Patent Publication Number: US-2009241157-A1

Title: Content distribution system, band control mediating apparatus, and band control method

Description:
TECHNICAL FIELD 
     The present invention relates to a content distribution system, a band control mediating apparatus and a band control method for realizing QoS (quality of service) guaranteed in streaming distribution. 
     BACKGROUND ART 
     In order to realize a streaming distribution of video data and audio data, a method is conventionally employed in which a sufficient network band is reserved for the distribution and a distributed packet is given a priority and transmitted on a network with priority, compared with other data communications. In particular, as a typical method of reserving the network band, the following two methods are known: a first method of directly reserving a pre-estimated band on a network prior to the distribution regardless of individual bands required for actual distribution, and a second method of directly instructing a network to reserve a necessary band prior to the distribution from a client terminal or a server. Also, a third method achieved by improving the second method is known, in which a necessary band is acquired by the client terminal or the server through an SIP (Session Initiation Protocol) and reserved prior to the streaming distribution. 
     The first method has an advantage that a network band is reserved without special consideration to the server and the client terminal. However, it is presumed that distributed video data and audio data always consumes a same bandwidth, and therefore, when a band used by actually distributed video data and audio data is much less than the reserved band, a difference between the reserved band and the used band is wasted. 
     The second method has an advantage of having no waste because the reserved network band is equal to a used network band. However, special consideration is required in the client terminal or the server to reserve the network band, and an interface portion with the network is required to be disposed in the client terminal and the server and to be adapted to fit to the network, since compatibility is not sufficient. RSVP (Resource reSerVation Protocol) is known as a method of reserving a band from the client terminal. There is also a method described in Japanese Patent Application Publication (JP-P2003-51846A) which represents a method of reserving a band from the server. 
     As the second method is known a method described in Japanese Patent Application Publication (JP-P2005-12655A) (Method and system for guaranteeing QoS in CDN through SIP session control, terminal apparatus, content distribution subsystem, SIP session control subsystem, and program). In the Japanese Patent Application Publication (JP-P2005-12655A), SIP is used as a session control protocol between the terminal apparatus and a content distribution subsystem, and an SIP session control subsystem mediates information exchanged by using SIP. Therefore, it is unnecessary for the terminal device and the content distribution subsystem to directly control a band, and it is advantageously sufficient that a standard protocol is installed in the terminal apparatus and the content distribution subsystem. However, the method disclosed in the Japanese Patent Application Publication (JP-P2005-12655A) uses SIP which was originally developed for voice communication and has not been widely disseminated for the purpose of streaming distribution. For this reason, developers of the terminal apparatus and the content distribution subsystem owe a risk of usage of SIP with little precedent. Also, there is a drawback of additional development/operation costs caused by newly providing a function for SIP. Further, in the Japanese Patent Application Publication (JP-P2005-12655A), a band is reserved prior to communication by RTSP (Realtime Streaming Protocol) which is a reproduction control protocol in the content distribution subsystem. Accordingly, in case of the content distribution subsystem which does not correspond to SIP as shown in Japanese Patent Application Publication (JP-P2005-12655A), a band is to be reserved based on band data received from the terminal apparatus. Therefore, there is a drawback in that the reserved band does not necessarily coincide with the band necessary for actual content transmission by the content distribution subsystem. 
     Related arts related to the network band control are disclosed in Japanese Patent Application Publications (JP-P2000-32048A, JP-P2002-344499A, JP-P2003-258879A and JP-P2004-289627A). 
     However, these related arts need understanding of a special message for band reservation or band control between a client terminal and a server, in addition to complicated band control procedures. Therefore, the client and the server cannot control a band by using an existing protocol. 
     DISCLOSURE OF INVENTION 
     An object of the present invention is to provide a content distribution system, a band control mediating apparatus and a band control method in which a band control is performed in a network by using an existing protocol. 
     Another object of the present invention is to provide a content distribution system, a band control mediating apparatus and a band control method, in which a band control can be performed in a network without requiring complicated band control procedures. 
     Yet another object of the present invention is to provide a content distribution system, a band control mediating apparatus and a band control method, in which a band corresponding to a transferred data amount can be reserved. 
     The content distribution system according to the present invention includes a client terminal, a server, a band control mediating apparatus and a first band control device. The band control mediating apparatus is arranged between the client terminal and the server, and relays a reproduction control protocol data of content data from the client terminal to the server. The first band control device is arranged in a first network to control a band in the first network. The band control mediating apparatus here requests the first band control device to control the band for a communication path through which content data is transferred, based on the reproduction control protocol data in the first network. In response to this request, the first band control device reserves a band for the communication path. 
     Furthermore, it is preferable that the server in response to the content data transfer request transmits the network band data required for transferring the content data to the client terminal via the band control mediating apparatus. In this case, the band control mediating apparatus determines a band controlled in the first band control device on the basis of the network band data. 
     Furthermore, the band control mediating apparatus may be arranged in a first network to which the band control unit belongs. In this case, the band control mediating apparatus requests the band control unit to control the band in the network to which the band control mediating apparatus belongs. Moreover, the content distribution system according to the present invention may further include a second band control unit which controls a band in a second network. In this case, the band control mediating apparatus requests the second band control unit to control the band for a communication path through which content data is transferred, based on the reproduction control protocol data in the second network. At this time, when the band control mediating apparatus is arranged in the first network, it is capable of requesting a band control with respect to the first band control unit and the second band control unit arranged in the first network and the second network, respectively. 
     The band control mediating apparatus according to the present invention is arranged between the client terminal and the server and includes an I/O interface which relays a reproduction control protocol data of content data from the client terminal to the server, and a CPU for analyzing the reproduction control protocol data and determining a band for the communication path through which the content data is transferred. The CPU transmits a band control request corresponding to the determined band to the first band control unit which controls a band in the first network, via the I/O interface. 
     Furthermore, it is preferable that the CPU analyzes a network band data required to transfer the content data in response to a content data transfer request to determine a band. 
     It is further preferable that the CUP analyzes a network band data required to transfer the content data in response to the content data transfer request to specify a network being present on a communication path through which the content data is transferred. 
     The CPU may further transmit the band control request to the second band control unit which controls the band in the second network. 
     A band control method according to the present invention includes a band control mediating apparatus arranged between a client terminal and a server relaying a reproduction control protocol data of a content data from the client terminal to the server, the band control mediating apparatus analyzing the reproduction control protocol data and determining a band for a communication path through which the content data is transferred, and the band control mediating apparatus transmitting a band control request corresponding to the band to the first band control unit which controls the band in the first network. 
     Furthermore, it is preferable that the determining a band includes analyzing a network band data required to transfer the content data in response to the content data transfer request and determining the band. 
     Furthermore, it is preferable that the transmitting a band control request includes analyzing a network band data required to transfer the content data in response to a content data transfer request, to specify a network on a communication path through which the content data is transferred. 
     It is further preferable to include the band control mediating apparatus transmitting the band control request to the second band control unit which controls the band in the second network. 
     The band control method according to the present invention preferably includes, in addition to the above method, the first band control unit reserving a band for the communication path through which content data is transferred in the first network in accordance with the request for band control. 
     It is further preferable to include the first band control device releasing the band reserved for the communication path through which the content data is transferred, in response to the band control request. 
     The reproduction control protocol data according to the present invention is preferably the RTSP (Realtime Streaming Protocol)-data. In this case, the content data is transferred from the server to the client terminal via the communication path corresponding to an RTP (Realtime Transport Protocol). 
