下一代网络(NGN)是目前通信网络发展的方向。NGN最大的优势就在于业务的优势以及网络融合带来网络建设运营维护成本降低的优势。传统固定电话网向NGN的演进通常分3个阶段和3个层面。3个阶段分别是从local交换网络层面上的演进,从长途网络层面上的演进,从网络接入层上的演进;3个层面分别是从local 交换网络层面上的演进,从长途网络层面上的演进,从网络接入层上的演进。固定电话网如何向NGN演进是固定电话网运营商最为关心的问题。 Next Generation Network (NGN) is the current direction of development of communication networks. The biggest advantage of NGN lies in the advantages of the business and the advantages brought by network convergence in reducing the cost of network construction, operation and maintenance. Traditional fixed telephone network to NGN evolution is usually divided into three stages and three levels. The three phases are the evolution from the local switching network level, the evolution from the long-distance network level, and the evolution from the network access level. The three levels are the evolution from the local switching network level. From the long-distance network level The evolution from the network access layer on the evolution. How the fixed telephone network evolves to NGN is the fixed telephone network operator most cares about the question.