ADTRAN Atlas 550 User Manual page 251

Appendix G. Glossary
each block and the result is sent along with the block. If the result does not check out at the other end,
the computer at the other end sends a request (a NAK-negative acknowledgment) to retransmit that
block again. If the block checks out, the computer send ACK (an acknowledgment). In this way, rela-
tively error-free transmissions can be accomplished.
61200305L1-1 ATLAS 550 User Manual G-11