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How does an ISP Work

Shah Newaz Alam Oct 08, 2018
For explaining how an ISP works, a detailed understanding of the different electronic components used in its functioning is required. There are various protocols and system models that need to be considered. Here is a simpler explanation of how an ISP works.
ISP stands for Internet Service Provider. These are the agencies that help you connect your computer to the Internet. The first cross-country link through the Internet was established in 1970. But, till date there are many people who are not aware of the working of the world wide web. The answer is the ISP, which connects you to the Internet.

What is an ISP?

ISPs are agencies that provide access to the Internet. They can be either privately owned, i.e., by an individual, or they can be group owned, i.e., by a group of individuals/community. The Internet is a huge network, formed by the interconnection of many small and big networks throughout the world.
There is a humongous quantity of data on the Internet, but it would have been pointless if we didn't have access to all this information. ISPs are the agencies that bridge this gap between us users, and the Internet. They provide the technology that is necessary for us to be able to access this information, as well add information and data on the Internet.
A simple analogy should make the concept easier to follow. Imagine you are in a huge mall where the goods are stored from floor 1 and above. You are standing on the ground floor. How do you get to the goods then? You can either take the stairs, the escalator or the elevator. These are the things which will take you where you want to go in the mall.
The mall is like the Internet, and the stairs, escalators and elevators are the ISPs. They take you where you want to go on the Internet.
The ISPs are classified based on the way in which they provide service to their customers. There are 5 types of ISPs:
  1. Dial-up ISP
  2. DSL ISP
  3. Cable/Fiber Optic ISP
  4. Wi-Fi ISP
  5. Satellite ISP
All of them have varying speeds and their own pros and cons. There are various terms related to the Internet. For explaining how an ISP works, certain terms need to be presented before starting with the actual working.

Terms Related to ISP


Every computer that connects to the Internet has to do so using a modem. The full form of modem is 'modulator-demodulator'. The function of the modem is synonymous to its name.
It modulates the data and converts it into digital form before passing on the information to the Internet service provider. The data that it receives from the Internet service provider is also in the form of digital signal, and so it demodulates the data.

IP Address

IP stands for Internet Protocol. Every computer that connects to the Internet is assigned an IP address by the ISP. When we type in the name of a particular website in our web browser, we are actually typing in the Internet Protocol address of the website.
The IP address in this case is the address of the server machine that holds the desired web pages. It is generally of the form 'n.n.n.n', where n stands for a number.


'Dynamic Host Control Protocol' in its abbreviated form is known as DHCP. A protocol is nothing but a set of rules that decides the process of doing a work.
The dynamic host control protocol is used by the ISP to assign temporary addresses to any of its subscribers who intend to connect to the Internet.

Backbone of ISP

This is the point that connects your ISP to the Internet. The ISPs buy a particular range of bandwidth for the working of its backbone. It is through this bandwidth that information is sent or received.

The ISP Facility

The Internet service provider carries out its entire functioning in a room called the data center. The advanced data centers consist of various equipment. A pool of modems inside the data center is used to connect every subscriber to the Internet.
Once a modem in the pool receives the information, it connects the subscriber to the backbone. The entire functioning of the modem pool is controlled by algorithms running in a computer to which the modems are connected. This setup of modems is generally referred to as the ISP port server.

How does an ISP Work?

Here is a simple steps to help you understand the working of an ISP...

1. Connect your computer to the network with the modem/router.
2. Modem sends request to the ISP.
3. ISP checks whether you have a static IP address.

4. If YES, your request is processed. If NO, the ISP communicates with the DHCP server and allots your computer a dynamic IP address.
5. Your request is processed by the ISP, i.e., the ISP figures out the IP address of the page that you are requesting.
6. Once it knows the IP address of the requested page, it refers to its own cache.
7. If the page is available in its cache, it transfers the data from that page to your IP address.
8. If it is not available in its cache, then it tracks the IP address that you have requested, and sends a request to that IP address.
9. If the server accepts the request, it allows data transfer to the ISP. If the request is declined, you have to try again.
10. Once the request is accepted by the server, the data is sent to the ISP.
11. The ISP then redirects this data to your IP address.
12. You now have the data on your computer.
Let's start with the procedure right from the local computer. Home computers connect to the ISP using telephone cables or broadband Internet connections. Large networks like that of educational institutes connect to the ISP using a D1 line. The way of logging into the ISP is same for both.
For connecting to the Internet, you will need a modem and an ISP subscription. Let's try to understand the entire procedure in a step-by-step process.
  • The first step is to login into the ISP using the user information provided to you by your ISP. Here, you enter the username, password and telephone number of the ISP.
  • Once the ISP receives your information in its modem pool, it verifies if you are an authentic user or not.
  • Once the user authentication process is done, the ISP provides you with a dynamic IP address using the DHCP.
  • If you have bought a static IP from your ISP, then this step is not required. However, buying a static IP will cost you a lot.
  • Now, you are allowed to browse any web page through your web browser. When you type in the name of the URL on the address bar, you are actually requesting for the IP address of the server machine, that holds those web pages.
  • The information is received at the modem pool. Once this information is received, the ISP connects the subscriber to the modem pool.
  • The requested server machine is reached through an array of dedicated lines and routers.
  • Once the ISP finds the required IP address, it transfers the requested web pages to the source IP address.
  • Some ISPs store every page that is requested by their users in their own cache. So the next time you request the same page, if it is still in the cache your request is directly fulfilled by the ISP without contacting the server.
  • If the page has been flushed from the cache, the above procedure is repeated.
ISPs have large caches and are transferring data to and from hundreds of computers at super fast speeds. A pause in their service can cause losses, and inconvenience to their customers, and their improper functioning can result in the network getting jammed! Hence, it is very important to maintain ISPs properly.
Cooling devices and backup power supplies are among the important components used by an ISP to ensure its smooth operation. These components are of utmost importance for the effective functioning of the ISP.