Examples of network protocols:

• HTTP - browse web pages
• HTTPS - browse web pages with encryption (with a layer of TLS encryption)
• SMTP - send and receive emails (very simple, similar to http)
• IMAP, POP3 - load emails from an inbox (also text based protocol)
• IRC - chat
• FTP - file transfer
• SSH - remote shell over an encrypted connection
• SSL - low-level secure data transfer (used by HTTPS)

They all have their "default" ports. FTP has a command port, designed to work like satellites. You have port 21 to listen on then it can open additional ports for the file transfer. With satellites, you have a lower, reliable frequency for the command opening, then a higher frequency with higher speed.

ports

Port is between 1 and 65535. On most system, to use a lower port number, you need higher, admin privileges.

• 21 - ftp (control port)
• 22 - ssh
• 25 - smtp
• 80 - http
• 443 - https
• 3306 - mysql
• 5432 - postgresql
• 5984 - couchdb
• 6667 - irc (the most typically used one)

$ nc -lp 1024
^C
$ nc -lp 1023
Can't grab 0.0.0.0:1023 with bind : Permission denied

nc is netcat to run commands. The above command tells to listen on that port. On 1013 it won't run.