EC2 instance: Connection timed out [closed]

I am getting and connection timed out error but I don't know why because I have checked my aws connection for port 22

Here is the error:

ssh: connect to host 3.110.156.211 port 22: Connection timed out

by using this command:

ssh -i pair1.pem ubuntu@3.110.156.211

and I am sure this is correct command because I have previously used the same command for the same and there was no such problem. I would like to connect to the EC2 instance again.