There can be instances where a remote host, has blocked ICMP traffic towards it. Due to which you cant ping the host, to check its presence. In this kind of a situation, what you can do to check the host's presence is to telnet to a known port or to try making a TCP connection to the host.
Whenever you try to establish a TCP connection to the remote host, the remote host will either accept the connection or refuse the connection by sending a RST package. Even this information is more than enough to confirm the presence of the host.
So below two methods can be used to determine whether the host is online or not, whenever PING is disabled or blocked.