Transfer device and program

Abstract

The purpose of the present disclosure is to salvage packets that might otherwise be discarded due to switching of a communication path and transmit the packets through a new path.　Therefore, the present disclosure provides a transfer device that transfers packets by switching packet communication paths, the transfer device having a transfer control unit that transfers packets waiting in a prescribed output buffer to another predetermined output buffer when at least one transfer condition is satisfied among a first transfer condition indicating that the number of packets waiting in the prescribed output buffer has exceeded a predetermined threshold value for a certain period of time, a second transfer condition indicating that the tendency to increase the number of packets waiting in the prescribed output buffer has continued for a certain period of time, and a third transfer condition indicating that the tendency to decrease the communication bandwidth of a prescribed output port corresponding to the prescribed output buffer has continued for a certain period of time.

Description

Transfer device and program

[0001] The present disclosure relates to a technique for reducing the discard of packets accumulated in an output buffer when switching a communication path in a transfer device mounted on an artificial satellite (satellite) or the like.

[0002] In a communication network where the network topology and link connectivity are dynamic, such as a non-terrestrial network (NTN: Non-Terrestrial Networks), the communication path of data (packets) flowing in the communication network frequently changes (Non-Patent Document 1).

[0003] Here, the communication situation of a low-earth orbit satellite over time will be described using FIG. 9. FIGS. 9(a), (b), and (c) show the positions of the respective satellites and the communication situation with the base station at times t1, t2, and t3, respectively. Note that t2 is about 3 minutes after t1, and t3 is about 3 minutes after t2.

[0004] As shown in FIG. 9(a), when the satellite 3b moves into the communicable range A of the ground station 7, communication is performed with the ground station 7. In this situation, the satellite 3b is close to the ground station 7 around the center of the communicable range A, and the communication band of the wireless link L22 is wide. Therefore, the possibility of packet transmission being delayed in the satellite 3b is low. In addition, the satellite 3b also communicates with other satellites (such as the satellite 3a) to construct a non-terrestrial network. Note that the satellite 3a is outside the communicable range A, so communication with the ground station 7 is impossible or difficult.

[0005] Subsequently, as shown in FIG. 9(b), when the satellite 3b moves to the right side on the paper surface, although it is within the communicable range A, the distance from the ground station 7 is far at the edge of the communicable range A, and the communication band of the wireless link L22 becomes narrow. Therefore, packets in the output buffer of the satellite 3b start to accumulate, and the possibility of packet transmission being delayed increases. In this case, a new satellite 3c is approaching within the communicable range A, but communication with the ground station 7 is still impossible or difficult.

[0006] Next, as shown in Figure 9(c), if satellite 3b moves further to the right on the paper, it will be outside the communication range A, and communication with ground station 7 will be impossible or difficult. On the other hand, satellite 3c is near the center of the communication range A, is close to ground station 7, and the communication bandwidth of wireless link L23 is wide. Therefore, the possibility of packet transmission delays is low for satellite 3c. Note that satellite 3d is outside the communication range A, so communication with ground station 7 is impossible or difficult.

[0007] RFC5714 "IP Fast Reroute Framework"<https: / / www.rfc-editor.org / rfc / rfc5714.html>

[0008] As described above, in Figure 9(b), packets waiting to be transmitted in the output buffer (queue) within the transmission device mounted on satellite 3b were not transmitted and were discarded due to switching of communication paths within the non-terrestrial network.

[0009] This disclosure is made in view of the above points, and aims to recover packets that would have been lost due to the switching of communication paths and transmit them over the new path.

[0010] To achieve the above objective, this disclosure provides a forwarding device that forwards packets by switching the communication path of packets, and has a forwarding control unit that forwards packets waiting in a predetermined output buffer to another predetermined output buffer when at least one of the following forwarding conditions is met: a first forwarding condition that the number of packets waiting in a predetermined output buffer exceeds a predetermined threshold for a certain period of time; a second forwarding condition that the number of packets waiting in the predetermined output buffer continues to increase for a certain period of time; and a third forwarding condition that the communication bandwidth at a predetermined output port corresponding to the predetermined output buffer continues to decrease for a certain period of time.

