Layered Architecture

The best  way to  understand  any complex system is to break  it into  pieces  and then analyze what they  do and  how they interact. The most logical approach for this is to  divide the overall  set of unction  into modular  components each of which is responsible for a particular  function. At the same time we also need to define  interfaces between  these  components  which  describe how  they fit together.

To understand  internet  architecture we will  take  an example  from our  daily  life. Every  day we  have  to deal  with complex systems. If  someone  want  to describe the metro railway  systems he she will  describe this complex  systems that has tokens baggage  checkers tracing machines  security personnel  pilots metro  train  metro  train control and a system  for routing  metro trains. In  other way this  system might be described as  the series of actions when  one travel from a metro trains. He she has to purchase a token get his  baggage cheeked goes for the train and eventually get loaded on to the  train. The  train then moves and is routed to its destination. After reaching to the destination at the baggage's collecting counter one claims for baggage. If  the trip was good  or bad  he she  gives  suggestions  to the  suggestions  sections  at the  station. In this systems  one moves to destination from  source.

In internet a  packet  is shipped from  source  host to destination host. According to the  figure 2.12, there  is a token  function  baggage  check  function  for the  passengers having  token  gate  function  for already  checked  passengers with  tokens and the  process continues.

Horizontal layering of metro railway  functionality  2.13 show the horizontal  manner each layer is combined with the  layer below. All this  process moves  step by  without  token  baggage check cannot be done  and without  token  gates  cannot  be loaded. Each layer provides  its service  by performing  certain  actions  within  that layer and by  using  the services  of the  layer  directly  below it.

A layered architecture allows  to discuss a well defined specific part of a large and complex system. This simplification  itself makes  its much easier to change the  implementation  of the  service provided by the layer.

The  ability  to change the implementation of service without  affecting other  components of the  systems  is another  important  advantage  of layering.