COMMUNICATION SYSTEM, COMMUNICATION METHOD, COMMUNICATION DEVICE, AND COMMUNICATION PROGRAM

Abstract

An objective of the present disclosure is to prevent the reduction of window sizes, thereby reducing the duration of the equality reduction caused by handover processes.　The present disclosure is a communication system wherein: a communication terminal communicates with any other communication terminal according to an allocated window size; and when the communication terminal performs a handover, the communication terminal stores a window size used before the handover or a window size defined on the basis of that window size, and then defines, on the basis of the stored window size, a window size that is to be used after the handover.

Description

[Technical field]

[0001] The present disclosure relates to a communication system in which a communication terminal communicates with an arbitrary communication device in accordance with an assigned window size. [Background technology]

[0002] Recent communication terminals are able to use multiple communication networks (hereinafter, sometimes referred to as NWs). By using a high-quality NW from among multiple NWs, the user's quality of experience is improved. In fact, it is possible to target a NW that is expected to have better quality for handover based on information such as the received signal strength of IEEE802.11 wireless LAN [see, for example, Non-Patent Document 1].

[0003] However, when handover to a network that is expected to have better quality is performed, a new TCP session is established and the application layer session is re-established, causing a temporary interruption in communication until these are completed. As a result, even if a handover is attempted to a network that should provide higher quality, communication quality will be degraded for a while after the switchover begins.

[0004] To prevent these session disconnections, Mobile IPv6 is a technology that performs encapsulation processing as if the IP address of the communication terminal remains unchanged, eliminating the need to re-establish a new TCP session and an application layer session [see non-patent document 2]. However, even when Mobile IPv6 is used, disconnection, connection, and IP address-related processing is performed in lower layer protocols during handover, so there will be temporary periods when communication is unavailable. Even if the session of the upper layer protocol is continued, when this communication unavailable period occurs, the upper layer protocol may recognize that a packet loss has occurred.

[0005] In the TCP protocol, when packet loss is detected, the window size is reduced, which causes the TCP throughput to drop and a time lag occurs before the throughput returns to normal. Therefore, the combination of existing technology to conceal IP address changes and the general TCP protocol makes it impossible to immediately enjoy high-quality communications in the handover destination network. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Keisuke Wakao, Kenichi Kawamura, Takatsune Moriyama, "Quality Prediction Technology for Optimal Use of Multiple Wireless Access Systems", NTT Technical Journal, April 2020, p.11-13 https: / / journal.ntt.co.jp / wp-content / uploads / 2020 / 05 / JN20200411.pdf [Non-Patent Document 2] IETF RFC2002 “IP mobility support”https: / / datatracker.ietf.org / doc / html / rfc2002 Summary of the Invention [Problem to be solved by the invention]

[0007] The present disclosure aims to reduce the time during which quality deteriorates due to handover processing. [Means for solving the problem]

[0008] The communication system of the present disclosure includes: A communication system in which a communication terminal communicates with an arbitrary communication device according to an assigned window size, When the communication terminal performs a handover, the communication terminal stores a window size before the handover or a window size determined based on the window size; The window size after the handover is determined based on the stored window size.

[0009] The communication method of the present disclosure includes: A method executed by a system in which a communication terminal communicates with a given communication device according to an assigned window size, comprising: When the communication terminal performs a handover, the window size before the handover is stored; The window size after the handover is determined based on the stored window size.

[0010] The communication device of the present disclosure functions as a communication terminal or a communication device provided in the communication system of the present disclosure. Effect of the Invention

[0011] According to the present disclosure, since the window size after handover is determined based on the window size before handover, the window size can be instantly restored, thereby reducing the time during which quality is degraded due to the handover process. [Brief description of the drawings]

[0012] [Figure 1] 1 shows an overview of a system according to an embodiment of the present invention. [Diagram 2] An example of a TCP window size when a temporary communication interruption occurs is shown below. [Diagram 3] 1 illustrates an example of a TCP window size according to the present disclosure. [Figure 4] FIG. 1 is a functional block diagram for implementing the present disclosure in downstream communication. [Diagram 5] FIG. 11 is a functional block diagram for implementing the present disclosure in upstream communication. [Figure 6] 13 is a flowchart of a terminal operation during downstream communication. [Figure 7] 11 is a flowchart showing the operation of a communication terminal and a communication destination server during upstream communication. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings are assumed to indicate the same components.

