An Investigation into Transport Protocols and Data Transport ...

6.2. Discussion and Deployment Considerations of New-TCP Algorithms130
A similar approach to H-TCP is taken with BicTCP, with almost zero
increase in cwnd as it approaches its w target . FAST, however, with its design
to stabilise the value of cwnd means that it is scalable with any buffer size.
But, this only applies when it is stable. In order to reach equilibrium, the (upto)
exponential increase in cwnd can cause serious implications for network
traffic. Again, this increase is determined by the value of α in the utility
function.
One way of preventing large losses as a result of small buffer allocations is
to utilise packet pacing [ASA00] whereby packets are not sent back-to-back
but spread out over each RTT to prevent the large number of sequential packets
drops due to drop-tail queuing mechanisms. However, findings in [ASA00]
suggest that applying global TCP pacing would result in large amounts of
TCP synchronisation due to the higher average queue occupancy of intermittent
routers. Synchronisation occurs when flows competing along a link
experience congestion at the same time, and as a result they all backoff together
and ramp-up together. Depending on the backoff factor of the flows (as
defined by H-TCP’s adaptive backoff factor), the link may be under-utilised
as a result of synchronisation.
The size of network queues is also important. As defined previously,
network queues are necessary to buffer the increase in packets caused by
the various algorithms’ increase parameters. Equation 5.6 states that for
Standard TCP, a queue provision equal to the bandwidth delay product is
necessary for 100% utilisation. Indeed, this requirement is often stipulated
in simulations involving network bulk transport [VS94]. However, [AKM04]
states that the inclusion of such large amounts of buffer memory is not feasible
due to physical size of Static RAM and the long latencies of DRAM.
This problem raises concerns for fast long distance networks as the required