In China,SDH system is adopted by Post and Telecommunication Ministry of China and Federal Telecommunication Corperation of China, so as to replace PDH system and expand capacity for better service.

• 邮电部、中国联合通信总公司均采用了同步数定等级(SDH)制,以取代准同步数字等级(PDH)制,扩大其通信系统容量,面向全国开放。