Communication methods, terminal devices, video management devices, communication systems, and programs

Abstract

This invention provides a communication method, terminal device, video management device, communication system, and program for appropriately transmitting image information from a video management device to a terminal device. [Solution] The communication method includes: an image request step in which the terminal device 3 transmits image request information to the video management device 1; a port identification step in which the terminal device 3 searches for and identifies an image acquisition port for acquiring image information transmitted from the video management device 1; a port number notification step in which, if the image acquisition port has been identified, the terminal device 3 generates port number information that identifies the identified image acquisition port and transmits it to the video management device 1; an image transmission step in which, once the video management device 1 has acquired the port number information, it identifies the image acquisition port based on the acquired port number information and transmits the image information to the image acquisition port of the terminal device 3; and an image acquisition step in which the terminal device 3 acquires image information transmitted from the video management device 1.

Description

Technical Field

[0001] The present invention relates to a communication method, a terminal device, a video management device, a communication system, and a program.

Background Art

[0002] A remote cooperative monitoring system has been proposed that includes a camera server, a camera switching device connected to the camera server, a plurality of cameras connected to the camera switching device, and a plurality of personal computers connected to the camera server via a network, and the personal computers access the camera server via the network and display the video of the cameras on the monitors of the plurality of personal computers (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in a remote cooperative monitoring system as described in Patent Document 1, when distributing video information from a camera server to a personal computer, if the port used for transmitting the video information in the personal computer is being used by another application, the video information cannot be transmitted using that port. In addition, security software is installed in many personal computers, and the use of a specific port may be restricted by the function of the security software. Therefore, in such a system, on the camera server side, it is required to provide a function for specifying a port that can be used for transmitting video information to a personal computer before transmitting the video information, so as to appropriately transmit the video information to the personal computer.

[0005] The present invention has been made in view of the above, and aims to provide a communication method, a terminal device, a video management device, a communication system, and a program for appropriately transmitting image information from a video management device to a terminal device. [Means for solving the problem]

[0006] To achieve the above objective, the communication method according to the present invention is A communication method between a video management device that manages image information indicating captured images taken by a camera, and a terminal device that can communicate with the video management device, The terminal device transmits image request information to the video management device requesting the transmission of the image information in an image request step, The terminal device performs a port identification step of searching for and identifying an image acquisition port for acquiring the image information transmitted from the video management device, If the terminal device can identify the image acquisition port, it performs a port number notification step of generating port number information that identifies the identified image acquisition port and sending it to the video management device. When the video management device obtains the port number information, it identifies the image acquisition port based on the obtained port number information and transmits the image information to the image acquisition port of the terminal device in an image transmission step. The terminal device includes an image acquisition step of acquiring the image information transmitted from the video management device to the image acquisition port.

[0007] From another perspective, the terminal device according to the present invention is: An image request unit transmits image request information to a video management device that manages image information representing captured images taken by a camera, which requests the transmission of the said image information. A port identification unit searches for and identifies an image acquisition port for acquiring the image information transmitted from the video management device, When the image acquisition port is identified, a port number notification unit generates port number information that identifies the identified image acquisition port and transmits it to the video management device. The system includes an image acquisition unit that acquires the image information transmitted from the video management device to the image acquisition port.

[0008] From another perspective, the communication system according to the present invention is: A video management device that manages image information showing captured images taken by a camera, The system comprises a terminal device capable of communicating with the aforementioned video management device, The aforementioned terminal device is An image request unit that sends image request information to the video management device requesting the transmission of the image information, A port identification unit searches for and identifies an image acquisition port for acquiring the image information transmitted from the video management device, When the image acquisition port is identified, a port number notification unit generates port number information that identifies the identified image acquisition port and transmits it to the video management device. The system includes an image acquisition unit that acquires the image information transmitted from the video management device to the image acquisition port, The aforementioned video management device is The image transmission unit obtains the port number information transmitted from the terminal device, identifies the image acquisition port based on the obtained port number information, and transmits the image information to the image acquisition port of the terminal device.

[0009] From another perspective, the program according to the present invention is: Computers, An image request unit transmits image request information to a video management device that manages image information indicating captured images taken by a camera, which requests the transmission of the said image information. A port identification unit searches for and identifies an image acquisition port for acquiring the image information transmitted from the video management device. When the image acquisition port is specified, a port number notification unit that generates port number information for identifying the specified image acquisition port and transmits it to the video management device. An image acquisition unit that acquires the image information transmitted to the image acquisition port from the video management device. Function as.

Effect of the Invention

[0010] According to the present invention, a terminal device searches for and specifies an image acquisition port for acquiring image information transmitted from a video management device, generates port number information for identifying the specified image acquisition port, and transmits it to the video management device. As a result, the video management device can transmit image information to the specified image acquisition port in the terminal device, so that the video management device can be prevented from continuously transmitting image information to a port that cannot be specified as an image acquisition port in the terminal device. Therefore, it is possible to suppress the state where the terminal device cannot acquire image information even though the video management device continues to transmit image information to the terminal device, so that the image information can be appropriately transmitted from the video management device to the terminal device.

Brief Description of the Drawings

[0011] [Figure 1] It is a diagram showing the configuration of a communication system according to an embodiment of the present invention. [Figure 2] It is a diagram showing the hardware configuration of a communication system according to an embodiment. [Figure 3] It is a diagram showing the functional configuration of a communication system according to an embodiment. [Figure 4] It is a diagram showing an example of information stored in the transmission success port number storage unit of a communication system according to an embodiment. [Figure 5] It is an operation explanatory diagram of a communication system according to an embodiment. [Figure 6] It is a sequence diagram showing the operation of a communication system according to an embodiment. [Figure 7] It is a sequence diagram showing the operation of a communication system according to an embodiment. [Figure 8] It is a diagram showing an example of an image for notifying that a port cannot be used, which is displayed on the display unit of the terminal device according to the embodiment. [Figure 9] It is a sequence diagram showing the operation of the communication system according to the embodiment. [Figure 10] It is a flowchart showing an example of the flow of video acquisition processing executed by the terminal device according to the embodiment. [Figure 11] It is a flowchart showing an example of the flow of video acquisition processing executed by the terminal device according to the embodiment. [Figure 12] It is a flowchart showing an example of the flow of video distribution processing executed by the video management device according to the embodiment. [Figure 13] It is an operation explanatory diagram of the communication system according to the modification example. [Figure 14] It is an operation explanatory diagram of the communication system according to the modification example.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, a communication method according to an embodiment of the present invention will be described in detail with reference to the drawings. The communication method according to this embodiment is a communication method performed between a video management device that manages image information indicating a captured image captured by a camera and a terminal device that can communicate with the video management device. This communication method includes an image request step in which the terminal device transmits image request information for requesting transmission of image information to the video management device to the video management device, a port identification step in which the terminal device searches for and identifies an image acquisition port for acquiring the image information transmitted from the video management device, a port number notification step in which the terminal device generates port number information for identifying the identified image acquisition port and transmits it to the video management device when the image acquisition port can be identified, an image transmission step in which the video management device identifies the image acquisition port based on the acquired port number information and transmits the image information to the image acquisition port of the terminal device, and an image acquisition step in which the terminal device acquires the image information transmitted to the image acquisition port of the terminal device from the video management device.

