Abstract: A change of switch plane operation is performed in a multi-plane cell switching node (20) which has a first switch plane (22); a second switch plane (24); and plural switch port interface units (26). In response to detection of a fault in the active switch plane, the passive switch plane sends a plane change cell to the plural switch port interface units, and stops egress traffic flow from the second switch plane. Upon receiving the plane change cell, each switch port interface unit redirects traffic cells sent from the active plane to the passive switch plane. Each switch port interface unit then determines when traffic cells destined thereto have been flushed from the first switch plane, and changes its active switch plane designation (so that the formerly passive switch plane becomes the active switch plane) so that egress traffic flow can begin from the formerly passive (now active) plane to the respective switch port interface units.

Abstract: Transmission is synchronized in a cell based switch of user cells which can include different numbers of data bits. The transmission is performed via a two-way link between functional entities which each includes a link control function containing functions for starting and controlling transmission of data on the link by sync cells which are exchanged between the link control functions. The exchange of sync cells is controlled by a sync state machine having three states. In a HUNT state, the link control function investigates a sync cell coming in from the link for establishing whether it agrees with a predetermined pattern for sync cells. In a PRESYNC state that starts after a sync cell contains the predetermined pattern has been found in the HUNT state, the link control function investigates a predetermined number thereafter incoming consecutive sync cells for establishing whether they contain the predetermined pattern. If this is not the case, the control process returns to the HUNT state.