How does Peplink works to monitor IPSec VPN beetween two sites, in tab STATUS

Product Discussion Peplink Balance
1

I have wondering how does Peplink works to monitor IPSec VPN beetween two sites, in tab STATUS

I created tunnel VPN from 192.168.30.12/32 and connect to 3 subnets
172.31.34.0/28
172.31.34.16/28
172.31.34.128/28
ipsec.png

In the status IPSec VPN is Connected. When I also attached 172.31.0.0/16 the status is also Connected

How the Peplink monitor that IPSec Connection connected beetween two connections?
Is it using PING from 192.168.30.12/32 to 172.31.0.0/16 or any others method, Peplink’s used?