Abstract:
The present invention relates to a satellite IP multicasting system and method for constructing an IP multicast network by a unit of internet node having a router for subscriber connection or a switch, and for transmitting a multicasting packet transmitted from a content provider into a local IP multicast network via a satellite. The satellite IP multicasting system features a backbone network, a content provider, a satellite network and a local network. The local network, which is interworked with the backbone network, is configured to multicasting protocol at a router or a switch, performs reverse path forwarding by static multicasting routing setup on a router or a switch connected to the satellite network via Ethernet and on a subscriber router or by IP designation of the same sub-net with source address of IP header of the multicast packet to an output port of a satellite data receiver and a port of a router connected to the satellite data receiver, and transmits the multicast packet into a terminal client.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an IP multicasting system, and more specifically, to a satellite IP multicasting system wherein satellite multicasting network is used to bypass backbone network of ISP and satellite network is interworked directly to local node of ISP, and method for constructing an IP multicast network by a unit of local node of ISP, that is, or by a unit of internet node having a router for subscriber connection and a switch, and for transmitting a multicasting packet transmitted from a content provider into a local IP multicast network via a satellite, and method for interworking satellite multicasting network and local access network. 
     2. Description of the Prior Art 
     In comparison with multicasting protocol, unicasting protocol is inefficient in terms of network traffic and transmission cost because the same data packet is replicated at a source server and is sent respectively to each subscriber who is connected to the source server, which causes network traffic in proportion to the number of concurrent connectors. 
     Despite the merit of IP multicasting protocol, it is very difficult to embody the solution on the whole internet network due to the network complexity of backbone network and possibility and impact of anomaly during new configuration process. 
     As shown in  FIG. 1 , a solution used in current internet broadcasting generally uses a unicasting system wherein a server of an internet broadcasting station exchanges data with a viewer. However, simultaneous connectors should share limited capacity of transmission network between the internet broadcasting station and connectors in the unicasting system. 
     Suppose that an internet broadcasting provider provides internet broadcasting service via a transmission network of 155 Mbps at a transmission speed of 512K, In this case, when simultaneous connectors are over 300, capacity of transmission network reaches the limit. 
     If the connectors exceed 300, the screen display is stopped or picture quality is degraded. As a result, a user cannot watch a normal screen. 
     Referring to  FIG. 1 , in the Contents Provider (hereinafter, referred to as “CP”) such as an internet broadcasting provider, a management server  14  and a media server  12  are connected to a router  10  constituting main nodes. The router  10  is connected to a router  22  of a backbone network  20 . The other terminal router  24  of the backbone network  20  is connected to a router  30  constituting networks of corporations or PC bang. 
     When the CP provides motion picture transmission service of 512 Kbps, and 15 subscribers 32 simultaneously connects with this service, a media server (main server) of the CP in unicasting protocol should transmit data to 15 clients 32, respectively. As a result, actually required capacity of transmission network is 7.680 Mbps (512 Kbps×15) in proportion to data to be transmitted and the number of simultaneous connectors. 
     The CP should secure a band of bottleneck interval (between the router  10  and the router  22  of the backbone network  20 ) so that simultaneous connectors may receive the service without delay. However, since it costs a great deal for security of sufficient band, the CP cannot but limit the number of simultaneous connectors or the content transmission speed. 
     In case of the band of bottleneck interval secured as 8 Mbps, if the number of simultaneous connectors exceeds 15, a required band exceeds 8 Mbps. As a result, a user cannot receive the normal motion picture service. 
     When contents such as internet broadcasting are provided with the unicast system, channels cannot be effectively used due to bottleneck phenomenon of network. The bottleneck phenomenon also causes the increase in CPU load of the media server  12  or the routers  10  and  22  of the CP for duplicating data as many as the number of clients. As a result, the unicast system is not suitable when the internet broadcasting has a lot of clients. 
     The security of required transmission band, the limit of subscribers and the enlargement of server capacity mainly degrade profitability of content providers. When subscribers of more than the transmission band are allowed for improvement of profitability, transmission delay occurs so that service of good quality cannot be provided. Additionally, the CP should reduce the amount of content data to attract subscribers as many as possible in a limited transmission line. As a result, the quality of image is degraded, and improvement of contents and internet broadcasting business is prevented. 
