TWI740547B - Stream media synchonization playing method and stream media synchonization playing system - Google Patents

Abstract

A stream media synchronization playing method and a stream media synchronization playing system are provided. The stream media synchronization playing method includes: selecting a stream media address on a unicast server and registering the stream media address to a multicast server by a control unit; generating a multicast stream media address according to the stream media address by the multicast server; receiving the multicast stream media address from the multicast server and transmitting the multicast stream media address to multiple playing terminals by the control unit; transmitting a stream media data to the multicast server by the unicast server, and transmitting the stream media data to the playing terminals by the multicast server; and decoding the stream media data and transmitting the decoded stream media data to multiple displays by the playing terminals.

Description

Streaming media synchronization playing method and streaming media synchronization playing system

The present invention relates to a method for synchronously playing streaming media and a system for synchronously playing streaming media, and more particularly to a method for synchronously playing streaming media and a system for synchronously playing streaming media for splicing display systems.

The video splicing wall is a large rectangular display wall composed of multiple liquid crystal displays (LCD) or light emitting diode (LED) displays. It has the advantages of high resolution and large size. It is used in security monitoring and Conference halls are used more frequently.

Many network cameras and streaming media servers in the security surveillance field usually work in unicast mode. As the number of playback terminals increases, the load of the streaming media unicast server becomes higher, which makes the time of streaming media data received by different terminals inconsistent, and eventually causes the playback screen to be out of sync. Unicast is a point-to-point connection between the client and the server. "Point-to-point" means that each client receives a remote stream from the server. Only when the client makes a request, the unicast stream is sent. Unicast is the communication between a single sender and a single receiver over the network. In the splicing wall layout of the distributed splicing display system, different terminals play the same streaming media. They and the streaming media server both transmit the media stream in unicast mode, so the media data is not sent out together, so the playback terminal The display may not be the same frame, and you will see the phenomenon of similar screen tearing as a whole.

Streaming media unicast has a limited load capacity, and ultimately cannot meet the needs of multiple terminals requesting streaming media. Although some IP cameras support multicast, if they are all set to multicast in the built-in monitoring system, the multicast address and port allocation need to be considered, which adds tedious work.

The sender and receiver in multicast transmission are point-to-multipoint network connections. A sender can transmit the same data to multiple receivers at the same time but only needs to copy the same data packet, thus improving the efficiency of data transmission and reducing the possibility of congestion in the backbone network. Multicast solves the problem of low efficiency in unicast and broadcast methods. When some users in the network require specific information, they request to join a multicast group. The sender of the multicast information only sends the information once. The multicast router uses the multicast routing protocol to establish a tree-type route for the multicast data packet. , The information to be transmitted begins to be copied and distributed at the fork as far as possible.

In view of this, the present invention proposes a stream media synchronization playback method and a stream media synchronization playback system. When a distributed display system is spliced into a large TV wall, the synchronization of the playback content of each playback terminal can be improved to reduce screen tearing. Phenomenon.

The present invention provides a method for synchronous playback of streaming media, which includes: selecting a streaming media address on a unicast server by a control unit, and registering the streaming media address to the multicast server; by the multicast server Generate a multicast streaming media address according to the streaming media address; receive the multicast streaming media address from the multicast server by the control unit, and transmit the multicast streaming media address to multiple playback terminals; The unicast server sends the streaming media data to the multicast server, and the multicast server multicasts the streaming media data to the playback terminal; and the playback terminal decodes the streaming media data and decodes the decoded Stream media data to multiple displays.

The present invention provides a stream media synchronous playback system, including: a control unit; a unicast server coupled to the control unit; a multicast server coupled to the control unit and the unicast server; multiple playback terminals coupled to To the control unit and the multicast server; and multiple displays, coupled to the playback terminal. The control unit selects the streaming media address on the unicast server, and registers the streaming media address to the multicast server; the multicast server generates the multicast streaming media address according to the streaming media address; the control unit Receive the multicast streaming media address from the multicast server, and send the multicast streaming media address to multiple playback terminals; the unicast server sends the streaming media data to the multicast server, and the multicast server Multicasting the streaming media data to the playback terminal; and the playback terminal decodes the streaming media data and transmits the decoded streaming media data to multiple displays.

