Cisco Systems Ltd This draft proposes a unified protocol layering approach for pseudo- wire emulation edge-to-edge (PWE3). It adopts the principle that PWE3 should be a single transport type operating over a common packet- switched network (PSN) service model using, wherever possible, existing IETF protocols. The draft defines the protocol layering model for pseudo-wires, guidelines for the design of a specific encapsulation type, and the service requirements on the underlying PSN tunneling mechanism.