Abstract: An apparatus having a buffer store connected to an input line upon which ATM cells are received, and an output line upon which ATM cells are transmitted is provided. A control device receives, for each cell, a channel identifier and a path identifier from which a first signal is generated indicative of a maximum delay value which is applied to the buffer store and used to schedule the particular cell for transmission on a calendar controlling a sustainable cell rate. The control device generates a second signal indicative of a minimum delay value which is applied to the buffer and, in conjunction with the first signal, is used to schedule the particular cell for transmission on a calendar controlling the peak cell rate. The apparatus can also handle routing information, where a group of channel connections define a Route which share a peak cell rate for the Route and are scheduled on the peak cell rate calendar.