7 Layers of the Osi Model

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The Seven Layers of the OSI Model
Kevin Ludwig
Bryant and Stratton College
TECH 140
Khaled Sabha
12.08.2009

There are seven layers in the OSI model. Each layer has a function or purpose that is used to set up a network. The International Organization for Standardization began to develop the OSI framework in 1984. The purpose was to have each layer interact with the layer directly beneath it. The layers are starting from the top: Application, Presentation, Session, Transport, Network, Data Link and Physical. The Application layer has the function of providing interface between software applications and network for interpreting the requests and requirements for applications. “This top layer defines the language and syntax that programs use to communicate with other programs.” (“OSI model, “2009, p.01). The Presentation layer allows hosts and applications to utilize a common language. It also performs encryption, formatting, and compression. “When the data are transmitted between different types of computer systems, the presentation layer negotiates and manages the way data is represented and encoded.” (OSI model, “2009, p.01). The Session layer establishes, maintains, and terminates user connections. The Transport layer ensures the precise delivery of data through flow control, segmentation and reassembly, error correction, and acknowledgement. “The lower layers may drop packets, but the transport layer performs a sequence check on the data and ensures that if a 12MB file is sent, the full 12MB is received.” (OSI model, “2009, p.01). The Network layer establishes network connections and translates network addresses into their physical counterparts and determines routing. In order to provide services to the Data Link layer, it must convert the logical network address into physical machine addresses, and vice versa on the receiving computer. The Data Link layer packages data in frames appropriate to network transmission method. “The data link is



References: OSI MODEL. (2009). In Computer Desktop Encyclopedia (p.01). Pennsylvania: Computer Language Company Inc. Network Protocols Handbook (2007). Protocols Guide: Iso Protocols in OSI7 Layers Reference Model. P 217-218.

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