What's the meaning of EST led indicator?

LEDs indicate the bridging quality:  

RG-EST350V2
a. SYS LED
Blinking: The system is initializing, restoring factory settings, upgrading or resetting.
On: The device is working properly.
Off: The device is not powered on.

b. LAN1/LAN2 LED
Off: The LAN port is not connected.
Blinking Green: Link is up. The port is sending or receiving data.
Solid Green: Link is up. The port is not sending or receiving data.

c. Signal LED (STR1/STR2/STR3)
STR1 Blinking/On: The device is bridged.
STR1 On: RSSI > -75 dBm
STR1 On + STR2 Blinking: RSSI > -73 dBm
STR1 On + STR2 On: RSSI > -71 dBm
STR1 On + STR2 On + STR3 Blinking: RSSI > -68dBm
STR1 On + STR2 On + STR3 On: RSSI > -64 dBm

RG-EST310V2
a. System LED
Blinking Green: The device is being booted.
Solid Green: The device is working properly.
b. LAN LED
Off: No cable is connected.
Blinking Green: Link is up. The port is sending or receiving data.
Solid Green: Link is up. The port is not sending or receiving data.
c. Signal LED
Off: No signal is detected.
Blinking: The signal is weak( ≤-78dBm).
Solid: (The stronger the signal gets, the more LEDs light up)
One LED on: -78dBm< RSSI ≤-72dBm
Two LEDs on: -72dBm< RSSI ≤-65dBm
Three LEDs on: >-65dBm

RG-EST100-E
a. SYS LED
Blinking: The system is initializing, restoring factory settings,
On: The device is working properly.
Off: The device is not powered on.
b. LAN1/LAN2 LED
Off: The LAN port is not connected.
Blinking Green: Link is up. The port is sending or receiving data.
Solid Green: Link is up. The port is not sending or receiving data.
c. Signal LED
LED off: No bridging
LED blinking: <-78dBm
One LED on:-78dBm<RSSI <-72dBm
Two LEDs on: -72dBm< RSSI <-65dBm
Three LEDs on: >-65dBm