This paper provides performance modeling and validation results for the the ns-3 model of the Licklider Transmission Protocol, the standard transport protocol used to provide transmission reliability in Delay Tolerant Networks (DTNs). DTNs are an emerging type of network used to provide communications in extreme environments characterized by very long round trip delays and intermittent connectivity. Evaluation of some target environments requires the use of modeling since high-fidelity testbeds can be impractical. To our knowledge, we provide the first LTP model for the ns-3 network simulator. In this paper, through a combination of simulation and real-time emulation, we verify and validate this new model of LTP and show that its performance is in line with previously published performance studies of LTP.