1. A method of determining a routing of data between at least two network elements of a telecommunications network, which are interconnected via a transmission path, the method comprising identifying a plurality of distinct transmission layers of a telecommunications model from which the transmission path is comprised, developing a reachability table by identifying a connection between each transmission element in each layer to other transmission elements in the same or a different layer of the transmission path, for each connection defining a set of communications parameters which define a cost of communicating data via the connection and allocating a weighting value for communicating data via the connection, for all possible routes between the two network elements along the transmission path via each of the layers modelling the effect of the connection for routing the data in accordance with the set of communications parameters for the connection and determining a weighted result along each path, and combining the weighted results to determine a metric of performance for each of the possible routes, and determining an optimum route from the best evaluated parameters.