How Layering Protocol Software Violates Separation of Concerns

We show how layering in communication software violates the principle of separating concerns. Examples illustrate that layering couples receiver-and sender functions, sharing message headers among layers creates dependencies between layers that largely compromise re-usability, QoS management is scattered over all layers, and layers are tightly coupled with the sub-system that executes it. Layering hence leads often to large and hardly re-usable modules, tangles possibly independent parts of code, and makes implemented protocols difficult and error-prone to extend.