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The Osi Reference Model

Autor:   •  August 8, 2017  •  1,012 Words (5 Pages)  •  895 Views

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Physical Layer (Layer 1)

Finally, layer one in the OSI Reference Model is the Physical Layer it defines the physical functions of a network such as functional interfaces, electrical/optical, and mechanical equipment. This layer is primarily concentrated on the transmission and reception of unstructured raw bit stream across a physical medium to another physical medium on the network. The physical layer carries signals for all of the higher layers. The High-Speed Serial Interface (HSSI) is one example of a standard interface working at the Physical Layer level ("The OSI Model's Seven Layers Defined and Functions Explained", 2014).

Packet-Filtering Routers and Firewalls

Packet-filtering routers and firewalls reside on layer three of the OSI Reference Model, which is the Network Layer. A packet-filtering router works like a firewall it allows only those packets to pass, which are allowed by configuration or for example a firewall policy. Packet-filtering inspects the IP address and TCP port for both source and destination and then depending on the configuration or policy the hardware will decide to route it through the network or not. Packet-filtering routers and firewalls are used to thwart unauthorized access protecting a network by controlling what a network will accept (Merkow & Breithaupt, 2006).


The seven layers of the OSI reference model created by IOS is a standard set of communication protocols it gives equipment from different manufactures and dissimilar networks the ability to communicate with each other. Throughout the model, control is sent from layer seven the application layer through the other layers until reaching the bottom physical layer. After the process has reached completion, it is then circulated back to the top of the hierarchy. Each of the seven layers defines a protocols function that is required to enable communication between computers over the internet. Layer three hosts packet-filtering routers and firewalls that control what is authorized to pass through into the network. Without the incorporation of set standards like the OSI Reference Model provides it would be difficult to create interoperability network devices.


Merkow, M., & Breithaupt, J. (2006). Information Security: Principles and Practices. Retrieved from, The University of Phoenix eBook

The OSI Model's Seven Layers Defined and Functions Explained. (2014). Retrieved from

Tuma, T. T., & Fajfar, I. I. (2000). A hands-on approach to teaching the basic OSI reference model.International Journal Of Electrical Engineering Education, 37(2), 157.


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