One can know current status of the PNR using the link given below.. This is very useful for ticket with Waiting list or RAC which will help them to know the berth allotment status online…
Passenger Current Status
Note:- Online PNR Status Enquiry is not available between 2300 hrs to 0500 hrs IST
http://www.indianrail.gov.in/pnr_stat_date.html