The success of peer-to-peer (P2P) applications hinges on users' willingness to contribute their network bandwidth to serve other peers. However if the upload data rate to other peers is too high it could severely degrade the download data rate, even if the downlink has abundant bandwidth available, especially in an asymmetric network such as ADSL. Experiments revealed that the download throughput degradation is in fact not caused by congestion in the uplink, but caused by increased queuing delay in the uplink path during high upload data rates. This paper tackles this problem by developing an adaptive algorithm to monitor the uplink queuing delay and adjust the upload data rate limit dynamically so that the download throughput will not be adversely affected. Experiments conducted using an open-source P2P software showed that the proposed algorithms can increase the downlink utilization over a wide range of network configurations (and over 200% increase in some cases) by automatically adjusting the upload data rate limit. The algorithms do not require any user intervention and can be readily incorporated into existing P2P systems.
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