Based on the above, in the streaming media synchronization playback method and streaming media synchronization playback system of the present invention, the control unit selects the streaming media address on the unicast server and registers the streaming media address to the multicast server to generate multiple The streaming media address is broadcast, and the playback terminal receives the multicast streaming media address from the control unit. The multicast server multicasts the streaming media data received from the unicast server to the playback terminal, and the playback terminal decodes the streaming media data and transmits the decoded streaming media data to multiple displays.

FIG. 1 is a block diagram of a system for synchronously playing streaming media according to an embodiment of the present invention.

Please refer to FIG. 1, a stream media synchronization playback system 100 according to an embodiment of the present invention includes a control unit 110, a unicast server 120, a multicast server 130, playback terminals 141 to 149, and a display 150. The display 150 in FIG. 1 is for illustration only. In an embodiment, each of the playback terminals 141 to 149 may be coupled to a display 150 respectively. The present invention also does not limit the number of playback terminals 141 to 149. Hereinafter, the playback terminal 140 represents one or more playback terminals 141 to 149.

In one embodiment, the control unit 110 selects a streaming media address on the unicast server 120, and registers the streaming media address to the multicast server 130. The streaming media address is, for example, a Uniform Resource Locator (URL) for streaming media. The multicast server 130 generates a multicast streaming media address according to the streaming media address. The control unit 110 receives the multicast streaming media address from the multicast server 130 and transmits the multicast streaming media address to a plurality of playback terminals 140. The unicast server 120 transmits the streaming media data to the multicast server 130, and the multicast server 130 multicasts the streaming media data to the playback terminal 140. The playback terminal 140 decodes the streaming media data and transmits the decoded streaming media data to the multiple displays 150.

In an embodiment, multiple playback terminals 140 can be spliced to form a spliced video wall, and the control unit 110 can edit the coordinate position of each playback terminal 140 on the large spliced video wall according to the resolution uploaded by the playback terminal 140 Each coordinate position message is sent to each playback terminal 140. In this way, each playback terminal 140 can determine its own coordinates on the splicing video wall, and determine whether the playback content falls within its own coordinate area, thereby determining whether the current playback terminal 140 needs to play streaming media and display content in a specific area.

In an embodiment, the streaming media registration function can be initiated by the control unit 110 actively. The user can select a streaming media and place it on the video wall for playback. If the play area occupies multiple play terminals 140, a registration service is required. If the play area only occupies one play terminal 140, the control unit 110 only needs to select the play terminal 140 in the rectangular area of the play content to directly play the original streaming media without using the multicast forwarding function. The playback terminal 140 that is not in the playback area does not perform any operation. If the user moves the playback content rectangle to multiple playback terminals, the control unit 110 needs to first send a shutdown instruction to stop the original streaming media playback, and then send a registered streaming media service to let the playback terminal 140 according to the coordinates of the streaming media The message determines whether the current playback terminal needs to perform playback.

In one embodiment, the playback terminal 140 may be a device that runs an operating system and executes an application program running on the operating system. The streaming media command can control the connection status of the playback terminal 140. In one embodiment, the streaming media command uses Real Time Streaming Protocol (RTSP) and may include multiple commands, for example, used to obtain specific session interactive services and streaming media formats supported by the server. Description, instructions for the multicast address and communication port of streaming media transmission, start, pause, stop and other functions.

Fig. 2 is a block diagram of a control unit according to an embodiment of the present invention.

1 and 2 at the same time, the control unit 110 of an embodiment of the present invention includes a device management module 111, a terminal layout module 112, and a control command module 113 to communicate with the outside world through a network component 114.

In an embodiment, the device management module 111 can perform the discovery, addition, modification, and deletion operations of the unicast server 120, the multicast server 130, and the playback terminal 140. The unicast server 120 can be a network camera, a digital video recorder (DVR), a network encoding box and other equipment and supports the Open Network Video Interface Forum (ONVIF) standard. Provide users with quick access to streaming media into the system. Regarding other network streaming media that do not support ONVIF, you can manually enter the URL of the streaming media to join the system and give it a different name for later playback management. The modification function supports editing and modification of streaming media URLs and aliases. This method can be used to update when the actual streaming media properties change.