[0014] An overview of the system according to this embodiment is shown in Fig. 1. In the communication system according to this embodiment, a communication terminal 93 communicates with a communication destination server 91. The communication terminal 93 is a communicable wireless communication terminal, and communicates with the communication destination server 91 according to an assigned window size. The communication destination server 91 is any communication device that can communicate with the communication terminal 93 according to the assigned window size.

[0015] The communication destination server 91 and the communication terminal 93 function as the communication device of the present disclosure. The communication device of the present disclosure can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided through a network. The program of the present disclosure is a program for realizing a computer as each functional unit of the device according to the present disclosure, and is a program for causing a computer to execute each step of the method executed by the device according to the present disclosure.

[0016] In this embodiment, an example is shown in which a communication destination server 91 is connected to NWs 92#1 and 92#2 through a network device such as a router 94, and a communication terminal 93 performs handover from the NW 92#1 to the NW 92#2.

[0017] When the communication terminal 93 performs handover from the NW 92#1 to the NW 92#1, S1: Disconnect the data link layer (L2) connection with NW92#1. S2: Perform L2 connection processing with NW92#2, S3: Assign an IP address in NW92#2 to the communication terminal 93, S4: A TCP session between the communication destination server 91 and the communication terminal 93 is established by the NW 92#2. S5: A session is re-established between the communication destination server 91 and the communication terminal 93 in the application layer.

[0018] In this way, when handover processing from NW 92#1 to NW 92#2 is performed, a new TCP session is established and an application layer session is re-established, causing a temporary communication interruption until the establishment of the new TCP session and the re-establishment of the application layer session. As a result, even if a handover is attempted to a network that should provide high quality, the communication quality will be degraded for a while after the switchover starts.

[0019] Figure 2 shows an example of the TCP window size when a temporary communication interruption occurs. During handover, disconnection, connection, and IP address-related processing is performed in the lower layer protocol, so a temporary communication interruption occurs. If this communication interruption occurs while a session of a higher layer protocol is continuing, the higher layer protocol may recognize that a packet loss has occurred. When the TCP protocol detects packet loss, it works to reduce the TCP window size, which reduces the TCP throughput. As a result, high-quality communication cannot be immediately enjoyed in the handover destination NW#2.

[0020] Therefore, in the present disclosure, as shown in FIG. 3, when a NW handover occurs, the previous TCP window size is stored at the start of the process, and is called up at the end of the handover. This allows the TCP window size after the handover to be quickly restored, and a high TCP throughput is obtained in a short time after switching. Therefore, the present disclosure reduces the quality degradation time in a NW handover, and enables active switching of the connection destination to a NW that is expected to be of high quality. The TCP window size may be stored in the communication terminal 93, the communication destination server 91, or a network device such as a proxy server. This will be described in detail below.

[0021] 4 is a functional block diagram for implementing the present disclosure in downstream communication. The communication destination server 91 includes a communication interface 11, an application 12, and a TCP / IP communication control unit 13. The communication terminal 93 includes a communication interface 31, an application 32, a TCP / IP communication control unit 33, a network control unit 34, and a TCP window storage unit 35. The network control unit 34 includes a network disconnection detection unit 341, a network connection detection unit 342, and a network selection unit 343.

[0022] 5 is a functional block diagram for implementing the present disclosure in upstream communication. The communication destination server 91 includes a communication interface 11, an application 12, a TCP / IP communication control unit 13, and a TCP window storage unit 15. The communication terminal 93 includes a communication interface 31, an application 32, a TCP / IP communication control unit 33, and a network control unit 34. The network control unit 34 includes a network disconnection detection unit 341, a network connection detection unit 342, and a network selection unit 343.

