Search some books about network simulation in the library.
Search the existed RFID simulator. Most of them are not on MAC level, but on application level, to help software programmer develop RFID application in real business case.
NS-2 needs C++ and OTcl. After brief reading of the NS2 manual, I found out C++ must be used to customize the protocol. It seems not enough time to build the project upon this simulator. Lots of project built up based on performance measurement by this simulator, which is the benefit in using this tool.
J-Sim is out of date, not enough reference can be a problem.
As to get familiar with simulator cost too much time, next step is to search the material in NS2 simulation, if these materials are insufficient in shortening the developing time, I may consider to build my own simulator, like the one we use in COMP5416