Whatever Internet connection you use (ADSL, cable, dial up, LAN, ...) a very important unique address is assigned to your PC : the IP Address (IP means "Internet Protocol").

IP Address: This is a number which is assigned to your automatically to your computer to identify your Internet Connection. An IP address is based on 4 numbers between 0 and 255. Each computer connected to the Internet has a unique IP Address as you can see on the drawing below.
Example : 178.34.29.10

IP Address: what is the link with Internet security ?
When you stay permanently connected to the Internet for a long duration, your computer keeps the same IP address. When keeping the same IP address for a long time, you attrack attention of hackers.

If your are connected to the Internet through ADSL, cable TV or LAN,  your PC usually contains an Ethernet card also called NIC (Network Interface Card). This card is an electronic device that makes the link between your ADSL or cable mode and the Internet.

Ethernet Address: This is simply the serial number of your Ethernet card. An Ethernet address is based on 6 numbers between 0 and 255.
Example: 233.34.78.178.4.253.97

Note: the Ethernet address of your PC is always the same. You can consider that the Ethernet address is permanently "written" inside the Ethernet card when manufacturing the card. This is different for the IP Address. The IP adress of your PC changes each time you re-connect yourself to the Internet. Note: some Internet service providers offer a service that allows you to get a fixed IP address that is to say an address which is always the same at each connection.

What is communication port ?

Any software that uses the Internet (Outlook, Internet Explorer, ...), exchanges data between your computer and other computers connected to the Internet. One of these computers can store your emails (such a computer is an email Server) before you read them with your email software. One of these computers can store the Web pages (such a computer is called a web Server) that you can read with your Internet navigation software.

Depending on the type of information exchanged between the software of your PC and the other computers of the Internet, specific communication channels also called "communication ports" are used. You can compare them to radio FM frequencies that allow to access to different types of information (Example : music, weather, news, ...)
Communication ports are associated to numbers like radio FM frequencies  (104.7 MHz, 105.5 MHz, ...).

Here are well known Internet communication ports : SMTP, POP3, HTTP et FTP
- The port used to send emails is the port 25. This port is called SMTP which means "Simple Mail Transfer Protocol".
- The port used to receive emails is the port 110. This port is called POP3 which means "Post Office Protocol version 3 ".
- The port used to access Web pages is the port 80. This port is called HTTP which means "Hyper Text Transfer Protocol".
- The port used to download and upload files is the port 21. This port is called FTP which means "File Transfer Protocol".

How do software use communication ports ?

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What is a communication protocol ?

A communication protocol is way to exchange data between to computers.

The most famous Internet communication protocols are TCP, UDP and ICMP.

TCP means "Transmission Control Protocol"
UDP means "User Datagram Protocol"
ICMP means "Internet Control Message Protocol"