Traffic multiplexing using timestamping
View Patent ↗Multiplexed traffic in a system where the maximum rate of all inputs exceeds the maximum rate of the output is processed via a separate queue for each input, and at any given forwarding clock cycle the earliest enqueued packet is forwarded via the output. In the event of congestion, a proportionally equal number of packets are dropped from each queue, where proportional equality corresponds to the number of packets dropped per number of packets enqueued. One implementation associates a time-stamp with each enqueued packet to indicate the time of enqueing relative to other enqueued packets. At any given forwarding clock cycle, the packet with the earliest time-stamp is forwarded.
1. An apparatus for multiplexing data units from a plurality of inputs onto an output having a transmission capacity less than the sum of the inputs, the apparatus comprising:
a plurality of queues configured to enqueue the data units from the inputs; and
a scheduler configured during any interval of time to prompt data unit drop for each queue in the plurality of queues that is non-empty in a manner that results in the ratio of the number of data units dropped in each non-empty queue in the plurality of queues divided by the number of data units enqueued in each non-empty queue in the plurality of queues is at least approximately equal for the interval of time.
2. The apparatus of claim 1 further including a clock operative to associate a time-stamp with each enqueued data unit indicating when the data unit was enqueued relative to other enqueued data units.
3. The apparatus of claim 2 wherein the clock comprises a counter.
4. The apparatus of claim 1 wherein the queues are FIFO queues, each having a head containing the respective earliest enqueued data unit for that queue, and wherein the scheduler is operative to compare the time-stamps of the data units at the heads of the queues to select and forward to the output the earliest enqueued data unit based on the time-stamps associated with those data units.
5. The apparatus of claim 1 wherein each queue is exclusively associated with a single respective one of the inputs.
6. A method for multiplexing data units from a plurality of inputs onto an output having a transmission capacity less than the sum of the inputs, the method comprising the steps of:
enqueueing data units from the inputs; and
during any interval of time, prompting data unit drop for each queue in the plurality of queues that is non-empty in a manner that results in the ratio of number of data units dropped in each non-empty queue in the plurality of queues divided by the number of data units enqueued in each non-empty queue in the plurality of queues is at least approximately equal for the interval of time.
7. The method of claim 6 further including the step of associating a time-stamp with each enqueued data unit indicating when the data unit was enqueued relative to other enqueued data units.
8. The method of claim 7 including the further step of a counter for associating a time-stamp with each enqueued data unit.
9. The method of claim 6 wherein the queues are FIFO queues, each having a head containing the respective earliest enqueued data unit for that queue, and including the further steps of comparing the time-stamps of the data units at the heads of the queues, and selecting and forwarding to the output the earliest enqueued data unit based on the time-stamps associated with those data units.
10. The method of claim 6 wherein each queue is exclusively associated with a single respective one of the inputs.
11. An apparatus for multiplexing data units from a plurality of inputs onto an output having a transmission capacity less than the sum of the inputs, the apparatus comprising:
a separate queue associated with each input, the queues operative to enqueue the data units from the associated inputs;
a clock circuit configured to associate a time-stamp with each enqueued data unit indicating time of receipt relative to other enqueued data units; and
a scheduler configured to select and forward for a given forwarding clock cycle the data unit having the earliest time-stamp, whereby a proportionally equal number of packets are dropped from each non-empty queue during a period of congestion.
12. A method for multiplexing data units from a plurality of inputs onto an output having a transmission capacity less than the sum of the inputs, the method comprising the steps of:
enqueueing a received data unit in one of a plurality of separate queues, each associated with a separate input;
associating a time-stamp with the enqueued data unit indicating time of receipt relative to other enqueued data units; and
selecting and forwarding for a given forwarding clock cycle the data unit having the earliest time-stamp,
whereby a proportionally equal number of packets are dropped from each non-empty queue in the plurality of queues during a period of congestion.