[0013] The communication system 10 according to this embodiment, as shown in Figure 1 for example, comprises four network cameras 2A, 2B, 2C, and 2D (hereinafter also referred to as network cameras 2, etc.), a video management device 1 connected to these network cameras 2, etc. via a network NW, and a terminal device 3. The network NW is, for example, a wired LAN (Local Area Network) conforming to the Ethernet standard. The network cameras 2, etc. are used, for example, as surveillance cameras to monitor production equipment. The network cameras 2, etc. comprise an imaging unit (not shown), a control unit (not shown), a memory (not shown), and a wired communication interface (not shown). The imaging unit has, for example, a lens barrel holding at least one lens and an image sensor (neither shown) positioned at the imaging position of at least one lens, and outputs image information indicating an image of a subject. The wired communication interface is connected to the network NW and transmits and receives data via the network NW. The memory temporarily stores image information indicating an image captured by the imaging unit. When the control unit receives the aforementioned image information from the imaging unit, it stores the input image information in the memory. Furthermore, the control unit performs processing to establish a link with the video management device 1 and processing to establish a session. After a session is established between the network camera 2, etc. and the video management device 1, the control unit identifies the image information to be transmitted from the image information stored in the memory each time a predetermined image transmission time arrives, and transmits the identified image information to the video management device 1. In this embodiment, the communication system 10 is described using four network cameras 2A, 2B, 2C, and 2D as an example, but the number of network cameras 2, etc. is not limited to these. Also, in this embodiment, the communication system 10 is described using a wired LAN conforming to the Ethernet standard as an example, but the network NW is not limited to this, and for example, it may be a connection by wired cable conforming to the HDMI® standard, or it may be configured by communication conforming to the wireless LAN standard compliant with IEEE802.11.

[0014] Figure 2 shows the hardware configuration of the video management device 1 and terminal device 3 according to the embodiment. Figure 3 shows the functional configuration of each device in the communication system 10 according to the embodiment. Hereinafter, the functions of the video management device 1 and terminal device 3 will be described in detail using Figures 2 and 3. The video management device 1 acquires image information showing images captured by network cameras 2, etc., via the network NW shown in Figure 1. The video management device 1 comprises a CPU 101, a main memory unit 102, an auxiliary memory unit 103, a wired communication interface (I / F) 106, a wireless module 107, and a bus 109 connecting each unit. The main memory unit 102 is composed of volatile memory such as RAM and is used as a working area for the CPU 101. The auxiliary memory unit 103 is composed of non-volatile memory such as ROM, or an SSD (Solid State Drive), HDD (Hard Disk Drive), etc., and stores a program for controlling the video management device 1. The wired communication interface 106 is connected to the network NW and transmits and receives data to and from the network camera 2, etc., via the network NW. The wireless module 107 communicates wirelessly with the terminal device 3 using a communication method that conforms to a wireless LAN standard such as IEEE 802.11. Note that communication between the video management device 1 and the terminal device 3 is not limited to the above wireless communication; it may also be communication via a wired LAN conforming to IEEE 802.3.

[0015] The CPU 101 functions as an image acquisition unit 111, a response unit 112, an image transmission unit 113, a port number acquisition unit 114, and a transmission stop request acquisition unit 115, as shown in Figure 3, by reading the program stored in the auxiliary storage unit 103 into the main storage unit 102 and executing it. The main storage unit 102 shown in Figure 2 has an image buffer 121 that temporarily stores image information transmitted from the network camera 2, etc., as shown in Figure 3. Here, the image buffer 121 stores the image information using, for example, a FIFO (First In First Out) method. Furthermore, the auxiliary storage unit 103 shown in Figure 2 has a transmission success port number storage unit 131 and a fixed port number storage unit 132, as shown in Figure 3. The transmission success port number storage unit 131 stores, for example as shown in Figure 4, IP address information indicating the IP address assigned to the terminal device 3 to which the image information was sent when the transmission of the image information by the image transmission unit 113 to the terminal device 3 was successful, and port number information indicating the port number of the terminal device 3 used to transmit the image information, in association with each other.

[0016] Returning to Figure 3, the fixed port number storage unit 132 stores port number information indicating a fixed port number pre-configured for transmitting image information. However, if the user has not registered a fixed port number, the fixed port number storage unit 132 does not store any port number information.

[0017] The image acquisition unit 111 acquires image information transmitted from the network camera 2, etc., each time a pre-set image transmission time arrives, after a link and session have been established between the video management device 1 and the network camera 2, etc. The image acquisition unit 111 then stores the acquired image information in the image buffer 121. For example, as shown in Figure 5, the image acquisition unit 111 acquires image information Fi (i=1,2,···) transmitted from the network camera 2, etc., each time an image transmission time arrives with a period dT1, for example, after the image request information described later transmitted from the terminal device 3 has been acquired, and sequentially stores the acquired image information Fi in the image buffer 121.

[0018] Returning to Figure 3, when the response unit 112 receives the image request information (described later) transmitted from the terminal device 3, it determines whether or not there is port number information stored in the successful transmission port number storage unit 131 or the fixed port number storage unit 132. If the response unit 112 determines that there is port number information stored in the successful transmission port number storage unit 131 or the fixed port number storage unit 132, it generates response information that includes the port number information stored in the successful transmission port number storage unit 131 or the fixed port number storage unit 132. Here, if both the successful transmission port number storage unit 131 and the fixed port number storage unit 132 store port number information, the response unit 112 generates response information that includes the port number information stored in the fixed port number storage unit 132. That is, the response unit 112 prioritizes including the port number information stored in the fixed port number storage unit 132 in the response information. On the other hand, if the response unit 112 determines that neither the successful transmission port number storage unit 131 nor the fixed port number storage unit 132 stores port number information, it generates response information that does not include port number information. Furthermore, the response unit 112 extracts the IP address information of the terminal device 3 that sent the image request information, which is included in the acquired image request information, and notifies the image transmission unit 113 of it.

