Now, a classical example which is quite interesting, but can be a little elaborate, concerns the FTP protocol. So, here is what happens when you want to get some kind of files from a server onto to your computer. You have to communicate channels.
Now, I do not really want to go at this stage in great detail, but of course in the course we have explained this formalism. So, I will just browse through these slides quickly to show how the various situations are described.