A method is described for synchronizing a clock of a client in a packet based communication network with respect to a reference time provided by a timeserver. Packets containing at least one timestamp indicating a sending time of the packet are sent from the timeserver and received at the client. Upon arrival of each packet at the client, the arrival time is determined and the delay between the timestamp and the arrival time is also determined for a first plurality of packets. A first variation of the delays of these packets is calculated and based on this calculation a first observation frame is defined whose size depends on the first variation of the packet delays. The first observation frame comprises a second plurality of delays associated with the first plurality of delays. Further, a first representative delay based on the second plurality of delays is determined. Based on the first representative delay a relation between the clock of the client and the reference time is calculated and the clock of the client is synchronized to the reference time based on the calculated relation.