Basically, QNX provides two protocols: TCP/IP and QNet.
QNX provides an implementation of the TCP/IP stack (npm-tcpip) relatively light, modular and using the common BSD Socket API (this API is the standar API for TCP/IP programing in the UNIX world). This implemenattion provides an NFS server/client, multicasting, support for IPsec security, IPv6, and so on.
Qnet is the QNX native networking protocol that extends the operating system message passing interprocess comunication (IPC) transparently through a networks of microkernels.
To understand how this protocol works, consider the case of a simple network with two nodes; one of them contains the client process, and the other one contains the server process. The client process creates a connection to the server, using the ConnectAttach() function call and then sends its messages using the MsgSend() function call (this network case works in the same way that in the single node case).
It is important to note that the POSIX calls such as open(), read(), write(), etc can be used too.