hi
Huawei OSN 3500 is used to carry traffic E1,E3,E4,STM-N, FE&GE access.
OSN 3500 convey telecom traffic, it uses MSTP(Multi standard transport protocol)to convey ethernet acess so NE can be converted to a an ethernet switch.
for these facts, we can pump E1 from BTS to BSC using OSN as carrier to convey telephone & data GSM.
Regards.