Support for connection types is implemented by connection files in

  /usr/lib/network/connections/

The file name determines the name of the connection type, so support
for the aviancarrier connection type will be provided by the file:

  /usr/lib/network/connections/aviancarrier

Files that implement support for a connection type should NOT be
executable. Such files should contain valid Bash code, among which two
functions, namely <connection_type>_up and <connection_type>_down. For
the aviancarrier file this would be:

  aviancarrier_up
  aviancarrier_down

These functions are responsible for bringing the network up and down,
respectively. When the functions are called, three bash files are
already sourced, so all functions and variables in those files are
available. The readily sourced files are:

  /usr/lib/network/network
  /usr/lib/network/globals
  /etc/netctl/<profile>

Here, <profile> is the profile file specifying the desired network
configuration.

A simple example of a connection file is that of the dummy connection
type.