| Summary: | 碩士 === 國立臺灣大學 === 資訊管理研究所 === 84 === The flourishing Internet applications make the widespread use
of the TCP/IP protocol. Recently, the increasing deployment of
ATM networks reflects that the users, demands for higher speed
and more reliable network quality. Therefore, performance of
TCP connections in high speed ATM networks is getting more and
more important. This research is trying to study the impacts of
congestion control mechanisms on the performance of TCP traffic
over ATM networks. ATM Forum classes the conventional data
transmission to ABR traffic; it means the cells of ABR traffic
will be dropped preferentially when the network experiences
congestion. The performance of ABR traffic may therefore be
affected seriously. Because the TCP protocol has its own
congestion avoidence mechanisms and sliding window control,
previous research indicates that the performance would become
even worse when these mechanisms are exercised. Therefore, it
becomes a consensus that the ATM layer should exercise some
congestion control when the input traffic load approaches the
network capacity. Close-loop feedback control is now commonly
agreed to be the most effective solution, which allows the
source to control the cell emission process directly according
to the network status carried back by the feedback information.
So the cell transmission rate can be adjusted flexibly. In this
research, We simulate the network operations via a simulation
program, and implement the full congestion control mechanisms
of the TCP and ATM layers. The goal is to study the TCP
performance in congestion controlled ATM networks, and to
evaluate the appropriateness and limitations of the various
control mechanisms.
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