     In order to solve the problem of the unicast system, a content delivery network (hereinafter, referred to as “CDN”) solution is suggested. 
     The CDN comprises streaming servers  26  individually disposed in various local nodes  28  of a backbone network  20  other than a media server (main server)  12  of a CP. The CDN provides contents from the most adjacent local node to a user by previously mirroring main contents to the streaming server  26  of the local node  28 . The CDN reduces a system (server, switch, router) path which a subscriber connects with and pass through, thereby decreasing transmission delay resulting from network traffic and distributing load of the media server  12  of the CP to simultaneous connection of subscribers. As a result, the quality of service to transmission speed and transmission delay is more or less improved. 
     If a user connects with a management server  14  of the CP hosting in the CDN to select motion picture watching, the management server  14  of the CP transmits a URL (uniform resource locator) of corresponding contents in the main node management system (not shown) into the user, and the user requires the corresponding contents to the main node management system of the CDN with the transmitted URL. 
     The main node management system of the CDN detects location of a user to transmit a URL of the optimum local node router  24 . If the user request contents to the local node router  24  corresponding to the URL transmitted from the CDN management system, the streaming server  26  of the local node router  24  transmits motion images into the user that requests the contents. 
     However, the above-described CDN has not solved the problems of unicast transmission systems. Although the media server  12  of the CP may load traffic to push multimedia contents into local nodes (e.g.  11  local nodes) using a leased channel, connectors should share the limited line capacity of networks from the streaming server  26  of the local node router  24  to subscribers like the above-mentioned problem of the unicast transmission system of  FIG. 1 . 
     Additionally, in proportion to the transmission speed and the number of simultaneous connectors, the transmission band required between the main server and various local node streaming servers should be hired from internal service providers or CDN providers. 
     In spite of the above-described problems such as traffic of network in the conventional unicast transmission system and the CDN solution, the limitation in the number of simultaneous connectors and the cost resulting from enlargement of capacity of leased channels, to embody an IP multicasting solution on the whole internet network is difficult in aspects of technology, time and cost. 
     As a result, it is difficult to smoothly provide content service for internal broadcasting or internet in education wherein multiple access is performed via the conventional internet network. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to embody an IP multicasting network from a content provider to a terminal subscriber by interworking a ground transmission network with a satellite multicasting network used to bypass the backbone network in which it is very difficult to embody multicasting protocol due to network complexity and high possibility of network anomaly. 
     It is another object of the present invention to embody a satellite IP multicasting network to overcome the limitation in transmission paths of content providers, capacity enlargement of servers and the number of simultaneous connectors. 
     It is still another object of the present invention to embody a IP multicasting network from a content provider to a terminal subscriber by embodying local IP multicasting network and interworking the local IP multicasting network with a satellite network. 
     In an embodiment, a satellite IP (Internet Protocol) multicasting system comprises a backbone network, a content provider, a satellite network and a local network. The content provider provides multimedia contents. The satellite network transmits contents provided from the content provider in the form of multicast packet to the local node of ISP. The local network, which is interworked with the backbone network, is configured to multicasting protocol at a router or switch, performs reverse path forwarding by static multicasting routing setup on a router connected to the satellite network via Ethernet and on a subscriber router or by designating IP of the same sub-net with source address of IP header of the multicast packet to an output port of a satellite data receiver and a port of a router connected to the satellite data receiver, and transmits the multicast packet into a terminal client. 
     Preferably, the satellite network comprises a satellite hub system, a satellite and a satellite reception system. The satellite hub system comprises a multimedia server for designating a multicast group address to the multimedia packet, an IP gateway for transforming the multimedia packet into transport stream data, a modulator for modulating the transport stream data and a satellite transmitter for wirelessly transmitting data. The satellite reception system comprises a satellite receiver for receiving a satellite modulating signal from the satellite and a satellite data receiver for demodulating a multicast packet made in the multimedia server from the satellite modulating signal and transmitting the multicast packet into a predetermined destination. 
