Video distribution system, repeating device, connection management device, repeating method, and connection management method

Abstract

To provide a video distribution system capable of realizing appropriate video communication.SOLUTION: A relay device 22 includes: a distribution request reception part 222 that receives a distribution request signal DM for requesting distribution of any video signal V from a terminal device 24 via a second network 20; an inquiry signal reception part 224 that receives an inquiry signal IQ for inquiring whether or not the distribution request signal DM has been received; a reply signal transmission part 226 that indicates whether or not the delivery request signal DM is received and, if it is received, returns a reply signal AS specifying a video signal V requested to be delivered in response to the inquiry signal IQ; and a video signal transfer part 228 that receives the video signal V corresponding to the delivery request signal DM from any of the delivery devices 12 and transmits the video signal V to the terminal device 24 via the second network 20. The relay device is provided to a video distribution system 101.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a video distribution system, a relay device, a connection management device, a relay method, and a connection management method.

Background Art

[0002] As background art in this technical field, Claim 1 of Patent Document 1 below states, "A server configured to be communicable with an imaging device belonging to a local area network and a terminal device belonging to a network other than the local area network, the server comprising means for receiving an inquiry about the presence or absence of a connection request to the imaging device periodically transmitted from the imaging device; means for, when receiving the inquiry from the imaging device, determining whether or not a connection request to the imaging device has been received from the terminal device, and maintaining a connection with the imaging device established based on the inquiry on condition that the determination result is affirmative; means for receiving imaging data captured by the imaging device transmitted from the imaging device using the maintained connection; and means for transmitting the received imaging data to the terminal device."

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 the above-described technology, there is a desire to realize more appropriate video distribution. This invention has been made in view of the above circumstances, and an object thereof is to provide a video distribution system, a relay device, a connection management device, a relay method, and a connection management method capable of realizing appropriate video distribution.

Means for Solving the Problems

[0005] To solve the above problems, the video distribution system of the present invention includes a first network, a second network, and a NAT device inserted between the first and second networks for performing mutual conversion between a first address in the first network and a second address in the second network, and a plurality of distribution devices each transmitting a video signal via the NAT device; a distribution request receiving unit that receives a distribution request signal for requesting distribution of any one of the video signals from a terminal device via the second network; a query signal receiving unit that receives a query signal for inquiring whether the distribution request signal has been received; and an answer signal transmitting unit that returns, in response to the query signal, an answer signal indicating whether the distribution request signal has been received and designating the video signal requested for distribution if the distribution request signal has been received. The video signal transfer unit receives the video signal corresponding to the distribution request signal from any one of the distribution devices and transmits the video signal to the terminal device via the second network. The relay device includes the above components, and the connection management device includes a query signal transmitting unit that repeatedly transmits the query signal to the relay device, an answer signal receiving unit that receives the answer signal from the relay device, and a distribution command transmitting unit that transmits a distribution command for commanding distribution of the video signal to the distribution device that outputs the designated video signal when any one of the video signals is designated in the answer signal. The video distribution system is characterized by comprising the above components.

Advantages of the Invention

[0006] According to the present invention, appropriate video distribution can be realized.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0008] [First Embodiment] 〈Configuration of the First Embodiment〉 FIG. 1 is a block diagram of a video distribution system 101 according to the first embodiment. The video distribution system 101 includes a plurality of (N) cameras 14-1 to 14-N, distribution devices 12-1 to 12-N, a NAT device 16, and a relay device 22 (computer). In the following description, a plurality of components, information, etc. having the same or similar functions and meanings may be denoted by the same reference numeral with "-" and alphanumeric characters, for example, "cameras 14-1, 14-N". However, when it is not necessary to distinguish these multiple components, etc., they may be denoted by omitting "-" and alphanumeric characters, for example, "camera 14".

