This paper describes a novel mechanism for achieving sufficient TCP performance in bulk data transfer in some asymmetrical environment without introducing additional functions in customer premises. On today's Internet, several types of broadband access media have an asymmetrical bandwidth characteristic, whereby the downstream link bandwidth is larger than the upstream. However, such an asymmetrical environment may cause TCP performance degradation due to upstream link congestion. To solve this problem, we propose a PEP-based approach to improve TCP file downloading throughput by reducing upstream traffic, using our “oversized MSS with compulsory IP fragmentation”technique. The results of our performance evaluation show that our experimental proxy implementation is capable of accelerating TCP throughput to about three times as fast as without the proxy.