[0019] When the port number acquisition unit 114 acquires port number information transmitted from the terminal device 3, it notifies the image transmission unit 113 of the acquired port number information. When the transmission stop request acquisition unit 115 acquires the image transmission stop request information described later from the terminal device 3, it notifies the image transmission unit 113 of the acquired image transmission stop request information.

[0020] When the image transmission unit 113 receives port number information from the port number acquisition unit 114, it selects image information to be sent to the terminal device 3 from the image information stored in the image buffer 121. The image transmission unit 113 then sends the selected image information to the image acquisition port, identified by the acquired port number information, at the IP address indicated by the IP address information notified by the response unit 112. Here, the image transmission unit 113, for example as shown in Figure 5, preferentially selects unsent image information Fi stored in the image buffer 121 from among the image information Fi stored in the image buffer 121, prioritizing the time of storage in the image buffer 121, and sends it to the terminal device 3. The image transmission unit 113 also repeats the selection of image information Fi and transmission to the terminal device 3 at the same period as the image transmission cycle dT1 of, for example, the network camera 2. Furthermore, the period dT4 between the time T0 when the response unit 112 acquires the image request information and the time T1 when the image information (F1 in Figure 5) is successfully transmitted to the terminal device 3 corresponds to the period during which the video management device 1 cannot transmit the image information Fi to the terminal device 3. After the response unit 112 acquires the image request information, all image information acquired during the period dT4, which is longer than the transmission cycle dT1 of the aforementioned network camera 2, is temporarily stored in the image buffer 121.

[0021] Returning to Figure 3, the image transmission unit 113, after transmitting image information to the terminal device 3, determines that the transmission of image information to the terminal device 3 has been successful if no new port number information is transmitted from the terminal device 3 within a predetermined time, and associates the IP address information notified by the response unit 112 with the port number information notified by the port number acquisition unit 114 and stores them in the successful transmission port number storage unit 131. Furthermore, when the image transmission unit 113 receives the aforementioned image transmission stop request information from the transmission stop request acquisition unit 115, it stops transmitting image information to the terminal device 3 accordingly.

[0022] Returning to Figure 2, terminal device 3 is a device for users to acquire and view image information captured by network cameras 2, etc., via video management device 1. Terminal device 3 is a personal computer capable of wireless communication with video management device 1 using a communication method conforming to the wireless LAN standard, such as IEEE 802.11, and comprises a CPU 301, a main memory unit 302, an auxiliary memory unit 303, a display unit 304, an input unit 305, a wireless module 307, and a bus 309 connecting each unit. The main memory unit 302 is composed of volatile memory such as RAM and is used as a working area for the CPU 301. The auxiliary memory unit 303 is composed of non-volatile memory such as ROM, or an SSD, HDD, etc., and stores a program for controlling terminal device 3. The display unit 304 is a display device having, for example, a liquid crystal display. The input unit 305 is an input device such as a keyboard. The wireless module 307 communicates wirelessly with the wireless module 107 of the video management device 1 using a communication method that conforms to a wireless LAN standard such as IEEE 802.11.

[0023] The CPU 301 reads the program stored in the auxiliary storage unit 303 into the main memory unit 302 and executes it, so that, as shown in Figure 3, it functions as an image request unit 311, a port identification unit 312, a port number notification unit 313, an image acquisition unit 314, a display control unit 315, a used port management unit 316, and a transmission stop request unit 317. Also, as shown in Figure 2, the main memory unit 302 stores port number information, which indicates port numbers already used by applications running on the terminal device 3 or port numbers prohibited by security software, in the port number management buffer 321, as shown in Figure 3, and associates it with port type information indicating the type of port related to the port number. This port type information indicates either a dynamic port, a registered port, or a well-known port. Here, port numbers 0 to 1023 are associated with port type numbers indicating well-known ports, and port numbers 1024 to 49151 are associated with port type numbers indicating registered ports. Registered ports are ports registered with IANA (Internet Assigned Numbers Authority). Furthermore, the auxiliary storage unit 303 shown in Figure 2 has an image storage unit 331 that stores image information transmitted from the video management device 1, as shown in Figure 3.

[0024] When a user requests video distribution via the input unit 305 to the video management device 1 to distribute captured images obtained by a network camera 2 or the like, the image request unit 311 receives the video distribution request and generates image request information requesting the transmission of image information. The image request unit 311 then transmits the generated image request information to the video management device 1.

[0025] When the port identification unit 312 receives response information transmitted from the video management device 1, it searches for and identifies an image acquisition port for acquiring image information transmitted from the video management device 1. When the port identification unit 312 receives response information, it determines whether or not the received response information includes port number information. If the received response information includes port number information, the port identification unit 312 identifies the port identified by the port number indicated by that port number information as the image acquisition port. On the other hand, if the received response information does not include port number information, or if the port identification unit 312 determines that it has failed to transmit image information to the port identified by the image acquisition unit 314 as the image acquisition port, it searches for an unused, free port among the multiple dynamic ports of the terminal device 3. Specifically, a situation in which it has failed to transmit image information to the identified port refers to an event in the operating status (status) of the video management device 1 where image information is not being transmitted, or an event where image information does not reach the terminal device 3 within a predetermined time. Here, the port identification unit 312 sends port number information indicating the port number identified by the port number notification unit 313 (as described later) to the video management device 1. If the image acquisition notification information described later is not sent from the image acquisition unit 314 within a predetermined period, the port identification unit 312 determines that the transmission of image information to the identified port has failed. The length of this predetermined period is set, for example, to 5 seconds or more and 10 seconds or less. The port identification unit 312 also selects one dynamic port from among multiple dynamic ports and repeatedly determines whether the selected dynamic port is an available port by referring to the port number information corresponding to the port type information indicating the dynamic port stored in the port number management buffer 321. When the port identification unit 312 determines that the selected dynamic port is an available port, it identifies the available port as an image acquisition port and notifies the port number notification unit 313 of the port number information indicating the port number of the available port.Furthermore, if the port identification unit 312 determines that it has failed to transmit image information to the identified image acquisition port, it selects another dynamic port, and if it determines that the selected dynamic port is one of the aforementioned available ports, it identifies that available port as the image acquisition port.

