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# 1.6 Layering Principle

### Layering 

![](/files/-MgXG8vPVXlDtHKpgwoj)

* E.x. flights: google flights --> airlines (abstract the details of each airlines) 
* E.x. postal service 
  * Mail 
  * Postal service 
  * Medias 
  * Mailman 
* Can improve each layer independently over time (the interface is the same)
* E.x. computer system 
  * Breakdown into functional components, each with well-defined roles 
  * Clear separations of concerns 
  * Each can be improved, updated over time 

![E.x. computer system ](/files/-MgXH4hzOQTm-UKaO60k)

* Break the layers boundary only if needed 

### Reasons for layering 

![](/files/-MgXIHbF26usHlWYDukn)

* p2p: specific to layered communication systems 
  * 4-layer: each layer communicate with its peer on the another system, using the delivery service provided by the layers below