     As described above, according to the present invention, a control to reserve a band is performed only by the band control mediating apparatus without requiring a complicated band control procedure. Furthermore, the band control is carried out based on a protocol (i.e. RTSP here) which is widely used in the existing streaming reproduction control, whereby the band control mediating apparatus does not need to understand a special protocol and message. The band control mediating apparatus which relays RTSP communication further controls a band in a network, which makes it possible for the client and the server to use an existing protocol and interface. 
     The present invention further determines the band to reserve in accordance with a streaming distribution request, and thus it is made possible to reserve the band corresponding to the actually transferred content data without having a redundant band. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing a configuration of a content distribution system according to a first exemplary embodiment of the present invention; 
         FIG. 2  is a flowchart showing an operation of an RTSP proxy server according to the first exemplary embodiment of the present invention; 
         FIG. 3A  is a sequence diagram showing an operation of reserving a band in the content distribution system according to the first exemplary embodiment of the present invention; 
         FIG. 3B  is a sequence diagram showing an operation of content distribution in the content distribution system according to the first exemplary embodiment of the present invention; 
         FIG. 4A  is a sequence diagram showing an operations of stopping the content distribution in the content distribution system according to the first exemplary embodiment of the present invention; 
         FIG. 4B  is a sequence diagram showing an operation of releasing the band in the content distribution system according to the first exemplary embodiment of the present invention; 
         FIG. 5  is a diagram showing a configuration of the content distribution system according to a second exemplary embodiment of the present invention; 
         FIG. 6A  is a sequence diagram showing an operation of reserving a band in the content distribution system according to the second exemplary embodiment of the present invention; 
         FIG. 6B  is a sequence diagram showing an operation of content distribute in the content distribution system according to the second exemplary embodiment of the present invention; 
         FIG. 7  is a sequence diagram showing an operation of stopping the content distribution in the content distribution system according to the second exemplary embodiment of the present invention; 
         FIG. 8  is a diagram showing a configuration of the content distribution system according to a third exemplary embodiment of the present invention; 
         FIG. 9A  is a sequence diagram showing an operation of reserving a band in the content distribution system according to the third exemplary embodiment of the present invention; 
         FIG. 9B  is a sequence diagram showing an operation of the content distribute in the content distribution system according to the third exemplary embodiment of the present invention; 
         FIG. 10  is a sequence diagram showing an operation of stopping the content distribution in the content distribution system according to the third exemplary embodiment of the present invention; 
         FIG. 11  is a diagram showing a configuration of the content distribution system according to a fourth exemplary embodiment of the present invention; 
         FIG. 12  is a sequence diagram showing an operation of reserving a band in the content distribution system according to the fourth exemplary embodiment of the present invention; 
         FIG. 13  is a sequence diagram showing an operation of stopping the content distribution in the content distribution system according to the fourth exemplary embodiment of the present invention; 
         FIG. 14  is a diagram showing a configuration of the content distribution system according to a fifth exemplary embodiment of the present invention; 
         FIGS. 15A and 15B  are a sequence diagram showing an operation of reserving a band in the content distribution system according to the fifth exemplary embodiment of the present invention; 
         FIG. 15C  is a sequence diagram showing an operation of content distribution in the content distribution system according to the fifth exemplary embodiment of the present invention; 
         FIG. 16  is a sequence diagram showing an operation of stopping the content distribution in the content distribution system according to the fifth exemplary embodiment of the present invention; and 
         FIGS. 17A and 17B  are a sequence diagram showing an operation of releasing the band in the content distribution system according to the fifth exemplary embodiment of the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, a content distribution system according to the present invention will be described in detail with reference to the attached drawings. Same or similar reference numbers are allocated to same or similar components in the drawings. The content distribution system performs streaming distribution of video and audio data via a network. 
     First Exemplary Embodiment 
     Referring to  FIGS. 1 to 4B , a content distribution system according to a first exemplary embodiment of the present invention will be described. The content distribution system according to the first exemplary embodiment includes two networks managed by different providers, in which data is distributed as a stream to a client terminal belonging to one of the networks from a server belonging to the other network. 
     (Configuration) 
       FIG. 1  is a block diagram showing a configuration of the content distribution system according to the first exemplary embodiment. Referring to  FIG. 1 , the content distribution system in the first exemplary embodiment includes an internet network  100  managed by a provider A (referred to as the internet network  100  hereinafter) and an internet network  200  managed by a provider B (referred to as the internet network  200  hereinafter). The internet network  100  includes an STB  10  which is a client terminal owned by a subscriber, a network band control unit  11  to control a band for a transmission path on the internet network  100 , and an RTSP proxy server  12  being a band control mediating unit. Although only one STB  10  is shown here, the internet network  100  may be provided with a plurality of STBs  10  owned by other subscribers. 
     Furthermore, the internet network  200  includes a VoD server  20  which is owned by a content provider and carries out streaming distribution of data to the STB  10 , a network band control unit  21  to control a band for a transmission path on the internet network  200 , and an RTSP proxy server  22  as a band control mediating unit (with functions similar to those of the RTSP proxy server  12 ). Although only one VoD server  20  is shown here, the internet network  200  may be provided with a plurality of VoD servers  20  owned by other content providers. 
     The RTSP proxy server  12  is arranged between the STB  10  and the VoD server  20  and has an RTSP protocol mediating function to transmit/receive data in an RTSP protocol. The RTSP proxy server  12  also controls the network band control unit  11  to execute a band control in place of the STB  10  and the VoD server  20  when data in a protocol requiring the band control passes through the internet network  100 , in mediating the data in the RTSP protocol. The RTSP proxy server  22  is similarly arranged between the STB  10  band the VoD Server  20 , and controls the network band control unit  21  to execute a band control in place of the STB  10  and the VoD server  20  when data in a protocol requiring the band control passes through the internet network  200 . Furthermore, each of the RTSP proxy servers  12  and  22  includes a storage unit  2  which stores a program, a CPU  1  which execute the program to perform an operation shown in  FIG. 2 , and an interface  3  which controls transmission of various kinds of commands specified by the CPU (i.e. request command and response command) and data (e.g. RTP data). The operation shown in  FIG. 2  will be described later. 
     The STB  10  is connected to the RTSP proxy server  12  via an RTSP communication path  13 . The RTSP proxy server  12  and the network band control unit  11  are connected via a band control protocol communication path  14 . The RTSP proxy server  12  and the RTSP proxy server  22  are connected via an RTSP communication path  50 . The RTSP proxy server  22  and the network band control unit  21  are connected via a band control protocol communication path  24 . The RTSP proxy server  22  and the VoD server  20  are connected via an RTSP communication path  23 . The VoD server  20  and the STB  10  are connected via an RTP communication path  60 . The band control protocol communication path  14  and the RTSP communication path  13  are both communication paths in the internet network  100 . Similarly, the band control protocol communication path  24  and the RTSP communication path  23  are both communication paths in the internet network  200 . Furthermore, an RTSP communication path  50  and the RTP (Realtime Transport Protocol) communication path  60  are both communication paths to connect the internet network  100  and an internet network  200  managed by different providers. 
     (Operations from Communication Connection to Communication Disconnection Through Content Distribution in the Content Distribution System) 
     Referring to  FIGS. 2 to 4B , an operation of the content distribution system according to the first exemplary embodiment of the present invention will be described in detail. Prior to description of the operation, an RTSP protocol and an RTP protocol will be described. The RTSP protocol is a reproduction control protocol of video/audio data as proposed in RFC2326. Content is specified to a server (i.e. VoD server  20  here) in response to a SETUP request  501 , and a bit rate data  500  which is a network band data required to reproduce the content is obtained as a response. Next, the reproduction of the content is specified from any portions of the content in response to a PLAY request. In addition, the content in reproduction is stopped in response to a STOP request  531 , and completion of a series of controls is declared in response to a TEARDOWN request. Furthermore, the RTP protocol is a protocol proposed in RFC3550 for the purpose of transporting video/audio data, and used for transporting video/audio data in the protocol such as MPEG2, MPEG4 and H.264, onto a payload of the format (i.e. data storage area) in the protocol. 