[0026] Furthermore, if the port identification unit 312 determines that all dynamic ports are in use, or that it has failed to transmit image information to all dynamic ports identified as image acquisition ports, it searches for an available port among the multiple registered ports of the terminal device 3. Here, the port identification unit 312 selects one registered port from among the multiple registered ports, and repeatedly determines whether the selected registered port is one of the aforementioned available ports by referring to the port number information corresponding to the port type information indicating the registered port stored in the port number management buffer 321. When the port identification unit 312 determines that the selected registered port is one of the aforementioned available ports, it identifies the available port as an image acquisition port and notifies the port number notification unit 313 of the port number information indicating the port number of the available port. Also, if the port identification unit 312 determines that it has failed to transmit image information to the registered port identified as an image acquisition port, it selects another registered port again, and when it determines that the selected registered port is one of the aforementioned available ports, it identifies the available port as an image acquisition port.

[0027] Furthermore, if the port identification unit 312 determines that all registered ports are in use, or that it has failed to transmit image information to all registered ports identified as image acquisition ports, it searches for an available port among the multiple well-known ports of the terminal device 3. Here, the port identification unit 312 selects one well-known port from among the multiple well-known ports, and repeatedly determines whether the selected well-known port is one of the aforementioned available ports by referring to the port number information corresponding to the port type information indicating the well-known port stored in the port number management buffer 321. When the port identification unit 312 determines that the selected well-known port is one of the aforementioned available ports, it identifies the available port as an image acquisition port and notifies the port number notification unit 313 of the port number information indicating the port number of the available port. Also, if the port identification unit 312 determines that it has failed to transmit image information to the well-known port identified as an image acquisition port, it selects another well-known port again, and when it determines that the selected well-known port is one of the aforementioned available ports, it identifies the available port as an image acquisition port.

[0028] Furthermore, if the port identification unit 312 determines that all well-known ports are in use, or that it has failed to transmit image information to all well-known ports identified as image acquisition ports, it notifies the display control unit 315 of a port unavailable notification.

[0029] When the port identification unit 312 identifies an image acquisition port, the port number notification unit 313 generates port number information that identifies the identified image acquisition port and transmits it to the video management device 1.

[0030] When the image acquisition unit 314 has successfully acquired image information transmitted from the video management device 1, it stores the acquired image information in the image storage unit 331. Here, as shown in Figure 5, the image acquisition unit 314 acquires the image information Fi acquired by the video management device 1 from the network camera 2, etc., at a time delayed by dT3 due to the delay time of passing through the image buffer 121 compared to the time T2 at which the video management device 1 acquired the information. Returning to Figure 3, the image acquisition unit 314 also notifies the port identification unit 312 of the image acquisition notification information.

[0031] The display control unit 315 uses the image information stored in the image storage unit 331 to form a camera image and display it on the display unit 304. As shown in Figure 5, as soon as the image information Fi is stored in the image storage unit 331, the display control unit 315 uses the image information Fi to form a camera image GFi (i=1,2,...) and displays it on the display unit 304. Here, the period dT2 for displaying the camera image GFi on the display unit 304 is set to be the same as the transmission period dT1 of the network camera 2, for example. Returning to Figure 3, when the port unavailable notification information is notified from the port identification unit 312, the display control unit 315 forms a port unavailable notification image G1 (described later) to notify the user that the port is unavailable on the terminal device 3 and displays it on the display unit 304.

[0032] When a user performs a video distribution stop operation via the input unit 305 to stop the transmission of image information Fi to the video management device 1, the transmission stop request unit 317 receives the video distribution stop operation, generates image transmission stop request information requesting the video management device 1 to stop transmitting image information Fi, and notifies the image request unit 311. The image request unit 311 then transmits the generated image transmission stop request information to the video management device 1. Note that the video distribution stop operation also includes the user ending the process without entering a port number by pressing the button BU2 shown in Figure 8, which will be described later.

[0033] Next, the operation of the communication system 10 according to this embodiment will be described with reference to Figures 6 to 8. First, as shown in Figure 6, suppose a user performs the aforementioned video distribution request operation to the input unit 305 of the terminal device 3. In this case, the terminal device 3 generates the aforementioned image request information (step S1), and the generated image request information is transmitted from the terminal device 3 to the video management device 1 (step S2). On the other hand, when the video management device 1 receives the image request information, it generates response information regarding the port number (step S3). Here, if the video management device 1 determines that there is port number information stored in the transmission success port number storage unit 131 or the fixed port number storage unit 132, it generates response information that includes the port number information stored in the transmission success port number storage unit 131 or the fixed port number storage unit 132. On the other hand, if the response unit 112 determines that neither the transmission success port number storage unit 131 nor the fixed port number storage unit 132 stores port number information, it generates response information that does not include port number information. Next, the generated response information is transmitted from the video management device 1 to the terminal device 3 (step S4). Meanwhile, terminal device 3 acquires response information and determines that the acquired response information does not include port number information (step S5). In this case, terminal device 3 selects one dynamic port (step S6). Then, if terminal device 3 determines that the selected dynamic port is an available port (step S7), it identifies the available port as an image acquisition port and generates port number information to identify the identified dynamic port (step S8). The generated port number information is then transmitted from terminal device 3 to video management device 1 (step S9).

[0034] Here, suppose that network camera 2 captures an image of the subject and generates image information (step S10), and that the generated image information is transmitted from network camera 2 to video management device 1 (step S11). In this case, when video management device 1 acquires the image information, it stores the acquired image information in image buffer 121. Next, suppose that video management device 1 selects image information Fi stored in image buffer 121 (step S12), and attempts to send the selected image information Fi to the image acquisition port indicated by the acquired port number information, but fails to send it. In this case, terminal device 3 determines that the transmission of image information Fi to the identified image acquisition port has failed (step S13). Then, terminal device 3 selects another dynamic port (step S6), and the processes from step S7 onwards described above are repeated as appropriate. After that, suppose that terminal device 3 determines that it has selected all of the multiple dynamic ports without acquiring the image information Fi transmitted from video management device 1 (step S14). In this case, terminal device 3 selects one registered port (step S15). Then, when terminal device 3 determines that the selected registered port is an available port (step S16), it identifies the available port as an image acquisition port and generates port number information to identify the identified registered port (step S17). The generated port number information is then transmitted from terminal device 3 to video management device 1 (step S18).