In one embodiment, the addition of the streaming media multicast server 130 and the playback terminal 140 can be implemented using a private agreement. The private agreement may include a search and discovery function, which can enumerate devices such as the multicast server 130 and the playback terminal 140 existing in the current network. The device information may include Internet Protocol (IP), port number, device Media Access Control (MAC) address, device type, and the resolution of the display 150 to which the playback terminal 140 is coupled. And other information. The IP and the communication port number are used for the control unit 110 to establish communication with the device and send different commands. The MAC address is a unique sign of the existence of a device. Since the device IP may change, the above-mentioned attribute information of the device will be automatically updated every time the device goes online to ensure that the control unit 110 can communicate normally with the newly added device.

In one embodiment, the terminal layout module 112 is used to determine the specific location of each playback terminal 140 in the spliced video wall. The splicing of multiple playback terminals 140 can realize a high-resolution display wall, which has good effects on security monitoring, conference halls and large exhibition halls, and is easy to implement. The control unit 110 can obtain the output resolution of each playback terminal 140 that has been added to the system. Fig. 3 is a schematic diagram of the coordinates of the playback terminal layout performed by the control unit according to an embodiment of the present invention. Please refer to Figure 3, the resolutions of the playback terminals 141 to 149 are all 1920*1080. The terminal layout module 112 lays out the play terminals 141 to 149 in a 3*3 manner, and sets the positions of the upper left corner and the lower right corner of the display 150 corresponding to the play terminals 141 to 149 on the x-axis and y-axis to indicate the specific layout positions. For example, the specific coordinates of the playback terminals 141 to 149 are (0,0), (1919,1079), (1920,0), (3839,1079), (3839,0), (5759,1079), (0,1080), (1919,2159), (1920,1080), (3839,2159), (3839,1080), (5759,2159), (0,2160), (1919,3239), (1920 ,2160), (3839,3239), (3839,2160), (5759,3239).

Referring to FIG. 2 again, the control instruction module 113 is used for playing management of different devices in the system, including playing in the splicing video wall, stopping playing, and moving.

Fig. 4 is a flowchart of a control unit executing a play instruction according to an embodiment of the present invention.

Referring to FIG. 4, in step S401, the control unit sends a streaming media registration instruction to the multicast server.

In step S402, the control unit sends the multicast streaming media address returned by the multicast server to the playback terminal.

In step S403, the playback terminal establishes a session communication with the multicast server according to the multicast streaming media address.

In step S404, the multicast server establishes a session with the unicast server and starts streaming media communication, receives data packets from the unicast server and sends them to the playback terminal by multicast.

In step S405, the playback terminal receives the streaming media data for playback and display.

Fig. 5 is a flowchart of a control unit executing a stop playing instruction according to an embodiment of the present invention.

Referring to FIG. 5, in step S501, the control unit sends a media closing instruction to the playback terminal.

In step S502, the playback terminal disconnects the communication with the multicast server and stops playing the content.

In step S503, the control unit sends a logout instruction to the multicast server to make the multicast server disconnect from the unicast server.

Please refer to FIG. 2 again, the control instruction module 113 can also perform the operation of moving the playing area. Specifically, if the cross-terminal (ie, cross-playing terminal 140) status of the play area changes, the control instruction module 113 needs to stop the play content and re-execute the preset play logic judgment. If the cross-terminal state of the play area remains unchanged, the control instruction module 113 directly sends a move play area instruction. The playing terminal 140 needs to determine by itself whether to stop playing.

Fig. 6 is a block diagram of a unicast server according to an embodiment of the invention.

6, the unicast server 120 may include an ONVIF device discovery module 121, a streaming media session module 122, a streaming media encoding RTP package sending module 123, and a network component 124. The ONVIF device discovery module 121 supports the ONVIF standard and is used to add devices such as network cameras. The ONVIF standard describes the model, interface, data type, and data interaction mode of online videos. The streaming media session module 122 can provide session interactive services. The streaming media encoding RTP encapsulation sending module 123 can encapsulate and send the streaming media data in Real-time Transport Protocol (RTP) packets. The network component 124 is, for example, a network chip. In one embodiment, audio and video streaming is performed using RTSP and RTP protocols. The RTSP protocol is used for media sessions to establish and control one or more time-synchronized continuous streaming media without sending continuous streaming itself. The RTP protocol specifies the standard data packet format for transmitting audio and video over the network and is created on the User Datagram Protocol (UDP). When the image data is compressed, the data is split according to RTP to generate a packet and send it out.

