How does the Internet work?
Augest 23, 2019
How does the Internet work? The videos you watch on youtube, traveled thousands of miles from
a Google data center to reach you. Let’s learn how the Internet works by getting to understand
the details of this data’s incredible journey.
Internet via satellite?
A data center, which can be thousands of miles away from you, this article stored inside it.
How does this data reach your mobile phone or laptop? An easy way to achieve this goal would
be with the use of satellites. From the data center, a signal could be sent to the satellite via an
antenna, and then from the satellite a signal could be sent to your mobile phone via another
antenna near to you, this is illustrated in Fig:1. However, this way of transmitting signals is not a good idea. Let’s see why.
The satellite is parked nearly 22,000 miles above the earth’s equator. So in order for the data
transmission to be successful the data would have to travel a total distance of 44000 miles.
Such a long distance of travel causes a significant delay in receiving the signal; more
specifically it causes huge latency, which is unacceptable for most Internet applications. Moreover, this type of communication is exposed to weather conditions, demands clear line of sight and offers low bandwidth.
Fig:1 An example of the internet via satellite
Internet via optical fiber cable
So if this webpage does not reach you via a satellite, then how does it actually get to you? Well it is
done with the help of a complicated network of optical fiber cables, which connect between the
data center and your device. Your phone could be connected to the Internet via cellular data or
any WiFi router, but ultimately, at some point, your phone will be connected to this network of
optical fiber cables (Fig:2A).
Fig:2A Optical fiber network across the globe
Fig: 2B A cross section view of optical fiber cable
What is SSD and server in data center?
Any youtube videos you watch, is stored inside a data center;
to be more specific it is stored in a solid-state device (SSD) within the data center (Fig: 3A). This SSD acts as the internal memory of a server. The server is simply a powerful computer (Fig: 3B), whose job is to
provide you the video, or other stored content, when you request it. Now the challenge is how to
transfer the data stored in the data center, specifically to your device, via the complex network
of optical fiber cables? Let’s see how this is done.
SSD is a memory device used in modern data center
Fig: 3B Server is a powerful computer used in data center
What is an IP address, how does it work?
Before proceeding further we should first understand an important concept, which is the concept
of an IP address. Every device that is connected to the Internet, whether it is a server, a
computer, or a mobile phone, is identified uniquely by a string of numbers known as an IP
Fig:4 All the devices connected to the internet have unique IP address
You can consider the IP address similar to your home address, i.e. the address that
uniquely identifies your home (Fig:5A). Any letter sent to you reaches you precisely because of your
home address. Similarly in the Internet world, an IP address acts as a shipping address through
which all information reaches its destination. Your Internet service provider will decide the IP
address of your device, and you are able to see what IP address your ISP has given to your
mobile phone or laptop (Fig:5B).
Fig: 5A In the internet, IP address acts as a shipping address
Fig: 5B An example of IP address of laptop and mobile
The server in the data center also has an IP address. The server stores a website, so you can
access any website just by knowing the server’s IP address. However, it is difficult for a person
to remember so many IP addresses, so to solve this problem, domain names like youtube.com,
facebook.com etc. are used which correspond to IP addresses, which are easier for us to remember than the long sequence of numbers. Another thing to notice here is that a server has
the capability of storing several websites (Fig: 6), and if the server consists of multiple websites, all the websites cannot be accessed with the server’s IP address. In such cases additional pieces of
information, host headers, are used to uniquely identify the website. However, for the giant
websites like facebook.com or youtube.com the entire data center infrastructure will be
dedicated to the storage of the particular website.
Fig:6 A single server can handle multiple small websites
The use of DNS server
To access the Internet, we always use domain names instead of the complex IP address numbers. From where does the Internet get IP addresses corresponding to our domain name requests? Well, for this purpose the Internet uses a huge phonebook known as DNS (Domain Name System). If you know a person’s name but don’t know their telephone number, you can simply look it up in a phone book (Fig:7A). The DNS server provides the same service to the Internet. Your Internet service provider or other organizations can manage the DNS server (Fig:7B).
