An Investigation into Transport Protocols and Data Transport ...

6.2. Discussion and Deployment Considerations of New-TCP Algorithms128
throughput at congestion: should the change of throughput at consecutive
congestion points be larger than 80%, then it sets β to 0.5 (as with Standard
TCP) to aid faster convergence to fairness.
Another important factor of scalability is the adaptation of the algorithms
at different network capacities (or more accurately with large cwnd
values). The design of HSTCP is explicitly such that you have to ‘tune’
the increase and decrease parameters depending on the required loss rates
against the response function (See Section 5.4.2). The current specification
of HSTCP suggests tuning appropriate for 10Gb/sec network flows. Whilst
Section A.2.3 suggests that it is currently not possible to reach such speeds,
even with the best currently available hardware, with time this is sure to
change. As such, when it becomes possible to enable network speeds greater
than 10Gb/sec (or in the unlikely even that the Internet becomes more lossy),
then all deployed versions of HSTCP will need to be ‘re-tuned’ to suit the
new networks available.
All of the other algorithms have no such problem in terms of utilisation.
However, with the larger cwnd values, an aggressive increase parameter may
require extra buffering to accommodate the extra packet bursts due to aggressive
algorithms, which may lead to a fundamental limit to the scalability
of the algorithm. This feature is most evident for ScalableTCP which has a
consistent large increase parameter.
FAST has a theoretical utilisation of 100% [JWL + 03, JWL04]. However,
a problem with the use of latency measurements to determine the incipient
stages of congestion is that unless one-way delay is used, both the forward
and reverse paths of the connection’s latency is measured. As such, should
the reverse path be congested, rather than the forward path, then FAST (and
TCP Vegas) suffers from low throughput as it cannot differentiate between