Abstract: A method of synchronising the filling of a queue, present at an interface between a packet network and a synchronous data link for storing packet identifiers identifying packets received from the packet network, to an incoming packet flow, the method comprising receiving a packet at said interface, identifying the sequence number of said packet, setting a read pointer, pointing to the next packet identifier to be read from the queue, to a value which is a predefined amount less than the identified sequence number. The method also provides a means for extending and reducing the average size of the queue in order to maintain the average size at an optimum level.