An Investigation into Transport Protocols and Data Transport ...

7.1. Metrics 136
7.1 Metrics
In this section, metrics which are considered important for the evaluation of
bulk data transport are presented and discussed.
7.1.1 Goodput
Define goodput, ¯x i , to be the mean rate of useful application layer data transferred
per unit time, such that for the i th flow, x i (t) is the rate of of useful
data sent in the time period t. More formally it is defined as the throughput
less losses.
∫
1 T
¯x i := lim x i (t)dt, (7.1)
T →∞ T 0
Another consideration is that as the number of flows increases, this can
be extended to define the aggregate goodput, ¯X, when there are n flows competing
along the same bottleneck to be:
¯X :=
n∑
¯x i (7.2)
i=1
Define the short-term average goodput as the exponentially weighted
moving average,
ˆx(t) i =
∫ t
0
exp[−λ(t − s)]x i (s)ds (7.3)
where λ is typically selected proportional to the bandwidth-delay product so
that the averaging window scales with the congestion epoch duration.
In order to convey the New-TCP dynamics over a range of cwnd values,
a range of network capacities and latencies should be investigated in order
to obtain a general perspective of this particular performance metric. The
effect of algorithmic mode switches from low to high speed regimes of the