An Investigation into Transport Protocols and Data Transport ...

7.2. Environment 141
of packets in flight as a result of large values of cwnd leads to a larger number
of packets that may be lost due to packet bursts and having a too aggressive
increase in α [KRB05].
It is important in order to prevent classical congestion collapse and improve
goodput that the fraction of retransmitted packets is kept low [FF99].
Therefore, given that, the i th TCP flow retransmits r i (k) bytes of data in the
duration s, define the ratio of retransmitted packets for s = 1, ..., t as:
ɛ i =
∑ t
s=1 r i(s)
∑ t
s=1 u i(s)
(7.10)
where u i (s) is the amount of data transfered during the period s of the
i th flow.
In order to give a comparable metric between stacks that achieve different
goodputs under identical network conditions, normalise all ɛ i by the total
goodput of all flows, ¯X, to give the total overhead, ξ:
ξ =
∑ n
i ɛ i
¯X
(7.11)
Therefore a low value of ξ is desirable and should not be much greater
than that of Standard TCP to facilitate the stability of the Internet.
7.2 Environment
The goal of this investigation is to be able to compare and contrast the
performance metrics of New-TCP algorithms against that of Standard TCP
in order to gauge the advantages and disadvantages of each.
In order to get a representation of the performance of these congestion