Abstract:
A network system according to the present invention comprises an IP encoder connected with a plurality of clients through a network. The IP encoder compresses and encodes inputted video information, forms a packet comprising the compressed and encoded video information, and multicasts the formed video information to the plurality of clients.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a network system and, more particularly, to a network system for distributing video (movie) information to clients through a network.  
           [0003]    2. Description of the Related Art  
           [0004]    In the field of a conventional monitor system using a network, when a video is shot by a camera is distributed to a plurality of clients, a video signal (video information) transmitted from the camera is temporarily stored in a storage device of a server. Thereafter, the server distributes the stored video information to each of the clients through the network.  
           [0005]    In the monitor system, display contents in a client require real-time properties. More specifically, a delay time from when a video is shot to when the video is displayed on the display device of the client is preferably short.  
           [0006]    However, the conventional technique has the following problem. More specifically, in the conventional technique, a server unitarily stores pieces of video information from a plurality of cameras in a storage device and, at the same time, distributes the video information stored in the storage device to a plurality of clients. For this reason, an amount of data per unit time which can be stored in the storage device by the server is limited. In addition, since the server executes a storing process and a distributing process at the same time, a processing load on the server is large, and an amount of data per unit time which can be distributed by the server is limited. Therefore, the length of the delay time when from the video is shot to when the video is displayed can not neglect.  
           [0007]    In addition, in the conventional technique, the clients request the server to redistribute the stored video information as needed. For the requests, the server executes a process for redistributing the video information, a load on the server increases, and the speeds of the storing process and the distributing process decrease. As a result, the delay time from the shooting to the displaying lengthen.  
         SUMMARY OF THE INVENTION  
         [0008]    It is an object of the present invention to provide a network system which can make a time for distributing video information to clients shorter than that of a conventional system.  
           [0009]    The first aspect of the present invention employs the following configuration to achieve the above object. More specifically, the present invention is a network system for distributing video information to a plurality of clients comprising a network for accommodating the plurality of clients, and an encoder connected to the network, wherein the encoder comprises a compression coding unit compressing and encoding to input video information, a packet forming unit forming a packet comprising the video information which is compressed and encoded, and a transmission unit multicasting the formed packet to the plurality of clients through the network.  
           [0010]    According to the present invention, since the video information is transmitted to the clients without being temporarily stored by a video server, display delay caused by a conventional storing process by a server does not occur. Therefore, a time from when the video information is acquired to when the video information is displayed can be shortened, real-time properties which can obtain a display more proper than that of a conventional system can be secured.  
           [0011]    In the present invention, part or all of the video information stored in the storage device may be stored by another storage device. The other storage device is a video server which is connected to the network, collects and stores the video information stored in the storage device, and distributes the stored video information at requests from clients.  
           [0012]    According to the present invention, the compression coding unit of the encoder may compress and encode a plurality of input video signals (a plurality of video information). More specifically, the compression coding unit may compress and encode to a plurality of video signals outputted from a certain video input device, and may compress and encode a plurality of video signals respectively transmitted from a plurality of video input devices.  
           [0013]    The second aspect of the present invention is a network system for distributing video information to a plurality of clients, comprising: an encoder compressing and encoding inputted video information, forming a packet comprising the compressed and encoded, and transmitting the formed packet to a network; and a concentrater accommodating the plurality of clients through communication lines, receiving the packet transmitted by the encoder through the network, and muluticasting the received packet to the plurality of clients.  
           [0014]    The third aspect of the present invention is an encoder for distributing video information to a plurality of clients through a network, comprising: a compression coding unit compressing and encoding inputted video information; a packet forming unit forming a packet comprising the compressed and encoded video information; and a transmission unit multicasting the formed packet to the plurality of clients. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a diagram of the entire configuration of a network system according to an embodiment.  
         [0016]    [0016]FIGS. 2A and 2B are diagrams of IP encoders shown in FIG. 1.  
         [0017]    [0017]FIG. 3 is an illustration showing a display example of a live screen.  
         [0018]    [0018]FIG. 4 is an illustration showing a display example of a video-on-demand screen.  
         [0019]    [0019]FIG. 5 is an illustration showing a display example of a video-on-demand screen.  
         [0020]    [0020]FIG. 6 is a diagram for explaining an operation example of in the network system shown in FIG. 1.  
         [0021]    [0021]FIG. 7 is a diagram for explaining an operation example of an on-demand display in the network system shown in FIG. 1.  
         [0022]    [0022]FIG. 8 is a diagram showing another configuration of a network system. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0023]    A preferred embodiment of the present invention will be described below with reference to the accompanying drawing.  
