Please Whitelist This Site?

I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)

If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.

If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.

Thanks for your understanding!

Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide


NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The Book is Here... and Now On Sale!

Get The TCP/IP Guide for your own computer.
The TCP/IP Guide

Custom Search







Table Of Contents  The TCP/IP Guide
 9  The Open System Interconnection (OSI) Reference Model
      9  Key OSI Reference Model Concepts

Previous Topic/Section
OSI Reference Model Networking Layers, Sublayers and Layer Groupings
Previous Page
Pages in Current Topic/Section
1
2
Next Page
Interfaces: Vertical (Adjacent Layer) Communication
Next Topic/Section

"N" Notation and Other OSI Model Layer Terminology
(Page 2 of 2)

Protocols and Interfaces

These words have special meaning within the context of the OSI model: a protocol represents communication between logical or physical devices at the same layer of the model while an interface represents information moving between adjacent layers within the same device.

Thus, in “N” notation, protocols represent communication between layer N on one device and layer N on another device, while interfaces deal with communication between layer N and N+1 or Layer N and N-1 on the same device. The topics on OSI protocols and OSI interfaces describe these issues much better.

Network Stacks

What do you get when you take a bunch of layers and put them all one on top of each other? Well, you get a stack. This term is used to refer to either the entire set of layers in a model or suite of technologies, or a partial set. Since each layer has protocols associated with it, this is also sometimes called the protocol stack.

Entities, Functions, Facilities and Services

These often-interchanged, somewhat vague terms refer to specific tasks or jobs performed at various layers in the model. An N-entity is a term that refers to a specific operation or job done at “layer N”. A function is basically the same thing. Facilities and services are what a layer provides to the layers above it. This is often expressed in N-notation as well: the “N+1” layer often uses a set of “N services” or “N facilities” provided by the “N” layer.

Making Sense of OSI Terminology

You may have just read all of that and said to yourself “why do they bother making this so complicated anyway?” Well, I can't really argue with you. Remember, I did say there was bad news here. Now that you know what all of this stuff is about, should you run into it you won't be… uh… too badly confused. J

Fortunately, the use of the buzzwords above is somewhat limited. Most references are to specific layer names or numbers, and in particular, the “N-1” and “N+1” stuff is rarely used in discussions of real-world technologies. However, it can be very useful in explaining the model itself, so you will see some of these terms as you read the rest of this chapter on the OSI model.


Previous Topic/Section
OSI Reference Model Networking Layers, Sublayers and Layer Groupings
Previous Page
Pages in Current Topic/Section
1
2
Next Page
Interfaces: Vertical (Adjacent Layer) Communication
Next Topic/Section

If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005

Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.