History and development
Al Gore may have laid claim to inventing the internet, but the groundwork for how modern computers connect and communicate was developed long before his famous comment. A base from which a major part of current computing interconnectivity was developed started in 1978 by the International Organization for Standardization. Their efforts gave rise to the OSI model. The acronym expands out to mean Open Systems Interconnection, a dual component framework credited to Northampton Community College’s Helen Yanulus. The OSI model are seven generic vertically stacked theoretic layers each providing data transmission functionality to the layer above or below. Each layer contains a set of systems, standards or protocols that communicate with corresponding entities in higher layers. As each successive layer depends on the one below, data cannot jump or skip layers. Currently, the Internet uses the more lax TCP/IP protocols that have absorbed some of the OSI model. Using the term “All People Seem to Need Data Processing”, the seven layers can be deduced as follows, starting from the bottom up.
Physical Layer
This is rather self explanatory as it defines the physical connection systems for a network at the end user. In its simplest form, layer 1 is responsible for standards relating to cabling and networking plugs. It also includes the voltages that can be broadcast across the network.
Data Layer
It is best to think of this layer as the one responsible for the creation of a network. The systems that facilitate data transmission between the networks themselves, like Hubs or Switches are found in this layer.
Network Layer
This is the last of the physical pieces of a network. This layer’s function is to direct the physical flow of the data, a job performed by Routers.
Transport Layer
Here data, as in the bits and bytes than move through the network, are prepared and addressed to their respective destinations. Other duties include delivery confirmation and error correction.
Session Layer
Once the data is prepped to move, both sender and destination must form a connection with each other. This is called a session. Once the physical and digital paths are confirmed the actual management of that path is handled here.
Presentation Layer
The data itself must be able to be read at the other end and that the job of this layer. At this point the syntax of the data will be chosen to allow its transmission and how it will be interpreted by the receiver. This would be the human equivalent of choosing what language, or a common language to communicate with another person.
Application Layer
This top layer is what the end user interacts with. When data is sent or received it has to be done so in manner that it’s applicable to the user. The platform on which data is created and received to be displayed on the computer is the realm of the application layer. For the user this would be the program, like an email client, that creates/receives/interprets/displays the data.