[0035] Next, suppose the video management device 1 selects image information Fi stored in the image buffer 121 (step S19) and attempts to send the selected image information Fi to the image acquisition port indicated by the acquired port number information, but fails to send it. In this case, the terminal device 3 determines that the transmission of image information Fi to the identified image acquisition port has failed (step S20). Then, as shown in Figure 7, the terminal device 3 selects another registered port (step S15), and the processes from step S16 onwards described above are repeated as appropriate. Subsequently, suppose the terminal device 3 determines that it has selected all of the multiple registered ports without acquiring image information transmitted from the video management device 1 (step S21). In this case, the terminal device 3 selects one well-known port (step S22). Then, if the terminal device 3 determines that the selected well-known port is an available port (step S23), it identifies the available port as an image acquisition port and generates port number information that identifies the identified well-known port (step S24). Then, the generated port number information is transmitted from terminal device 3 to video management device 1 (step S25).

[0036] Subsequently, the video management device 1 selects image information Fi stored in the image buffer 121 (step S26), and attempts to send the selected image information Fi to the image acquisition port indicated by the acquired port number information, but fails to send it. In this case, the terminal device 3 determines that the transmission of image information Fi to the identified image acquisition port has failed (step S27). Then, the terminal device 3 selects another well-known port (step S22), and the processes from step S23 onwards described above are repeated as appropriate. Subsequently, the terminal device 3 determines that it has selected all of the multiple well-known ports without acquiring the image information Fi transmitted from the video management device 1 (step S28). In this case, the terminal device 3 forms the aforementioned port unavailable notification image G1 and displays it on the display unit 304 (step S29). Here, the terminal device 3 displays a port unavailable notification image G1 on the display unit 304, for example, as shown in Figure 8. This port unavailable notification image G1 includes an input field B1 for the user to enter a port number that has become available after the user has removed the restriction on the image acquisition port by some means, a button BU1 (update settings) which is selected when updating the port identified by the entered port number to an available state, and a button BU2 (exit) which is selected when the user terminates the process without entering a port number. Here, the means of removing the aforementioned restriction on the image acquisition port may be, for example, opening a port that is already in use, or changing the settings of an application (e.g., security software) that restricts the use of a specific port.

[0037] Furthermore, as shown in Figure 9, the video management device 1 selects image information Fi stored in the image buffer 121 (step S26), and assumes that the image information Fi, which has been set to the image acquisition port indicated by the acquired port number information, has been successfully transmitted from the video management device 1 to the terminal device 3 (step S30). In this case, the video management device 1 associates the IP address information of the terminal device 3 that sent the image request information with the port number information acquired from the terminal device 3 and stores it in the successful transmission port number storage unit 131 (step S31). Meanwhile, the terminal device 3 determines that it has successfully transmitted the image information (step S32) and stores the acquired image information Fi in the image storage unit 331. Then, the terminal device 3 uses the newly stored image information in the image storage unit 331 to form a camera image and displays it on the display unit 304 (step S33).

[0038] Next, suppose that the network camera 2 captures an image of the subject and generates image information (step S34), and that the generated image information is transmitted from the network camera 2 to the video management device 1 (step S35). In this case, when the video management device 1 acquires the image information, it stores the acquired image information in the image buffer 121. Subsequently, the video management device 1 selects the image information Fi stored in the image buffer 121 (step S36), and the image information Fi set for the aforementioned image acquisition port is transmitted from the video management device 1 to the terminal device 3 (step S37). Meanwhile, the terminal device 3 stores the acquired image information Fi in the image storage unit 331. Then, the terminal device 3 uses the newly stored image information Fi in the image storage unit 331 to form a camera image and displays it on the display unit 304 (step S38).

[0039] Next, the video acquisition process performed by the terminal device 3 according to this embodiment will be described in detail with reference to Figures 10 and 11. This video acquisition process is started, for example, after power is turned on to the terminal device 3 and the application for displaying the aforementioned camera image on the display unit 304 is launched. First, as shown in Figure 10, the image request unit 311 determines whether or not it has received the aforementioned video distribution request operation performed by the user via the input unit 305 (step S101). Here, as long as the image request unit 311 determines that it has not received the video distribution request operation (step S101: No), the process in step S101 is repeatedly executed. On the other hand, if the image request unit 311 determines that it has received the video distribution request operation (step S101: Yes), it generates image request information requesting the transmission of image information. Then, the image request unit 311 transmits the generated image request information to the video management device 1 (step S102).

[0040] Next, the port identification unit 312 obtains response information regarding the port number transmitted from the video management device 1 (step S103), and determines whether or not the obtained response information includes port number information (step S104). If the port identification unit 312 determines that the obtained response information does not include port number information (step S104: No), the process in step S107, described later, is executed. On the other hand, if the port identification unit 312 determines that the obtained response information includes port number information (step S104: Yes), it identifies the port identified by the port number indicated by the port number information as the image acquisition port. Then, the port number notification unit 313 generates port number information that identifies the identified image acquisition port and sends it to the video management device 1 (step S105). Subsequently, the port identification unit 312 determines whether or not the transmission of image information Fi to the port identified as the image acquisition port has failed (step S106). If the port identification unit 312 determines that it has successfully transmitted image information Fi to the port identified as the image acquisition port (step S106: No), the process in step S126, described later, is executed.

[0041] On the other hand, suppose the port identification unit 312 determines that it has failed to transmit image information Fi to the port it has identified as the image acquisition port (step S106: Yes). In this case, the port identification unit 312 selects one dynamic port from among multiple dynamic ports (step S107), and refers to the port number information stored in the port number management buffer 321 to determine whether the selected dynamic port is the aforementioned free port (step S108). If the port identification unit 312 determines that the selected dynamic port is a port in use (step S108: No), the process in step S107 is executed again. On the other hand, if the port identification unit 312 determines that the selected dynamic port is a free port (step S108: Yes), it identifies the port identified by the port number indicated by the port number information as the image acquisition port. The port number notification unit 313 then generates port number information that identifies the identified image acquisition port and sends it to the video management device 1 (step S109). Subsequently, the port identification unit 312 determines whether or not it failed to transmit image information Fi to the port identified as the image acquisition port (step S110). If the port identification unit 312 determines that it succeeded in transmitting image information Fi to the port identified as the image acquisition port (step S110: No), the process in step S126, described later, is executed. On the other hand, suppose the port identification unit 312 determines that it failed to transmit image information Fi to the dynamic port identified as the image acquisition port (step S110: Yes). In this case, the port identification unit 312 determines whether or not it has selected all of the multiple dynamic ports (step S111). If the port identification unit 312 determines that there are dynamic ports that have not yet been selected (step S111: No), the process in step S107 is executed again.

