In this paper we present a novel design technique, and combined routing and flow control algorithms, for congestion-free packet switched networks. The design is based on the construction of multiple virtual rings, under the constraint that the path between any two nodes is either confined to a single ring, or traverses exactly two rings (passing through a single bridge node). Our best designs are constructed by using Finite Generalized Quadrangles of combinatorial design theory, together with a scaling algorithm for realizing networks of arbitrary size. The target topology is obtained by taking the edge union of the multiple virtual rings. Capitalizing on the underlying topological properties, we design routing, flow and access control protocols. We prove that the proposed network architecture, coupled with our protocols, ensures that (i) no loss due to congestion occurs inside a network, under arbitrary traffic patterns; (ii) all the packets reach their destinations within bounded tim...