Various new transport protocols have been proposed with the aim of the efficient use of abundant resources in fast long-distance networks, and a number of experiments to investigate the performances of those protocols have already been reported. However, they have mainly focused on the throughput characteristics of a single connection or under a stable condition, and thus, more variety of throughput characteristics in actual network environments should be investigated aiming at practical use. Therefore, in this paper, the throughput characteristics of some practical high-speed transport protocols, High-Speed TCP (HSTCP), Scalable TCP, and Simple Available Bandwidth Utilization Library (SABUL) with multiple connections or with changes of competitive traffic are investigated through experiments on the Japan Gigabit Network (JGN), an open testbed in Japan, using implementations available to the public. For TCP-based protocols, the influence of the receiver-side OS (TCP implementation) on throughput performance is also investigated, which is of practical importance from the deployment viewpoint. On the basis of the results of these experiments, some considerations on transport protocols for fast long-distance networks are given.