At the time when the sailing schedule is published, the shipping line may not know which ships will perform all the voyages specified, especially the ones in the schedule which are furthest into the future. Against the vessel name they may show a vessel TBN (to be nominated) or a vessel TBA (to be advised), or simply a TBN or a TBA. In the case of a parcel service, the line may advertise a TBN and charter in a (suitable) ship only once the quantity of cargo is known.