An Investigation into Transport Protocols and Data Transport ...

6.1. Survey of New-TCP Algorithms 116
6.1.3 H-TCP
H-TCP [LS04a] was designed to address the issues of the slow transient convergence
between similar flows of HSTCP and ScalableTCP.
H-TCP is based on the same idea of HSTCP and ScalableTCP such that
the rate at which TCP allows packets into the network should reflect the
prevailing network conditions. What is unique about H-TCP is the fact
that it incorporates a mode-switch between a Standard TCP regime and
that of a faster mode for each and every congestion epoch (whereas HSTCP
and ScalableTCP incorporates a switch from Standard TCP mode to their
relevant ‘high-speed’ modes if the cwnd is larger than some value).
The H-TCP can be encompassed in the following algorithm:
2(1 − β) × α(∆)
ACK: cwnd ← cwnd + (6.7)
cwnd
LOSS: cwnd ← β × cwnd (6.8)
with
α(∆) =
β =
⎧
⎪⎨ 1 ∆ ≤ ∆ L
⎪⎩ max(ᾱ(∆)T min , 1) ∆ > ∆ L (6.9)
⎧
⎪⎨ 0.5 | B(k+1)−B(k)
¯ | > ∆
B(k)
B
⎪⎩ min( T min
T max
, β max ) otherwise
(6.10)
∆ is the (real) time since the last congestion epoch and ∆ L is a constant
parameter. T min and T max are the flows’ minimum and maximum experienced
latencies and B(k) and B(k+1) are the measured goodputs of the H-TCP flow
at the moment of congestion for the previous and current epoch respectively.