1. A method of generating and applying a set of policy rules for enforcement by a policy enforcement function at a node of a communication network, said node routing packet flows to and from users of the network, the method comprising: at a service level control function, determining source and destination addressing information for a packet flow to be transported through said node; sending said determined addressing information to a policy rules generating function, the policy rules generating function maintaining or having access to service and mobility policies for users of the communication network; at the policy rules generating function, generating said set of policy rules on the basis of the source and destination addressing information and the appropriate service and mobility policies, the rules specifying a route optimization policy; and sending the generated set of policy rules to the policy enforcement function; and applying the set of policy rules to traffic flows to determine whether or not route optimization is allowed.