STS (Standard Transfer Specification) is a standard transmission protocol for prepaid meters, established in South Africa in 1997, standardized as IEC62055 by the International Standards Association, becoming the only public prepaid transmission standard in the world. Most of the African countries use STS meters, and they are also used in some countries in Southeast Asia, and Yongtailong as an old enterprise exporting energy meters has a series of STS energy meters to meet the needs of different markets.