Why is the RLOS LED is on when performing a loop at E1 port ?
RLOS LED is the synchronous alarm indicator of E1 port, and it is on or flashes if E1 link is not synchronous or without synchronization; otherwise, it is down. When E1 port works in non-frame mode, RLOS LED does not indicate the synchronization status and it should be down consistently. By default, E1 port uses line clock. When a loop occurs to the line, the LED cannot get the clock signals, so RLOS LED is always on. After setting the clock mode of the port to master, RLOS LED will be down then.