The equipment part of this system includes at least a data sending net point, a data receiving net, a net link, RAIN device and a transferring net communicating between them. The RAIN device consists of 2/4/8 pieces of PPP physical link I/O ports, the processing branch, the stack branch, the exchanging part and the low cost redundancy net array comm. protocol. The method part of this system discloses practical steps to increase the bandwidth. It can be applied in numerous nets. Without the support of the accessing end, it piles efficiently up the bandwidth, manages the link and possesses efficient toleration ability. On the basis of the protocol, this system suits various business requirements and adds functions, such as the abnormal processing, authentication, encryption and QOS. Its practicability and reliability are good and it costs low.