Manual:Queues - Burst

Theory

To understand burst it is necessary to be aware of 5 concepts:

1. burst-limit (NUMBER) : maximal upload/download data rate which can be reached while the burst is active
2. burst-time (TIME) : period of time, in seconds, over which the average data rate is calculated. (This is NOT the time of actual burst)
3. burst-threshold (NUMBER) : when average data rate is below this value - burst is allowed, as soon as average data rate reach this value - burst is denied. (basically this is burst on/off switch). For optimal burst behavior this value should above limit-at value and below max-limit value
4. average-rate (read-only) : Every 1/16 part of the burst-time, the router calculates the average data rate of each class over the last burst-time seconds.
5. actual-rate (read-only) : actual traffic transfer rate of the queue

To simplify calculations for examples we will use limit-at=1M, max-limit=2M, burst-threshold=1500k, burst-limit=4M

Example Burst-time=8s

Average rate is calculated every 1/16 of burst time, so in this case 0,5s

Zero second - average-rate=(0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0)/8=0Kbps, average-rate < burst-threshold -> Burst is allowed -> Actual-rate=4Mbps (2Mb per 0,5sek)

0,5 second - average-rate=(0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+2)/8=250Kbps, average-rate < burst-threshold -> Burst is allowed -> Actual-rate=4Mbps (2Mb per 0,5sek)

1,0 second - average-rate=(0+0+0+0+0+0+0+0+0+0+0+0+0+0+2+2)/8=500Kbps, average-rate < burst-threshold -> Burst is allowed -> Actual-rate=4Mbps (2Mb per 0,5sek)

1,5 second - average-rate=(0+0+0+0+0+0+0+0+0+0+0+0+0+2+2+2)/8=750Kbps, average-rate < burst-threshold -> Burst is allowed -> Actual-rate=4Mbps (2Mb per 0,5sek)

2,0 second - average-rate=(0+0+0+0+0+0+0+0+0+0+0+0+2+2+2+2)/8=1000Kbps, average-rate < burst-threshold -> Burst is allowed -> Actual-rate=4Mbps (2Mb per 0,5sek)

2,5 second - average-rate=(0+0+0+0+0+0+0+0+0+0+0+2+2+2+2+2)/8=1250Kbps, average-rate < burst-threshold -> Burst is allowed -> Actual-rate=4Mbps (2Mb per 0,5sek)

3,0 second - average-rate=(0+0+0+0+0+0+0+0+0+0+2+2+2+2+2+2)/8=1500Kbps, average-rate = burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

3,5 second - average-rate=(0+0+0+0+0+0+0+0+0+2+2+2+2+2+2+1)/8=1625Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

4,0 second - average-rate=(0+0+0+0+0+0+0+0+2+2+2+2+2+2+1+1)/8=1750Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

4,5 second - average-rate=(0+0+0+0+0+0+0+2+2+2+2+2+2+1+1+1)/8=1875Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

5,0 second - average-rate=(0+0+0+0+0+0+2+2+2+2+2+2+1+1+1+1)/8=2000Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

5,5 second - average-rate=(0+0+0+0+0+2+2+2+2+2+2+1+1+1+1+1)/8=2125Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

6,0 second - average-rate=(0+0+0+0+2+2+2+2+2+2+1+1+1+1+1+1)/8=2250Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

6,5 second - average-rate=(0+0+0+2+2+2+2+2+2+1+1+1+1+1+1+1)/8=2375Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

7,0 second - average-rate=(0+0+2+2+2+2+2+2+1+1+1+1+1+1+1+1)/8=2500Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

7,5 second - average-rate=(0+2+2+2+2+2+2+1+1+1+1+1+1+1+1+1)/8=2625Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

8,0 second - average-rate=(2+2+2+2+2+2+1+1+1+1+1+1+1+1+1+1)/8=2750Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

8,5 second - average-rate=(2+2+2+2+2+1+1+1+1+1+1+1+1+1+1+1)/8=2625Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

9,0 second - average-rate=(2+2+2+2+1+1+1+1+1+1+1+1+1+1+1+1)/8=2500Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

9,5 second - average-rate=(2+2+2+1+1+1+1+1+1+1+1+1+1+1+1+1)/8=2375Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

10,0 second - average-rate=(2+2+1+1+1+1+1+1+1+1+1+1+1+1+1+1)/8=2250Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

10,5 second - average-rate=(2+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1)/8=2125Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

11,0 second - average-rate=(1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1)/8=2000Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

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19,0 second - average-rate=(1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1)/8=2000Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=0Mbps (0Mb per 0,5sek)