FIG. 7 is a block diagram of a multicast server according to an embodiment of the invention.

1 and 7, the multicast server 130 includes a device discovery module 131, a registration and deregistration service module 132, a session module 133, a media data reading module 134, a multicast forwarding module 135, and a network Component 136. The device discovery module 131 describes the device network IP address, device MAC address, and device type according to a predetermined protocol. The registration and deregistration service module 132 accepts the registration command from the control unit 110 to register the streaming media address and generate the multicast streaming media address, and interacts with the unicast server 120 after receiving the playback command from the playback terminal 140. And receiving a logout command to stop receiving the streaming media data of the unicast server 120. The session module 133 includes a registration command, a logout command, a play command, a pause command, and a stop command. The media data reading module 134 uses the RTP encapsulation format to process the streaming media data. The multicast forwarding module 135 receives the play instruction from the play terminal 140 and determines whether the streaming media corresponding to the play instruction is in the forwarding state. If the streaming media is not in the forwarding state, it establishes a session communication with the unicast server 120 to obtain audiovisual data Send out in multicast mode. The network component 136 is, for example, a network chip.

Fig. 8 is a block diagram of a playback terminal according to an embodiment of the present invention.

Referring to FIG. 8, the playback terminal 140 includes a streaming media player 810, which is executed on the hardware abstraction layer 840, the operating system 830, and the application layer 820. The bottom layer of the playback terminal 140 includes a processor 851, a network card 852, a power supply 853, an audio component 854, and a display component 855. The display component 855 is coupled to the display 860. The streaming media player 810 includes a device instruction module 811, a streaming media acquisition module 812, a media decoding module 813, and a display module 814. The device instruction module 811 performs device discovery and control instruction processing of the playback terminal 140. Device discovery can be achieved with a private agreement. The control unit 110 sends a device discovery request instruction in a fixed format and the playback terminal 140 can send a corresponding response. The returned information includes information such as network IP, port number, device MAC address, and device type. The control unit 110 can establish a connection communication with the playback terminal 140 according to the returned message. The control instruction processing of the play terminal 140 is used to receive play control instructions from the control unit 110, including adding, deleting, and moving play sources. The playback terminal 140 determines whether to perform a playback operation according to whether there is an overlapping area between the current terminal coordinate position and the playback source. The delete command can stop the video streaming. The movement command will update the display according to the overlapping area of the playback source and the current terminal, and the display area coordinates need to be converted to absolute coordinates in the current terminal to be displayed correctly. It is worth noting that the coordinates sent by the control unit 110 correspond to the coordinates of the entire spliced video wall.

The streaming media acquisition module 812 uses RTSP and RTP protocols. The RTSP protocol works as a client server and supports a variety of control commands, such as pause/continue, back, forward, etc. The RTSP protocol is a multimedia playback control protocol that allows users to control when playing real-time data downloaded from the Internet. The RTSP protocol is an application layer protocol and provides an extensible framework to enable streaming media to be controlled and on-demand. However, the RTSP protocol itself is not used to transmit streaming media data and uses the sub-protocols of the RTSP protocol RTP and Real-Time Transmission Control Protocol (Real-Time Transmission Control Protocol). Time Transport Control Protocol (RTCP) provides services to complete the transmission of streaming media data. RTP and RTCP transmit data through UDP and RTSP transmits data through Transmission Control Protocol (TCP). RTP is used to transmit data in real time. The information provided by RTP includes: timestamp, serial number, and payload format (that is, the encoding format used to describe the data). RTCP is used for Quality of Service (QoS) feedback and synchronized media streaming. Compared with RTP, the bandwidth occupied by RTCP is very small (for example, 5% of RTP). The RTP data packets received by the playback terminal are transmitted via UDP, so packet loss or disorder may occur. If a packet occurs, the received data packet cannot be reassembled into a complete video compression packet (for example, an H.264 data packet), and other data of the same video frame has to be discarded.

