Week 2: Day 004 - OSI Layers 4-7

Hello again! So I was not able to post yesterday since I was taking my English entry test for NOVA, but now I'm back, and I will finish off my independent lesson on the OSI Layers. I will also likely make another post to make up for yesterday, so be alert for two consecutive posts!

So, let's start out with Layer 4, (since last time I went through up to the Network layer) this is known as the "Transport" layer. This layer has the responsibility of chopping up, organizing, and sending data. Usually the amount of data is too large for a single frame, so the data must be broken and put into several frames for sending. Once this process is complete the sending computer will give the data to the NIC. When the receiving computer gets the data it will recognize this packets are being sent to it, and will verify that the data is not corrupted. This entire process is directed by the "transport protocol", the protocol is set to give each packet a sequence number. The process proves to be one of the most important as it is responsible for the assembling and disassembling of data.

Next, there is Layer 5 which is known as the "Session" layer. A network has many systems, and usually they are talking to each other very often. For example, say there was a printer connected to someone's PC. The system must direct all the files and print jobs to the correct programs and software. Basically, the system layer will take care of all of this, or handle all the sessions in other words. It may also name your system to make the process for the user a lot easier. In general, this layer is important for handling many necessary processes people perform in a network.

Now, on to Layer 6, called the "Presentation" layer. To begin, I am grateful that computers with Mac OS and Windows can communicate with each other despite the many differences, thanks to today's networks. It means less problems for techs, and less interaction of me with Macs (haha.) To summarize what the Presentation layer is meant for, it handles conversion of data into formats that are compatible with a system on the network. This was a problem back then, and it drove many crazy, which is why I say I'm grateful. File formats like PDF were ones that put forth a universally usable document between operating systems. So, this is important for say a Mac to transfer a document to a Windows computer, and for the document to be readable.

Finally, Layer 7! This is the "Application" Layer. Putting this very simply, this part of the network is the most visible one (obviously.) It's pretty much in the name, software applications are very involved in this layer. This is definitely an important part of the OSI Model because you need an application to move files to another computer to begin with! For example, on Windows 7 you have the "Network" application, and I've used it several times before. If you want to go on the internet, well you need a web browser (for sure)! Programs like Google Chrome and Mozilla Firefox specialize in this. To be blunt this layer is mainly for the user. It's hard to believe that this is the 21st Century and people still don't know how to bloody use Windows or Mac OS. Now some applications also have the abilities to encrypt and authenticate data coming and leaving your device. But as we all know these tasks are given to individual applications that only have a certain task. To finally close my analysis of the Application layer, I have to make this clear --- The word "application" in this sense does not refer to the computer applications, just the software that enables the applications to co-operate with the network. This now concludes my lesson on the OSI Model (yay!).