The invention describes a method of performing re-synchronisations on a DSL line to optimise the synchronisation rate of the line. The line is monitored over a period of time, and a stable SNR margin is determined, below which the line is observed to lose synchronisation. Historical synchronisation rates and associated SNR margins for the line are recorded, and the highest stable synchronisation rate is determined as the historical synchronisation rate that does not have any associated SNR margins below the stable SNR margin. The method attempts to optimise the synchronisation rate of the line towards this highest stable synchronisation rate. To do this, the current target SNR margin imposed by DLM is identified, for example, by interrogating the DLM system or by noting the SNR margin on the line immediately after the most recent synchronisations. Assuming the current synchronisation rate on the line is less than the highest stable rate, then the synchronisation rate is optimised by triggering a synchronisation of the line when the SNR margin is greater than the target SNR margin plus an additional predetermined amount. The result should be an increase in the synchronisation rate, and can be repeated until the synchronisation rate reaches the highest stable synchronisation rate.