This function enables station numbers (calling numbers, connected numbers, but not called numbers) signaled in the context of internode traffic to be modified. It thus supports network-wide features in networks with open numbering plans. For example, the function can be used to ensure the "correct" display of the caller’s station number on the called subscriber’s station. For instance, if number extensions are set in the originating node and if no modification takes place at the transit node, this means that the station number can be extended (e.g. by means of the node code) irrespective of the call route. However, to operate a network with nodes that cannot handle station number modification (such as variants ealier than SP300 V3.3), it may be necessary for numbers to be extended or reduced in transit nodes or destination nodes. Central Office trunk accesses necessitate the option of modifying station numbers even on the "inbound" side.