Jonathan's reply is correct, but to be more precise, 1718 is for multicast signaling and 1719 is for unicast signaling.  I noted that the documentation he referenced is actually wrong, as it presently says that 1718 is for unicast traffic.  I'll see if I can get that corrected.  A correct listing of ports is shown here: http://www.packetizer.com/in/q119.html.

Virtually every real-world deployment I've seen uses unicast for discovery, registration, etc., so port 1719 is probably the only port you need.  That said, there has been confusion over these ports for years in the industry, so most devices will listen for traffic on both ports and you might encounter some devices that send unicast traffic to port 1718. While I recommend proper usage, I would expect that both ports might be used interchangeably.

Cheers!

Paul