The media decoding module 813 can select a corresponding decoder according to different types of audio or video. Each encoded data packet contains a time stamp. In one embodiment, the movie stream timestamp can be used as a reference clock to control the media decoding speed and achieve synchronous media playback. When the playback terminal 140 obtains a frame of data through the RTSP and RTP protocols, it can record the system local clock and the time stamp of the media stream as a reference clock. In this way, it is necessary to convert the streaming time stamp of each media data packet into a local time stamp according to the reference clock during decoding and add a time delay, where the time delay is used for buffer storage and synchronization. If the error between the converted time stamp and the current local clock is within the preset threshold, it is determined that decoding is required. If the time after conversion is greater than the current local clock, there is no need to continue to wait for decoding. If the converted time stamp is less than the current local clock, it means that the current frame is decoded too late and needs to be discarded.

The display module 814 displays the decoded image according to the position of the playback source in the spliced video wall.

To sum up, in the streaming media synchronization playback method and streaming media synchronization playback system of the present invention, the control unit selects the streaming media address on the unicast server and registers the streaming media address to the multicast server to A multicast streaming media address is generated, and the playback terminal receives the multicast streaming media address from the control unit. The multicast server multicasts the streaming media data received from the unicast server to the playback terminal, and the playback terminal decodes the streaming media data and transmits the decoded streaming media data to multiple displays. Therefore, the streaming media synchronization playback method and streaming media synchronization playback system of the present invention can solve the problem of unsynchronized display system images caused by insufficient streaming media service capabilities in a distributed splicing display system, and use a smaller network The transmission load allows the distributed splicing display system to play streaming media smoothly.

Although the present disclosure has been disclosed in the above embodiments, it is not intended to limit the present disclosure. Anyone with ordinary knowledge in the technical field can make some changes and modifications without departing from the spirit and scope of this disclosure. Therefore, The scope of protection of this disclosure shall be subject to those defined by the attached patent scope.

100: Streaming media synchronization playback system 110: control unit 120: Unicast server 130: Multicast server 140, 141~149: Play terminal 150: display 111: Device Management Module 112: Terminal layout module 113: Control Command Module 114: network components S401~S405: Steps for the control unit to execute playback instructions S501~S503: The control unit executes the steps to stop playing instructions 121: ONVIF device discovery module 122: Streaming media session module 123: Streaming media encoding RTP package sending module 124: network components 131: Device Discovery Module 132: Register and deregister service modules 133: Conversation Module 134: Media data reading module 135: Multicast forwarding module 136: network components 810: Streaming Media Player 811: Equipment Command Module 812: Streaming Media Acquisition Module 813: Media Decoding Module 814: display module 820: application layer 830: operating system 840: Hardware Abstraction Layer 851: processor 852: network card 853: Power 854: Audio component 855: display component 860: display

FIG. 1 is a block diagram of a system for synchronously playing streaming media according to an embodiment of the present invention. Fig. 2 is a block diagram of a control unit according to an embodiment of the present invention. Fig. 3 is a schematic diagram of the coordinates of the playback terminal layout performed by the control unit according to an embodiment of the present invention. Fig. 4 is a flowchart of a control unit executing a play instruction according to an embodiment of the present invention. Fig. 5 is a flowchart of a control unit executing a stop playing instruction according to an embodiment of the present invention. Fig. 6 is a block diagram of a unicast server according to an embodiment of the invention. FIG. 7 is a block diagram of a multicast server according to an embodiment of the invention. Fig. 8 is a block diagram of a playback terminal according to an embodiment of the present invention.

100: Streaming media synchronization playback system

110: control unit

120: Unicast server

130: Multicast server

140, 141~149: Play terminal

150: display

Claims (14)

