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.
