A method of operating a Call Session Control Function node within an IP Multimedia Subsystem network. The method comprises establishing a first session corresponding to a first IP Multimedia Subsystem communication service using a first Application Server, receiving a request for a further session corresponding to a further IP Multimedia Subsystem communication service, and forwarding said request to a further Application Server. Said further Application Server is additionally notified that said first communication service is ongoing and of the nature of said first session.