In the near future we are faced with the challenge to provide SIP based services in heterogeneous IP networks. Call signaling as well as media transport for Voice over IP (VoIP) must traverse interconnected IPv4 and IPv6 network domains to work successfully. Indeed there are several classical IPv6 transition techniques but are they appropriate for voice interaction? On the one hand SIP signaling requires reliable IP interworking as mostly UDP is used as the transport protocol of choice and on the other hand VoIP undergoes harsh conditions in terms of delay, jitter and packet loss which makes it hard to guarantee adequate voice and interaction quality.

In this paper we consider both the theoretical and practical aspects regarding different approaches for transitioning SIP over heterogeneous IP networks. In order to evaluate the strength and weaknesses we designed a testbed architecture that enables us to investigate many transition scenarios in a very simple way. Thus we are able to conduct performance evaluation and characterization which are important issues for the Next Generation Network (NGN).