In a method of estimating a bit rate (f1) of a digital signal conveyed through a SONET network between an originating node and a terminating node, the digital signal received by the originating node is processed to determine a result of a first function of the signal bit rate (f1) and a respective Tx local reference frequency (f2) of the originating node. A result of a second function of the Tx local reference frequency (f2) and a respective Rx local reference frequency (f3) of the terminating node is calculated. Finally, a result of a third function of the respective first and second function results is calculated, to derive an estimate of the signal bit rate (f4) relative to the Rx local reference frequency (f3).