The invention provides a coordination layer of coordinating entities provided intermediate the admission control interfaces of the transport network domains, and any QoS signaller which signals QoS requests on behalf of the application layer. The coordination layer acts to distribute an admission control request across the multiple transport network domains by the use of coordination request messages containing the admission control request being forwarded through the coordination layer of coordinating entities. At each coordinating entity the admission control request is passed on to the admission control interface of the transport network which the coordinating entity serves, and an admission control response obtained. This admission control response is then combined with admission control responses from the other domains which are propagated through the coordination layer via coordination messages. The result is that the coordination layer acts to combine the various admission control responses into a combined response, which can be provided back to the QoS signaller (or other requesting entity). Thus, coordination of admission control across multiple transport network domains is achieved, without a QoS signaller having to contact each individual domain.