The packet channels carry either RLC data blocks or RLC/MAC control blocks (except PRACH and PTCCH UL, which use an access burst instead of normal bursts). Each of these radio blocks is mapped after channel coding and interleaving onto four radio frames (called radio blocks because they carry logical radio blocks).

The mapping in time of the packet logical channels carried by the same PDCH is defined by a multiframe structure. The multiframe structure for PDCH consists of a cycle of 52 successive TDMA frames, divided into 12 blocks (of four frames each), and 4 idle frames. The multiplexing of the packet channels on a PDCH is not fixed like in the GSM system. It is managed by some parameters and the following block order: B0, B6, B3, B9, B1, B7, B4, B10, B2, B8, B5, and B11. For example, if the cell has four PBCCH blocks, those will be carried by the blocks B0, B6, B3, and B9 (on the same time slots indicated in SI 13 on BCCH).

The idle frames are used by the mobile station for signal measurements and Base Station Identity Code (BSIC) decoding on the SCH of neighboring cells (idle 2 and 4) or for TA update (sending an access burst on PTCCH uplink in idle 1 or 3 and receiving an RLC/MAC control block on PTCCH DL in idle 1 and 3 of two successive multiframes, which equals four frames in total).

The multiframe for PDCH consists of...