A PDP context shall be activated before data can be transmitted or received for this PDP context. 在发送和接收数据之前必须激活对应的分组数据协议上下文。
From practice, it concludes that data controlling mechanism of Netfilter can succeed in managing and filtering the whole data under Linux. 模块可以实现对固定端口,网页访问以及不同数据协议类型的数据进行管理和控制。