In this paper, a new MAC protocol for OBS networks is introduced, described and evaluated. Into operation, DAOBS avoids burst collisions in the core of the network by controlling the way OBS nodes access the optical channel. Assuming no wavelength conversion capabilities in the network, DAOBS is assessed and compared to standard deflection routing through simulations. From the results, DAOBS offers zero collisions at low-to-medium network loads without excessively deteriorating the burst end-to-end delay. This makes DAOBS particularly useful either in network scenarios where the increased costs related to wavelength converters arise as prohibitive, or as a mid-term OBS network solution until wavelength conversion becomes sufficiently mature.