[0042] On the other hand, suppose the port identification unit 312 determines that it has selected all of the multiple dynamic ports (step S111: Yes). In this case, the port identification unit 312 selects one registered port from among the multiple registered ports (step S112), and refers to the port number information stored in the port number management buffer 321 to determine whether the selected registered port is an available port or not (step S113). If the port identification unit 312 determines that the selected registered port is a port in use (step S113: No), the process in step S112 is executed again. On the other hand, if the port identification unit 312 determines that the selected registered port is an available port (step S113: Yes), it identifies the port identified by the port number indicated by the port number information as the image acquisition port. Then, the port number notification unit 313 generates port number information that identifies the identified image acquisition port and sends it to the video management device 1 (step S114). Next, the port identification unit 312 determines whether or not it failed to transmit image information to the port identified as the image acquisition port (step S115). If the port identification unit 312 determines that it succeeded in transmitting image information Fi to the port identified as the image acquisition port (step S115: No), the process in step S126, described later, is executed. On the other hand, suppose the port identification unit 312 determines that it failed to transmit image information Fi to the registered port identified as the image acquisition port (step S115: Yes). In this case, the port identification unit 312 determines whether or not it has selected all of the multiple registered ports (step S116). If the port identification unit 312 determines that there are still registered ports that have not been selected (step S116: No), the process in step S112 is executed again.

[0043] On the other hand, suppose the port identification unit 312 determines that it has selected all of the multiple registered ports (step S116: Yes). In this case, as shown in Figure 11, the port identification unit 312 selects one well-known port from among the multiple well-known ports (step S117), and refers to the port number information stored in the port number management buffer 321 to determine whether the selected well-known port is an available port or not (step S118). If the port identification unit 312 determines that the selected well-known port is an in-use port (step S118: No), the process in step S117 is executed again. On the other hand, if the port identification unit 312 determines that the selected well-known port is an available port (step S118: Yes), it identifies the port identified by the port number indicated by the port number information as the image acquisition port. The port number notification unit 313 then generates port number information that identifies the identified image acquisition port and sends it to the video management device 1 (step S119). Next, the port identification unit 312 determines whether or not it failed to transmit image information Fi to the port identified as the image acquisition port (step S120). If the port identification unit 312 determines that it succeeded in transmitting image information Fi to the port identified as the image acquisition port (step S120: No), the process in step S126, described later, is executed. On the other hand, suppose the port identification unit 312 determines that it failed to transmit image information Fi to the well-known port identified as the image acquisition port (step S120: Yes). In this case, the port identification unit 312 determines whether or not it has selected all of the multiple well-known ports (step S121). If the port identification unit 312 determines that there are still well-known ports that have not yet been selected (step S121: No), the process in step S117 is executed again.

[0044] On the other hand, suppose the port identification unit 312 determines that it has selected all of the multiple well-known ports (Step S121: Yes). In this case, the display control unit 315 forms the aforementioned port unavailable notification image G1 and displays it on the display unit 304 (Step S122).

[0045] Next, the port number notification unit 313 determines whether an update operation has been performed in which the user has entered a specific port number into the input field B1 of the port unavailable notification image G1 displayed on the display unit 304 via the input unit 305 and selected the button image BU1 to update the port to an usable state (step S123). Here, the port number notification unit 313 determines that the aforementioned update operation has been performed (step S123: Yes). In this case, if the port number entered in input field B1 is a dynamic port (step S124: Yes), the process proceeds to step S109; if it is a registered port (step S124: No, and step S125: Yes), the process proceeds to step S114; and if it is a well-known port (step S125: No), the process proceeds to step S119. On the other hand, if the operation to select the button image BU2 shown in Figure 8 has been performed (step S123: No), the port number notification unit 313 terminates the process without entering a port number and proceeds to step S129 via Yes in step S128.

[0046] Furthermore, the port identification unit 312 determines in step S120 that it has successfully transmitted image information to the port identified as the image acquisition port (step S120: No). In this case, the image acquisition unit 314 acquires the image information transmitted from the video management device 1 and stores the acquired image information in the image storage unit 331 (step S126). Then, the display control unit 315 uses the newly stored image information in the image storage unit 331 to form a camera image and display it on the display unit 304 (step S127). Subsequently, the transmission stop request unit 317 determines whether or not it has accepted the aforementioned video distribution stop operation performed by the user via the input unit 305, such as when a series of image acquisitions have been completed (step S128). If the transmission stop request unit 317 determines that it has not accepted the video distribution stop operation (step S128: No), the process in step S126 is executed again. On the other hand, when the transmission stop request unit 317 determines that it has received a video distribution stop operation (step S128: Yes), it generates the aforementioned image transmission stop request information and sends it to the video management device 1 (step S129), and after temporarily ending the video acquisition process, it waits for the image distribution process to start again through the process in step S101.

[0047] Next, the video distribution process performed by the video management device 1 according to this embodiment will be described in detail with reference to Figure 12. This video distribution process is started, for example, when power is turned on to the video management device 1. Although not shown in Figure 12, the image acquisition unit 111 of the video management device 1, in parallel with the video distribution process, acquires image information transmitted from the network camera 2, etc., each time the aforementioned image transmission time arrives, and stores the acquired image information in the image buffer 121. First, the response unit 112 determines whether or not it has acquired the aforementioned image request information transmitted from the terminal device 3 (step S201). Here, unless the response unit 112 has acquired the image request information (step S201: No), the process in step S201 is repeated. On the other hand, if the response unit 112 determines that it has acquired the image request information (step S201: Yes), it determines whether or not there is port number information stored in the transmission success port number storage unit 131 or the fixed port number storage unit 132 (step S202). Here, if the response unit 112 determines that there is port number information stored in the successful transmission port number storage unit 131 or the fixed port number storage unit 132 (step S202: Yes), it generates response information that includes the port number information stored in the successful transmission port number storage unit 131 or the fixed port number storage unit 132. Subsequently, the response unit 112 sends the generated response information to the terminal device 3 (step S203), and then the process of step S205, described later, is executed. On the other hand, if the response unit 112 determines that the successful transmission port number storage unit 131 or the fixed port number storage unit 132 does not store port number information (step S202: Yes), it generates response information that does not include port number information and sends the generated response information to the terminal device 3 (step S204).

