  We present a formal model to represent and solve the unicast/multicast
routing problem in networks with Quality of Service (QoS) requirements. To
attain this, first we translate the network adapting it to a weighted graph
(unicast) or and-or graph (multicast), where the weight on a connector
corresponds to the multidimensional cost of sending a packet on the related
network link: each component of the weights vector represents a different QoS
metric value (e.g. bandwidth, cost, delay, packet loss). The second step
consists in writing this graph as a program in Soft Constraint Logic
Programming (SCLP): the engine of this framework is then able to find the best
paths/trees by optimizing their costs and solving the constraints imposed on
them (e.g. delay < 40msec), thus finding a solution to QoS routing problems.
Moreover, c-semiring structures are a convenient tool to model QoS metrics. At
last, we provide an implementation of the framework over scale-free networks
and we suggest how the performance can be improved.
