Patent Publication Number: US-2007097955-A1

Title: Method and apparatus for ip multicast relay of live tv streaming traffic in a tv-over-ip environment

Description:
REFERENCE TO RELATED APPLICATIONS  
      This application is related to copending applications Ser. Nos. 10/826,519 carrying attorney docket no. U001 100084 entitled METHOD AND APPARATUS FOR A LOOSELY COUPLED, SCALABLE DISTRIBUTED MULTIMEDIA STREAMING SYSTEM filed on Apr. 16, 2004 and 10/826,520 entitled METHOD AND APPARATUS FOR MEDIA CONTENT DISTRIBUTION IN A DISTRIBUTED MULTIMEDIA STREAMING SYSTEM carrying attorney docket no. U001 100085 filed on Apr. 16, 2004, both applications having a common assignee with the present application, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION—FIELD OF THE INVENTION  
      This invention relates generally to the field of distributed multimedia streaming and more particularly to distribution of live TV multicast programming using unicast methods to tunnel through network segments without multicast support.  
     BACKGROUND OF THE INVENTION—DESCRIPTION OF THE RELATED ART  
      Broadcast of live TV programming is desirable for TV-over-IP applications. Many networks are enabled for multicast transmission to support direct streaming of the live broadcast. However, for many networks in the infrastructure end-to-end IP multicast from a live TV head-end to the set top box (STB) at the customer premises is not supported. In certain segments of the network routing can only be accomplished by unicast methods. However, for optimized management and efficiency, a centralized live TV head-end is desirable as opposed to introducing live TV multicast through multiple head ends dispersed through the system. Consequently, it is desirable to support unicast IP traffic to tunnel through segments of the network where multicast is not supported to deliver live TV strams from a single head-end to the entire IPTV network.  
     SUMMARY OF THE INVENTION  
      The present invention provides a system for live TV transmission over IP networks which incorporates a head end real-time encoding/transcoding server for converting live TV encoded data streams with root multicast relay servers receiving multicast data streams from the encoding/transcoding server. Multicast stream output is provided to a first set of relay servers through multicast capable routers and the root multicast servers provide unicast stream output to a second set of relay servers through unicast limited routers. The first and second sets of relay servers provide unicast and multicast stream output for child servers or local access networks. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
       FIG. 1  is a block diagram of a network system for multi-media streaming in which the present invention is employed;  
       FIG. 2  is a diagram network elements having multicast and unicast capability for operation of the present invention; and  
       FIG. 3  is a flow diagram of the process for operation of a multicast relay server according to the present invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1  demonstrates one embodiment of a network system designated a Media Switch with incorporates groups of media stations configured for use in a number of geographical areas or cities  102  served. A complete description of the Media Switch is disclosed in companion application Ser. No. 10/826,520 entitled METHOD AND APPARATUS FOR MEDIA CONTENT DISTRIBUTION IN A DISTRIBUTED MULTIMEDIA STREAMING SYSTEM having a common assignee with the current application, the contents of which are fully incorporated herein by reference. Each city employs a series of media stations  104  interconnected through the metropolitan area network (MAN)  106 . Each media station serves a number of subscribers having media consoles or STBs  108 . Each subscriber has a primary media station to serve its streaming requests. Additionally, each city incorporates on-line support layer elements including a media location registry (MLR)  110 , a home media station  112  and a content manager  114  in a data center (DC)  116 . For the embodiment shown, a principal city  102 ′ is chosen as a headquarters site. Associated with that site is a Media Asset Management (MAM) system  118 . In alternative embodiments, multiple cities incorporate a MAM for introduction of content into the system.  
      The MAM determines when and where to distribute a program. The CM publishes the program at the time specified by the MAM and the MLR identifies the location of the data for distribution.  
      Live TV broadcasts are a subset of the media streaming performed by the Media Switch. Multicast transmission within the MAN or between various cities each having a separate MAN may not be possible where the network connections will not support multicast.  FIG. 2  demonstrates the configuration of the overall network in a generalized form and with certain router served segments (designated  200 ) supporting multicast and other segments having only unicast capability which require relay by unicast (designated  202 )  
      Live TV signals through a real-time encoding/transcoding server  204  are turned into encoded video streams carried by IP multicast traffic in the head-end local network  206 . Multiple computer servers form multiple tree topology clusters through the open networks with three servers as the root servers  208   a,    208   b  and  208   c  (Root Multicast Relay Server  1 ,  2 ,  3 ), that are physically attached to the head-end live TV stream multicast network. Intermediate servers  211   a  and  211   b  (Middle Multicast Relay Server  1 - 1  and  2 - 1 ) are present in middle networks  210   a,  and  210   c.  The leaf servers  212   a,    212   b  and  212   c  (Leaf Multicast Relay Server  1 - 1 - 1 ,  2 - 1 - 1  and  3 - 1 ) in the cluster are attached to the edge access networks.  
      A centralized configuration server  214 , which may be incorporated as a portion of the Network Management System (NMS)] in the Media Switch application, controls the topology of the relay servers. When a relay server boots up, the topology from the configuration server is transmitted and stored in the relay server. Each relay server has the knowledge of its immediate precedent server and its immediate descendant servers in the cluster.  
      From the configuration server, along with the cluster topology, a relay server also receives the IP addresses and port numbers from which the sourced live TV streams that its precedent server forwards will be received. In addition, a relay server also obtains the IP addresses and port numbers to which it will send the received live TV streams for receipt by its descendant servers.  