     Referring to  FIGS. 3A and 3B , a flow from communication line connection to video data/audio data reproduction in the content distribution system according to the present invention will be described. First, the STB  10  selects stream data (i.e. RTP data  600 ) of contents (i.e. video data/audio data) desired by a subscriber of the STB  10  to reproduce from a portal server (not shown), and obtains identifier data on the VoD server  20  for storing the content, and the content in the VoD server  20 . 
     Next, the STB  10  transmits a SETUP request  501  to the VoD server  20  via the RTSP proxy servers  12  and  22  (steps S 101  to S 103 ). Here, the SETUP request  501  includes an identifier data of the VoD server  20  which stores a content data obtained in advance and desired to be reproduced, the content in the VoD server  20 , and the STB  10  being a distribution destination of the content. 
     More specifically, the STB  10  transmits to the RTSP proxy server  12 , the SETUP request  501  which specifies content data desired to be reproduced (step S 101 ). The RTSP proxy server  12  transmits the SETUP request  501  to the RTSP proxy server  22  corresponding to an identifier of the VoD server  20  included in the SETUP request  501  (step S 102 ). At the step S 102 , the RTSP proxy server  12  detects the VoD server  20  as a distribution source of the content data from the SETUP request  501  based on the RTSP protocol. The RTSP proxy server  22  in the internet network  200  to which the VoD server  20  belongs is then determined as a transmission destination of the SETUP request  501 . The RTSP proxy server  22  similarly detects the VoD server  20  as a transmission destination from the SETUP request  501  based on the RTSP protocol to transmit the SETUP request  501  to the VoD server  20  (step S 103 ). 
     In response to the received SETUP request  501 , the VoD server  20  transmits a SETUP response  502  and the bit rate data  500  to the STB  10  as a content request source (steps S 104  to S 112 ). At this time, the SETUP response  502  and the bit rate data  500  are transmitted to the STB  10  via the RTSP proxy servers  22  and  12 . The RTSP proxy servers  22  and  12  control the network control units  21  and  11  to reserve a network band for the RTP communication path  60  in response to the SETUP response  502  and the bit rate data  500 . 
     Details of the operation at the steps S 104  to S 112  will be described below. In response to the received SETUP request  501 , the VoD server  20  transmits the SETUP response  502  and the bit rate data  500  to the RTSP proxy server  22  (step S 104 ). Here, the bit rate data  500  includes network band data required for transmission/reproduction of content requested by the SETUP request  501  and desired to be reproduced. 
     In response to the received SETUP response  502 , the RTSP proxy server  22  extracts a network band data included in the bit rate data  500 , and transmits a band reserving request  511  to the network band control unit  21  based on the network band data (step S 105 ). The network band control unit  21  controls a band on the internet network  200  in response to the band reserving request  511  to reserve a network band for the RTP communication path  60  (used for RIP data transmission) used for transmitting the RTP data  600  in the internet network  200  (step S 106 ). After reserving the band, the network band control unit  21  transmits a band reserving response  512  to the RTSP proxy server  22  (step S 107 ). 
     Upon receiving the band reserving response  512 , the RTSP proxy server  22  transmits the SETUP response  502  and the bit rate data  500  to the RTSP proxy server  12  (step S 108 ). The RTSP proxy server  12  extracts the network band data included in the bit rate data  500  based on a band control protocol in response to the received SETUP response  502 , and transmits a band reserving request  513  to the network band control unit  11  based on the network band data (step S 109 ). The network band control unit  11  controls a band on the internet network  100  on the basis of the received band reserving request  513 , and reserves a network band for the RTP communication path  60  to transmit the RTP data  600  on the internet network  100  (step S 110 ). Furthermore, after reserving the band, the network band control unit  11  transmits a band reserving response  514  to the RTSP proxy server  12  (step S 111 ). 
     Upon receiving the band reserving response  514 ; the RTSP proxy server  12  transmits the SETUP response  502  and the bit rate data  500  to the STB  10  (step S 112 ). 
     Next, referring to  FIG. 3B , the STB  10  which has confirmed a band reserved for the RTP communication path  60  by the SETUP response  502  transmits a PLAY request  521  to the VoD server  20  via the RTSP proxy servers  12  and  22  for streaming reproduction of the target content data (steps S 113  to S 115 ). Here, the PLAY request  521  includes an identifier data on the VoD server  20  which stores content data desired to be reproduced, and the content of the VoD server  20 . 
     More specifically, the STB  10  transmits to the RTSP proxy server  12  the PLAY request  521  which specifies content data desired to be reproduced (step S 113 ). The RTSP proxy server  12  transmits the PLAY request  521  to the RTSP proxy server  22  corresponding to an identifier of the VoD server  20  included in the PLAY request  521  (step S 114 ). AT the step S 114 , the RTSP proxy server  12  detects the VoD server  20  as a distribution source of content data based on an RTSP protocol in response to the PLAY request  521 . The RTSP proxy server  22  in the internet network  200  to which the VoD server  20  belongs is then determined as a transmission destination of the PLAY request  521 . Similarly, the RTSP proxy server  22  detects the VoD server  20  as a transmission destination based on the RTSP protocol in response to the PLAY request  521  to transmit the PLAY request  521  to the VoD server  20  (step S 115 ). 
     Upon receiving the PLAY request  521 , the VoD server  20  starts RTP distribution of video data/audio data of the content specified in the PLAY request  521  by using the RTP communication path  60  which has a reserved band (step S 116 ). Thereafter, a video/audio data stream (i.e. RTP data  600 ) of the content requested by the PLAY request  521  is transmitted on the RTP communication path  60  until receiving a protocol data for changing the reproduced content such as a STOP request  531 , or reaching a tail end of the RTP data  600  (step  117 ). The VoD server  20  transmits a PLAY response  522  to the STB  10  via the RTSP proxy servers  22  and  12  in the RTP distribution (steps S 118  to S 120 ). 
     Next, referring to  FIGS. 4A and 4B , an operation of the video/audio stop request to communication line disconnection in the content distribution system according to the present invention explanation will be made for. The STB  10  which desires to stop distribution of video/audio data transmits the STOP request  531  to the VoD server  20  being a content stream distribution source. At this time, the STB  10  transmits the STOP request  531  to the VoD server  20  via the RTSP proxy servers  12  and  22  (steps S 121  to S 123 ). Here, the STOP request  531  includes an identifier data on the VoD server  20  as a distribution source of content data, and the content in the VoD server  20 . 
     More specifically, the STB  10  transmits to the RTSP proxy server  12  the STOP request  531  which specifies content data subjected to stop distribution (step S 121 ). The RTSP proxy server  12  transmits the STOP request  531  to the RTSP proxy server  22  corresponding to an identifier of the VoD server  20  included in the STOP request  531  (step S 122 ). At the step S 122 , the RTSP proxy server  12  detects the VoD server  20  as a distribution source of content data based on an RTSP protocol in response to the STOP request  531 . The RTSP proxy server  22  in the internet network  200  to which the VoD server  20  belongs is then determined as a transmission destination of the STOP request  531 . Similarly, the RTSP proxy server  22  detects the VoD server  20  as a transmission destination based on the RTSP protocol in response to the STOP request  531  to transmit the STOP request  531  to the VoD server  20  (step S 123 ). 
