ONC is based on calling conventions used in Unix and the C programming language. It serializes data using the External Data Representation (XDR), which has also found some use to encode and decode data in files that are to be accessed on more than one platform. ONC then delivers the XDR payload using either UDP or TCP. Access to RPC services on a machine are provided via a port mapper that listens for queries on a well-known port (number 111) over UDP and TCP.
