A node in a computer network predefines a threshold number (Max) as the maximum number of allowed call set up messages (CSMs) to be processed from a plurality of sources by the network node, and predefines a time frame window as the time within which no more than the threshold number (Max) CSMs are accepted for processing by the network node. The node detects each new incoming CSM in the network node. The node rejects each new incoming CSM if the number of CSMs accepted for processing during the current time frame window equals the threshold number (Max). Otherwise, the node accepts each new incoming CSM that is not rejected. Also the node rejects each new incoming CSM if the number of CSMs currently being processed by the network node equals the threshold number (Max).