[0009] Each camera 14 is installed, for example, in a monitoring target facility 10 such as a factory. The distribution devices 12-1 to 12-N are, for example, server machines, and are connected to a private network 18 (first network) of the IP protocol provided in the monitoring target facility 10. Then, the distribution devices 12-1 to 12-N output, as video signals V-1 to V-N, the videos captured by the cameras 14-1 to 14-N via the private network 18 as needed.

[0010] The relay device 22 and the terminal device 24 are connected to a public network 20 (second network) of the IP protocol, which is the Internet, for example. The relay device 22 is, for example, a server device that provides cloud services. The terminal device 24 is, for example, a personal computer, a mobile information terminal, etc. operated by a user.

[0011] The NAT device 16 is inserted between the private network 18 and the public network 20, and has a NAT (Network Address Translation) function that mutually converts the private IP address in the private network 18 and the global IP address in the public network 20. Further, the NAT device 16 has a NAPT (Network Address Port Translation) function that mutually converts port numbers in addition to IP addresses.

[0012] When the user wants to receive video distribution on the terminal device 24, the user designates one or more of the video signals V-1 to V-N and transmits a distribution request signal DM to the relay device 22. Then, the relay device 22 stores the received distribution request signal DM together with the reception time.

[0013] The distribution device 12-1 (computer, connection management device) includes a video transmission unit 126, an inquiry signal transmission unit 132 (inquiry signal transmission process), a response signal reception unit 134 (response signal reception process), and a distribution command transmission unit 136 (distribution command transmission process). The inquiry signal transmission unit 132 repeatedly transmits an inquiry signal IQ to the relay device 22 at a predetermined cycle via the NAT device 16. This inquiry signal IQ is a signal for inquiring whether the relay device 22 has received the above-described distribution request signal DM.

[0014] The response signal reception unit 134 receives a response signal AS returned by the relay device 22 in response to the inquiry signal IQ. The response signal AS is a signal indicating whether the relay device 22 has received a new distribution request signal DM from the terminal device 24 after the timing when the relay device 22 last transmitted the response signal AS. When the relay device 22 has received a new distribution request signal DM, the response signal AS includes information specifying one or more video signals V-k (where 1 ≤ k ≤ N) for which distribution has been requested.

[0015] When the video transmission unit 126 in the distribution device 12-1 includes the designation of the video signal V-1 in the response signal AS, it outputs the video signal V-1 via the relay device 22. Here, the response signal AS may include designations other than the video signal V-1, that is, one or more commands among the video signals V-2 to V-N. In this case, the distribution command transmission unit 136 outputs a distribution command VC for instructing video distribution to the distribution devices 12-2 to 12-N corresponding to these designations, respectively.

[0016] The distribution device 12-2 (computer) includes a distribution command reception unit 124 and a video transmission unit 126. The distribution command reception unit 124 receives the distribution command VC addressed to itself. Also, the video transmission unit 126 outputs the video signal V-2 corresponding to the distribution command VC addressed to itself. Although the configurations of the distribution devices 12-3 to 12-N (computers) are not shown, they are configured in the same manner as the distribution device 12-2. That is, when the distribution command reception unit 124 of the distribution device 12-k (where 2 ≤ k ≤ N) receives the distribution command VC addressed to itself, the video transmission unit 126 of the distribution device 12-k starts outputting the video signal V-k.

[0017] The relay device 22 includes a distribution request reception unit 222, an inquiry signal reception unit 224, a response signal transmission unit 226, and a video signal transfer unit 228. The distribution request reception unit 222 receives the distribution request signal DM supplied from the terminal device 24 via the public network 20 and stores the received distribution request signal DM. The inquiry signal reception unit 224 receives the inquiry signal IQ from the distribution device 12-1 via the NAT device 16.

[0018] When the inquiry signal reception unit 224 receives the inquiry signal IQ, the response signal transmission unit 226 outputs the response signal AS to the distribution device 12-1 based on the distribution request signal DM stored in the distribution request reception unit 222. The video signal transfer unit 228 receives the video signals V-1 to V-N supplied from the distribution devices 12-1 to 12-N and transfers them to the terminal device 24.

