It has now become the extensively – used session establishment protocol of VoIP and further been adopted to be the core protocol of session control for the Next Generation Network ( NGN) due to its characteristic advantages of simplicity, preferable expansibility, and toilless realization. 它固有的诸如简单性、良好的扩展性以及比较容易实现等优点已被下一代网络采用作为其核心呼叫控制协议,成为当前使用最流行的VoIP会话建立协议。