A method for assessing performance of a cell in a network in which data is passed between layers in a protocol stack implemented by the cell. The method comprises calculating a data efficiency of data passing through a physical layer in the protocol stack via one or more higher layers in the protocol stack based on a comparison of a number of physical resource data units allocated to that data at the physical layer with a data throughput of one or more of the layers of the protocol stack. The method further comprises calculating an average efficiency by averaging the data efficiency over a predetermined time and normalizing the average efficiency with respect to a predetermined efficiency so as to generate a normalized average efficiency. The method also comprises comparing the normalized average efficiency with a target threshold and adjusting the operation of the cell if the normalized average efficiency differs from the target threshold by greater than a threshold amount.