[0019] Figure 2 is a block diagram of the computer 980. The distribution device 12, the relay device 22, the terminal device 24 shown in FIG. 1, and the connection management device 13 (see FIG. 4) in the second embodiment described later all include one or more computers 980 shown in FIG. 2. In FIG. 2, the computer 980 includes a CPU 981, a storage unit 982, a communication I / F (interface) 983, an input / output I / F 984, and a media I / F 985. Here, the storage unit 982 includes a RAM 982a, a ROM 982b, and an SSD (Solid State Drive) 982c.

[0020] The communication I / F 983 is connected to a communication circuit 986. The input / output I / F 984 is connected to an input / output device 987. The media I / F 985 reads and writes data from and to a recording medium 988. The ROM 982b stores an IPL (Initial Program Loader) or the like executed by the CPU. The SSD 982c stores application programs, various data, and the like. The CPU 981 realizes various functions by executing application programs and the like read from the SSD 982c into the RAM 982a.

[0021] <Operation of the First Embodiment> When the user of the terminal device 24 wishes to distribute any of the video signals V-1 to V-N, a distribution request signal DM specifying the desired video signal V-k (where 1 ≤ k ≤ N) is transmitted to the relay device 22 via the public network 20. The relay device 22 stores the received distribution request signal DM.

[0022] The distribution device 12-1 has a function of managing the connection relationship between the relay device 22 and each distribution device 12, in addition to the function of distributing the video signal V-1. That is, the distribution device 12-1 transmits an inquiry signal IQ to the relay device 22 at a predetermined cycle via the NAT device 16. This inquiry signal IQ is a signal for inquiring whether the relay device 22 has received any distribution request signal DM. When the relay device 22 receives the inquiry signal IQ, it outputs a response signal AS to the distribution device 12-1 via the NAT device 16.

[0023] The response signal AS is a signal indicating whether a new distribution request signal DM has been received after the timing when the relay device 22 last transmitted the response signal AS. Further, when the distribution request signal DM is received, the response signal AS includes information specifying one or more video signals V for which distribution is requested. When the distribution device 12-1 receives the response signal AS, it determines whether any video signal V is specified in the response signal AS. Then, when the designation of the video signal V-1 is included in the response signal AS, a distribution command VC for instructing the output of the video signal V-1 is supplied to the video transmission unit 126 in its own device. Also, when any designation among the video signals V-2 to V-N is included in the response signal AS, a distribution command VC for instructing the output of the video signal V is output to the corresponding one of the distribution devices 12-2 to 12-N.

[0024] The distribution device 12-k (where 1 ≤ k ≤ N) that has received the distribution command VC transmits a connection request to the relay device 22 via the NAT device 16. As a result, a new connection is established between the distribution device 12-k and the relay device 22. Also, the relay device 22 transmits a connection request to the terminal device 24. As a result, a new connection is established between the relay device 22 and the terminal device 24. Next, the distribution device 12-k distributes the video signal V-k to the terminal device 24 via the relay device 22 by means of these newly established connections.

[0025] Figure 3 is a flowchart showing an example of the process executed in the first embodiment. In step S2 of Figure 3, the distribution device 12-1 transmits an inquiry signal IQ to the relay device 22. Here, it is assumed that the relay device 22 has not received a new distribution request signal DM after the timing (not shown) when it last transmitted the response signal AS. In this case, in step S4, the relay device 22 transmits a response signal AS indicating that there is no distribution request to the distribution device 12-1.

[0026] Thereafter, in step S10, it is assumed that a distribution request signal DM for requesting distribution of the video signal V-3 is transmitted from the terminal device 24 to the relay device 22. In this case, the relay device 22 stores this distribution request signal DM. Thereafter, in step S12, it is assumed that the distribution device 12-1 transmits an inquiry signal IQ to the relay device 22 again.

