Abstract: A telecommunications system includes a mobile network having a plurality of portable communication devices, and a fixed network which includes a signaling agent, a plurality of directory agents, and a plurality of spaced apart attachment points to which the mobile network can attach. In use, each directory agent stores a routing table for routing data to a respective mobile communication device associated with that directory agent. When the point of attachment of the mobile network changes, the mobile network sends a change-of-address message to the signaling agent. In response, the signaling agent is configured to forward the change of address to each directory agent, so that each can update its routing table to take into account the changed point of attachment of the mobile network.