     It is preferable that the router of the local network declares multicast packet as well as multicasting protocol to be static multicast routing to a start source IP for proper RPF check or designates IP of the same sub-net with source address of IP header of the multicast packet to an output port of a satellite data receiver and a port of a router connected to the satellite data receiver. 
     In an embodiment, an IP multicasting method of a multicast packet of a router in a local network interworked with a backbone network comprises performing unilateral reverse path forwarding with static multicast routing declaration of the router to the multicast packet or with IP designation of the same sub-net with source address of IP header of the multicast packet to an output port of a satellite data receiver and a port of a router connected to the satellite data receiver, wherein the declaration or the designation is constituted of a source IP of a destination media server of the multicast packet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and further advantages of the invention may be better understood by referring to the following description, in conjunction with the accompanying drawings, wherein: 
         FIG. 1  illustrates a conventional unicast transmission method; 
         FIG. 2  illustrates the conventional CDN-type service; 
         FIG. 3  illustrates a satellite IP multicasting system according to a preferred embodiment of the present invention; 
         FIG. 4  illustrates the multicasting packet transmission operation according to an embodiment of the present invention; 
         FIGS. 5   a  through  5   d  illustrate the multicasting group authentication process according to an embodiment of the present invention; and 
         FIG. 6  illustrates the traffic state according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In an embodiment, multimedia contents to be streamed from a CP to a satellite transmission system is transmitted with a multimedia packet. The satellite transmission system transmits a satellite modulating signal corresponding to the multimedia packet via a satellite into a satellite reception system. The satellite reception system demodulates the satellite modulating signal into the multimedia packet to transmit the demodulated signal into a local IP multicasting network. The local IP multicasting network forwards the multimedia packet into a terminal router. 
     Referring to  FIG. 3 , the content providers  100   a  and  100   b  such as internet broadcasting station or cyber university connected to a backbone network  200  comprise a management server  102 , a streaming server  104  and a router  106 . 
     The management server  102  controls networks, internet connection, authentication and streaming. The streaming server  104  provides multimedia contents, interworked with control of the management server  102 . Here, the multimedia packet is preferably transmitted with unicasting or multicasting protocol. 
     The backbone network  200  comprises a plurality of switches  202  and a plurality of routers  204 . The terminal router  204  constitutes a main node connected to the router  106 . The terminal router  206  of the backbone network  200  is connected to a local network  600 . 
     The multimedia packet transmitted from the CP  100   a  and  100   b  with unicasting protocol is transmitted via the main node of the backbone network  200  into a router  310  of a satellite transmission system  300 . Here, the backbone network  200  identifies a destination address of the multimedia packet to transmit the multimedia packet into a destination router  310 . 
     The above multimedia packet is transformed into a satellite modulating signal in the satellite transmission system  300 . The satellite transmission system  300  comprises a multimedia server  312 , an IP gateway  313 , a modulator  316  and a satellite transmitter  318 , which are connected to the router  310 , via a network each other. The satellite transmission system  300  performs a unilateral transmission into a local network  600 . 
     The multimedia server  312  designates a multicast group address to transform the multimedia packet transmitted with unicasting protocol into a multicasting packet, and determines a transmission speed of contents depending on packet residual period in the network, that is, TTL values and on required service quality. 
     The IP gateway  314  performs a statistical multiplexing function on multicast data transmitted from the multimedia server  312  and a CAS (Conditional Access System) function. The IP gateway  314  also attaches a program identifier to various multicast data to transform the data into a MPEG-2 transport stream signal, and then transmits the stream signal into the modulator  316 . 
     For communication with a satellite  400 , the modulator  316  modulates the MPEG-2 transport stream signal into a DVB-S signal and transmits the DVB-S signal into the satellite transmitter  318 . 
     The satellite transmitter  318  sends data to the satellite  400  by a predetermined carrier frequency signal. 
     The multimedia server  312  designates a multicast group address to he multimedia packet transmitted from the satellite transmission system  300  with the unicast protocol. The IP gateway  314  transforms the multimedia packet into the transport stream data. The transport stream data are modulated in the modulator  316 , and then sent from the satellite transmitter  318 . 
