> 5.5.3 | Message Sequence Charts for Error Recovery Mode

> List of state variables and frame types used in this chapter
> V(S) Send state variable
> The send state variable denotes the sequence number of the next in-sequence UIH_E frame to be transmitted.
> V(R) Receive state variable
> The receive state variable denotes the sequence number of the next UIH_E frame expected to be received.
> V(A) Acknowledge state variable
> The acknowledge state variable denotes the sequence number of the next non-acknowledged UIH_E frame within the send window.
> RR[N(R)] Receive Ready frame with the receive sequence number
> The receive sequence number indicates the N(S) sequence number of the next expected UIH_E frame.
> RNR[N(R)] Receive Not Ready frame with the receive sequence number
> The receive sequence number indicates the N(S) sequence number of the next expected UIH_E frame.
> REJ[N(R)] Reject frame with the receive sequence number
> A station receiving an REJ frame shall initiate sequential retransmission of UIH_E frames starting with the UIH_E frame indicated by the N(R) contained in the REJ frame.
> T1 Acknowledgement timer for starting the UIH_E frame retransmission
> I[N(S), N(R)] I frame (Information frame) with two sequence numbers:
> - N(S) is the send sequence number of the I frame
> - N(R) is the receive sequence number of the next expected I frame to be received.
> Consequently, N(R) indicates that the I frames numbered up to N(R) -1 inclusive have been received correctly.
> Figure 16: Data transmission in one direction
> Figure 17: Data transmission in both directions
> Figure 18: Data transmission to busy station
> Figure 19: Data transmission to busy station with Receive Ready missing
> Figure 20: Data transmission to busy station with Receive Not Ready missing
> Figure 21: Data transmission to busy station with T1 timer expired
> Figure 22: Data transmission with Receive Ready missing, scenario 1
> Figure 23: Data transmission with Receive Ready missing, scenario 2
> Figure 24: Sequence error