| Control Channels |
Channel Types |
Usage |
| Broadcast Control Channel (BCCH) |
Broadcast downlink
(Base station to mobile)
|
Continually broadcasts, on the downlink, information including base station identity, frequency allocations, and frequency-hopping sequences. |
| Frequency Correction Channel (FCCH) |
Broadcast downlink |
Used to synchronise the mobile to the time slot structure of a cell by defining the boundaries of burst periods, and the time slot numbering. Every cell in a GSM network broadcasts exactly one FCCH and one SCH, which are by definition on time slot number 0 (within a TDMA frame). |
| Synchronisation Channel (SCH) |
Broadcast downlink |
| Random Access Channel (RACH) |
Common uplink
(Mobile to base station)
|
Slotted Aloha channel used by the mobile to request access to the network.
(p.s. I love that term "Aloha"; appropriate and to the point)
|
| Paging Channel (PCH) |
Common downlink
(Base station to mobile)
|
Used to alert the mobile station of an incoming call. |
| Access Grant Channel (AGCH) |
Broadcast downlink |
Used to allocate an SDCCH to a mobile for signalling (in order to obtain a dedicated channel), following a request on the RACH. |
| Slow Associated Control Channel (SACCH) |
Uplink and downlink |
In every traffic channel. Used for low rate, non critical signaling. |
| Fast Associated Control Channel (FACCH) |
Uplink and downlink |
"A high rate signaling channel, used during call establisment, subscriber authentication, and for handover comands." Macario |
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