     For the satellite  400  up-linked with the satellite transmission system  300  and down-linked with the satellite reception system  500  are used INMARSAT having a frequency band of L/S band (upward 1.5 Ghz, downward 1.5 Ghz/2.5 Ghz), INTELSAT of C band (upward 6 Ghz, downward 4 Ghz), Koreasat Mugunghwa No. 1 and 2 of Ku band (upward 14 Ghz, downward 12 Ghz) or Koreasat Mugunghwa No. 3 of Ka band (upward 30 Ghz, downward 20 Ghz). A satellite having the optimum frequency band may also be selected in consideration of economical efficiency and applicability to systems depending on intentions of manufacturers. 
     The satellite reception system  500  comprises a satellite receiver  510  and a satellite data receiver  520 . The satellite receiver  510  transmits a signal received from the satellite  400  into the designated satellite data receiver  520 . The satellite data receiver  520  demodulates the multicast packet made in the multimedia server  312  from the satellite modulating signal to transmit the demodulated packet into the local network  600 . 
     The local network  600  comprises an internet network node  610 , sub-networks  650  and  670 , routers  630  and  640  and subscriber terminals  635  and  645 . The internet network node  610  comprises a router or a switch for local nodes of ISP, that is, for subscriber connections. The sub-networks  650  and  670  are connected to an optical terminal station  620  connected to the internet network node  610 . The routers  630  and  640  are comprised in PC bang connected to the internet network node  610 . Here, the sub-network  650  comprises an optical terminal station  652  connected to the optical terminal station  620 , and the sub-network  670  comprises an optical terminal station  672  connected to the optical terminal station  620 . The optical terminal station  652  is connected to a router  654 , a switch  656 , a switching hub  658  and LAN cards  660 . The optical terminal station  672  is connected to a router  674 , a switch  676 , a concentrator  678 , modems  680  and LAN cards  682 . 
     The internet network node  610  comprises a router  206  connected to the backbone network  200 , a plurality of switches  612  and  618 , and routers  614  and  616  connected to subscribers. 
     In the above-described local network  600 , the multicast packet demodulated in the satellite data receiver  520  is multicast into a terminal of a corresponding subscriber through the switches  612  and  618  and the routers  614  and  616  of the internet network node  610 . 
     In the local network  600 , the router of the local network declares the multicast packet to be static multicast routing to a source address or designates IP of the same sub-net with source address of IP header of the multicast packet to an output port of a satellite data receiver and a port of a router connected to the satellite data receiver. 
     Specifically, the routers  614  and  616  of the internet network node  610 , and the routers  630 ,  640 ,  654  and  674  of the lower network judge whether data is a multicast packet. When the data is a multicast packet, the routers declare the multicast packet to be static multicast routing to an IP of the source address or designates IP of the same sub-net with source address of IP header of the multicast packet to an output port of a satellite data receiver and a port of a router connected to the satellite data receiver. 
     Referring to  FIG. 4 , a router R 1  corresponds to the first routers  614  and  616  of  FIG. 3 , and a router R 2  corresponds to the second routers  630 ,  640 ,  654  and  674  of  FIG. 1 . 
     In case of the multicast packet, the router R 1  declares static multicasting routing to IP of an output port of the satellite data receiver  520 . The router R 2  declares the multicasting routing to the source address to be static multicast routing to a serial interface IP of the router R 1  or designates IP of the same sub-net with source address of IP header of the multicast packet to an output port of a satellite data receiver and a port of a router connected to the satellite data receiver. 
     The router R 2  sets a predetermined traffic to be transmitted not by repeated packet duplication but by once packet duplication between the routers R 1  and R 2 , that is, the serial interval. 
     In other words, only one packet is duplicated even when all clients are connected to the same multimedia contents in e0 of the router R 2 . 
     The source address of the multicasting routing is used to send traffic to a group represented by a multicast group address. The multicast router determines directions toward the source and the clients. 
     Here, the transmission into the receiver is RPF (Reverse Path Forwarding). 
     The RPF helps the router to properly distribute traffic toward the receiver. If the multicast packet is entered, the router checks the RPF. If the check result is normal, the packet is forwarded. Otherwise, the packet is dropped. 