     Upon receiving the STOP request  531 , the VoD server  20  stops a video/audio data stream (i.e. RTP data  600 ) transmitted through the RTP communication path  60  (i.e. RTP distribution stop: step S 124 ). Furthermore, after stopping RTP distribution, the VoD server  20  transmits a STOP response  532  to the STB  10  via the RTSP proxy servers  22  and  12  (steps S 125  to S 127 ). 
     Referring to  FIG. 4B , the STB  10  which has received the STOP response  532 , transmits a STEARDOWN request  541  to the VoD server  20  via the RTSP proxy servers  12  and  22  (steps S 128  to S 130 ). Here, the STEARDOWN request  541  includes identifier data on the VoD server  20  as a transmission source of the STOP response  532 , content subjected to stop in the VoD server  20 , and the STB  10  as a request source to stop distribution, or more precisely includes information which specifies the RTP communication path  60  subjected to disconnect. 
     To be more specific, the STB  10  transmits the STEARDOWN request  541  to the RTSP proxy server  12  (step S 128 ). The RTSP proxy server  12  transmits the STEARDOWN request  541  to the RTSP proxy server  22  corresponding to an identifier of the VoD server  20  included in the STEARDOWN request  541  (step S 129 ). At step S 129 , the RTSP proxy server  12  detects the VoD server  20  as a distribution source of content data based on an RTSP protocol in response to the STEARDOWN request  541 . The RTSP proxy server  22  in the internet network  200  to which the VoD server  20  belongs, is then determined as a transmission destination of the STEARDOWN request  541 . Similarly, the RTSP proxy server  22  detects the VoD server  20  as a transmission destination based on the RTSP protocol in response to the STEARDOWN request  541  to transmit the STEARDOWN request  541  to the VoD server  20  (step S 123 ). 
     The VoD server  20  which has received the TEARDOWN request  541  prepares for disconnection of the RTP communication path  60  and transmits a TEARDOWN response  542  to the STB  10  as a line disconnection request source (steps S 131  to S 139 ). At this time, the TEARDOWN response  542  is transmitted to the STB  10  via the RTSP proxy servers  22  and  12 . The RTSP proxy servers  22  and  12  control the network control units  21  and  11  in response to the TEARDOWN response  542  and release a network band used for the RTP communication path  60  to distribute content (i.e. RTP data  600 ). 
     The operation from the steps S 131  to S 139  will be described below in detail. In response to the received TEARDOWN response  541 , the VoD server  20  transmits the TEARDOWN response  542  to the RTSP proxy server  22  (step S 131 ). Here, the TEARDOWN response  542  includes the network band data on the RTP communication path  60  used for transmission of content (i.e. RTP data  600 ). 
     The RTSP proxy server  22  extracts a network band data on the RTP communication path  60  included in the received TEARDOWN response  542  based on a band control protocol to transmit to the network band control unit  21  a band releasing request  551  based on the network band data (step S 132 ). The network band control unit  21  controls a band on the internet network  200  in response to the band releasing request  551  to release a network band reserved for the RTP communication path  60  in the internet network  200  (step S 133 ). Furthermore, after releasing the band, the network band control unit  21  transmits a band releasing response  552  to the RTSP proxy server  22  (step S 134 ). 
     Upon receiving the band releasing response  552 , the RTSP proxy server  22  disconnects communication with the VoD server  20  via the RTSP communication path  23 , and transmits the TEARDOWN response  542  to the RTSP proxy server  12  (step S 135 ). The RTSP proxy server  12  extracts the network band data from the received TEARDOWN response  542  based on the band control protocol to transmit a band releasing request  553  to the network band control unit  11  based on the network band data (step S 136 ). At this time, the RTSP proxy server  12  disconnects communication with the RTSP proxy server  22  via the RTSP communication path  50  in response to the TEARDOWN response  542 . The network band control unit  11  controls a band on the internet network  100  on the basis of the received band releasing request  553  to release the network band reserved on the internet network  100  for the RTP communication path  60  (step S 137 ). Furthermore, after releasing the band, the network band control unit  11  transmits a band releasing response  554  to the RTSP proxy server  12  (step S 138 ). 
     Upon receiving the band releasing response  554 , the RTSP proxy server  12  transmits the TEARDOWN response  542  to the STB  10  (step S 139 ). Upon receiving the TEARDOWN response  542 , the STB  10  disconnects communication with the RTSP proxy server  12  via the RTSP communication path  13 , and ends a series of reproduction controls started from the SETUP request  501 . 
     As stated above, the content distribution system according to the present invention does not use a client terminal (i.e. STB  10  here) or a server (i.e. VoD server  20  here) to directly communicate with a network to reserve a band, without changing specifications of the client terminal and the server in a large scale even if the client terminal and the server are arranged in different networks. Even if a server is unable to deal with the SIP, it is possible to reserve a band required for content distribution as requested by the server on condition that the RTSP communication standardly used in streaming distribution is available. Furthermore, a band is reserved in response to a request from a client side, which means only a band required for streaming distribution of video data/audio data is reserved in a network. Therefore, the present invention is excellent in efficient network usage. 
     (Operation of RTSP Proxy Server) 
     Operations of the RTSP proxy servers  12  and  22  will be described in detail with reference to  FIG. 2 .  FIG. 2  is a flowchart showing an operation of receiving a request/response in the RTSP proxy servers  12  and  22 . In the following description, the RTSP proxy server  12  will be used as an example, while description for the RSTP proxy server  22  is omitted since the operation of the server  22  is the same manner as that of the RTSP proxy server  12 . In the following description, it should be noted that an “STB side” refers to the STB  10  side and a “VoD server side” refers to the VoD Server  20  side or the RTSP proxy server  22  side. However, in case of the RSTP proxy server  22 , the “STB side” refers to the STB  10  side or the RTSP proxy server  12  side and the “VoD server side” refers to the VoD server  20  side. 
     The RTSP proxy server  12  receives an RTSP protocol request or response from the STB side (step S 1 ). The RTSP proxy server  12  confirms the content of the received request or response by performing analysis through the following steps S 2  to S 7 . More specifically, she RTSP proxy server  12  analyzes whether the content is an electronic message requesting to reserve a network band, an electronic message requesting to release a network band, or another electronic message, from data in the video/audio data reproduction control protocol relayed between the STB side and the VoD server side. 
     When a request/response received in the step S 1  is a request necessary to reserve a band (Yes in step S 2 ), a band reserving request is transmitted to the network band control unit  11  connected to the RTSP proxy server  12  via the band control protocol communication path (step S 3 ). That is, the RTSP proxy server  12  transmits the band reserving request  513  to the network band control unit  11  in response to the SETUP response  502  transmitted from the VoD side. Furthermore, when an received request/response is a request necessary to release the band (No in step S 2  and Yes in step S 3 ), a band releasing request is transmitted to the network band control unit  11  connected to the RTSP proxy server  12  itself via the band control protocol communication path (step S 4 ). That is, the RTSP proxy server  12  transmits the band releasing request  553  to the network band control unit  11  in response to the TEARDOWN response  542  transmitted from the VoD side. In the step S 3  or the step S 5 , the RTSP proxy server  12  determines a band to reserve or release on the basis of the received bit rate data  500 , and transmits the band reserving/releasing request. 
     When the request/response received in the step S 1  is an electronic message related to another request or response, the RTSP proxy server  12  analyzes a transmission source and a transmission destination of the request/response to determine a transfer destination of the received electronic message (step S 6 ). At this time, when the received request/response is a request/response transmitted from the VoD side (Yes in step S 6 ), the RTSP proxy server  12  transfers this request or response to the STB side (step S 7 ). For example, the RTSP proxy server  12  which has received the PLAY response  522  and the STOP response  532  transfers the PLAY response  522  and the STOP response  532  to the STB side. 