         [0024]    [Entire Configuration of Network System] 
         [0025]    [0025]FIG. 1 is a diagram of the configuration of a network system according to the embodiment of the present invention. The network system shown in FIG. 1 is used as a monitor system for monitoring video images photographed by a plurality of cameras C 1  to C 4  (corresponding to video input devices according to the present invention) by first clients  1  to  3 .  
         [0026]    The concrete configuration is as follows. The first clients  1  to  3  are accommodated in a LAN (100 BASE-TX: corresponding to the network according to the present invention)  7 . The LAN  7  also accommodates a video server  8  (corresponding to another storage device according to the present invention), a management system (corresponding to the management device according to the present invention)  9 , and a distribution server  10 . The LAN  7 , the first clients  1  to  3 , the video server  8 , the management system  9 , and the distribution server  10  constitute a center system in the monitor system.  
         [0027]    The LAN  7  accommodates IP encoders  11  to  14  (corresponding to the encoder according to the present invention), and video images (video information) from the cameras C 1  to C 4  are distributed to the first clients  1  to  3  through the LAN  7 .  
         [0028]    The IP encoder  11  is connected to the camera C 1  through a CODEC  15  and a WAN (e.g., INS64 or DA128)  16 . The IP encoder  12  is connected to the camera C 2  through a CODEC  17  and a WAN  16  (corresponding to another network according to the present invention). The IP encoder  13  is connected to a camera C 3  through a video signal transmission network (video signal transmission network)  18 . The IP encoder  14  is connected to the camera C 4  through the video signal transmission network  18 .  
         [0029]    The distribution server  10  is connected to second clients  4  to  6  through the Internet  19 . The constituent elements shown in FIG. 1 will be independently described below.  
         [0030]    &lt;Camera&gt; 
         [0031]    The cameras C 1  to C 4  are arranged at specific monitoring positions to photograph events occurring at the monitoring positions. For example, when the monitor system according to the embodiment is used as a monitor system for a traffic state, the cameras C 1  to C 4  are arranged at junctions or the like, respectively.  
         [0032]    Each of the cameras C 1  to C 4  has a microphone and a loudspeaker, and outputs an NTSC signal including a photographed video image (video) and a sound.  
         [0033]    The NTSC signal output from the camera C 1  is input to the CODEC  15 , and the NTSC signal output from the camera C 2  is input to the CODEC  17 . On the other hand, the NTSC signals output from the cameras C 3  and C 4  are received by the IP encoder  13  or the IP encoder  14  through the video signal transmission network  18 .  
         [0034]    &lt;CODEC&gt; 
         [0035]    The CODECs  15  and  17  convert the NTSC signal output from the camera C 1  or the camera C 2  into a transmission signal (to be referred to as an “H. 320 signal” hereinafter) based on a protocol of H. 320, and outputs the converted H. 320 signal. The H. 320 signals output from the CODECs  15  and  17  are received by the IP encoder  11  or the IP encoder  12  through the WAN  16 .  
         [0036]    &lt;IP Encoder&gt; 
         [0037]    [0037]FIG. 2A is a diagram of the configuration of each of the IP encoders  11  and  12  shown in FIG. 1. The IP encoder  11  will be described as an example. The IP encoder  11  comprises an interface circuit (I/F)  21  on the camera side, a CODEC  22  connected to the I/F  21 , an MPEG encoder  23  (corresponding to the compression coding unit according to the present invention) connected to the CODEC  22 , a packet forming unit  24  connected to the MPEG encoder  23 , an I/F  25  (corresponding to the transmission unit according to the present invention) on the LAN  7  side connected to the packet forming unit  24 , a hard disk drive (HDD: including a hard disk: corresponding to the storage device according to the present invention)  26 , and a control unit  29  including a CPU  27  and a main memory (MM)  28 .  
         [0038]    The CODEC  22  converts the H. 320 signal received from the WAN  16  through the I/F  21  into an NTSC signal to input the NTSC signal to the MPEG encoder  23 .  
         [0039]    The MPEG encoder  23  performs compression coding to the input NTSC signal to convert the NTSC signal into MPEG (MPEG  1  or MPEG  4 ) data (corresponding to video information). The MPEG data is input to the packet forming unit  24  and stored in the hard disk drive  26 .  
         [0040]    The packet forming unit  24  forms and outputs a packet including the MPEG data input from the MPEG encoder  23 . When the packet forming unit  24  distributes a video image photographed by the camera C 1  to the first clients  1  to  3  on real time, the packet forming unit  24  forms a UDP multicast packet including the MPEG data of the video images. On the other hand, when the packet forming unit  24  transfers the MPEG data stored in the HDD  26  to the video server  8 , the packet forming unit  24  forms a TCP packet including the MPEG data.  
