European Journal of Control (2010)2:185–187 # 2010 EUCA Discussion on: ‘‘A Control Based Solution for Integrated Dynamic Capacity Assignment, Congestion Control and Scheduling in Wireless Networks’’ Daniel Simon 1,  , Mongi Ben Gaı¨d 2,  1 INRIA, Grenoble Rhône-Alpes, France; 2 IFP, Rueil-Malmaison, France This paper is a contribution in the emerging domain of control, computing and networking co-design. More specifically it presents a closed-loop control design to guarantee the Quality of Service (QoS) for a set of wireless-based networked nodes. The proposed design jointly handles several sub-objectives, i.e. dynamic capacity assignment, congestion control and scheduling packets on links, to maximize a cost function as the overall objective. As usual, control design involves several steps such as the formalization of the control objective, the choice of a suitable abstraction (model) of the system, the identification of the available and signi- ficant output signals that can be used for control purpose (sensors and probes) and the selection of the actuators able to modify the system’s state. Note that when the plant is made of computing devices, sensors and actuators are software probes and functions which can be implemented at a moderate cost. However making such control system effective needs to keep the control complexity and associated com- munication induced overheads low compared with a statically tuned system, as the control related budget is a part of the overall computing and networking cost. Indeed control theoretic approaches are tradition- ally based on models of the addressed plant. A model (often a set of differential or difference equations) is first chosen. Then, an identification phase is under- taken in order to experimentally determine the model parameters. Control design is performed based on the identified model, and using well known control design methodologies. For example, in control approaches for computing systems, e.g. [5], queuing processes modeling introduces dynamics in the computing system model. Existing modeling frameworks has been reused to model computing and networking devices, e.g. linear models and fluid modeling. Beyond linear models, non-linear models has been successively used to better handle and control undesirable phe- nomena like trashing [7]. However, conversely with the traditional targets of control systems, e.g. mechanics or electrical systems involving complex dynamics, computing systems such as stacks of tasks to be executed or messages to be transmitted often have a static (or a simple dynamic) behavior. Thus modeling w.r.t. dynamic aspects can be kept elementary, as in this paper where the control laws (for congestion avoidance and for air interface assignment) are build step by step to satisfy the involved quality of service requirements. Understanding the dynamics of the addressed phe- nomena (if any) is disregarded in this paper. The proposed approach only relies on the knowledge of plant inputs and outputs, and on well known con- straints (and cost functions) which are related to the QoS satisfaction. Therefore it might be seen as a model free control approach. The main contribution is to handle jointly two dif- ferent problems using a hierarchical and coordinated control structure. The proposed approach may be seen as a heuristic to this difficult QoS formalization and solving problem. The communication load  E-mail: Daniel.Simon@inrialpes.fr  E-mail: mongi.ben-gaid@ifp.fr