We study a problem of sequential frame detection in an asynchronous framework, where a single frame of length N slots is transmitted uniformly in a large interval of known size A slots. In this setup, we seek to characterize the scaling needed of N and the channel (input) parameters for asynchronous optimal frame synchronization. We note that the framework permits a natural trade-off between N and \alpha , where \alpha is the synchronization threshold of the channel (usually parameterized by the channel input). We present a general framework that permits this trade-off and then characterize the scaling needed of both N and \alpha as a function of the asynchronism period A. Finally, we apply our results to the AWGN channel as an illustration. © 1997-2012 IEEE.