Initialization guarantees that the correct sequence numbers are used in processes on both ends. Layer 2 protocol maintain the correct sequence of information due to many different types of error. Firstly, if frames lost more than three consecutive times, the re-establishment of the LAP will be done under the assumption that the connection has failed. Secondly, a timer mechanism and preset values of time-out intervals detect lost frames in the transmit direction. Thirdly, frames received out of sequence denote a lost frame in the receive direction.
Unacknowledged operation uses unnumbered information frame.
Information transfer in the acknowledged operation can be done with either a single or multiple frame transmission. In acknowledge information transfer service, information from the network layer is transferred in frames that are not acknowledged by the receiver. This provides fast data transfer but neither flow control nor error recovery. However, in acknowledged information transfer service, upper layer information is transferred in numbered frames that are acknowledged by the receiver. This service is used only with point to point communication.