To fully understand how Internet works, we use a case scenario to help us. Say you have a notebook and you want to connect to the Internet. The first thing you need to do is to get an IP address for your notebook so that you can setup your network connection.
Where do you get your IP address? – From you network administrator or automatically when your notebook is connected to the LAN. There is a DHCP (Dynamic Host Configuration Protocol) server in your network in order to automatic assignment of IP address to your notebook.
The DHCP assigns a temporary non-public IP address for your notebook. The gateway machine IP address is also provided to set up the network connection and this process is done automatically by the DHCP server. If this server is not available then you have to configure the network connection manually.
The gateway machine uses NAT (Network Address Translation) to translate the non-public IP address so that your notebook can communicate with the computer connected on the Internet.
On your browser, you type a web site address say www.google.com , your browser running on your notebook begins to send and receive packets of information to and from Google's website. The web site address is called URL (Uniform Resource Locator).
The URL is a user human readable host name that reference to a machine on the internet. URL consists of the host name and the domain name. Using our earlier example, www.google.com: "www" is the host name and "google.com" is the domain name.
The URL is translated into an IP address. The Domain Name Server (DNS) is used to maintain the hostname to IP mapping.
You will notice that domain name will include a dot followed by a 3 characters generic name referred to as top-level-domain (TLD) name. And depend on where the domain name is registered, and additional dot and country code (2 characters) is added after the TLD. These 2 sections of the domain name is referred as country code top-level-domain (ccTLD). For example www.google.com.sg is registered and maintain by Singapore. Each ccTLD is maintained by their respective country government.
The 2 characters country code is maintain by ISO-3166 standard committee under ISO. The TLD name is managed by ICANN, Internet Corporation for Assigned Names and Numbers.
When you use the Web or send an email, you used the domain name. In your network there is a DNS that you use to translate the URL to the IP address. Your network DNS get this mapping information from the Authoritative DNS. This DNS is the central database for the domain and other DNS updates the address mapping information on a regular timing, usually once a day.
The ccTLD name servers maintain the Authoritative DNS information. The Individual host name is recorded in the Authoritative DNS which in turn propagated to all other DNS in the Internet.
When you try to access to a web site, your web browser will query the DNS server in your network for the IP address. The DNS will access to the TLD Name Server if the domain name is not found in its database. Once the IP address is known, your notebook can start to communicate with the web server or email server. Your network DNS can be in your LAN or provided by your Internet Service Provider (ISP).
The DHCP is normally including the router which also provides a modem to connect to the ISP using public telephone network. ISP provides connectivity to the Internet.
There are many ways to connect to the Internet; my case study shows you one way where you can subscribe to an Internet service from your local ISP from your home or your office.
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