[0048] Subsequently, the port number acquisition unit 114 acquires the port number information after the response information has been sent (step S205) and notifies the image transmission unit 113 of the acquired port number information. When the image transmission unit 113 receives the port number information, it selects the image information to be sent to the terminal device 3 from the image information stored in the image buffer 121. The image transmission unit 113 then sends the selected image information to the image acquisition port identified by the acquired port number information at the IP address indicated by the notified IP address information (step S206). Next, after sending the image information to the terminal device 3, the port number acquisition unit 114 associates the IP address information notified by the response unit 112 with the port number information notified by the port number acquisition unit 114 and stores them in the successful transmission port number storage unit 131 (step S207). Step S207 is the step when image information transmission is successful, based on the port number information received in the port number information generation and transmission steps (S109, S114, or S119) by terminal device 3 in Figures 10 and 11, by sending to the said port number.

[0049] Subsequently, the transmission stop request acquisition unit 115 determines whether or not it has acquired the aforementioned image transmission stop request information from the terminal device 3 (step S208). If the transmission stop request acquisition unit 115 determines that it has not acquired the image transmission stop request information (step S208: No), the process in step S206 is executed again. On the other hand, if the transmission stop request acquisition unit 115 determines that it has acquired the image transmission stop request information (step S208: Yes), it notifies the image transmission unit 113 of the acquired image transmission stop request information. The image transmission unit 113 then stops selecting image information and transmitting the selected image information to the terminal device 3 in response (step S209). Next, the process returns to step S201 and waits for a request for image distribution processing.

[0050] As described above, in the communication system 10 according to this embodiment, the terminal device 3 searches for and identifies an image acquisition port for acquiring image information transmitted from the video management device 1, generates port number information that identifies the identified image acquisition port, and transmits it to the video management device 1. As a result, the video management device 1 can transmit image information to the image acquisition port based on the port number information received from the terminal device 3, thereby preventing the video management device 1 from continuously transmitting image information to a port that cannot be used as an image acquisition port on the terminal device 3. Therefore, it is possible to prevent a situation in which the terminal device 3 is unable to acquire image information despite the video management device 1 continuously transmitting it to the terminal device 3, thereby enabling the video management device 1 to appropriately transmit image information to the terminal device 3.

[0051] Although embodiments of the present invention have been described above, the present invention is not limited to the configuration of the embodiments described above. For example, if the aforementioned transmission failure period dT4 occurs, the video management device 1 may, after the transmission failure period has elapsed, transmit the image information stored in the image buffer 121 during the transmission failure period to the terminal device 3 with a transmission cycle shorter than the transmission cycle described above. Specifically, as shown in Figure 13, the video management device 1 transmits the image information F1, F2, and F3 stored in the image buffer 121 during the transmission failure period dT4 to the terminal device 3 with a transmission cycle dT21 shorter than the transmission cycle dT1 of the network camera 2, etc., after the transmission failure period dT4 has elapsed. Note that in Figure 13, the same components as in the embodiments are denoted by the same reference numerals as in Figure 5.

[0052] With this configuration, all image information stored in the image buffer 121 during the transmission-unavailable period can be delivered to the terminal device 3 relatively quickly, thereby reducing the deterioration of video quality caused by missing camera images displayed on the display unit 304 of the terminal device 3.

[0053] Furthermore, in this embodiment, the image information stored in the image buffer 121 is assumed to be either I-frame information indicating an I-frame, P-frame information indicating a P-frame, or B-frame information indicating a B-frame. In this case, the video management device 1 may transmit only the I-frame information from the image information stored in the image buffer 121 during the transmission-unavailable period dT4 to the terminal device 3. Specifically, as shown in Figure 14, the image information F1, F2, and F3 stored in the image buffer 121 during the transmission-unavailable period dT4 are assumed to consist of I-frame information, P-frame information, and B-frame information, respectively. Note that in Figure 14, the same components as in the embodiment are denoted by the same reference numerals as in Figure 5. In this case, after the transmission-unavailable period dT4 has elapsed, the video management device 1 transmits only the I-frame information of the image information F1, F2, and F3 stored in the image buffer 121 during the transmission-unavailable period dT4 to the terminal device 3.

[0054] With this configuration, all of the I-frame information necessary to form the camera image from the image buffer 121 stored during the transmission-unavailable period can be delivered to the terminal device 3 relatively early, so that the minimum camera image stored during the transmission-unavailable period can be displayed on the display unit 304 of the terminal device 3.

[0055] The various functions of the video management device 1 and terminal device 3 according to the present invention can be realized using a computer system equipped with a wireless communication module, without requiring a dedicated system. For example, the video management device 1 and terminal device 3 that perform the above-mentioned operations may be configured by distributing a program for performing the above operations to a computer connected to a network, stored on a non-temporary recording medium (such as a CD-ROM) that can be read by the computer system, and then installing the program into the computer system.

[0056] Furthermore, the method of providing the program to the computer is arbitrary. For example, the program may be uploaded to a server on a communication line and distributed to the computer via the communication line. The computer then launches this program and executes it under the control of the OS, just like any other application. In this way, the computer functions as the video management device 1 and terminal device 3 that perform the processes described above.

