I would like to know if Digi one supports iec 870 protocol
Well, if your host can encapsulate the serial form into TCP or UDP, then you can use any Digi as a remote serial port. IEC 870 (and also DNP3) are designed for tolerant timing, so this works fine. The RealPort driver can be used for an application that only understands serial port (and/or requires RS-232 control signals be driven at the remote device).
However, none of our products can “convert” between a serial and non-serial version. I am more familar with DNP3, where there are differences between EIA-232 form and UDP form.