How Do You Explain The Purpose Of The Osi Model?

By Author: Jonathan Simpson
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The reference model used by most Intelligence Technology (IT) experts to explain the functions of both networks and their applications is the Open System Interconnection, or OSI model. This concept was originally developed for the purpose of describing an entire range of protocols for production networks. The expense and intricacy of the programming process required to successfully define this network made this descriptive project unfeasible. Furthermore, while the OSI designers quibbled over individual responsibilities of the application's features, the Transmission Control Protocol/Internet Protocol, or TCP/IP, became the world's standard instead.

The OSI model is structured to contain seven layers. These are, from layers 7 to 1, Application, Presentation, Session, Transport, Network, Data Link, and Physical. Many people utilize the first letter of each layer to form the following mnemonic: ‘All People Seem To Need Data Processing'.

Each of the layers has a unique function:

1. Layer Seven: This layer is the Application Layer, and controls certain services for the terminal user, including file ...
... transfer applications, electronic mail and messaging software, access to virtual terminals, and the management of computer networks. The typical computer user interacts with the model on this layer.
2. Layer Six: This layer, denoted as the Presentation Layer, controls the definition of network host communication syntax. Encryption, as well as compression functions, operate on this layer.
3. Layer Five: This layer, known as the Session Layer, controls the establishment of interacting process communications between two or more hosts in a network.
4. Layer Four: This is the transport Layer for the OSI model. This layer manages the processes of message delivery between hosts in a network. Other processes that occur at this layer include file fragmentation and their reassembly.
5. Layer Three: This layer is the Network Layer. The purpose of this layer is to establish data transfer paths throughout the entire network. This is the layer at which routers function.
6. Layer Two: This layer, known as the Data Link Layer, manages the communication processes that occur between contiguous nodes in a network. Devices that operate at this level include hubs and switches.
7. Layer One: This layer is the Physical Layer. It manages the coordination of bit-level communication among network nodes. Items that are found at this layer include types of cable or connectors, as well as pin- outs and voltage specifications.

How Does the OSI Model Affect Modern Computers?

Unfortunately, this model is not very well correlated with the real computer world. This is true because a large number of current protocols were already being produced when the model was developed. Some of these, including TCP/IP, were developed to solve actual problems encountered by standard computer users. In contrast, the OSI model was structured to fulfill the academic functions desired by academic professionals. While this model is seriously lacking, it is the sole commonly acknowledged method used to describe networked applications. describes networked applications.

The most effective way to approach this model is to map the layers to actual processes as accurately as possible. Unfortunately, however, programmers do not commonly agree about which layers of this model are best mapped to each real-world protocol. For example, programmers could argue ad infinitum regarding which layer is best mapped to SSH. The following, however, is this author's best judgment regarding which layers best map to current commonly used protocols:

In contrast, the TCP/IP model is much more reflective of the practical process of networking.:

Unfortunately, however, people who reference the TCP/IP model frequently learn that very few others actually have any idea what they are saying. To understand better why the OSI model ought to be laid to rest next to Beta Videotape Recorders and BASIC programming, read Kill the Beast: Why the Seven-Layer Model Must Die.