NOVELTY - The cell has inner and outer circulation circuits (14, 16) to circulate coolant i.e. deionised water, within and outside of a stack (2) of electrochemical cells (4). Hydrogen and air supply circuits (8, 10) supply hydrogen and air to the cells. A main housing (20) is mounted on an end plate (6.1) and forms a sealed space (V) partially filled with water. The supply circuits pass via the space, and are submerged in the water to exchange heat with the water. A portion (10.1) of the air supply circuit transfers water in the coolant from outside toward inside of the circuit to humidify air.    USE - Fuel cell e.g. proton exchange membrane fuel cell (claimed) for use as an energy source in a motor vehicle to supply power to an electric propulsion motor and as a mobile energy source in camping and military campaign applications.    ADVANTAGE - The cell utilizes the coolant as humidification and reheating unit of reactive gas filled in a reservoir placed directly on one of the end plates into which cooling circuit is opened after being crossed through the stack of cells, thus reducing the number of distinct devices, connections and length of the devices, and hence reducing size of the cell. The design of the cell saves space for realizing humidification and heating functions, and reduces the number and space of tubes to facilitate accessibility to different elements of the cell.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a device for optimizing the routing of a stream exchanged between two nodes in a telecommunication network    (2) a computer program recorded on a storage medium comprising instructions for executing a method for optimizing the routing of a stream exchanged between two nodes in a telecommunication network.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic sectional view of a fuel cell.    Sealed space (V)    Stack of electrochemical cells (2)    Electrochemical cells (4)    End plates (6.1, 6.2)    Hydrogen supply circuit (8)    Air supply circuit (10)    Portion of air supply circuit (10.1)    Inner coolant circulation circuit (14)    Outer coolant circulation circuit (16)    Main housing (20)