Part 02 – OSI Intro

In this section we'll begin to dissect the OSI (Open Systems Interconnect) reference model. As its name implies, it's an open standard maintained by the ISO (International Standards Organization) used to ensure interoperability of network devices. Such interoperability means that a wireless router from Linksys can be swapped out for similar products from the likes of Netgear or Edimax without missing a beat. As previously discussed, the various layers of the OSI model define specific functions handled exclusively at each layer. This specialization is referred to as "encapsulation." So much has to happen in order to transfer data, that no one device or protocol is expected to handle it all. We'll see how various network devices map to the individual OSI layers. The data payload size remains the same as it's passed down and up through the 7 layers of the reference model. Headers are added to the data payload as it gets passed up the layers. This packaging up of data is the encapsulation process. At the upper layers (5-7) the data payload plus headers is referred to as a PDU (protocol data unit). As we move down towards the physical layer, headers are stripped off during the sending process. We have a segment at the transport layer, packet at the network layer, frame at the datalink layer, and finally, bits at the physical layer. The unpackaging process is referred to as "decapsulation." It should be noted, that in terms of the CISSP exam, it's important to understand the security threats and specific attacks that exist at each layer. There are several nifty mnemonic devices for remembering each of the OSI layers. One of the more popular is "All People Seem To Need Data Processing" which translates to: Application, Presentation, Session, Transport, Network, Datalink, and Physical layers. Feel free to come up with one that works for you!
Learn on the go.
The app designed for the modern cyber security professional.
Get it on Google Play Get it on the App Store

Our Revolution

We believe Cyber Security training should be free, for everyone, FOREVER. Everyone, everywhere, deserves the OPPORTUNITY to learn, begin and grow a career in this fascinating field. Therefore, Cybrary is a free community where people, companies and training come together to give everyone the ability to collaborate in an open source way that is revolutionizing the cyber security educational experience.

Cybrary On The Go

Get the Cybrary app for Android for online and offline viewing of our lessons.

Get it on Google Play

Support Cybrary

Donate Here to Get This Month's Donor Badge

Skip to toolbar

We recommend always using caution when following any link

Are you sure you want to continue?