We demonstrate and validate that concurrent and parallel transmissions are feasible for low data-rate impulse-radio ultra-wide band (IR-UWB) physical layers. The optimal organization for a low data-rate IR-UWB network is to allow for concurrent transmissions at the link layer, and to use interference mitigation techniques at the physical layer. Indeed, low data-rate IR-UWB physical layers can suffer from multi-user interference (MUI), especially in near-far scenarios. Therefore, we perform an experimental validation with a packet-based, low data-rate IR-UWB physical layer testbed. Our results clearly demonstrate that concurrent IR-UWB transmissions are possible. This shows that completely uncoordinated low data-rate IR-UWB networks are feasible. We also demonstrate that, in the presence of MUI, an interference mitigation scheme at the physical layer is indeed necessary. In particular, because it is the first component for the proper reception of a packet, we focus on packet detection and timing acquisition. We show that a traditional scheme is not robust against multi-user interference and prevents concurrent transmissions. On the contrary, a scheme designed to take MUI into account, even with a very simple interference mitigation scheme, allows for concurrent transmissions, even in strong near-far scenarios.