In this paper we describe a study of an end-to-end architecture in a packet network where congestion is signalled to all contributing users, who then react accordingly. We assume a generic form of packet marking, where congested nodes set a single bit in the packets flowing them using ECN (Explicit Congestion Notification). We briefly describe how allowing greater freedom to the end-systems lays the foundation for a differential QoS framework as a possible future extension to ECN. Not surprisingly, this QoS is a function of the user-network interaction. Focussing on a specific class of user behaviors, related to streaming applications, we decompose this interaction at the relevant timescales, relying both on simulations and dynamical system models. Results indicate that within the framework, single-bit notification achives end-to-end QoS differentiation, approaching proportionally fair sharing of bandwidth.