The AI3 project aims to achieve effective and fair bandwidth usage of its relatively narrow satellite links by all the partners in this project and the best possible end-to-end communication quality under limited resources. It is difficult to realize them as the operation of it is shared by all the partners with heterogeneous traffic demands and policies, as the network includes many traffic engineering(TE) facilities for traffic shaping or priority queuing in various points. In this paper we monitor the retransmission rate of TCP flows in a passive mode to obtain estimated packet loss rate of each flow and partner, and try to analyze the actual reason that affects end-to-end communications in a real-world environment. The results obtained in this paper is considered as a first step of reflecting TCP retransmission monitoring to improve operation, focusing on a certain partner, ITB, who has the largest traffic demand in AI3. The effectivity of the method is approved by the experimental configuration tuning.