[0023] The application 32 is an application used by the communication terminal 93. The application 12 is a function provided in the communication destination server 91 that enables the application 32 to be executed.

[0024] The communication interfaces 11 and 31 are any interfaces capable of TCP / IP communication, such as IEEE802.3, IEEE802.11, 3GPP 5G NR, etc.

[0025] The TCP / IP communication control units 13 and 33 are functional units that control a general TCP / IP protocol. On the receiving side, the TCP window size is notified to the sending side.

[0026] The network disconnection detection unit 341 is a functional unit that detects a network disconnection and triggers storage of the TCP window size. The network connection detection unit 342 is a functional unit that detects the completion of a network connection and triggers application of the stored TCP window. The network selection unit 343 is a functional unit that estimates and selects a network that allows communication of higher quality than the immediately preceding connected network. The method of estimating and selecting a network is arbitrary and is not specified in this disclosure.

[0027] For upstream communication, as shown in Fig. 4, communication terminal 93 is provided with TCP window storage unit 35. On the other hand, for upstream communication, as shown in Fig. 5, communication destination server 91 is provided with TCP window storage unit 15. TCP window storage unit 35 is a functional unit that, upon receiving an external trigger, saves the immediately previous TCP window size and sets parameters for TCP / IP communication control unit 33. TCP window storage unit 15 is a functional unit that, upon receiving an external trigger, saves the immediately previous TCP window size and sets parameters for TCP / IP communication control unit 13.

[0028] 6 is a flowchart of the operation of the communication terminal 93 during downstream communication. The network control unit 34 judges, based on some NW selection algorithm, whether switching to a different NW than the already connected NW will enable higher quality communication. For example, there is a method described in Non-Patent Document 1. When executing NW switching, the TCP window size at that time is notified to the TCP window storage unit 35, and the TCP window storage unit 35 stores it (S11).

[0029] The TCP / IP communication unit 33 performs a process of disconnecting from NW#1 (S12), and a process of connecting to NW#2 (S13). When the network control unit 34 has completed the process of connecting to the switching destination NW (IP address-related settings) (S13), it instructs the TCP window storage unit 35 to call up the TCP window size (S14). The TCP window storage unit 35 notifies the TCP / IP communication unit 33 of the called-up value of the TCP window size before switching (S15), and the TCP / IP communication control unit 33, upon receiving the notification, notifies the TCP / IP communication control unit 13 of the communication destination server 91 of the update of the TCP window size. After that, general TCP / IP communication is performed.

[0030] As a result, in downstream communication from the communication destination server 91, the amount of data that can be transmitted before returning an ack (TCP window size) can be instantly restored, and high TCP throughput can be achieved immediately after switching.

[0031] The notification of the TCP window size in step S11 may be performed after step S12. For example, the notification of the TCP window size may be triggered by the completion of a disconnection process of a connected NW.

[0032] The window size after handover is not limited to the window size immediately before handover, but may be a window size determined based on the window size before handover. For example, it may be the maximum window size within a certain period before handover. If the algorithm of the NW selection unit 343 can predict the expected quality after NW switching in detail, a value higher than the window size before switching may be stored.

[0033] 7 is a flowchart showing the operation of the communication terminal 93 and the communication destination server 91 during upstream communication. The network control unit 34 of the communication terminal 93 judges, based on some NW selection algorithm, whether or not switching to a different NW than the already connected NW 92#1 will enable higher quality communication.

[0034] When NW switching is performed, the network control unit 34 of the communication terminal 93 executes a disconnection advance notice to the communication destination server 91. The disconnection advance notice is a notice to the effect that a disconnection of the communication network will occur, and includes information on the TCP window size at that time. Upon receiving the disconnection advance notice, the communication destination server 91 stores the received TCP window size in the TCP window storage unit 15 (S21).

