Search The Site

OSI Model explained in laymans terms

There are a total of seven layers in the OSI Model. Before we can diagnose any network issues we must first understand the seven different layers involved in networking. Each layer of the OSI Model has individual characteristics and tasks it is responsible for. Each layer must communicate with the layer directly above it and below it through a series of standards and protocols. I will explain the layers in layman's terms so you can grasp the idea quicker. The seven layers are as follows:

  • Physical Layer: Specifies how data is processed into bits and physically transferred over medium, such as cables for example thinnet, thicknet, unshielded twisted pairs (UTP), etc. Maintains the physical link between systems.
  • Data Link: Provides the link for how data, packaged into frames is communicated through hardware to be transported across a medium. A network data frame, aka packet, includes checksum, source and destination address, and data. The data link layer communicates with nic adapters, and manages physical layer communications between connecting systems, it also handles all error notifications.
  • Network: Responsible for determining addressing on the network, determining the routes that information will take on its journey, and managing network traffic congestion. Internet protocol (IP) is responsible for routing, directing data-grams from one network to another. Data at this level is packaged into packets.
  • Transport: Responsible for breaking the data into segments, establishing an end-to-end logical connection between machines, and providing for error handling. Two transport protocols, Transmission Control Protocol (TCP) and User Datagram Protocol (UDP), sits at the transport layer.
  • Session: Determines how two devices establish, maintain and manage a connection – how they talk to each other. These connections are called sessions. The session protocol defines the format of the data sent over the connections.
  • Presentation: Concerned with how data is converted and formatted for data transfer. Examples of format conversions include ASCII text for documents and .gif and JPG for images. This layer performs code conversion, data translation, compression and encryption. It is basically responsible for converting local representation of data to its canonical form and vice versa.
  • Application: Provides network services to user applications. Provides network services to the end-users. Mail, ftp, telnet, DNS, NIS, NFS are examples of some of the network applications it uses.

Now that we have a better understanding of the layers involved in networking it is much easier to troubleshoot. Learn how to troubleshoot networking issues in Vista.