Periodic call auction mandated for illiquid securities, with defined session mechanics and penalties to protect market integrity. Trading in identified illiquid scrips must occur only through periodic call auction sessions with quarterly identification, two trading days' notice for entry or exit, a minimum period before exit, hourly sessions with specified windows for order entry and matching, purging of unmatched orders, intraday price bands subject to tightening for surveillance, circuit-breaker cancellation and resumption rules, and a penalty regime for self-matching collected into an investor protection fund.