Hi, If the list allows attachments, this mail contains a PDF with NDL represented in UML. Allow me to quickly guide you through it. The different colours represent different schema (topology, layer, domain, capability and physical schema). You will see a slight gray band; this may serve as a guide: it represents a hierarchy: - At the top administrative domains, thus organizations offering services. - Each admin domain may contain one or more network domains; abstract representations of the data plane. - Network Domains can contain one or more Devices. - Devices may contain one or more SwitchMatrices, each representing the dynamic switching capability at a specific layer. - Networks, Devices, and SwitchMatrices contain one or more Interfaces. All Interfaces are *logical* interfaces, not physical interfaces. The superclass of Interfaces is Connection Points; we distinguish between: - static interfaces (e.g. a laser at a specific wavelength) - configurable interfaces (e.g. a tunable laser) - a potential mux interface; a "shorthand" notation to specify many equal interfaces. E.g. the 4096 possible logical interfaces for each VLAN in a tagged Ethernet interface. - an instantiated mux interface. An instantiation of a potential mux interface (e.g. a configured VLAN). We are happy with the way we represent layers and adaptation between (logical) interfaces: each is specified by 3 properties: the server interface, the client interface, and the (type of) adaptation (e.g. 1000base-X or 10Gbase-R for Ethernet over Fiber). We still struggle with the "horizontal" connections between interfaces: the linkTo, and connectedTo, and Link objects. linkTo is a shorthand to describe two "directly connected" interfaces (a link connection). "connectedTo" describes a more abstracted connection between two interfaces (a network connection; there may be hops in between). The Link and BroadcastSegment allow explicit description of Links. If you have any more questions, please ask! Finally, I've been talking a bit about ITU-T recommendation G.805. We've put a short introduction to G.805 online: http://www.science.uva.nl/~fdijkstr/publications/G805-introduction.pdf (it lacks the final layout, but the text is ready). Regards, Freek, Jeroen and Paola