Innovative solutions for unified communications Due to the ongoing massive growth of the global Internet, the latest Internet Protocol version 6 (IPv6) is considered as a key technology for the delivery of next generation communications. Digital Economy © Shutterstock 6NET was the largest European project to demonstrate that continued growth of the Internet can be met by using new IPv6 technology. However, regardless of the numerous advantages of deploying IPv6 technology, IPv6-only networks will only be introduced gradually. During the relatively long transition period IPv4 and IPv6 networks will need to coexist and be able to communicate with each other. In this context, research work at the Fraunhofer Institute for Open Communication Systems (FOKUS) focused on providing a technical solution that would enable Voice over IP (VoIP) services beyond IPv4 networks. VoIP offers a promising alternative to conventional telephone services, but also a rich suite of IP-based services, such as instant messaging, multimedia conferences and application data exchange. To support VoIP services between IPv4 and IPv6 networks, the Session Initiation Protocol (SIP) was deployed. Session Initiation Protocol has been designed as a multimedia protocol that could take advantage of the distributed architecture of popular Internet applications, with URLs for naming and text-based messaging. As a protocol only, SIP defines how sessions, including telephone calls are to be created, modified and terminated. To authenticate registered users before establishing a VoIP session, the open-source SIP Express Router (SER) was extended to serve as an access control element in an IPv6 network. To support communication between IPv4 only networks and IPv6 only networks, a dedicated gateway was developed for translating and routing SIP messages. Finally, an adequate replacement of high-end phones was developed, supporting the integration of Internet telephony service into a PC. The 'Bonephone' is a software application designed to allow easy customisation to the specific needs of a user and importantly, to be used over different hard- and software platforms. The public was encouraged to access a VoIp server through the popular www.iptel.gr website, where they could request a VoIP identity and put to the test VoIP services from their IPv6 network. Over the course of the 6NET project the deployed systems had demonstrated the versatility required from VoIP systems, operating seamlessly between IPv4 and IPv6 networks.