[0011] As explained above, the present invention has the effect of recovering packets that would have been lost due to switching of communication paths and transmitting them over the new path.

[0012] This is an overall configuration diagram of the communication system in the embodiment. This is a configuration diagram of a transfer device mounted on a satellite according to the first embodiment. This is a conceptual diagram showing a route information management table. This is a conceptual diagram showing packet transfer control processing. This is an electrical hardware configuration diagram of the transfer device. This is a flowchart showing the processing according to the first embodiment. This is a configuration diagram of a transfer device mounted on a satellite according to the second embodiment. This is a flowchart showing the processing according to the second embodiment. This is a diagram showing the communication status of a low Earth orbit satellite over time.

[0013] Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the embodiments shown below, and various modifications are possible without departing from the technical spirit of the invention. Since the drawings are for conceptual explanation of the present invention, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for ease of understanding.

[0014] ●First Embodiment First, the first embodiment will be described using Figures 1 to 6.

[0015] [Overall Configuration of the Communication System] Figure 1 is an overall configuration diagram of the communication system in the embodiment. In space, artificial satellites 3a and 3b can communicate via wireless link L11, and satellites 3b and 3c can communicate via wireless link L12. As a result, a non-terrestrial network 90 is constructed by satellites 3a, 3b, 3c, etc. Meanwhile, on the ground, a terrestrial network 100 such as the Internet is constructed, and a ground station 7 is installed as part of this network.

[0016] In Figure 1, satellite 3b is within the communication range A of ground station 7 and is communicating with ground station 7. In this situation, satellite 3b is close to ground station 7, near the center of communication range A, and has a wide communication bandwidth for wireless link L22 (see Figure 9(a)). As a result, for example, if satellite 3a receives data (packets) from a ground station other than ground station 7, satellite 3a forwards the data to satellite 3, satellite 3b forwards the data to ground station 7, and ground station 7 forwards the data to the destination terminal via the terrestrial network. Communication in the reverse route is also possible.

[0017] [Configuration of the Transfer Device in the First Embodiment] Next, the configuration of the transfer device mounted on the satellite will be described using Figures 2 and 3. Figure 2 is a diagram of the configuration of the transfer device mounted on the satellite according to the first embodiment.

[0018] A forwarding device consists of one or more computers and functions as a router, a packet switch that forwards packets by switching the communication path of those packets.

[0019] As shown in Figure 2, the transfer device 30a has a plurality of input ports p11, p12, ..., p1m, and a plurality of input buffers b11, b12, ..., b1m corresponding to each of these. The transfer device 30a also has a plurality of output ports p21, p22, ..., p2n, and a plurality of output buffers b21, b22, ..., b2n corresponding to each of these. The plurality of output ports p21, p22, ..., p2n are referred to as "output port group p2", and any output port among the plurality of output ports p21, p22, ..., p2n is referred to as "output port p20". Similarly, the plurality of output buffers b21, b22, ..., b2n are referred to as "output buffer group b2", and any output buffer among the plurality of output buffers b21, b22, ..., b2n is referred to as "output buffer b20".

[0020] Furthermore, the transfer device 30a includes a transfer processing unit 31 and a transfer control unit 33a. The transfer processing unit 31 and the transfer control unit 33a may each be electronic circuits, or they may be functions implemented by instructions from the processor 1004 shown in Figure 5 based on a program.

[0021] Furthermore, the transfer device 30a has a route information management DB 39 in its storage unit, which is either an auxiliary storage device 1002 or a memory device 1003 as shown in Figure 5. The content of the information managed by the route information management DB 39 is set for each satellite and therefore differs for each satellite.

[0022] <Route Information Management DB 39> Here, we will explain the route information management table that constitutes the route information management DB 39 using Figure 3. Figure 3 is a conceptual diagram showing the route information management table.

[0023] As shown in Figure 3, the routing information management table manages the time, destination IP address, and forwarding output port number in association. The "time" indicates the scheduled time of the communication route change. This time may be the number of seconds elapsed since the reference time (for example, 0:00). The "destination IP address" indicates the IP address of the destination terminal or other device to which the packet will ultimately be delivered. The "forwarding output port number" is associated with one of the other satellites.

