The DTN model is implemented as a set of classes in the ns-2 simulator. The model was developed in order to study the deployment of DTN on top of traditional, Internet-based networks and can be useful in experimenting with issues such as: storage space management, custody acceptance and rejection reporting, routing strategies, retransmission timeouts, and bundle fragmentation. The underlying network topology is assumed to be static and, thus, this model is inappropriate for testing routing algorithms in ad-hoc network settings, at least for the time being. Implementation of a full-fledged routing scheme is part of future development plans. The DTN model supports both TCP and UDP convergence layers.
TCP Convergence Layer：http://www.dtnrg.org/docs/code/DTN2/doc/manual/cl-tcp.html