19,5 second - average-rate=(1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+0)/8=1875Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=0Mbps (0Mb per 0,5sek)

20,0 second - average-rate=(1+1+1+1+1+1+1+1+1+1+1+1+1+1+0+0)/8=1750Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=0Mbps (0Mb per 0,5sek)

20,5 second - average-rate=(1+1+1+1+1+1+1+1+1+1+1+1+1+0+0+0)/8=1625Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=0Mbps (0Mb per 0,5sek)

21,0 second - average-rate=(1+1+1+1+1+1+1+1+1+1+1+1+0+0+0+0)/8=1500Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=0Mbps (0Mb per 0,5sek)

21,5 second - average-rate=(1+1+1+1+1+1+1+1+1+1+1+0+0+0+0+0)/8=1375Kbps, average-rate < burst-threshold -> Burst is allowed -> Actual-rate=0Mbps (0Mb per 0,5sek)

22,0 second - average-rate=(1+1+1+1+1+1+1+1+1+1+0+0+0+0+0+0)/8=1250Kbps, average-rate < burst-threshold -> Burst is allowed -> Actual-rate=0Mbps (0Mb per 0,5sek)

22,5 second - average-rate=(1+1+1+1+1+1+1+1+1+0+0+0+0+0+0+0)/8=1125Kbps, average-rate < burst-threshold -> Burst is allowed -> Actual-rate=0Mbps (0Mb per 0,5sek)

23,0 second - average-rate=(1+1+1+1+1+1+1+1+0+0+0+0+0+0+0+0)/8=1000Kbps, average-rate < burst-threshold -> Burst is allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

23,5 second - average-rate=(1+1+1+1+1+1+1+0+0+0+0+0+0+0+0+1)/8=1000Kbps, average-rate < burst-threshold -> Burst is allowed -> Actual-rate=4Mbps (2Mb per 0,5sek)

24,0 second - average-rate=(1+1+1+1+1+1+0+0+0+0+0+0+0+0+1+2)/8=1125Kbps, average-rate < burst-threshold -> Burst is allowed -> Actual-rate=4Mbps (2Mb per 0,5sek)

24,5 second - average-rate=(1+1+1+1+1+0+0+0+0+0+0+0+0+1+2+2)/8=1250Kbps, average-rate < burst-threshold -> Burst is allowed -> Actual-rate=4Mbps (2Mb per 0,5sek)

25,0 second - average-rate=(1+1+1+1+0+0+0+0+0+0+0+0+1+2+2+2)/8=1375Kbps, average-rate < burst-threshold -> Burst is allowed -> Actual-rate=4Mbps (2Mb per 0,5sek)

25,5 second - average-rate=(1+1+1+0+0+0+0+0+0+0+1+2+2+2+2+2)/8=1500Kbps, average-rate = burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

26,0 second - average-rate=(1+1+0+0+0+0+0+0+0+1+2+2+2+2+2+1)/8=1500Kbps, average-rate = burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

26,5 second - average-rate=(1+0+0+0+0+0+0+0+1+2+2+2+2+2+1+1)/8=1500Kbps, average-rate = burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

27,0 second - average-rate=(0+0+0+0+0+0+0+1+2+2+2+2+2+1+1+1)/8=1500Kbps, average-rate = burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

27,5 second - average-rate=(0+0+0+0+0+0+1+2+2+2+2+2+1+1+1+1)/8=1625Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

28,0 second - average-rate=(0+0+0+0+0+1+2+2+2+2+2+1+1+1+1+1)/8=1750Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

28,5 second - average-rate=(0+0+0+0+1+2+2+2+2+2+1+1+1+1+1+1)/8=1875Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

29,0 second - average-rate=(0+0+0+1+2+2+2+2+2+1+1+1+1+1+1+1)/8=2000Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

29,5 second - average-rate=(0+0+1+2+2+2+2+2+1+1+1+1+1+1+1+1)/8=2125Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

30,0 second - average-rate=(0+1+2+2+2+2+2+1+1+1+1+1+1+1+1+1)/8=2250Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

30,5 second - average-rate=(1+2+2+2+2+2+1+1+1+1+1+1+1+1+1+1)/8=2375Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

30,5 second - average-rate=(2+2+2+2+2+1+1+1+1+1+1+1+1+1+1+1)/8=2375Kbps, average-rate > burst-threshold -> Burst not allowed -> Actual-rate=2Mbps (1Mb per 0,5sek)

Example Burst-time=16s