         [0041]    The I/F  25  transmits the packet (UDP multicast packet or the TCP packet) input from the packet forming unit  24  to the LAN  7 .  
         [0042]    In this manner, the MPEG data of the video image photographed by the camera C 1  is multicasted without being temporarily stored. In this manner, a present video image (live video image) photographed by the camera C 1  is distributed to the first clients  1  to  3 . Therefore, the first clients  1  to  3  can display the live video image of the camera C 1  with a delay time which is shorter than that of a conventional system.  
         [0043]    The HDD  26  stores the MPEG data of a predetermined period of time (e.g., 2 hours) output from the MPEG encoder  23  while updating the MPEG data at any time. The MPEG data stored in the HDD  26  is transferred to the videoserver  8  at a predetermined timing.  
         [0044]    The control unit  29  is constituted by the CPU  27 , the MM  28 , a ROM (not shown), and the like. When the CPU  27  executes an operating system (OS) or a firmware recorded on the ROM to control a data format conversion process performed by the CODEC  22  and the MPEG encoder  23 , a packet forming process performed by the packet forming unit  24 , a write/read process of MPEG data performed by the HDD  26 , and the like.  
         [0045]    [0045]FIG. 2B is a diagram of the configuration of the IP encoder  13  shown in FIG. 1. The IP encoder  13  is the same as the IP encoder  11  except that the IP encoder  13  does not comprise the CODEC  22 . However, the IP encoder  13  does not transmit a TCP packet including the MPEG data stored in the HDD  26  to the video server  8 , and the IP encoder  13  forms a TCP packet including the MPEG data stored in the HDD  26  to transmit the TCP packet to the LAN  7  at a request of on-demand distribution from the first client  1 .  
         [0046]    The IP encoder  14  has the same configuration as that of the IP encoder  13  except that the IP encoder  14  does not comprise the HDD  26 . The IP encoder  14  performs only transmission (real-time distribution of a live video image) of a UDP multicast packet including MPEG data.  
         [0047]    In place of the above configuration, the MPEG data stored in the HDDs  26  of the IP encoders  11  and  12  may be designed to be distributed to the first clients on demand. The MPEG data stored in the HDD  26  of the IP encoder  13  may be designed to be transferred to the video server  8 . The IP encoder  14  may comprise the HDD  26 , so that the MPEG data stored in the HDD  26  is collected and stored by the video server  8  or distributed on demand to the first clients.  
         [0048]    The CODEC  22  is an option which is mounted when the IP encoder receives an H. 320 signal. The CODEC  22  is not required when the IP encoder receives an NTSC signal.  
         [0049]    In this embodiment, the MPEG encoder  23  is designed to convert an NTSC signal into MPEG data. However, the MPEG encoder  23  may be designed to convert an H. 261 signal into MPEG data.  
         [0050]    &lt;First Client&gt; 
         [0051]    Each of the first clients  1  to  3  is constituted by a personal computer (PC) comprising a display for displaying video images photographed by the cameras C 1  to C 4 , a workstation (WS), a computer corresponding to a host device.  
         [0052]    [0052]FIG. 3 is an illustration showing a display example of a live screen  31 . The live screen can be substantially united into one window-like user interface as shown in FIG. 3. In the window-like live screen  31  as described above, an image display unit which can display a video image at a desired point (area) and an operation unit (illustrated on the right side toward the screen in FIG. 3) comprising interactive function buttons. If necessary, a plurality of live screens  31  of different area video images to be displayed can be also opened (displayed).  
         [0053]    Each of the first clients  1  to  3  operates the plurality of function buttons arranged on the operation portion on the live screen  31  with a pointing device or the like, so that the display devices of various live screens  31  can be selected. More specifically, searching and selection of an area to be displayed, camera control operations such as enlargement/reduction of an area video image which is being displayed, movement of an image pickup angle, and adjustment of focus can be performed, past video images stored in the IP encoder (to be also described) or the video server  8  can be referred to, and write, edition, and the like of a comment document can be performed.  
         [0054]    Each of the first clients  1  to  3  has a video image distribution request function  34  (see FIG. 6). More specifically, each of the first clients  1  to  3  requests the management system  9  to perform real-time distribution of video images photographed by the cameras C 1  to C 4 .  
         [0055]    Each of the first clients  1  to  3  has a stream receiving function  35  (see FIG. 6). More specifically, the first clients  1  to  3  receive UDP multicast packets multicasted from the IP encoders  11  to  14 , and display video images based on MPEG data included in the packets on the live screen  31  (see FIG. 3) of the display. In this manner, a video image at a monitoring position is displayed on real time.  
