It works like the cli interface in asterisk, it has the same commands,
although only some are meaningful like "link status" and others are not
meaningful like "show channels".

When you invoke mtp3cli, it sends the command to mtp3d on the service port,
and then prints the result. You invoke like

mtp3cli link status (corresponding to asterisk cli "ss7 link status"), or
mtp3cli link up (corresponding to asterisk cli "ss7 link up").