An Investigation into Transport Protocols and Data Transport ...

6.1. Survey of New-TCP Algorithms 114
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ssthresh
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(a) Congestion Window
(b) AIMD Parameters
Figure 6.1: cwnd dynamic of HSTCP (Single flow on Dummynet, link capacity
200Mbit/sec, RTT 150ms, queue size 500 packets.)
6.1.2 ScalableTCP
ScalableTCP [Kel03] defines a mechanism by which the number of RTTs
to recover from a loss event is independent of the of the link bandwidth.
The design of ScalableTCP ensures that the recovery time required at any
throughput is approximately a constant regardless of the RTT of the connection.
It therefore ensures a degree of scalability of the algorithm regardless
of the link capacity of the path that enables ScalableTCP to outperform
standard TCP.
The generalised ScalableTCP window update algorithm responds to each
acknowledgment received in which congestion has not been detected with the
update:
ACK: cwnd ← cwnd + α (6.5)
LOSS: cwnd ← β × cwnd (6.6)
where α is a constant with 0 < α < 1 and β is a constant with 0.5 < β < 1.
The scaling property applies for any choice of the constants α and β. The