A method of alternative routing of a service request in connection with a pool 1 of integrated core network nodes. Before a serving radio access node routes a service request to the core network node serving a mobile station it checks if there are any idle terrestrial transmission resources available between the serving radio access node and the serving core network node. If idle resources are available, the service request is routed to the serving core network node. If no idle resources are available, the service request is rerouted to a selected one of the other core network nodes the pool that has idle resources available. The selected core network node receives the service request, recognizes it contains no temporary identification (TMSI) number associated with it and therefore sends an identity request to the mobile station. The identity request triggers the mobile station initiate an update location registration at the selected core network node or at any of the other core network nodes in the pool. The selected core network node or said other network node now acts as serving core network node for the mobile station. Next time the mobile station makes a service request the radio access node routes it to said selected or said other network node to which it hopefully are idle terrestrial transmission resources available.