GSM Combined channel configuration
This page describes GSM combined channel configuration for TS0. It covers 51 frame multiframe structure mentioning FCCH,SCH,BCCH,CCCH,SDCCH,SACCH channel mapping on TS0 for both downlink and uplink.
As mentioned in GSM Channel types signaling channels SDCCH are combined with (FCCH+SCH+BCCH+CCCH) on time slot TS0.
In this configuration, position of FCCH+SCH+BCCH is not changed, but CCCH capacity is reduced from 9 blocks to mere 3 blocks. This 6 blocks are used by 4 blocks of SDCCH and 2 blocks of SACCH.
In the downlink CCCH gives a way for signaling channels(SDCCH/SACCH) and similarly in the uplink RACH gives a way for these signaling channels as shown in the figure below.