EGPRS Switched Radio Block Loopback mode defines two Sub-modes of operation - Radio Block Loopback ON and Radio Block Loopback OFF. When the EGPRS Switched Radio Block Loopback mode is initiated, the MS shall enter the Radio Block Loopback ON sub-mode.
When the EGPRS SRB Loopback Sub-mode is set to ON, the MS shall receive all radio blocks and, before they pass through the decoding process, shall send them to the test set using the same uplink resources as the existing uplink TBF. The radio blocks shall be resent on the very next block period regardless of USF or TFI decoding.The radio blocks shall also pass through the decoding process and if the RLC/MAC header is successfully decoded shall be sent to RLC/MAC. When in Radio Block Loopback Sub-mode ON, the MS should not send any control messages or data from RLC/MAC to its own Physical Link layer for transmission.When the EGPRS SRB Loopback Sub-mode is set to OFF, the MS shall not loopback any radio blocks received.
The GPIB command to set the EGPRS SRB Loopback Sub-Mode is CALL:FUNCtion:CONNection:SRBLoopback:SUBMode .