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

Seconds (s)	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
Actual Rate (Mbps)	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4
Average Rate (Mbps)	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4
Burst Allowed	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Yes

(0+0+0+0+0+0+0+0)/8=0Mbps

Example Burst-time=16s