客户必须提供确定的技术安装以及所要求的通信连接，并将其保持在有效状态。
The defined technical installations as well as the required communications connections must be made available and kept in an operative state by the customer.
所研制的这套系统采用了先进的状态检查技术，实时地对进出内部网络的电子邮件和传输文件等进行分析，并根据需要对通信内容进行审计，以及对通信连接进行控制。
It adopts advanced technology of state check, analyses the emails and files passing in and out real-time, audits the communicated content according to requirement, controls the network connects.
其次，对SIP这个NGN软交换的核心协议进行深入的研究，分析SIP消息包的结构，理解SIP协议中规定的通信连接流程和状态机维护过程，建立了一个遵循协议规定的SIP协议栈模型。
Soft Switch and SIP that is mainstream application protocol in NGN are studied. The structure of SIP message and process of building connection are introduced, a SIP stack model is set to program.
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