This paper describes a novel mechanism for achieving sufficient TCP performance over some asymmetrical environment without any modification in customer premises. In today?s Internet, several types of access media have an asymmetrical bandwidth characteristic, where the down-stream link bandwidth is larger than the upstream. However, such asymmetrical environment may cause TCP performance degradation due to upstream link congestion. In order to solve this problem, we propose a PEP (Performance Enhancement Proxy) based approach to improve TCP downloading throughput by reducing upstream traffic using our compulsory IP fragmentation technique. The results of our performance evaluation show that our experimental proxy implementation is capable of accelerating TCP throughput about three times faster comparing to the case without the proxy.