• _{error correction is:}
• _{receiving modem detecting an error and requesting retransmission}
• _{transmitting modem retransmitting the incorrect data}
• _{Discrete ARQ}
• _{define (ACK,NAK)}
• _{Continuous ARQ (no WAITING for ACK,NAK)}
• _{only if error is detected is NAK with block number sent back to transmitter}
• _{flow control}
  • _{controls flow of data into and out of buffer memory}
• _{forward error correction}
  • _{transmits redundant data so the receiving modem can also correct the data transmission}
  • _{various techniques are used to convey this 'redundant' data}