The INET framework for the widely used OMNeT++ simulation environment supports discrete event simulation for IP-based networks. This paper describes an implementation of the Stream Control Transmission Protocol (SCTP) within this framework. SCTP is a new transport protocol originally designed for signaling transport in telephony networks. The simulation model and parameters of the SCTP implementation in INET are discussed in detail. The INET framework has also been extended to support external interfaces. These interfaces allow to set up hybrid scenarios where simulated nodes communicate with real external IP-based nodes. This new feature was used to test the simulation against multiple SCTP implementations at the last SCTP Interoperability tests. Other methods that were used to verify the SCTP simulation are finally discussed.