随着社会经济的发展，人们对通信业务的需求量也越来越大，业务种类早已由电话语音业务扩展到数据、传真、计算机、图像等业务，如何经济、高效地提供用户满意的接入网，已经成为通信业关注的焦点。 接入网是指用户网络接口与业务节点之间实现传送承载功能的网络实体。随着接入 With the development of society and economy, people are also in increasing demand for communication services. The types of services have long been extended from telephone voice services to data, fax, computer and image services. How to provide user-friendly access cost-effectively and efficiently Network, has become the focus of the communications industry. An access network refers to a network entity that carries a function of carrying and bearing between a user network interface and a service node. With access