Ns is a discrete event simulator targeted at networking research. Ns provides substantial support for simulation of TCP, routing, and multicast protocols over wired and wireless (local and satellite) networks.
An implementation of the GSD service discovery protocol for the network simulator ns2 (http://www.isi.edu/nsnam/ns/). The protocol core is written in c++ whereas simulation settings and scenarios can be set up via OTCL scripts -- as usual in ns2.