A fault tolerant queue system for buffering data in a packet switch with a common buffer memory for one or more output ports from the switch uses a number of pointers identifying storing positions in the buffer memory. Multiple copies of the same pointer are handled in a controlled way by using a multiple pointer list where the number of copies included in the system of respective pointers are recorded. A maintenance function checks that the number of copies of a pointer agrees with the value recorded in the multiple pointer list for the respective pointer. The maintenance function cyclically checks all pointers and appurtenant buffer positions, one at the time. This is preceded by an initiation procedure during which the pointer is taken out of operation by filtering out the pointer from the flow of pointers which from output queue lists for queueing pointers in queue to the output ports of the memory are returned to the idle list, until the queue system has been emptied of each copy of the pointer in question. Thereupon, the number of returned copies of the pointer in question is compared with the value in the multiple pointer list. The maintenance function can thereafter work in accordance with one or more operating modes for performing the cyclical control.
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