Figure 2 shows the connection model for synchronous transparent CS data. In general all the user data bits are conveyed between the MT and the IWF as they are received from the TE. This implies that the RLC SDU/ Iu UP frame is transparent.
Figure 3 shows the connection model for asynchronous transparent CS data. The rate adaptation function RA0 from
TS 44.021 (adapted to the RLC SDU size) is used for converting between asynchronous data and a synchronous bit stream. End-to-end flow control is not applicable in UTRAN Iu mode, thus no status bits are conveyed over RAN/UTRAN (see
TS 27.001).
Figure 4 shows the connection model for asynchronous non-transparent CS data.