The OSI Model
The OSI Model
The OSI model describes how data flows in a network. From the top, highest level containing applications for the everyday user down to the bottom level of the physical connections, data and information passes through every layer which in turn can talk to the layers above and below it. Every layer is made up of complicated software. When that software and its components receive information, commonly called packets, from another source it checks it and then sends it back through if necessary (Breithaupt & Merkow, 2006, Chapter 12). The OSI Model is comprised of seven layers, each distinctly different but yet each function and communicate with the others.
The application layer is the one most computer users are the most familiar with, whether it is known to them or not. This is where user forward software operates, such as ...view middle of the document...
This layer also handles any restart and recovery functions necessary.
The transport layer provides integrity for point-to-point data transmissions. The transmission control protocol lives in this layer, working to allow the connecting of two computers with each other. During this connection the computers will stream data to each other, the integrity and order of that data being maintained by the TCP.
The network layer monitors and decides what path data will take. Controlling the operation of the subnet makes sure the data goes to the correct placed based on a variety of factors present and identified by the software.
Data link layer
The data link layer is responsible for establishing communication between devices, converting that transferred information to deliverable data to the lowest layer, the physical layer.
The physical layer is the lowest of the OSI model. This layer manages the sending and receiving of a raw stream of data and information through a network. This layer consists of the various mechanical, optical, electrical, and functional interfaces that carry the information to all of the higher layers.
Packet-filtering routers and firewalls
Packet-filtering routers and firewalls control the flow of data at differing layers. The transport and network layers often come into play first, as this is where a firewall will ascertain if the packets are from a trusted source or not. Firewalls know little about the information contained in the packet at this level, but provide an amount of security nonetheless. Packet filtering looks more in-depth into the content of the packets. When the packets flow through the filter it is analyzed according to a pre-set standard. If information does not match or does not meet a certain quality the packet is denied, not going any further into the system.
Breithaupt, J., & Merkow, M. (2006). Information Security: Principles and Practicies. Retrieved from The University of Phoenix eBook Collection.