A GSM TCH carries speech and data
traffic. Of each 26-frame multiframe, 24 frames are used for
TCHs, one is used for the slow associated control
channel (SACCH) and one is unused.
A GSM full-rate TCH (TCH/F) has a raw rate of 22.8 Kbps, with
a useable rate of 9.6 Kbps for data (or approximately
13 Kbps for speech). One full-rate TCH is
allocated one slot in each frame.
A GSM half-rate traffic
channel (TCH/H) has a raw rate of 11.4 Kbps,
with a useable rate of 4.8 Kbps for data. A
half-rate TCH is allocated one slot in every
second frame.