#overviewofnetworking

We all use the Internet every day, -we work on the Internet. It is definitely not that black box.  It’s something more like this:

The Internet is a network that facilitates the transmission of information amongst billions of devices worldwide. It’s a network of networks, but what exactly is it made out of, how does it transmit that information?

In order to understand these things, we decided to break down a GET request, the simplest of HTTP requests and follow it step by step, from the moment that an individual client opens up the browser on his/her computer, to the browser requesting a page from a server, to the server responding back with the requested page.

 YOUR COMPUTER:

We’ll start by taking a look at how your request travels through the client side protocols on your home computer: 

This stack above represents a few of the different protocols that take place inside your client computer when you click on a link to MAKE an HTTP request.This stack represents a few of the different protocols that take place inside your client computer when you click on a link to MAKE an HTTP request.

We start out in the application layer. This is the first layer of abstraction which includes the browser and the DNS. This is where the application code runs. Data from here is passed on to the next layer.

TCP layer breaks down data into data packets, which ARE more manageable, pieces of data. It attaches a header to each packet assigning it a destination port. This is the way we organize all the messages that are BEING sent out over the Internet. Ports are a way of multiplexing, or specifying different recipients at the same location. Ports allow your computer to use more than one network service at the same time.

Similarly to TCP, the Internet Protocol layer, above,  packages data and tells it where to go. THIS time by means of an IP address. THE packets from the IP layer are called datagrams and they contain two pieces:

the payload which is your information, 

and the header which determines the IP address your information will go to.

The main role of the PHYSICAL layer is to translate binary packet  data into network signals.  Those signals may be, electrical, radio waves, or light as in the case of optic fiber networks. THAT is mind blowing awesomeness right there!

And, all this is happening  right in your very own computer :)

YOUR HOME NETWORK:

As we leave your personal computer,  we connect to the home network with the following set of hardware:  the switch, the firewall, the router, and modem. The four of which  can exist as a single box.

(That Linksys might look familiar some of to you)

A switch creates a LAN, or a local area network. It acts as a controller which allows it’s networked computers to talk to each other.

The firewall acts as decision engine, deciding what data traffic to allow in and out of the LAN.

A router (“a hop”) serves as a dispatcher. It chooses the best path for the information to travel, by using dynamic routing protocol. The router makes sure that information doesn’t go where it isn’t needed.

The modem (MODulator-DEModulator), is responsible for creating the SIGNAL that ACTUALLY gets transmitted and then decoded to recreate the information at its new destination. It takes YOUR digital data and turns it into a modulated signal. 

THE INTERNET SERVICE PROVIDER:

The modulated signal goes to an ISP (or internet service provider ).  You actually contract with an ISP to access the Internet. While your home network isn’t directly connected to the Internet, your ISP owns a mesh network of routers which are. This redundancy of routers provides multiple paths for the information to travel. If there’s a problem with one router, the packet can navigate around it.

FINALLY, THE INTERNET!

Now,  at this point we are on the Internet and we’re able to answer our initial question…The Internet is just a series of routers owned by different entities.  They connect different LANS to each other.

Hoewever, we still don’t have our information. Here, data packets containing our request go from router to router, each time getting closer to it’s destination.

Of course, we still don’t have this information on our home computer, we’ve merely located where it is on the server, but to get back from here, the process is pretty much the same but in reverse.

We’re guided out of the server computer and through the same series of switches and routers back onto the Internet and eventually to the network of our home computer.

We then navigate our protocol stack in reverse until we finally end up at the application layer of our home machine—our browser, where we can see the information we requested.

Finally, we hop into the network of the company whose information we’re requesting. We then go through the company’s firewall and get routed onto the network that the server containing the information we requested is on. 

Then our data packets go through a switch and finally get onto the individual server containing the information we want.

Within that server computer, we navigate the very same protocols that we talked about on the client side, this time proceeding from the bottom up.

 We are routed by hardware up into the IP layer which guides us via IP address. Then our data is directed to the correct port and into the server’s application layer. Hooray! We’re here, we made it!

And what exactly was it that we were requesting? Well, it looks like it was this image, which is a much, much, simpler explanation of what the Internet is - it came out of Sir Tim Berners Lee’s head, and it’s full of cats.