In this paper, some new schemes for communication systems using error-
detecting codes are described. These schemes employ hybrid strategies
for the retransmission of the codewords detected in error, and combine
the advantages of the go-back-N and selective protocols. The memory,
introduced at the receiver side, enhances their performance with respe
ct to the classical schemes. The results show that the protocols descr
ibed in this paper permit the achievement of a net improvement with re
spect to other similar schemes.