     When the request/response received in the step S 1  is not a request/response transmitted from the VoD side (No in step S 6 ), the RTSP proxy server  12  confirms whether this request/response is a response from the network band control unit (step S 8 ). At this time, when the received request/response is a response from the network band control unit  11  (Yes in step S 8 ), the RTSP proxy server  12  transfers a response signal corresponding to this response to the STB side. For example, when the received response is the band reserving response  514  transmitted from the network band control unit  11 , the RTSP proxy server  12  transfers the SETUP response  502  corresponding to the band reserving response  514  to the STB side. 
     When the request/response received in the step S 1  is neither any request/response from the VoD server side nor a response from the network band control unit (No in step S 8 ), the RTSP proxy server  12  transfers the received request/response to the VoD server side (step S 9 ). For example, the RTSP proxy server  12  receives the SETUP request  501 , the PLAY request  521 , the STOP request  531  or the TEARDOWN request  541  and transfers the SETUP request  501 , the PLAY request  521 , the STOP request  531  or the TEARDOWN request  541  to the VoD server side. 
     Although the flow is ended after the step S 7  or S 8  in  FIG. 2 , the RTSP proxy server  12  is made to loop to the step S 1  so as to wait for a request/response again. In this case, the loop operation is desirably continued until a legitimate reason is given to disconnect the network (such as reception of the TEARDOWN response and no response from a communication counter end for a predetermined period of time). 
     Second Exemplary Embodiment 
     Configuration 
     Referring to  FIGS. 5 to 7 , a content distribution system according to a second exemplary embodiment of the present invention will be described. Referring to  FIG. 5 , the content distribution system in the second exemplary embodiment has a configuration in which the RTSP proxy server  12  is not arranged in the internet network  100  and the RTSP proxy server  22  is arranged only in the internet network  200  in the configuration according to the first exemplary embodiment. That is, the second exemplary embodiment is configured to have the RTSP proxy server  22  only in the network provided with the VoD server  20 . In this case, the RTSP proxy server  22  requests both of the network band control unit  11 , which controls a network band on the internet network  100 , and the network band control unit  21 , which controls a network band on the internet network  200 , to reserve/release a band. Therefore, an RTSP communication path  53  and a band control protocol communication path  54  are used to connect the RTSP proxy server  22  to the STB  10  and the network band control unit  11  respectively. Other configurations in the connection are similar to those of the first exemplary embodiment. 
     The description of operation of the RTSP proxy server  22  in the second exemplary embodiment will be omitted as being similar to that of the first exemplary embodiment. 
     (Operations from Communication Connection to Content Distribution to Communication Disconnection in the Content Distribution System) 
     Referring to  FIGS. 6A to 7 , an operation in the content distribution system according to the second exemplary embodiment of the present invention will be described in detail. In the second exemplary embodiment, one RTSP proxy server  22  requests two of the network band control units  11  and  21  to reserve/release a network band for the RTP communication path  60 . Referring to  FIG. 6A , the STB  10  carries out a content request and transmits the SETUP request  501  to the VoD server  20  via the RSTP proxy server  22  (steps S 201  and S 202 ). In response to the received SETUP request  501 , the VoD server  20  transmits the SETUP response  502  and the bit rate data  500  to the STB  10  via the RTSP proxy server  22  (steps S 203  to S 210 ). 
     The details of the operation from the steps S 203  to S 210  will be described below. In response to the received SETUP request  501 , the VoD server  20  transmits the SETUP response  502  and the bit rate data  500  to the RTSP proxy server  22  (step S 203 ). In response to the received SETUP response  502 , the RTSP proxy server  22  extracts a network band data included in the bit rate data  500  based on a network band control protocol, and transmits the band reserving request  511  to the network band control unit  21  based on the network band data (step S 204 ). The network band control unit  21  controls a band on the internet network  200  in response to the band reserving request  511 , and reserves a network band for the RTP communication path  60  to transmit the RTP data  600  on the internet network  200  (step S 205 ). After reserving the band, the network band control unit  21  transmits the band reserving response  512  to the RTSP proxy server  22  (step S 206 ). 
     Upon receiving the band reserving response  512 , the RTSP proxy server  22  extracts a network band data included in the bit rate data  500  based on a band control protocol, and transmits to the network band control unit  11  the band reserving request  513  based on the network band data (step S 207 ). The network band control unit  11  controls a band on the internet network  100  based on the received band reserving request  513 , and reserves a network band for the RTP communication path  60  used for transmitting the RTP data  600  on the internet network  100  (step S 208 ). Furthermore, after reserving the band, the network band control unit  11  transmits the band reserving response  514  to the RTSP proxy server  22  (step S 209 ). 
     Upon receiving the band reserving response  514 , the RTSP proxy server  22  transmits the SETUP response  502  and the bit rate data  500  to the STB  10  (step S 210 ). 
     Subsequently, referring to  FIG. 6B , the STB  10  confirms a band reserved for the RTP communication path  60  in response to the SETUP response  502  and transmits the PLAY request  521  to the VoD server  20  via the RTSP proxy server  22  to realize streaming reproduction of target content data (steps S 211  and S 212 ). Upon receiving the PLAY request  521 , the VoD server  20  starts RTP distribution of video data/audio data of the content data specified by the PLAY request  521 , using the RTP communication path  60  which has a reserved band (step S 213 ). Thereafter, a video data/audio data stream of the content (i.e. RTP data  600 ) requested by the PLAY request  521  is transmitted on the RTP communication path  60  until receiving a protocol data for changing the reproduced content such as the STOP request  531 , or reaching the tail end of the RTP data  600  (step S 214 ). In starting RTP distribution, the VoD server  20  transmits the PLAY response  522  to the STB  10  via the RTSP proxy server  22  (steps S 215  and S 216 ). 
     An operation from video data/audio-data stop request to communication line disconnection in the content distribution system according to the present invention (in the second exemplary embodiment) referring to  FIG. 7 . will be Explained next The STB  10  which desires to stop video data/audio data distribution transmits the STOP request  531  to the VoD server  20  being a content stream distribution source via the RTSP proxy server  22  (steps S 221  and S 222 ). Upon receiving the STOP request  531 , the VoD server  20  stops the video data/audio data stream (i.e. RTP data  600 ) transmitted by the RTP communication path  60  (i.e. RTP distribution stop: step S 223 ). Furthermore, after stopping the RTP distribution, the VoD server  20  transmits the STOP response  532  to the STB  10  via the RTSP proxy server  22  (steps S 224  and S 225 ). 
     The STB  10  receives the STOP response  532  and transmits the STEARDOWN request  541  to the VoD server  20  via the RTSP proxy server  22  (steps S 226  and S 227 ). Upon receiving the TEARDOWN request  541 , the VoD server  20  prepares for disconnection of the RTP communication path  60  and transmits the TEARDOWN response  542  to the STB  10  which is a line disconnection request source (steps S 228  to S 235 ). More specifically, the TEARDOWN response  542  is transmitted to the RTSP proxy server  22  (step S 228 ). The RTSP proxy server  22  extracts a network band data included in the received TEARDOWN response  542  on the RTP communication path  60  based on a band control protocol to transmit the band releasing request  551  based on the network band data to the network band control unit  21  (step S 229 ). The network band control unit  21  controls a band on the internet network  200  in response to the band releasing request  551 , and releases the network band reserved on the internet network  200  for the RTP communication path  60  (step S 230 ). After releasing the band, the network band control unit  21  transmits the band releasing response  552  to the RTSP proxy server  22  (step S 231 ). 