         [0056]    The user of the first clients  1  to  3  refers to the displayed real-time video image, so that the user can monitor the present state of the monitoring position. Each of the first clients  1  to  3  comprises a loudspeaker for outputting a sound to output a sound obtained by -microphones held by the cameras C 1  to C 4  from the loudspeaker. The first clients  1  to  3  store the video images which are distributed on real time in the storage devices held by the first clients  1  to  3  as needed.  
         [0057]    The first client  1  has an on-demand operation function  39  (see FIG. 7). More specifically, the first client  1  requests the video server  8  to provide (on-demand distribution) desired MPEG data (video image) stored in the video server  8 . Thereafter, when the first client  1  receives the video image stored in the video server  8 , the video image is displayed on a video-on-demand screen  32  (VOD screen  32 : see FIG. 4) of the display. In this manner, the user of the first client  1  can refer to the past video image of the monitoring position.  
         [0058]    The first client  1  requests the on-demand operation function  39  to provide (on-demand distribution) of images (to be referred to as “library images”) edited and stored by the video server  8 . Thereafter, when the first client  1  acquires the library images stored in the video server  8 , the library images are on the VOD screen  32  (see FIG. 5).  
         [0059]    In addition, the first client  1  requests the on-demand operation function  39  to perform on-demand distribution of a desired video image stored in the HDD  26  of the IP encoder  13 . Thereafter, when the first client  1  acquires the desired video image stored in the HDD  26  of the IP encoder  13 , the video image is displayed on the VOD screen  32  (see FIG. 4) of the display device. In this manner, the user of the first client  1  can also refer to the past video image of the monitoring position. The first client  1  stores the video image or the library images subjected to on-demand distribution in the storage device held by the first client  1  as needed.  
         [0060]    When the user of the first client  1  requests on-demand distribution, the user designates a monitoring position or a camera and a photographing period (start time and end time) of the camera. In this case, a request message for on-demand distribution including the information of the camera and the photographing period is supplied from the first client  1  to the management system  9 . The management system  9  specifies a position where a corresponding video image is stored on the basis of the information of the camera and the photographing period, and acquires the corresponding video image from the specific position to give the video image to the first client In this example, when the first client  1  requests a video image of the camera C 1  or the camera C 2 , the management system  9  acquires a desired video image stored in the video server  8 . In contrast to this, when the first client  1  requires a video image of the camera C 3 , the management system  9  acquires a desired video image stored in the HDD  26  of the IP encoder  13 .  
         [0061]    The first client  1  can display the video images or the library images which are distributed to the live screen  31  on demand. In contrast to this, the first client  1  can display a video image subjected to stream distribution (real-time distribution) on the VOD screen  32 . In addition, the live screen  31  and the VOD screen  32  can also be displayed at once. In this manner, the user of the first client  1  can refer to a present video image, a past video image, and a library image at once.  
         [0062]    &lt;Video Server&gt; 
         [0063]    The video server  8  is constituted by using a computer comprising a storage device (not shown) such as an HDD functioning as an image database (image DB  82 : see FIGS. 6 and 7). The video server  8  has a correction/storage function (video storage function  81 : see FIG. 6) of MPEG data (video image) stored in the HDD  26  of the IP encoder.  
         [0064]    More specifically, the video server  8 , according to a predetermined schedule (e.g., a collection interval of 3 to 5 minutes) or an external trigger (e.g., an instruction from the management system  9  or the first client  1 ), requests the IP encoders  11  and  12  to transfer the MPEG data stored in the HDD  26 , and stores the MPEG data transferred at the request to the image DB  82  as a video image file. The schedule is formed by the management system  9  and registered on the video server  8 .  
         [0065]    The video server  8  has a video data edition function. More specifically, the video server  8  executes a cut process for images, a merge process, and a capture process for still images by using the video image file stored in the image DB  82 . The video server  8  also performs a superimpose process, a telop insertion process, an inter-media synchronization process (SMIL or the like), audio edition, frame adjustment, and the like if necessary. The video server  8  stores library images formed by an edition process using the video data edition function in the image DB  82  as a library image file.  
         [0066]    The video server  8  has an on-demand distribution function  85  (see FIG. 7). More specifically, the video server  8 , at a request from the management system  9  which receives an on-demand distribution request from the first client  1 , reads a corresponding video file or a corresponding library image file from the image DB  82  to distribute the file to the first client  1 .  
         [0067]    In place of the above configuration, the first clients  1  to  3  may directly request the video server  8  to perform on-demand distribution of the video file or the library image file stored in the image DB  82 .  
         [0068]    In addition, the video server  8 , at a request from the distribution server  10 , reads the corresponding video image file or the corresponding library image file from the image DB  82  to give the file to the distribution server  10 . At this time, the distribution server  10  the video image file or the library image file received from the video server  8  to the second clients  4  to  6  or any one of the second clients  4  to  6  through the Internet  19 .  
