23.0343GPPHigh Speed Circuit Switched Data (HSCSD)Release 17Stage 2TS
In GERAN Iu mode a Radio bearer reconfiguration procedure is used for forwarding the new channel configuration to the mobile station, regardless whether the position of the main channel is changed or not.
Figure 8a depicts the procedures for a successful resource upgrading and downgrading for an ongoing HSCSD call in GERAN Iu mode, in case the position of the main TCH/F remains unchanged.
Figure 8a: Resource upgrading and downgrading in GERAN Iu mode, the position of the main channel unchanged
The outcome of the procedure shall be reported to the MSC by means of an Iu UP rate control procedure (see 3GPP TS 25.415 ). The BSC shall set the maximum rate permitted downlink over the Iu interface according to the new HSCSD configuration, i.e. according to the AIUR to be used by the IW function when the communication is resumed after the handover. The BSC shall use the same RAB subflow combination in uplink direction.
For a transparent call in GERAN Iu mode, the resource upgrading or downgrading is not applicable since the AIUR remains unchanged during the call, and the allowed radio interface data rate is set by the MSC.