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This paper indicates a desired scheduler buffer size which minimizes the overall packet blocking probability of optical burst switching (OBS) networks based on forward resource reservation (FRR). A packet is blocked either if it arrives at the edge buffer that is full or if the control packet (CP) corresponding to the burst including the packet arrives to find the scheduler buffer full. In conventional one-way reservation schemes, simply increasing the size of a scheduler buffer in which CPs are enqueued may avoid its overflow, but it involves increasing per-hop delay because buffering a CP prolongs to process it, thus increasing the burst delay. In FRR-based OBS networks, since the burst assembly procedure at edge nodes and the resource reservation by CPs at core nodes are processed in parallel, the packet blocking probability can be reduced with no increased delay. To analyze the FRR-based scheme, we develop an edge node model comprising a set of independent edge buffers that feed bursts to core networks and their CPs to a scheduler. We demonstrate that for a set of parameters, an optimal scheduler buffer size exists and depends on the number of packets comprising a burst and the packet arrival rate, and that the minimum packet blocking probability is much lower than that of non-FRR-based OBS systems.