It was not a walk in. It was a scheduled walk-in. HR allowed only to the candidates who had mail letter from Ariba HR.
Rounds:
1) Written Test: 1 hour, 60 question. Consists of mix of apptitude, and java questions. Looks like cut off was 30
2) Technical Interview
3) Telephone Interview
4) HR Interview
You will be on hold after every round. We get to know only if we clear the round.