BIC TCP
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BIC TCP (Binary Increase Congestion control) is one of the congestion control algorithms that can be used for Transmission Control Protocol (TCP). BIC is optimized for high-speed networks with high latency: so-called long fat networks. For these networks, BIC has significant advantage over previous congestion control schemes in correcting for severely underutilized bandwidth.[1]
BIC implements a unique congestion window (cwnd) algorithm. This algorithm tries to find the maximum cwnd by searching in three parts: binary search increase, additive increase, and slow start. When a network failure occurs, the BIC uses multiplicative decrease in correcting the cwnd.[2]
BIC TCP is implemented and used by default in Linux kernels 2.6.8 and above. The default implementation was again changed to CUBIC TCP in the 2.6.19 version.
Algorithm
[edit ]Define the following variables:
Smax: the maximum increment Smin: the minimum increment wmax: the maximum window size β: multiplicative window decrease factor cwnd: congestion window size bic_inc: window increment per RTT (round trip time)
At every RTT interval update cwnd with the following:
If no packets are dropped, the congestion window (cwnd) increases in three distinct ways: binary search increase, additive increase, and slow start. In each step, one is used as an increment.
One step of increasing cwnd:
if (cwnd < wmax) // binary search OR additive bic_inc = (wmax - cwnd) / 2; else // slow start OR additive bic_inc = cwnd - wmax; if (bic_inc > Smax) // additive bic_inc = Smax; else if (bic_inc < Smin) // binary search OR slow start bic_inc = Smin; cwnd = cwnd + (bic_inc / cwnd);
If one or more packets are dropped, the cwnd is reduced using multiplicative decrease. This requires β, which is used in decreasing cwnd by (×ばつβ)%. In the case of two flows, one with a large cwnd and the other a small cwnd, fast convergence is used to decrease the greater cwnd flow's wmax at a greater rate than the smaller cwnd's flow to allow faster convergence of the greater cwnd's flow when increasing its cwnd.
One step of decreasing cwnd:
if (cwnd < wmax) // fast convergence wmax = cwnd * (2-β) / 2; else wmax = cwnd; cwnd = cwnd * (1-β);
See also
[edit ]References
[edit ]- ^ "BIC FAQ". www4.ncsu.edu. Archived from the original on December 12, 2018. Retrieved December 25, 2018.
- ^ "Binary increase congestion control (BIC) for fast long-distance networks - IEEE Conference Publication". doi:10.1109/INFCOM.2004.1354672. S2CID 11750446.
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External links
[edit ]- [1] Home Page.