     Upon receiving the band releasing response  552 , the RTSP proxy server  22  disconnects communication with the VoD server  20  via the RTSP communication path  23 . Furthermore, the RTSP proxy server  22  extracts a network band data included in the received TEARDOWN response  542  based on the band control protocol, and transmits the band releasing request  553  based on the network band data to the network band control unit  11  (step S 232 ). The network band control unit  11  controls a band on the internet network  100  based on the received band releasing request  553 , and releases a network band reserved for the RTP communication path  60  on the internet network  100  (step S 233 ). Furthermore, after releasing the band, the network band control unit  11  transmits the band releasing response  554  to the RTSP proxy server  22  (step S 234 ). Upon receiving the band releasing response  554 , the RTSP proxy server  22  transmits the TEARDOWN response  542  to the STB  10  (step S 139 ). Upon receiving the TEARDOWN response  542 , the STB  10  disconnects communication with the RTSP proxy server  22  via the RTSP communication path  53 , and ends a series of reproduction controls started from the SETUP request  501 . 
     As stated above, even if there is no RTSP proxy server arranged in the network to which the STB  10  belongs, the RTSP proxy server  22  in the network to which the VoD server  20  belongs relays communication between the STB  10  and the VoD server  20 , and controls the network control units  11  and  21  to reserve or release a network band. Therefore, it is unnecessary for the STB  10  or the VoD server  20  to directly communicate to reserve or release a network band even if no RTSP proxy server is arranged in the network to which the STB  10  belongs. Moreover, even if the STB  10  or the VoD server  20  is arranged in different networks, specifications are not changed in a large scale in the STB  10  and the VoD server  20 . 
     Third Exemplary Embodiment 
     Configuration 
     Referring to  FIGS. 8 to 10 , the content distribution system according to a third exemplary embodiment of the present invention will be described. Referring to  FIG. 8 , the content distribution system in the third exemplary embodiment has a configuration in which the RTSP proxy server  22  is not arranged in the internet network  200  and the RTSP proxy server  12  is arranged only in the internet network  100 , as compared with the configuration according to the first exemplary embodiment. That is, the third exemplary embodiment is configured to have the RTSP proxy server  12  only in the network provided with the STB  10 . In this case, the RTSP proxy server  12  requests both of the network band control unit  11 , which controls the network band on the internet network  100 , and the network band control unit  21 , which controls a network band on the internet network  200 , to reserve/release a band in the same manner with the second exemplary embodiment. Accordingly, an RTSP communication path  63  and a band control protocol communication path  64  are used to connect the RTSP proxy server  12  to the VoD server  20  and the network band control unit  21  respectively. Other configurations in the connection are similar to those of the first exemplary embodiment. 
     The description of the operation of the RTSP proxy server  12  in the third exemplary embodiment will be omitted as being similar to that of the first exemplary embodiment. 
     (Operation from Communication Connection to Content Distribution to Communication Disconnection in the Content Distribution System) 
     Referring to  FIGS. 9A to 10 , an operation of the content distribution system according to the third exemplary embodiment of the present invention will be described in detail. In the third exemplary embodiment, one RTSP proxy server  12  requests two of the network band control units  11  and  21  to reserve/release a network band for the RTP communication path  60  in the same manner as the second exemplary embodiment. Accordingly, the operations of the third exemplary embodiment (steps S 301  to S 335 ) are similar to those (steps S 201  to S 235 ) of the second exemplary embodiment respectively. However, the RTSP proxy server  22 , the RTSP communication path  53  and the band control protocol communication path  54  in the second exemplary embodiment are replaced with the RTSP proxy server  12 , the RTSP communication path  63  and the band control protocol communication path  64  in the third exemplary embodiment respectively. 
     As stated above, the STB  10  or the VoD server  20  may not communicate directly to reserve or release a network band even if the RTSP proxy server is not present in the network to which the VoD server  20  for distributing content data belongs in the third exemplary embodiment. Moreover, even in case of arranging the STB  10  or the VoD server  20  in a different network, specifications are not changed in a large scale in the STB  10  and the VoD server  20 . 
     Fourth Exemplary Embodiment 
     Configuration 
     Referring to  FIGS. 11 to 13 , the content distribution system according to a fourth exemplary embodiment of the present invention will be described. The fourth exemplary embodiment is configured only by the single internet network  100  in place of the . . . plurality of the internet networks present in the first exemplary embodiment. That is, the content distribution system in the fourth exemplary embodiment has a configuration in which the STB  10  and the VoD server  20  are arranged in the same internet network  100  having one each of the network band control unit  11  and the RTSP proxy server  12 . In this case, the RTSP proxy server  12  requests only the network band control unit  11 , which controls the network band on the internet network  100 , to reserve/release a band. Accordingly, RTSP communication paths  13  and  15  are used to connect the RTSP proxy server  12  to the STB  10  and the VoD server  20  respectively, while using a band control protocol communication path  14  to connect the RTSP proxy server  12  to the network band control unit  11 , and using an RTP communication path  61  for transmitting the RTP data  600  to connect the STB  10  and the VoD server  20 . It should be noted that the RTP communication path  61  is configured in the same network (i.e. internet network  100  here). 
     The description of an operation of the RTSP proxy server  12  in the fourth exemplary embodiment will be omitted as being similar to that of the first exemplary embodiment. 
     (Operation from Communication Connection to Content Distribution to Communication Disconnection in the Content Distribution System) 
     Referring to  FIGS. 12 and 13 , the content distribution system according to the fourth exemplary embodiment of the present invention will be described in detail. In the fourth exemplary embodiment, one RTSP proxy server  12  requests one network band control unit  11  to reserve/release a network band for the RTP communication path  60 . Accordingly, the operations of the fourth exemplary embodiment (i.e. steps S 401  to S 432 ) are similar to those obtained by removing the steps S 204  to S 206  and the steps S 229  to S 231  from the operations of the second exemplary embodiment (i.e. steps, S 201  to S 235 ). However, the RTSP proxy server  22 , the RTSP communication path  53 , the band control protocol communication path  54  and the RTP communication path  60  in the second exemplary embodiment are replaced with the RTSP proxy server  12 , the RTSP communication path  13 , the band control protocol communication path  14  and the RTP communication path  63  in the fourth exemplary embodiment, respectively. 
     As stated above, according to the fourth exemplary embodiment, it is possible for the RTSP proxy server  12  to relay communication related to reserving/releasing a network band between the STB  10  and the VoD server  20 , and control the network band control unit  11  to reserve/release a network band even in the same network. 
     Fifth Exemplary Embodiment 
     Configuration 
     Referring to  FIGS. 14 to 17B , the content distribution system according to a fifth exemplary embodiment of the present invention will be described. Referring to  FIG. 14 , the content distribution system in the fifth exemplary embodiment is further provided with another internet network (e.g. internet network  300  managed by a provider C) between the STB  10  and the VoD server  20  in the configuration according to the first exemplary embodiment. Here, the internet network  300  managed by the provider C (to be referred to as the internet network  300 , hereinafter) includes a network band control unit  31  which controls a network band on the internet network  300 , and an RTSP proxy server  32  which relays RTSP communication between the RTSP proxy servers  12  and  22  and controls the network band control unit  31 . That is, the RTSP proxy servers  12 ,  22  and  32  relay RTSP communication between the STB  10  and the VoD server, and control the network band control units  11 ,  21  and  31  in the networks to which the RTSP proxy servers  12 ,  22  and  32  belong respectively so as to reserve or release a network band for an RTP communication path  62  in the networks (i.e. internet networks  100 ,  200  and  300 ). Accordingly, RTSP communication paths  51  and  52  are connected with the RTSP proxy server  32  to the RTSP servers  12  and  21 , respectively, while the RTP communication path  62  provided for communication of the RTP data  600  is used to connect the STB  10  and the VoD server  20 . Other configurations in the connection are similar to those of the first exemplary embodiment. 