[0024] <Transfer Processing Unit 31> The transfer processing unit 31 refers to the route information stored in the route information management DB 39, reads the destination output port number based on the set time and destination IP address, and switches the packet (data) stored in one of the input buffers b11, b12, ..., b1m to one of the multiple output buffers b21, b22, ..., b2n according to the read output port number and transfers it.

[0025] <Transfer Control Unit 33a> The transfer control unit 33a monitors the communication bandwidth of each port in the output port group p2, as well as the output buffer group b2. If the transfer control unit 33a determines that the transfer conditions have been met based on these monitoring (transfer determination), it retrieves packets that are stuck in a predetermined output buffer and transfers them to another predetermined output buffer (transfer control processing).

[0026] (Transfer Judgment) If the transfer conditions are met, it indicates that at least one of the following first to third transfer conditions is met. Note that each "certain time" is, for example, 10 seconds. (1) First transfer condition: The number of packets waiting in a predetermined output buffer exceeds a predetermined threshold for a certain period of time. (2) Second transfer condition: The increasing trend in the number of packets waiting in a predetermined output buffer continues for a certain period of time. (3) Third transfer condition: The decreasing trend in communication bandwidth at a predetermined output port corresponding to a predetermined output buffer continues for a certain period of time. (Transfer Control Processing) Furthermore, the packet transfer control processing will be explained using Figure 4. Note that the buffer shown in Figure 4 is just an example, and may be any other buffer in the output buffer group b2.

[0027] When the transfer conditions are met, the transfer control unit 33a temporarily transfers (including duplication) the packets stored in a predetermined output buffer to buffer 34 using FIFO (First In, First Out), and sets the read indicator d1 and the write indicator d2 to the start and end positions of the duplicated packets, respectively. If the transfer control unit 33a is an electronic circuit, buffer 34 is a buffer within this electronic circuit or a part of the memory device 1003 shown in Figure 5. On the other hand, if the transfer control unit 33a is a function implemented by a program, buffer 34 is a part of the memory device 1003 shown in Figure 5.

[0028] Furthermore, when additional packets are generated in the output buffer b21, the transfer control unit 33a duplicates the additional packets in address order starting from the location of the write indicator d2, and sets the write indicator d2 to the end of the additional packets.

[0029] Furthermore, the transfer control unit 33a reads each packet stored in the buffer 34 sequentially from the read indicator d1 to the write indicator d2, and transfers (including duplication) them sequentially using FIFO from the empty area of ​​the predetermined output buffer b22.

[0030] [Hardware Configuration] Next, Figure 5 shows the electrical hardware configuration diagram of the transfer device 30a. Figure 5 is an electrical hardware configuration diagram of the transfer device.

[0031] As shown in Figure 5, the transfer device 30a includes a drive device 1000, an auxiliary storage device 1002, a memory device 1003, a processor 1004, an interface device 1005, a display device 1006, an input device 1007, an output device 1008, etc., which are all interconnected by the bus 1010.

[0032] The program that enables processing on the computer is provided on a recording medium 1001, such as a CD-ROM or memory card. When the recording medium 1001 containing the program is set in the drive device 1000, the program is installed from the recording medium 1001 to the auxiliary storage device 1002 via the drive device 1000. However, the program does not necessarily have to be installed from the recording medium 1001; it may also be downloaded from another computer via a communication network (non-terrestrial network 90, terrestrial network 100). The auxiliary storage device 1002 stores the installed program as well as necessary files and data.

[0033] When a program startup command is received, the memory device 1003 reads the program from the auxiliary storage device 1002 and stores it. The processor 1004 implements the functions related to the memory device 1003 according to the program stored in the memory device 1003. The processor 1004 may include not only a CPU (Central Processing Unit) but also a GPU (Graphics Processing Unit).

[0034] The interface device 1005 is used as an interface for connecting to a communication network, etc. The display device 1006 displays a GUI (Graphical User Interface) or the like, programmed by the user. The input device 1007 consists of a keyboard and mouse, buttons, or a touch panel, and is used to input various operation instructions. The output device 1008 outputs the calculation results to the outside.

