The present invention relates to a solution to the problem of providing CCBS services over GVNS. In a network service with routing code recalculation a supplementary subscriber service involving an interaction between two subscribers. Knowledge of a subscriber access code, used in a called subscriber local remote exchange, is required in a calling subscriber local exchange. A subscriber access code is generated by modification of a called subscriber routing code, used by said calling subscriber local exchange. Said modification occurs in a transit node of said network service. An interworking problem is then overcome by providing a relay CCBS applications service element (CCBS-ASE), in a GVNS transit node, and arranging for end-to-end signalling to be replaced by two TC dialogues, one between the calling partys LE and the relay CCBS-ASE and the other between the called partys LE and the relay CCBS-ASE.