     The description of operations of the RTSP proxy server  32  in the fifth exemplary embodiment will be omitted as being similar to those of the RTSP proxy server  12  in the first exemplary embodiment. 
     (Operations from Communication Connection to Content Distribution to Communication Disconnection in the Content Distribution System) 
     Referring to  FIGS. 15A to 17B , operations of the content distribution system according to the fifth exemplary embodiment of the present invention will be described in detail. The STB  10  in the fifth exemplary embodiment receives content distribution from the VoD server  20  in the internet network  200  which differs from the internet network  100  to which the STB  10  belongs, in the same manner as the first exemplary embodiment. The STB  10  in the fifth exemplary embodiment receives content distribution via the other internet network  300 . Therefore, an operation to reserve a network band for the RTP communication path  62  (i.e. steps S 501  to S 517 ) are provided by adding to an operation similar to the communication connection operation in the first exemplary embodiment (i.e. steps S 101  to S 112 ), an operation of relaying RTSP communication between the STB  10  and the VoD server by the RTP proxy server  32  (i.e. steps S 503 , S 510  and S 513 ), and an operation of reserving a network band for the RTP communication path  62  in the internet network  300  (i.e. steps S 510  to S 512 ). 
     Operations which differ from those of the first exemplary embodiment will be described below. Referring to  FIG. 15A , the STB  10  transmits the SETUP request  501  to the VoD server  20  via the RTSP proxy servers  12 ,  32  and  22  (steps S 501  to S 504 ). Furthermore, referring to  FIG. 15B , the VoD server  20  transmits the SETUP response  502  to the SETUP request  501  and the bit rate data  500  to the STB  10  via the RTSP proxy servers  22 ,  32  and  11  (steps S 508  to S 517 ). At this time, the RTSP proxy server  32  receives the SETUP response  502  and the bit rate data  500  and controls the network band control unit  31  so as to release a network band for the RTP communication path  62  on the internet network  300  (steps S 510  to S 512 ). 
     The RTSP proxy servers  12 ,  22  and  32  are thus capable of relaying RTSP communication between the STB  10  and the VoD server and reserving the network band on the internet networks  100 ,  200  and  300  to which the RTSP proxy servers  12 ,  22  and  32  belong, respectively. 
     Referring to  FIG. 15C , an operation to distribute content (i.e. RTP data  600 ) in the fifth exemplary embodiment (steps S 518  to S 527 ) is provided by adding to an operation similar to that of the first exemplary embodiment (steps S 113  to S 120 ), an operation of relaying RTSP communication between the STB  10  and the VoD server by the RTP proxy server  32  (steps S 520  and S 526 ). That is, the STB  10  transmits the PLAY request  521  to the VoD server  20  via the RTSP proxy servers  12 ,  32  and  22  (steps S 518  to S 521 ). Furthermore, the VoD server  20  transmits the PLAY response  522  to the PLAY request  521  to the STB  10  via the RTSP proxy servers  22 ,  32  and  11  (steps S 524  to S 527 ). 
     Referring to  FIGS. 16 to 17B , an operation to stop distribution of content (i.e. RTP data  600 ) in the fifth exemplary embodiment (steps S 531  to S 556 ) is provided by adding to an operation similar to that of the first exemplary embodiment (steps S 121  to S 139 ), an operation of relaying RTSP communication between the STB  10  and the VOD server by the RTP proxy server  32  (steps S 533 , S 538  and S 552 ), and an operation of releasing a network band reserved for the RTP communication path  62  on the internet network  300  (steps S 549  to S 551 ). 
     The STB  10  transmits the STOP request  531  to the VoD server  20  via the RTSP proxy servers  12 ,  32  and  22  (steps S 531  to S 534 ). Furthermore, the VoD server  20  transmits the STOP response  532  for the STOP request  531 ′ to the STB  10  via the RTSP proxy servers  22 ,  32  and  11  (steps S 536  to S 539 ). Furthermore, the STB  10  transmits the TEARDOWN request  541  to the VoD server  20  via the RTSP proxy servers  12 ,  32  and  22  (steps S 540  to S 543 ). Furthermore, the VoD server  20  transmits the TEARDOWN response  542  for the TEARDOWN request  541  to the STB  10  via the RTSP proxy servers  22 ,  32  and  11  (steps S 544  to S 556 ). At this time, the RTSP proxy server  32  receives the TEARDOWN response  542  and controls the network band control unit  31  to release the network band reserved for the RTP communication path  62  on the internet network  300  (steps S 549  to S 551 ). 
     As stated above, even if the number of networks on a content data communication path (i.e. RTP communication path  62 ) is increased, the RTSP proxy server  22  arranged in the added network (i.e. internet network  300  here) is used to relay RTSP communication and control a band therein. Therefore, it is unnecessary for the STB  10  or the VoD server  20  to directly communicate to reserve or release a network band. Moreover, even if the STB  10  or the VoD server  20  is arranged in a different network, specifications are not changed in a large scale in the STB  10  or the VoD server  20 . 
     The present invention may have another specific configuration without being limited to the first to fifth exemplary embodiments described above in detail, and changes made in a range without deviating from the scope of the present invention are also included in the present invention. Providers used in the above exemplary embodiments are simply different by the internet network  100  managed by a provider A, the internet network  200  managed by a provider B, and the internet network  300  managed by a provider C, as an example, but more than one internet networks may be owned by a single provider. Each of the internet networks may be different by a provider referring to the number of subscribers who subscribe each network and in association with firewall setting for company users or the like. 
     Furthermore, a NAT or NAPT router may be arranged in front of and behind each of the RTSP proxy servers. In this case, each of the RTSP proxy servers operates by converting a communication address (or address and port) included in an RTSP protocol to an address (or address and port) obtained before NAT (or NAPT) conversion. 
     Referring to  FIGS. 8 to 10 , an example of the conversion will be described below by using the content distribution system configured according to the third exemplary embodiment. It is assumed here that the NAT router is present in the RTSP communication path  13 . Furthermore, the description will be made on an assumption that the STB  10  has the local address of 192.168.1.1 in the NAT router and the global address of 10.10.10.200 on the outside of the NAT router, while the VoD server  20  has the local address of 192.168.1.250 in the NAT router and the global address of 10.10.10.250 on the outside of the NAT. In addition, the STB  10  is assumed to obtain the global address of the VoD server  20  and an identifier of content which is desired to be reproduced, from a portal server prior to transmission of the SETUP request  501  at the step S 301 . Furthermore, it is assumed that a correspondence between the local address and the global address before and after the NAT conversion can be obtained by asking the network band control unit  11  in case of conversion by the NAT router in the internet network  100 . 
     In response to the SETUP request  501  is transmitted from the STB  10  to the RTSP proxy server  12 , the following RTSP message is transmitted. In this example, “destination” described in the transport field contains a value which specifies the STB  10  as a transmission destination of content of the VoD server  20 . The STB  10  describes a transmission destination address of the STB itself by the local address in the NAT router because the type of the global address distributed by the NAT router is unknown. 