         [0069]    In this embodiment, all the video images temporarily stored in the HDDs  26  of the IP encoders  11  and  12  are stored in the video server  8 . However, when users of the first clients  1  who do not require video images older than video images of the period in which video images can be stored in the HDDs  26  of the IP encoders  11  and  12 , i.e., when it is satisfactory that the video images stored in the HDDs  26  of the IP encoders  11  and  12  are used, the video server  8  may not be arranged. Even in the above case, the video server  8  may be prepared to store a video image required for editing the library images or only a video image which is specially required.  
         [0070]    &lt;Management System&gt; 
         [0071]    The management system  9  is constituted by using a computer such as a PC or a WS. The management system  9  has a schedule forming/managing function. More specifically, the management system  9  forms a schedule of storage of video images to register the schedule in the video server  8 .  
         [0072]    In place of this configuration, the management system  9  may form schedules of MPEG data transfer performed by the IP encoders  11  and  12  to register the schedules in the IP encoders  11  and  12 . The IP encoders  11  and  12 , according to the registered schedules, may transfer the MPEG data stored in the HDDs  26  to the video server  8 .  
         [0073]    The management system  9  has a video image distribution request management function  51  (see FIG. 6) for performing communication management between the first clients  1  to  3  and the IP encoders  11  to  14 . More specifically, the management system  9  gives an instruction for transmitting a UDP multicast packet to the corresponding first client at request of stream distribution (real-time distribution) from the first clients  1  to  3  to a specific IP encoder. In this manner, the first client which requests stream distribution can receive the stream (UDP multicast packet) of video images from the specific IP encoder.  
         [0074]    The management system  9  instructs the IP encoders  11  to  14  to stop real-time-distribution to the specific first client at a request from the first client or as needed. For this reason, the IP encoder which receives the instruction stops real-time distribution the specific first client.  
         [0075]    As described above, the management system  9  controls stream distribution (real-time distribution) to the first clients  1  to  3  by the video image distribution request management function  51 . For this reason, a video image photographed by a certain camera can be prevented from being provided to a certain first client.  
         [0076]    The management system  9  has an on-demand management function  56  (see FIG. 7). More specifically, the management system  9  requests the video server  8  or the IP encoder  13  to supply stored MPEG data (video image file) or a library image file to the first client  1  in place of the management system  9  at a request of on-demand distribution from the first client  1  (representative request of distribution).  
         [0077]    In addition, the management system  9  controls on-demand distribution to the first clients  1  to  3  by the on-demand management function  56 . More specifically, the management system  9  can select a first client which receives a video image or a library image distributed on demand from the video server  8  or the IP encoder  13  by the on-demand management function  56 .  
         [0078]    In this example, only the first client  1  is set to receive a video image or a library image distributed on demand. In addition, the setting of the first client  2  and/or the first clients  3  can be changed such that the first client  2  and/or the first client  3  receives a video image or the like distributed on demand. Video images stored in the HDDs  26  of the IP encoders  11  and  12  can also set to be distributed to the first clients  1  to  3  or at least one of the first clients  1  to  3  on demand.  
         [0079]    When the management system  9  is set to receive on-demand distribution request messages from a plurality of first clients, and the management system  9  simultaneously receive the plurality of distribution request messages, the management system  9  executes a process for the distribution requests in the order based on priority information included in these messages. More specifically, the management system  9  extracts pieces of priority information from the messages and executes a process (representative request of distribution) to the distribution request in the order of priority.  
         [0080]    The management system  9  limits a video image or an image supplied from the video server  8  to the distribution server  10 . More specifically, the management system  9  gives an instruction that only a specific type of video image or image to the distribution server  10  to the video server  8 . At this time, the video server  8  receives the provided request only when the type of video image or image which is distributed by the distribution server  10  to be provided is a specific type instructed by the management system  9 .  
         [0081]    In place of the above configuration, on-demand distribution of video images stored in the video server  8  or the HDD  26  may be performed to the first clients  2  and  3 , and the video image stored in the HDD  26  of the IP encoder  13  may be collected and stored in the video server  8 . In this case, when each of the first clients  1  to  3  gives the on-demand distribution request message to the management system  9 , the management system  9  generates a representative request of distribution as follows on the basis of photographing time designated by the message.  
         [0082]    More specifically, when a desired video image is stored in only the HDD  26  of the IP encoder, the management system  9  gives the representative request of distribution to the corresponding IP encoder. In contrast to this, when the desired video image is stored in only the video server  8 , and when the desired video image is stored in the HDD  26  and the video server  8 , the management system  9  gives a representative request of distribution to the video server  8 .  
