The Supervisor-based Network Surveillance (SNS) scheme is a semi-centralized network surveillance scheme for detecting the health status of the computing components in a distributed real-time (RT) system. An implementation of the SNS scheme in a middleware architecture, named ROAFTS (Real-time Object-Oriented Adaptive Fault-Tolerance Support), has been underway in the authors' lab. ROAFTS is a middleware subsystem which is layered above a COTS (Commercial-off-the-shelf) operating system (OS), such as Windows XP or UNIX, and functions as the core of a reliable RT execution engine for fault-tolerant (FT) distributed RT applications. The applications supported by ROAFTS are structured as a network of RT objects, named Time-triggered Message-triggered Objects (TMOs). The structure of the prototype implementation of the SNS scheme is discussed first, then a rigorous analysis of the time bounds for fault detection and recovery is provided.