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The use of the control theory tools for traffic control in communication networks, for example, the congestion control in internet protocol (IP) routers, has given rise to challenging issues in the time-delay system framework. In this study, the authors propose to design a linear time-delay observer for traffic monitoring in transmission control protocol/active queue management (TCP/AQM) networks. More precisely, the authors focus on a bottleneck topology consisting of long-lived TCP communications through a router. The developed mechanism, located at the router, aims at supervising the network via TCP flow estimations as well as detecting a class of anomalies. This issue is formulated as a stability problem for multiple delayed systems and appropriate robust control tools such as quadratic separation are adopted to address it. Then, some simulations via the network simulator NS-2 and an emulation experiment support the proposed methodology.