Intermittent Periodic Transmission (IPT forwarding) has been proposed as an efficient packet relay method for wireless backhaul. In the IPT forwarding, a source node sends packets to a destination node with a certain time interval (IPT duration) so that signal interference between relay nodes that send packets simultaneously are reduced and frequency reuse is realized which brings about the improvement of system throughput. However, optimum IPT duration setting for each node is a difficult problem which is not solved adequately yet. In this paper, we propose a new IPT duration setting protocol which employs some training packets to search the optimum IPT duration for each node. Simulation and experimental results show that the proposed method is not only very effective but also practical for wireless backhaul.