Uplink Common Packet Channel
The uplink common packet channel (CPCH) is an extension to the RACH channel that is
intended to carry packet-based user data in the uplink direction.
The reciprocal channel providing the data in the downlink direction is the FACH. In the physical layer, the main differences to the RACH are the use of fast power control, a physical layer-based collisiondetection mechanism and a CPCH status monitoring procedure.
The uplink CPCH transmission may last several frames in contrast with one or two frames for the RACH message.