[0027] In this case, the relay device 22 has received a new distribution request signal DM in step S10 after the timing (step S4) when the response signal AS was transmitted last time. Therefore, in step S14, the relay device 22 transmits a response signal AS indicating that "there is a distribution request for the video signal V-3" to the distribution device 12-1.

[0028] When the distribution device 12-1 receives the response signal AS, it outputs a distribution command VC to the distribution device 12-3 corresponding to the specified video signal V-3 in step S20. When this distribution command VC is supplied, the distribution device 12-3 transmits a connection request to the relay device 22 in step S22. Thereby, a new connection is established between the distribution device 12-3 and the relay device 22.

[0029] Next, in step S24, the relay device 22 transmits a connection request to the terminal device 24. Thereby, a new connection is established between the relay device 22 and the terminal device 24. Next, in step S26, the distribution device 12-3 distributes the video signal V-3 to the terminal device 24 via the relay device 22 by means of these newly established connections.

[0030] [Second Embodiment] FIG. 4 is a block diagram of a video distribution system 102 according to the second embodiment. In the following description, parts corresponding to those of the first embodiment described above may be denoted by the same reference numerals and the description thereof may be omitted. The video distribution system 102 includes, similar to the video distribution system 101 of the first embodiment, a plurality of (N units) cameras 14-1 to 14-N, distribution devices 12-1 to 12-N, a NAT device 16, and a relay device 22. Further, the video distribution system 102 includes a connection management device 13 (computer).

[0031] Similar to that of the above-described first embodiment, the distribution device 12-1 has a function of distributing the video signal V-1. However, in the second embodiment, the connection management device 13 is responsible for the function of managing the connection relationship between the relay device 22 and each distribution device 12. That is, in this embodiment, the configuration of the distribution device 12-1 is the same as the functions of the other distribution devices 12-2 to 12-N, and includes the above-described distribution command receiving unit 124 and video transmission unit 126.

[0032] On the other hand, the distribution device 12-1 of this embodiment is not provided with an inquiry signal transmission unit 132, a response signal reception unit 134, and a distribution command transmission unit 136, and these components are included in the connection management device 13. Accordingly, the inquiry signal transmission unit 132 provided in the connection management device 13 repeatedly transmits an inquiry signal IQ to the relay device 22 at a predetermined cycle via the NAT device 16. When the relay device 22 receives the inquiry signal IQ, it outputs a response signal AS to the connection management device 13 via the NAT device 16.

[0033] The response signal reception unit 134 of the connection management device 13 receives the response signal AS. And when any video signal V-k (where 1 ≤ k ≤ N) is specified in the response signal AS, the distribution command transmission unit 136 of the connection management device 13 outputs a distribution command VC for instructing the distribution of the video signal V-k to the corresponding distribution device 12-k. The configuration of the video distribution system 102 other than that described above is the same as that of the video distribution system 101 of the first embodiment (see FIG. 1).

[0034] The operation of the second embodiment is the same as that of the first embodiment (see Fig. 3). However, in the second embodiment, the communication in steps S2, S4, S12, and S14 is the communication between the connection management device 13 and the relay device 22. Also, in step S20, the transmission source that transmits the distribution command VC to the distribution device 12-3 is the connection management device 13.

[0035] [Comparative Example] Next, in order to clarify the effects of this embodiment, a comparative example will be described. This comparative example applies the technology described in the above-mentioned Patent Document 1. The hardware configuration of the comparative example is the same as that of the first embodiment described above (see Fig. 1). However, in this comparative example, the distribution devices 12-1 to 12-N are different in that they output inquiry signals IQ-1 to IQ-N (see Fig. 5) to the relay device 22 respectively. The inquiry signals IQ-1 to IQ-N in this comparative example are signals that individually inquire whether there is a distribution request for each video signal V-1 to V-N. Also, the relay device 22 outputs response signals AS-1 to AS-N in response to each of the inquiry signals IQ-1 to IQ-N.

