An Investigation into Transport Protocols and Data Transport ...

6.3. Summary 134
capacity - however, at what cost? [CJ89] states that MIMD based algorithms
may have serious convergence, and hence unfairness issues. FAST has a
theoretical network utilisation of 100% - but is based on TCP Vegas which,
despite its various advantages, was never widely deployed for general usage
due to its inability to compete against aggressive flows, and hence the user
perception of throughput was lower. Also TCP Vegas suffers from poor
performance when the path is asymmetric [FLcL01].
So why cannot users simply choose their own algorithm to use? Indeed,
this appears to be the situation at present as new congestion control algorithms
appear all the time. However, very little research has been conducted
to gauge the effectiveness of these algorithms against each other in similar
network conditions. Furthermore, most of the analysis of New-TCP algorithms
are centred around simulation based studies. Whilst the modeling of
new algorithms in simulations is no doubt necessary, there may be physical
limitations of running TCP protocols at high speeds - which may have negative
consequences on network stability. For example, the aggressive increases
of some of the algorithms may cause global synchronisation which will in fact
lower network utilisation rather than increase it [ASA00].
Therefore, there is a clear need to test these algorithms on real hardware
in realistic environments, and possibly on real Internet networks. The goal
of such an investigation should not only focus on the performance in terms of
throughput achieved, but also on other factors such as fairness, how quickly
algorithms converge to fairness and the potential for congestion collapse.