What is 1xRTT (Single Carrier Radio transmission technology)?

Single Carrier Radio Transmission Technology (1xRTT) is a mode of CDMA 2000 wireless communications standard that has a single (1x) 1.25 MHz channel. This single channel is meant for data transmission. Sometimes it is also referred to as 2.5 G standard. This was later on replaced by 3G technologies such as 1xEV-DO and 4G technologies like LTE.