Analysis of High-Speed Data Transfer Protocol Algorithms
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Date
2004-05-20
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Abstract
High-performance networks offer the promise of connectivity at speeds of 40 Gbps or more. However, effective use of the bandwidth they offer is a challenge since no reliable transport protocol is well suited for such environments. The most popular reliable protocol currently available is standard TCP/IP. However, studies show that standard TCP performs poorly in high bandwidth long delay networks, i.e., in long distance backbone networks. The maximum bandwidth utilization of TCP in such often environments is less than 10% of the provided bandwidth. Thus, to utilize the provided bandwidth effectively, new protocols and algorithms have been proposed.
SABUL is one of the hybrid protocols designed to overcome TCP performance issues in high bandwidth, long delay environments. SABUL uses a variant of MIMD (Multiplicative Increase and Multiplicative Decrease) as its congestion control algorithm, and implements loss rate as a congestion indicator.
Unfortunately, assessment of SABUL properties is mostly empirical, and not comprehensive. Similar appears to be the case with many new protocols being developed in this space. While emprical work is very useful, it can very easily miss some key behavioral aspects of the protocol, especially when it is used in diverse situations. This work remedies this problem by suggesting a generalizable framework for systematic study of protocols intented for use in a high bandwidth, long delay environment. The framework is presented through a full theoretical, and some experimental, assessment of SABUL congestion control algorithm.
The framework is divided into three sections: mathematical analysis of the (SABUL) congestion control algorithm, simulation and experimental analysis of the (SABUL) congestion control algorithm, and improvement of the (SABUL) congestion control algorithm. The mathematical analysis is done by using deterministic and stochastic models. These models are used to assess (SABUL) properties such as bandwidth utilization, self-fairness, and aggressiveness/responsiveness. To validate mathematical models, simulations and experimental analyses are performed. The results explain SABUL throughput oscillations, derive bounds on its aggressiveness/responsiveness, show that SABUL can be self-fair, and identify conditions under which SABUL may exhibit excessive packet loss.
Moreover, the results show several drawbacks of SABUL such as high rate fluctuation and rate synchronization which cause loss of throughput which was not observed in the analytical model but was observed in subsequent experiments. Based on this information, we suggest how SABUL congestion control algorithm can be modified to improve its bandwidth utilization.
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Keywords
bandwidth, MIMD, high speed long delay network, TCP/IP, congestion control
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Degree
PhD
Discipline
Computer Engineering