     SETUP rtsp://10.10.10.202:554/1 RTSP/1.0 
     CSeq: 4 
     Transport: RTP/AVP/UDP; unicast; destination=192.168.1.1; client_port=19000 
     The RTSP proxy server  12  is connected to the STB  10  by TCP in receiving the SETUP request  501  and recognizes the global address of the STB connected by a SOCKET interface for use in the TCP connection to replace the address described in “destination” transmitted by the SETUP request  501  with the global address recognized by the SOCKET interface. The replaced RTSP message is transmitted to the VoD server  20  as the SETUP request  501 . The RTSP message obtained at this time is as shown below: 
     SETUP rtsp://10.10.10.202.554/1 RTSP/1.0 
     CSeq: 4 
     Transport: RTP/AVP/UDP; unicast; destination=10.10.10.200; client_port=19000 
     Upon receiving the SETUP request  501 , the VoD server  20  includes a transmission source address and a port of a video/audio data stream transmitted from the server itself in the SETUP response  502  so as to transmit to the RTSP proxy server  12 . Shown below is the SETUP response  502 . An address described in “Source” here is the global address of the VoD server  20  as a transmission source. 
     RTSP/1.0 200 OK 
     CSeq: 4 
     Session: 1796-35902448 
     Transport: RTP/AVP/UDP; unicast; destination=10.10.10.250; source=10.10.10.202; client_port=19000; server_port=3590; bitrate=8545088 
     Public: OPTIONS, DESCRIBE, SETUP, PLAY, PAUSE, GET_PARAMTER, GET_DATA, TEARDOWN 
     VersionSupport: NEC/1.0 
     Upon receiving the SETUP response  502  and the bit rate data  500 , the RTSP proxy server  12  specifies a “bitrate” value included in the SETUP response  502  and the bit rate data  500  as a band value to reserve a band for the RTP communication path  60  used in RTP communication on the internet network  200 , and simultaneously specifies a combination of specific addresses and ports so as to transmit the band reserving request  511  to the network band control unit  21 . The combination of addresses and ports at this time includes the global address (10.10.10.202) and the port (3590) of the VoD server  20  serving as a transmission source, and the global address (10.10.10.250) and the port (19000) of the STB  10  serving as a transmission destination. 
     The network band control unit  21  reserves a network band on the internet network  200  in response to the content of the band reserving request  511  so as to transmit the band reserving response  512  to the RTSP proxy server  12 . 
     To reserve the network band on the internet network  100 , upon receiving the band reserving response  512 , the RTSP proxy server  12  specifies as a band value, the “bitrate” value included in SETUP response  502  and the bit rate data  500  received beforehand, and simultaneously specifies a combination of specific addresses and ports so as to transmit the band reserving request  513  to the network band control unit  11 . The combination of addresses and ports at this time includes the global address (10.10.10.202) and the port (3590) of the VoD server  20  serving as a transmission source, and the local address (192.168.1.1) and the port (19000) of the STB  10  serving as a transmission destination. This combination of specified addresses may also include the global address (10.10.10.250) for the network on the STB side and the local address (192.168.1.250) for the network on the VoD server side, depending on the NAT router and the network band control unit  11  to be mounted. 
     The network band control unit  11  reserves the network band on the internet network  100  in response to the content of the band reserving request  513  so as to transmit the band reserving response  514  to the RTSP proxy server  12 . 
     Upon receiving the band reserving response  514 , the RTSP proxy server  12  converts the global address of the VoD server  20 , which is included in the SETUP response  502  and the bit rate data  500 , to the aforementioned local address in the NAT router in the internet network  100 . The conversion is executed from a corresponding-relationship between the local address and the global address in the inside and outside of NAT by inquiring the network band control unit  11 . Next, the RTSP proxy server  12  uses the converted value. The converted RTSP message is transmitted to the STB  10  as the SETUP response  502  and the bit rate data  500 . Shown below are the SETUP response  502  and the bit rate data  500 . A value in “source” here is converted to the local address of the VoD server  20  in the NAT router. 
     RTSP/1.0 200 OK 
     CSeq: 4 
     Session: 1796-35902448 
     Transport: RTP/AVP/UDP; unicast; destination=192.168.1.1; source=192.168.1.250; client_port=19000; server_port=3590; bitrate=8545088 
     Public: OPTIONS, DESCRIBE, SETUP, PLAY, PAUSE, GET_PARAMTER, GET_DATA, TEARDOWN 
     VersionSupport: NEC/1.0 
     Upon receiving the SETUP response  502  and the bit rate data  500 , the STB  10  executes a process of receiving a video/audio data stream (i.e. in RTP protocol) transmitted from the “source” address and “service port” port number described therein by using the “destination” address and “client_port” address. 
     The NAT conversion example in communication connection is as described above. In a band releasing operation starting from the TEARDOWN request  541 , a combination of respective addresses and ports of the STB  10  and the VoD server  20  used in reserving the above band starting from the SETUP response  502  may be used to instruct the release of the band. Furthermore, when a NAPT router is used in place of the NAT router, it is obvious to add a port conversion process to an address conversion process in the similar method. 
     Furthermore, in the configuration shown in the third exemplary embodiment, not only the VoD server  20  but also any VoD servers may be desired by the STB  10  for reproduction, which means that the RTSP proxy server  12  does not always know the address of the network band control unit  21  from the beginning. In such a case, a method may be employed to obtain a corresponding relationship between the VoD server  20  and the network band control unit  21  by using a directory service such as a DNS server. Described below will be an example of a method to solve the address of the network band control unit  21  in the case of using a DNS server. 
     The DNS server realizes a relationship between the VoD server and the network band control unit  21  by using a following corresponding table. It is assumed here that the VoD server  20  has an addres&#39;s expressed in an FQDN format as “hi-mpeg-server.com” and an IP address expressed as “10.10.10.202”, while the network band control unit  21  has an address in the FQDN format as “hi-mpeg-server.com.racs” and an IP address expressed as “10.20.3.81”. 
     The table stores following address relationships: 
     hi-mpeg-server.com 
     hi-mpeg-server.com.racs 
     Firstly, the RTSP proxy server  12  is used to obtain the FQDN format address expressed as “hi-mpeg-server.com” with respect to the IP address “10.10.10.202” of the VoD server  20  from the DNS server. Next, “.racs” is added to the FQDN address expressed as “hi-mpeg-server.com” so as to obtain “hi-mpeg-server.com.racs”. This “hi-mpeg-server.com.racs” is equal to the FQDN format address expression of the network band control unit  21 . Next, the IP address expressed as “10.20.3.81” with respect to the FQDN format address of the network band control unit  21  expressed as “hi-mpeg-server.com.racs” is obtained from the DNS server. The IP address thus obtained is used to transmit the band reserving request  511  or the like to the network band control unit  21 . 
     The aforementioned method converts the IP address of the VoD server  20  to the FQDN format for once and further adds fixed ending (i.e. “racs” in the above example) to the FQDN format so as to set the network band control unit  21  in the FQDN format corresponding to the VoD server  20 , whereby a corresponding relationship between each VoD server and the network band control unit in the internet network  200  operated by the provider B can be easily set and obtained by using only a standard DNS server. 
     As stated above, the present invention makes a control for reserving a band only by the RTSP proxy server without requiring complicated band control procedures. Furthermore, band control is also carried out based on a . . . protocol (i.e. RTSP protocol here) widely used in the existing streaming reproduction control, so that a device which controls a band does not need to know a special protocol and message. Moreover, the RTSP proxy server which relays RTSP communication makes a band control in a network, thereby allowing a client terminal and a server to use an existing protocol and interface. Furthermore, a band to be reserved is determined according to a streaming distribution request, which allows a band corresponding to the actually transferred content data to be reserved without reserving a redundant band.