Sweep Ping

To sweep ping and findout which hosts are up

nmap -sP 192.168.0.0/24

This will find out all hosts that are up in the subnet 192.168.0.0/24. It uses ICMP and TCP Ack to findout this. If you need to do it using ICMP alone then

nmap -sP -PI 192.168.0.0/24