It is used for the one E4 to STM-1 or three E3 to STM-1. E3, E4 interfaces conform to the protrol signed by PDH system. The interface adopts Siemens-type L9 coaxial as physical connector, and optic interface is used for STM-1 physical connector. Wavelength is 1310nm or 1550nm. 19 inches in width, 1U in height, the power supply can be of AC220V or DC-48V. The LED indicator on the front panel to indicate the working conditions and the alarming. The overhead processing of the STM-1 is not used by STM1/E4E3.