A method (10, 30, 40, 50, 60, 70, 80, 90, 100, 110, 140) of controlling optical signal power levelling in an optical communication network node in a chain of a plurality of optical communication network nodes, wherein the optical communication network node is configured to apply an optical attenuation, α, to a pass-through optical signal, the method comprising: a. performing the following steps i. to iii. until an attenuation variation value, Δα, is greater than a preselected attenuation variation threshold value (18, 32, 34, 36, 122), Δα TH: i. measuring (12, 112) an optical signal power of an optical signal; ii. calculating (14, 114) a difference, ΔP, between the measured optical signal power and a target optical signal power; iii. calculating (16, 42, 62, 116) a value for the attenuation variation, Δα, to be applied to the optical attenuation taking account of ΔP; b. obtaining a current value of the optical attenuation, α n, and obtaining (22, 38, 44, 46, 52, 82, 84, 92, 126, 128, 142) a new optical attenuation value, α n+1, in dependence on the current value of the optical attenuation, a current value of the attenuation variation, Δα n, and at least an earlier value of the attenuation variation, Δα n-1; wherein the obtaining the new optical attenuation value, α n+1, comprises obtaining the new value of the optical attenuation value, α n+1, only if the earlier value of the attenuation variation, Δα n-1, and the current value of the attenuation variation, Δα n are greater than the preselected attenuation variation threshold value, Δα TH; and c. generating (24, 128) a control signal arranged to configure the node to apply the new optical attenuation value, α n+1. a. performing the following steps i. to iii. until an attenuation variation value, Δα, is greater than a preselected attenuation variation threshold value (18, 32, 34, 36, 122), Δα TH: i. measuring (12, 112) an optical signal power of an optical signal; ii. calculating (14, 114) a difference, ΔP, between the measured optical signal power and a target optical signal power; iii. calculating (16, 42, 62, 116) a value for the attenuation variation, Δα, to be applied to the optical attenuation taking account of ΔP; i. measuring (12, 112) an optical signal power of an optical signal; ii. calculating (14, 114) a difference, ΔP, between the measured optical signal power and a target optical signal power; iii. calculating (16, 42, 62, 116) a value for the attenuation variation, Δα, to be applied to the optical attenuation taking account of ΔP; b. obtaining a current value of the optical attenuation, α n, and obtaining (22, 38, 44, 46, 52, 82, 84, 92, 126, 128, 142) a new optical attenuation value, α n+1, in dependence on the current value of the optical attenuation, a current value of the attenuation variation, Δα n, and at least an earlier value of the attenuation variation, Δα n-1; wherein the obtaining the new optical attenuation value, α n+1, comprises obtaining the new value of the optical attenuation value, α n+1, only if the earlier value of the attenuation variation, Δα n-1, and the current value of the attenuation variation, Δα n are greater than the preselected attenuation variation threshold value, Δα TH; and c. generating (24, 128) a control signal arranged to configure the node to apply the new optical attenuation value, α n+1.