1. A method of constructing an end-to-end routing path across multiple packet switched domains supporting one or more connection oriented technologies, the method comprising: generating a domains topology identifying all possible domains, the border elements of those domains and the inter-domain links; receiving a request for computation of a path from a source entity in a first domain to a destination entity in a second domain; removing from the domains topology all domains and inter-domain links that cannot or are unlikely to feature in the requested path; computing candidate intra-domain paths for each remaining domain; mapping each candidate intra-domain path to a logical link defined by its two ends, one end being a border element and the other being a border element or the source or destination entity; determining attributes for each logical link; determining attributes of the remaining inter-domain links; generating a virtual network topology by combining the logical links and their associated attributes with the remaining inter-domain links and their associated attributes; and determining a best end-to-end route by analysing said virtual network topology.