     The satellite data receiver  520  transmits the multicast packet from the media server  312  into the router R 1 . Without specific setup of routing, the router R 1  cannot perform a normal RPF check on the multimedia packet. 
     Since the interval between the IP gateway  314  and the satellite data receiver  520  is a unilateral interval via a satellite network, the network between the router R 1  and the media server  312  is disconnected. Thus, even when the multicast packet reaches the router R 1 , the router R 1  does not perform a proper RPF process because the router R 1  does not have a unicast routing table to the source. As a result, the router R 1  does not forward but drops the multimedia packet when the router R 1  configures multicasting protocol. 
     In an embodiment, the filtering in the routers R 1  and R 2  and the proper setup of TTL values to channel address represented by the group in the media server  312  prevent all hosts from being senders. Therefore, an inflow of the multicast packet from subscriber terminals is intercepted. 
     The unilateral multicast routing is set by the static multicast routing for the proper RPF check in the routers R 1  and R 2  or by IP designation of the same sub-net with source address of IP header of the multicast packet to an output port of a satellite data receiver and a port of a router connected to the satellite data receiver. As a result, the RPF drop resulting from the network disconnection due to unilateral characteristic of satellite interval can be prevented. 
     In case of the router R 1  [cisco router], the IP multicasting setting is done as presented below:
         ip multicasting   int e0   ip pim sparse-mode   int el   ip pim sparse-mode   int s0   ip pim sparse-mode   ip mroute [source ip address] [ip address of Ethernet connection port to the router R 1  of the satellite data receiver]       

     Otherwise, IP of the same sub-net with source address of IP header of the multicast packet can be designated to an output port of a satellite data receiver and a port of a router connected to the satellite data receiver. 
     Although the cisco routers are exemplified for the router setup herein, the setup may be changed depending on equipment and the same principle is applied. 
     Referring to  FIG. 5   a , contents are transmitted into a terminal subscriber client of the local network through path A of  FIG. 5   a.    
     A subscriber authenticated as a predetermined multicast group connects with the management server  102  of the CP  100   a  via the wide area network  610  and the backbone network  200  through path B of  FIG. 5   b  in order to request IGMP (Internet Group Management Protocol). When the subscriber is proved to be legitimate, the management server  102  of the CP  100   a  performs authentication through path C of  FIG. 5C , and authorizes the subscriber to enter the multicast group. A user proved to be legitimate through the above authentication process may receive a multicast packet transmitted into LAN of the local network  600  through path D of  FIG. 5   d.    
     As shown in  FIG. 6 , contents corresponding to a channel, for example motion picture of 512K can be transmitted depending on unicast protocol from the streaming server  104  of the CP through the router  106  and the terminal router of the backbone network  200  to the satellite transmission system  300 . The satellite signal is unilaterally transmitted between the satellite transmission system  300  and the satellite reception system  500 . The traffic of 512K is transmitted into terminal clients by each path included in the local network  600 . 
     Since only a multicast packet is transmitted into a terminal client, the number of simultaneous connectors is not limited, and the bottleneck phenomenon resulting from the large number of simultaneous connectors from the CP to the internet network or in each interval of the local network does not occur. As a result, the traffic of the whole network may be improved. 
     The embodiment of the present invention may be selectively applied in case of multimedia contents which require real time transmission, and may be also applied with the unicast transmission system in case of non-real time transmission. 
     Other embodiment according to the present invention may be variously provided. Specifically, a case wherein the local network according to an embodiment is applied to the CDN. In other words, if the static multicast routing declaration applied to the CDN is performed in the local network, the contents transmitted via the conventional unicast protocol may be transmitted via the multicast protocol according to an embodiment of the present invention. 
     Accordingly, an IP multicasting system according to an embodiment of the present invention enables the efficient and stabilized operation of networks due to reduction of multimedia traffic on the whole network for communication operator. 
     Additionally, according to an embodiment of the present invention, the network environment satisfactory to content providers that require transmission of high capacity multimedia data such as internet broadcasting, tele-education or multi-user internet game. 
     While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and described in detail herein. However, it should be understood that the invention is not limited to the particular forms disclosed. Rather, the invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined in the appended claims.