Editing FAST TCP (section)

==Strengths and weaknesses==
Delay-based algorithms can, in principle, maintain a constant window size, avoiding the oscillations inherent in loss-based algorithms.  However, they also detect congestion earlier than loss-based algorithms, since delay corresponds to partially filled [[Buffer (telecommunication)|buffers]], while loss results from totally filled buffers.  This can be either a strength or a weakness.  If the only protocol used in a network is delay-based, then the inefficiency of loss can be avoided; however, if loss-based and delay-based protocols share the network,<ref>{{cite web
 | last = Tang
 | first = Ao
 | author2 = Wang, Jiantao
 | author3 = Low, Steven H.
 | author4 = Chiang, Mung
 | name-list-style = amp
 |date= March 2005
 | title = Network Equilibrium of heterogeneous congestion control protocols
 | work = IEEE INFOCOM
 | location = Miami, FL
 | url = http://www.sisl.caltech.edu/pubs/controlprotocol.pdf
 }}
</ref> then delay-based algorithms tend to be less aggressive.  This can be overcome by suitable choice of parameters, leading to complex interactions studied by Tang et al.

Delay measurements are also subject to jitter as a result of [[operating system]] scheduling, or [[Computer bus|bus]] contention.

Whether the strengths or weaknesses prevail is not clear, and depends in large part on the particular scenario.

Propagation delay is used in the FAST window control algorithm. In a clean network, the queueing delay maintained by existing FAST flows may be mistaken as part of the propagation delay by new flows that join later, as shown in ns-2 simulations in.<ref name=":0">L. Tan, C. Yuan, and M. Zukerman, “FAST TCP: fairness and queuing issues,” IEEE Commun. Lett., vol. 9, no. 8, pp. 762–764, Aug. 2005.</ref> The effect of this estimation error is equivalent to modifying the underlying utility functions to favor new flows over existing flows. Method to eliminate this error is suggested in.<ref name=":0" />