DTT means Digital Terrestial Transmission. Our normal transmission is analogue, but in many countries the terrestial transmission is digitised. In India also DD had planned for DTT & probably started test transmission in Delhi & Chennai.
DTT advantages are like we can transmit data along with Audio/Video which not possible in Analog. Data could be EPG, Text information like News, Weather, scores, etc. Also Multi-Audio & Stereo Audio is possible in DTT.
I think DTT Signals is Available in Chennai. i think its need a Very Small Antenna, Few years back i have seen the News about DTT in DD News.