3.1.5.11 Acknowledged Sequence ID (bNRcv) Processing
If the TRANS_USERDATA_HEADER bSeq sequence ID is valid, the bNRcv field SHOULD be inspected. All previously sent TRANS_USERDATA_HEADER packets that are covered by the bNRcv sequence ID, that is, those packets that had been sent with bSeq values less than bNRcv (accounting for 8-bit counter wrapping) are acknowledged. These packets do not have to be remembered any longer, and their retry timers can be canceled.