Rising for the third straight session the Sensex at the Bombay Stock Exchange gained 106 points, or 0.5 percent, to close at 20,898, on buying by funds, and better-than-expected, second quarter GDP growth.The Nifty at the National Stock Exchange advanced 42 points, or 0.7 percent, to 6,218.Stock markets in Japan, China, Hong Kong, South Korea and Singapore ended mixed.