To give the channel a unique identifier you must type in a number in the port text field which represents the port used by this channel. The port must be between 1 and 65535 and it must be unused in your network. Make sure that this port is not closed on any router/firewall used between just:connect and the interface client. Note that each channel must have a different port number assigned. Using the same port number for two channels will result in an error. We recommend to avoid any number under 1024 as these are listed as "well known ports" and used by standards such as HTTP and FTP:

http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers

We would recommend to start with 5000 or 10000.