Saturday, January 11, 2014

The Internet!!

Internet – the network of networks has become so ubiquitous that most of us are wired to it all the time. Millions of people around the globe use internet for anything and everything like chatting with a friend, sharing pictures with the dear ones, working in a collaborative environment, banking, shopping and even robbing J.  It is amazing to see that in a short period of time internet has evolved with has evolved with its wide range of offering.  However did you know how does this huge network of networks communicate and are able to exchange information with each other?  What’s the backbone of this magical network?

If you did not know, don’t worry, I hope by the end of this post you would definitely get to know at least the basics of how this magical network works.

TCP/IP (Transmission Control Protocol /Internet Protocol) architecture lays the backbone of internet.  So what is this TCP/IP?

TCP /IP is a suite of communication protocols that help the computers on the internet to network and communicate with each other. It is layered architecture starting with the Link layer (aka physical layer), then to the Internetwork layer, Transport Layer and ending up with the Application Layer, with each layer servicing the layer above.

Theoretically this sounds easy, but how does this conceptually work?  While I was thinking on how to explain this I saw a baggage advertisement on TV, and then it struck to me that even the baggage that we checkin during a flight journey, also runs through a small network of baggage and is delivered safely to us at the destination airport. Have we ever seen how the bag we check in arrives right at the other end? Similarly we simply checkin our request via home network and then end up back with the right information at our desk. How does this all happen? Magic??

Below I have tried to unlock this magic by doing a comparative study of Baggage Handling System (BHS) and the internet architecture. I hope this example helps us understand in simple terms on how TCP/IP suite functions. Before jumping into the explanation, let’s have some analogies between the Conveyor network and Internet architecture.

Internet (TCP/IP)
Conveyor network (BHS)
Data
Packets
Bags
Source and Destination address
Barcode
Internet Protocol address (IP)
Link
Airline Baggage Belt
DSL, Modem
Route
Router
Pusher
Reliable Transport
Scanners/BHS
TCP
Application
Email, Hyper text documents
Loading the plane
Heart
TCP/IP
BHS

When we checkin the bags at the respective airline counter, the airline agent checks our itinerary and prints a tag and attaches to each of the bags.  This tag consists of a unique bar code, the holds the details of the source and destination address.  In the same way once we submit a data onto the internet it is broken into packets (like individual bags) and is labeled with a unique address i.e the Internet Protocol Address for it to traverse to the required destination.

How does the flow of information start?

As we have a airline baggage belt running at the counter, that takes forward the checked in bags, we have the Link layer of the TCP/IP that actually Links one node to the other in the internet and moves packets from one network to the other.  The DSL at home, Wi-Fi at cafes, Ethernet etc. forms the Link layer.
Thereon the individual airline bags get merged into the common Conveyor network which transports number of bags from various other airlines to the respective airplanes, in a way similar to our data gets pushed into the internet to make its way to the destination.

The conveyor belt system at various junctions has got some agents called the PUSHERS that scan the bags, checks the barcode, and routes the bags to the right belt of respective airline. Similarly the network agents called ROUTERS at various nodes of internet inspect the IP address, lift the packets and route them to the right destination in a best effort way. These routers that move the packets onto the right network form the Network layer of TCP/IP and there on as the network is established the packets move further up via the Transport layer just like the bags move on the right track in the conveyor network.

As the bags move they pass through a set of scanners and once the baggage are scanned the BHS tracks its movement providing a reliable transport. Similarly the Transmission control protocol at the transport layer monitors + co-ordinates the movement of packets and assures a reliable delivery.

End of the Main Terminal conveyor system is a conveyor that loads your bag into a passing (Destination Coded Vehicle) DCV which quickly moves your bags to an off-ramp at the gate. Like Network interface adapters, DSLs, these DCVs are something similar to the link layer technologies, connecting 2 end points, and take the baggage from the conveyor belt system to the plane. These DCVs contain unique number just like the Media access addresses of linkers to identify themselves on the internet.

The bags delivered at the gate could be compared to the data that we receive as data input to the application layer. The bags then make their way down a short conveyor to a sorting station where the baggage handlers load the bags onto carts or into special containers that go right into the airplane.

While loading the plane, the baggage are sorted at the sorting station( as per their need/application) and those that are for transfer are passed into a different bay area than those that would be headed to baggage claim. Similarly the data we receive at the application layer are either presented as a web page via the Hyper Text Transfer Protocol (HTTP) or as an email via Simple Mail Transfer Protocol (SMTP), or as a file via the File Transfer Protocol (FTP). All these protocols HTTP, FTP, SMTP and many such forms the application layer.

Since the bags already come sorted, they then get offloaded into their respective baggage claim belts at the destination and arrive to us safely.

Most of the times all the bags are delivered safely at the destination (if the BHS uses stronger reliability standards like TCP), however if the BHS standards are unreliable like the Internet Protocol (IP) then there are chances that few bags/packets are missed during the transport.

A short summary of the above process has been represented below pictorially.  I hope now you have got at least a little knowledge on the underlying network technology of the internet and how it functions. 


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