Here I write about EVDO (HSD) reverse channel in short or summarize defination.

The reverse link for 1xEV-DO has a structure similar to that for CDMA2000. In EV-DO all signalling is performed on the data channel and this means that there is no Dedicated Control Channel. The data channel can support 5 data rates which are separated in powers of 2 from 9.6 to 153.6 kbps. These rates are achieved by varying the repeat factor. The highest rate uses a Turbo coder with lower gain. The following channels are transmitted in addition to those used with 1X:

Reverse Rate Indicator (RRI) Channel – This indicates the data rate of the Reverse Data Channel.

Acknowledgement (Ack) Channel – This channel is transmitted after the AT detects a frame with the preamble detailing it to be the recipient of the data.

Data Rate Control (DRC) Channel – This channel contains a four bit word in each slot to allow the choice of 12 different
transmission rates.