[0035] [Processing according to the first embodiment] Next, the processing according to the first embodiment will be explained using Figure 6. Figure 6 is a flowchart of the processing according to the first embodiment. Here, we show the case where all of the above transfer conditions (1) to (3) are met, but at least one of the transfer conditions (1) to (3) may be met.

[0036] S11: The transfer control unit 33a monitors the number of pending data (packets) in each output buffer b20.

[0037] S12: The transfer control unit 33a determines whether the number of packets waiting in the output buffer b20 has exceeded a predetermined threshold for a certain period of time (transfer condition (1)). If the number of packets waiting has not exceeded the predetermined threshold for a certain period of time (NO), the process returns to S11.

[0038] S13: In processing S12, if the number of waiting packets exceeds a predetermined threshold for a certain period of time (YES), the forwarding control unit 33a determines whether the increasing trend in the number of waiting packets in the predetermined output buffer b20 that has exceeded the threshold for a certain period of time has continued for a certain period of time (forwarding condition (2)). If the increasing trend in the number of waiting packets has not continued for a certain period of time (NO), the process returns to S11.

[0039] S14: If, in processing S13, the increasing trend in the number of waiting packets continues for a certain period of time (YES), the transfer control unit 33a monitors the communication bandwidth of a predetermined output port p20 (e.g., output port p21) corresponding to a predetermined output buffer b20 (e.g., output buffer b21).

[0040] S15: The transfer control unit 33a determines whether the decreasing trend in communication bandwidth at a predetermined output port p20 continues for a certain period of time (transfer condition (3)). If the decreasing trend in communication bandwidth at the predetermined output port p20 does not continue for a certain period of time (NO), the process returns to S11.

[0041] S16: In process S15, if the decreasing trend of the communication bandwidth at the predetermined output port p20 continues for a certain period of time (YES), the transfer control unit 33a satisfies the transfer conditions (1) and (2), and within the predetermined output buffer b20 that satisfies the transfer condition (3) at the corresponding predetermined output port p20, the data (packet) waiting in the buffer is transferred to another predetermined output buffer (for example, output buffer b22) as shown in FIG. 4.

[0042] [Main Effects of the First Embodiment] As described above, according to this embodiment, the transfer control unit 33a transfers the data (packet) waiting in the predetermined output buffer that satisfies the transfer conditions to another predetermined output buffer, thereby preventing the data from being discarded without being transmitted due to the switching of the communication path within the non-terrestrial network 90. As a result, it is possible to rescue the packets that might have been discarded due to the communication path switching. Also, in a dynamic network, the packet arrival rate can be increased.

[0043] ● Second Embodiment Next, the second embodiment will be described using FIGS. 7 and 8. FIG. 7 is a configuration diagram of a transfer device mounted on a satellite according to the second embodiment.

[0044] As shown in FIG. 7, since the transfer device 30b according to the second embodiment has basically the same configuration as the transfer device 30a according to the first embodiment, the differences will be described.

[0045] The transfer device 30b has a transfer control unit 33b whose processing content is different from that of the transfer control unit 33a instead of the transfer control unit 33a of the transfer device 30b. Otherwise, it is the same as the transfer device 30a. Note that the transfer control unit 33b may be an electronic circuit, similar to the transfer control unit 33a, or a function realized by an instruction from the processor 1004 shown in FIG. 5 based on a program. Also, since the transfer device 30b has the same hardware configuration as the transfer device 30a, the description thereof will be omitted. Therefore, the transfer control unit 33b will be described below.

[0046] [Configuration of Transfer Device in Second Embodiment] <Transfer Control Unit 33b> The transfer control unit 33b refers to the path information stored in the path information management DB 39 and checks the planned change of the communication path involving the switching of the output port number due to the change of the set time (record). Then, when the transfer control unit 33b determines that it is a predetermined time (for example, 1 second before) before the planned change time of the communication path, it transfers (including duplication) the data (packet) waiting in the predetermined output buffer b20 corresponding to the predetermined output port p20 to another output buffer (for example, output buffer b22) corresponding to the output port of the transfer destination. Note that the transfer method is the same as that of the first embodiment (see FIG. 4).

