Explaining the reasons for the four-hour long halt in trading on Wednesday, the National Stock Exchange (NSE) said that the instability of telecom links impacted the online risk management system. In a statement on Thursday, the exchange said that it has multiple telecom links with two service providers to ensure redundancy and it received communication of instability of all their links from both the service providers.

"While there was no impact to the trading system, this instability resulted in an impact to the online risk management system, which also is configured in a High Availability mode. Given that the online risk management system was unavailable, market functioning could not continue normally and hence had to be shut down," it said.

NSE said that it was continuously working on resolution of the problem and once the same was resolved, it made an announcement with respect to re-opening of the markets.

It further said that it is awaiting detailed root cause analysis from telecom service providers and vendors regarding this incident.

"NSE is in close contact with SEBI and keeping them updated of developments," it said.

On Wednesday, NSE halted trade at around 11.40 a.m. till 3.30 p.m. due to the glitch, following which SEBI has sought a detailed root cause analysis on the incident from the exchange.

The capital market regulator also told NSE to explain the reasons for trading not migrating to the disaster recovery site.

Meanwhile, the key Indian equity indices opened on a positive note on Thursday with the BSE Sensex rising over 500 points.

The Nifty50 on the National Stock Exchange also rose above the 15,000 mark.

Healthy buying activity was witnessed in metal, IT, banking and finance stocks.