Method and an apparatus for shaping the output traffic in a fixed length cell switching network node

A network node supports switching fixed length information cells between a source unit and a destination unit. The invention uses two lookup tables called the active and the standby calendars for each of said output line. Each entry in the calendars represents the position of one cell in the output cell stream which will be sent onto said output lines. While the active calendar is controlling the network cell multiplexing onto a node output line, the standby calendar is updated at each traffic change by looking for a calendar free position for the new traffic starting with a targeted theoretical entry position. A Free Location Table (700) is used, storing the calendar organized by pages. The standby calendar updating starts with reading a Free Location Table page pointed at by the most significant bits of the theoretical entry. Should said page contain only ones (i.e., no free cell position) looking for the nearest page containing at least one zero (i.e., free cell position) and updating the Table and standby calendar accordingly, and then swapping calendars.