Drop-insert slot structure, modular design,16/32/48/64 E1 optional, convenience for expansion 16 uni-directional E1 per DTU board (E1 interface board) 75 Ohm and 120 Ohm optional E1 link can receive signal=-43dB, which is also after spanning 2KΩ impedance and 120m transmission cable Unblocked 2048Ts exchange network Providing cross connect of any time slot within any E1;Providing multifarious connection method including uni-directional, bi-directional. multicast and loopback; Under the mode of receiving clock extraction, system clock source auto-following can be implemented( A maximum of eight priority classes can be configured preliminarily) 19 inch 2U