中文摘要：

软交换是下一代网络中的核心技术，SIP协议在软交换中起着十分重要的作用，但SIP协议的NAT穿越一直影响着软交换业务的迅速普及。虽然目前解决NAT穿越的方案很多，但都存在着一定的局限性。本文介绍了适合目前软交换网络环境的SBC和ALG方案，并给出了一种基于ALG方案的具体实现。本方案已经成功应用于我们开发的高端防火墙并投入了市场。

英文摘要：

Softswitch is the core technology of NGN （Next Generation Network）. And SIP （Session Initiation Protocol） plays an important role in softswitch. The NAT （Network Address Translator） traversal for SIP has been an operational im- pact on the rapid popularization of the softswitch service. In this paper, we introduce St3C （Session Border Controller） and ALG （Application Level Gateway）to solve this problem since it is more suitable for the current softswitch network environment, and we also give an implementation of ALG. This solution has been adopted successfully in our high-end firewall and has been put into the market.