         [0083]    In this manner, when the first clients  1  to  3  give on-demand distribution request messages to the management system  9 , the first clients  1  to  3  can receive a desired video image without considering a storage position of the desired video image.  
         [0084]    The function of the management system  9  is given to the video server  8 , so that the management system  9  can also be omitted. However, in order to reduce the processing load on the video server  8 , the management system  9  is arranged independently of the video server  8 .  
         [0085]    &lt;Distribution Server&gt; 
         [0086]    The distribution server  10  is arranged by using a computer. The distribution server  10  functions as the proxy server of the second clients  4  to  6  connected through the Internet  19 .  
         [0087]    More specifically, at requests from the second clients  4  to  6 , the distribution server  10  receives a video image or image corresponding to the request from the video server  8  to transmits the video image or the image to the corresponding second client.  
         [0088]    When a request from any one of the second clients  4  to  6  is made by the setting of the distribution server  10  or an external trigger, the distribution server  10  acquires a video image or an image corresponding to the request to multicast the video image or the image to the second clients  4  to  6 .  
         [0089]    The distribution server  10 , by the setting of the distribution server  10  or an external trigger, receives a specific kind of image from the video server  8  according to a predetermined schedule and transmits each of the second clients  4  to  6  or any one of the second clients  4  to  6 .  
         [0090]    The distribution server  10  stops distribution of a video image or an image corresponding to a specific second client according to an external trigger (e.g., an instruction from the management system  9 ).  
         [0091]    In place of the above configuration, the following configuration may be used. That is, the distribution server  10  receives a video image stored in the HDD of an IP encoder to transmit the video image to the second client.  
         [0092]    &lt;Second Client&gt; 
         [0093]    Each of the second clients  4  to  6  is constituted by a PC, a WS, a mobile computer or the like comprising a display. Each of the second clients  4  to  6  requests the distribution server  10  to distribute a video image, so that each of the second clients  4  to  6  receives video images of the cameras C 1  to C 4  stored in the video server  8  to display the video images on the display.  
         [0094]    &lt;Other&gt; 
         [0095]    In the network system shown in FIG. 1, the first client  1  executes control (pan adjustment of a camera, tilt adjustment, and volume adjustment of a microphone and a loudspeaker) of the cameras C 1  and C 3 .  
         [0096]    More specifically, the first client  1  operates a monitor screen to request the management system  9  to control the camera C 1 . A this time, the management system  9  outputs a control signal for the camera C 1 . The output control signal is input to the camera C 1  through the LAN  7  and the CODEC  22 , the WAN  16 , and the CODEC  15  of the IP encoder  11 , and an operation depending on the control signal is executed in the camera C 1 .  
         [0097]    When the first client  1  requests the management system  9  to control the camera C 3 , a control signal from the management system  9  is input to the camera C 3 , and the camera C 3  operates on the basis of the control signal.  
         [0098]    [Operation in Network System] 
         [0099]    An operation in the network system will be described below.  
         [0100]    &lt;Live Video Image Display&gt; 
         [0101]    [0101]FIG. 6 is a diagram for explaining an operation example of a live video image display and video storage in the network system shown in FIG. 1. In FIG. 6, as the operation example, an example in which-a video image photographed by the camera C 1  is displayed as a live video image (real-time display) by the first client  1 .  
         [0102]    As shown in FIG. 6, when the live video image is displayed, the first client  1  functions as a device comprising the video image distribution request function  34 , the stream receiving function  35 , a browser  36 , a network interface (I/F)  37  to the LAN  7 , an MPEG viewer  38 , and a cameral control function such that a processor (not shown) (e.g., a CPU) held by the first client  1  executes a program.  
         [0103]    The management system  9  functions as a device comprising the video image distribution request management function  51 , a network interface (I/F)  52  to the LAN  7 , a WWW server  53 , a DBMS  54 , management information  55 , a camera operation information management function, and a camera control right management function such that a processor (not shown) (e.g., a CPU) held by the management system  9  executes a program.  
         [0104]    In addition, the IP encoder  11  functions as a device comprising I/Fs  21  and  25 , the HDD  26 , a stream distribution function  41 , a video storage function  42 , and a camera control function such that the CPU  27  executes a program.  
         [0105]    The stream distribution function  41  is realized by the CODEC  22 , the MPEG encoder  23 , the packet forming unit  24 , and the control unit  29 , and the video storage function  42  is realized by the packet forming unit  24 , the HDD  26 , and the control unit  29 .  
         [0106]    At the first, a user of the first client  1  inputs a video image distribution request of the camera C 1  to the first client  1 . At this time, the video image distribution request function  34  forms a real-time distribution request message of a video image photographed by the camera C 1  and transmits the real-time distribution request message from the I/F  37  to the management system  9 . The transmitted request message is received by the I/F  52  of the management system  9  through the LAN  7  to give the request message to the video image distribution request management function  51 .  
