The case where the next DTN router cannot accept custody is an important one. This situation could occur for many reasons, such as running out of storage space or only accepting custody in certain conditions. The way to deal with this is to send the packet onwards if it is able, just like a normal router would, otherwise the packet should be
silently dropped. The lack of a custody response for the dropped packet will cause the current custody holder to perform a retransmission at a later time when it might be possible to accept custody again.