OSI Model

 



Open System Interconnection (OSI) model. First introduced in 1984

1. Application
2. Presentation
3. Session
4. Transport
5. Network
6. Data Link
7. Physical

Acronym :

All People Seem To Need Data Processing (top down)  

Please Do Not Throw Sausage Pizza Away (bottom up)

Functions of OSI model : 

•  helps to break down network functions
•  create standards for equipment manufacturing 
•  allow vendors to focus in specialized area of network

Application Layer :   

• provide interface with application to work in network
•  provide network access to application

Presentation Layer :   

•  generi-fies the data by attributable / give data tag that everyone understand
•  encryption (generic) services

Session Layer : 

• start and end session
• keep different session separate

Application ,Presentation , Session - these 3 are least important, handled by OS

Transport Layer : ( most important)

• describe how data is sent ( reliably/unreliably)

reliable - get acknowledgment  

unreliable - don't get acknowledgment ( real time application , VOIP , streaming  ) dropping is not crucial 

     

• defines well know services ( port number)

Network Layer :

• provide "logical addressing" ( ip addressing)
• find best path for destination 

Data Link Layer :

• provide "physical addressing" (mac address)
• ensure data is error-free

Physical Layer :

• provide access to cable
• convert all/features to bits(0,1)