将多个汇聚层连接起来

B、为整个城域网提供一个高速、安全与具有QoS保障能力的数据传输环境

C、提供宽带城域网的用户访问Internet所需要的路由服务

D、根据接入层的用户流量进行本地路由、过滤、流量均衡

-Connect multiple convergence layer B, for the entire metropolitan area to provide a high-speed, security and QoS support capabilities with data transmission environment C, to provide broadband access to Internet users MAN routing services required D, according to the access layer local user traffic routing, filtering, traffic equilibrium