Packet scheduling system for digital video broadcasting

Abstract

A system and method for processing multiple client flows to a single outbound link is provided. Specifically, a scheduler enforces a maximum symbol rate on the aggregate output flow. Inbound client flows are scheduled for output based upon individual quality of service parameters. For each round of scheduling, packets configured for a first bandwidth range are processed in a first pass and packets configured for a second bandwidth range are processed in a second pass. The packets are placed into frames before transmission. A comparison of the actual symbol usage with the estimated symbol is made and used to determine how to schedule inbound client flows for the second pass of the round.

1 . A device, comprising:
 a first input buffer to store a first input stream;   a second input buffer to store a second input stream;   a scheduling multiplexer coupled to the first input buffer and the second input buffer to schedule a plurality of packets for transmission based upon an estimated quota of symbol consumption;   an output buffer coupled to the scheduling multiplexer to store packets scheduled for transmission; and   a framer coupled to the output buffer to generate a baseband frame and further configured to determine an actual symbol consumption based on a MODCOD for the baseband frame.   
     
     
         2 . The device of  claim 1 , wherein the framer communicates the actual symbol consumption to the scheduling multiplexer. 
     
     
         3 . The device of  claim 2 , wherein the scheduling multiplexer uses the actual symbol consumption to determine a next estimated quota of symbol consumption for a next transmission round. 
     
     
         4 . The device of  claim 1 , further comprising a packetizer coupled to the output buffer to generate MPEG-2 transport stream packets. 
     
     
         5 . The device of  claim 1 , further comprising a modulator coupled to the framer to convert a flow of baseband frames to a stream of radio frequency symbols. 
     
     
         6 . A system, comprising:
 N buffers, wherein N is an integer greater than one, wherein each of N buffers is coupled to a client to receive an input stream;   a scheduling multiplexer coupled to N buffers configured to schedule a plurality of input stream packets for transmission to a single outbound link of a network based on an estimated symbol consumption on an outbound link during a present round;   a packetizer coupled to the multiplexer configured to convert a plurality of input stream packets to MPEG-2 transport stream packets; and   a framer coupled to the packetizer configured to place the MPEG-2 transport stream packets into one or more baseband frames (BBFRAMEs), wherein the framer determines an actual symbol consumption number for the one or more baseband frames and transmits the actual symbol consumption number to the scheduling multiplexer.   
     
     
         7 . The system of  claim 6 , further comprising:
 a modulator coupled to the framer to transmit the BBFRAMEs to the single outbound link   
     
     
         8 . The system of  claim 6 , wherein the input stream comprises internet protocol data. 
     
     
         9 . The system of  claim 6 , wherein scheduling multiplexer is configured to schedule input stream packets for transmission based upon the estimated symbol consumption, wherein the scheduled packets for transmission require less than the estimated symbol consumption. 
     
     
         10 . The system of  claim 9 , wherein the framer determines a MODCOD for transmitting at least one of the baseband frames and is configured to determine the actual symbol consumption value based in part on the MODCOD used. 
     
     
         11 . The system of  claim 6 , wherein the scheduling multiplexer is configured to adjust the estimated symbol consumption of a next transmission round if the estimated symbol consumption for the present transmission round differs from the actual symbol consumption value received from the framer. 
     
     
         12 . The system of  claim 11  wherein the scheduling multiplexer adjusts the estimated symbol consumption of a next transmission round if the estimated symbol consumption differs from the actual symbol consumption value by exceeding a threshold level. 
     
     
         13 . The system of  claim 11 , wherein the scheduling multiplexer decreases the estimated symbol consumption of the next transmission round if the actual symbol consumption value is greater than the estimated symbol consumption.