it is fully optional...you may even complaint to indian railways,if you wish,stating that you were asked for tips during the journey...it is a personal choice,if you are satisfied and pleased with their service you may tip them or else not...in my recent trip by hwh ypr express...pantry staff asked for tip,bt 2 of my co pax suffered from bowel upset with the stale and cold food provided...hence i did not tip them...and instead tipped the cleaning staff with rs.20 for the wonderful job done and cleanliness maintained in the running train...so,it depends on you and only you