by one or more processors of an apparatus having one or more processors, that causes the apparatus to function as the communication control apparatus according to any one of claims 1 to 8 .

Images