[0036] Fig. 5 is a flowchart showing an example of the process executed in this comparative example. In step S102 of Fig. 5, the distribution device 12-1 transmits an inquiry signal IQ-1 to the relay device 22. Here, it is assumed that the relay device 22 has not received a new distribution request signal DM for the video signal V-1 since the timing (not shown) of the previous transmission of the response signal AS-1. In this case, in step S104, the relay device 22 transmits a response signal AS-1 indicating that "there is no distribution request for the video signal V-1" to the distribution device 12-1.

[0037] After that, similarly, in steps S106 to S122, the distribution device 12-k (where 2 ≤ k ≤ N) transmits an inquiry signal IQ-k to the relay device 22. Here, it is assumed that the relay device 22 has not received a new distribution request signal DM for the video signal V-k after the timing (not shown) of transmitting the response signal AS-k last time. In this case, the relay device 22 transmits a response signal AS-k indicating that "there is no distribution request for the video signal V-k" to the distribution device 12-k.

[0038] Thereafter, in step S130, it is assumed that a distribution request signal DM for requesting the distribution of the video signal V-3 is transmitted from the terminal device 24 to the relay device 22. In this case, the relay device 22 stores this distribution request signal DM. Thereafter, in step S132, it is assumed that the distribution device 12-3 transmits an inquiry signal IQ-3 to the relay device 22 again.

[0039] In this case, the relay device 22 has received a new distribution request signal DM for requesting the distribution of the video signal V-3 in step S130 after the timing (step S110) of transmitting the response signal AS-3 last time. Therefore, in step S134, the relay device 22 transmits a response signal AS-3 indicating that "there is a distribution request for the video signal V-3" to the distribution device 12-3.

[0040] When the distribution device 12-3 receives this response signal AS-3, it distributes the video signal V-3 using the same connection as the connection used in steps S132 and S134. That is, the distribution device 12-3 distributes the video signal V-3 to the terminal device 24 via the relay device 22.

[0041] Thus, in this comparative example, each of the distribution devices 12-1 to 12-N exchanges inquiry signals IQ-1 to IQ-N and response signals AS-1 to AS-N with the relay device 22. For this reason, when the number (N) of video signals V that can be selected by the relay device 22 is large, there is a problem that the traffic of the inquiry signal IQ and the response signal AS increases between the distribution device 12 and the relay device 22.

[0042] [Effect of Embodiment] According to the first and second embodiments described above as described above, the video distribution systems 101 and 102 are a first network (18), a second network (20), and a NAT device 16 inserted between the first and second networks 18 and 20 for mutually converting a first address PA in the first network (18) and a second address GA in the second network (20), and a plurality of distribution devices 12 each transmitting a video signal V a distribution request receiving unit 222 that receives a distribution request signal DM for requesting distribution of any video signal V from the terminal device 24 via the second network (20), a query signal receiving unit 224 that receives a query signal IQ for inquiring whether the distribution request signal DM has been received, and an answer signal transmitting unit 226 that returns an answer signal AS indicating whether the distribution request signal DM is being received and designating the video signal V for which distribution has been requested if it is being received, in response to the query signal IQ, and a video signal transfer unit 228 that receives the video signal V corresponding to the distribution request signal DM from any one of the distribution devices 12 and transmits it to the terminal device 24 via the second network (20). a query signal transmitting unit 132 that repeatedly transmits a query signal IQ to the relay device 22, an answer signal receiving unit 134 that receives an answer signal AS from the relay device 22, and a distribution command transmitting unit 136 that transmits a distribution command VC for commanding distribution of the video signal V to the distribution device 12 that outputs the designated video signal V when any video signal V is designated in the answer signal AS.

