How do computers talk to each other via the Internet?
The Internet is composed of millions of computers, located all across the globe, communicating and transmitting information over a variety of computing systems, platforms, and networking equipment. Each of these computers (unless they are connecting via an intranet) will have a unique IP address.
IP addresses are 32-bit numbers, containing four octets (8 bit numbers) separated by a full stop. Each computer with a direct internet connection will have a unique IP address, (e.g. 207.68.156.61). Some computers have temporary addresses, such as when you connect to your ISP through a modem. Others have permanent addresses, and some even have their own unique domain names (e.g.www.microsoft.com).
An IP address allows us to uniquely identify a device or system connected to the Internet. If I wanted to connect to a specific IP address, and send a message, I could do so. Without an IP address, my message would have no way of reaching its destination - a bit like leaving the address off a letter or parcel.
Often, computers connected to the Internet provide services. This page is provided by a web server, for example. Because computers are capable of providing more than one type of service, we need a way to uniquely identify each service. Like an IP address, we use a number. We call this number a port. Common services (such as HTTP, FTP, Telnet, SMTP) have well known port numbers. For example, most web servers use port 80. Of course, you can use any port you like - there's no rule that says you must use 80.
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| Figure 1.0 - Ports help computers identify which service data is for. |
