The Pre-Congestion Notification Architecture document defines a PCN domain and the PCN-ingress and PCN-egress nodes that form its boundary. The present document is an attempt to describe the detailed behaviour of the PCN boundary nodes. It is a contribution toward the PCN WG milestone: "Suggested Flow Admission and Termination Boundary Mechanisms". This first version is expected to evolve with discussion and further thought toward a more precise and prescriptive view of boundary node behaviour.