专线业务是数据通信业务的主要收入来源之一，以往较为常见的专线接入方式多为DDN、FR等窄带专线。由于DDN、FR等网络在建设上存在资金投入大、技术复杂、周期长等问题致使价格较高，并且最高只有２M的带宽，已经不能满足企业级用户对高带宽数据通信的需要。ADSL是XDSL技术中最 Dedicated line services are one of the main sources of revenue for data communications services. In the past, the more common dedicated line access methods were mostly narrow-band dedicated lines such as DDN and FR. Due to the large capital investment, complex technology and long period of network construction such as DDN and FR, the price is high and the maximum bandwidth is only 2M, which can not meet the needs of enterprise level users for high bandwidth data communication. ADSL is the most XDSL technology