-/* Random Early Detection (RED) algorithm.
- =======================================
-
- Source: Sally Floyd and Van Jacobson, "Random Early Detection Gateways
- for Congestion Avoidance", 1993, IEEE/ACM Transactions on Networking.
-
- This file codes a "divisionless" version of RED algorithm
- as written down in Fig.17 of the paper.
-
-Short description.
-------------------
-
- When a new packet arrives we calculate the average queue length:
-
- avg = (1-W)*avg + W*current_queue_len,
-
- W is the filter time constant (chosen as 2^(-Wlog)), it controls
- the inertia of the algorithm. To allow larger bursts, W should be
- decreased.
-
- if (avg > th_max) -> packet marked (dropped).
- if (avg < th_min) -> packet passes.
- if (th_min < avg < th_max) we calculate probability:
-
- Pb = max_P * (avg - th_min)/(th_max-th_min)
-
- and mark (drop) packet with this probability.
- Pb changes from 0 (at avg==th_min) to max_P (avg==th_max).
- max_P should be small (not 1), usually 0.01..0.02 is good value.
-
- max_P is chosen as a number, so that max_P/(th_max-th_min)
- is a negative power of two in order arithmetics to contain
- only shifts.
-
-
- Parameters, settable by user: