I worked at COVAD during the night shift as a tech support agent and started in a large cubicle farm building with a open floor plan that meant you could see the entire building. It was a bit like working in a convention hall.
Because I worked nights, it was more like working in an abandoned convention hall.
The drive home was a lonely one through miles of country road before hitting the highway. The check engine light liked to flash menacingly as I drove my aging Geo Storm across the windy roads.
I would have rather listened to anyone else but me reading about the OSI model from a fat book with tissue thin pages that promised that I would pass the CISCO certification exam. Still, learning about the OSI model meant not thinking about breaking down near the haunted farm house in the middle of the night.
OSI model stands for Open Systems Interconnection model. Knowing this model gives a few advantages when trouble shooting a network. It makes you sound very smart to the guy that doesn’t understand it, and it helps with understanding the technical aspects of how systems interact.
I like to imagine it as a seven story office building where each floor supports the other in the process of communication. I like to imagine it is run by an army of monkeys.
The first floor is called the physical layer. The physical layer is concerned with hardware. If you can touch it in the real world, it is part of the physical layer. The thing that is in your hand right now is part of the physical layer. The physical layer creates the raw data, loads it into bins, and sends the whole thing up to floor two the Data Link Layer.
The data link layer is in charge of taking that raw data and delivering it through the physical layer. It is great for describing things that are plugged into each other. Imagine our raw data coming off the elevator from floor one. An army of monkeys grab the data from the bin and box them up in a way so that they can be sent across the network and not run into each other. These monkeys then put the boxes in the elevator and send it on up to floor three.
Floor three is called the Network layer. The network layer is in charge of taking the little boxes and writing the correct address on it. Instead of using a postal address, the monkeys use an IP address.
Floor four is called the Transport Layer. On this floor, the monkeys are responsible for delivering the little boxes to the correct IP address.
They send the little boxes using a system called TCP/IP. The TCP part is called the Transport Control Protocol (TCP). Its job is to deliver the little boxes using the internet protocol (IP) address the monkeys put on the boxes.
The Session Layer sits on floor five and is a bit like a traffic controller. From way up near the top of the building, they are able to control when, how, and for how long each connection will take.
The Presentation layer is on floor six, where all the little boxes are unpacked again before being shoved back in the elevator.
Floor seven is where the final product is made. The Application layer is responsible for connecting applications together. Here the monkeys are responsible for taking the unpacked boxes and assembling them into things like email, websites, video, and pictures of your mom.