Short message exchange capability is required for control plane operations of several applications in ATM networks, such as multimedia networking, Intelligent Network-based services, and to support mobility in wireless ATM networks. Existing methods to transport such messages between ATM nodes typically suffer from the disadvantages of excessive management complexity (for provisioned virtual circuits), and/or of incurring large latencies (for switched virtual circuits). In this paper, we propose a new method for connectionless transport in ATM networks using the routing data that is present in all ATM switches. The “connectionless-ATM (CL-ATM)∝ transport technique encapsulates messages into CL-ATM packets containing the source and destination ATM end system addresses in their header. By adding a CL-ATM packet forwarding module, ATM switches can be upgraded to “ATM switch routers∝ enabling them to support both connection-oriented and connectionless transport modes. Routing data collected by the PNNI (Private Network-Network Interface) routing protocol is used to route datagram packets from one ATM switch router to the next. Since the proposed solution defines a generic network-layer connectionless protocol that can be used to transport datagrams generated by any application, it can also be used for IP-over-ATM transport.