poll and epoll are like select.
While through select you can establish only 1024 connections using poll and epoll we can establish 200,000 connections
In places where we need more no. of socket poll and epoll are prefered
Though they are only available at Linux.
One sample site I got is
http://publib.boulder.ibm.com/infocenter/iseries/v6r1m0/index.jsp?topic=/rzab6/example.htm
Anyone visiting can refer this it is good.