What is an OSI Model?

In the late 70's, a model was introduced that have proven to be useful in past and present periods. The open system interconnection (OSI) model is reference model that illustrates communications between two end users in a network. This model can be used for building new products and comprehending networks. (WhatIsThis, 2007)

The Open System Interconnection model separates the mechanisms of telecommunications into seven layers. The seven layers are grouped into two sections. The first segment of layers is called upper layers. The upper layers handle messages that are received or sent by the user. The second segment of layers is called the lower layers. The lower layers handle messages that travel through the host. The host computer messages are sent through the upper layers but messages that are sent to another host are not sent through those upper layers they are simply forwarded to the other host. (WhatIsThis, 2007)

The seven layers of the OSI Models are: Application, Presentation, Session, Network, Data-Link, and Physical. The seven layers each serves its own purpose and provides a specific service.

Layer 7 - Application Layer

The Application layer supports the application and end users processes.

Layer 6 - Presentation Layer

The presentation layer provides translation from application to networks and networks to the application

Layer 5 - Session Layer

The session layer manages the connection between applications

Layer 4 - Transport Layer

The transport layer provides clear data transfers between hosts, error recovery and flow control.

Layer 3 - Network Layer

The network layer offers virtual circuits for transmitting data from computers or other devices. The layer also provides switching and routing technologies.

Layer 2 - Data-Link Layer

The data-link layer encodes and decodes data packets into bits.

Layer 1 - Physical Layer

The physical layer communicates the electrical impulse, light or radio signal via the network at the electrical and mechanical level.

(WhatIsThis, 2007)

The OSI model has been useful and received high remarks but they have also received some criticism. The critique involves the complexity of the seven layers and implementation. It's believed that the complex layers takes away from its efficiency. Due to a difficult manipulation, the over complex model presents implementation issues. (Critics, 2007) The OSI model has received criticism for its complexity but has still proven to be practical for some purposes. The effectiveness of the model has allowed it to remain effective for current users.

References:

Critics of OSI and TCP/IP models and Protocols (2007) Retrieved on 02 December 2007 from http://www.et.put.poznan.pl/tcpip/architecture/archi_critics.htm

WhatIsThis.com, (2007) The OSI Model Illustrated Retrieved on 02 December 2007 from http://whatis.techtarget.com/definition/0,,sid9_gci523729,00.html