Packet scheduling system for digital video broadcasting
View Patent ↗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 method for scheduling input flows in a scheduling multiplexer, comprising the steps of:
receiving a plurality of input flows at a first input buffer and a second input buffer associated with the scheduling multiplexer;
receiving an actual symbol consumption value from a framer transmitting a first plurality of packets previously multiplexed by the scheduling multiplexer and provided to a packetizer which in turn provides the first plurality of packets to the framer;
determining a present estimated symbol quota value in the scheduling multiplexer based on comparing the actual symbol consumption value with a previous estimated symbol quota,
wherein said present estimated symbol quota value is reduced relative to the previous estimated symbol quota if the actual symbol consumption value was greater than the previous estimated symbol quota, and
wherein said present estimated symbol quota value is increased relative to the previous estimated symbol quota if the actual symbol consumption was less than then previous estimated symbol quota; and
multiplexing a first number of bits from the first input buffer with a second number of bits from the second input buffer based on the present estimated symbol quota value.
2. The method of claim 1 wherein the framer transmits the packets at an indicated modulation and coding (MODCOD) and determines the actual symbol consumption value based on the MODCOD used to transmit the first plurality of packets.
3. The method of claim 2 wherein the framer transmits the actual symbol consumption value to the scheduling multiplexer.
4. The method of claim 1 wherein said present estimated symbol quota value is maintained if the actual symbol consumption is the same as the previous estimated symbol quota.
5. The method of claim 1 where the first plurality of packets comprise MPEG-2 packets.
6. The method of claim 1 wherein each input flow is associated with a respective scheduled modulation and coding (MODCOD) and the framer transmits at least one input flow in a baseband frame using a MODCOD lower than the respective scheduled MODCOD.