         [0107]    In this case, the video image distribution request management function  51  refers to the management information  55  to check whether the video image distribution request management function  51  may accept the request from the first client  1  or not. The video image distribution request management function  51  accepts the request, the video image distribution request management function  51  updates the management information  55  by the check result.  
         [0108]    Thereafter, the video image distribution request management function  51  transmits a real-time distribution request message from the I/F  52  to the IP encoder  11 . The transmitted request message is received by the I/F  25  of the IP encoder through the LAN  7  and received by the stream distribution function  41 .  
         [0109]    In this case, the stream distribution function  41  adds the address of the first client  1  to the destination address of a UDP multicast packet transmitted to the LAN  7 . Thereafter, when the H. 320 signal of a video image photographed by the camera C 1  is input to the I/F  21 , the stream distribution function  41  forms a UDP multicast packet including MPEG data corresponding to the H. 320 signal to multicast the UDP multicast packet from the I/F  25  to the LAN  7 . The multicasted UDP multicast packet is received by the I/F  37  of the first client  1  and input to the stream receiving function  35  through the browser  36 .  
         [0110]    In this case, the stream receiving function  35  extracts the MPEG data from the UDP multicast packet to give the MPEG data to the MPEG viewer  38 . At this time, the MPEG viewer  38  displays a live video image of the camera C 1  based on the MPEG data on the live screen  31  which is displayed on the display in advance (see FIG. 3).  
         [0111]    In this manner, a user of the first client  1  refers to the video image which is lively displayed, so that the user can monitor an event occurring at a point (area) at which the camera C 1  is arranged.  
         [0112]    &lt;Video Storage&gt; 
         [0113]    An operation example of video storage in the network system shown in FIG. 1 will be described below with reference to FIG. 6. As shown in FIG. 6, in a video storage operation, a CPU (not shown) held by the video server  8  executes a program, so that the video server  8  functions as a device comprising a video storage function  81 , an image DB  82 , and I/Fs  83  and  84 .  
         [0114]    In FIG. 6, the stream distribution function  41  of the IP encoder  11  receives the H. 320 signal of the video image photographed by the camera C 1 , forms MPEG data corresponding to the received H. 320 signal, and gives the MPEG data to the video storage function  42 .  
         [0115]    In this case, the video storage function  42  stores the MPEG data received from the stream distribution function  41  in the hard disk in the HDD  26 . In this manner, the video image of the camera C 1  is stored in the HDD  26  of the IP encoder  11 .  
         [0116]    On the other hand, the video storage function  81  of the video server  8  is started according to a schedule which is recorded by the management system  9  in advance to form a MPEG data transfer request message. The formed request message is given to the video storage function  42  through the I/F  83 , the LAN  7 , and the I/F  25 .  
         [0117]    The video storage function  42  reads MPEG data to be transferred from the HDD  26 , forms a TCP packet including the read MPEG data, and transmits the TCP packet from the I/F  25  to the LAN  7 . The transmitted TCP packet is received by the I/F  83  of the video server  8  through the LAN  7  and given to the video storage function  81 .  
         [0118]    The video storage function  81  extracts the MPEG data from the TCP packet to store the MPEG data as a video image file in the image DB  82 . An operation similar to this is also performed between the video server  8  and the IP encoder  12 . Therefore, the MPEG data stored in the HDDs  26  by the IP encoders  11  and  12  are stored in the image DB  82  of the video server  8 .  
         [0119]    &lt;On-demand Display&gt; 
         [0120]    [0120]FIG. 7 is a diagram for explaining an operation example of an on-demand display in the network system shown in FIG. 1. FIG. 7 shows an operation example in which the first client  1  accepts on-demand distribution from the video server  8 .  
         [0121]    As shown in FIG. 7, in an on-demand display, the first client  1  functions as a device comprising the browser  36 , the I/F  37 , the MPEG viewer  38 , and the on-demand operation function  39 .  
         [0122]    The video server  8  functions as a device comprising the image DB  82 , the I/Fs  83  and  84 , the on-demand distribution function  85 , and a VOD server  87 . In addition, the management system  9  functions as a device comprising the I/F  52 , the WWW server  53 , the DBMS  54 , the management information  55 , the on-demand management function  56 , and a meta-data  57 .  
         [0123]    As a presumption, the VOD screen  32  shown in FIGS. 4 and 5 is displayed on the display of the first client  1 . A user of the first client  1  operates buttons displayed on the VOD screen  32  to execute a file selection operation or a stream operation.  
