Most congestion control research emphasizes incremental changes to TCP. There are several notable efforts addressing TCP’s shortcomings.
XCP is significantly different from the proposals described above. By introducing explicit, non-binary feedback from the network to the endpoints, XCP achieves several important functional and performance advantages.
First, XCP offers superior performance. While all the proposals allow large BDP flows to ramp up to broadband rates more rapidly than current TCP, XCP is the most responsive in both start-up and "steady-state" operation, and is able to obtain the maximum performance supported by the infrastructure, under the widest range of challenging conditions.
Second, XCP, rather than being a modification or tuning of TCP, introduces a novel and general framework for resource management. XCP's basic building blocks can be used by a range of protocols with different semantics, meeting the high-performance communication needs of the vast majority of scientific and commercial applications.
Third, XCP, by making bandwidth allocation explicit, provides fairness to "equal" flows when TCP would not, and implements a nearly cost-free service differentiation mechanism when that is what is required. [Katabi03] suggests ways in which this simple and powerful unified bandwidth allocation strategy can support traditional QoS concepts such as tiered service levels and bandwidth guarantees.
Of course, these advantages
do not come without cost. XCP's tradeoff is some additional complexity in the
network routers and switches. It is the core thesis of this proposal, and the
goal of our work, to rigorously demonstrate that this additional complexity
is minor and manageable, and that the resulting advantages are profound.
[Floyd] Sally Floyd. “HighSpeed
TCP for Large Congestion Windows,” Internet draft draft-floyd-tcp-highspeed-02.txt,
work in progress, February 2003.
[Jain] Amit Jain and Sally
Floyd. “Quick-Start for TCP and IP,” Internet draft draft-amit-quick-start-02.txt,
work in progress, October 2002.
[Kelly] Tom Kelly. “Scalable
TCP: Improving Performance in Highspeed Wide Area Networks,” Submitted
for publication, December 2002,
[Low03] C. Jin, D. Wei,
S. H. Low, G. Buhrmaster, J. Bunn, D. H. Choe, R. L. A. Cottrell, J. C. Doyle,
W. Feng, O. Martin, H. Newman, F. Paganini, S. Ravot, S. Singh. “Fast
TCP: From Theory to Experiments,” submitted to IEEE Communications Magazine,
April 1, 2003,
last modified: May 12, 2003