The transport layer may comprise one or more transport providers at the same time. The identifier parameter of the transport provider passed to the t_open() function determines the required transport provider. To keep the applications portable, the identifier parameter of the transport provider should not be hard-coded into the application source code.
Currently, the only valid value for the identifier parameter for the t_open() function is /dev/tcp, indicating the TCP transport provider. Even though no device with this pathname actually exists, the library uses this value to determine which transport provider to use.