 Reliability in either of these modes is optionally and/or additionally guaranteed by the lower layer Bluetooth BDR/EDR air interface by configuring the number of retransmissions and flush timeout (time after which the radio will flush packets).In-order sequencing is guaranteed by the lower layer.The EL2CAP specification adds an additional "enhanced retransmission mode" (ERTM) to the core specification, which is an improved version of retransmission and flow control modes.