说明：  华为培训新员工的教材《数据通信技术》，不可多得的经验型教材，适合有一定基础的通信技术人员阅读。请勿用于商业用途。
(Huawei training materials for new employees " data communication" , a rare experience-based teaching materials, suitable for a foundation of communication and technical personnel to read. Do not for commercial purposes.)