| Summary: | In this work, we focus on congestion control mechanisms in Transmission Control
Protocol (TCP) for emerging very-high bandwidth-delay product networks and suggest
several congestion control schemes for parallel and single-flow TCP. Recently, several
high-speed TCP proposals have been suggested to overcome the limited throughput
achievable by single-flow TCP by modifying its congestion control mechanisms.
In the meantime, users overcome the throughput limitations in high bandwidth-delay
product networks by using multiple parallel TCP flows, without modifying TCP itself.
However, the evident lack of fairness between the high-speed TCP proposals (or
parallel TCP) and existing standard TCP has increasingly become an issue.
In many scenarios where flows require high throughput, such as grid computing
or content distribution networks, often multiple connections go to the same or nearby
destinations and tend to share long portions of paths (and bottlenecks). In such cases
benefits can be gained by sharing congestion information. To take advantage of this
additional information, we first propose a collaborative congestion control scheme for
parallel TCP flows. Although the use of parallel TCP flows is an easy and effective
way for reliable high-speed data transfer, parallel TCP flows are inherently unfair
with respect to single TCP flows. In this thesis we propose, implement, and evaluate
a natural extension for aggregated aggressiveness control in parallel TCP flows.
To improve the effectiveness of single TCP flows over high bandwidth-delay product networks without causing fairness problems, we suggest a new TCP congestion
control scheme that effectively and fairly utilizes high bandwidth-delay product networks
by adaptively controlling the flowÂs aggressiveness according to network situations
using a competition detection mechanism. We argue that competition detection
is more appropriate than congestion detection or bandwidth estimation. We further
extend the adaptive aggressiveness control mechanism and the competition detection
mechanism from single flows to parallel flows. In this way we achieve adaptive aggregated
aggressiveness control. Our evaluations show that the resulting implementation
is effective and fair.
As a result, we show that single or parallel TCP flows in end-hosts can achieve
high performance over emerging high bandwidth-delay product networks without requiring
special support from networks or modifications to receivers.
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