How HTTP works:
1. A GET command is performed.
2. It accepts the URI that has been entered by the user.
3. It extracts the Fully Qualified Domain Name (FQDN) and usus a Domain Name System (DNS) to translate it into an Internet Protocol (IP).
4. A GET request is then sent for the web resource that has been specified in the URI, which is sent to a web server using the appropriate IP address (Usually port 80 unless another port number is specified).
5. The user recieves the file returned by the web server.
6. It displays all of the file’s contents in a web browser, being sructured and styled correctly.
7. If the file contains other URI’s, like a reference to a graphic, then the browser will issue another GET command to recieve these files.
FTP – The File Transfer Protocol:
FTP is an application layer protocol thatenables files on one host to be transfered to another host or client.
It uses ports 21 for commands, and port 20 for transferring data.
Telnet is a puirely text based protocol that can be used to manage remote devices, read-only files, and sending/recieving emails.
It uses commands like LIST, GET, and RETR.
POP 3 and SMTP:
POP3 stands for Post-Office Protocol Version 3, SMTP stands for Simple Mail Transfer Protocol. Both are used to send and recieve email. For example:
If Person A sends an email to Person B, the email Person A sends will be sent using SMTP. This will then be stored on the email’s web server. Person B will recieve the email using POP3.
HTTPS stands for Hyper-Text Transfer Protocol over Secure Socket Layer. This encrypts and decrypts user page requests, and the page returned by the web server.
It uses port 43 instead of port 80.