[0043] Thus, the answer signal transmitting unit 226 of the relay device 22 in each embodiment returns an answer signal AS designating the video signal V for which distribution has been requested, in response to the query signal IQ. Further, the distribution command transmitting unit 136 of the connection management device (12-1, 13) transmits a distribution command VC for commanding distribution of the video signal V to the distribution device 12 that outputs the designated video signal V. Thereby, traffic between the relay device 22 and the distribution device 12 can be suppressed, and appropriate video distribution can be realized.

[0044] [Modification Example] The present invention is not limited to the above-described embodiments, and various modifications are possible. The above-described embodiments are examples for easy understanding and explanation of the present invention, and are not necessarily limited to those having all the configurations described. Also, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, a part of the configuration of each embodiment can be deleted, or additional or replacement of other configurations is possible. Also, the control lines and information lines shown in the figures indicate those considered necessary for explanation, and do not necessarily show all the control lines and information lines required on the product. In fact, it may be considered that almost all the configurations are interconnected. Possible modifications to the above embodiments are, for example, as follows.

[0045] (1) Since the hardware of the distribution device 12, the connection management device 13, and the relay device 22 in the above embodiment can be realized by a general computer, a program for executing the processing corresponding to each of the above flowcharts and other various processes described above, etc. may be stored in a storage medium (a computer-readable recording medium recording the program), or distributed via a transmission path.

[0046] (2) The SSD 982c in the computer 980, which is provided in all of the distribution device 12, the connection management device 13, the relay device 22, and the terminal device 24 in the above embodiment, may be replaced with a storage medium such as a magnetic disk such as an HDD (Hard Disk Drive), a flash memory such as a USB flash drive or a memory card, an optical disk such as a CD (Compact Disc) or a DVD (Digital Versatile Disc), or a magnetic tape such as an LTO (Linear Tape-Open). Also, one computer 980 may be provided with a plurality of storage media by combining these storage media.

[0047] (3) Although the processing corresponding to each of the above block diagrams and each flowchart, and other various processes described above were described as software processing using a program in the above embodiment, part or all of them may be replaced with hardware processing using an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array).

[0048] (4) In each of the above embodiments, each distribution device 12-1 to 12-N outputs one system of video signals V-1 to V-N, but one distribution device 12 may output a plurality of systems of video signals V.

[0049] (5) In each of the above embodiments, each distribution device 12-1 to 12-N is connected to one camera 14-1 to 14-N, respectively, but one distribution device 12 may be connected to a plurality of cameras 14.

[0050] (6) In each of the above embodiments, the camera 14 connected to the distribution device 12 is not limited to a camera for monitoring purposes, but may also be a camera provided in a portable information terminal, a wearable camera that can be worn on the body by wearing it on a helmet or goggles, a camera provided in a drone (an unmanned aircraft capable of remote control or autonomous flight), an in-vehicle camera mounted on a vehicle, etc.

[0051] (7) In each of the above embodiments, the video signals V-1 to V-N were captured by the camera 14, but the video signals V-1 to V-N may be, for example, recorded video.

Explanation of Reference Numerals

[0052] 12 Distribution device (computer) 12-1 Distribution device (computer, connection management device) 13 Connection management device (computer) 16 NAT device 18 Private Network (First Network) 20 Public Network (Second Network) 22 Relay Device (Computer) 24 Terminal Device 101, 102 Video Distribution System 132 Inquiry Signal Transmitter (Inquiry Signal Transmission Process) 134 Response Signal Receiver (Response Signal Reception Process) 136 Distribution Command Transmitter (Distribution Command Transmission Process) 222 Distribution Request Receiver (Distribution Request Reception Process) 224 Inquiry Signal Receiver (Inquiry Signal Reception Process) 226 Response Signal Transmitter (Response Signal Transmission Process) 228 Video Signal Transfer Unit (Video Signal Transfer Process) V Video Signal AS Response Signal DM Distribution Request Signal PA First Address (Private IP Address) GA Second Address (Global IP Address) IQ Inquiry Signal VC Distribution Command

