求翻译：NS2 的模拟也分为两个层次：一个是基于Otcl 编程层次，利用NS 已有的网络元素实现模拟，无需对NS 本身进行修改，只要编写Otcl 脚本；另一个层基于C++和Otcl 编程的层次，如果没有所需的网络元素，就需要首先对NS 进行扩展，添加所需要的网络元素，然后再编写Otcl 脚本是什么意思？

ns2 simulation is divided into two levels: one is based on otcl programming level, the use of ns-existing network elements for analog, no need to modify ns itself, as long as write otcl script; another layer based on the level of c + + and otcl programming not have the required network elements need

NS 2 analog is also divided into two levels: one is based on programd Otcl NS level, the use of the network elements to simulate NS itself, you don't need to be modified, as long as script writing Otcl; another layer based on C++ and Otcl programming level, if you do not have the necessary network e

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NS2 simulation is also divided into two levels: one is based on Otcl programming levels, implementation of simulation with NS network elements that you already have, without having to make modifications to NS itself, as long as the writing Otcl scripts; based on another layer of Otcl and C++ program

正在翻译，请等待...