As originally designed for wired networks, TCP (transmission control protocol) congestion control mechanism is triggered into action when packet loss is detected. This implicit assumption for packet loss mostly due to network congestion does not work well in Mobile Ad Hoc Network, where there is a comparatively high likelihood of packet loss due to high bit error rate (BER) and node roaming. Such non-congestion packet loss, when dealt with by congestion control mechanism, causes poor TCP performance in MANET. All improvement mechanisms have two distinct phases: problem detection and problem solving. This paper attempts to address this problem by first summarizing over several major reasons for such mis-behavior, an in-depth analysis and the detailed comparison between different solutions are proposed to improve at each of the two phases. Finally, some new research directions for optimizing TCP performance in MANET (mobile ad hoc network) are suggested.