Network infrastructures are nowadays getting more and more complex as security considerations and technical needs like network address translation are blocking traffic and protocols in IP-based networks. Applications in such networks should transparently overcome these limitations. Examples for such applications range from simple chat clients to collaborative work environments spanning different enterprises with different heterogeneous network infrastructure and different security policies, e.g., different firewalls with different configurations. Overlay networks are a convenient way to overcome this problem. In many cases, diverse barriers like multiple facing firewalls would require significant user knowledge to establish a connection. Self-organizing peer-to-peer networks appear to be a convenient solution, but contemporary systems still have limitations in overcoming connectivity problems in heterogeneous networks. Thus, we introduce a self-organizing peer-to-peer infrastructure th...