A domain name server to be connected to a telecommunication network, the server comprising a memory for storing the names of network elements constituting the management domain of the domain name server and the IP addresses corresponding to the names, and a processor for mapping the received access point name to the stored network element IP address. The domain name server is arranged to identify a name included in a session request as an Internet address related to a certain service and map the network element name to a certain IP address of the management domain of another network, the IP address corresponding to the access point of the server. The invention enables provision of service to several separately managed networks by one service sub-system, which minimizes the amount of work required to establish and manage the hardware needed to provide service.