         [0124]    In this manner, the on-demand operation function  39  acquires specific information of a monitoring position (camera) designated by the user and information of a photographing period to form an on-demand distribution request message including the acquired information. The formed request message is transmitted to the LAN  7  through the browser  36  and the I/F  37  and received by the on-demand management function  56  through the I/F  52  and the WWW server  53  of the management system  9 .  
         [0125]    In this case, the on-demand management function  56  refers to the management information  55  and the meta-data  57  to specify a monitoring position included in the request message of the first client  1  and a storage position of a video image corresponding to the information of the photographing period. In this example, it is assumed that the video image is stored in the image DB  82  of the video server  8 .  
         [0126]    Thereafter, the on-demand management function  56  acquires data required to form a representative request message from the management information  55  and the metadata  57  and updates the management information  55  or the metadata  57  as needed.  
         [0127]    Thereafter, the on-demand management function  56  forms a representative request message of distribution of a video image or a library image to the video server  8  on the basis of information (information of a monitoring position and a photographing period) included in the message from the first client  1  and information obtained from the management information  55  and the metadata  57 .  
         [0128]    The formed representative request message is transmitted to the LAN  7  through the WWW server  53  and the I/F  52  and received by the on-demand distribution function through the I/F  84  of the video server  8 .  
         [0129]    In this case, the on-demand operation function  39  refers to the information included in the representative request message to detect a corresponding video image file (or a library image file) from the image DB  82 .  
         [0130]    The detected video file is transmitted from the on-demand distribution function  85  to the LAN  7  through the VOD server  87  and the I/F  84 . In this manner, on-demand distribution of a video image to the first client  1  is performed.  
         [0131]    The video file transmitted to the LAN  7  is received by the on-demand operation function  39  through the I/F  37  and the browser  36  of the first client  1 . At this time, the on-demand operation function  39  gives the received video image file to the MPEG viewer  38 .  
         [0132]    In this case, the MPEG viewer  38  displays a video image (past video image) based on the video image file in the VOD screen  32  displayed on the display device (file reception and stream display). In this manner, the user of the first client  1  can refer to a desired video image.  
         [0133]    [Operation of Embodiment] 
         [0134]    In the network system according to the embodiment of the present invention, information (video information) of video images photographed by the cameras C 1  to C 4  are multicasted from the IP encoders  11  to  14  to the first clients  1  to  3  without being temporarily stored.  
         [0135]    In this manner, unlike a conventional system, delay caused such that the video information is temporarily stored and then distributed does not occur. For this reason, a delay time from when a video image is photographed to when the video image is displayed by a client can be reduced in comparison with the conventional system.  
         [0136]    Therefore, a proper reaction faster than that of the conventional system can be made to an event occurring for the monitoring position. When video information is multicasted, the video information can be distributed to clients faster than distribution performed by repeating uni-casting to a plurality of destinations.  
         [0137]    When the HDDs  26  are arranged in the IP encoders  11  to  13 , unlike a conventional system, video images need not be simultaneously stored in a server. In addition, the video server  8  does not perform real-time distribution.  
         [0138]    In this manner, the processing load on the video server  8  is smaller than that of a conventional system. For this reason, when the video server  8  is requested to perform on-demand distribution, the processing load on the video server  8  does not increase unlike the conventional system. For this reason, a process for an on-demand distribution request is prevented from being delayed.  
         [0139]    In addition, when it is satisfactory that video images stored in the HDD  26  are used, the video server  8  for on-demand distribution of the video image is not necessary. For this reason, the cost required to construct a network system can be suppressed.  
         [0140]    The network system of the present invention can be constituted as the network configuration shown in FIG. 8. More specifically, the network system can be constituted as follows. That is, the camera C 1  and the IP encoder  11  are directly connected to each other, the IP encoder  11  is connected to a line concentrater (router)  19   a  through a network  16   a  (corresponding to another network in the second invention), and the line concentrater (router)  19   a  is connected to clients  1   a  to in constituting a center system and the LAN  7  accommodating the video server  8  and the management system  9 .  
         [0141]    In the network configuration shown in FIG. 8, when the IP encoder  11  is designed to store a video image photographed by the camera C 1  without any condition, the center system performs monitoring by a real-time display. When a user recognizes the occurrence of an event, the video image can be collected from the HDD  26  to the video server  8  in the IP encoder As described above, only a video image required for the video server  8  can be designed to be stored. For this reason, a network (LAN  7 ) used to collect video images can be efficiently used. More specifically, lines can be prevented from being continuously busy due to video image collection performed by a video server.  
         [0142]    In the network configuration shown in FIG. 8, unlike the network configuration shown in FIG. 1, the IP encoder  11  transmits video information including multicast designation to the line concentrater (router)  19   a,  and the router  19   a  multicasts the video information to the clients  1   a  to  1   n.