[0047] [Processing of Second Embodiment] Subsequently, the processing according to the second embodiment will be described using FIG. 8. FIG. 8 is a flowchart showing the processing according to the second embodiment.

[0048] S21: The transfer control unit 33b refers to the path information stored in the path information management DB 39 and checks the planned change of the communication path involving the switching of the output port number due to the change of the set time (record).

[0049] S22: The transfer control unit 33b determines whether it is a predetermined time (for example, 1 second before) before the planned change time of the communication path. If it is not a predetermined time before the planned change time of the communication path (NO), the process returns to S21.

[0050] S23: In S22, if it is a predetermined time before the planned change time of the communication path (YES), the transfer control unit 33b transfers (including duplication) the data (packet) waiting in the predetermined output buffer b20 corresponding to the predetermined output port p20 to another output buffer corresponding to the output port of the transfer destination.

[0051] [Main Effects of Second Embodiment] As described above, according to this embodiment, the same effects as those of the first embodiment are achieved.

[0052] [Supplementary Note] The present invention is not limited to the above-described embodiments, and for example, the following configurations or processes (operations) may be used.

[0053] (1) The route information stored in the route information management DB39 (initial route information, updated route information) may be obtained from a designated server or the like in a data center located within the terrestrial network shown in Figure 1.

[0054] (2) In the above embodiment, the control of a communication device mounted on a satellite was described, but it is also applicable to the control of a communication device mounted on an unmanned aerial vehicle such as a drone that flies in a disaster area, etc.

[0055] (3) Furthermore, it is applicable not only to non-terrestrial networks but also to mobile networks. For example, in a mobile network, when a terminal such as a smartphone changes to a different base station due to a handover, it is thought that a port switch occurs in the transmission equipment that makes up the base station. The transmission equipment is a high-performance transmission equipment called EPC (Evolved Packet Core) in the case of LTE (Long Term Evolution) and UPF (User Plane Function) in the case of 5G. In this case, if the transmission equipment is so congested that packets are waiting in the buffer (queue), the above embodiment can recover the packets in the original buffer and suppress retransmission.

[0056] (4) The transfer devices 30a and 30b can also be implemented by a computer and a program, but it is also possible to provide the program by recording it on a (non-temporary) recording medium, and it is also possible to provide the program via a communication network (non-terrestrial network 90, terrestrial network 100).

[0057] (5) The hardware processor 1004 may be single or multiple.

[0058] 3a, 3b, 3c, 3d (artificial) satellites 30a, 30b Transfer device 31 Transfer processing unit 33a, 33b Transfer control unit 39 Route information management DB (example of route information management unit) b21, b22, ..., b2n Output buffers p21, p22, ..., p2n Output ports

Claims

1. A packet forwarding device that forwards packets by switching the communication path of packets, the forwarding device having a forwarding control unit that forwards packets waiting in a predetermined output buffer to another predetermined output buffer when at least one of the following forwarding conditions is met: a first forwarding condition that the number of packets waiting in a predetermined output buffer exceeds a predetermined threshold for a certain period of time; a second forwarding condition that the number of packets waiting in the predetermined output buffer continues to increase for a certain period of time; and a third forwarding condition that the communication bandwidth at a predetermined output port corresponding to the predetermined output buffer continues to decrease for a certain period of time.

2. A forwarding device that forwards packets by switching the communication path of packets, the forwarding device having a forwarding control unit that refers to route information which includes at least the scheduled time for the change of the communication path and the number of the output port of the forwarding destination, and when it is a predetermined time before the scheduled time for the change, forwards packets waiting in a predetermined output buffer to another output buffer corresponding to the output port of the forwarding destination.

3. The forwarding device according to claim 1 or 2 is a forwarding device that switches the communication path of a packet in a non-terrestrial network where the network topology and link connectivity are dynamic.

4. A program for a computer to implement the transfer device described in claim 1 or 2.

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