Trigger ports

[WNxBigs]

My router has the following

[Trigger port][ucp/tcp] [Public port][udp/tcp]

What are the trigger ports for
UDP 6500
TCP 6667
UDP 27900
UDP 27901
TCP 28910
TCP 29900
TCP 29901
UDP 29910
TCP 29920

I have had a nosey around and can't find anything on this