A separate module called RTnet provides the drivers (only two network drivers are supported) and the protocols (IP, ARP, UDP and ICMP) over Ethernet. The API is quiet similar to the sockets API: rt_socket(), rt_connect(), rt_sendmsg(), etc. Current version of RTnet only works with Linux kernel version 2.2.x.
RTAI has extended its API to allow true remote (other host) procedure call RPC. New API functions has been added with the following syntax: replace the first two letters of the function name (for example: given the rt_mbx_send(), the new function RT_mbx_send() has been added); and the new function has two new parameters: node and port. This feature do not comply with any communication standard.