An Investigation into Transport Protocols and Data Transport ...

6.1. Survey of New-TCP Algorithms 119
cwnd and ssthresh (packets)
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cwnd
ssthresh
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Time (seconds)
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Time (seconds)
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(a) Congestion Window
(b) AIMD Parameters
Figure 6.3: cwnd dynamic of H-TCP (Single flow on Dummynet, link capacity
200Mbit/sec, RTT 150ms, queue size 500 packets.)
speed mode a period ∆ i later. After this period, the growth of cwnd is
polynomial in nature, reaching very high values before loss is induced and
the cycle begins again. The adaptive backoff is also shown, with an initial
value of 0.5 and later set to 0.8 due to the (relatively) large queue which
means that the ratio of the minimum and maximum latencies is capped by
the algorithm.
6.1.4 BicTCP
BicTCP [XHR04] attempts to address an issue with HSTCP and ScalableTCP
whereby competing flows would starve the throughput of a Standard TCP
flow due to the faster growth of cwnd.
The implementation of BicTCP is based around two separate algorithms;
A binary search to determine the optimal cwnd size, and an additive increase
to ensure fast convergence and RTT-fairness.
Binary search is used to determine whether the current sending rate (or
window) is larger than the network capacity. This is achieved with a variable
w target that holds a value halfway between the values of cwnd just before and