[0035] In addition, the storage of the TCP window size in step S21 may be a form in which the communication destination server 91 autonomously stores the previous TCP window size or the maximum TCP window size within a certain period of time when a data packet from the communication terminal 93 does not arrive for a certain period of time.

[0036] The TCP / IP communication control unit 33 performs a process of disconnecting from the NW#1 (S22), and a process of connecting to the NW#2 (S23). When the communication terminal 93 has completed the process of connecting to the switching destination NW92#2 (IP address related settings), the communication terminal 93 notifies the communication destination server 91 of the completion of the connection.

[0037] Here, if the communication terminal 93 and the NW are equipped with an IP address continuity function such as Mobile IPv6, the past TCP session continues, so that communication confirmation is performed based on the data sent from the communication terminal 93. If the IP address continuity function is not equipped, a temporary terminal ID is also notified when the advance disconnection notice is sent, and after a new TCP session is established with the communication destination server 91, the terminal ID is resent, thereby recognizing that the notice is from the same communication terminal 93.

[0038] TCP / IP communication control unit 13 of communication destination server 91 acquires the TCP window size stored in TCP window storage unit 15. TCP / IP communication control unit 13 of communication destination server 91 notifies TCP / IP communication control unit 33 of communication terminal 93 of an update of the TCP window size so as to update the TCP window size to the acquired TCP window size. After that, general TCP / IP communication is performed.

[0039] As a result, in upstream communication from the communication terminal 93, the amount of data that can be transmitted before returning an ack (TCP window size) is instantly restored, and high TCP throughput is achieved immediately after switching.

[0040] This disclosure is expected to be applied in combination with a system that can predict the quality of the network after switching, such as that described in Non-Patent Document 1, and thereby convert the high quality of the network after switching into an improvement in the quality of experience. This combination makes it possible to control the network while minimizing the load on terminals and the network, since it is not necessary to check the quality by sending traffic to the destination network in advance or to increase the TCP window size. [Industrial Applicability]

[0041] The present disclosure can be applied to the information and communications industry. [Explanation of symbols]

[0042] 11, 31: Communication interface 12, 32: Application 13, 33: TCP / IP communication control section 15, 35: TCP window storage 34: Network control section 341: Network disconnection detection unit 342: Network connection detection unit 343: Network selection section 91: Destination server 92: Communication Network 93: Communication terminal 94: Router

Claims

1. A communication system in which a communication terminal communicates with an arbitrary communication device according to an assigned window size, The communication device includes: When the communication terminal performs a handover, a window size for establishing a connection with the communication terminal is stored for a predetermined time after the connection with the communication terminal is disconnected; When the connection with the communication terminal is resumed at the predetermined time, establishing a connection with the communication terminal based on the stored window size. Communication systems.

2. The communication terminal includes: storing a window size before the handover or a window size determined based on the window size; After the handover, notifying the communication device of the stored window size; the communication device establishes a connection with the communication terminal by using the window size notified by the communication terminal; The communication system according to claim 1 .

3. The communication terminal issues a notice of disconnection to the communication device before the handover; When the communication device receives the advance notice of disconnection, the communication device stores a window size before the handover; After the handover, the communication device establishes a connection with the communication terminal using the stored window size. The communication system according to claim 1 .

4. A communication device that communicates with a communication terminal according to an assigned window size, storing a window size used to establish a connection with the communication terminal for a predetermined time period after the connection with the communication terminal is disconnected; When the connection with the communication terminal is resumed at the predetermined time, the stored window size is used to establish the connection with the communication terminal. Communications equipment.

5. A communication program for causing a computer to realize each of the functional units of the communication device according to claim 4.

6. A method executed by a system in which a communication terminal communicates with a given communication device according to an assigned window size, comprising: The communication device includes: When the communication terminal performs a handover, a window size for establishing a connection with the communication terminal is stored for a predetermined time after the connection with the communication terminal is disconnected; When the connection with the communication terminal is resumed at the predetermined time, establishing a connection with the communication terminal based on the stored window size. Communication methods.

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