      For segments without multicast capability, the root relay servers (Root Multicast Relay Server  1 ,  2  and  3 ) receive the live TV streams from the head-end IP multicast network and send the streams to their immediate descendant servers through unicast IP traffic in areas that multicast IP are not supported.  
      Each intermediate relay server receives the live TV streams from its immediate precedent server through unicast IP traffic and relays those streams to its immediate descendant servers through unicast IP. Concurrently, the relay server also multicasts out the received live TV streams to the access network it is attached to.  
      Each leaf relay server receives the live TV streams from its immediate precedent server through unicast IP traffic and multicasts out to the access network to which it is attached. A relay server has the capability to relay multiple streams at the same time with the input stream to the relay server either unicast or multicast depending on the networks that it is connected to. All relay servers provide multicast TV streams to customer premises if the access networks that they are connected to support multicast.  
      As specific examples referencing  FIG. 2 , the head-end network  206  incorporates the live TV signals through a Head End real-time encoding/transcoding server  204  which are turned into encoded video streams. These streams are controlled and stored in content server  216 . The configuration server communications with all of the servers in the system for topology management. Head end network  206  communicates through routers  218 . Router 1  handles traffic with a first intermediate network  210   a  through router 2 . Each of the intermediate or leaf networks may be a MAN as previously described. Router 1  is multicast capable, however, subsequent routers in the network stream, router 2  which serves network  210   a  and router 3  which serves a second intermediate network  210   b  are not multicast capable. Consequently, to service network  210   a  root multicast relay server  1  (RMRS  1 ) in the head-end network communicates with middle multicast relay server  1 - 1  (MMRS  1 - 1 ) using unicast IP traffic. MMRS  1 - 1  then distributes the data to the elements in access network  210   a  which has internal multicast capability including a content server  216   a,  which for the embodiment shown employs a media engine and media director as defined in patent application Ser. No. 10/826,519 entitled METHOD AND APPARATUS FOR A LOOSELY COUPLED, SCALABLE DISTRIBUTED MULTIMEDIA STREAMING SYSTEM, for storage of the data streams and DSLAM  220   a  for communication to a representative STB  222   a.    
      Similarly, router 6  which connects leaf network  210   b  to the system is not multicast capable. However, rather than requiring direct communication with the root multicast relay server to stream data to the network, the configuration server has provided data for communication by leaf multicast relay server  1 - 1 - 1  with middle multicast relay server  1 - 1 . MMRS 1 - 1  forwards by unicast IP traffic the broadcast streams to LMRS  1 - 1 - 1 . LMRS  1 - 1 - 1  then transmits the data to the elements of network  210   b  using the internal multicast capability of the network. Again, an exemplary content server  216   b  and a DSLAM  220   b  for communication with STB  222   b  are shown.  
      Router 3  and router 7  similarly support networks  210   c  and  210   d  respectively. However, multicast transmission capability is not available. Therefore, unicast transmission must again be employed. In network  210   c,  MMRS  2 - 1  receives unicast data from the Root multicast relay server  2  (RMRS  2 )  208   b  in head end network  206 . As with MMRS  1 - 1 , MMRS  2 - 1  distributes the data streams received to its own access network  210   c  using multicast trafficking and provides unicast transmission to LMRS  2 - 1 - 1  in network  210   d.  LMRS  2 - 1 - 1  then distributes the data within its access network by multicast.  
      Router 4  is multicast capable and root multicast relay server  3  receives live TV multicast data directly from the head end. Since RMRS  3  receives the live TV multicast data directly over multicast route, it is designated as a Root Multicast Relay Server even though not located in the head end local network. RMRS  3  then distributes the data to the elements in access network  210   e  including a content server  216   e  for storage of the data streams and DSLAM  220   e  for communication to a representative STB  222   e.    
      Network  210   f  is also a leaf network since router 5  does not support multicast transmission. LMRS 3 - 1  therefore receives unicast data from RMRS 3  and then distributes the data as multicast traffic within its access network  210   f.    
      Each multicast relay server in the system has the capability to receive and transmit either multicast or unicast traffic. The designation of root, middle or leaf is determined solely based on the skip level from the head end network.  FIG. 3  shows the communication sequence for the relay servers in the network. On boot-up, the relay server obtains the multicast IP and Port of all TV channels from the configuration server  302 . Additionally, the multicast relay server tree topology map is obtained from the configuration server to establish parent relay servers from which communications are received and child relay servers to which communications are forwarded  304 .  
      The relay server starts processing the channels  306  based on the data received from the configuration server. A determination is made  308  if all channels have been processed. If so, the relay server stops processing  310  until new configuration data is received. If not, the data for the next channel is accessed  312 . A determination is made if the current node (i.e. the relay server) has a parent server providing unicast data  314 . If not, reception of the unicast data stream on the designate port for that channel is terminated  316  and the incoming multicast stream for that channel is received from the channel&#39;s multicast group  318 .  
      If the relay server does have a parent server, incoming multicast stream traffic is terminated  320  and the incoming data stream for that channel is received as a unicast stream on the port designated for the channel  322 . The received data for the channel is then re-multicast to the elements of the access network for the relay server  324 .  
      A determination is made if the relay server has children for unicast transmission  326 . If no child server is present, processing is directly returned to block  308  for the next channel. If a child server has been defined by the configuration server, the unicast stream received is transmitted to the port designated for that channel on each of the children for that relay server  328 . Processing is then returned to block  308  for the next channel.  
      Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the following claims.