[0057] Although embodiments and variations of the present invention have been described above, the present invention is not limited thereto. The present invention includes embodiments and variations that are appropriately combined, and those that are appropriately modified thereto. [Industrial applicability]

[0058] This invention is suitable for surveillance systems using network cameras. [Explanation of Symbols]

[0059] 1: Video management device, 2A, 2B, 2C, 2D: Network cameras, 3: Terminal device, 10: Communication system, 101, 301: CPU, 102, 302: Main memory unit, 103, 303: Auxiliary memory unit, 106: Wired communication interface, 107, 307: Wireless module, 109, 309: Bus, 111: Image acquisition unit, 112: Response unit, 113: Image transmission unit, 114: Port number acquisition unit, 115: Transmission stop Request acquisition unit, 121: Image buffer, 131: Successful transmission port number storage unit, 132: Fixed port number storage unit, 304: Display unit, 305: Input unit, 311: Image request unit, 312: Port identification unit, 313: Port number notification unit, 314: Image acquisition unit, 315: Display control unit, 316: Used port management unit, 317: Transmission stop request unit, 321: Port number management buffer, 331: Image storage unit, NW: Network

Claims

1. A communication method between a video management device that manages image information indicating captured images taken by a camera, and a terminal device that can communicate with the video management device, The terminal device transmits image request information to the video management device requesting the transmission of the image information in an image request step, The terminal device performs a port identification step of searching for and identifying an image acquisition port for acquiring the image information transmitted from the video management device, If the terminal device can identify the image acquisition port, it performs a port number notification step of generating port number information that identifies the identified image acquisition port and sending it to the video management device. When the video management device obtains the port number information, it identifies the image acquisition port based on the obtained port number information and transmits the image information to the image acquisition port of the terminal device in an image transmission step. The terminal device includes an image acquisition step of acquiring the image information transmitted from the video management device to the image acquisition port, Communication method.

2. In the port identification step, the terminal device, The system searches for available ports among multiple dynamic ports, and upon detecting such available ports, it identifies the detected available ports as the image acquisition ports. If no available port is detected among the multiple dynamic ports, the system searches for a available port among a number of pre-registered ports, and when a available port is detected, it identifies the detected available port as the image acquisition port. If no available port is found among the multiple registered ports, the system searches for a available port among the multiple well-known ports, and if a available port is found, it identifies the found available port as the image acquisition port. The communication method according to claim 1.

3. If no available port is detected among the plurality of well-known ports, the notification step further includes forming a port unavailable notification image to inform the user that the image acquisition port cannot be set and displaying it on the display unit of the terminal device. The communication method according to claim 2.

4. The video management device performs a determination step of determining whether or not the transmission of the image information to the terminal device was successful, The video management device further includes a storage step of storing in a port number storage unit, in association with the address information indicating the address assigned to the terminal device to which the image information is sent, and the port number information transmitted from the terminal device to which the image information is sent. The communication method according to any one of claims 1 to 3.

5. The video management device performs an image information acquisition step in which it acquires the image information transmitted from the camera at a predetermined first transmission cycle, The video management device transmits the acquired image information to the terminal device in the first transmission cycle in the image information transmission step, If, after the video management device has acquired the image request information, a transmission failure period occurs that is longer than the first transmission cycle and during which the image information cannot be transmitted to the terminal device, the device performs a temporary storage step of temporarily storing the image information acquired during the transmission failure period in an image buffer. The video management device further includes the step of transmitting the image information stored in the image buffer to the terminal device after the transmission unavailable period has elapsed. The communication method according to any one of claims 1 to 3.

6. In the step of transmitting the image information stored in the temporary storage step to the terminal device, the video management device transmits the image information to the terminal device with a second transmission cycle shorter than the first transmission cycle. The communication method according to claim 5.

7. The aforementioned image information is one of the following: I-frame information indicating an I-frame, P-frame information indicating a P-frame, and B-frame information indicating a B-frame. In the step of transmitting the image information stored in the temporary storage step to the terminal device, the video management device transmits only the I-frame information to the terminal device. The communication method according to claim 5.

8. An image request unit transmits image request information to a video management device that manages image information representing captured images taken by a camera, which requests the transmission of the said image information. A port identification unit searches for and identifies an image acquisition port for acquiring the image information transmitted from the video management device, When the image acquisition port is identified, a port number notification unit generates port number information that identifies the identified image acquisition port and transmits it to the video management device. The system includes an image acquisition unit that acquires the image information transmitted from the video management device to the image acquisition port. Terminal device.

9. A video management device that manages image information showing captured images taken by a camera, An image acquisition unit that acquires the image information transmitted from the camera at a predetermined first transmission cycle, An image transmission unit obtains port number information from a terminal device that identifies an image acquisition port for acquiring the image information identified by the terminal device, identifies the image acquisition port based on the obtained port number information, and transmits the image information to the image acquisition port of the terminal device in the first transmission cycle. If a period of non-transmission occurs that is longer than the first transmission cycle and the image information cannot be transmitted to the terminal device, the system includes an image buffer that temporarily stores the image information acquired from the camera during the period of non-transmission. If the image transmission unit experiences a period of transmission failure, it transmits the image information stored in the image buffer to the terminal device after the period of transmission failure has elapsed. Video management device.

10. A video management device that manages image information showing captured images taken by a camera, The system comprises a terminal device capable of communicating with the aforementioned video management device, The aforementioned terminal device is An image request unit that sends image request information to the video management device requesting the transmission of the image information, A port identification unit searches for and identifies an image acquisition port for acquiring the image information transmitted from the video management device, When the image acquisition port is identified, a port number notification unit generates port number information that identifies the identified image acquisition port and transmits it to the video management device. The system includes an image acquisition unit that acquires the image information transmitted from the video management device to the image acquisition port, The aforementioned video management device is The image transmission unit obtains the port number information transmitted from the terminal device, identifies the image acquisition port based on the obtained port number information, and transmits the image information to the image acquisition port of the terminal device. Communication system.

11. Computers, An image request unit transmits image request information to a video management device that manages image information indicating captured images taken by a camera, which requests the transmission of the said image information. A port identification unit searches for and identifies an image acquisition port for acquiring the image information transmitted from the video management device. When the image acquisition port is identified, a port number notification unit generates port number information that identifies the identified image acquisition port and transmits it to the video management device. An image acquisition unit that acquires the image information transmitted from the video management device to the image acquisition port. A program designed to function as such.

12. Computers, Image acquisition unit that acquires image information transmitted from the camera at a pre-set first transmission cycle. An image transmission unit obtains port number information from a terminal device that identifies an image acquisition port for acquiring the image information identified by the terminal device, identifies the image acquisition port based on the obtained port number information, and transmits the image information to the image acquisition port of the terminal device at the first transmission cycle. If a period of non-transmission occurs that is longer than the first transmission cycle and the image information cannot be transmitted to the terminal device, an image buffer temporarily stores the image information acquired from the camera during the period of non-transmission. It is a program designed to function as such. If the image transmission unit experiences a period of transmission failure, it transmits the image information stored in the image buffer to the terminal device after the period of transmission failure has elapsed. program.

Images