Communication channels are known to impose a number of constraints on control objectives when explicitly considered in feedback loops. One recent line of work considers the problem of feedback stabilisation subject to a channel signal-to-noise ratio (SNR) constraint. The present paper extends such formulation to study the stabilisability of digital output feedback loops and sampled-data output feedback loops. We then quantify the difference in channel capacity between the present setting and the discrete-time output feedback loop setting. This difference is known to represent a fundamental limitation in control over networks performance. © 2010 AACC.