To produce ciphertexts, two modes of encryption are appliedblock ciphers, which encrypt a fixed size block of plaintext at a time, and stream ciphers, which encrypt stream data, one or more bits at a time. As one of stream ciphers, the cipher feedback (CFB) mode is implemented by a block cipher via multiple stages, and in each stage, 1bit or a number of bits of plaintext are encrypted at a time. Throughout this paper, the study will focus upon the error performance of the stream-based CFB under two sliding-window protocols, go-back-N and selective-reject, in an error channel in terms of throughput. We model the performance of the CFB in terms of application-level throughput and derive the number of stages needed to achieve the optimal throughput, under a given error rate in an error channel. Copyright (c) 2012 John Wiley & Sons, Ltd.