What is Selective Reject (SREJ)?
Selective Reject (SREJ) is an optional, advanced LAPM (V.42) error correction capability that allows the receiving modem to request retransmission of a given block while continuing to receive later blocks; i.e., to receive the retransmission late (out of order). Without it, the entire transmission has to start over at the retransmitted block, which can result in later blocks being resent unnecessarily. Hence, Selective Reject can improve throughput where there is a significant error rate, particularly over links with long delays (e.g., satellite links). Not all modems support Selective Reject, which is typically found only in high-end products.
