The Asynchronous Reliable Delivery Protocol (ARDP) is a communication protocol used by the Prospero Directory Service, as well as other systems such as NetCheque, NetCash, and PPV.
ARDP is designed for a request/response style of interaction, where in the common case, the client sends a request message to a server using as few packets as possible, and then receives a reply message from the server. The server can queue requests and send the packets composing the response message as data becomes available. In the meantime, the server can process other requests. In the current implementation, each request message sent by a machine from a particular port has its own connection id.
ARDP, which is layered on top of the Internet User Datagram Protocol (UDP), is designed so that in the common case, the additional overhead of guaranteeing reliability is as small as possible. In other words, ARDP's goal is to provide reliability without incurring the overhead of setting up/tearing down a TCP connection. Unless special processing is required, the header is kept small, and unless a packet is lost, no additional packets are sent.
For more details on ARDP, click on the "Frequently Asked Questions" button below.