A method for synchronously playing streaming media, including: A control unit selects a streaming media address on a unicast server, and registers the streaming media address to a multicast server; Generating a multicast streaming media address according to the streaming media address by the multicast server; Receiving the multicast streaming media address from the multicast server by the control unit, and transmitting the multicast streaming media address to multiple playback terminals; Sending a stream of streaming media data to the multicast server via the unicast server, and multicasting the streaming media data to the playback terminals via the multicast server; and The playback terminals decode the streaming media data and transmit the decoded streaming media data to multiple displays. The method for synchronously playing streaming media according to claim 1, wherein the control unit discovers and adds the unicast server, a multicast server, and the playback terminals in a network. The method for synchronous playback of streaming media according to claim 1, wherein the control unit adds all the playback terminals on the line, and forms a spliced video wall according to the playback terminals, wherein the control unit marks each of the playback terminals The terminal is splicing a position information of the video wall and transmitting the position information to each of the playback terminals. The method for synchronously playing streaming media according to claim 1, wherein the unicast server includes a network camera, and the control unit is implemented through an Open Network Video Interface Forum (ONVIF) standard Add the webcam, where the open web video connector forum standard describes a model, an interface, a data type, and a data interaction mode of a web video. The method for synchronously playing streaming media according to claim 1, wherein the multicast server includes: A device discovery module, which describes a device network IP address, a device MAC address, and a device type according to a predetermined protocol; A registration and deregistration service module accepts a registration command from the control unit to register the streaming media address and generate the multicast streaming media address, and then communicate with the broadcast terminal after receiving a playback command from the playback terminals. The unicast server interacts and receives a logout command to stop receiving the streaming media data of the unicast server; A session module, including the registration command, the logout command, a play command, a pause command, and a stop command; A media data reading module that uses a Real-time Transport Protocol (RTP) encapsulation format to process the streaming media data; and A multicast forwarding module that receives a play instruction from the play terminals and determines whether a stream of media corresponding to the play instruction is already in a forwarding state, and if the streaming media is not in the forwarding state, it will communicate with the unicast server The device establishes a session communication to obtain an audio-visual data. The streaming media synchronous playback method of claim 1, wherein the playback terminals receive the streaming media data in a multicast manner, and a packet corresponding to the streaming media data is encapsulated in the real-time transmission protocol encapsulation format. , And the packet is transmitted through a User Datagram Protocol (UDP). The method for synchronous playback of streaming media according to claim 1, wherein the control unit, the multicast server, and the playback terminals are coupled to a network that supports multicast, and the unicast server is coupled to a Local area network or a public network. A synchronous playback system for streaming media, including: A control unit; A unicast server, coupled to the control unit; A multicast server, coupled to the control unit and the unicast server; Multiple playback terminals, coupled to the control unit and the multicast server; and Multiple displays, coupled to the playback terminals, where The control unit selects a streaming media address on the unicast server, and registers the streaming media address to the multicast server; The multicast server generates a multicast streaming media address according to the streaming media address; The control unit receives the multicast streaming media address from the multicast server, and transmits the multicast streaming media address to the playback terminals; The unicast server sends a stream of streaming media data to the multicast server, and the multicast server multicasts the streaming media data to the playback terminals; and The playback terminals decode the streaming media data and transmit the decoded streaming media data to the displays. The stream media synchronous playback system according to claim 8, wherein the control unit discovers and adds the unicast server, a multicast server, and the playback terminals in a network. The streaming media synchronous playback system according to claim 8, wherein the control unit adds all the playback terminals on the line, and forms a spliced video wall according to the playback terminals, wherein the control unit marks each of the playback terminals The terminal is splicing a position information of the video wall and transmitting the position information to each of the playback terminals. The streaming media synchronous playback system according to claim 8, wherein the unicast server includes a network camera, and the control unit is implemented through an Open Network Video Interface Forum (ONVIF) standard Add the webcam, where the open web video connector forum standard describes a model, an interface, a data type, and a data interaction mode of a web video. The streaming media synchronous playback system according to claim 8, wherein the multicast server includes: A device discovery module, which describes a device network IP address, a device MAC address, and a device type according to a predetermined protocol; A registration and deregistration service module accepts a registration command from the control unit to register the streaming media address and generate the multicast streaming media address, and then communicate with the broadcast terminal after receiving a playback command from the playback terminals. The unicast server interacts and receives a logout command to stop receiving the streaming media data of the unicast server; A session module, including the registration command, the logout command, a play command, a pause command, and a stop command; A media data reading module that uses a Real-time Transport Protocol (RTP) encapsulation format to process the streaming media data; and A multicast forwarding module that receives a play instruction from the play terminals and determines whether a stream of media corresponding to the play instruction is already in a forwarding state, and if the streaming media is not in the forwarding state, it will communicate with the unicast server The device establishes a session communication to obtain an audio-visual data. The streaming media synchronous playback system according to claim 8, wherein the playback terminals receive the streaming media data in a multicast manner, and a packet corresponding to the streaming media data is encapsulated in the real-time transmission protocol encapsulation format. , And the packet is transmitted through a User Datagram Protocol (UDP). The streaming media synchronous playback system according to claim 8, wherein the control unit, the multicast server and the playback terminals are coupled to a network supporting multicast, and the unicast server is coupled to a Local area network or a public network.

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