The Sensex at the Bombay Stock Exchange jumped 311 points, or 1.8 per cent, to 17,456 in early trade, today, on fresh buying by funds and retail investors at lower levels, amid rising Asian markets. Later, the Sensex remained firm, and stood 315 points, or 1.8 per cent in the positive zone, at 17,461 in afternoon deals, a short while ago.