TCH in GSM

TCH stands for a traffic channel in GSM.


This article describes the GSM traffic channel. Traffic channel carries digitally encoded user data or user speech on the forward and reverse link.


TCH support two types of information rates, they are
  • Full rate ( TCH/F )
  • Half rate ( TCH/H )
TCH is a group of 26 consecutive TDMA frame, called multi-frame of the 26 TDMA frames, 24 are used as TCH frames, one frame (thirteen ) is for SACCH and 26th is the unused or idle frame.
TCH data transmitted in 26 consecutive frames

1. Full rate TCH  (TCH/F)
Full rate speech channel  (TCH/FS) - At 13 Kbps the full rate speech channel is digitized. After channel coding, full rate speech channel carries 22.8 Kbps.

Full rate data channel (TCH/F9.6), Full rate data channel (TCH/F4.8), Full rate data channel (TCH/F2.4) channel carries the data at the speed of 9.6 Kbps, 4.8Kbps, 2.4Kbps respectively.

After channel coding is applied is converted to data transferred rate at up to 22.8 Kbps.

2. Half rate TCH (TCH/H)

Half rate speech channel (TCH/HS) - At 6.5 Kbps the half rate speech channel is digitized. After channel coding, half rate speech channel carries up to 11.4 Kbps.

Hull rate data channel ( TCH/H4.8), Full rate data channel (TCH/H2.4) channels carry the data at the speed of 4.8 Kbps, 2.4 Kbps respectively.

After channel coding is applied is converted to data transferred rate at up to 11.4 Kbps.