The Sensex at the Bombay Stock Exchange was trading 51 points in the green zone, at 17,450, a shortwhile ago. The BSE benchmark index rose by nearly 89 points in early trade today on fresh buying by funds and retailers amid a firming trend in Asian markets. The 30-share barometer, had lost 31 points in yesterday's trading.Similarly, the wide-based National Stock Exchange index, Nifty was up by 18 points, to 5,297.