Chapter 6: Telecommunications and Network Security - OSI Layers

OSI stands for Open Systems Interconnection. There are various functions and protocols of the OSI model and the study guide states that if you want to take the exam, you will need be be pretty familiar with these.

Application - in charge of file transfer, network management, and fulfilling network requests. My favorite protocol example here is HTTP, because I am familiar with it and understand how it works for the most part.

Presentation - Handles data formats, and encryption. ASCII is one standard that is concerned with the presentation aspect of OSI.

Session - This layer sets up the connection of applications. A good protocol example here is SQL.

Transport - This is like an agreement between two computers. How much stuff will be sent is a concern, as well as how the receiving end will verify and handle the data.

Network -Main responsibility here is to tell the packet where it needs to go, and to get it to its correct destination. An IP address is a good example for this one.

Data Link - Changes the data into LAN or WAN frames for transfer and sets up how a computer will gain access to a network. Ethernet is one protocol that is associated with this layer.

Physical - The conversion of bits to actual electrical signals for transmission. A familiar term that you is in use here would be a digital subscriber line (DSL).

http://compnetworking.about.com/od/basicnetworkingconcepts/l/blbasics_osimod.htm