Claims

Claim 1 A plurality of distribution devices each transmitting a video signal, via a first network, a second network, and a NAT device inserted between the first and second networks for performing mutual conversion between a first address in the first network and a second address in the second network; A relay device comprising: a distribution request receiving unit that receives, via the second network, a distribution request signal for requesting distribution of any one of the video signals from a terminal device; an inquiry signal receiving unit that receives an inquiry signal for inquiring whether the distribution request signal has been received; an answer signal transmitting unit that returns, in response to the inquiry signal, an answer signal indicating whether the distribution request signal has been received and specifying the video signal requested for distribution if received; and a video signal transfer unit that receives the video signal corresponding to the distribution request signal from any one of the distribution devices and transmits the video signal to the terminal device via the second network; A connection management device comprising: an inquiry signal transmitting unit that repeatedly transmits the inquiry signal to the relay device; an answer signal receiving unit that receives the answer signal from the relay device; and a distribution command transmitting unit that transmits, to the distribution device that outputs the specified video signal if any one of the video signals is specified in the answer signal, a distribution command for commanding distribution of the video signal. A video distribution system characterized by the above. Claim 2 A video signal transfer unit that, when receiving the video signal from any one of a plurality of distribution devices each transmitting a video signal via a first network, a second network, and a NAT device inserted between the first and second networks for performing mutual conversion between a first address in the first network and a second address in the second network, transfers the received video signal to a terminal device; A distribution request receiving unit that receives, via the second network, a distribution request signal for requesting distribution of any one of the video signals from the terminal device; An inquiry signal receiving unit that receives an inquiry signal for inquiring whether the distribution request signal has been received; An answer signal transmitting unit that returns, in response to the inquiry signal, an answer signal indicating whether the distribution request signal has been received and specifying the video signal requested for distribution if received. A relay device characterized by the above. Claim 3 A query signal transmission unit that repeatedly transmits a query signal for inquiring whether a relay device has received a distribution request signal for requesting distribution of any one of a plurality of video signals via a first network, a second network, and a NAT device inserted between the first and second networks for performing mutual conversion between a first address in the first network and a second address in the second network. An answer signal receiving unit that receives, from the relay device, an answer signal indicating whether the distribution request signal has been received in response to the query signal, and specifying the video signal for which distribution has been requested if the answer signal has been received. A distribution command transmission unit that, when any one of the video signals is specified in the answer signal, transmits a distribution command for instructing distribution of the video signal to a distribution device that is connected to the first network and outputs the specified video signal. A connection management device characterized by the above.

4. A video signal transfer process of transferring a received video signal to a terminal device when the video signal is received from any one of a plurality of distribution devices each transmitting a video signal via a first network, a second network, and a NAT device inserted between the first and second networks for performing mutual conversion between a first address in the first network and a second address in the second network. A distribution request receiving process of receiving a distribution request signal for requesting distribution of any one of the video signals from the terminal device via the second network. A query signal receiving process of receiving a query signal for inquiring whether the distribution request signal has been received. Causing a computer to execute an answer signal transmission process of returning, in response to the query signal, an answer signal indicating whether the distribution request signal has been received and specifying the video signal for which distribution has been requested if the answer signal has been received. A relay method characterized by the above.

5. A query signal transmission process of repeatedly transmitting a query signal for inquiring whether a relay device has received a distribution request signal for requesting distribution of any one of a plurality of video signals via a first network, a second network, and a NAT device inserted between the first and second networks for performing mutual conversion between a first address in the first network and a second address in the second network. An answer signal receiving process of receiving, from the relay device, an answer signal indicating whether the distribution request signal is received in response to the inquiry signal, and specifying the video signal for which the distribution is requested if the answer signal is received; When any of the video signals is specified in the answer signal, a distribution command transmitting process of transmitting a distribution command for instructing distribution of the video signal to a distribution device connected to the first network and outputting the specified video signal, to cause a computer to execute; A connection management method characterized by the above.

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