OSI Model Overview If you have ever studied or read about networking, you know that in order for machines to communicate properly, hundreds of questions and regulations must be set by protocols. In order to make this possible and manageable, the Open Standards Interconnection (OSI) model was created in 1977 by the International Organization for Standardization. The OSI model makes networking manageable, and breaks the questions down into seven smaller groups, called layers. Also, the OSI model is used as a baseline for protocols, and can be used to understand how TCP/IP works. Diving Into the Seven Layers: The 7 layers of the OSI model are as follows: [*]Application [*]Presentation [*]Session [*]Transport [*]Network [*]Data-Link [*]Physical Lets kick it off with the first layer, Application. The Application Layer In short, the Application layer deals with communication between applications (didn't see that coming, did you?). It receives and requests data, and is the layer that all of the other layers "work" for, in that they ready the info for transferring to the other program's Application layer. Also, the other layers decode the information for the Application layer, when data is coming in. The Presentation Layer The Presentation layer basically does what it says. It gets packets ready to be presented. It makes sure the packets are in the correct syntax, structure, and language for being transferred or sent up to the Application layer. It either translates the data for the Application layer, or compresses it to send down to the Session layer. The Session Layer The Session layer controls the "formalities" of communication. The protocols present in this layer set up the sessions, or connections. They deal with how to establish the connection, what to do with the connection, and then when/how to break down the connection when communication is over. Also, it checks for errors during connection and puts control headers (a header is basically an address and instructions) on the packets during data exchange. The Transport Layer The Transport layer is directly under the Session layer, and guarantees that packets are received. Also, it can send acknowledgement that the packets have been received. The protocols in this layer give the ability to be able to establish, maintain, and end a connection/session. The Network Layer Next down the ladder is the Network Layer. This layer reads the address on the packets and routs them to the correct destination. Also, it reassembles or fragments packets as needed, depending on whether they are coming in or going out. It is also responsible for moving the data packets from source to destination and across networks as needed. The Data-Link Layer Here, the packets are prepared for final delivery to the recipient. They are encapsulated in the proper format and addressed. Protocols in this layer also aid in error detection. Inside this layer are two sublayers, the LLC (Logical Link Control) sublayer and the MAC (Media Access Control) sublayer. The LLC is responsible for communication between the Network layer protocols and the method of transfer, such as Ethernet. The MAC sublayer is responsible for communication with the physical media (hardware). The Physical Layer This is where the dirty work takes place. The Physical layer controls the actual data bits moving from the network card on your computer onto the actual network, and vice versa. Think of this layer as a person on an assembly line, taking the ready and packed boxes and placing them onto a conveyor belt to be sent on their way; or as a person taking packages off of an assembly line to be unpacked. ~~~~~ As I said, just a quick introduction to the OSI model. Once I've read and learned more, I'll post more about this, hopefully in a more detailed and comprehensive paper. I apologize for any mistakes or miscommunications/typos. ~ Cro Shoutz to: #suidrewt