A level of supply chain nodes. For example, a supply chain with two independent factory warehouses and nine wholesale warehouses delivering product to 350 retail stores is a supply chain with three echelons between the factory and the end customer. One echelon consists of the two independent factory warehouses.One echelon consists of the nine wholesale warehouses. One echelon consists of the 350 retail stores. Each echelon adds operating expense, holds inventory, adds to the cycle time, and expects to make a profit.