An Investigation into Transport Protocols and Data Transport ...

6.2. Discussion and Deployment Considerations of New-TCP Algorithms124
eliminate the variance of T q , it is smoothed such that,
¯T (k + 1) = η(t k )T (k) + (1 − η(t k )) ¯T (k) (6.20)
where η(t k ) = 50 is a design paramter of FAST.
Window changes are implemented over two RTTs and adjusted such that
at maximum cwnd doubles in each RTT (i.e. slow start) such that α(w, T q ) =
aw when the queuing delay T q is zero. However, this growth only occurs until
T q > 0, after which α(w, T q ) = α where α is a constant which determines
the number of packets per flow that is (attempted to be) maintained in the
network buffers at equilibrium.
This rudimentary definition of α means that the bottleneck queue size
needs to scale with the number of competing FAST flows. Therefore, in order
for n competing FAST flows to reach equilibrium and stabilise, a queue-size
of at least n × α is required. In the current [JWL04] version of FAST, a
simple algorithm to tune α based on the achieved throughput is used.
Throughout this study, the default parameters of γ = 50 is used, and that
α(w, T q ) is calculated from the measured goodput of the FAST flow. More
specifically, the value of α(w, T q ) changes such that it is set to 8, 20 or 200
when the measured goodput is less than 10Mbit/sec, less than 100Mbit/sec
and greater than 100Mbit/sec respectively.
6.2 Discussion and Deployment Considerations
of New-TCP Algorithms
The optimisation of high performance, high throughput network transport
protocols is very important. There is a clear need to maximise the net-