Fig: 7A DNS server is similar to the phonebook
Fig: 7B DNS server stores IP addresses corresponding to domain name
Let’s have a recap of the whole operation. You enter the domain name; the browser sends a
request to the DNS server to get the corresponding IP address; after getting the IP address your
browser simply forwards the request to the data center, more specifically to the respective
server as shown in Fig:8. To save time in the future, your browser also saves this IP address in its cache memory so it will be there next time you want to access that particular site.
Fig:8 Working of DNS server is illustrated here
Journey of data from data center to mobile or laptop
Once the server gets a request to access a particular website, the data flow starts. The data is
transferred in digital format via optical fiber cables, more specifically in the form of light pulses(Fig: 9A). These light pulses sometimes have to travel thousands of miles via the optical fiber cable to
reach their destination. During their journey they often have to go through tough terrains such as
hilly areas or under the sea. There are a few global companies(Oragne, AT&T, Verizon, Google, etc.) who lay and maintain these optical cable networks. The optical fiber cables are laid with the help of plow. A plow is dropped deep into the sea from the ship (Fig: 9B), and this plow creates a trench on the seabed into which is placed the optical fiber cable (Fig:9C). In fact, this complex optical cable network is the backbone of the Internet.
Fig:9A The data is transferred in digital format via optical fiber cables
Fig:9B A plow is dropped into the sea from the ship
Fig :9C Plow creates a trench on the seabed to placed the optical fiber cable
These optical fiber cables, carrying the light, are stretched across the seabed to your doorstep, where they are connected to a router. The router converts these light signals to electrical signals. An Ethernet cable is then used to transmit the electrical signals to your laptop as shown in Fig: 10A. However, if you are accessing the Internet using cellular data, from the optical cable the signal has to be sent to a cell tower, and from the cell tower the signal reaches your cellphone in the form of electromagnetic waves as shown in Fig: 10B.
Fig:10A When accessing the internet using WiFi, signal reaches your laptop via router
Fig:10B When accessing the internet using cellular data, signal reaches your cellphone via cell tower
What is ICANN?
ICANN stands for Internet Corporation for Assigned Names and Numbers. Since the Internet is a global network, it has become important to have an organisation to manage things like: IP address assignment, domain name registration etc. This is all managed by an institution called, ICANN, located in the USA.
What is packet technology?
One amazing thing about the Internet is its efficiency in transmitting data when compared with
cellular and landline communication technologies. This video you are watching from the Google
data center is sent to you in the form of a huge collection of 0s and 1s. What makes the data
transfer in the Internet efficient is the way in which these 0s and 1s are chopped up into small
chunks known as packets and transmitted (Fig:12).
Fig:12 Representation of an image in digital form
Let’s assume, these streams of 0s and 1s are divided into different packets by the server where
each packet consists of 6 bits (Fig:13A). Along with the bits of the video, each packet also consists of the
sequence number and the IP addresses of the server and your phone. With this information, the
packets are routed towards your phone. It's not necessary that all packets are routed through
the same path, and each packet independently takes the best route available at that time as shown in Fig:13B. Upon reaching your phone, the packets are reassembled according to their sequence number. If it is
the case that any packets fail to reach your phone, an acknowledgement is sent from your
phone to resend the lost packets.
Fig:13A Streams of 0s and 1s are divided into different packet
Fig:13B Data transmission in the form of packets
What are the internet protocols?
Now compare this with a postal network with a good infrastructure, but the customers do not
follow the basic rules regarding the destination addresses. In this scenario letters won’t be able
to reach the correct destination. Similarly in the Internet we use something called protocols for
the management of this complex flow of data packets (Fig:14). The protocols set the rules for data
packet conversion, attachment of the source and destination addresses to each packet, and the
rules for routers etc. For different applications, the protocols used are different.
Fig:14 Internet uses protocols for managing flow of data packets