In this paper, the authors first provide a close form differentiate formula to analyze the buffer requirement for zero loss of TCP in networks with high bandwidth delay product. Then, A Token Based Fast-TCP algorithm is analyzed and modeled in WANs when the window size is smaller than Bandwidth-Delay Products (BDP) or in satellite networks where window size is not allowed to be larger than BDP because link errors. It proves that Token Based ACKs delay algorithm not only reduce buffer occupancy largely, but also gain the average same throughput as TCP with infinite buffer size as well. The authors also apply the analysis to multiple connection case that is not included in previous work.