这是NS2的学习资料，里面讲述了NS2的框架，并且可以从中学习到如何添加代码-This is the NS2 of learning materials, which describes the framework of NS2, and can learn how to add code

NS2的学习代码，其中的几个例子，挺不错的-NS2 learning code, one of the few examples of very good