What is Routing in Computer Networks? - Protocol and Working of Routers

How is it possible for every piece of data to be delivered to you reliably?

For plunging directly into Routing, we need to look into a few things before. Say you want to play a music from a website. It seems like your computer connects directly to the website's server and it sends you a song on a direct dedicated line. But actually, that's not how the Internet works!

Network Packet in Routing:

Information on the Internet goes from one computer to another in what we call a packet of information. A packet travels from one place to another on the Internet. As we move from place to another in a car. Depending on traffic congestion, you might choose or to forced to take a different path to get to the same place. Similarly as you can transport in a car, a lot of kinds of information could be sent with packets with the help of routing but there are some restrictions. 

For instance, if you need to move a space shuttle from where it was built to where it will be launched. The shuttle won't fit in one truck, so it needs to be broken into pieces and transported. Trucks could all take different routes and might get to the destination at different times. But once all the pieces are there, you can resemble the pieces into the complete shuttle to launch. On the Internet, the details work similarly. 

If you have a very large image that you need to send to or upload, that image might be made up of 10s of millions of bits of 1s and 0s. Which are too many to send along in one packet. The computer sending the image can quickly break it into thousands of smaller parts known as packets. Unlike cars and trucks these packets don't choose their routes. Each packet in routing has the Internet address of where it came from and where its going.

What is Routing?

If the Internet were made up of direct, dedicated connections it would be impossible to keep things working as millions of users join. Since there is no surety that each wire and computer is working all the time. Instead, data travel on the Internet in a much less direct fashion.
Many many years ago, in early 1970s Bob Kehn and Vint Cerf begin working on the design of what we now call the Internet. They had the responsibility and the opportunity to design Internet's protocol and architecture. So they persisted in participating in the Internet's growth and evolution for all of this time up to, and including present.

      "The information transfers among computers very amazingly"

It does not require a set path to follow, in fact, your path might amendment within the inside of a PC to PC spoken communication. Routers, on the web, act as traffic managers to let the packets moving through the network smoothly. If one route is congested, individual packets may travel different routes through the Internet. Then they may arrive at the destination at little bit different times or even out of order.

Types of Routing: 

Default Routing: A type of routing which sends all IP requests to a single fixed Default Gateway.

Static Routing: A type of fixed routing in which path selection and routing is controlled manually by network admin.

Dynamic Routing: A type of routing in which path selection and routing is controlled by Protocols.

How Router Works?

As part of the Internet Protocol, every router keeps track of multiple paths for sending packets and chooses the cheapest available path for each piece of data. Which is based on destination IP address for the packets. Cheapest in this case, does not mean cost but time and non-technical factors such as politics and relationships between companies. Often the best route for data to travel is not necessarily the most direct having options, makes the network fault tolerant.
Which means that the packets can keep sending packets even if anyone goes horribly wrong. This is the basis for a key principle of the Internet, Reliability.

Now what if you want to request some data and not everything is delivered? Say you want to listen to a song. How can you be 100% sure all the data will be delivered so the song plays perfectly. Here we need something called Routing Protocols.

TCP-Transmission Control Protocol in Routing:

Transmission Control Protocol (TCP) manages the sending and receiving of all your data as packets. Think of it as guaranteed mail service. When you request a song on your device, the server sends a song broken up into many packets. When your packet arrive, TCP does a full inventory and sends back the acknowledgements of each packets received. If all packets are there, TCP signs for your delivery. If TCP finds some packets are missing, it won't sign, otherwise your song won't sound good or portion of the song could be missing. 

For each missing or incomplete packet, server will resend them. Once TCP verifies the delivery of many packets for that song, your song will start to play. TCP and Router systems are scalable, they can work with 8 or 8 billion devices. In fact, because of these principles of fault tolerance and redundancy, the more Routers we add, more reliable the Internet becomes. Whats also great is we can grow and scale the Internet without interrupting services for anybody using it. 
The Internet is made up of hundreds of thousands of networks and billions of computers and devices connected physically. 

These different systems make up the Internet connect to each other, communicate with each other, and work together. Due to the standards of sending data around on the Internet. Computer devices, or routers along the Internet help all the packets make their way to the destination. Where they are reassembled, if necessary, in order. This happens billions of times a day, whether you and others are sending email, visiting a web page, or doing a video call. Even, when sensors or devices on the Internet talk to each other.